Positive electrode active material and electrolyte composition for lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a composition of a positive electrode active material and an electrolyte for a lithium ion battery, which comprises lithium iron phosphate positive electrode active material particles and a non-aqueous electrolyte, the lithium iron phosphate positive electrode active material particles comprise a lithium iron phosphate matrix with an olivine structure, a conductive carbon phase dispersed in the lithium iron phosphate matrix and an inorganic lithium ion conductor shell layer continuously wrapping the outer surface of the lithium iron phosphate matrix; the inorganic lithium ion conductor shell layer comprises one or more of Li3PO4, Li2SiO3, LiAlPO4 and a solid solution of Li3PO4, Li2SiO3 and LiAlPO4; the non-aqueous electrolyte comprises an organic carbonate solvent, a lithium salt and a high-temperature stable additive; the organic carbonate solvent comprises ethylene carbonate, ethyl methyl carbonate and fluoroethylene carbonate; the lithium salt comprises lithium hexafluorophosphate and lithium difluorophosphate and / or lithium difluoro (oxalato) borate; the high-temperature stable additive is an organophosphate compound.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a composition of positive electrode active material and electrolyte for lithium-ion batteries. Background Technology

[0002] Lithium iron phosphate (LiFePO4) has been widely used in power batteries and energy storage due to its excellent structural stability, safety, and cycle life as a cathode material for lithium-ion batteries. However, its intrinsic electronic conductivity and lithium-ion diffusion coefficient are relatively low, and severe polarization occurs at high rates, limiting power performance. At the same time, under high temperature and high SOC storage conditions, side reactions such as electrolyte oxidation decomposition and trace Fe dissolution can still occur at the cathode interface, leading to capacity decay and gas evolution, which affects battery life and safety.

[0003] Existing technologies primarily improve conductivity and rate performance through carbon coating, metal doping, and nanoparticles. Some also improve interfacial stability through TiO2 doping and LiNbVO2 coating. However, these generally employ a "surface carbon shell" structure, where the carbon layer is directly exposed to the electrolyte, which can exacerbate interfacial side reactions at high temperatures. Furthermore, the electrolyte systems mostly still use the conventional EC / EMC+LiPF6 system, lacking a dedicated high-temperature stable formulation matched to the cathode structure. Current solutions struggle to effectively balance high rate performance, high energy density, and high-temperature storage safety.

[0004] Therefore, it is necessary to propose a new technical route that combines an internal conductive network, an outer inorganic lithium-ion conductor shell, and a high-temperature stable electrolyte from the perspective of the synergistic design of the cathode microstructure and electrolyte formulation.

[0005] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0006] This disclosure provides at least one composition of a positive electrode active material and an electrolyte for use in lithium-ion batteries.

[0007] In a first aspect, embodiments of this disclosure provide a composition of positive electrode active material and electrolyte for lithium-ion batteries, comprising: lithium iron phosphate positive electrode active material particles and a non-aqueous electrolyte; the lithium iron phosphate positive electrode active material particles comprising an olivine-structured lithium iron phosphate matrix, a conductive carbon phase dispersed within the lithium iron phosphate matrix, and an inorganic lithium-ion conductor shell continuously wrapped around the outer surface of the lithium iron phosphate matrix; the inorganic lithium-ion conductor shell comprising one or more of Li3PO4, Li2SiO3, LiAlPO4, and their solid solutions; the non-aqueous electrolyte comprising an organic carbonate solvent, a lithium salt, and a high-temperature stabilizing additive; the organic carbonate solvent comprising ethylene carbonate, ethyl methyl carbonate, and fluoroethylene carbonate; the lithium salt comprising lithium hexafluorophosphate, lithium difluorophosphate, and / or lithium difluorooxalate borate; and the high-temperature stabilizing additive being an organic phosphate compound.

[0008] In one optional embodiment, EDS cross-sectional analysis is performed on the lithium iron phosphate cathode active material particles. In the surface region of 10 nm from the outer surface of the particles inward, the atomic fraction of carbon is less than 5 at%, while in the internal region with a radius of 0.5 μm centered on the geometric center of the particles, the atomic fraction of carbon is greater than or equal to 10 at%, and the atomic fraction of carbon in the internal region is at least twice that of the surface region. This characterizes the particles as having a structural gradient of "internal conductive carbon phase - outer inorganic shell". The average thickness of the inorganic lithium-ion conductor shell is 5-20 nm. In the non-aqueous electrolyte, the volume fraction of fluoroethylene carbonate in the total carbonate solvent is 10-25 vol%, the molar fraction of lithium difluorophosphate and / or lithium difluorooxalate borate in the total lithium salt is 5-25 mol%, and the mass fraction of organophosphate high-temperature stabilizing additives in the total electrolyte mass is 2-10 wt%.

[0009] In one optional embodiment, the secondary particle D50 of the lithium iron phosphate cathode active material particles is 2.5-6.0 μm, and the primary particle size is 50-300 nm.

[0010] In one alternative embodiment, the conductive carbon phase comprises amorphous carbon and / or carbon with a low degree of graphitization, wherein the intensity ratio of the D peak to the G peak, I_D / I_G, is 1.0-1.8 in the Raman spectrum.

[0011] In one optional embodiment, the inorganic ionic conductor shell is an amorphous or nanocrystalline shell, which appears as 2 in X-ray diffraction patterns. θ =Broad diffuse peak in the range of 15-35°.

[0012] In one optional embodiment, the total carbon mass fraction in the lithium iron phosphate cathode active material particles is 1.0-3.5 wt%.

[0013] In one optional embodiment, the volume ratio of ethylene carbonate, ethyl methyl carbonate, and fluoroethylene carbonate in the non-aqueous electrolyte is 2–3:4–6:1–2; and the total concentration of the lithium salt is 1.0–1.4 mol·L⁻¹. -1 The molar fraction of lithium difluorophosphate or lithium difluorooxalate borate is 5-25 mol; the high-temperature stabilizing additive includes one or more of trimethyl phosphate, triethyl phosphate, and trimethyl nitrate, and the total amount added is 2-10 wt% of the electrolyte mass.

[0014] Secondly, this disclosure also provides a method for preparing lithium iron phosphate cathode active material particles as described above, comprising: [the method involves] mixing Fe... 2+ A soluble iron salt solution and a phosphorus source solution are reacted in the presence of an oxidant to obtain an iron phosphate precursor. The iron phosphate precursor is mixed and dispersed with a lithium source and an organic carbon source, and then spray-dried to obtain a carbon-containing precursor powder. The carbon-containing precursor powder is sintered at 600-750°C under an inert or weakly reducing atmosphere to form LiFePO4 matrix particles containing an internal conductive carbon phase. The obtained LiFePO4 matrix particles are contacted with an inorganic shell precursor solution containing Li3PO4 and / or Li2SiO3 and / or LiAlPO4 to enrich the precursor on the surface of the LiFePO4 matrix particles. The precursor-enriched material is heat-treated at 350-500°C to transform the inorganic shell precursor on the surface of the LiFePO4 matrix particles into a continuous inorganic ionic conductor shell, thereby obtaining the lithium iron phosphate cathode active material particles.

[0015] Thirdly, embodiments of this disclosure also provide a lithium-ion battery, comprising: a positive electrode, a negative electrode, and an electrolyte; the positive electrode comprises lithium iron phosphate positive active material particles and a positive electrode binder as described above; the negative electrode comprises negative active material particles and a negative electrode binder; and the electrolyte is the non-aqueous electrolyte as described in claim 1.

[0016] In one optional embodiment, the compaction density of the negative electrode sheet is 1.2-1.7 g / cm³. 3 The negative electrode active material particles contain 5%-35% silicon and carbon by mass; the negative electrode binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber, accounting for 0.5%-3% of the negative electrode sheet by mass; and the ratio of the capacity N of the negative electrode sheet to the capacity P of the positive electrode sheet, N / P, is 1.02-1.20.

[0017] The beneficial effects of this invention are that the composition of the positive electrode active material and electrolyte for lithium-ion batteries achieves spatial separation of the electron and lithium-ion transport paths through the synergistic design of "conductive carbon phase inside the particles + outer layer of Li3PO4 / Li2SiO3 / LiAlPO4 inorganic lithium-ion conductor shell + high-temperature stable electrolyte containing FEC and LiPO2F2". This ensures low polarization at high rates and significantly suppresses electrolyte oxidation and structural corrosion during high-temperature storage, enabling the battery to have excellent capacity retention and safety under high-rate and long-term storage conditions at 60°C.

[0018] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, 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 scope of protection of the present invention.

[0021] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0022] In this document, as used herein, expressions such as “at least one of…” modify the entire list of elements when following a list of elements, rather than individual elements in the list. For example, the expression “at least one of a, b, and c” should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.

[0023] The terminology used herein is for the purpose of describing specific exemplary configurations only and is not intended to be limiting. As used herein, the singular articles “a,” “an,” and “the” may also be intended to include plural forms unless otherwise clearly stated herein. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically identified as such. Additional or alternative steps may be employed.

[0024] In this article, the abbreviations and Chinese names of some compounds are as follows: ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), trimethyl phosphate (TMP), and triethyl phosphate (TEP).

[0025] The following describes some embodiments of the present invention in detail. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0026] This disclosure provides a composition of positive electrode active material and electrolyte for lithium-ion batteries, comprising: lithium iron phosphate positive electrode active material particles and a non-aqueous electrolyte; the lithium iron phosphate positive electrode active material particles comprising an olivine-structured lithium iron phosphate matrix, a conductive carbon phase dispersed within the lithium iron phosphate matrix, and an inorganic lithium-ion conductor shell continuously wrapped around the outer surface of the lithium iron phosphate matrix; the inorganic lithium-ion conductor shell comprising one or more of Li3PO4, Li2SiO3, LiAlPO4, and their solid solutions; the non-aqueous electrolyte comprising an organic carbonate solvent, a lithium salt, and a high-temperature stabilizing additive; the organic carbonate solvent comprising ethylene carbonate, ethyl methyl carbonate, and fluoroethylene carbonate; the lithium salt comprising lithium hexafluorophosphate, lithium difluorophosphate, and / or lithium difluorooxalate borate; and the high-temperature stabilizing additive being an organic phosphate compound.

[0027] In some embodiments, specifically, EDS cross-sectional analysis is performed on the lithium iron phosphate cathode active material particles. In the surface region of 10 nm from the outer surface of the particles, the atomic fraction of carbon is less than 5 at%, while in the internal region with a radius of 0.5 μm centered on the geometric center of the particles, the atomic fraction of carbon is greater than or equal to 10 at%, and the atomic fraction of carbon in the internal region is at least twice that of the surface region. This characterizes the particles as having a structural gradient of "internal conductive carbon phase - outer inorganic shell". The average thickness of the inorganic lithium-ion conductor shell is 5-20 nm. In the non-aqueous electrolyte, the volume fraction of fluoroethylene carbonate in the total carbonate solvent is 10-25 vol%, the molar fraction of lithium difluorophosphate and / or lithium difluorooxalate borate in the total lithium salt is 5-25 mol%, and the mass fraction of organophosphate high-temperature stabilizing additives in the total electrolyte mass is 2-10 wt%.

[0028] In some embodiments, specifically, the secondary particle D50 of the lithium iron phosphate cathode active material particles is 2.5-6.0 μm, and the primary particle size is 50-300 nm.

[0029] In some embodiments, specifically, the conductive carbon phase comprises amorphous carbon and / or carbon with a low degree of graphitization, wherein the intensity ratio of the D peak to the G peak, I_D / I_G, is 1.0-1.8 in the Raman spectrum.

[0030] In some embodiments, specifically, the inorganic ionic conductor shell is an amorphous or nanocrystalline shell, which appears as 2 in X-ray diffraction patterns. θ =Broad diffuse peak in the range of 15-35°.

[0031] In some embodiments, specifically, the total carbon mass fraction in the lithium iron phosphate cathode active material particles is 1.0-3.5 wt%.

[0032] In some embodiments, specifically, in the non-aqueous electrolyte, the volume ratio of ethylene carbonate, ethyl methyl carbonate, and fluoroethylene carbonate is 2–3:4–6:1–2; and the total concentration of the lithium salt is 1.0–1.4 mol·L⁻¹. -1 The molar fraction of lithium difluorophosphate or lithium difluorooxalate borate is 5-25 mol; the high-temperature stabilizing additive includes one or more of trimethyl phosphate, triethyl phosphate, and trimethyl nitrate, and the total amount added is 2-10 wt% of the electrolyte mass.

[0033] This disclosure also provides a method for preparing lithium iron phosphate cathode active material particles as described above, comprising: [the method involves] mixing Fe-containing... 2+A soluble iron salt solution and a phosphorus source solution are reacted in the presence of an oxidant to obtain an iron phosphate precursor. The iron phosphate precursor is mixed and dispersed with a lithium source and an organic carbon source, and then spray-dried to obtain a carbon-containing precursor powder. The carbon-containing precursor powder is sintered at 600-750°C under an inert or weakly reducing atmosphere to form LiFePO4 matrix particles containing an internal conductive carbon phase. The obtained LiFePO4 matrix particles are contacted with an inorganic shell precursor solution containing Li3PO4 and / or Li2SiO3 and / or LiAlPO4 to enrich the precursor on the surface of the LiFePO4 matrix particles. The precursor-enriched material is heat-treated at 350-500°C to transform the inorganic shell precursor on the surface of the LiFePO4 matrix particles into a continuous inorganic ionic conductor shell, thereby obtaining the lithium iron phosphate cathode active material particles.

[0034] This disclosure also provides a lithium-ion battery, comprising: a positive electrode, a negative electrode, and an electrolyte; the positive electrode comprises lithium iron phosphate positive active material particles and a positive electrode binder as described above; the negative electrode comprises negative active material particles and a negative electrode binder; and the electrolyte is the non-aqueous electrolyte as described in claim 1.

[0035] In some embodiments, specifically, the compaction density of the negative electrode sheet is 1.2-1.7 g / cm³. 3 The negative electrode active material particles contain 5%-35% silicon and carbon by mass; the negative electrode binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber, accounting for 0.5%-3% of the negative electrode sheet by mass; and the ratio of the capacity N of the negative electrode sheet to the capacity P of the positive electrode sheet, N / P, is 1.02-1.20.

[0036] 1. Preparation of FePO4, the precursor of iron phosphate 1.1 Raw materials and proportions (based on Fe = 1 mol) Ferrous sulfate heptahydrate FeSO4·7H2O: 278g (approximately 1.0 mol Fe) 2+ ); Phosphoric acid H3PO4 (mass fraction 85%): approximately 67 mL (equivalent to approximately 1.0 mol H3PO4); Hydrogen peroxide solution (H2O2) (30% by mass): approximately 115g (equivalent to approximately 1.0 mol H2O2); Deionized water: approximately 2.0 L as solvent.

[0037] 1.2 Operating Procedures Dissolved iron salts Add 1.5L of deionized water to a 5L glass-lined reactor; add 278g of FeSO4·7H2O and stir (300rpm) at room temperature (20-25℃) until completely dissolved to obtain a light green solution; add phosphorus source and oxidant, and slowly add about 67mL of 85% H3PO4 dropwise, controlling the dropwise addition time to 30min, and controlling the temperature of the reaction system at 40-50℃; then add about 115g of 30% H2O2 solution dropwise, controlling the system temperature not to exceed 60℃ during the dropwise addition process to prevent violent decomposition.

[0038] Reaction and aging The reaction was continued at 50 °C for 3 h, and a light yellow FePO4·xH2O precipitate was formed.

[0039] Main reaction: FeSO4 + H3PO4 + H2O2 → FePO4·xH2O↓ + H2SO4 + (1−x)H2O Solid-liquid separation and washing After the reaction is complete, filter while hot, collect the filter cake, and wash it repeatedly with deionized water.

[0040] Drying and pre-calcination The filter cake was dried in an oven at 120℃ for 10 h to obtain FePO4·xH2O powder; the dried powder was then placed in a muffle furnace and heated in air at 5℃·min. -1 The temperature was raised to 500℃ and held for 4 hours to obtain amorphous FePO4 powder. The FePO4 powder weighed to obtain approximately 150.8 g, corresponding to an Fe content of approximately 1.0 mol, which was used as the basis for subsequent batching.

[0041] 2. Preparation of internal carbon-containing LiFePO4 / C matrix 2.1 Raw materials and proportions Based on a Fe content of 1 mol in FePO4: FePO4 powder: 150.8g (1.0mol Fe); Lithium carbonate (Li₂CO₃): 38.1 g (approximately 0.515 mol, providing 1.03 mol Li₂CO₃). + (Li:Fe≈1.03:1). Sucrose (carbon source): 7.5g (approximately 5 wt% of FePO4 mass); Deionized water: Approximately 3.0L.

[0042] 2.2 Operating Procedures Pulping and ball milling Add 3.0 L of deionized water to a 5 L ball mill jar, then add 150.8 g FePO4, 38.1 g Li2CO3 and 7.5 g sucrose in sequence, and add zirconia balls (5-10 mm in diameter). The slurry to grinding ball mass ratio is about 1:3. Wet ball mill at 300 rpm for 6 hours to uniformly disperse FePO4, Li2CO3 and sucrose, and obtain a stable precursor slurry (solid content about 25-30 wt%).

[0043] Spray drying The precursor slurry was fed into a spray drying tower via a peristaltic pump, with the following settings: inlet air temperature: 220℃, outlet air temperature: 110℃, and feed rate: approximately 15 mL / min. -1 Atomization method: dual-fluid nozzle or pressure nozzle, atomization pressure of about 0.3-0.4MPa; the collected precursor dry powder is nearly spherical with a particle size D50 of about 5-8μm.

[0044] Sintering forms LiFePO4 / C The precursor powder was evenly spread in the alumina boat, with the thickness controlled at 1–1.5 cm.

[0045] Push the crucible into the center of the tube furnace and introduce a N2 / H2 (95 / 5) mixture at a flow rate of 200-300 mL / min. -1 Replace 30 minutes in advance.

[0046] At 5℃·min -1 Heating to 700℃ and holding for 8 hours completes the formation of LiFePO4 and the carbonization of the organic carbon source. LiFePO4 formation: FePO4 + Li2CO3 → LiFePO4 + CO2↑ Sucrose pyrolysis and carbonization: C 12 H 22 O 11 →12C + 11H₂O↑ + a small amount of CO₂↑ Grinding and air jet milling are used to control the secondary particle size D50 to approximately 4.0 μm.

[0047] Elemental analysis confirmed that the total carbon content was approximately 2.0 wt%, mainly distributed at the grain boundaries and pores inside the particles, with a lower carbon content on the surface.

[0048] 3. Li3PO4-Li2SiO3 Inorganic Shell Coating 3.1 Preparation of shell precursor solution Based on 200g of LiFePO4 / C powder, the target shell layer has a molar ratio of Li3PO4:Li2SiO3 of 7:3.

[0049] Lithium monophosphate (LiH₂PO₄): approximately 7.3 g (approximately 0.07 mol); molar mass approximately 10⁴ g·mol⁻¹ -1 ; Lithium silicate Li₂SiO₃: approximately 3.0 g (approximately 0.03 mol); Ethanol / deionized water mixed solvent (volume ratio 1:1): 500 mL.

[0050] step: 7.3 g LiH2PO4 and 3.0 g Li2SiO3 were added to 500 mL of ethanol / water mixed solvent; ultrasonically dispersed for 30 min to form a uniform shell precursor mixed solution; the overall Li3PO4:Li2SiO3 molar ratio was approximately 7:3, corresponding to the target shell Li3PO4-Li2SiO3 glassy mixture.

[0051] 3.2 Wet coating The above shell precursor solution was added to a 2L reactor with mechanical stirring; 200g of LiFePO4 / C powder was slowly added under stirring (about 300 rpm) and stirring was continued for 2 hours to allow the shell precursor ions to be fully adsorbed on the particle surface; the solid was collected by vacuum filtration or centrifugation, while retaining a small amount of solvent to keep it moist.

[0052] 3.3 Low-temperature heat treatment to form the shell The wet powder was pre-dried in a vacuum drying oven at 80℃ for 6 hours to remove most of the solvent; the dried powder was then placed in a box furnace and purged with N2 atmosphere; the drying process was carried out at 2℃·min -1 The temperature was raised to 450℃ and held for 3 hours. During the heat treatment, some of the surface LiH2PO4 underwent condensation and dehydration to form Li3PO4, which simultaneously interpenetrated with Li2SiO3 to form a Li3PO4-Li2SiO3 glassy shell. The schematic reaction is as follows: LiH2PO4 dehydration condensation: 3LiH2PO4 → Li3PO4 + 2H3PO4 (In the actual system, LiH2PO4 and Li2SiO3 undergo multi-step condensation and glass transition processes during heating, which can be approximated as the formation of a mixed inorganic phase of Li3PO4-Li2SiO3 on the particle surface.) After naturally cooling to room temperature, the average thickness of the shell, as measured by TEM cross-section, is approximately 10 nm, and the shell continuously coats the surface of the particles. In XPS surface analysis (0-10 nm), the C atom fraction was <5 at%, and the P+Si+Li atom fraction was >30 at%; Using FIB-TEM / EDS line scanning, the C atom fraction in the internal 0.5μm region was ≥10 at%, which was at least twice that of the surface layer, forming a gradient structure of "inner carbon – outer inorganic shell".

[0053] Thus, the positive electrode active material particles were obtained: LFP / C@Li3PO4-Li2SiO3.

[0054] 4. Preparation of high-temperature stable electrolyte 4.1 Solvent Ratio Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) were mixed in a volume ratio of EC:EMC:FEC = 2:5:1, with FEC accounting for approximately 12.5 vol of the total solvent volume.

[0055] 4.2 Lithium Salt and Additive Ratio Lithium hexafluorophosphate (LiPF6) and lithium difluorophosphate (LiPO2F2) The total lithium salt concentration was set at 1.2 mol·L⁻¹. -1 The molar fraction of LiPO2F2 in all lithium salts is 15 mol%, that is, the molar ratio of LiPF6:LiPO2F2 is approximately 85:15.

[0056] Organic phosphate additives: such as trimethyl phosphate (TMP) or triethyl phosphate (TEP), added at 5 wt% of the total electrolyte mass.

[0057] 4.3 Preparation steps Under dry, inert atmosphere (such as Ar) conditions, EC, EMC and FEC are measured and mixed evenly in a volume ratio of 2:5:1.

[0058] Slowly add pre-weighed LiPF6 and LiPO2F2 while stirring, keeping the temperature below 40℃, until completely dissolved.

[0059] Add TMP or TEP to achieve a mass fraction of 5 wt%, and continue stirring for 30 minutes.

[0060] Filter through a 0.2μm microporous membrane and store in a sealed container for later use.

[0061] 1. Method for manufacturing positive electrode plates: Positive electrode active material, conductive carbon black, carbon nanotubes and polyvinylidene fluoride (PVDF) were taken and thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2 to obtain a positive electrode coating material. The positive electrode coating material was then coated onto a 12.0 μm thick aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained. 2. Negative electrode manufacturing method: The negative electrode sheet comprises a negative current collector copper foil and a negative electrode coating material coated on both sides of the copper foil. By mass percentage, the negative electrode coating material comprises 10.0% deposited silicon carbon, 76.0% graphite, 0.75% of the aforementioned conductive agent, 0.75% conductive carbon black, 1.0% thickener sodium carboxymethyl cellulose (CMC), 0.75% binder polyacrylic acid (PAA), and 0.75% binder styrene-butadiene rubber (SBR). These substances are added to deionized water and stirred to form the negative electrode coating material, with a solid content of 42%. The negative electrode coating material is then coated onto both sides of the negative current collector (copper foil), dried, and cold-pressed to form the negative electrode sheet with a compaction density of 1.5 g / cm³. 3 ; 3. Diaphragm: A high-porosity membrane is selected, in which the thickness of the PE base membrane is 9μm, the thickness of the ceramic coating on both sides of the base membrane is 1.0μm, and the thickness of the PVDF coating is 1.0μm.

[0062] 5. Assembly of lithium-ion batteries: After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator according to a set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to a pre-made connecting piece by welding and then installed into a metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, the lithium-ion battery described in Example 1 is obtained. This lithium-ion battery uses a cylindrical casing with an external dimension of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specification.

[0063] Example 2: The difference between this example and Example 1 is that only the shell composition is changed: the molar ratio of LiH2PO4 to Li2SiO3 is adjusted from 7:3 to 5:5, while the other raw material ratios and process conditions remain the same.

[0064] Example 3: The difference between this example and Example 1 is that only the molar ratio of LiH2PO4:Li2SiO3 is adjusted to 9:1, while the rest remains the same.

[0065] Comparative Example 1 Compared with Example 1, this comparative example only uses Li2SiO3 as the shell precursor, that is, the amount of LiH2PO4 is 0, and the total amount of shell added is equivalent to that of Example 1.

[0066] Example 4: The difference between this example and Example 1 is that this example only reduces the total amount of shell precursor added by about 20%, keeps the molar ratio of LiH2PO4:Li2SiO3 at 7:3 and the heat treatment conditions unchanged, and the average thickness of the shell measured by TEM is about 7 nm. Everything else is the same as in Example 1.

[0067] Example 5: The difference between this example and Example 1 is that the total amount of shell precursor added is increased by about 40%, while the molar ratio and heat treatment remain unchanged, and the average shell thickness is increased to about 15 nm. Everything else is the same as in Example 1.

[0068] Comparative Example 2 The difference between this embodiment and Embodiment 1 is that this comparative example significantly reduces the amount of shell precursor used, and the shell thickness measured by TEM is only about 3 nm, with discontinuous shells in some areas. Everything else is the same as in Embodiment 1.

[0069] Example 6: The difference between this example and Example 1 is that the amount of sucrose added is reduced from 5 wt% of FePO4 mass to about 3.8 wt%, while other conditions remain unchanged. The total carbon content is about 1.5 wt%, and everything else is the same as in Example 1.

[0070] Example 7: The difference between this example and Example 1 is that the amount of sucrose added is increased to 7 wt% of FePO4 mass, and the total carbon content is about 2.5 wt%. Everything else is the same as in Example 1.

[0071] Comparative Example 3: The difference between this example and Example 1 is that the amount of sucrose added is reduced to 2 wt% of the FePO4 mass, while other conditions are the same as in Example 1, and the total carbon content is only about 0.8 wt%. Everything else is the same as in Example 1.

[0072] Example 8: The difference between this example and Example 1 is that this example only adjusts the volume ratio of EC:EMC:FEC to about 2:6:1 and the volume fraction of FEC to about 10%. Everything else is the same as in Example 1.

[0073] Example 9: The difference between this example and Example 1 is that the EC:EMC:FEC ratio is adjusted to approximately 2:4.5:1.5, and the FEC volume fraction is approximately 18%. Everything else is the same as in Example 1.

[0074] Comparative Example 4 The difference between this embodiment and Embodiment 1 is that the ratio of EC:EMC:FEC in this comparative example is adjusted to approximately 3:6:0.5, and FEC is only about 5 vol%. Everything else is the same as in Embodiment 1.

[0075] Example 10: The difference between this example and Example 1 is that the molar ratio of LiPF6:LiPO2F2 is adjusted to 90:10, the molar fraction of LiPO2F2 is approximately 10%, and the total lithium salt concentration is 1.2 mol·L⁻¹. -1 Everything else remains the same as in Example 1.

[0076] Example 11: The difference between this example and Example 1 is that the molar ratio of LiPF6:LiPO2F2 is adjusted to 80:20, the molar fraction of LiPO2F2 is about 20%, and the total lithium salt concentration is kept unchanged. Everything else is the same as in Example 1.

[0077] Comparative Example 5 The difference between this comparative example and Example 1 is that this comparative example uses only 1.2 mol·L⁻¹. -1 LiPF6 was used as the lithium salt, without the addition of LiPO2F2, and everything else was the same as in Example 1.

[0078] test: First, discharge the lithium-ion battery to a constant current of 2.5V to ensure it is in a safe state, reducing the risk of short circuits or thermal runaway during disassembly. Carefully disassemble the battery within a glove box (protected by argon or other inert atmosphere) and remove the positive electrode from the cylindrical cell. Use plastic tweezers to peel off the electrode, avoiding damage to the active material layer. Next, cut the removed positive electrode to an appropriate size and soak it in anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible byproducts. After removing the electrode, gently wipe the surface with lint-free paper, then replace with fresh DMC solution, repeating the soaking-wiping process three times to ensure no residual contaminants remain on the electrode surface. Subsequently, rinse the electrode with anhydrous ethanol and wipe it again to further remove solvent and impurities. After cleaning, place the electrode in a glove box and let it stand for 48 hours to ensure it is completely dry, preventing interference from residual solvent in subsequent tests. After drying, the positive electrode active material layer is gently scraped off using a plastic scraper to ensure the collected powder is uncontaminated. The scraped powder is transferred to a centrifuge tube containing anhydrous ethanol and ultrasonically dispersed for 30 minutes in an ultrasonic cleaner to further remove any possible residual electrolyte, binder, and impurities. After ultrasonic treatment, the sample is centrifuged (at 5000 rpm for 2 minutes), the supernatant is discarded, and the powder is redispersed with anhydrous ethanol, ultrasonicated again for 10 minutes, and then centrifuged again. This process is repeated three times to ensure the purity of the powder sample. Finally, the precipitate is collected and transferred to a vacuum drying oven and dried at 80°C for 12 hours to ensure complete removal of residual solvents. The dried powder is placed in a sealed bag or sealed sample box, immediately removed from the glove box, and the sample is quickly subjected to XRD, XPS, Raman, and HRTEM tests.

[0079] Specific XRD measurement method: A copper target X-ray diffractometer (Cu-Kα radiation, 1.54 Å, tube voltage 40 kV, tube current 40 mA) was used. The sample was uniformly dispersed on a silicon substrate, and XRD was measured at 2... θ XRD patterns were acquired at a scan rate of 2° / min within the range of 15°-70°.

[0080] The specific method for determining the intensity (height) of elemental characteristic peaks in XPS spectra: XPS testing was performed using a PHI-5000 Versa Probe instrument, with Al Kα (1486.6 eV) as the X-ray source and a power of 150 W (15 kV × 10 mA). The test included full-spectrum scanning (0–1100 eV, step size 1 eV), background subtraction was performed using Shirley background correction, and C 1s (284.8 eV) was used as an internal standard for data normalization and elemental quantitative analysis.

[0081] Raman spectral analysis: A 532nm laser was used as the excitation source, with the laser power set to 1–5mW to avoid sample ablation. The sample was uniformly dispersed on a silicon substrate. The laser was applied at a depth of 500–1700 cm⁻¹. -1 Raman spectra were collected within the range, with a spectral resolution set to 1 cm⁻¹. -1 The instrument performs 3-5 scans to improve the signal-to-noise ratio. It uses an XYZ automatic displacement platform for precise focusing and performs pre-scanning on a silicon wafer (520.7 cm²). -1 Calibration is performed to ensure data accuracy.

[0082] The determination methods for HRTEM and HRTEM-EDS are as follows: The powder sample is ultrasonically dispersed in ethanol, and the suspension is dropped onto a copper microgrid (3 mm in diameter) and dried. In a 200 kV transmission electron microscope, the high-resolution mode is selected, and the coating layer is determined and its thickness is measured by selected area electron diffraction (SAED) and fast Fourier transform (FFT). At the same time, the EDS spectrometer is turned on, and the acquisition time is set to ≥30 seconds / point and the beam current is ≤1 nA. Elemental surface scan or line scan is performed to determine the distribution of Fe, N, B and C.

[0083] Test method for electrode compaction density: First, the positive electrode sheet, after being washed with dimethyl carbonate and vacuum dried, was cut into six standard-sized square samples (2.0cm × 2.0cm). Next, the active material on both sides of three of these square samples was removed, and they were rinsed with ethanol, dried, weighed, and their average mass M1 was calculated. Simultaneously, the average thickness L1 of the samples was measured using a micrometer. Then, the mass of the remaining three square samples was weighed, and their average mass M2 was calculated. The average thickness L2 of these samples was also measured. The electrode sheet thickness was calculated as L2 - L1 (in cm). The compaction density of the electrode sheet was also calculated. Unit: g / cm 3 .

[0084] Performance testing methods: 1C discharge specific capacity: Assemble a 2032 coin cell by combining the positive electrode, separator, lithium sheet, and electrolyte. Under 25°C conditions, charge at a rate of 0.1C to 3.65V, let stand for 10 minutes, discharge at 0.1C to 2.5V, repeat 2 cycles, charge at a rate of 1C to 3.65V, let stand for 10 minutes, discharge at 1C to 2.5V, and record the 1C discharge specific capacity at this time.

[0085] 5C Capacity Retention R5C: Place the battery in a 45℃ constant temperature chamber for 6 hours and test according to the following steps: (1) First round of constant current and constant voltage charging: charge at a constant current of 0.1C to 3.65V, then switch to constant voltage charging until the current drops to 0.01C.

[0086] (2) Let it stand for 30 minutes after charging is complete.

[0087] (3) Perform constant current discharge, and discharge to 2.5V at a rate of 0.1C.

[0088] (4) Charging and discharging process: constant current charging at a rate of 1C to 3.65V, then constant voltage charging until the current drops to 0.1C.

[0089] (5) Let it stand for another 30 minutes.

[0090] (6) Discharge at a constant current rate of 5C to 2.5V.

[0091] Capacity retention rate: The capacity measured in (6) / the capacity measured in (3) * 100% is the 5C capacity retention rate R5C (%).

[0092] Capacity retention rate R after 28 days of full-charge storage at 60℃ 60 ℃ (%): The battery that has completed step (2) above was placed in a 60℃ constant temperature chamber for 28 days, cooled to 25℃, and then discharged at 0.1C to obtain the storage capacity Qafter, which was compared with the capacity Qbefore measured in (3) (average of 3 parallel samples): R 60 ℃ = Q_after / Q_before × 100%.

[0093] Table 1 Parameter Variation Table

[0094] Table 2 Performance Comparison Table

[0095] As shown in Table 2, comparing Examples 1-3 with Comparative Example 1, it can be seen that the molar ratio of Li3PO4 to Li2SiO3 in the shell is a key balancing factor between interfacial performance and rate performance. Example 1 uses a ratio of approximately 7:3, achieving a good compromise between 5C capacity retention and 60℃ storage retention. Example 2 increases the Li2SiO3 ratio to 5:5, further reducing the interfacial resistance and slightly improving high-rate discharge, but due to the decrease in the phosphate phase ratio, the chemical inertness and anti-dissolution ability of the shell are slightly reduced, and high-temperature storage deteriorates slightly. Example 3 increases the Li3PO4 ratio to 9:1, making the shell closer to the properties of lithium phosphate, enhancing the interfacial oxidation resistance and HF corrosion resistance, and significantly improving high-temperature storage, but the overall ionic conductivity of the shell decreases slightly, leading to increased polarization at high rates. Comparative Example 1 uses only a Li2SiO3 shell, showing significant performance degradation under both high-temperature and high-rate conditions, indicating that without the chemical stability support of Li3PO4, the shell is prone to cracking or structural degradation, making it difficult to protect the LFP matrix for a long time. Therefore, it can be summarized that Li3PO4 is responsible for providing chemical stability and interfacial passivation, while Li2SiO3 mainly provides higher Li content. + Migration capability and a certain degree of mechanical flexibility must coexist within a certain proportion in order to simultaneously achieve high-rate and high-temperature storage performance.

[0096] Comparing Examples 1, 4, and 5 with Comparative Example 2, it can be seen that the shell thickness directly determines the Li + The cross-shell diffusion resistance is related to the integrity and density of the shell. In Example 1, an average thickness of approximately 10 nm achieved a good balance between AC impedance and high-temperature storage. In Example 4, the thickness was reduced to approximately 7 nm, resulting in a further decrease in interfacial charge transfer impedance as shown by EIS and an improvement in 5C discharge capacity. However, after long-term storage at 60 °C, some particles exhibited localized shell discontinuities or pinholes, leading to localized contact between the electrolyte and the active phase, resulting in additional side reactions and a slight decrease in capacity retention. In Example 5, the thickness was increased to approximately 15 nm, and Li... + With increased diffusion distance of the shell, interfacial impedance rises, resulting in a slight sacrifice in rate performance. However, the shell's barrier effect against solvent decomposition products and HF is significantly enhanced, leading to a marked reduction in high-temperature storage degradation. In Comparative Example 2, the shell thickness is only about 3 nm, and TEM reveals large areas of discontinuity, essentially losing its electrolyte barrier function. High-temperature storage performance deteriorates severely, and even with good short-term rate performance, it cannot meet durability requirements. Therefore, the thickness of the inorganic shell must be controlled above a lower limit to ensure continuity, while avoiding excessive thickness to prevent significant ion transport impedance.

[0097] Comparing Examples 1, 6, and 7 with Comparative Example 3, it can be seen that the total content of the internal conductive carbon phase determines the continuity of the electron transport network inside the particle and the balance of the active material content per unit mass. In Example 1, the total carbon content is about 2 wt%, mainly distributed in the grain boundaries and micropores through sucrose carbonization, which can build an electron channel that runs through the particle, while retaining a high LiFePO4 volume fraction. Therefore, the 1C specific capacity and 5C capacity retention are both at a high level. In Example 6, the carbon content is reduced to about 1.5 wt%. The four-probe conductivity is slightly lower, the interfacial charge transfer impedance is slightly higher, and the 5C discharge is slightly reduced. However, due to the slight decrease in the proportion of inactive phase, the volumetric energy density and high-temperature storage performance are slightly improved. In Example 7, the carbon content is increased to about 2.5 wt%. The conductive framework is more continuous, the electron transport is smoother, and the polarization at high rates is further reduced. However, the excessive carbon phase dilutes the active material content, slightly reducing the discharge specific capacity. At the same time, it increases the carbon interfacial area in contact with the electrolyte, which slightly enhances the side reactions during high-temperature storage. Comparative Example 3 contains only about 0.8 wt% carbon, resulting in highly discrete internal and external conductive paths. Microscopically, this manifests as a significant increase in interparticle contact resistance and internal potential gradient, leading to capacity collapse even at high rates. In summary, it can be concluded that there is a clear lower and upper limit window for internal carbon content, with the range of approximately 1.5-2.5 wt% balancing electronic conductivity, active material ratio, and interfacial stability.

[0098] Comparing Examples 1, 8, and 9 with Comparative Example 4, it is evident that the volume fraction of FEC in the solvent system significantly affects the composition and mechanical stability of the inter-electrode interface film, thus influencing high-rate and high-temperature storage behavior. In Example 1, FEC accounts for approximately 12.5% ​​of the total solvent, inducing the formation of CEI and SEI rich in fluorine-containing inorganic components on both the positive and negative electrode surfaces. This enhances the film's density and elasticity, making the interface less prone to cracking under repeated volume changes and high-temperature conditions; simultaneously, the overall solvent viscosity remains at a low level, and Li... + Migration number and overall conductivity have limited impact on rate performance. In Example 8, the FEC was reduced to approximately 10%, slightly decreasing the proportion of fluorine-containing components in the interfacial film. This reduced the film's self-healing ability during high-temperature storage and resulted in slightly lower capacity retention, but the rate performance remained essentially unchanged. In Example 9, the FEC was increased to approximately 18%, forming a thicker, fluorine-rich layer between the positive electrode shell and the electrolyte. This enhanced the ability to suppress solvent oxidation and metal dissolution, significantly improving capacity retention at 60°C. However, slight changes in the viscosity and dissolution structure of the solvent system led to a slight decrease in electrolyte conductivity, resulting in a slight increase in polarization at high rates. In Comparative Example 4, the FEC was only about 5%, lacking sufficient fluorine-containing inorganic phase support at the interface, resulting in PF6... -The acidic species and intermediate products generated during decomposition are difficult to passivate in time, leading to continuous interface deterioration and significant capacity decay during high-temperature storage. This indicates that the FEC content should not be too low or too high; a reasonable balance between interface stability and ion transport can be achieved in the range of approximately 10-20 vol%, especially when it is close to 12-15 vol%.

[0099] Comparing Examples 1, 10, and 11 with Comparative Example 5, it is evident that the molar fraction of LiPO2F2 in the lithium salt system plays a crucial role in constructing a stable fluorinated phosphate-rich interfacial film and inhibiting the high-temperature decomposition of LiPF6. In Example 1, LiPO2F2 accounts for approximately 15% of the total lithium salt molar fraction, continuously providing PO2F2 during charge-discharge and high-temperature resting processes. - Intermediate species, such as LiF and Li, participate in the generation of LiF- and Li-containing compounds on the positive electrode shell surface and the negative electrode surface. x PO y F z The stable inorganic phase effectively passivates the active surface and inhibits the accumulation of corrosive species such as HF and POF3, thus maintaining high rate performance while exhibiting outstanding high-temperature storage capacity retention. Example 10 reduced this proportion to approximately 10%, and the interface repair capability was still significantly better than the single LiPF6 system, but the reconstruction and compensation speed of the film structure during high-temperature resting was somewhat weakened, resulting in a slightly lower storage retention rate. Example 11 increased LiPO2F2 to approximately 20%, resulting in more complete formation of the interface inorganic film at high temperatures and further improving the capacity retention rate. However, with the increase in deep decomposition products of LiPO2F2 and the decrease in electrolyte anion mobility, the overall conductivity decreased slightly, leading to a slight sacrifice in specific capacity and rate performance. Comparative Example 5 contained no LiPO2F2, using only LiPF6, and under high-temperature conditions, PF6... - Continuous decomposition generates HF and phosphorus-containing intermediates that react with the positive electrode shell and the negative electrode SEI, resulting in a fragile and irreversibly damaged interfacial film and a significant decrease in storage capacity at 60°C. Therefore, controlling LiPO2F2 within the range of approximately 5-25 mol%, especially close to 10-20 mol%, can significantly improve high-temperature interfacial stability and storage safety while maintaining electrolyte conductivity.

[0100] This invention designs polyaniline and Fe 2+ A five-membered chelate coordination structure is formed, and the BO-Fe structure is guided by boric acid to achieve synergistic repair of grain boundary defects in lithium iron phosphate cathode materials. This method has mild preparation conditions, strong structural stability, and the formed bonding structure has clear reverse characterization features, significantly improving electrochemical performance under high-temperature conditions.

[0101] In summary, the composition of the positive electrode active material and electrolyte for lithium-ion batteries achieves spatial separation of the electron and lithium-ion transport paths through a synergistic design of "conductive carbon phase inside the particles + outer Li3PO4 / Li2SiO3 / LiAlPO4 inorganic lithium-ion conductor shell + high-temperature stable electrolyte containing FEC and LiPO2F2". This ensures low polarization at high rates and significantly suppresses electrolyte oxidation and structural corrosion during high-temperature storage, resulting in excellent capacity retention and safety of the battery under both high-rate and long-term storage conditions at 60°C.

[0102] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A composition of positive electrode active material and electrolyte for lithium-ion batteries, characterized in that, include: Lithium iron phosphate cathode active material particles and non-aqueous electrolyte; The lithium iron phosphate cathode active material particles include an olivine-structured lithium iron phosphate matrix, a conductive carbon phase dispersed inside the lithium iron phosphate matrix, and an inorganic lithium-ion conductor shell continuously wrapped around the outer surface of the lithium iron phosphate matrix. The inorganic lithium-ion conductor shell includes one or more of Li3PO4, Li2SiO3, LiAlPO4 and their solid solutions; The non-aqueous electrolyte includes an organic carbonate solvent, a lithium salt, and a high-temperature stabilizing additive. The organic carbonate solvents include ethylene carbonate, ethyl methyl carbonate, and fluoroethylene carbonate. The lithium salt includes lithium hexafluorophosphate, lithium difluorophosphate, and / or lithium difluorooxalate borate. The high-temperature stabilizing additive is an organophosphate compound.

2. The composition of positive electrode active material and electrolyte for lithium-ion batteries as described in claim 1, characterized in that, EDS cross-sectional analysis of the lithium iron phosphate cathode active material particles revealed that the atomic fraction of carbon was less than 5 at%, in the surface region of 10 nm from the outer surface of the particles to the inner surface, while the atomic fraction of carbon was greater than or equal to 10 at%, in the internal region with a radius of 0.5 μm centered on the geometric center of the particles. Furthermore, the atomic fraction of carbon in the internal region was at least twice that in the surface region. This characterizes the particles as having a structural gradient of "internal conductive carbon phase - outer inorganic shell". The average thickness of the inorganic lithium-ion conductor shell is 5-20 nm. In the non-aqueous electrolyte, the volume fraction of fluoroethylene carbonate in the total carbonate solvent is 10-25 vol, the molar fraction of lithium difluorophosphate and / or lithium difluorooxalate borate in the total lithium salt is 5-25 mol, and the mass fraction of organophosphate high-temperature stabilizing additives in the total electrolyte is 2-10 wt%.

3. The composition of positive electrode active material and electrolyte for lithium-ion batteries as described in claim 1, characterized in that, The secondary particle D50 of the lithium iron phosphate cathode active material particles is 2.5-6.0 μm, and the primary particle size is 50-300 nm.

4. The composition of positive electrode active material and electrolyte for lithium-ion batteries as described in claim 1, characterized in that, The conductive carbon phase includes amorphous carbon and / or carbon with low graphitization, and the intensity ratio of the D peak to the G peak, I_D / I_G, is 1.0-1.8 in the Raman spectrum.

5. The composition of positive electrode active material and electrolyte for lithium-ion batteries as described in claim 1, characterized in that, The inorganic ionic conductor shell is an amorphous or nanocrystalline shell, which appears as 2 in the X-ray diffraction spectrum. θ =Broad diffuse peak in the range of 15-35°.

6. The composition of positive electrode active material and electrolyte for lithium-ion batteries as described in claim 1, characterized in that, The total carbon mass fraction in the lithium iron phosphate cathode active material particles is 1.0-3.5 wt%.

7. The composition of positive electrode active material and electrolyte for lithium-ion batteries as described in claim 1, characterized in that, In the non-aqueous electrolyte, the volume ratio of ethylene carbonate, ethyl methyl carbonate, and fluoroethylene carbonate is 2-3:4-6:1-2. The total concentration of the lithium salt is 1.0-1.4 mol·L⁻¹. -1 The molar fraction of lithium difluorophosphate or lithium difluorooxalate borate is 5-25 mol%. The high-temperature stabilizing additive includes one or more of trimethyl phosphate, triethyl phosphate, and trimethyl nitrate phosphate, with a total addition amount of 2-10 wt% of the electrolyte mass.

8. A method for preparing lithium iron phosphate cathode active material particles as described in claim 1, characterized in that, include: Fe 2+ A soluble iron salt solution reacts with a phosphorus source solution in the presence of an oxidant to obtain an iron phosphate precursor. The iron phosphate precursor was mixed and dispersed with a lithium source and an organic carbon source, and then spray-dried to obtain a carbon-containing precursor powder. The carbon-containing precursor powder is sintered at 600-750°C under an inert or weakly reducing atmosphere to form LiFePO4 matrix particles containing an internal conductive carbon phase. The obtained LiFePO4 matrix particles are contacted with an inorganic shell precursor solution containing Li3PO4 and / or Li2SiO3 and / or LiAlPO4, so that the precursor is enriched on the surface of the LiFePO4 matrix particles. The precursor enrichment material is heat-treated at 350-500℃ to transform the inorganic shell precursor into a continuous inorganic ionic conductor shell on the surface of the LiFePO4 matrix particles, thereby obtaining the lithium iron phosphate cathode active material particles.

9. A lithium-ion battery, characterized in that, include: Positive electrode, negative electrode, and electrolyte; The positive electrode sheet comprises lithium iron phosphate positive electrode active material particles and a positive electrode binder as described in claim 1; The negative electrode sheet includes negative electrode active material particles and a negative electrode binder; The electrolyte is the non-aqueous electrolyte as described in claim 1.

10. The lithium-ion battery as described in claim 9, characterized in that, The compacted density of the negative electrode sheet is 1.2-1.7 g / cm³. 3 ; The mass percentage of silicon and carbon in the negative electrode active material particles is 5%-35%; The negative electrode binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber, accounting for 0.5%-3% of the mass of the negative electrode sheet; Furthermore, the ratio N / P of the capacity N of the negative electrode to the capacity P of the positive electrode is 1.02-1.20.

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