A lithium-ion battery

Abstract

This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery with good fast-charging cycle performance and high-temperature storage performance. The lithium-ion battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte; the positive electrode includes a positive electrode active material, which includes a phosphate compound; 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, and the solvent includes a compound shown in 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, 160≤D≤220. The lithium-ion battery provided by this invention has high energy density and also achieves excellent high-temperature storage performance and fast-charging cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery with good fast-charging cycle performance, high-temperature storage performance, and high energy density. Background Technology

[0002] In the field of power lithium-ion batteries, phosphate cathodes, represented by lithium iron phosphate, have advantages over nickel-cobalt-manganese ternary cathodes in terms of longer cycle life, better safety, and higher cost-effectiveness. However, phosphate cathodes have poor rate performance and lower specific capacity than ternary cathodes. With the development of the new energy vehicle market, the industry is increasingly focused on improving the rate performance and energy density of lithium-ion batteries to meet consumer demands for fast charging performance and driving range in new energy vehicles. One common method 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 and improve lithium-ion diffusion efficiency. For example, the thickness of existing fast-charging lithium iron phosphate electrode sheets is generally less than 150μm. However, this leads to a decrease in the active material loading per unit area of ​​the electrode sheet, sacrificing the battery's energy density. Therefore, finding a way to improve battery rate performance without degrading energy density is a hot research direction in the field of power lithium-ion batteries. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a lithium-ion battery with good fast-charging cycle performance, high-temperature storage performance, and high energy density.

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

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

[0006] The positive electrode sheet includes a positive electrode material layer containing a positive electrode active material, the positive electrode active material including 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 comprises a first additive, a lithium salt, and a non-aqueous organic solvent;

[0008] The lithium salt comprises lithium hexafluorophosphate and lithium difluorosulfonylimide; the first additive comprises at least one of compounds 1 to 5:

[0009]

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

[0011]

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

[0013] The lithium-ion battery satisfies:

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

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

[0016] B represents the mass percentage of lithium difluorosulfonylimide in the non-aqueous electrolyte, in %;

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

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

[0019] The lithium-ion battery of this invention uses phosphate compounds as the positive electrode active material, a sulfur-containing compound with a specific structure as the first additive in the non-aqueous electrolyte, lithium hexafluorophosphate and lithium bisfluorosulfonylimide as the co-salt, and a short-chain carboxylic acid ester compound as shown in structural formula 1 as the non-aqueous organic solvent. Through extensive research, the inventors discovered that when the relationship between the mass percentage A of the first additive in the non-aqueous electrolyte, the mass percentage B of lithium bisfluorosulfonylimide, 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, and 160≤D≤220, a phosphate-based positive electrode lithium-ion battery with strong high-temperature storage performance and fast-charge 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 low viscosity, which can reduce the resistance to lithium ion movement. Lithium bisfluorosulfonyl imide (LiFSI) has a large anion, which weakens the interaction between the anion and cation, making it easier to ionize and generate free lithium ions in the electrolyte. Combining the compound shown in Structural Formula 1 with LiFSI can significantly improve the ionic conductivity of the electrolyte and enhance the fast-charge cycle performance of the battery. Furthermore, the first additive with a specific structure will form a thermally stable, dense, and thin protective film on the negative electrode surface during battery formation, preventing side reactions between the negative electrode and the carboxylic acid ester solvent, thereby avoiding the degradation of the battery's high-temperature performance by the compound shown in Structural Formula 1. Simultaneously, the combination of the first additive and LiFSI can form a dense, thin protective film rich in inorganic LiF during battery formation, which can efficiently conduct lithium ions through the protective film, reducing the internal resistance at the electrode-electrolyte interface. By limiting the solvent, lithium salt, and additives in the non-aqueous electrolyte as described above, good fast-charging performance can be achieved even with a thicker positive electrode, avoiding a sacrifice in battery energy density. When the mass percentages A (first additive), B (lithium bis(fluorosulfonyl)imide), C (compound shown in structural formula 1), and D (thickness of the positive electrode material layer) in the non-aqueous electrolyte are in a synergistic state, a lithium-ion battery can achieve high energy density with a thicker battery electrode, while also maintaining good high-temperature storage performance and fast-charging cycle performance. Preferably, the lithium-ion battery satisfies: 3 ≤ C / (10A+B) + D / 100 ≤ 8.

[0020] A sulfur-containing compound with a specific structure, used as the first additive, forms a dense and thin protective film with strong thermal stability on the surface of the negative electrode during battery formation. This helps prevent side reactions between the negative electrode and carboxylic acid ester solvents, thereby avoiding the degradation of the battery's high-temperature performance by the carboxylic acid ester solvents. If the mass percentage A% of the first additive is too low, a dense interface film that completely covers the surface of the negative electrode cannot be formed, resulting in insufficient protection. If the mass percentage A% of the first additive is too high, the interface film will be too thick, leading to increased internal resistance and deterioration of 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 any combination of these values; preferably, the mass percentage A% of the first additive in the non-aqueous electrolyte is 0.05% to 1%.

[0021] Replacing some lithium hexafluorophosphate with lithium difluorosulfonylimide (Li₂F₃) offers several advantages. Li₂F₃ has a large anion, which weakens the interaction between cations and anions, making it easier to ionize in the electrolyte to produce free lithium ions. This helps improve the electrolyte's ionic conductivity and enhances the battery's fast-charging cycle performance. However, if the mass percentage (B%) of Li₂F₃ is too low, it will not significantly improve fast-charging performance; conversely, if the mass percentage (B%) is too high, it will cause corrosion of the positive electrode current collector aluminum foil. Specifically, the mass percentage B% of lithium difluorosulfonylimide 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 any combination of these values; preferably, the mass percentage B% of lithium difluorosulfonylimide in the non-aqueous electrolyte is 2% to 5%.

[0022] The non-aqueous electrolyte contains 9% to 14% lithium hexafluorophosphate by mass. 。 Preferably, the mass percentage of lithium hexafluorophosphate is greater than the mass percentage of lithium difluorosulfonylimide. Lithium hexafluorophosphate can form a passivation film on the surface of the positive electrode current collector aluminum foil, inhibiting the corrosion effect of lithium difluorosulfonylimide on the aluminum foil during charging and discharging.

[0023] The compound shown in Structural Formula 1, as a non-aqueous organic solvent, is a short-chain carboxylic acid ester solvent with low viscosity, which can reduce the resistance to lithium-ion movement and help improve the ionic conductivity of the electrolyte. However, short-chain carboxylic acid ester solvents have poor electrochemical stability and are prone to side reactions with the highly lithium-intercalated negative electrode at high temperatures, leading to deterioration in high-temperature storage and high-temperature cycling performance. If the mass percentage C% of the compound shown in Structural Formula 1 is too low, it cannot significantly reduce viscosity; if the mass percentage C% of the compound shown in Structural Formula 1 is too high, the degradation in high-temperature storage is too severe. Therefore, when the mass percentages of additives, solvents, and lithium salts in the non-aqueous electrolyte are in a synergistic state, a phosphate-based positive electrode lithium-ion battery with strong high-temperature storage performance and fast-charge cycling 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 any combination 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 electrode, the main factors limiting fast charging of batteries are the diffusion efficiency of lithium ions in the electrode active material and the resistance to lithium ion transport across the phase boundary at the electrode-electrolyte interface. The industry often shortens the lithium ion conduction path and improves lithium ion diffusion efficiency by reducing the thickness of the positive electrode material layer, thereby improving fast-charging cycle performance. However, this leads to a decrease in the active material loading per unit area of ​​the electrode, sacrificing the battery's energy density; for example, the thickness of the positive electrode material layer in fast-charging applications is generally below 150 μm. In this invention, a first additive with a specific structure is used in conjunction with LiFSI to form a dense, thin, and inorganic LiF-rich protective film during battery formation. This film can efficiently conduct lithium ions across the protective film, reducing the internal resistance at the electrode-electrolyte interface, thus enabling better fast-charging performance even with thicker electrodes. 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 any combination 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 structural formula 1 includes one or more of the following compounds:

[0026]

[0027] Preferably, the compound represented by structural formula 1 includes at least one of compound 1-1, compound 1-2, or compound 5, namely at least one of methyl acetate, ethyl acetate, or ethyl propionate. More preferably, the compound represented by structural formula 1 includes at least ethyl acetate. Compared to other carboxylic acid ester compounds, ethyl acetate not only has a lower viscosity, which reduces the resistance to lithium-ion movement and helps improve the ionic conductivity of the electrolyte, but also helps stabilize the cathode structure. Therefore, while improving the fast-charging performance of lithium-ion batteries, it can also simultaneously improve their high-temperature performance, thereby improving the overall performance of the electrochemical device.

[0028] In the field of power lithium-ion batteries, phosphate cathodes have advantages over nickel-cobalt-manganese ternary cathodes, including longer cycle life, better safety, and higher cost-effectiveness. However, phosphate cathodes have poor rate performance, mainly due to their poor conductivity. Improving the rate performance of lithium iron phosphate cathode batteries could, to some extent, compensate for the gap with ternary cathodes, making them more competitive in the market. This invention, by limiting the solvent, lithium salt, and additives in the non-aqueous electrolyte, achieves strong high-temperature storage performance and fast-charge cycle performance without sacrificing the energy density of phosphate cathode lithium-ion batteries. Specifically, in some embodiments of this invention, the cathode active material includes LiFePO4 and 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 further includes lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiPO2F2, LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiCl, LiBr, LiI, LiClO4, and LiB 10 Cl 10The electrolyte contains at least one of the following: LiAlCl4, lithium chloroborane, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, and lithium tetraphenylborate. Preferably, the total lithium salt content in the non-aqueous electrolyte is 9.5% to 20%. Controlling the total lithium salt content within this range allows the electrolyte conductivity to be controlled within an optimal range.

[0030] In some embodiments of the present invention, the non-aqueous electrolyte further includes auxiliary additives, which include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and borate compounds.

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

[0032] In some preferred embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0033] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by structural formula 3 below:

[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 one of the following: hydrogen atom, halogen atom, or C1-C5 group.

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

[0037]

[0038] In some preferred embodiments, the phosphate ester compound includes at least one of the compounds represented by structural formula 3:

[0039]

[0040] In structural formula 3, R 31 R 32 R 33Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; more preferably, the compound represented by structural formula 3 includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, triargylpropyl phosphate, diargylpropylmethyl phosphate, diargylpropylethyl phosphate, diargylpropylpropyl phosphate, diargylpropyltrifluoromethyl phosphate, diargylpropyl-2,2,2-trifluoroethyl phosphate, diargylpropyl-3,3,3-trifluoropropyl phosphate, diargylpropylhexafluoroisopropyl 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(trimethylsilane)borate and tris(triethylsilane)borate.

[0042] In some embodiments of the present invention, the content of the auxiliary additive is 0.01% to 10% based on the total mass of the non-aqueous electrolyte as 100%. Preferably, the content is 0.1% to 5%; more preferably, the content is 0.1% to 2%. Specifically, the content of any optional substance in the auxiliary additive can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, or any combination of these values.

[0043] Specifically, in some embodiments of the present invention, the positive electrode sheet further includes a positive electrode binder and a positive electrode conductive agent. The positive electrode binder includes one or more of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber. The positive electrode conductive agent includes one or more of the following: conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0044] Specifically, in some embodiments of the present invention, the positive electrode sheet further includes a positive current collector, and the positive electrode material layer is disposed on the surface of the positive current collector. The positive current collector includes a metallic material capable of conducting electrons; preferably, the positive 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, wherein the negative electrode active material is any one or more of silicon-based materials and carbon materials. The silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon materials, and silicon alloy materials; preferably, the silicon material is nano-silicon material; preferably, the silicon oxide material is SiO₂. x Materials, wherein 0 ≤ x < 2; preferably, the silicon-carbon material is: a silicon-based material containing silicon and carbon materials, and / or containing SiO2. y The silicon-based material is a carbon material, wherein 0 ≤ y < 2; preferably, the silicon alloy material is a Mg2Si alloy material and / or an Fe2Si alloy material. The carbon material is selected from one or more of artificial graphite, natural graphite, composite graphite, graphene, and hard carbon; preferably, the carbon material is an artificial graphite material.

[0046] Specifically, in some embodiments of the present invention, the negative electrode material layer further includes a negative electrode binder, a negative electrode conductive agent, and a negative electrode current collector. The material of the negative electrode current collector can be the same as that of the positive electrode current collector, and will not be described again here. The negative electrode binder and the negative electrode conductive agent can be the same as those of the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described again here.

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

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

[0049] The lithium-ion battery of the present invention uses lithium hexafluorophosphate and lithium bisfluorosulfonylimide as a co-salt, a sulfur-containing compound with a specific structure as a first additive, and a short-chain carboxylic acid ester compound as shown in structural formula 1 as a solvent. The relationship between the mass percentage A of the first additive, the mass percentage B of lithium bisfluorosulfonylimide, the mass percentage C of the compound shown in structural formula 1, and the thickness D of the positive electrode material layer in the non-aqueous electrolyte satisfies the following conditions: 2.8≤C / (10A+B)+D / 100≤14, 0.05≤A≤2, 0.5≤B≤6, 24≤C≤56, 160≤D≤220. During battery formation, a dense and thin protective film rich in inorganic LiF can be formed, efficiently conducting lithium ions through the protective film, reducing the internal resistance at the electrode-electrolyte interface, overcoming the poor rate performance of phosphates as positive electrode materials, and achieving both superior high-temperature storage performance and fast-charge cycle performance. Furthermore, the battery has a high energy density. It breaks away from the industry's common practice of reducing the thickness of the positive electrode to improve lithium-ion diffusion efficiency, enabling better fast charging performance even with thicker electrodes. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0051] Example 1

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

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

[0054] Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and ethyl acetate (EA) were 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)) were added. Based on the total weight of the non-aqueous electrolyte (100%), the content of compound 1 was 0.5%, the content of VC was 3%, and the content of FEC was 0.5%; the content of the solvent ethyl acetate (compounds 1-2) was 35%, the content of lithium bis(fluorosulfonyl)imide was 5%, and the total content of lithium salts was 16.8%.

[0055] 2) Preparation of the positive electrode:

[0056] The positive electrode active material LiFePO4, conductive carbon black Super-P, and 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 uniformly coated on both sides of an aluminum foil current collector, and after drying, calendering, and vacuum drying, aluminum leads were welded on using an ultrasonic welding machine to obtain a positive electrode sheet with a thickness of 180 μm.

[0057] 3) Preparation of the negative electrode:

[0058] Artificial graphite, conductive carbon black Super-P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95:1:1.5:2.5 to obtain the negative electrode active material. These materials were then dispersed in deionized water to obtain the negative electrode slurry. The negative electrode slurry was coated onto both sides of a copper foil, dried, rolled, and vacuum dried, and then nickel leads were soldered on using an ultrasonic welder to obtain the negative electrode sheet.

[0059] 4) Cell fabrication:

[0060] A three-layer separator of polypropylene, polyethylene and polypropylene with a thickness of 20μm is placed between the positive plate and the negative plate. Then, the sandwich structure composed of the positive plate, the negative plate and the separator is wound up, and the wound body is flattened and put into an aluminum foil packaging bag. It is then vacuum baked at 85℃ for 48h to obtain the cell to be injected with electrolyte.

[0061] 5) Electrolyte injection and formation of the battery cell:

[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-sealed, and left to stand at 45°C for 48 hours. Then, the first charge is performed 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 rating:

[0064] The cell was left to stand at 45°C for 48 hours, then vacuum sealed again to remove the gas generated by the formation, and then charged at a constant current of 0.2C to 3.65V, and then charged at a constant voltage until the current dropped to 0.05C. After resting for 5 minutes, it was discharged at a constant current of 0.2C to 2.5V to obtain a lithium iron phosphate positive electrode / graphite negative electrode lithium-ion battery.

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

[0066] This embodiment and comparative example are used to illustrate the lithium-ion battery disclosed in this invention. They include most of the operating steps in the above embodiment 1, and the total lithium salt content 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 each embodiment and comparative example were subjected to the following performance tests:

[0068] (1) High-temperature storage performance test

[0069] At 25℃, the battery was charged to 3.65V using a 1C constant current and constant voltage method (cutoff current 0.05C), and then discharged to 2.5V using a 1C constant current and constant voltage method. The discharge capacity of the battery was recorded. After charging the battery to 3.65V again using a 1C constant current and constant voltage method (cutoff current 0.05C), the battery was placed in an oven at 60℃ for 30 days. After the battery was removed and cooled, it was discharged to 2.5V using a 1C constant current method at 25℃. The discharge capacity of the battery was recorded.

[0070] High-temperature storage capacity retention rate (%) = Discharge capacity after 30 days of storage at 60℃ / Discharge capacity before storage × 100%

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

[0072] At 25°C, the battery is charged at a constant current of 4C until it reaches 80% SOC, then charged at a constant current and constant voltage of 1C to 3.65V (cutoff current 0.05C), and then discharged at a constant current of 1C to 2.5V. This process is used to continuously perform cyclic charge-discharge tests, and the discharge capacity of each cycle is recorded.

[0073] Cycle capacity retention (%) = Current cycle discharge capacity / Initial cycle discharge capacity × 100%

[0074] Record the capacity retention rate after 800 cycles.

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

[0076] At 45°C, the battery is charged at a constant current of 4C until it reaches 80% SOC, then charged at a constant current and constant voltage of 1C to 3.65V (cutoff current 0.05C), and then discharged at a constant current of 1C to 2.5V. This process is used to continuously perform cyclic charge-discharge tests, and the discharge capacity of each cycle is recorded.

[0077] Cycle capacity retention (%) = Current cycle discharge capacity / Initial cycle discharge capacity × 100%

[0078] Record the capacity retention rate after 800 cycles.

[0079] Test Results

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

[0081] Table 1

[0082]

[0083]

[0084]

[0085] Note: " / " in the table indicates that the item does not exist.

[0086] The test results of Examples 1-19 and Comparative Examples 1-13 show that the lithium-ion battery of the present invention, using lithium hexafluorophosphate and lithium difluorosulfonylimide as co-salts, a sulfur-containing compound with a specific structure as the first additive, and a short-chain carboxylic acid ester compound as a solvent, and limiting the relationship between the mass percentage A of the first additive, the mass percentage B of 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 in the non-aqueous electrolyte to satisfy 2.8≤C / (10A+B)+D / 100≤14, 0.05≤A≤2, 0.5≤B≤6, 24≤C≤56, 160≤D≤220, can achieve a high energy density for the lithium-ion battery under a relatively thick battery electrode, while also taking into account good high-temperature storage performance and fast-charge cycle performance.

[0087] As can be seen from the test results of Example 1 and Comparative Examples 1 to 13, when any of the following parameters in a lithium-ion battery—A (mass percentage of the first additive in the non-aqueous electrolyte), B (mass percentage of lithium salt LiFSI), C (type and mass percentage of the compound shown in structural formula 1), and D (thickness of the positive electrode material layer)—does not meet the specified range, or when the value of the relationship C / (10A+B)+D / 100 is too large or too small, it is impossible to guarantee the formation of a dense, thin, and inorganic LiF-rich protective film during battery formation. This prevents the efficient conduction of lithium ions through the protective film, thus failing to reduce the internal resistance at the electrode-electrolyte interface and hindering the achievement of good high-temperature storage performance and fast-charge cycle performance of the lithium-ion battery.

[0088] When the mass percentage of the first additive (A), the mass percentage of lithium salt LiFSI (B), the type and mass percentage of the compound shown in structural formula 1 (C), the thickness of the cathode material layer (D), 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, and 170≤D≤200, a dense, thin, and inorganic LiF-rich protective film can be better formed during battery formation. This allows the battery to achieve high energy density while also maintaining superior high-temperature storage performance and fast-charge cycle performance. This demonstrates a strong correlation between the mass percentage of the first additive (A), the mass percentage of lithium salt LiFSI (B), the type and mass percentage of the compound shown in structural formula 1 (C), and the thickness of the cathode material layer (D) in improving the high-temperature storage performance and fast-charge cycle performance of lithium-ion batteries.

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

[0090] Table 2

[0091]

[0092] As shown in Table 2, when the mass percentage content A of the first additive, the mass percentage content B of lithium salt LiFSI, the mass percentage content C of the compound shown in structural formula 1, the thickness D of the cathode 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-charge cycle performance of lithium-ion batteries, indicating that the battery system of the present invention has universality for different additives.

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

[0094] Table 3

[0095]

[0096] As shown in Table 3, when the mass percentages of the first additive (A), lithium bis(fluorosulfonyl)imide (B), the compound shown in Structural Formula 1 (C), the thickness of the cathode material layer (D), 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. This indicates that the battery system of the present invention has universal applicability to different solvents in non-aqueous electrolytes. However, 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 Examples 1 and Examples 29-34; the difference between Examples 29-34 and Example 1 lies in the relevant parameters in Table 1.

[0098] Table 4

[0099]

[0100] As shown in Table 4, when the mass percentages of the first additive (A), lithium bis(fluorosulfonyl)imide (B), the compound shown in structural formula 1 (C), the thickness of the cathode material layer (D), and the value of the relationship C / (10A+B)+D / 100 meet the relevant requirements, the addition of 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 has universality for different auxiliary additives.

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

[0102] Table 5

[0103]

[0104]

[0105] As shown in Table 5, when the mass percentages of the first additive (A), lithium bis(fluorosulfonyl)imide (B), the compound shown in structural formula 1 (C), the thickness of the cathode material layer (D), and the value of the relationship C / (10A+B)+D / 100 meet the relevant requirements, the addition of different types of cathode active materials 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 has universality for different cathode active materials.

[0106] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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 embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A lithium-ion battery, characterized in that, Includes positive electrode, negative electrode, and non-aqueous electrolyte; The positive electrode sheet includes a positive electrode material layer containing a positive electrode active material, the positive electrode active material including 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 comprises a first additive, a lithium salt, and a non-aqueous organic solvent; The lithium salt includes lithium hexafluorophosphate and lithium difluorosulfonylimide; the first additive includes at least one of compound 1 to compound 5: The non-aqueous organic solvent includes the compound shown in structural formula 1: Wherein, R3 is an alkyl or fluoroalkyl group with ≤2 carbon atoms, R4 is an alkyl group with ≤3 carbon atoms, and the total number of carbon atoms in R3 and R4 is ≤4. The lithium-ion battery satisfies: 2.8≤C / (10A+B)+D / 100≤14, 0.05≤A≤2, 0.5≤B≤6, 24≤C≤56, 160≤D≤220; In the formula: A is the mass percentage of the first additive in the non-aqueous electrolyte, in %; B represents the mass percentage of lithium difluorosulfonylimide in the non-aqueous electrolyte, in %; C represents the mass percentage of the compound shown in structural formula 1 in the non-aqueous electrolyte, in %; D represents 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 satisfies: 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 difluorosulfonylimide 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 170μm to 200μm.

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

8. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte contains 9% to 14% lithium hexafluorophosphate by mass.

9. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte further includes auxiliary additives, which include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and borate ester compounds; and / or, Based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additives is 0.01% to 10%; and / or, The cyclic sulfate compounds include at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate; and / or, The sulfonyl lactone compounds include at least one selected from 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone; and / or, The cyclic carbonate compounds include at least one of the following: vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by 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 one of the following: hydrogen atom, halogen atom, C1-C5 group; and / or, The phosphate ester compounds include at least one of the compounds shown in structural formula 4 below: In structural formula 4, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; and / or, The borate esters include at least one of tris(trimethylsilane)borate and tris(triethylsilane)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, and LiB 10 Cl 10 At least one of LiAlCl4, lithium chloroborane, and lithium tetraphenylborate.

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