An electrolyte

Abstract

The present application discloses an electrolyte, belonging to the technical field of batteries. The electrolyte of the present application introduces a lithium supplement material while regulating the anion composition in the components. The lithium supplement material has high solubility and strong stability. When the electrolyte is applied to a secondary battery, efficient lithium supplementation can be achieved, and at the same time, the CEI impedance in the battery can be preferably reduced, and the overall electrochemical performance can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to an electrolyte solution. Background Art

[0002] The lithium supplementation technology for lithium-ion batteries refers to introducing a lithium-containing compound to release active lithium in addition to the positive electrode active material in the battery, so as to compensate for the active lithium consumed by the positive electrode active material when forming the SEI film, thereby reducing the irreversible loss of the battery capacity and improving the battery cycle performance. Currently, the main lithium supplementation technologies are positive electrode lithium supplementation and negative electrode lithium supplementation, that is, the lithium supplementation material is arranged on the positive electrode sheet or the negative electrode sheet. However, in the process of electrode sheet production, the uniformity and safety of the arrangement of the lithium supplementation material need to be considered, the preparation cost becomes higher, and at the same time, the difficulty of subsequent recovery of the electrode active material increases.

[0003] The electrolyte lithium supplementation technology refers to dissolving the lithium supplementation material in the electrolyte solution and performing lithium supplementation through the lithium ions in the electrolyte solution. Compared with the electrode sheet lithium supplementation, the operation difficulty is low, the operable space is large, and the recovery difficulty is low. However, the current electrolyte lithium supplementation technology still cannot replace the electrode sheet lithium supplementation technology due to defects such as low solubility of the lithium supplementation material, poor system stability, and high overall impedance. Summary of the Invention

[0004] The purpose of the present application is to overcome the deficiencies of the prior art and provide an electrolyte solution. The electrolyte solution introduces a lithium supplementation material and simultaneously regulates the anion composition in the components. The lithium supplementation material has high solubility and strong stability. When the electrolyte solution is applied to secondary batteries, it can achieve efficient lithium supplementation, and at the same time, it can preferably reduce the CEI impedance in the battery and improve the overall electrochemical performance.

[0005] To achieve the above purpose, in the first aspect of the present application, the present application provides an electrolyte solution, including a lithium supplementation material and a composite anion;

[0006] The lithium supplementation material includes M x T y , where 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;

[0007] The composite anion includes BOB - (bis(oxalato)borate ion), PO2F2 - (difluorophosphate), ODFB - (difluorooxalato borate), FSI - (bis(fluorosulfonyl)imide), TFSI - (bis(trifluoromethylsulfonyl)imide), ODFP - (difluorodioxalato phosphate), FNFSI -([(FSO2)(n-C4F9SO2)N] - )、BF4 - (tetrafluoroborate), PF6 - (hexafluorophosphate), FEA - (1,1,1-trifluoro-N-[2-[2-(2-methoxyethoxy)ethoxy)]ethyl]methanesulfonamide) of at least four kinds.

[0008] The beneficial effects of this application are as follows:

[0009] This application provides an electrolyte. When introducing a lithium supplement material and simultaneously regulating the anion composition in the components, the lithium supplement material has high solubility and strong stability. When this electrolyte is applied to a secondary battery, efficient lithium supplementation can be achieved. At the same time, the CEI impedance in the battery can be preferably reduced, and the overall electrochemical performance can be improved. Specific embodiments

[0010] 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 some, but not all, of the embodiments of this application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this application.

[0011] In this application, among the technically characterized descriptions in an open-ended manner, it includes both a closed technical solution composed of the listed features and an open technical solution including the listed features.

[0012] In this application, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of this range, as well as each value between such minimum and maximum values. Further, when the range refers to an integer, it includes each integer between the minimum and maximum values of this range. In addition, when providing multiple ranges to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0013] The following further elaborates this application with specific embodiments:

[0014] An electrolyte, comprising a lithium supplement material and a composite anion;

[0015] The lithium supplement material includes M x T y , where 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;

[0016] The composite anion includes BOB - , PO2F2 - , ODFB - , FSI - , TFSI - , ODFP - , FNFSI - , BF4 - , PF6 - , FEA - and at least four of them.

[0017] Compared with the cathode lithium supplement technology, the electrolyte lithium supplement technology theoretically has many advantages such as low operation difficulty, large adjustable space, and convenient recycling. However, to achieve sufficient lithium supplement effect, it is necessary to introduce sufficient lithium-containing compounds into the electrolyte while ensuring that these compounds will not precipitate before lithium supplement activation. However, due to the presence of lithium salts in traditional electrolytes, there are technical bottlenecks in the addition of lithium supplement materials in the electrolyte. To solve the above problems, the technical solution of this application introduces a lithium supplement material M x T y (It should be noted that the lithium supplement additive M x T y in this application is not a pure lithium compound in the traditional sense, but a compound containing metal ions that can achieve reversible deintercalation behavior in secondary batteries. It can contain but is not limited to lithium ions. As is well known to those skilled in the art, monovalent metal ions such as Li, Na, and K can all achieve reversible deintercalation during charge and discharge, and the main role of the lithium supplement material is to make up for the irreversible loss of active ions caused by the formation of the SEI film. Using compounds corresponding to non-lithium ions containing Na or K ions can also achieve the lithium supplement behavior of secondary batteries, so they can be used as lithium supplement materials) as a component to supplement active reversible metal ions, and at the same time, anions are oxidized to release electrons to supplement active electrons; in order to improve the solubility and stability of the lithium supplement material in the electrolyte, the technical solution of this application introduces composite anions for compounding, and improves the mixing entropy in the overall electrolyte by limiting the number of types of anions, and finally achieves good electrolyte stability and lithium supplement effect.

[0018] In addition, the anions in M x T y will be oxidized during lithium supplementation to form anion elements and become a part of the CEI film on the positive electrode plate. The ion conduction performance of this component is poor, which will increase the overall impedance of the CEI film and reduce the charge and discharge efficiency of the overall secondary battery. By constructing a specific composite anion system electrolyte, it can be based on the entropy disorder during the reaction to achieve the same effect as M x T yThe anions therein form a competitive relationship, forming a certain amount of low-impedance inorganic salts on the CEI film. Eventually, after introducing the lithium supplement material into the electrolyte and achieving lithium supplementation, the overall ionic conductivity can still be maintained at a relatively high level, improving the fast charging performance of the corresponding secondary battery.

[0019] In some embodiments, the number of types of the composite anions in the electrolyte ≤ 8.

[0020] Further preferably, the number of types of the composite anions in the electrolyte is one of 4, 5, 6, 7, 8 or the range value of any two of them.

[0021] As described above, the number of types of the composite anions will affect the overall mixing entropy of the electrolyte, thereby affecting the oxidation degree of the anions in the lithium supplement material and the overall lithium supplementation efficiency of the lithium supplement material. After optimization, when the number of types of the composite anions is within the above range, the lithium supplement material can achieve the best lithium supplementation effect. At the same time, the ionic transport efficiency of the electrolyte is relatively high, the stability is high, the kinetic performance of the secondary battery after the electrolyte is applied to the secondary battery is excellent, the impedance is small, and the cycle life is longer.

[0022] In some embodiments, the composite anions include PO2F2 - , FSI - , TFSI - , FNFSI - , BF4 - , PF6 - , FEA - and at least four of them.

[0023] When the composite anions are compounded with the lithium supplement material, in addition to considering the mixing entropy in the electrolyte, the application effect of the composite anions themselves also needs to be considered. When preferably compounding the electrolyte with the above types of composite anions, the stability of the electrolyte at high temperatures can be effectively improved, the probability of side reactions occurring in the secondary battery at high temperatures can be reduced, thereby improving its safety and working life at high temperatures.

[0024] Further preferably, the composite anions include FSI - , TFSI - , FNFSI - and FEA - .

[0025] In addition to the thermal stability of the composite anion, when formulating the composite electrolyte, the ionic radius of the composite anion also needs to be considered, because the size of the ionic radius will cause differences in the dissociation efficiency between the composite anion and lithium ions, and the ionic conductivity of the electrolyte will also change. When the above composite anion is preferably selected, the ionic conductivity of the obtained electrolyte can be further improved. When this electrolyte is applied to a secondary battery, better kinetic performance, lower impedance, and longer cycle life can be achieved.

[0026] In a specific embodiment of the present application, the composite anion can be derived from a metal salt containing the composite anion, or it can be an inorganic and / or organic compound that can decompose in the electrolyte solvent and precipitate the corresponding composite anion.

[0027] For example, in some embodiments, the composite anion is derived from a lithium salt containing the corresponding composite anion. More specifically, the FSI - can be derived from the lithium salt LiFSI.

[0028] In some embodiments, the electrolyte satisfies: 5 ≤ x × n ≤ 14; where n is the number of types of composite anions in the electrolyte.

[0029] Further preferably, x × n is one of 5, 7, 8, 9, 10, 12, 14 or a range value of any two of them.

[0030] Lithium supplement material M x T y A Lewis acid-base solvent system is formed among the metal cations, anions, and the compounded composite anions in the lithium supplement material. In this system, the unit molar amount of the metal cations in the lithium supplement material affects its solubility, and also changes the competition degree between the corresponding anions and the composite anions. When the electrolyte preferably satisfies the above relationship, it can make the electrolyte maintain a lower impedance of the positive electrode CEI film while taking into account a higher solubility of the lithium supplement material.

[0031] In some embodiments, the lithium supplement material includes M x P y and the composite anion includes at least four of FSI - , TFSI - , FNFSI - , BF4 - , FEA - .

[0032] When the lithium supplement material contains phosphorus anions, the above-mentioned preferred composite anions are selected for compounding. These anions can improve the diversity of the components of the CEI film when the CEI film is formed on the positive electrode, making the CEI film have a lower impedance and corresponding better secondary battery kinetic performance.

[0033] In some embodiments, the lithium supplement material includes M x S y , and the composite anion includes PO2F2 - , FSI - , TFSI - and a fourth component, and the fourth component is at least one of BOB - , ODFB - , ODFP - , FNFSI - , BF4 - , PF6 - , FEA - .

[0034] When the lithium supplement material contains sulfur, selecting the above-mentioned several preferred composite anions for compounding can effectively further improve the compatibility between the lithium supplement material and other components of the electrolyte, making the lithium supplement effect of the material better.

[0035] In some embodiments, the lithium supplement material includes at least one of Li3P, Li4P, Li5P, Li6P, Li7P, Li7P3, Li2S4, Li2S6, Li2S8.

[0036] In some embodiments, the electrolyte further includes a solvent.

[0037] In some embodiments, the solvent includes at least one of carbonate solvents, carboxylate solvents, ether solvents, sulfone solvents, nitrile solvents, phosphate solvents.

[0038] Exemplarily, the carbonate solvents include but are not limited to at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC); the carboxylate solvents include but are not limited to at least one of ethyl acetate, methyl formate, 1,4-butyrolactone; the ether solvents include but are not limited to at least one of dimethyltetrahydrofuran, tetrahydrofuran, 1,2-dimethoxyethane; the sulfone solvents include but are not limited to at least one of methyl sulfone, dimethyl sulfoxide; the nitrile solvents include but are not limited to at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, 1,3,6-hexanetricarbonitrile; the phosphate solvents include but are not limited to at least one of trimethyl phosphate, triethyl phosphate.

[0039] Further preferably, the solvent may further include, but is not limited to, at least one of fluorinated derivatives of carbonate solvents, fluorinated derivatives of carboxylate solvents, fluorinated derivatives of ether solvents, fluorinated derivatives of sulfone solvents, fluorinated derivatives of nitrile solvents, and fluorinated derivatives of phosphate solvents.

[0040] Exemplarily, the fluorinated derivative of the carbonate solvent includes, but is not limited to, fluoroethylene carbonate (FEC).

[0041] In the embodiments of the present application, a secondary battery is further provided, including the electrolyte of the present application.

[0042] In some embodiments, the battery further includes a positive electrode plate and a negative electrode plate; the positive electrode plate includes a positive electrode material, and the negative electrode plate includes a negative electrode material.

[0043] In some embodiments, the positive electrode plate includes a current collector and a positive electrode material layer;

[0044] Further preferably, the positive electrode material layer includes a positive electrode material, a binder, and a conductive agent.

[0045] In some embodiments, the negative electrode plate includes a current collector and a negative electrode material layer;

[0046] Further preferably, the negative electrode material layer includes a negative electrode material, a binder, a thickening agent, and a conductive agent.

[0047] In some embodiments, the positive electrode material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt manganese oxide doped with lithium iron phosphate, lithium iron phosphate, lithium iron phosphate doped with lithium manganese iron phosphate, and lithium manganese iron phosphate.

[0048] The electrolyte of the present application has universality when paired with the positive electrode material, mainly relying on the mixing entropy regulation and interaction between the lithium supplementing material and the composite anion. Whether it is a ternary system material or a lithium iron phosphate-based or lithium manganese iron phosphate-based positive electrode material, the lithium supplementing effect and stability during application can be effectively improved, so that the finally obtained secondary battery has excellent electrochemical performance.

[0049] In some embodiments, the positive electrode material includes at least one of lithium nickel cobalt manganese oxide and doped lithium nickel cobalt manganese oxide, and in the electrolyte, the lithium supplementing material includes Li3P.

[0050] Further preferably, the lithium supplementing material includes Li3P, and the composite anion includes BOB - , PO2F2 - , BF4 - and PF6 - .

[0051] When the positive electrode material includes a ternary system material, selecting a lithium supplement material such as Li3P with an oxidation potential lower than the lithium deintercalation potential of the ternary system material can make the oxidation time node of the lithium supplement material later when the positive electrode CEI film is formed, thereby having a better control level over the impedance of the CEI film; on the other hand, the above-mentioned preferred composite anion can further cooperate with the ternary system material and inhibit the dissolution of transition metal ions in the ternary system material, and the formed CEI film component has a better protection effect on the positive electrode material, better interface stability, and better cycle stability of the obtained secondary battery.

[0052] In some embodiments, the positive electrode material includes at least one of lithium iron phosphate and doped lithium iron phosphate, and in the electrolyte, the lithium supplement material includes Li2S4.

[0053] Further preferably, the composite anion includes FSI - , TFSI - , FNFSI - and FEA - .

[0054] The lithium deintercalation potential of the lithium iron phosphate-based material is about 3.2V. When Li2S4 is preferably used as the lithium supplement material, in addition to slowing down the formation node of S elemental on the CEI film and reducing the impedance of the CEI film, it can also compound with the above-mentioned preferred composite anion to improve the thermal stability of the overall electrolyte, give full play to the advantages of the lithium iron phosphate-based material, and further improve the long-term thermal stability of the final secondary battery.

[0055] In some embodiments, the positive electrode material includes at least one of lithium manganese iron phosphate and doped lithium manganese iron phosphate, and in the electrolyte, the lithium supplement material includes Li5P.

[0056] Further preferably, the composite anion includes PO2F2 - , FSI - , TFSI - , FNFSI - and PF6 - .

[0057] When Li5P is preferably used as the lithium supplement material for compounding with the lithium manganese iron phosphate-based material, the oxidation potential of this component is lower than the lithium deintercalation potential of the lithium manganese iron phosphate-based positive electrode material, so the impedance of the CEI film of the positive electrode pole piece can be lower and the compatibility with the positive electrode pole piece is better.

[0058] In some embodiments, in the electrolyte, the mass content of the lithium supplement material based on the total mass of the electrolyte is 0.01 to 15%.

[0059] In some specific embodiments, partial structures of the lithium supplement material are shown in the following formulas I-1 to I-8:

[0060]

[0061]

[0062] It should be noted that in the technical solution of this application, the types and mass contents of the lithium supplement materials are confirmed by a high performance liquid chromatography - mass spectrometry (HPLC - MS) instrument. The specific method is as follows:

[0063] The electrolyte sample is injected into an Agilent Infinity III liquid chromatography - mass spectrometry (LC - MS) instrument using a micro - syringe for type (qualitative) and content (quantitative) testing:

[0064] ① Obtaining the MS standard curve and the LC peak area - concentration curve: Prepare EMC solutions with different concentrations from Formula I - 1 to I - 8 and inject them into the above - mentioned liquid chromatography - mass spectrometry instrument respectively to obtain the MS spectra and LC spectra of the standard substances. Integrate the peak areas in the LC spectra (routine processing of test data by the test software) to obtain the peak areas. Make a linear graph of the peak areas and concentrations of the standard substances with different concentrations to obtain the standard LC peak area - concentration curve.

[0065] ② Type determination: Inject the electrolyte to be tested into the above - mentioned liquid chromatography - mass spectrometry instrument to obtain the LC spectrum and MS spectrum of the electrolyte to be tested. Compare the MS spectrum of the electrolyte to be tested with the standard MS spectrum to determine whether the additives of Formula I - 1 to I - 8 are contained in the electrolyte to be tested (for example, if a corresponding peak appears at the position of the peak of Formula I - 1 in the standard spectrum in the MS spectrum of the electrolyte to be tested, it is determined that the electrolyte to be tested contains the lithium supplement additive of Formula I - 1, and so on for other components).

[0066] ③ Mass content determination:

[0067] Integrate the peaks in the LC spectrum of the electrolyte to be tested to obtain the peak area. According to the standard LC peak area - concentration curve, knowing the peak area, the concentration of the substance to be tested can be obtained.

[0068] When the electrolyte is present in a secondary battery, the following method is used to collect the electrolyte:

[0069] First, discharge the secondary battery: Use a battery charge - discharge device to discharge the battery. Discharge conditions: current 0.3C, and the cut - off voltage is set according to the characteristics of the active material system. For example: lithium iron phosphate / graphite system: 2.5V;

[0070] lithium manganese iron phosphate / graphite system: 2.5V;

[0071] lithium nickel cobalt manganese oxide / graphite system: 2.8V;

[0072] Lithium nickel cobalt manganese oxide / silicon-based system: 2.8V;

[0073] After recording the battery number / barcode, disassemble the battery in a glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm) to collect the electrolyte.

[0074] 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 pipette 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'ao De Technology Co., Ltd.) can be used to continuously apply pressure until free electrolyte appears, and then collect the electrolyte into the sample tube and seal it.

[0075] In some embodiments, in the electrolyte, the testing method for the type quantity of the composite anion and the mass content of the salt containing the composite anion is as follows:

[0076] Determine the type and concentration of anions: Inject the collected electrolyte into the sample pool 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).

[0077] 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.

[0078] In some embodiments, the mass content of the salt containing the composite anion corresponding to the composite anion in the electrolyte is 1 - 20%.

[0079] 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.

[0080] In some embodiments, the lithium iron manganese phosphate includes LiFe e Mn f PO4, where 0 < e < 1, 0 < f < 1, e + f = 1.

[0081] In some embodiments, the negative electrode material includes at least one of carbon-based materials, silicon-based materials, and lithium titanate.

[0082] Exemplarily, 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 monoxide, and silicon-carbon composite materials.

[0083] Those skilled in the art can also use other methods to prepare the negative electrode material according to the actual situation, or directly purchase commercially available products.

[0084] The following further elaborates the present invention with specific examples, and these examples should not be construed as limiting the scope claimed by the present invention:

[0085] Example 1

[0086] A battery, and the preparation method includes the following steps:

[0087] (1) Preparation of the positive electrode sheet: Dispersing the positive electrode material lithium nickel cobalt manganese oxide LiNi 0.6 Mn 0.2 Co 0.2 O2, conductive agent SP, and binder polyvinylidene fluoride in a mass ratio of 97.8:1.2:1 in N-methylpyrrolidone, dispersing under vacuum and stirring to prepare a slurry, and then coating both sides of the current collector aluminum foil, followed by rolling and cutting to obtain the positive electrode sheet;

[0088] (2) Preparation of the negative electrode sheet: Dispersing the negative electrode material artificial graphite, conductive agent SP, thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber in a mass ratio of 96.5:2.2:0.2:1.1 in water, dispersing under vacuum and stirring to prepare a slurry, and then coating both sides of the current collector copper foil, followed by rolling and cutting to obtain the negative electrode sheet;

[0089] (3) Preparation of the separator: Using a PP separator with an average pore size of 2 μm and an air permeability of 300 s / 100 mL, and an alumina ceramic coating is provided on the separator;

[0090] (4) Preparation of the electrolyte: Mixing ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3:5:2 as the solvent; then adding lithium salts containing specific composite anions with the mass contents recorded in Table 1 respectively, and finally adding a lithium supplement material and mixing evenly to obtain the electrolyte, as shown in Table 1, where n is BOB in the electrolyte - , PO2F2 - , ODFB - , FSI - , TFSI - , ODFP - , FNFSI- , BF4 - , PF6 - , FEA - The number of types of these composite anions, where x is the unit mole number of the metal element in the lithium supplement material (for example, when the lithium supplement material is Li3P7, x = 3).

[0091] (5) Stack and wind the positive electrode sheet, separator (coated side facing the positive electrode sheet), and negative electrode sheet in sequence to assemble into an electric core (the alumina coating of the separator faces the positive electrode). Place the electric core into an outer packaging shell, inject the electrolyte after drying, and obtain the battery after vacuum packaging, standing, formation, and constant volume.

[0092] Examples 2 to 18

[0093] A battery, which is only different from Example 1 in that the component composition of the electrolyte is different, and the results are shown in Table 1.

[0094] Example 19

[0095] A battery, and the preparation method includes the following steps:

[0096] (1) Preparation of the positive electrode sheet: Disperse the positive electrode material lithium iron phosphate LiFePO4, conductive agent SP, and binder polyvinylidene fluoride in N-methylpyrrolidone according to a mass ratio of 97.8:1.2:1, vacuum stir to prepare a slurry, and then coat it on both sides of the current collector aluminum foil. After rolling and cutting, the positive electrode sheet is obtained;

[0097] (2) Preparation of the negative electrode sheet: Disperse the negative electrode material artificial graphite, conductive agent SP, thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber in water according to a mass ratio of 96.5:2.2:0.2:1.1, vacuum stir to prepare a slurry, and then coat it on both sides of the current collector copper foil. After rolling and cutting, the negative electrode sheet is obtained;

[0098] (3) Preparation of the separator: Use a PP separator with an average pore size of 2 μm and a gas permeability of 300 s / 100 mL; an alumina ceramic coating is provided on the separator;

[0099] (4) Preparation of the electrolyte: Mix ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3:5:2 as the solvent; then add lithium salts containing specific composite anions with the mass contents recorded in Table 1 respectively, and finally add a lithium supplement material with a specific mass content and mix evenly to obtain the electrolyte;

[0100] (5) Stack and wind the positive electrode sheet, separator (coated side facing the positive electrode sheet), and negative electrode sheet in sequence to assemble into an electric core, place the electric core into an outer packaging shell, inject the electrolyte after drying, and obtain the battery after vacuum packaging, standing, formation, and constant volume.

[0101] Examples 20 - 28

[0102] A battery, which is only different from Example 19 in that the component composition of the electrolyte is different, and the results are shown in Table 1.

[0103] Example 29

[0104] A battery, the preparation method of which includes the following steps:

[0105] (1) Preparation of the positive electrode sheet: Lithium iron manganese phosphate LiFe 0.5 Mn 0.5 PO4, a conductive agent SP, and a binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone according to a mass ratio of 97.8:1.2:1, and a slurry is prepared by vacuum stirring. Then, it is coated on both sides of a current collector aluminum foil, and after rolling and cutting, the positive electrode sheet is obtained;

[0106] (2) Preparation of the negative electrode sheet: Artificial graphite as the negative electrode material, a conductive agent SP, a thickener sodium carboxymethyl cellulose, and a binder styrene-butadiene rubber are dispersed in water according to a mass ratio of 96.5:2.2:0.2:1.1, and a slurry is prepared by vacuum stirring. Then, it is coated on both sides of a current collector copper foil, and after rolling and cutting, the negative electrode sheet is obtained;

[0107] (3) Preparation of the separator: A PP separator with an average pore size of 2 μm and an air permeability of 300 s / 100 mL is used;

[0108] (4) Preparation of the electrolyte: Ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate are mixed as solvents according to a volume ratio of 3:5:2; then, a lithium salt containing a specific composite anion with the mass content recorded in Table 1 is added respectively, and finally, a lithium supplement material with a specific mass content is added and mixed evenly to obtain the electrolyte;

[0109] (5) The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in sequence to assemble an electric core. The electric core is placed in an outer packaging shell, dried, and then the electrolyte is injected. After vacuum packaging, standing, forming, and constant volume, the battery is obtained.

[0110] Examples 30 - 36

[0111] A battery, which is only different from Example 29 in that the component composition of the electrolyte is different, and the results are shown in Table 1.

[0112] Example 37

[0113] A battery, which is only different from Example 1 in that the component composition of the electrolyte is different, and the results are shown in Table 1.

[0114] Comparative Examples 1 - 3

[0115] A battery, which is only different from that of Example 1 in that the component composition of the electrolyte is different, and the results are shown in Table 1.

[0116] Comparative Examples 4-6

[0117] A battery, which is only different from that of Example 19 in that the component composition of the electrolyte is different, and the results are shown in Table 1.

[0118] Comparative Examples 7-9

[0119] A battery, which is only different from that of Example 29 in that the component composition of the electrolyte is different, and the results are shown in Table 1.

[0120] Table 1

[0121]

[0122]

[0123]

[0124]

[0125]

[0126] Effect Example

[0127] The batteries obtained in each of the examples and comparative examples were tested as follows:

[0128] (1) Positive electrode sheet CEI impedance test: The battery was charged at a constant current and constant voltage at a rate of 0.3C to the upper limit voltage on a LAND charge and discharge system, with the cut-off current ≤ 0.05C; then discharged at a rate of 0.3C to the lower limit voltage, and the above steps were repeated 3 times, and the actual discharge capacity of the third time was used as the discharge capacity of the battery; subsequently, it was charged at a rate of 0.3C to 50% of the third discharge capacity; based on the different positive electrode materials used in the battery, the upper and lower limits of the working voltage were different:

[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 2.8-4.25 V; Examples 19-28 and Comparative Examples 4-6 correspond to 2.5-3.65 V; Examples 29-36 and Comparative Examples 7-9 correspond to 2.5-4.25 V.

[0132] Subsequently, the battery was removed, the electrode tabs were wrapped with insulating glue, and then transferred to a vacuum glove box (H2O ≤ 0.01 ppm, O2 ≤ 0.01 ppm) to disassemble the positive electrode sheet. The positive electrode sheet was placed in a polytetrafluoroethylene box containing DMC for cleaning, naturally dried, cut into circular pieces with a diameter of 9 mm and sealed; the circular pieces were stacked and assembled into a symmetric battery in the order of circular piece, electrolyte (10 μL), separator, electrolyte (10 μL), and circular piece with the same type of separator and electrolyte as those in the batteries obtained in each example and comparative example. After standing for 24 h, an impedance spectrum was measured using a CS310X multi-channel electrochemical workstation under the conditions of an amplitude of 5 mV and a frequency of 100,000-0.1 Hz; after obtaining the impedance spectrum, the value of the horizontal axis when -Z” = 0 was taken as R1, and the inflection point of the ellipse, i.e., the minimum value of the curve, was taken as R2; the impedance R of the positive electrode CEI = R2 - R1

[0133] (2) Cycle capacity retention rate: Set the working environment at 60 °C, charge the battery to the upper limit voltage at a constant current and constant voltage of 1C rate on a LAND (Blue Electric) charge-discharge system, with the cut-off current less than or equal to 0.05C; then discharge it to the lower limit voltage at a 1C rate; repeat the above steps 1000 times, and count the discharge capacity at the 1000th time. The discharge capacity retention rate (%) after 1000 cycles = 100% × discharge capacity A1 at the 1000th cycle / discharge capacity A0 at the first cycle;

[0134] Based on the different positive electrode materials used in the battery, the upper and lower limits of the working voltage are different:

[0135] LiFePO4: 2.5 V to 3.65 V; LiFe 0.5 Mn 0.5 PO4: 2.5 V to 4.25 V;

[0136] LiNi 0.6 Mn 0.2 Co 0.2 O2: 2.8 V to 4.25 V.

[0137] Examples 1-18, Example 37, and Comparative Examples 1-3 correspond to 2.8-4.25 V; Examples 19-28 and Comparative Examples 4-6 correspond to 2.5-3.65 V; Examples 29-36 and Comparative Examples 7-9 correspond to 2.5-4.25 V.

[0138] The test results are shown in Table 2.

[0139] Table 2

[0140]

[0141]

[0142] It can be seen from Table 2 that:

[0143] (1) When the electrolyte described in this application is applied to secondary batteries, efficient lithium supplementation can be achieved, while reducing the impedance of the CEI film layer in the battery. The CEI film impedance on the positive electrode plate in the ternary system secondary batteries corresponding to the products of Examples 1 to 18 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%, up to more than 86%; for the lithium iron phosphate system secondary batteries corresponding to Examples 19 to 28, the CEI film impedance on the positive electrode plate 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%, up to more than 88%; for the lithium manganese iron phosphate system secondary batteries corresponding to Examples 29 to 36, the CEI film impedance on the positive electrode plate can be maintained within the range of 45 mΩ, and the capacity retention rate after 1000 cycles at 1C rate can reach more than 78.5%, up to more than 81%. This is mainly due to the application of lithium supplementation materials and the specific selection of composite anions in the electrolyte, enabling the lithium supplementation materials to achieve good solubility and stability in the electrolyte, and forming a competitive relationship with the anions in the lithium supplementation materials based on entropy disorder, forming a certain amount of low-impedance inorganic salts on the CEI film. Finally, after lithium supplementation, the electrolyte can still maintain a relatively high overall ionic conductivity, improving the fast charging performance of the corresponding secondary batteries; in contrast, although composite anions are also introduced in each comparative example product, due to insufficient quantity or improper selection of types, regardless of whether the total amount of additives is the same as that of the example products, the ideal entropy disorder of the electrolyte system cannot be achieved, the formed CEI film has a higher impedance, and the cycle life of the secondary battery is also much shorter than that of the example products.

[0144] (2) From the comparison among the products of Examples 1 to 18, it can be seen that selecting composite anions including FSI - , TFSI - , FNFSI - and FEA - can achieve better battery kinetic performance and cycle life based on the optimization of ionic radius size. When the positive electrode material includes ternary system materials, selecting a lithium supplementation material such as LiP3 with an oxidation potential lower than the lithium deintercalation potential of the ternary system materials can make the oxidation time node of the lithium supplementation material later when the positive electrode CEI film is formed, thereby having a better control level of the CEI film impedance; on the other hand, when LiP3 is selected as the lithium supplementation material, it can be seen from Examples 4 to 7 that further optimizing to include BOB -PO2F2 - 、BF4 - and PF6 - The composite anions contained therein cooperate with the ternary materials to effectively inhibit the dissolution of transition metal ions in the ternary materials, and the CEI membrane components formed thereby have better protection effects on the positive electrode materials, better interface stability, and better cycle performance of the resulting secondary battery.

[0145] Lithium Supplement Material M x T y The metal cations, anions and the compounded composite anions in the lithium supplement material form a Lewis acid-base solvent system. The unit molar amount of the metal cations in the lithium supplement material affects its solubility, and also changes the degree of competition between the corresponding anions and the composite anions. When the product of the unit molar number of the metal element in the lithium supplement material and the number of types of composite anions in the electrolyte is preferably 5 to 14, the corresponding battery comprehensive performance will also be better. The number of types of composite anions itself will affect the overall mixing entropy of the electrolyte, thereby affecting the oxidation degree of anions in the lithium supplement material and the overall lithium supplement efficiency of the lithium supplement material. When the number of types of composite anions is within 8, the lithium supplement material can achieve a better lithium supplement effect. At the same time, the electrolyte has a high ion transmission efficiency and high stability. The secondary battery after the electrolyte is applied to the secondary battery has excellent kinetic performance, small impedance and longer cycle life.

[0146] (3) According to the products of Examples 19 to 28 and Examples 29 to 36, it can be seen that when the corresponding battery systems are lithium iron phosphate system and lithium iron manganese phosphate system, the lithium supplement materials corresponding to the electrolyte are Li2S4 and LiP5, which have better effects. This is because the lithium de-lithiation potential of lithium iron phosphate materials is about 3.2V. When Li2S4 is used as the lithium supplement material, it can not only slow down the formation of S single substance on the CEI film and reduce the impedance of the CEI film, but also reduce the resistance of the CEI film. - TFSI - 、FNFSI - and FEA - When LiP5 is used as a lithium supplement material for compounding lithium iron phosphate materials, the oxidation potential of this component is lower than the delithiation potential of lithium iron phosphate positive electrode materials, so it can also reduce the impedance of the CEI film. - 、FSI - TFSI - 、FNFSI - and PF6 - The composite anions included can achieve better electrochemical performance.

Claims

1. An electrolyte, characterized in that, It includes a lithium supplement material and a composite anion; The lithium supplement material includes M x T y , where 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 is BOB - , PO2F2 - , ODFB - , FSI - , TFSI - , ODFP - , FNFSI - , BF4 - , PF6 - , FEA - and at least four of the following 2. The electrolyte according to claim 1, characterized in that, The number of types of the composite anion in the electrolyte ≤ 8.

3. The electrolyte according to claim 1, wherein The composite anion includes PO2F2 - , FSI - , TFSI - , FNFSI - , BF4 - , PF6 - , FEA - and at least four of the following 4. The electrolyte according to claim 3, wherein The composite anion includes FSI - , TFSI - , FNFSI - and FEA - .

5. The electrolyte according to claim 1, wherein The electrolyte satisfies: 5 ≤ x×n ≤ 14; where n is the number of types of the composite anion in the electrolyte.

6. The electrolyte according to claim 1, wherein The lithium supplement material includes M x P y , and the composite anion includes at least four of FSI - , TFSI - , FNFSI - , BF4 - , FEA - .

7. The electrolyte according to claim 1, wherein The lithium supplement material includes M x S y , and the composite anion includes PO2F2 - , FSI - , TFSI - and a fourth component, and the fourth component is BOB - , ODFB - , ODFP - , FNFSI - , BF4 - , PF6 - , FEA - at least one of them.

8. A secondary battery, characterized in that, It includes the electrolyte according to any one of claims 1 to 6; the secondary battery further includes a positive electrode plate and a negative electrode plate; the positive electrode plate includes a positive electrode material, and the negative electrode plate includes a negative electrode material.

9. The secondary battery according to claim 8, characterized in that, The positive electrode material includes at least one of lithium nickel cobalt manganese oxide, doped lithium nickel cobalt manganese oxide, lithium iron phosphate, doped lithium iron phosphate, lithium manganese iron phosphate, and doped lithium manganese iron phosphate.

10. The secondary battery according to claim 9, wherein The positive electrode material includes at least one of lithium nickel cobalt manganese oxide and doped lithium nickel cobalt manganese oxide, and in the electrolyte, the lithium supplement material includes Li3P.

11. The secondary battery according to claim 10, wherein The composite anion includes BOB - , PO2F2 - , BF4 - and PF6 - .

12. The secondary battery according to claim 9, wherein The positive electrode material includes at least one of lithium iron phosphate and doped lithium iron phosphate, and in the electrolyte, the lithium supplement material includes Li2S4.

13. The secondary battery according to claim 12, wherein The composite anion includes FSI - , TFSI - , FNFSI - and FEA - .

Images