An electrolyte, its preparation method and application, and a battery

Abstract

The present invention discloses an electrolyte, a preparation method and application thereof, and a battery, belonging to the technical field of electrolytes. The electrolyte includes a multifunctional additive, and the multifunctional additive includes a fluoroester containing an unsaturated bond and a sulfonic acid group or a sulfuric acid group. The multifunctional additive can form a film preferentially compared to traditional film-forming additives, which helps to form a thinner and denser solid electrolyte interface film and improve 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 helps to reduce the decomposition and oxygen release 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 helps 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

Technical Field

[0001] This invention relates to the field of electrolyte technology, and more specifically, to an electrolyte, its preparation method and application, and a battery. Background Art

[0002] In the fields of new energy power and energy storage, lithium-ion batteries have become the most widely used rechargeable batteries due to their high energy density and portability. However, currently commercialized lithium-ion batteries are struggling to meet the ever-increasing demands for battery energy and lifespan. Since a significant reason for battery energy decay and shortened lifespan is the loss of active lithium in the system, lithium replenishment using positive and negative electrode materials has been extensively studied as a method to compensate for this loss. Compared to lithium metal replenishment at the negative electrode, lithium replenishment at the positive electrode has lower requirements for processes and the environment, can be directly introduced without altering existing process conditions, and has lower operating costs, making it more advantageous.

[0003] Commonly used positive electrode lithium replenishers include lithium ferrite (Li5FeO4, LFO), lithium nickel oxide (Li2NiO2, LNO), and lithium peroxide (Li2O2, LLO). These lithium replenishers decompose when the voltage is reached during the first charge, releasing Li. + To compensate for the loss of active lithium during the formation stage, oxygen free radicals and oxygen molecules are generated. The oxygen free radicals combine with the electrolyte solvent to form intermediates and produce reducing gas at the negative electrode. Most of the gas is removed by vacuuming after formation. However, batteries containing lithium replenishing agents (mainly LFO) still have serious gas generation problems in later cycles and high-temperature storage. This gas generation comes from the unused lithium replenishing agents continuing to decompose after formation, generating oxygen free radicals and oxygen, which causes gas generation at the negative electrode.

[0004] Currently, solutions to the above problems may include the following methods:

[0005] (1) Introduction of oxygen radical scavenging additives. The main reason for gas generation in the positive electrode lithium replenishment system is that the lithium replenishment not fully consumed during the formation stage is continuously consumed during subsequent cycle storage, generating oxygen radicals. These radicals and electrolyte solvent (EC) combine to form intermediate products, which then generate reducing gases at the negative electrode. By introducing oxygen radical scavenging additives into the electrolyte, the additives can complex with the generated oxygen radicals, preventing them from easily migrating to the negative electrode for reduction, thereby reducing gas generation. However, when the amount of oxygen radical scavenging additives added is small, the oxygen radicals cannot be completely eliminated. When the amount added is large, the impedance increases significantly, which will degrade the gas electrochemical performance of the battery (such as rate capability and cycle performance).

[0006] (2) Reduce the amount of LFO lithium replenisher added to reduce the delithiation content of the lithium replenisher (control the charging voltage); or replace part of the LFO with LNO. However, the lithium replenishment capacity of LNO (theoretical specific capacity is about 400 mAh / g) is much lower than that of LFO (theoretical specific capacity is about 867 mAh / g). Whether reducing the amount of LFO added, replacing LFO with LNO, or reducing the delithiation content of the lithium replenisher, the lithium replenishment efficiency will be low and the performance improvement will not be obvious.

[0007] (3) Reducing the formation current can ensure that the lithium supplement reacts fully, thereby avoiding continuous decomposition and gas generation during subsequent use. However, this method has a more complex process flow, a much longer formation time, a much higher production cost, and a lower production efficiency.

[0008] In view of this, the present invention is proposed. Summary of the Invention

[0009] The purpose of this invention is to provide an electrolyte, its preparation method and application, and a battery, in order to solve or improve the above-mentioned technical problems.

[0010] This invention can be implemented as follows:

[0011] In a first aspect, the present invention provides an electrolyte comprising additives, the additives including multifunctional additives, the multifunctional additives including fluorinated esters containing unsaturated bonds, and the fluorinated esters having sulfonic acid groups or sulfuric acid groups.

[0012] In an optional embodiment, the multifunctional additive includes at least one of unsaturated fluorosulfates and unsaturated fluorosulfonates.

[0013] In an optional embodiment, the multifunctional additive includes at least one of the following: fluoroethylene sulfate containing an unsaturated bond, fluoropropylene sulfate containing an unsaturated bond, fluorobis(propylene) sulfate containing an unsaturated bond, fluorobis(propanesulfonate) lactone containing an unsaturated bond, fluorobutanesulfonate lactone containing an unsaturated bond, and fluorobis(butanesulfonate) lactone containing an unsaturated bond.

[0014] In an optional embodiment, the multifunctional additive includes at least one of the following compounds:

[0015]

[0016] In this compound, 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.

[0017] In an optional embodiment, the multifunctional additive is present in the electrolyte at a concentration of 0.2 wt% to 5 wt%.

[0018] In an optional embodiment, the multifunctional additive is present in the electrolyte at a concentration of 1 wt% to 2 wt%.

[0019] In an optional embodiment, the additives also include film-forming additives.

[0020] In an optional embodiment, the film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

[0021] In an optional embodiment, the content of the film-forming additive in the electrolyte is 0.2 wt% to 5 wt%.

[0022] In an optional embodiment, the content of the film-forming additive in the electrolyte is 2wt% to 3wt%.

[0023] In an optional embodiment, the electrolyte may further include a carbonate solvent.

[0024] 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).

[0025] In an optional embodiment, the carbonate solvent content in the electrolyte is 70 wt% to 87 wt%.

[0026] In an optional embodiment, the carbonate solvent content in the electrolyte is 75 wt% to 85 wt%.

[0027] In an optional embodiment, the electrolyte further includes a lithium salt.

[0028] In optional embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium difluorooxalate borate (LiODFB), lithium difluorobis(oxalate) phosphate (LiODFP), lithium difluorophosphate (LiPO2F2), and lithium dioxalate borate (LiBOB).

[0029] In an optional embodiment, the lithium salt content in the electrolyte is 8 wt% to 20 wt%.

[0030] In an optional embodiment, the lithium salt content in the electrolyte is 10wt% to 15wt%.

[0031] Secondly, the present invention provides a method for preparing an electrolyte as described in any of the foregoing embodiments, comprising the following steps: mixing the components of the electrolyte.

[0032] In an optional embodiment, the additive is added to a mixed solution formed by lithium salt and carbonate solvent.

[0033] Thirdly, the present invention provides an application of the electrolyte as described in any of the foregoing embodiments, for example, it can be used in the preparation of batteries.

[0034] Fourthly, the present invention provides a battery containing the electrolyte of any of the foregoing embodiments.

[0035] In optional embodiments, 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.

[0036] The beneficial effects of this invention include:

[0037] The multifunctional additive provided by this invention contains fluorine, which tends to form lithium fluoride during film formation. This helps to lower the lithium-ion diffusion barrier, increase the mechanical stability of the solid electrolyte interface film, prevent lithium dendrite formation, and improve electrochemical performance. Furthermore, this multifunctional additive contains sulfonic acid or sulfuric acid groups, which helps to reduce battery impedance and improve battery high-temperature cycling and storage performance.

[0038] Furthermore, the multifunctional additive proposed in this invention possesses a lower least unoccupied molecular orbital (LUMO) level, allowing it to preferentially form films compared to traditional film-forming additives. This facilitates the formation of thinner and denser solid electrolyte interface films, preventing the reduction of oxygen free radical-electrolyte solvent intermediates at the negative electrode, thereby reducing side reactions and mitigating the problem of reducing gases generated by oxygen free radical-electrolyte solvent intermediates at the negative electrode. This multifunctional additive can form films not only at the negative electrode but also at the positive electrode, which helps reduce the decomposition and oxygen release of the positive electrode lithium replenishment agent during cyclic storage.

[0039] Batteries with the electrolyte provided by this invention can improve the problem of gas generation during storage, have a low volume expansion rate after storage, and also have low internal resistance and better cycle performance. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1The graph shows the volume expansion rate of the batteries corresponding to Examples 1-12 and Comparative Examples 1-5 of the present invention after storage at 55°C for 20 days. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0043] The electrolyte, its preparation method, its application, and the battery provided by this invention will be described in detail below.

[0044] This invention proposes an electrolyte comprising additives, including multifunctional additives, which include fluorinated esters containing unsaturated bonds, and the fluorinated esters having sulfonic acid groups or sulfuric acid groups.

[0045] The number of unsaturated bonds can be one, two, or more. The number of sulfonic acid groups and sulfuric acid groups can be one, two, or more.

[0046] This multifunctional additive contains fluorine, which tends to form lithium fluoride during film formation. This helps lower the lithium-ion diffusion barrier, increases the mechanical stability of the solid electrolyte interface film, prevents lithium dendrite formation, and improves electrochemical performance. Furthermore, this multifunctional additive contains sulfonic acid or sulfuric acid groups, which help reduce battery impedance and improve battery high-temperature cycling and storage performance.

[0047] Furthermore, the multifunctional additive proposed in this invention possesses a lower least unoccupied molecular orbital (LUMO) level, allowing it to preferentially form films compared to traditional film-forming additives. This facilitates the formation of thinner and denser solid electrolyte interface films, preventing the reduction of oxygen free radical-electrolyte solvent intermediates at the negative electrode, thereby reducing side reactions and mitigating the problem of reducing gases generated by oxygen free radical-electrolyte solvent intermediates at the negative electrode. This multifunctional additive can form films not only at the negative electrode but also at the positive electrode, which helps reduce the decomposition and oxygen release of the positive electrode lithium replenishment agent during cyclic storage.

[0048] In some alternative embodiments, the multifunctional additive includes at least one of unsaturated fluorosulfates and unsaturated fluorosulfonates. For example, the multifunctional additive may, by way of example but not limitation, include at least one of unsaturated vinyl fluorosulfate, unsaturated propylene fluorosulfate, unsaturated propylene fluorodisulfate, unsaturated fluorodipropanesulfonate lactone, unsaturated fluorobutanesulfonate lactone, and unsaturated fluorodibutanesulfonate lactone.

[0049] For example, the multifunctional additive includes at least one of the following compounds:

[0050]

[0051] In this compound, 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.

[0052] In some embodiments, the content of the multifunctional additive in the electrolyte can be from 0.2 wt% to 5 wt%, such as 0.2 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%, or other values ​​within the range of 0.2 wt% to 5 wt%. In some preferred embodiments, the content of the multifunctional additive in the electrolyte is 1 wt% to 2 wt%.

[0053] Furthermore, the additives provided by the present invention also include film-forming additives.

[0054] In some embodiments, the film-forming additive may, by way of example but not limitation, include at least one of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate. Alternatively, other conventional film-forming additives used in electrolytes in the art may also be used.

[0055] In some embodiments, the content of the film-forming additive in the electrolyte can be from 0.2 wt% to 5 wt%, such as 0.2 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%, or other values ​​within the range of 0.2 wt% to 5 wt%. In some preferred embodiments, the content of the film-forming additive in the electrolyte is 2 wt% to 3 wt%.

[0056] Furthermore, the electrolyte provided by the present invention also includes carbonate solvents.

[0057] In some embodiments, the carbonate solvent may, by way of example but not limitation, include at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate, preferably at least two. Alternatively, other conventional carbonate solvents used in electrolytes in the art may also be used.

[0058] In some embodiments, the content of the carbonate solvent in the electrolyte can be 70 wt% to 87 wt%, such as 70 wt%, 75 wt%, 80 wt%, 85 wt%, or 87 wt%, or other values ​​within the range of 70 wt% to 87 wt%. In some preferred embodiments, the content of the carbonate solvent in the electrolyte is 75 wt% to 85 wt%.

[0059] Furthermore, the electrolyte provided by this invention also includes a lithium salt. The lithium salt is a conductive lithium salt.

[0060] In some embodiments, the lithium salt may, by way of example but not limitation, include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium difluorooxalate borate, lithium difluorobis(oxalate) phosphate, lithium difluorophosphate, and lithium di(oxalate) borate. Alternatively, other conventional lithium salts used in electrolytes in the art may also be used.

[0061] In some embodiments, the lithium salt content in the electrolyte can be 8 wt% to 20 wt%, such as 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, or 20 wt%, or other values ​​within the range of 8 wt% to 20 wt%. In some preferred embodiments, the lithium salt content in the electrolyte is 10 wt% to 15 wt%.

[0062] Building upon the above, the electrolyte provided by this invention retains traditional carbonate solvents, commonly used lithium salts, and conventional film-forming additives, without altering the existing lithium replenishment system formation process. This ensures that the basic physical properties of the electrolyte, such as viscosity, conductivity, and density, remain largely unchanged, having no impact on the manufacturing process. Furthermore, the electrolyte provided by this invention guarantees sufficient lithium replenishment without altering the LFO addition amount; and it eliminates the need to introduce additives with high impedance, such as TMP, which could negatively affect electrochemical performance. By introducing specific multifunctional additives (unsaturated fluorosulfates or unsaturated fluorosulfonates), this electrolyte effectively reduces gas production, lowers battery impedance, and extends high-temperature cycle life without affecting other performance characteristics.

[0063] Accordingly, the present invention also provides a method for preparing the above-mentioned electrolyte, comprising the following steps: mixing the components of the electrolyte.

[0064] In some implementations, all components of the electrolyte can be mixed at once.

[0065] In other embodiments, the electrolyte components can be mixed in batches to ensure thorough and uniform mixing. For example, additives can be added to a mixed solution formed by lithium salt and carbonate solvent. Specifically, lithium salt is first added to carbonate solvent to form a mixed solution; then additives (including multifunctional additives and film-forming additives) are added to this mixed solution.

[0066] Furthermore, the present invention provides an application of the above-mentioned electrolyte, for example, it can be used in the preparation of batteries.

[0067] The aforementioned battery can be a lithium-ion battery.

[0068] Accordingly, the present invention also provides a battery containing the above-mentioned electrolyte.

[0069] This battery can be a lithium-ion battery.

[0070] It should be noted that the positive electrode material of the above-mentioned battery may, by way of example but not limitation, 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, by way of example but not limitation, include graphite negative electrode material, silicon-carbon negative electrode material, or silicon-oxygen negative electrode material.

[0071] Batteries with the electrolyte provided by this invention can improve the problem of gas generation during storage, have a low volume expansion rate after storage, and also have low internal resistance and better cycle performance.

[0072] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0073] Example 1

[0074] This embodiment provides an electrolyte, denoted as: LiPF6 (1mol / L) + EC / EMC / DMC (30:30:40 vol%) + 2% VC + 0.5% vinyl fluoroethylene sulfate.

[0075] The structural formula of vinyl fluoroethylene sulfate is: In R1 and R2, one is F and the other is vinyl.

[0076] The preparation of the electrolyte includes: adding conductive lithium salt lithium hexafluorophosphate (LiPF6) at a concentration of 1 mol / L to a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (by volume percentage, EC:EMC:DMC = 30%:30%:40%), and dissolving it completely to form a mixed solution; then adding vinylene carbonate (VC) and vinyl fluorosulfate to the mixed solution, wherein the amount of vinylene carbonate added is 2% of the total mass of the electrolyte, and the amount of vinyl fluorosulfate added is 0.5% of the total mass of the electrolyte.

[0077] That is, the electrolyte consists of 0.5 wt% multifunctional additives, 2 wt% film-forming additives, 85 wt% carbonate solvents (25.5 wt% EC + 25.5 wt% EMC + 34 wt% DMC) and 12.5 wt% lithium salt.

[0078] Example 2

[0079] The electrolyte provided in this embodiment is denoted as: LiPF6 (1mol / L) + EC / EMC / DMC (30:30:40 vol%) + 2% VC + 1% vinyl fluoroethylene sulfate.

[0080] The preparation method and process of this electrolyte are the same as in Example 1, except that the amount of vinyl fluoroethylene sulfate used is different.

[0081] That is, the electrolyte consists of 1 wt% multifunctional additives, 2 wt% film-forming additives, 84.5 wt% carbonate solvents (25.35 wt% EC + 25.35 wt% EMC + 33.8 wt% DMC) and 12.5 wt% lithium salt.

[0082] Example 3

[0083] The electrolyte provided in this embodiment is denoted as: LiPF6 (1mol / L) + EC / EMC / DMC (30:30:40 vol%) + 2% VC + 2% vinyl fluoroethylene sulfate.

[0084] The preparation method and process of this electrolyte are the same as in Example 1, except that the amount of vinyl fluoroethylene sulfate used is different.

[0085] That is, the electrolyte consists of 2 wt% multifunctional additives, 2 wt% film-forming additives, 83.5 wt% carbonate solvents (25.05 wt% EC + 25.05 wt% EMC + 33.4 wt% DMC) and 12.5 wt% lithium salt.

[0086] Example 4

[0087] The difference between this embodiment and Embodiment 1 is that the multifunctional additive is replaced with... Where R1 is vinyl and R2 is F.

[0088] Example 5

[0089] The difference between this embodiment and Embodiment 1 is that the multifunctional additive is replaced with... Wherein, R1 is F, R2 is F, R3 is vinyl, and R4 is F.

[0090] Example 6

[0091] The difference between this embodiment and Embodiment 1 is that the multifunctional additive is replaced with... Wherein, R1 is vinyl, R2 is F, R3 is F, and R4 is F.

[0092] Example 7

[0093] The difference between this embodiment and Embodiment 1 is that the multifunctional additive is replaced with... Where R1 is F, R2 is vinyl, and R3 is F.

[0094] Example 8

[0095] The difference between this embodiment and Embodiment 1 is that the multifunctional additive is replaced with... Wherein, R1 is F, R2 is vinyl, R3 is F, and R4 is F.

[0096] Example 9

[0097] The difference between this embodiment and Example 1 is that the electrolyte consists of 2 wt% multifunctional additives, 3 wt% film-forming additives, 85 wt% carbonate solvents (30 wt% EC + 55 wt% DMC) and 10 wt% lithium salt.

[0098] Example 10

[0099] The difference between this embodiment and Example 1 is that the electrolyte consists of 2 wt% multifunctional additives, 3 wt% film-forming additives, 78 wt% carbonate solvents (20 wt% EC + 58 wt% EMC) and 17 wt% lithium salt.

[0100] Example 11

[0101] The difference between this embodiment and Example 1 is that the electrolyte consists of 5 wt% of a multifunctional additive, 5 wt% of a film-forming additive, 70 wt% of a carbonate solvent (32.5 wt% EC + 37.5 wt% DMC) and 20 wt% of a lithium salt.

[0102] Example 12

[0103] The difference between this embodiment and Example 1 is that the electrolyte consists of 0.2 wt% of a multifunctional additive, 4.8 wt% of a film-forming additive, 87 wt% of a carbonate solvent (27 wt% EC + 24 wt% EMC + 36 wt% DMC) and 8 wt% of a lithium salt.

[0104] Comparative Example 1

[0105] The electrolyte provided in this comparative example is denoted as: LiPF6 (1 mol / L) + EC / EMC / DMC (30:30:40 vol%) + 2% VC.

[0106] The preparation method and process of this electrolyte are the same as in Example 1, except that the only additive is vitamin C.

[0107] That is, the electrolyte consists of 2 wt% film-forming additives, 85.32 wt% carbonate solvents (25.6 wt% EC + 25.65 wt% EMC + 34.2 wt% DMC) and 12.5 wt% lithium salt.

[0108] Comparative Example 2

[0109] The electrolyte provided in this comparative example is denoted as: LiPF6 (1 mol / L) + EC / EMC / DMC (30:30:40 vol%) + 2% VC + 1% methyl phosphite (TMP).

[0110] The preparation method and process of this electrolyte are the same as in Example 2, except that the multifunctional additive is replaced with TMP.

[0111] That is, the electrolyte consists of 1 wt% of multifunctional additive (TMP), 2 wt% of film-forming additive, 84.5 wt% of carbonate solvent (25.35 wt% EC + 25.35 wt% EMC + 33.8 wt% DMC) and 12.5 wt% lithium salt.

[0112] Comparative Example 3

[0113] The difference between this comparative example and Example 1 is that: multifunctional additive In this compound, R1 and R2 are both vinyl groups, and this multifunctional additive does not contain F.

[0114] Comparative Example 4

[0115] The difference between this comparative example and Example 1 is that the electrolyte consists of 6 wt% multifunctional additives, 2 wt% film-forming additives, 79.5 wt% carbonate solvents (23.85 wt% EC + 23.85 wt% EMC + 31.8 wt% DMC) and 12.5 wt% lithium salt.

[0116] Comparative Example 5

[0117] The difference between this comparative example and Example 1 is that the electrolyte consists of 0.1 wt% of a multifunctional additive, 2 wt% of a film-forming additive, 85.4 wt% of a carbonate solvent (25.62 wt% EC + 25.62 wt% EMC + 34.16 wt% DMC) and 12.5 wt% of a lithium salt.

[0118] Test case

[0119] The electrolytes provided in Examples 1-12 and Comparative Examples 1-5 were injected into 5Ah lithium-filling pouch cells. The positive electrode was LFP + 2wt% LFO, and the negative electrode was graphite. The electrolyte injection coefficient was 4g / Ah. After formation and degassing, the cells were subjected to DC resistance (DCR), cycle life, and storage performance tests. The results are shown in Table 1 and... Figure 1 As shown.

[0120] Table 1 Test Results As shown in Table 1, the volume expansion rate of batteries in Examples 1-3 after 20 days at 55°C was significantly lower than that in Comparative Example 1 due to the addition of the multifunctional additive vinyl fluoroethylene sulfate. This indicates that the preferential film-forming characteristic of the multifunctional additive can indeed prevent the reduction of oxygen free radical-electrolyte solvent intermediate at the negative electrode, thereby reducing side reactions. The higher the amount of multifunctional additive added, the more significant the improvement in gas production. The addition of TMP oxygen-scavenging free radicals in Comparative Example 2 can also reduce gas production and lower the battery volume expansion rate, but the effect is worse than that of the multifunctional electrolyte used in Examples 1-3.

[0121] The DCR data for Examples 1-3 showed no significant increase compared to Comparative Example 1, while Comparative Example 2 showed a significant increase in DCR. This indicates that compared to the commonly used additive TMP for suppressing gas production, the SEI film formed by the multifunctional additive has lower impedance and less impact on battery electrical performance. In the examples, the higher the amount of multifunctional additive added, the greater the battery DCR.

[0122] Cycling data at 45°C showed that the capacity retention rates of Examples 1-3 were higher than those of Comparative Examples 1-2, indicating that the multifunctional additive can effectively improve high-temperature performance and extend service life. When the multifunctional additive concentration was higher (2%), the cycle retention rate decreased due to an increase in DCR.

[0123] As can be seen from Examples 1 and Examples 5-12, the use of the multifunctional additive provided by the present invention and the dosage range provided in this application are all beneficial to improving the storage gas generation problem of positive electrode lithium-ion batteries, reducing battery DCR, and improving 45°C cycle performance.

[0124] The electrolyte incorporating the multifunctional additive provided by this invention can effectively improve the gas generation problem during storage in lithium-ion batteries, reduce the battery DCR, and improve cycle performance at 45°C. The preferred amount of the multifunctional additive is 1%.

[0125] As can be seen from Example 1 and Comparative Example 3, if the multifunctional additive does not contain F, it will lead to gas generation problems during storage and a high expansion rate.

[0126] As can be seen from Example 1 and Comparative Examples 4-5, if the amount of multifunctional additive is inappropriate, the storage gas generation, DCR and cycle performance of the battery will not be effectively improved.

[0127] In summary, the electrolyte provided by this invention has at least the following advantages:

[0128] (1) It retains the traditional carbonate solvent, commonly used lithium salt, and conventional film-forming additive system, so that the basic physical properties of the electrolyte, such as viscosity, conductivity, and density, will not change significantly. Using this electrolyte does not require changing the existing lithium replenishment system formation scheme and has no impact on the existing process.

[0129] (2) This electrolyte effectively improves the gas generation problem during storage in the positive electrode lithium replenishment system; the multifunctional additive participates in the negative electrode film formation and has a lower LUMO energy level than conventional film-forming additive VC, enabling preferential film formation and the formation of a thinner and denser SEI. Furthermore, this additive contains F, which tends to generate LiF-rich SEI. This type of SEI film has strong mechanical properties and is more dense. Covering the negative electrode surface, it can prevent the formation of intermediates by oxygen free radicals generated from the decomposition of the positive electrode lithium replenishment agent and the generation of gas during reduction at the negative electrode. This additive also participates in the positive electrode film formation, protecting the positive electrode and reducing oxygen release from the decomposition of the positive electrode lithium replenishment agent during the later stages of cycle storage.

[0130] (3) It solves the problem of increased impedance caused by conventional gas-generating additives. The novel multifunctional additives contained in this electrolyte contain sulfuric acid groups or sulfonic acid groups, which participate in film formation with lower SEI impedance and help reduce battery internal resistance.

[0131] (4) The problem of deteriorated cycle performance caused by side reactions resulting from gas production has been solved. The multifunctional additives in this electrolyte contain sulfuric acid or sulfonic acid groups, which help improve the high-temperature cycle and storage performance of the battery. The LiF-rich SEI film can reduce Li + The diffusion energy barrier facilitates lithium-ion diffusion, allowing it to be more uniformly embedded in the negative electrode and preventing the formation of lithium dendrites. This characteristic also helps extend the battery's cycle life and slow down degradation.

[0132] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes additives, and the additives include multifunctional additives; The multifunctional additive is selected from: or ; In this compound, 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, and R1 to R4 are not simultaneously F.

2. The electrolyte according to claim 1, characterized in that, The multifunctional additive is present in the electrolyte at a concentration of 0.2 wt% to 5 wt%.

3. The electrolyte according to claim 2, characterized in that, The multifunctional additive is present in the electrolyte at a concentration of 1 wt% to 2 wt%.

4. The electrolyte according to claim 1, characterized in that, The additives also include film-forming additives.

5. The electrolyte according to claim 4, characterized in that, The film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

6. The electrolyte according to claim 4, characterized in that, The film-forming additive is present in the electrolyte at a concentration of 0.2 wt% to 5 wt%.

7. The electrolyte according to claim 6, characterized in that, The film-forming additive is present in the electrolyte at a concentration of 2 wt% to 3 wt%.

8. The electrolyte according to claim 1, characterized in that, The electrolyte also includes carbonate solvents.

9. The electrolyte according to claim 8, characterized in that, The carbonate solvents include at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

10. The electrolyte according to claim 8, characterized in that, The carbonate solvent is present in the electrolyte at a concentration of 70 wt% to 87 wt%.

11. The electrolyte according to claim 10, characterized in that, The carbonate solvent is present in the electrolyte at a concentration of 75 wt% to 85 wt%.

12. The electrolyte according to claim 1, characterized in that, The electrolyte also includes lithium salt.

13. The electrolyte according to claim 12, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium perchlorate, lithium difluorooxalate borate, lithium difluorobis(oxalate) phosphate, lithium difluorophosphate, and lithium di(oxalate) borate.

14. The electrolyte according to claim 13, characterized in that, The lithium salt content in the electrolyte is 8wt%~20wt%.

15. The electrolyte according to claim 14, characterized in that, The lithium salt content in the electrolyte is 10wt%~15wt%.

16. A method for preparing an electrolyte as described in any one of claims 1 to 15, characterized in that, The following steps are involved: The components of the electrolyte are mixed.

17. The preparation method according to claim 16, characterized in that, The additive is added to a mixed solution formed by lithium salt and carbonate solvent.

18. The application of an electrolyte as described in any one of claims 1 to 15, characterized in that, The electrolyte is used to manufacture batteries.

19. A battery, characterized in that, The battery contains the electrolyte according to any one of claims 1 to 15.

20. The battery according to claim 19, 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.

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