electrolyte

Abstract

The present invention belongs to the technical field of batteries. Provided is an electrolyte. A lithium-replenishing material is introduced into the electrolyte, and the composition of anions in the components of the electrolyte is also regulated and controlled. The lithium-replenishing material has high solubility and high stability. When applied to a secondary battery, the electrolyte can achieve efficient lithium replenishment and can also reduce the impedance of a CEI in the battery, thereby improving the overall electrochemical performance.

Description

An electrolyte

[0001] This application claims priority to Chinese Patent Application No. 202411939301.0, filed on December 26, 2024, entitled “An Electrolyte”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, specifically to an electrolyte. Background Technology

[0003] Lithium-ion battery replenishment technology refers to introducing lithium-containing compounds into the battery, in addition to the positive electrode active material, to release active lithium. This compensates for the active lithium consumed by the positive electrode active material during the formation of the SEI film, thereby reducing irreversible capacity loss and improving battery cycle performance. Currently, the main lithium replenishment technologies are positive electrode replenishment and negative electrode replenishment, which involve placing the replenishing material on the positive or negative electrode sheet. However, this technology requires consideration of the uniformity and safety of the replenishing material placement during electrode production, increasing manufacturing costs and making subsequent recycling of the electrode active material more difficult.

[0004] Electrolyte-based lithium replenishment technology involves dissolving lithium replenishment materials in an electrolyte, allowing lithium to be replenished through the presence of lithium ions in the electrolyte. Compared to electrode-based lithium replenishment, it is easier to operate, offers greater operational flexibility, and is easier to recycle. However, current electrolyte-based lithium replenishment technologies suffer from drawbacks such as low solubility of lithium replenishment materials, poor system stability, and high overall impedance, and therefore cannot replace electrode-based lithium replenishment technology. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the existing technology and provide an electrolyte. The electrolyte introduces a lithium-replenishing material and controls the anion composition of the components. The lithium-replenishing material has high solubility and strong stability. When the electrolyte is applied to a secondary battery, it can achieve efficient lithium replenishment and can also preferably reduce the CEI impedance in the battery, thereby improving the overall electrochemical performance.

[0006] To achieve the above objectives, in a first aspect of this application, an electrolyte is provided, comprising a lithium-replenishing material and a composite anion;

[0007] The lithium replenishment material includes M x T y M includes at least one of Li, Na, and K, T includes at least one of P and S, 1≤x≤3, 1≤y≤8, and x and y are integers;

[0008] The composite anion includes BOB. - (dioxoborate ion), PO2F2 - (difluorophosphate), ODFB- (difluorooxalate borate), FSI - (bis(fluorosulfonyl)imide), TFSI - (bis(trifluoromethanesulfonyl)imide), ODFP - (difluorodioxanol phosphate), FNFSI - ([(FSO2)(n-C4F9SO2)N] - ), BF4 - (Tetrafluoroborate), PF6 - (hexafluorophosphate), FEA - At least four of the following are selected from (1,1,1-trifluoro-N-[2-[2-(2-methoxyethoxy)ethoxy)]ethyl]methanesulfonamide).

[0009] The beneficial effects of this application are as follows:

[0010] This application provides an electrolyte in which a lithium-replenishing material is introduced and the anion composition of the component is controlled. The lithium-replenishing material has high solubility and strong stability. When applied to a secondary battery, the electrolyte can achieve efficient lithium replenishment and can also preferably reduce the CEI impedance in the battery, thereby improving the overall electrochemical performance. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0012] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0013] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0014] The present application is further illustrated below with specific embodiments:

[0015] An electrolyte comprising a lithium-supplementing material and a composite anion;

[0016] The lithium replenishment material includes M x T y M includes at least one of Li, Na, and K, T includes at least one of P and S, 1≤x≤3, 1≤y≤8, and x and y are integers;

[0017] The composite anion includes BOB. - PO2F2 - ODFB - FSI - TFSI - ODFP - ,FNFSI - BF4 - PF6 - FEA - At least four of them.

[0018] Compared to electrode-based lithium replenishment technology, electrolyte-based lithium replenishment technology theoretically offers advantages such as lower operational difficulty, greater controllability, and easier recovery. However, to achieve sufficient lithium replenishment, it is necessary to introduce enough lithium-containing compounds into the electrolyte while ensuring that these compounds do not precipitate before lithium replenishment activation. However, since traditional electrolytes already contain lithium salts, the addition of lithium replenishment materials presents a technical bottleneck. To address these issues, the technical solution of this application introduces a lithium replenishment material M into the electrolyte. x T y (It should be noted that the lithium supplementation additive M described in this application) x T y This is not a pure lithium compound in the traditional sense, but a compound containing metal ions that can achieve reversible insertion / extraction behavior in secondary batteries. It may contain, but is not limited to, lithium ions. As is known to those skilled in the art, monovalent metal ions such as Li, Na, and K can all achieve reversible insertion / extraction during charge and discharge. The main function of lithium replenishment materials is to compensate for the irreversible loss of active ions caused by the formation of the SEI film. Compounds containing Na or K ions (non-lithium ions) can also achieve lithium replenishment behavior in secondary batteries and can therefore be used as lithium replenishment materials. As a component to supplement reversibly active metal ions, the oxidation of anions releases electrons to replenish active electrons. In order to improve the solubility and stability of lithium replenishment materials in electrolytes, the technical solution of this application introduces composite anions for compounding. By limiting the number of types of anions, the mixing entropy in the overall electrolyte is increased, ultimately achieving good electrolyte stability and lithium replenishment effect.

[0019] In addition, M x T yThe anions in the electrolyte undergo oxidation during lithium replenishment, forming elemental anions that become part of the CEI film on the positive electrode. This component has poor ion conductivity, leading to an increase in the overall impedance of the CEI film and reducing the overall charge / discharge efficiency of the secondary battery. However, by constructing a specific composite anion electrolyte system, it is possible to achieve [something related to M] based on entropy disorder during the reaction process. x T y The anions in the electrolyte compete with each other, forming a certain amount of low-resistance inorganic salts on the CEI film. Ultimately, after the lithium replenishment material is introduced into the electrolyte and lithium replenishment is achieved, it can still maintain a high overall ionic conductivity, thereby improving the fast charging performance of the corresponding secondary battery.

[0020] In some embodiments, the number of types of the composite anions in the electrolyte is ≤8.

[0021] More preferably, the number of types of the composite anions in the electrolyte is one of 4, 5, 6, 7, 8 or any two of them.

[0022] As mentioned above, the types and quantities of composite anions affect the overall mixing entropy of the electrolyte, thereby affecting the oxidation degree of anions in the lithium replenishment material and the overall lithium replenishment efficiency of the lithium replenishment material. Through optimization, when the types and quantities of composite anions are within the above range, the lithium replenishment material can achieve the best lithium replenishment effect. At the same time, the electrolyte has high ion transport efficiency and high stability. The secondary battery after the electrolyte is applied to the secondary battery has excellent kinetic performance, low impedance, and longer cycle life.

[0023] In some embodiments, the composite anion includes PO2F2. - FSI - TFSI - ,FNFSI - BF4 - PF6 - FEA - At least four of them.

[0024] When compound anions are combined with lithium replenishment materials, in addition to considering the mixing entropy in the electrolyte, the application effect of the compound anions themselves also needs to be considered. When the above-mentioned types of compound anions are selected to compound the electrolyte, the stability of the electrolyte at high temperature can be effectively improved, the probability of side reactions occurring in secondary batteries at high temperature can be reduced, thereby improving its safety and service life at high temperature.

[0025] More preferably, the composite anion includes FSI. - TFSI - ,FNFSI - and FEA - .

[0026] Besides the thermal stability of the composite anions, the ionic radius of the composite anions also needs to be considered when compounding electrolytes. This is because the size of the ionic radius will lead to differences in the dissociation efficiency between the composite anions and lithium ions, thus affecting the ionic conductivity of the electrolyte. When the aforementioned composite anions are optimized, the ionic conductivity of the resulting electrolyte can be further improved. When this electrolyte is applied to secondary batteries, it can achieve better kinetic performance, lower impedance, and longer cycle life.

[0027] In specific embodiments of this application, the composite anion may originate from a metal salt containing the composite anion, or from an inorganic and / or organic compound that can decompose in the electrolyte solvent and precipitate the corresponding composite anion.

[0028] For example, in some embodiments, the complex anion originates from a lithium salt containing the corresponding complex anion; more specifically, the FSI - It can be derived from lithium salt LiFSI.

[0029] In some embodiments, the electrolyte satisfies: 5 ≤ x × n ≤ 14; where n is the number of different types of complex anions in the electrolyte.

[0030] More preferably, the range of x×n is one or any two of 5, 7, 8, 9, 10, 12, 14.

[0031] Lithium supplement material M x T y The metal cations, anions, and compounded anions in the electrolyte form a Lewis acid-base solvent system. In this system, the molar amount of metal cations in the lithium-supplementing material affects its solubility and also changes the degree of competition between the corresponding anions and the compound anions. When the electrolyte preferably satisfies the above relationship, it can maintain the impedance of the positive electrode CEI film at a low level while taking into account the higher solubility of the lithium-supplementing material.

[0032] In some embodiments, the lithium replenishment material includes M x P y The composite anion includes FSI - TFSI - ,FNFSI - BF4 - FEA - At least four of them.

[0033] When the lithium replenishment material contains phosphorus anions, the above-mentioned preferred composite anions are selected for compounding. These anions can improve the diversity of CEI film composition when the positive electrode forms a CEI film, resulting in a lower impedance of the CEI film and better dynamic performance of the corresponding secondary battery.

[0034] In some embodiments, the lithium replenishment material includes M x S y The composite anion includes PO2F2 - FSI - TFSI - and the fourth component, wherein the fourth component is BOB - ODFB - ODFP - ,FNFSI - BF4 - PF6 - FEA - At least one of them.

[0035] When the lithium replenishment material contains sulfur, selecting the above-mentioned preferred composite anions for compounding can effectively further improve the compatibility of the lithium replenishment material with other components of the electrolyte, resulting in a better lithium replenishment effect.

[0036] In some embodiments, the lithium replenishing material includes at least one of Li3P, Li4P, Li5P, Li6P, Li7P, Li7P3, Li2S4, Li2S6, and Li2S8.

[0037] In some embodiments, the electrolyte further includes a solvent.

[0038] In some embodiments, the solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

[0039] Exemplary examples include, but are not limited to, at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); carboxylic acid ester solvents include, but are not limited to, at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; ether solvents include, at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; sulfone solvents include, at least one of methyl sulfone and dimethyl sulfoxide; nitrile solvents include, at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrionitrile; and phosphate ester solvents include, at least one of trimethyl triphosphate and triethyl phosphate.

[0040] More preferably, the solvent may also include, but is not limited to, at least one of carbonate solvent fluorinated derivatives, carboxylic acid ester solvent fluorinated derivatives, ether solvent fluorinated derivatives, sulfone solvent fluorinated derivatives, nitrile solvent fluorinated derivatives, and phosphate ester solvent fluorinated derivatives.

[0041] For example, the carbonate solvent fluorinated derivatives include, but are not limited to, fluoroethylene carbonate (FEC).

[0042] The embodiments described in this application also provide a secondary battery, including the electrolyte described in this application.

[0043] In some embodiments, the battery further includes a positive electrode and a negative electrode; the positive electrode includes a positive electrode material, and the negative electrode includes a negative electrode material.

[0044] In some embodiments, the positive electrode includes a current collector and a positive electrode material layer;

[0045] More preferably, the positive electrode material layer includes a positive electrode material, a binder, and a conductive agent.

[0046] In some embodiments, the negative electrode sheet includes a current collector and a negative electrode material layer;

[0047] More preferably, the negative electrode material layer includes a negative electrode material, a binder, a thickener, and a conductive agent.

[0048] In some embodiments, the cathode material comprises at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt manganese oxide mixed with lithium iron phosphate, lithium iron phosphate, lithium iron phosphate mixed with lithium manganese iron phosphate, and lithium manganese iron phosphate.

[0049] The electrolyte described in this application is universally applicable when paired with cathode materials. It mainly relies on the mixing entropy regulation and interaction between the lithium replenishing material and the composite anion. Whether it is a ternary material or a lithium iron phosphate or lithium manganese iron phosphate cathode material, it can effectively improve the lithium replenishment effect and stability during application, thereby giving the final secondary battery excellent electrochemical performance.

[0050] In some embodiments, the cathode material includes at least one of lithium nickel cobalt manganese oxide and doped lithium nickel cobalt manganese oxide, and the lithium replenishing material in the electrolyte includes Li3P.

[0051] More preferably, the lithium supplement material comprises Li3P, and the composite anion comprises BOB. - PO2F2 - BF4 - and PF6 - .

[0052] When the cathode material includes a ternary material, selecting Li3P, a lithium replenishment material with an oxidation potential lower than that of the ternary material, allows for a later oxidation time of the lithium replenishment material during the formation of the cathode CEI film, thereby providing better control over the impedance of the CEI film. On the other hand, the aforementioned preferred composite anion can further complement the ternary material and suppress the dissolution of transition metal ions in the ternary material. Furthermore, the CEI film composition formed by it provides better protection for the cathode material, exhibits better interface stability, and results in better cycle stability of the secondary battery.

[0053] In some embodiments, the cathode material includes at least one of lithium iron phosphate and doped lithium iron phosphate, and the lithium replenishing material in the electrolyte includes Li2S4.

[0054] More preferably, the composite anion includes FSI. - TFSI - ,FNFSI - and FEA - .

[0055] The delithiation potential of lithium iron phosphate materials is around 3.2V. When Li2S4 is preferred as the lithium replenishment material, in addition to slowing down the formation node of elemental sulfur on the CEI film and reducing the impedance of the CEI film, it can also be combined with the above-mentioned preferred composite anions to improve the overall thermal stability of the electrolyte, give full play to the advantages of lithium iron phosphate materials, and further improve the long-term thermal stability of the final secondary battery.

[0056] In some embodiments, the cathode material includes at least one of lithium manganese iron phosphate and doped lithium manganese iron phosphate, and the lithium replenishing material in the electrolyte includes Li5P.

[0057] More preferably, the composite anion includes PO2F2. - FSI - TFSI - ,FNFSI - and PF6 - .

[0058] When Li5P is preferred as a lithium supplement material for compounding lithium manganese iron phosphate materials, its oxidation potential is lower than that of lithium manganese iron phosphate cathode materials. Therefore, the CEI film impedance of the cathode can be lower and the compatibility with the cathode can be better.

[0059] In some embodiments, the lithium replenishing material in the electrolyte has a mass content of 0.01 to 15% based on the total mass of the electrolyte.

[0060] In some specific embodiments, the partial structure of the lithium replenishment material is shown in formulas I-1 to I-8:

[0061] It should be noted that in the technical solution of this application, the type and mass content of the lithium replenishment material were confirmed by high performance liquid chromatography-mass spectrometry, and the specific method is as follows:

[0062] Electrolyte samples were injected using a microsyringe into an Agilent Infinity III liquid chromatography-mass spectrometry (LC-MS) system for qualitative and quantitative analysis of the electrolyte composition.

[0063] ① Obtaining MS standard curves and LC peak area-concentration curves: EMC solutions of different concentrations were prepared using formulas I-1 to I-8 and injected into the aforementioned liquid chromatography-mass spectrometry (LC-MS) instrument. MS and LC spectra of the standards were obtained, and the peak areas in the LC spectra were integrated (a routine data processing step in the testing software) to obtain the peak areas. Linearity graphs were plotted between the peak areas and concentrations of the standards at different concentrations to obtain the standard LC peak area-concentration curves.

[0064] ② Specimen identification: Inject the electrolyte to be tested into the above-mentioned liquid chromatography-mass spectrometry (LC-MS) instrument to obtain the LC and MS spectra of the electrolyte to be tested. Compare the MS spectrum of the electrolyte to be tested with the MS spectrum of the standard to determine whether the electrolyte to be tested contains additives of formulas I-1 to I-8 (for example, if the MS spectrum of the electrolyte to be tested shows a peak at the position of the peak of formula I-1 in the standard spectrum, then the electrolyte to be tested is determined to contain lithium supplementation additive of formula I-1, and other components are deduced in the same way).

[0065] ③ Determination of mass content:

[0066] The peak area is obtained by integrating the peaks in the LC spectrum of the electrolyte to be tested. Based on the standard LC peak area-concentration curve, the concentration of the analyte can be determined from the known peak area.

[0067] When electrolyte is present in a secondary battery, it is collected using the following method:

[0068] First, the secondary battery is discharged: Use a battery charging and discharging device to discharge the battery. Discharge conditions: current 0.3C, cut-off voltage is set according to the characteristics of the active material system, for example: lithium iron phosphate / graphite system: 2.5V;

[0069] Lithium manganese iron phosphate / graphite system: 2.5V;

[0070] Lithium nickel cobalt manganese oxide / graphite system: 2.8V;

[0071] Lithium nickel cobalt manganese oxide / silicon-based system: 2.8V;

[0072] After recording the battery number / barcode, disassemble the battery in the glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm) to collect the electrolyte.

[0073] Collecting the electrolyte: There are the following two methods for collecting the electrolyte: After removing the battery cover plate, ① If there is free electrolyte, use a straw to collect the electrolyte into a 5 mL sample tube and seal it with sealing tape to prevent electrolyte leakage. ② If there is no free electrolyte, a hydraulic press (FY-30 hydraulic press from Beijing Heng Aode Technology Co., Ltd.) can be used to continuously apply pressure until free electrolyte appears, collect the electrolyte into the sample tube and seal it.

[0074] In some embodiments, in the electrolyte, the test method for the type quantity of the composite anion and the mass content of the salt containing the composite anion is as follows:

[0075] Determine the type and concentration of anions: Inject the collected electrolyte into the sample cell of a Thermo Fisher Dionex TM Aquion TM IC ion chromatograph, test the ion chromatogram curve of the electrolyte sample, and determine the type (quantity) of the composite anion by comparing with the database built in the chromatograph; determine the concentration corresponding to the salt containing the anion, that is, the mass content, through the peak area curve (peak area - concentration curve).

[0076] When the electrolyte exists in a secondary battery, the same method as above is used to collect the electrolyte, which will not be elaborated here.

[0077] In some embodiments, the mass content of the salt containing the composite anion corresponding to the composite anion in the electrolyte is 1 - 20%.

[0078] In some embodiments, at least one of the lithium nickel cobalt manganese oxide and the doped lithium nickel cobalt manganese oxide includes LiNi a Mn b Co c N d O2, where 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 ≤ d < 0.1, a + b + c + d = 1 and N is at least one of Al, Na, Ti, Nb, Zr, W, Fe, Cr.

[0079] In some embodiments, the lithium iron manganese phosphate includes LiFe e Mn f PO4, where 0 < e < 1, 0 < f < 1, e + f = 1.

[0080] In some embodiments, the negative electrode material includes at least one of a carbon-based material, a silicon-based material, and lithium titanate.

[0081] For example, the carbon-based material may be at least one of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, and soft carbon; the silicon-based material may be at least one of elemental silicon, silicon suboxide, and silicon-carbon composite materials.

[0082] Those skilled in the art may also use other methods to prepare negative electrode materials, or directly purchase commercially available products, depending on the actual situation.

[0083] The present invention is further illustrated below with specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention:

[0084] Example 1

[0085] A battery, the preparation method comprising the following steps:

[0086] (1) Preparation of the positive electrode: The positive electrode material is lithium nickel cobalt manganese oxide (LiNiO2). 0.6 Mn 0.2 Co 0.2 O2, conductive agent SP, and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97.8:1.2:1. The mixture is then vacuum stirred to prepare a slurry, which is subsequently coated on both sides of the current collector aluminum foil. After rolling and cutting, the positive electrode sheet is obtained.

[0087] (2) Preparation of negative electrode sheet: The negative electrode material artificial graphite, conductive agent SP, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.5:2.2:0.2:1.1, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after rolling and cutting, the negative electrode sheet is obtained.

[0088] (3) Preparation of the diaphragm: A PP diaphragm with an average pore size of 2μm and an air permeability of 300s / 100mL is used, and the diaphragm is coated with an alumina ceramic coating.

[0089] (4) Preparation of electrolyte: Ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate are mixed in a volume ratio of 3:5:2 as a solvent; then lithium salts containing specific composite anions as listed in Table 1 are added respectively; finally, lithium supplementing material is added and mixed evenly to obtain the electrolyte, as shown in Table 1, where n is the BOB content in the electrolyte. - PO2F2 - ODFB - FSI - TFSI - ODFP - ,FNFSI - BF4 - PF6 - FEA -The number of these composite anions, where x is the number of moles of the metal element in the lithium replenishment material (for example, when the lithium replenishment material is Li3P7, x = 3).

[0090] (5) The positive electrode, separator (coating side facing the positive electrode), and negative electrode are stacked, wound, and assembled into a battery cell in sequence (alumina coating of the separator facing the positive electrode). The battery cell is placed in the outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, and volume adjustment, the battery is obtained.

[0091] Examples 2-18

[0092] A battery differs from Example 1 only in that the electrolyte composition is different, as shown in Table 1.

[0093] Example 19

[0094] A battery, the preparation method comprising the following steps:

[0095] (1) Preparation of positive electrode sheet: The positive electrode material lithium iron phosphate LiFePO4, conductive agent SP and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97.8:1.2:1. The slurry is prepared by vacuum stirring, and then coated on both sides of the current collector aluminum foil. After rolling and cutting, the positive electrode sheet is obtained.

[0096] (2) Preparation of negative electrode sheet: The negative electrode material artificial graphite, conductive agent SP, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.5:2.2:0.2:1.1, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after rolling and cutting, the negative electrode sheet is obtained.

[0097] (3) Preparation of the diaphragm: A PP diaphragm with an average pore size of 2μm and an air permeability of 300s / 100mL is used; the diaphragm is coated with an alumina ceramic coating;

[0098] (4) Preparation of electrolyte: Ethylene carbonate, methyl ethyl carbonate and diethyl carbonate are mixed in a volume ratio of 3:5:2 as solvent; then lithium salts containing specific composite anions with the mass content recorded in Table 1 are added respectively; finally, lithium supplementing material with a specific mass content is added and mixed evenly to obtain the electrolyte.

[0099] (5) The positive electrode, separator (coated side facing the positive electrode), and negative electrode are stacked, wound and assembled into a battery cell in sequence. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing, formation and volume adjustment, the battery is obtained.

[0100] Examples 20-28

[0101] A battery differs from Example 19 only in that the electrolyte composition is different, as shown in Table 1.

[0102] Example 29

[0103] A battery, the preparation method comprising the following steps:

[0104] (1) Preparation of the positive electrode: The positive electrode material is lithium manganese iron phosphate (LiFePO4). 0.5 Mn 0.5 PO4, conductive agent SP, and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97.8:1.2:1. The mixture is then vacuum stirred to prepare a slurry, which is subsequently coated on both sides of the current collector aluminum foil. After rolling and cutting, the positive electrode sheet is obtained.

[0105] (2) Preparation of negative electrode sheet: The negative electrode material artificial graphite, conductive agent SP, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are dispersed in water at a mass ratio of 96.5:2.2:0.2:1.1, and a slurry is prepared by vacuum stirring. The slurry is then coated on both sides of the current collector copper foil, and after rolling and cutting, the negative electrode sheet is obtained.

[0106] (3) Preparation of the diaphragm: PP diaphragm with an average pore size of 2μm and an air permeability of 300s / 100mL was used.

[0107] (4) Preparation of electrolyte: Ethylene carbonate, methyl ethyl carbonate and diethyl carbonate are mixed in a volume ratio of 3:5:2 as solvent; then lithium salts containing specific composite anions with the mass content recorded in Table 1 are added respectively; finally, lithium supplementing material with a specific mass content is added and mixed evenly to obtain the electrolyte.

[0108] (5) The positive electrode, separator and negative electrode are stacked and wound in sequence to form a battery cell. The battery cell is placed in the outer packaging shell, dried and injected with electrolyte. After vacuum sealing, standing, formation and volume adjustment, the battery is obtained.

[0109] Examples 30-36

[0110] One battery differs from Example 29 only in that the electrolyte composition is different, as shown in Table 1.

[0111] Example 37

[0112] A battery differs from Example 1 only in that the electrolyte composition is different, as shown in Table 1.

[0113] Comparative Examples 1-3

[0114] A battery differs from Example 1 only in that the electrolyte composition is different, as shown in Table 1.

[0115] Comparative Examples 4-6

[0116] A battery differs from Example 19 only in that the electrolyte composition is different, as shown in Table 1.

[0117] Comparative Examples 7-9

[0118] One battery differs from Example 29 only in that the electrolyte composition is different, as shown in Table 1.

[0119] Table 1

[0120] Example of effect

[0121] The batteries obtained in each embodiment and comparative example were tested as follows:

[0122] (1) Positive electrode CEI impedance test: The battery is charged to the upper limit voltage at a constant current and constant voltage rate of 0.3C on a LAND charge-discharge system, with a cutoff current ≤0.05C; then discharged to the lower limit voltage at a rate of 0.3C, and the above steps are repeated 3 times. The actual discharge capacity of the third discharge is taken as the discharge capacity of the battery; then charged at a rate of 0.3C to 50% of the third discharge capacity; the upper and lower limits of the working voltage vary depending on the positive electrode material used in the battery.

[0123] LiFePO4: 2.5V~3.65V; LiFe 0.5 Mn 0.5 PO4: 2.5V~4.25V;

[0124] LiNi 0.6 Mn 0.2 Co 0.2 O2: 2.8V~4.25V;

[0125] Examples 1-18, Example 37, and Comparative Examples 1-3 correspond to 2.8-4.25V; Examples 19-28 and Comparative Examples 4-6 correspond to 2.5-3.65V; Examples 29-36 and Comparative Examples 7-9 correspond to 2.5-4.25V.

[0126] The battery was then removed, and the tabs were wrapped with insulating glue before being transferred to a vacuum glove box (H2O≤0.01ppm, O2≤0.01ppm) to disassemble the positive electrode. The electrode was then cleaned in a PTFE box containing DMC, allowed to air dry, and cut into 9mm diameter discs, which were then sealed. The discs, along with the same separator and electrolyte as those used in the examples and comparative examples, were stacked in the following order: disc, electrolyte (10μL), separator, electrolyte (10μL), disc, and then disc again to assemble a symmetrical battery. After standing for 24 hours, the impedance spectrum was tested using a CS310X multichannel electrochemical workstation at an amplitude of 5mV and a frequency of 100000-0.1Hz. After obtaining the impedance spectrum, the value of the horizontal axis when -Z”=0 was selected as R1, and the inflection point of the ellipse, i.e., the minimum value of the curve, was R2. The impedance of the positive electrode CEI was R=R2-R1.

[0127] (2) Cycle capacity retention rate: Set the working environment to 60℃, charge the battery to the upper limit voltage at a constant current and constant voltage of 1C on the LAND charging and discharging system, and cut off the current less than or equal to 0.05C; then discharge to the lower limit voltage at a constant current and voltage of 1C; repeat the above steps 1000 times, and count the discharge capacity of the 1000th cycle. The discharge capacity retention rate (%) after 1000 cycles = 100% × discharge capacity A1 at 1000 cycles / discharge capacity A0 at the first cycle;

[0128] The upper and lower limits of the operating voltage vary depending on the positive electrode material used in the battery.

[0129] LiFePO4: 2.5V~3.65V; LiFe 0.5 Mn 0.5 PO4: 2.5V~4.25V;

[0130] LiNi 0.6 Mn 0.2 Co 0.2 O2: 2.8V~4.25V.

[0131] Examples 1-18, Example 37, and Comparative Examples 1-3 correspond to 2.8-4.25V; Examples 19-28 and Comparative Examples 4-6 correspond to 2.5-3.65V; Examples 29-36 and Comparative Examples 7-9 correspond to 2.5-4.25V.

[0132] The test results are shown in Table 2.

[0133] Table 2

[0134] As can be seen from Table 2:

[0135] (1) When the electrolyte described in this application is applied to secondary batteries, it can achieve efficient lithium replenishment while reducing the impedance of the CEI film layer in the battery. In the ternary secondary batteries corresponding to the products in Examples 1-18, the CEI film impedance on the positive electrode can be maintained within the range of 66 mΩ, and the capacity retention rate after 1000 cycles at 1C rate can reach more than 78%, with a maximum of more than 86%. In the lithium iron phosphate secondary batteries corresponding to Examples 19-28, the CEI film impedance on the positive electrode can be maintained within the range of 47 mΩ, and the capacity retention rate after 1000 cycles at 1C rate can reach more than 85%, with a maximum of more than 88%. In the lithium manganese iron phosphate secondary batteries corresponding to Examples 29-36, the CEI film impedance on the positive electrode can be maintained within the range of 45 mΩ, and the capacity retention rate after 1000 cycles at 1C rate can reach more than 85%. The efficiency can reach over 78.5%, with a maximum of over 81%. This is mainly attributed to the application of lithium-replenishing materials in the electrolyte and the specific selection of composite anions. This allows the lithium-replenishing materials to achieve good solubility and stability in the electrolyte. Furthermore, based on entropy disorder, they compete with the anions in the lithium-replenishing materials, forming a certain amount of low-resistance inorganic salts on the CEI film. Ultimately, this allows the electrolyte to maintain a high overall ionic conductivity after lithium replenishment, improving the fast-charging performance of the corresponding secondary battery. In contrast, although the comparative products also introduced composite anions, due to insufficient variety and quantity, or improper selection of varieties, regardless of whether the total amount of additives was the same as that of the example products, they could not achieve the ideal entropy disorder of the electrolyte system. The resulting CEI film had higher impedance, and the cycle life of the secondary battery was far inferior to that of the example products.

[0136] (2) As can be seen from the comparison between the products in Examples 1 to 18, the selection of products including FSI is more suitable. - TFSI - ,FNFSI - and FEA - The inclusion of composite anions allows for optimization based on ionic radius size, resulting in superior battery kinetic performance and cycle life. When the cathode material includes a ternary material, selecting LiP3, a lithium replenishment material with an oxidation potential lower than the delithiation potential of the ternary material, allows for a later oxidation time of the lithium replenishment material during CEI film formation, thus providing better control over the CEI film impedance. Furthermore, when LiP3 is selected as the lithium replenishment material, as seen in Examples 4-7, further optimization includes BOB. - PO2F2 - BF4 - and PF6 - The composite anions, combined with ternary materials, can effectively suppress the dissolution of transition metal ions in ternary materials, and the CEI film composition formed by it has a better protective effect on the cathode material, better interface stability, and better cycle performance of the resulting secondary battery.

[0137] Lithium supplement material M x T y The lithium-replenishing material forms a Lewis acid-base solvent system with metal cations, anions, and compounded anions. The molar amount of metal cations in the lithium-replenishing material affects its solubility and alters the competition between the corresponding anions and compound anions. When the product of the molar amount of metal elements in the lithium-replenishing material and the number of different types of compound anions in the electrolyte is preferably between 5 and 14, the overall battery performance is better. The number of different types of compound anions affects the overall mixing entropy of the electrolyte, thus influencing the oxidation degree of anions in the lithium-replenishing material and the overall lithium-replenishing efficiency. When the number of different types of compound anions is less than 8, the lithium-replenishing material can achieve better lithium-replenishing effect, while the electrolyte has high ion transport efficiency and stability. The secondary battery after the electrolyte is applied to the secondary battery exhibits excellent kinetic performance, low impedance, and longer cycle life.

[0138] (3) As can be seen from the products of Examples 19-28 and Examples 29-36, when the battery systems are lithium iron phosphate and lithium manganese iron phosphate respectively, the lithium replenishing materials corresponding to the electrolyte are Li2S4 and LiP5, which are more effective. This is because the delithiation potential of lithium iron phosphate materials is around 3.2V, while Li2S4, as a lithium replenishing material, can not only slow down the formation node of elemental sulfur on the CEI film and reduce the impedance of the CEI film, but also, if FSI is included... - TFSI - ,FNFSI - and FEA - When combined with other composite anions, LiP5 can enhance the overall thermal stability of the electrolyte, fully leveraging the advantages of lithium iron phosphate materials and further improving the long-term cycle performance of the final secondary battery. When LiP5 is used as a lithium supplement material in combination with lithium manganese iron phosphate materials, its oxidation potential is lower than the delithiation potential of the lithium manganese iron phosphate cathode material, thus also reducing the impedance of the CEI film. This can be achieved when combined with other materials, including PO2F2. - FSI - TFSI - ,FNFSI - and PF6 - The inclusion of complex anions can achieve better electrochemical performance.

Claims

1. An electrolyte, characterized in that, Including lithium-supplementing materials and composite anions; The lithium replenishment material includes M x T y M includes at least one of Li, Na, and K, T includes at least one of P and S, 1≤x≤3, 1≤y≤8, and x and y are integers; The composite anion includes BOB. - PO2F2 - ODFB - FSI - TFSI - ODFP - ,FNFSI - BF4 - PF6 - FEA - At least four of them.

2. The electrolyte as described in claim 1, characterized in that, The number of different types of the composite anions in the electrolyte is ≤8.

3. The electrolyte as described in claim 1, characterized in that, The composite anion includes PO2F2 - FSI - TFSI - ,FNFSI - BF4 - PF6 - FEA - At least four of them.

4. The electrolyte as described in claim 3, characterized in that, The composite anion includes FSI. - TFSI - ,FNFSI - and FEA - .

5. The electrolyte as described in claim 1, characterized in that, The electrolyte satisfies the following condition: 5 ≤ x × n ≤ 40; where n is the number of different types of complex anions in the electrolyte.

6. The electrolyte as described in claim 5, characterized in that, The electrolyte satisfies the following condition: 5 ≤ x × n ≤ 14.

7. The electrolyte as described in claim 1, characterized in that, The lithium replenishment material includes M x P y The composite anion includes FSI - TFSI - ,FNFSI - BF4 - FEA - At least four of them.

8. The electrolyte as described in claim 1, characterized in that, The lithium replenishment material includes M x S y The composite anion includes PO2F2 - FSI - TFSI - and the fourth component, wherein the fourth component is BOB - ODFB - ODFP - ,FNFSI - BF4 - PF6 - FEA - At least one of them.

9. The electrolyte as described in claim 1, characterized in that, The lithium replenishment material includes at least one of Li3P, Li4P, Li5P, Li6P, Li7P, Li7P3, Li2S4, Li2S6, and Li2S8.

10. The electrolyte according to any one of claims 1-9, characterized in that, The electrolyte also includes a solvent, which includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

11. The electrolyte as described in claim 10, characterized in that, The carbonate solvents include at least one of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the carboxylic acid ester solvents include at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; the ether solvents include at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; the sulfone solvents include at least one of methyl sulfone and dimethyl sulfoxide; the nitrile solvents include at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrionitrile; and the phosphate ester solvents include at least one of trimethyl triphosphate and triethyl phosphate.

12. The electrolyte as described in claim 10 or 11, characterized in that, The solvent also includes at least one of the following: carbonate solvent fluorinated derivatives, carboxylic acid ester solvent fluorinated derivatives, ether solvent fluorinated derivatives, sulfone solvent fluorinated derivatives, nitrile solvent fluorinated derivatives, and phosphate ester solvent fluorinated derivatives.

13. The electrolyte as described in claim 12, characterized in that, The carbonate solvent fluorinated derivatives include fluoroethylene carbonate.

14. A secondary battery, characterized in that, The secondary battery includes the electrolyte as described in any one of claims 1 to 13; the secondary battery further includes a positive electrode and a negative electrode; the positive electrode includes a positive electrode material, and the negative electrode includes a negative electrode material.

15. The secondary battery as described in claim 14, characterized in that, The cathode material includes at least one of lithium nickel cobalt manganese oxide, doped lithium nickel cobalt manganese oxide, lithium iron phosphate, doped lithium iron phosphate, and doped lithium manganese iron phosphate.

16. The secondary battery as described in claim 15, characterized in that, The cathode material includes at least one of lithium nickel cobalt manganese oxide and doped lithium nickel cobalt manganese oxide, and the electrolyte contains lithium 3P as the lithium replenishing material.

17. The secondary battery as described in claim 16, characterized in that, The composite anion includes BOB. - PO2F2 - BF4 - and PF6 - .

18. The secondary battery as described in claim 15, characterized in that, The cathode material includes at least one of lithium iron phosphate and doped lithium iron phosphate, and the electrolyte contains Li2S4 as the lithium replenishing material.

19. The secondary battery as described in claim 18, characterized in that, The composite anion includes FSI. - TFSI - ,FNFSI - and FEA - .

20. The secondary battery as described in claim 15, characterized in that, The cathode material includes at least one of lithium manganese iron phosphate and doped lithium manganese iron phosphate, and the electrolyte contains Li5P as the lithium replenishing material.

21. The secondary battery as described in claim 20, characterized in that, The composite anion includes PO2F2 - FSI - TFSI - ,FNFSI - and PF6 - .

22. The secondary battery as described in claim 20, characterized in that, The lithium replenishing material has a mass content of 0.01% to 15% based on the total mass of the electrolyte.

23. The secondary battery as described in claim 20, characterized in that, The mass content of the salt containing the complex anion in the electrolyte is 1-20%.

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