A lithium-ion battery

Abstract

This invention belongs to the field of lithium battery technology, specifically relating to a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the current collector. The positive electrode material layer includes lithium cobalt oxide containing Ti, and based on the mass of the positive electrode material layer, the mass content of Ti is u ppm, 100≤u≤2000. The non-aqueous electrolyte includes lithium salt, fluoroethylene carbonate, fluorocarboxylic acid ester, and a first additive. The first additive includes a compound shown in structural formula 1. The mass percentages of the first additive (A%), fluoroethylene carbonate (B%), and fluorocarboxylic acid ester (C%) satisfy: 0.3≤25, and 100≤u≤2000, 0.05≤A≤3, 5≤B≤30, 15≤C≤65. The lithium-ion battery provided by this invention exhibits synergistic effects among its parameters, achieving a balance between high-temperature cycle performance and safety performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a lithium-ion battery with excellent high-temperature cycle performance and safety performance. Background Technology

[0002] Lithium cobalt oxide (LiCoO2, LCO) has long dominated the portable consumer electronics lithium-ion battery market due to its excellent overall electrochemical performance. The urgent need for longer battery life in end devices is driving the development of LCO systems towards higher voltage (≥4.5V), which can significantly increase battery energy density by more than 20%, making it a key technology for achieving high energy density. However, high-voltage conditions can trigger irreversible phase transitions, lattice structure collapse, and the release of reactive oxygen species in LCO materials. Simultaneously, it exacerbates electrolyte oxidation and decomposition, as well as interfacial side reactions, ultimately creating a vicious cycle of material structure degradation and intensified electrolyte side reactions. This leads to battery capacity decay, reduced cycle life, and deteriorated safety performance.

[0003] Currently, the mainstream solvent systems for commercial electrolytes are mainly carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC). These solvents can form a stable solid electrolyte interface (SEI) with the graphite anode, have excellent solubility for lithium salts, and possess suitable ionic conductivity and viscosity, thus becoming the mainstream choice in the industry. However, these solvents exhibit extremely poor stability at high voltages, undergoing significant irreversible oxidative decomposition above 4.4 V, making them unsuitable for high-voltage LCO systems. Furthermore, they are prone to decomposition and gas generation at high temperatures, exhibiting poor thermal stability and significantly exacerbating the risks of battery gas expansion and thermal runaway. Insufficient compatibility between electrolytes and high-voltage LCO systems has become a core bottleneck restricting their industrial application. Therefore, there is an urgent need to develop a lithium cobalt oxide lithium-ion battery suitable for high-voltage systems with good high-temperature cycle performance and safety. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a lithium-ion battery to solve the problems of poor high-temperature cycle performance and poor safety performance of existing high-voltage lithium cobalt oxide lithium-ion batteries.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] A lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte; The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer includes lithium cobalt oxide containing Ti element. Based on the mass of the positive electrode material layer, the mass content of Ti element is uppm, 100≤u≤2000. The non-aqueous electrolyte comprises lithium salt, fluoroethylene carbonate, fluorocarboxylic acid ester, and a first additive. Based on the mass of the non-aqueous electrolyte, the mass percentage of the first additive is A%, the mass percentage of the fluoroethylene carbonate is B%, and the mass percentage of the fluorocarboxylic acid ester is C%. The first additive comprises a compound represented by structural formula 1: Structural Formula 1 Where X is selected from or R1 and R2 are each independently selected from H, ,or R1 and R2 are not both selected from H, and X, R1 and R2 contain at least one sulfur atom; The lithium-ion battery satisfies the following condition: 0.3≤ ≤25, and 0.05≤A≤3, 5≤B≤30, 15≤C≤65.

[0007] The lithium-ion battery provided by this invention uses lithium cobalt oxide containing Ti as the positive electrode active material, and adds the compound shown in structural formula 1 as the first additive to the non-aqueous electrolyte, and uses fluoroethylene carbonate and fluorocarboxylic acid ester as solvents, which is beneficial to form an inorganic / organic composite interface film on the positive electrode surface that combines rigidity and flexibility, thereby improving the high-temperature performance and safety performance of the battery. The presumed reasons are as follows: On the one hand, fluoroethylene carbonate can preferentially construct a LiF-rich inorganic film on the LCO cathode, providing a rigid and stable interfacial film and improving high-temperature performance; however, the inorganic film is prone to cracking due to volume strain during charge and discharge, and fluoroethylene carbonate is prone to ring-opening reactions at high temperatures, increasing gas production during high-temperature storage; to solve this problem, an appropriate amount of Ti element is added to lithium cobalt oxide. Ti ions can preferentially occupy Co sites, significantly enhancing the structural stability of the layered oxide, inhibiting particle cracking caused by abrupt changes in cell volume, buffering volume stress, protecting the stability of the interfacial film, and also inhibiting the irreversible H1-3 phase transition that occurs at the cathode under high SOC, reducing the reactivity between the cathode and the electrolyte, and inhibiting the decomposition of the electrolyte and gas production at high temperatures; on the other hand, the first additive can form a sulfur-containing organic interfacial film rich in CS bonds on the LCO surface, providing a flexible structure and alleviating the layered structure. The volume expansion of oxide particles makes the interfacial film less prone to breakage, but the organic film structure is loose and unstable at high temperatures. However, by combining the first additive with fluoroethylene carbonate, the two work together to form a stable inorganic / organic composite interfacial film on the LCO cathode surface, balancing rigidity and flexibility. This effectively suppresses side reactions between the cathode and the electrolyte, reduces heat accumulation from local side reactions, and improves the battery's high-temperature performance and thermal safety. Furthermore, the combination of fluorocarboxylic acid ester and fluoroethylene carbonate, with its high content of fluorinated solvent, improves the stability of the electrolyte, suppresses the continuous oxidative decomposition of the electrolyte under high voltage, and inhibits gas generation during high-temperature storage. At the same time, the fluorinated solvent also has a lower Li+ solvation capacity, which can increase the anion content in the solvation sheath, change the solvation structure, promote the formation of LiF, suppress electrolyte side reactions, and further improve the battery's high-temperature and safety performance. Based on the interactions between Ti, the first additive, fluoroethylene carbonate, and fluorocarboxylic acid esters in the cathode material layer, the inventors discovered through extensive research that when the mass content u of Ti, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid esters in the cathode material layer satisfy 0.3 ≤ When the temperature is ≤25, and 100≤u≤2000, 0.05≤A≤3, 5≤B≤30, and 15≤C≤65, the resulting lithium-ion battery has excellent high-temperature cycle performance and safety performance.

[0008] Preferably, when the lithium-ion battery satisfies 0.6≤ When the value is ≤20, the synergistic improvement effect among the parameters is optimal, thereby better suppressing interfacial side reactions, reducing local reaction heat accumulation, and thus improving the battery's high-temperature cycling and safety performance.

[0009] In some embodiments, when the mass content u of Ti element in the cathode material layer is too high, Ti element will accumulate on the surface of lithium cobalt oxide, forming a high-resistivity phase, hindering lithium-ion transport and degrading cycle performance. When the mass content u of Ti element in the cathode material layer is too low, it is impossible to effectively suppress the structural distortion and oxygen evolution of lithium cobalt oxide material under high voltage, making it difficult to stabilize the lattice oxygen environment. At the same time, the suppression effect on side reactions between electrolytes is insufficient, resulting in poor cycle stability and high-temperature performance of lithium-ion batteries. Specifically, the mass content u ppm of Ti element is 100 ppm, 200 ppm, 300 ppm, 500 ppm, 700 ppm, 1000 ppm, 1300 ppm, 1500 ppm, 1700 ppm, 2000 ppm, or any combination of these values.

[0010] In a preferred embodiment, the Ti element mass content u ppm is 200 ppm to 1500 ppm. Within this range, Ti element on the surface and at grain boundaries of lithium cobalt oxide can better improve interface stability and reduce side reactions between electrolytes, thereby better enhancing high-temperature cycling stability and safety performance.

[0011] In some embodiments, Ti is added to the lithium cobalt oxide material in the form of doping and / or coating.

[0012] In some embodiments, the non-aqueous electrolyte includes fluoroethylene carbonate as a solvent. Fluoroethylene carbonate preferentially forms a LiF-rich inorganic film on the lithium cobalt oxide cathode, providing a rigid and stable interface film. This interface film effectively blocks direct contact between the electrolyte and the cathode active material, significantly inhibiting oxidative decomposition, gas generation, and cathode transition metal dissolution of the electrolyte under high voltage and high temperature conditions, preventing a continuous increase in impedance due to repeated damage and repair of the interface film. Simultaneously, the rigid and stable interface film alleviates lattice strain and structural distortion of the lithium cobalt oxide material during charge-discharge cycles, maintaining the integrity of the cathode interface structure. Therefore, it can significantly improve the high-temperature cycle stability and safety performance of the battery. If the mass percentage (B%) of fluoroethylene carbonate in the non-aqueous electrolyte is too low, a LiF-rich inorganic film cannot be constructed at the positive electrode, resulting in insufficient protection of the positive electrode, difficulty in suppressing high-temperature side reactions, poor interface stability, and a significant decrease in battery cycle life and safety performance. If the mass percentage (B%) of fluoroethylene carbonate in the non-aqueous electrolyte is too high, an excessively thick and poorly dense interface film is easily formed on the electrode surface, leading to a surge in interface impedance, increased battery polarization, and faster cycle degradation. Specifically, the mass percentage (B%) of fluoroethylene carbonate in the non-aqueous electrolyte is 5%, 7%, 10%, 13%, 15%, 17%, 20%, 23%, 25%, 27%, 30%, or any combination of these values. In a preferred embodiment, the mass percentage (B%) of fluoroethylene carbonate is 7% to 25%.

[0013] In some embodiments, the non-aqueous electrolyte includes fluorocarboxylic acid esters as solvents. Fluorocarboxylic acid esters can improve the electrolyte's resistance to oxidative decomposition and effectively suppress side reactions on the positive electrode surface, thereby improving the cycle life of lithium-ion batteries. Simultaneously, high oxidation stability can reduce thermal side reactions and heat accumulation, lowering the risk of thermal runaway and improving the safety performance of lithium-ion batteries. If the mass percentage (C%) of fluorocarboxylic acid esters in the non-aqueous electrolyte is too high, the high viscosity of the solvent itself and weakened lithium-ion solvation ability will lead to a significant decrease in the electrolyte's ionic conductivity. This will worsen the problems of increased polarization and accelerated capacity decay during high-temperature cycling. Furthermore, excessively high content will weaken the electrolyte's wettability and film stability at the electrode interface, which is detrimental to the overall control of interfacial side reactions at high temperatures and may even exacerbate local gas generation and internal pressure increases, adversely affecting the battery's high-temperature cycling performance and safety performance. Conversely, if the mass percentage (C%) of fluorocarboxylic acid esters is too low, it cannot sufficiently improve the electrolyte's oxidation stability and cannot effectively suppress side reactions on the positive electrode surface. Specifically, the mass percentage (C%) of the fluorocarboxylic acid ester is 15%, 17%, 20%, 23%, 25%, 27%, 30%, 33%, 35%, 37%, 40%, 43%, 45%, 47%, 50%, 53%, 55%, 57%, 60%, 63%, 65%, or any combination of these values. In a preferred embodiment, the mass percentage (C%) of the fluorocarboxylic acid ester is 20% to 55%.

[0014] In some embodiments, the fluorocarboxylic acid ester is selected from one or more of ethyl 2,2-difluoroacetate, 2,2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, 2,2-difluoroethyl propionate, and 2,2,2-trifluoroethyl propionate.

[0015] In some embodiments, introducing the compound shown in Structural Formula 1 as a first additive into the non-aqueous electrolyte can form a sulfur-containing organic interfacial film rich in CS bonds on the lithium cobalt oxide surface. This provides a flexible structure, mitigates particle volume expansion changes, makes the interfacial film less prone to breakage, suppresses interfacial side reactions, reduces local heat accumulation from side reactions, and improves the battery's high-temperature performance and safety performance. If the mass percentage A% of the first additive in the non-aqueous electrolyte is too low, the film formation will be defective and unable to effectively suppress side reactions; if the mass percentage A% of the first additive is too high, the film will be too thick, increasing impedance, causing local heat generation during charging and discharging, deteriorating safety performance. Furthermore, excessive additive is unstable and decomposes at high temperatures, increasing safety risks. Specifically, the mass percentage A% of the first additive is 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, or any combination of these values. In a preferred embodiment, the mass percentage A% of the first additive is 0.1% to 2%.

[0016] In some embodiments, the compound represented by structural formula 1 is selected from one or more of the following compounds: .

[0017] In some embodiments, due to the strong electron-withdrawing properties of fluorine atoms, fluorinated solvents themselves possess higher flash points, thermal stability, and oxidation resistance. Therefore, when the amounts of fluoroethylene carbonate and fluorocarboxylic acid esters further satisfy 35 ≤ B + C ≤ 70, the stability of the electrolyte can be improved, and the oxidative decomposition of the electrolyte under high pressure can be suppressed. Simultaneously, the fluorinated solvent also has lower Li₂O₃ content. + Solvency increases the anion content in the solvation sheath and alters the solvation structure, thereby promoting LiF formation, forming a dense interfacial film, and improving the battery's high-temperature cycle performance. Simultaneously, because fluorinated solvents have higher viscosity and lower lithium salt solubility, it is necessary to balance the content of fluoroethylene carbonate and fluorocarboxylic acid esters. The ratio of fluoroethylene carbonate to fluorocarboxylic acid esters must satisfy 1.5 ≤ C / B ≤ 5.5 to ensure the electrolyte can fully dissolve the lithium salt while maintaining suitable conductivity and viscosity. If C / B < 1.5, the electrolyte viscosity is too high, making wetting difficult and prone to lithium plating, thus degrading the battery's high-temperature cycle and safety performance. If C / B > 5.5, the lithium salt may not dissolve.

[0018] In some embodiments, the non-aqueous electrolyte further includes a second additive, which is a nitrile compound. The nitrile compound includes at least one selected from butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, butanetrionitrile, and hexanetrionitrile. The nitrile compound can complex with the transition metal ion Co, masking highly active sites to form a protective layer, effectively preventing direct contact between the electrolyte and the positive electrode material, thereby avoiding oxidative decomposition of the electrolyte, and simultaneously preventing hydrofluoric acid corrosion of the positive electrode material and the dissolution of Co ions from the positive electrode material. The mass percentage D% of the second additive is 2 ≤ D ≤ 5. When the mass percentage D% of the second additive is too low, the second additive cannot cover the active sites, providing insufficient protection; when the mass percentage D% of the second additive is too high, nitrile compound molecules accumulate on the positive electrode surface, hindering lithium-ion transport and degrading cycle performance. Specifically, the mass percentage D% of the second additive is 2.0%, 2.3%, 2.5%, 2.7%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, 5.0%, or a range of any two of these values.

[0019] In a preferred embodiment, the mass percentage D% of the second additive is 3 ≤ D ≤ 5.

[0020] In some embodiments, the first additive can synergistically interact with nitrile compounds. The first additive preferentially forms a film on the positive electrode, while the nitrile additive can complex with the positive electrode active sites at film formation defects, synergistically suppressing side reactions at the electrode interface. At the same time, the two synergistically enhance the stability of the electrode interface, reduce the heat of film decomposition reaction, and improve thermal safety performance. When the first additive and the second additive satisfy 2.5≤A+D≤6, the high-temperature cycling and safety performance of the battery can be better improved.

[0021] In some preferred embodiments, the nitrile compound is hexanetrionitrile. Hexanetrionitrile has three -CN groups, exhibiting stronger coordination ability and forming a stable stereochelate protective structure, thus providing stronger protection.

[0022] In some embodiments, the charging cut-off voltage of the lithium-ion battery is ≥4.53V. The lithium-ion battery provided by the present invention is applicable to high-voltage systems. The lower limit of the voltage for a high-voltage battery with a charging cut-off voltage of 4.5V or higher is typically 4.53V or higher, preferably 4.55V or higher. The upper limit is not particularly limited, but is typically 6V or lower, preferably 5V or lower, and particularly preferably 4.8V or lower. When the charging cut-off voltage is higher than this lower limit, the energy density improvement effect and cycle characteristics are good.

[0023] In some embodiments, the non-aqueous electrolyte further includes a non-fluorinated carboxylic acid ester, which includes at least one selected from ethyl acetate, ethyl propionate, and propyl propionate. Adding a non-fluorinated carboxylic acid ester to the non-aqueous electrolyte is beneficial for improving its viscosity, increasing lithium-ion transport rate, suppressing material structure breakage caused by uneven lithium intercalation, and improving the battery's high-temperature cycle life.

[0024] In some embodiments, based on the mass of the non-aqueous electrolyte, the mass content of the non-fluorinated carboxylic acid ester is E%, 2≤E≤40. When the mass content E% of the non-fluorinated carboxylic acid ester in the non-aqueous electrolyte is too high, the electrolyte stability is insufficient, interfacial reactions increase, active lithium is consumed, impedance increases, thereby deteriorating the battery's cycle performance. When the mass content E% of the non-fluorinated carboxylic acid ester in the non-aqueous electrolyte is too low, the effect on improving electrolyte viscosity is limited, making it difficult to effectively improve the lithium-ion transport rate, and also unable to fully suppress the material structure damage caused by uneven lithium intercalation, which is also detrimental to improving battery cycle performance. Specifically, the mass content E% of the non-fluorinated carboxylic acid ester in the non-aqueous electrolyte is 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any combination of these values.

[0025] In a preferred embodiment, the mass content (E%) of non-fluorinated carboxylic acid esters in the non-aqueous electrolyte is 5 ≤ ​​E ≤ 25, which is beneficial to further improve the viscosity of the non-aqueous electrolyte, increase the lithium-ion transport rate, suppress material structure breakage caused by uneven lithium intercalation, and improve the high-temperature cycle life of the battery.

[0026] In some embodiments, by controlling the ratio of fluorinated solvents (fluoroethylene carbonate and fluorocarboxylic acid esters) to non-fluorinated carboxylic acid esters to satisfy the relationship 1≤(B+C) / E≤8, it is beneficial to obtain a better solvation structure, promote the formation of inorganic interface films, and improve the high-temperature performance and safety performance of batteries.

[0027] In some embodiments, the non-aqueous electrolyte does not contain ethylene carbonate. Ethylene carbonate is unstable under high temperature and pressure, easily producing byproducts such as ethylene and carbonates, and further reacting with the positive and negative electrodes to generate a large amount of Joule heat, causing safety thermal problems. This invention uses a fluorinated solvent to replace ethylene carbonate, which has the ability to quench free radicals at high temperatures, achieving a flame retardant effect.

[0028] In some embodiments, the compaction density of the positive electrode material layer is 3.9~4.4 g / cm³. 3 By controlling the compaction density of the positive electrode material layer within this range, it can be adapted to the aforementioned non-aqueous electrolyte, reducing stress concentration within the electrode that could lead to particle breakage, ensuring good electrolyte wetting to promote lithium-ion transport, and reducing interfacial impedance growth. Specifically, the compaction density of the positive electrode material layer is 3.9 g / cm³. 3 4.0 g / cm3 4.1 g / cm 3 4.2 g / cm 3 4.3 g / cm 3 4.4 g / cm 3 Or a range consisting of any two of these values.

[0029] In some embodiments, the non-aqueous electrolyte further includes auxiliary additives, which include at least one of sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, and borate compounds.

[0030] In some preferred embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone.

[0031] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate.

[0032] In some preferred embodiments, the phosphate ester compound includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, and tripropyne phosphate.

[0033] In some preferred embodiments, the borate ester compound includes at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0034] In some embodiments, the electrolyte salt is selected from LiPF6, LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAlCl4, LiCF3SO3, Li2B 10 Cl 10 At least one of the following: lower aliphatic lithium carboxylates; and / or, Based on the mass of the non-aqueous electrolyte (100%), the mass percentage content of the electrolyte salt is 5% to 20%. Specifically, the mass percentage content of the electrolyte salt can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any combination thereof. In a preferred embodiment, the mass percentage content of the electrolyte salt is 8% to 18%.

[0035] The lithium-ion battery provided by this invention uses lithium cobalt oxide containing Ti as the positive electrode active material. A compound of structural formula 1 is added as a first additive, and fluoroethylene carbonate and fluorocarboxylic acid ester are added as solvents to a non-aqueous electrolyte. Furthermore, the relationship between the mass content u of Ti, the mass percentage A of the first additive, the mass percentage B of the fluoroethylene carbonate, and the mass percentage C of the fluorocarboxylic acid ester in the positive electrode material layer is defined as 0.3 ≤ When the values ​​are ≤25, 100≤u≤2000, 0.05≤A≤3, 5≤B≤30, and 15≤C≤65, the parameters work synergistically to form an inorganic / organic composite interface film that balances rigidity and flexibility on the cathode surface. The resulting lithium-ion battery exhibits excellent high-temperature cycle performance and safety performance. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0037] Unless otherwise specified, all reagents, materials, and instruments used in the following description are conventional reagents, materials, and instruments, all of which are commercially available. The reagents involved can also be synthesized using conventional synthetic methods. Unless otherwise specified, the methods in the examples are conventional methods in the art. Monomers conforming to this invention are commercially available.

[0038] Example 1 This embodiment provides a method for preparing a lithium-ion battery, including the following steps: 1. Preparation of non-aqueous electrolyte: FEC (fluoroethylene carbonate), ethyl 2,2-difluoroacetate (fluorocarboxylic acid ester), and propyl propionate (non-fluorocarboxylic acid ester) were mixed, and then lithium hexafluorophosphate was added, followed by compound 1 (first additive). The total weight of the non-aqueous electrolyte was 100%, the mass percentage of lithium hexafluorophosphate was 15%, and the contents of FEC, ethyl 2,2-difluoroacetate and the first additive were shown in Table 1. The balance was propyl propionate.

[0039] 2. Preparation of the positive electrode: Lithium cobalt oxide (LCO), conductive carbon black Super-P, and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 97:1.5:1.5. The LCO contains Ti. These materials were then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain the positive electrode slurry. The slurry was uniformly coated onto both sides of an aluminum foil current collector to form a positive electrode material layer. After drying, calendering, and vacuum drying, aluminum leads were welded on using an ultrasonic welder to obtain the positive electrode sheet. Ti was added to the LCO as a dopant. The Ti content in the positive electrode material layer was controlled by adjusting the amount of Ti doping in the LCO. In this embodiment, the Ti content in the positive electrode material layer was 540 ppm. The compaction density of the positive electrode material layer was controlled by adjusting the coating amount and the calendering pressure. In this embodiment, the compaction density of the positive electrode material layer was 4.1 g / cm³. 3 .

[0040] 3. Preparation of the negative electrode: Artificial graphite, conductive carbon black Super-P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95:1:1.5:2.5. These were then dispersed in deionized water to obtain a negative electrode slurry. The slurry was coated onto both sides of a copper foil, dried, calendered, vacuum dried, and finally welded with nickel leads using an ultrasonic welder to obtain the negative electrode sheet.

[0041] 4. Cell fabrication: A separator is placed between the positive and negative electrode plates. Then, the sandwich structure consisting of the positive and negative electrode plates and the separator is wound up. The wound body is flattened and placed in an aluminum foil packaging bag. It is then vacuum baked at 85°C for 48 hours to obtain the battery cell to be injected with electrolyte.

[0042] 5. Electrolyte injection and formation of battery cells: In a glove box where the moisture and oxygen content are controlled below 10 ppm, the non-aqueous electrolyte prepared above is injected into the battery cell, vacuum sealed, and left to stand at 45°C for 48 hours. Then, the first charge is performed according to the following steps: 0.1C constant current charging for 45 minutes, 0.2C constant current charging for 30 minutes, and 0.5C constant current charging for 75 minutes.

[0043] 6. Cell capacity rating: The cell was left to stand at 45°C for 48 hours, then vacuum sealed again to remove the gas generated by the formation, and then charged at a constant current of 0.2C to 4.5V, and then charged at a constant voltage until the current dropped to 0.05C. After resting for 5 minutes, it was discharged at a constant current of 0.2C to 3.0V to obtain a lithium cobalt oxide cathode / graphite lithium-ion battery.

[0044] Examples 2-24 Examples 2-24 illustrate the lithium-ion non-aqueous electrolyte, lithium-ion battery and preparation method disclosed in this invention, including most of the operation steps in Example 1. The difference is that the content of Ti element, fluoroethylene carbonate, fluorocarboxylic acid ester, second additive and non-fluorocarboxylic acid ester in the positive electrode material layer are as shown in Examples 2-24 of Table 1.

[0045] Comparative Examples 1-12 Comparative Examples 1-12 are used to illustrate the lithium-ion non-aqueous electrolyte, lithium-ion battery and preparation method disclosed in this invention. Comparative Examples 1-12 include most of the operation steps in Example 1, the difference being that: the content of Ti element, the content of fluoroethylene carbonate, the content of fluorocarboxylic acid ester, the content of the second additive and the content of non-fluorocarboxylic acid ester in the positive electrode material layer are as shown in Comparative Examples 1-12 in Table 1. The difference between Comparative Example 5 and Example 1 is that ethylene carbonate is used instead of fluoroethylene carbonate, that is, the content of fluoroethylene carbonate in Comparative Example 5 is 0, the content of ethylene carbonate is 20%, and the rest is the same as in Example 1. The difference between Comparative Example 8 and Example 1 is that ethyl acetate is used instead of ethyl 2,2-difluoroacetate. That is, the content of ethyl 2,2-difluoroacetate in Comparative Example 8 is 0, and the content of ethyl acetate is 40%, while the rest is the same as in Example 1.

[0046] Table 1 shows the parameters required for preparing lithium-ion batteries in Examples 1-24 and Comparative Examples 1-12. The differences between Examples 2-24 and Comparative Examples 1-12 and Example 1 lie in the relevant parameters in Table 1, specifically: the Ti content in the cathode material layer, the content of the first additive, the content of fluorinated carboxylic acid esters, the content of non-fluorinated carboxylic acid esters, and the related formulas. The values ​​of B+C, C / B, and (B+C) / E.

[0047] Table 1 Note: "-" in the table indicates that the item does not exist.

[0048] Performance testing: The lithium-ion batteries prepared above were subjected to the following performance tests: 1. High-temperature cycling performance: After capacity testing, the lithium-ion batteries were placed in a 45℃ environment and left to stand for 2 hours. Then, they were charged at a constant current and constant voltage of 1C to 4.53V, with a cutoff current of 0.05C. After resting for 5 minutes, they were discharged at a constant current of 1C to 3V. The initial discharge capacity was recorded as C1, and the initial battery thickness as h1. This 1C / 1C charge-discharge cycle was repeated 500 times, and the discharge capacity on the 500th cycle was recorded as C2, and the battery thickness as h2. Ten lithium-ion batteries were tested in each group, and the average value was taken. The formulas for capacity retention and volume expansion rate are as follows: Capacity retention rate (%) = C2 / C1 × 100%; Volume expansion rate (%) = (h2-h1) / h1×100%.

[0049] 2. 130℃ hot box test: The lithium-ion battery was placed in a constant temperature environment of 25°C and left to stand for 30 minutes. It was then discharged at a constant current of 0.2C to 3V, left to rest for 5 minutes, and charged at a constant current and voltage of 0.2C to 4.53V, with a cutoff current of 0.02C. The battery was then placed in a high-temperature chamber and heated to 130°C at a rate of 5°C ± 2°C / min, and maintained for 30 minutes. The battery status was observed. If the battery opened its valve, caught fire, or exploded, the test was considered a failure. If the battery did not open its valve, catch fire, or explode, the test was considered a success. Ten batteries were tested for each example and comparative example. The pass rate (%) = (number of passes / 10) × 100%.

[0050] Table 2 shows the test results obtained from Examples 1-24 and Comparative Examples 1-12.

[0051] Table 2 As shown in Table 2, the test results indicate that using lithium cobalt oxide containing Ti as the positive electrode active material, adding the compound shown in structural formula 1 as the first additive to the non-aqueous electrolyte, and using fluoroethylene carbonate and fluorocarboxylic acid ester as solvents, and defining the relationship between the mass content u of Ti element, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid ester in the positive electrode material layer, are as follows: Satisfying 0.3≤ When the values ​​are ≤25, 100≤u≤2000, 0.05≤A≤3, 5≤B≤30, and 15≤C≤65, the parameters work synergistically to form an inorganic / organic composite interface film that balances rigidity and flexibility on the cathode surface. The resulting lithium-ion battery exhibits excellent high-temperature cycle performance and safety performance.

[0052] The test results of Example 1 and Comparative Examples 1-12 show that when any one or two of the following parameters in the cathode material layer—the mass content u of Ti, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid ester—do not meet the specified range, or the relationship between them is not met, the following conditions will be met. If the value is too large or too small, an inorganic / organic composite interface film that balances rigidity and flexibility cannot be formed on the positive electrode surface, ultimately resulting in the lithium-ion battery being unable to achieve both excellent high-temperature cycle performance and safety performance.

[0053] When the mass content u of Ti element in the cathode material layer, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid ester are given, and the relationship is... The value further satisfies 0.6≤ When the values ​​of ≤20, 200≤u≤1500, 0.1≤A≤2, 7≤B≤25, and 20≤C≤55 are used, the synergistic improvement effect among the parameters is optimal, thereby better suppressing interfacial side reactions, reducing local reaction heat accumulation, and thus improving the high-temperature cycle and safety performance of the battery.

[0054] When the amounts of fluoroethylene carbonate and fluorocarboxylic acid ester are further satisfied with 35≤B+C≤70 and 1.5≤C / B≤5.5, the stability of the electrolyte can be better improved, the high-temperature cycle performance of the battery can be improved, and the electrolyte can be guaranteed to fully dissolve lithium salt while taking into account appropriate conductivity and viscosity, thus better optimizing the high-temperature cycle and safety performance of the battery.

[0055] When the non-aqueous electrolyte further includes non-fluorinated carboxylic acid esters, and the content of non-fluorinated carboxylic acid esters E and the content of fluorinated solvents (content of fluorinated ethylene carbonate B and content of fluorinated carboxylic acid esters C) satisfy 2≤E≤40 and / or 1≤(B+C) / E≤8, it is beneficial to obtain a better solvation structure, promote the formation of inorganic interface film, and improve the high-temperature performance and safety performance of the battery.

[0056] As can be seen from the test results of Example 1 and Comparative Example 5, when ethylene carbonate is used to replace fluoroethylene carbonate, ethylene carbonate is unstable under high temperature and high pressure, and easily produces byproducts such as ethylene and carbonates. Furthermore, it reacts with the positive and negative electrodes to generate a large amount of Joule heat, causing safety thermal problems and degrading the high temperature performance and safety performance of the battery.

[0057] As can be seen from the test results of Example 1 and Comparative Example 8, when ethyl acetate is used instead of ethyl 2,2-difluoroethyl acetate, ethyl acetate is unstable under high temperature and high pressure, easily decomposes, and further reacts with the positive and negative electrodes to generate a large amount of Joule heat, causing safety thermal problems and degrading the high temperature performance and safety performance of the battery.

[0058] Examples 25-33 Examples 25-33 include most of the operational steps in Example 1, except that: 1. The electrolyte also includes a second additive, 1,3,6-hexanetrionitrile; 2. The mass content of Ti element, the content of fluoroethylene carbonate, the content of fluorocarboxylic acid ester, the content of the second additive, the content of non-fluorocarboxylic acid ester, and the content of the second additive in the cathode material layer are different, as shown in Table 3.

[0059] Comparative Example 13 The difference between Comparative Example 13 and Example 1 is that Comparative Example 13 does not contain the first additive.

[0060] Table 3 shows the parameters required for preparing lithium-ion batteries in Examples 1, 25-33, and Comparative Example 13. The differences between Examples 25-33 and Comparative Example 13 and Example 1 lie in the relevant parameters in Table 3, specifically: the Ti content in the cathode material layer, the content of the first additive, the content of fluorinated carboxylic acid esters, the content of fluorinated carboxylic acid esters, the content of non-fluorinated carboxylic acid esters, and the relevant relationships. The values ​​of B+C, C / B, and (B+C) / E.

[0061] Table 3 Note: "-" in the table indicates that the item does not exist.

[0062] Performance testing The lithium-ion batteries prepared in Examples 1, 25-33 and Comparative Example 13 were tested according to the performance test method of Example 1, and the test results were filled in Table 4.

[0063] Table 4 The test results in Table 4 show the relationship between the mass content u of Ti element, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid ester in the cathode material layer. When the corresponding conditions are met, a second additive is further introduced. When the content D of the second additive satisfies 2≤D≤5 and / or 2.5≤A+D≤6, the nitrile compound can complex with the transition metal ion Co, masking the highly active sites to form a protective layer, effectively preventing direct contact between the electrolyte and the positive electrode material, thereby avoiding the oxidative decomposition of the electrolyte. It also has a synergistic effect with the first additive, improving the stability of the electrode interface, reducing the heat of membrane decomposition reaction, and improving thermal safety performance. This results in a lithium-ion battery that balances superior high-temperature cycle performance and safety performance.

[0064] As can be seen from the test results of Example 1 and Comparative Example 13, if the second additive is directly used to replace the first additive, it is difficult to improve the flexibility of the interface film, the volume expansion rate deteriorates, and it is also difficult to achieve the synergistic effect of the first additive and fluoroethylene carbonate, which seriously affects the thermal safety performance of the battery.

[0065] Examples 34-37 Examples 34-37 include most of the operational steps in Example 25, except that the type of the second additive is different from that in Example 25. Specifically, the type of the second additive is different, as shown in Table 5.

[0066] Performance testing The lithium-ion batteries prepared in Examples 34-37 were tested according to the performance test method of Example 1. The test results obtained in Examples 25 and 34-37 are filled in Table 5.

[0067] Table 5 The test results in Table 5 show the relationship between the mass content u of Ti element, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid ester in the cathode material layer. When the corresponding conditions are met, adding different types of nitrile compounds as second additives can yield lithium-ion batteries that balance superior high-temperature cycle performance and safety performance, demonstrating that the battery system of the present invention is universally applicable to different types of second additives.

[0068] Examples 38-43 Examples 38-43 are used to illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1. The difference is that the type of the first additive is different from that in Example 1, as shown in Table 6.

[0069] Performance testing The lithium-ion batteries prepared in Examples 38-43 were tested according to the performance test method of Example 1. The test results obtained in Examples 1 and 38-43 are filled in Table 6.

[0070] Table 6 The test results in Table 6 show the relationship between the mass content u of Ti element, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid ester in the cathode material layer. When the corresponding conditions are met, adding different types of first additives can yield lithium-ion batteries that balance superior high-temperature cycle performance and safety performance, demonstrating that the battery system of the present invention has universal applicability to different types of first additives.

[0071] Examples 44-47 Examples 44-47 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1. The difference is that the type of fluorocarboxylic acid ester is different from that in Example 1, as shown in Table 7.

[0072] Performance testing The lithium-ion batteries prepared in Examples 44-47 were tested according to the performance test method of Example 1. The test results obtained in Examples 1 and 44-47 are filled in Table 7.

[0073] Table 7 The test results in Table 7 show the relationship between the mass content u of Ti element, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid ester in the cathode material layer. When the corresponding conditions are met, the addition of different types of fluorinated carboxylic acid esters can yield lithium-ion batteries that balance superior high-temperature cycle performance and safety performance, demonstrating that the battery system of the present invention is universally applicable to different types of fluorinated carboxylic acid esters.

[0074] Example 48 Example 48 includes most of the steps in Example 1, except that the type of non-fluorinated carboxylic ester is different from that in Example 1, as shown in Table 8.

[0075] Performance testing The lithium-ion battery prepared in Example 48 was subjected to performance testing according to the performance testing method of Example 1. The test results obtained in Example 1 and Example 48 are filled in Table 8.

[0076] Table 8 The test results in Table 8 show the relationship between the mass content u of Ti element, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid ester in the cathode material layer. When the corresponding conditions are met, adding either propyl propionate or ethyl propionate, a non-fluorinated carboxylic acid ester, can result in a lithium-ion battery that balances superior high-temperature cycle performance and safety performance.

[0077] Examples 49-55 Examples 49-55 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1. The difference is that the compaction density of the positive electrode material layer is different from that in Example 1, as shown in Table 9.

[0078] Performance testing The lithium-ion batteries prepared in the above embodiments were subjected to performance tests according to the performance test method of Example 1. The test results obtained in Examples 1 and 49-55 are filled in Table 9.

[0079] Table 9 The test results in Table 9 show the relationship between the mass content u of Ti element, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid ester in the cathode material layer. When the corresponding conditions are met, the compaction density of the cathode material layer is further limited to 3.9~4.4 g / cm³. 3 When compatible with the aforementioned non-aqueous electrolyte, it reduces stress concentration within the electrode that could lead to particle breakage. Good electrolyte wetting promotes lithium-ion transport and reduces interfacial impedance growth, resulting in a lithium-ion battery that balances high-temperature cycle performance and safety. When the compaction density of the positive electrode material layer is less than 3.9 g / cm³... 3 Increased porosity in the cathode material layer leads to more side reactions, deterioration of cycle performance, and greater volume expansion; when the compaction density of the cathode material layer exceeds 4.4 g / cm³... 3 This results in poor electrolyte wettability and deterioration of cycle performance.

[0080] Examples 56-57 Examples 56-57 include most of the operating steps in Example 1, except that the electrolyte also includes auxiliary additives, as shown in Table 10.

[0081] Performance testing The lithium-ion batteries prepared in the above embodiments were subjected to performance tests according to the performance test method of Example 1. The test results obtained in Examples 1 and 56-57 are filled in Table 10.

[0082] Table 10 Note: "-" in the table indicates that the item is not present; "DTD" in the table represents vinyl sulfate; "PS" represents 1,3-propanesulfonate lactone.

[0083] The test results in Table 10 show the relationship between the mass content u of Ti element, the mass percentage A of the first additive, the mass percentage B of fluoroethylene carbonate, and the mass percentage C of fluorocarboxylic acid ester in the cathode material layer. When the corresponding conditions are met, adding different types of auxiliary additives can yield lithium-ion batteries that balance superior high-temperature cycle performance and safety performance, demonstrating that the battery system of the present invention is universally applicable to different types of auxiliary additives.

[0084] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A lithium-ion battery, characterized in that, Includes positive electrode, negative electrode, membrane, and non-aqueous electrolyte; The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer includes lithium cobalt oxide containing Ti element. Based on the mass of the positive electrode material layer, the mass content of Ti element is u ppm, and 100≤u≤2000. The non-aqueous electrolyte comprises lithium salt, fluoroethylene carbonate, fluorocarboxylic acid ester, and a first additive. Based on the mass of the non-aqueous electrolyte, the mass percentage of the first additive is A%, the mass percentage of the fluoroethylene carbonate is B%, and the mass percentage of the fluorocarboxylic acid ester is C%. The first additive comprises a compound represented by structural formula 1: Structural Formula 1 Where X is selected from or R1 and R2 are each independently selected from H, ,or R1 and R2 are not both selected from H, and X, R1 and R2 contain at least one sulfur atom; The lithium-ion battery satisfies the following condition: 0.3≤ ≤25, and 0.05≤A≤3, 5≤B≤30, 15≤C≤65.

2. The lithium-ion battery as described in claim 1, characterized in that, The lithium-ion battery satisfies the following condition: 0.6≤ ≤20.

3. The lithium-ion battery as described in claim 1, characterized in that, The mass content u ppm of the Ti element satisfies 200 ≤ u ≤ 1500; and / or, The mass percentage A% of the first additive satisfies 0.1 ≤ A ≤ 2; and / or, The mass percentage B% of the fluoroethylene carbonate satisfies 7 ≤ B ≤ 25; and / or, The mass percentage (C%) of the fluorocarboxylic acid ester satisfies 20 ≤ C ≤ 55.

4. The lithium-ion battery as described in claim 1, characterized in that, The fluorocarboxylic acid ester is selected from one or more of ethyl 2,2-difluoroethyl acetate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, 2,2-difluoroethyl propionate, and 2,2,2-trifluoroethyl propionate; and / or, The compound represented by structural formula 1 is selected from one or more of the following compounds: 。 5. The lithium-ion battery as described in claim 1, characterized in that, The fluoroethylene carbonate and fluorocarboxylic acid esters satisfy the following conditions: 35≤B+C≤70, 1.5≤C / B≤5.

5.

6. The lithium-ion battery as described in claim 1, characterized in that, The non-aqueous electrolyte further includes a second additive, which is a nitrile compound. The nitrile compound includes at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, butanetrionitrile, and hexanetrionitrile. Based on the mass of the non-aqueous electrolyte, the mass percentage of the second additive is D%, 2≤D≤5. Preferably, 2.5≤A+D≤6.

7. The lithium-ion battery as described in claim 1, characterized in that, The charging cutoff voltage of the lithium-ion battery is ≥4.53V.

8. The lithium-ion battery as described in claim 1, characterized in that, The non-aqueous electrolyte also includes non-fluorinated carboxylic acid esters, which include at least one of ethyl acetate, ethyl propionate, and propyl propionate. Based on the mass of the non-aqueous electrolyte, the mass content of the non-fluorinated carboxylic acid ester is E%, 2≤E≤40. Preferably, the fluoroethylene carbonate, fluorocarboxylic acid ester, and non-fluorocarboxylic acid ester satisfy the following condition: 1≤(B+C) / E≤8.

9. The lithium-ion battery as described in claim 1, characterized in that, The lithium-ion battery meets the following conditions: The non-aqueous electrolyte does not contain ethylene carbonate; and / or, The compaction density of the positive electrode material layer is 3.9~4.4 g / cm³. 3 .

10. The lithium-ion battery as described in claim 1, characterized in that, The non-aqueous electrolyte further includes auxiliary additives, which include at least one of sulfonyl lactone compounds, cyclic carbonate compounds, phosphate ester compounds, and borate ester compounds; and / or, The sulfonyl lactone compounds include at least one selected from 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone; and / or, The cyclic carbonate compounds include at least one of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; and / or, The phosphate ester compounds include at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, and triargyl phosphate; and / or, The borate esters include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

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