Electrolyte for high-nickel positive electrode, lithium ion battery and electrolyte injection method thereof

Abstract

This application provides an electrolyte for a high-nickel cathode, a lithium-ion battery, and a method for injecting the electrolyte, relating to the field of battery manufacturing technology. The method for injecting the lithium-ion battery employs a first injection process and a second injection process to inject a first electrolyte with a high concentration of lithium salt and a second electrolyte with a lower viscosity. This not only forms a dense CEI layer on the surface of the high-nickel cathode, but also significantly reduces the overall viscosity of the electrolyte by adding low-viscosity linear carbonate through the second injection. This improves the ion mobility of the cell during cycling, thereby improving kinetic performance and effectively alleviating the problem of increased internal resistance caused by the high viscosity resulting from the high concentration of lithium salt.

Description

Technical Field

[0001] This application relates to the field of battery manufacturing technology, and in particular to an electrolyte for a high-nickel cathode, a lithium-ion battery, and a method for electrolyte injection therein. Background Technology

[0002] Using high-nickel layered oxide (Ni>80%) cathodes is an ideal way to improve the energy density of lithium-ion batteries. However, pursuing higher energy density from layered oxides comes at the cost of cathode stability. Gas generation under high charge conditions leading to volume changes and cathode interface reactions can exacerbate electrolyte oxidation, transition metal dissolution, structural rebuilding, and particle breakage, resulting in poorer cycle storage performance of the cell.

[0003] In existing technologies, transition metal complex additives are introduced to mitigate the negative effects of high-nickel cathodes, or high-concentration lithium salt electrolytes are used to improve the internal stability of the cell. However, introducing transition metal complex additives increases the internal resistance of the cell, and using high-concentration lithium salt electrolytes reduces the cell's conductivity, further increasing its internal resistance and thus affecting the battery's kinetic and overall performance.

[0004] Therefore, there is an urgent need to provide an electrolyte for high-nickel cathodes, a lithium-ion battery, and a method for electrolyte injection thereof, which can improve the negative effects of high-nickel cathodes and enhance the cycle storage performance of the cell, while also avoiding the problem of increased internal resistance of the battery, thereby improving the dynamic performance and overall performance of the battery. Summary of the Invention

[0005] This application provides an electrolyte for a high-nickel cathode, a lithium-ion battery, and a method for injecting the electrolyte, in order to solve the problem of increased internal resistance of the battery while the negative effects of the high-nickel cathode are present, thereby improving the dynamic performance and overall performance of the battery.

[0006] In a first aspect, this application provides an electrolyte for a high-nickel cathode, a first electrolyte; the first electrolyte is used in the first electrolyte filling process of a lithium-ion battery, wherein the first electrolyte includes lithium salt, solvent, and film-forming additive, wherein the lithium salt content is 12%-18% of the total amount of the first electrolyte, the solvent content is 77%-83% of the total amount of the first electrolyte, and the film-forming additive content is 1.2%-4% of the total amount of the first electrolyte.

[0007] The above scheme enables the first electrolyte to be used in the initial electrolyte injection process of lithium-ion batteries. This stepwise injection process helps to precisely control the proportion of each component in the electrolyte and optimize its physicochemical properties to meet the application requirements of high-nickel cathode materials in lithium-ion batteries under high energy density, high voltage, and wide temperature range. Specifically, lithium salt accounts for 12%-18% of the total first electrolyte, solvent content is 77%-83%, and film-forming additive content is 1.2%-4%. These formulations and their concentrations, after formation, can generate a dense CEI structure rich in inorganic matter, effectively preventing negative impacts such as dissolution of the cathode transition metal and structural damage during battery operation. Simultaneously, it can form a stable SEI (solid electrolyte interface), achieving the effect of protecting the high-nickel cathode material and improving battery performance.

[0008] In one possible design, the lithium salt is lithium bis(fluorosulfonyl)imide or lithium hexafluorophosphate; the solvent consists of propylene carbonate, ethylene carbonate and ethyl methyl carbonate; and the film-forming additive consists of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate and lithium difluorooxalate borate.

[0009] Through the above-described scheme, lithium bisfluorosulfonyl imide (LiFSI) exhibits high thermal and electrochemical stability. LiFSI can form a stable SEI film, which is beneficial for improving battery cycle performance. At high concentrations, LiFSI can provide more lithium ions, contributing to improved rate performance and low-temperature performance. High-concentration LiFSI electrolyte can form a LiF-rich solid electrolyte interface, thereby improving the compatibility of the positive and negative electrode interfaces. Lithium hexafluorophosphate (LiPF6) exhibits good ionic conductivity and chemical stability.

[0010] Propylene carbonate (PC) possesses a high dielectric constant and a low melting point (-49°C), which enables it to provide excellent ion migration and low-temperature performance when used as a solvent in electrolytes. Ethylene carbonate (EC) has a high dielectric constant, which is beneficial for improving the ionic conductivity of the electrolyte. Ethyl methyl carbonate (EMC) exhibits good overall performance, including low viscosity and good electrochemical stability, which helps to improve the charge-discharge efficiency and cycle life of batteries.

[0011] Vinylene carbonate (VC) is an electrochemically reducing additive with a higher reduction potential than the organic solvents in the electrolyte. It preferentially undergoes electrochemical reduction on the electrode surface, forming a high-performance SEI film. Fluoroethylene carbonate (FEC) can form a LiF-rich SEI film in the battery, improving cycle performance and safety. 1,3-Propanesulfonate lactone (PS), as a film-forming additive, can improve the battery's room-temperature cycle performance. Vinyl sulfate (DTD) significantly improves high-temperature cycle performance, thus enhancing its effectiveness. LiDFOB has high solubility and conductivity, forming a passivation film on the Al foil surface and inhibiting electrolyte oxidation.

[0012] In one possible design, the lithium salt concentration is 2M-6M; in the solvent: the content of propylene carbonate is 2%-5% of the total amount of the first electrolyte, the content of ethylene carbonate is 22%-28% of the total amount of the first electrolyte, and the content of methyl ethyl carbonate is 67%-73% of the total amount of the first electrolyte; in the film-forming additives: the content of vinylene carbonate is 0.2%-0.5% of the total amount of the first electrolyte, the content of fluoroethylene carbonate is 0.5%-1% of the total amount of the first electrolyte, the content of 1,3-propanesulfonyl lactone is 0.8%-1.5% of the total amount of the first electrolyte, the content of vinyl sulfate is 1%-2% of the total amount of the first electrolyte, and the content of lithium difluorooxalate borate is 0.3%-0.6% of the total amount of the first electrolyte.

[0013] The above method achieves a lithium salt concentration of 2M-6M, which provides good electrolyte performance. Higher lithium salt concentrations increase the lithium-ion content of the electrolyte, thereby improving the battery's rate performance and low-temperature performance. Simultaneously, high-concentration electrolytes help form a stable SEI film, enhancing the battery's cycle stability and safety.

[0014] Using a solvent composed of PC, EC, and EMC, with PC content of 2%-5%, can better alleviate the problem of electrolyte decomposition at high temperatures. EC content of 22%-28% and EMC content of 67%-73% can balance the characteristics of different solvents to optimize the overall performance of the electrolyte, including ionic conductivity, low-temperature performance, and electrochemical stability, thereby improving the performance and safety of lithium-ion batteries.

[0015] With a VC content of 0.2%–0.5%, FEC content of 0.5%–1%, PS content of 0.8%–1.5%, and DTD content of 1%–2%, this combination of film-forming additives optimizes SEI film formation and improves the electrochemical performance of the battery through different mechanisms and functions. VC and FEC form the SEI film through electrochemical reduction, PS and DTD improve the stability of the SEI film through chemical reaction, while LiDFOB improves the cycle performance and safety of the battery by forming a LiF-rich SEI film. The content ratio of these additives is designed according to their role and effect in the battery. By adjusting the ratio of each additive, the defects caused by excessive content of any one additive are avoided, thereby ensuring the optimal performance of the battery under different conditions. Especially in lithium-ion batteries with high-nickel cathode materials, these additives help improve the kinetic and overall performance of the battery.

[0016] In one possible design, the first electrolyte also includes a wetting additive, the content of which is 0.3%-1% of the total amount of the first electrolyte.

[0017] Through the above methods, wetting additives can reduce the surface tension of the electrolyte, improve its wetting and penetration capabilities on the electrodes, thereby enhancing the electrochemical performance of the battery. Adding wetting agents can effectively shorten the battery electrolyte filling time and significantly improve the battery's cycle performance. However, when the wetting agent content reaches 1%, it will negatively impact cycle performance. Therefore, controlling the wetting additive content within the range of 0.3%-1% can ensure battery performance while avoiding potential problems caused by excessive addition.

[0018] In one possible design, the wetting additive is fluorobenzene.

[0019] Through the above-described scheme, fluorobenzene, as a wetting additive, can optimize the contact between the electrolyte and electrode materials, thereby improving the battery's kinetic performance. It can improve the wettability of the electrolyte on the electrode materials, thus enhancing the battery's charge-discharge performance and cycle stability. The introduction of fluorobenzene not only solves the problem of lithium-ion and PC co-intercalation in graphite but also improves the physicochemical properties of the electrolyte, exhibiting excellent compatibility with both graphite and NCM811.

[0020] Secondly, this application provides an electrolyte for a high-nickel cathode, including a second electrolyte, which is a linear carbonate solvent, and the second electrolyte is used in the second electrolyte injection process of a lithium-ion battery.

[0021] The above-described solution, by providing a second electrolyte in the second electrolyte injection process, replenishes the electrolyte inside the battery, restoring its original conductivity and electrochemical performance. Linear carbonate solvents possess low viscosity and good electrochemical stability, contributing to improved ionic conductivity of the electrolyte and low-temperature performance of the battery. In particular, the use of linear carbonate solvents in the second electrolyte injection process ensures that high-nickel cathode materials meet the stability and compatibility requirements for operation at high voltages. This allows lithium-ion batteries with high-nickel cathode materials to meet the application requirements of high energy density, high voltage, and wide temperature ranges, further optimizing the electrolyte environment and improving the battery's kinetic and low-temperature performance, thereby enhancing the overall battery performance.

[0022] In one possible design, the linear carbonate solvent is diethyl carbonate or methyl ethyl carbonate.

[0023] Through the above examples, diethyl carbonate (DEC), as a linear carbonate solvent, exhibits low viscosity and good electrochemical stability. The lower viscosity of DEC contributes to improving the ionic conductivity of the electrolyte and the low-temperature performance of the battery. Ethyl methyl carbonate (EMC), as a linear carbonate solvent, is used in combination with cyclic carbonates to improve the physicochemical properties of the electrolyte. EMC provides good electrolyte stability and electrochemical performance, while also contributing to improved battery charge-discharge efficiency and cycle life.

[0024] In one possible design, when the linear carbonate solvent is diethyl carbonate and methyl ethyl carbonate, the ratio of methyl ethyl carbonate to diethyl carbonate is 1:1.

[0025] Through the above scheme, EMC, due to its lower viscosity, helps to improve the ionic conductivity of the electrolyte, while DEC helps to improve the high-temperature performance of the electrolyte. Since high-nickel cathode material batteries have high requirements for electrolyte stability and compatibility when operating at high voltages, a 1:1 ratio of DEC to EMC allows the high-nickel cathode material to maintain the overall performance of the electrolyte while also improving its thermal stability to a certain extent, reducing the occurrence of transesterification reactions. By balancing the characteristics of different solvents to optimize the overall performance of the electrolyte, the overall performance of the battery can be improved, including cycle stability, charge / discharge efficiency, and safety.

[0026] Thirdly, this application provides a method for injecting electrolyte into a lithium-ion battery. The method includes the following steps: forming a pouch cell and drying the pouch cell; performing a first electrolyte injection process, which includes injecting a first electrolyte into the pouch cell, sealing, allowing it to stand, and forming it to form a first cell, wherein the first electrolyte is any of the aforementioned first electrolytes; and performing a second electrolyte injection process, which includes injecting a second electrolyte into the first cell and performing a second sealing to obtain a lithium-ion battery, wherein the second electrolyte is any of the aforementioned second electrolytes.

[0027] The above scheme requires drying the pouch cells before electrolyte injection to ensure the battery is free of moisture and prevent performance degradation. Considering the characteristics of high-nickel cathode materials, a first electrolyte is used for the initial electrolyte injection of the pouch cells. This first electrolyte comprises lithium salt, solvent, and film-forming additives, with lithium salt content at 12%-18%, solvent content at 77%-83%, and film-forming additive content at 1.2%-4%. After injection, the cells undergo sealing, settling, formation, and aging processes to form the first cell. A second electrolyte is then used for the second electrolyte injection of the first cell. The second electrolyte is a linear carbonate solvent, used for secondary sealing and capacity testing, ultimately yielding a lithium-ion battery. The first electrolyte injection primarily forms stable SEI and CEI films, improving the battery's cycle stability and safety. The second electrolyte injection further optimizes the electrolyte environment by injecting a lower-viscosity linear carbonate solvent, improving the battery's kinetic and low-temperature performance. By precisely controlling the proportions of each component in the electrolyte, the battery's electrochemical stability, cycle life, and safety can be effectively managed.

[0028] In one possible design, the injection coefficient is 3g / Ah-4g / Ah, and the ratio of the first injection to the second injection is 82-88 to 12-18.

[0029] With the above scheme, the electrolyte injection coefficient is 3g / Ah-4g / Ah, meaning that 3 grams of electrolyte are injected per ampere-hour (Ah) of battery capacity. A suitable electrolyte injection coefficient optimizes the battery's internal resistance, cycle life, and safety performance. The ratio of the first to second electrolyte injection is 82-88:12-18, meaning that the first injection accounts for approximately 82% to 88% of the total electrolyte volume, while the second injection accounts for approximately 12% to 18%. This stepwise electrolyte injection process allows for more precise control of the electrolyte environment inside the battery, optimizing battery performance. For example, the first injection may focus more on forming stable SEI and CEI films, while the second injection may focus more on replenishing the electrolyte to further improve the battery's high-temperature performance and cycle stability. This injection method optimizes battery performance at different stages to improve overall battery performance and reliability.

[0030] Fourthly, this application provides a lithium-ion battery, including a lithium-ion battery obtained by any of the above-mentioned liquid injection methods.

[0031] The beneficial effects of the lithium-ion battery provided in the fourth aspect and the various possible designs of the fourth aspect can be found in the beneficial effects of the third aspect and the various possible implementations of the third aspect, and will not be repeated here.

[0032] The above description is merely an overview of the technical solutions of the embodiments of this application. In order to better understand the technical means of the embodiments of this application and to implement them in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the embodiments of this application more obvious and understandable, specific implementation methods of this application are described below. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is a flowchart of a method for injecting electrolyte into a lithium-ion battery according to one embodiment of this application. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims and drawings of this application are intended to cover non-exclusive inclusion.

[0037] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of the phrase "embodiment" in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0038] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists, A and B exist simultaneously, or B exists. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0039] The terms "first," "second," etc., in the specification, claims, or the accompanying drawings of this application are used to distinguish different objects, rather than to describe a specific order, and may explicitly or implicitly include one or more of the features.

[0040] In the description of this application, unless otherwise stated, "multiple" means two or more (including two), and similarly, "multiple groups" means two or more (including two groups).

[0041] It is known that increased internal resistance of the battery cell is detrimental to dynamic performance, mainly referring to the fact that increased internal resistance reduces the battery's charging and discharging efficiency and power output capability. Specifically, increased internal resistance leads to the following problems.

[0042] Increased internal resistance leads to more Joule heat being generated when current flows through the battery, causing the battery temperature to rise. This increased temperature not only affects battery performance but can also impact battery safety and lifespan.

[0043] Increased internal resistance leads to a greater voltage drop during battery discharge, thereby reducing the battery's actual operating voltage and affecting its output power and discharge time.

[0044] Increased internal resistance means that during charging and discharging, the resistance encountered by the current flowing through the battery increases, which leads to reduced charging and discharging efficiency and a decrease in the battery's usable capacity.

[0045] The kinetic performance of a battery refers to its performance under high-rate charge and discharge conditions. Increased internal resistance leads to increased polarization during high-rate charge and discharge, thereby reducing the battery's kinetic performance.

[0046] The ionic conductivity of the electrolyte determines the battery's internal resistance and rate capability. The electrolyte conductivity is inversely proportional to the solvent viscosity and is also affected by the lithium salt concentration and anion size. Decreased ionic conductivity means a reduced migration ability of lithium ions in the electrolyte, leading to an increase in the battery's internal resistance.

[0047] A decrease in electrolyte ionic conductivity increases the difficulty of lithium-ion desolvation, leading to increased charge transfer impedance and hindering the formation of the negative electrode graphite SEI film.

[0048] A decrease in electrolyte ionic conductivity can affect the battery's charge and discharge efficiency and power output capability. Especially at low temperatures, the increased viscosity and decreased conductivity of the electrolyte are detrimental to lithium ion transport, further increasing the battery's internal resistance.

[0049] Therefore, a decrease in electrolyte ionic conductivity directly leads to an increase in battery internal resistance, thereby affecting the battery's kinetic and overall performance. Optimizing the electrolyte ionic conductivity is thus a key factor in improving battery performance. In related technologies, introducing transition metal complex additives increases the cell's internal resistance, and using high-concentration lithium salt electrolytes reduces cell conductivity, further increasing internal resistance and impacting the battery's kinetic and overall performance.

[0050] In view of this, embodiments of this application provide an electrolyte for a high-nickel cathode, a lithium-ion battery, and a method for injecting the electrolyte. In the method, a high-concentration lithium salt electrolyte composed of a first electrolyte and a second electrolyte is injected using a two-stage injection method. This not only forms a dense CEI layer on the surface of the high-nickel cathode, but also significantly reduces the overall viscosity of the electrolyte by adding low-viscosity linear carbonate during the second injection. This improves the ion mobility of the cell during cycling, thereby improving the kinetic performance and effectively alleviating the problem of increased battery internal resistance caused by the high viscosity due to the high concentration of lithium salt.

[0051] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below.

[0052] Example 1

[0053] This embodiment provides an electrolyte for a high-nickel cathode, a first electrolyte; the first electrolyte is used in the first electrolyte filling process of a lithium-ion battery, wherein the first electrolyte includes lithium salt, solvent, and film-forming additive, wherein the lithium salt content is 12%-18% of the total amount of the first electrolyte, the solvent content is 77%-83% of the total amount of the first electrolyte, and the film-forming additive content is 1.2%-4% of the total amount of the first electrolyte.

[0054] The above scheme enables the first electrolyte to be used in the initial electrolyte injection process of lithium-ion batteries. This stepwise injection process helps to precisely control the proportion of each component in the electrolyte and optimize its physicochemical properties to meet the application requirements of high-nickel cathode materials in lithium-ion batteries under high energy density, high voltage, and wide temperature range. Specifically, lithium salt accounts for 12%-18% of the total first electrolyte, solvent content is 77%-83%, and film-forming additive content is 1.2%-4%. These formulations and their concentrations, after formation, can generate a dense CEI structure rich in inorganic matter, effectively preventing negative impacts such as dissolution of the cathode transition metal and structural damage during battery operation. Simultaneously, it can form a stable SEI (solid electrolyte interface), achieving the effect of protecting the high-nickel cathode material and improving battery performance.

[0055] In this embodiment, the lithium salt is lithium difluorosulfonylimide or lithium hexafluorophosphate; the solvent is composed of propylene carbonate, ethylene carbonate and ethyl methyl carbonate; the film-forming additive is composed of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonyl lactone, ethylene sulfate and lithium difluorooxalate borate.

[0056] Through the above-described scheme, lithium bisfluorosulfonyl imide (LiFSI) exhibits high thermal and electrochemical stability. LiFSI can form a stable SEI film, which is beneficial for improving battery cycle performance. At high concentrations, LiFSI can provide more lithium ions, contributing to improved rate performance and low-temperature performance. High-concentration LiFSI electrolyte can form a LiF-rich solid electrolyte interface, thereby improving the compatibility of the positive and negative electrode interfaces. Lithium hexafluorophosphate (LiPF6) exhibits good ionic conductivity and chemical stability.

[0057] Propylene carbonate (PC) possesses a high dielectric constant and a low melting point (-49°C), which enables it to provide excellent ion migration and low-temperature performance when used as a solvent in electrolytes. Ethylene carbonate (EC) has a high dielectric constant, which is beneficial for improving the ionic conductivity of the electrolyte. Ethyl methyl carbonate (EMC) exhibits good overall performance, including low viscosity and good electrochemical stability, which helps to improve the charge-discharge efficiency and cycle life of batteries.

[0058] Vinylene carbonate (VC) is an electrochemically reducing additive with a higher reduction potential than the organic solvents in the electrolyte. It preferentially undergoes electrochemical reduction on the electrode surface, forming a high-performance SEI film. Fluoroethylene carbonate (FEC) can form a LiF-rich SEI film in the battery, improving cycle performance and safety. 1,3-Propanesulfonate lactone (PS), as a film-forming additive, can improve the battery's room-temperature cycle performance. Vinyl sulfate (DTD) significantly improves high-temperature cycle performance, thus enhancing its effectiveness. LiDFOB has high solubility and conductivity, forming a passivation film on the Al foil surface and inhibiting electrolyte oxidation.

[0059] In this embodiment, the concentration of lithium salt is 2M-6M. For example, the concentration of lithium salt can be 2M, 3.5M, 4M, 5M or 6M.

[0060] In this embodiment, the solvent contains: propylene carbonate at 2%-5% of the total amount of the first electrolyte, ethylene carbonate at 22%-28% of the total amount of the first electrolyte, and methyl ethyl carbonate at 67%-73% of the total amount of the first electrolyte; the film-forming additive contains: vinylene carbonate at 0.2%-0.5% of the total amount of the first electrolyte, fluoroethylene carbonate at 0.5%-1% of the total amount of the first electrolyte, 1,3-propanesulfonyl lactone at 0.8%-1.5% of the total amount of the first electrolyte, vinyl sulfate at 1%-2% of the total amount of the first electrolyte, and lithium difluorooxalate borate at 0.3%-0.6% of the total amount of the first electrolyte.

[0061] For example, the content of propylene carbonate can be 2%, 3%, 4%, or 5% of the total amount of the first electrolyte. The content of ethylene carbonate can be 23%, 24%, 25%, 27%, or 28% of the total amount of the first electrolyte. The content of methyl ethyl carbonate can be 67%, 68%, 69%, 70%, 71%, 72%, or 73% of the total amount of the first electrolyte.

[0062] For example, in the film-forming additives: the content of vinylene carbonate can be 0.2%, 0.3%, 0.4%, or 0.5% of the total amount of the first electrolyte; the content of fluoroethylene carbonate can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1% of the total amount of the first electrolyte; the content of 1,3-propanesulfonyl lactone can be 0.8%, 0.9%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5% of the total amount of the first electrolyte; the content of vinyl sulfate can be 1%, 1.2%, 1.3%, 1.5%, or 2% of the total amount of the first electrolyte; and the content of lithium difluorooxalate borate can be 0.3%, 0.4%, 0.5%, or 0.6% of the total amount of the first electrolyte.

[0063] The above method achieves a lithium salt concentration of 2M-6M, which provides good electrolyte performance. Higher lithium salt concentrations increase the lithium-ion content of the electrolyte, thereby improving the battery's rate performance and low-temperature performance. Simultaneously, high-concentration electrolytes help form a stable SEI film, enhancing the battery's cycle stability and safety.

[0064] Using a solvent composed of PC, EC, and EMC, with PC content of 2%-5%, can better alleviate the problem of electrolyte decomposition at high temperatures. EC content of 22%-28% and EMC content of 67%-73% can balance the characteristics of different solvents to optimize the overall performance of the electrolyte, including ionic conductivity, low-temperature performance, and electrochemical stability, thereby improving the performance and safety of lithium-ion batteries.

[0065] For example, the PC content can be 2%, 3%, 4%, or 5%.

[0066] For example, EC can be 22%, 23%, 25%, 26%, or 28%.

[0067] For example, EMC can be 67%, 68%, 69%, 70%, or 71% or 73%.

[0068] With a VC content of 0.2%–0.5%, FEC content of 0.5%–1%, PS content of 0.8%–1.5%, and DTD content of 1%–2%, this combination of film-forming additives optimizes SEI film formation and improves the electrochemical performance of the battery through different mechanisms and functions. VC and FEC form the SEI film through electrochemical reduction, PS and DTD improve the stability of the SEI film through chemical reaction, while LiDFOB improves the cycle performance and safety of the battery by forming a LiF-rich SEI film.

[0069] For example, the vitamin C content can be 0.2%, 0.3%, 0.4%, or 0.5%.

[0070] For example, the PS content can be 0.8%, 0.9%, 1.0%, 1.2%, 1.4%, or 1.5%.

[0071] For example, the DTD content can be 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%.

[0072] The proportions of these additives are designed based on their roles and effects in the battery. By adjusting their proportions, the defects caused by an excessive amount of one additive are avoided, thereby ensuring the optimal performance of the battery under different conditions. In particular, in lithium-ion batteries with high-nickel cathode materials, these additives help improve the battery's dynamic performance and overall performance.

[0073] In this embodiment, the first electrolyte also includes a wetting additive, the content of which is 0.3%-1% of the total amount of the first electrolyte.

[0074] For example, the content of the wetting additive can be 0.3%, 0.5%, 0.7%, 0.8% or 1% of the total amount of the first electrolyte.

[0075] Through the above methods, wetting additives can reduce the surface tension of the electrolyte, improve its wetting and penetration capabilities on the electrodes, thereby enhancing the electrochemical performance of the battery. Adding wetting agents can effectively shorten the battery electrolyte filling time and significantly improve the battery's cycle performance. However, when the wetting agent content reaches 1%, it will negatively impact cycle performance. Therefore, controlling the wetting additive content within the range of 0.3%-1% can ensure battery performance while avoiding potential problems caused by excessive addition.

[0076] Based on the above embodiments, this embodiment also provides an electrolyte for a high-nickel cathode, including a second electrolyte, which is a linear carbonate solvent, and the second electrolyte is used in the second electrolyte injection process of a lithium-ion battery.

[0077] The above-described solution, by providing a second electrolyte in the second electrolyte injection process, replenishes the electrolyte inside the battery, restoring its original conductivity and electrochemical performance. Linear carbonate solvents possess low viscosity and good electrochemical stability, contributing to improved ionic conductivity of the electrolyte and low-temperature performance of the battery. In particular, the use of linear carbonate solvents in the second electrolyte injection process ensures that high-nickel cathode materials meet the stability and compatibility requirements for operation at high voltages. This allows lithium-ion batteries with high-nickel cathode materials to meet the application requirements of high energy density, high voltage, and wide temperature ranges, further optimizing the electrolyte environment and improving the battery's kinetic and low-temperature performance, thereby enhancing the overall battery performance.

[0078] In this embodiment, the linear carbonate solvent is diethyl carbonate or methyl ethyl carbonate.

[0079] Through the above examples, diethyl carbonate (DEC), as a linear carbonate solvent, exhibits low viscosity and good electrochemical stability. The lower viscosity of DEC contributes to improving the ionic conductivity of the electrolyte and the low-temperature performance of the battery. Ethyl methyl carbonate (EMC), as a linear carbonate solvent, is used in combination with cyclic carbonates to improve the physicochemical properties of the electrolyte. EMC provides good electrolyte stability and electrochemical performance, while also contributing to improved battery charge-discharge efficiency and cycle life.

[0080] Based on the first electrolyte and the second electrolyte provided in the above embodiments, this embodiment also provides a method for injecting electrolyte into a lithium-ion battery, the method comprising:

[0081] Step 1: Form a pouch cell and dry the pouch cell.

[0082] The steps involved in forming a pouch cell include:

[0083] First, NCM811 (composed of nickel, cobalt and manganese in a ratio of 8:1:1) is used as the main positive electrode material. It is mixed with conductive agent and binder, and homogenized with NMP to obtain positive electrode slurry. The positive electrode slurry is coated on aluminum foil and then dried, rolled, slit and die-cut to obtain positive electrode sheet.

[0084] Then, graphite is used as the main negative electrode material and mixed with conductive agent, binder and dispersant respectively. The mixture is homogenized with deionized water to obtain negative electrode slurry. The negative electrode slurry is coated on carbon-coated copper foil and then dried, rolled, slit and die-cut to obtain negative electrode sheet.

[0085] Finally, a microporous polypropylene membrane is used as the separator, and the positive electrode, negative electrode and separator are processed through stacking-hot pressing-baking-liquid injection-high temperature standing-formation-aging-capacity grading-OCV process to form a lithium-ion battery.

[0086] Step 2, perform the first electrolyte injection process, which includes injecting the first electrolyte into the soft-pack battery cell, sealing, standing, and forming to form the first battery cell; wherein, the first electrolyte is any of the first electrolytes mentioned above.

[0087] Step 3, perform a second electrolyte injection process, which includes injecting a second electrolyte into the first cell and performing a second sealing to obtain a lithium-ion battery, wherein the second electrolyte is any of the second electrolytes mentioned above.

[0088] The above approach requires drying the pouch cells before electrolyte injection to ensure the battery is free of moisture and prevent performance degradation. Considering the characteristics of high-nickel cathode materials, a first electrolyte is used for the initial electrolyte injection process. This first injection primarily forms stable SEI and CEI films, improving the battery's cycle stability and safety. A second electrolyte is then used for the second electrolyte injection process, further optimizing the electrolyte environment. Injecting a low-viscosity linear carbonate solvent during the second injection improves the battery's kinetic and low-temperature performance. By precisely controlling the proportions of each component in the electrolyte, the battery's electrochemical stability, cycle life, and safety can be effectively managed.

[0089] In one possible design, the injection coefficient is 3g / Ah-4g / Ah, and the ratio of the first injection to the second injection is 82-88 to 12-18.

[0090] With the above scheme, the electrolyte injection ratio is 3g / Ah-4g / Ah, which means that 3 to 4 grams of electrolyte are needed to fill each ampere-hour (Ah) of battery capacity. A suitable electrolyte injection ratio optimizes the battery's internal resistance, cycle life, and safety performance. The ratio of the first to the second electrolyte injection is 82-88 to 12-18. This ratio means that the first injection accounts for approximately 82% to 88% of the total electrolyte volume, while the second injection accounts for approximately 12% to 18%.

[0091] For example, the electrolyte injected in the first injection may account for 82%, 83%, 84%, 85%, 86%, 87%, or 88% of the total electrolyte volume, while the electrolyte injected in the second injection may account for approximately 12%, 13%, 14%, 15%, 16%, or 18% of the total electrolyte volume.

[0092] This stepwise electrolyte injection process allows for more precise control of the electrolyte environment inside the battery, optimizing battery performance. For example, the first injection may focus on forming stable SEI and CEI films, while the second injection may focus on replenishing the electrolyte to further improve the battery's high-temperature performance and cycle stability. By using this injection method, battery performance can be specifically optimized at different stages to improve the overall performance and reliability of the battery.

[0093] Based on the above embodiments, this application also provides a lithium-ion battery, including a lithium-ion battery obtained by any of the above-described liquid injection methods. Since the liquid injection method and its effects have been described in detail in the preceding embodiments, this application will not repeat them here.

[0094] Example 2

[0095] Based on the above embodiments, this embodiment provides a lithium-ion battery, obtained through the following liquid injection method:

[0096] To manufacture a 5Ah soft-pack battery cell, the electrolyte is injected at a ratio of 3g / Ah.

[0097] The first electrolyte injection process is carried out, which includes injecting the first electrolyte into the soft-pack battery cell to obtain the first battery cell;

[0098] A second electrolyte injection process is performed, which includes injecting a second electrolyte into the first cell and then sealing it a second time to obtain a lithium-ion battery.

[0099] In this embodiment, the ratio of the first electrolyte in the first injection process to the second electrolyte in the second injection process is 85:15.

[0100] In this embodiment, the electrolyte used for the high-nickel cathode includes a first electrolyte, which includes lithium salt, solvent, film-forming additive, and wetting additive.

[0101] The lithium salt used is 3MLiFSi, the solvent is PC:EC:EMC = 5:25:70, the film-forming additives are 0.3% VC, 0.6% FEC, 1% PS, 1.5% DTD, and 0.6% LiODFB, and the wetting additive is 0.5% fluorobenzene FB.

[0102] In this embodiment, the electrolyte used for the high-nickel cathode also includes a second electrolyte, which includes DEC and EMC, and the ratio of DEC to EMC is 1:1.

[0103] The obtained lithium-ion batteries were subjected to electrochemical tests, and the test results are shown in Table 1.

[0104] Example 3

[0105] In the lithium-ion battery provided in this embodiment, the lithium salt of the first electrolyte in the first electrolyte injection process is 2M LiFSi. That is, the difference between this embodiment and Embodiment 2 is that the lithium salt of the first electrolyte in the first electrolyte injection process in Embodiment 2 is 3M LiFSi, while the lithium salt of the first electrolyte in the first electrolyte injection process in Embodiment 3 is 2M LiFSi. All other aspects are the same as in Embodiment 1.

[0106] The obtained lithium-ion batteries were subjected to electrochemical tests, and the test results are shown in Table 1.

[0107] Example 4

[0108] In the lithium-ion battery provided in this embodiment, the lithium salt used in the first electrolyte during the first electrolyte injection process is 5M LiFSi. That is, the difference between this embodiment and Embodiment 2 is that in Embodiment 2, the lithium salt used in the first electrolyte during the first electrolyte injection process is 3M LiFSi, while in Embodiment 4, the lithium salt used in the first electrolyte during the first electrolyte injection process is 5M LiFSi. All other aspects are the same as in Embodiment 2.

[0109] The obtained lithium-ion batteries were subjected to electrochemical tests, and the test results are shown in Table 1.

[0110] Example 5

[0111] In the lithium-ion battery provided in this embodiment, the lithium salt of the first electrolyte in the first electrolyte injection process is 3M LiPF6. That is, the difference between this embodiment and embodiment 2 is that the lithium salt of the first electrolyte in the first electrolyte injection process in embodiment 2 is 3M LiFSi, while the lithium salt of the first electrolyte in embodiment 5 is 3M LiPF6. All other aspects are the same as in embodiment 2.

[0112] The obtained lithium-ion batteries were subjected to electrochemical tests, and the test results are shown in Table 1.

[0113] Example 6

[0114] In the lithium-ion battery provided in this embodiment, the lithium salt used in the first electrolyte of the first electrolyte injection process is 1.5M LiPF6 and 1.5M LiFSi. That is, the difference between Example 6 and Example 2 is that the lithium salt used in the first electrolyte of Example 2 in the first electrolyte injection process is 3M LiFSi, while the lithium salt used in the first electrolyte of Example 6 is 1.5M LiPF6 and 1.5M LiFSi. All other aspects are the same as in Example 2.

[0115] The obtained lithium-ion batteries were subjected to electrochemical tests, and the test results are shown in Table 1.

[0116] Example 7

[0117] In the lithium-ion battery provided in this embodiment, the solvent for the first electrolyte in the first electrolyte injection process is EC:EMC = 30:70. That is, the difference between Example 7 and Example 2 is that the solvent for the first electrolyte in the first electrolyte injection process in Example 2 is PC:EC:EMC = 5:25:70, while the solvent for the first electrolyte in Example 7 is EC:EMC = 30:70. All other aspects are the same as in Example 2.

[0118] The obtained lithium-ion batteries were subjected to electrochemical tests, and the test results are shown in Table 1.

[0119] Example 8

[0120] The lithium-ion battery provided in this embodiment does not include a wetting additive in the first electrolyte during the first electrolyte injection process. That is, the difference between Example 8 and Example 2 is that 0.5% FB is used as a wetting additive in the first electrolyte injection process of Example 2, while the first electrolyte in Example 8 does not include a wetting additive; all other aspects are the same as in Example 2.

[0121] The obtained lithium-ion batteries were subjected to electrochemical tests, and the test results are shown in Table 1.

[0122] Comparative Example 1

[0123] The lithium-ion battery provided in Comparative Example 1 uses the same electrolyte injection method as that in Example 2, including the lithium salt and its concentration, solvent ratio, and types and amounts of additives. The only difference is that the comparative example only uses the first electrolyte injection process to obtain the lithium-ion battery. The specific electrolyte injection method of Comparative Example 1 is as follows:

[0124] A method for injecting electrolyte into a lithium-ion battery is provided, comprising:

[0125] To manufacture a 5Ah soft-pack battery cell, the electrolyte is injected at a ratio of 3g / Ah.

[0126] The first electrolyte injection process involves injecting a first electrolyte and a second electrolyte into a pouch cell to obtain a lithium-ion battery.

[0127] The obtained lithium-ion batteries were subjected to electrochemical tests, and the test results are shown in Table 1.

[0128] Performance testing:

[0129] Specific capacity utilization (mAh / g): This refers to the ratio of the electrical capacity that the active materials inside a battery can release to their mass, and is commonly used to measure the performance of battery materials. In lithium-ion batteries, this typically involves the specific capacity utilization of the positive and negative electrode materials, i.e., how much electrical energy (mAh / g) can be released or stored per gram of material.

[0130] In this test, the battery cell was charged and discharged at a rate of 0.33C before testing, and the specific capacity of the battery cell was calculated based on the discharge capacity and the mass of the active material.

[0131] Capacity retention rate after 500 cycles at 45℃ (1C / 1C): This refers to the capacity retention rate of the battery cell after 500 cycles of charging and discharging at a rate of 1C at 45℃.

[0132] 60℃ Storage Retention Rate (60D): The ratio of a fully charged battery cell stored in a 60℃ constant temperature chamber for 60 days and then discharged to its initial capacity is calculated.

[0133] 55℃ Storage Volume Expansion (60D): Fully charged cells are placed in a 55℃ constant temperature chamber for 60 days. The volume expansion rate of the cells after storage is calculated by the water displacement method, thereby evaluating the gas production performance of the battery.

[0134] The lithium-ion batteries obtained in Examples 2, 3, 4, 5, 6, 7, 8 and Comparative Example 1 were tested for the above performance indicators, and the results are shown in Table 1.

[0135] Table 1:

[0136]

[0137] As can be seen from Table 1:

[0138] A comparison of the results from Examples 2 to 8 and Comparative Example 1 shows that the lithium-ion battery obtained using the liquid injection method provided in this application outperforms conventional lithium-ion batteries in terms of standard capacity utilization, 500-cycle capacity retention, storage retention, and storage volume expansion performance. The secondary liquid injection method effectively improves the cell's cycle and storage performance and suppresses gas generation.

[0139] The comparison results of Examples 2, 3 and 4 show that the effect of choosing 3MLiFSi as the lithium salt is better than that of 2MLiFSi and 5MLiFSi. This is because the concentration of lithium salt that is too high or too low will affect the lithium ion content of the electrolyte, thereby affecting the cycle stability and safety of the battery.

[0140] The comparison results of Examples 2 and 5 and 6 show that the effect of choosing MLiFSi as the lithium salt may be better than LiPF6 or a combination of MLiFSi and LiPF6.

[0141] The comparison results of Examples 2 and 7 show that replacing EC with PC can alleviate electrolyte decomposition at high temperatures. Specifically, the PC content in the solvent is ≤5%, which can improve the battery's cycle stability, storage retention rate, and gas generation suppression.

[0142] The comparison results of Examples 2 and 8 show that the introduction of fluorobenzene not only improves the wetting of the electrode by the electrolyte, but also alleviates the co-intercalation problem of Li+-PC on graphite, which can make the battery cycle stability, storage retention rate and gas generation suppression better.

[0143] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An electrolyte for high-nickel cathodes, characterized in that, include: First electrolyte; The first electrolyte is used in the first electrolyte filling process of a lithium-ion battery. The first electrolyte comprises lithium salt, solvent, and film-forming additives. The lithium salt content is 12%-18% of the total first electrolyte, the solvent content is 77%-83% of the total first electrolyte, and the film-forming additive content is 1.2%-4% of the total first electrolyte. The solvent is composed of propylene carbonate, ethylene carbonate, and ethyl methyl carbonate. Specifically, the propylene carbonate content is 2%-5% of the total first electrolyte, the ethylene carbonate content is 22%-28% of the total first electrolyte, and the ethyl methyl carbonate content is 67%-73% of the total first electrolyte. It also includes a second electrolyte, which is a linear carbonate solvent. The second electrolyte is used in the second electrolyte filling process of the lithium-ion battery, wherein the linear carbonate solvent is diethyl carbonate and / or methyl ethyl carbonate.

2. The electrolyte according to claim 1, characterized in that, The lithium salt is lithium bis(fluorosulfonyl)imide or lithium hexafluorophosphate; The film-forming additive is composed of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, and lithium difluorooxalate borate.

3. The electrolyte according to claim 2, characterized in that, The concentration of the lithium salt is 2M-6M; The film-forming additive contains: vinylene carbonate at a content of 0.2% to 0.5% of the total amount of the first electrolyte, fluoroethylene carbonate at a content of 0.5% to 1% of the total amount of the first electrolyte, and 1,3 The content of propane sulfonate lactone is 0.8% to 1.5% of the total amount of the first electrolyte, the content of vinyl sulfate is 1% to 2% of the total amount of the first electrolyte, and the content of lithium difluorooxalate borate is 0.3% to 0.6% of the total amount of the first electrolyte.

4. The electrolyte according to claim 1, characterized in that, The first electrolyte also includes a wetting additive, the content of which is 0.3%-1% of the total amount of the first electrolyte.

5. The electrolyte according to claim 4, characterized in that, The wetting additive is fluorobenzene.

6. The electrolyte according to claim 1, characterized in that, When the linear carbonate solvent is diethyl carbonate and methyl ethyl carbonate, the ratio of diethyl carbonate to methyl ethyl carbonate is 1:

1.

7. A method for injecting electrolyte into a lithium-ion battery, characterized in that, The method includes the following steps: A soft-pack battery cell is formed, and the soft-pack battery cell is dried. The first electrolyte injection process includes injecting a first electrolyte into the soft-pack battery cell, sealing, settling, and forming to form a first battery cell, wherein the first electrolyte is the first electrolyte as described in any one of claims 1-6. A second electrolyte injection process is performed, which includes injecting a second electrolyte into the first cell and performing a second sealing to obtain a lithium-ion battery, wherein the second electrolyte is the second electrolyte as described in any one of claims 1-6.

8. The injection method according to claim 7, characterized in that, The electrolyte injection coefficient is 3g / Ah-4g / Ah, and the ratio of the total amount of the first electrolyte in the first injection process to the total amount of the second electrolyte in the second injection process is 82-88 to 12-18.

9. A lithium-ion battery, characterized in that, Lithium-ion batteries including those obtained by the liquid injection method according to claim 7 or 8.

Images