A lithium-ion battery

Abstract

The application discloses a lithium ion battery, which comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte, the negative electrode comprises a negative electrode material, the negative electrode material comprises a negative electrode active material and a coating layer, the coating layer comprises an ion-conducting material, and the inorganic component in the coating layer accounts for greater than or equal to 80 wt%; the electrolyte comprises a non-aqueous organic solvent and a lithium salt, the non-aqueous organic solvent comprises a solvent with high dielectric constant and low viscosity and ethylene carbonate, the volume fraction of the solvent with high dielectric constant and low viscosity in the non-aqueous organic solvent is greater than or equal to 10%, and the volume fraction of the ethylene carbonate in the non-aqueous organic solvent is less than or equal to 10%; and the concentration of lithium bisfluorosulfonylimide and / or lithium bis(trifluoromethylsulfonyl)imide in the lithium salt is less than or equal to 0.1 mol / L. By matching the negative electrode material with the specific type of coating layer and the electrolyte with the specific composition, the lithium ion battery has good fast-charging performance, and the risk of explosion and fire during thermal runaway of the battery is reduced.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion secondary battery technology, and relates to a lithium-ion battery, and more particularly to a high-safety fast-charging lithium-ion battery. Background Technology

[0002] Lithium-ion rechargeable batteries have advantages such as high energy density, long cycle life, and environmental friendliness, and have become the main energy storage device for new energy vehicles. The spontaneous combustion of batteries or battery explosions after collisions in new energy vehicles is a serious concern. Based on the responsibility for user safety and to guide the healthy development of my country's new energy industry, the new national standard for power lithium-ion batteries (GB / T 45565—2025) came into effect on November 1, 2025, further strengthening the safety performance requirements for batteries and prohibiting explosions and fires in the event of thermal runaway.

[0003] When a lithium-ion battery experiences thermal runaway, the electrolyte and the lithium-intercalated anode react violently, generating a large amount of heat and gas, exacerbating the severity of the thermal runaway. The heat generation from ethylene carbonate and lithium bis(fluorosulfonyl)imide in the electrolyte is particularly significant. Furthermore, ethylene carbonate plays a role in dissociating lithium salts and solubilizing lithium ions in the electrolyte; simply reducing ethylene carbonate and lithium bis(fluorosulfonyl)imide leads to a significant decrease in electrolyte conductivity, making it difficult to maintain fast-charging performance. On the other hand, while coating graphite with alumina can reduce the reaction intensity between the anode and electrolyte during thermal runaway to some extent, alumina coating can also block the lithium-ion intercalation / deintercalation pathway on the graphite surface, affecting the battery's fast-charging and rate performance. Other electrolyte safety improvement measures, such as flame-retardant electrolytes, utilize expensive phosphazene compounds and large amounts of phosphate esters or flame-retardant fluorinated solvents, which have disadvantages such as low electrolyte conductivity or decreased electrochemical stability, making large-scale industrial application difficult.

[0004] Therefore, it is necessary to provide a lithium-ion battery that has good fast-charging performance and reduces the risk of battery explosion and fire in the event of battery thermal runaway, which is an urgent technical problem to be solved. Summary of the Invention

[0005] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a lithium-ion battery, and more particularly to provide a high-safety fast-charging lithium-ion battery.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises a negative electrode material, the negative electrode material comprises a negative electrode active material and a coating layer covering the negative electrode active material, the coating layer comprises an ion-conducting material, and the inorganic component in the coating layer accounts for ≥80 wt%;

[0008] The electrolyte comprises a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent comprises a solvent with a high dielectric constant and low viscosity and ethylene carbonate. The volume percentage of the solvent with a high dielectric constant and low viscosity in the non-aqueous organic solvent is ≥10%, and the volume percentage of ethylene carbonate in the non-aqueous organic solvent is ≤10%. The lithium salt optionally comprises lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide, and the concentration of lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is ≤0.1 mol / L.

[0009] The solvent with high dielectric constant and low viscosity satisfies the following conditions: dielectric constant ≥ 20, viscosity μ ≤ 0.5CP at 25℃.

[0010] In this invention, the inorganic component in the coating layer accounts for ≥80wt%, for example, it can be 80wt%, 82wt%, 84wt%, 85wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, 95wt%, 96wt%, 98wt%, 99wt%, or 100wt%, etc.

[0011] In this invention, the volume percentage of the solvent with high dielectric constant and low viscosity in the non-aqueous organic solvent is ≥10%, for example, it can be 10%, 12%, 13%, 14%, 15%, 17%, 18%, 20%, 22%, 24%, 25%, 28%, or 30%, etc.

[0012] In this invention, the solvent with high dielectric constant and low viscosity satisfies the following conditions: dielectric constant ≥ 20, for example, it can be 20, 22, 25, 27, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85 or 90, etc.; viscosity μ ≤ 0.5CP at 25℃, for example, it can be 0.5CP, 0.4CP, 0.3CP, 0.2CP or 0.1CP, etc.

[0013] In this invention, lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide may be optionally included. This means that lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide may not be included, or it may include one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. When lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide are included, the concentration of lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is ≤0.1 mol / L, for example, it may be 0.1 mol / L, 0.08 mol / L, 0.06 mol / L, 0.05 mol / L, 0.04 mol / L, 0.02 mol / L, 0.01 mol / L, or 0 mol / L, etc. The phrase "the concentration of lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is 0 mol / L" means that the electrolyte does not contain lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide.

[0014] This invention, by employing a negative electrode material with a specific type of coating layer and an electrolyte with a specific composition, enables lithium-ion batteries to exhibit excellent fast-charging performance and reduces the risk of explosion and fire during thermal runaway. The technical principles are as follows: First, the coating layer on the surface of the negative electrode active material includes an ion-conducting material with an inorganic component ratio ≥80%, thus providing sufficient thermal stability. This coating layer effectively prevents contact between the electrolyte and the negative electrode during thermal runaway, reducing heat generation from the reaction between the negative electrode and the electrolyte. Furthermore, its excellent ion-conducting properties enhance ion transport, improving fast-charging and cycle performance. Second, in the electrolyte, ethylene carbonate is used to dissociate lithium salts and solvate lithium ions. By replacing ethylene carbonate with a solvent of high dielectric constant and low viscosity to participate in the inner solvation of lithium ions, the amount of ethylene carbonate used is reduced, which helps to reduce the exothermic reaction between ethylene carbonate and the negative electrode during thermal runaway. Moreover, compared to using ethylene carbonate alone, it can increase the dielectric constant of the electrolyte, reduce the viscosity of the electrolyte, and increase the conductivity of the electrolyte instead of decreasing it; lithium salt can provide migratable lithium ions, and by controlling the presence of no or only a small amount of lithium bisfluorosulfonylimide and / or lithium bistrifluoromethanesulfonylimide (concentration ≤0.1mol / L), the risk of heat generation from their reaction with the negative electrode can be reduced. Therefore, the synergistic use of the negative electrode material and electrolyte of the present invention can enable the battery to have good fast charging performance, while reducing the risk of explosion and fire in the event of battery thermal runaway.

[0015] Preferably, the lithium-ion conductivity of the coating layer is ≥10. -2 mS / cm, for example, could be 10 -2 mS / cm, 3×10 - 2 mS / cm, 5×10 -2 mS / cm, 7×10-2 mS / cm, 10 -1 mS / cm, 3×10 -1 mS / cm, 5×10 -1 mS / cm, 6×10 -1 mS / cm, 7×10 -1 mS / cm, 8×10 -1 mS / cm, 9×10 -1 mS / cm or 1mS / cm. The electronic conductivity of the coating layer is ≤10. - 5 mS / cm, for example, could be 10 -5 mS / cm, 3×10 -5 mS / cm, 5×10 -5 mS / cm, 7×10 -5 mS / cm, 10 -6 mS / cm, 3×10 -6 mS / cm, 5×10 -6 mS / cm, etc.

[0016] The coating layer of the present invention has lithium-ion conduction function but no electron transport function, which can prevent the electrolyte from being oxidized and ensure that the negative electrode material has good ion transport performance.

[0017] Preferably, the mass percentage of the ion-conducting material relative to the negative electrode active material is 1wt% to 10wt%, for example, it can be 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, or 10wt%, etc., preferably 3wt% to 7wt%. If the content of the ion-conducting material is too low, it will lead to uneven coating of the solid electrolyte layer on the surface of the negative electrode material, poor temperature resistance, and reduced safety performance; if the content of the ion-conducting material is too high, it will lead to increased impedance and reduced fast charging performance.

[0018] Preferably, the ion-conducting material includes at least one of artificial SEI materials and solid electrolyte materials.

[0019] Preferably, the artificial SEI material includes at least one of Li3BO3, Li2B4O7, LiAlO2, lithium sulfonate, and lithium phosphate.

[0020] Preferably, the solid electrolyte material includes lithium titanium aluminum phosphate (Li... 1.3 Al 0.3 Ti 1.7(PO4)3, LATP), lithium lanthanum zirconium oxide (Li7La3Zr2O) 12 LLZO), lithium phosphorus oxy nitrogen (LiPON), LiPS or lithium germanium phosphorus sulfide (Li 10 GeP2S 12 At least one of LGPS.

[0021] Preferably, the coating layer coats the negative electrode active material in an in-situ or non-in-situ manner. When the coating method is non-in-situ coating, the particle size D50 of the negative electrode active material is defined as D50. c The particle size D50 of the negative electrode material is defined as D50. p The particle size D50 of the ion-conducting material is defined as D50. s D50 c / D50 s ≥50, 1.01≤D50 p / D50 c ≤1.05. For example, D50 c / D50 s It can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 115, 120, 125, 130, 135, 140, 145, or 150, etc. D50 p / D50 c It can be 1.01, 1.02, 1.03, 1.04, or 1.05, etc.

[0022] In this invention, a coating layer can be formed on the surface of the negative electrode active material using either in-situ or non-in-situ coating methods. In-situ coating refers to the coating material being formed on the surface of the negative electrode active material. If a non-in-situ coating method is used, a more uniform and continuous coating layer can be obtained by controlling the relationship between the particle size D50 of the negative electrode active material (the bulk material before coating), the negative electrode material (the material after coating), and the ion-conducting material, thereby ensuring the coating effect.

[0023] Preferably, the coating layer further includes an adhesive and a carbon material. The adhesive can bond and fix the ion-conducting material and the carbon material to each other on the surface of the negative electrode active material. The carbon material can provide electron transport performance. Preferably, a one-dimensional carbon material is used, as it is easier to penetrate the coating layer, providing a good electron transport particle size, reducing the amount of carbon material used, and ensuring good electrochemical performance of the negative electrode material.

[0024] This invention does not specifically limit the type of carbon material; for example, it may be carbon nanotubes and / or carbon fibers.

[0025] Preferably, the adhesive comprises B2O3 and / or a lithium boron oxide composite.

[0026] Preferably, the carbon material accounts for 8% to 12% of the mass of the coating layer, for example, it can be 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5% or 12%.

[0027] Preferably, the negative electrode material is prepared by the following method, which includes the following steps:

[0028] The negative electrode active material, ion-conducting material, optional binder raw material and optional carbon material are mixed and sintered to form a coating layer on the surface of the negative electrode active material, thus obtaining the negative electrode material.

[0029] Preferably, the sintering temperature is 450℃~500℃, for example, it can be 450℃, 460℃, 470℃, 480℃, 490℃ or 500℃.

[0030] Preferably, the adhesive raw material is B2O3.

[0031] Preferably, the binder accounts for 8% to 15% of the mass of the ion-conducting material, for example, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. Compared to binders using organic components, this invention uses B2O3 to form an inorganic binder, which is beneficial for improving the thermal stability of the negative electrode material. Furthermore, during the preparation process, B2O3 may react with lithium-containing components to form lithium boron oxide complexes, which are beneficial for ion transport.

[0032] This invention does not specifically limit the type of negative electrode active material. For example, it can be at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon carbide, silicon suboxide, tin alloy, and fluorinated graphite, wherein the graphite can be natural graphite and / or artificial graphite. It should be noted that the negative electrode active material of this invention is not limited to the types listed above; other commonly used negative electrode active materials in the art are also applicable to this invention.

[0033] In one embodiment, the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector, wherein the negative electrode material layer includes the negative electrode material.

[0034] In one embodiment, the negative current collector includes any one of copper foil, carbon-coated copper foil, composite copper foil, or carbon-coated composite copper foil, wherein the composite copper foil is formed by combining copper foil with other film layers.

[0035] In one embodiment, the negative electrode material layer further includes a first binder, a first thickener, and a first conductive agent.

[0036] In one embodiment, the first adhesive comprises styrene-butadiene rubber.

[0037] In one embodiment, the first thickener comprises carboxymethyl cellulose.

[0038] In one embodiment, the first conductive agent includes at least one of conductive carbon black, carbon nanotubes, carbon fibers, and graphene.

[0039] Preferably, the electrolyte has an ionic conductivity ≥13 mS / cm at 25°C, for example, it can be 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, 19 mS / cm, 20 mS / cm, 21 mS / cm, 22 mS / cm, 23 mS / cm, 24 mS / cm, 25 mS / cm, 26 mS / cm, 27 mS / cm, 28 mS / cm, 29 mS / cm, or 30 mS / cm, etc.

[0040] Preferably, the solvent with high dielectric constant and low viscosity includes at least one of acetonitrile, propionitrile, n-butyronitrile, and isobutyronitrile.

[0041] Preferably, the high dielectric constant and low viscosity solvent accounts for ≥10% and ≤30% of the volume of the non-aqueous organic solvent, more preferably ≥15% and ≤30%. If the content of the high dielectric constant and low viscosity solvent is too low, it will reduce the fast charging performance; if the content of the high dielectric constant and low viscosity solvent is too high, it will lead to excessively high reactivity between the electrolyte and the negative electrode, resulting in poor high-temperature cycle performance of the battery cell, increased gas production, and other performance degradation.

[0042] Preferably, the volume percentage of the ethylene carbonate in the non-aqueous organic solvent is ≥5% and ≤10%.

[0043] Preferably, the non-aqueous organic solvent further includes other solvents, which include at least one of carbonates, carboxylic esters, chain ethers, cyclic ethers, lactones, nitriles, ionic liquids, phosphate esters, fluorocarbonates, fluorocarboxylic esters, fluoroethers, and fluoronitriles.

[0044] Preferably, the other solvents include at least one selected from propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, methyl acetate, ethyl formate, ethyl propionate, propyl propionate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetrahydrofuran, dioxapentane, crown ether, γ-butyrolactone, succinic acid, glutaronitrile, adiponitrile, hexanetrionitrile, trimethyl phosphate, triethyl phosphate, fluoroethylene carbonate, trifluoroethyl methyl ethyl carbonate, difluoroethyl ethyl acetate, tetrafluoroethyl-tetrafluoropropyl ether, and fluoroacetonitrile.

[0045] Preferably, the lithium salt further includes at least one selected from lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate borate), and lithium tetrafluoroborate. In this invention, the lithium salt serves to dissociate lithium ions in the electrolyte.

[0046] Preferably, the concentration of the lithium salt is ≥1.2 mol / L, for example, it can be 1.2 mol / L, 1.25 mol / L, 1.3 mol / L, 1.35 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 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, or 3 mol / L, etc. In this invention, the concentration of the lithium salt should not be too low to ensure sufficient ionic conductivity.

[0047] Preferably, the electrolyte further includes additives, which include at least one of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, ethylene dicarbonate, ethylene sulfate, propylene sulfate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, ethylene disulfate, dimethyl methanesulfonate, ethylene disulfate, lithium difluorophosphate (LiPO2F2), lithium nitrate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, lithium tetrafluoroborate, lithium difluorosulfonylimide, lithium fluorosulfonate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, and tetravinylsilane.

[0048] Preferably, the additive has a mass percentage of 3wt% to 10wt% in the electrolyte, for example, it can be 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, or 10wt%.

[0049] In this invention, by adding an appropriate amount of additives to form a film on the surface of the positive or negative electrode, which works in conjunction with the electrolyte, the battery can be guaranteed to have good fast charging performance while also having good room temperature cycling, high temperature cycling and high temperature storage performance.

[0050] Compared with existing technologies, the present invention has the following beneficial effects:

[0051] (1) This invention, by using a negative electrode material with a specific type of coating layer and an electrolyte with a specific composition, enables lithium-ion batteries to have good fast-charging performance and reduces the risk of explosion and fire during battery thermal runaway. The technical principle is as follows: First, the coating layer on the surface of the negative electrode active material includes ion-conducting materials and the proportion of inorganic components is ≥80%. Therefore, the coating layer has sufficient thermal stability. This coating layer can effectively prevent the contact between the electrolyte and the negative electrode during thermal runaway, reduce the heat generated by the reaction between the negative electrode and the electrolyte, and has good ion-conducting characteristics, which can improve ion transport and improve fast-charging performance and cycle performance. Second, in the electrolyte, ethylene carbonate is used to dissociate lithium salt and solubilize lithium ions. By using a solvent with a high dielectric constant and low viscosity to replace ethylene carbonate, it participates in the inner solubilization of lithium ions, reducing the amount of ethylene carbonate used and reducing the exothermic reaction between ethylene carbonate and the negative electrode during thermal runaway. Moreover, compared to using ethylene carbonate alone, it can increase the dielectric constant of the electrolyte, reduce the viscosity of the electrolyte, and increase the conductivity of the electrolyte instead of decreasing it; lithium salt can provide migratable lithium ions, and by controlling the presence of no or only a small amount of lithium bisfluorosulfonylimide and / or lithium bistrifluoromethanesulfonylimide (concentration ≤0.1mol / L), the risk of heat generation from their reaction with the negative electrode can be reduced. Therefore, the synergistic use of the negative electrode material and electrolyte of the present invention can enable the battery to have good fast charging performance, while reducing the risk of explosion and fire in the event of battery thermal runaway.

[0052] (2) The lithium-ion battery of the present invention has good thermal stability. According to ARC testing, the self-generated heat initiation temperature (T1) of the cell is above 87.5℃; the thermal runaway acceleration inflection point temperature (T2) is above 235℃; and the thermal runaway trigger temperature (T3) is above 255℃. Moreover, the lithium-ion battery of the present invention has the advantages of good fast charging performance, good room temperature cycle performance, good high temperature cycle performance, and good high temperature storage performance. The charging time from 0 to 80% SOC at 25℃ is less than 15.7 min, preferably less than 14.8 min; the retention rate after 1000 cycles at 25℃ is above 91.7%; the retention rate after 1000 cycles at 45℃ is above 86.7%; and the capacity recovery rate after 30 days of storage at 60℃ is above 89.5%. Detailed Implementation

[0053] The technical solution of the present invention will be further described in detail below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0054] To facilitate comparison of the performance differences between the embodiments and comparative examples, lithium iron phosphate is selected as the positive electrode material and graphite as the negative electrode active material in this paper. It should be noted that this is only an example and is not a limitation on the types of positive electrode materials and negative electrode active materials of the present invention. Other commonly used positive electrode materials and negative electrode active materials in the art are also applicable to the present invention.

[0055] The embodiments of the present invention do not specifically limit the structure and composition of the positive electrode. For example, in one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the surface of the positive electrode current collector, wherein the positive electrode material layer includes a positive electrode material.

[0056] In one embodiment, the positive current collector includes any one of aluminum foil, carbon-coated aluminum foil, composite aluminum foil, or carbon-coated composite aluminum foil, wherein the composite aluminum foil is formed by combining aluminum foil with other film layers.

[0057] In one embodiment, the cathode material is lithium iron phosphate.

[0058] In one embodiment, the positive electrode material layer further includes a second binder and a second conductive agent.

[0059] In one embodiment, the second adhesive is polyvinylidene fluoride (PVDF).

[0060] In one embodiment, the second conductive agent includes at least one of conductive carbon black, carbon nanotubes, carbon fibers, and graphene.

[0061] In this embodiment of the invention, the separator has electronic insulation properties and a porous structure, allowing lithium ions to be transferred between the positive and negative electrodes via an electrolyte. Its composition can be an organic polymer membrane, such as polyethylene, polypropylene, or polysaccharides, or an inorganic fiber, such as glass fiber or alumina fiber; its structure can be a homogeneous single-layer porous structure, a heterogeneous single-layer porous structure, or a heterogeneous multilayer porous structure.

[0062] In this embodiment of the invention, the lithium-ion battery further includes a packaging shell. The invention does not specifically limit the shape and material of the packaging shell; for example, the material of the packaging shell can be an aluminum shell, a steel shell, or a plastic shell, and the shape of the packaging shell can be square, cylindrical, polygonal, or an irregular three-dimensional geometric structure. In one embodiment, the packaging shell uses an aluminum-plastic soft-pack packaging.

[0063] In the following examples, LiFSI is lithium difluorosulfonylimide, EC is ethylene carbonate, EMC is ethyl methyl carbonate, DMC is dimethyl carbonate, EA is ethyl acetate, ACN is acetonitrile, VC is vinylene carbonate, FEC is fluoroethylene carbonate, and PS is 1,3-propanesulfonic acid lactone.

[0064] The following are typical but non-limiting embodiments:

[0065] In the following embodiments, the lithium-ion conductivity of the coating layer is ≥10. -2 mS / cm, the electronic conductivity of the coating layer is ≤10 -5 mS / cm. Solvents with high dielectric constant and low viscosity satisfy the following conditions: dielectric constant ≥ 20, viscosity μ ≤ 0.5CP at 25℃.

[0066] Example 1

[0067] This embodiment provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative electrode material, which comprises a negative electrode active material (graphite with a particle size D50 of 0.50). c D50 c =15μm) and a coating layer covering the negative electrode active material, wherein the particle size D50 of the negative electrode material is D50. p D50 p =15.4μm, the coating layer includes an ion-conducting material and carbon nanotubes (CNTs), the ion-conducting material being lithium aluminum titanium phosphate (LATP, particle size D50 is D50). s D50 s =200nm), the LATP accounts for 5% of the mass of graphite, the CNT accounts for 10% of the mass of the coating layer, and the inorganic component in the coating layer accounts for ≥100wt%.

[0068] The electrolyte (see Table 1 for composition) includes a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent includes a solvent with a high dielectric constant and low viscosity and ethylene carbonate. The solvent with a high dielectric constant and low viscosity is ACN (dielectric constant ≥ 20, viscosity μ ≤ 0.5CP at 25°C).

[0069] This embodiment also provides a method for preparing the above-mentioned lithium-ion battery, including the following steps:

[0070] Preparation of negative electrode material: LATP and B2O3 are mixed, wherein the mass ratio of B2O3 to LATP (i.e., the mixing ratio of B2O3) is 10%, and a mixture is obtained. Then, the mixture is thoroughly mixed with graphite and CNT, and sintered at 475℃ for 3 hours under Ar atmosphere. During sintering, B2O3 melts and connects LATP and CNT to the graphite surface and may be partially converted into lithium boron oxide composite, thus obtaining the negative electrode material.

[0071] Preparation of the negative electrode sheet: The negative electrode material, conductive carbon black, carboxymethyl cellulose, and styrene-butadiene rubber were mixed evenly in water at a mass ratio of 96:1:1.3:1.7 to obtain a negative electrode slurry. The negative electrode slurry was coated onto a 5 μm thick copper foil, with a single-sided coating areal density of 10.68 mg / cm³. 2 After drying, it is rolled to a compaction density of 1.55 g / cm³. 3 The negative electrode sheet with a size of 53mm×104mm was obtained by die cutting and then dried for later use.

[0072] Preparation of positive electrode sheet: Lithium iron phosphate, carbon nanotubes, conductive carbon black and PVDF are mixed evenly in NMP at a mass ratio of 96.5:0.5:1:2 to obtain positive electrode slurry. The positive electrode slurry is coated on both sides of a 12μm thick carbon-coated aluminum foil with a single-sided coating density of 22.5mg / cm2. After drying, it is rolled to a thickness of 192μm, die-cut to obtain a positive electrode sheet with a size of 50mm×100mm, and then dried for later use.

[0073] Preparation of electrolyte: Mix the components of the electrolyte evenly according to the formula to obtain the electrolyte.

[0074] The positive electrode, negative electrode, and separator are stacked to form a battery cell, which is then packaged in an aluminum-plastic film pouch and injected with electrolyte to obtain a 4.0 Ah lithium-ion battery. The lithium-ion battery is then tested after formation.

[0075] Examples 2-3

[0076] The difference between this embodiment and Embodiment 1 is that the electrolyte composition is changed.

[0077] Example 4

[0078] The difference between this embodiment and Embodiment 1 is that the amount of LATP is changed so that the mass ratio of LATP to graphite is 2%.

[0079] Example 5

[0080] The difference between this embodiment and Embodiment 1 is that the amount of LATP is changed so that the mass ratio of LATP to graphite is 10%.

[0081] Example 6

[0082] The difference between this embodiment and Example 1 is that, in the preparation method, the mass ratio of B2O3 to LATP is 20%.

[0083] Example 7

[0084] The difference between this embodiment and Example 1 is that, in the preparation method, B2O3 is replaced with polymethyl methacrylate (PMMA), and the sintering temperature is adjusted from 450°C to 180°C. In this embodiment, the inorganic component in the coating layer accounts for 90 wt%.

[0085] Example 8

[0086] The difference between this embodiment and Embodiment 1 is that LATP is replaced with LLZO, and the D50 of the LLZO used is... s The wavelength is 100nm, and the mass ratio of LLZO to graphite is 8%.

[0087] Examples 9-10

[0088] The difference between this embodiment and Embodiment 1 is that the electrolyte composition is changed.

[0089] The electrolyte composition involved in Examples 1-10 of this invention is shown in Table 1.

[0090] Example 11

[0091] The difference between this embodiment and Embodiment 1 is that the D50 of graphite... c The D50 of LATP is 10 μm. s The wavelength is 200 nm. The D50 of the negative electrode material in this embodiment is... p It is 10.4 μm.

[0092] Comparative Example 1

[0093] The difference between this comparative example and Example 1 is that the graphite was not coated in the preparation method. The electrolyte composition was also changed.

[0094] Comparative Example 2

[0095] The difference between this comparative example and Example 1 is that the graphite was not coated.

[0096] Comparative Example 3

[0097] The difference between this comparative example and Example 1 is that the composition of the electrolyte is changed.

[0098] Comparative Examples 4-5

[0099] The difference between this comparative example and Example 1 is that the composition of the electrolyte is changed.

[0100] Comparative Example 6

[0101] The difference between this comparative example and Example 1 is that, in the preparation method, B2O3 is replaced with polymethyl methacrylate (PMMA), the mass ratio of PMMA to LATP is 30%, and the sintering temperature is adjusted from 450°C to 180°C. In this comparative example, the inorganic component in the coating layer accounts for 70 wt%.

[0102]

[0103] Note: The content of each component in the non-aqueous organic solvent is based on the total volume of the non-aqueous organic solvent, and the content of each component in the additive is based on the total mass of the electrolyte.

[0104] The lithium-ion batteries of Examples 1-11 and Comparative Examples 1-7 were tested as follows:

[0105] ①ARC Test: The lithium-ion battery is fully charged to 3.65V at a 1 / 3C rate. The fully charged lithium-ion battery is placed in the calorimetric chamber of the Accelerated Adiabatic Calorimeter (ARC), and its position is adjusted to ensure that the lithium-ion battery does not contact the chamber body or upper and lower walls. The following steps are performed in sequence: 1) The temperature is increased from room temperature to 65±0.5℃ at a rate of 5℃ / min, and then left to stand for 60min; then the temperature is increased by 5℃ at a rate of 5℃ / min and held at this temperature for 15min. The temperature rise rate of the lithium-ion battery is monitored during this process. If the temperature rise exceeds 0.3℃ within 15min (i.e., the temperature rise rate ≥ 0.02℃ / min), it is considered that a self-exothermic reaction has occurred inside the cell, and this temperature is marked as T. onset If the temperature rise rate is ≤0.02℃ / min, continue to raise the temperature by 5℃ and repeat the above process until the temperature rise rate is ≥0.02℃ / min. Record the temperature at this point as T. onset ;2) When the cell reaches T onset After the temperature is reached, the equipment automatically switches to the adiabatic tracking mode. During this process, the instrument adjusts the heating power in real time to ensure that the temperature difference between the sample and the furnace cavity is ≤0.01℃. The temperature (T) changes with time (t) and the temperature rise rate (dT / dt) changes with time are recorded throughout the process. 3) When the temperature rises to 400℃ or the temperature change rate of the cell within 5 minutes is ≤0.1℃ / s, the test is terminated.

[0106] Data was read during the adiabatic tracking mode process, and a temperature rise rate curve was plotted (the horizontal axis is temperature, and the vertical axis is the temperature rise rate, where the temperature rise rate is the ratio of temperature to time). The temperature point corresponding to the first temperature rise rate reaching ≥0.1℃ / min was extracted and marked as T1. The inflection point of the temperature rise rate between 1-10℃ / min in the temperature rise rate curve was read and marked as T2. The temperature point of the temperature rise rate >60℃ / min (i.e., the temperature rise per second exceeds 1℃) in the temperature rise rate curve was read and marked as T3. T1, T2, and T3 were obtained, representing the cell's self-generated heat initiation temperature, thermal runaway acceleration inflection point temperature, and thermal runaway trigger temperature, respectively. The higher T1, T2, and T3 are, the better the thermal stability of the lithium-ion battery.

[0107] ②25℃ Three-electrode charging capability test: The lithium-ion battery is charged at a constant current rate of 3C starting from 0% SOC, while the potential of the lithium reference electrode is monitored until the potential of the negative electrode drops to 2mV relative to the potential of the lithium reference electrode. Then the charging current is gradually reduced to maintain the potential of the negative electrode relative to the potential of the lithium reference electrode at 2mV until the cell is fully charged to 3.65V. The charging time (min) from 0 to 80% SOC is recorded to obtain the cell's maximum charging capability.

[0108] ③ 25℃ / 45℃ Cycling Test: Cycling tests were conducted at 25℃ and 45℃ respectively. The cycle voltage range of the lithium-ion battery is 2.5-3.65V. The charge-discharge regime was stepped charging and 1C discharging. Specifically, 2C was used for charging from 0-80% SOC, 1.5C for 80-85% SOC, 1C for 85-90% SOC, 0.75C for 90-95% SOC, and 0.5C for 95-100% SOC. The discharge capacity C1 of the first cycle and C2 of the 1000th cycle at 25℃ were recorded. 1000 And calculate the capacity retention rate after 1000 cycles at 25°C. Capacity retention rate after 1000 cycles at 25°C = C 1000 / C1×100%. Record the discharge capacity C1 during the first week at 45℃. ＇ and the discharge capacity C at week 1000 1000 ＇ Calculate the capacity retention rate after 1000 cycles at 25°C and the capacity retention rate after 1000 cycles at 45°C = C 1000 ＇ / C1 ＇ ×100%.

[0109] ④ 60℃ Storage Test: The lithium-ion battery was fully charged to 100% SOC and stored at 60℃ for 30 days. Capacity retention and recovery rate tests were then conducted. The test method was as follows: 1) Before the cell was first placed in the 60℃ constant temperature chamber, it was left to stand in a 25℃ environment for more than 4 hours. It was then first charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage until the current rate was <0.05C. After standing for 10 minutes, it was discharged at a constant current of 0.33C to 2.5V. This charging and discharging method was repeated for three weeks until a full charge was achieved. The discharge capacity of the last week was recorded as the initial capacity. The cell was then stored in the 60℃ constant temperature chamber for 30 days. After storage, the battery cells are removed from the 60℃ constant temperature chamber and placed in a 25℃ environment to cool for more than 4 hours. They are first charged with a constant current of 0.33C to 3.65V and then charged with a constant voltage until the current ratio is <0.05C. After standing for 10 minutes, they are discharged with a constant current of 0.33C to 2.5V. The discharge capacity at this time is marked as the recovery capacity. The capacity recovery rate is calculated as recovery capacity / initial capacity × 100%.

[0110] Based on the above embodiments and comparative examples, the specific experimental results are summarized in Table 2 below.

[0111]

[0112] This invention, by employing a negative electrode material with a specific type of coating layer and combining it with an electrolyte of a specific composition, enables lithium-ion batteries to have excellent fast-charging performance, room-temperature cycling performance, high-temperature cycling performance, and high-temperature storage performance, while reducing the risk of explosion and fire during battery thermal runaway.

[0113] A comparison of Examples 1 and 4-5 shows that if the LATP content is too low (Example 4), it will lead to uneven coating on the surface of the negative electrode material, affecting the high-temperature cycling, high-temperature storage and thermal stability of the battery cell in ARC testing; if the LATP content is too high (Example 5), it will lead to increased impedance and increased charging time of 0-80% SOC at 25℃, which means a reduction in the battery cell's ultimate charging capability.

[0114] A comparison between Example 1 and Example 7 shows that, compared to using an organic binder (Example 7), using B2O3 to form an inorganic binder (Example 1) is beneficial for improving the thermal stability of the negative electrode material. At the same time, during the preparation process, B2O3 may react with lithium-containing components to form a lithium boron oxide complex, which is beneficial for ion transport. Therefore, Example 1 has better fast charging performance and thermal stability.

[0115] A comparison between Example 1 and Example 10 shows that the volume ratio of ACN is preferably ≥15% and ≤30%, which can better improve the fast charging performance of the battery.

[0116] In Comparative Example 2, the lack of graphite coating increased the risk of reaction between the negative electrode and the electrolyte. In Comparative Example 3, ACN was not used to replace part of the EC in the electrolyte, and the LiFSI content was 0.4 mol / L, which not only resulted in a lower conductivity than in Example 1 but also increased the risk of reaction between the negative electrode and the electrolyte. Comparative Example 1, which neither coated the graphite nor used an electrolyte with the same composition as Comparative Example 3, had worse safety performance than Comparative Examples 1 and 2.

[0117] In Comparative Example 4, EMC was used to replace part of EC in the electrolyte, and ACN was not added, resulting in a lower conductivity than in Example 1.

[0118] In Comparative Example 5, the LiFSI content in the electrolyte was 0.4 mol / L. Although this slightly increased the conductivity of the electrolyte, it also increased the heat generation between LiFSI and the negative electrode, thus reducing the safety performance of the battery.

[0119] In Comparative Example 6, due to the excessively large particle size of LATP, the D50... c / D50 s =30, affecting the coating effect. Even with an increase in the coating amount of LATP compared to Example 1, it is still impossible to achieve complete and uniform coating, resulting in a decrease in the safety and electrochemical performance of the battery.

[0120] In Comparative Example 7, the inorganic component in the coating layer accounted for less than 80 wt%, which led to a decrease in the thermal stability of the coating layer, and consequently a decrease in the thermal stability of the negative electrode material, resulting in a risk of explosion and fire in the event of thermal runaway. Moreover, the extensive use of PMMA as a binder resulted in a decrease in fast-charging performance.

[0121] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode includes a negative electrode material, which comprises a negative electrode active material and a coating layer covering the negative electrode active material, wherein the lithium-ion conductivity of the coating layer is ≥10. -2 mS / cm, the electronic conductivity of the coating layer is ≤10 -5 mS / cm, the coating layer includes an ion-conducting material, which includes at least one of artificial SEI material and solid electrolyte material, and the inorganic component in the coating layer accounts for ≥80 wt%; The electrolyte comprises a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent comprises a solvent with a high dielectric constant and low viscosity and ethylene carbonate. The volume percentage of the solvent with a high dielectric constant and low viscosity in the non-aqueous organic solvent is ≥10% and ≤30%. The volume percentage of ethylene carbonate in the non-aqueous organic solvent is ≥5% and ≤10%. The lithium salt optionally comprises lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide, and the concentration of lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is ≤0.1 mol / L. The solvent with high dielectric constant and low viscosity satisfies the following conditions: dielectric constant ≥ 20, viscosity μ ≤ 0.5CP at 25℃.

2. The lithium-ion battery according to claim 1, characterized in that, The mass percentage of the ion-conducting material relative to the negative electrode active material is 1wt% to 10wt%.

3. The lithium-ion battery according to claim 2, characterized in that, The mass percentage of the ion-conducting material relative to the negative electrode active material is 3wt%~7wt%.

4. The lithium-ion battery according to claim 1, characterized in that, The artificial SEI material includes at least one of Li3BO3, Li2B4O7, LiAlO2, lithium sulfonate, and lithium phosphate; and / or, The solid electrolyte material includes at least one of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, lithium phosphorus oxy nitrogen, LiPS, or lithium germanium phosphorus sulfide; and / or, The coating layer can coat the negative electrode active material in an in-situ or non-in-situ manner. When the coating method is non-in-situ coating, the particle size D50 of the negative electrode active material is defined as D50. c The particle size D50 of the negative electrode material is defined as D50. p The particle size D50 of the ion-conducting material is defined as D50. s D50 c / D50 s ≥50, 1.01≤D50 p / D50 c ≤1.

05.

5. The lithium-ion battery according to claim 1, characterized in that, The coating layer also includes carbon materials and adhesives; and / or, The adhesive comprises B2O3 and / or a lithium boron oxide complex; and / or, The carbon material accounts for 8% to 12% of the mass of the coating layer.

6. The lithium-ion battery according to claim 1, characterized in that, The negative electrode material is prepared by the following method, which includes the following steps: The negative electrode active material, ion-conducting material, optional binder raw material and optional carbon material are mixed and sintered to form a coating layer on the surface of the negative electrode active material, thus obtaining the negative electrode material.

7. The lithium-ion battery according to claim 6, characterized in that, The sintering temperature is 450℃~500℃; and / or, The adhesive raw material is B2O3; and / or, The adhesive accounts for 8% to 15% of the mass of the ion-conducting material.

8. The lithium-ion battery according to claim 1, characterized in that, The electrolyte has an ionic conductivity ≥13 mS / cm at 25°C; and / or, The high dielectric constant, low viscosity solvent includes at least one of acetonitrile, propionitrile, n-butyronitrile, and isobutyronitrile.

9. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous organic solvent also includes other solvents, including at least one of carbonates, carboxylic esters, chain ethers, cyclic ethers, lactones, nitriles, ionic liquids, phosphate esters, fluorocarbonates, fluorocarboxylic esters, fluoroethers, and fluoronitriles.

10. The lithium-ion battery according to claim 9, characterized in that, The other solvents include at least one selected from propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, methyl acetate, ethyl formate, ethyl propionate, propyl propionate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetrahydrofuran, dioxapentane, crown ether, γ-butyrolactone, succinic acid, glutaronitrile, adiponitrile, hexanetrionitrile, trimethyl phosphate, triethyl phosphate, fluoroethylene carbonate, trifluoroethyl methyl ethyl carbonate, difluoroethyl ethyl acetate, tetrafluoroethyl-tetrafluoropropyl ether, and fluoroacetonitrile.

11. The lithium-ion battery according to claim 1, characterized in that, The lithium salt further includes at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate borate), and lithium tetrafluoroborate; and / or, The concentration of the lithium salt is ≥1.2 mol / L.

12. The lithium-ion battery according to any one of claims 1-11, characterized in that, The electrolyte further includes additives, which include at least one of the following: vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, ethylene dicarbonate, vinyl sulfate, propylene sulfate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl disulfate, dimethyl methanesulfonate, vinyl disulfate, lithium difluorophosphate, lithium nitrate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, lithium tetrafluoroborate, lithium difluorosulfonylimide, lithium fluorosulfonate, tris(trimethylsilyl)boronic acid ester, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, and tetravinylsilane; and / or, The additive accounts for 3wt% to 10wt% of the mass of the electrolyte.

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