CN118738557A - An electrolyte, preparation method and application thereof, and battery - Google Patents

Abstract

The invention discloses an electrolyte, a preparation method and application thereof, and a battery, and belongs to the technical field of electrolytes. The electrolyte includes a multifunctional additive, and the multifunctional additive includes a fluorinated ester containing an unsaturated bond and a sulfonic acid group or a sulfuric acid group. The multifunctional additive can form a film preferentially compared to a traditional film-forming additive, which helps to form a thinner and denser solid electrolyte interface film, and improves the problem of oxygen free radical-electrolyte solvent intermediates generating reducing gas at the negative electrode. The multifunctional additive can form a film at the negative electrode and the positive electrode, which is beneficial to reduce the decomposition and deoxygenation of the positive electrode lithium supplement during the cycle storage process. The multifunctional additive contains a sulfonic acid or sulfuric acid group, which helps to reduce the battery impedance and improve the high-temperature cycle and storage performance of the battery; the fluorine element contained therein tends to generate lithium fluoride during film formation, which is beneficial to reduce the lithium ion diffusion energy barrier, increase the mechanical stability of the solid electrolyte interface film, avoid the formation of lithium dendrites, and improve the electrochemical performance.

Description

An electrolyte, preparation method and application thereof, and battery

Technical Field

The present invention relates to the technical field of electrolytes, and in particular to an electrolyte, a preparation method and application thereof, and a battery.

Background Art

In the field of new energy power and energy storage, lithium-ion batteries have become the most widely used secondary batteries due to their high energy density and portability. However, currently commercial lithium-ion batteries are difficult to meet people's increasingly high requirements for battery energy and life. Since an important reason for battery energy decay and shortened life is the loss of active lithium in the system, lithium replenishment of positive and negative electrode materials has been widely studied as a method to compensate for the loss of active lithium. Compared with lithium metal replenishment of the negative electrode, positive electrode replenishment has low requirements for process and environment, and can be directly introduced without changing the existing process conditions, with lower cost of use and more advantages.

Commonly used positive electrode lithium supplements include lithium ferrite Li ₅ FeO ₄ (LFO), lithium nickelate Li ₂ NiO ₂ (LNO), and lithium peroxide Li ₂ O ₂ (LO). These lithium supplements will decompose when the first charge reaches a certain voltage, releasing Li ⁺ to make up for the active lithium lost in the formation stage, while generating oxygen free radicals and oxygen molecules. The oxygen free radicals will form intermediates with the electrolyte solvent and generate reducing gas at the negative electrode. Most of the gas will be vacuumed out after the formation is completed. However, batteries containing lithium supplements (mainly LFO) still have serious gas production problems in later cycles and high-temperature storage. This part of the gas production comes from the unconsumed lithium supplements that continue to decompose after formation to produce oxygen free radicals and oxygen-induced gas production at the negative electrode.

At present, the solutions to the above problems may include the following:

(1) Introducing oxygen free radical capture additives. The main reason for gas production in the positive electrode lithium supplement system is that the lithium supplement that is not completely consumed in the formation stage is continuously consumed during the subsequent cycle storage process, generating oxygen free radicals. The free radicals and the electrolyte solvent (EC) form intermediate products and generate reducing gases at the negative electrode. By introducing oxygen free radical capture additives into the electrolyte, the generated oxygen free radicals can be complexed, making it impossible for them to move smoothly to the negative electrode to be reduced, thereby reducing gas production. However, when the amount of free radical capture additive added is small, the oxygen free radicals cannot be completely eliminated. When a large amount is added, the impedance increases significantly, which will deteriorate the gas electrochemical performance of the battery (such as rate and cycle performance).

(2) Reduce the amount of LFO added to reduce the lithium content of the lithium supplement (control the charging voltage); or replace part of LFO with LNO. However, the lithium supplement amount of LNO (theoretical specific capacity is about 400mAh/g) is much lower than that of LFO (theoretical specific capacity is about 867mAh/g). Whether reducing the amount of LFO added, replacing LFO with LNO, or reducing the lithium content of the lithium supplement, the lithium supplement efficiency will be low and the performance improvement will not be obvious.

(3) Reducing the formation current can allow the lithium supplement to react fully, thereby avoiding continuous decomposition during subsequent use and causing gas production. However, this method has a more complicated process flow, greatly prolongs the formation time, greatly increases production costs, and reduces production efficiency.

In view of this, the present invention is proposed.

Summary of the invention

The object of the present invention is to provide an electrolyte, a preparation method and application thereof, and a battery to solve or improve the above-mentioned technical problems.

The present invention can be implemented like this:

In a first aspect, the present invention provides an electrolyte, the electrolyte includes an additive, the additive includes a multifunctional additive, the multifunctional additive includes a fluoroester containing an unsaturated bond, and the fluoroester has a sulfonic acid group or a sulfuric acid group.

In an alternative embodiment, the multifunctional additive includes at least one of an unsaturated fluorinated sulfate and an unsaturated fluorinated sulfonate.

In an optional embodiment, the multifunctional additive includes at least one of fluoroethylene sulfate containing an unsaturated bond, fluoropropylene sulfate containing an unsaturated bond, fluoropropylene bissulfate containing an unsaturated bond, fluorobispropane sultone containing an unsaturated bond, fluorobutane sultone containing an unsaturated bond, and fluorobisbutane sultone containing an unsaturated bond.

In an alternative embodiment, the multifunctional additive comprises at least one of the following compounds:

Wherein, the substituents R1 to R4 are independently selected from F, vinyl, 1-propenyl, 2-propenyl, ethynyl, 1-propynyl or 2-propynyl, and at least one substituent in each compound is F.

In an optional embodiment, the content of the multifunctional additive in the electrolyte is 0.2 wt % to 5 wt %.

In an optional embodiment, the content of the multifunctional additive in the electrolyte is 1 wt% to 2 wt%.

In an alternative embodiment, the additive further comprises a film-forming additive.

In an alternative embodiment, the film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)phosphate, and tris(trimethylsilyl)borate.

In an optional embodiment, the content of the film-forming additive in the electrolyte is 0.2 wt % to 5 wt %.

In an optional embodiment, the content of the film-forming additive in the electrolyte is 2 wt % to 3 wt %.

In an optional embodiment, the electrolyte further includes a carbonate solvent.

In an optional embodiment, the carbonate solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).

In an optional embodiment, the content of the carbonate solvent in the electrolyte is 70 wt % to 87 wt %.

In an optional embodiment, the content of the carbonate solvent in the electrolyte is 75 wt % to 85 wt %.

In an optional embodiment, the electrolyte further includes a lithium salt.

In an optional embodiment, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium perchlorate (LiClO ₄ ), lithium difluorooxalatoborate (LiODFB), lithium difluorobis(oxalatophosphate) (LiODFP), lithium difluorophosphate (LiPO ₂ F ₂ ), and lithium dioxalatoborate (LiBOB).

In an optional embodiment, the content of lithium salt in the electrolyte is 8 wt % to 20 wt %.

In an optional embodiment, the content of lithium salt in the electrolyte is 10 wt % to 15 wt %.

In a second aspect, the present invention provides a method for preparing an electrolyte as described in any one of the aforementioned embodiments, comprising the following steps: mixing components of the electrolyte.

In an optional embodiment, the additive is added to a mixed solution formed by the lithium salt and the carbonate solvent.

In a third aspect, the present invention provides an application of an electrolyte according to any one of the aforementioned embodiments, for example, it can be used to prepare a battery.

In a fourth aspect, the present invention provides a battery comprising the electrolyte of any one of the aforementioned embodiments.

In an optional embodiment, the positive electrode material of the battery includes lithium iron phosphate positive electrode material, ternary positive electrode material, lithium cobalt oxide positive electrode material or lithium manganese oxide positive electrode material; or, the negative electrode material of the battery includes graphite negative electrode material, silicon carbon negative electrode material or silicon oxygen negative electrode material.

The beneficial effects of the present invention include:

The multifunctional additive provided by the present invention contains fluorine element, which tends to generate lithium fluoride during film formation, which is beneficial to reduce the lithium ion diffusion barrier, increase the mechanical stability of the solid electrolyte interface film, avoid the formation of lithium dendrites, and improve the electrochemical performance. In addition, the multifunctional additive contains sulfonic acid or sulfuric acid groups, which helps to reduce battery impedance and improve battery high temperature cycle and storage performance.

In addition, the multifunctional additive proposed in the present invention has a lower lowest unoccupied molecular orbital (LUMO energy level), and can form a film preferentially compared to traditional film-forming additives, which helps to form a thinner and denser solid electrolyte interface film, and can prevent the oxygen free radical-electrolyte solvent intermediate from being reduced at the negative electrode, thereby reducing the occurrence of side reactions and improving the problem of oxygen free radical-electrolyte solvent intermediate generating reducing gas at the negative electrode. The multifunctional additive can form a film not only at the negative electrode, but also at the positive electrode, which is beneficial to reduce the decomposition and deoxygenation of the positive electrode lithium supplement during the cycle storage process.

The battery with the electrolyte provided by the present invention can improve the problem of gas generation during storage, and has a low volume expansion rate after storage. In addition, the battery also has a low internal resistance and better cycle performance.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

FIG. 1 is a graph showing the volume expansion rate of batteries corresponding to Examples 1 to 12 and Comparative Examples 1 to 5 in the test examples of the present invention after storage at 55° C. for 20 days.

DETAILED DESCRIPTION

In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

The electrolyte provided by the present invention, its preparation method and application, and the battery are described in detail below.

The present invention provides an electrolyte. The electrolyte comprises an additive. The additive comprises a multifunctional additive. The multifunctional additive comprises a fluoroester containing an unsaturated bond. The fluoroester has a sulfonic acid group or a sulfuric acid group.

The number of unsaturated bonds may be 1, 2 or more, and the number of sulfonic acid groups and sulfuric acid groups may be 1, 2 or more.

The multifunctional additive contains fluorine, which tends to generate lithium fluoride during film formation, which is beneficial to reduce the lithium ion diffusion barrier, increase the mechanical stability of the solid electrolyte interface film, avoid the formation of lithium dendrites, and improve the electrochemical performance. In addition, the multifunctional additive contains sulfonic acid or sulfuric acid groups, which helps to reduce battery impedance and improve battery high-temperature cycle and storage performance.

In addition, the multifunctional additive proposed in the present invention has a lower lowest unoccupied molecular orbital (LUMO energy level), and can form a film preferentially compared to traditional film-forming additives, which helps to form a thinner and denser solid electrolyte interface film, and can prevent the oxygen free radical-electrolyte solvent intermediate from being reduced at the negative electrode, thereby reducing the occurrence of side reactions and improving the problem of oxygen free radical-electrolyte solvent intermediate generating reducing gas at the negative electrode. The multifunctional additive can form a film not only at the negative electrode, but also at the positive electrode, which is beneficial to reduce the decomposition and deoxygenation of the positive electrode lithium supplement during the cycle storage process.

In some optional embodiments, the multifunctional additive includes at least one of unsaturated fluorosulfate and unsaturated fluorosulfonate. For example, the multifunctional additive may exemplarily but not limitatively include at least one of fluorosulfate vinyl ester containing unsaturated bonds, fluorosulfate propylene ester containing unsaturated bonds, fluorobissulfate propylene ester containing unsaturated bonds, fluorobispropane sultone containing unsaturated bonds, fluorobutane sultone containing unsaturated bonds, and fluorobisbutane sultone containing unsaturated bonds.

Exemplarily, the multifunctional additive includes at least one of the following compounds:

Wherein, the substituents R1 to R4 are independently selected from F, vinyl, 1-propenyl, 2-propenyl, ethynyl, 1-propynyl or 2-propynyl, and at least one substituent in each compound is F.

In some embodiments, the content of the multifunctional additive in the electrolyte can be 0.2wt% to 5wt%, such as 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%, etc., or other values within the range of 0.2wt% to 5wt%. In some preferred embodiments, the content of the multifunctional additive in the electrolyte is 1wt% to 2wt%.

Furthermore, the additives provided by the present invention also include film-forming additives.

In some embodiments, the film-forming additive may illustratively but not limitatively include at least one of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)phosphate and tris(trimethylsilyl)borate. In addition, it may also be other conventional film-forming additives used in electrolytes in the art.

In some embodiments, the content of the film-forming additive in the electrolyte can be 0.2wt% to 5wt%, such as 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%, etc., or other values within the range of 0.2wt% to 5wt%. In some preferred embodiments, the content of the film-forming additive in the electrolyte is 2wt% to 3wt%.

Furthermore, the electrolyte provided by the present invention also includes a carbonate solvent.

In some embodiments, the carbonate solvent may illustratively but not limitatively include at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate, preferably at least two. In addition, it may also be other conventional carbonate solvents used in the electrolyte of the present invention.

In some embodiments, the content of carbonate solvent in the electrolyte can be 70wt% to 87wt%, such as 70wt%, 75wt%, 80wt%, 85wt% or 87wt%, etc., or other values within the range of 70wt% to 87wt%. In some preferred embodiments, the content of carbonate solvent in the electrolyte is 75wt% to 85wt%.

Furthermore, the electrolyte provided by the present invention also includes a lithium salt. The lithium salt is a conductive lithium salt.

In some embodiments, the lithium salt may illustratively but not limitatively include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), lithium difluorophosphate, and lithium dioxalatoborate. In addition, other conventional lithium salts used in electrolytes in the art may also be used.

In some embodiments, the content of lithium salt in the electrolyte can be 8wt% to 20wt%, such as 8wt%, 10wt%, 12wt%, 15wt%, 18wt% or 20wt%, etc., or other values within the range of 8wt% to 20wt%. In some preferred embodiments, the content of lithium salt in the electrolyte is 10wt% to 15wt%.

As mentioned above, the electrolyte provided by the present invention retains the traditional carbonate solvents, commonly used lithium salts and conventional film-forming additives, and there is no need to change the existing lithium replenishment system formation process, so that the basic physical parameters such as viscosity, conductivity, density, etc. of the electrolyte will not change significantly, and there is no impact on the process. In addition, the electrolyte provided by the present invention can ensure sufficient lithium replenishment without changing the amount of LFO added; and there is no need to introduce additives with large impedance such as TMP to affect the electrochemical performance. The electrolyte introduces a specific multifunctional additive (unsaturated fluorinated sulfate or unsaturated fluorinated sulfonate) to ensure that the battery effectively reduces gas production, reduces battery impedance, and extends high-temperature cycle life without affecting other performances.

Correspondingly, the present invention also provides a method for preparing the above-mentioned electrolyte, comprising the following steps: mixing the components of the electrolyte.

In some embodiments, all components of the electrolyte may be mixed at once.

In some other embodiments, the components of the electrolyte may be mixed in batches to ensure that the materials are fully mixed. For example, the additive may be added to a mixed solution formed by a lithium salt and a carbonate solvent. Specifically, the lithium salt is first added to the carbonate solvent to form a mixed solution; and then the additive (including a multifunctional additive and a film-forming additive) is added to the mixed solution.

In addition, the present invention provides an application of the above electrolyte, for example, it can be used to prepare a battery.

The battery mentioned above may be a lithium-ion battery.

Correspondingly, the present invention also provides a battery, which contains the above-mentioned electrolyte.

The battery may be a lithium-ion battery.

It should be noted that the positive electrode material of the above-mentioned battery may exemplarily but not limitatively include lithium iron phosphate positive electrode material, ternary positive electrode material, lithium cobalt oxide positive electrode material or lithium manganese oxide positive electrode material. Similarly, the negative electrode material of the above-mentioned battery may exemplarily but not limitatively include graphite negative electrode material, silicon carbon negative electrode material or silicon oxygen negative electrode material.

The battery with the electrolyte provided by the present invention can improve the problem of gas generation during storage, and has a low volume expansion rate after storage. In addition, the battery also has a low internal resistance and better cycle performance.

The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

Example 1

This embodiment provides an electrolyte solution, which is: LiPF ₆ (1 mol/L)+EC/EMC/DMC (30:30:40 vol%)+2% VC+0.5% vinyl fluorosulfate.

Among them, the structural formula of vinyl fluorosulfate is Of _R1 and _R2 , one is F and the other is vinyl.

The preparation of the electrolyte comprises: adding a conductive lithium salt lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 mol/L into a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) (in volume percentage, EC:EMC:DMC=30%:30%:40%), and fully dissolving to form a mixed solution; and then adding vinylene carbonate (VC) and vinyl fluorosulfate to the mixed solution, wherein the amount of vinylene carbonate added is 2% of the mass of the entire electrolyte, and the amount of vinyl fluorosulfate added is 0.5% of the mass of the entire electrolyte.

That is, the electrolyte consists of 0.5 wt % of a multifunctional additive, 2 wt % of a film-forming additive, 85 wt % of a carbonate solvent (25.5 wt % of EC+25.5 wt % of EMC+34 wt % of DMC) and 12.5 wt % of a lithium salt.

Example 2

The electrolyte provided in this embodiment is recorded as: LiPF ₆ (1 mol/L)+EC/EMC/DMC (30:30:40 vol%)+2% VC+1% vinyl fluorosulfate.

The preparation method and process of the electrolyte are the same as those of Example 1, except that the amount of vinyl fluorosulfate is different.

That is, the electrolyte consists of 1 wt% of a multifunctional additive, 2 wt% of a film-forming additive, 84.5 wt% of a carbonate solvent (25.35 wt% of EC+25.35 wt% of EMC+33.8 wt% of DMC) and 12.5 wt% of a lithium salt.

Example 3

The electrolyte provided in this embodiment is recorded as: LiPF ₆ (1 mol/L)+EC/EMC/DMC (30:30:40 vol%)+2% VC+2% vinyl fluorosulfate.

The preparation method and process of the electrolyte are the same as those of Example 1, except that the amount of vinyl fluorosulfate is different.

That is, the electrolyte consists of 2 wt % of a multifunctional additive, 2 wt % of a film-forming additive, 83.5 wt % of a carbonate solvent (25.05 wt % of EC+25.05 wt % of EMC+33.4 wt % of DMC) and 12.5 wt % of a lithium salt.

Example 4

The difference between this embodiment and embodiment 1 is that the multifunctional additive is replaced by Among them, _R1 is vinyl and _R2 is F.

Example 5

The difference between this embodiment and embodiment 1 is that the multifunctional additive is replaced by Among them, _R1 is F, _R2 is F, _R3 is vinyl, and _R4 is F.

Example 6

The difference between this embodiment and embodiment 1 is that the multifunctional additive is replaced by Among them, _R1 is vinyl, _R2 is F, _R3 is F, and _R4 is F.

Example 7

The difference between this embodiment and embodiment 1 is that the multifunctional additive is replaced by Among them, _R1 is F, _R2 is vinyl, and _R3 is F.

Example 8

The difference between this embodiment and embodiment 1 is that the multifunctional additive is replaced by Among them, _R1 is F, _R2 is vinyl, _R3 is F, and _R4 is F.

Example 9

The difference between this embodiment and embodiment 1 is that the electrolyte consists of 2wt% of a multifunctional additive, 3wt% of a film-forming additive, 85wt% of a carbonate solvent (30wt% of EC+55wt% of DMC) and 10wt% of a lithium salt.

Example 10

The difference between this embodiment and embodiment 1 is that the electrolyte consists of 2 wt% of a multifunctional additive, 3 wt% of a film-forming additive, 78 wt% of a carbonate solvent (20 wt% of EC+58 wt% of EMC) and 17 wt% of a lithium salt.

Embodiment 11

The difference between this embodiment and embodiment 1 is that the electrolyte consists of 5wt% of a multifunctional additive, 5wt% of a film-forming additive, 70wt% of a carbonate solvent (32.5wt% of EC+37..5wt% of DMC) and 20wt% of a lithium salt.

Example 12

The difference between this embodiment and embodiment 1 is that the electrolyte consists of 0.2wt% of a multifunctional additive, 4.8wt% of a film-forming additive, 87wt% of a carbonate solvent (27wt% of EC+24wt% of EMC+36wt% of DMC) and 8wt% of a lithium salt.

Comparative Example 1

The electrolyte provided in this comparative example is recorded as: LiPF ₆ (1 mol/L)+EC/EMC/DMC (30:30:40 vol%)+2%VC.

The preparation method and process of the electrolyte are the same as those of Example 1, except that the additive is only VC.

That is, the electrolyte consists of 2 wt % of film-forming additives, 85.32 wt % of carbonate solvents (25.6 wt % of EC+25.65 wt % of EMC+34.2 wt % of DMC) and 12.5 wt % of lithium salt.

Comparative Example 2

The electrolyte provided in this comparative example is recorded as: LiPF ₆ (1 mol/L)+EC/EMC/DMC (30:30:40 vol%)+2% VC+1% methyl phosphite (TMP).

The preparation method and process of the electrolyte are the same as those of Example 2, except that the multifunctional additive is replaced by TMP.

That is, the electrolyte consists of 1 wt% of a multifunctional additive (TMP), 2 wt% of a film-forming additive, 84.5 wt% of a carbonate solvent (25.35 wt% of EC+25.35 wt% of EMC+33.8 wt% of DMC) and 12.5 wt% of a lithium salt.

Comparative Example 3

The difference between this comparative example and Example 1 is that the multifunctional additive In the embodiment, _R1 and _R2 are both vinyl groups, and the multifunctional additive does not contain F.

Comparative Example 4

The difference between this comparative example and Example 1 is that the electrolyte consists of 6wt% of a multifunctional additive, 2wt% of a film-forming additive, 79.5wt% of a carbonate solvent (23.85wt% of EC+23.85wt% of EMC+31.8wt% of DMC) and 12.5wt% of a lithium salt.

Comparative Example 5

The difference between this comparative example and Example 1 is that the electrolyte consists of 0.1wt% of a multifunctional additive, 2wt% of a film-forming additive, 85.4wt% of a carbonate solvent (25.62wt% of EC+25.62wt% of EMC+34.16wt% of DMC) and 12.5wt% of a lithium salt.

Test example

The electrolytes provided in Examples 1 to 12 and Comparative Examples 1 to 5 were respectively injected into 5Ah lithium supplement system soft pack batteries, the positive electrode of the battery was LFP + 2wt% LFO, the negative electrode was graphite, and the injection coefficient was 4g/Ah. After the battery was formed and vented, the DC impedance (DCR), cycle, storage and other performance tests were performed. The results are shown in Table 1 and Figure 1.

Table 1 Test results

As can be seen from Table 1: Due to the addition of the multifunctional additive vinyl fluorosulfate, the volume expansion rate of the battery at 55°C for 20 days in Examples 1 to 3 is significantly lower than that in Comparative Example 1, indicating that the preferential film-forming property of the multifunctional additive can indeed prevent the oxygen free radical-electrolyte solvent intermediate from being reduced at the negative electrode, thereby reducing the occurrence of side reactions. The more the multifunctional additive is added, the more obvious the improvement effect on gas production. The addition of TMP oxygen capture free radicals in Comparative Example 2 can also reduce gas production and reduce the volume expansion rate of the battery, but the effect is worse than that of the multifunctional electrolyte used in Examples 1 to 3.

From the DCR data, there is no significant increase in Examples 1 to 3 compared with Comparative Example 1, while the DCR of Comparative Example 2 has increased significantly, indicating that compared with the commonly used additive TMP for inhibiting gas production, the SEI film formed by the multifunctional additive has a lower impedance and has less impact on the battery electrical performance. The higher the amount of multifunctional additive added in the embodiment, the greater the battery DCR.

The 45°C cycle data show that the capacity retention rates of Examples 1 to 3 are higher than those of Comparative Examples 1 to 2, indicating that the multifunctional additive can effectively improve high temperature performance and extend service life. When the multifunctional additive is added at a higher concentration (2%), the cycle retention rate decreases due to the increase in DCR.

It can be seen from Examples 1 and 5 to 12 that the use of the multifunctional additive provided by the present invention and the dosage range provided in this application are beneficial to improving the storage gas generation problem of the positive lithium battery, reducing the battery DCR, and improving the 45°C cycle performance.

The electrolyte containing the multifunctional additive provided by the present invention can effectively improve the storage gas generation problem of the positive electrode lithium supplemented battery, reduce the battery DCR, and improve the 45° C. cycle performance. The preferred addition amount of the multifunctional additive is 1%.

It can be seen from Example 1 and Comparative Example 3 that if the multifunctional additive does not contain F, it will cause storage gas generation problems and a high expansion rate.

It can be seen from Example 1 and Comparative Examples 4 to 5 that if the amount of the multifunctional additive is inappropriate, the storage gas generation, DCR and cycle performance of the battery will not be effectively improved.

In summary, the electrolyte provided by the present invention has at least the following advantages:

(1) The traditional carbonate solvent, common lithium salt and conventional film-forming additive system are retained, so that the basic physical parameters of the electrolyte, such as viscosity, conductivity, density, etc., will not change significantly. When using this electrolyte, there is no need to change the existing lithium replenishment system formation plan, and there is no impact on the existing process.

(2) The electrolyte effectively improves the storage gas generation problem of the positive electrode lithium replenishment system; the multifunctional additive participates in the negative electrode film formation and has a lower LUMO energy level than the conventional film-forming additive VC, which can preferentially form a film and form a thinner and denser SEI. In addition, the additive also contains F elements, which tend to generate LiF-rich SEI. This type of SEI film has strong mechanical properties and is more dense. Covering the surface of the negative electrode can prevent the oxygen free radicals generated by the decomposition of the positive electrode lithium replenisher from forming intermediates and reducing gas at the negative electrode; the additive also participates in the positive electrode film formation, protects the positive electrode, and reduces the decomposition and oxygenation of the positive electrode lithium replenisher in the later stage of cycle storage.

(3) The problem of increased impedance caused by conventional gas production additives has been solved. The new multifunctional additives contained in the electrolyte contain sulfuric acid groups or sulfonic acid groups, and the SEI impedance involved in film formation is low, which helps to reduce the internal resistance of the battery.

(4) The problem of deterioration of cycle performance due to side reactions caused by gas production has been solved. The multifunctional additive contained in the electrolyte contains sulfuric acid groups or sulfonic acid groups, which helps to improve the high-temperature cycle and storage performance of the battery. The LiF-rich SEI film can reduce the energy barrier for Li ⁺ diffusion, facilitate the diffusion of lithium ions, and make them more evenly embedded in the negative electrode to avoid the formation of lithium dendrites. This feature also helps to extend the cycle life of the battery and slow down the attenuation.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. An electrolyte, characterized in that the electrolyte comprises an additive, the additive comprises a multifunctional additive, the multifunctional additive comprises a fluoroester containing an unsaturated bond, and the fluoroester has a sulfonic acid group or a sulfuric acid group. 2. The electrolyte according to claim 1, characterized in that the multifunctional additive comprises at least one of an unsaturated fluorinated sulfate and an unsaturated fluorinated sulfonate; Preferably, the multifunctional additive comprises at least one of fluoroethylene sulfate containing an unsaturated bond, fluoropropylene sulfate containing an unsaturated bond, fluoropropylene bissulfate containing an unsaturated bond, fluorobispropane sultone containing an unsaturated bond, fluorobutane sultone containing an unsaturated bond, and fluorobisbutane sultone containing an unsaturated bond; Preferably, the multifunctional additive comprises at least one of the following compounds: Wherein, the substituents R1 to R4 are independently selected from F, vinyl, 1-propenyl, 2-propenyl, ethynyl, 1-propynyl or 2-propynyl, and at least one substituent in each compound is F. 3. The electrolyte according to claim 1 or 2, characterized in that the content of the multifunctional additive in the electrolyte is 0.2wt% to 5wt%, preferably 1wt% to 2wt%. 4. The electrolyte according to claim 1 or 2, characterized in that the additive further comprises a film-forming additive; Preferably, the film-forming additive comprises at least one of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)phosphate and tris(trimethylsilyl)borate; Preferably, the content of the film-forming additive in the electrolyte is 0.2 wt% to 5 wt%, preferably 2 wt% to 3 wt%. 5. The electrolyte according to claim 1 or 2, characterized in that the electrolyte further comprises a carbonate solvent; Preferably, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate; Preferably, the content of the carbonate solvent in the electrolyte is 70wt% to 87wt%, more preferably 75wt% to 85wt%. 6. The electrolyte according to claim 1 or 2, characterized in that the electrolyte further comprises a lithium salt; Preferably, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), lithium difluorophosphate and lithium dioxalatoborate; Preferably, the content of the lithium salt in the electrolyte is 8wt% to 20wt%, more preferably 10wt% to 15wt%. 7. A method for preparing an electrolyte according to any one of claims 1 to 6, characterized in that it comprises the following steps: mixing the components of the electrolyte; Preferably, the additive is added into a mixed solution formed by the lithium salt and the carbonate solvent. 8. Use of the electrolyte according to any one of claims 1 to 6, characterized in that the electrolyte is used to prepare a battery. 9. A battery, characterized in that the battery contains the electrolyte according to any one of claims 1 to 6. 10. The battery according to claim 9 is characterized in that the positive electrode material of the battery includes lithium iron phosphate positive electrode material, ternary positive electrode material, lithium cobalt oxide positive electrode material or lithium manganese oxide positive electrode material; or, the negative electrode material of the battery includes graphite negative electrode material, silicon-carbon negative electrode material or silicon-oxygen negative electrode material.