Pressure-resistant electrolyte and lithium ion battery using same

Abstract

The application provides a kind of pressure-resistant electrolyte, electrolyte includes organic solvent component, lithium salt component and additive component, additive component includes functional additive A;The general structure of functional additive A is: Wherein, R11, R12, R13 independently selected from hydrogen or C1-C4 alkyl or C1-C4 substituted alkyl, R2 is cyanomethyl or cyanoethyl, at least one of R3, R4 includes carbon-carbon double bond;The molar mass of functional additive A is 180-280, in the pressure-resistant electrolyte, the mass ratio of the functional additive A is 0.3wt.-%-1wt.-%. Functional additive A can form CEI film, SEI film on the surface of positive electrode and negative electrode of lithium ion battery respectively, effectively reduce electrode interface side reaction in the process of lithium ion battery cycle, in addition, functional additive A shows obvious superiority under high pressure application condition, so that the pressure-resistant electrolyte of the present application can effectively improve the capacity attenuation and voltage drop of battery product in the process of high pressure cycle.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a pressure-resistant electrolyte and a lithium ion battery using the same. BACKGROUND

[0002] With the increasing demand for energy density of lithium ion batteries for pure electric vehicles, hybrid electric vehicles and portable energy storage devices, people expect to develop lithium ion batteries with higher energy density and power density to realize long-lasting endurance and energy storage of electric devices. High working voltage is one of the methods to improve the energy density of lithium ion batteries, and under high working voltage, the electrolyte needs to have good oxidation resistance and stable electrochemical window to ensure that the lithium ion battery maintains stable circulation under high voltage.

[0003] However, the commercialized lithium ion battery electrolyte is generally composed of carbonate organic solvents and lithium hexafluorophosphate (LiPF6), and the carbonate solvents are mainly composed of chain carbonates dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and cyclic carbonates propylene carbonate (PC), ethylene carbonate (EC) and the like. However, the oxidation potential of the above organic solvents is low, and they are easily oxidized and decomposed under high voltage, which makes it difficult to exist stably, resulting in reduced performance of lithium ion batteries containing these solvents in the electrolyte.

[0004] The pressure resistance of the commercialized electrolyte can be improved in the following ways:

[0005] (1) The concentration of lithium salt in the electrolyte containing carbonate solvents is increased, the number of complexed solvent molecules is increased, the oxidation resistance of the complexed solvent molecules is enhanced, and the stability of the electrolyte is enhanced. In addition, the high-concentration electrolyte has enhanced flame retardancy compared to the traditional electrolyte, and the safety of the battery is improved.

[0006] (2) New high-voltage electrolyte solvents are used to replace carbonate solvents, such as sulfone, nitrile, ionic liquid and fluorinated electrolyte. These new system electrolytes can meet the demand of high voltage to some extent.

[0007] (3) High-voltage electrolyte additives can be added to the traditional carbonate electrolyte, which can preferentially decompose on the surface of the positive electrode to form a CEI film during battery cycling, thereby protecting the integrity of the high-voltage electrode material to some extent, and reducing the side reactions caused by the contact between the high-voltage positive electrode and the electrolyte.

[0008] Although the above-mentioned methods can improve the high-voltage resistance of electrolyte to some extent, they all have certain limitations. High lithium salt concentration will cause high cost and low safety of electrolyte. The solvents of sulfonyl and ionic liquid have relatively high melting points, which leads to performance decline at low temperature. The incompatibility of nitrile and graphite negative electrode also limits the practical application of new solvent system electrolyte. Fluorine-containing solvents are prone to produce corrosive HF by-products that destroy the positive electrode interface, leading to the dissolution of transition metal ions and rapid performance degradation of lithium metal batteries. In comparison, high-voltage multifunctional additives can simply and effectively improve the high-voltage resistance of electrolyte. However, the high-voltage electrolyte additives available on the market are single positive electrode film-forming additives, and the types are relatively few. Therefore, the development of new practical multifunctional high-voltage electrolyte additives is still a problem to be solved. SUMMARY

[0009] The present application provides a kind of electrolyte and the lithium ion battery of application thereof, the electrolyte has good stability, and can form the CEI film, SEI film of can performance excellent at lithium ion battery positive electrode, negative electrode respectively, thereby can effectively reduce the positive and negative electrode interface side reaction of lithium ion battery under high voltage working condition, improve the high voltage application performance of lithium ion battery.

[0010] According to the first aspect of the present application, a voltage-resistant electrolyte is provided, the electrolyte comprising an organic solvent component, a lithium salt component and an additive component, the additive component comprising a functional additive A; the structural general formula of the functional additive A is: Wherein, R11, R12, R13 are independently selected from hydrogen or C1-C4 alkyl or C1-C4 substituted alkyl, R2 is cyanomethyl or cyanoethyl, at least one of R3, R4 comprises a carbon-carbon double bond; the molar mass of the functional additive A is 180-280, and in the voltage-resistant electrolyte, the mass fraction of the functional additive A is 0.3wt.% to 1wt.%. In the structure of the functional additive A, the olefin structure corresponding to the carbon-carbon double bond is easy to reduce to form a dense and uniform SEI film, inhibiting the reduction of transition metal ions on the negative electrode surface, thereby reducing the interface side reaction. The oxygen-silicon bond functional group can react with the moisture generated by the electrolyte to form O-Si-O material on the positive electrode surface, which can promote the formation of stable CEI film, thereby effectively reducing the side reaction between the positive electrode and the electrolyte. At the same time, the oxygen-silicon bond can also eliminate water and hydrofluoric acid in the electrolyte, reducing the harm caused by them and improving the high-voltage cycling process. In addition to having both positive and negative electrode film-forming properties, compared with the commonly used silicon-oxygen electrolyte additives and olefin electrolyte additives, the functional additive A can exhibit obvious superiority under high-voltage application conditions, so that the voltage-resistant electrolyte of the present application can effectively improve the capacity attenuation and voltage drop of the battery product during high-voltage cycling.

[0011] Preferably, the general structure of the functional additive A is wherein R5 is hydrogen or C1-10 alkyl or C1-10 alkoxy or C1-10 halogenated alkyl or C1-10 halogenated alkoxy, and R6 is alkyl or substituted alkyl. By further optimizing the chemical structure of the functional additive A, the capacity retention of the battery product based on the pressure-resistant electrolyte provided in the present solution is improved under high-temperature and high-pressure application conditions.

[0012] Preferably, the general structure of the functional additive A is R7, R8, R9, R10 are independently selected from hydrogen or C1-10 alkyl or C1-10 alkoxy or C1-10 halogenated alkyl or C1-10 halogenated alkoxy.

[0013] Preferably, the additive component further comprises a sulfur-containing additive and a vinylene carbonate, wherein the sulfur-containing additive comprises at least one of vinyl sulfonate (DTD), 1,3-propane sulfonate lactone (PS), 1,3-propylene sulfonate lactone (PST), and the carbonate additive comprises vinylene carbonate (VC); the lithium salt component comprises lithium hexafluorophosphate (LiPF6) and a lithium salt additive, and the lithium salt additive comprises at least one of lithium bisfluorosulfonylimide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium bisoxalate borate (LiBOB), and lithium difluorodioxalate phosphate (LiODFP).

[0014] Preferably, the sulfur-containing additive comprises 1,3-propane sulfonate lactone. Based on the functional additive A selected in the present solution, the introduction of PS into the electrolyte formula can significantly improve the positive and negative film-forming auxiliary effect of the functional additive A.

[0015] Preferably, the lithium salt additive comprises lithium difluorophosphate. Based on the application of the functional additive A, lithium difluorophosphate is further selected as the lithium salt additive, and the functional additive A and lithium difluorophosphate together act as positive and negative surface film-forming substances, and the two synergistically improve the positive and negative film-forming effect.

[0016] Preferably, the mass ratio of the functional additive A, the sulfur-containing additive, and the lithium salt additive is 0.3-1:0.5-3:0.5-1. By adjusting the ratio of the functional additive A, the sulfur-containing additive, and the lithium salt additive, the compactness of the SEI film can be further improved while keeping the film-forming impedance at a low level.

[0017] Preferably, the organic solvent component comprises cyclic carbonates, chain carbonates, and chain carboxylic acid esters.

[0018] Preferably, the cyclic carbonate includes fluoroethylene carbonate and ethylene carbonate, the chain carbonate includes diethyl carbonate, the chain carboxylic acid ester includes diethyl carbonate, and the chain carboxylic acid ester includes ethyl difluoroacetate; in the pressure-resistant electrolyte, the total mass of fluoroethylene carbonate and ethylene carbonate: the mass of diethyl carbonate: the mass of ethyl difluoroacetate = 1-15: 2-70: 5-20. Based on the CEI film formed on the surface of the battery positive electrode by the functional additive A, the positive electrode can be reliably protected, and on this basis, by optimizing the solvent component, not only can the cycle performance of the pressure-resistant electrolyte be further improved, but also a good dissolution medium can be provided for various active ingredients in the electrolyte, and the film formation quality of the positive electrode CEI film and the negative electrode SEI film can be improved.

[0019] According to a second aspect of the present application, a lithium ion battery is provided, which includes the pressure-resistant electrolyte as described above. The lithium ion battery provided by the present application has good high-voltage application performance and can maintain good cycle stability under high-voltage application conditions. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, not all.

[0021] Embodiment 1

[0022] According to the mass percentage of the components, the electrolyte formula used in this embodiment is as follows: functional additive A 0.5%, VC 0.5%, LiPO2F2 0.5%, PS 2%, lithium hexafluorophosphate (LiPF6) 15%, and the rest is the organic solvent component. Among them, the organic solvent component in the above electrolyte formula is composed of fluoroethylene carbonate, ethylene carbonate, diethyl carbonate, and ethyl difluoroacetate, wherein, calculated based on the total mass of the organic solvent being 100%, the mass percentage of fluoroethylene carbonate is 5%, the mass percentage of ethylene carbonate is 20%, the mass percentage of diethyl carbonate is 65%, and the mass percentage of ethyl difluoroacetate is 10%. The functional additive A in the above formula is used as a variable to set different experimental groups, which are respectively labeled as: experimental group 1-1, experimental group 1-2, experimental group 1-3, experimental group 1-4, experimental group 1-5, experimental group 1-6, and experimental group 1-7. The functional additive A used in each of the above experimental groups is shown in Table 1.

[0023] Table 1. Number of each experimental group in this embodiment and the corresponding functional additive A used

[0024]

[0025]

[0026] Each experimental group is prepared according to the electrolyte formula composition used by each group. First, the materials used to prepare the organic solvent component are mixed uniformly to obtain the organic solvent component. Then, under an argon atmosphere at 10°C, the formula amount of VC, PS, LiPO2F2, functional additive A, and LiPF6 is added to the organic solvent component, the temperature is maintained at 10°C, and the mixture is stirred until the solid materials are fully dissolved to obtain a uniform solution, thereby preparing the electrolyte.

[0027] Comparative Example 1

[0028] This comparative example uses the electrolyte formula used in Example 1 as a reference, and uses functional additive A in the electrolyte formula as a variable to set up control group 1-1, control group 1-2, control group 1-3, and control group 1-4. The difference between the electrolyte formula used in the above control groups and the electrolyte formula used in Example 1 is:

[0029] Control group 1-1 omits functional additive A in the electrolyte formula of Example 1, and replaces functional additive A in the electrolyte formula of Example 1 with the same amount of organic solvent component used to form the electrolyte formula used by control group 1-1;

[0030] Control group 1-2 and control group 1-3, as shown in Table 2, respectively replace functional additive A in the electrolyte formula of Example 1 with different types of silicon oxide compounds in the same amount to form the electrolyte formula used by control group 1-2 and control group 1-3, respectively;

[0031] Control group 1-4 replaces functional additive A in the electrolyte formula of Example 1 with VC in the same amount to form the electrolyte formula used by control group 1-4.

[0032] Table 2. Numbering of each experimental group in this example and the corresponding silicon oxide compound used by each group

[0033]

[0034] In addition to the above differences, the other materials in the electrolyte formula used by control group 1-1, control group 1-2, control group 1-3, and control group 1-4 are consistent with the materials and proportions used in the electrolyte formula of Example 1.

[0035] The control group 1-1 and the control group 1-4 are prepared according to the electrolyte formula composition used, the materials used to prepare the organic solvent component are mixed uniformly to obtain the organic solvent component, then VC, PS, LiPO2F2, LiPF6 in the formula amount are added to the organic solvent component under the condition of 10 ℃ and argon atmosphere, the temperature is kept at 10 ℃, the mixture is fully stirred until the solid materials are fully dissolved to obtain a uniform solution, and the electrolyte is prepared.

[0036] The control group 1-2 and the control group 1-3 are prepared according to the electrolyte formula composition used, the materials used to prepare the organic solvent component are mixed uniformly to obtain the organic solvent component, then VC, PS, LiPO2F2, silicon oxide compound, LiPF6 in the formula amount are added to the organic solvent component under the condition of 10 ℃ and argon atmosphere, the temperature is kept at 10 ℃, the mixture is fully stirred until the solid materials are fully dissolved to obtain a uniform solution, and the electrolyte is prepared.

[0037] Preparation example 1

[0038] The electrolyte prepared in the present preparation example for lithium ion battery is the electrolyte prepared in example 1 and comparative example 1. The method for preparing lithium ion battery in the present preparation example is as follows:

[0039] Graphite is used as the negative active material, graphite, conductive agent acetylene black, binder CMC, SBR are prepared into negative electrode slurry in the mass percentage of 94:1:2:3, the negative electrode slurry is coated on the copper foil current collector, vacuum dried to obtain the negative electrode sheet; 0.25Li2MnO3·0.75LiMn 0.375 Ni 0.375 Co 0.25 O2 is used as the positive active material, the positive active material, conductive agent acetylene black, binder PVDF are prepared into positive electrode slurry in the mass ratio of 94:3:3, the positive electrode slurry is coated on the aluminum foil current collector, vacuum dried to obtain the positive electrode sheet; the electrolyte prepared in example 1 and comparative example 1 is used to assemble soft package battery with the above-mentioned positive electrode sheet, the negative electrode sheet and Celgard2400 separator.

[0040] Test example 1

[0041] 1. Test object

[0042] The soft package battery prepared in preparation example 1 is used as the test object.

[0043] 2. Test item

[0044] The new Wei charge and discharge test cabinet is used to test the cycle performance of the test object.

[0045] (1) Normal temperature cycle performance test

[0046] The test object was charged at 25°C at 0.5C (nominal capacity) to a voltage of 4.6V, then charged at 4.6V to a current of ≤0.05C, and after a 10 min rest, discharged at 1C to a cut-off voltage of 2.5V, which was one charge-discharge cycle. The test object was subjected to 1000 charge-discharge cycles at 25°C under the above conditions.

[0047] The capacity retention rate (%) of the test object after N cycles = (discharge capacity of the Nth cycle / first discharge capacity) x 100%, and N is the cycle number of the lithium ion battery.

[0048] The average voltage (V) of the test object after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, and N is the cycle number of the lithium ion battery.

[0049] (2) High temperature cycle performance test

[0050] The test object was charged at 45°C at 1.0C (nominal capacity) to a voltage of 4.6V, then charged at 4.6V to a current of ≤0.05C, and after a 10 min rest, discharged at 1C to a cut-off voltage of 2.5V, which was one charge-discharge cycle. The test object was subjected to 800 charge-discharge cycles at 45°C under the above conditions.

[0051] The capacity retention rate (%) of the test object after N cycles = (discharge capacity of the Nth cycle / first discharge capacity) x 100%, and N is the cycle number of the lithium ion battery.

[0052] The average voltage (V) of the test object after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, and N is the cycle number of the lithium ion battery.

[0053] 3. Test results

[0054] The test results are shown in Table 3. Under the same test conditions, the cycle capacity retention rate of the lithium ion battery using the electrolyte prepared in experimental group 1-1, experimental group 1-2, experimental group 1-3, experimental group 1-4, experimental group 1-5, and experimental group 1-6 was higher in the test object of the present test example.

[0055] The electrolyte prepared in experimental group 1-1, experimental group 1-2, experimental group 1-3, experimental group 1-4, experimental group 1-5, and experimental group 1-6 all contained a compound having a general structure according to functional additive (functional additive A), in the above general structure, R11, R12, R13 are independently selected from hydrogen or C1-C4 alkyl or C1-C4 substituted alkyl, R2 is cyanomethyl or cyanoethyl, at least one of R3, R4 includes a carbon-carbon double bond. The electrolyte prepared in experimental group 1-1, experimental group 1-2, experimental group 1-3, experimental group 1-4, experimental group 1-5, experimental group 1-6 is applied in the working process of the lithium ion battery, the carbon-carbon double bond in the functional additive A corresponding to the olefin structure is easy to reduce to form a dense and uniform SEI film, and the reduction of transition metal ions on the negative electrode surface is inhibited, thereby reducing the interface side reaction, and the oxygen-silicon bond functional group in the functional additive A can react with the moisture generated by the electrolyte to form O-Si-O material on the positive electrode surface, which can promote the formation of stable CEI film, thereby effectively reducing the side reaction between the positive electrode and the electrolyte, and the above oxygen-silicon bond can also eliminate water and hydrofluoric acid in the electrolyte, reduce the harm caused by them, and improve the high voltage cycle process.

[0056] The test results show that under the same test conditions, the lithium ion battery prepared by using the electrolyte of control group 1-1 has the lowest cycle capacity retention rate. Control group 1-4 also does not use silicon oxide compounds as raw materials in the preparation of electrolyte, but the difference between control group 1-4 and control group 1-1 is that the raw materials for preparing the electrolyte of control group 1-4 also include VC, which is a commonly used olefin SEI film forming agent in the prior art. However, from the test results, under the same test conditions, compared with the lithium ion battery using the electrolyte of control group 1-1, the lithium ion battery using the electrolyte of control group 1-4 does not have a very obvious improvement in the corresponding measured cycle capacity retention rate, which indicates that under high voltage working conditions, only by adding SEI film forming agent to the electrolyte is not enough to effectively improve the cycle performance of the lithium ion battery.

[0057] The control group 1-2 and the control group 1-3 both use silicon oxide compounds as raw materials in the preparation of electrolyte, but from the material structure shown in Table 2, it can be clearly seen that the molecular structure of the silicon oxide compound VIII and the silicon oxide compound IX used by the control group 1-2 and the control group 1-3 respectively does not conform to the general structure formula of the functional additive A. Among them, although the molecular structure of the silicon oxide compound VIII used by the control group 1-2 also contains silicon-oxygen bond, carbon-carbon double bond and cyano group, from the molecular structure, the arrangement and connection mode of the above functional groups in the molecular structure of the silicon oxide compound VIII are different from the general structure formula of the functional additive A. The molecular structure of the silicon oxide compound IX used by the control group 1-3 does not contain carbon-carbon double bond, and there is a significant difference between its molecular structure and the general structure formula of the functional additive A. From the test results, under the same test conditions, compared with the lithium ion batteries using the electrolyte of the experimental group 1-1, the experimental group 1-2, the experimental group 1-3, the experimental group 1-4, the experimental group 1-5 and the experimental group 1-6 respectively, the cycle capacity retention rate of the lithium ion battery using the electrolyte of the control group 1-2 and the control group 1-3 is obviously lower. The test results show that compared with general silicon oxide compounds, the functional additive A used in the preparation of electrolyte in the experimental group 1-1, the experimental group 1-2, the experimental group 1-3, the experimental group 1-4, the experimental group 1-5 and the experimental group 1-6 makes these electrolytes exhibit superior cycle characteristics under high pressure application conditions.

[0058] As described above, based on the test results of the present test example, the lithium ion batteries using the electrolyte prepared by the experimental group 1-1, the experimental group 1-2, the experimental group 1-3, the experimental group 1-4, the experimental group 1-5 and the experimental group 1-6 respectively can all maintain good cycle stability under different temperature conditions. In the above experimental groups, the difference is the silicon oxide compound used for preparing the electrolyte, based on the above difference, the electrolyte prepared by the above experimental groups and the lithium ion batteries using the same also have certain differences in cycle stability and working voltage. Among the lithium ion batteries using the electrolyte prepared by the above experimental groups, under the same test conditions, the lithium ion batteries using the electrolyte prepared by the experimental group 1-1, the experimental group 1-2 and the experimental group 1-3 can achieve higher cycle capacity retention rate and higher average voltage. The molecular structure of the silicon oxide compound used in the preparation of electrolyte in the experimental group 1-1, the experimental group 1-2 and the experimental group 1-3 conforms to the following general formula The molecular structure of the silicon oxide compound used in the experimental group 1-4, the experimental group 1-5, the experimental group 1-6, and the experimental group 1-7 does not comply with the general formula. Further, compared with the electrolyte of the control group 1-1, the electrolyte prepared in the experimental group 1-1 can improve the capacity retention rate of the lithium ion battery to the greatest extent. And under the same test conditions, the lithium ion battery using the electrolyte prepared in the experimental group 1-1 can achieve the highest average voltage. In summary, in the case of using the silicon oxide compound belonging to the functional additive A as the raw material to prepare the electrolyte, by further selecting the silicon oxide compound with a specific molecular structure to participate in the preparation of the electrolyte, the cycle performance and the average voltage of the lithium ion battery using such electrolyte under high voltage working conditions can be further improved.

[0059] Table 3. Test result statistics of test example 1

[0060]

[0061] Example 2

[0062] In this embodiment, the electrolyte formula used in the experimental group 1-1 of example 1 is used as a reference, and the sulfur-containing additive included in the formula is used as a variable to set the experimental group 2-1, the experimental group 2-2, and the experimental group 2-3. The electrolyte formula used in the experimental group 2-1 and the experimental group 2-2 is different from the electrolyte formula used in the experimental group 1-1 of example 1 in that a different kind of sulfur-containing additive is used to replace the PS in the electrolyte formula of the experimental group 1-1 of example 1 in equal mass, wherein the sulfur-containing additive used in the experimental group 2-1 is PST, and the sulfur-containing additive used in the experimental group 2-2 is DTD. The electrolyte formula used in the experimental group 2-3 is different from the electrolyte formula used in the experimental group 1-1 of example 1 in that the electrolyte formula of the experimental group 2-3 does not contain a sulfur-containing additive. With the electrolyte formula used in the experimental group 1-1 of example 1 as a reference, the PS contained in the electrolyte formula is removed, and the content of the PS in the electrolyte formula is supplemented with the organic solvent component used in the electrolyte formula in equal mass, and the electrolyte formula thus obtained is used as the electrolyte formula used in the experimental group 2-3.

[0063] The experimental group 2-1, the experimental group 2-2, and the experimental group 2-3 are prepared according to the electrolyte formula used in each group. First, the materials for preparing the organic solvent component are mixed uniformly to obtain the organic solvent component. Then, under the condition of 10°C and argon atmosphere, the VC, the sulfur-containing additive, LiPO2F2, the silicon oxide compound I, and LiPF6 in the formula amount are added to the organic solvent component, the temperature is kept at 10°C, and the mixture thus obtained is stirred thoroughly until the solid materials are fully dissolved to obtain a uniform solution, thereby preparing the electrolyte.

[0064] Comparative Example 2

[0065] This example takes the electrolyte formulation adopted by the control group 1-1 of Comparative Example 1 as a reference, and sets control group 2-1, control group 2-2, control group 2-3 with the sulfur-containing additive included in the formulation as a variable. The electrolyte formulation adopted by control group 2-1, control group 2-2 is different from the electrolyte formulation adopted by the control group 1-1 of Comparative Example 1 in that a different kind of sulfur-containing additive is used to replace PS in the electrolyte formulation of the control group 1-1 of Comparative Example 1 in equal mass, wherein the sulfur-containing additive used by control group 2-1 is PST, and the sulfur-containing additive used by control group 2-2 is DTD. The electrolyte formulation adopted by control group 2-3 is different from the electrolyte formulation adopted by the control group 1-1 of Comparative Example 1 in that the electrolyte formulation of control group 2-3 does not contain a sulfur-containing additive. Taking the electrolyte formulation adopted by the control group 1-1 of Comparative Example 1 as a reference, the PS contained in the electrolyte formulation is removed, and the originally contained amount of PS in the electrolyte formulation is supplemented with the organic solvent component used in the electrolyte formulation in equal mass, and the electrolyte formulation thus obtained is used as the electrolyte formulation adopted by control group 2-3.

[0066] Control group 2-1, control group 2-2, control group 2-3 are prepared according to the electrolyte formulation adopted by each of them, respectively. First, the materials for preparing the organic solvent component are mixed uniformly to obtain the organic solvent component, then under the argon atmosphere at 10°C, the VC, sulfur-containing additive, LiPO2F2, LiPF6 in the formulation amount are added to the organic solvent component, the temperature is kept at 10°C, the mixture thus obtained is stirred thoroughly until the solid materials are fully dissolved to obtain a uniform solution, and thus the electrolyte is prepared.

[0067] Preparation Example 2

[0068] The electrolyte prepared in this preparation example for lithium ion battery is the electrolyte prepared in Example 2 and Comparative Example 2. Lithium ion batteries are prepared according to the method of preparing lithium ion batteries in Preparation Example 1 using the electrolyte prepared in Example 2 and Comparative Example 2, except that the electrolyte used is different. The other materials used and the related process steps for preparing lithium ion batteries in this preparation example are consistent with those in Preparation Example 1.

[0069] Test Example 2

[0070] 1. Test object

[0071] The soft pack battery prepared in Preparation Example 2 is used as the test object.

[0072] 2. Test items

[0073] The cycle performance test of the test object is carried out using the new Wei charge and discharge test cabinet.

[0074] (1) Normal temperature cycle performance test

[0075] The relevant operations in Test Example 1 were kept unchanged.

[0076] (2) High temperature cycle performance test

[0077] The relevant operations in Test Example 1 were kept unchanged.

[0078] 3. Test results

[0079] The test results are shown in Table 4. In order to facilitate comparison, the high temperature cycle performance test results of the lithium ion battery provided with the electrolyte based on the experimental group 1-1 of Example 1 and the control group 1-1 of Comparative Example 1 in Test Example 1 are shown in Table 4. Therefore, the electrolyte formulations of the experimental group 2-3 and the control group 2-3 do not contain sulfur-containing additives, so the positions corresponding to the experimental group 2-3 and the control group 2-3 in the content of sulfur-containing additives in Table 4 are represented by “-”.

[0080] In the electrolytes of the experimental group 1-1, the experimental group 2-1, the experimental group 2-2 and the experimental group 2-3, the experimental group 2-3 does not contain sulfur-containing additives, and the experimental group 1-1, the experimental group 2-1 and the experimental group 2-2 respectively contain different types of sulfur-containing additives. Among them, the sulfur-containing additive used for preparing the electrolyte of the experimental group 1-1 is PS, the sulfur-containing additive used for preparing the electrolyte of the experimental group 2-1 is PST, and the sulfur-containing additive used for preparing the electrolyte of the experimental group 2-2 is DTD. Based on the above differences, under the same test conditions, the capacity retention of the lithium ion battery using the experimental group 2-1 electrolyte and the experimental group 2-2 electrolyte is lower than that of the lithium ion battery using the experimental group 2-3 electrolyte, but the lithium ion battery using the experimental group 1-1 electrolyte can achieve higher capacity retention and higher average voltage. Therefore, in the electrolyte system based on functional additive A, not all sulfur-containing additives can improve the cycle performance of the electrolyte. Among them, the use of PS and additive A can improve the cycle performance of the electrolyte, improve the cycle stability and average voltage of the lithium ion battery using the same.

[0081] The electrolyte of the control group 2-3 does not contain sulfur-containing additive, the electrolyte of the control group 1-1, the electrolyte of the control group 2-1 and the electrolyte of the control group 2-2 respectively contain different types of sulfur-containing additives, wherein the sulfur-containing additive used for preparing the electrolyte of the control group 1-1 is PS, the sulfur-containing additive used for preparing the electrolyte of the control group 2-1 is PST, and the sulfur-containing additive used for preparing the electrolyte of the control group 2-2 is DTD. Based on the above differences, the cycle performance and average voltage of the lithium ion battery using the above electrolyte under high voltage working condition are also different. However, under the same test conditions, the capacity retention rate of the lithium ion battery using the electrolyte without sulfur-containing additive (control group 2-3) is the highest, and the capacity retention rate of the lithium ion battery using the electrolyte containing PS (control group 1-1) is the lowest.

[0082] The above comparison shows that the effects of the further addition of sulfur-containing additives on the performance of the electrolyte and the lithium ion battery using the same are different based on whether the electrolyte contains functional additive A. For the electrolyte containing functional additive A, PS as a sulfur-containing additive can play a positive and negative electrode film forming auxiliary role on functional additive A, which is obviously better than other sulfur-containing additives, thereby making the electrolyte and the lithium ion battery using the same have better cycle characteristics.

[0083] Table 4. Test result statistics of test example 2

[0084]

[0085] Example 3

[0086] The electrolyte formulation adopted by the experimental group 1-1 of the embodiment 1 is taken as the reference, and the lithium salt additive included in the formulation is taken as the variable, and the experimental group 3-1, the experimental group 3-2, the experimental group 3-3 and the experimental group 3-4 are set. The electrolyte formulation adopted by the experimental group 3-1, the experimental group 3-2 and the experimental group 3-3 is compared with the electrolyte formulation adopted by the experimental group 1-1 of the embodiment 1, and the difference is that the LiPO2F2 in the electrolyte formulation of the experimental group 1-1 of the embodiment 1 is replaced by the lithium salt additive of different types in equal mass. The lithium salt additive adopted by the experimental group 3-1 is LiFSI, the lithium salt additive adopted by the experimental group 3-2 is LiBOB, and the lithium salt additive adopted by the experimental group 3-3 is LiODFP. The difference between the electrolyte formulation adopted by the experimental group 3-4 and the electrolyte formulation adopted by the experimental group 1-1 of the embodiment 1 is that the electrolyte formulation of the experimental group 3-4 does not contain the lithium salt additive, that is, the only lithium-containing raw material in the electrolyte formulation of the experimental group 3-4 is LiPF6. The electrolyte formulation adopted by the experimental group 3-4 is compared with the electrolyte formulation adopted by the experimental group 1-1 of the embodiment 1, and the LiPO2F2 contained in the electrolyte formulation is removed, and the content of the LiPO2F2 in the electrolyte formulation is supplemented by the organic solvent component in equal mass, and the electrolyte formulation thus obtained is used as the electrolyte formulation adopted by the experimental group 3-4.

[0087] The experimental group 3-1, the experimental group 3-2, the experimental group 3-3 and the experimental group 3-4 are prepared according to the electrolyte formulation adopted by each group. First, the materials for preparing the organic solvent component are mixed uniformly to obtain the organic solvent component. Then, VC, PS, lithium salt additive, silicon oxide compound I and LiPF6 in the formulation amount are added to the organic solvent component under the condition of 10℃ and argon atmosphere, the temperature is kept at 10℃, the mixture is stirred thoroughly until the solid materials are dissolved completely to obtain a uniform solution, and the electrolyte is prepared.

[0088] Preparation Example 3

[0089] The electrolyte prepared in the preparation example 3 is used to prepare the lithium ion battery. The lithium ion battery is prepared according to the method of the preparation example 1, and the difference is that the electrolyte adopted is different. The other materials and related process steps adopted by the lithium ion battery prepared in the preparation example are consistent with those of the preparation example 1.

[0090] Test Example 3

[0091] 1. Test object

[0092] The soft package battery prepared in the preparation example 3 is taken as the test object.

[0093] 2. Test item

[0094] The new Wei discharge test cabinet is used to test the cycle performance of the test object.

[0095] (1) Normal temperature cycle performance test

[0096] The relevant operations in Test Example 1 are kept consistent.

[0097] (2) High temperature cycle performance test

[0098] The relevant operations in Test Example 1 are kept consistent.

[0099] 3. Test results

[0100] The test results are shown in Table 5. In order to facilitate comparison, the high temperature cycle performance test results of the lithium ion battery based on the electrolyte provided by Experimental Group 1-1 in Example 1 are shown in Table 5. Since the electrolyte formulation of Experimental Group 3-4 does not contain a lithium salt additive, the content related to the lithium salt additive in Table 5 is represented by “-” for the position of Experimental Group 3-4.

[0101] Under the same test conditions, compared with the lithium ion battery using the electrolyte of Experimental Group 3-4 without a lithium salt additive, the lithium ion batteries using the electrolytes of Experimental Group 1-1, Experimental Group 3-1, Experimental Group 3-2, and Experimental Group 3-3 can achieve higher capacity retention rates. Further, by comparing the test data of the lithium ion batteries using the electrolytes of Experimental Group 1-1, Experimental Group 3-1, Experimental Group 3-2, and Experimental Group 3-3, it can be seen that the electrolyte of Experimental Group 1-1 uses LiPO2F2 as a lithium salt additive, and the lithium ion battery using it has a significantly higher capacity retention rate than the lithium ion batteries using other electrolytes under the same conditions. In the electrolyte formulation of Experimental Group 1-1, based on the application of functional additive A, LiPO2F2 is further selected as a lithium salt additive. In the electrolyte thus prepared, functional additive A and LiPO2F2 together act as positive and negative electrode surface film forming substances. When the above electrolyte is used under high voltage working conditions, functional additive A and LiPO2F2 in the electrolyte synergistically enhance the positive and negative electrode film forming effect, thereby enabling the lithium ion battery using the electrolyte provided by Experimental Group 1-1 of Example 1 to achieve significantly better cycle stability compared to other lithium ion batteries.

[0102] Table 5. Test result statistics of Test Example 3

[0103]

[0104] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application is described in detail with reference to the above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently, and these modifications or replacements are within the protection scope of the present application.

Claims

1. A voltage-resistant electrolyte, characterized in that: The electrolyte comprises an organic solvent component, a lithium salt component, and an additive component, wherein the additive component comprises a functional additive A; The general structural formula of the functional additive A is: R11, R12, and R13 are independently selected from hydrogen or C1-C4 alkyl or C1-C4 substituted alkyl, R2 is cyanomethyl or cyanoethyl, and at least one of R3 and R4 includes a carbon-carbon double bond. The molar mass of the functional additive A is 180 to 280, and the mass percentage of the functional additive A in the voltage-resistant electrolyte is 0.3 wt.% to 1 wt.%.

2. The voltage-resistant electrolyte as described in claim 1, characterized in that: The general structural formula of the functional additive A is: R5 is hydrogen or C1-10 alkyl or C1-10 alkoxy or C1-10 halogenated alkyl or C1-10 halogenated alkoxy, and R6 is alkyl or substituted alkyl.

3. The voltage-resistant electrolyte as described in claim 2, characterized in that: The general structural formula of the functional additive A is: R7, R8, R9, and R10 are independently selected from hydrogen or C1-10 alkyl or C1-10 alkoxy or C1-10 halogenated alkyl or C1-10 halogenated alkoxy.

4. The voltage-resistant electrolyte as described in claim 1, characterized in that: The additive components also include sulfur-containing additives and vinylene carbonate, wherein the sulfur-containing additives include at least one of vinyl sulfate, 1,3-propanesulfonate lactone, and 1,3-propenesulfonate lactone, and the carbonate additives include vinylene carbonate. The lithium salt component includes lithium hexafluorophosphate and lithium salt additives, wherein the lithium salt additives include at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium dioxaborate, and lithium difluorodioxaborate.

5. The voltage-resistant electrolyte as described in claim 4, characterized in that: The sulfur-containing additives include 1,3-propanesulfonate lactone.

6. The voltage-resistant electrolyte as described in claim 4, characterized in that: The lithium salt additive includes lithium difluorophosphate.

7. The voltage-resistant electrolyte as described in claim 4, characterized in that: The ratio of functional additive A to sulfur-containing additive to lithium salt additive is calculated by mass ratio as follows: 0.3-1: 0.5-3: 0.5-1.

8. The voltage-resistant electrolyte as described in claim 4, characterized in that: The organic solvent components include cyclic carbonates, chain carbonates, and chain carboxylic esters.

9. The voltage-resistant electrolyte as described in claim 8, characterized in that: The cyclic carbonates include fluoroethylene carbonate and ethylene carbonate, the chain carbonates include diethyl carbonate, and the chain carboxylic acid esters include ethyl difluorocarbonate; in the voltage-resistant electrolyte, the total mass of fluoroethylene carbonate and ethylene carbonate: the mass of diethyl carbonate: the mass of ethyl difluorocarbonate = 1~15: 2~70: 5~20.

10. A lithium-ion battery, characterized in that: The lithium-ion battery includes the pressure-resistant electrolyte as described in any one of claims 1 to 9.

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