A lithium-ion battery

Abstract

To overcome the problems of increased battery impedance and high-temperature capacity decay caused by defects in the carbon material on the surface of existing lithium manganese iron phosphate batteries, this invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material comprises lithium manganese iron phosphate coated with a carbon coating layer. Raman spectroscopy shows that the positive electrode active material satisfies: 0.5 ≤ I D / I G ≤1.1, where I D 1300 cm⁻¹ in Raman spectra ‑1 Up to 1400cm ‑1 The peak intensity of the inner D peak, I G 1530 cm⁻¹ in Raman spectrum ‑1 Up to 1630cm ‑1 The peak intensity of the inner G peak, the non-aqueous electrolyte includes a non-aqueous solvent, a lithium salt, and additives, the additives including compounds shown in structural formula 1; the lithium-ion battery satisfies the following conditions: 0.25≤f / (x*c)≤5, and 1≤c≤6, 0.5≤f≤5, 0.5<x≤0.8. The lithium-ion battery provided by this invention has low impedance and excellent high-temperature stability.

Description

Technical Field

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

[0002] Lithium-ion batteries possess advantages such as high specific capacity, low self-discharge, long lifespan, and no memory effect, making them the most widely used electrochemical devices. In recent years, lithium iron phosphate (LiFePO4) materials have been used as cathode materials in pure electric vehicles or hybrid electric vehicles due to their high safety and long cycle performance, and their installed capacity has been increasing year by year. However, the specific capacity and discharge plateau of lithium iron phosphate are relatively low, making it unsuitable for systems with high energy density requirements. Doping lithium iron phosphate with manganese can improve the material's rate performance and low-temperature performance. Simultaneously, thanks to the increased voltage plateau (4.1V vs 3.4V), the theoretical energy density of LMFP materials is 10-20% higher than that of LFP. However, the electronic transition bandgap of manganese is larger than that of iron, which reduces the material's conductivity. To achieve lower impedance in lithium-ion secondary batteries with lithium manganese iron phosphate cathodes, carbon coating is typically applied during the preparation stage to form a conductive network and conductive channels, improving the material's conductivity.

[0003] However, the carbon materials coating the surface of lithium manganese iron phosphate are prone to defects during the preparation process. These defects, as active sites in lithium-ion batteries, will aggravate the side reactions of the electrolyte on the surface of the lithium manganese iron phosphate material. Especially at high temperatures, the side reactions will accelerate the consumption of active lithium, eventually leading to rapid capacity decay of the battery at high temperatures. On the other hand, more side reactions will block the lithium conduction channels of the carbon material or destroy the structure of the carbon material (increase the disorder), that is, generate more defects, causing the battery impedance to increase and the battery performance to deteriorate. Summary of the Invention

[0004] To address the problem of increased battery impedance and high-temperature capacity decay caused by defects in the surface carbon material of existing lithium manganese iron phosphate batteries, this invention provides a lithium-ion battery.

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

[0006] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material comprises lithium manganese iron phosphate (LiMn) coated with a carbon coating layer. x Fe 1-x PO4, where 0.5 < x ≤ 0.8, and by Raman spectroscopy, the positive electrode active material satisfies: 0.5 ≤ I D / I G ≤1.1, where I D 1300 cm⁻¹ in Raman spectra -1 Up to 1400cm-1 The peak intensity of the inner D peak, I G 1530 cm⁻¹ in Raman spectrum -1 Up to 1630cm -1 The peak intensity of the inner G peak;

[0007] The non-aqueous electrolyte comprises a non-aqueous solvent, a lithium salt, and an additive, wherein the additive comprises a compound shown in structural formula 1:

[0008]

[0009] R1 to R6 are each independently selected from hydrogen, halogen, C1 to C5 hydrocarbon group or C1 to C5 halohydrocarbon group; and at least one of R1 to R6 contains halogen.

[0010] The lithium-ion battery meets the following conditions:

[0011] 0.25≤f / (x*c)≤5, and 1≤c≤6, 0.5≤f≤5, 0.5<x≤0.8;

[0012] Where c is the mass percentage of the carbon coating layer in the cathode material layer, in %;

[0013] f represents the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in %;

[0014] x represents the proportion of manganese replacing iron in lithium manganese iron phosphate.

[0015] Optionally, the lithium-ion battery meets the following conditions:

[0016] 0.6≤f / (x*c)≤2.5.

[0017] Optionally, the mass percentage c of the carbon coating layer in the positive electrode material layer is 2% to 5%.

[0018] Optionally, the mass percentage f of the compound represented by structural formula 1 in the non-aqueous electrolyte is 2% to 4%.

[0019] Optionally, the ratio x of manganese replacing iron in the lithium manganese iron phosphate is 0.6 to 0.7.

[0020] Optionally, the compound represented by structural formula 1 is selected from at least one of the following compounds:

[0021]

[0022]

[0023] Optionally, the compaction density of the positive electrode material layer is 2.0 g / cm³. 3~4.4g / cm 3 .

[0024] Optionally, the additive may further include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and nitrile compounds.

[0025] Optionally, the content of the additive is 0.01% to 30% based on the total mass of the non-aqueous electrolyte as 100%.

[0026] Optionally, the cyclic sulfate compound is selected from vinyl sulfate, propylene sulfate, methyl vinyl sulfate, etc. At least one of them;

[0027] The sulfonyl lactone compound is selected from at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone.

[0028] The cyclic carbonate compounds are selected from vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, or other compounds with the following structure.

[0029] At least one of the compounds shown in Formula 2:

[0030]

[0031] In structural formula 2, 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;

[0032] The phosphate ester compound is selected from at least one of tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, or the compound shown in structural formula 3:

[0033]

[0034] In structural formula 3, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33At least one of them is an unsaturated hydrocarbon group;

[0035] The borate ester compound is selected from at least one of tris(trimethylsilane)borate ester and tris(triethylsilane)borate ester;

[0036] The nitrile compound is selected from at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitrile.

[0037] According to the lithium-ion battery provided by the present invention, a specific I-type process is performed on the outer layer of lithium manganese iron phosphate. D / I G A carbon coating layer is formed by coating the positive electrode material with a valuable carbon material to obtain a positive electrode active material. Simultaneously, a compound with structural formula 1 is added as an additive to the non-aqueous electrolyte. D / I G The value can reflect the degree of defects and graphitization of the carbon coating layer, I D The value is the peak intensity of peak D, which is the positive Raman peak with a shift range of 1300 cm⁻¹. -1 Up to 1400cm -1 The peak is caused by the radial breathing mode of the symmetric stretching vibration of the sp2 carbon atom in the aromatic ring (structural defect), I G The value is the peak intensity of peak G, which is the positive Raman peak with a shift range of 1530 cm⁻¹. -1 Up to 1630cm -1 The peak is caused by the stretching vibration between sp2 carbon atoms, which corresponds to the vibration of the E2g optical phonon (in-plane vibration of carbon atoms) at the center of the Brillouin zone. D / I G A higher I value indicates that the coated carbon layer has more defects and a higher degree of disorder. D / I G The value depends on the carbon source used in preparing the positive electrode active material, as well as the preparation method and process conditions, etc. D / I G Excessive concentration can lead to a situation where even the addition of additives shown in Formula 1 cannot completely suppress the negative effects of increased side reactions, thus degrading the battery's high-temperature performance. D / I G While a very small Ig value does not have a significant negative impact on battery performance, it places stringent requirements on the carbon source and processing conditions (for example, using carbon nanotubes to coat the positive electrode active material can increase Ig). D / I G When the Ig value reaches below 0.1, it significantly increases costs, hindering commercial application and widespread adoption. The inventors, through extensive research, discovered that when using Ig values ​​of 0.5-1.1... D / I GWhen carbon materials are used as the carbon coating layer of the positive electrode, and the mass percentage c of the carbon coating layer in the positive electrode material layer, the mass percentage f of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the proportion x of manganese replacing iron in lithium manganese iron phosphate satisfy the conditions 0.25≤f / (x*c)≤5, 1≤c≤6, 0.5≤f≤5, and 0.5<x≤0.8, the resulting lithium-ion battery of lithium manganese iron phosphate system has lower impedance and excellent high-temperature storage performance. It is speculated that this is because a higher proportion x of manganese replacing iron in lithium manganese iron phosphate material can effectively improve the battery charge and discharge platform, thereby increasing the battery energy density, but the conductivity will decrease, and manganese ions will be more easily dissolved, aggravating battery side reactions. The carbon coating layer can improve the impedance increase problem caused by the increased proportion of manganese replacing iron, but excessively high carbon content means that... With the reduction of positive electrode active material, defects on the carbon coating layer, acting as active sites, exacerbate positive electrode side reactions, thereby blocking lithium conduction channels in the carbon coating layer and even damaging its structure (increasing disorder). Ultimately, this leads to a further increase in defects in the carbon coating layer, resulting in rapid battery impedance growth and rapid capacity decay. However, the additive in Structural Formula 1 possesses an ordered carbon structure with benzene rings, which are not easily decomposed into a film at the positive / negative electrode / electrolyte interface during charge / discharge. Instead, it readily binds to active sites on the carbon coating layer surface, thus suppressing surface side reactions caused by defects in the carbon coating layer. This reduces the degradation of the graphitization degree of the carbon material by side reactions at high temperatures, allowing the carbon coating layer to improve conductivity without degrading the battery's high-temperature performance, even with certain initial defects. Therefore, by limiting the positive electrode active material I... D / I G By relating the mass percentage c of the carbon coating layer in the positive electrode material layer, the mass percentage f of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the ratio x of manganese replacing iron in lithium manganese iron phosphate, lithium-ion batteries with manganese iron phosphate system can achieve both low impedance and high temperature stability. Attached Figure Description

[0038] Figure 1 This is the Raman spectrum of the positive electrode provided by the present invention. Detailed Implementation

[0039] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0040] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material comprises lithium manganese iron phosphate (LiMn) coated with a carbon coating layer.x Fe 1-x PO4, where 0.5 < x ≤ 0.8, and by Raman spectroscopy, the positive electrode active material satisfies: 0.5 ≤ I D / I G ≤1.1, where I D 1300 cm⁻¹ in Raman spectra -1 Up to 1400cm -1 The peak intensity of the inner D peak, I G 1530 cm⁻¹ in Raman spectrum -1 Up to 1630cm -1 The peak intensity of the inner G peak;

[0041] The non-aqueous electrolyte comprises a non-aqueous solvent, a lithium salt, and an additive, wherein the additive comprises a compound shown in structural formula 1:

[0042]

[0043] R1 to R6 are each independently selected from hydrogen, halogen, C1 to C5 hydrocarbon group or C1 to C5 halohydrocarbon group; and at least one of R1 to R6 contains halogen.

[0044] The lithium-ion battery meets the following conditions:

[0045] 0.25≤f / (x*c)≤5, and 1≤c≤6, 0.5≤f≤5, 0.5<x≤0.8;

[0046] Where c is the positive electrode material layer

[0047] The mass percentage of the medium carbon coating layer, in %;

[0048] f represents the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in %;

[0049] x represents the proportion of manganese replacing iron in lithium manganese iron phosphate.

[0050] The positive electrode active material I D / I G This mainly reflects the lattice defect degree and crystallinity of the carbon coating layer on the surface of lithium manganese iron phosphate. The manganese content in the positive electrode active material and the I content of the positive electrode active material... D / I GThe compounds represented by Structural Formula 1 in the non-aqueous electrolyte exhibit interactions with each other on the performance of lithium-ion batteries. In lithium manganese iron phosphate materials, a higher proportion (x) of manganese replacing iron effectively improves the battery's charge-discharge platform, thereby increasing energy density, but it also reduces conductivity. Furthermore, manganese ions are more easily dissolved, exacerbating battery side reactions. While a surface carbon coating can mitigate the increased impedance caused by the higher proportion of manganese replacing iron, excessively high carbon content means a reduction in positive electrode active material. Additionally, defects in the carbon coating act as active sites, leading to aggravated positive electrode side reactions, which can block lithium conduction channels in the carbon coating or even damage its structure (increasing disorder). This ultimately leads to a further increase in defects in the carbon coating layer, creating a vicious cycle that results in rapid increase in battery impedance and rapid capacity decay. However, the additive in Structural Formula 1 possesses an ordered carbon structure with benzene rings, which are not easily decomposed into a film at the positive / negative electrode / electrolyte interface during charge / discharge. Instead, it readily binds to active sites on the surface of the carbon coating layer, thereby suppressing surface side reactions caused by defects in the carbon material of the coating layer. This reduces the degradation of the graphitization degree of the carbon material by side reactions at high temperatures, allowing the carbon coating layer to improve conductivity without degrading the high-temperature performance of the battery, even with certain initial defects. The inventors discovered through extensive research that when a specific I... D / I G When a carbon material is used as the carbon coating layer of the positive electrode, and the mass percentage c of the carbon coating layer in the positive electrode material layer, the mass percentage f of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the proportion x of manganese replacing iron in lithium manganese iron phosphate satisfy the conditions 0.25≤f / (x*c)≤5, 1≤c≤6, 0.5≤f≤5, and 0.5<x≤0.8, the resulting lithium-ion battery system of lithium manganese iron phosphate has low impedance and excellent high-temperature storage performance.

[0051] In the description of this invention, the positive electrode active material may include only lithium manganese iron phosphate material, or it may be a mixture of lithium manganese iron phosphate material and other positive electrode active materials. Specifically, based on the total mass of the positive electrode active material, the mass ratio of lithium manganese iron phosphate is 50% or more. More preferably, based on the total mass of the positive electrode active material, the mass ratio of lithium manganese iron phosphate is 60% or more, which can further improve the safety performance and dynamic performance of lithium-ion batteries.

[0052] In a preferred embodiment, the lithium-ion battery satisfies the following conditions:

[0053] 0.6≤f / (x*c)≤2.5.

[0054] When the mass percentage c of the carbon coating layer in the cathode material layer, the mass percentage f of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the proportion x of manganese replacing iron in lithium manganese iron phosphate meet the above conditions, it is beneficial to further improve the energy density, rate performance, and high-temperature storage performance of lithium-ion batteries.

[0055] In a specific embodiment, the mass percentage c of the carbon coating layer in the positive electrode material layer can be 1.0%, 1.2%, 1.4%, 1.7%, 1.9%, 2.0%, 2.1%, 2.2%, 2.4%, 2.7%, 2.8%, 2.9%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.1%, 4.5%, 4.8%, 5.0%, 5.2%, 5.5%, 5.6%, 5.8%, or 6.0%.

[0056] In a preferred embodiment, the mass percentage c of the carbon coating layer in the positive electrode material layer is 2% to 5%.

[0057] Carbon is a commonly used conductive material. By utilizing conductive carbon and lithium manganese iron phosphate to construct a fast conductive network, electrons can rapidly migrate between active materials during charging and discharging, reducing the battery's internal resistance and polarization during charging and discharging. Furthermore, surface carbon coating can effectively inhibit the aggregation and growth of modified material particles, thereby maintaining the nanostructure of the particles and effectively reducing Li... + The diffusion distance within the active particles contributes to the material's superior rate capability. Carbon materials, such as carbon black (SP) or carbon nanotubes, used as conductive agents in the cathode material layer, possess high specific surface area, highly ordered structure, high purity, and excellent conductivity. Furthermore, the conductive agent forms point contacts with the cathode active material, meaning the conductive carbon material has almost no impact on the battery's high-temperature performance. However, the preparation process of the carbon coating layer for the cathode active material generates numerous defects. Specifically, the ID / IG value of the carbon material in the cathode material layer largely depends on the carbon coating layer. When the mass percentage of the carbon coating layer is too high, these defects act as active sites, exacerbating side reactions of the electrolyte at the cathode. Decomposition products can block the lithium conduction channels of the carbon coating layer and even destroy its ordered structure, leading to a significant increase in battery impedance and rapid capacity decay due to the consumption of active lithium. Conversely, when the mass percentage of the carbon coating layer is too low, a conductive network cannot be effectively established, resulting in excessive battery impedance and polarization, increased heat generation during charging and discharging, and similarly, degraded battery performance.

[0058] In specific embodiments, the mass percentage f of the compound represented by structural formula 1 in the non-aqueous electrolyte can be 0.5%, 0.8%, 0.9%, 1.0%, 1.2%, 1.4%, 1.7%, 1.9%, 2.1%, 2.2%, 2.4%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.9%, 4.1%, 4.3%, 4.6%, 4.9%, or 5.0%.

[0059] In a preferred embodiment, the mass percentage f of the compound represented by structural formula 1 in the non-aqueous electrolyte is 2% to 4%.

[0060] The compound shown in Structural Formula 1 is not consumed during the first charge / discharge cycle or battery cycling. Instead, it readily combines with defects in the carbon coating layer of the positive electrode active material. Due to its ordered carbon structure and benzene rings, it reduces defects in the carbon coating material and the occurrence of surface side reactions. This reduces the degradation of the graphitization degree of the carbon material by side reactions at high temperatures, ultimately fully leveraging the increased conductivity of the carbon material while maintaining excellent high-temperature storage performance. If the content of the compound shown in Structural Formula 1 in the non-aqueous electrolyte is too high, it will increase the electrolyte viscosity, affecting the conduction rate of lithium ions in the liquid phase and interfacial film, increasing battery impedance and polarization. Excessive polarization will lead to incomplete charging and discharging of the battery, thus reducing the initial capacity of the battery. If the content of the compound shown in Structural Formula 1 in the non-aqueous electrolyte is too low, it will be difficult to provide good protection for the carbon coating layer, exacerbating the side reactions of the positive electrode and destroying the orderliness of the carbon coating layer. More defects will further aggravate the side reactions, forming a vicious cycle, causing the battery capacity to decay rapidly at high temperatures.

[0061] In the description of this invention, the term "the proportion x of manganese replacing iron in the lithium manganese iron phosphate" refers to the proportion of manganese in the lithium manganese iron phosphate, calculated with the total amount of manganese and iron in the lithium manganese iron phosphate being 1.

[0062] In specific embodiments, the ratio x of manganese replacing iron in the lithium manganese iron phosphate can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, or 0.8.

[0063] In a preferred embodiment, the ratio x of manganese replacing iron in the lithium manganese iron phosphate is 0.6 to 0.7.

[0064] Replacing iron with manganese in lithium iron phosphate (LFP) batteries improves the charge-discharge platform and increases energy density. However, excessive manganese leads to a decrease in iron ion content, resulting in lower conductivity. Furthermore, manganese ions are more readily dissolved than iron ions and catalyze electrolyte decomposition, exacerbating side reactions and degrading battery performance. Conversely, insufficient manganese content results in low energy density, hindering commercial applications.

[0065] In some embodiments, the positive electrode active material I D / I G The value can be obtained through the following testing methods:

[0066] In any region of size 100μm×100μm on the positive electrode, the peak intensity ratio I of the D peak to the G peak measured by Raman spectroscopy is... D / I G And take the average value.

[0067] For details, see Figure 1 The image shown is a Raman spectrum of the positive electrode provided in an embodiment of the present invention.

[0068] In some embodiments, the compound represented by structural formula 1 is selected from at least one of the following compounds:

[0069]

[0070]

[0071] In some embodiments, the compaction density of the positive electrode material layer is 2.0 g / cm³. 3 ~4.4g / cm 3 .

[0072] More preferably, the compaction density of the positive electrode material layer is 2.3 g / cm³. 3 ~4.2g / cm 3 .

[0073] In some implementations, the double-sided areal density of the positive electrode material layer is 20 mg / cm³. 2 ~70mg / cm 2 More preferably, the double-sided areal density of the positive electrode material layer is 30 mg / cm³. 2 ~50mg / cm 2 .

[0074] In some embodiments, the positive electrode material layer further includes a positive electrode binder, which includes at least one of polyvinylidene fluoride, copolymers of polyvinylidene fluoride, polytetrafluoroethylene, copolymers of polyvinylidene fluoride-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of polyvinylidene fluoride-tetrafluoroethylene, copolymers of polyvinylidene fluoride-trifluoroethylene, copolymers of polyvinylidene fluoride-trichloroethylene, copolymers of polyvinylidene fluoride-fluorinated vinylidene, copolymers of polyvinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, etc.; acrylic resins; sodium hydroxymethyl cellulose; nitrile rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers, polyvinyl acetate, syndiotactic-1,2-polybutadiene, and ethylene-vinyl acetate.

[0075] In some embodiments, the positive electrode material layer further includes a positive electrode conductive agent, which includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0076] In some embodiments, the positive current collector is selected from a metallic material that can conduct electrons. Preferably, the positive current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive current collector is selected from aluminum foil.

[0077] In some embodiments, the negative electrode includes a negative electrode material layer containing a negative electrode active material.

[0078] The negative electrode active material includes at least one of carbon-based, silicon-based, tin-based, and lithium-based negative electrodes. Carbon-based negative electrodes may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; silicon-based negative electrodes may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; tin-based negative electrodes may include tin, tin-carbon, tin-oxygen, and tin metal compounds; lithium-based negative electrodes may include metallic lithium or lithium alloys. Specifically, lithium alloys may be at least one of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys.

[0079] In some embodiments, the graphite includes, but is not limited to, one or more of natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. The natural graphite may be flake graphite, flaky graphite, soil graphite, and / or graphite particles obtained by using these graphites as raw materials and subjecting them to spheroidization, densification, or other treatments. The artificial graphite may be obtained by graphitizing organic materials such as coal tar pitch, heavy coal-based crude oil, atmospheric residue, heavy petroleum-based crude oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polystyrene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene ether, furfuryl alcohol resin, phenolic resin, and imide resin at high temperatures. The amorphous carbon can be amorphous carbon particles obtained by heat treatment at a temperature range (400–2200°C) using easily graphitizable carbon precursors such as tar and pitch as raw materials, or amorphous carbon particles obtained by heat treatment using difficult-to-graphitize carbon precursors such as resin as raw materials. The carbon-coated graphite can be obtained by mixing natural and / or artificial graphite with carbon precursors such as tar, pitch, and resin (organic compounds), and heat treatment at a temperature range (400–2300°C) at least once. The obtained natural and / or artificial graphite is used as the core graphite, and amorphous carbon is used to coat it to obtain a carbon-graphite composite. The carbon-graphite composite can be in the form where the entire or part of the surface of the core graphite is coated with amorphous carbon, or it can be in the form of multiple primary particles composited using carbon derived from the aforementioned carbon precursors as a binder. Alternatively, carbon-graphite composites can be obtained by reacting hydrocarbon gases such as benzene, toluene, methane, propane, and volatile aromatic compounds with natural and / or artificial graphite at high temperatures, causing carbon to deposit on the graphite surface. The graphite-coated graphite can be obtained by mixing natural and / or artificial graphite with carbon precursors of easily graphitized organic compounds such as tar, asphalt, and resin, and subjecting the mixture to one or more heat treatments at approximately 2400–3200°C. Using the resulting natural and / or artificial graphite as the core graphite, and coating the entire or part of the surface of the core graphite with graphitized materials, graphite-coated graphite can be obtained. The resin-coated graphite can be obtained by mixing natural and / or artificial graphite with resin, drying at a temperature below 400°C, and using the resulting natural and / or artificial graphite as the core graphite, coating the core graphite with resin, etc. The aforementioned organic compounds, such as tar and asphalt resin, can be listed as carbonizable organic compounds selected from coal-based heavy crude oil, direct-flow heavy crude oil, decomposed petroleum heavy crude oil, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polystyrene, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins.

[0080] In some embodiments, the silicon material is one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon.

[0081] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer.

[0082] The selectable ranges of the negative electrode adhesive and negative electrode conductive agent are the same as those of the positive electrode adhesive and positive electrode conductive agent, and will not be repeated here.

[0083] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer is formed on the surface of the negative electrode current collector.

[0084] The negative electrode current collector is selected from a metallic material that can conduct electrons. Preferably, the negative electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0085] In some embodiments, the compaction density of the negative electrode material layer is 1.0 g / cm³. 3 ~2.0g / cm 3 More preferably, the compaction density of the negative electrode material layer is 1.4 g / cm³. 3 ~1.8g / cm 3 .

[0086] In some embodiments, the double-sided areal density of the negative electrode material layer is 10 mg / cm³. 2 ~35mg / cm 2 More preferably, the areal density of the negative electrode material layer is 15 mg / cm³. 2 ~30mg / cm 2 .

[0087] In some embodiments, the non-aqueous organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents.

[0088] In some embodiments, the ether solvent includes cyclic ethers or chain ethers, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. The cyclic ethers may specifically include, but are not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ethers may specifically include, but are not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. Ether compounds can be used alone or in any combination and ratio of two or more. There are no particular restrictions on the amount of ether compounds added; it is arbitrary as long as it does not significantly impair the performance of the high-pressure lithium-ion battery of this invention. Typically, the volume ratio is 1% or more, preferably 2% or more, and more preferably 3% or more when the non-aqueous solvent volume ratio is 100%. Furthermore, the volume ratio is typically 30% or less, preferably 25% or less, and more preferably 20% or less. When using two or more ether compounds in combination, the total amount of ether compounds should meet the above-mentioned range. When the amount of ether compounds added is within the above-mentioned preferred range, it is easy to ensure the improved ionic conductivity resulting from the increased lithium-ion dissociation degree and reduced viscosity of the chain ethers. Additionally, when the negative electrode active material is a carbon-based material, the phenomenon of co-intercalation between the chain ethers and lithium ions can be suppressed, thus enabling the input / output characteristics and charge / discharge rate characteristics to reach an appropriate range.

[0089] In some embodiments, the nitrile solvent may be, but is not limited to, at least one of acetonitrile, glutaronitrile, and malononitrile.

[0090] In some embodiments, the carbonate solvent includes cyclic carbonates or chain carbonates. Cyclic carbonates may specifically include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); chain carbonates may specifically include, but are not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of cyclic carbonates is not particularly limited and is arbitrary within a range that does not significantly impair the performance of the lithium-ion battery of the present invention. However, when using only one type, its lower limit relative to the total volume of the non-aqueous electrolyte solvent is typically 3% or more, preferably 5% or more. By setting this range, a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, making it easier to achieve good high-current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery. Furthermore, the upper limit is typically 90% or less, preferably 85% or less, and more preferably 80% or less. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, thereby contributing to enhanced stability during high-temperature storage. The content of the chain carbonate is not particularly limited, but relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 15% or more by volume, preferably 20% or more, and more preferably 25% or more. Furthermore, it is typically 90% or less by volume, preferably 85% or less, and more preferably 80% or less. By keeping the chain carbonate content within the above range, it is easier to achieve an appropriate viscosity for the non-aqueous electrolyte, suppressing the decrease in ionic conductivity, and thus contributing to achieving a favorable range of output characteristics for the non-aqueous electrolyte battery. When using two or more chain carbonates in combination, it is sufficient to ensure that the total amount of chain carbonate meets the above range.

[0091] In some embodiments, fluorine-containing chain carbonates (hereinafter referred to as "fluorinated chain carbonates") are also preferably used. There is no particular limitation on the number of fluorine atoms in a fluorinated chain carbonate as long as it is 1 or more, but it is generally 6 or less, preferably 4 or less. When a fluorinated chain carbonate has multiple fluorine atoms, these fluorine atoms can be bonded to the same carbon atom or to different carbon atoms. Examples of fluorinated chain carbonates include dimethyl fluorinated carbonate derivatives, methyl ethyl fluorinated carbonate derivatives, and diethyl fluorinated carbonate derivatives.

[0092] Carboxylic acid ester solvents include cyclic carboxylic acid esters and / or chain carbonates. Examples of cyclic carboxylic acid esters include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonates include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0093] In some embodiments, the sulfone solvent includes cyclic sulfones and chain sulfones. Preferably, in the case of cyclic sulfones, it is typically a compound with 3 to 6 carbon atoms, more preferably 3 to 5 carbon atoms; in the case of chain sulfones, it is typically a compound with 2 to 6 carbon atoms, more preferably 2 to 5 carbon atoms. There are no particular limitations on the amount of sulfone solvent added, and it is arbitrary within a range that does not significantly impair the performance of the lithium-ion battery of the present invention. Relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 0.3% or more by volume, preferably 0.5% or more by volume, more preferably 1% or more by volume. Furthermore, it is typically 40% or less by volume, preferably 35% or less by volume, more preferably 30% or less by volume. When using two or more sulfone solvents in combination, the total amount of sulfone solvent should satisfy the above range. When the amount of sulfone solvent added is within the above range, a non-aqueous electrolyte with excellent high-temperature storage stability is tended to be obtained.

[0094] In a preferred embodiment, the non-aqueous organic solvent is a mixture of cyclic carbonates and chain carbonates.

[0095] In some embodiments, the lithium salt is selected from LiPF6, LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAlCl4, LiCF3SO3, Li2B 10 Cl 10 At least one of LiSO3F, LiTOP (lithium trioxarate phosphate), LiDODFP (lithium difluorodioxarate phosphate), LiOTFP (lithium tetrafluorooxarate phosphate), and lower aliphatic carboxylic acid lithium salts.

[0096] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 8 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, the concentration of the lithium salt in the non-aqueous electrolyte can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L.

[0097] In some embodiments, the additive further includes at least one selected from cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and nitrile compounds;

[0098] Preferably, the content of the additive is 0.01% to 30% based on the total mass of the non-aqueous electrolyte (100%).

[0099] In some embodiments, the cyclic sulfate compound is selected from vinyl sulfate, propylene sulfate, methyl vinyl sulfate, etc. At least one of them;

[0100] The sulfonyl lactone compound is selected from at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone.

[0101] The cyclic carbonate compounds are selected from vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, or other compounds with the following structure.

[0102] At least one of the compounds shown in Formula 2:

[0103]

[0104] In structural formula 2, 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;

[0105] The phosphate ester compound is selected from at least one of tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, or the compound shown in structural formula 3:

[0106]

[0107] In structural formula 3, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group;

[0108] In a preferred embodiment, the phosphate ester compound represented by structural formula 3 may be at least one of the following: triargyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0109] The borate ester compound is selected from at least one of tris(trimethylsilane)borate ester and tris(triethylsilane)borate ester;

[0110] The nitrile compound is selected from at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitrile.

[0111] In other embodiments, the additive may also include other additives that can improve battery performance: for example, additives that improve battery safety performance, such as flame retardant additives like fluorophosphates and cyclophosphonitriles, or overcharge prevention additives like tert-amylbenzene and tert-butylbenzene.

[0112] It should be noted that, unless otherwise specified, the content of any one of the optional substances in the additive in the non-aqueous electrolyte is generally less than 10%, preferably 0.1-5%, and more preferably 0.1% to 2%.

[0113] In some embodiments, the additive includes fluoroethylene carbonate, and the amount of fluoroethylene carbonate added is 0.01% to 30% based on 100% of the total mass of the non-aqueous electrolyte.

[0114] In some embodiments, the battery further includes a separator located between the positive electrode and the negative electrode.

[0115] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0116] The present invention will be further illustrated by the following examples.

[0117] Table 1

[0118]

[0119]

[0120]

[0121] Example 1

[0122] This embodiment is used to illustrate the lithium-ion battery and its preparation method disclosed in this invention.

[0123] 1) Preparation of positive electrode sheet

[0124] Step 1: Add PVDF as a binder to NMP solvent and stir thoroughly to obtain PVDF adhesive.

[0125] Step 2: Add the conductive agent (super P+CNT) and positive electrode active material to the PVDF adhesive, and stir thoroughly to obtain the positive electrode slurry. The mass ratio of positive electrode active material, conductive carbon black Super-P and positive electrode binder is 96:2:2. The selection of positive electrode active material is shown in Table 1.

[0126] Step 3: The prepared positive electrode slurry is evenly coated on aluminum foil, and then dried, rolled, die-cut or slit to obtain the positive electrode sheet.

[0127] 2) Preparation of negative electrode sheet

[0128] Step 1: Weigh out each material according to the negative electrode sheet ratio of graphite (Shanghai Shanshan, FSN-1): conductive carbon (super P): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 96.3:1.0:1.2:1.5 (mass ratio).

[0129] Step 2: First, add CMC to pure water at a solid content of 1.5% and stir thoroughly (e.g., stirring time 120 min) to prepare a transparent CMC solution.

[0130] Step 3: Add conductive carbon (super P) to the CMC adhesive solution and stir thoroughly (e.g., stirring time 90 min) to prepare the conductive adhesive.

[0131] Step 4: Continue adding graphite and stir thoroughly to obtain the desired negative electrode slurry.

[0132] Step 5: The prepared negative electrode slurry is evenly coated on copper foil, and then dried, rolled, die-cut or slit to obtain the negative electrode sheet.

[0133] 3) Preparation of non-aqueous electrolyte

[0134] Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC = 1:1:1. 2% VC (ethylene carbonate) was added, along with additives in the mass percentages shown in Table 1. Then, lithium hexafluorophosphate (LiPF6) was added until the molar concentration reached 1 mol / L.

[0135] 4) Lithium-ion cell manufacturing

[0136] The prepared positive electrode sheet and the prepared negative electrode sheet are assembled into a stacked soft-pack battery cell.

[0137] 5) Electrolyte injection and formation of battery cells

[0138] In a glove box with the dew point controlled below -40°C, the electrolyte prepared above was injected into the cell, vacuum sealed, and left to stand for 72 hours. Then, the first charge was performed according to the following steps: 0.05C constant current charging for 180 min, 0.1C constant current charging for 120 min, 0.2C constant current charging for 120 min, followed by a second vacuum sealing, and then a full charge at 0.2C (100% SOC). After resting at room temperature for 72 hours, a full discharge at 0.2C (0% SOC) was performed.

[0139] Examples 2-26

[0140] Examples 2-26 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences:

[0141] The positive electrode active material and non-aqueous electrolyte additives shown in Examples 2-26 of Table 1 were used.

[0142] Comparative Examples 1-19

[0143] Comparative Examples 1-19 are used to illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1, with the following differences:

[0144] The positive electrode active material and non-aqueous electrolyte additives shown in Comparative Examples 1 to 19 in Table 2 were used.

[0145] Performance testing

[0146] The lithium-ion batteries prepared above were subjected to the following performance tests:

[0147] The positive electrode active material I D / I GThe testing method for the value is as follows: An area of ​​100μm × 100μm is selected on the positive electrode sheet. The positive electrode sheet within this area is scanned using a laser confocal Raman spectroscopy microscope. The D and G peaks of all positive electrode material particles within this area are obtained. The data is processed using LabSpec software to obtain the peak intensities of the D and G peaks for each positive electrode active material particle, which are respectively I0 and I0. D and I G The Raman spectrometer's laser wavelength can range from 532 nm to 785 nm. Ig of all positive electrode active material particles measured within this range was... D and I G The average of the ratios is used to obtain I. D / I G value.

[0148] The carbon coating content in the cathode material layer:

[0149] Remove the positive electrode sheet, then scrape about 5g of the positive electrode active material with a spoon and test the carbon content (%) using a carbon-sulfur analyzer (Wuxi Chuangxiang Analytical Instrument Co., Ltd.).

[0150] Internal resistance test at 0℃:

[0151] At 25℃, the lithium-ion battery was left to stand for 4 hours, then charged at a constant current rate of 0.5C to the upper cutoff voltage (e.g., 4.2V), and then charged at a constant voltage until the current was less than or equal to 0.05C. At this point, the battery's state of charge (SOC) was 100%. Afterward, it was discharged at a constant current rate of 0.5C to the lower limit voltage (e.g., 2.5V), and the discharge capacity at room temperature was recorded as C0. The battery was then charged to 100% SOC using the same charging method, and then discharged at a constant current rate of 0.5C to terminate the discharge when the capacity reached C0 / 2 cutoff. At this point, the battery's SOC was 50%. The battery with 50% SOC was left to stand at 0℃ for 6 hours, and the following tests were performed at 0℃:

[0152] Charge at 0.1C constant current for 10 seconds and then let stand for 40 seconds; discharge at 0.1C constant current for 10 seconds and then let stand for 40 seconds, and record the termination voltage V1.

[0153] Charge at 0.2C constant current for 10s and then let stand for 40s; discharge at 0.2C constant current for 10s and then let stand for 40s, and record the termination voltage V2.

[0154] Charge at 0.5C constant current for 10 seconds and then let stand for 40 seconds; discharge at 0.5C constant current for 10 seconds and then let stand for 40 seconds, and record the termination voltage V3.

[0155] Plot a straight line with the current on the x-axis and the discharge termination voltage on the y-axis. The slope of the line is 0℃DCIR.

[0156] High-temperature storage performance test:

[0157] Before the high-temperature storage test, the lithium-ion batteries prepared in the examples and comparative examples were charged and discharged at a 1C rate for three cycles within the charge / discharge cutoff voltage range. The discharge capacity of the last cycle was recorded as the battery capacity C1 before the test. Finally, the batteries were charged to full capacity at a 1C rate. The test batteries were placed in an oven at 60°C for 30 days. After the high-temperature storage was completed, the batteries were discharged at a 1C rate to the cutoff voltage range, and the discharged capacity was recorded as the battery capacity C2 after the test. The high-temperature storage capacity retention rate was calculated using the following formula:

[0158] Capacity retention rate (%) after 30 days of storage at 60℃ = C2 / C1*100%.

[0159] (1) The test results obtained from Examples 1-15 and Comparative Examples 1-6 and 10-15 are filled in Table 2.

[0160] Table 2

[0161]

[0162]

[0163] The test results from Examples 1-15 and Comparative Examples 1-6 and 10-19 show that using I0.5-1.1 D / I G When a carbon material is used as the carbon coating layer for the positive electrode, and the mass percentage c of the carbon coating layer in the positive electrode material layer, the mass percentage f of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the proportion x of manganese replacing iron in lithium manganese iron phosphate satisfy the conditions 0.25≤f / (x*c)≤5, 1≤c≤6, 0.5≤f≤5, and 0.5<x≤0.8, the resulting lithium-ion battery exhibits low impedance and high high-temperature storage capacity retention. It is speculated that this is because manganese in the lithium manganese iron phosphate material replaces iron to a certain extent, leading to an increase in impedance. Therefore, it is necessary to adjust the carbon coating layer content to meet the conductivity requirements of the positive electrode active material. D / I GUnder certain conditions, the presence of manganese exacerbates the degradation of battery stability at high temperatures. However, the additive in Structural Formula 1 has an ordered carbon structure with benzene rings, which are not easily decomposed during charging and discharging. Instead, it readily binds to the active sites on the surface of the carbon coating layer, thereby suppressing the occurrence of surface side reactions caused by defects in the carbon coating layer. This reduces the degradation of the graphitization degree of the carbon material by side reactions at high temperatures, allowing the carbon coating layer to improve conductivity without degrading the battery's high-temperature performance, even with certain initial defects. Ultimately, by balancing the mass percentage c of the carbon coating layer in the cathode material layer, the mass percentage f of the compound shown in Structural Formula 1 in the non-aqueous electrolyte, and the proportion x of manganese replacing iron in lithium manganese iron phosphate, the lithium-ion battery achieves a balance between low impedance, excellent energy density, and high-temperature stability.

[0164] The test results from Examples 1-3 and Examples 4-15 show that when the mass percentage c of the carbon coating layer in the positive electrode material layer, the mass percentage f of the compound shown in Structural Formula 1 in the non-aqueous electrolyte, and the proportion x of manganese replacing iron in lithium manganese iron phosphate further satisfy the conditions 0.6≤f / (x*c)≤2.5, 2≤c≤5, 2≤f≤4, and 0.6<x≤0.7, the impedance of the obtained lithium-ion battery is further reduced, and the capacity retention rate under high temperature storage is also maintained at a high level.

[0165] The test results of Comparative Examples 1, 2, 5, and 10–15 show that when the values ​​of f, x, and c do not meet the constraint of 0.25 ≤ f / (x*c) ≤ 5, it will lead to the deterioration of battery impedance and high-temperature stability. This indicates that there is an interaction between the mass percentage c of the carbon coating layer in the cathode material layer, the mass percentage f of the compound shown in Structural Formula 1 in the non-aqueous electrolyte, and the proportion x of manganese replacing iron in lithium manganese iron phosphate. Only when the three reach a good balance can they significantly improve the impedance and high-temperature stability of lithium-ion batteries. The test results from Comparative Examples 3-4 and 6 show that when any of the parameters f, x, and c exceeds the specified range, even if the requirement of the relationship 0.25≤f / (x*c)≤5 is met, the capacity retention rate of the lithium-ion battery under high-temperature storage conditions is poor, and the impedance increases. This indicates that when the mass percentage c of the carbon coating layer in the positive electrode material layer, the mass percentage f of the compound shown in Structural Formula 1 in the non-aqueous electrolyte, and the proportion x of manganese replacing iron in lithium manganese iron phosphate are too high or too low, they will all affect the protective effect of the compound shown in Structural Formula 1 on the carbon coating layer against defects, leading to surface side reactions, blocking lithium conduction channels, and increasing impedance.

[0166] (2) The test results obtained from Examples 3-6 and Comparative Examples 16-19 are filled in Table 3.

[0167] Table 3

[0168]

[0169]

[0170] The test results from Examples 3-6 and Comparative Examples 16-19 show that in the battery system provided by the present invention, when the carbon material of the selected carbon coating layer is I D / I G An excessively high I value can lead to a deterioration in the performance of lithium-ion batteries, indicating that when the I value of the positive electrode active material is too high... D / I G When the value is too high, the defects and disorder of the carbon coating layer are too great, so that adjusting the carbon coating layer content, manganese content, and the content of the compound shown in structural formula 1 cannot fully solve the electrolyte decomposition problem caused by its defects. Furthermore, when the I of the positive electrode active material is too high... D / I G When the value is too low, the compound shown in Formula 1 has limited effect on improving the protection of the carbon coating layer. Therefore, adjusting the relationship 0.25≤f / (x*c)≤5 will not significantly improve the battery performance. On the contrary, using too low I D / I G Using high-value carbon materials as the carbon coating layer for the positive electrode significantly increases costs, which is not conducive to commercial use and widespread adoption.

[0171] (3) The test results obtained from Examples 16-18 and Comparative Examples 7-9 are filled in Table 4.

[0172] Table 4

[0173] Example 16 410.7 89.7 Example 17 413.3 84.5 Example 18 380.5 90.4 Comparative Example 7 457.4 86.3 Comparative Example 8 340.9 82.3 Comparative Example 9 382.7 82.1

[0174] The test results of Examples 16-18 and Comparative Examples 7-9 show that in the battery system provided by the present invention, when different positive electrode active materials containing lithium manganese iron phosphate are used, and the mass percentage c of the carbon coating layer in the positive electrode material layer, the mass percentage f of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the ratio x of manganese element replacing iron element in lithium manganese iron phosphate satisfy the conditions 0.25≤f / (x*c)≤5, 1≤c≤6, 0.5≤f≤5, and 0.5<x≤0.8, compared with Comparative Examples 7-9 which do not meet these conditions, the lithium-ion batteries obtained in Examples 16-18 have lower impedance and higher high-temperature storage capacity retention, indicating that the battery system provided by the present invention has universality for different positive electrode active materials containing lithium manganese iron phosphate.

[0175] (4) The test results obtained in Examples 1, 19 to 21 are filled in Table 5.

[0176] Table 5

[0177] Example 1 425.2 89.4 Example 19 415.5 92.4 Example 20 426.4 91.5 Example 21 430.1 91.4

[0178] As can be seen from the test results of Examples 1 and 19-21, in the battery system provided by the present invention, the addition of fluoroethylene carbonate (FEC), ethylene sulfate (DTD), or 1,3-propane sulpholactone (PS) can further reduce the battery impedance and improve the high-temperature storage stability of the battery. This indicates that the performance enhancement mechanism of other additives is different from that of the compound shown in Structural Formula 1. Fluoroethylene carbonate (FEC), ethylene sulfate (DTD), or 1,3-propane sulpholactone (PS) are mainly used for surface film formation of the positive and negative electrode active material layers, while the compound shown in Structural Formula 1 is used to combine with the carbon coating layer to avoid electrolyte decomposition caused by defects in the carbon coating layer, thereby improving the performance of lithium-ion batteries from different dimensions.

[0179] (4) The test results obtained in Examples 1, 22-26 are filled in Table 5.

[0180] Table 5

[0181] Example 1 425.2 89.4 Example 22 429.7 88.8 Example 23 431.5 88.5 Example 24 434.8 87.8 Example 25 439.6 87.5 Example 26 433.5 87.0

[0182] The test results from Examples 1 and 22-26 show that, in the battery system provided by this invention, when different compounds of structural formula 1 are used, and the mass percentage c of the carbon coating layer in the positive electrode material layer, the mass percentage f of the compound of structural formula 1 in the non-aqueous electrolyte, and the ratio x of manganese element replacing iron element in lithium manganese iron phosphate satisfy the conditions 0.25≤f / (x*c)≤5, 1≤c≤6, 0.5≤f≤5, and 0.5<x≤0.8, the resulting lithium-ion batteries all have good electrochemical performance, indicating that the battery system provided by this invention has universality for different compounds of structural formula 1.

[0183] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The electrolyte includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material includes lithium manganese iron phosphate (LiMn) coated with a carbon coating layer. x Fe 1- x PO4, where 0.5 < x ≤ 0.8, the positive electrode active material satisfies the following condition through Raman spectroscopy: 0.5 ≤ I D / I G ≤1.1, where I D 1300 cm⁻¹ in Raman spectra -1 Up to 1400cm -1 The peak intensity of the inner D peak, I G 1530 cm⁻¹ in Raman spectrum -1 Up to 1630cm -1 The peak intensity of the inner G peak; The non-aqueous electrolyte comprises a non-aqueous solvent, a lithium salt, and an additive, wherein the additive comprises a compound shown in structural formula 1: Structural Formula 1 R1 to R6 are each independently selected from hydrogen, halogen, C1 to C5 hydrocarbon group or C1 to C5 halohydrocarbon group; and at least one of R1 to R6 contains halogen. The lithium-ion battery meets the following conditions: 0.25≤f / (x*c)≤5, and 1≤c≤6, 0.5≤f≤5, 0.6≤x≤0.7; Where c represents the mass percentage of the carbon coating layer in the cathode material layer, expressed in % . f represents the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in percentages (%). x represents the proportion of manganese replacing iron in lithium manganese iron phosphate.

2. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery meets the following conditions: 0.6≤f / (x*c)≤2.

5.

3. The lithium-ion battery according to claim 1, characterized in that, The mass percentage c of the carbon coating layer in the cathode material layer is 2%~5%.

4. The lithium-ion battery according to claim 1, characterized in that, The mass percentage f of the compound represented by structural formula 1 in the non-aqueous electrolyte is 2% to 4%.

5. The lithium-ion battery according to claim 1, characterized in that, The compound represented by structural formula 1 is selected from at least one of the following compounds: 。 6. The lithium-ion battery according to claim 1, characterized in that, The compaction density of the positive electrode material layer is 2.0 g / cm³. 3 ~4.4 g / cm 3 .

7. The lithium-ion battery according to claim 1, characterized in that, The additives also include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and nitrile compounds.

8. The lithium-ion battery according to claim 7, characterized in that, Based on the total mass of the non-aqueous electrolyte as 100%, the content of the additive is 0.01% to 30%.

9. The lithium-ion battery according to claim 7, characterized in that, The cyclic sulfate compounds are selected from vinyl sulfate, propylene sulfate, methyl vinyl sulfate, etc. , At least one of them; The sulfonyl lactone compound is selected from at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone. The cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, or the compound shown in structural formula 2. Structural Formula 2 In structural formula 2, 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; The phosphate ester compound is selected from at least one of tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, or the compound shown in structural formula 3: Structural Formula 3 In structural formula 3, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group; The borate ester compound is selected from at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate; The nitrile compound is selected from at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitrile.

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