An electrolyte, a secondary battery, and an electrical device

Abstract

This application provides an electrolyte, a secondary battery, and an electrical device, belonging to the field of new energy technology. This application weakens the solvation ability of the electrolyte and reduces the reaction between the solvent and Li by adding a specific co-solvent. + The coordination effect weakens the interaction between the solvent and Li. + Coordination competitiveness allows more anions to bind with Li. + Coordination leads to the formation of more aggregated ion pairs, thereby improving the coulombic efficiency and cycle life of the battery; at the same time, the F-containing functional groups of the cosolvent used can form a LiF interface layer between the negative and positive electrodes of the battery, which helps to improve the cycle stability of the battery.

Description

Technical Field

[0001] This application belongs to the field of new energy technology and relates to an electrolyte, a secondary battery and an electrical device. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles and energy storage due to their high energy density, good cycle performance, rapid charging and discharging capabilities, and environmental friendliness. In recent years, the rapid development of the electric vehicle industry has driven the development and advancement of lithium-ion battery technology, which is the core of energy supply. The market demands increasingly higher performance from lithium-ion batteries, such as higher coulombic efficiency and better cycle performance. Therefore, it is necessary to develop a technology to effectively improve their coulombic efficiency and cycle performance. Summary of the Invention

[0003] Based on the deficiencies of the existing technology, the purpose of this application is to provide an electrolyte, a secondary battery, and an electrical device.

[0004] To achieve the above objectives, in a first aspect, this application provides an electrolyte comprising a main solvent, a co-solvent, a diluent, and a lithium salt, wherein the co-solvent comprises at least one compound of formula I.

[0005]

[0006] In Equation I, x is an integer from 0 to 2.

[0007] In some embodiments, the co-solvent includes at least one of compound A, compound B, and compound C.

[0008]

[0009] In some embodiments, the mass ratio of the main solvent, the co-solvent, and the diluent is 1:(0.4-1.5):(5-12).

[0010] In some embodiments, the Raman spectrum of the electrolyte is in the range of 745-760 cm⁻¹. -1 It exhibits characteristic peaks of aggregated ion pair structure within the wavelength range.

[0011] In some embodiments, the aggregated ion pair content is ≥60%.

[0012] In some embodiments, the main solvent includes at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and fluoroethylene carbonate.

[0013] In some embodiments, the diluent includes at least one selected from 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis(2,2,2-trifluoroethyl ether), fluorobenzene, difluorobenzene, and trifluoromethoxybenzene.

[0014] In some embodiments, at least one of conditions S1 to S2 is satisfied:

[0015] S1. The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonate)imide, lithium tetrafluoroborate, lithium perchlorate, and lithium trifluoromethanesulfonate;

[0016] S2. The concentration of the lithium salt in the electrolyte is 1-3 mol / L.

[0017] In a second aspect, a secondary battery is provided, which includes the electrolyte.

[0018] Thirdly, an electrical device is provided, including the secondary battery, which serves as a power supply for the electrical device.

[0019] Compared with the prior art, the beneficial effects of this application are as follows: This application weakens the solvation ability of the electrolyte by adding a specific co-solvent to the electrolyte, thereby reducing the reaction between the solvent and Li. + The coordination effect weakens the interaction between the solvent and Li. + The competitive advantage of coordination leads to more anions reacting with Li. + Coordination leads to the formation of more aggregated ion pairs (AGG) structures, improving the coulombic efficiency and cycle life of the battery. At the same time, the F-containing functional groups in the cosolvent can form a LiF interface layer between the negative and positive electrodes of the battery, which helps to improve the cycle stability of the battery. Attached Figure Description

[0020] Figure 1 This is a synthetic route diagram for compound I;

[0021] Figure 2 The NMR 1H and NMR 1F spectra of DPE-F5 (i.e., compound of formula C) are shown.

[0022] Figure 3 A comparison of the coulombic efficiencies of Li-Cu half-cells using GSE1 electrolyte and STD1 electrolyte;

[0023] Figure 4 A comparison of the cycle performance of Li-NCM monolayer pouch cells using GSE1 electrolyte and STD1 electrolyte. Detailed Implementation

[0024] To better illustrate the purpose, technical solutions, and advantages of this application, the following description, in conjunction with specific embodiments and comparative examples, aims to provide a detailed understanding of the content of this application, rather than limiting it. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this application. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this application are commonly used reagents and instruments. In this application, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0025] This application provides an electrolyte comprising a main solvent, a co-solvent, a diluent, and a lithium salt, wherein the co-solvent comprises at least one compound of formula I.

[0026]

[0027] In Equation I, x is an integer from 0 to 2.

[0028] This application adds a specific co-solvent to the electrolyte, whose solvation ability is weaker than that of the main solvent. Therefore, its introduction weakens the solvation ability of the electrolyte and reduces the solubility of the solvent and Li. + The coordination effect weakens the interaction between the solvent and Li. + The competitive advantage of coordination leads to more anions reacting with Li. + Coordination leads to the formation of more aggregated ion pairs (AGG) structures, thereby improving the coulombic efficiency and cycle life of the battery. Furthermore, the F-containing functional groups in the aforementioned cosolvent can form a LiF interfacial layer between the negative and positive electrodes, contributing to improved cycle stability.

[0029] The electrolyte in this application has a higher content of aggregated ion pairs compared to traditional electrolytes with the same lithium salt concentration due to the introduction of a specific cosolvent, resulting in higher battery coulombic efficiency and better cycle performance.

[0030] In some embodiments, the co-solvent comprises at least one of compound A, compound B, and compound C.

[0031]

[0032] When the cosolvent includes at least one of compounds of formula A, B, and C, the content of aggregated ion pairs in the electrolyte is higher, the battery coulombic efficiency is higher, and the cycle performance is better. The effects of compounds of formula A, B, and C on increasing the content of aggregated ion pairs in the electrolyte, improving battery coulombic efficiency, and improving battery cycle performance are all progressively stronger.

[0033] In some embodiments, the synthetic route for preparing the compound of formula I is as follows: Figure 1 As shown, it includes the following steps:

[0034] At -20 to 10°C, 4-toluenesulfonyl chloride, isopropoxyethanol and alkaline catalyst were added to the first solvent and stirred to obtain a white suspension. The suspension was then extracted with a second solvent. The organic layer obtained from the extraction was removed from the solvent to obtain intermediate product I (Ts-2-iPE).

[0035] At -20 to 10°C, fluorinated alcohol CF3CH (2-x) F x CH2OH (x is an integer from 0 to 2) and NaH are dissolved in a third solvent, and the reaction is stirred until no more bubbles are produced to obtain sodium fluoroalkoxide CF3CH. (2-x) F x CH2ONa was added, and then intermediate I was added. The mixture was heated to produce a brown precipitate, which was then extracted with a fourth solvent. The organic layer obtained from the extraction was then removed from the solvent to obtain compound I.

[0036] In one embodiment, the alkaline catalyst includes at least one of KOH and NaOH.

[0037] In one embodiment, the molar ratio of 4-toluenesulfonyl chloride, isopropoxyethanol and alkaline catalyst is (0.4-0.5):0.4:(0.4-0.5).

[0038] In one embodiment, the molar concentration of 4-toluenesulfonyl chloride in the first solvent is 1-2M.

[0039] In one embodiment, the first solvent includes at least one of dichloromethane and acetonitrile.

[0040] In one embodiment, the reaction of 4-toluenesulfonyl chloride and isopropoxyethanol to generate intermediate I was carried out under ice bath conditions.

[0041] In one embodiment, the reaction time for generating intermediate I using 4-toluenesulfonyl chloride and isopropoxyethanol is 4 to 12 hours.

[0042] In one embodiment, during the preparation of intermediate product I, after extraction with a second solvent, the solvent is removed from the extracted organic layer by rotary evaporation.

[0043] In one embodiment, the second solvent includes at least one of dichloromethane and acetonitrile.

[0044] In one embodiment, fluoroalcohol CF3CH (2-x) F x CH2OH includes at least one of CF3CH2CH2OH, CF3CHFCH2OH, and CF3CF2CH2OH.

[0045] In one embodiment, fluorinated alcohol CF3CH is used (2-x) F x CH2OH and NaH react to produce sodium fluoride alcohol CF3CH (2-x) F x The reaction of CH2Ona was carried out under ice bath conditions.

[0046] In one embodiment, sodium fluoroalkoxide CF3CH (2-x) F x CH2ONa includes at least one of CF3CH2CH2ONa, CF3CHFCH2ONa, and CF3CF2CH2ONa.

[0047] In one embodiment, fluoroalcohol CF3CH (2-x) F x The molar ratio of CH2OH to NaH is 1:1.

[0048] In one embodiment, the fluoroalcohol has a molar concentration of 1-3 M in the third solvent.

[0049] In one embodiment, the third solvent includes at least one of tetrahydrofuran (THF) and 2-methyltetrahydrofuran.

[0050] In one embodiment, the heating reaction is carried out at a temperature of 40–70°C for a duration of 4–16 hours.

[0051] In one embodiment, the fourth solvent includes at least one of dichloromethane and acetonitrile.

[0052] In one embodiment, during the preparation of compound I using intermediate product I, the solvent removal method for the extracted organic layer after extraction with a fourth solvent includes vacuum distillation.

[0053] In one embodiment, the mass ratio of the main solvent, co-solvent, and diluent is 1:(0.4-1.5):(5-12).

[0054] When the mass ratio of the main solvent to the co-solvent is in the range of 1:(0.4-1.5), such as 1:0.4, 1:0.6, 1:0.8, 1:1, 1:1.3, 1:5, or any two of these ranges, it can induce more anions to react with Li while ensuring that the electrolyte has high ionic conductivity. + Coordination leads to the formation of more aggregated ion pairs, resulting in better coulombic efficiency and cycle performance of the battery.

[0055] When the mass ratio of the main solvent to the diluent is in the range of 1:(5-12), such as 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12 or any two of the above values, the electrolyte viscosity is better, the ionic conductivity is higher, and the role of the main solvent can be better utilized, thereby improving the coulombic efficiency and cycle performance of the battery.

[0056] In some embodiments, the mass fraction of the main solvent in the electrolyte is 5% or more, such as 5%, 7%, 9%, 11%, 13%, 15%, 17%, 18%, 19%, 20%, or any two of these values ​​forming a range.

[0057] The Raman spectrum of the electrolyte is in the range of 745-760 cm⁻¹. -1 The electrolyte exhibits characteristic peaks of aggregated ion pair structure within a wavelength range. In some embodiments, the aggregated ion pair content is ≥60%, such as a range formed by any two values ​​of 60%, 62%, 64%, 66%, 68%, 70%, 72%, 75%, or higher. The aggregated ion pair content is calculated as: (Peak area of ​​aggregated ion pair characteristic peak in the Raman spectrum of the electrolyte / Peak area of ​​lithium salt characteristic peak) × 100%.

[0058] In some embodiments, the main solvent includes at least one of ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and fluoroethylene carbonate (FEC).

[0059] In some embodiments, the diluent includes at least one selected from 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFE), bis(2,2,2-trifluoroethyl ether) (BTFE), fluorobenzene (FB), difluorobenzene (DFB), and trifluoromethoxybenzene (TFMB).

[0060] In some embodiments, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonate)imide (LiTFSI), lithium tetrafluoroborate, lithium perchlorate, and lithium trifluoromethanesulfonate.

[0061] In some embodiments, the concentration of lithium salt in the electrolyte is 1-3 mol / L, such as 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 18 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, or any two of the above values. Even at lower electrolyte concentrations, such as within the 1-3 mol / L range, the content of aggregated ion pairs is higher than that of conventional high-salt electrolytes; simultaneously, the lower lithium salt concentration results in a more suitable electrolyte viscosity, higher ionic conductivity, and lower cost.

[0062] The electrolyte may be free of other additives or may contain other commonly used additives, such as fluorinated additives, nitrogen-containing additives, and self-polymerizing additives. For example, fluorinated additives include at least one of fluoroethylene carbonate, dimethyl fluorocarbonate, fluorocarbamate, and lithium difluorooxalate borate; nitrogen-containing additives include at least one of lithium nitrate, isosorbide dinitrate, and trimethyl azidosilane; and self-polymerizing additives include at least one of dioxapentane and trioxane.

[0063] In some embodiments, the method for preparing the electrolyte includes the following steps:

[0064] Under an inert atmosphere, the main solvent, co-solvent, and diluent are first mixed and dispersed to obtain a mixed solvent. Then, lithium salt is added to the obtained mixed solvent and dispersed to obtain an electrolyte.

[0065] This application also provides a secondary battery comprising the above-described electrolyte. Due to the use of the electrolyte, the secondary battery exhibits higher coulombic efficiency and better cycle performance.

[0066] The secondary battery also includes a negative electrode. This application does not impose any particular limitation on the negative electrode; any commonly used negative electrode in the art can be used. In some embodiments, the negative electrode includes a lithium metal negative electrode. Lithium metal negative electrodes possess an ultra-high theoretical specific capacity (3860 mAh·g). -1 It also features a low redox potential (-3.04 V vs. standard hydrogen electrode) and a low density (0.534 g·cm³). -3Lithium metal is considered an ideal negative electrode in lithium batteries. However, the high chemical and electrochemical activity of lithium metal itself can cause harmful side reactions between the lithium metal negative electrode and the electrolyte, continuously consuming lithium metal and electrolyte, and causing uneven lithium deposition, leading to dendrite growth, increasing the specific surface area of ​​the lithium metal negative electrode, and accelerating interfacial side reactions between the negative electrode and the electrolyte. The secondary batteries in these embodiments, due to the use of the aforementioned electrolyte, have a higher content of aggregated ion pairs in the electrolyte. These aggregated ion pairs preferentially reduce the lithium metal negative electrode compared to the solvent, constructing a fast-conducting SEI dominated by inorganic matter, inducing more uniform lithium deposition, and improving the battery's coulombic efficiency and cycle life. Simultaneously, the F-containing functional groups of the co-solvent in the electrolyte can form a LiF interfacial layer between the negative and positive electrodes, contributing to improved battery cycle stability.

[0067] The secondary battery also includes a positive electrode. This application does not impose any particular limitation on the positive electrode; any commonly used positive electrode in the art can be used. In some embodiments, the positive electrode includes a current collector and a positive electrode material layer disposed on at least one side of the current collector. The positive electrode material layer comprises a ternary material, which includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. The molar amount of nickel in the ternary material / the total molar amount of nickel, cobalt, manganese, and aluminum is ≥0.8, such as 0.8, 0.82, 0.84, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96, or any two of the above values ​​forming a range.

[0068] In some embodiments, the negative electrode includes a lithium metal negative electrode, and the positive electrode includes a current collector and a positive electrode material layer disposed on at least one side of the current collector. The positive electrode material layer comprises a ternary material, which includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. The molar amount of nickel in the ternary material / the total molar amount of nickel, cobalt, manganese, and aluminum is ≥0.8 (e.g., 0.8, 0.82, 0.84, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96, or any two of the above values ​​within a range). The secondary batteries of these embodiments achieve stable battery cycling within a voltage range of 2.5-4.25V.

[0069] The secondary battery also includes a separator located between the positive and negative electrode plates to separate them and prevent short circuits caused by contact. This application does not impose any particular limitation on the separator; any commonly used separator in the art can be used. In some embodiments, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, etc.

[0070] This application also provides an electrical device, including the aforementioned secondary battery, which serves as the power supply for the electrical device.

[0071] The present application will be further illustrated below through specific embodiments, wherein the co-solvent DPE-F is used. x+3 The preparation method is as follows:

[0072] DPE-F5 (i.e., compound C): Under ice bath conditions, 0.44 mol of 4-toluenesulfonyl chloride (Ts-Cl), 0.5 mol of potassium hydroxide and 0.4 mol of isopropoxyethanol (2-iPE) were added to 250 mL of dichloromethane and stirred for 4 h to obtain a white suspension. The suspension was extracted with dichloromethane, and the organic layer obtained by rotary evaporation was used to obtain intermediate product I (Ts-2-iPE), with a yield >98% (mol / mol, the same below).

[0073] Under ice bath conditions, 0.4 mol of fluoroalcohol CF3CF2CH2OH and 0.4 mol of NaH were dissolved in 150 mL of THF solvent and stirred until no bubbles were generated to obtain sodium fluoroalcohol CF3CF2CH2ONa. Then, 0.4 mol of intermediate product I was added, and the mixture was heated at 60 °C for 12 h to obtain a brown precipitate. The precipitate was extracted with dichloromethane, and the organic layer obtained by extraction was distilled under reduced pressure to obtain the final product DPE-F5 with a yield >95%.

[0074] DPE-F4 (i.e., compound B): The preparation method differs from DPE-F5 in that the co-solvent DPE-F... x+3 In the process, an equimolar amount of fluorinated alcohol CF3CHFCH2OH was used to replace fluorinated alcohol CF3CF2CH2OH, and the yield of DPE-F4 was >95%.

[0075] DPE-F3 (i.e., compound A): The preparation method differs from DPE-F5 in that the co-solvent DPE-F... x+3 In the process, an equimolar amount of fluorinated alcohol CF3CH2CH2OH was used to replace fluorinated alcohol CF3CF2CH2OH, and the yield of DPE-F4 was >95%.

[0076] Example 1

[0077] At 25°C, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), the main solvent, co-solvent, and diluent were measured separately according to the mass ratio of main solvent:co-solvent:diluent = 1.5:1:12, stirred to obtain a mixed solvent. Then, 1 L of this mixed solvent was taken and 1.5 mol of LiFSI was added, and stirred until completely dissolved to obtain the electrolyte. The main solvent was ethylene glycol dimethyl ether (DME), the co-solvent was DPE-F5, and the diluent was 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE).

[0078] Examples 2-9

[0079] The difference from Example 1 is that the mass ratio of the main solvent, co-solvent, and diluent used in the preparation of the electrolyte is different, as detailed in Table 1.

[0080] Examples 10-12

[0081] The difference from Example 1 is that the mass ratio (if any) of the main solvent, co-solvent and diluent used in the preparation of the electrolyte and the concentration of lithium salt in the electrolyte are different, as detailed in Table 1.

[0082] Examples 13-14

[0083] The difference from Example 1 is that the types of co-solvents used in the preparation of the electrolyte are different, as detailed in Table 1.

[0084] Examples 15-16

[0085] The difference from Example 1 is that the types of diluents used in the preparation of the electrolyte and the mass ratio of the main solvent, co-solvent and diluent are different, as detailed in Table 1.

[0086] Examples 17-21

[0087] The difference from Example 1 is that the types of main solvents, and / or diluents, and / or lithium salts used in the preparation of the electrolyte are different, as detailed in Table 1.

[0088] Comparative Example 1

[0089] The difference from Example 1 is that no co-solvent was used in the preparation of the electrolyte, and the mass ratio of the main solvent to the diluent is different, as detailed in Table 1.

[0090] Comparative Example 2

[0091] Unlike Example 1, no diluent was used in the preparation of the electrolyte, as detailed in Table 1.

[0092] Comparative Example 3

[0093] The difference from Example 1 is that no diluent was used in the preparation of the electrolyte, and the lithium salt concentration in the electrolyte is different, as detailed in Table 1.

[0094] Comparative Example 4

[0095] The difference from Example 1 lies in the type of co-solvent used in the preparation of the electrolyte. The co-solvent used in this comparative example is (CH3)2CHOCH2OCH2CH2CF3 (TFMPP), with the following structural formula:

[0096]

[0097] The electrolytes obtained in Examples 1 to 21 are recorded as GSE1 electrolyte, GSE2 electrolyte, GSE3 electrolyte, ... GSE21 electrolyte (i.e., the electrolyte obtained in Example x is recorded as GSEx electrolyte); the electrolytes obtained in Comparative Examples 1 to 4 are recorded as STD1 electrolyte, STD2 electrolyte, STD3 electrolyte, and STD4 electrolyte.

[0098] Test case

[0099] The electrolytes obtained in the above embodiments and comparative examples were subjected to the following performance tests:

[0100] (1) Nuclear magnetic resonance test

[0101] Take 0.05 mL of DPE-F x+3 A series of solvents were mixed with 0.5 mL of deuterated chloroform, dispersed, injected into NMR tubes, and sealed. NMR H-spectroscopy and NMR F-spectroscopy were then performed. The test results for DPE-F5 solvent are as follows: Figure 2 As shown.

[0102] (2) AGG content test in electrolyte

[0103] A small amount of electrolyte was drawn using a capillary tube, and Raman spectroscopy was performed to characterize the sample. The results were analyzed at approximately 750 cm⁻¹. -1 The characteristic peaks of aggregated ion pair (AGG) structures were observed, and the AGG content was quantitatively determined.

[0104] (3) Average Coulomb efficiency test

[0105] A copper counter electrode was obtained by cutting a 6μm copper foil. The copper counter electrode, a separator (PP separator), and a 200μm lithium metal negative electrode were stacked in sequence and placed in a battery case. 30μL of electrolyte was added dropwise using a pipette. The battery was then pressurized and sealed using a button cell sealing machine at a pressure of 30 kPa to produce a lithium-copper half-cell. The coulombic efficiency of the resulting lithium-copper half-cell was then tested. The specific test method is as follows: At 25℃, the lithium-copper half-cell was subjected to a pressure test at 1 mA·cm⁻¹. -2 First, deposit 3 mAh·cm at the current density. -2 Lithium-to-copper current collector, charged to 1V, recorded lithium stripping capacity as C1mAh·cm⁻¹ -2 Coulomb efficiency CE1% = C1 / 3 × 100%; repeat this cycle 50 times, and calculate the average coulomb efficiency CE from the 6th to the 50th cycle. Ave. %, where the coulombic efficiency of GSE1 and STD1 electrolytes is as follows: Figure 3 As shown.

[0106] (4) Battery cycle stability test

[0107] LiNi, the positive electrode active material 0.92 Co0.07 Mn 0.01 O2 (NCM), conductive agent acetylene black (Super P), and binder polyvinylidene fluoride (PVDF) in the mass ratio of LiNi 0.92 Co 0.07 Mn 0.01 O2:Super P:PVDF = 90:6:4 was mixed evenly and dispersed in 1-methyl-2-pyrrolidone (NMP) to prepare a black slurry. The resulting black slurry was coated on both sides of an aluminum foil, then baked, rolled, and cut to obtain the positive electrode sheet with a surface capacity of 4.5 mAh / cm². 2 ;

[0108] The prepared positive electrode sheet, separator (PP separator), and 20μm lithium metal negative electrode sheet are stacked in sequence so that each positive electrode film layer and negative electrode film layer are covered with a separator. Then, they are stacked into a cell, hot-pressed, and the tabs are welded and put into an outer packaging shell. After baking and drying, GSE1 electrolyte is injected at a volume of 2g / Ah. Then, after standing, formation, aging and capacity testing, a single-layer soft-pack lithium-high nickel ternary full cell is made.

[0109] A single-layer soft-pack lithium-high nickel ternary full battery was charged and discharged at 25℃ with a charging rate of 0.5C, a discharging rate of 0.2C, and a voltage range of 2.5-4.25V. The capacity retention rate of the nth cycle was recorded as (discharge specific capacity of the nth cycle / discharge specific capacity of the first cycle) × 100%. The number of cycles when the capacity retention rate decays to 80% is the battery cycle life.

[0110] The test results are shown in Table 1.

[0111] Table 1

[0112]

[0113]

[0114] As can be seen from the above data, the electrolytes in the embodiments of this application have high AGG content, and the batteries used have high coulombic efficiency and good cycle performance. For example, when the AGG content is above 60%, the average coulombic efficiency is above 99.10%, and the cycle life is above 80 cycles.

[0115] As can be seen from the comparison of Examples 1 to 5, the mass ratio of the main solvent to the co-solvent affects the AGG content, average coulombic efficiency, and cycle life in the electrolyte. When the mass ratio is in the range of 1:(0.4-1.5), the AGG content in the electrolyte is higher, the average coulombic efficiency is higher, and the cycle life is longer.

[0116] A comparison of Examples 1 to 9 shows that the mass ratio of the main solvent to the diluent affects the AGG content, average coulombic efficiency, and cycle life in the electrolyte. When the mass ratio is in the range of 1:(5-12), the AGG content in the electrolyte is higher, the average coulombic efficiency is higher, and the cycle life is longer.

[0117] Comparative Example 1 had a lower AGG content, lower average coulombic efficiency, and shorter cycle life because the electrolyte did not contain a co-solvent.

[0118] Comparative Examples 2 and 3, because the electrolyte does not contain a diluent, even if the lithium salt concentration is increased to make the AGG content in the electrolyte higher, the average coulombic efficiency is still low and the cycle life is still short.

[0119] Comparative Example 4, due to the use of other co-solvents, had a lower AGG content in the electrolyte, resulting in a lower average coulombic efficiency and a shorter cycle life.

[0120] Depend on Figure 3 It can be seen that, compared to the electrolyte in Comparative Example 1, the coulombic efficiency is higher when using the electrolyte in Example 1. Figure 4 It can be seen that, compared with the electrolyte of Comparative Example 1, the electrolyte of Example 1 has better cycle performance.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. An electrolyte, characterized by, The electrolyte comprises a main solvent, a co-solvent, a diluent and a lithium salt, wherein the co-solvent comprises at least one of the compounds of Formula I, Ⅰ ； In Formula I, x is an integer from 0 to 2. The electrolyte has a Raman spectrum having a peak in the range of 745-760 cm -1 characteristic of an aggregated ion pair structure.

2. The electrolyte of claim 1, wherein The co-solvent comprises at least one of the compounds of Formula A, Formula B and Formula C, 3. The electrolyte of claim 1, wherein The mass ratio of the main solvent, the co-solvent and the diluent is 1 : (0.4-1.5) : (5-12).

4. The electrolyte of claim 1, wherein The content of the aggregated ion pairs is ≥60%.

5. The electrolyte of claim 1, wherein The main solvent comprises at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and fluoroethylene carbonate.

6. The electrolyte of claim 1, wherein The diluent comprises at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis (2,2,2-trifluoroethyl ether), fluorobenzene, difluorobenzene and trifluoromethoxybenzene.

7. The electrolyte of claim 1, wherein At least one of the following conditions S1-S2 is satisfied: S1. The lithium salt comprises at least one of lithium bisfluorosulfonylimide, lithium bistrifluoromethylsulfonylimide, lithium tetrafluoroborate, lithium perchlorate and lithium trifluoromethylsulfonate; S2. The concentration of the lithium salt in the electrolyte is 1-3 mol / L.

8. A secondary battery, characterized by, The secondary battery comprises the electrolyte according to any one of claims 1-7.

9. An electric device, characterized by The secondary battery according to claim 8 is used as a power supply for the power-consuming device.

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