Lithium-ion electrolyte additive, lithium-ion electrolyte and preparation method thereof, lithium battery and electrical equipment

Abstract

The application provides a lithium ion electrolyte additive, a lithium ion electrolyte and a preparation method thereof, a lithium battery and an electrical equipment, and relates to the field of lithium batteries. The lithium ion electrolyte additive is 5-trifluoromethylpyridine-2-lithium trimethylborate. The preparation method comprises the following steps: mixing 2-hydroxy-5-trifluoromethylpyridine, lithium bis(trimethylsilyl)amide and a first organic solvent, and stirring and reacting to obtain 5-trifluoromethylpyridine-2-lithium hydroxide; and dropping trimethyl borate into a second organic solvent containing 5-trifluoromethylpyridine-2-lithium hydroxide, and reacting to obtain 5-trifluoromethylpyridine-2-lithium trimethylborate. The additive has a low oxidation potential, can form an effective CEI film before LNMO deintercalates lithium ions, thereby inhibiting the decomposition of the electrolyte in the subsequent reaction, reducing the generation of harmful substances HF, and further protecting the structure of the material.

Description

Technical Field

[0001] This application relates to the field of lithium batteries, and more particularly to a lithium-ion electrolyte additive, a lithium-ion electrolyte and its preparation method, a lithium battery and electrical equipment. Background Technology

[0002] Lithium-ion batteries boast the highest energy density per unit volume of rechargeable batteries to date, and after more than 20 years of development, they have been widely used as power sources for portable electronic devices. However, several issues remain to be addressed for lithium-ion batteries used in automotive applications, such as specific energy density, lifespan, cost, and safety. Numerous targeted studies have been conducted to meet these requirements, including nanomaterials for improved rate performance, gel polymer electrolytes and solid electrolytes for enhanced safety, and organic lithium-intercalation materials for recyclable battery materials. In these studies, energy and power density are primary considerations. Improving specific energy density is essential for the development of lighter and smaller batteries, and is also an effective measure to reduce battery production costs. Conversely, increasing power density is fundamental to the evolution of lithium-ion batteries from mobile power sources to dedicated power sources.

[0003] 5V high-voltage cathode materials are a general term for cathode materials whose charge-discharge platform is in the 5V region. Using 5V cathode materials can simultaneously improve the operating voltage of a single battery cell, as well as its power and energy density. Spinel-structured LiNi... 0.5 Mn 1.5 O4 (LNMO) materials originate from Ni doping of LiMn2O4, due to their low cost (inexpensive raw materials and simple synthesis conditions) and 3D lithium-ion migration channels (high Li... + (migration rate), 147.6 mAh g -1 With its theoretical capacity and high potential plateau (high energy density) of 4.7V, it is considered a highly promising cathode material for power lithium-ion batteries. However, the oxidative stability of the LiPF6 / carbonate electrolyte system mainly depends on the composition of the solvent system in the electrolyte, while the electrochemical stability of binary or multi-component organic carbonate solvent mixtures is around 4.5V (vs. Li / Li). + The following is a brief overview. To improve the oxidative stability of electrolytes, researchers initially attempted to partially replace organic carbonate solvents with organic solvent molecules possessing high oxidative stability to form new electrolyte systems. However, due to limitations such as high viscosity, low conductivity, inability to form an SEI film at the graphite electrode interface, and high cost, research and application remain at the basic research level. Compared to using sulfones, organic nitriles, and fluorinated organic solvents to replace carbonate solvent molecules to form new electrolyte systems, the method of using functional additive molecules to form a controllable and highly stable interfacial film is clearly more feasible and effective.

[0004] Boron-based additives have attracted widespread attention due to their excellent oxidation properties, good film-forming ability, and inhibition of electrolyte decomposition. Synthesizing multifunctional boron-containing electrolyte additives to significantly improve the performance of high-voltage LNMO cathode materials is a feasible method, and also provides a new approach for the targeted synthesis of additives that meet specific requirements. Summary of the Invention

[0005] The purpose of this application is to provide a lithium-ion electrolyte additive, a lithium-ion electrolyte and its preparation method, a lithium battery and electrical equipment to solve the above-mentioned problems.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] A lithium-ion electrolyte additive, wherein the lithium-ion electrolyte additive is lithium 5-trifluoromethylpyridine-2-trimethylborate.

[0008] This application also provides a method for preparing the lithium-ion electrolyte additive, comprising:

[0009] 2-hydroxy-5-trifluoromethylpyridine, bis(trimethylsilyl)aminolithium and a first organic solvent were mixed and stirred to obtain 5-trifluoromethylpyridine-2-hydroxylithium;

[0010] Trimethyl borate was added dropwise to a second organic solvent containing the 5-trifluoromethylpyridine-2-hydroxylithium to obtain the 5-trifluoromethylpyridine-2-trimethylborate lithium.

[0011] Preferably, the first organic solvent and the second organic solvent comprise diethyl ether.

[0012] This application also provides a lithium-ion electrolyte, comprising the aforementioned lithium-ion electrolyte additive, a conductive lithium salt, and a third organic solvent.

[0013] Preferably, the third organic solvent comprises cyclic carbonates and / or linear carbonates;

[0014] Preferably, the cyclic carbonate includes ethylene carbonate, and the linear carbonate includes at least one of methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0015] Preferably, the conductive lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium difluorooxalate borate, lithium hexafluoroarsenate, and lithium difluorophosphate.

[0016] Preferably, the concentration of the conductive lithium salt in the lithium-ion electrolyte is 0.6 mol / L to 2 mol / L.

[0017] Preferably, the content of lithium 5-trifluoromethylpyridine-2-trimethylborate in the lithium-ion electrolyte is 0.1g / 100ml-0.3g / 100ml.

[0018] This application also provides a method for preparing the lithium-ion electrolyte, comprising:

[0019] The lithium-ion electrolyte additive, the conductive lithium salt, and the third organic solvent are mixed;

[0020] Preferably, the third organic solvent is purified and dehydrated before use;

[0021] Preferably, the purification, impurity removal, and dehydration treatment is carried out using at least one of molecular sieves, calcium hydride, activated carbon, lithium hydride, anhydrous calcium oxide, calcium chloride, phosphorus pentoxide, alkali metals, or alkaline earth metals.

[0022] This application also provides a lithium battery, including a positive electrode, a negative electrode, a separator, and the lithium-ion electrolyte;

[0023] Preferably, the positive electrode material used in the positive electrode includes lithium oxide, the negative electrode material used in the negative electrode includes metallic lithium or graphite, and the separator includes either a polyethylene separator or a polypropylene separator.

[0024] Preferably, the cathode material is an LNMO cathode material.

[0025] This application also provides an electrical device, including the aforementioned lithium battery.

[0026] Compared with the prior art, the beneficial effects of this application include:

[0027] The lithium-ion electrolyte additive provided in this application uses lithium 5-trifluoromethylpyridine-2-trimethylborate as a film-forming additive for the lithium-ion cathode material LNMO. Because this additive has a low oxidation potential, it can form an effective CEI film before lithium ion insertion / extraction in LNMO, thereby inhibiting electrolyte decomposition in subsequent reactions, reducing the generation of harmful HF, and thus protecting the material's structure. It belongs to the category of additives used to improve the interface film of 5V-level LNMO cathode materials.

[0028] The method for preparing lithium-ion electrolyte additives provided in this application involves a two-step reaction with stirring at room temperature to synthesize a novel lithium-ion electrolyte additive, lithium 5-trifluoromethylpyridine-2-trimethylborate, with a yield of over 70% and a purity of over 95%.

[0029] The lithium-ion electrolyte provided in this application contains the aforementioned lithium-ion electrolyte additives, conductive lithium salts, and a third organic solvent, which can effectively achieve the above-mentioned effects.

[0030] The method for preparing the lithium-ion electrolyte provided in this application is simple to operate.

[0031] The lithium battery and electrical equipment provided in this application have excellent electrical performance. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0033] Figure 1 For LTFMP 1 Results of H NMR testing;

[0034] Figure 2 For LTFMP 13 Results of C NMR testing;

[0035] Figure 3 For LTFMP 11 Results of B NMR testing;

[0036] Figure 4 The cycling results of the LNMO / Li half-cell in Comparative Example 1 and Example 3 are shown in the graph.

[0037] Figure 5 The efficiency graphs of LNMO / Li half-cells during cycling in Comparative Example 1 and Example 3 are shown.

[0038] Figure 6 The graph shows the change in cycle capacity of the LNMO / Li half-cell as a function of the number of cycles in Comparative Example 1.

[0039] Figure 7 The graph shows the change in cycle capacity of the LNMO / Li half-cell as a function of the number of cycles in Example 3.

[0040] Figure 8 The first cycle comparison diagram of the LNMO / Li half-cell in Comparative Example 1 and Example 3;

[0041] Figure 9 The second comparison diagram of the cyclic voltammetry test of LNMO / Li half-cell in Comparative Example 1 and Example 3;

[0042] Figure 10 A comparison graph showing the linear scan test of the LNMO cathode half-cell in Comparative Example 1 and Example 3;

[0043] Figure 11 The HOMO and LUMO plots are obtained from DFT theoretical calculations;

[0044] Figure 12 The image shows a comparison of TEM tests performed on the LNMO cathode after 200 cycles in Comparative Example 1 and Example 3, without cycling.

[0045] Figure 13 The image shows a comparison of SEM results of LNMO cathodes after 200 cycles in Comparative Example 1 and Example 3, without cycling.

[0046] Figure 14 XPS test comparison chart of LNMO cathode after 200 cycles in Comparative Example 1 and Example 3;

[0047] Figure 15 Comparison graphs of linear scan tests performed on graphite anodes in Comparative Example 1 and Example 3;

[0048] Figure 16 The graph shows the cycling results of the Graphite / Li half-cell in Comparative Example 1 and Example 3;

[0049] Figure 17 The graph shows the cycling results of the LNMO / Graphite full cell in Comparative Example 1 and Example 3;

[0050] Figure 18 The efficiency graphs for LNMO / Graphite full cells in Comparative Example 1 and Example 3 are shown. Detailed Implementation

[0051] As used in this article:

[0052] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0053] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0054] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0055] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0056] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0057] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0058] A lithium-ion electrolyte additive, wherein the lithium battery electrolyte additive is lithium 5-trifluoromethylpyridine-2-trimethylborate.

[0059] This application also provides a method for preparing the lithium-ion electrolyte additive, comprising:

[0060] 2-hydroxy-5-trifluoromethylpyridine, bis(trimethylsilyl)aminolithium and a first organic solvent were mixed and stirred to obtain 5-trifluoromethylpyridine-2-hydroxylithium;

[0061] Trimethyl borate was added dropwise to a second organic solvent containing the 5-trifluoromethylpyridine-2-hydroxylithium to obtain the 5-trifluoromethylpyridine-2-trimethylborate lithium.

[0062] The reaction equation is shown below:

[0063]

[0064] In an optional embodiment, the first organic solvent and the second organic solvent comprise diethyl ether.

[0065] This application also provides a lithium-ion electrolyte, comprising the aforementioned lithium-ion electrolyte additive, a conductive lithium salt, and a third organic solvent.

[0066] The lithium-ion electrolyte, except for containing a conductive lithium salt, can have the same composition as conventionally known lithium-ion electrolytes. That is, conventionally known lithium-ion battery electrolytes can be used. This lithium-ion electrolyte is formed by dissolving a lithium-ion electrolyte in an organic solvent.

[0067] The organic solvent is not particularly limited to any organic solvent commonly used in lithium-ion battery electrolytes, such as carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, xolane compounds, etc. In particular, suitable solvents include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, vinylene carbonate, and mixtures thereof. Among these examples, the use of one or more organic solvents selected from carbonates and ethers, in particular, results in excellent electrolyte solubility, dielectric constant, and viscosity, and high battery charge / discharge efficiency, and is therefore preferred.

[0068] In an optional embodiment, the third organic solvent comprises cyclic carbonates and / or linear carbonates;

[0069] In an optional embodiment, the cyclic carbonate includes ethylene carbonate, and the linear carbonate includes at least one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0070] In some embodiments, the organic solvent may be selected as a cyclic carbonate solvent ethylene carbonate (EC) and a linear carbonate solvent ethyl methyl carbonate (EMC) or diethyl carbonate (DEC) in a mass ratio of (0.5 to 1.5):(0.5 to 1.5); more preferably, it may be 3:5:2.

[0071] In an optional embodiment, the conductive lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium difluorooxalate borate, lithium hexafluoroarsenate, and lithium difluorophosphate.

[0072] In one optional embodiment, the concentration of the conductive lithium salt in the lithium-ion battery electrolyte is 0.6 mol / L to 2 mol / L.

[0073] Optionally, the concentration of the conductive lithium salt in the lithium-ion battery electrolyte can be any value between 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, or 0.6 mol / L-2 mol / L.

[0074] In an optional embodiment, the content of lithium 5-trifluoromethylpyridine-2-trimethylborate in the lithium-ion battery electrolyte is 0.1g / 100ml-0.3g / 100ml.

[0075] Optionally, the content of lithium 5-trifluoromethylpyridine-2-trimethylborate in the lithium-ion battery electrolyte can be any value between 0.1g / 100ml, 0.2g / 100ml, 0.3g / 100ml, or 0.1g / 100ml-0.3g / 100ml.

[0076] This application also provides a method for preparing the lithium-ion electrolyte, comprising:

[0077] The lithium-ion electrolyte additive, the conductive lithium salt, and the third organic solvent are mixed;

[0078] In an optional embodiment, the third organic solvent is purified to remove impurities and water before use;

[0079] In an optional embodiment, the purification and dehydration treatment is carried out using at least one of molecular sieves, calcium hydride, activated carbon, lithium hydride, anhydrous calcium oxide, calcium chloride, phosphorus pentoxide, alkali metals, or alkaline earth metals.

[0080] In some embodiments, the molecular sieve is type, type or type.

[0081] This application also provides a lithium battery, including a positive electrode, a negative electrode, a separator, and the lithium-ion electrolyte;

[0082] In an optional embodiment, the positive electrode material used in the positive electrode includes lithium oxide, the negative electrode material used in the negative electrode includes metallic lithium or graphite, and the separator includes either a polyethylene separator or a polypropylene separator.

[0083] As a positive electrode active material, it can contain various lithium-containing oxides, such as: Li 1-x MnO2, Li1-x Mn2O4, Li 1- x CoO2, Li 1-x NiO2, LiV2O3 and their derivatives, and stable free radical compounds. It should be noted that 'x' in these positive electrode active materials represents a number from 0 to 1. As the conductive material for the positive electrode, graphite microparticles, acetylene black, Ketjen black, carbon nanofibers, and amorphous carbon microparticles such as needle coke can be used, but are not limited to these.

[0084] The positive electrode can be made by suspending a positive electrode mixture containing positive electrode active material, conductive agent and binder in a suitable solvent and mixing it, coating the slurry-forming material on one or both sides of the current collector and drying it.

[0085] Examples of adhesives include, but are not limited to, PVDF, ethylene-propylene-diene copolymer (EPDM), SBR, acrylonitrile-butadiene rubber (NBR), and fluororubber.

[0086] As a solvent for dispersing positive electrode active materials, organic solvents commonly used to dissolve binders can be used. Examples include: NMP, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc., but not limited to these. In addition, sometimes dispersants, thickeners, etc. are added to water, and the active material is slurried using PTFE or the like.

[0087] In one optional embodiment, the cathode material is an LNMO cathode material.

[0088] By comparing cathode materials such as NCM811, NCM622, LCO, and LNMO, numerous experiments have demonstrated that, with the addition of additives in the same mass ratio, LNMO cathode material exhibits the best electrochemical performance.

[0089] The lithium battery provided in this application is not subject to any special shape restrictions and can be used as a battery of various shapes such as coin-shaped, cylindrical, and triangular.

[0090] This application also provides an electrical device, including the aforementioned lithium battery.

[0091] It should be noted that the electrical equipment referred to in this application does not simply refer to equipment that has the aforementioned lithium battery installed on it, such as electric vehicles, electric bicycles, power banks, and other electronic devices (such as mobile phones, tablets, and electronic watches), but also includes equipment that is not loaded on the device body but is powered by lithium batteries, or equipment that stores energy through lithium batteries, such as energy storage battery packs or energy storage power stations.

[0092] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0093] Example 1

[0094] This embodiment provides a lithium-ion electrolyte additive, which is lithium 5-trifluoromethylpyridine-2-trimethylborate.

[0095] Its preparation method is as follows:

[0096] A solution of 2-hydroxy-5-trifluoromethylpyridine and lithium bis(trimethylsilyl)aminoamino was mixed at a molar ratio of 1:1 and added to 25 mL of diethyl ether. The mixture was stirred for 24 h, filtered, and the intermediate product was washed three times with diethyl ether and dried to obtain 5-trifluoromethylpyridine-2-hydroxylithium. The dried 5-trifluoromethylpyridine-2-hydroxylithium was then added to 25 mL of diethyl ether, and the same molar amount of trimethyl borate was slowly added dropwise. The mixture was stirred for 12 h to obtain the target product, 5-trifluoromethylpyridine-2-trimethylborate, which was then filtered, washed, and dried.

[0097] The final product, lithium 5-trifluoromethylpyridine-2-trimethylborate, was added to an appropriate amount of deuterated dimethyl sulfoxide, dissolved, and then tested. 1 H NMR, 13 C NMR, 11 B NMR is used to analyze the purity of the product and calculate the yield.

[0098] The results are as follows Figure 1 , Figure 2 , Figure 3 As shown. The yield of the final target product is over 70%, and its color is pure white. This was determined through NMR analysis. 1 In the 1H NMR spectrum, the most prominent feature is the H characteristic peak of the target product, indicating that the purity of the product is above 95%. 13 C and 11 The characteristic peak of B also confirms that the final product does not contain impurities.

[0099] Example 2

[0100] This embodiment provides a lithium-ion electrolyte, the preparation method of which is as follows:

[0101] (1) The cyclic carbonate solvent ethylene carbonate (EC) and the linear carbonate solvents ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC = 3:5:2, and purified by molecular sieve, calcium hydride and lithium hydride to remove impurities and water (moisture <10ppm).

[0102] (2) At room temperature, the conductive lithium salt LiPF6 is dissolved in the solvent obtained in step (1), the final concentration of the conductive lithium salt is 1.0 mol / L, stirred evenly, and allowed to stand to obtain a common electrolyte.

[0103] (3) Add lithium 5-trifluoromethylpyridine-2-trimethylborate to the ordinary electrolyte prepared in step (2) at a dosage of 0.1 wt.% of the ordinary electrolyte to obtain the final electrolyte.

[0104] Example 3

[0105] This embodiment provides a lithium-ion electrolyte, the preparation method of which is as follows:

[0106] (1) The cyclic carbonate solvent ethylene carbonate (EC) and the linear carbonate solvents ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC = 3:5:2, and purified by molecular sieve, calcium hydride and lithium hydride to remove impurities and water (moisture <10ppm).

[0107] (2) At room temperature, the conductive lithium salt LiPF6 is dissolved in the solvent obtained in step (1), the final concentration of the conductive lithium salt is 1.0 mol / L, stirred evenly, and allowed to stand to obtain a common electrolyte.

[0108] (3) Add lithium 5-trifluoromethylpyridine-2-trimethylborate to the ordinary electrolyte prepared in step (2) at a dosage of 0.2 wt.% of the ordinary electrolyte to obtain the final electrolyte.

[0109] Example 4

[0110] This embodiment provides a lithium-ion electrolyte, the preparation method of which is as follows:

[0111] (1) The cyclic carbonate solvent ethylene carbonate (EC) and the linear carbonate solvents ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC = 3:5:2, and purified by molecular sieve, calcium hydride and lithium hydride to remove impurities and water (moisture <10ppm).

[0112] (2) At room temperature, the conductive lithium salt LiPF6 is dissolved in the solvent obtained in step (1), the final concentration of the conductive lithium salt is 1.0 mol / L, stirred evenly, and allowed to stand to obtain a common electrolyte.

[0113] (3) Add lithium 5-trifluoromethylpyridine-2-trimethylborate to the ordinary electrolyte prepared in step (2) at a dosage of 0.3 wt.% of the ordinary electrolyte to obtain the final electrolyte.

[0114] Comparative Example 1

[0115] The ordinary electrolyte obtained in Example 3 was used as a control.

[0116] Preparation of positive electrode: LiNi 0.5 Mn 1.5 O4 (LNMO), polytetrafluoroethylene adhesive (PVDF), and conductive agent acetylene black were dissolved in an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1. The slurry was evenly coated onto the current collector aluminum foil, dried in an oven at 80°C for 1 hour, and then transferred to a vacuum dryer at 120°C for 12 hours to make electrode sheets with a diameter of 12 mm for later use.

[0117] Preparation of negative electrode sheet: Graphite, polytetrafluoroethylene adhesive (PVDF) and conductive agent acetylene black are dissolved in an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1. The slurry is evenly coated on the current collector aluminum foil, dried in an oven at 80℃ for 1 hour, and then transferred to a vacuum dryer at 120℃ for 12 hours to make electrode sheets with a diameter of 12 mm for later use.

[0118] The prepared positive and negative electrode sheets were assembled with the electrolytes of Example 3 and Comparative Example 1, respectively (using Celgard 2400 separators), to obtain Li / LNMO half-cells. Cyclic tests were performed, and the results are as follows: Figure 4 , Figure 5 , Figure 6 and Figure 7 As shown.

[0119] from Figure 4 As can be seen from the data, after 150 cycles, the LNMO half-cell cyclicated in the ordinary electrolyte of Comparative Example 1 exhibits significant capacity decay, with the capacity retention rate after 200 cycles being only 32.5% of the initial value. In contrast, the cycling performance of the LNMO half-cell in the electrolyte of Example 3 clearly demonstrates that the electrolyte of Example 3 significantly improves the cycling stability of the LNMO / Li half-cell. Comparison of efficiency graphs shows that the battery cyclicated in the electrolyte of Example 3 exhibits better lithium-ion intercalation / deintercalation reversibility, indicating that the electrolyte of Example 3 can effectively suppress side reactions, thereby reducing polarization and maintaining capacity performance.

[0120] Figure 8 , Figure 9 , Figure 10 and Figure 11The results of CV and LSV tests for the LNMO / Li half-cell in the electrolytes of Comparative Example 1 and Example 3 are shown. The CV comparison in the first round clearly shows that the activated half-cell in the electrolyte of Example 3 exhibits a significant oxidation current at 4.0 V, indicating that the electrolyte of Example 3 can oxidize earlier. The same result is confirmed in the LSV comparison chart. The results calculated using DFT theory also demonstrate that the product obtained in Example 1 has the highest HOMO energy and is more easily oxidized and decomposed compared to the three components in the ordinary electrolyte of Comparative Example 1.

[0121] Figure 12 , Figure 13 , Figure 14 The figures show the TEM, SEM, and XPS analysis results of the LNMO cathode material after cycling in the ordinary electrolyte and the final electrolyte of the LNMO / Li half-cell. After 200 cycles, the LNMO electrode surface in the ordinary electrolyte of Comparative Example 1 was covered with a large amount of decomposition products, forming an uneven interfacial film with a thickness between 17.4 and 68.4 nm. In contrast, the LNMO electrode after cycling in the electrolyte of Example 3 had an appearance close to the fresh surface morphology, and the interfacial film was uniform and thin. This indicates that the CEI film obtained by preferential decomposition of the electrolyte in Example 3 has the effect of inhibiting electrolyte decomposition, thereby improving the cycle stability of the battery. XPS comparative analysis revealed that the ordinary electrolyte in Comparative Example 1 had a large number of EC / DEC / EMC decomposition products on its surface, such as CO (C1s, 284.8 eV; O 1s, 532.0 eV) and C=O (C 1s, 289.1 eV; O 1s, 533.6 eV), while the electrolyte in Example 3 contained characteristic peaks of BF, BO, and N, indicating that the products in Example 1 were effective components for constructing the interfacial film.

[0122] Figure 15 , Figure 16 , Figure 17 and Figure 18 The LSV and cycling plots for Li / Graphite, and the cycling and efficiency plots for LNMO / Graphite, show that the electrolyte in Example 3 also preferentially reduces the electrolyte and significantly improves the cycling stability of the negative electrode. After 300 cycles, the capacity retention of the full cell increased from 28.6% to 57.6%.

[0123] Comparative Example 2

[0124] Existing boron-based additives, such as LiBOB, retain only 50.8% of their capacity in LNMO / Graphite full cells after 75 cycles, while LTFMP additives retain 57.6% of their capacity after 300 cycles. TMSB exhibits slightly better cycling performance in LNMO / Li half cells than LTFMP, but it does not significantly improve the performance of the graphite anode or the overall battery life. Lithium difluorooxalate borate generates a large amount of CO2 gas during full battery cycling, affecting subsequent capacity retention and safety performance. Existing boron-based additives, such as LiBOB, retain only 50.8% of their capacity in LNMO / Graphite full cells after 75 cycles, while LTFMP additives retain 57.6% of their capacity after 300 cycles. TMSB exhibits slightly better cycling performance in LNMO / Li half cells than LTFMP, but it does not significantly improve the performance of the graphite anode or the overall battery life. Lithium difluorooxalate borate generates a large amount of CO2 gas during full battery cycling, affecting subsequent capacity retention and safety performance.

[0125] Finally, it should be noted that 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 or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0126] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A lithium-ion electrolyte additive for lithium batteries with LNMO as the cathode material, characterized in that, The lithium-ion electrolyte additive is lithium 5-trifluoromethylpyridine-2-trimethylborate; The structural formula of the lithium 5-trifluoromethylpyridine-2-trimethylborate is as follows: .

2. A method for preparing a lithium-ion electrolyte additive for a lithium battery with LNMO as the cathode material, as described in claim 1, characterized in that, include: 2-hydroxy-5-trifluoromethylpyridine, bis(trimethylsilyl)aminolithium and a first organic solvent were mixed and stirred to obtain 5-trifluoromethylpyridine-2-hydroxylithium; Trimethyl borate was added dropwise to a second organic solvent containing lithium 5-trifluoromethylpyridine-2-hydroxyl, and the reaction was stirred to obtain lithium 5-trifluoromethylpyridine-2-trimethylborate. The first organic solvent and the second organic solvent include diethyl ether.

3. A lithium-ion electrolyte for a lithium battery with LNMO as the cathode material, characterized in that, Includes the lithium-ion electrolyte additive, conductive lithium salt, and third organic solvent for lithium batteries with LNMO cathode material as described in claim 1; The third organic solvent includes cyclic carbonates and / or linear carbonates.

4. The lithium-ion electrolyte for a lithium battery with LNMO as the positive electrode material according to claim 3, characterized in that, The cyclic carbonates include ethylene carbonate, and the linear carbonates include at least one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

5. The lithium-ion electrolyte for a lithium battery with LNMO as the positive electrode material according to claim 3, characterized in that, The conductive lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium difluorooxalate borate, lithium hexafluoroarsenate, and lithium difluorophosphate.

6. The lithium-ion electrolyte for a lithium battery with LNMO as the positive electrode material according to claim 3, characterized in that, The concentration of the conductive lithium salt in the lithium-ion electrolyte is 0.6 mol / L-2 mol / L.

7. The lithium-ion electrolyte for a lithium battery with LNMO as the positive electrode material according to any one of claims 3-6, characterized in that, The content of lithium 5-trifluoromethylpyridine-2-trimethylborate in the lithium-ion electrolyte is 0.1g / 100ml - 0.3g / 100ml.

8. A method for preparing a lithium-ion electrolyte for a lithium battery with LNMO as the cathode material, as described in any one of claims 3-7, characterized in that, include: The lithium-ion electrolyte additive for lithium batteries with LNMO cathode material, the conductive lithium salt, and the third organic solvent are mixed.

9. The method for preparing a lithium-ion electrolyte for a lithium battery with LNMO as the cathode material according to claim 8, characterized in that, The third organic solvent is purified to remove impurities and water before use.

10. The method for preparing a lithium-ion electrolyte for a lithium battery with LNMO as the cathode material according to claim 9, characterized in that, The purification, impurity removal, and dehydration treatment is carried out using at least one of molecular sieves, calcium hydride, activated carbon, lithium hydride, anhydrous calcium oxide, calcium chloride, phosphorus pentoxide, alkali metals, or alkaline earth metals.

11. A lithium battery with LNMO as the cathode material, characterized in that, Includes a positive electrode, a negative electrode, a separator, and a lithium-ion electrolyte as described in any one of claims 3-7 for a lithium battery with LNMO as the positive electrode material.

12. The lithium battery with LNMO as the cathode material according to claim 11, characterized in that, The negative electrode material used includes lithium metal or graphite, and the separator includes either a polyethylene separator or a polypropylene separator.

13. An electrical-related device, characterized in that, Lithium batteries including those with LNMO as the cathode material as described in claim 11 or 12.

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