WO2023053773A1 - リチウムイオン二次電池 - Google Patents
リチウムイオン二次電池 Download PDFInfo
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- WO2023053773A1 WO2023053773A1 PCT/JP2022/031487 JP2022031487W WO2023053773A1 WO 2023053773 A1 WO2023053773 A1 WO 2023053773A1 JP 2022031487 W JP2022031487 W JP 2022031487W WO 2023053773 A1 WO2023053773 A1 WO 2023053773A1
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- Prior art keywords
- negative electrode
- secondary battery
- ion secondary
- current collector
- based material
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 26
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 26
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- 239000007773 negative electrode material Substances 0.000 claims abstract description 26
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- 229910012733 LiCo1/3Mn1/3Ni1/3O2 Inorganic materials 0.000 description 1
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Images
Classifications
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- Y02E60/10—Energy storage using batteries
Definitions
- the present disclosure relates to lithium ion secondary batteries.
- the electrodes of lithium-ion secondary batteries generally have a metal current collector and a mixture layer formed on the surface of the current collector.
- the mixture layer contains, in addition to the active material as the main component, a conductive agent interposed between the active materials to form a conductive path.
- Patent Literature 1 discloses a technique of including carbon nanotubes as a conductive agent in a negative electrode mixture layer in order to maintain a conductive path between negative electrode active materials even after repeated charging and discharging.
- the purpose of the present disclosure is to provide a high-capacity, long-life lithium-ion secondary battery.
- a lithium ion secondary battery that is one aspect of the present disclosure includes a positive electrode, a negative electrode, a separator that separates the positive electrode and the negative electrode from each other, and an electrolyte.
- a negative electrode mixture layer formed on a surface, the negative electrode mixture layer including a negative electrode active material having a discharge capacity of 400 mAh/g to 750 mAh/g and a conductive agent; and the negative electrode active material being a carbon-based material. and a silicon-based material, the thickness of the negative electrode current collector is 4 ⁇ m to 12 ⁇ m, the 1% proof stress of the negative electrode current collector is 300 MPa to 700 MPa, and the conductive agent contains carbon nanotubes. .
- a lithium-ion secondary battery which is one embodiment of the present disclosure, has a high capacity and can suppress a decrease in battery capacity due to repeated charging and discharging.
- FIG. 1 is a cross-sectional view of a lithium-ion secondary battery that is an example of an embodiment
- FIG. FIG. 4 is a diagram showing the relationship between strain and stress when a tensile test is performed on a negative electrode current collector.
- the present inventors have further studied and found that even when the proportion of the silicon-based material in the negative electrode active material is increased to increase the discharge capacity of the negative electrode to 400 mAh / g to 750 mAh / g, carbon nanotubes and a predetermined negative electrode The present inventors have found that the use of a current collector can suppress breakage and elongation of the negative electrode due to repeated charging and discharging.
- a negative electrode current collector having a thickness of 4 ⁇ m to 12 ⁇ m and a 1% yield strength of 300 MPa to 700 MPa is used to suppress the expansion of the negative electrode, and carbon nanotubes maintain a conductive path, thereby reducing cycle characteristics. can be suppressed.
- cycle characteristics refer to changes in battery capacity due to repeated charging and discharging.
- a cylindrical battery in which the wound electrode body 14 is housed in a cylindrical outer can 16 with a bottom is exemplified, but the outer casing of the battery is not limited to a cylindrical outer can. It may be an exterior can (square battery), a coin-shaped exterior can (coin-shaped battery), or an exterior body (laminate battery) composed of a laminate sheet including a metal layer and a resin layer. Further, the electrode body may be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated with separators interposed therebetween.
- FIG. 1 is a diagram schematically showing a cross section of a lithium ion secondary battery 10 that is an example of an embodiment.
- the lithium ion secondary battery 10 includes a wound electrode body 14, an electrolyte, and an outer can 16 that accommodates the electrode body 14 and the electrolyte.
- the electrode body 14 has a positive electrode 11 , a negative electrode 12 , and a separator 13 , and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween.
- the outer can 16 is a bottomed cylindrical metal container that is open on one side in the axial direction.
- the side of the sealing member 17 of the battery will be referred to as the upper side
- the bottom side of the outer can 16 will be referred to as the lower side.
- the electrolyte includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.
- non-aqueous solvents include esters, ethers, nitriles, amides, and mixed solvents of two or more thereof.
- the non-aqueous solvent may contain a halogen-substituted product obtained by substituting at least part of the hydrogen atoms of these solvents with halogen atoms such as fluorine.
- non-aqueous solvents include ethylene carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), mixed solvents thereof, and the like.
- a lithium salt such as LiPF 6 is used as the electrolyte salt.
- the electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte.
- the positive electrode 11, the negative electrode 12, and the separator 13, which constitute the electrode assembly 14, are all strip-shaped elongated bodies, and are alternately laminated in the radial direction of the electrode assembly 14 by being spirally wound.
- the negative electrode 12 is formed with a size one size larger than that of the positive electrode 11 in order to prevent deposition of lithium. That is, the negative electrode 12 is formed longer than the positive electrode 11 in the longitudinal direction and the width direction (transverse direction).
- the separator 13 is formed to have a size at least one size larger than that of the positive electrode 11, and two separators 13 are arranged so as to sandwich the positive electrode 11 therebetween.
- the electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.
- Insulating plates 18 and 19 are arranged above and below the electrode body 14, respectively.
- the positive electrode lead 20 extends through the through hole of the insulating plate 18 toward the sealing member 17
- the negative electrode lead 21 extends through the outside of the insulating plate 19 toward the bottom of the outer can 16 .
- the positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 electrically connected to the internal terminal plate 23, serves as the positive electrode terminal.
- the negative electrode lead 21 is connected to the inner surface of the bottom of the outer can 16 by welding or the like, and the outer can 16 serves as a negative electrode terminal.
- the outer can 16 is a bottomed cylindrical metal container that is open on one side in the axial direction.
- a gasket 28 is provided between the outer can 16 and the sealing member 17 to ensure hermeticity inside the battery and insulation between the outer can 16 and the sealing member 17 .
- the outer can 16 is formed with a grooved portion 22 that supports the sealing member 17 and has a portion of the side surface projecting inward.
- the grooved portion 22 is preferably annularly formed along the circumferential direction of the outer can 16 and supports the sealing member 17 on its upper surface.
- the sealing member 17 is fixed to the upper portion of the outer can 16 by the grooved portion 22 and the open end of the outer can 16 that is crimped to the sealing member 17 .
- the sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are layered in order from the electrode body 14 side.
- Each member constituting the sealing member 17 has, for example, a disk shape or a ring shape, and each member other than the insulating member 25 is electrically connected to each other.
- the lower valve body 24 and the upper valve body 26 are connected at their central portions, and an insulating member 25 is interposed between their peripheral edge portions.
- the positive electrode 11, the negative electrode 12, and the separator 13, which constitute the lithium ion secondary battery 10, will be described in detail below, particularly the negative electrode 12.
- the positive electrode 11 has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector.
- a foil of a metal such as aluminum or an aluminum alloy that is stable in the potential range of the positive electrode 11, a film having the metal on the surface layer, or the like can be used.
- the positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder, and is preferably provided on both sides of the positive electrode current collector excluding the current collector exposed portion to which the positive electrode lead is connected.
- the thickness of the positive electrode mixture layer is, for example, 50 ⁇ m to 150 ⁇ m on one side of the positive electrode current collector.
- the positive electrode 11 is formed by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like to the surface of a positive electrode current collector, drying the coating film, and then compressing the positive electrode mixture layer to form a positive electrode. It can be produced by forming on both sides of the current collector.
- the positive electrode active material is mainly composed of lithium transition metal composite oxide.
- Elements other than Li contained in the lithium-transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In , Sn, Ta, W, Si, P and the like.
- An example of a suitable lithium-transition metal composite oxide is a composite oxide containing at least one of Ni, Co, and Mn. Specific examples include lithium-transition metal composite oxides containing Ni, Co, and Mn, and lithium-transition metal composite oxides containing Ni, Co, and Al.
- Examples of the conductive agent contained in the positive electrode mixture layer include carbon-based particles such as carbon black, acetylene black, ketjen black, carbon nanotubes, graphene, and graphite.
- Examples of the binder contained in the positive electrode mixture layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. . These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or salts thereof, polyethylene oxide (PEO), and the like.
- the negative electrode 12 has a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector.
- the negative electrode mixture layers are preferably provided on both sides of the negative electrode current collector.
- the thickness of the negative electrode current collector is 4 ⁇ m to 12 ⁇ m.
- the thickness of the negative electrode mixture layer is, for example, 50 ⁇ m to 150 ⁇ m on one side of the negative electrode current collector.
- the negative electrode current collector it is possible to use foils of metals such as copper and copper alloys that are stable in the potential range of the negative electrode, films with such metals arranged on the surface layer, and the like.
- the negative electrode current collector is preferably copper.
- the crystal grain size of copper as the negative electrode current collector is preferably 0.2 ⁇ m to 2 ⁇ m. The crystal grain size can be measured using SEM-EBSD (electron beam backscatter diffraction method) or the like.
- the 1% yield strength of the negative electrode current collector is 300 MPa to 700 MPa.
- the 1% yield strength is the yield strength (1%) measured by the JIS Z 2241 metal material tensile test method.
- FIG. 2 is a schematic diagram showing the relationship between strain and stress when a tensile test was performed on the negative electrode current collector.
- the 1% proof stress is the stress value when the strain is 1%.
- the 1% yield strength of the negative electrode current collector can be adjusted by, for example, the thickness of the negative electrode current collector and the crystal grain size of the material of the negative electrode current collector.
- the breaking elongation of the negative electrode current collector is, for example, 2% to 9%.
- the elongation at break is a value expressed as a percentage obtained by dividing the elongation amount of the test piece broken by the tensile test by the length of the test piece before the tensile test. is the distortion value of
- the negative electrode mixture layer includes a negative electrode active material with a discharge capacity of 400 mAh/g to 750 mAh/g and a conductive agent.
- the negative electrode active material includes a carbon-based material and a silicon-based material.
- the negative electrode active material may contain materials other than carbon-based materials and silicon-based materials that can occlude and release Li.
- the ratio of the silicon-based material in the negative electrode active material may be 5% by mass to 30% by mass with respect to the total of the carbon-based material and the silicon-based material.
- a negative electrode active material mixed in such a ratio has the above discharge capacity.
- the discharge capacity CA (mAh/g) of the negative electrode active material, the thickness CT ( ⁇ m) of the negative electrode current collector, and the 1% proof stress CM (N/mm 2 ) of the negative electrode current collector are calculated as CA/(CM ⁇ CT). It is preferable to satisfy the relationship ⁇ 0.3.
- the carbon-based material may be at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon.
- natural graphite or artificial graphite which is excellent in charge/discharge stability and has a low irreversible capacity, is preferable.
- natural graphite include flake graphite, massive graphite, earthy graphite, etc.
- artificial graphite include massive artificial graphite, graphitized mesophase carbon microbeads, and the like.
- silicon-based materials include Si metal alloyed with Li, metal compounds containing Si, and composite oxides containing Si.
- Silicon-based materials include, for example, an ion-conducting phase, silicon particles dispersed within the ion-conducting phase, and a coating layer covering the surface of the ion-conducting phase.
- the ion-conducting phase is, for example, at least one selected from the group consisting of a silicate phase, an amorphous carbon phase, and a silicide phase.
- SiO which is an example of a silicon-based material, has a particle structure in which fine silicon particles are dispersed in a silicate phase.
- Suitable SiO has a sea-island structure in which fine silicon particles are dispersed substantially uniformly in an amorphous silicon oxide matrix, and is represented by the general formula SiO x (0 ⁇ x ⁇ 2).
- the silicate phase is composed of an aggregate of finer particles than silicon particles.
- the content of silicon particles is preferably 35% by mass to 75% by mass with respect to the total mass of SiO from the viewpoint of compatibility between battery capacity and cycle characteristics.
- the ion-conducting phase may contain at least one element selected from the group consisting of alkali metal elements and Group 2 elements.
- a compound represented by the general formula Li 2z SiO (2+z) (0 ⁇ z ⁇ 2) is a silicon-based material, and has a sea-island structure in which fine Si particles are substantially uniformly dispersed in a lithium silicate matrix. have.
- the lithium silicate phase is composed of an aggregate of finer particles than silicon particles. As in the case of SiO, the content of silicon particles is preferably 35% by mass to 75% by mass with respect to the total mass of the Li 2z SiO (2+z) compound.
- Si--C which is another example of a silicon-based material, has a grain structure in which fine silicon particles are dispersed in an amorphous carbon phase.
- Suitable Si--C has a sea-island structure in which fine silicon particles are substantially uniformly dispersed in an amorphous carbon phase matrix.
- the content of Si particles is preferably 35% by mass to 75% by mass with respect to the total mass of Si—C from the viewpoint of increasing the capacity.
- the ion-conducting phase contains the element M, which is B, Al, Zr, Nb, Ta, V, La, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F, and W may be at least one selected from the group consisting of
- constituent materials of the coating layer include carbon materials, metals, and metal compounds, and carbon materials such as amorphous carbon are particularly preferable.
- the coating layer can be formed by, for example, a CVD method using acetylene, methane, or the like, or a method of mixing silicon compound particles with coal pitch, petroleum pitch, phenol resin, or the like and subjecting the mixture to heat treatment.
- the coating layer may be formed by fixing a conductive filler such as carbon black to the surface of the ion conductive phase using a binder.
- the conductive agent contained in the negative electrode mixture layer contains carbon nanotubes (CNT).
- the conductive agent may contain carbon black, acetylene black, ketjen black, graphite, etc. in addition to CNT, but preferably contains only CNT. CNTs form good conductive paths in the negative electrode mixture layer and contribute to lowering the resistance of the negative electrode mixture layer.
- the CNTs may be either multi-walled CNTs (MWCNTs) or single-walled CNTs (SWCNTs), preferably SWCNTs. Both SWCNTs and MWCNTs may be included in the negative electrode mixture layer.
- MWCNTs multi-walled CNTs
- SWCNTs single-walled CNTs
- the average fiber diameter of CNT is, for example, 0.01 nm to 5 nm. If the average fiber diameter of CNTs is within the range, the effect of improving cycle characteristics is enhanced compared to the case of using CNTs having an average fiber diameter outside the range.
- the average fiber diameter of CNTs is obtained by selecting 100 CNTs from a cross-sectional image of the negative electrode mixture layer, measuring the diameters, and averaging the measured values.
- the content of CNTs in the negative electrode mixture layer is, for example, 0.005% by mass to 0.6% by mass with respect to the total amount of the negative electrode active material. If the CNT content is within this range, it is possible to increase the content of the negative electrode active material while ensuring a conductive path in the negative electrode mixture layer, thereby improving the cycle characteristics and increasing the battery capacity. be able to.
- the negative electrode mixture layer may further contain a binder.
- a binder As the binder contained in the negative electrode mixture layer, fluororesin, PAN, polyimide, acrylic resin, polyolefin, or the like can be used as in the case of the positive electrode 11, but styrene-butadiene rubber (SBR) is preferably used.
- SBR styrene-butadiene rubber
- the negative electrode mixture layer may further contain CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), and the like.
- PAA polyacrylic acid
- PVA polyvinyl alcohol
- the separator 13 separates the positive electrode 11 and the negative electrode 12 from each other.
- a porous sheet having ion permeability and insulation is used for the separator 13 .
- Specific examples of porous sheets include microporous thin films, woven fabrics, and non-woven fabrics.
- Suitable materials for the separator 13 include polyolefins such as polyethylene, polypropylene, copolymers of ethylene and ⁇ -olefin, and cellulose.
- the separator 13 may have either a single layer structure or a laminated structure.
- a heat-resistant layer containing inorganic particles, a heat-resistant layer made of a highly heat-resistant resin such as aramid resin, polyimide, polyamideimide, or the like may be formed on the surface of the separator 13 .
- a lithium transition metal composite oxide represented by LiCo 1/3 Mn 1/3 Ni 1/3 O 2 was used as the positive electrode active material. 98 parts by mass of a positive electrode active material, 1 part by mass of acetylene black, and 1 part by mass of polyvinylidene fluoride are mixed, and N-methyl-2-pyrrolidone (NMP) is used as a dispersion medium to prepare a positive electrode mixture slurry. was prepared. Next, the positive electrode mixture slurry is applied to both sides of a positive electrode current collector made of aluminum foil, the coating film is dried and compressed, and then cut into a predetermined electrode size. A positive electrode having a layer formed thereon was produced. An exposed portion where the surface of the current collector was exposed was provided in the center of the positive electrode in the longitudinal direction, and the positive electrode lead was welded to the exposed portion.
- NMP N-methyl-2-pyrrolidone
- the negative electrode mixture slurry was applied to both sides of a copper foil having a thickness of 6 ⁇ m as a negative electrode current collector, and the coating film was dried and compressed. After that, it was cut into a predetermined electrode size to prepare a negative electrode having negative electrode mixture layers formed on both sides of the negative electrode current collector. An exposed portion where the current collector surface was exposed was provided at the longitudinal end of the negative electrode, and the negative electrode lead was welded to the exposed portion.
- Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4.
- An electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF 6 ) in the mixed solvent at a concentration of 1 mol/liter.
- Examples 2 to 5 Comparative Examples 1 to 4>
- Tables 1 to 3 the ratio of the mass of SiO to the total mass of artificial graphite and SiO is changed, and copper foils with different characteristics (thickness, 1% proof stress, elongation at break) are used, A test cell was produced and evaluated in the same manner as in Example 1, except that the CNT content was changed.
- Table 1 also shows the discharge capacities of the negative electrode active materials in Examples and Comparative Examples.
- Tables 1 to 3 show the evaluation results of the test cells of Examples and Comparative Examples.
- Table 1 shows the results when the ratio of the silicon-based material is 8% by mass, and the capacity deterioration rate of Example 1 is a relative value based on the capacity deterioration rate of Comparative Example 1 (100). be.
- Table 2 shows the results when the ratio of the silicon-based material was 15% by mass. ) is a relative value.
- Table 3 shows the results when the ratio of the silicon-based material is 20% by mass, and the capacity deterioration rate of Example 5 is a relative value based on the capacity deterioration rate of Comparative Example 4 (100). be.
- test cell of the example had a lower capacity deterioration rate than the test cell of the comparative example.
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Abstract
Description
正極11は、正極集電体と、正極集電体の表面に形成された正極合剤層とを有する。正極集電体には、アルミニウム、アルミニウム合金など、正極11の電位範囲で安定な金属の箔、当該金属を表層に配置したフィルム等を用いることができる。正極合剤層は、正極活物質、導電剤、及び結着剤を含み、正極リードが接続される部分である集電体露出部を除く正極集電体の両面に設けられることが好ましい。正極合剤層の厚みは、正極集電体の片側で、例えば50μm~150μmである。正極11は、正極集電体の表面に正極活物質、導電剤、及び結着剤等を含む正極合剤スラリーを塗布し、塗膜を乾燥させた後、圧縮して正極合剤層を正極集電体の両面に形成することにより作製できる。
負極12は、負極集電体と、負極集電体の表面に形成された負極合剤層とを有する。負極合剤層は、負極集電体の両面に設けられることが好ましい。負極集電体の厚みは、4μm~12μmである。負極合剤層の厚みは、負極集電体の片側で、例えば50μm~150μmである。
セパレータ13は、正極11及び負極12を相互に隔離する。セパレータ13には、イオン透過性および絶縁性を有する多孔性シートが用いられる。多孔性シートの具体例としては、微多孔薄膜、織布、不織布等が挙げられる。セパレータ13の材質としては、ポリエチレン、ポリプロピレン、エチレンとαオレフィンの共重合体等のポリオレフィン、セルロースなどが好適である。セパレータ13は、単層構造、積層構造のいずれであってもよい。セパレータ13の表面には、無機粒子を含む耐熱層、アラミド樹脂、ポリイミド、ポリアミドイミド等の耐熱性の高い樹脂で構成される耐熱層などが形成されていてもよい。
[正極の作製]
正極活物質として、LiCo1/3Mn1/3Ni1/3O2で表されるリチウム遷移金属複合酸化物を用いた。98質量部の正極活物質と、1質量部のアセチレンブラックと、1質量部のポリフッ化ビニリデンとを混合し、分散媒としてN-メチル-2-ピロリドン(NMP)を用いて、正極合剤スラリーを調製した。次に、当該正極合剤スラリーをアルミニウム箔からなる正極集電体の両面に塗布し、塗膜を乾燥、圧縮した後、所定の電極サイズに切断し、正極集電体の両面に正極合剤層が形成された正極を作製した。なお、正極の長手方向中央部に集電体表面が露出した露出部を設け、当該露出部に正極リードを溶接した。
人造黒鉛とSiOx(0<x≦2)とを92:8の質量比で混合し、これを負極活物質として用いた。この負極活物質の放電容量は、430mAh/gであった。また、導電剤としては、平均繊維径が0.1nmのカーボンナノチューブ(CNT)を用いた。負極活物質と、CNTと、カーボンナノチューブカルボキシメチルセルロース(CMC)と、スチレンブタジエンゴム(SBR)のディスパージョンとを、100:0.05:1:1の固形分質量比で混合し、分散媒として水を用いて、負極合剤スラリーを調製した。当該負極合剤スラリーを負極集電体としての厚み6μmの銅箔の両面に塗布し、塗膜を乾燥、圧縮した。その後、所定の電極サイズに切断し、負極集電体の両面に負極合剤層が形成された負極を作製した。なお、負極の長手方向端部に集電体表面が露出した露出部を設け、当該露出部に負極リードを溶接した。
エチレンカーボネート(EC)と、エチルメチルカーボネート(EMC)と、ジメチルカーボネート(DMC)とを、3:3:4の体積比で混合した。当該混合溶媒に対して、六フッ化リン酸リチウム(LiPF6)を1モル/リットルの濃度となるように溶解させて、電解質を調製した。
上記正極の露出部にアルミニウム製のリードを、負極の所定の位置にニッケル製のリードをそれぞれ取り付け、ポリエチレン製のセパレータを介して正極と負極を渦巻き状に巻回して巻回型の電極体を作製した。この電極体を有底円筒形状の外装缶内に収容し、上記電解質を注入した後、外装缶の開口部にガスケットを介して封口体を取り付け、円筒形の試験セルを作製した。
環境温度25℃の下、上記の試験セルを、0.2Itで4.2Vまで定電流充電した後、4.2Vで0.02Itまで定電圧充電した。その後、0.2Itで2.5Vまで定電流放電した。この充放電を1サイクルとして、200サイクル行い、下記式により容量劣化率を求めた。
容量劣化率=(1サイクル目の放電容量-200サイクル目の放電容量)/1サイクル目の放電容量×100
負極の作製において、表1~3に示すように、人造黒鉛とSiOの総質量に対するSiOの質量の割合を変化させ、特性(厚み、1%耐力、破断伸び)の異なる銅箔を使用し、CNTの含有率を変化させたこと以外は、実施例1と同様にして試験セルを作製し、評価を行った。表1には、実施例及び比較例における負極活物質の放電容量も併せて示す。
Claims (12)
- 正極と、負極と、前記正極及び前記負極を相互に隔離するセパレータと、電解質とを備え、
前記負極は、負極集電体と、前記負極集電体の表面に形成された負極合剤層とを有し、
前記負極合剤層は、放電容量が400mAh/g~750mAh/gの負極活物質と、導電剤とを含み、
前記負極活物質は、炭素系材料とケイ素系材料とを含み、
前記負極集電体の厚みが、4μm~12μmであり、前記負極集電体の1%耐力が、300MPa~700MPaであり、
前記導電剤がカーボンナノチューブを含む、リチウムイオン二次電池。 - 前記負極活物質の放電容量CA(mAh/g)、前記負極集電体の厚みCT(μm)、及び、前記負極集電体の1%耐力CM(N/mm2)が、CA/(CM×CT)<0.3の関係を満たす、請求項1に記載のリチウムイオン二次電池。
- 前記炭素系材料が、天然黒鉛、人造黒鉛、ソフトカーボン、及びハードカーボンからなる群より選択される少なくとも1種である、請求項1又は2に記載のリチウムイオン二次電池。
- 前記ケイ素系材料は、イオン伝導相と、前記イオン伝導相内に分散しているシリコン粒子と、前記イオン伝導相の表面を覆うコーティング層とを含む、請求項1~3のいずれか1項に記載のリチウムイオン二次電池。
- 前記イオン伝導相が、シリケート相、非晶質炭素相、及びシリサイド相からなる群より選択される少なくとも1種である、請求項4に記載のリチウムイオン二次電池。
- 前記イオン伝導相が、アルカリ金属元素及び第2族元素からなる群より選択される少なくとも1種の元素を含む、請求項4又は5に記載のリチウムイオン二次電池。
- 前記イオン伝導相が、元素Mを含み、前記元素Mは、B、Al、Zr、Nb、Ta、V、La、Y、Ti、P、Bi、Zn、Sn、Pb、Sb、Co、Er、F、及びWからなる群より選択される少なくとも1種である、請求項4~6のいずれか1項に記載のリチウムイオン二次電池。
- 前記負極活物質における前記ケイ素系材料の割合が、前記炭素系材料と前記ケイ素系材料の合計に対して、5質量%~30質量%である、請求項1~7のいずれか1項に記載のリチウムイオン二次電池。
- 前記負極集電体が、結晶粒径が0.2μm~2μmの銅である、請求項1~8のいずれか1項に記載のリチウムイオン二次電池。
- 前記負極集電体の破断伸びが2%~9%である、請求項1~9のいずれか1項に記載のリチウムイオン二次電池。
- 前記カーボンナノチューブの平均繊維径が0.01nm~5nmである、請求項1~10のいずれか1項に記載のリチウムイオン二次電池。
- 前記負極合剤層における前記カーボンナノチューブの含有率は、前記負極活物質の総量に対して、0.005質量%~0.6質量%である、請求項1~11のいずれか1項に記載のリチウムイオン二次電池。
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JP2007035472A (ja) | 2005-07-28 | 2007-02-08 | Matsushita Electric Ind Co Ltd | リチウム二次電池、リチウム二次電池用負極材料および負極ならびにその製造方法 |
WO2013047432A1 (ja) * | 2011-09-27 | 2013-04-04 | 三洋電機株式会社 | リチウム二次電池 |
WO2020195335A1 (ja) * | 2019-03-28 | 2020-10-01 | パナソニックIpマネジメント株式会社 | 非水電解質二次電池用負極および非水電解質二次電池 |
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JP2007035472A (ja) | 2005-07-28 | 2007-02-08 | Matsushita Electric Ind Co Ltd | リチウム二次電池、リチウム二次電池用負極材料および負極ならびにその製造方法 |
WO2013047432A1 (ja) * | 2011-09-27 | 2013-04-04 | 三洋電機株式会社 | リチウム二次電池 |
WO2020195335A1 (ja) * | 2019-03-28 | 2020-10-01 | パナソニックIpマネジメント株式会社 | 非水電解質二次電池用負極および非水電解質二次電池 |
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CN117038848A (zh) * | 2023-10-08 | 2023-11-10 | 宁德时代新能源科技股份有限公司 | 负极极片、二次电池以及用电装置 |
CN117038848B (zh) * | 2023-10-08 | 2024-03-29 | 宁德时代新能源科技股份有限公司 | 负极极片、二次电池以及用电装置 |
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