Lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, relates to a lithium ion battery, and particularly relates to a lithium ion battery with relatively good fast-charge cycle performance and high-temperature storage performance. The lithium ion battery comprises a positive plate, a negative plate and a non-aqueous electrolyte, the positive plate comprises a positive active material, and the positive active material comprises a phosphate compound; the non-aqueous electrolyte comprises a first additive, a lithium salt and a non-aqueous organic solvent; the lithium salt comprises lithium hexafluorophosphate and lithium bis (fluorosulfonyl) imide; the first additive comprises at least one of compounds 1-5, and the solvent comprises a compound as shown in a structural formula 1; the lithium ion battery satisfies the following conditions: 2.8 < = C / (10A + B) + D / 100 < = 14, 0.05 < = A < = 2, 0.5 < = B < = 6, 24 < = C < = 56, and 160 < = D < = 220. The lithium ion battery provided by the invention is high in energy density, and has relatively excellent high-temperature storage performance and fast-charge cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery with good fast-charging cycle performance and high-temperature storage performance and high energy density. Background Art

[0002] In the field of power lithium-ion batteries, phosphate cathodes represented by lithium iron phosphate have the advantages of longer cycle life, better safety, and higher cost performance compared to nickel-cobalt-manganese ternary cathodes, but the rate performance of phosphate cathodes is poor, and the specific capacity is not as good as that of ternary cathodes. With the development of the new energy vehicle market, the industry is paying more and more attention to how to improve the rate performance and energy density of lithium-ion batteries to meet consumers' demand for fast charging performance and cruising range of new energy vehicles. One of the commonly used methods to improve the rate performance of phosphate cathode batteries is to reduce the thickness of the cathode material layer to shorten the lithium ion conduction path to improve the lithium ion diffusion efficiency. For example, the thickness of the existing fast-charging lithium iron phosphate electrode is generally less than 150μm, but this leads to a decrease in the active material loading per unit area of ​​the cathode, sacrificing the energy density of the battery. Therefore, finding a way to improve the battery rate performance without degrading the energy density is a hot research direction in the field of power lithium-ion batteries. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a lithium-ion battery with good fast charging cycle performance and high temperature storage performance and high energy density.

[0004] The present invention adopts the following technical scheme.

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

[0006] The positive electrode sheet comprises a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material comprises a phosphate compound LiFe 1-x-y Mn x M y PO4, wherein 0≤x≤0.8, 0≤y≤0.05, and M includes any one or more of Co, B, Ga, F, W, Zr, Mg, Na, Pb, K, Al, Cr, Ba, Ca, Ni, Sr, Ti, Zn, Si, V, Mo, or Nb;

[0007] The non-aqueous electrolyte includes a first additive, a lithium salt and a non-aqueous organic solvent;

[0008] The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; the first additive includes at least one of Compounds 1 to 5:

[0009]

[0010] The non-aqueous organic solvent includes a compound shown in structural formula 1:

[0011]

[0012] Wherein, R3 is an alkyl group or a fluoroalkyl group having a carbon number ≤ 2, R4 is an alkyl group having a carbon number ≤ 3, and the total number of carbon atoms in R3 and R4 is ≤ 4;

[0013] The lithium-ion battery meets the following requirements:

[0014] 2.8≤C / (10A+B)+D / 100≤14, 0.05≤A≤2, 0.5≤B≤6, 24≤C≤56, 160≤D≤220;

[0015] Wherein: A is the mass percentage of the first additive in the non-aqueous electrolyte, in %;

[0016] B is the mass percentage of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte, in %;

[0017] C is the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in %;

[0018] D is the thickness of the positive electrode material layer, in μm.

[0019] The lithium ion battery of the present invention uses a phosphate compound as a positive electrode active material, a sulfur-containing compound with a specific structure as a first additive in a non-aqueous electrolyte, lithium hexafluorophosphate and lithium bisfluorosulfonyl imide as a common salt, and a short-chain carboxylic acid ester compound shown in structural formula 1 as a non-aqueous organic solvent. The inventors have found through extensive research that when the relationship between the mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of lithium bisfluorosulfonyl imide, the mass percentage C of the compound shown in structural formula 1, and the thickness D of the positive electrode material layer satisfies 2.8≤C / (10A+B)+D / 100≤14, 0.05≤A≤2, 0.5≤B≤6, 24≤C≤56, 160≤D≤220, a phosphate positive electrode lithium ion battery with strong high-temperature storage performance and fast charging cycle performance can be obtained without sacrificing energy density. It is speculated that the short-chain carboxylic acid ester solvent shown in Structural Formula 1 has a lower viscosity, which can reduce the resistance to the movement of lithium ions, while lithium bis(fluorosulfonyl)imide (LiFSI) has a large anion, which weakens the interaction between anions and cations, making it easy to ionize in the electrolyte to generate free lithium ions. The combination of the compound shown in Structural Formula 1 and LiFSI can significantly improve the electrolyte ion conductivity and improve the fast charging cycle performance of the battery. In addition, the first additive with a specific structure will form a thermally stable, dense and thin protective film on the surface of the negative electrode during the battery formation process, preventing the negative electrode from having side reactions with the carboxylic acid ester solvent, thereby avoiding the compound shown in Structural Formula 1 from deteriorating the high temperature performance of the battery; at the same time, the first additive is used in combination with LiFSI to form a dense and thin protective film rich in inorganic substances LiF during the battery formation process, which can efficiently conduct lithium ions through the protective film and reduce the internal resistance of the electrode-electrolyte interface. By limiting the solvent, lithium salt and additive in the non-aqueous electrolyte as mentioned above, it is possible to achieve good fast charging performance under the condition of thicker positive electrode sheets, thus avoiding the sacrifice of battery energy density. When the mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of lithium bis(fluorosulfonyl)imide, the mass percentage C of the compound shown in structural formula 1, and the thickness D of the positive electrode material layer are in a synergistic state, it is possible to achieve a lithium-ion battery with a higher energy density under thicker battery sheets, while taking into account good high-temperature storage performance and fast charging cycle performance. Preferably, the lithium-ion battery satisfies: 3≤C / (10A+B)+D / 100≤8.

[0020] The sulfur-containing compound with a specific structure is used as the first additive. During the battery formation process, a thermally stable, dense and thin protective film will be generated on the surface of the negative electrode, which helps to prevent the negative electrode from having side reactions with carboxylic acid ester solvents, thereby avoiding the carboxylic acid ester solvents from deteriorating the high temperature performance of the battery. If the mass percentage A% of the first additive is too little, a dense interface film that completely covers the surface of the negative electrode cannot be generated, and the protective effect is insufficient; if the mass percentage A% of the first additive is too much, the interface film will be too thick, resulting in an increase in the internal resistance of the battery and deterioration of the cycle performance. Specifically, the mass percentage A% of the first additive in the non-aqueous electrolyte is 0.05%, 0.3%, 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.5%, 1.6%, 1.8%, 2% or a range consisting of any two of these values; preferably, the mass percentage A% of the first additive in the non-aqueous electrolyte is 0.05% to 1%.

[0021] Lithium bis(fluorosulfonyl)imide is used to replace part of lithium hexafluorophosphate. Lithium bis(fluorosulfonyl)imide has large anions, which weaken the interaction between anions and cations, making it easy to ionize in the electrolyte to produce free lithium ions, which helps to improve the electrolyte ion conductivity and improve the fast charging cycle performance of the battery. If the mass percentage B% of lithium bis(fluorosulfonyl)imide is too low, it will not have a significant effect on improving the fast charging performance; if the mass percentage B% of lithium bis(fluorosulfonyl)imide is too high, the problem of corroding the positive electrode current collector aluminum foil will be exposed. Specifically, the mass percentage B% of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.7%, 3%, 3.2%, 3.5%, 3.6%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.7%, 6% or a range consisting of any two of these values; preferably, the mass percentage B% of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is 2% to 5%.

[0022] The mass percentage of lithium hexafluorophosphate in the non-aqueous electrolyte is 9% to 14%. 。 Preferably, the mass percentage of the lithium hexafluorophosphate is greater than the mass percentage of the lithium bis(fluorosulfonyl)imide, and the lithium hexafluorophosphate can form a passivation film on the surface of the positive electrode current collector aluminum foil to inhibit the corrosion of the lithium bis(fluorosulfonyl)imide on the aluminum foil during the charge and discharge process.

[0023] The compound shown in Structural Formula 1 is a non-aqueous organic solvent, and the short-chain carboxylic acid ester solvent has a low viscosity, which can reduce the resistance to the movement of lithium ions and help to improve the ionic conductivity of the electrolyte. However, the short-chain carboxylic acid ester solvent has poor electrochemical stability and is prone to side reactions with the negative electrode in a highly lithium-intercalated state at high temperatures, resulting in degradation of high-temperature storage and high-temperature cycle performance. If the mass percentage C% of the compound shown in Structural Formula 1 is too small, it will not have a significant effect on reducing viscosity; if the mass percentage C% of the compound shown in Structural Formula 1 is too much, the degradation for high-temperature storage is too serious. Therefore, when the mass percentages of additives, solvents, and lithium salts in the non-aqueous electrolyte are in a synergistic state, a phosphate positive electrode lithium-ion battery with strong high-temperature storage performance and fast-charging cycle performance can be obtained without sacrificing energy density. Specifically, the mass percentage C% of the compound represented by structural formula 1 in the non-aqueous electrolyte is 24%, 25%, 28%, 30%, 32%, 34%, 35%, 37%, 39%, 40%, 42%, 45%, 48%, 50%, 52%, 54%, 56% or a range consisting of any two of these values; preferably, the mass percentage C% of the compound represented by structural formula 1 in the non-aqueous electrolyte is 24% to 40%.

[0024] From the perspective of the pole piece, the main factors limiting the fast charging of the battery are the diffusion efficiency of lithium ions in the electrode active material and the resistance of lithium ion transmission across the phase boundary at the electrode-electrolyte interface. The industry often reduces the thickness of the positive electrode material layer to shorten the lithium ion conduction path and improve the lithium ion diffusion efficiency to improve the fast charging cycle performance. However, this results in a decrease in the active material loading per unit surface area of ​​the positive electrode, sacrificing the energy density of the battery. For example, the thickness of the fast-charging positive electrode material layer is generally below 150μm. In the present invention, a first additive with a specific structure is used in combination with LiFSI to form a dense, thin, and inorganic LiF-rich protective film during the battery formation process. It can efficiently conduct lithium ions through the protective film and reduce the internal resistance of the electrode-electrolyte interface, so that a thicker pole piece can also have better fast charging performance. Specifically, the thickness D of the positive electrode material layer of the lithium ion battery is 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm or a range consisting of any two of these values. Preferably, the thickness D of the positive electrode material layer of the lithium ion battery is 170 μm to 200 μm.

[0025] In some embodiments of the present invention, the compound represented by the structural formula 1 includes one or more of the following compounds:

[0026]

[0027] Preferably, the compound shown in the structural formula 1 includes at least one of compound 1-1, compound 1-2 or compound-5, that is, at least one of methyl acetate, ethyl acetate, or ethyl propionate. More preferably, the compound shown in the structural formula 1 includes at least ethyl acetate. Compared with other carboxylate compounds, ethyl acetate not only has a lower viscosity, can reduce the resistance to the movement of lithium ions, help to improve the ionic conductivity of the electrolyte, but also is beneficial to stabilize the positive electrode structure. Therefore, while improving the fast charging performance of lithium-ion batteries, it can also improve its high temperature performance at the same time, thereby improving the overall performance of electrochemical devices.

[0028] In the field of power lithium-ion batteries, phosphate positive electrodes have the advantages of longer cycle life, better safety, and higher cost performance compared to nickel-cobalt-manganese ternary positive electrodes, but the rate performance of phosphate positive electrodes is poor, which is mainly due to their poor conductivity. If the rate performance of lithium iron phosphate positive electrode batteries can be improved, it can make up for the gap with ternary positive electrodes to a certain extent and be more competitive in the market. The present invention limits the solvents, lithium salts, and additives in the non-aqueous electrolyte to achieve strong high-temperature storage performance and fast charging cycle performance without sacrificing the energy density of phosphate positive electrode lithium-ion batteries. Specifically, in some embodiments of the present invention, the positive electrode active materials include LiFePO4, LiFe 0.6 Mn 0.4 PO4、LiFe 0.5 Mn 0.5 PO4、LiFe 0.2 Mn 0.8 PO4、LiFe 0.4 Mn 0.6 PO4、LiFe 0.4 Mn 0.55 Zr 0.05 PO4、LiFe 0.4 Mn 0.55 Mg 0.05 PO4、LiFe 0.4 Mn 0.55 Na 0.05 PO4、LiFe 0.4 Mn 0.55 Zn 0.05 PO4、LiFe 0.4 Mn 0.55 Al 0.05 PO4、LiFe 0.4 Mn 0.55 Co 0.05 PO4、LiFe 0.4 Mn 0.55 B 0.05 PO4、LiFe 0.4 Mn 0.55 Ga 0.05PO4、LiFe 0.4 Mn 0.55 F 0.05 PO4、LiFe 0.4 Mn 0.55 W 0.05 PO4、LiFe 0.4 Mn 0.55 Pb 0.05 PO4、LiFe 0.4 Mn 0.55 K 0.05 PO4、LiFe 0.4 Mn 0.55 Cr 0.05 PO4、LiFe 0.4 Mn 0.55 Ba 0.05 PO4、LiFe 0.4 Mn 0.55 Ca 0.05 PO4、LiFe 0.4 Mn 0.55 Ni 0.05 PO4、LiFe 0.4 Mn 0.55 Sr 0.05 PO4、LiFe 0.4 Mn 0.55 Ti 0.05 PO4、LiFe 0.4 Mn 0.55 Si 0.05 PO4、LiFe 0.4 Mn 0.55 V 0.05 PO4、LiFe 0.4 Mn 0.55 Mo 0.05 PO4 or LiFe 0.4 Mn 0.55 Nb 0.05 Any one or more of PO4.

[0029] Specifically, in some embodiments of the present invention, the lithium salt also includes lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiPO2F2, LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiCl, LiBr, LiI, LiClO4, LiB 10 Cl 10At least one of LiAlCl4, lithium chloroborane, lithium carboxylate with less than 4 carbon atoms, and lithium tetraphenylborate. Preferably, the total content of lithium salt in the non-aqueous electrolyte is 9.5-20%. Controlling the total content of lithium salt within the above range can control the conductivity of the electrolyte within the optimal range.

[0030] In some embodiments of the present invention, the non-aqueous electrolyte further includes an auxiliary additive, and the auxiliary additive includes at least one of a cyclic sulfate ester compound, a sultone compound, a cyclic carbonate compound, a phosphate ester compound and a borate ester compound.

[0031] In some preferred embodiments, the cyclic sulfate ester compound includes at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate.

[0032] In some preferred embodiments, the sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, and propenyl-1,3-sultone.

[0033] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate and the compound shown in the following structural formula 3:

[0034]

[0035] In the structural formula 2 shown, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group.

[0036] In some preferred embodiments, the compound represented by structural formula 2 includes at least one of the following compounds 2-1 to 2-6:

[0037]

[0038] In some preferred embodiments, the phosphate compound includes at least one of the compounds shown in the following structural formula 3:

[0039]

[0040] In the structural formula 3, R 31 , R 32 , R 33Each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number of 1 to 3; more preferably, the compound shown in the structural formula 3 includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate and diallyl hexafluoroisopropyl phosphate.

[0041] In some preferred embodiments, the borate ester compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

[0042] In some embodiments of the present invention, based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additive is 0.01% to 10%. Preferably, the content is 0.1% to 5%; more preferably, the content is 0.1% to 2%. Specifically, the content of any one of the optional substances 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 a range consisting of any two of these values.

[0043] Specifically, in some embodiments of the present invention, the positive electrode sheet further includes a positive electrode binder and a positive electrode conductor. The positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a thermoplastic resin such as thermoplastic polyimide, polyethylene and polypropylene; an acrylic resin; and one or more of styrene butadiene rubber. The positive electrode conductor includes one or more of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0044] Specifically, in some embodiments of the present invention, the positive electrode sheet further includes a positive electrode current collector, and the positive electrode material layer is disposed on the surface of the positive electrode current collector. The positive electrode current collector includes a metal material that can conduct electrons, and preferably, the positive electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0045] Specifically, in some embodiments of the present invention, the negative electrode sheet includes a negative electrode material layer containing a negative electrode active material, and the negative electrode active material is any one or more of a silicon-based material and a carbon material. The silicon-based material is selected from one or more of a silicon material, a silicon oxide material, a silicon-carbon material, and a silicon alloy material; preferably, the silicon material is a nano-silicon material; preferably, the silicon oxide material is SiO x Material, wherein 0≤x<2; preferably, the silicon-carbon material is: a silicon-based material containing silicon and carbon materials, and / or a silicon-based material containing SiO y and a silicon-based material of a carbon material, wherein 0≤y<2; preferably, the silicon alloy material is a Mg2Si alloy material and / or a 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.

[0046] Specifically, in some embodiments of the present invention, the negative electrode material layer further includes a negative electrode binder, a negative electrode conductor and a negative electrode current collector. The material of the negative electrode current collector may be the same as that of the positive electrode current collector, which will not be described in detail here. The negative electrode binder and the negative electrode conductor may be the same as the positive electrode binder and the positive electrode conductor, respectively, which will not be described in detail here.

[0047] Specifically, in some embodiments of the present invention, the lithium-ion battery further includes a diaphragm, and the diaphragm is located between the positive electrode and the negative electrode.

[0048] The separator is an existing conventional separator, selected from one or more of a ceramic separator, a polymer separator, a non-woven fabric, and an inorganic-organic composite separator, for example, a single-layer polypropylene (PP) separator, a single-layer polyethylene (PE) separator, a double-layer PP / PE separator, a double-layer PP / PP separator, and a triple-layer PP / PE / PP separator.

[0049] The lithium ion battery of the present invention uses lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide as a common salt, uses a sulfur-containing compound of a specific structure as a first additive, uses a short-chain carboxylic acid ester compound shown in structural formula 1 as a solvent, and limits the relationship between the mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of lithium bis(fluorosulfonyl)imide, the mass percentage C of the compound shown in structural formula 1, and the thickness D of the positive electrode material layer to satisfy 2.8≤C / (10A+B)+D / 100≤14, 0.05≤A≤2, 0.5≤B≤6, 24≤C≤56, and 160≤D≤220. During the battery formation process, a dense and thin protective film rich in inorganic substance LiF can be formed, lithium ions are efficiently conducted through the protective film, the internal resistance of the electrode-electrolyte interface is reduced, the defect of poor rate performance of phosphates as positive electrode materials is overcome, so that it takes into account both excellent high-temperature storage performance and fast charging cycle performance, and the battery has a higher energy density. It breaks the industry's common method of reducing the thickness of the positive electrode to improve the lithium ion diffusion efficiency, allowing the use of thicker electrodes to achieve better fast charging performance. DETAILED DESCRIPTION

[0050] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0051] Example 1

[0052] The method for preparing a lithium-ion battery in this embodiment comprises the following steps:

[0053] 1) Preparation of non-aqueous electrolyte:

[0054] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and ethyl acetate (EA) are mixed, and then lithium salts (lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI)) and additives (Compound 1, vinylene carbonate (VC) and fluoroethylene carbonate (FEC)) are added. Based on the total weight of the non-aqueous electrolyte as 100%, the content of Compound 1 is 0.5%, the content of VC is 3%, and the content of FEC is 0.5%; the content of the solvent ethyl acetate (Compound 1-2) is 35%, the content of lithium bis(fluorosulfonyl)imide is 5%, and the total content of lithium salts is 16.8%.

[0055] 2) Preparation of positive electrode:

[0056] The positive electrode active material LiFePO4, the conductive carbon black Super-P and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on both sides of the aluminum foil current collector, dried, rolled, vacuum dried, and welded with an ultrasonic welder. The aluminum lead wire was obtained to obtain a positive electrode sheet, and the thickness of the positive electrode material layer was 180μm.

[0057] 3) Preparation of negative electrode sheet:

[0058] The negative electrode active material artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 95:1:1.5:2.5. Then they are dispersed in deionized water to obtain negative electrode slurry. The negative electrode slurry is coated on both sides of the copper foil, dried, rolled, vacuum dried, and welded with nickel lead wires using an ultrasonic welder to obtain a negative electrode sheet.

[0059] 4) Preparation of battery cells:

[0060] A three-layer separator made of polypropylene, polyethylene and polypropylene with a thickness of 20 μm is placed between the positive plate and the negative plate, and then the sandwich structure consisting of the positive plate, the negative plate and the separator is wound. The wound body is flattened and placed in an aluminum foil packaging bag, and vacuum-baked at 85°C for 48 hours to obtain a battery cell to be injected with liquid.

[0061] 5) Battery filling and formation:

[0062] In a glove box where the moisture and oxygen content are controlled below 10 ppm, the non-aqueous electrolyte prepared above is injected into the battery cell, vacuum packaged, and left to stand at 45°C for 48 hours. Then, the conventional formation of the first charge is carried out according to the following steps: 0.05C constant current charging for 2 hours, 0.1C constant current charging for 1 hour, and 0.2C constant current charging for 1 hour.

[0063] 6) Cell capacity division:

[0064] The battery cell was left at 45°C for 48h, then vacuum sealed for a second time to remove the generated gas, then charged to 3.65V at a constant current of 0.2C, then charged at a constant voltage until the current dropped to 0.05C, and after being left for 5min, discharged to 2.5V at a constant current of 0.2C to obtain a lithium iron phosphate positive electrode / graphite negative electrode lithium ion battery.

[0065] Examples 2 to 48 and Comparative Examples 1 to 17

[0066] This embodiment and comparative example are used to compare and illustrate the lithium-ion battery disclosed in the present invention, including most of the operating steps in the above-mentioned embodiment 1, and the total content of lithium salt in the non-aqueous electrolyte is the same. The differences are: the type of positive electrode active material, the composition of the non-aqueous electrolyte and the content of each component, the auxiliary additives and the thickness of the positive electrode material layer, as shown in Tables 1 to 5.

[0067] The lithium-ion batteries prepared in the examples and comparative examples were subjected to the following performance tests:

[0068] (1) High temperature storage performance test

[0069] At 25°C, charge the battery to 3.65V (cut-off current 0.05C) with 1C constant current and constant voltage, and discharge it to 2.5V with 1C constant current, and record the discharge capacity of the battery. Then charge the battery to 3.65V (cut-off current 0.05C) with 1C constant current and constant voltage, and place it in a 60°C oven. Take it out after 30 days, and after the battery cools down, discharge it to 2.5V with 1C constant current at 25°C, and record the discharge capacity of the battery.

[0070] High temperature storage capacity retention rate (%) = discharge capacity after storage at 60°C for 30 days / discharge capacity before storage × 100%

[0071] (2) Normal temperature fast charging cycle life test

[0072] At 25°C, charge the battery with a 4C constant current until the battery is at 80% SOC, then charge it with a 1C constant current and constant voltage to 3.65V (cut-off current 0.05C), and then discharge it with a 1C constant current to 2.5V. Use this process to continuously perform cyclic charge and discharge tests, and record the discharge capacity of each cycle.

[0073] Cycle capacity retention rate (%) = current cycle discharge capacity / first cycle discharge capacity × 100%

[0074] The capacity retention rate was recorded after 800 cycles.

[0075] (3) High temperature fast charging cycle life test

[0076] At 45°C, charge the battery with a 4C constant current until the battery is at 80% SOC, then charge it with a 1C constant current and constant voltage to 3.65V (cut-off current 0.05C), and then discharge it with a 1C constant current to 2.5V. Use this process to continuously perform cyclic charge and discharge tests, and record the discharge capacity of each cycle.

[0077] Cycle capacity retention rate (%) = current cycle discharge capacity / first cycle discharge capacity × 100%

[0078] The capacity retention rate was recorded after 800 cycles.

[0079] Test Results

[0080] Table 1 shows the test results of Examples 1 to 19 and Comparative Examples 1 to 13; the differences between Examples 2 to 19 and Comparative Examples 1 to 13 and Example 1 are the relevant parameters in Table 1.

[0081] Table 1

[0082]

[0083]

[0084]

[0085] Note: “ / ” in the table means there is no such item.

[0086] It can be seen from the test results of Examples 1 to 19 and Comparative Examples 1 to 13 that the lithium ion battery of the present invention uses lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide as a common salt, a sulfur-containing compound of a specific structure as a first additive, and a short-chain carboxylic acid ester compound shown in Structural Formula 1 as a solvent, and limits the relationship between the mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of the lithium salt LiFSI, the mass percentage C of the compound shown in Structural Formula 1, and the thickness D of the positive electrode material layer to satisfy 2.8≤C / (10A+B)+D / 100≤14, 0.05≤A≤2, 0.5≤B≤6, 24≤C≤56, and 160≤D≤220. It can be achieved that the lithium ion battery has a higher energy density under a thicker battery pole piece, and takes into account good high temperature storage performance and fast charging cycle performance.

[0087] It can be seen from the test results of Example 1 and Comparative Examples 1 to 13 that in a lithium-ion battery, when any of the parameters A, the mass percentage content of the first additive in the non-aqueous electrolyte, B, the mass percentage content of the lithium salt LiFSI, C, the type and mass percentage content of the compound shown in Structural Formula 1, and D, the thickness of the positive electrode material layer, do not meet the range or the value of the relationship C / (10A+B)+D / 100 is too large or too small, it is impossible to ensure that a dense, thin, and inorganic LiF-rich protective film is formed during the battery formation process, and it is impossible to efficiently conduct lithium ions through the protective film, thereby failing to achieve the effect of reducing the internal resistance of the electrode-electrolyte interface, and failing to achieve good high-temperature storage performance and fast charging cycle performance of the lithium-ion battery.

[0088] When the mass percentage A of the first additive, the mass percentage B of the lithium salt LiFSI, the type and mass percentage C of the compound shown in the structural formula 1, the thickness D of the positive electrode material layer and the value of the relationship C / (10A+B)+D / 100 further satisfy 3≤C / (10A+B)+D / 100≤8, 0.05≤A≤1, 2≤B≤5, 24≤C≤40, 170≤D≤200, a dense and thin protective film rich in inorganic substance LiF can be better formed during the battery formation process, and the battery has a higher energy density while taking into account better high-temperature storage performance and fast-charge cycle performance. It shows that the mass percentage A of the first additive, the mass percentage B of the lithium salt LiFSI, the type and mass percentage C of the compound shown in the structural formula 1, and the thickness D of the positive electrode material layer have a strong correlation in improving the high-temperature storage performance and fast-charge cycle performance of lithium-ion batteries.

[0089] Table 2 shows the test results of Example 1 and Examples 20 to 23; the difference between Examples 20 to 23 and Example 1 lies in the relevant parameters in Table 1.

[0090] Table 2

[0091]

[0092] It can be seen from the measurement results in Table 2 that when the mass percentage A of the first additive, the mass percentage B of the lithium salt LiFSI, the mass percentage C of the compound shown in structural formula 1, the thickness D of the positive electrode material layer and the value of the relationship C / (10A+B)+D / 100 meet the relevant requirements, adding different types of first additives can optimize the high temperature storage performance and fast charging cycle performance of the lithium-ion battery, indicating that the battery system of the present invention is universal for different additives.

[0093] Table 3 shows the test results of Example 1, Examples 24 to 28 and Comparative Examples 14 to 16; the differences between Examples 24 to 28 and Comparative Examples 14 to 16 and Example 1 are the relevant parameters in Table 1.

[0094] Table 3

[0095]

[0096] From the measurement results in Table 3, it can be seen that when the mass percentage A of the first additive, the mass percentage B of lithium bis(fluorosulfonyl)imide, the mass percentage C of the compound shown in Structural Formula 1, the thickness D of the positive electrode material layer and the value of the relationship C / (10A+B)+D / 100 meet the relevant requirements, adding different types of solvents shown in Structural Formula 1 can optimize the high temperature storage performance and fast charge cycle performance of lithium ion batteries, indicating that the battery system of the present invention is universal for different solvents in non-aqueous electrolytes. When the carbon chain of the carboxylic acid ester is too long, it will affect the high temperature cycle performance of the lithium ion battery.

[0097] Table 4 shows the test results of Example 1 and Examples 29 to 34; the difference between Examples 29 to 34 and Example 1 lies in the relevant parameters in Table 1.

[0098] Table 4

[0099]

[0100] It can be seen from the measurement results in Table 4 that when the mass percentage A of the first additive, the mass percentage B of lithium bis(fluorosulfonyl)imide, the mass percentage C of the compound shown in structural formula 1, the thickness D of the positive electrode material layer and the value of the relationship C / (10A+B)+D / 100 meet the relevant requirements, adding different types of auxiliary additives can optimize the high temperature storage performance and fast charging cycle performance of lithium-ion batteries, indicating that the battery system of the present invention is universal for different auxiliary additives.

[0101] Table 5 shows the test results of Example 1 and Examples 35 to 44; the difference between Examples 35 to 44 and Example 1 lies in the relevant parameters in Table 1.

[0102] Table 5

[0103]

[0104]

[0105] It can be seen from the measurement results in Table 5 that when the mass percentage A of the first additive, the mass percentage B of lithium bis(fluorosulfonyl)imide, the mass percentage C of the compound shown in structural formula 1, the thickness D of the positive electrode material layer and the value of the relationship C / (10A+B)+D / 100 meet the relevant requirements, adding different types of positive electrode active materials can optimize the high temperature storage performance and fast charging cycle performance of the lithium-ion battery, indicating that the battery system of the present invention is universal for different positive electrode active materials.

[0106] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0107] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A lithium ion battery, characterized in that: Including positive electrode sheet, negative electrode sheet and non-aqueous electrolyte; The positive electrode sheet comprises a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material comprises a phosphate compound LiFe 1-x-y Mn x M y PO4, wherein 0≤x≤0.8, 0≤y≤0.05, and M includes any one or more of Co, B, Ga, F, W, Zr, Mg, Na, Pb, K, Al, Cr, Ba, Ca, Ni, Sr, Ti, Zn, Si, V, Mo, or Nb; The non-aqueous electrolyte includes a first additive, a lithium salt and a non-aqueous organic solvent; The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; the first additive includes at least one of Compounds 1 to 5: The non-aqueous organic solvent includes a compound shown in structural formula 1: Wherein, R3 is an alkyl group or a fluoroalkyl group having a carbon number ≤ 2, R4 is an alkyl group having a carbon number ≤ 3, and the total number of carbon atoms in R3 and R4 is ≤ 4; The lithium-ion battery meets the following requirements: 2.8≤C / (10A+B)+D / 100≤14, 0.05≤A≤2, 0.5≤B≤6, 24≤C≤56, 160≤D≤220; Wherein: A is the mass percentage of the first additive in the non-aqueous electrolyte, in %; B is the mass percentage of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte, in %; C is the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in %; D is the thickness of the positive electrode material layer, in μm.

2. The lithium ion battery according to claim 1, characterized in that: The lithium-ion battery meets the following requirements: 3≤C / (10A+B)+D / 100≤8.

3. The lithium-ion battery according to claim 1, characterized in that The mass percentage A% of the first additive in the non-aqueous electrolyte is 0.05% to 1%.

4. The lithium-ion battery according to claim 1, characterized in that The mass percentage B% of lithium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is 2% to 5%.

5. The lithium-ion battery according to claim 1, characterized in that: The mass percentage C% of the compound represented by structural formula 1 in the non-aqueous electrolyte is 24% to 40%.

6. The lithium-ion battery according to claim 1, characterized in that The thickness D of the positive electrode material layer is 170 μm to 200 μm.

7. The lithium-ion battery according to claim 1, characterized in that: The compound represented by the structural formula 1 includes one or more of the following compounds:

8. The lithium-ion battery according to claim 1, characterized in that The mass percentage of lithium hexafluorophosphate in the non-aqueous electrolyte is 9% to 14%.

9. The lithium-ion battery according to claim 1, characterized in that: The non-aqueous electrolyte further includes an auxiliary additive, wherein the auxiliary additive includes at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound and a borate compound; and / or, Based on the total mass of the non-aqueous electrolyte being 100%, the content of the auxiliary additive is 0.01% to 10%; and / or, The cyclic sulfate ester compound includes at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate; and / or, The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone and propenyl-1,3-sultone; and / or, The cyclic carbonate compound includes at least one of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate and the compound shown in the following structural formula 3: In the structural formula 3 shown, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 Each is independently selected from a hydrogen atom, a halogen atom, a C1-C5 group; and / or, The phosphate compound includes at least one of the compounds shown in the following structural formula 4: In the structural formula 4, R 31 , R 32 , R 33 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, m is a natural number from 1 to 3; and / or, The borate ester compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

10. The lithium ion battery according to claim 1, characterized in that: The lithium salts also include lithium bis(trifluoromethanesulfonyl imide), LiPO2F2, LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiCl, LiBr, LiI, LiClO4, LiB 10 Cl 10 , LiAlCl4, lithium chloroborane, and lithium tetraphenylborate.

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