A method for injecting electrolyte into a lithium battery

Abstract

This invention discloses a method for electrolyte injection into lithium batteries, relating to the field of lithium battery technology. The invention introduces lithium perfluorobutyl sulfonate (PFBS-Li) as a wetting functional additive for primary electrolyte injection. Combined with vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, and tris(trimethylsilyl)phosphate, it achieves better wetting effects, ensuring a specific relationship between the primary electrolyte injection volume and the PFBS-Li content in the first electrolyte. By increasing the primary electrolyte injection volume to create a rich electrolyte wetting state, the proportion of PFBS-Li in the primary electrolyte injection is reduced, ensuring the degree of electrolyte wetting of the electrodes and reducing localized electrode drying. Before formation, a portion of the electrolyte is extracted under negative pressure to prevent excessive decomposition of the electrolyte during formation, which could lead to unstable conditions such as gas generation.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to a method for injecting electrolyte into a lithium battery. Background Technology

[0002] In battery manufacturing, ensuring the electrolyte wets the electrodes is a crucial step that directly affects battery performance and lifespan. In high-density systems and other systems, the high compaction density of the electrodes reduces the contact area between the electrolyte and the electrode material, making it more difficult for the electrolyte to distribute evenly. This can lead to localized drying, affecting the uniformity of SEI film formation and causing a decrease in interfacial stability.

[0003] Electrolyte components mainly consist of lithium salts, solvents, and additives. Different components play different roles, especially additives, which are numerous and varied, each with its own function and interactions. Therefore, to fully utilize their respective roles, some battery manufacturers employ a secondary electrolyte injection process to achieve better battery performance. The formation process is a crucial step in forming the solid electrolyte interphase (SEI, CEI) film between the positive and negative electrodes. Incomplete electrolyte wetting after injection can easily lead to uneven solid electrolyte film formation, increased side reactions, and failure to protect electrode materials, thereby accelerating electrode material corrosion and dissolution and shortening battery life.

[0004] In some currently disclosed two-electrode injection techniques, the injection efficiency or wetting ability of the first-electrode is improved by reducing the amount or viscosity of the first-electrode injection. However, these methods all increase the proportion of the second-electrode injection, which increases the difficulty of injecting the second-electrode injection. This can easily lead to poor film formation after the first injection or uneven dispersion after the second injection, thus affecting the battery performance.

[0005] Therefore, there is an urgent need to improve the electrolyte injection process to ensure the wetting effect of each injection while improving the uniformity of electrolyte distribution, the uniformity of SEI film formation, and the interfacial stability, thereby improving the battery's electrical performance.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method for injecting electrolyte into lithium batteries, which aims to improve the uniformity and interfacial stability of SEI film formation and enhance electrochemical performance.

[0008] This invention is implemented as follows:

[0009] In a first aspect, the present invention provides a method for injecting electrolyte into a lithium battery, comprising:

[0010] First, the battery is injected with electrolyte once, then left to stand for a while before some electrolyte is extracted. After that, the battery undergoes formation, aging, and a second electrolyte injection in sequence.

[0011] The electrolyte injected during the first injection process is the first electrolyte, and the electrolyte injected during the second injection process is the second electrolyte.

[0012] The first electrolyte contains a first lithium salt, a first solvent, and a first additive, the first additive including vinylene carbonate and lithium perfluorobutyl sulfonate;

[0013] The ratio of the single injection volume to the total injection volume is controlled as Y, the mass fraction of lithium perfluorobutyl sulfonate in the first electrolyte is X%, and X×Y≥3.1 is controlled, with Y ranging from 1.1 to 1.4.

[0014] In an optional implementation, the value of X ranges from 2.3 to 3.2;

[0015] And / or, the value of Y ranges from 1.2 to 1.3.

[0016] In an optional embodiment, the first additive in the first electrolyte further includes fluoroethylene carbonate, ethylene sulfate, and tris(trimethylsilyl) phosphate; the mass fraction of vinylene carbonate is 1%-3%, and the mass fractions of fluoroethylene carbonate, ethylene sulfate, and tris(trimethylsilyl) phosphate are all 0.3%-1.0%.

[0017] And / or, the concentration of the first lithium salt is 0.5 mol / L to 3.0 mol / L;

[0018] And / or, the first lithium salt is selected from at least one of lithium hexafluorophosphate and lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide;

[0019] And / or, the mass fraction of the first solvent in the first electrolyte is 70%-80%;

[0020] And / or, the first solvent includes ethylene carbonate and a first other solvent, the first other solvent being selected from at least one of propylene carbonate, ethyl methyl carbonate and dimethyl carbonate, wherein the volume ratio of ethylene carbonate to the first other solvent is 1:(1.8-5.6).

[0021] In an optional embodiment, the first electrolyte further contains a first auxiliary additive, which is selected from at least one of bis(trimethylsilyl)methane disulfonate, benzenesulfonyltrifluoromethane, triphenyl phosphate, propylene sulfite, lithium difluorophosphate, lithium difluorooxalate borate, and lithium difluorophosphate oxalate; the mass fraction of the first auxiliary additive in the first electrolyte is 0.3%-1.0%.

[0022] In an optional embodiment, the second electrolyte contains a second lithium salt, a second solvent, and a second additive, wherein the second additive includes vinylene carbonate and a second auxiliary additive.

[0023] In the second electrolyte, the mass fraction of vinylene carbonate is 10%-20%, and the mass fraction of the second auxiliary additive is 0%-4%.

[0024] In an optional embodiment, the second auxiliary additive is selected from at least one of fluoroethylene carbonate and ethylene sulfate;

[0025] And / or, the mass fraction of the second auxiliary additive is 2%-4%.

[0026] In an optional embodiment, the concentration of the second lithium salt in the second electrolyte is 0.5 mol / L to 3.0 mol / L;

[0027] And / or, the second lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide;

[0028] And / or, the second solvent includes ethylene carbonate and a second other solvent, the second other solvent being selected from at least one of propylene carbonate, ethyl methyl carbonate and dimethyl carbonate, wherein the volume ratio of ethylene carbonate and the second other solvent is 1:(1.8-5.6).

[0029] In an optional implementation, after one injection, the solution is left to stand at 40°C-50°C for 12-24 hours.

[0030] In an optional embodiment, after extracting a portion of the electrolyte, the ratio of the remaining injected electrolyte to the total injected electrolyte is controlled to be (85-95):100, and after a second injection, the amount of electrolyte in the battery reaches the total injected electrolyte.

[0031] And / or, by drawing out a portion of the electrolyte injected during the first injection process using a negative pressure method.

[0032] In an optional implementation, during the formation process, the state of charge (SOC) during the formation stage is controlled to 78%-82%.

[0033] And / or, after the formation is complete, control the aging temperature at 40℃-50℃ and the aging time at 12h-24h.

[0034] This invention offers the following advantages: It introduces lithium perfluorobutyl sulfonate (PFBS-Li) as a wetting functional additive for primary electrolyte injection. Combined with vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, and tris(trimethylsilyl)phosphate, it achieves better wetting, ensuring a specific relationship between the primary electrolyte injection volume and the PFBS-Li content in the first electrolyte. By increasing the primary electrolyte injection volume, a rich-wetting state is created, reducing the proportion of PFBS-Li in the primary electrolyte injection, ensuring the degree of electrolyte wetting of the electrode, and reducing localized electrode drying. Before formation, a portion of the electrolyte is extracted under negative pressure to prevent excessive electrolyte decomposition and unstable conditions such as gas generation during formation. The electrolyte injection method provided by this invention improves both the electrolyte wetting effect and the electrolyte distribution uniformity, reducing localized drying, promoting the uniformity of SEI film formation during formation, improving interface stability, and thus enhancing the battery's electrochemical performance. Detailed Implementation

[0035] 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.

[0036] This invention provides a method for electrolyte injection into a lithium battery, comprising the following steps: first, the battery is injected with electrolyte once, then left to stand for a period of time before a portion of the electrolyte is extracted; subsequently, formation, aging, and a second electrolyte injection are performed sequentially. Each step is described below:

[0037] S1, One-time injection

[0038] The inventors optimized the composition of the first electrolyte by performing a single electrolyte injection on the battery: the first electrolyte contains a first lithium salt, a first solvent, and a first additive, the first additive including vinylene carbonate (VC) and lithium perfluorobutyl sulfonate (PFBS-Li).

[0039] It should be noted that the first electrolyte contains more functional additives, which aid in film formation and the wettability of the first electrolyte injection. Various film-forming additives, such as VC, contribute to film formation, while PFBS-Li improves the wettability of the electrolyte to the electrode, thus improving the wettability during the first electrolyte injection. The additives also contain sulfonic acid groups (SO3). -The polar effect of sulfonic acid groups: Sulfonic acid groups have strong polarity and hydrophilicity, which can reduce the interfacial tension between the electrolyte and the electrode (such as graphite / silicon-carbon anode), and enhance the electrolyte's ability to penetrate the micropores on the electrode surface; sulfonic acid groups optimize the electrolyte spreading effect on the electrode surface by forming hydrogen bonds or electrostatic adsorption with hydroxyl groups (-OH) or metal oxides on the electrode surface. The synergistic effect of perfluorobutyl (-CF2CF2CF2CF3): Fluorinated terminal groups have low surface energy and high hydrophobicity, which can reduce side reactions (such as gas generation) between the electrolyte and the electrode, while improving fluidity by reducing the overall viscosity of the electrolyte.

[0040] Furthermore, the ratio of the single injection volume to the total injection volume is controlled to be Y, that is, the single injection volume is Y times the total injection volume. The value of Y ranges from 1.1 to 1.4, such as 1.1, 1.2, 1.3, 1.4, etc., preferably 1.2-1.3. The mass fraction of lithium perfluorobutyl sulfonate in the first electrolyte is X%, and X×Y≥3.1 is controlled to allow the additive to exert its effect of improving wetting.

[0041] It should be noted that for PFBS-Li to exert its wetting-improving effect as a wetting additive, a certain total substance content needs to be reached within the battery. This is related to the amount of additive added (X) and the amount of electrolyte injected (Y). The additive content and the amount of electrolyte injected need to satisfy the formula X×Y≥3.1 for the additive to exert its wetting-improving effect. Specifically, when X = 2.3-3.2 (e.g., 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, etc.) and Y = 1.1-1.25, the wettability of the electrolyte injection and the best electrochemical performance can be achieved.

[0042] When Y = 1.1-1.3 (e.g., 1.25), a larger amount of electrolyte in a single injection creates a rich wetting environment, which is beneficial for better wetting. When X = 2.4-2.7 (e.g., 2.6), the additive ratio in a single injection will not be too high, so it will not affect the electrolyte viscosity and desolvation process. The rich environment is guaranteed, and the total amount of additive is sufficient to exert its effect of improving wetting.

[0043] If the amount of electrolyte injected in a single injection decreases (i.e., Y decreases), the additive content needs to be increased (X increases). Excessive PFBS-Li content in a single injection will increase electrolyte viscosity due to the highly polar sulfonic acid groups and fluorinated alkyl chains, leading to a decrease in lithium-ion migration rate. It may even compete with lithium salts (such as LiPF6) for solubility, interfering with Li... + The solvation-desolvation process.

[0044] If the additive content is reduced (i.e., X becomes smaller), the amount of liquid injected in one injection increases (Y becomes larger). If the amount of liquid injected in one injection is too large, it will lead to a significant increase in the injection time. In particular, when the amount of liquid injected is greater than 130% of the total amount of liquid injected, the subsequent injection time will increase significantly, affecting the injection efficiency. Similarly, it will lead to excessively high total content in other groups, affecting the performance of the battery cell.

[0045] Specifically, the total electrolyte volume can be calculated using conventional methods, such as a standard of 4.5g of electrolyte per Ah of battery capacity. The type of lithium battery is not limited; it can be any common lithium battery type, such as pouch lithium-ion batteries or aluminum-cased lithium-ion batteries, or other rechargeable batteries. Specifically, it can be a lithium iron phosphate battery, but is not limited to this.

[0046] In a preferred embodiment, the first additive further includes fluoroethylene carbonate (FEC), vinyl sulfate (DTD), and tris(trimethylsilyl)phosphate (TMSP). By adding FEC, DTD, and TMSP, these film-forming additives contribute to the formation of a better SEI film during the initial impregnation process. In the first electrolyte, the mass fraction of vinylene carbonate (VC) is 1%-3%, such as 1%, 2%, 3%, etc.; the mass fractions of fluoroethylene carbonate (FEC), vinyl sulfate (DTD), and tris(trimethylsilyl)phosphate (TMSP) are all 0.3%-1.0%, and the mass fractions of FEC, DTD, and TMSP can be the same or different, and can be independently 0.3%, 0.5%, 0.8%, 1.0%, etc.

[0047] In some embodiments, the first lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and the first lithium salt can be any one or more of the above. The concentration of the first lithium salt is 0.5 mol / L-3.0 mol / L, such as 0.5 mol / L, 1.0 mol / L, 2.0 mol / L, 3.0 mol / L, etc., and the concentration of the second lithium salt is 0.2 mol / L-0.5 mol / L, such as 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, etc.

[0048] In some embodiments, the first solvent is a mixed solvent formed by ethylene carbonate (EC) and a first other solvent. The first other solvent is selected from at least one of propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), and can be any one or more of the above. The volume ratio of the first ethylene carbonate to the first other solvent is 1:(1.8-5.6), and this volume ratio is preferably within this range, which is beneficial to improving the electrochemical performance of the battery. The total amount of the first solvent in the first electrolyte is 70%-80% by mass, such as 70%, 73%, 75%, 78%, 80%, etc.

[0049] In some embodiments, the first electrolyte further contains a first auxiliary additive, which is selected from at least one of bis(trimethylsilyl)methane disulfonate (MMDS), benzenesulfonyltrifluoromethane (PST), triphenyl phosphate (TPP), propylene sulfite (PS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiODFB), and lithium difluorophosphate oxalate (LiODFP). The first auxiliary additive can be any one or more of the above, all of which can improve the wetting effect of the first electrolyte to a certain extent. The mass fraction of the first auxiliary additive in the first electrolyte is 0.3%-1.0%, such as 0.3%, 0.5%, 0.8%, 1.0%, etc.

[0050] S2, High-temperature storage

[0051] After one injection, let it stand for a period of time to allow the first electrolyte to fully wet the surface.

[0052] In some embodiments, the sample is left to stand at 40°C-50°C for 12-24 hours to improve the wetting effect. Specifically, the standing temperature can be 40°C, 43°C, 45°C, 48°C, 50°C, etc., and the standing time can be 12 hours, 15 hours, 18 hours, 20 hours, 24 hours, etc.

[0053] S3. Extract a portion of the electrolyte.

[0054] Before formation, some electrolyte is extracted to reduce the total amount of electrolyte in the battery before formation. Excess electrolyte will exacerbate side reactions on the negative electrode surface during the formation stage, forming an excessively thick and unstable SEI film. This will lead to an increase in interfacial impedance, and the decomposition of excess electrolyte will produce gases such as CO and CO2, resulting in increased gas production.

[0055] In some embodiments, a portion of the electrolyte injected during the initial injection process is extracted using a negative pressure method. This method is convenient and easy to implement. The ratio of the remaining injected electrolyte volume to the total injected electrolyte volume is controlled at (85-95):100, such as 85:100, 88:100, 90:100, 93:100, 95:100, etc. Specifically, the remaining injected electrolyte volume = initial injected electrolyte volume - extracted volume. Controlling the remaining injected electrolyte volume to 90% is preferable to avoid excessive electrolyte decomposition during formation, which could lead to unstable conditions such as gas production.

[0056] S4, transformation

[0057] The formation is carried out using conventional formation methods, and the specific process is not limited.

[0058] In some embodiments, during the formation process, the SOC of the formation stage is controlled to 78%-82%, such as 78%, 80%, 82%, etc. This means that during the initial charging (formation) of the battery, the State of Charge (SOC) is artificially controlled to reach only 80%, rather than being fully charged (100% SOC).

[0059] S5, High-Temperature Aging

[0060] After the formation process is complete, the SEI film is aged to make it more stable.

[0061] In some embodiments, the aging temperature is controlled at 40℃-50℃, such as 40℃, 43℃, 45℃, 48℃, 50℃, etc.; the aging time is 12h-24h, such as 12h, 15h, 20h, 24h, etc.

[0062] S6, Secondary Injection

[0063] The battery undergoes a second electrolyte injection, bringing the total electrolyte level inside the battery to 100% of the total injected volume. This second injection is defined as the second injected volume plus the remaining electrolyte after extraction. The electrolyte injected during the second injection is called the second electrolyte, and its composition may differ from the first electrolyte.

[0064] In some embodiments, the second electrolyte contains a second lithium salt, a second solvent, and a second additive. The second additive includes vinylene carbonate (VC) and a second auxiliary additive. A higher VC content in the second electrolyte helps repair the interface film damaged during cycling and reduces active lithium loss. In the second electrolyte, the mass fraction of vinylene carbonate is 10%-20%, such as 10%, 13%, 15%, 18%, 20%, etc.; the mass fraction of the second auxiliary additive is 0%-4%, such as 0%, 1%, 2%, 3%, 4%, etc., preferably 2%-4%. The second auxiliary additive is selected from at least one of fluoroethylene carbonate (FEC) and ethylene sulfate (DTD), and can be any one or more of these. Adding the second auxiliary additive helps repair the SEI film and maintain the cycle performance of the battery cell in subsequent cycles.

[0065] In some embodiments, the second lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluoromethanesulfonyl)imide. The second lithium salt can be any one or more of the above. The concentration of the second lithium salt in the second electrolyte is 0.5 mol / L-3.0 mol / L, such as 0.5 mol / L, 1.0 mol / L, 2.0 mol / L, 3.0 mol / L, etc.

[0066] In some embodiments, the second solvent includes ethylene carbonate (EC) and a second other solvent, which is selected from at least one of propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). The second other solvent can be any one or more of the above. The volume ratio of ethylene carbonate to the second other solvent is 1:(1.8-5.6).

[0067] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0068] It should be noted that the lithium battery preparation process in the following examples and comparative treatments is as follows: (1) Preparation of positive electrode sheet: Lithium iron phosphate, conductive carbon black (Super P), binder (polyvinylidene fluoride PVDF), and conductive agent (carbon nanotubes CNT) are mixed in a mass ratio of 97.15:2:0.5:0.35 to obtain a positive electrode slurry. The positive electrode slurry is coated on both sides of an aluminum foil with a thickness of 13 μm, and the coating density is 307 mg / 1540.25 mm. 2After drying, a positive electrode sheet is obtained. (2) Preparation of negative electrode sheet: Graphite, conductive agent (Super P), binder (styrene-butadiene rubber SBR), and binder (sodium carboxymethyl cellulose CMC) are mixed in a mass ratio of 96.2:0.8:1.8:1.2 to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of a copper foil with a thickness of 6 μm, and the coating density is 146 mg / 1540.25 mm. 2 After drying, a negative electrode sheet is obtained. (3) The positive and negative electrode sheets are stacked, with about 20 layers for the positive electrode and one more layer for the negative electrode, forming a cell structure. (4) Packaging: The cell is packaged with aluminum-plastic film to obtain a dry cell without liquid filling.

[0069] The total electrolyte injection volume is calculated based on 4.5g of electrolyte per Ah of battery capacity. For a battery capacity of 5Ah, the total electrolyte injection volume is 22.5g.

[0070] Example 1

[0071] This embodiment provides a method for injecting electrolyte into a lithium battery, the steps of which are as follows:

[0072] (1) In the initial electrolyte filling, the first electrolyte is used, and the initial filling volume is controlled at 125% of the total filling volume (i.e., Y = 1.25). The mass fraction of PFBS-Li in the first electrolyte is 2.6 wt% (i.e., X = 2.6), and X × Y = 3.25. The composition of the first electrolyte is as follows: 0.9 M LiPF6 and 0.2 M LiFSI are dissolved in a solvent composed of EC, EMC, and DMC (volume ratio of 1:1:2). The other additives are 2% VC, 1% FEC, 0.5% DTD, 0.5% TMSP, 0.5% MMDS, and 2.6% PFBS-Li by mass fraction.

[0073] (2) After one injection, leave at 45°C for 24 hours.

[0074] (3) A portion of the electrolyte injected at one time is extracted by drawing negative pressure. The initial injection volume minus the extraction volume equals the remaining injection volume at one time, which is 90% of the total injection volume.

[0075] (4) Perform formation and control the SOC during the formation stage to 80%. The specific formation process is as follows: constant current charging at 0.05C to 10% SOC, constant current charging at 0.1C to 30% SOC, and constant current charging at 0.2C to 80% SOC.

[0076] (5) After the formation is completed, the battery is aged at high temperature for 24 hours at 45°C.

[0077] (6) The battery is injected with electrolyte a second time. The amount of electrolyte injected a second time plus the amount of electrolyte remaining after the first injection = 100% of the total electrolyte volume. The electrolyte injected during the second injection is called the second electrolyte. The composition of the second electrolyte is as follows: 0.9M LiPF6 and 0.2M LiFSI are dissolved in a solvent composed of EC, EMC and DMC (in a ratio of 1:1:2). By mass fraction, the content of other additives is 2% VC and 1% FEC.

[0078] Example 2

[0079] The only difference from Example 1 is the injection volume and PFBS-Li content in step (1). In Example 2, the initial injection volume was controlled at 115% of the total injection volume (Y = 1.15), the PFBS-Li content was 2.8 wt% (X = 2.8), and X × Y = 3.22.

[0080] Compared with Example 1 and Example 2, the lower level of the rich electrolyte environment and the higher PFBS-Li content in electrolyte A will affect the solvation structure. The specific battery performance is shown in Table 1.

[0081] Example 3

[0082] The only difference from Example 1 is the injection volume and PFBS-Li content in step (1). In Example 3, the initial injection volume was controlled at 135% of the total injection volume (Y = 1.35), the PFBS-Li content was 2.3 wt% (X = 2.3), and X × Y = 3.105.

[0083] Compared with Example 1 and Example 3, the single injection content was too high, the injection was more difficult, the injection efficiency was lower, and the total content of other components such as VC was too high, which was adsorbed on the electrode surface and affected film formation. The specific battery performance is shown in Table 1.

[0084] Example 4

[0085] The only difference from Example 1 is the injection volume and PFBS-Li content in step (1). In Example 4, the initial injection volume was controlled at 140% of the total injection volume (Y = 1.40), the PFBS-Li content was 3.2 wt% (X = 3.2), and X × Y = 4.48.

[0086] Comparing Examples 1 and 4, increasing the total liquid injection volume to 140% increases the PFBS-Li content by 3.2 wt%, resulting in X*Y = 4.5, which is significantly higher than 3.1. The total amount of PFBS-Li is high, satisfying the calculation formula. However, the high liquid injection volume and high component ratio have certain negative impacts; specific battery performance is shown in Table 1.

[0087] Example 5

[0088] The only difference from Example 1 is the injection volume and PFBS-Li content in step (1). In Example 5, the initial injection volume was controlled at 135% of the total injection volume (Y = 1.35), the PFBS-Li content was 2.6 wt% (X = 2.6), and X × Y = 3.51.

[0089] Comparing Example 1 and Example 5, the PFBS-Li content of electrolyte A is appropriate, X×Y=3.51, and the total amount of PFBS-Li after one injection is high, which meets the calculation formula. However, a higher injection volume makes injection more difficult and reduces injection efficiency. The total content of other components such as VC is too high, which has certain negative effects.

[0090] Example 6

[0091] The only difference from Example 1 is the injection volume and PFBS-Li content in step (1). In Example 6, the initial injection volume was controlled at 125% of the total injection volume (Y = 1.25), the PFBS-Li content was 2.8 wt% (X = 2.8), and X × Y = 3.5.

[0092] Comparing Example 1 and Example 6, the electrolyte injection volume is appropriate and has a certain level of rich electrolyte environment. However, the high PFBS-Li content of electrolyte A will affect the solvation structure. The specific battery performance is shown in Table 1.

[0093] Comparative Example 1

[0094] The only difference from Example 1 is that PFBS-Li is not added to the first electrolyte.

[0095] Compared with Example 1 and Comparative Example 1, simply increasing the amount of electrolyte injected without adding PFBS-Li additives cannot achieve the effect of rich electrolyte wetting. The interfacial tension between the electrolyte and the electrode is relatively large, and the improvement of the wetting effect is very limited. The improvement of electrochemical performance is not obvious, as shown in Table 1.

[0096] Comparative Example 2

[0097] The only difference from Example 1 is that in step (1), the initial injection volume is controlled at 90% of the total injection volume, i.e., Y = 0.9, X = 2.6, X × Y = 2.34.

[0098] Compared with Example 1 and Comparative Example 2, although PFBS-Li additive was added, the amount of liquid injected was small, and a rich liquid wetting environment was not formed. Moreover, the total amount of additive was too small to exert its effect of improving wetting. The specific electrochemical performance is shown in Table 1.

[0099] Comparative Example 3

[0100] The only difference from Example 1 is that formation is performed first, and then the electrolyte is extracted, that is, the order of steps (3) and (4) is reversed.

[0101] Compared with Example 1 and Comparative Example 3, the presence of more electrolyte during formation resulted in more side reactions and increased impedance. Excess electrolyte exacerbates side reactions on the negative electrode surface during formation, leading to an excessively thick and unstable SEI film. This increases interfacial impedance, and the decomposition of excess electrolyte generates gases such as CO and CO2, resulting in increased gas production. Specific battery performance is shown in Table 1.

[0102] Comparative Example 4

[0103] The only difference from Example 1 is that PFBS-Li in the first electrolyte is replaced with an equal amount of FB (fluorobenzene) additive. FB can reduce the surface tension of the electrolyte, reduce the contact angle between the electrolyte and the graphite electrode, and improve the wettability of the electrolyte on the graphite negative electrode.

[0104] The performance of the lithium batteries was obtained from the test examples and comparative examples, and the results are shown in Table 1.

[0105] Table 1 shows the performance test results of the lithium batteries obtained in the examples and comparative examples.

[0106]

[0107]

[0108] It can be seen that the present invention introduces lithium perfluorobutyl sulfonate into the first electrolyte and controls X×Y≥3.1, which can significantly improve the electrochemical performance of the battery. When Y=1.10-1.25 and X=2.6-2.8, it can increase the wettability of the electrolyte and achieve the best electrochemical performance.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the 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. A method for injecting electrolyte into a lithium battery, characterized in that, include: First, the battery is injected with electrolyte once, then left to stand for a while before some electrolyte is extracted. After that, the battery undergoes formation, aging, and a second electrolyte injection in sequence. The electrolyte injected during the first injection process is the first electrolyte, and the electrolyte injected during the second injection process is the second electrolyte. The first electrolyte contains a first lithium salt, a first solvent, and a first additive, wherein the first additive includes vinylene carbonate and lithium perfluorobutyl sulfonate; The ratio of the single injection volume to the total injection volume is controlled as Y, the mass fraction of lithium perfluorobutyl sulfonate in the first electrolyte is X%, and X×Y≥3.1 is controlled, with Y ranging from 1.1 to 1.4 and X ranging from 2.3 to 3.

2.

2. The method for injecting electrolyte into a lithium battery according to claim 1, characterized in that, The value of Y ranges from 1.2 to 1.

3.

3. The method for injecting electrolyte into a lithium battery according to claim 1 or 2, characterized in that, The first additive in the first electrolyte further includes fluoroethylene carbonate, ethylene sulfate, and tris(trimethylsilyl) phosphate; the mass fraction of vinylene carbonate is 1%-3%, and the mass fractions of fluoroethylene carbonate, ethylene sulfate, and tris(trimethylsilyl) phosphate are all 0.3%-1.0%. And / or, the concentration of the first lithium salt is 0.5 mol / L to 3.0 mol / L; And / or, the first lithium salt is selected from at least one of lithium hexafluorophosphate and lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide; And / or, the mass fraction of the first solvent in the first electrolyte is 70%-80%; And / or, the first solvent includes ethylene carbonate and a first other solvent, the first other solvent being selected from at least one of propylene carbonate, ethyl methyl carbonate and dimethyl carbonate, wherein the volume ratio of ethylene carbonate to the first other solvent is 1:(1.8-5.6).

4. The method for injecting electrolyte into a lithium battery according to claim 3, characterized in that, The first electrolyte also contains a first auxiliary additive, which is selected from at least one of bis(trimethylsilyl)methane disulfonate, benzenesulfonyltrifluoromethane, triphenyl phosphate, propylene sulfite, lithium difluorophosphate, lithium difluorooxalate borate, and lithium difluorophosphate oxalate; the mass fraction of the first auxiliary additive in the first electrolyte is 0.3%-1.0%.

5. The method for injecting electrolyte into a lithium battery according to claim 1, characterized in that, The second electrolyte contains a second lithium salt, a second solvent, and a second additive, wherein the second additive includes vinylene carbonate and a second auxiliary additive. In the second electrolyte, the mass fraction of vinylene carbonate is 10%-20%, and the mass fraction of the second auxiliary additive is greater than 0% and less than or equal to 4%.

6. The method for injecting electrolyte into a lithium battery according to claim 5, characterized in that, The second auxiliary additive is selected from at least one of fluoroethylene carbonate and ethylene sulfate; And / or, the mass fraction of the second auxiliary additive is 2%-4%.

7. The method for injecting electrolyte into a lithium battery according to claim 5, characterized in that, The concentration of the second lithium salt in the second electrolyte is 0.5 mol / L-3.0 mol / L; And / or, the second lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide; And / or, the second solvent includes ethylene carbonate and a second other solvent, the second other solvent being selected from at least one of propylene carbonate, ethyl methyl carbonate and dimethyl carbonate, wherein the volume ratio of ethylene carbonate and the second other solvent is 1:(1.8-5.6).

8. The method for injecting electrolyte into a lithium battery according to claim 1, characterized in that, After the first injection, the solution is left to stand at 40℃-50℃ for 12h-24h.

9. The method for injecting electrolyte into a lithium battery according to claim 1, characterized in that, After extracting part of the electrolyte, the ratio of the remaining electrolyte volume to the total electrolyte volume is controlled to be (85-95):

100. After the second electrolyte injection, the electrolyte volume in the battery reaches the total electrolyte volume. And / or, by drawing out a portion of the electrolyte injected during the first injection process using a negative pressure method.

10. The method for injecting electrolyte into a lithium battery according to claim 1, characterized in that, During the formation process, the state of charge (SOC) during the formation stage is controlled to 78%-82%; And / or, after the formation is complete, control the aging temperature at 40℃-50℃ and the aging time at 12h-24h.

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