Secondary electrolyte, electrolyte injection method and lithium ion battery

Abstract

The application discloses a kind of secondary liquid injection electrolyte, injection method and lithium ion battery, the secondary liquid injection electrolyte includes, electrolyte A for primary injection and electrolyte B for secondary injection;The first additive in the electrolyte A is fluoroethylene carbonate, and the second additive includes lithium difluorophosphate and at least one of vinyl sulfate or methanedimethanesulfonate;The first additive in the electrolyte B includes at least one of unsaturated phosphate or unsaturated phosphite or unsaturated borate, and the second additive is one or two of lithium difluorophosphate, lithium difluorobisoxalate phosphate or lithium tetrafluorophosphate;By electrolyte A and electrolyte B composition design realizes additive "targeting" film formation, make the best of advantages and avoid shortcomings, improve the film formation efficiency of positive electrode additive, avoid the problem that bidirectional film formation additive participates in negative electrode film formation and causes battery DCR sharp increase.

Description

Technical Field

[0001] This invention relates to the field of battery electrolyte technology, specifically to a secondary electrolyte, an electrolyte injection method, and a lithium-ion battery. Background Technology

[0002] Range anxiety has always been a key factor limiting the widespread adoption of new energy vehicles, primarily determined by the energy density of the power battery. The energy density of a power battery is directly related to the selection of positive and negative electrode materials. Based on different positive electrode materials, commercially available power batteries are currently divided into lithium iron phosphate batteries and ternary lithium batteries. Among them, ternary lithium batteries dominate the high-end vehicle market due to their energy density advantage. To further improve battery energy density, a more mature approach is to use high-nickel or high-voltage positive electrode materials (LiNi). x Co y Mn (1-x-y) O2) Matching silicon-based anode materials (SiO2) x However, problems such as positive electrode instability under high voltage / high nickel and silicon expansion of negative electrode severely limit the cycle performance and calendar life of the battery, especially under high temperature conditions.

[0003] Optimizing the structure of positive and negative materials and designing electrolyte formulations are two key approaches to addressing the high-temperature performance limitations of ternary lithium batteries. Material optimization strategies are relatively clear, primarily aiming to improve the structural stability of the battery during high-temperature cycling or storage. Examples include single-crystalization, metal ion doping, surface coating, and gradient structure design for the positive electrode, and carbon coating, silicon suboxide pre-lithiation, and porous carbon-deposited silicon for the negative electrode. Electrolyte formulation strategies, however, present greater design challenges due to the need to consider factors from both the positive and negative electrodes. For power batteries using silicon negative electrode materials, the most critical factor limiting their electrical performance is the repeated damage and formation of the solid electrolyte interphase (SEI) caused by the expansion of the silicon-based negative electrode during cycling. Electrolyte design primarily uses fluoroethylene carbonate (FEC) as a sacrificial additive to improve battery cycle performance. However, FEC itself has long thermal stability and is prone to decomposition to produce HF, which further deteriorates the battery's high-temperature performance. To address the instability of the cathode structure under high voltage / high temperature, the main strategy in electrolyte design is to add boron- or phosphorus-containing additives to form a stable and dense electrochemical interface (CEI) to suppress side reactions at the cathode interface. Unsaturated B / P ester additives can form a dense and stable CEI on the cathode surface, which has a significant effect on improving the dissolution of cathode metal ions and interfacial side reactions. However, due to the presence of unsaturated bonds, these additives often participate in cathode film formation. Current processes use a single-fill method. If too much is added, it will severely deteriorate the battery's DC internal resistance (DCR); if too little is added, the amount consumed in anode film formation will be insufficient for the CEI reaction. Therefore, this severely restricts the application of these additives in power batteries.

[0004] In existing technologies, some methods utilize borates and unsaturated phosphate compounds in high-voltage nickel-manganese lithium-ion battery systems to maintain the stability and oxidation resistance of the positive electrode structure, suppress electrolyte decomposition, and improve battery cycle life. Other methods employ a combination of multiple additives, including fluorinated cyclic carbonates, phosphate compounds containing unsaturated hydrocarbon groups, boron-containing lithium salt additives, and secondary additives, which have significantly improved the battery's high-temperature performance. In these secondary additives, at least one is selected from trinitrile compounds and cyclic carboxylic anhydrides.

[0005] While the above solutions have improved battery performance to some extent through the targeted selection and combination of additives, they still have several problems such as low additive utilization and increased DCR. Therefore, the development of high-efficiency electrolytes and batteries that take into account both silicon-based anodes and high-nickel / high-voltage ternary cathodes remains a key technical challenge that the industry urgently needs to address. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a secondary electrolyte, an electrolyte injection method, and a lithium-ion battery, including electrolyte A for primary electrolyte injection and electrolyte B for secondary electrolyte injection. The additive combination of electrolyte A and electrolyte B is improved, and the secondary battery prepared with the obtained electrolyte exhibits excellent performance in fast charging, high-temperature cycling, and other aspects.

[0007] The technical solution of the present invention is as follows:

[0008] In a first aspect of the present invention, a secondary electrolyte is provided, comprising electrolyte A for primary electrolyte injection and electrolyte B for secondary electrolyte injection; wherein electrolyte A accounts for 78% to 92% of the total electrolyte mass of the battery, and electrolyte B accounts for 8% to 22% of the total electrolyte mass of the battery, and both electrolyte A and electrolyte B comprise lithium salt, solvent and additives.

[0009] The first additive in electrolyte A is fluoroethylene carbonate, and the second additive contains lithium difluorophosphate and at least one selected from ethylene sulfate and methane disulfonate.

[0010] The first additive in the electrolyte B includes at least one of unsaturated phosphate ester and unsaturated phosphite ester or unsaturated borate ester, and the second additive is one or two of lithium difluorophosphate, lithium difluorobis(oxalate) phosphate and lithium tetrafluoro(oxalate) phosphate.

[0011] To address several issues in cycling and high-temperature performance of high-energy-density batteries, particularly high-nickel or high-voltage cathode-matched silicon-based anode systems, a secondary electrolyte design scheme is proposed. This scheme can solve the application problems of unsaturated phosphate esters, unsaturated phosphites, or unsaturated borate esters in the electrolyte of this system.

[0012] In some embodiments of the present invention, the first additive, fluoroethylene carbonate, accounts for 1% to 15% of the total mass of electrolyte A; preferably 6% to 8%.

[0013] The second additive, lithium difluorophosphate, accounts for 0.5% to 1.2% of the total mass of the electrolyte, and the second additive, vinyl sulfate and / or methane disulfonate, accounts for 0.5% to 2.5% of the total mass of electrolyte A; preferably 0.8% to 1%.

[0014] Specifically, the amount of the first additive, fluoroethylene carbonate (FEC), is directly related to the type and proportion of silicon in the negative electrode.

[0015] Specifically, the amount of the first additive, fluoroethylene carbonate (FEC), is positively correlated with the amount of silicon-based material added to the negative electrode. If silicon suboxide (SiOx) is used as the negative electrode, the mass fraction of FEC in electrolyte A to the mass fraction of SiOx in the negative electrode is 2:1 to 1:2. If porous carbon-deposited silicon is used as the negative electrode, the mass fraction of FEC in electrolyte A to the mass fraction of porous carbon-deposited silicon in the negative electrode is 1:2 to 1:5. If the mass fraction of SiOx in the negative electrode is 5%, the mass percentage of FEC in electrolyte A is 2.5% to 10%, preferably 4% to 7%.

[0016] In some embodiments of the present invention, the additives in electrolyte A further include one or more of the following: vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), tris(trimethylsilane) phosphate (TMSP), lithium difluorooxalate borate (LiODFB), lithium difluorobis(oxalate) phosphate, lithium tetrafluorooxalate phosphate, succinic anionyl (SN), adiponitrile (ADN), 1,3,6-hexanetrionitrile (HTCN), and 1,2-bis(2-cyanoethoxy)ethane (DENE), in an amount of 0.2% to 2% of the total mass of electrolyte A.

[0017] In some embodiments of the present invention, the first additive in the electrolyte B is at least one selected from triargyl phosphate (TPP), triallyl phosphate, tris(2-cyanoethyl) phosphate, triargyl phosphite, triallyl phosphite, tris(2-cyanoethyl) phosphite, triargyl phosphate, triallyl borate, and tris(2-cyanoethyl) borate. The amount of the first additive added is 0.2% to 2% of the total mass of electrolyte B, preferably 0.2% to 0.8%.

[0018] Specifically, the unsaturated functional groups of the first additive in electrolyte B are alkynyl, alkenyl, or cyano groups. These additives can form a dense CEI film at the positive electrode, mitigating the dissolution of transition metal ions and the decomposition of FEC at the positive electrode under high temperature and pressure conditions, thus improving the battery's cycle performance, especially high-temperature cycle performance. However, these additives not only participate in CEI formation but also in SEI formation at the negative electrode, thereby worsening the battery's DCR. In electrolyte design, if the content is too low, it will preferentially participate in SEI formation, leading to a significant reduction in the amount participating in CEI formation, making it difficult to exert its beneficial effects; if the content increases, it will severely worsen SEI impedance, affecting the battery's fast charging and cycle performance. It is known that SEI formation mainly occurs before the first charge to 3.4V. Through a two-fill design, these unsaturated additives are concentrated in the second-fill electrolyte, avoiding the main drawback of increased battery DCR caused by the use of these additives in existing single-fill solutions, while significantly improving their efficiency in CEI formation and reducing electrolyte costs.

[0019] In some embodiments of the present invention, the amount of the second additive added to the electrolyte B is 0.2% to 1.5% of the total mass of the electrolyte B; preferably 0.3% to 0.7%.

[0020] Preferably, the electrolyte B also includes fluoroethylene carbonate (FEC) as an additive, with an addition amount of 1% to 15%; more preferably 3% to 7%.

[0021] Using phosphorus-containing lithium salt compounds as the second additive in secondary electrolyte B can synergistically increase the content of lithium phosphate-like structural components in CEI, which have superconducting lithium-ion properties, thereby further reducing the battery's DCR.

[0022] In some embodiments of the present invention, the lithium salt is at least one selected from lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium tetrafluoroborate (LiBF4);

[0023] Preferably, the lithium salt is one or both of lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI).

[0024] In some embodiments of the present invention, the lithium salt accounts for 10% to 20% of the total mass of electrolyte A or electrolyte B, preferably 12% to 16%.

[0025] In some embodiments of the present invention, the solvent is two or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, ethyl acetate, methyl acetate, propyl acetate, methyl propionate, propyl propionate, and ethyl propionate.

[0026] The amount of solvent added to electrolyte A is 70% to 88% of the total mass of electrolyte A, preferably 75% to 85%; the amount of solvent added to electrolyte B is 75% to 88% of the total mass of electrolyte B, preferably 82% to 87%.

[0027] In a second aspect of the invention, a method for injecting a secondary electrolyte is provided, comprising:

[0028] Determine the total amount of electrolyte required for the battery based on the battery capacity and the electrolyte injection coefficient. Inject electrolyte A of mass "m * total electrolyte volume" into the battery to be injected, and soak it at 45°C for ≥24 hours. Where m represents the proportion of electrolyte A to the total electrolyte volume of the battery.

[0029] Set the formation current to 3.4V or higher (e.g., charge at 0.05C for 36 minutes, then charge at 0.1C to 3.4V and cut off), and the aging time is ≥3h;

[0030] Electrolyte B, with a mass of “(1-m)*total injection volume”, is injected into the formed and aged battery to complete the secondary injection, where 1-m represents the proportion of electrolyte B to the total injection volume of the battery.

[0031] In a third aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the secondary electrolyte described in the first aspect.

[0032] One or more technical solutions of the present invention have the following beneficial effects:

[0033] (1) This invention achieves "targeted" film formation of additives through the composition design of electrolyte A and electrolyte B, leveraging the strengths and avoiding the weaknesses, thereby improving the film formation efficiency of the positive electrode additives and avoiding the problem of a sharp increase in battery DCR caused by bidirectional film-forming additives participating in the negative electrode film formation. The high-energy-density ternary battery prepared by this secondary electrolyte injection exhibits significantly improved overall performance, especially high-temperature performance.

[0034] (2) This invention, through a two-cell design, concentrates the addition of this type of unsaturated additive to the two-cell electrolyte, thereby avoiding the main drawback of increased battery DCR caused by the use of this type of additive in the existing single-cell design. At the same time, it significantly improves the efficiency of its participation in CEI generation and reduces electrolyte costs. Furthermore, by using a phosphorus-containing lithium salt compound as the second additive in the two-cell electrolyte of this design, it can synergistically work with the aforementioned unsaturated additive to increase the content of lithium phosphate-like structural components in the CEI. This structure has superconducting lithium-ion properties, further reducing battery DCR.

[0035] (3) Based on the electrolyte B formulation, the present invention has conducted extensive verification on the electrolyte A formulation and screened out a combination of additives with strong matching. The secondary battery prepared using the secondary electrolyte of the present invention exhibits excellent performance in fast charging, high temperature cycling and other aspects. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments.

[0037] The secondary electrolyte provided by this invention is used to prepare lithium-ion batteries with embedded multilayer negative electrode sheets. The specific preparation process is as follows:

[0038] Preparation of the positive electrode: Polyvinylidene fluoride (PVDF), conductive agent (Super P), carbon nanotubes (CNTs), and positive electrode material (NMC, nickel content 90%) are added to N-methylpyrrolidone (NMP) in a mass ratio of 1.5%:0.5%:0.5%:97.5% and mixed evenly to form a slurry. The slurry is then coated onto an aluminum foil current collector. The surface density of the positive electrode on one side is 180±3 g / m². 2 Cold-pressed to 3.5g / m³ 3 After punching, the positive electrode sheet is obtained.

[0039] Preparation of the negative electrode sheet: Sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), styrene-butadiene rubber latex (SBR), conductive agent (Super P), single-walled carbon nanotubes (SWCNTs), and silicon suboxide (SiO2) are mixed. x Add graphite and N2 at a mass ratio of 0.4%:1.6%:0.8%:0.94%:0.06%:96.2% to deionized water, stir thoroughly to mix evenly, coat the slurry onto a copper foil current collector, determine the negative electrode surface density according to an N / P ratio of 1.12, and cold press to 1.55 g / m³. 3 After punching, the negative electrode sheet is formed.

[0040] Preparation of the reference electrolyte:

[0041] Electrolyte A was prepared according to the mass ratio of LiPF6:LiFSI:EC:DMC:EMC:FEC:DTD:LiODFB:LiPO2F2:TPP of 10.0%:4.5%:19.5%:37.0%:19.5%:7.0%:1.0%:0.5%:0.8%:0.2%, ensuring strict moisture control (<1ppm) and temperature below 30℃ throughout the preparation process;

[0042] Electrolyte B was prepared according to the mass ratio of LiPF6:LiFSI:EC:DMC:EMC:DTD:LiPO2F2:LiODFP:TPP:tris(2-cyanoethyl) phosphate of 10.0%:4.5%:19.5%:37.5%:19.5%:7%:1.0%:0.5%:0.5%.

[0043] Comparative Examples 1-4 represent a single-injection electrolyte scheme; Examples 1-10 maintain the same formulation of the baseline electrolyte A, only adjusting the formulation of electrolyte B; Examples 11-14 maintain the same formulation of the baseline electrolyte B, only adjusting the formulation of electrolyte A. Specific electrolyte schemes are shown in Table 1. Table 1

[0044]

[0045]

[0046] Preparation of the battery to be injected with electrolyte: The separator, negative electrode, and positive electrode are stacked in a "Z" shape to obtain the bare cell to be injected with electrolyte. The cell is then packaged in aluminum-plastic film and baked to obtain the battery to be injected with electrolyte. The designed capacity of the battery to be injected with electrolyte is 2Ah.

[0047] The implementation of the two-injection scheme: the electrolyte injection coefficient is calculated at 2.5g / Ah, and liquid A is calculated as accounting for 90% of the total injection volume, i.e., 4.5g.

[0048] Inject 4.5g of solution A into the battery cell to be injected, seal it, and then immerse it at 45°C for 36 hours.

[0049] After soaking, the battery was formed at 0.2C (0.4A) until the voltage cutoff was 3.4V, and then aged at 45℃ for 12 hours.

[0050] 0.5g of solution B was injected into the battery after it had undergone formation and aging. The battery was then left at 25°C for 36 hours and then charged and discharged normally to obtain the battery to be tested.

[0051] Testing of lithium-ion batteries:

[0052] DCR test: Charge the battery to 4.0V with constant current and constant voltage, let it stand for 6 hours, and then test the battery's DC internal resistance.

[0053] Rate charging performance test: The battery was charged at 1C and 3C constant current and constant voltage to 4.25V, with a cutoff current of 0.05C, and then discharged at 1C to 2.8V. The capacity ratio of constant current charging was calculated. A soft-pack three-electrode was fabricated, and the charging time at different rates was tested. By data aggregation, the maximum charging current at different SOCs was determined. The optimal stepped charging scheme (6 stages) was determined for different batteries, and the shortest charging time from 10% to 90% SOC was determined.

[0054] Normal temperature / high temperature cycling performance test: The capacity retention rate was tested at 25℃ and 45℃ for different cycles of 1C charge and discharge. The cutoff voltage for charge and discharge was 2.8V to 4.25V, and the cutoff current for constant voltage charging was 0.05C.

[0055] Negative electrode transition metal deposition test: After the battery is cycled at 45℃ for 1000 times, it is discharged to 2.8V, the battery is disassembled, the negative electrode powder is collected, ICP is tested, and the Ni element content is recorded.

[0056] The test data for the examples and comparative examples are shown in Table 2.

[0057] Table 2

[0058]

[0059] The results showed that, compared with Comparative Example 1, increasing the TPP content by 0.3% improved the high-temperature performance of the cell, mainly due to the increased TPP content participating in the positive electrode film formation. However, the cell's DCR and fast-charging performance deteriorated significantly, which was directly related to the deterioration of the negative electrode film formation impedance caused by the increased TPP content. Compared with Comparative Example 1, Comparative Example 3 effectively reduced the battery DCR and improved the battery's fast-charging and cycle performance by increasing the LiODFP and TPP composite film formation at the positive electrode. However, LiODFP also suffered from consumption during negative electrode film formation, which significantly affected its improvement effect. Compared with Comparative Example 3, Comparative Example 4 further added tris(2-cyanoethyl) phosphate to the electrolyte formulation. The cyano complexation effect had a certain inhibitory effect on metal ion dissolution, improving the battery's high-temperature performance. However, due to the relatively high viscosity of tris(2-cyanoethyl) phosphate, it deteriorated the battery's DCR and fast-charging performance to some extent.

[0060] Electrolyte A was used as a reference electrolyte formulation, and Examples 1-3 conducted single-variable experiments on the TPP content in electrolyte B. Compared with the comparative examples, it was found that the two-injection scheme significantly improved the battery's fast charging and high-temperature cycling performance. Among them, Example 2 showed the best overall performance, proving that the optimal addition amount of TTP in the electrolyte under this scheme is 0.5%. Further analysis of the battery performance comparison results showed that Example 3 had the highest TPP content in electrolyte B compared to the comparative examples, but the cell DCR was still low. This also confirms that the increase in battery DCR caused by TPP is mainly due to its participation in negative electrode film formation. At the same time, compared with comparative examples 1-3, the improvement in high-temperature cycling performance and metal dissolution further confirms that the two-injection scheme combined with formation voltage control can achieve directional control of additives that can form films on both the positive and negative electrodes.

[0061] Compared to Example 2, Examples 4-6 added lithium salt additives to the electrolyte, and single-factor experiments were conducted on their content. It was found that using a combination of LiODFB and TPP in electrolyte B effectively reduced the battery DCR and thus improved fast-charging performance. Overall, an addition of 0.5% showed the best effect. In Example 7, compared to Example 5, LiODFP was used instead of LiODFB. This resulted in a slight deterioration in high-temperature cycling performance and metal dissolution, but significantly improved DCR and rate performance. This was mainly because the increased P component in the CEI was more conducive to improving interfacial impedance, and the increased presence of electrolyte B components, due to their stronger complexing ability, had a more significant inhibitory effect on metal ion dissolution. In Examples 8-10, the electrolyte B formulation, based on Example 7, added tris(2-cyanoethyl) phosphate. The purpose was to utilize the complexing effect of low-impedance polycyano compounds to alleviate the problem of transition metal ion dissolution during ternary battery cycling, especially during high-temperature cycling. Experimental results also proved the effectiveness of this design. Compared to other embodiments, the Ni content deposited on the negative electrode after high-temperature cycling is significantly reduced, and the corresponding high-temperature cycling performance of the battery is also significantly improved. However, due to the high viscosity of tri(2-cyanoethyl) phosphate, the battery DCR will be slightly deteriorated. As the amount added increases, the degree of deterioration will also increase. Overall, the battery cell of Example 9 (i.e., the amount of tri(2-cyanoethyl) phosphate added is 0.5%) has the best overall performance.

[0062] Electrolyte B from Example 9, which has been verified to have superior overall performance, was selected as the baseline electrolyte. The formulation of solution A was adjusted to further verify the optimal solution of the two-injection scheme. Examples 11 and 12 verified the effect of FEC addition in solution A on battery performance. The results showed that a high FEC content is beneficial for improving room temperature cycling, while a low FEC content is more beneficial for high temperature cycling. This is mainly related to the instability of FEC at high temperatures. In practical applications, the amount of FEC added can also be adjusted according to different end-user requirements for battery cycling. Examples 13 and 14 investigated the effects of DTD and LiPO2F2 on battery performance, respectively. The results showed that in a high-nickel-to-silicon anode battery system, both are indispensable. The absence of either in solution A severely degrades the battery's cycling performance. In summary, combined with the examples, this invention has verified the two-injection scheme design from multiple aspects. Compared with existing schemes, it significantly improves the effect of unsaturated phosphate / boronate / phosphite additives that focus on improving the cathode interface, resulting in a significant improvement in the overall battery performance.

[0063] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A secondary electrolyte solution, characterized by comprising: The electrolyte A for one-time injection and the electrolyte B for two-time injection are included; wherein the electrolyte A accounts for 78% to 92% of the total injection mass of the battery, and the electrolyte B accounts for 8% to 22% of the total injection mass of the battery; the electrolyte A and the electrolyte B both include lithium salt, solvent and additive; The first additive in the electrolyte A is fluoroethylene carbonate, and the second additive includes lithium difluorophosphate and at least one selected from vinyl sulfate and methanedimethylenesulfonate; In the electrolyte A, the first additive fluoroethylene carbonate accounts for 1% to 15% of the total mass of the electrolyte A; The second additive lithium difluorophosphate accounts for 0.5% to 1.2% of the total mass of the electrolyte, and the second additive vinyl sulfate and / or methanedimethylenesulfonate accounts for 0.5% to 2.5% of the total mass of the electrolyte A; the additive in the electrolyte A further includes one or more of vinyl sulfite, 1,3-propanesultone, tris(trimethylsilyl)phosphate, lithium difluoro(oxalato)borate, lithium difluorobis(oxalato)phosphate, lithium tetrafluorobis(oxalato)phosphate, butanedinitrile, hexanedinitrile, 1,3,6-hexanetrinitrile and 1,2-bis(2-cyanoethoxy)ethane, and the addition amount is 0.2% to 2% of the total mass of the electrolyte A; The first additive in the electrolyte B includes at least one of unsaturated phosphate ester and unsaturated phosphite ester or unsaturated borate ester, and the second additive is one or two of lithium difluorophosphate, lithium difluorobis(oxalato)phosphate and lithium tetrafluorobis(oxalato)phosphate; The first additive in the electrolyte B is at least one of tripropargyl phosphate, triallyl phosphate, tris(2-cyanoethyl)phosphate, tripropargyl phosphite, triallyl phosphite, tris(2-cyanoethyl)phosphite, tripropargyl borate, triallyl borate and tris(2-cyanoethyl)borate, and the addition amount of the first additive is 0.2% to 2% of the total mass of the electrolyte B; The addition amount of the second additive in the electrolyte B is 0.2% to 1.5% of the total mass of the electrolyte B; The additive in the electrolyte B further includes fluoroethylene carbonate, and the addition amount is 1% to 15%.

2. The secondary electrolyte solution of claim 1, wherein The lithium salt is at least one of lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium bis(trifluoromethylsulfonyl)imide and lithium tetrafluoroborate. The lithium salt is one or two of lithium hexafluorophosphate and lithium bisfluorosulfonimide.

3. The secondary electrolyte solution of claim 1, wherein The lithium salt accounts for 10% to 20% of the total mass of the electrolyte A or the electrolyte B.

4. The secondary electrolyte solution of claim 1, wherein The solvent is two or more of vinyl carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, ethyl acetate, methyl acetate, propyl acetate, methyl propionate, propyl propionate and ethyl propionate; The addition amount of the solvent in the electrolyte A accounts for 70% to 88% of the total mass of the electrolyte A; and the addition amount of the solvent in the electrolyte B accounts for 75% to 88% of the total mass of the electrolyte B.

5. The method of claim 1-4, wherein the method is characterized by, It includes: The total injection amount of the electrolyte required by the battery is determined according to the battery capacity and the injection coefficient, the electrolyte A with the mass of "m*total injection amount" is injected into the battery to be injected, and the immersion time at 45℃ is ≥24h; wherein m represents the proportion of the electrolyte A in the total injection amount of the battery; The formation current is set to form to 3.4V or above voltage, and the aging time is greater than or equal to 3h; The electrolyte B with the mass of "(1-m)*total injection amount" is injected into the battery after formation and aging, to complete secondary injection; wherein, 1-m represents the proportion of the electrolyte B in the total injection amount of the battery.

6. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, characterized by, The electrolyte is the secondary injection electrolyte according to any one of claims 1-4.

Images