Lithium ion battery
Incorporating an acrylamide compound in the electrolyte of lithium-ion batteries with silicon-containing electrodes forms a uniform SEI, addressing volume changes and improving cycle life and capacity retention.
Patent Information
- Application Number
- JP2023221547
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-12-27
- Publication Date
- 2025-07-09
AI Technical Summary
Lithium-ion batteries using silicon-containing materials as negative electrodes face challenges in maintaining high capacity while improving charge-discharge cycle life due to volume expansion and contraction, leading to SEI cracking and gas generation.
Incorporating an acrylamide compound with a specific chemical structure into the non-aqueous electrolyte to form a uniform SEI on the silicon-containing negative electrode, suppressing electrolyte decomposition and promoting rapid SEI reformulation during expansion and contraction.
Enhances charge-discharge cycle characteristics by reducing gas generation and maintaining capacity retention, as evidenced by improved capacity retention rates and reduced volume expansion.
Smart Images
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Abstract
Description
Technical Field
[0001] The present application relates to a lithium-ion battery.
Background Art
[0002] In recent years, lithium-ion batteries have been used not only as power sources for electronic devices such as smartphones and personal computers but also as power sources for transportation devices such as automobiles, and there is a demand for further increased capacity.
[0003] Currently, in lithium-ion batteries using graphite as the negative electrode that are in practical use, the capacity is close to the theoretical capacity, and it is difficult to further significantly increase the capacity. Therefore, the development of lithium-ion batteries using materials that alloy with Li, such as Si, as the negative electrode has been progressing. On the other hand, such negative electrodes have large expansion and contraction of the negative electrode volume during charge and discharge. The volume change of the negative electrode may cause cracks in the film (SEI) at the electrode / electrolyte interface. When the electrolyte decomposition reaction and the consumption of lithium ions proceed during the crack repair process, problems such as a decrease in the charge-discharge cycle life and gas generation occur. In particular, in the case of a Si negative electrode, the capacity and the life are in a trade-off relationship, and it is required to increase the life while showing a high capacity.
[0004] To solve such problems, several methods have been developed. One approach to suppressing gas generation is to reduce the nanosize of the negative electrode active material particles (Patent Document 1). Another approach is to use a Si-based carbon composite material (Patent Document 2). However, although both have a certain effect on suppressing gas generation, the capacity retention rate is still insufficient.
Prior Art Documents
Patent Documents
[0005]
Patent Document 1
Patent Document 2
Summary of the Invention
Problems to be Solved by the Invention
[0006] The present disclosure has been made to solve the problems of the prior art as described above, and an object thereof is to provide a lithium-ion battery with improved charge-discharge cycle characteristics while using a Si-containing material as a negative electrode active material.
Means for Solving the Problems
[0007] As a result of intensive studies on the above problems, the present inventors have found that in a lithium-ion battery using a Si-containing material as a negative electrode active material, the charge-discharge cycle characteristics can be improved by including an acrylamide compound having a specific chemical structure in a non-aqueous electrolyte, and have completed the present invention.
[0008] In order to solve the above problems, the present disclosure includes the following configurations.
[0009] The lithium-ion battery according to the present embodiment includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte contains a compound represented by the following general formula A.
[0010]
Chemical formula
[0011] (In the formula, R1 and R2 may be the same or different and are each an organic group having 1 to 6 carbon atoms containing a CH3 group or an OH group at the terminal or H) In the negative electrode, the negative electrode active material consists only of a silicon-containing material.
[0012] In one embodiment, in the compound represented by the general formula A, R1 and R2 may each independently be any of H, a CH3 group, or a CH2OH group.
[0013] In one embodiment, the silicon-containing material is Si or SiO x (0 < x < 2) may also be possible.
[0014] In one embodiment, the mass ratio of the compound represented by the general formula A to the mass of the non-aqueous electrolyte may be 0.1% by mass or more and 2.0% by mass or less.
[0015] In one embodiment, the non-aqueous electrolyte may further contain a cyclic carbonate and a chain carbonate.
[0016] In one embodiment, the non-aqueous electrolyte may further contain a lithium salt.
Advantages of the Invention
[0017] According to the present disclosure, the charge-discharge cycle characteristics of a lithium-ion battery using an Si-containing material as a negative electrode active material can be improved.
Modes for Carrying Out the Invention
[0018] A lithium-ion battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte contains a compound represented by the following general formula A.
[0019]
Chemical Formula
[0020] In the formula, R1 and R2 may be the same or different and are an organic group having 1 to 6 carbon atoms containing a CH3 group or an OH group at the terminal or H. In the negative electrode, the negative electrode active material consists only of a silicon-containing material.
[0021] [Electrolyte] A lithium-ion battery according to the present disclosure includes a non-aqueous electrolyte, and the non-aqueous electrolyte contains a compound represented by the following general formula A.
[0022]
Chemical Formula
[0023] In the formula, R1 and R2 may be the same or different, and are an organic group having 1 to 6 carbon atoms containing a CH3 group or an OH group at the terminal or H.
[0024] In this specification, examples of the organic group include a chain saturated hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group. Further, the organic group may have a substituent, and may be a substituted chain saturated hydrocarbon group, a substituted alicyclic hydrocarbon group, a substituted aromatic hydrocarbon group, etc. in which at least a part of the hydrogen atoms bonded to the carbon atoms constituting these groups are replaced with a substituent.
[0025] Without being bound by a specific theory, in the lithium ion battery according to the present disclosure, by including the compound represented by the general formula A in the electrolytic solution, a film-like and uniform SEI is formed on the surface of the negative electrode active material, and the decomposition reaction of the electrolytic solution, which is a side reaction, is suppressed. In particular, when the negative electrode active material consists only of a silicon-containing material, the expansion and contraction of the negative electrode active material during charge and discharge become large. However, when the compound represented by the general formula A is included in the electrolytic solution, even if the negative electrode active material expands and contracts and cracks occur in the SEI, the formation of a new SEI can be promptly promoted. As a result, gas generation in the battery can be suppressed, and the charge and discharge cycle characteristics can be improved.
[0026] When R1 and R2 are an organic group having 1 to 6 carbon atoms or H, the promotion of SEI formation by the compound represented by the general formula A suppresses the decomposition reaction of the electrolytic solution, which is a side reaction, and suppresses gas generation.
[0027] In one embodiment, in General Formula A, R1 and R2 may be the same or different, and may be an organic group having 1 to 5 carbon atoms containing a CH3 group or an OH group at the terminal or H. In another embodiment, R1 and R2 are preferably each independently H, a CH3 group, or a CH2OH group. When the number of carbon atoms of R1 and R2 is small, the decomposition reaction of the compound represented by General Formula A further decreases. For example, the number of carbon atoms of R1 and R2 may be 0 or more and 6 or less, 0 or more and 5 or less, or 0 or more and 3 or less. Here, a carbon number of 0 means hydrogen.
[0028] Preferably, in General Formula A, R1 may be H or a CH3 group.
[0029] Most preferably, the compound represented by the general formula A may be N,N-dimethylacrylamide or N-(hydroxymethyl)acrylamide.
[0030] The ratio of the mass of the compound represented by General Formula A to the mass of the non-aqueous electrolyte is calculated according to the following Formula 1. [Formula 1] (Ratio of the mass of the compound represented by General Formula A to the mass of the non-aqueous electrolyte) (mass%) = (mass of the compound represented by General Formula A) (g) / (total mass of the non-aqueous electrolyte) (g)
[0031] Preferably, the ratio of the mass of the compound represented by General Formula A to the mass of the non-aqueous electrolyte may be 0.1 mass% or more and 2.0 mass% or less. For example, the content of the compound represented by General Formula A contained in the non-aqueous electrolyte can be identified by gas chromatography, NMR, FT-IR, etc. In one embodiment, the ratio of the mass of the compound represented by General Formula A to the mass of the non-aqueous electrolyte may be 0.1 mass% or more and 1.0 mass% or less. The mass ratio may be, for example, 0.5 mass% or more and 2.0 mass% or less, or 1.0 mass% or more and 2.0 mass% or less.
[0032] The non-aqueous electrolyte used in the lithium-ion battery according to the present disclosure preferably contains at least one selected from cyclic carbonates and chain carbonates as a solvent. More preferably, the non-aqueous electrolyte contains a cyclic carbonate and a chain carbonate.
[0033] Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), methyl vinylene carbonate, ethyl vinylene carbonate, 1,2-diethyl vinylene carbonate, vinyl ethylene carbonate (VEC), 1-methyl-2-vinyl ethylene carbonate, 1-ethyl-2-vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1,1-divinyl ethylene carbonate, 1,2-divinyl ethylene carbonate, 1,1-dimethyl-2-methylene ethylene carbonate, 1,1-diethyl-2-methylene ethylene carbonate, ethynyl ethylene carbonate, 1,2-diethynyl ethylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, chloroethylene carbonate, and combinations thereof.
[0034] Examples of the chain carbonate include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate, methyl butyl carbonate, diethyl carbonate (DEC), ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, propyl butyl carbonate, and combinations thereof.
[0035] The non-aqueous electrolyte may also contain a carbonate containing a fluorine atom as a cyclic carbonate or a chain carbonate. Examples of the carbonate containing a fluorine atom include fluorovinylene carbonate, trifluoromethylvinylene carbonate, fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, 4-fluoro-1,3-dioxolan-2-one, trans- or cis-4,5-difluoro-1,3-dioxolan-2-one, 4-ethynyl-1,3-dioxolan-2-one, methyl-2,2,2-trifluoroethyl carbonate, and combinations thereof.
[0036] In particular, among the carbonates, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents. Ethylene carbonate and propylene carbonate have a high dielectric constant and easily dissociate lithium salts in the electrolyte. When such cyclic carbonates are mixed with chain carbonates having a low viscosity and a low dielectric constant, such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, at an appropriate ratio, an electrolyte having a high electrical conductivity can be produced.
[0037] The non-aqueous electrolyte of the present disclosure may contain a mixture of a cyclic carbonate and a chain carbonate. The ratio of the cyclic carbonate to the total of the cyclic carbonate and the chain carbonate is preferably 5% by volume or more and 95% by volume or less, and more preferably 10% by volume or more and 90% by volume or less.
[0038] The non-aqueous electrolyte of the present disclosure can further contain an ester compound. Examples of the ester compound include carboxylic acid esters and the like. Examples of the carboxylic acid ester include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl valerate, ethyl valerate, propyl valerate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, ε-caprolactone, compounds in which a part of the hydrogen of these carboxylic acid esters is substituted with fluorine, and combinations thereof.
[0039] In addition to the above, the non-aqueous electrolyte of the present disclosure can contain other solvents, such as ether compounds such as cyclic ethers or chain ethers, polyethers, sulfur-containing solvents, and phosphorus-containing solvents, without particular limitation as long as the object of the present disclosure is not impaired.
[0040] Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran. Further, the non-aqueous electrolyte of the present disclosure can further contain a chain ether. Examples of the chain ether include dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.
[0041] The non-aqueous electrolyte used in the lithium-ion battery according to the present disclosure can contain an electrolyte generally used in lithium-ion batteries. The electrolyte acts as a medium for transporting ions involved in electrochemical reactions in the lithium-ion battery. Preferably, the non-aqueous electrolyte used in the lithium-ion battery according to the present disclosure contains a lithium salt as an electrolyte.
[0042] The lithium salt contained in the non-aqueous electrolyte used in the lithium-ion battery according to the present disclosure is, for example, LiPF6, LiBF4, LiB 12 F 12, LiAsF6, LiFSO3, Li2SiF6, LiCF3CO2, LiCH3CO2, LiCF3SO3, LiC4F9SO3, LiCF3CF2SO3, LiCF3(CF2)7SO3, LiCF3CF2(CF3)2CO, Li(CF3SO2)2CH, LiNO3, LiN(CN)2, LiN(FSO2)2, LiN(F2SO2)2, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiC(CF3SO2)3, LiP(CF3)6, LiPF(CF3)5, LiPF2(CF3)4, LiPF3(CF3)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2C2O4, LiBC4O8, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2, LiSbF6, LiAlO4, LiAlF4, LiSCN, LiClO4, LiCl, LiF, LiBr, LiI, LiAlCl4, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), etc. can be included. In one embodiment, the electrolyte used in the lithium-ion battery according to the present disclosure contains LiTFSI as a lithium salt. The lithium salt can be used alone or in combination of a plurality of lithium salts.
[0043] The content of the electrolyte is not particularly limited, but can be contained in an amount of 0.1 mol / L or more and 5 mol / L or less, preferably 0.5 mol / L or more and 3 mol / L or less, more preferably 0.5 mol / L or more and 2 mol / L or less, based on the total amount of the non-aqueous electrolyte. By setting the amount of the electrolyte within the above range, sufficient battery characteristics can be obtained.
[0044] In the lithium-ion battery according to the present disclosure, the non-aqueous electrolyte may contain at least one additional additive. Examples of the additional additive include a flame retardant, a wetting agent, a stabilizer, a corrosion inhibitor, a gelling agent, an overcharge prevention agent, and a negative electrode film forming additive.
[0045] [Negative electrode] The negative electrode used in the lithium-ion battery of the present disclosure can be manufactured, for example, by coating a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, a solvent, etc. on a negative electrode current collector, and then drying and rolling.
[0046] The negative electrode current collector generally may have a thickness of 3 μm or more and 500 μm or less. The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing a chemical change in the lithium-ion battery of the present disclosure. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, similar to the positive electrode current collector, the binding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and it may be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven bodies.
[0047] In the lithium-ion battery according to the present disclosure, the negative electrode active material is made of a silicon-containing material. As the silicon-containing material, for example, Si, SiO x (0 < x < 2), Si-A alloy (where A is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), and a mixture of at least one of these and SiO2 can be used. Preferably, the silicon-containing material may be Si or SiO x (0 < x < 2). Most preferably, the silicon-containing material may be Si.
[0048] The negative electrode active material is preferably contained in an amount of 80% by mass or more and 99% by mass or less, more preferably 90% by mass or more and 99% by mass or less, based on the total mass of the solid content in the negative electrode slurry.
[0049] The binder is a component that aids in the binding between the conductive material, the negative electrode active material, and the current collector. The binder is preferably contained in an amount of 1% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 10% by mass or less, based on the total mass of the solid content in the negative electrode slurry. Examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluorine rubber. The binder can be used alone or in combination of a plurality of compounds.
[0050] The conductive material is a component for further improving the conductivity of the negative electrode active material. The conductive material can be contained in an amount of 0.1% by mass or more and 20% by mass or less, for example 0.5% by mass or more and 10% by mass or less, for example 1% by mass or more and 3% by mass or less, based on the total mass of the solid content in the negative electrode slurry. The conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the lithium ion battery. Examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.
[0051] The solvent used for the negative electrode slurry is not particularly limited as long as it can form a slurry of the negative electrode active material, binder, conductive material, etc. as the negative electrode material. For example, water or organic solvents such as NMP and alcohol can be used. Also, the negative electrode slurry can be used in an amount that provides a suitable viscosity. For example, it can be used in an amount such that the solid content concentration in the slurry is 50% by mass or more and 75% by mass or less, preferably 50% by mass or more and 65% by mass or less.
[0052] [Positive Electrode] The positive electrode used in the lithium-ion battery of the present disclosure can be manufactured, for example, by coating a positive electrode slurry containing a positive electrode active material, binder, conductive material, and solvent, etc. on a positive electrode current collector, and then drying and rolling.
[0053] The positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the lithium-ion battery of the present disclosure. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used.
[0054] The positive electrode active material is a compound capable of reversibly occluding and releasing lithium. Specifically, it may include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium composite metal oxide includes lithium-manganese-based oxides (for example, LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (for example, LiCoO2, etc.), lithium-nickel-based oxides (for example, LiNiO2, etc.), lithium-nickel-manganese-based oxides (for example, LiNi 1-y1 Mn y1 O2 (where 0 < y1 < 1), LiMn 2-z1 Ni z O4 (where 0 < Z1 < 2), etc.), lithium-nickel-cobalt-based oxides (for example, LiNi 1-y2 Co y2O2 (where 0 < y2 < 1), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-y3 Mn y3 O2 (where 0 < y3 < 1), LiMn 2-z2 Co z2 O4 (where 0 < Z2 < 2), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p1 Co q1 Mn r1 )O2 (where 0 < p1 < 1, 0 < q1 < 1, 0 < r1 < 1, p1 + q1 + r1 = 1), or Li(Ni p2 Co q2 Mn r2 )O4 (where 0 < p2 < 2, 0 < q2 < 2, 0 < r2 < 2, p2 + q2 + r2 = 2), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p3 Co q3 Mn r3 M S3 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p3, q3, r3, and s3 are atomic fractions of independent elements, 0 < p3 < 1, 0 < q3 < 1, 0 < r3 < 1, 0 < s3 < 1, p3 + q3 + r3 + s3 = 1), etc.), and these may be included alone or two or more of them may be included.
[0055] Preferably, from the viewpoint of being able to enhance the capacity characteristics and stability of the battery, the lithium composite metal oxide may be a lithium composite metal oxide containing a nickel-containing metal and lithium. Specifically, lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium-nickel-cobalt-aluminum oxides (e.g., Li(Ni0.8 Co 0.15 Al 0.05 ) Such as O2 can be used. In particular, it is preferable in terms of cost to use lithium-nickel-manganese-cobalt oxide or lithium-nickel-cobalt-aluminum oxide, which are ternary materials of nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA).
[0056] The positive electrode active material is preferably contained in an amount of 80% by mass or more and 99% by mass or less, more preferably 90% by mass or more and 99% by mass or less, based on the total mass of the solid content in the positive electrode slurry. By setting the content of the positive electrode active material within the above range, high energy density and capacity can be obtained.
[0057] The binder is a component that helps bind the positive electrode active material and conductive material, etc., and bind to the current collector. The binder is preferably contained in an amount of 1% by mass or more and 30% by mass or less based on the total mass of the solid content in the positive electrode slurry. Examples of the binder include polyvinylidene fluoride (PVdF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluorine rubber, etc.
[0058] The conductive material is a substance that imparts conductivity without inducing chemical changes in the lithium-ion battery of the present disclosure. The conductive material is preferably contained in an amount of 0.5% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 20% by mass or less, for example 1% by mass or more and 5% by mass or less, based on the total mass of the solid content in the positive electrode slurry. By containing the conductive material in the above range of content, the electrical conductivity of the positive electrode is improved. Also, by containing the conductive material in the above range of content, a lithium-ion secondary battery with high energy density and capacity can be obtained.
[0059] Examples of the conductive material include carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, and graphite with a developed crystal structure; conductive fibers such as carbon fibers and metal fibers; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.
[0060] The solvent of the positive electrode slurry is not limited as long as it can form a slurry with the positive electrode active material, binder, conductive material, etc. as the positive electrode material. For example, organic solvents such as NMP (N-methyl-2-pyrrolidone), DMF (dimethylformamide), acetone, dimethylacetamide, and water can be used. In addition, the positive electrode slurry can be used in an amount that provides a suitable viscosity. For example, it can be used in an amount such that the solid content concentration in the slurry is 10% by mass or more and 60% by mass or less, preferably 20% by mass or more and 50% by mass or less.
[0061] [Separator] In the lithium ion battery according to the present disclosure, a separator may be interposed between the positive electrode and the negative electrode.
[0062] The separator of the lithium ion battery of the present disclosure plays a role of blocking internal short circuits between both electrodes and impregnating the electrolyte. The separator may be formed by mixing a polymer resin, a filler, and a solvent to produce a separator composition and then directly coating and drying the separator composition on the upper part of the electrode. Alternatively, the separator may be formed by casting and drying the separator composition on a support and then laminating the separator film peeled from the support on the upper part of the electrode.
[0063] As the separator, a normal porous polymer film that has been conventionally used as a separator, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer may be used alone or these may be laminated and used, or a normal porous nonwoven fabric, for example, a nonwoven fabric such as high melting point glass fiber and polyethylene terephthalate fiber may be used, but it is not limited thereto.
[0064] The pore diameter of the porous separator is generally 0.01 μm or more and 50 μm or less, and the porosity may be 5% or more and 95% or less. Also, the thickness of the porous separator may generally be in the range of 5 μm or more and 300 μm or less.
[0065] [Lithium-ion battery] The outer shape of the lithium-ion battery of the present disclosure is not particularly limited, and it may be cylindrical, rectangular, pouch-shaped, or coin-shaped, etc.
Examples
[0066] Hereinafter, the present disclosure will be described more specifically using examples and comparative examples, but the scope of the present disclosure is not limited to the examples.
[0067] <1. Fabrication of lithium-ion battery> (Examples 1 to 12) (1) Fabrication of positive electrode 96.5% by mass of NCM(622) ternary positive electrode material (Li(Ni 0.6 Co 0.2 Mn 0.2 )O2), 1.5% by mass of acetylene black as a conductive carbon material, and 2% by mass of polyvinylidene fluoride as a binder were dispersed in an N-methyl-2-pyrrolidone solvent to prepare a positive electrode slurry. The prepared positive electrode slurry was uniformly coated on an Al foil, dried by heating under vacuum, and then pressed to obtain a positive electrode.
[0068] (2) Fabrication of negative electrode As the negative electrode active material, 96.0% by mass of Si, as the conductive carbon material, 1.0% by mass of graphite, and as the binder, 1.5% by mass of styrene-butadiene rubber and 1.5% by mass of carboxymethyl cellulose were dispersed in water to prepare a negative electrode slurry. The prepared negative electrode slurry was uniformly coated on a Cu foil, dried by heating under vacuum, and then pressed to obtain a negative electrode.
[0069] (3) Preparation of the electrolyte Using a mixture of 10% by volume of ethylene carbonate (EC), which is a cyclic carbonate, and 90% by volume of ethyl methyl carbonate (EMC), which is a chain carbonate, as the solvent, and dissolving LiTFSI as the solute so that the salt concentration becomes 1 mol / L as the base electrolyte. To this, an additive represented by the general formula A was added so as to have a predetermined concentration with respect to the mass of the entire electrolyte to obtain an electrolyte. The specific structure and addition amount of the additive are shown in Table 1 below.
[0070]
Table 1
[0071] (4) Fabrication of the lithium-ion battery Using the above positive electrode plate, negative electrode plate, and electrolyte, and a polyolefin film as the separator, a pouch cell with an opposing area of about 12 cm 2 was fabricated.
[0072] (Comparative Example 1) A lithium-ion battery was fabricated in the same manner as in Example 1, except that the electrolyte was prepared without adding the additive represented by the general formula A to the base electrolyte.
[0073] <2. Evaluation of the lithium-ion battery> (1) Charge-discharge cycle test Using the fabricated lithium-ion batteries of Examples 1 to 12 and Comparative Example 1, a charge-discharge cycle test was conducted at 45 °C with a charge upper limit voltage of 4.3 V and a discharge lower limit voltage of 2.8 V. However, at 300 cycles, in order to confirm the exact capacity, the test was conducted using a constant current of 0.1C. From the measured capacity, the capacity retention rate was calculated according to Equation 2 below. [Equation 2] (Capacity retention rate) (%) = (Discharge capacity after 300 cycles / Initial discharge capacity) × 100
[0074] In addition, the volume change of the pouch cell before and after the cycle test was measured, and the volume expansion rate was calculated according to Equation 3 below to evaluate the influence of gas generation due to side reactions. [Equation 3] (Volume expansion rate) (%) = (Volume of pouch cell after 300 cycles / Volume of pouch cell before cycle test) × 100
[0075] The measurement results of the capacity retention rate and the volume expansion rate are shown in Table 2.
[0076]
Table 2
[0077] From Table 2, it was found that the batteries of Examples 1 to 12 had a higher capacity retention rate after 300 cycles than the battery of Comparative Example 1. Also, from Table 2, it was found that the batteries of Examples 1 to 12 had less gas generation due to side reactions such as the decomposition of the electrolyte and SEI, and a lower volume expansion rate after 300 cycles than the battery of Comparative Example 1.
[0078] (2) Measurement of battery resistance increase rate Using the lithium-ion batteries of Examples 1 to 12 and Comparative Example 1 prepared in <1. Fabrication of Lithium-Ion Batteries>, the charge cut-off voltage was set to 4.3 V and the discharge cut-off voltage was set to 2.8 V at a constant current of 0.5 C at 25 °C to confirm the discharge capacity, and the battery was stored in an oven at 60 °C in a fully charged state with the charge cut-off voltage set to 4.3 V at a constant current of 0.5 C. After storage for 4 weeks, the remaining capacity of the lithium secondary battery was measured by discharging at a constant current of 0.1 C at 25 °C, and the battery resistance increase rate (Equation 4) was evaluated. [Equation 4] (Battery resistance increase rate) (%) = (Battery resistance after storage at 60 °C for 4 weeks / Initial battery resistance) × 100 In addition, for a lithium secondary battery that was subjected to a charge-discharge cycle test of 300 cycles at 45 °C in the same manner as the charge-discharge cycle test, the remaining capacity was measured by discharging at a constant current of 0.1 C at 25 °C, and the battery resistance increase rate (Equation 5) was measured. [Equation 5] (Battery resistance increase rate) (%) = (Battery resistance after 300 cycles / Initial battery resistance) × 100
[0079] The results are shown in Table 3 below.
[0080]
Table 3
[0081] From Table 3, it was found that the batteries of Examples 1 to 12 had a lower resistance increase rate after storage at 60 °C and a lower resistance increase rate after the 45 °C 300-cycle test than the battery of Comparative Example 1.
Industrial Applicability
[0082] The lithium-ion battery according to the present disclosure is useful because the charge-discharge cycle characteristics are improved by forming an SEI on the surface of the negative electrode active material.
Claims
1. a positive electrode, a negative electrode, a non-aqueous electrolyte, comprising, wherein the non-aqueous electrolyte contains a compound represented by the following general formula A: 【Chemical 1】 (wherein, R １ and R ２ may be the same or different, a C H at the end ３ an organic group having 1 to 6 carbon atoms or H which contains a group or an OH group a lithium-ion battery, wherein in the negative electrode, the negative electrode active material consists only of a silicon-containing material.
2.
3. In the compound represented by the general formula A, R １ and R ２ are each independently H, CH ３ group or CH ２ OH group, and the lithium ion battery according to claim 1.
4. The silicon-containing material is Si or SiO ｘ The lithium ion battery according to claim 1, wherein x satisfies 0 < x < 2. The lithium-ion battery according to claim 1, wherein a mass ratio of the compound represented by the general formula A to the mass of the non-aqueous electrolyte is 0.1% by mass or more and 2.0% by mass or less.
5. The lithium-ion battery according to claim 1, wherein the non-aqueous electrolyte further contains a cyclic carbonate and a chain carbonate.
6. The lithium-ion battery according to claim 1, wherein the non-aqueous electrolyte further contains a lithium salt.
Citation Information
Patent Citations
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