A battery and an electrical device

Abstract

This invention provides a battery and an electrical device, comprising a positive electrode sheet, which includes a positive current collector and a positive active material layer disposed on the positive current collector, the positive active material layer including a positive active material, the positive active material including iron; and an electrolyte comprising a first additive, a second additive, and a third additive, the first additive including a phosphate ester compound, the second additive including a fluorinated lithium salt compound, and the third additive including an amide compound; the first additive irreversibly complexes dissolved Fe. 2+ / Fe 3+ The first additive removes ions and eliminates HF, H2O, and free protons generated by its catalysis, effectively reducing the acidity of the electrolyte; the second additive preferentially reduces on the negative electrode surface to form a high ion conductivity SEI film, avoiding the formation of an electronic insulating deposition layer at low temperatures and ensuring charge transfer kinetics; the third additive preferentially adsorbs on the iron exposure sites on the positive electrode surface, physically covering and passivating the active center, inhibiting iron from participating in the disproportionation reaction.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to a battery and an electrical device. Background Technology

[0002] With the rapid development of lithium-ion batteries towards higher energy density, wider temperature range, and longer lifespan, the introduction of transition metal elements (such as iron) into cathode materials to regulate structural stability and electrochemical performance has become an important strategy. However, the presence of iron in the cathode system has significant environmentally dependent hazards, and can trigger multiple interface and bulk degradation mechanisms under different operating conditions, severely restricting the overall performance of the battery.

[0003] Specifically, under low temperature conditions (such as 0°C), the dissolved Fe 2+ / Fe 3+ Lithium ions readily react with electrolyte decomposition products (such as LiF, organic carbonate reduction products, etc.), generating electronically insulating deposits that accumulate at the electrode / electrolyte interface. This significantly increases interfacial impedance, hindering the co-transport of lithium ions and electrons, leading to intensified battery polarization and a sharp drop in capacity. During high-temperature cycling, iron ions pass through Fe... 2+ / Fe 3+ Reversible valence change behavior catalyzes the oxidative decomposition of electrolytes (especially carbonate solvents), accelerating the generation of gas and acidic byproducts (such as HF, H2O and free protons). The latter further erodes the cathode lattice structure, inducing the dissolution of transition metals and the collapse of layered structures. During long-term storage, iron ions can participate in disproportionation reactions or react with residual moisture / acidic substances, consuming active lithium and forming irreversible byproducts, causing open-circuit voltage (OCV) decay and increased self-discharge.

[0004] The aforementioned multi-scenario and multi-mechanism iron-induced failure pathways demonstrate that single-functional additives cannot provide comprehensive protection. Therefore, overcoming these technical problems and shortcomings is a key issue that needs to be addressed. Summary of the Invention

[0005] In view of the problem that the cycle performance of lithium-ion batteries deteriorates significantly under high and low temperature environments in the prior art, the present invention provides a battery and an electrical device.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: This invention provides a battery, comprising: A positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on the positive current collector, the positive active material comprising a positive active material, the positive active material being doped with and / or coated with iron. An electrolyte comprising a first additive, a second additive, and a third additive, wherein the first additive comprises a phosphate ester compound, the second additive comprises a fluorinated lithium salt compound, and the third additive comprises an amide compound.

[0007] Optionally, the mass content X of iron in the positive electrode active material layer is in the range of 1ppm-2000ppm.

[0008] Optionally, taking the total mass of the electrolyte as 100%, the percentage content of the first additive in the electrolyte is denoted as A, in %, and the value of A ranges from 0.1 to 1.5; the percentage content of the second additive in the electrolyte is denoted as B, in %, and the value of B ranges from 0.1 to 1; the percentage content of the third additive in the electrolyte is denoted as C, in %, and the value of C ranges from 1 to 8.

[0009] Optionally, the values ​​of A, B, C, and X satisfy the following conditions: Equation 1: (A+B+C) / X≥0.005; Equation 2: 0.1 ≤ (A+B) / C ≤ 1.6; Equation 3: 0.1≤A / B≤8.

[0010] Optionally, the phosphate ester compounds include one or more of the following: monoethyl phosphate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(2,2,2-trifluoroethyl) phosphite, vinyl phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, ethyl(tetrafluoroethyl) phosphate, triphenyl phosphate, and diethyl vinyl phosphate.

[0011] Optionally, the fluorinated lithium salt compound includes one or more of lithium difluorooxalate borate, lithium difluorobis(oxalate) phosphate, and lithium tetrafluorooxalate phosphate.

[0012] Optionally, the amide compounds include one or more of acrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and methacrylamide.

[0013] Optionally, the positive electrode active material includes transition metal lithium oxides doped with and / or coated with iron.

[0014] Optionally, the chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M(1-y-z) O2, where -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; Wherein, M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr, and M includes at least Fe.

[0015] Another aspect of the present invention provides an electrical device comprising a battery as described above.

[0016] According to the battery provided by the present invention, the P=O and / or PH functional groups in the first additive of this application can irreversibly complex dissolved Fe. 2+ / Fe 3+ The first additive removes ions and eliminates HF, H2O, and free protons generated by catalysis, effectively reducing electrolyte acidity and inhibiting transition metal dissolution and electrode corrosion from the source. The second additive preferentially reduces on the negative electrode surface to form a highly ionicly conductive SEI film rich in LiF and BO / PO components, blocking Fe ions from migrating to the negative electrode interface, avoiding the formation of an electronic insulating deposition layer at low temperatures, and ensuring charge transfer kinetics. The third additive preferentially adsorbs on the iron exposure sites on the positive electrode surface through strongly polar amide groups, physically covering and passivating the active centers, inhibiting the loss of active lithium and open-circuit voltage decay caused by iron participating in the disproportionation reaction.

[0017] The combined use of three types of additives produces a super-synergistic effect: (1) Fluorinated lithium salt compounds first form a highly ion-conductive, LiF-rich interfacial layer on the electrode surface; amide molecules enhance interfacial adhesion and regulate film uniformity through strong adsorption; phosphate ester compounds then fill micropores and defects, improving the density and chemical stability of the CEI / SEI film, and jointly constructing a super-stable composite interfacial structure; (2) The gel network formed by the polymerization of amide compounds effectively confines phosphate ester molecules, suppressing unnecessary side reactions during cycling, while retaining their gas-phase / condensed-phase flame-retardant function, and the highly conductive LiF formed by fluorinated lithium salts... + The interface ensures rapid ion transport; (3) Under thermal runaway or high-temperature abuse conditions, the phosphate ester thermally decomposes and releases PO free radicals, interrupting the combustion chain reaction (gas phase flame retardant), the amide crosslinking promotes the formation of a dense carbon layer (condensed phase flame retardant), and the fluorine-containing components enhance the overall interface thermal stability. The three mechanisms work together to achieve efficient thermal protection. Detailed Implementation

[0018] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0019] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0020] In one embodiment, the present invention provides a battery comprising: The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive active material, which is doped with and / or coated with iron. It should be noted that the different amounts of iron in the positive electrode active layer are to simulate different application scenarios and manufacturing systems.

[0021] Preparation process: Taking lithium cobalt oxide particles as an example, a certain amount of iron oxide is added to the lithium cobalt oxide particles, and pre-calcination is carried out at 400℃ to 600℃ for 20 to 40 minutes to preliminarily decompose the precursor. In an oxygen atmosphere, the temperature is further increased to 900℃-1100℃, and high-temperature sintering is carried out for 8 to 10 hours to complete iron doping.

[0022] Test method for iron content in active material layer: After the battery is manufactured, it is disassembled after being discharged. Take 5mg of positive electrode active material layer and add 3mL of concentrated sulfuric acid and 3mL of concentrated nitric acid in sequence. Heat to 180℃ until the solution is clear and transparent. After cooling, add water to make up to 50mL and send the sample for testing. The iron content is tested using an ICP (Inductively Coupled Plasma Emission Spectrometer).

[0023] The electrolyte includes a first additive, a second additive, and a third additive. The first additive includes phosphate ester compounds, the second additive includes fluorinated lithium salt compounds, and the third additive includes amide compounds.

[0024] The positive electrode active material of this application is doped with iron and / or surface-coated. In low-temperature environments (e.g., 0°C and below), the introduction of iron optimizes the electronic structure and lithium-ion diffusion channels of the positive electrode material, improving intrinsic conductivity and interfacial charge transfer kinetics. Simultaneously, the formed iron-based surface coating layer exhibits good ion conductivity and chemical stability, effectively suppressing excessive reduction and decomposition of the electrolyte at low temperatures and reducing the deposition of high-resistivity byproducts at the interface, thereby alleviating low-temperature polarization and improving discharge capacity retention and rate performance. In high-temperature environments (e.g., above 45°C, especially 60°C and above), iron doping enhances the thermodynamic stability of the positive electrode lattice, suppressing oxygen evolution and irreversible phase transitions during high-voltage charging and discharging. Furthermore, by occupying specific lattice sites in the transition metal layer, iron reduces Ni... 4+ The surface enrichment of highly reactive species weakens their catalytic oxidation effect on the electrolyte; in addition, the iron-based coating can act as a physical barrier to prevent direct contact between the positive electrode and the electrolyte, significantly inhibiting the dissolution of transition metals and HF corrosion, slowing down the growth of interfacial impedance, and improving high-temperature cycling stability and storage performance.

[0025] The first additive, phosphate ester compounds, preferentially undergo oxidation reactions on the surface of high-voltage cathode materials, constructing a dense cathode electrolyte interface (CEI) film rich in lithium polyphosphate in situ. This CEI film effectively inhibits the continuous decomposition of the electrolyte at high potentials and significantly blocks the dissolution of transition metal ions from the cathode lattice, thereby improving the cycle stability and capacity retention of the battery. Simultaneously, the P=O and / or P–H functional groups contained in the molecular structure of the phosphate ester compounds can irreversibly capture harmful impurities such as residual or generated HF and H2O in the electrolyte system, effectively reducing electrolyte acidity and alleviating interfacial corrosion of electrode materials, especially high-nickel cathodes, further enhancing the long-term electrochemical performance of the battery. Furthermore, under high-temperature or thermal runaway conditions, phosphate ester compounds can pyrolyze to generate PO· radicals, interrupting the combustion chain reaction through a gas-phase free radical capture mechanism; simultaneously, they promote the formation of a dense carbon layer at the electrode / electrolyte interface, exerting a condensed-phase flame-retardant effect. The synergistic effect of these dual flame-retardant mechanisms significantly improves the thermal safety of lithium-ion batteries.

[0026] The second additive is a fluorinated lithium salt compound, which is not used as the main salt in the electrolyte but is specifically used for film formation control. This compound can simultaneously electrochemically decompose on the surfaces of the positive and negative electrodes, constructing in situ a dense and stable solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) film rich in lithium fluoride (LiF) and boron-oxygen (BO) components. This composite interfacial film effectively inhibits the continuous decomposition of the electrolyte, the dissolution of transition metals, and the degradation of the electrode structure, significantly improving the cycle life and coulombic efficiency of the battery. In addition, the fluorinated lithium salt compound has a unique anionic structure, combining high lithium-ion conductivity and a wide electrochemical stability window, which not only reduces the battery's internal resistance, improves rate performance and low-temperature discharge capability, but also stably adapts to high-voltage cathode materials. It has excellent thermal stability and can form an effective passivation layer on the surface of the aluminum current collector, preventing aluminum foil corrosion at high potentials and ensuring the long-term reliability of the battery.

[0027] The third additive is an amide compound, whose synergistic value is reflected in three aspects: (1) The strong polar amide groups in the molecule preferentially adsorb onto the electrode surface to form a physical protective layer, suppress electrolyte side reactions and effectively maintain the structural integrity of the graphite negative electrode; (2) Under electrochemical or thermal triggering conditions, it polymerizes to construct a three-dimensional cross-linked polymer skeleton, imprison free electrolyte molecules, suppress lithium dendrite growth, and endow the interface with excellent mechanical strength; (3) Under high temperature conditions, it promotes cross-linking to form carbon, forms a condensed phase thermal barrier, and has a synergistic effect with phosphate ester flame retardant components, significantly enhancing the thermal safety of the battery.

[0028] The P=O and / or PH functional groups in the first additive can irreversibly complex dissolved Fe. 2+ / Fe 3+ The first additive removes ions and eliminates HF, H2O, and free protons generated by catalysis, effectively reducing electrolyte acidity and inhibiting transition metal dissolution and electrode corrosion from the source. The second additive preferentially reduces on the negative electrode surface to form a highly ionicly conductive SEI film rich in LiF and BO / PO components, blocking Fe ions from migrating to the negative electrode interface, avoiding the formation of an electronic insulating deposition layer at low temperatures, and ensuring charge transfer kinetics. The third additive preferentially adsorbs on the iron exposure sites on the positive electrode surface through strongly polar amide groups, physically covering and passivating the active centers, inhibiting the loss of active lithium and open-circuit voltage decay caused by iron participating in the disproportionation reaction.

[0029] The combined use of three types of additives produces a super-synergistic effect: (1) Fluorinated lithium salt compounds first form a highly ion-conductive, LiF-rich interfacial layer on the electrode surface; amide molecules enhance interfacial adhesion and regulate film uniformity through strong adsorption; phosphate ester compounds then fill micropores and defects, improving the density and chemical stability of the CEI / SEI film, and jointly constructing a super-stable composite interfacial structure; (2) The gel network formed by the polymerization of amide compounds effectively confines phosphate ester molecules, suppressing unnecessary side reactions during cycling, while retaining their gas-phase / condensed-phase flame-retardant function, and the highly conductive LiF formed by fluorinated lithium salts... + The interface ensures rapid ion transport; (3) Under thermal runaway or high-temperature abuse conditions, the phosphate ester thermally decomposes and releases PO free radicals, interrupting the combustion chain reaction (gas phase flame retardant), the amide crosslinking promotes the formation of a dense carbon layer (condensed phase flame retardant), and the fluorine-containing components enhance the overall interface thermal stability. The three mechanisms work together to achieve efficient thermal protection.

[0030] In one embodiment, the mass content X of iron in the positive electrode active material layer ranges from 1 ppm to 2000 ppm.

[0031] Specifically, the iron content in the positive electrode active material layer is any one value or a range of any two values ​​from 1ppm, 5ppm, 10ppm, 50ppm, 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm, 1500ppm, 1600ppm, 1700ppm, 1800ppm, 1900ppm, or 2000ppm; in a preferred embodiment, the iron content in the positive electrode active material layer is 100ppm-500ppm.

[0032] When the iron content in the positive electrode active material layer is 1ppm-2000ppm, the iron exists in trace doping or surface coating forms, which can effectively stabilize the crystal structure, improve electron / ion conductivity, and form a protective passivation layer at the electrode / electrolyte interface. This improves the battery's cycle stability, rate performance, and high-temperature storage characteristics, while avoiding significant side reactions and achieving synergistic optimization of performance gains and interface compatibility. When the iron content in the positive electrode active material layer is greater than 2000ppm, excess iron is easily dissolved into Fe during charge and discharge. 2+ / Fe 3+Iron ions react with electrolyte reduction products at low temperatures to form electronically insulating deposits, hindering interfacial charge transfer. During high-temperature cycling, they catalyze electrolyte oxidation and decomposition through variable valence catalysis, releasing free protons and accelerating transition metal dissolution. In the storage phase, they participate in disproportionation reactions, consuming active lithium and causing open-circuit voltage decay. These multi-scenario side reactions significantly degrade battery cycle life, coulombic efficiency, and thermal stability, offsetting or even reversing the beneficial effects of iron introduction.

[0033] Therefore, the present invention preferably controls the iron content in the positive electrode active material layer to be strictly within the range of 1 ppm to 2000 ppm, so as to give full play to its advantages of structural stability and interface regulation, while avoiding the multi-dimensional failure mechanism induced by high concentration of iron, and ensuring the comprehensive performance and reliability of the battery under high voltage, wide temperature range and long cycle operation conditions.

[0034] In one embodiment, the total mass of the electrolyte is denoted as 100%, the percentage of the first additive in the electrolyte is denoted as A, with the unit being %, and the value of A ranges from 0.1 to 1.5; the percentage of the second additive in the electrolyte is denoted as B, with the unit being %, and the value of B ranges from 0.1 to 1; the percentage of the third additive in the electrolyte is denoted as C, with the unit being %, and the value of C ranges from 1 to 8.

[0035] Specifically, the percentage content of the first additive in the electrolyte is any one value or a range of any two values ​​selected from 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, or 1.5%; in a preferred embodiment, the percentage content of the first additive in the electrolyte is 0.3%-1.2%.

[0036] When the first additive accounts for 0.1%-1.5% of the electrolyte, this phosphate ester compound can preferentially oxidize on the positive electrode surface, forming a dense CEI film rich in lithium polyphosphate in situ, effectively inhibiting electrolyte decomposition and transition metal dissolution; at the same time, it can fully remove acidic impurities such as HF / H2O from the system, and release PO free radicals and promote char formation under thermal abuse conditions, achieving synergistic flame retardancy of the gas phase and condensed phase, significantly improving the high-voltage stability, cycle life and thermal safety of the battery, without causing significant negative impact on ionic conductivity or low-temperature performance; when the first additive accounts for less than 0.1% of the electrolyte, its coverage at the electrode interface is insufficient, making it difficult to form a continuous and effective protective film, and its ability to remove HF / H2O is limited, failing to effectively inhibit side reactions and transition metal dissolution; at the same time, it inhibits... The flammability is weak, and under extreme conditions such as high temperature or overcharge, it is difficult to trigger an effective free radical capture and carbonization mechanism, resulting in insignificant improvement in battery interface stability, cycle performance, and safety performance, which cannot meet the application requirements of high energy density batteries. When the first additive accounts for more than 1.5% of the electrolyte, the excess phosphate ester compounds are prone to uncontrolled reduction and decomposition on the negative electrode surface, generating a thick and high-resistivity SEI layer, increasing the interface impedance, and deteriorating the rate and low-temperature performance. At the same time, its high viscosity and low dielectric constant characteristics may reduce the overall ionic conductivity of the electrolyte and continuously consume active lithium during long-term cycling, leading to a decrease in initial coulombic efficiency and accelerated capacity decay. In addition, the excess additive may undergo cross-linking or polymerization side reactions at high temperatures, producing gas or deposits, which may reduce battery reliability.

[0037] Specifically, the percentage content of the second additive in the electrolyte is any one value or a range of any two values ​​selected from 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, or 1%; in a preferred embodiment, the percentage content of the second additive in the electrolyte is 0.2%-0.8%.

[0038] When the second additive accounts for 0.1%-1% of the electrolyte, this fluorinated lithium salt compound can simultaneously and controllably decompose on the surfaces of the positive and negative electrodes, forming a dense, highly ion-conducting SEI / CEI composite interface film rich in LiF and BO components. This effectively inhibits the continuous oxidation / reduction decomposition of the electrolyte and the degradation of the electrode structure. Simultaneously, its anionic structure improves the lithium-ion transference number and overall conductivity without significantly increasing viscosity, broadening the electrochemical window, adapting to high-voltage positive electrode systems, and forming a stable passivation layer on the surface of the aluminum current collector to prevent high-voltage corrosion. This synergistically improves the battery's cycle life, coulombic efficiency, rate performance, and high-temperature storage stability. When the second additive accounts for less than 0.1% of the electrolyte... At a concentration of %, the concentration is insufficient to form a continuous and effective protective film on the electrode surface. The interfacial film formation is incomplete, failing to effectively block side reactions. This results in problems such as transition metal dissolution, increased interfacial impedance, and loss of active lithium not being adequately suppressed. Simultaneously, the passivation effect on aluminum current collectors is weak, making them prone to pitting or oxidation under high voltage, affecting the long-term reliability of the battery. Furthermore, the improvement in ionic conductivity and electrochemical window is limited, making it difficult to support high-voltage and high-rate applications. When the second additive accounts for more than 1% of the electrolyte, excessive fluorinated lithium salt may cause an increase in electrolyte viscosity and a shift in lithium salt dissociation equilibrium, which in turn reduces ion migration rate. At the same time, its excessive decomposition can easily form an excessively thick or non-uniform LiF-rich SEI layer on the negative electrode, increasing interfacial impedance and deteriorating low-temperature and rate performance. In addition, some fluorinated anions may participate in side reactions at high concentrations, generating gases or insoluble deposits, affecting the battery's gas generation behavior and cycle consistency.

[0039] Specifically, the percentage of the third additive in the electrolyte is any one value or a range of any two values ​​from 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5% or 8%; in a preferred embodiment, the percentage of the third additive in the electrolyte is 2%-5%.

[0040] When the third additive accounts for 1% to 8% of the electrolyte, this amide compound preferentially adsorbs onto the electrode interface through its highly polar amide groups, forming a physical barrier to inhibit solvent co-intercalation and side reactions. Moderate polymerization under electrochemical or thermally triggered conditions constructs a gel phase with a three-dimensional network structure, effectively confining free electrolyte molecules, inhibiting lithium dendrite growth, and enhancing interfacial mechanical strength. Simultaneously, it promotes cross-linking to carbon at high temperatures, producing a synergistic effect with phosphate ester flame retardants, significantly improving the battery's thermal stability and safety performance, while maintaining controllable influence on ion transport kinetics. When the third additive accounts for less than 1% of the electrolyte, its adsorption coverage is insufficient, making it difficult to form an effective interfacial protective layer. If the concentration of amide is too low, it cannot form a continuous gel network, resulting in weak dendrite suppression and electrolyte confinement effects. Its high-temperature carbonization ability is limited, making it difficult to form a dense condensed phase barrier, thus failing to fully realize its functions in safety protection and interface stability. When the third additive accounts for more than 8% of the electrolyte, excessive amide monomers significantly increase electrolyte viscosity, hindering lithium-ion diffusion and leading to severe degradation of rate performance and low-temperature discharge capability. Over-polymerization may cause electrolyte gelation or even localized solidification, resulting in poor wetting and a sharp increase in interfacial contact resistance. Furthermore, high-concentration amides may undergo irreversible side reactions during cycling, consuming active lithium and generating byproducts, reducing initial coulombic efficiency and long-term cycling stability.

[0041] In one embodiment, the values ​​A, B, C, and X satisfy the following condition: Equation 1: (A+B+C) / X≥0.005; Equation 2: 0.1 ≤ (A+B) / C ≤ 1.6; Equation 3: 0.1≤A / B≤8.

[0042] Specifically, the value range of (A+B+C) / X is any one point value or any two point values ​​from 0.005, 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or 10.5.

[0043] When the value of (A+B+C) / X ranges from 0.005 to 10.5, this ratio reflects the "functional compensation strength" of the additive system relative to the iron impurity level in the cathode. Within this range, phosphate esters effectively remove Fe... 2+ / Fe 3+The HF and free protons generated by catalysis are used to construct a flame-retardant CEI; fluorinated lithium salts form a highly conductive LiF-rich interface film, inhibiting iron-induced electronic insulation deposition; amide compounds stabilize the interface and imprison dissolved metal ions through adsorption and polymerization; these three components dynamically match the iron content, avoiding both insufficient additives leading to protection failure and excessive introduction causing kinetic degradation, thus achieving a balance between high voltage stability, long cycle life, and high thermal safety. When the value of (A+B+C) / X is less than 0.005, it indicates that the total amount of additives is severely insufficient relative to the iron content in the cathode. In this case, the first, second, and third additives cannot produce a synergistic effect and cannot effectively passivate the multi-scenario side reactions caused by iron dissolution: Fe at low temperatures 2+ The insulating layer formed by the reduction products of the electrolyte was not suppressed, and the interfacial impedance increased sharply; Fe during high-temperature cycling 2+ / Fe 3+ Catalytic oxidation continues, accelerating electrolyte decomposition and loss of active lithium; iron-involved disproportionation reactions during storage are also not blocked, leading to significant open-circuit voltage decay. Overall, the battery exhibits rapid cycle capacity decay, low coulombic efficiency, and poor thermal stability, failing to meet the requirements of high-reliability applications; when the value of (A+B+C) / X is greater than 10.5, excessive decomposition of phosphate esters increases SEI impedance and deteriorates low-temperature performance; excessively high concentrations of fluorinated lithium salts lead to increased electrolyte viscosity and decreased ionic conductivity; excessive polymerization of amide monomers causes electrolyte gelation, resulting in poor wettability, hindered lithium-ion transport, and even inducing lithium plating or internal short-circuit risks.

[0044] Specifically, the value of ((A+B) / C) is any one value or a range of any two values ​​from 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or 1.6; in a preferred embodiment, the value of ((A+B) / C) is 0.3-0.8.

[0045] When the value of (A+B) / C ranges from 0.1 to 1.6, within this range, the three components form a highly efficient and complementary interface regulation system: phosphate esters and fluorinated lithium salts preferentially construct a high-ion-conductivity CEI / SEI bottom layer rich in LiF and lithium polyphosphate; amide compounds are moderately adsorbed and polymerized to form a three-dimensional network structure with mechanical strength, stabilizing the interface and confining the electrolyte; together, the three components achieve a dense, stable, highly conductive, and flame-retardant composite interface film, significantly improving the electrochemical performance and thermal safety of the battery under high voltage, wide temperature range, and long-term cycling. When the value of (A+B) / C is less than 0.1, it indicates that the amide additive (C) is relatively excessive, while the film-forming / flame-retardant functional components (A+B) are severely insufficient. At this point, although a strong gel network structure can be formed, the lack of sufficient LiF-rich and lithium polyphosphate interface substrates leads to high ion transport impedance at the electrode / electrolyte interface, resulting in significant degradation of rate and low-temperature performance. The CEI / SEI film lacks density and chemical stability, and cannot effectively inhibit electrolyte oxidation and decomposition and transition metal dissolution. Although it has the ability to form carbon at high temperatures, the lack of PO· free radical gas-phase flame retardancy and thermal stabilization effect of fluorine-containing components limits the overall improvement in thermal safety. When the value of (A+B) / C is greater than 1.6, it indicates that the film-forming / flame-retardant component (A+B) is relatively excessive, while the amide polymer component (C) is insufficient. In this case, although a highly conductive interface film rich in LiF and lithium polyphosphate can be formed, it lacks effective three-dimensional polymer network support, resulting in insufficient interfacial mechanical strength and difficulty in suppressing film rupture caused by lithium dendrite penetration or volume expansion. Excess phosphate ester and fluorinated lithium salt can easily lead to an increase in side reactions, such as excessively thick negative electrode SEI, increased gas production, and decreased initial coulombic efficiency. Although it has good gas-phase flame retardant ability at high temperatures, the condensed phase char layer is weak, which cannot form an effective thermal insulation barrier, thus limiting the effect of suppressing thermal runaway.

[0046] Specifically, the value of A / B is any one point value or any two point values ​​from 0.1, 0.2, 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5 or 8; in a preferred embodiment, the value of A / B is 0.2-0.8.

[0047] When the A / B ratio ranges from 0.1 to 8, within this range, the fluorinated lithium salt film-forming additive (B), with its high reducing activity, preferentially decomposes on the negative electrode surface, constructing a dense, LiF-rich, and highly ionicly conductive SEI framework in situ. This effectively passivates the graphite surface and inhibits solvent co-intercalation. This stable interface provides a good foundation for the electrochemical behavior of the subsequent phosphate ester additive (A), preventing uncontrollable reduction side reactions at the negative electrode. Simultaneously, the phosphate ester additive, as a highly efficient flame retardant and positive electrode auxiliary film-forming agent, forms a lithium polyphosphate-rich CEI film on the positive electrode side and releases PO· radicals under thermal abuse conditions to achieve gas-phase flame retardancy, compensating for the shortcomings of fluorinated lithium salts in high-temperature safety and positive electrode interface protection. The two components have a clear division of labor, are spatially and temporally ordered, and complement each other's functions, ultimately achieving a super-synergistic effect of "1+1>2". This significantly improves the battery's thermal safety and lifespan while ensuring high-rate and long-cycle electrochemical performance. When A / B < 0.1, it indicates that the content of phosphate ester additives (A) is too low relative to fluorinated lithium salts (B). Although fluorinated lithium salts can form excellent SEI films, the phosphate ester concentration in the system is insufficient to support effective flame retardant function. When A / B > 8, it indicates that the fluorinated lithium salt film-forming additive (B) is relatively severely insufficient. In this case, although the phosphate ester content is sufficient, the lack of sufficient fluorinated lithium salt to construct a high-quality SEI framework in the initial cycle results in a loose, porous, and unevenly composed interfacial film on the graphite anode surface, rich in organic reduction products rather than highly conductive LiF. Such SEI films not only fail to effectively prevent the continuous decomposition of the electrolyte, but also become obstacles to lithium-ion migration due to their low ionic conductivity, resulting in a significant increase in interfacial impedance. This manifests as a decrease in initial coulombic efficiency, deterioration in low-temperature performance, intensified cycle polarization, and even the induction of lithium dendrite growth. Simultaneously, phosphate esters are prone to excessive reduction on the negative electrode surface lacking stable SEI protection, generating gases or high-resistivity byproducts, further degrading battery performance and reliability.

[0048] In one embodiment, the phosphate ester compound includes one or more of the following: monoethyl phosphate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tri(2,2,2-trifluoroethyl) phosphate, tri(2,2,2-trifluoroethyl) phosphite, vinyl phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, ethyl(tetrafluoroethyl) phosphate, triphenyl phosphate, and diethyl vinyl phosphate.

[0049] Phosphate esters (such as tris(2,2,2-trifluoroethyl) phosphate, vinyl phosphate, bis(2,2,2-trifluoroethyl)methyl phosphate, etc.) combine high oxidation stability, strong HF scavenging ability, and excellent flame retardancy. Fluorophosphates (such as tris(2,2,2-trifluoroethyl) phosphate) have high C–F bond energy and excellent thermo / electrochemical stability, and can be stably filmed at high voltage (≥4.5 V), while releasing PO· free radicals to achieve efficient gas-phase flame retardancy. Vinyl / alkyl substituted phosphates (such as diethyl vinyl phosphate) can participate in CEI crosslinking through in-situ polymerization, thereby improving the film density and mechanical strength; Phosphate ester compounds are selected, which have multifunctional structures (such as P=O, P–H, C=C) that can simultaneously achieve interfacial film formation, acidic impurity capture and free radical quenching, resulting in high functional integration.

[0050] In one embodiment, the fluorinated lithium salt compound includes one or more of lithium difluorooxalate borate, lithium difluorobis(oxalate) phosphate, and lithium tetrafluorooxalate phosphate.

[0051] The anions in fluorinated lithium salt compounds contain BO, PO, and F atoms, which are reduced at the negative electrode to form compounds rich in LiF and Li. x BO y Li x PO y Its high ion conductivity SEI significantly reduces interfacial impedance; it forms a stable CEI containing B / P / F during positive electrode oxidation, inhibiting transition metal dissolution and oxygen release; it has self-passivation capability for aluminum current collectors, preventing high-voltage corrosion; compared with traditional LiPF6, its thermal decomposition temperature is higher, improving the intrinsic safety of the electrolyte.

[0052] In one embodiment, the amide compound includes one or more of acrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acryloyloxyethyltrimethylammonium chloride, and methacrylamide.

[0053] Amide compounds possess strong polarity, polymerizability, and thermal responsiveness; among them, the amide group (–CONH2 / –CONR2) has strong adsorption capacity, preferentially covering the active sites of the electrode and inhibiting solvent co-intercalation and side reactions; Double-bonded structures (such as acrylamides) can undergo free radical polymerization under electrochemical or thermal triggering to form a three-dimensional cross-linked network, which impounds the electrolyte, inhibits dendrites, and enhances the interfacial mechanical strength. Functional groups such as sulfonic acid groups and hydroxymethyl groups (such as AMPS and NMA) further enhance lithiophilicity, char-forming ability, and high-temperature stability, and produce a synergistic flame-retardant effect with phosphate esters in the condensed phase.

[0054] In one embodiment, the electrolyte further includes a lithium salt, which includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluorophosphate, lithium bis(oxalate-borate), lithium difluorooxalate-borate, lithium tetrafluoroborate, and lithium difluorodi(oxalate-borate). Using the above-mentioned lithium salt has the effects of providing a stable lithium ion source, promoting the formation of a dense SEI film, and improving the ionic conductivity and thermal stability of the electrolyte.

[0055] It should be noted that this application does not impose any particular limitation on the preparation method of the electrolyte. Those skilled in the art can prepare the electrolyte using conventional technical means, such as mixing the raw materials evenly according to the specified ratio.

[0056] In one embodiment, the electrolyte further includes an organic solvent, which includes one or more of the following: ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0057] Specifically, the aforementioned organic solvents are selected primarily to dissolve the first additive, the second additive, the third additive, and the lithium salt.

[0058] In one embodiment, the positive electrode active material further includes a transition metal lithium oxide doped and / or coated with iron.

[0059] In this application, there is no particular limitation on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, iron plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper. In one embodiment, the positive electrode current collector is a metallic material.

[0060] In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent and a positive electrode binder.

[0061] In some embodiments, the type of positive conductive agent mentioned in this invention is not limited, and any known conductive agent can be used.

[0062] In some embodiments, the positive electrode conductive agent mentioned in this invention includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene.

[0063] In one embodiment, the type of positive electrode binder mentioned in this invention is not limited, and any known positive electrode binder can be used.

[0064] In some embodiments, the positive electrode binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0065] In one embodiment, the chemical formula of the transition metal lithium oxide is Li. 1+x Ni y Co z M (1-y-z) O2, where -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; M is selected from one or more of iron, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0066] Using the aforementioned transition metal lithium oxides as positive electrode active materials has the advantages of high specific capacity, high operating voltage, and structural stability. It can be matched with high-capacity silicon-based negative electrodes to jointly achieve high energy density of the battery.

[0067] In one embodiment, the battery further includes a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a negative active material, which includes, but is not limited to, one or more combinations of graphite, hard carbon, silicon, silicon suboxide, silicon-carbon composite material, and lithium titanate. It is preferably designed in conjunction with the positive electrode and the functionalized electrolyte to maximize the overall performance of the battery. In this invention, there are no particular limitations on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, iron foil, stainless steel foil, titanium foil, foamed iron, foamed copper, or composite current collector, etc.

[0068] In some preferred embodiments, the negative current collector comprises copper foil.

[0069] In some embodiments, the negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector, and the negative electrode active material layer further includes a negative electrode conductive agent, a negative electrode binder, a negative electrode thickener, and a negative electrode solvent.

[0070] The negative electrode conductive agent includes at least one of the following carbon materials: natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene.

[0071] Negative electrode binders include styrene-butadiene latex, etc. Negative electrode thickeners include CMC, etc. Negative electrode solvents include deionized water, etc.

[0072] In one embodiment, a separator is also included, which is located between the positive electrode and the negative electrode.

[0073] This application does not impose any particular restrictions on the material and shape of the diaphragm, as long as it does not significantly impair the effectiveness of this application.

[0074] In some embodiments, the diaphragm includes a porous sheet-like or non-woven material with excellent liquid retention properties. The diaphragm includes resin or glass fiber diaphragm materials, including but not limited to polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc.

[0075] In some embodiments, the lithium-ion battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte described above.

[0076] In one embodiment, another aspect of the present invention provides an electrical device including a battery as described above.

[0077] Specifically, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0078] The present invention will be further illustrated by the following examples.

[0079] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Materials not specified in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0080] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0081] In the following embodiments, the reagents, materials and instruments used, unless otherwise specified, are commercially available or can be obtained through synthesis methods known in the art.

[0082] Table 1. Design of battery components for Examples 1-21 and Comparative Examples 1-15; Table 2. Design of electrolyte components for Examples 2, 22-26 and Comparative Examples 16-18; Example 1 This embodiment illustrates the lithium-ion battery disclosed in this invention, and includes the following operational steps: Preparation of positive electrode sheet Lithium cobalt oxide doped with iron, acetylene black (SuperP) as the positive electrode active material, and polyvinylidene fluoride (PVDF) binder are mixed evenly at a mass ratio of 97:1.5:1.5 and then evenly dispersed with 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry. The mixed slurry is coated on both sides of an aluminum foil current collector, and then baked, rolled, and cut into sheets to obtain the positive electrode sheet.

[0083] The specific values ​​of iron content in the added positive electrode active material are shown in Table 1.

[0084] It should be noted that the different iron contents in the positive electrode active layer set in Table 1 are to simulate different application scenarios and manufacturing systems. The value of X can be adjusted by adding elemental iron to the positive electrode slurry for different positive electrode active materials.

[0085] Preparation of negative electrode sheet Artificial graphite (anode active material), acetylene black (Super P) (anode conductive agent), CMC (thickener), and SBR (anode binder) (anode binder) are mixed evenly in a mass ratio of 94:2:1.2:2.8 and then evenly dispersed with deionized water to form a uniform anode slurry. The mixed slurry is coated on both sides of a copper foil current collector, and then baked, rolled, and cut into sheets to obtain the anode sheet.

[0086] Preparation of electrolyte a. Mix ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (EP), and diethyl carbonate (DEC) in a mass ratio of 10:20:40:30 to form a mixed solvent. Remove water using a molecular sieve and set aside. Add 1M LiPF6 and mix thoroughly. b. Add 0.1% of the initiator azobisisobutyronitrile (as a percentage of the colorless and transparent liquid content) and the first additive, the second additive, and the third additive (the types and amounts of the first additive, the second additive, and the third additive are shown in Table 1 and Table 2) to the colorless and transparent liquid obtained in step a to obtain the electrolyte.

[0087] Manufacturing of lithium-ion batteries The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets. After winding and welding the tabs, a bare cell is obtained. The bare cell is placed in an aluminum-plastic film for liquid injection, encapsulation, and high-temperature curing at 60°C for 8 hours to obtain a lithium-ion battery.

[0088] Examples 2-26 Examples 2-21 illustrate the lithium-ion battery disclosed in this invention, including most of the operations in Example 2, except that: The percentage of the first additive (A / %), the percentage of the second additive (B / %), the percentage of the third additive (C / %), the content of iron in the positive electrode active material (X / ppm), the value of A / B, the value of (A+B) / C, and the value of (A+B+C) / X in Examples 2-21 are all referenced in Table 1.

[0089] Examples 22-26 illustrate the lithium-ion battery disclosed in this invention, including most of the operations in Example 2, except that: The types of the first additive, the second additive, and the third additive in Examples 22-26 are all referred to in Table 2.

[0090] Comparative Examples 1-18 Comparative Examples 1-15 are used to illustrate the lithium-ion battery disclosed in this invention, including most of the operations in Example 2, the differences being: The percentage of the first additive (A / %), the percentage of the second additive (B / %), the percentage of the third additive (C / %), the content of iron in the positive electrode active material (X / ppm), the value of A / B, the value of (A+B) / C, and the value of (A+B+C) / X in Comparative Examples 1 to 15 are all referenced in Table 1.

[0091] Comparative Examples 16-18 are used to illustrate the lithium-ion battery disclosed in this invention, including most of the operations in Example 2, except that: The types of the first, second, and third additives in Comparative Examples 16-18 are all referenced in Table 2.

[0092] The method for testing the iron content in the positive electrode active material layer is as follows: After the battery is manufactured and discharged, it is disassembled. Take 5 iron positive electrode active material layers and add 3 mL of concentrated sulfuric acid and 3 mL of concentrated nitric acid in sequence. Heat to 180°C until the solution is clear and transparent. After cooling, add water to make up to 50 mL and send the sample for testing. The iron content is tested using an ICP (Inductively Coupled Plasma Emission Spectrometer).

[0093] Performance testing The following performance tests were performed on Examples 1-26 and Comparative Examples 1-18 prepared above: 60℃ Storage Performance Test The lithium-ion batteries prepared in the above embodiments and comparative examples were charged at 25°C at a rate of 1C to the cutoff voltage, with a cutoff current of 0.025C, and left to stand for 5 minutes. The thickness H1 of the lithium-ion battery was then measured. After that, the batteries were stored at 60°C for 60 days, and the thickness H2 of the lithium-ion battery was measured after the storage period.

[0094] Thickness expansion rate = [(H2-H1) / H1]×100%.

[0095] 45℃ Cyclic Performance Test The lithium-ion batteries prepared in the above embodiments and comparative examples were charged and discharged at 45°C at a rate of 1C / 1C within the charge and discharge cutoff voltage range. The discharge capacity of the first cycle was recorded as C1, and the discharge capacity of the Nth cycle was recorded as C2. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R2 = C2 / C1. The number of cycles of the lithium-ion battery when the cycle capacity retention rate R2 was 70% was recorded.

[0096] 0℃ Cyclic Performance Test The lithium-ion batteries prepared in the above embodiments and comparative examples were charged and discharged at 0°C at a rate of 1C / 1C within the charge and discharge cutoff voltage range. The discharge capacity of the first cycle was recorded as Y1, and the discharge capacity of the Nth cycle was recorded as Y2. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate of the Nth cycle, X2 = Y2 / Y1. The number of cycles of the lithium-ion battery when the cycle capacity retention rate X2 was 80% was recorded.

[0097] The test results are shown in Table 3.

[0098] Table 3 Battery performance test results of Examples 1-26 and Comparative Examples 1-18 Comparing Example 2 and Comparative Example 1, it can be seen that when the present invention uses the first additive (phosphate ester compound), the battery can cycle at 10°C to 80% capacity retention for 1020 cycles, and the thickness expansion rate at 60°C is 3.2%; when the first additive is absent, the cycle number drops to 780 cycles, and the thickness expansion rate increases to 5.8%, indicating that the phosphate ester compound can effectively participate in the formation of a thermally stable SEI film, suppress electrolyte decomposition and gas generation at high temperatures, and significantly improve cycle life and safety performance.

[0099] Comparing Example 2 and Comparative Example 2, it can be seen that when the present invention uses the second additive (fluorinated lithium salt compound), the battery cycle count at 10°C is 1020 cycles, and the expansion rate at 60°C is 3.2%; when the second additive is not present, the cycle count drops to 810 cycles, and the expansion rate increases to 6.1%. This indicates that the fluorinated lithium salt compound can form a dense protective film rich in LiF at the positive and negative electrode interfaces, effectively inhibiting the dissolution of transition metals and corrosion of aluminum current collectors, thereby improving high-voltage cycle stability and thermal storage performance.

[0100] Comparing Example 2 and Comparative Example 3, it can be seen that when the present invention uses a third additive (amide compound), the number of cycles at 10°C reaches 1020 cycles; when the third additive is absent, the number of cycles drops significantly to 690 cycles, and the expansion rate increases to 4.5%, indicating that the amide compound weakens Li through coordination. + - Solvent molecule binding energy promotes the desolvation process, significantly improves low-temperature ion transport dynamics, and preferentially oxidizes to form a stable CEI film under high voltage.

[0101] Comparing Example 2 and Comparative Example 4, it can be seen that when the electrolyte contains the first additive, the second additive, and the third additive, the cycle count is 1020 cycles, the expansion rate is 3.2%, and the overall battery performance is optimal. When the electrolyte does not contain the first additive, the second additive, and the third additive, the cycle count is only 520 cycles, and the expansion rate is as high as 8.3%. This proves that the three types of additives work together through a synergistic mechanism of "flame retardant film formation + interface enhancement + solvation regulation" to achieve a comprehensive performance improvement in high safety, long life, and wide temperature range.

[0102] Comparative Examples 1-5, Comparative Example 7, and Comparative Example 11 show that when the first additive accounts for 0.1%-1.5% of the electrolyte, the battery cycle count at 10°C remains at 980-1020 cycles, and the expansion rate at 60°C is controlled at 3.2%-3.8%. When the first additive accounts for less than 0.1% of the electrolyte, the cycle count drops to 720 cycles, and the expansion rate reaches 5.2%, indicating that incomplete film formation cannot effectively suppress side reactions. When the first additive accounts for more than 1.5% of the electrolyte, the cycle count drops to 850 cycles, and the expansion rate rises to 6.0%, indicating that excessive phosphate esters damage the graphite layered structure, inducing co-intercalation or gas evolution.

[0103] Comparative Examples 2, 6-8, 8, and 12 show that when the second additive accounts for 0.1%-1% of the electrolyte, the cycle count reaches 960-970 cycles, and the expansion rate is 3.3%-3.5%. When the second additive accounts for less than 0.1% of the electrolyte, the cycle count drops to 750 cycles, and the expansion rate is 5.5%, due to the discontinuity of the LiF film at the interface and insufficient positive electrode protection. When the second additive accounts for more than 1% of the electrolyte, the cycle count drops to 880 cycles, and the expansion rate is 4.9%, due to increased electrolyte viscosity, decreased ionic conductivity, and potential exacerbation of aluminum corrosion.

[0104] Comparative Examples 2, 9-12, and 9-10 show that when the third additive accounts for 1% to 8% of the electrolyte, the cycle count is 940–950 cycles and the expansion rate is 3.6%–4.0%. When the third additive accounts for less than 1% of the electrolyte, the cycle count is only 700 cycles because the solvation regulation effect is weak and the low-temperature desolvation energy barrier is high. When the third additive accounts for more than 8% of the electrolyte, the cycle count drops to 820 cycles and the expansion rate increases dramatically to 7.5% because the amide compounds undergo oxidative decomposition at high potentials, generating gas that causes the battery cell to swell.

[0105] Comparing Examples 2, 13-17, and Comparative Example 5, it can be seen that when the iron content in the positive electrode active material layer is 1ppm-2000ppm, the high and low temperature cycling cycles are 990-1020 cycles, the expansion rate is 3.2%-3.8%, and the battery performance is stable. At low temperatures, the number of cycles is lower, and the thickness expansion rate is higher. When the iron content in the positive electrode active material layer is greater than 2000ppm, the number of cycles drops sharply to 760 cycles, and the expansion rate reaches 6.5%, due to the presence of Fe. 3+ Catalytic oxidation and decomposition of the electrolyte accelerates the destruction of the positive electrode structure and the generation of gas, resulting in a decrease in battery cycle life and a deterioration in high and low temperature storage performance.

[0106] Comparing Examples 2, 18-19, 6, and 12, it can be seen that when the A / B ratio is in the range of 0.05-8, the battery performance is good. When A / B < 0.05: the second additive is excessive, the cycle life drops to 730 cycles, and aluminum current collector corrosion is easily triggered; when A / B > 8: the first additive is excessive, the cycle life drops to 880 cycles, negative electrode compatibility deteriorates, and the initial efficiency decreases.

[0107] Comparing Examples 2, 20-21, and 13-14, it can be seen that when the value of (A+B) / C is in the range of 0.1-1.6, the interface protection and solvation regulation are balanced. When the value of (A+B) / C is less than 0.1: the proportion of the third additive is too high, the cycle count is only 710 cycles, and the high voltage stability is insufficient; when the value of (A+B) / C is greater than 1.6, the first two types of additives are excessive, the cycle count is 840 cycles, the expansion rate is 5.0%, ion migration is hindered, and the rate performance decreases.

[0108] Comparing Examples 2, 16, and 15, it can be seen that when the value of (A+B+C) / X is greater than 0.005, the total amount of additive is sufficient to cover the electrode surface and form an effective protective layer, resulting in excellent cycle performance. When the value of (A+B+C) / X is less than 0.005, the number of cycles is only 740, because the additive coverage is insufficient and the interfacial side reactions are not effectively suppressed.

[0109] Comparing Examples 2, 22-23 and Comparative Example 16, it can be seen that when the first additive of the present invention is a phosphate ester compound, it has both flame retardancy and film-forming ability, and expands by 3.2% after 1020 cycles; when the first additive is fluoroethylene carbonate, the number of cycles drops to 860 cycles and the expansion rate is 5.5%. This is because neither of them has flame retardancy, and FEC is prone to decomposition to produce HF under high voltage, which corrodes the positive electrode.

[0110] Comparing Examples 2, 24 and 17, it can be seen that when the second additive of the present invention is a fluorinated lithium salt compound, it can simultaneously improve conductivity and interface stability; when the second additive is lithium nitrate, the cycle number is 890 cycles and the expansion rate is 5.2%, because LiDFP is corrosive to aluminum current collectors at high concentrations and has low conductivity.

[0111] Comparing Examples 2, 25-26 and Comparative Example 18, it can be seen that when the third additive of the present invention is an amide compound, it has excellent low-temperature performance and low expansion rate; when the third additive is succinic anionylene, the expansion rate is as high as 8.0% after 780 cycles. This is because succinic anionylene is prone to electrochemical polymerization at >4.3 V, generating a large amount of gas, which leads to severe swelling.

[0112] This system achieves comprehensive improvements in battery performance in terms of high and low temperature cycling, interface stability, and safety by strictly controlling the contents of the first additive (A), the second additive (B), the third additive (C), and the mass content of iron in the positive electrode active material layer (X), so that (A+B+C) / X≥0.005, 0.1≤(A+B) / C≤1.6, and 0.1≤A / B≤8. It is especially suitable for high energy density lithium-ion battery applications.

[0113] 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 battery, characterized in that, include A positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on the positive current collector, the positive active material comprising a positive active material, the positive active material being doped with and / or coated with iron. An electrolyte comprising a first additive, a second additive, and a third additive, wherein the first additive comprises a phosphate ester compound, the second additive comprises a fluorinated lithium salt compound, and the third additive comprises an amide compound.

2. The battery according to claim 1, characterized in that, The mass content X of iron in the positive electrode active material layer is in the range of 1ppm-2000ppm.

3. The battery according to claim 2, characterized in that, The total mass of the electrolyte is denoted as 100%. The percentage of the first additive in the electrolyte is denoted as A, with the unit being %, and the value of A ranges from 0.1 to 1.

5. The percentage of the second additive in the electrolyte is denoted as B, with the unit being %, and the value of B ranges from 0.1 to 1. The percentage of the third additive in the electrolyte is denoted as C, with the unit being %, and the value of C ranges from 1 to 8.

4. The battery according to claim 3, characterized in that, The values ​​of A, B, C, and X satisfy the following conditions: Equation 1: (A+B+C) / X≥0.005; Equation 2: 0.1 ≤ (A+B) / C ≤ 1.6; Equation 3: 0.1≤A / B≤8.

5. The battery according to claim 1, characterized in that, The phosphate ester compounds include one or more of the following: monoethyl phosphate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tri(2,2,2-trifluoroethyl) phosphate, tri(2,2,2-trifluoroethyl) phosphite, vinyl phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, ethyl(tetrafluoroethyl) phosphate, triphenyl phosphate, and diethyl vinyl phosphate.

6. The battery according to claim 1, characterized in that, Fluorinated lithium salt compounds include one or more of lithium difluorooxalate borate, lithium difluorobis(oxalate) phosphate, and lithium tetrafluorooxalate phosphate.

7. The battery according to claim 1, characterized in that, The amide compounds include one or more of acrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acryloyloxyethyltrimethylammonium chloride, and methacrylamide.

8. The battery according to claim 1, characterized in that, The positive electrode active material includes transition metal lithium oxides doped with and / or coated with iron.

9. The battery according to claim 8, characterized in that, The chemical formula of the transition metal lithium oxide is Li 1+ x Ni y Co z M (1-y-z) O2, where -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; Wherein, M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr, and M includes at least Fe.

10. An electrical device, characterized in that, Includes the battery as described in any one of claims 1 to 9.

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