Lithium ion battery

Abstract

The invention belongs to the technical field of new energy batteries, and particularly relates to a lithium ion battery. The lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and a non-aqueous electrolyte, the positive electrode comprises a positive electrode material layer containing a positive electrode active material, and the positive electrode active material comprises lithium iron phosphate; the compaction density of the positive electrode material layer is X; the negative electrode comprises a negative electrode material layer containing a negative electrode active material, and the compaction density of the negative electrode material layer is Y; the non-aqueous electrolyte comprises an additive, a lithium salt and an organic solvent; the additive comprises vinylene carbonate and a first additive as shown in a structural formula 1; the lithium ion battery satisfies the following conditions: 0.15 < = ((a / b) 1 / 2) / (X / Y) < = 20, 1.45 < = X / Y < = 2.0, 0.05 < = a < = 5, 0.05 < = b < = 5, 2.5 < = X < = 2.85, and 1.40 < = Y < = 1.75. The lithium ion battery provided by the invention has excellent cycle performance and safety performance.

Description

Technical Field

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

[0002] Lithium iron phosphate (LFP) batteries, with their advantages of long cycle life, high thermal stability, and low cost per watt-hour, have become one of the dominant technologies in modern energy storage systems. Due to the specific application scenarios of energy storage systems, extremely high requirements are placed on the cycle life and thermal safety of batteries. This is especially true in large-scale energy storage power stations at the megawatt-hour level and above, where not only are stringent standards for cycle performance met, but there is also a high risk of thermal runaway. Therefore, how to further improve the cycle life and enhance the safety performance of lithium-ion batteries has become a critical issue that urgently needs to be addressed. At the same time, improving these two aspects of performance will also help reduce end-product production costs and alleviate the pressure on companies in the battery recycling process. To address these challenges, there is an urgent need to provide system solutions that meet the requirements of long cycle life and high safety performance. Summary of the Invention

[0003] Therefore, the purpose of this invention is to provide a lithium-ion battery that addresses the problem of how to further improve the cycle life and safety performance of lithium iron phosphate batteries.

[0004] To achieve the above objectives, the present invention adopts the following technical solution.

[0005] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte;

[0006] The positive electrode includes a positive electrode material layer comprising a positive electrode active material, wherein the positive electrode active material includes lithium iron phosphate; the compaction density of the positive electrode material layer is X g / cm³. 3 ;

[0007] The negative electrode includes a negative electrode material layer containing a negative electrode active material, and the compaction density of the negative electrode material layer is Y g / cm³. 3 ;

[0008] The non-aqueous electrolyte includes additives, lithium salts, and organic solvents;

[0009] The additives include vinylene carbonate and a first additive shown in structural formula 1;

[0010] Structural Formula 1,

[0011] Wherein, at least one of R2, R2, R4, and R5 is selected from halogen atoms, -CF3, -COCH3, -COCF3, -COOCH3, -NHCOCF3, -NO2, -COH, -SO3H, -CCl3, and maleimide groups, and the others are each independently selected from H, C1-C12 alkyl or haloalkyl, C5-C7 cycloalkyl or halocycloalkyl, C2-C12 alkenyl or haloalkenyl, C1-C12 alkoxy or haloalkoxy, aromatic hydrocarbon groups and their derivatives.

[0012] R1 is selected from any one of H, C1-C12 alkyl or haloalkyl, C5-C7 cycloalkyl or halocycloalkyl, C2-C12 alkenyl or haloalkenyl, C1-C12 alkoxy or haloalkoxy, aromatic hydrocarbon groups and their derivatives.

[0013] Based on the mass of the non-aqueous electrolyte, the mass percentage of the first additive is a%, and the mass percentage of the vinylene carbonate is b%.

[0014] The lithium-ion battery satisfies: 0.15 ≤ ((a / b)) 1 / 2 ) / (X / Y)≤20, 1.45≤X / Y≤2.0, and 0.05≤a≤5, 0.05≤b≤5, 2.5≤X≤2.85, 1.40≤Y≤1.75.

[0015] The lithium-ion battery of this invention uses vinylene carbonate and the first additive shown in structural formula 1 as additives, and limits the content of vinylene carbonate and the first additive, as well as the compaction density and ratio of the positive electrode material layer and the negative electrode material layer. Through extensive research, the inventors discovered that when the ratio of the compaction density X of the positive electrode material layer to the compaction density Y of the negative electrode material layer (X / Y), the mass percentage of the first additive (a%), and the mass percentage of vinylene carbonate (b%) satisfy: 0.15 ≤ ((a / b) 1 / 2When X / Y ≤ 20, and 0.05 ≤ a ≤ 5, 0.05 ≤ b ≤ 5, 1.45 ≤ X / Y ≤ 2.0, 2.5 ≤ X ≤ 2.85, and 1.40 ≤ Y ≤ 1.75, the parameters work synergistically to achieve a lithium-ion battery that balances cycle performance and safety. The reason for this is that, on the one hand, by adjusting the ratio of the positive to negative electrode compaction density, the lithium-ion transport barrier at the electrode material ends can be reduced, while optimizing the ion transport path and increasing the active sites of lithium ions at the positive / negative electrode material ends; on the other hand, by using a combination of vinylene carbonate and the first additive shown in Formula 1, an interface film with certain electrochemical stability and ultra-high thermal stability is formed on the surface of the positive and negative electrodes of the battery, thereby further enhancing the cycle life and safety performance of the battery. In summary, this invention achieves a synergistic effect among various parameters by limiting the content of vinylene carbonate and the first additive shown in structural formula 1 in the non-aqueous electrolyte, and the ratio of the compaction density of the positive electrode material layer to the negative electrode material layer, within a certain range. This results in a lithium-ion battery that balances excellent long-cycle performance and safety. Preferably, the lithium-ion battery satisfies: 0.3 ≤ ((a / b) 1 / 2 ) / (X / Y)≤9.

[0016] Vinylene carbonate (VC), as a key additive in lithium iron phosphate systems, can form a film on the negative electrode superior to ethylene carbonate, and the resulting interfacial film exhibits good electrochemical stability, which is fundamental for achieving long-cycle performance. When the VC content is too low, a complete and dense SEI film cannot form on the negative electrode surface, leading to the continuous decomposition of some electrolyte on the negative electrode surface, resulting in decreased battery cycle performance, reduced coulombic efficiency, and potentially even lithium dendrite growth, posing safety hazards. When the VC content is too high, excessive VC will over-polymerize on the negative electrode surface, forming an excessively thick SEI film, increasing interfacial impedance, reducing the battery's rate performance and low-temperature performance, and consuming a large amount of active lithium, resulting in a significant decrease in battery capacity. Specifically, the mass percentage b% of VC is 0.05%, 0.08%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or any combination of these values. Preferably, the mass percentage (b%) of the vinylene carbonate is 0.1% to 4%. Within this range, the battery can form a stable and dense SEI film on the negative electrode surface, effectively suppressing the continuous decomposition of the electrolyte, while maintaining good cycle life, coulombic efficiency, and rate performance.

[0017] A single battery cell made with the aforementioned lithium iron phosphate positive electrode active material has a cell capacity ≥300Ah. For large-scale energy storage power stations at the megawatt-hour level and above, the required cell capacity is 300Ah and above. However, the introduced high-capacity cells release more heat than conventional capacity cells during long-term cycling. Over time, this makes the interfacial film formed by VC at the negative electrode unstable under such long-term heat release, leading to cycling failure. At the same time, long-term heat accumulation can cause battery safety issues. The compound described in Structural Formula 1 is a benzoxazine compound. This type of compound has the effect of thermally intelligent film formation. It can form a stable CEI / SEI coating on the surface of the positive and negative electrodes, blocking the contact between the positive and negative electrode active materials and the electrolyte. Specifically, when the temperature exceeds 80°C, the benzoxazine compound can polymerize under thermal initiation to form a phenol-rich polybenzoxazine with flame-retardant function, thereby reducing the reactivity of the positive and negative electrode materials and further preventing thermal runaway. Meanwhile, introducing the compound of Structural Formula 1 as the first additive can inhibit the decomposition of the interfacial film formed at the VC negative electrode at high temperatures, ensuring a long cycle life of the battery. Moreover, the phenolic structure with flame-retardant function formed by benzoxazine compounds at the positive and negative electrodes has certain electrochemical stability and ultra-high thermal stability, which can further enhance the battery cycle life and improve the battery safety performance. However, when the content of the compound shown in Structural Formula 1 is too low, its thermal intelligent response film formation effect is insufficient, and it cannot form a sufficiently complete and effective CEI / SEI protective layer inside the battery. Under long-term high-temperature operation, it is difficult to effectively inhibit the decomposition of the VC interfacial film, and the protection effect on the positive and negative electrode materials is limited. It also cannot provide sufficient flame-retardant effect in the early stage of thermal runaway. Therefore, the effect on extending cycle life and improving safety performance is not obvious. When the content of the compound described in Structural Formula 1 is too high, the excess compound may undergo partial polymerization or excessive film formation prematurely at normal operating temperatures, increasing the internal resistance of the battery and leading to a decrease in initial capacity and rate performance. Specifically, the mass percentage a% of the compound represented by structural formula 1 is 0.05%, 0.08%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or any combination of these values. Preferably, the mass percentage a% of the compound represented by structural formula 1 is 0.1% to 3%. Within this range, the additive can ensure no significant negative impact on battery performance at normal temperatures, and can rapidly and effectively exert its thermally responsive polymerization function when the battery temperature rises abnormally (e.g., exceeding 80°C), forming a stable, highly barrier-resistant, and flame-retardant protective layer. This not only effectively stabilizes the SEI film formed by VC and significantly extends the cycle life of large-capacity cells under harsh operating conditions, but also provides a crucial thermal safety barrier for the battery system, achieving the best balance between cycle performance and safety performance.

[0018] Specifically, as one embodiment of the present invention, the first additive includes any one or more of the following compounds:

[0019]

[0020]

[0021] Specifically, the preparation method of the first additive shown in structural formula 1, taking compound 1 as an example, includes the following steps:

[0022] (1) Synthesize N,N-dimethylethanolamine from aniline and paraformaldehyde in 1,4-dioxane (under alkaline conditions, heating at 40°C).

[0023]

[0024] (2) Dissolve p-trifluoromethylphenol in 1,4-dioxane, and then mix it with N,N-dimethylethanolamine and stir the mixture to obtain compound 1 (under alkaline conditions, heating at 90°C).

[0025]

[0026] (3) After the reactants are cooled, the solvent is removed by rotary evaporation, followed by washing in dichloromethane and sodium chloride aqueous solution, and then drying to obtain the product.

[0027] To obtain the other compounds shown in structural formula 1, simply replace aniline with Replace trifluoromethylphenol with .

[0028] Wherein, at least one of R2, R2, R4, and R5 is selected from halogen atoms, -CF3, -COCH3, -COCF3, -COOCH3, -NHCOCF3, -NO2, -COH, -SO3H, -CCl3, and maleimide groups, and the others are each independently selected from H, C1-C12 alkyl or haloalkyl, C5-C7 cycloalkyl or halocycloalkyl, C2-C12 alkenyl or haloalkenyl, C1-C12 alkoxy or haloalkoxy, aromatic hydrocarbon groups and their derivatives.

[0029] R1 is selected from any one of H, C1-C12 alkyl or haloalkyl, C5-C7 cycloalkyl or halocycloalkyl, C2-C12 alkenyl or haloalkenyl, C1-C12 alkoxy or haloalkoxy, aromatic hydrocarbon groups and their derivatives.

[0030] Additives can form an interfacial film between the positive and negative electrodes due to their intrinsic properties. However, the quality of film formation is affected by material parameters. By adjusting the parameters of the positive and negative electrode materials, the additives can better form a film at the interface. Therefore, in this invention, the compaction density X of the positive electrode material layer is controlled to be 2.5~2.85 g / cm³. 3 Specifically, the compaction density X of the positive electrode material layer is 2.5 g / cm³. 3 2.52g / cm 3 2.55g / cm 3 2.6g / cm 3 2.65g / cm 3 2.70 g / cm 3 2.75g / cm 3 2.80g / cm 3 2.85g / cm 3 Or a range of any two of these values; preferably, the compaction density X of the positive electrode material layer is 2.55~2.7 g / cm³. 3 The compaction density Y of the negative electrode material layer was controlled to be 1.40~1.75 g / cm³. 3 Specifically, the compaction density Y of the negative electrode material layer is 1.40 g / cm³. 3 1.43 g / cm 3 1.45g / cm 3 1.50g / cm 3 1.55g / cm 3 1.60g / cm 3 1.65g / cm 3 1.70g / cm 3 1.75g / cm 3 Or a range of any two of these values; preferably, the compaction density Y of the negative electrode material layer is 1.45~1.65 g / cm³. 3 .

[0031] By adjusting the ratio of positive electrode compaction density to negative electrode compaction density, the resistance to lithium ion transport at the electrode material end can be reduced, while the ion transport path can be optimized, and the active sites of lithium ions at the positive / negative electrode material ends can be increased, providing a good interfacial environment for the first additive and VC negative electrode film formation shown in Formula 1. When the ratio X / Y of the compaction density of the positive electrode material layer to that of the negative electrode material layer is too small, it means that the positive electrode compaction is relatively low or the negative electrode compaction is relatively high. This may lead to an imperfect electron conduction path and insufficient active sites in the positive electrode. At the same time, it makes the capacity of the negative electrode relatively excessive compared to the positive electrode. During charging, the driving force for lithium ion insertion on the negative electrode side is insufficient, which is not conducive to the formation of a dense and stable SEI film and may cause lithium plating. When the ratio X / Y of the compaction density of the positive electrode material layer to that of the negative electrode material layer is too large, it means that the positive electrode compaction is too high or the negative electrode compaction is relatively insufficient. This may lead to difficulties in the transport of lithium ions in the dense positive electrode and increased polarization. Their preferential insertion or extraction on the positive electrode surface will aggravate electrolyte decomposition and form an unstable CEI film. At the same time, the barren negative electrode structure cannot provide enough space and channels for the uniform insertion of lithium ions, which can easily lead to local overcharging and rapid capacity decay. Specifically, the ratio X / Y of the compaction density of the positive electrode material layer to that of the negative electrode material layer is 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 2.0, or any combination of these values. Preferably, the ratio X / Y of the compaction density of the positive electrode material layer to that of the negative electrode material layer is 1.6 to 1.8. Within this range, the ion transport kinetics and structural stability between the positive and negative electrodes achieve an optimal balance, and the lithium-ion flow is uniformly distributed at the interface. This creates an ideal interfacial chemical environment for the first additive and vinylene carbonate to synergistically construct a stable, low-resistance CEI / SEI film on both sides, thereby significantly improving the battery's cycle life, rate performance, and safety.

[0032] In some embodiments of the present invention, the organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents;

[0033] In some preferred embodiments, the ether solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0034] In some preferred embodiments, the nitrile solvent includes one or more of acetonitrile, propionitrile, butyronitrile, adiponitrile, glutaronitrile, ethoxypropionitrile, and 3-methoxypropionitrile;

[0035] In some preferred embodiments, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluoroethylene carbonate.

[0036] In some preferred embodiments, the carboxylic acid ester solvent includes one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0037] In some preferred embodiments, the sulfone solvent includes one or more of sulfolane, dimethyl sulfoxide, 2-methylsulfolane, and 3-methylsulfolane.

[0038] Based on the non-aqueous electrolyte by mass of 100%, the content of the organic solvent is 20% to 80%. In specific embodiments, the mass percentage of the organic solvent is within any two of 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or more. Preferably, the content of the organic solvent is 20% to 60%.

[0039] In some embodiments of the present invention, the lithium salt is selected from at least one of LiPF6, LiBF4, LiFSI, LiBOB, LiDFOB, LiPO2F2, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, and LiN(SO2F)2.

[0040] In the non-aqueous electrolyte, the concentration of the lithium salt is 0.1~4 mol / L. In specific embodiments, the concentration of the lithium salt is within the range of 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3.0 mol / L, 3.2 mol / L, 3.4 mol / L, 3.6 mol / L, 3.8 mol / L, 4 mol / L, or any two of the above.

[0041] In some embodiments of the present invention, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is located on both sides of the positive electrode current collector. The positive electrode current collector includes a metallic material capable of conducting electrons. Preferably, the positive electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0042] In some embodiments of the present invention, the positive electrode further includes a positive electrode binder and a positive electrode conductive agent. The positive electrode binder includes one or more 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. The positive electrode conductive agent includes one or more of the following: conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0043] In some embodiments of the present invention, the non-aqueous electrolyte further includes auxiliary additives, which include at least one selected from cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and borate ester compounds. Adding these auxiliary additives to the electrolyte allows them to participate in the film-forming process together with the first additive and vinylene carbonate, further enhancing the stability of the protective film and thus further improving the battery's high-temperature storage performance and fast-charge cycle performance.

[0044] In some preferred embodiments, the cyclic sulfate compound includes at least one of 4-methyl vinyl sulfate, vinyl sulfate, and propylene sulfate.

[0045] In some preferred embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0046] In some preferred embodiments, the cyclic carbonate compound includes at least one of ethylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, methylene carbonate, trifluoromethyl vinyl carbonate, diethylene carbonate, and a compound represented by structural formula 2 below:

[0047] Structural Formula 2,

[0048] In the structural formula 2 shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group.

[0049] In some preferred embodiments, the compound represented by structural formula 2 includes at least one of the compounds represented by compounds 2-1 to 2-6 below:

[0050]

[0051] Compound 2-1, Compound 2-2, Compound 2-3

[0052]

[0053] Compounds 2-4, 2-5, and 2-6.

[0054] In some preferred embodiments, the phosphate ester compound includes at least one of the compounds shown in structural formula 3:

[0055] Structural Formula 3

[0056] In structural formula 3, R 31 R 32 R 33 Each independent group is selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; more preferably, the compound represented by structural formula 3 includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, triargylpropyl phosphate, diargylmethyl phosphate, diargylethyl phosphate, diargylpropyl phosphate, diargyltrifluoromethyl phosphate, diargyl-2,2,2-trifluoroethyl phosphate, diargyl-3,3,3-trifluoropropyl phosphate, diargylhexafluoroisopropyl 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 diallylhexafluoroisopropyl phosphate.

[0057] In some preferred embodiments, the borate ester compound includes at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0058] Specifically, in some embodiments of the present invention, the content of the auxiliary additive is 0.01-10% based on the total mass of the non-aqueous electrolyte as 100%. Preferably, the content is 0.1-5%; more preferably, the content is 0.1-2%. Specifically, the content of any optional substance in the auxiliary additive can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, or any combination of these values.

[0059] In some embodiments of the present invention, the negative electrode active material is any one or more of silicon-based materials and carbon materials. The silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon materials, and silicon alloy materials; preferably, the silicon material is a nano-silicon material; preferably, the silicon oxide material is SiO₂. x Materials, wherein 0 ≤ x < 2; preferably, the silicon-carbon material is: a silicon-based material containing silicon and carbon materials, and / or containing SiO2. y The silicon-based material is a carbon material, wherein 0 ≤ y < 2; preferably, the silicon alloy material is a Mg2Si alloy material and / or an Fe2Si alloy material. The carbon material is selected from one or more of artificial graphite, natural graphite, composite graphite, graphene, and hard carbon; preferably, the carbon material is an artificial graphite material.

[0060] Specifically, in some embodiments of the present invention, the negative electrode material layer further includes a negative electrode binder, a negative electrode conductive agent, and a negative electrode current collector. The material of the negative electrode current collector can be the same as that of the positive electrode current collector, and will not be described again here. The negative electrode binder and the negative electrode conductive agent can be the same as those of the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described again here.

[0061] Specifically, in some embodiments of the present invention, the lithium-ion battery further includes a separator located between the positive electrode and the negative electrode.

[0062] The diaphragm is a conventional diaphragm, selected from one or more of polymer diaphragms, non-woven fabrics, and inorganic-organic composite diaphragms. For example, a single-layer polypropylene (PP) diaphragm, a single-layer polyethylene (PE) diaphragm, a double-layer PP / PE diaphragm, a double-layer PP / PP diaphragm, or a triple-layer PP / PE / PP diaphragm.

[0063] In some embodiments of the present invention, the voltage range of the lithium-ion battery is between 2.0 and 3.65V.

[0064] The lithium-ion battery provided in this invention uses vinylene carbonate and the first additive shown in structural formula 1 as additives, and limits the mass percentage of the first additive described in structural formula 1 (a%) and the mass percentage of vinylene carbonate (b%) in the non-aqueous electrolyte, as well as the relationship between the ratio of the compaction density X of the positive electrode material layer to the compaction density Y of the negative electrode material layer (X / Y) to satisfy 0.15 ≤ ((a / b)). 1 / 2 When 1.45 ≤ X / Y ≤ 2.0, and 0.05 ≤ a ≤ 5, 0.05 ≤ b ≤ 5, 2.5 ≤ X ≤ 2.85, and 1.40 ≤ Y ≤ 1.75, the safety performance of the battery can be improved while ensuring a long cycle life, greatly reducing the risk of thermal runaway of lithium-ion batteries, and achieving the goal of improving the safety performance of electrochemical energy storage devices. The various parameters achieve a synergistic effect, thus obtaining a lithium-ion battery that balances excellent long cycle performance and safety performance. Detailed Implementation

[0065] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0066] Example 1

[0067] I. The method for preparing the lithium-ion battery in this embodiment includes the following steps:

[0068] 1. Preparation of electrolyte

[0069] Ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) were mixed in a mass ratio of EC:DEC:PC:PP:EP = 10:25:25:20:20. Then, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L. Finally, a certain amount of additives (4% by mass of vinylene carbonate and 0.5% by mass of compound 1, the first additive shown in structural formula 1) was added based on the total mass of the electrolyte.

[0070] 2. Preparation of the positive electrode plate

[0071] Lithium iron phosphate, conductive agent (super P+CNT), and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 93:4:3, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry was uniformly coated on both sides of an aluminum foil, and after drying, calendering, and vacuum drying, aluminum leads were welded on using an ultrasonic welder to obtain the positive electrode plate. The compaction density of the positive electrode material layer was 2.6 g / cm³. 3 .

[0072] 3. Preparation of the negative electrode plate

[0073] Artificial graphite (anode active material), Super-P conductive carbon black, styrene-butadiene rubber (SBR) binder, and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5 and then dispersed in deionized water to obtain a cathode slurry. The slurry was coated on both sides of a copper foil, dried, calendered, and vacuum dried, and then nickel leads were welded on using an ultrasonic welder to obtain the cathode plate. The compaction density of the cathode material layer was 1.5 g / cm³. 3 .

[0074] 4. Cell fabrication

[0075] A three-layer separator with a thickness of 20 μm is placed between the positive and negative plates. Then, the sandwich structure composed of the positive plate, negative plate and separator is wound up, and the wound body is flattened and placed in an aluminum foil packaging bag. It is then vacuum baked at 75°C for 48 hours to obtain the cell to be injected with electrolyte.

[0076] 5. Electrolyte injection and formation of battery cells

[0077] In a glove box with a dew point controlled below -40°C, the electrolyte prepared above was injected into the battery cell, vacuum-sealed, and left to stand for 24 hours. Then, the first charge formation was performed under the following conditions: formation temperature of 40°C to 85°C, and formation pressure of 2 to 8 kg / cm³. 2 The charging current is 0.05C~0.12C, and the discharging current is 0.1C~0.3C.

[0078] Examples 1-25, Comparative Examples 1-14

[0079] Examples 1-25 and Comparative Examples 1-14 are used to illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1, the difference being: the content of the first additive a%, the content of vinylene carbonate b%, the compaction density X of the positive electrode material layer, the compaction density Y of the negative electrode material layer, the ratio X / Y of the compaction density of the positive electrode material layer to the compaction density of the negative electrode material layer, and the relationship ((a / b)). 1 / 2 The value of ) / (X / Y).

[0080] II. Performance Testing:

[0081] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to the following performance tests, including high-temperature cycle performance test, high-temperature storage performance test, and low-temperature performance test. The specific test methods for each test are as follows:

[0082] 1. High-temperature cycling performance test

[0083] The lithium-ion batteries prepared in each embodiment and comparative example were placed in an oven at a constant temperature of 45°C and charged at a constant current of 1C to 3.65V, then charged at a constant voltage until the current dropped to 0.02C, and then discharged at a constant current of 1C to 2.5V. This cycle was repeated, and the discharge capacity of the first discharge and the last discharge were recorded.

[0084] Calculate the capacity retention during high-temperature cycling using the following formula:

[0085] Capacity retention rate = (Final discharge capacity / First discharge capacity) × 100%.

[0086] 2. Room temperature cycling performance test

[0087] The lithium-ion batteries prepared in each embodiment and comparative example were placed in an oven at a constant temperature of 25°C and charged to 3.65V with a constant current and constant voltage of 1C, with a cutoff current of 0.05C. Then they were discharged to 2.5V with a constant current of 1C. This cycle was repeated, and the discharge capacity of the first discharge and the last discharge were recorded.

[0088] Calculate the capacity retention rate during ambient temperature cycling using the following formula:

[0089] Capacity retention rate = (Final discharge capacity / First discharge capacity) × 100%.

[0090] 3. High-temperature storage performance test

[0091] The formed lithium-ion battery was charged to 3.65V at room temperature using a constant current and constant voltage (0.5C), and the initial battery thickness was measured. Then, it was discharged to 2.5V using a constant current and constant voltage (0.5C), and the initial discharge capacity and initial battery thickness were measured. After storage at 60℃ for 30 days, the battery thickness after storage was measured. The battery was then discharged to 2.5V using a constant current and constant voltage (0.5C), and the battery's retention capacity was measured. Finally, the battery was charged to 3.65V using a constant current and constant voltage (0.5C), and then discharged to 2.5V using a constant current and constant voltage (1C), and the retention capacity, recovery capacity, and battery thickness after storage were measured. The calculation formula is as follows:

[0092] Battery capacity retention rate (%) = Retained capacity / Initial discharge capacity × 100%;

[0093] Battery capacity recovery rate (%) = Recovered capacity / Initial discharge capacity × 100%;

[0094] Thickness expansion rate (%) = (Battery thickness after storage - Initial battery thickness) / Initial battery thickness × 100%.

[0095] 4. Low-temperature performance test

[0096] At 25℃, the formed battery was charged to 3.65V using a 1C constant current and constant voltage method, and then discharged to 2.5V using a 1C constant current method, and the discharge capacity was recorded. Then, it was charged to 3.65V using a 1C constant current and constant voltage method, placed in an environment at -20℃ for 12 hours, and then discharged to 2.0V using a 0.5C constant current method, and the discharge capacity was recorded.

[0097] The low-temperature discharge efficiency value at -20℃ is calculated as follows: 0.5C discharge capacity (-20℃) / 1C discharge capacity (25℃) × 100%.

[0098] Test Results: Table 1 shows the parameters required for preparing lithium-ion batteries in Examples 1-15 and Comparative Examples 1-14. The differences between Examples 2-15 and Comparative Examples 1-14 and Example 1 lie in the relevant parameters in Table 1. The remaining parameters and preparation steps are the same as those described in Example 1. The specific differences are: the mass percentage of the first additive a%, the mass percentage of vinylene carbonate b%, the compaction density X of the positive electrode material layer, the compaction density Y of the negative electrode material layer, the ratio X / Y of the compaction density X of the positive electrode material layer to the compaction density Y of the negative electrode material layer, and the relationship ((a / b)). 1 / 2 The value of ) / (X / Y).

[0099] Table 1

[0100] Group First additive content a / % Vinylene carbonate content b / % <![CDATA[The compaction density of the positive electrode sheet is X g / cm 3 > <![CDATA[Negative electrode sheet compaction density Y g / cm 3 > X / Y <![CDATA[((a / b) 1 / 2 ) / (X / Y)]]> Example 1 0.5 4 2.60 1.5 1.73 0.613 Example 2 0.05 5 2.50 1.4 1.79 0.179 Example 3 0.1 4.5 2.55 1.45 1.76 0.262 Example 4 1 3.5 2.65 1.6 1.66 0.885 Example 5 1.5 3 2.70 1.65 1.64 1.157 Example 6 2 2.5 2.75 1.7 1.62 1.447 Example 7 2.5 2 2.80 1.75 1.60 1.789 Example 8 3 1.5 2.85 1.75 1.63 2.303 Example 9 3.5 1 2.52 1.4 1.80 3.367 Example 10 4 0.5 2.54 1.75 1.45 4.105 Example 11 4.5 0.1 2.85 1.43 1.99 13.369 Example 12 5 0.05 2.80 1.4 2.00 20.000 Example 13 3.8 0.1 2.55 1.75 1.46 8.982 Example 14 0.05 5 2.55 1.65 1.55 0.155 Example 15 0.15 4.5 2.55 1.45 1.76 0.321 Comparative Example 1 / 4 2.60 1.5 1.73 / Comparative Example 2 3 / 2.55 1.65 1.55 / Comparative Example 3 0.03 4.5 2.75 1.4 1.96 0.160 Comparative Example 4 5.1 4 2.80 1.65 1.70 1.916 Comparative Example 5 3.5 0.03 2.50 1.7 1.47 15.884 Comparative Example 6 0.2 5.2 2.70 1.65 1.64 0.321 Comparative Example 7 3.5 5 2.45 1.65 1.48 1.242 Comparative Example 8 0.05 5 2.90 1.7 1.71 0.171 Comparative Example 9 3.5 4.5 2.50 1.35 1.85 1.633 Comparative Example 10 4 0.05 2.75 1.8 1.53 13.665 Comparative Example 11 4 0.5 2.50 1.75 1.43 4.041 Comparative Example 12 4.5 0.1 2.85 1.4 2.04 13.656 Comparative Example 13 0.05 5 2.51 1.73 1.45 0.145 Comparative Example 14 5 0.05 2.85 1.4 2.04 20.357

[0101] Note: " / " indicates that the item does not exist.

[0102] The performance test results of the lithium-ion batteries prepared in Examples 1-15 and Comparative Examples 1-14 are shown in Table 2.

[0103] Table 2

[0104] Group High-temperature cycling capacity retention (%) Capacity retention during ambient temperature cycling / % High-temperature storage battery capacity retention rate / % Storage battery capacity recovery rate / % Thickness expansion rate / % Low-temperature discharge efficiency value at -20℃ / % Example 1 90.5 95.5 95.1 96.3 0.8 43.0 Example 2 84.5 89.3 93.0 94.1 2.0 30.0 Example 3 85.9 91.8 94.1 94.6 1.6 34.5 Example 4 89.1 94.8 95.1 95.7 0.9 39.3 Example 5 89.5 94.6 94.5 95.8 1.0 39.8 Example 6 88.0 94.1 94.6 95.9 0.8 41.0 Example 7 89.5 95.0 95.1 96.0 0.7 42.5 Example 8 89.3 94.2 94.0 95.2 1.0 40.2 Example 9 88.9 94.0 94.1 94.9 1.0 40.0 Example 10 88.6 93.9 93.9 94.2 1.3 39.1 Example 11 83.8 88.9 92.8 93.6 2.3 29.5 Example 12 83.4 88.5 92.2 93.1 2.7 28.5 Example 13 85.0 90.0 93.5 94.0 1.5 35.4 Example 14 84.5 88.0 93.0 93.6 1.8 32.7 Example 15 88.6 94.0 94.2 95.3 1.0 38.4 Comparative Example 1 75.2 78.4 80.1 82.2 3.5 22.8 Comparative Example 2 72.1 74.6 76.7 78.9 4.2 20.9 Comparative Example 3 78.9 79.7 81.5 83.1 3.1 23.8 Comparative Example 4 80.2 81.1 82.1 84.0 3.0 25.8 Comparative Example 5 73.4 75.3 77.4 79.5 3.9 21.8 Comparative Example 6 80.4 83.6 80.2 83.4 3.1 25.2 Comparative Example 7 84.5 90.5 92.0 92.8 1.2 37.5 Comparative Example 8 82.3 84.2 85.4 88.6 2.3 30.7 Comparative Example 9 84.5 90.5 92.0 92.8 1.2 37.5 Comparative Example 10 82.3 84.2 85.4 88.6 2.3 30.7 Comparative Example 11 85.6 90.2 91.2 90.2 2.7 32.1 Comparative Example 12 81.2 85.2 87.5 88.6 2.5 25.5 Comparative Example 13 80.4 83.5 85.2 86.1 4.3 28.5 Comparative Example 14 79.1 80.6 827.0 82.9 4.7 26.9

[0105] As shown in Table 2, the lithium-ion battery provided by the present invention uses vinylene carbonate and the first additive shown in structural formula 1 as additives, and the ratio of the compaction density X of the positive electrode material layer to the compaction density Y of the negative electrode material layer, X / Y, the mass percentage content a of the first additive, the mass percentage content b of vinylene carbonate, and the relationship (a / b) are used. 1 / 2 The expression ) / (X / Y) satisfies: 0.15 ≤ ((a / b) 1 / 2When ) / (X / Y)≤20, and 0.05≤a≤5, 0.05≤b≤5, 1.45≤X / Y≤2.0, 2.5≤X≤2.85, and 1.40≤Y≤1.75, the parameters work synergistically to obtain a lithium-ion battery that balances cycle performance and safety performance.

[0106] As can be seen from the test results of Example 1 and Comparative Examples 1-14, when any one or more parameters, such as the ratio of the compaction density X of the positive electrode material layer to the compaction density Y of the negative electrode material layer (X / Y), the mass percentage content a of the first additive, and the mass percentage content b of vinylene carbonate, do not meet the specified range, or when the relationship between them (a / b) is not met, the test results will be negative. 1 / 2 If the value of ) / (X / Y) is too large or too small, it will not be able to increase the active sites of lithium ions at the ends of the positive and negative electrode materials, and it will not be able to form an interface film with certain electrochemical stability and ultra-high thermal stability on the surface of the positive and negative electrodes of the battery. Therefore, it will not be able to enhance the cycle life and safety performance of the battery.

[0107] The ratio of the compaction density X of the positive electrode material layer to the compaction density Y of the negative electrode material layer, X / Y, the mass percentage content of the first additive a, the mass percentage content of vinylene carbonate b, and the relationship (a / b) are given. 1 / 2 The value of (a / b) further satisfies: 0.3 ≤ (a / b) / (X / Y) 1 / 2 When ) / (X / Y)≤9, and 0.1≤a≤3, 0.1≤b≤4, 1.6≤X / Y≤1.8, 2.55≤X≤2.7, and 1.45≤Y≤1.65, the ion transport kinetics and structural stability between the positive and negative electrodes can be better balanced, and the lithium ion flow is uniformly distributed at the interface. This creates an ideal interfacial chemical environment for the first additive and vinylene carbonate to synergistically construct a stable and low-resistance CEI / SEI film on both sides, thereby significantly improving the cycle life, rate performance and safety of the battery.

[0108] Table 3 shows the parameters required for preparing lithium-ion batteries in Examples 1 and 16-22. The difference between Examples 16-22 and Example 1 lies in the relevant parameters in Table 3. The remaining parameters and preparation steps are the same as those described in Example 1. The specific difference is the type of the first additive. The performance test results of the lithium-ion batteries prepared in Examples 1 and 16-22 are shown in Table 3.

[0109] Table 3

[0110] Group First type of additive High-temperature cycling capacity retention (%) Capacity retention during ambient temperature cycling / % High-temperature storage battery capacity retention rate / % Storage battery capacity recovery rate / % Thickness expansion rate / % Low-temperature discharge efficiency value at -20℃ / % Example 1 Compound 1 90.5 95.5 95.1 96.3 0.8 43.0 Example 16 Compound 2 90.5 95.5 95.1 96.3 0.8 43.0 Example 17 Compound 3 89.3 94.1 94.5 95.3 0.9 42.0 Example 18 Compound 4 89.5 94.3 94.4 95.2 0.9 42.4 Example 19 Compound 5 89.4 94.5 94.7 95.6 0.8 41.8 Example 20 Compound 6 89.2 94.4 94.1 95.4 0.9 42.6 Example 21 Compound 7 89.1 94.7 94.3 95.7 0.8 41.4 Example 22 Compound 8 88.9 94.0 94.1 95.1 1.0 42.0

[0111] As shown in Table 3, the ratio of the compaction density X of the positive electrode material layer to the compaction density Y of the negative electrode material layer, X / Y, the mass percentage content of the first additive a, the mass percentage content of vinylene carbonate b, and the relationship (a / b) are given. 1 / 2 When X / Y meets the corresponding conditions, adding different types of benzoxazine compounds as the first additive can yield lithium-ion batteries that maintain good high-temperature performance while also ensuring good safety performance. This demonstrates that the battery system of the present invention has universal applicability to different types of first additives.

[0112] Table 4 shows the parameters required for preparing lithium-ion batteries in Examples 1 and 23-25. The difference between Examples 23-25 ​​and Example 1 lies in the relevant parameters in Table 4. The remaining parameters and preparation steps are the same as those described in Example 1. The specific difference is the type and content of auxiliary additives. The performance test results of the lithium-ion batteries obtained in Examples 1 and 23-25 ​​are shown in Table 4.

[0113] Table 4

[0114] Group Auxiliary additives and their content High-temperature cycling capacity retention (%) Capacity retention during ambient temperature cycling / % High-temperature storage battery capacity retention rate / % Storage battery capacity recovery rate / % Thickness expansion rate / % Low-temperature discharge efficiency value at -20℃ / % Example 1 / 90.5 95.5 95.1 96.3 0.8 43.0 Example 23 0.5% DTD 91.3 96.0 95.6 96.8 0.6 43.4 Example 24 0.5% MMDS 91.4 96.1 95.8 96.5 0.6 43.5 Example 25 0.5% PS 91.0 95.8 95.4 96.4 0.7 42.9

[0115] As shown in Table 4, the ratio of the compaction density X of the positive electrode material layer to the compaction density Y of the negative electrode material layer, X / Y, the mass percentage content of the first additive a, the mass percentage content of vinylene carbonate b, and the relationship (a / b) are given. 1 / 2 When X / Y meets the corresponding conditions, adding different types of auxiliary additives can yield lithium-ion batteries that maintain good high-temperature performance while also ensuring good safety performance. This demonstrates that the battery system of the present invention has universal applicability to different types of auxiliary additives.

[0116] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A lithium-ion battery, characterized by, The non-aqueous electrolyte comprises an additive, a lithium salt and an organic solvent. The positive electrode includes a positive electrode material layer including a positive electrode active material, the positive electrode active material including lithium iron phosphate; a compacted density of the positive electrode material layer is X g / cm 3 ; The negative electrode includes a negative electrode material layer containing a negative electrode active material, the compaction density of the negative electrode material layer is Y g / cm 3 ; The non-aqueous electrolyte comprises an additive, a lithium salt and an organic solvent. The additive comprises vinylene carbonate and a first additive represented by structural formula 1. Structure 1, At least one of R2, R2, R4 and R5 is selected from a halogen atom, -CF3, -COCH3, -COCF3, -COOCH3, -NHCOCF3, -NO2, -COH, -SO3H, -CCl3, a maleimide group, and the rest are each independently selected from any one of H, a C1-C12 alkyl or halogenated alkyl, a C5-C7 cycloalkyl or halogenated cycloalkyl, a C2-C12 alkenyl or halogenated alkenyl, a C1-C12 alkoxy or halogenated alkoxy, an aromatic hydrocarbon group and derivatives thereof. R1 is selected from any one of H, a C1-C12 alkyl or halogenated alkyl, a C5-C7 cycloalkyl or halogenated cycloalkyl, a C2-C12 alkenyl or halogenated alkenyl, a C1-C12 alkoxy or halogenated alkoxy, an aromatic hydrocarbon group and derivatives thereof. The mass percentage of the first additive is a%, and the mass percentage of the vinylene carbonate is b%, based on the mass of the non-aqueous electrolyte. The lithium ion battery satisfies: 0.15 ≤ ((a / b) 1 / 2 ) / (X / Y) ≤ 20, and 0.05 ≤ a ≤ 5, 0.05 ≤ b ≤ 5, 1.45 ≤ X / Y ≤ 2.0, 2.5 ≤ X ≤ 2.85, 1.40 ≤ Y ≤ 1.

75.

2. The lithium-ion battery of claim 1, wherein, The first additive comprises any one or more of the following compounds:

3. The lithium-ion battery of claim 1, wherein, The lithium ion battery satisfies: 0.3 ≤ ((a / b) 1 / 2 ) / (X / Y) ≤ 9.

4. The lithium-ion battery of claim 1, wherein, The mass percentage a% of the first additive satisfies 0.1≤a≤3.

5. The lithium-ion battery of claim 1, wherein, The mass percentage b% of the fluorinated carbonate satisfies 0.1≤b≤4.

6. The lithium-ion battery of claim 1, wherein, The ratio of the compaction densities of the positive electrode material layer and the negative electrode material layer satisfies 1.6≤X / Y≤1.

8.

7. The lithium-ion battery of claim 1, wherein, The compacted density X g / cm3 of the positive electrode material layer 3 satisfies: 2.55 ≤ X ≤ 2.7; the compacted density Y g / cm3 of the negative electrode material layer 3 satisfies: 1.45 ≤ Y ≤ 1.

65.

8. The lithium-ion battery of claim 1, wherein, A single battery cell made of the lithium iron phosphate positive electrode active material has a capacity of ≥300 Ah.

9. The lithium-ion battery of claim 1, wherein, The organic solvent comprises at least one of an ether solvent, a nitrile solvent, a carbonate solvent, a carboxylic acid ester solvent and a sulfone solvent; and / or, The lithium salt is selected from at least one of LiPF6, LiBF4, LiFSI, LiBOB, LiDFOB, LiPO2F2, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3 and LiN(SO2F)2.

10. The lithium-ion battery of claim 1, wherein, The non-aqueous electrolyte further comprises an auxiliary additive, and the auxiliary additive comprises at least one of a cyclic sulfate compound, a sulfonic acid lactone compound, a cyclic carbonate compound, a phosphate ester compound and a borate ester compound; and / or, The content of the auxiliary additive is 0.01-10%, based on the total mass of the non-aqueous electrolyte; and / or, The cyclic sulfate compound comprises at least one of 4-methyl vinyl sulfate, vinyl sulfate and propylene sulfate; and / or, The sulfonic acid lactone compound comprises at least one of 1,3-propane sulfonic acid lactone, 1,4-butane sulfonic acid lactone and propylene-1,3-sulfonic acid lactone; and / or, The cyclic carbonate compound comprises at least one of vinylene carbonate, fluorinated vinylene carbonate, vinylene ethylene carbonate, methylene vinylene carbonate, trifluoromethyl vinylene carbonate, bis vinylene carbonate and a compound represented by structural formula 2: Structural Formula 2, In the illustrated structural formula 2, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 are each independently selected from one of a hydrogen atom, a halogen atom, a C1-C5 group; and / or, The phosphate ester compound includes at least one of compounds represented by the following formula 3: Structural Formula 3 In the structural formula 3, R 31 , R 32 , R 33 are each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 )3, and m is a natural number from 1 to 3; and / or, The borate ester compound includes at least one of tris(trimethylsilyl) borate and tri(triethylsilyl) borate.

Images