ABSTRACT
Abstract
A secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution. The negative electrode includes a silicon-containing material and a plurality of single-walled carbon nanotubes. The single-walled carbon nanotubes have a maximum outer diameter of 5 nanometers or less.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a continuation of PCT patent application no. PCT/JP2020/039452, filed on Oct. 21, 2020, which claims priority to Japanese patent application no. JP2019-195409, filed on Oct. 28, 2019, the entire contents of which are being incorporated herein by reference.
BACKGROUND
The present technology relates to a negative electrode for a secondary battery, and a secondary battery.
Various kinds of electronic equipment, including mobile phones, have been widely used. Such widespread use has promoted the development of a secondary battery that is smaller in size and lighter in weight and allows for a higher energy density, as a power source. The secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution. The negative electrode includes a negative electrode active material and a negative electrode binder.
A configuration of the secondary battery influences a battery characteristic. Accordingly, the configuration of the secondary battery has been considered in various ways. For example, silicon monoxide is used as the negative electrode active material, and a single-walled carbon nanotube is used as a negative electrode conductor in order to obtain, for example, sufficient charge and discharge capacities. Further, a negative electrode active material which includes composite particles and carbon nanotubes is used in order to obtain, for example, a superior lifetime characteristic. The carbon nanotubes in the negative electrode active material are directly grown on surfaces of the composite particles that include, for example, silicon and natural graphite.
SUMMARY
The present application relates to a negative electrode for a secondary battery, and a secondary battery.
Consideration has been given in various ways to solve problems of the secondary battery; however, a battery capacity characteristic, an electric resistance characteristic, and a cyclability characteristic of the secondary battery each still remain insufficient. Accordingly, there is still room for improvement in terms of those characteristics.
The present technology has been made in view of such an issue, and is directed to providing a negative electrode for a secondary battery, and a secondary battery that are each able to increase the battery capacity and improve the electric resistance characteristic, the cyclability characteristic, or both according to an embodiment.
A negative electrode for a secondary battery according to an embodiment of the technology includes a silicon-containing material and a plurality of single-walled carbon nanotubes. The single-walled carbon nanotubes have a maximum outer diameter of 5 nm or less.
A secondary battery according to an embodiment of the technology includes a positive electrode, an electrolytic solution, and a negative electrode. The negative electrode includes a configuration similar to the configuration of the negative electrode for the secondary battery according to an embodiment of the technology described above.
The term âsilicon-containing materialâ used herein is a generic term for a material including silicon (Si) as a constituent element. Thus, the silicon-containing material may be a simple substance of silicon, a compound of silicon, an alloy of silicon, or a mixture of two or more thereof.
According to the negative electrode for the secondary battery or the secondary battery of an embodiment of the technology, the negative electrode includes the silicon-containing material and the plurality of single-walled carbon nanotubes. The single-walled carbon nanotubes have a maximum outer diameter of 5 nm or less. Accordingly, it is possible to increase the battery capacity and improve the electric resistance characteristic, the cyclability characteristic, or both.
Note that effects of the technology are not necessarily limited to the effects described above and may include any of a series of suitable effects including described below in relation to the technology.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a perspective view of a configuration of a secondary battery of a laminated-film type according to an embodiment of the technology.
FIG. 2 is a sectional view of a configuration of a wound electrode body illustrated in FIG. 1 .
FIG. 3 is a plan view of a configuration of each of a positive electrode and a negative electrode illustrated in FIG. 2 .
FIG. 4 is a plan view for describing an orientation of a negative electrode conductor in the secondary battery according to an embodiment of the technology.
FIG. 5 is a plan view for describing an orientation of the negative electrode conductor in a first comparative example.
FIG. 6 is a plan view for describing an orientation of the negative electrode conductor in a second comparative example.
FIG. 7 is a flowchart for describing a procedure for preparing a negative electrode mixture slurry.
FIG. 8 is a sectional view of a configuration of another secondary battery of a cylindrical type according to an embodiment of the technology.
FIG. 9 is a perspective view of a configuration of a secondary battery of another laminated-film type according to a modification according to an embodiment.
FIG. 10 is a sectional view of a configuration of a stacked electrode body illustrated in FIG. 9 .
FIG. 11 is a block diagram illustrating a configuration of an application example of the secondary battery, which is a battery pack including a single battery.
FIG. 12 is a block diagram illustrating a configuration of an application example of the secondary battery, which is a battery pack including an assembled battery.
FIG. 13 is a block diagram illustrating a configuration of an application example of the secondary battery, which is an electric vehicle.
FIG. 14 illustrates a RBM spectrum and a five-point average differential spectrum of a negative electrode active material layer in Experiment example 3 in which the negative electrode conductor was single-walled carbon nanotubes, the negative electrode conductor was introduced at earlier introduction, and no five-point average differential peak was detected.
FIG. 15 illustrates a RBM spectrum and a five-point average differential spectrum of a negative electrode active material layer in Experiment example 2 in which the negative electrode conductor was single-walled carbon nanotubes, the negative electrode conductor was introduced at later introduction, and a five-point average differential peak was detected.
FIG. 16 illustrates a RBM spectrum and a five-point average differential spectrum of a single-walled carbon nanotube in which a five-point average differential peak was detected.
FIG. 17 illustrates a RBM spectrum and a five-point average differential spectrum of a negative electrode active material layer in a reference example in which no negative electrode conductor was introduced and no five-point average differential peak was detected.
DETAILED DESCRIPTION
One or more embodiments of the present technology are described below in detail with reference to the drawings.
First, a description is given of a secondary battery according to an embodiment of the technology. Note that a negative electrode for a secondary battery according to an embodiment of the technology (hereinafter simply referred to as a ânegative electrodeâ) is a part or one component of the secondary battery described here, and is thus described together below.
The secondary battery described here is a secondary battery that obtains a battery capacity by utilizing insertion and extraction of an electrode reactant. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte.
In the secondary battery, a charge capacity of the negative electrode is greater than a discharge capacity of the positive electrode in order to prevent accidental precipitation of the electrode reactant on a surface of the negative electrode in the middle of charging. In other words, an electrochemical capacity per unit area of the negative electrode is set to be greater than an electrochemical capacity per unit area of the positive electrode.
The electrode reactant is not limited to a particular kind and may be a light metal such as an alkali metal or an alkaline earth metal. In the following, a description is given of an example case where the electrode reactant is lithium. A secondary battery that utilizes insertion and extraction of lithium serving as the electrode reactant is a so-called lithium-ion secondary battery.
First, a secondary battery of a laminated-film type (a so-called laminated cell) is described. The secondary battery of the laminated-film type includes an outer package member having softness or flexibility, that is, an outer package film 20 as an outer package member for containing a battery device.
FIG. 1 is a perspective view of a configuration of the secondary battery of the laminated-film type. FIG. 2 illustrates a sectional configuration of a wound electrode body 10 illustrated in FIG. 1 . FIG. 3 illustrates a plan configuration of each of a positive electrode 11 and a negative electrode 12 illustrated in FIG. 2 .
Note that FIG. 1 illustrates a state where the wound electrode body 10 and the outer package film 20 are separated away from each other. FIG. 2 illustrates only a portion of the wound electrode body 10 . FIG. 3 illustrates a state where the positive electrode 11 and the negative electrode 12 are separated away from each other. In FIG. 3 , the positive electrode 11 and the negative electrode 12 are each reduced in size in a longitudinal direction.
As illustrated in FIG. 1 , the secondary battery has the outer package film 20 having a pouch-shape in which a battery device of a wound type (the wound electrode body 10 ) is contained. A positive electrode lead 14 and a negative electrode lead 15 are coupled to the wound electrode body 10 . The positive electrode lead 14 and the negative electrode lead 15 are each led out from inside to outside the outer package film 20 in a similar direction.
The outer package film 20 is a single film foldable in a direction of an arrow R indicated by a dash-dot-dash line illustrated in FIG. 1 . The outer package film 20 has a depression 20 U. The depression 20 U is a so-called deep drawn part designed to contain the wound electrode body 10 therein.
Specifically, the outer package film 20 is a laminated film including three layers: a fusion-bonding layer, a metal layer, and a surface protective layer that are laminated in this order from an inner side. In a state where the outer package film 20 is folded in the direction of the arrow R, the outer edges of the fusion-bonding layer are fusion-bonded to each other. The fusion-bonding layer includes a polymer compound such as polypropylene. The metal layer includes a metal material such as aluminum. The surface protective layer includes a polymer compound such as nylon. Note that the number of layers laminated into the outer package film 20 is not limited to three. The outer package film 20 may include one layer (a single layer), two layers, or four or more layers.
A sealing film 21 is interposed between the outer package film 20 and the positive electrode lead 14 , and a sealing film 22 is interposed between the outer package film 20 and the negative electrode lead 15 . The sealing films 21 and 22 are members for preventing outside air from entering. The sealing films 21 and 22 include, without limitation, a polyolefin resin having adherence to the positive electrode lead 14 and the negative electrode lead 15 . Examples of the polyolefin resin include polyethylene, polypropylene, modified polyethylene, and modified polypropylene. Note that the sealing film 21 , the sealing film 22 , or both may be omitted.
As illustrated in FIGS. 1 and 2 , the wound electrode body 10 includes the positive electrode 11 , the negative electrode 12 , a separator 13 , and an electrolytic solution. The electrolytic solution is a liquid electrolyte. In the wound electrode body 10 , the positive electrode 11 and the negative electrode 12 are stacked on each other with the separator 13 interposed therebetween, and the stack of the positive electrode 11 , the negative electrode 12 , and the separator 13 is wound. The positive electrode 11 , the negative electrode 12 , and the separator 13 are each impregnated with the electrolytic solution.
As illustrated in FIG. 2 , the positive electrode 11 includes a positive electrode current collector 11 A, and two positive electrode active material layers 11 B provided on respective opposite sides of the positive electrode current collector 11 A. However, the positive electrode active material layer 11 B may be provided on only one of the opposite sides of the positive electrode current collector 11 A.
The positive electrode current collector 11 A includes one or more of electrically conductive materials including, without limitation, aluminum, nickel, and stainless steel. The positive electrode active material layer 11 B includes one or more of positive electrode active materials into which lithium is insertable and from which lithium is extractable. The positive electrode active material layer 11 B may further include a material such as a positive electrode binder or a positive electrode conductor.
Although the positive electrode active material is not limited to a particular kind, the positive electrode active material is a lithium-containing compound such as a lithium-containing transition metal compound. The lithium-containing transition metal compound includes lithium and one or more of transition metal elements, and may further include one or more of other elements. The other elements are not limited to particular kinds as long as they are one or more of any elements excluding a transition metal element. In particular, it is preferable that the other elements be elements belonging to Groups 2 to 15 in the long period periodic table. Note that the lithium-containing
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a continuation of PCT patent application no. PCT/JP2020/039452, filed on Oct. 21, 2020, which claims priority to Japanese patent application no. JP2019-195409, filed on Oct. 28, 2019, the entire contents of which are being incorporated herein by reference.
BACKGROUND
The present technology relates to a negative electrode for a secondary battery, and a secondary battery.
Various kinds of electronic equipment, including mobile phones, have been widely used. Such widespread use has promoted the development of a secondary battery that is smaller in size and lighter in weight and allows for a higher energy density, as a power source. The secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution. The negative electrode includes a negative electrode active material and a negative electrode binder.
A configuration of the secondary battery influences a battery characteristic. Accordingly, the configuration of the secondary battery has been considered in various ways. For example, silicon monoxide is used as the negative electrode active material, and a single-walled carbon nanotube is used as a negative electrode conductor in order to obtain, for example, sufficient charge and discharge capacities. Further, a negative electrode active material which includes composite particles and carbon nanotubes is used in order to obtain, for example, a superior lifetime characteristic. The carbon nanotubes in the negative electrode active material are directly grown on surfaces of the composite particles that include, for example, silicon and natural graphite.
SUMMARY
The present application relates to a negative electrode for a secondary battery, and a secondary battery.
Consideration has been given in various ways to solve problems of the secondary battery; however, a battery capacity characteristic, an electric resistance characteristic, and a cyclability characteristic of the secondary battery each still remain insufficient. Accordingly, there is still room for improvement in terms of those characteristics.
The present technology has been made in view of such an issue, and is directed to providing a negative electrode for a secondary battery, and a secondary battery that are each able to increase the battery capacity and improve the electric resistance characteristic, the cyclability characteristic, or both according to an embodiment.
A negative electrode for a secondary battery according to an embodiment of the technology includes a silicon-containing material and a plurality of single-walled carbon nanotubes. The single-walled carbon nanotubes have a maximum outer diameter of 5 nm or less.
A secondary battery according to an embodiment of the technology includes a positive electrode, an electrolytic solution, and a negative electrode. The negative electrode includes a configuration similar to the configuration of the negative electrode for the secondary battery according to an embodiment of the technology described above.
The term âsilicon-containing materialâ used herein is a generic term for a material including silicon (Si) as a constituent element. Thus, the silicon-containing material may be a simple substance of silicon, a compound of silicon, an alloy of silicon, or a mixture of two or more thereof.
According to the negative electrode for the secondary battery or the secondary battery of an embodiment of the technology, the negative electrode includes the silicon-containing material and the plurality of single-walled carbon nanotubes. The single-walled carbon nanotubes have a maximum outer diameter of 5 nm or less. Accordingly, it is possible to increase the battery capacity and improve the electric resistance characteristic, the cyclability characteristic, or both.
Note that effects of the technology are not necessarily limited to the effects described above and may include any of a series of suitable effects including described below in relation to the technology.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a perspective view of a configuration of a secondary battery of a laminated-film type according to an embodiment of the technology.
FIG. 2 is a sectional view of a configuration of a wound electrode body illustrated in FIG. 1 .
FIG. 3 is a plan view of a configuration of each of a positive electrode and a negative electrode illustrated in FIG. 2 .
FIG. 4 is a plan view for describing an orientation of a negative electrode conductor in the secondary battery according to an embodiment of the technology.
FIG. 5 is a plan view for describing an orientation of the negative electrode conductor in a first comparative example.
FIG. 6 is a plan view for describing an orientation of the negative electrode conductor in a second comparative example.
FIG. 7 is a flowchart for describing a procedure for preparing a negative electrode mixture slurry.
FIG. 8 is a sectional view of a configuration of another secondary battery of a cylindrical type according to an embodiment of the technology.
FIG. 9 is a perspective view of a configuration of a secondary battery of another laminated-film type according to a modification according to an embodiment.
FIG. 10 is a sectional view of a configuration of a stacked electrode body illustrated in FIG. 9 .
FIG. 11 is a block diagram illustrating a configuration of an application example of the secondary battery, which is a battery pack including a single battery.
FIG. 12 is a block diagram illustrating a configuration of an application example of the secondary battery, which is a battery pack including an assembled battery.
FIG. 13 is a block diagram illustrating a configuration of an application example of the secondary battery, which is an electric vehicle.
FIG. 14 illustrates a RBM spectrum and a five-point average differential spectrum of a negative electrode active material layer in Experiment example 3 in which the negative electrode conductor was single-walled carbon nanotubes, the negative electrode conductor was introduced at earlier introduction, and no five-point average differential peak was detected.
FIG. 15 illustrates a RBM spectrum and a five-point average differential spectrum of a negative electrode active material layer in Experiment example 2 in which the negative electrode conductor was single-walled carbon nanotubes, the negative electrode conductor was introduced at later introduction, and a five-point average differential peak was detected.
FIG. 16 illustrates a RBM spectrum and a five-point average differential spectrum of a single-walled carbon nanotube in which a five-point average differential peak was detected.
FIG. 17 illustrates a RBM spectrum and a five-point average differential spectrum of a negative electrode active material layer in a reference example in which no negative electrode conductor was introduced and no five-point average differential peak was detected.
DETAILED DESCRIPTION
One or more embodiments of the present technology are described below in detail with reference to the drawings.
First, a description is given of a secondary battery according to an embodiment of the technology. Note that a negative electrode for a secondary battery according to an embodiment of the technology (hereinafter simply referred to as a ânegative electrodeâ) is a part or one component of the secondary battery described here, and is thus described together below.
The secondary battery described here is a secondary battery that obtains a battery capacity by utilizing insertion and extraction of an electrode reactant. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte.
In the secondary battery, a charge capacity of the negative electrode is greater than a discharge capacity of the positive electrode in order to prevent accidental precipitation of the electrode reactant on a surface of the negative electrode in the middle of charging. In other words, an electrochemical capacity per unit area of the negative electrode is set to be greater than an electrochemical capacity per unit area of the positive electrode.
The electrode reactant is not limited to a particular kind and may be a light metal such as an alkali metal or an alkaline earth metal. In the following, a description is given of an example case where the electrode reactant is lithium. A secondary battery that utilizes insertion and extraction of lithium serving as the electrode reactant is a so-called lithium-ion secondary battery.
First, a secondary battery of a laminated-film type (a so-called laminated cell) is described. The secondary battery of the laminated-film type includes an outer package member having softness or flexibility, that is, an outer package film 20 as an outer package member for containing a battery device.
FIG. 1 is a perspective view of a configuration of the secondary battery of the laminated-film type. FIG. 2 illustrates a sectional configuration of a wound electrode body 10 illustrated in FIG. 1 . FIG. 3 illustrates a plan configuration of each of a positive electrode 11 and a negative electrode 12 illustrated in FIG. 2 .
Note that FIG. 1 illustrates a state where the wound electrode body 10 and the outer package film 20 are separated away from each other. FIG. 2 illustrates only a portion of the wound electrode body 10 . FIG. 3 illustrates a state where the positive electrode 11 and the negative electrode 12 are separated away from each other. In FIG. 3 , the positive electrode 11 and the negative electrode 12 are each reduced in size in a longitudinal direction.
As illustrated in FIG. 1 , the secondary battery has the outer package film 20 having a pouch-shape in which a battery device of a wound type (the wound electrode body 10 ) is contained. A positive electrode lead 14 and a negative electrode lead 15 are coupled to the wound electrode body 10 . The positive electrode lead 14 and the negative electrode lead 15 are each led out from inside to outside the outer package film 20 in a similar direction.
The outer package film 20 is a single film foldable in a direction of an arrow R indicated by a dash-dot-dash line illustrated in FIG. 1 . The outer package film 20 has a depression 20 U. The depression 20 U is a so-called deep drawn part designed to contain the wound electrode body 10 therein.
Specifically, the outer package film 20 is a laminated film including three layers: a fusion-bonding layer, a metal layer, and a surface protective layer that are laminated in this order from an inner side. In a state where the outer package film 20 is folded in the direction of the arrow R, the outer edges of the fusion-bonding layer are fusion-bonded to each other. The fusion-bonding layer includes a polymer compound such as polypropylene. The metal layer includes a metal material such as aluminum. The surface protective layer includes a polymer compound such as nylon. Note that the number of layers laminated into the outer package film 20 is not limited to three. The outer package film 20 may include one layer (a single layer), two layers, or four or more layers.
A sealing film 21 is interposed between the outer package film 20 and the positive electrode lead 14 , and a sealing film 22 is interposed between the outer package film 20 and the negative electrode lead 15 . The sealing films 21 and 22 are members for preventing outside air from entering. The sealing films 21 and 22 include, without limitation, a polyolefin resin having adherence to the positive electrode lead 14 and the negative electrode lead 15 . Examples of the polyolefin resin include polyethylene, polypropylene, modified polyethylene, and modified polypropylene. Note that the sealing film 21 , the sealing film 22 , or both may be omitted.
As illustrated in FIGS. 1 and 2 , the wound electrode body 10 includes the positive electrode 11 , the negative electrode 12 , a separator 13 , and an electrolytic solution. The electrolytic solution is a liquid electrolyte. In the wound electrode body 10 , the positive electrode 11 and the negative electrode 12 are stacked on each other with the separator 13 interposed therebetween, and the stack of the positive electrode 11 , the negative electrode 12 , and the separator 13 is wound. The positive electrode 11 , the negative electrode 12 , and the separator 13 are each impregnated with the electrolytic solution.
As illustrated in FIG. 2 , the positive electrode 11 includes a positive electrode current collector 11 A, and two positive electrode active material layers 11 B provided on respective opposite sides of the positive electrode current collector 11 A. However, the positive electrode active material layer 11 B may be provided on only one of the opposite sides of the positive electrode current collector 11 A.
The positive electrode current collector 11 A includes one or more of electrically conductive materials including, without limitation, aluminum, nickel, and stainless steel. The positive electrode active material layer 11 B includes one or more of positive electrode active materials into which lithium is insertable and from which lithium is extractable. The positive electrode active material layer 11 B may further include a material such as a positive electrode binder or a positive electrode conductor.
Although the positive electrode active material is not limited to a particular kind, the positive electrode active material is a lithium-containing compound such as a lithium-containing transition metal compound. The lithium-containing transition metal compound includes lithium and one or more of transition metal elements, and may further include one or more of other elements. The other elements are not limited to particular kinds as long as they are one or more of any elements excluding a transition metal element. In particular, it is preferable that the other elements be elements belonging to Groups 2 to 15 in the long period periodic table. Note that the lithium-containing transition metal compound may be an oxide, or may be, for example, one of a phosphoric acid compound, a silicic acid compound, or a boric acid compound.
Specific examples of the oxide include LiNiO 2 , LiCoO 2 , LiCo 0.98 Al 0.01 Mg 0.01 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.8 Co 0.15 Al 0.05 O 2 , LiNi 0.33 Co 0.33 Mn 0.33 O 2 , Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O 2 , Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O 2 , and LiMn 2 O 4 . Specific examples of the phosphoric acid compound include LiFePO 4 , LiMnPO 4 , LiFe 0.5 Mn 0.5 PO 4 , and LiFe 0.3 Mn 0.7 PO 4 .
The positive electrode binder includes one or more of materials including, without limitation, a synthetic rubber and a polymer compound. Examples of the synthetic rubber include a styrene-butadiene-based rubber, a fluorine-based rubber, and ethylene propylene diene. Examples of the polymer compound include polyvinylidene difluoride and polyimide.
The positive electrode conductor includes an electrically conductive material such as a carbon material. Examples of the carbon material include graphite, carbon black, acetylene black, and Ketjen black. The positive electrode conductor may be a material such as a metal material or an electrically conductive polymer as long as the material has an electrically conductive property.
The positive electrode active material layer 11 B is provided on a portion of the positive electrode current collector 11 A on one side of the positive electrode current collector 11 A. Accordingly, a portion of the positive electrode current collector 11 A on which the positive electrode active material layer 11 B is not provided is exposed without being covered with the positive electrode active material layer 11 B.
Specifically, as illustrated in FIG. 3 , the positive electrode current collector 11 A extends in a longitudinal direction (X-axis direction) and includes a covered portion 11 AX and paired uncovered portions 11 AY. The covered portion 11 AX is a portion which is located at the middle portion of the positive electrode current collector 11 A in the longitudinal direction and on which the positive electrode active material layer 11 B is formed. The paired uncovered portions 11 AY are portions which are located at respective ends of the positive electrode current collector 11 A in the longitudinal direction and on which the positive electrode active material layer 11 B is not formed. Accordingly, the covered portion 11 AX is covered with the positive electrode active material layer 11 B, whereas the paired uncovered portions 11 AY are exposed without being covered with the positive electrode active material layer 11 B. In FIG. 3 , the positive electrode active material layer 11 B is slightly shaded.
As illustrated in FIG. 2 , the negative electrode 12 includes a negative electrode current collector 12 A, and two negative electrode active material layers 12 B provided on respective opposite sides of the negative electrode current collector 12 A. However, the negative electrode active material layer 12 B may be provided only on one of the opposite sides of the negative electrode current collector 12 A.
The negative electrode current collector 12 A includes one or more of electrically conductive materials including, without limitation, copper, aluminum, nickel, and stainless steel. The negative electrode active material layer 12 B includes a negative electrode active material into which lithium is insertable and from which lithium is extractable, and a negative electrode conductor. The negative electrode active material layer 12 B may further include materials including, without limitation, a negative electrode binder.
The negative electrode active material includes a silicon-containing material. A reason for this is that a high theoretical capacity (i.e., battery capacity) is obtained.
As described above, the term âsilicon-containing materialâ is a generic term for a material including silicon as a constituent element. The silicon-containing material may be a simple substance of silicon, a compound of silicon, an alloy of silicon, or a mixture of two or more thereof. Specific examples of the alloy of silicon and the compound of silicon include SiB 4 , SiB 6 , Mg 2 Si, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , CaSi 2 , CrSi 2 , Cu 5 Si, FeSi 2 , MnSi 2 , NbSi 2 , TaSi 2 , VSi 2 , WSi 2 , ZnSi 2 , SiC, Si 3 N 4 , Si 2 N 2 O, SiO v (0<v<2), and LiSiO. Note that the range of v may be 0.2<v<1.4.
It is preferable, in particular, the silicon-containing material include silicon oxide represented by SiO v (0<v<2) described above. It is more preferable that the silicon-containing material include SiO. A reason for this is that the amount of expansion or contraction at the time of charging and discharging is relatively small.
The negative electrode active material may further include one or more of other materials including, without limitation, a carbon-containing material and a metal-based material. Note that the silicon-containing material described above is excluded from the metal-based material described here.
The term âcarbon-containing materialâ is a generic term for a material including carbon as a constituent element. Note that a material including both silicon and carbon as constituent elements shall be classified as the silicon-containing material, not as the carbon material. Additionally, the negative electrode conductor (single-walled carbon nanotubes) described below shall be excluded from the carbon-containing material described here. Specific examples of the carbon-containing material include graphitizable carbon, non-graphitizable carbon, and graphite. The graphite may be natural graphite, artificial graphite, or both. The graphite is a carbon material having an average interplanar spacing d002 of less than 0.34 nm. The graphitizable carbon is a carbon material having an average interplanar spacing d002 of 0.34 nm or greater and 0.36 nm or less. The non-graphitizable carbon is a carbon material having an average interplanar spacing d002 of 0.37 nm or greater.
It is preferable, in particular, that the carbon-containing material include graphite in order to increase the battery capacity and in order to form an electrically conductive network. Further, it is preferable that the carbon-containing material include a material that includes graphite particles of which surfaces are covered with a covering material, that is, covered particles, in order to reduce reactivity of the surface of the graphite to the electrolytic solution. The covering material includes one or more of materials including, without limitation, graphitizable carbon and non-graphitizable carbon. The thickness of the covering material is not limited to a particular thickness. However, it is preferable, in particular, that the thickness of the covering material be 10% or less of the radius of the covered particle, i.e., 10% or less of the distance from the surface of the covered particle to the center of the covered particle.
The term âmetal-based materialâ is a generic term for a material that includes one or more of metal elements and metalloid elements that are each able to form an alloy with lithium, as a constituent element or constituent elements. The metal-based material may thus be a simple substance, an alloy, a compound, or a mixture of two or more thereof. The metal-based material may include one or more of non-metallic elements. Specific examples of the metal element and the metalloid element include tin.
It is preferable, in particular, that the negative electrode active material include the carbon-containing material together with the silicon-containing material. A reason for this is that expansion or contraction of the negative electrode active material layer 12 B is reduced at the time of charging and discharging while a high battery capacity is secured, as compared with a case where the negative electrode active material includes only the silicon-containing material.
The negative electrode conductor includes single carbon nanotubes, which are carbon substances each having a fiber shape (a tubular shape), i.e., so-called single-walled carbon nanotubes (SWCNT). Thus, the negative electrode active material layer 12 B includes the single-walled carbon nanotubes serving as the negative electrode conductor, together with the silicon-containing material serving as the negative electrode active material. A reason for this is that, in a case where the negative electrode active material is in the form of particles, the particles of the negative electrode active material are electrically coupled to each other via the single-walled carbon nanotubes. This increases electron conductivity between the particles of the negative electrode active material, resulting in an increase in electrical conductivity of the negative electrode active material layer 12 B.
The number of the single-walled carbon nanotubes per unit weight is greater than the number of multi-walled carbon nanotubes (MWCNT) per unit weight. Accordingly, using the single-walled carbon nanotubes as the negative electrode conductor sufficiently increases the electrical conductivity of the negative electrode active material layer 12 B.
The negative electrode conductor may further include the multi-walled carbon nanotubes described above in addition to the single-walled carbon nanotubes. The multi-walled carbon nanotubes encompass nanotubes including double-walled (DW) carbon nanotubes.
The single-walled carbon nanotubes have a maximum outer diameter of 5 nm or less. That is, although the outer diameter (thickness) of each of the single-walled carbon nanotubes is not limited to a particular outer diameter, a maximum value of the outer diameters of the single-walled carbon nanotubes is 5 nm or less. Note that, the single-walled carbon nanotubes each have an outer diameter of approximately 1 nm to approximately 2 nm. The double-walled carbon nanotubes each have an outer diameter of approximately 5 nm to approximately 6 nm. The multi-walled carbon nanotubes each have an outer diameter of 10 nm to 200 nm both inclusive.
A reason for this is that the dispersibility of the single-walled carbon nanotubes in the negative electrode active material layer 12 B is secured and the particles of the negative electrode active material are thus easily electrically coupled to each other via the single-walled carbon nanotubes. This markedly increases the electron conductivity between the particles of the negative electrode material, and thus markedly increases the electrical conductivity of the negative electrode active material layer 12 B, as compared with a case where the dispersibility of the single-walled carbon nanotubes in the negative electrode active material layer 12 B is insufficient.
That is, in the case where the dispersibility of the single-walled carbon nanotubes in the negative electrode active material layer 12 B is insufficient, the single-walled carbon nanotubes are easily entangled with each other. This causes the outer diameter of the single-walled carbon nanotubes to increase easily, resulting in a maximum outer diameter of greater than 5 nm. In contrast, in a case where the dispersibility of the single-walled carbon nanotubes in the negative electrode active material layer 12 B is sufficient, the single-walled carbon nanotubes are prevented from being easily entangled with each other. This helps to prevent an increase in the outer diameter of the single-walled carbon nanotubes, resulting in a maximum outer diameter of 5 nm or less.
The maximum outer diameter of the single-walled carbon nanotubes is determined as follows. First, the negative electrode active material layer 12 B is observed with a microscope such as a scanning electron microscope (SEM). Thereafter, the outer diameter of the single-walled carbon nanotube is measured at ten different points on the basis of the result of observation (a micrograph) of the negative electrode active material layer 12 B. Lastly, a maximum value is identified from the outer diameters measured at the ten points, and is set as the maximum outer diameter.
For the secondary battery described here, it is preferable that a physical property (the presence or absence of a five-point average differential peak described below) of the negative electrode 12 be properly controlled by controlling the orientation of the negative electrode conductor (the single-walled carbon nanotubes) into an appropriate state in order to further increase the electrical conductivity of the negative electrode 12 (the negative electrode active material layer 12 B). The physical property of the negative electrode 12 is to be described in detail later.
The content of the negative electrode conductor (the single-walled carbon nanotubes) in the negative electrode active material layer 12 B is not limited to a particular content. However, it is preferable, in particular, that the content of the negative electrode conductor (the single-walled carbon nanotubes) be 0.01 wt % to 0.03 wt % both inclusive. A reason for this is that the single-walled carbon nanotubes are prevented from being easily entangled with each other, and it thus becomes easier to control the orientations of the single-walled carbon nanotubes into appropriate states.
The negative electrode active material layer 12 B is provided over the entire negative electrode current collector 12 A on one side of the negative electrode current collector 12 A. Accordingly, the negative electrode current collector 12 A is entirely covered with the negative electrode active material layer 12 B without being exposed.
Specifically, as illustrated in FIG. 3 , the negative electrode current collector 12 A extends in the longitudinal direction (X-axis direction), and the negative electrode active material layer 12 B includes paired unopposed portions 12 BZ. The paired unopposed portions 12 BZ are opposed to the paired uncovered portions 11 AY. That is, the paired unopposed portions 12 BZ are not opposed to the positive electrode active material layer 11 B and thus do not contribute to charging and discharging reactions. In FIG. 3 , the negative electrode active material layer 12 B is darkly shaded.
The negative electrode active material layer 12 B is entirely provided on the negative electrode current collector 12 A, whereas the positive electrode active material layer 11 B is provided on only a portion (the covered portion 11 AX) of the positive electrode current collector 11 A, in order to prevent lithium extracted from the positive electrode active material layer 11 B at the time of charging from precipitating on the surface of the negative electrode 12 .
As illustrated in FIG. 2 , the separator 13 is interposed between the positive electrode 11 and the negative electrode 12 . The separator 13 allows lithium to pass therethrough while preventing short circuiting between the positive electrode 11 and the negative electrode 12 caused by contact between the positive electrode 11 and the negative electrode 12 . The separator 13 is a porous film including one or more of synthetic resins including, without limitation, polytetrafluoroethylene, polypropylene, and polyethylene. The separator 13 may be a multi-layer film including two or more of such porous films stacked on each other.
The electrolytic solution includes a solvent and an electrolyte salt. Note that the electrolytic solution may further include various additives.
The solvent includes one or more of non-aqueous solvents (organic solvents). An electrolytic solution including the non-aqueous solvent(s) is a so-called non-aqueous electrolytic solution.
Examples of the non-aqueous solvent include esters and ethers. More specifically, examples of the non-aqueous solvent include a carbonic-acid-ester-based compound, a carboxylic-acid-ester-based compound, and a lactone-based compound. Examples of the carbonic-acid-ester-based compound include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of the carboxylic-acid-ester-based compound include ethyl acetate, ethyl propionate, and ethyl trimethylacetate. Examples of the lactone-based compound include γ-butyrolactone and γ-valerolactone. Examples of the ethers other than the lactone-based compounds described above include 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane.
Examples of the non-aqueous solvent further include an unsaturated cyclic carbonic acid ester, a halogenated carbonic acid ester, a sulfonic acid ester, a phosphoric acid ester, an acid anhydride, a nitrile compound, and an isocyanate compound. A reason for this is that the chemical stability of the electrolytic solution increases. Specific examples of the non-aqueous solvent include vinylene carbonate, vinylethylene carbonate, methylene ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, 1,3-propane sultone, trimethyl phosphate, succinic anhydride, sulfobenzoic anhydride, acetonitrile, succinonitrile, and hexamethylene diisocyanate.
The electrolyte salt includes one or more of light metal salts including, without limitation, a lithium salt. Examples of the lithium salt include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(fluorosulfonyl)imide (LiN(FSO 2 ) 2 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 ) 2 ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF 3 SO 2 ) 3 ), and lithium bis(oxalato)borate (LiB(C 2 O 4 ) 2 ). Although the content of the electrolyte salt is not limited to a particular content, the content of the electrolyte salt is 0.3 mol/kg to 3.0 mol/kg both inclusive with respect to the solvent. A reason for this is that high ion conductivity is obtainable.
The positive electrode lead 14 is coupled to the positive electrode 11 (the positive electrode current collector 11 A), and the negative electrode lead 15 is coupled to the negative electrode 12 (the negative electrode current collector 12 A). The positive electrode lead 14 includes one or more of electrically conductive materials including, without limitation, aluminum, and the negative electrode lead 15 includes one or more of electrically conductive materials including, without limitation, copper, nickel, and stainless steel. The positive electrode lead 14 and the negative electrode lead 15 each have a shape such as a thin plate shape or a meshed shape.
As described above, it is preferable for the secondary battery that the physical property (the presence or absence of the five-point average differential peak) of the negative electrode 12 be properly controlled by controlling the orientation of the negative electrode conductor (the single-walled carbon nanotubes) into an appropriate state in order to further increase the electrical conductivity of the negative electrode 12 (the negative electrode active material layer 12 B).
Specifically, the negative electrode active material layer 12 B is analyzed by Raman spectroscopy to thereby measure a Raman spectrum of the negative electrode active material layer 12 B in a radial breathing mode (RBM). The Raman spectrum is defined by a horizontal axis representing a Raman shift (cm â1 ) and a vertical axis representing a Raman intensity. Thereafter, five-point average differentiation of the Raman spectrum in the RBM is acquired. The five-point average differentiation is defined by a horizontal axis representing a Raman shift (cm â1 ) and a vertical axis representing of a five-point average differential value of the Raman intensity. Hereinafter, the Raman spectrum in the RBM is referred to as a âRBM spectrumâ, and the five-point average differentiation of the Raman spectrum in the RBM is referred to as a âfive-point average differential spectrumâ.
The âfive-point average differentiationâ described above is a calculation process in which the calculation of an average value of values at five latest points (five Raman intensities) based on a plurality of pieces of data (Raman intensities) of the RBM spectrum and the calculation of a differential value of the average value are repeated.
A peak is thereby detected in the five-point average differential spectrum in the range of Raman shift from 165 cm â1 to 185 cm â1 both inclusive. Hereinafter, the peak described here is referred to as a âfive-point average differential peakâ.
That is, in a case where the orientations of the single-walled carbon nanotubes in the negative electrode active material layer 12 B are controlled into appropriate states, the five-point average differential peak is detected in the five-point average differential spectrum. In contrast, in a case where the orientations of the single-walled carbon nanotubes in the negative electrode active material layer 12 B are not controlled into appropriate states, no five-point average differential peak is detected in the five-point average differential peak spectrum. Accordingly, it is possible to determine whether or not the orientations of the single-walled carbon nanotubes are controlled into appropriate states on the basis of whether or not the five-point average differential spectrum is detected.
Note that the five-point average differential peak is a peak defined by three inflection points: a first inflection point, a second inflection point, and a third inflection point. That is, the five-point average differential peak is a peak having an upward convex shape determined on the basis of the three inflection points. The first inflection point is an inflection point located at a position where the Raman shift is smaller than that at the top of the peak. A decrease in the five-point average differential value before the first inflection point turns into an increase in the five-point average differential value at the first inflection point. The second inflection point is an inflection point located at the top of the peak. An increase in the five-point average differential value before the second inflection point turns into a decrease in the five-point average differential value at the second inflection point. The third inflection point is an inflection point located at a position where the Raman shift is larger than that at the top of the peak. A decrease in the five-point average differential value before the third inflection point turns into an increase in the five-point average differential value at the third inflection point.
That is, in a case where the five-point average differential value varies so that the five-point average differential spectrum has an upward convex shape in the range of Raman shift of 165 cm â1 to 185 cm â1 both inclusive, the upward convex portion defined by the three inflection points corresponds to the five-point average differential peak; whereas an upward convex portion defined by two or less inflection points does not correspond to the five-point average differential peak.
Now, the orientation of the negative electrode conductor (the single-walled carbon nanotubes) described above is described in detail. FIGS. 4 to 6 each illustrate a plan configuration of main components of the negative electrode active material layer 12 B for describing the orientation of the negative electrode conductor. Described here as the main components of the negative electrode active material layer 12 B are negative electrode active materials 121 each including a carbon-containing material, a negative electrode active material 122 including a silicon-containing material, and negative electrode conductors 123 each including a single-walled carbon nanotube.
FIG. 4 illustrates a case where the physical property of the negative electrode 12 is properly controlled (the present embodiment). FIGS. 5 and 6 illustrate respective cases where the physical property of the negative electrode 12 is not properly controlled (a first comparative example and a second comparative example). Note that, in each of FIGS. 4 to 6 , the negative electrode active materials 121 are slightly shaded, whereas the negative electrode active material 122 is darkly shaded.
In the present embodiment in which the amount of the negative electrode conductors 123 in a negative electrode mixture slurry is an appropriate amount in a manufacturing process of the negative electrode 12 (a forming process of the negative electrode active material layer 12 B) described later, the negative electrode conductors 123 are dispersed substantially uniformly in the negative electrode mixture slurry. This prevents the single-walled carbon nanotubes from being easily entangled with each other as described above, resulting in a maximum outer diameter of 5 nm or less. Further, since the negative electrode conductors 123 are appropriately dispersed in the negative electrode active material layer 12 B as illustrated in FIG. 4 , the orientation of each of the negative electrode conductors 123 is controlled into an appropriate state.
In this case, the negative electrode conductors 123 are each in line contact with each of the negative electrode active materials 121 and 122 because the negative electrode conductors 123 are dispersed substantially uniformly. The negative electrode active materials 121 are thus easily electrically coupled to each other via the negative electrode conductors 123 , and the negative electrode active materials 121 and 122 are easily electrically coupled to each other via the negative electrode conductors 123 . This increases the electrical conductivity of the negative electrode 12 . The physical property of the negative electrode 12 is thus properly controlled, and therefore the five-point average differential peak is detected in the five-point average differential spectrum in the range of Raman shift of 165 cm â1 to 185 cm â1 both inclusive.
In contrast, in a case where the negative electrode conductors 123 in an appropriate amount are not dispersed substantially uniformly in the negative electrode mixture slurry, the negative electrode conductors 123 are not appropriately dispersed in the negative electrode active material layer 12 B, as illustrated in FIGS. 5 and 6 . The orientation of each of the negative electrode conductors 123 is therefore not controlled into an appropriate state.
Specifically, in the first comparative example in which the amount of the negative electrode conductors 123 is insufficient, as illustrated in FIG. 5 , the negative electrode conductors 123 are each in line contact with each of the negative electrode active materials 121 and 122 ; however, the negative electrode conductors 123 are localized only in the vicinity of the negative electrode active material 122 due to poor dispersion of the negative electrode conductors 123 . As a result, although it is easy for the negative electrode active materials 121 and 122 to be electrically coupled to each other via the negative electrode conductors 123 , it is difficult for the negative electrode active materials 121 to be electrically coupled to each other via the negative electrode conductors 123 . This decreases the electrical conductivity of the negative electrode 12 . The physical property of the negative electrode 12 is thus not properly controlled, and therefore no five-point average differential peak is detected in the five-point average differential spectrum in the range of Raman shift of 165 cm â1 to 185 cm â1 both inclusive.
In the second comparative example in which the amount of the negative electrode conductors 123 is excessive, as illustrated in FIG. 6 , the negative electrode conductors 123 are each in line contact with each of the negative electrode active materials 121 and 122 due to substantially uniform dispersion of the negative electrode conductors 123 . This allows the negative electrode active materials 121 to be easily electrically coupled to each other via the negative electrode conductors 123 and allows the negative electrode active materials 121 and 122 to be easily electrically coupled to each other via the negative electrode conductors 123 .
However, in this case where the amount of the negative electrode conductors 123 is excessive, the single-walled carbon nanotubes are easily entangled with each other, resulting in a maximum outer diameter of greater than 5 nm, as described above. Moreover, a solid electrolyte interphase (SEI) film is formed on the surface of each of the negative electrode conductors 123 due to excessive dispersion of the negative electrode conductors 123 , resulting in an increase in the total amount of the SEI films formed in the negative electrode active material layer 12 B. This increases the reaction resistance of the negative electrode 12 , which rather decreases the electrical conductivity of the negative electrode 12 . The physical property of the negative electrode 12 is thus not properly controlled, and therefore no five-point average differential peak is detected in the five-point average differential spectrum in the range of Raman shift of 165 cm â1 to 185 cm â1 both inclusive.
Although a Raman spectroscopic apparatus used to measure the RBM spectrum is not limited to a particular type, the Raman spectroscopic apparatus is, for example, a laser Raman microscope RAMAN-11 manufactured by Nanophoton Corporation. Although measurement conditions are not limited to particular conditions, an excitation wavelength is set to 532 nm, and grating is set to 600 gr/mm. The Raman spectroscopic apparatus is able to acquire the five-point average differential spectrum on the basis of the RBM spectrum by using a calculation function for conducting a calculation process in which the differential value described above is calculated.
As described above, whether or not the five-point average differential peak is detected in the five-point average differential spectrum is determined on the basis of the forming method of the negative electrode active material layer 12 B (including a procedure for preparing the negative electrode mixture slurry used to form the negative electrode active material layer 12 B). The forming method of the negative electrode active material layer 12 B is to be described later.
In a case of analyzing the negative electrode active material layer 12 B by Raman spectroscopy to measure the RBM spectrum, the secondary battery is disassembled to thereby collect the negative electrode active material layer 12 B, a measurement target, from the secondary battery.
In this case, it is preferable to use a secondary battery whose number of charging and discharging cycles (the number of charging and discharging reactions repeated) is 50 or less, as the secondary battery for measurement. A reason for this is that the orientations of the single-walled carbon nanotubes are easily maintained in the states at the time of formation of the negative electrode 12 without being influenced by the charging and discharging reactions. This allows the orientations of the single-walled carbon nanotubes to be examined in a stable and reproducible manner.
In a case where the number of charging and discharging cycles of the secondary battery is unknown, i.e., where it is difficult to identify the number of charging and discharging cycles of the secondary battery ex-post facto, it is preferable to use a new (unopened) secondary battery rather than a used (opened) secondary battery. The number of charging and discharging cycles of a new secondary battery is not much more than several cycles at most. Using a new secondary battery thus allows the orientations of the single-walled carbon nanotubes to be examined in a stable and reproducible manner.
Further, it is preferable to use the unopposed portion 12 BZ illustrated in FIG. 3 as the negative electrode active material layer 12 B for measurement. A reason for this is that the unopposed portion 12 BZ has little involvement in the charging and discharging reactions and the orientations of the single-walled carbon nanotubes are thus easily maintained in the states at the time of formation of the negative electrode 12 without being influenced by the charging and discharging reactions. This allows the orientations of the single-walled carbon nanotubes to be examined in a stable and reproducible manner.
Upon charging the secondary battery, lithium is extracted from the positive electrode 11 , and the extracted lithium is inserted into the negative electrode 12 via the electrolytic solution. Upon discharging the secondary battery, lithium is extracted from the negative electrode 12 , and the extracted lithium is inserted into the positive electrode 11 via the electrolytic solution.
In a case of manufacturing the secondary battery, the positive electrode 11 and the negative electrode 12 are fabricated, following which the secondary battery is assembled according to a procedure described below.
First, the positive electrode active material is mixed with, on an as-needed basis, a material such as the positive electrode binder or the positive electrode conductor to thereby obtain a positive electrode mixture. Thereafter, the positive electrode mixture is put into a solvent such as an organic solvent to thereby prepare a positive electrode mixture slurry in a paste form. Lastly, the positive electrode mixture slurry is applied on each of opposite sides of the positive electrode current collector 11 A to thereby form the positive electrode active material layer 11 B. Thereafter, the positive electrode active material layer 11 B may be compression-molded by a roll pressing machine. In this case, the positive electrode active material layer 11 B may be heated. The positive electrode active material layer 11 B may be compression-molded multiple times. The positive electrode active material layer 11 B is thereby formed on each of the opposite sides of the positive electrode current collector 11 A. As a result, the positive electrode 11 is fabricated.
FIG. 7 il
CLAIMS
Claims ( 9 )
The invention claimed is:
1 . A secondary battery comprising:
a positive electrode; a negative electrode including a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode current collector material, a first negative electrode active material, and a second negative electrode active material, wherein the first negative electrode active material includes a silicon-containing material, wherein the second negative electrode active material includes a carbon-containing material, and wherein the negative electrode current collector material is a plurality of single-walled carbon nanotubes, the plurality of single-walled carbon nanotubes are entangled to define an entangled single-walled carbon nanotubes structure, wherein the entangled single-walled carbon nanotubes structure having a maximum outer diameter of 5 nanometers or less, a peak is detected in a range of Raman shift of 165 cm â1 or greater and 185 cm â1 or less in five-point average differentiation of a Raman spectrum of the negative electrode active material layer in a radial breathing mode, the Raman spectrum being measured by Raman spectroscopy; and an electrolytic solution.
2 . The secondary battery according to claim 1 , wherein the silicon-containing material includes a silicon oxide represented by SiO v where v is greater than 0 and less than 2.
3 . The secondary battery according claim 1 , wherein the negative electrode active material layer includes a content of the single-walled carbon nanotubes from about 0.01 wt % to about 0.03 wt %.
4 . The secondary battery according to claim 3 , wherein the silicon-containing material is Si, SiC or a silicon oxide represented by SiO v where v is greater than 0 and less than 2, and wherein the carbon-containing material is graphite.
5 . The secondary battery according to claim 4 , wherein an amount of the silicon-containing material is from 6.5 wt % to 25 wt %, wherein an amount of the carbon-containing material is from 75 wt % to 93.5 wt %.
6 . The secondary battery according to claim 5 , wherein the silicon-containing material is SiO.
7 . A negative electrode for a secondary battery, the negative electrode comprising:
a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode current collector material, a first negative electrode active material, and a second negative electrode active material, wherein the first negative electrode active material includes a silicon-containing material, wherein the second negative electrode active material includes a carbon-containing material, and wherein the negative electrode current collector material is a plurality of single-walled carbon nanotubes, the plurality of single-walled carbon nanotubes are entangled to define an entangled single-walled carbon nanotubes structure, wherein the entangled single-walled carbon nanotubes structure having a maximum outer diameter of 5 nanometers or less, and a peak is detected in a range of Raman shift of 165 cm â1 or greater and 185 cm â1 or less in five-point average differentiation of a Raman spectrum of the negative electrode active material layer in a radial breathing mode, the Raman spectrum being measured by Raman spectroscopy.
8 . The negative electrode according to claim 7 , wherein the silicon-containing material includes a silicon oxide represented by SiO v where v is greater than 0 and less than 2.
9 . A secondary battery comprising:
a positive electrode; a negative electrode including a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode current collector material, a first negative electrode active material, and a second negative electrode active material, wherein the first negative electrode active material includes a silicon-containing material to provide a dispersed negative electrode material to which a thickening agent is added thereby providing a solid content of the dispersed negative electrode material of 35 wt % to 50 wt %, wherein the second negative electrode active material includes a carbon-containing material, wherein the negative electrode current collector material is a plurality of single-walled carbon nanotubes that are dispersed in the dispersed negative electrode material, wherein the plurality of single-walled carbon nanotubes are entangled to define an single-walled entangled carbon nanotubes structure, and wherein the entangled single-walled carbon nanotubes structure having a maximum outer diameter of 5 nanometers or less, a peak is detected in a range of Raman shift of 165 cm â1 or greater and 185 cm â1 or less in five-point average differentiation of a Raman spectrum of the negative electrode active material layer in a radial breathing mode, the Raman spectrum being measured by Raman spectroscopy; and an electrolytic solution.
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