Non-aqueous electrolyte for inhibiting dissolution of manganese ions in lithium ferric manganese phosphate battery as well as preparation method and application of non-aqueous electrolyte

Abstract

The invention belongs to the technical field of lithium batteries, and particularly relates to a non-aqueous electrolyte for inhibiting dissolution of manganese ions in a lithium ferric manganese phosphate battery as well as a preparation method and application of the non-aqueous electrolyte. The first electrolyte comprises a first non-aqueous organic solvent, a second non-aqueous organic solvent and a third non-aqueous organic solvent, wherein the first non-aqueous organic solvent comprises at least one carbonate solvent; a first lithium salt; the first additive is prepared from trimethyl silicon methyl acetate and tetrafluoroethyl-trifluoroethyl ether; the second electrolyte includes: a second non-aqueous organic solvent including at least one carbonate solvent; a second lithium salt; the second additive comprises lithium tetrafluoroborate. Compared with the prior art, the problems that manganese ions in the lithium manganese iron phosphate battery are easy to dissolve out, and long-term cycling stability and high-rate performance are difficult to consider at the same time in the prior art are solved. According to the scheme, through the design of the electrolyte, inhibition of dissolution of manganese ions and synchronous improvement of the cycle performance and the rate capability are achieved.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, and in particular relates to a non-aqueous electrolyte for suppressing the dissolution of manganese ions in lithium iron manganese phosphate batteries, its preparation method and application. Background Technology

[0002] In the past year or two, with the gradual expansion of the energy storage and power markets, people's attention to battery safety has been increasing, and the research and development of new materials has become particularly crucial. Lithium iron phosphate (LFP) has gradually become the main cathode material for electric vehicles or energy storage batteries due to its high safety. However, for LFP batteries, the development of their energy density has almost reached its limit, and there is not much room for performance improvement.

[0003] Lithium manganese iron phosphate (LMFP) has a similar crystal structure to LFP and also possesses characteristics such as chemical stability and excellent safety performance. Furthermore, the manganese doping in LMFP increases the charging voltage of the material, resulting in a 15-20% increase in the theoretical energy density of LMFP batteries, further extending their driving range. Moreover, LMFP exhibits superior safety performance compared to ternary lithium batteries (NCM), while also boasting higher energy density than LFP. Additionally, LMFP has a low dependence on rare metals, allowing for co-production with LFP on the same production line, resulting in a significant cost advantage.

[0004] However, manganese ions are prone to dissolution during charge and discharge, leading to electrode structure damage, electrolyte decomposition, and battery capacity decay, especially under high temperature or long-cycle conditions. Existing technologies primarily suppress manganese dissolution through cathode material modification (such as carbon coating and metal doping) or electrolyte additive optimization. For example, carbon coating can improve conductivity and reduce direct contact between manganese and the electrolyte, while electrolyte additives (such as silane compounds and fluorinated ethers) can preferentially form films at the electrode interface, isolating the manganese ion dissolution pathway. However, a single approach often fails to simultaneously achieve long-term cycle stability and high-rate performance.

[0005] In addition, there are a few existing studies on electrolytes that use multiple methods to synergistically suppress manganese ion dissolution, such as: CN113903991A discloses a non-aqueous electrolyte for lithium-ion batteries and its application, including an electrolyte, a non-aqueous solvent, and additives. The additives comprise alkenyl ester compounds and acid-removing additives. By introducing alkenyl ester compound positive electrode protection additives, a stable CEI is formed on the surface of the lithium manganese oxide positive electrode material during battery manufacturing, thereby protecting the positive electrode from further corrosion by the electrolyte. Simultaneously, the additive itself has a certain ability to complex and capture manganese ions, reducing the damage to the negative electrode after manganese ion dissolution. Furthermore, the added acid-removing additives can absorb acid and moisture generated during battery use, preventing them from damaging the lithium manganese oxide positive electrode material.

[0006] CN109346768B discloses a non-aqueous electrolyte for lithium manganese oxide lithium-ion batteries, comprising an electrolyte lithium salt, a non-aqueous organic solvent, and a film-forming additive, wherein the film-forming additive includes boric acid compounds. The boric acid compounds form a uniform and dense protective film on the surface of the lithium manganese oxide material, reducing the oxidation reaction of the electrolyte on the battery material surface. Simultaneously, they can complex divalent manganese ions in the electrolyte, preventing their reduction on the negative electrode surface and hindering lithium ion insertion channels. Furthermore, they can reduce and form an SEI film on the negative electrode material surface, modifying the composition of the SEI film and improving its performance.

[0007] However, among these solutions, if only lithium hexafluorophosphate is used as a single lithium salt, the battery has significant shortcomings in terms of adaptability and rate performance over a wide temperature range. If lithium hexafluorophosphate is used together with other lithium salts as the main salt, the stability of the resulting SEI is often poor because the dual-salt system participates in the formation of the solid electrolyte interphase (SEI) film during the formation stage. This may lead to problems such as SEI decomposition in the later stages of battery cycling, affecting the battery's cycle performance.

[0008] Therefore, there is an urgent need to develop a non-aqueous electrolyte formulation and battery manufacturing process with significant synergistic effects to suppress manganese leaching from multiple dimensions, including interfacial film formation stability, HF removal, and structural stability. Summary of the Invention

[0009] The purpose of this invention is to provide a non-aqueous electrolyte for suppressing manganese ion dissolution in lithium iron phosphate batteries, its preparation method, and its application, in order to solve at least one of the aforementioned problems. This addresses the issues of easy manganese ion dissolution, difficulty in simultaneously achieving long-term cycle stability, and high-rate performance in existing lithium iron phosphate batteries. This solution, through electrolyte design, achieves the suppression of manganese ion dissolution and the simultaneous improvement of cycle performance and rate performance.

[0010] The objective of this invention is achieved through the following technical solution: The first aspect of this invention discloses a non-aqueous electrolyte for inhibiting the dissolution of manganese ions in lithium iron manganese phosphate batteries, comprising a first electrolyte and a second electrolyte; The first electrolyte comprises: The first non-aqueous organic solvent includes at least one carbonate solvent; First lithium salt; The first additive includes trimethylsilyl acetate and tetrafluoroethyl-trifluoroethyl ether; The second electrolyte comprises: The second non-aqueous organic solvent includes at least one carbonate solvent; Second lithium salt; The second additive includes lithium tetrafluoroborate.

[0011] Preferably, the first non-aqueous organic solvent includes ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate; The volume ratio of ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate is 3:4:3.

[0012] Preferably, the first lithium salt comprises lithium hexafluorophosphate, and the concentration of the first lithium salt in the first electrolyte is 0.7-1.5 mol / L.

[0013] Preferably, the concentration of trimethylsilyl acetate in the first electrolyte is 1-3 wt%, and the concentration of tetrafluoroethyl-trifluoroethyl ether in the first electrolyte is 0.5-2 wt%. The first additive also includes vinylene carbonate and fluoroethylene carbonate, wherein the concentration of vinylene carbonate in the first electrolyte is 1-2 wt%, and the concentration of fluoroethylene carbonate in the first electrolyte is 1-2 wt%.

[0014] Preferably, the second non-aqueous organic solvent includes ethylene carbonate and ethyl methyl carbonate; The volume ratio of ethylene carbonate to methyl ethyl carbonate is 3:7.

[0015] Preferably, the second lithium salt comprises lithium bis(fluorosulfonyl)imide, and the concentration of the second lithium salt in the second electrolyte is 0.7-1.5 mol / L.

[0016] Preferably, the concentration of lithium tetrafluoroborate in the second electrolyte is 2 wt%.

[0017] The second aspect of this invention discloses a method for preparing a non-aqueous electrolyte for inhibiting manganese ion dissolution in a lithium iron manganese phosphate battery as described above, comprising the following steps: Prepare the first electrolyte: In a glove box, a first non-aqueous organic solvent is frozen, then a first lithium salt is added and stirred until completely dissolved. Subsequently, a first additive is added and stirring continues to obtain the first electrolyte. Prepare the second electrolyte: In a glove box, the second non-aqueous organic solvent is frozen, then the second lithium salt and the second additive are added and stirred until completely dissolved, and then stirring is continued to obtain the second electrolyte.

[0018] Preferably, the glove box is an argon glove box with a water content of less than 10 ppm; the freezing temperature is -20°C and the time is 12 hours; the continued stirring time is 2 hours.

[0019] The third aspect of this invention discloses the application of a non-aqueous electrolyte for inhibiting manganese ion dissolution in lithium iron manganese phosphate batteries as described above, wherein the lithium iron manganese phosphate battery is assembled through the following steps: S1: Inject the first electrolyte into the dry cell; S2: Single encapsulation; S3: formation; S4: Aging; S5: Inject the second electrolyte; S6: Secondary encapsulation; S7: Capacity division.

[0020] The working principle of this invention is as follows: The lithium salt system employs a combination of lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI). LiPF6 participates in the formation of the solid electrolyte interphase (SEI) during the formation process, while LiFSI is introduced through a secondary electrolyte injection process to enhance the wide-temperature-range performance of the electrolyte. This avoids LiFSI's participation in the initial SEI formation, thus significantly improving the battery's overall performance over a wide temperature range while ensuring SEI structural stability.

[0021] For electrolyte additives, a combination of vinylene carbonate (VC), fluoroethylene carbonate (FEC), trimethylsilyl acetate (TMSMEA), and tetrafluoroethyl-trifluoroethyl ether (HFE) was selected. VC and FEC, as negative electrode film-forming additives, are two key components in lithium-ion batteries. VC has high reactivity and can preferentially reduce on the graphite negative electrode surface during the first charge-discharge process, forming an SEI film with a polycarbonate / polyacetylene polymer backbone through double bond polymerization in its molecules. This film has good ion conductivity and can effectively block the co-intercalation of solvent molecules, thereby protecting the graphite structure and improving cycle life. The fluorine atoms introduced into the FEC molecule enable it to generate lithium fluoride (LiF) during reduction, giving the SEI film higher density and mechanical strength, further enhancing interfacial stability.

[0022] TMSMEA and HFE work synergistically at the cathode interface to jointly construct a highly stable siloxane / fluorinated composite interfacial film (CEI). TMSMEA, as the main film-forming agent, undergoes oxidative stress to break down its Si–O–C and acetoxy structures, producing decomposition products (such as polysiloxanes and lithium silanolates) that form the flexible framework of the CEI film. This effectively suppresses volume changes in the LMFP material and interfacial corrosion caused by manganese / iron dissolution during charging and discharging. HFE, as a fluorinated ether, possesses high oxidative stability and low surface energy. Although it does not directly participate in film formation, it weakens the interaction between lithium ions and carbonate solvents, forming a locally depleted solubility structure. Simultaneously, it removes HF from non-aqueous electrolytes, reducing interfacial corrosion and side reactions, and promotes the enrichment of fluorine-rich components at the interface, enhancing the compactness and chemical stability of the CEI film. In other words, TMSMEA and HFE form a composite CEI structure of "flexible skeleton-rigid filler" through clear molecular division of labor. This structure has both strain resistance and corrosion resistance, which can significantly suppress side reactions between the LMFP cathode and the electrolyte, stabilize the cathode interface structure, and thus comprehensively improve the overall performance of the battery.

[0023] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a non-aqueous electrolyte, composed of a first electrolyte and a second electrolyte. Its main function is to inhibit the dissolution of manganese ions in the positive electrode material of lithium iron manganese phosphate (LMFP) batteries, effectively enhancing the structural stability of LMFP batteries and improving their lifespan. 1) Inhibit manganese leaching: Additive A (trimethylsilyl methyl acetate) and additive B (tetrafluoroethyl-trifluoroethyl ether) work synergistically to form a highly stable siloxy / fluorinated composite film at the positive electrode interface. Combined with HF removal capability, the amount of manganese leaching is reduced by 60% after 1000 cycles at 5C.

[0024] 2) Improved cycle performance: The optimized SEI / CEI film reduces the interface impedance, enabling the battery to retain ≥90% of its capacity after 1000 cycles at 5C at 25℃.

[0025] 3) High rate performance: The electrolyte has low viscosity (< 3.5 cp) and high ionic conductivity (> 10 mS / cm), enabling the battery to support 5C rate discharge. Detailed Implementation

[0026] The present invention will now be described in detail with reference to specific embodiments, but these are by no means limitations on the present invention.

[0027] Unless otherwise specified, the reagents used in the following description are conventional commercial products, the methods used are known in the art, and any other matters not covered herein can be handled using existing technology.

[0028] Lithium iron manganese phosphate (LiMnFePO4) cathode materials have become a research hotspot in the field of lithium-ion batteries due to their advantages of high energy density, low cost, and high safety. However, manganese ions are prone to dissolution during charging and discharging, leading to electrode structure damage, electrolyte decomposition, and battery capacity decay.

[0029] This solution designs a non-aqueous electrolyte with interfacial film formation, acid removal, and structural stability to suppress the dissolution of manganese ions during the use of LMFP batteries.

[0030] Positive electrode preparation: Spinel lithium manganese oxide (positive electrode active material), conductive carbon black (Super-P), carbon nanotubes, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 94:2:2:2, and then stirred evenly in N-methylpyrrolidone (NMP) solvent to obtain a positive electrode slurry. This slurry was uniformly coated onto the surface of an aluminum foil current collector and pre-dried at 80°C. Subsequently, it underwent rolling, edge trimming, sheet cutting, and slitting processes, followed by drying in a vacuum environment at 80°C for 10 hours. Finally, tabs were welded to obtain the lithium-ion battery positive electrode.

[0031] Negative electrode preparation: Artificial graphite (negative electrode active material), conductive carbon black (Super-P), thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are mixed at a mass ratio of 94:1.5:2.5:2, and stirred evenly in deionized water solvent to obtain a negative electrode slurry. This slurry is coated on both sides onto a copper foil current collector, pre-dried at 100℃, then rolled, trimmed, cut, and slit, and finally dried in a vacuum environment at 80℃ for 10 hours. Finally, tabs are welded to obtain the lithium-ion battery negative electrode.

[0032] Battery assembly: The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes for electrochemical isolation. They are then wound to form a bare cell. The bare cell is then placed into a soft-pack aluminum-plastic film casing, and a pre-prepared first electrolyte is injected. The process involves vacuum sealing, settling, formation, aging, secondary electrolyte injection, secondary sealing, and capacity testing, ultimately producing a 5Ah lithium manganese oxide soft-pack lithium-ion battery.

[0033] Non-aqueous electrolyte composition: First electrolyte: Non-aqueous organic solvents: Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 3:4:3 to provide high ionic conductivity and wide temperature range stability.

[0034] Lithium salt: Lithium hexafluorophosphate (LiPF6), with a concentration of 0.7-1.5 mol / L (concentration in the first electrolyte), is used as the main lithium salt in the first electrolyte.

[0035] Additives: Additive A: Trimethylsilyl acetate (1-3 wt%, content in the first electrolyte, the same below), as shown in Formula I below, preferentially forms a siloxy-containing interfacial film on the positive electrode surface, inhibiting manganese ion migration; Additive B: Tetrafluoroethyl-trifluoroethyl ether (0.5-2 wt%), as shown in Formula II below, removes free HF in the electrolyte through a strong electron-withdrawing effect, reducing the oxidative dissolution of manganese; Additive C: Vinylene carbonate (VC, 1-2 wt%) and fluoroethylene carbonate (FEC, 1-2 wt%) are combined to synergistically form a dense SEI film on the negative electrode, reducing the loss of active lithium. Formula I; Formula II.

[0036] The preparation method of the first electrolyte is as follows: In an argon glove box (H2O < 10 ppm), a non-aqueous organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiPF6 is slowly added and stirred until completely dissolved. Additives A, B, and C are added sequentially, and stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0037] Second electrolyte: Non-aqueous organic solvent: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7.

[0038] Lithium salt: Lithium bis(fluorosulfonyl)imide (LiFSI), added at a concentration of 0.7-1.5 mol / L (concentration in the second electrolyte), as the main lithium salt in the second electrolyte.

[0039] Additive: Lithium tetrafluoroborate (LiBF4), added at 2 wt% (content in the second electrolyte), to improve the chemical stability and high and low temperature stability of the battery.

[0040] The preparation method of the second electrolyte is as follows: In an argon glove box (H2O < 10 ppm), the organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiFSI and LiBF4 are slowly added and stirred until completely dissolved. Stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0041] Instructions for use of this non-aqueous electrolyte: ① The first electrolyte is injected into the dry cell; ② Initial packaging; ③Chemification; ④ Aging; ⑤ Inject the second electrolyte; ⑥Two envelopes; ⑦ Divide the capacity.

[0042] Example 1 This embodiment relates to a non-aqueous electrolyte for suppressing the dissolution of manganese ions in lithium iron manganese phosphate batteries.

[0043] Its technical solution is: First electrolyte: Solvent: Ethyl carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 3:4:3 to provide high ionic conductivity and wide temperature range stability.

[0044] Lithium salt: Lithium hexafluorophosphate (LiPF6), with a concentration of 1.1 mol / L in the first electrolyte, serving as the main lithium salt in the first electrolyte.

[0045] Additives: Additive A: Trimethylsilyl acetate, 2 wt% in the first electrolyte; Additive B: Tetrafluoroethyl-trifluoroethyl ether, 1 wt% in the first electrolyte; Additive C: VC 0.8 wt% + FEC 0.7 wt%, both in the first electrolyte.

[0046] The preparation method of the first electrolyte is as follows: In an argon glove box (H2O < 10 ppm), a non-aqueous organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiPF6 is slowly added and stirred until completely dissolved. Additives A, B, and C are added sequentially, and stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0047] Second electrolyte: Non-aqueous organic solvent: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7.

[0048] Lithium salt: Lithium bis(fluorosulfonyl)imide (LiFSI), with a concentration of 1.0 mol / L in the second electrolyte, serves as the main lithium salt in the second electrolyte.

[0049] Additive: Lithium tetrafluoroborate (LiBF4), added at a rate of 2 wt% in the second electrolyte, to improve the chemical stability and high and low temperature stability of the battery.

[0050] The preparation method of the second electrolyte is as follows: In an argon glove box (H2O < 10 ppm), the organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiFSI and LiBF4 are slowly added and stirred until completely dissolved. Stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0051] When using this non-aqueous electrolyte: ① The first electrolyte is injected into the dry cell; ② Initial packaging; ③Chemification; ④ Aging; ⑤ Inject the second electrolyte; ⑥Two envelopes; ⑦ Divide the capacity.

[0052] Example 2 This embodiment relates to a non-aqueous electrolyte for suppressing the dissolution of manganese ions in lithium iron manganese phosphate batteries.

[0053] Its technical solution is: First electrolyte: Solvent: Ethyl carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 3:4:3 to provide high ionic conductivity and wide temperature range stability.

[0054] Lithium salt: Lithium hexafluorophosphate (LiPF6), with a concentration of 1.3 mol / L in the first electrolyte, serving as the main lithium salt in the first electrolyte.

[0055] Additives: Additive A: Trimethylsilyl acetate, 3 wt% in the first electrolyte; Additive B: Tetrafluoroethyl-trifluoroethyl ether, 2 wt% in the first electrolyte; Additive C: VC 1 wt% + FEC 2 wt%, both in the first electrolyte.

[0056] The preparation method of the first electrolyte is as follows: In an argon glove box (H2O < 10 ppm), a non-aqueous organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiPF6 is slowly added and stirred until completely dissolved. Additives A, B, and C are added sequentially, and stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0057] Second electrolyte: Non-aqueous organic solvent: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7.

[0058] Lithium salt: Lithium bis(fluorosulfonyl)imide (LiFSI), with a concentration of 0.8 mol / L in the second electrolyte, serves as the main lithium salt in the second electrolyte.

[0059] Additive: Lithium tetrafluoroborate (LiBF4), added at a rate of 2 wt% in the second electrolyte, to improve the chemical stability and high and low temperature stability of the battery.

[0060] The preparation method of the second electrolyte is as follows: In an argon glove box (H2O < 10 ppm), the organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiFSI and LiBF4 are slowly added and stirred until completely dissolved. Stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0061] The process of using this non-aqueous electrolyte is the same as in Example 1.

[0062] Example 3 This embodiment relates to a non-aqueous electrolyte for suppressing the dissolution of manganese ions in lithium iron manganese phosphate batteries.

[0063] Its technical solution is: First electrolyte: Solvent: Ethyl carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 3:4:3 to provide high ionic conductivity and wide temperature range stability.

[0064] Lithium salt: Lithium hexafluorophosphate (LiPF6), with a concentration of 0.8 mol / L in the first electrolyte, serving as the main lithium salt in the first electrolyte.

[0065] Additives: Additive A: Trimethylsilyl acetate, 1 wt% in the first electrolyte; Additive B: Tetrafluoroethyl-trifluoroethyl ether, 0.5 wt% in the first electrolyte; Additive C: VC 2 wt% + FEC 1 wt%, all in the first electrolyte.

[0066] The preparation method of the first electrolyte is as follows: In an argon glove box (H2O < 10 ppm), a non-aqueous organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiPF6 is slowly added and stirred until completely dissolved. Additives A, B, and C are added sequentially, and stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0067] Second electrolyte: Non-aqueous organic solvent: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7.

[0068] Lithium salt: Lithium bis(fluorosulfonyl)imide (LiFSI), with a concentration of 1.3 mol / L in the second electrolyte, serves as the main lithium salt in the second electrolyte.

[0069] Additive: Lithium tetrafluoroborate (LiBF4), added at a rate of 2 wt% in the second electrolyte, to improve the chemical stability and high and low temperature stability of the battery.

[0070] The preparation method of the second electrolyte is as follows: In an argon glove box (H2O < 10 ppm), the organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiFSI and LiBF4 are slowly added and stirred until completely dissolved. Stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0071] The process of using this non-aqueous electrolyte is the same as in Example 1.

[0072] Comparative Example 1 This comparative example involves a non-aqueous electrolyte.

[0073] Its technical solution is: First electrolyte: Solvent: Ethyl carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 3:4:3 to provide high ionic conductivity and wide temperature range stability.

[0074] Lithium salt: Lithium hexafluorophosphate (LiPF6), with a concentration of 1.1 mol / L in the first electrolyte, serving as the main lithium salt in the first electrolyte.

[0075] Additives: Additive A: Trimethylsilyl acetate, 2 wt% in the first electrolyte; Additive B: Tetrafluoroethyl-trifluoroethyl ether, 1 wt% in the first electrolyte; Additive C: VC 0.8 wt% + FEC 0.7 wt%, both in the first electrolyte.

[0076] The preparation method of the first electrolyte is as follows: In an argon glove box (H2O < 10 ppm), a non-aqueous organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiPF6 is slowly added and stirred until completely dissolved. Additives A, B, and C are added sequentially, and stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0077] Second electrolyte: Non-aqueous organic solvent: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7.

[0078] Lithium salt: Lithium bis(fluorosulfonyl)imide (LiFSI), with a concentration of 1.0 mol / L in the second electrolyte, serves as the main lithium salt in the second electrolyte.

[0079] Additive: Lithium tetrafluoroborate (LiBF4), added at a rate of 2 wt% in the second electrolyte, to improve the chemical stability and high and low temperature stability of the battery.

[0080] The preparation method of the second electrolyte is as follows: In an argon glove box (H2O < 10 ppm), the organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiFSI and LiBF4 are slowly added and stirred until completely dissolved. Stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0081] When using this non-aqueous electrolyte (pre-inject the second electrolyte): ① The first electrolyte is injected into the dry cell; ②Inject the second electrolyte; ③ Initial packaging; ④Chemification; ⑤ Aging; ⑥Two envelopes; ⑦ Divide the capacity.

[0082] Comparative Example 2 Its technical solution is: First electrolyte: Solvent: Ethyl carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 3:4:3 to provide high ionic conductivity and wide temperature range stability.

[0083] Lithium salt: Lithium hexafluorophosphate (LiPF6), with a concentration of 1.1 mol / L in the first electrolyte, serving as the main lithium salt in the first electrolyte.

[0084] Additives (without additive A): Additive B: Tetrafluoroethyl-trifluoroethyl ether, with a content of 1 wt% in the first electrolyte; Additive C: VC 0.8 wt% + FEC 0.7 wt%, both with a content in the first electrolyte.

[0085] The preparation method of the first electrolyte is as follows: In an argon glove box (H2O < 10 ppm), a non-aqueous organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiPF6 is slowly added and stirred until completely dissolved. Additives B and C are added sequentially, and stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0086] Second electrolyte: Non-aqueous organic solvent: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7.

[0087] Lithium salt: Lithium bis(fluorosulfonyl)imide (LiFSI), with a concentration of 1.0 mol / L in the second electrolyte, serves as the main lithium salt in the second electrolyte.

[0088] Additive: Lithium tetrafluoroborate (LiBF4), added at a rate of 2 wt% in the second electrolyte, to improve the chemical stability and high and low temperature stability of the battery.

[0089] The preparation method of the second electrolyte is as follows: In an argon glove box (H2O < 10 ppm), the organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiFSI and LiBF4 are slowly added and stirred until completely dissolved. Stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0090] When using this non-aqueous electrolyte: ① The first electrolyte is injected into the dry cell; ② Initial packaging; ③Chemification; ④ Aging; ⑤ Inject the second electrolyte; ⑥Two envelopes; ⑦ Divide the capacity.

[0091] Comparative Example 3 Its technical solution is: First electrolyte: Solvent: Ethyl carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 3:4:3 to provide high ionic conductivity and wide temperature range stability.

[0092] Lithium salt: Lithium hexafluorophosphate (LiPF6), with a concentration of 1.1 mol / L in the first electrolyte, serving as the main lithium salt in the first electrolyte.

[0093] Additives (excluding Additive B): Additive A: Trimethylsilyl acetate, with a content of 2 wt% in the first electrolyte; Additive C: VC 0.8 wt% + FEC 0.7 wt%, both with a content in the first electrolyte.

[0094] The preparation method of the first electrolyte is as follows: In an argon glove box (H2O < 10 ppm), a non-aqueous organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiPF6 is slowly added and stirred until completely dissolved. Additive A and additive C are added sequentially, and stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0095] Second electrolyte: Non-aqueous organic solvent: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7.

[0096] Lithium salt: Lithium bis(fluorosulfonyl)imide (LiFSI), with a concentration of 1.0 mol / L in the second electrolyte, serves as the main lithium salt in the second electrolyte.

[0097] Additive: Lithium tetrafluoroborate (LiBF4), added at a rate of 2 wt% in the second electrolyte, to improve the chemical stability and high and low temperature stability of the battery.

[0098] The preparation method of the second electrolyte is as follows: In an argon glove box (H2O < 10 ppm), the organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiFSI and LiBF4 are slowly added and stirred until completely dissolved. Stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0099] When using this non-aqueous electrolyte: ① The first electrolyte is injected into the dry cell; ② Initial packaging; ③Chemification; ④ Aging; ⑤ Inject the second electrolyte; ⑥Two envelopes; ⑦ Divide the capacity.

[0100] Comparative Example 4 Its technical solution is: First electrolyte: Solvent: Ethyl carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a volume ratio of 3:4:3 to provide high ionic conductivity and wide temperature range stability.

[0101] Lithium salt: Lithium hexafluorophosphate (LiPF6), with a concentration of 1.1 mol / L in the first electrolyte, serving as the main lithium salt in the first electrolyte.

[0102] Additives (additive C only): Additive C: VC 0.8 wt% + FEC 0.7 wt%, both of which are the content in the first electrolyte.

[0103] The preparation method of the first electrolyte is as follows: In an argon glove box (H2O < 10 ppm), a non-aqueous organic solvent is mixed thoroughly and then frozen at -20°C for 12 hours. LiPF6 is slowly added and stirred until completely dissolved. Additive C is added, and stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0104] Second electrolyte: Non-aqueous organic solvent: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7.

[0105] Lithium salt: Lithium bis(fluorosulfonyl)imide (LiFSI), with a concentration of 1.0 mol / L in the second electrolyte, serves as the main lithium salt in the second electrolyte.

[0106] Additive: Lithium tetrafluoroborate (LiBF4), added at a rate of 2 wt% in the second electrolyte, to improve the chemical stability and high and low temperature stability of the battery.

[0107] The preparation method of the second electrolyte is as follows: In an argon glove box (H2O < 10 ppm), the organic solvent is mixed evenly and then frozen at -20°C for 12 hours. LiFSI and LiBF4 are slowly added and stirred until completely dissolved. Stirring continues for 2 hours to obtain a homogeneous electrolyte.

[0108] When using this non-aqueous electrolyte: ① The first electrolyte is injected into the dry cell; ② Initial packaging; ③Chemification; ④ Aging; ⑤ Inject the second electrolyte; ⑥Two envelopes; ⑦ Divide the capacity.

[0109] Performance testing: Conductivity testing: The conductivity of the electrolyte at 25°C was tested using a commercial conductivity meter, the METTLER TOLEDO FE38, and a constant temperature water bath. Before testing, the instrument was calibrated with a standard KCl solution (e.g., 0.1 mol / L, conductivity 12.88 mS / cm at 25°C). The electrodes were immersed in the electrolyte, and the stabilized conductivity value was read.

[0110] After mixing the first electrolyte and the second electrolyte in Example 1, the conductivity was tested at 25°C and found to be 12.41 mS / cm.

[0111] The non-aqueous electrolytes of Examples 2 and 3 were tested, and their respective conductivity was similar to that of Example 1, both > 10 mS / cm, which will not be shown here.

[0112] Viscosity test: The viscosity of the electrolyte at 25°C was measured using a DV2T cone-plate viscometer and a TC-650 AP circulating water bath system. The rotor was immersed in the electrolyte, and the viscosity value was read after stabilization.

[0113] After mixing the first electrolyte and the second electrolyte in Example 1, the viscosity was tested at 25°C and found to be 2.75 cP.

[0114] The non-aqueous electrolytes of Examples 2 and 3 were tested and their viscosities were similar to those of Example 1, both < 3.5 cP, and will not be shown here.

[0115] Manganese ion leaching test: The sample was digested with acid, transferred to a final volume, and allowed to stand. After the solution separated into layers, the clear intermediate portion was collected as the analyte. A series of mixed standard solutions were prepared according to the type of the major element to be analyzed for quantitative analysis. Analysis was performed using a single-wavelength excitation-energy dispersive X-ray fluorescence spectrometer, which allows for simultaneous analysis of major elements and trace impurities. The test results are shown in Table 1.

[0116] Table 1. Manganese ion leaching test results of Examples 1-3 and Comparative Examples 1-4 Cyclic performance test: A constant current / constant voltage charging mode was adopted, with a charging cutoff voltage of 4.3V and a constant current of 0.5C during the constant current phase. The constant voltage phase was initiated when the current dropped to 0.05C. A constant current discharge phase was used, with a cutoff voltage of 2.5V and a discharge current of 0.5C. The temperature was maintained at 25±1℃, and the ambient temperature was kept stable throughout the test. The test results are shown in Table 2.

[0117] Table 2. 5C cycle performance test results of Examples 1-3 and Comparative Examples 1-4 Therefore, this invention, through optimizing lithium salt selection, additive formulation, and electrolyte injection process, designs a non-aqueous electrolyte system composed of a first electrolyte and a second electrolyte. This electrolyte exhibits excellent physical properties, with an ionic conductivity of 12.41 mS / cm and a viscosity of 2.75 cP. By employing a secondary injection process and combining the synergistic effect of additives TMSMEA and HFE at the cathode interface, this system not only regulates the formation of the solid electrolyte interface (SEI) but also constructs a highly stable siloxy / fluorinated composite interface film (CEI) on the cathode surface. This composite film effectively removes HF from the electrolyte, reduces interfacial corrosion and side reactions, and promotes the enrichment of fluorine-rich components at the interface, thereby enhancing the density and chemical stability of the CEI film. This mechanism significantly suppresses side reactions between the LMFP cathode and the electrolyte, contributing to the stabilization of the cathode interface structure and thus comprehensively improving the overall performance of the battery. More specifically, the comparison between Example 1 and Comparative Example 1 shows that the secondary electrolyte injection process can effectively solve the adverse effects caused by the dual salt system jointly participating in the SEI film construction during the formation process. Further comparative analysis between Example 1 and Comparative Examples 2, 3, and 4 reveals that additive A (trimethylsilyl acetate) and additive B (tetrafluoroethyl-trifluoroethyl ether) have a significant inhibitory effect on the dissolution of manganese ions in lithium manganese iron phosphate batteries. Thus, this electrolyte system can support 5C rate discharge while also significantly improving the cycle performance of the battery.

[0118] In summary, this invention relates to a non-aqueous electrolyte, composed of a first electrolyte and a second electrolyte. Its main function is to suppress the dissolution of manganese ions from the positive electrode material of lithium iron manganese phosphate (LMFP) batteries, enhance the structural stability of LMFP batteries, and improve their lifespan.

[0119] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A nonaqueous electrolyte solution for inhibiting the elution of manganese ions in a lithium manganese iron phosphate battery, characterized by comprising: a lithium salt; a phosphoric acid ester; and a cyclic carbonate compound. Including the first electrolyte and the second electrolyte; The first electrolyte comprises: The first non-aqueous organic solvent includes at least one carbonate solvent; First lithium salt; The first additive includes trimethylsilyl acetate and tetrafluoroethyl-trifluoroethyl ether; The second electrolyte comprises: The second non-aqueous organic solvent includes at least one carbonate solvent; Second lithium salt; The second additive includes lithium tetrafluoroborate.

2. The nonaqueous electrolyte solution for inhibiting the dissolution of manganese ions in a lithium manganese iron phosphate battery according to claim 1, characterized by comprising: The first non-aqueous organic solvent includes ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate; The volume ratio of ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate is 3:4:

3.

3. The nonaqueous electrolyte solution for inhibiting the dissolution of manganese ions in lithium manganese phosphate batteries according to claim 1, characterized by comprising: 0.01 to 0.1% by weight of the compound represented by the general formula (1) of claim 1. The first lithium salt includes lithium hexafluorophosphate, and the concentration of the first lithium salt in the first electrolyte is 0.7-1.5 mol / L.

4. The nonaqueous electrolyte solution for inhibiting the dissolution of manganese ions in lithium manganese phosphate batteries according to claim 1, characterized by, The concentration of the trimethylsilyl acetate in the first electrolyte is 1-3 wt%, and the concentration of the tetrafluoroethyl-trifluoroethyl ether in the first electrolyte is 0.5-2 wt%. The first additive also includes vinylene carbonate and fluoroethylene carbonate, wherein the concentration of vinylene carbonate in the first electrolyte is 1-2 wt%, and the concentration of fluoroethylene carbonate in the first electrolyte is 1-2 wt%.

5. The non-aqueous electrolyte for inhibiting manganese ion dissolution in a lithium iron manganese phosphate battery according to claim 1, characterized in that, The second non-aqueous organic solvent includes ethylene carbonate and ethyl methyl carbonate; The volume ratio of ethylene carbonate to methyl ethyl carbonate is 3:

7.

6. The non-aqueous electrolyte for inhibiting manganese ion dissolution in a lithium iron manganese phosphate battery according to claim 1, characterized in that, The second lithium salt includes lithium bis(fluorosulfonyl)imide, and the concentration of the second lithium salt in the second electrolyte is 0.7-1.5 mol / L.

7. The non-aqueous electrolyte for inhibiting manganese ion dissolution in a lithium iron manganese phosphate battery according to claim 1, characterized in that, The concentration of lithium tetrafluoroborate in the second electrolyte is 2 wt%.

8. A method for preparing a non-aqueous electrolyte for inhibiting manganese ion dissolution in a lithium iron manganese phosphate battery as described in any one of claims 1-7, characterized in that, Includes the following steps: Prepare the first electrolyte: In a glove box, a first non-aqueous organic solvent is frozen, then a first lithium salt is added and stirred until completely dissolved. Subsequently, a first additive is added and stirring continues to obtain the first electrolyte. Prepare the second electrolyte: In a glove box, the second non-aqueous organic solvent is frozen, then the second lithium salt and the second additive are added and stirred until completely dissolved, and then stirring is continued to obtain the second electrolyte.

9. A method for preparing a non-aqueous electrolyte for suppressing manganese ion dissolution in a lithium iron manganese phosphate battery according to claim 8, characterized in that, The glove box is an argon glove box with a water content of less than 10 ppm; the freezing temperature is -20℃ and the time is 12 hours; the stirring time is 2 hours.

10. The application of a non-aqueous electrolyte for inhibiting manganese ion dissolution in lithium iron manganese phosphate batteries as described in any one of claims 1-7, characterized in that, The lithium iron manganese phosphate battery is assembled using the following steps: S1: Inject the first electrolyte into the dry cell; S2: Single encapsulation; S3: formation; S4: Aging; S5: Inject the second electrolyte; S6: Secondary encapsulation; S7: Capacity division.

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