Positive electrode for secondary battery and secondary battery
阅读说明：本技术 二次电池用正极和二次电池 (Positive electrode for secondary battery and secondary battery ) 是由 武泽秀治 盐崎朝树 于 2018-04-11 设计创作，主要内容包括：二次电池用正极具备正极集电体和正极复合材料层,正极复合材料层具有第1正极复合材料层和第2正极复合材料层。第1正极复合材料层包含由含有Ni、Co、Al和Li的化合物A构成的正极活性物质。第2正极复合材料层配置在第1正极复合材料层与正极集电体之间、且包含含有上述化合物A和比容量(mAh/g)以及平均粒径小于上述化合物A的含Li化合物B的正极活性物质。上述化合物A中,Ni相对于除Li以外的金属元素的总摩尔数的比例为82摩尔％以上,上述化合物B的平均粒径为上述化合物A的平均粒径的55％以下。(The positive electrode for a secondary battery comprises a positive electrode current collector and a positive electrode composite material layer, wherein the positive electrode composite material layer comprises a 1 st positive electrode composite material layer and a 2 nd positive electrode composite material layer. The 1 st positive electrode composite material layer contains a positive electrode active material composed of a compound a containing Ni, Co, Al, and Li. The 2 nd positive electrode composite material layer is disposed between the 1 st positive electrode composite material layer and the positive electrode current collector, and contains a positive electrode active material containing the compound A, a specific capacity (mAh/g) and a Li-containing compound B having an average particle diameter smaller than that of the compound A. In the compound A, the proportion of Ni to the total number of moles of metal elements other than Li is 82 mol% or more, and the average particle diameter of the compound B is 55% or less of the average particle diameter of the compound A.)
1. A positive electrode for a secondary battery, comprising a positive electrode current collector and a positive electrode composite material layer,
the positive electrode composite material layer has a 1 st positive electrode composite material layer and a 2 nd positive electrode composite material layer, the 1 st positive electrode composite material layer contains a positive electrode active material composed of a compound A containing Ni, Co, Al and Li, the 2 nd positive electrode composite material layer is arranged between the 1 st positive electrode composite material layer and the positive electrode current collector and contains a positive electrode active material containing the compound A and a specific capacity (mAh/g) and a Li-containing compound B having an average particle diameter smaller than that of the compound A,
in the compound A, the proportion of Ni to the total number of moles of metal elements other than Li is 82 mol% or more,
the average particle diameter of the compound B is 55% or less of the average particle diameter of the compound A.
2. The positive electrode for a secondary battery according to claim 1, wherein the compound B comprises at least any one of the following compounds: a compound containing Ni, Co, Mn and Li; a compound containing Ni, Co, Al and Li in which the proportion of Ni to the total number of moles of metal elements other than Li is less than 82 mol%.
3. The positive electrode for a secondary battery according to claim 1 or 2, wherein the content of the compound B is in a range of 1% by mass to 50% by mass with respect to the total amount of the positive electrode composite material layer.
4. The positive electrode for a secondary battery according to any one of claims 1 to 3, wherein the specific capacity of the compound B is in a range of 60% to 98% of the specific capacity of the compound A.
5. The positive electrode for a secondary battery according to any one of claims 1 to 4, wherein the 2 nd positive electrode composite material layer contains an insulating inorganic material.
6. The positive electrode for a secondary battery according to any one of claims 1 to 5, wherein a ratio of a thickness of the 1 st positive electrode composite layer to a total of thicknesses of the positive electrode composite layers is 40% to 95%, and a ratio of a thickness of the 2 nd positive electrode composite layer to a total of thicknesses of the positive electrode composite layers is 5% to 60%.
7. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte,
the positive electrode is the positive electrode for a secondary battery according to any one of claims 1 to 6.
Technical Field
The present invention relates to a technique of a positive electrode for a secondary battery and a secondary battery.
Background
For example, patent document 1 proposes a nonaqueous electrolyte secondary battery including a positive electrode for a lithium secondary battery including a current collecting substrate and a positive electrode coating film including a plurality of composite material layers on the current collecting substrate, the positive electrode coating film including two or more lithium-containing compounds having different heat generation starting temperatures as positive electrode active materials, at least 1 of the two or more lithium-containing compounds having a heat generation starting temperature of 300 ℃ or higher, and at least 1 of the lithium-containing compounds having a heat generation starting temperature of 300 ℃ or higher in a 1 st composite material layer closest to the current collecting substrate. According to the nonaqueous electrolyte secondary battery of patent document 1, it is possible to suppress an increase in battery temperature when an internal short circuit occurs.
Disclosure of Invention
However, as a positive electrode active material that can realize a high capacity of a secondary battery, a Li-containing compound having a high Ni content is useful. On the other hand, a Li-containing compound having a high Ni content is poor in thermal stability. Therefore, when a secondary battery using a Li-containing compound having a high Ni content as a positive electrode active material has an internal short circuit, the conventional technique may not sufficiently suppress an increase in battery temperature.
Accordingly, an object of the present disclosure is to provide a positive electrode for a secondary battery, which can suppress a rise in battery temperature when an internal short circuit occurs even when a Li-containing compound having a high Ni content is used as a positive electrode active material, and a secondary battery including the positive electrode.
A positive electrode for a secondary battery according to one aspect of the present disclosure includes a positive electrode current collector and a positive electrode composite material layer, the positive electrode composite material layer including a 1 st positive electrode composite material layer and a 2 nd positive electrode composite material layer, the 1 st positive electrode composite material layer including a positive electrode active material composed of a compound a containing Ni, Co, Al, and Li, the 2 nd positive electrode composite material layer being disposed between the 1 st positive electrode composite material layer and the positive electrode current collector and including a positive electrode active material containing the compound a, a specific capacity (mAh/g), and a Li-containing compound B having an average particle diameter smaller than that of the compound a, a ratio of Ni to a total number of moles of metal elements other than Li in the compound a being 82 mol% or more, and an average particle diameter of the compound B being 55% or less of the average particle diameter of the compound a.
A secondary battery according to one embodiment of the present disclosure includes a positive electrode, a negative electrode, and an electrolyte, and the positive electrode is the above-described positive electrode for a secondary battery.
According to one aspect of the present disclosure, even when a Li-containing compound having a high Ni content is used as a positive electrode active material, it is possible to suppress a rise in battery temperature when an internal short circuit occurs.
Drawings
Fig. 1 is a sectional view of a secondary battery as an example of the embodiment.
Fig. 2 is a cross-sectional view of a positive electrode as an example of the embodiment.
Detailed Description
A compound containing Ni, Co, Al, and Li in which the proportion of Ni is 82 mol% or more with respect to the total number of moles of metal elements other than Li is useful as a positive electrode active material capable of realizing a high capacity of a secondary battery. However, such a Li-containing compound having a high Ni content is likely to be thermally decomposed by heat generated by an internal short circuit of the secondary battery, and therefore, the battery temperature at the time of the internal short circuit is further increased. As a result of intensive studies, the present inventors have found that a Li-containing compound having a specific capacity smaller than that of the Li-containing compound having a high Ni content and an average particle diameter of 55% or less of the average particle diameter of the Li-containing compound having a high Ni content has extremely high thermal stability as compared with the Li-containing compound having a high Ni content, and have conceived a secondary battery positive electrode of the embodiment described below.
A positive electrode for a secondary battery according to one aspect of the present disclosure includes a positive electrode current collector and a positive electrode composite material layer, the positive electrode composite material layer including a 1 st positive electrode composite material layer and a 2 nd positive electrode composite material layer, the 1 st positive electrode composite material layer including a positive electrode active material composed of a compound a containing Ni, Co, Al, and Li, the 2 nd positive electrode composite material layer being disposed between the 1 st positive electrode composite material layer and the positive electrode current collector and including a positive electrode active material containing the compound a, a specific capacity (mAh/g), and a Li-containing compound B having an average particle diameter smaller than that of the compound a, a ratio of Ni to a total number of moles of metal elements other than Li in the compound a being 82 mol% or more, and an average particle diameter of the compound B being 55% or less of the average particle diameter of the compound a.
According to the above secondary battery positive electrode, even when a conductive foreign matter or the like having a negative electrode potential reaches the positive electrode current collector and causes an internal short circuit, since the Li-containing compound having a very high thermal stability (the compound B) is disposed around the Li-containing compound having a high Ni content (the compound a) in the 2 nd positive electrode composite material layer, thermal decomposition of the Li-containing compound having a high Ni content (the compound a) in the 2 nd positive electrode composite material layer can be suppressed. In addition, since the 2 nd positive electrode composite material layer containing the Li-containing compound (the compound B) having extremely high thermal stability prevents the Li-containing compound (the compound a) having a high Ni content in the 1 st positive electrode composite material layer from coming into direct contact with the positive electrode current collector, thermal decomposition of the Li-containing compound (the compound a) having a high Ni content in the 1 st positive electrode composite material layer is also suppressed. Therefore, in the positive electrode for a secondary battery according to one embodiment of the present disclosure, a Li-containing compound having a high Ni content is used as the positive electrode active material, but the increase in battery temperature at the time of occurrence of an internal short circuit can be suppressed.
An example of the embodiment will be described in detail below. The drawings referred to in the description of the embodiments are schematic representations, and the dimensional ratios and the like of the components depicted in the drawings may differ from the actual dimensions.
Fig. 1 is a sectional view of a secondary battery as an example of the embodiment. The secondary battery 10 shown in fig. 1 includes: a wound electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween; an electrolyte; insulating plates 17 and 18 disposed above and below the electrode body 14; and a battery case for housing the above members. The battery case is composed of a case main body 15 having a bottomed cylindrical shape and a sealing body 16. As an alternative to the wound electrode body 14, another electrode body may be used, such as a laminated electrode body in which positive electrodes and negative electrodes are alternately laminated with separators interposed therebetween. Examples of the battery case include: cylindrical, square, coin-shaped, button-shaped, and other metal cases; a resin case (laminate type battery) formed by laminating resin sheets, and the like.
The case main body 15 is, for example, a bottomed cylindrical metal container. A gasket 27 is provided between the case main body 15 and the sealing body 16 to ensure the sealing property inside the battery case. The case main body 15 preferably has a protruding portion 21 formed by pressing the side surface portion from the outside and supporting the sealing member 16, for example. The protrusion 21 is preferably formed in a ring shape along the circumferential direction of the case main body 15, and supports the sealing body 16 on the upper surface thereof.
Sealing body 16 includes filter 22 having filter opening 22a formed therein, and a valve body disposed on filter 22. The valve body closes the filter opening 22a of the filter 22, and breaks when the internal pressure of the battery rises due to heat generation caused by an internal short circuit or the like. In the present embodiment, the valve body is provided with a lower valve body 23 and an upper valve body 25, and further provided with an insulating member 24 disposed between the lower valve body 23 and the upper valve body 25, and a cap 26 having a cap opening 26 a. Each member constituting sealing body 16 has, for example, a disk shape or a ring shape, and members other than insulating member 24 are electrically connected to each other. Specifically, the filter 22 and the lower valve body 23 are joined to each other at their respective peripheral edges, and the upper valve body 25 and the cover 26 are also joined to each other at their respective peripheral edges. The lower valve body 23 and the upper valve body 25 are connected to each other at their central portions, and the insulating member 24 is interposed between the peripheral portions. When the internal pressure rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 23 is broken at the thin portion, the upper valve body 25 expands toward the cap 26 and separates from the lower valve body 23, and the electrical connection between the two is cut off.
In the secondary battery 10 shown in fig. 1, a positive electrode lead 19 attached to the positive electrode 11 extends to the sealing member 16 side through a through hole of the insulating plate 17, and a negative electrode lead 20 attached to the negative electrode 12 extends to the bottom side of the case body 15 through the outside of the insulating plate 18. For example, positive electrode lead 19 is connected to the lower surface of filter 22, which is the bottom plate of sealing body 16, by welding or the like, and cover 26, which is the top plate of sealing body 16 electrically connected to filter 22, serves as a positive electrode terminal. The negative electrode lead 20 is connected to the bottom inner surface of the case main body 15 by welding or the like, and the case main body 15 serves as a negative electrode terminal.
[ Positive electrode ]
Fig. 2 is a cross-sectional view of a positive electrode as an example of the embodiment. The positive electrode 11 includes a positive electrode current collector 30 and a positive electrode mixture layer 32. The positive electrode composite material layer 32 includes a 1 st positive electrode composite material layer 32a and a 2 nd positive electrode composite material layer 32b provided between the 1 st positive electrode composite material layer 32a and the positive electrode current collector 30.
As the positive electrode current collector 30, a foil of a metal stable in the potential range of the positive electrode, such as aluminum or an aluminum alloy, or a film in which the metal is disposed on the surface layer, may be used. The positive electrode current collector 30 has a thickness of, for example, about 10 μm to 100 μm.
The 1 st positive electrode composite material layer 32a constituting the positive electrode composite material layer 32 contains a positive electrode active material composed of a compound a containing Ni, Co, Al, and Li. In addition, the 1 st positive electrode composite material layer 32a preferably contains a binder in view of ensuring the mechanical strength of the 1 st positive electrode composite material layer 32a by binding the positive electrode active materials to each other, improving the adhesion between the 1 st positive electrode composite material layer 32a and the 2 nd positive electrode composite material layer 32b, and the like. In addition, the 1 st positive electrode composite material layer 32a preferably contains a conductive material from the viewpoint of improving the conductivity of the layer and the like.
The compound a containing Ni, Co, Al, and Li is not particularly limited as long as it contains Ni, Co, Al, and Li and the proportion of Ni to the total number of moles of metal elements other than Li is 82 mol% or more, and is represented by, for example, the following general formula.
LixNiyCoαAlβMγO2-z (1)
Wherein x, y, alpha, beta, gamma and z respectively satisfy 0.95 < x < 1.2, 0.82 < y < 1, 0 < alpha < 0.15, 0 < beta < 0.03, 0 < gamma < 0.02, y + alpha + beta + gamma is 1 and 0 < z < 0.05. In the formula, M is not particularly limited as long as it is at least 1 element other than Li, Ni, Co and Al, and examples thereof include at least 1 element selected from the group consisting of Fe, Mg, Ti, Cr, Cu, Ze, Sn, Zr, Nb, Mo, Ta, W, Na, K, Ba, Sr, Bi, Be and B.
The 2 nd positive electrode composite material layer 32b constituting the positive electrode composite material layer 32 contains a positive electrode active material containing: the compound a containing Ni, Co, Al, and Li (hereinafter sometimes referred to as compound a) and the Li-containing compound B are described above. The 2 nd positive electrode composite material layer 32b may contain a binder material, a conductive material, or the like.
The Li-containing compound B is a Li-containing compound having a specific capacity smaller than that of the compound a and having an average particle diameter smaller than that of the compound a (hereinafter sometimes referred to as compound B).
The average particle size of the compound B may be 55% or less of the average particle size of the compound a, and from the viewpoint of further improving the thermal stability of the compound B and further suppressing thermal decomposition of the compound a, the range of 1/5 to 1/2 is preferable, and the range of 1/3 to 1/2 is more preferable. The average particle diameter is a volume average particle diameter measured by a laser diffraction method, and is a median particle diameter in which a volume cumulative value in a particle diameter distribution is 50%. The average particle diameters of the compound a and the compound B can be measured, for example, using a laser diffraction scattering particle size distribution measuring instrument (manufactured by horiba ltd.).
The average particle diameters of the compound a and the compound B are not particularly limited as long as the above relationship is satisfied, and the following ranges are particularly preferable. The average particle diameter of the compound a is preferably in the range of, for example, 1 μm to 50 μm, and more preferably in the range of 5 μm to 20 μm, from the viewpoint of thermal stability of the compound a, high capacity of the battery, and the like. The average particle diameter of the compound B is preferably in the range of, for example, 0.5 to 25 μm, and more preferably in the range of 2.5 to 10 μm, from the viewpoint of the thermal stability of the compound B and the like.
The specific capacity of the compound B is not particularly limited as long as it is smaller than the specific capacity of the compound a, and from the viewpoint of further improving the thermal stability of the compound B and further suppressing the thermal decomposition of the compound a, the specific capacity of the compound a is preferably in the range of 60% to 98%, and more preferably in the range of 70% to 90%. The specific capacity of compound A (the specific capacity of compound B) means the capacitance (mAh/g) per 1g of compound A (compound B). The specific capacity measurement will be described in the examples section.
Examples of the compound B include a lithium-containing compound containing a transition metal element such as Co, Mn, and Ni, and from the viewpoint of thermal stability of the compound B, for example, at least one of the following is preferably contained: a compound containing Ni, Co, Mn and Li; a compound containing Ni, Co, Al and Li in which the proportion of Ni to the total number of moles of metal elements other than Li is less than 82 mol%; a compound comprising a core portion containing a compound of Ni, Co, Al and Li and a shell portion disposed on a surface of the core portion containing a compound of Ni, Co, Mn and Li.
From the viewpoint of thermal stability, the compound containing Ni, Co, Mn, and Li is preferably a compound containing Ni, Co, Mn, and Li in which the proportion of Ni to the total number of moles of metal elements other than Li is less than 82 mol%, and is represented by, for example, the following general formula.
LixNiyCoαMnβMγO2-z (2)
Wherein x, y, alpha, beta, gamma and z respectively satisfy 0.95 < x < 1.2, 0.3 < y < 0.82, 0 < alpha < 0.4, 0 < beta < 0.4, 0 < gamma < 0.02, y + alpha + beta + gamma is 1 and 0 < z < 0.05. y is more preferably 0.3. ltoreq. y.ltoreq.0.6. In the formula, M is not particularly limited as long as it is at least 1 element other than Li, Ni, Co and Mn, and examples thereof include at least 1 element selected from the group consisting of Fe, Mg, Ti, Cr, Cu, Ze, Sn, Zr, Nb, Mo, Ta, W, Na, K, Ba, Sr, Bi, Be and B. When the compound of the general formula (2) is used as the compound B, the average particle diameter of the compound B is preferably in the range of 1/5 to 1/2, more preferably in the range of 1/3 to 1/2.
The compound containing Ni, Co, Al, and Li, in which the proportion of Ni to the total number of moles of metal elements other than Li is less than 82 mol%, is represented by, for example, the following general formula.
LixNiyCoαAlβMγO2-z (3)
Wherein x, y, alpha, beta, gamma and z respectively satisfy 0.95 < x < 1.2, 0.6 < y < 0.82, 0 < alpha < 0.2, 0 < beta < 0.15, 0 < gamma < 0.02, y + alpha + beta + gamma is 1 and 0 < z < 0.05. In the formula, M is not particularly limited as long as it is at least 1 element other than Li, Ni, Co and Al, and examples thereof include at least 1 element selected from the group consisting of Fe, Mg, Ti, Cr, Cu, Ze, Sn, Zr, Nb, Mo, Ta, W, Na, K, Ba, Sr, Bi, Be and B.
As the compound B, for example, LiCoO can be mentioned in addition to the above-mentioned compounds2、LixCoyM1-yOz、LiMnO2、LiMn2O4、LixMn2-yMyO4、LiMPO4、Li2MPO4F (M is at least 1 of Na, Mg, Sc, Y, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb and B, x is more than 0 and less than or equal to 1.2, Y is more than 0 and less than or equal to 0.9, z is more than or equal to 2.0 and less than or equal to 2.3) and the like. Among the compounds comprising a core portion containing a compound of Ni, Co, Al and Li and a shell portion containing a compound of Ni, Co, Mn and Li disposed on the surface of the core portion, the compound of Ni, Co, Al and Li of the core portion is preferably a compound of the above general formula (1) or (3), and the compound of Ni, Co, Mn and Li of the shell portion is preferably a compound of the above general formula (2).
The content of the compound B is preferably in the range of 1 to 50 mass%, and more preferably in the range of 3 to 30 mass%, relative to the total amount of the positive electrode composite material layer 32. When the content of the compound B is less than 1% by mass, the amount of the compound B disposed around the compound a in the 2 nd positive electrode composite material layer 32B becomes small, and the thermal decomposition of the compound a at the time of the internal short circuit may not be suppressed and the battery temperature may become higher than when the content of the compound B satisfies the above range. When the content of the compound B exceeds 30 mass%, the content of the compound a in the positive electrode composite material layer 32 becomes small, and the battery capacity may be decreased as compared with the case where the content of the compound a satisfies the above range.
The content of the compound a is preferably in the range of 50 to 99 mass%, and more preferably in the range of 70 to 97 mass% with respect to the total amount of the positive electrode composite material layer 32, from the viewpoints of suppressing a decrease in battery capacity and an increase in battery temperature at the time of an internal short circuit.
The 2 nd positive electrode composite material layer 32b preferably contains an insulating inorganic material. By including the insulating inorganic material in the 2 nd positive electrode composite material layer 32b, when a conductive foreign matter or the like having a negative electrode potential reaches the positive electrode current collector 30 and an internal short circuit occurs, the 2 nd positive electrode composite material layer 32b becomes a large resistance component, and therefore it is considered that an increase in short-circuit current between the positive electrode and the negative electrode can be suppressed, and an increase in battery temperature at the time of the internal short circuit can be further suppressed.
The insulating inorganic material preferably has a thickness of, for example, 1012Examples of the inorganic material having a resistivity of not less than Ω cm include metal oxide particles, metal nitride particles, metal fluoride particles, and insulating magnetic particles. Examples of the metal oxide particles include aluminum oxide, titanium oxide, zirconium oxide, silicon oxide, manganese oxide, magnesium oxide, and nickel oxide. Examples of the metal nitride particles include boron nitride, aluminum nitride, magnesium nitride, and silicon nitride. Examples of the metal fluoride particles include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, barium fluoride, aluminum hydroxide, and boehmite. Examples of the insulating magnetic particles include Ni-Cu-Zn ferrite. The insulating inorganic material preferably contains at least one of aluminum oxide, titanium oxide, silicon oxide, and manganese oxide, and more preferably contains at least aluminum oxide, from the viewpoints of insulation, a high melting point, and a lower oxidizing power than the positive electrode active material.
The content of the insulating inorganic material is preferably in the range of 1 to 20 mass% with respect to the total amount of the positive electrode composite material layer, for example. When the content of the insulating inorganic material is less than 1% by mass, the effect of suppressing the increase in the battery temperature at the time of the internal short circuit is small as compared with the case where the above range is satisfied, and when the content of the insulating inorganic material exceeds 20% by mass, the capacity of the battery may be decreased as compared with the case where the above range is satisfied.
Examples of the conductive material used for the 1 st positive electrode composite material layer 32a and the 2 nd positive electrode composite material layer 32b include carbon-based particles such as Carbon Black (CB), Acetylene Black (AB), ketjen black, and graphite. These may be used alone or in combination of two or more.
Examples of the binder used for the 1 st positive electrode composite material layer 32a and the 2 nd positive electrode composite material layer 32b include fluorine-based resins such as Polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), Polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, and polyolefin-based resins. These resins may be mixed with carboxymethylcellulose (CMC) or a salt thereof (CMC-Na, CMC-K, CMC-NH)4And the like, and may be a partially neutralized salt), polyethylene oxide (PEO), and the like. These may be used alone or in combination of two or more.
The ratio of the thickness of the 1 st positive electrode composite material layer 32a to the total of the positive electrode composite material layer thicknesses is preferably 40% to 95%, and particularly preferably 50% to 90%. The ratio of the thickness of the 2 nd positive electrode composite material layer 32b to the total of the positive electrode composite material layer thicknesses is preferably 5% to 60%, and particularly preferably 10% to 50%.
An example of a method for producing positive electrode 11 will be described. First, a slurry for the 2 nd positive electrode composite material layer containing the compound a, the compound B, and the like is applied on the positive electrode current collector 30 and dried to form the 2 nd positive electrode composite material layer 32B, and the formed 2 nd positive electrode composite material layer 32B is rolled. Then, a slurry for a 1 st positive electrode composite material layer containing the compound a is applied on the 2 nd positive electrode composite material layer 32b and dried to form a 1 st positive electrode composite material layer 32a, and the formed 1 st positive electrode composite material layer 32a is rolled. The positive electrode 11 can be obtained as described above.
[ negative electrode ]
The negative electrode 12 includes a negative electrode current collector such as a metal foil, and a negative electrode composite material layer formed on the negative electrode current collector. As the negative electrode current collector, a foil of a metal such as copper that is stable in the potential range of the negative electrode, a film in which the metal is disposed on the surface layer, or the like can be used. The negative electrode composite layer contains, for example, a negative electrode active material, a binder, a thickener, and the like.
The negative electrode 12 is obtained, for example, as follows: the negative electrode active material layer is formed by coating a negative electrode active material slurry containing a negative electrode active material, a thickener, and a binder on a negative electrode current collector, drying the coating, and rolling the negative electrode active material slurry. The negative electrode current collector may have negative electrode composite material layers on both surfaces thereof.
The negative electrode active material is not particularly limited as long as it is a material capable of absorbing and releasing lithium ions, and examples thereof include: lithium alloys such as metallic lithium, lithium-aluminum alloys, lithium-lead alloys, lithium-silicon alloys, and lithium-tin alloys; carbon materials such as graphite, coke, and organic-substance fired bodies; SnO2、SnO、TiO2And the like. These may be used alone or in combination of two or more.
As the binder contained in the negative electrode mixture layer, a fluorine-based resin, PAN, a polyimide-based resin, an acrylic resin, a polyolefin-based resin, or the like can be used as in the case of the positive electrode. When preparing the negative electrode composite slurry using an aqueous solvent, Styrene Butadiene Rubber (SBR), CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, or the like, and may be a partially neutralized salt), polyvinyl alcohol (PVA), or the like is preferably used.
[ separator ]
As the separator 13, for example, a porous sheet having ion permeability and insulation properties is used. Specific examples of the porous sheet include a microporous film, a woven fabric, and a nonwoven fabric. As the material of the separator, olefin resin such as polyethylene and polypropylene, cellulose, and the like are preferable. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Further, a multilayer separator including a polyethylene layer and a polypropylene layer may be used, and a separator in which a surface of the separator is coated with a material such as an aramid resin or ceramics may be used.
[ electrolyte ]
The electrolyte includes a solvent and an electrolyte salt dissolved in the solvent. The electrolyte is not limited to a liquid electrolyte (nonaqueous electrolyte solution), and may be a solid electrolyte using a gel polymer or the like. Examples of the solvent include a nonaqueous solvent such as an ester, an ether, a nitrile such as acetonitrile, an amide such as dimethylformamide, and a mixed solvent of two or more of these, and water. The nonaqueous solvent may contain a halogen substituent in which at least part of hydrogen in the solvent is substituted with a halogen atom such as fluorine.
Examples of the esters include: cyclic carbonates such as Ethylene Carbonate (EC), Propylene Carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ -butyrolactone and γ -valerolactone; and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, Methyl Propionate (MP), ethyl propionate, and γ -butyrolactone.
Examples of the ethers include: cyclic ethers such as 1, 3-dioxolane, 4-methyl-1, 3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1, 2-butylene oxide, 1, 3-dioxane, 1, 4-dioxane, 1,3, 5-trioxane, furan, 2-methylfuran, 1, 8-cineole, and crown ether; and chain ethers such as 1, 2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methylphenyl ether, ethylphenyl ether, butylphenyl ether, amylphenyl ether, methoxytoluene, benzylethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1, 2-diethoxyethane, 1, 2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1-dimethoxymethane, 1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.
As the halogen substituent, fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates such as fluorinated chain carbonates, fluorinated chain carboxylates such as Fluorinated Methyl Propionate (FMP), and the like are preferably used.
The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiBF4、LiClO4、LiPF6、LiAsF6、LiSbF6、LiAlCl4、LiSCN、LiCF3SO3、LiCF3CO2、Li(P(C2O4)F4)、LiPF6-x(CnF2n+1)x(x is more than 1 and less than 6, n is 1 or 2) and LiB10Cl10LiCl, LiBr, LiI, chloroborane lithium, lower aliphatic carboxylic acid lithium, Li2B4O7、Li(B(C2O4)F2) Borate salts, LiN (SO)2CF3)2、LiN(C1F2l+1SO2)(CmF2m+1SO2) And { l, m is an integer of 1 or more }, and the like. The lithium salt may be used alone or in combination of two or more. Among these, LiPF is preferably used from the viewpoint of ion conductivity, electrochemical stability, and the like6. The concentration of the lithium salt is preferably 0.8 to 1.8mol per 1 liter of the solvent.