Lithium ion battery

Abstract

In order to solve the problem that an existing lithium ion battery is insufficient in fast charging performance, the invention provides a lithium ion battery which comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, the negative electrode comprises a negative electrode material layer, the negative electrode material layer comprises a negative electrode active material, the negative electrode active material comprises graphite and hard carbon, the graphitization degree X of the graphite is 0.55-0.85, the graphitization degree X (hard carbon) of the hard carbon is 0.2-0.5; the ratio of X graphite to X hard carbon is 1.3-3.8; the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, the non-aqueous organic solvent comprises EC and PC, and the additive comprises VC, FEC and a boron-containing additive; the lithium ion battery satisfies the following conditions: 1 < = a / b < = 12, and 2 < = c / d < = 15. According to the lithium ion battery provided by the invention, through regulation and control of the negative electrode component and the electrolyte component, the function of rapid lithium intercalation at the negative electrode side is realized, and the rapid charging service life of the lithium ion battery is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, and specifically relates to a lithium-ion battery. Background Technology

[0002] In the current stage of rapid development of the global "green economy," the penetration rate of new energy vehicles is constantly increasing, and the installed capacity of power batteries for new energy vehicles has maintained an annual growth rate of over 30% in recent years. With the substantial increase in market demand, "energy replenishment anxiety" regarding new energy vehicles has frequently attracted consumers' attention in recent years. The current 1-3C charging technology can no longer meet consumers' charging needs for new energy vehicles, and the energy replenishment demand has driven the development of battery technology towards 4C+ fast charging.

[0003] Mainstream research indicates that negative electrode failure is a key issue limiting fast charging in lithium-ion batteries. During charging, lithium is extracted from the positive electrode and diffuses to the negative electrode interface in the electrolyte as solvated lithium. After desolvation, it migrates to the negative electrode particles, where it gains electrons and is stored as lithium intercalation compounds, thus converting electrical energy. The rate-determining step in this process is the formation of lithium intercalation compounds on the negative electrode particles. For fast charging, the lithium intercalation capability of graphite negative electrodes with highly ordered layered graphitized structures is limited under fast charging conditions. At high current densities, the highly graphitized structure of the graphite negative electrode increases the resistance to the intercalation of desolvated lithium ions at the negative electrode end face. The kinetics of lithium ions at the graphite end face are hindered, and lithium ions that cannot be intercalated in time accumulate on the negative electrode surface. This results in some lithium ions being unable to extract and losing capacity. The lithium deposited on the surface increases electrolyte side reactions, further reducing battery capacity and causing fast charging cycle failure. Summary of the Invention

[0004] To address the issue of insufficient fast-charging performance of existing lithium-ion batteries, this invention provides a lithium-ion battery.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0006] On one hand, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode comprises a negative electrode material layer, the negative electrode material layer comprising a negative electrode active material, the negative electrode active material comprising graphite and hard carbon, wherein the degree of graphitization of the graphite is X. 石墨 The graphitization degree X of hard carbon is 0.55–0.85. 硬碳 The value is 0.2 to 0.5; and X 石墨 :X 硬碳 =1.3~3.8;

[0007] The non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt, and additives. The non-aqueous organic solvent includes EC and PC, and the additives include VC, FEC, and boron-containing additives.

[0008] The lithium-ion battery meets the following conditions:

[0009] 1≤a / b≤12, 2≤c / d≤15;

[0010] Wherein, a is the mass percentage of graphite in the negative electrode active material;

[0011] b is the sum of the mass percentages of EC and VC in the non-aqueous electrolyte;

[0012] c represents the mass percentage of hard carbon in the negative electrode active material;

[0013] d represents the sum of the mass percentages of PC and FEC in the non-aqueous electrolyte.

[0014] Optionally, the lithium-ion battery meets the following conditions:

[0015] 1.5≤a / b≤10, 4≤c / d≤12.

[0016] Optionally, the mass percentage a of graphite in the negative electrode active material is 55% to 95%, and the mass percentage c of hard carbon in the negative electrode active material is 5% to 45%.

[0017] Optionally, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of EC is 5% to 35%, and the mass percentage of VC is 0.1% to 3%.

[0018] Optionally, based on the total mass of the non-aqueous electrolyte as 100%, the sum of the mass percentages of EC and VC, b, is 5.5% to 36%.

[0019] Optionally, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of PC is 2% to 20%, and the mass percentage of FEC is 0.05% to 2%.

[0020] Optionally, based on the total mass of the non-aqueous electrolyte as 100%, the sum of the mass percentages of PC and FEC, d, is 3% to 20%.

[0021] Optionally, based on the total mass of the non-aqueous electrolyte, the mass percentage of the boron-containing additive is 0.05% to 2%.

[0022] Optionally, the boron-containing additive includes one or more of LiODFB, LiBF4, LiBOB, and TMSB.

[0023] Optionally, the negative electrode active material further includes at least one of silicon-based negative electrode, tin-based negative electrode, and lithium negative electrode.

[0024] The lithium-ion battery provided by the present invention uses a mixture of graphite and hard carbon as the negative electrode active material. The graphitized region of the graphite material provides high capacity, while the non-graphitized region of the hard carbon material provides a fast lithium intercalation channel. By comprehensively controlling the graphitization ratio of graphite and hard carbon, the lithium intercalation capacity and lithium intercalation rate of the negative electrode can be effectively improved, the lithium intercalation resistance of the negative electrode can be reduced, the lithium ion storage space can be expanded, and the lithium intercalation capacity and lithium intercalation rate of the negative electrode can be improved, thereby reducing the risk of lithium plating failure caused by the lithium storage characteristics of the negative electrode. Meanwhile, since graphite and hard carbon are different types of negative electrode active materials, there is a lithium-ion migration barrier between them, leading to an increase in impedance and affecting the high-rate charge-discharge performance of the battery. Furthermore, existing electrolyte systems struggle to simultaneously form stable interfacial films on the surfaces of both negative electrode active materials. Through extensive experimentation, the inventors discovered that when EC and PC are used as non-aqueous organic solvents, and VC, FEC, and boron-containing additives are used as additives, and the mass percentages of graphite (a), hard carbon (c), EC and VC in the non-aqueous electrolyte (b), and PC and FEC in the non-aqueous electrolyte (d) satisfy the condition 1 ≤ a, the following conditions can be met. When / b≤12 and 2≤c / d≤15, a lithium-ion battery with excellent cycle life under high-rate charge-discharge conditions can be obtained. This is presumably because under these conditions, EC and VC can form an interface film on the graphite surface that facilitates rapid lithium-ion migration, while PC and FEC can form a highly stable interface film on the hard carbon surface. This isolates the negative electrode active material and the non-aqueous electrolyte, reducing side reactions of the non-aqueous electrolyte on the negative electrode surface. Furthermore, the boron-containing additive forms a network structure through boron atom centers, organically combining the graphite and hard carbon interfaces to create a continuous and stable ion migration path, reducing the risk of failure due to negative electrode interface channel blockage or side reactions causing active lithium consumption. By regulating the negative electrode and electrolyte components, rapid lithium intercalation on the negative electrode side can be achieved, improving the fast-charge life of the lithium-ion battery. Detailed Implementation

[0025] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] An embodiment of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes graphite and hard carbon, wherein the degree of graphitization of the graphite is X. 石墨 The graphitization degree X of hard carbon is 0.55–0.85. 硬碳 The value is 0.2 to 0.5; and X 石墨 :X 硬碳 =1.3~3.8.

[0027] In the description of this invention, the term graphitization degree X is used. 石墨 And graphitization degree X 硬碳 Defined as I measured by Raman spectroscopy G / (I D +I G Ratio, I G Raman spectroscopy was used to measure the carbon material at 1500–1700 cm⁻¹ -1 The peak intensity, I D Raman spectroscopy was used to measure the carbon material in the range of 1200–1500 cm⁻¹. -1 The peak intensity.

[0028] Controlling the graphitization ratio X of graphite and hard carbon 石墨 :X 硬碳 A ratio of 1.3 to 3.8 can improve the lithium intercalation capacity and rate of the negative electrode. The reasonable range for the graphitization degree ratio of graphite to hard carbon is 1.3 to 3.8. Below the lower limit of this range, the hard carbon material has fewer non-graphitized regions for fast lithium intercalation, resulting in poor fast charging performance. Above the upper limit of this range, excessive non-graphitized regions increase the probability of battery side reactions.

[0029] The non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt, and additives. The non-aqueous organic solvent includes EC (ethylene carbonate) and PC (propylene carbonate), and the additives include VC (ethylene carbonate), FEC (fluoroethylene carbonate), and boron-containing additives.

[0030] The lithium-ion battery meets the following conditions:

[0031] 1≤a / b≤12, 2≤c / d≤15;

[0032] Wherein, a is the mass percentage of graphite in the negative electrode active material;

[0033] b is the sum of the mass percentages of EC and VC in the non-aqueous electrolyte;

[0034] c represents the mass percentage of hard carbon in the negative electrode active material;

[0035] d represents the sum of the mass percentages of PC and FEC in the non-aqueous electrolyte.

[0036] The lithium-ion battery uses a mixture of graphite and hard carbon as the negative electrode active material. The graphitized region of the graphite material provides high capacity, while the non-graphitized region of the hard carbon material provides a fast lithium intercalation channel. By comprehensively controlling the graphitization ratio of graphite and hard carbon, the lithium intercalation capacity and rate of the negative electrode can be effectively improved, the lithium intercalation resistance of the negative electrode can be reduced, the lithium ion storage space can be expanded, and the risk of lithium plating failure caused by the lithium storage characteristics of the negative electrode can be reduced. Meanwhile, since graphite and hard carbon are different types of negative electrode active materials, there is a lithium-ion migration barrier between them, leading to an increase in impedance and affecting the high-rate charge-discharge performance of the battery. Furthermore, existing electrolyte systems struggle to simultaneously form stable interfacial films on the surfaces of both negative electrode active materials. Through extensive experimentation, the inventors discovered that when EC and PC are used as non-aqueous organic solvents, and VC, FEC, and boron-containing additives are used as additives, and the mass percentages of graphite (a), hard carbon (c), EC and VC in the non-aqueous electrolyte (b), and PC and FEC in the non-aqueous electrolyte (d) satisfy the condition 1 ≤ a, the following conditions can be met. When / b≤12 and 2≤c / d≤15, a lithium-ion battery with excellent cycle life under high-rate charge-discharge conditions can be obtained. This is presumably because under these conditions, EC and VC can form an interface film on the graphite surface that facilitates rapid lithium-ion migration, while PC and FEC can form a highly stable interface film on the hard carbon surface. This isolates the negative electrode active material and the non-aqueous electrolyte, reducing side reactions of the non-aqueous electrolyte on the negative electrode surface. Furthermore, the boron-containing additive forms a network structure through boron atom centers, organically combining the graphite and hard carbon interfaces to create a continuous and stable ion migration path, reducing the risk of failure due to negative electrode interface channel blockage or side reactions causing active lithium consumption. By regulating the negative electrode and electrolyte components, rapid lithium intercalation on the negative electrode side can be achieved, improving the fast-charge life of the lithium-ion battery.

[0037] In a preferred embodiment, the lithium-ion battery satisfies the following conditions:

[0038] 1.5≤a / b≤10, 4≤c / d≤12.

[0039] The EC and VC are used to provide an interface for rapid lithium-ion migration on the graphite surface. If the a / b value is below the lower limit of this range, excessive EC and VC will form a high-resistivity interface at the negative electrode, reducing the battery's capacity retention rate during high-rate charging. If the a / b value is above the upper limit of this range, EC and VC are insufficient to form a stable film, and the battery may experience active lithium loss during high-rate charge and discharge, leading to high-temperature cycle degradation. The PC and FEC provide a stable interface in localized areas of hard carbon. If the c / d value is below the lower limit of this range, high PC content can easily damage the graphite structure and degrade room-temperature cycle performance. If the c / d value is above the upper limit of this range, PC and FEC are insufficient to form a stable film on the hard carbon of the negative electrode, and side reactions of the electrolyte will occur at the hard carbon interface, increasing gas generation during high-temperature storage of the battery.

[0040] When the mass percentages of graphite (a), hard carbon (c), EC and VC in the non-aqueous electrolyte (b), and PC and FEC (d) further satisfy the above conditions, it is beneficial to fully leverage the synergistic effect between EC, PC, VC, FEC and boron-containing additives, improve the density of the interfacial film on the graphite and hard carbon surfaces, further enhance the stability and high-temperature stability of the negative electrode graphite and hard carbon under high-rate charge and discharge, form a continuous and stable ion migration path on the negative electrode side, reduce the failure risk of active lithium consumption caused by negative electrode interface channel blockage or side reactions, and comprehensively improve the fast-charging life of lithium-ion batteries.

[0041] In some embodiments, the mass percentage a of graphite in the negative electrode active material is 55% to 95%, and the mass percentage c of hard carbon in the negative electrode active material is 5% to 45%.

[0042] In specific embodiments, the mass percentage 'a' of graphite in the negative electrode active material can be 5%, 53%, 55%, 60%, 63%, 65%, 70%, 73%, 75%, 78%, 80%, 83%, 85%, 90%, 93%, 95%, or 100%; the mass percentage 'c' of hard carbon in the negative electrode active material can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 27%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 37%, 39%, 40%, 41%, 42%, 43%, 44%, or 45%.

[0043] In the aforementioned negative electrode active material, if the proportion of graphite is too high, it will lead to an increase in the resistance to lithium intercalation; if the proportion of hard carbon is too high, it will reduce the battery's lithium storage capacity. Therefore, by comprehensively controlling the composition and structure of the negative electrode active material, the risk of lithium plating failure caused by the lithium storage characteristics of the negative electrode can be reduced.

[0044] In some embodiments, based on the total mass of the non-aqueous electrolyte, the mass percentage of EC is 5% to 35%, and the mass percentage of VC is 0.1% to 3%.

[0045] In some embodiments, the sum of the mass percentages of EC and VC, b, is 5.5% to 36% based on the total mass of the non-aqueous electrolyte as 100%.

[0046] The EC and VC are used to form an interface film on the graphite surface to protect the graphite. If the content of the EC or VC in the non-aqueous electrolyte is too low, it is difficult to form a stable interface film on the graphite surface. If the content of the EC or VC in the non-aqueous electrolyte is too high, it is easy to cause the thickness of the interface film on the graphite surface to be too large, thereby increasing the impedance, which is also not conducive to improving the high-rate performance of the battery.

[0047] In some embodiments, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of PC is 2% to 20%, and the mass percentage of FEC is 0.05% to 2%.

[0048] In some embodiments, the sum of the mass percentages of PC and FEC, d, is 3% to 20% based on the total mass of the non-aqueous electrolyte being 100%.

[0049] The PC and FEC are used to form an interface film on the hard carbon surface to protect the hard carbon. If the content of the PC or FEC in the non-aqueous electrolyte is too low, it is difficult to form a stable interface film on the hard carbon surface; if the content of the PC or FEC in the non-aqueous electrolyte is too high, it will affect the stability of the film formed on the graphite surface.

[0050] In some embodiments, the boron-containing additive has a mass percentage content of 0.05% to 2% based on the total mass of the non-aqueous electrolyte (100%).

[0051] In a specific embodiment, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the boron-containing additive can be 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.7%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.8%, or 2%.

[0052] If the content of boron-containing additives in the non-aqueous electrolyte is less than 0.05%, the resulting interfacial network structure is unstable, and the battery deteriorates due to high-temperature gas generation. If the content of boron-containing additives in the non-aqueous electrolyte is greater than 2%, it will increase the thickness of the interfacial passivation layer, increase battery impedance and fast-charging polarization, and reduce fast-charging performance.

[0053] In some embodiments, the boron-containing additive includes one or more of LiODFB (lithium difluorooxalate borate), LiBF4, LiBOB (lithium bis(oxalate borate), and TMSB (tris(trimethylsilane)borate).

[0054] In some embodiments, the lithium salt includes LiPF6, LiTFSI, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, and Li2B. 10 Cl 10 At least one of lithium chloroborane, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, or lithium tetraphenylborate.

[0055] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 4 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, in the non-aqueous electrolyte, the concentration of the lithium salt can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.45 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, or 2.5 mol / L.

[0056] In some embodiments, the non-aqueous organic solvent has a mass content of 65% to 90% based on the total mass of the non-aqueous electrolyte being 100%.

[0057] Specifically, based on the total mass of the non-aqueous electrolyte as 100%, the mass content of the non-aqueous organic solvent can be 65%, 68%, 71%, 74%, 76%, 78%, 79%, 80%, 81.5%, 82%, 84%, 85%, 86%, 87%, 89%, or 90%.

[0058] In some embodiments, the non-aqueous organic solvent further includes at least one of ether solvents, nitrile solvents, carboxylic acid ester solvents, and sulfone solvents.

[0059] In some embodiments, the ether solvent includes cyclic ethers or chain ethers, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. The cyclic ethers may specifically include, but are not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ethers may specifically include, but are not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. Ether compounds can be used alone, or in any combination and ratio of two or more.

[0060] In some embodiments, the nitrile solvent may be, but is not limited to, at least one of acetonitrile, glutaronitrile, and malononitrile.

[0061] In some embodiments, the carboxylic acid ester solvent includes cyclic carboxylic acid esters and / or chain carbonates. Examples of cyclic carboxylic acid esters include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonates include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0062] In some embodiments, the sulfone solvent includes cyclic sulfones and chain sulfones. Preferably, in the case of cyclic sulfones, it is typically a compound with 3 to 6 carbon atoms, more preferably 3 to 5 carbon atoms; in the case of chain sulfones, it is typically a compound with 2 to 6 carbon atoms, more preferably 2 to 5 carbon atoms. There are no particular limitations on the amount of sulfone solvent added, and it is arbitrary within a range that does not significantly impair the performance of the lithium-ion battery of the present invention. Relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 0.3% or more by volume, preferably 0.5% or more by volume, more preferably 1% or more by volume. Furthermore, it is typically 40% or less by volume, preferably 35% or less by volume, more preferably 30% or less by volume. When using two or more sulfone solvents in combination, the total amount of sulfone solvent should satisfy the above range. When the amount of sulfone solvent added is within the above range, a non-aqueous electrolyte with excellent high-temperature storage stability is tended to be obtained.

[0063] In some embodiments, the additive further includes at least one of cyclic sulfate compounds, sulfonyl lactone compounds, phosphate compounds, and nitrile compounds.

[0064] In some embodiments, the content of the additive is 0.01% to 10% based on the total mass of the non-aqueous electrolyte as 100%.

[0065] In some embodiments, the cyclic sulfate compound includes at least one of vinyl sulfate, propylene sulfate, and methyl vinyl sulfate.

[0066] In some embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone.

[0067] In some embodiments, the phosphate ester compound includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, or the compound shown in structural formula 1:

[0068]

[0069] In structural formula 1, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group.

[0070] In a preferred embodiment, the phosphate ester compound represented by structural formula 3 may be at least one of the following: triargyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0071] In some embodiments, the nitrile compound includes at least one selected from succinic acid, glutaronitrile, hexanetrionitrile, adiponitrile, heptacyanide, octadionitrile, nonadionitrile, and sebaconitrile.

[0072] In other embodiments, the additive may also include other additives that can improve battery performance: for example, additives that improve battery safety performance, such as flame retardant additives like fluorophosphates and cyclophosphonitriles, or overcharge prevention additives like tert-amylbenzene and tert-butylbenzene.

[0073] In some embodiments, the positive electrode includes a positive electrode material layer, the positive electrode material layer including a positive electrode active material, the positive electrode active material being selected from LiFe. 1-x’ M' x’ PO4, LiMn 2-y’ M y’ O4 and LiNi x Co y Mn z M 1-x-y-z At least one of O2, wherein M' is selected from at least one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V, or Ti, and M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V, or Ti, and 0≤x'<1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1. In a specific embodiment, the positive electrode active material may be selected from LiCoO2, LiFePO4, LiFe 0.4 Mn 0.6 PO4, LiMn2O4, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 At least one of O2.

[0074] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0075] The positive electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0076] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0077] In some embodiments, the positive current collector comprises a metallic material capable of conducting electrons. Preferably, the positive current collector comprises at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive current collector is selected from aluminum foil.

[0078] In some embodiments, the negative electrode active material further includes at least one of a silicon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode. The silicon-based negative electrode may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials; the tin-based negative electrode may include tin, tin-carbon, tin-oxygen, and tin metal compounds; the lithium negative electrode may include metallic lithium or lithium alloys. Specifically, the lithium alloy may be at least one of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys.

[0079] In some embodiments, the silicon material is one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon.

[0080] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode active material layer covers the surface of the negative electrode current collector. The negative electrode current collector includes a metallic material capable of conducting electrons; preferably, the negative electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel; in a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0081] In some embodiments, the negative electrode active material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended to obtain the negative electrode active material layer. The negative electrode binder and the negative electrode conductive agent can be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described in detail here.

[0082] In some embodiments, the battery further includes a separator located between the positive electrode and the negative electrode.

[0083] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0084] The present invention will be further illustrated by the following examples.

[0085] Table 1

[0086]

[0087]

[0088]

[0089] Example 1

[0090] This embodiment illustrates the preparation method of the lithium-ion battery disclosed in this invention, including the following operations:

[0091] 1) Preparation of non-aqueous electrolyte:

[0092] Electrolyte was prepared by mixing non-aqueous organic solvent, lithium salt, and additives. The selection and content of non-aqueous organic solvent and additives are shown in Table 1. Dimethyl carbonate and ethyl methyl carbonate were used to make up the balance.

[0093] 2) Preparation of the positive electrode:

[0094] LiNi, the positive electrode active material, is mixed in a certain mass ratio. 0.6 Co 0.2 Mn 0.2 O2, conductive carbon black Super-P, and binder PVDF (mass ratio 96:2:2) are dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil, and after drying, calendering, and vacuum drying, the positive electrode is obtained.

[0095] 3) Preparation of the negative electrode:

[0096] A mixture of negative electrode active material, conductive carbon black Super-P, binder SBR, and CMC (mass ratio 97:1:2) was mixed in a certain mass ratio. The negative electrode active material consisted of graphite and hard carbon. The mass fraction ratio of graphite to hard carbon in the negative electrode active material and the degree of graphitization of graphite and hard carbon are shown in Table 1. The mixture was dispersed in deionized water to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil, and after drying, rolling, and vacuum drying, a negative electrode plate was obtained.

[0097] 4) Lithium-ion battery manufacturing: The positive electrode with the welding tab, the separator, and the negative electrode with the welding tab are stacked in sequence, wound, and sealed with aluminum-plastic film to obtain the cell. The above-mentioned electrolyte is injected into the cell, and after aging, formation, jig shaping, and secondary sealing, it is made into a lithium-ion battery.

[0098] Examples 2-20

[0099] Examples 2-20 illustrate the preparation method of the lithium-ion battery disclosed in this invention, including most of the operation steps in Example 1, with the following differences:

[0100] Table 1 shows the selection of non-aqueous organic solvents, additives and their amounts, and negative electrode active materials in the non-aqueous electrolyte.

[0101] Comparative Examples 1-11

[0102] Comparative Examples 1-11 are used to illustrate the preparation method of the lithium-ion battery disclosed in this invention, including most of the operation steps in Example 1, with the following differences:

[0103] Table 1 shows the selection of non-aqueous organic solvents, additives and their amounts, and negative electrode active materials in the non-aqueous electrolyte.

[0104] Performance testing

[0105] The lithium-ion batteries prepared above were subjected to the following performance tests:

[0106] 1) Rate charging capacity retention rate: With the battery at room temperature, charge it at a constant current of 0.2C to 4.4V, then charge it at a constant voltage of 0.05C, and discharge it at 0.2C to 3V. The charging capacity is recorded as C1; charge it at a constant current of 5C to 4.4V, then charge it at a constant voltage of 0.05C, and discharge it at 1C to 3V. The charging capacity is recorded as C2; the rate charging capacity retention rate is C2 / C1.

[0107] 2) Room temperature fast charging cycle life test: The battery is placed at room temperature, charged at 5C constant current to 4.4V and then charged at constant voltage to 0.05C, and discharged at 1C to 3V. The charging capacity is measured as C3. After the nth cycle of charging and discharging, the charging capacity is measured as Cn. Cn / C3 = 80%, and the 5C rate fast charging room temperature cycle life is n.

[0108] 3) High-temperature fast charging cycle life test: The battery is placed in a constant temperature environment of 45℃, charged at 5C constant current to 4.4V and then charged at constant voltage to 0.05C, and discharged at 1C to 3V. The charging capacity is measured as C4. After the mth charge and discharge cycle, the charging capacity is measured as Cm. Cm / C4=80%, and the high-temperature cycle life of 5C fast charging is m.

[0109] 4) High-temperature storage gas generation rate test: Place the battery at room temperature and let it stand for 2 hours, then test the volume V1. Transfer it to 60℃ for storage for 30 days, and let it stand at room temperature for 2 hours, then test the volume V2. High-temperature storage gas generation rate = (V2-V1) / V1*100%.

[0110] (1) The test results obtained from Examples 1 to 17 and Comparative Examples 1 to 11 are filled in Table 2.

[0111] Table 2

[0112]

[0113]

[0114] The test results of Examples 1-17 and Comparative Examples 1-11 show that in a battery system using a mixture of graphite and hard carbon as the negative electrode active material and EC and PC as the non-aqueous organic solvent, when VC, FEC, and boron-containing additives are added to the non-aqueous electrolyte as additives, and when the mass percentages of graphite (a), hard carbon (c), EC and VC (b), and PC and FEC (d) in the non-aqueous electrolyte satisfy the following relationships: 1≤a / b≤12, 2≤c / d≤15, the resulting lithium-ion battery exhibits excellent cycle life and high-temperature electrochemical performance under high-rate charge-discharge conditions. It is speculated that under these conditions, EC and VC can form an interface film on the graphite surface that allows for rapid migration of lithium ions, while PC and FEC can form a highly stable interface film on the hard carbon surface. This is used to isolate the negative electrode active material and the non-aqueous electrolyte, reduce the side reactions of the non-aqueous electrolyte on the negative electrode surface, and reduce the failure risk of active lithium consumption caused by the blockage of the negative electrode interface channel or side reactions. This is conducive to the simultaneous formation of a stable interface film on the surface of the two negative electrode active materials.

[0115] A comparison of the test results from Examples 1-1 and Examples 12-17 shows that in Examples 12-17, when one or more parameters of a, b, c, and d exceed the specified ranges (55% ≤ a ≤ 95%, 5.5% ≤ b ≤ 36%, 5% ≤ c ≤ 45%, 3% ≤ d ≤ 20%), the lithium-ion batteries obtained show a certain degree of decrease in lifespan during high-rate charge-discharge cycles compared to Examples 1-11. This indicates that when the mass percentage of graphite a and the mass percentage of hard carbon in the negative electrode active material exceed the specified ranges, the lithium-ion battery lifespan decreases to some extent compared to Examples 1-11. c. When the sum of the mass percentages of EC and VC in the non-aqueous electrolyte (b) and the sum of the mass percentages of PC and FEC (d) are too high or too low, it will affect the film density, stability, and ion permeability of the interface film on the surface of the negative electrode material layer, leading to uneven film formation and increased impedance. When the conditions 55%≤a≤95%, 5.5%≤b≤36%, 5%≤c≤45%, and 3%≤d≤20% are met, the resulting lithium-ion battery has the best electrochemical performance under high temperature and high rate charge / discharge conditions.

[0116] The test results from Comparative Examples 1 to 18 show that even if the values ​​of a, b, c, and d all meet their parameter range limits, excessively large or small a / b or c / d values ​​will lead to the deterioration of the high-temperature performance and high-rate charge-discharge performance of lithium-ion batteries. This indicates that there is an interaction between the mass percentage of graphite (a) in the negative electrode active material, the mass percentage of hard carbon (c), the sum of the mass percentages of EC and VC in the non-aqueous electrolyte (b), and the sum of the mass percentages of PC and FEC (d). Only when the four reach a good balance can they significantly improve the high-temperature performance and high-rate charge-discharge performance of lithium-ion batteries.

[0117] The test results of Comparative Examples 9-11 show that the graphitization degree of graphite and hard carbon is higher than that of X. 石墨 :X 硬碳 The addition of boron-containing additives has a significant impact on the lithium-ion battery system provided by this invention. Specifically, the boron-containing additives form a network structure through the boron atom centers, organically combining the graphite interface and the hard carbon interface to form a continuous and stable ion migration path. By adapting the graphitization degree of graphite and hard carbon, a better ion conduction effect can be achieved.

[0118] (2) The test results obtained in Examples 3, 18-20 are filled in Table 3.

[0119] Table 3

[0120]

[0121] As can be seen from the test results of Examples 3, 18-20, in the lithium-ion battery system provided by the present invention, when different boron-containing additives are used, and when the mass percentage of graphite a, the mass percentage of hard carbon c, the sum of the mass percentages of EC and VC in the negative electrode active material b, and the sum of the mass percentages of PC and FEC d in the non-aqueous electrolyte satisfy the following relationships: 1≤a / b≤12, 2≤c / d≤15, they can all significantly improve the high-rate discharge performance and high-temperature cycle performance of the lithium-ion battery. This indicates that the boron element contained in different boron-containing additives has a universally applicable improving effect on the battery system of the present invention.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized by, A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, the negative electrode active material includes graphite and hard carbon, the graphite has a graphitization degree X 石墨 of 0.55 to 0.85, the hard carbon has a graphitization degree X 硬碳 of 0.2 to 0.5; and X 石墨 : X 硬碳 = 1.3 to 3.

8. The non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, the non-aqueous organic solvent comprises EC and PC, and the additive comprises VC, FEC and a boron-containing additive; The lithium ion battery satisfies the following conditions: 1≤a / b≤12, 2≤c / d≤15; wherein a is the mass percentage of graphite in the negative electrode active material; b is the sum of the mass percentages of EC and VC in the non-aqueous electrolyte; c is the mass percentage of hard carbon in the negative electrode active material; d is the sum of the mass percentages of PC and FEC in the non-aqueous electrolyte.

2. The lithium-ion battery of claim 1, wherein, The lithium ion battery satisfies the following conditions: 1.5≤a / b≤10, 4≤c / d≤12.

3. The lithium-ion battery of claim 1, wherein, The mass percentage a of graphite in the negative electrode active material is 55% to 95%, and the mass percentage c of hard carbon in the negative electrode active material is 5% to 45%.

4. The lithium-ion battery of claim 1, wherein, The mass percentage of EC is 5% to 35%, and the mass percentage of VC is 0.1% to 3%, based on the total mass of the non-aqueous electrolyte.

5. The lithium-ion battery of claim 1 or 4, wherein, The sum b of the mass percentages of EC and VC is 5.5% to 36%, based on the total mass of the non-aqueous electrolyte.

6. The lithium-ion battery of claim 1, wherein, The mass percentage of PC is 2% to 20%, and the mass percentage of FEC is 0.05% to 2%, based on the total mass of the non-aqueous electrolyte.

7. The lithium-ion battery of claim 1, wherein, The sum d of the mass percentages of PC and FEC is 3% to 20%, based on the total mass of the non-aqueous electrolyte.

8. The lithium-ion battery of claim 1, wherein, The mass percentage of the boron-containing additive is 0.05% to 2%, based on the total mass of the non-aqueous electrolyte.

9. The lithium-ion battery of claim 1, wherein, The boron-containing additive comprises one or more of LiODFB, LiBF4, LiBOB and TMSB.

10. The lithium-ion battery of claim 1, wherein, The negative electrode active material further comprises at least one of a silicon-based negative electrode, a tin-based negative electrode and a lithium negative electrode.

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