Electrolyte for lithium iron manganese phosphate battery and lithium ion battery

Abstract

This invention relates to an electrolyte for lithium iron phosphate batteries and a lithium-ion battery, belonging to the field of lithium-ion battery technology. The electrolyte includes lithium salt, a non-aqueous solvent, and additives. The non-aqueous solvent is characterized by comprising one or more asymmetric fluorosulfonate compounds; the additives are carbonate additives and / or nitrile additives. This invention addresses the capacity decay problem caused by manganese leaching at high temperatures in lithium iron phosphate batteries by using LiFSI to prevent HF generation at the source, thus inhibiting manganese leaching. Simultaneously, a fluorosulfonate is introduced as a co-solvent. On the one hand, it decomposes at the positive electrode to form a protective film rich in sulfur components, effectively inhibiting the corrosion of aluminum foil by LiFSI. On the other hand, the fluorosulfonate can participate in the regulation of lithium-ion solvation structure and synergistically construct a stable positive and negative electrode interface film, significantly improving the battery's high-temperature cycle stability and high-temperature storage performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more particularly to an electrolyte for lithium manganese iron phosphate batteries and a lithium-ion battery. Background Technology

[0002] With the rapid development of new energy vehicles and large-scale energy storage, the market has placed higher demands on the energy density, safety, and cost of lithium-ion batteries. Lithium manganese iron phosphate (LFP) ) as lithium iron phosphate ( LFP is an upgraded alternative material. By introducing Mn elements into LFP, the working voltage platform can be increased from 3.4V (vs Li+ / Li) to 4.1V, and the theoretical energy density can be increased by 15-20%. At the same time, it inherits the excellent olivine structure stability and thermal safety of LFP, and is regarded as an important development direction for the next generation of power battery cathode materials.

[0003] However, the commercialization of LMFP materials faces severe challenges, the most critical of which is the rapid performance degradation caused by the dissolution of manganese ions at high temperatures. Research suggests that manganese dissolution is primarily driven by two factors: firstly, the intrinsic Jahn-Teller effect of the material... The first is lattice distortion; the second is the trace water (H2O) in the electrolyte that is difficult to completely remove and the conventional lithium salt lithium hexafluorophosphate (LiPo). Hydrolysis reaction occurs. The process generates highly corrosive hydrofluoric acid (HF). HF severely corrodes the LMFP cathode, accelerating the dissolution of manganese and iron. The dissolved Mn2+ migrates to the anode, catalyzing electrolyte decomposition and damaging the solid electrolyte interphase (SEI) film. This leads to irreversible consumption of active lithium, a sharp increase in battery impedance, and ultimately a significant drop in capacity. More critically, this study found an abnormally high hydrogen content (approximately 10%) in the gas produced after high-temperature storage of the LMFP system. This is more likely due to the reduction of moisture within the system, rather than the traditionally believed ring-opening decomposition of the EC solvent. This further highlights the severity of the chain reaction triggered by moisture in the LMFP system.

[0004] To address these challenges, existing technologies mainly focus on two aspects: material modification and electrolyte optimization. In the field of electrolytes, some solutions have been disclosed in existing technologies. For example, Chinese patent application CN120565808A discloses an electrolyte that improves the high-temperature cycle performance of lithium manganese iron phosphate batteries by introducing additives with specific structures to form a CEI film on the positive electrode. Chinese patent application CN120261708A discloses an electrolyte for lithium manganese iron phosphate batteries that inhibits manganese dissolution by adding multifunctional compounds. Chinese patent application CN119786733A improves manganese deposition on the negative electrode by regulating the relationship between the negative electrode film-forming additives and the positive electrode material, solvent, and lithium salt. In addition, some studies have attempted to use lithium bis(fluorosulfonyl)imide (LiFSI) as a substitute. By leveraging its high thermal stability and resistance to hydrolysis, the generation of HF can be avoided at the source.

[0005] However, existing technologies still have significant shortcomings. First, most strategies remain at the "end-of-pipe treatment" level, that is, physically blocking HF erosion through film-forming additives or consuming moisture through dehydrating agents, but they fail to fundamentally solve the problem. The fundamental problem is its thermodynamic instability and inevitable decomposition upon contact with water. Secondly, although LiFSI is highly anticipated, it faces two major technical bottlenecks in practical applications: Aluminum foil current collector corrosion problem: Under high voltage (>4.2V), LiFSI will corrode aluminum foil, leading to battery performance degradation or even failure; Interface stability issues: The pure LiFSI system lacks sufficient oxidation stability under high voltage, making it difficult to form a sufficiently dense protective film. Therefore, how to leverage the advantages of LiFSI in inhibiting manganese leaching while addressing the associated aluminum foil corrosion and high-voltage instability problems is a pressing technical challenge for the industry.

[0006] Literature reports mostly focus on LiFSI and The strategy of mixing different types of electrolytes has been adopted, but this has not completely eliminated the source of HF. Currently, few technical solutions systematically design lithium iron phosphate electrolytes from the dual perspectives of "inhibiting manganese leaching at the source" and "in-situ corrosion prevention of aluminum foil". Summary of the Invention

[0007] In order to overcome the above-mentioned defects of the prior art, the present invention provides an electrolyte for lithium manganese iron phosphate batteries and a lithium-ion battery to solve the problems mentioned in the background art.

[0008] To achieve the above-mentioned objectives, the present invention provides an electrolyte for lithium manganese iron phosphate batteries, comprising a lithium salt, a non-aqueous solvent, and additives. The non-aqueous solvent comprises an asymmetric fluorosulfonate compound, wherein the asymmetric fluorosulfonate compound is one or more compounds represented by the following general structural formula (I); the additives are carbonate additives and / or nitrile additives. (I) in, Selected from fluoroalkyl groups with 1-4 carbon atoms, and and The carbon chain length difference of the groups is greater than or equal to 1 carbon atom, and the dipole moment of the asymmetric fluorosulfonate compound is in the range of 3.2-4.5D.

[0009] Furthermore, the asymmetric fluorosulfonate compound is 2,2,2-trifluoroethyltrifluoromethane sulfonate and / or 2,2,2-trifluoroethyltrifluoropropane sulfonate.

[0010] Furthermore, the asymmetric fluorosulfonate compound accounts for 5% to 15% of the solvent volume of the electrolyte.

[0011] Furthermore, the non-aqueous solvent also includes a carbonate solvent, wherein the carbonate solvent is any one or a mixture of two or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0012] Furthermore, the concentration of the lithium salt in the electrolyte is 0.8–1.2 mol / L.

[0013] Furthermore, the carbonate additive is at least one of vinylene carbonate, fluoroethylene carbonate, and vinyl ethylene carbonate; the nitrile additive is at least one of adiponitrile, succinic anion, benzonitrile, hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, and ethylene glycol bis(propionitrile) ether; and the additive accounts for 0.5% to 5% of the mass percentage of the electrolyte.

[0014] A lithium-ion battery, comprising the electrolyte for a lithium manganese iron phosphate battery.

[0015] Furthermore, the positive electrode material of the lithium-ion battery is lithium manganese iron phosphate. , where 0.5 < x < 0.8.

[0016] Furthermore, the negative electrode material of the lithium-ion battery is one of graphite, silicon carbide, silicon suboxide, or metallic lithium.

[0017] Furthermore, the lithium-ion battery has an upper limit of operating voltage of 4.3V, a lower limit of discharge voltage of 2.5V, and an operating temperature range of -20~70℃.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention eliminates the problem of easy hydrolysis and acid production. The technology employs LiFSI, which has extremely high thermal and chemical stability. The hydrolysis pathway of LiFSI does not produce HF, thus cutting off the chemical corrosion of the LMFP cathode by HF at the source and greatly inhibiting the intrinsic dissolution of manganese ions. This is a fundamental innovation that distinguishes it from existing "end-of-pipe treatment" technologies.

[0019] 2. This invention creatively introduces fluorosulfonate TTMS as a co-solvent, rather than a simple additive. TTMS preferentially decomposes under high voltage, forming a dense protective layer on the aluminum foil surface containing AlF3 and sulfur-containing organic / inorganic complexes. This ingeniously and efficiently solves the long-standing aluminum foil corrosion problem of LiFSI systems, enabling the safe and stable application of LiFSI in high-voltage LMFP systems.

[0020] 3. The introduction of TTMS reconstructs the solvation structure of Li+. The interaction between its sulfonyl group and Li+ makes the Li+ solvent coordination environment more uniform, and the electron-withdrawing effect of the trifluoromethyl group lowers the desolvation energy barrier, improving lithium-ion transport kinetics. At the same time, the S and F species generated by TTMS decomposition participate in the formation of the positive and negative electrode interface film, constructing a thinner, more stable, and lower impedance CEI / SEI film, effectively blocking the crosstalk of dissolved manganese ions.

[0021] 4. Through the synergistic effect of the above multiple mechanisms, the LMFP / graphite battery using the electrolyte of this invention can maintain a capacity retention rate of over 90% after 200 cycles at 45°C, and a capacity recovery rate of over 95% after 30 days of storage at 60°C. The gas production is also higher than that of traditional... The system cost was reduced by more than 60%, and the overall performance was significantly improved. Attached Figure Description

[0022] Figure 1 The CV curves of the electrolytes in Example 1 and Comparative Examples 1-2 of this invention are shown. Figure 2 The LMFP / graphite pouch cells of Example 1 and Comparative Examples 1-2 of this invention have 100 charge-discharge cycles at 45°C. Figure 3 This is a comparison chart of the storage capacity recovery rate of LMFP / graphite pouch cells in Examples 1-2 and Comparative Examples 1-2 of the present invention at 60°C. Figure 4This is a comparison chart of the gas production of LMFP / graphite soft-pack batteries from Examples 1-2 and Comparative Examples 1-2 after storage at 60°C. Figure 5 This is a comparison diagram of the dissolution of transition metal ions in Example 1 and Comparative Examples 1-2 of the present invention; Figure 6 The -20°C low-temperature charge-discharge curves are for Embodiment 1 and Comparative Examples 1-2 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the invention, but not all embodiments. The embodiments of the present invention are described below with reference to the accompanying drawings.

[0024] This invention achieves a systematic solution to the high-temperature failure problem of lithium manganese iron phosphate systems through the synergistic design of LiFSI and a specific fluorosulfonate TTMS. Specifically, this invention abandons the traditional method of easily hydrolyzing and producing acid. By employing intrinsically stable LiFSI as the lithium salt, the generation pathway of HF is cut off at its source, greatly suppressing the core failure point of manganese ion dissolution induced by acid. This is the fundamental reason for the performance breakthrough of this invention. However, using LiFSI alone will face new problems such as aluminum foil corrosion under high pressure and insufficient interface stability. To address this, this invention creatively introduces fluorosulfonate TTMS as a multifunctional co-solvent, whose function is manifested on three levels: First, at the positive electrode interface, fluorosulfonate TTMS, due to its weaker oxidation stability, can preferentially undergo oxidative decomposition compared to carbonate solvents. The trifluoromethyl and sulfonate groups in its molecule participate in the construction of a layer rich in... The dense and low-resistance positive electrode electrolyte interface film containing sulfur components not only physically prevents direct contact between the electrolyte and the positive electrode, inhibiting the corrosion of the positive electrode by residual moisture and other side reactions, but also cleverly solves the corrosion problem of aluminum foil current collectors caused by LiFSI. Secondly, at the solvation structure level, the sulfonyl group in the fluorosulfonate TTMS molecule has a high electron-donating ability and can effectively participate in the solvation coordination of Li+, while the strongly electron-withdrawing trifluoromethyl group at its end significantly reduces the binding energy between Li+ and the coordination solvent. This unique coordination mechanism reconstructs the solvation sheath of Li+, promoting the rapid desolvation process of Li+ at the electrode interface, thereby reducing the interfacial charge transfer impedance. Finally, at the negative electrode interface, the reduction decomposition products of fluorosulfonate TTMS participate in the construction of the SEI film, forming a thin, tough, and stable interface layer with high sulfur content. This layer effectively passivates the negative electrode surface. Even if trace amounts of manganese ions dissolve from the positive electrode and migrate to the negative electrode, they can be effectively blocked by this dense SEI layer, inhibiting their catalytic decomposition of the electrolyte and the "crosstalk" effect that damages the SEI. In summary, this invention, through a dual strategy of "LiFSI source suppression of manganese dissolution" and "multiple interface protection and kinetic optimization of fluorosulfonate TTMS," not only eradicates the corrosion of HF on the LMFP positive electrode but also simultaneously solves the application bottleneck of high-stability LiFSI salts, ultimately achieving a comprehensive improvement in the high-temperature cycling, high-temperature storage performance, and interface stability of LMFP batteries. Example 1

[0025] A method for preparing a lithium-ion battery, specifically including: Battery cell preparation: The purchased dry-cell batteries (without electrolyte filling) were placed in a 45℃ vacuum drying oven and left to stand for 12 hours to remove moisture. The positive electrode of the dry-cell batteries was a mixture of lithium iron manganese oxide, a positive electrode active material, in a mass ratio of 93:4:3. The positive electrode slurry is prepared by mixing LMFP (artificial graphite), conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP). The slurry is then uniformly coated onto both sides of an aluminum foil, followed by drying, calendering, and vacuum drying to obtain the positive electrode sheet. The negative electrode of the dry cell is prepared by mixing artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in a 92:2:3:3 mass ratio, followed by dispersion in deionized water to obtain the negative electrode slurry. This slurry is coated onto both sides of a copper foil, followed by drying, calendering, and vacuum drying to obtain the negative electrode sheet. The positive and negative electrode sheets are then stacked to assemble and seal the battery, resulting in the dry cell.

[0026] The preparation of the electrolyte for lithium manganese iron phosphate batteries specifically includes the following steps: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and compound 1 (2,2,2-trifluoroethyltrifluoromethanesulfonate) as shown in formula (1) were mixed in a volume ratio of EC:EMC:TTMS = 30:60:10. Lithium bis(fluorosulfonyl)imide (LiFSI) was then added to a molar concentration of 1 mol / L. Subsequently, 2% fluoroethylene carbonate (FEC), 2% ethylene carbonate (VES), and 2% adiponitrile (ADN) were added. The electrolyte was named TTMS.

[0027] Equation (1) The steps for electrolyte injection, formation, and capacity testing of battery cells are as follows: (1) Transfer the dried battery cell to a glove box with a moisture content of less than 10 ppm, cut open the seal, and inject the electrolyte prepared in this embodiment into the battery cell at a rate of 4.3 g / Ah. The amount of electrolyte should be sufficient to fill the gaps in the battery cell. (2) After liquid injection, the battery cell is transferred to the vacuum device inside the glove box. The pressure is slowly reduced and maintained at a low pressure of -88 kPa for 20 minutes. Then, heat sealing is performed under vacuum conditions. The vacuum level is less than -88 kPa, and the heat sealing time is 3-5 seconds. The sealing temperature of the upper and lower blades is 160℃. After the first sealing, the battery cell with the air bladder facing upwards is left to stand in a 25℃ environment for 24 hours. The weight is measured by the water displacement method (m1). (3) Perform the following steps: charge to 3.95V at a constant current of 0.02C in a test chamber at 45℃, then let stand for 8 hours, and weigh m2 by water displacement method; (4) Transfer the formed and weighed cells to the glove box, cut open the air bag to remove the air and then reseal it. Pay attention to the sealing effect. Keep the sealing position 1.00±0.50mm away from the edge and weigh m3. (5) After the secondary sealing, the battery cell is divided into two parts according to the following steps: 0.1C constant current charging to 4.25V, then constant voltage charging to cutoff current 0.05C, then stand for 10 minutes, then 0.1C constant current discharge to 3.0V, then constant voltage discharge to cutoff current 0.05C. Example 2

[0028] Compared with Example 1, the preparation method of lithium-ion battery is the same as that in Example 1, in the preparation of electrolyte, 10% by volume of compound 1 (2,2,2-trifluoroethyltrifluoromethanesulfonate) is replaced by 10% by volume of compound 2 (2,2,2-trifluoroethyltrifluoropropanesulfonate) (Formula 2), and this electrolyte is named TTPS.

[0029] CF3CF2-O-SO2-CH2CH2CF3......Formula (2) Comparative Example 1 The preparation method of the lithium-ion battery is the same as that in Example 1. In the preparation of the electrolyte, the 10% volume fraction of compound 1 (2,2,2-trifluoroethyltrifluoromethanesulfonate) in Example 1 is replaced with 10% volume fraction of ethyl methyl carbonate (EMC), that is, EC:EMC=30:70. This electrolyte is named Base. Everything else is the same as in Example 1.

[0030] Comparative Example 2 The method for preparing lithium-ion batteries differs from Comparative Example 1 in that LiFSI in Comparative Example 1 is replaced with... Everything else is the same as in Comparative Example 1. Example 3

[0031] The preparation method of lithium-ion battery is the same as in Example 1, except that the volume fraction of compound 1 (2,2,2-trifluoroethyltrifluoromethanesulfonate) in Example 1 is changed from 10% to 15%, the volume fraction of EMC is 55%, and the rest is the same as in Example 1. Example 4

[0032] The preparation method of lithium-ion battery is the same as in Example 1, except that the volume fraction of compound 1 (2,2,2-trifluoroethyltrifluoromethanesulfonate) in Example 1 is changed from 10% to 5%, the volume fraction of EMC is 65%, and the rest is the same as in Example 1. Example 5

[0033] The preparation method of the lithium-ion battery is the same as in Example 1, except that the concentration of lithium salt LiFSI in Example 1 is changed from 1 mol / L to 0.8 mol / L. Example 6

[0034] The preparation method of the lithium-ion battery is the same as in Example 1, except that the concentration of lithium salt LiFSI in Example 1 is changed from 1 mol / L to 1.2 mol / L. Example 7

[0035] The preparation method of lithium-ion battery is the same as in Example 1, except that the mass fraction of fluoroethylene carbonate (FEC), vinylene carbonate (VES) and adiponitrile (AND) additives in Example 1 is changed from 2% to 5%. Example 8

[0036] The preparation method of lithium-ion battery is the same as in Example 1, except that the mass fraction of fluoroethylene carbonate (FEC), vinylene carbonate (VES) and adiponitrile (AND) additives in Example 1 is changed from 2% to 0.5%. Example 9

[0037] The method for preparing lithium-ion batteries, compared with Example 1, involves using lithium iron manganese phosphate in Example 1. / / Replace the graphite pouch battery with the positive electrode The battery is the same as in Example 1. Example 10

[0038] The method for preparing lithium-ion batteries, compared with Example 1, involves using lithium iron manganese phosphate in Example 1. / / Replace the graphite pouch battery with the positive electrode The battery is the same as in Example 1.

[0039] The performance of the batteries applied in Examples 1-10 and Comparative Examples 1-2 was tested (activation film formation was performed by cycling at 0.05°C for three cycles before each test), including: I. High-Temperature (45℃) Cycling Performance Set the test chamber to 45℃, charge at 0.5C to 4.25V, then charge at a constant voltage of 4.25V until the current drops to 0.05C (50mA), followed by discharge at 0.5C to 3.0V. Repeat this cycle 200 times, recording the discharge capacity of the first cycle and the discharge capacity of the 200th cycle. Calculate the battery cycle capacity retention rate using the following formula: Capacity retention rate = (Discharge capacity at the 200th discharge / Discharge capacity at the 1st discharge) * 100%.

[0040] Table 2. High-temperature cycling performance test results: II. High-Temperature (60℃) Storage Capacity Recovery Performance After storing the battery in a test chamber at 60°C for 60 days, charge it to 4.25V at 0.5C, then charge it at a constant voltage of 4.25V until the current drops to 0.05C (50mA), followed by discharging it to 3.0V at 0.5C. Repeat this cycle 200 times, record the discharge capacity of the 200th cycle, and calculate the battery cycle capacity recovery rate using the following formula.

[0041] Capacity recovery rate = (Discharge capacity at the 200th discharge after storage / Discharge capacity at the 1st discharge before storage) * 100%.

[0042] Table 3 High-Temperature Storage Capacity Recovery Rate: To further verify the corrosion behavior of the non-aqueous solvent of the lithium-ion battery electrolyte on aluminum foil, the present invention also tested the cyclic voltammetry (CV) curve of the electrolyte.

[0043] The CV curve testing method is as follows: A three-electrode system was assembled using aluminum foil as the working electrode and lithium metal as the counter and reference electrodes. Linear scan voltammetry was performed with a scan rate of 0.1 mV / s and a voltage range of OCV to 6 V.

[0044] Figure 1 The Al-Li-Li three-electrode CV curves of Example 1 and Comparative Examples 1-2 are shown. Figure 1 It can be seen that, using Comparative Example 2 showed a lower current density and better aluminum foil stability across the entire voltage range. However, Comparative Example 1, using LiFSI, exhibited a sharp increase in current density after the voltage exceeded 3.75V, indicating severe corrosion of the aluminum foil. Using Example 1, the corrosion current was compared to that of Comparative Example 2. The systems are very similar, and no significant corrosion current was observed under high voltage, indicating that the introduction of TTMS successfully formed an effective protective layer on the aluminum foil surface, inhibiting the corrosion of the aluminum foil by LiFSI.

[0045] Figure 2 The charge-discharge curves of the LMFP / graphite pouch cells of Example 1 and Comparative Examples 1-2 after 100 cycles at 45°C are shown. As can be seen from the figures, Comparative Example 2 ( The battery in the first example (LiFSI system, without TTMS) exhibited significant capacity decay after 100 high-temperature cycles, and a marked increase in polarization voltage between charge and discharge plateaus, indicating severe side reactions at the electrode interface and a significant increase in impedance. The battery in Comparative Example 1 (LiFSI system, without TTMS) showed extremely poor cycle performance and the most severe capacity decay due to aluminum foil corrosion. In contrast, the battery using Example 1 of this invention (LiFSI + 10% TTMS) maintained a high discharge capacity after 100 high-temperature cycles, with a stable charge-discharge curve plateau and a low polarization voltage, demonstrating excellent high-temperature cycle stability and interface compatibility.

[0046] Figure 3 This is a comparison chart of the capacity recovery rates of LMFP / graphite pouch cells from Examples 1-2 and Comparative Examples 1-2 after 60 days of storage at 60°C. The chart shows that Comparative Example 2 (…) The capacity recovery rate of the first system was only 45%, indicating that electrolyte decomposition, interfacial side reactions, and manganese dissolution during high-temperature storage led to severe irreversible capacity loss. The capacity recovery rate of Comparative Example 1 (LiFSI system, without TTMS) was even lower, at only 29%, due to the sharp increase in battery internal resistance and severe interfacial damage caused by the corrosion of aluminum foil by LiFSI under high voltage. In contrast, the capacity recovery rates of Examples 1 and 2 of this invention reached 68% and 65%, respectively, significantly higher than the Comparative Example group. This demonstrates that the asymmetric fluorosulfonate co-solvent introduced in this invention can effectively protect the positive and negative electrode interfaces and suppress side reactions during high-temperature storage, thereby significantly improving capacity recovery capability.

[0047] Figure 4 This is a comparison graph showing the gas production of LMFP / graphite pouch cells from Examples 1-2 and Comparative Examples 1-2 after 60 days of storage at 60°C. The graph clearly shows that Comparative Example 2 (…) The system has a high gas production rate, which is mainly attributed to... Hydrolysis and electrolyte decomposition side reactions at high temperatures were observed. Comparative Example 1 (LiFSI system, without TTMS) showed higher gas production, due to the chain reaction triggered by LiFSI corrosion of the aluminum foil and the continuous decomposition of the electrolyte caused by interfacial instability. In contrast, the gas production of Examples 1 and 2 of this invention was significantly reduced, by approximately 60% or more compared to Comparative Example 2. This result fully demonstrates that the introduction of TTMS and TTPS can effectively suppress electrolyte decomposition and gas production from side reactions at high temperatures, and the stable interfacial film formed has a significant blocking effect on gas generation.

[0048] Figure 5 This is a comparison graph showing the amount of transition metal ions dissolved in the negative electrode of LMFP / graphite pouch cells from Examples 1 and Comparative Examples 1-2 after 200 cycles at 45°C, measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). The graph shows that Comparative Example 2 (LiPF6 system) showed higher Mn and Fe content in its negative electrode, indicating that a large amount of transition metal ions dissolved from the positive electrode and migrated and deposited to the negative electrode. Comparative Example 1 (LiFSI system, without TTMS) also showed a high amount of transition metal ion dissolution in its negative electrode, even higher in some samples, due to interface instability exacerbating the manganese dissolution process. In contrast, the dissolution of Mn and Fe in the negative electrode of Example 1 was extremely low, reduced by more than 90% compared to Comparative Example 2. This result directly proves that the present invention, through the synergistic effect of LiFSI suppressing HF generation at the source and TTMS constructing a stable interface, fundamentally suppresses manganese dissolution from the LMFP positive electrode and its crosstalk effect to the negative electrode, thus achieving a systematic solution to the high-temperature failure problem of LMFP batteries.

[0049] Figure 6 For comparison of low-temperature performance, Comparative Example 2 ( The battery (system) exhibits a significant decrease in discharge capacity, a marked drop in discharge plateau voltage, and a relatively high polarization voltage at -20°C. This is mainly due to... The ionic conductivity of the base electrolyte decreases significantly at low temperatures, and the interfacial impedance increases. The battery in Comparative Example 1 (LiFSI system, without TTMS) almost cannot discharge normally at -20°C, exhibiting extremely low discharge capacity. This is because the corrosion of the aluminum foil by LiFSI leads to a sharp increase in the battery's internal resistance, and the lack of a stable interfacial film severely hinders ion transport at low temperatures. In contrast, the battery using Example 1 of this invention maintains a high discharge capacity at -20°C, with a high and stable discharge plateau voltage and a low polarization voltage, demonstrating excellent low-temperature discharge performance.

[0050] In summary, the present invention achieves significant technical effects in inhibiting aluminum foil corrosion, improving high-temperature cycling stability, enhancing high-temperature storage performance, improving low-temperature performance, reducing gas generation, and inhibiting the dissolution of transition metal ions through the synergistic effect of LiFSI and asymmetric fluorosulfonates TTMS / TTPS, fully verifying the advanced nature and inventiveness of the technical solution of the present invention.

[0051] The technical solution of the present invention has been described above in conjunction with specific embodiments. However, it should be noted that the above descriptions are only for explaining the solution of the present invention and should not be construed as a specific limitation on the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can conceive of other specific embodiments or equivalent substitutions of the present invention without creative effort, and all such embodiments or substitutions will fall within the scope of protection of the present invention.

Claims

1. An electrolyte for lithium iron phosphate batteries, comprising lithium salt, a non-aqueous solvent, and additives, characterized in that, The non-aqueous solvent includes an asymmetric fluorosulfonate compound, which is one or more of the compounds represented by the following general formula (I); the additive is a carbonate additive and / or a nitrile additive: （I） in, Selected from fluoroalkyl groups with 1-4 carbon atoms, and and The carbon chain length difference of the groups is greater than or equal to 1 carbon atom, and the dipole moment of the asymmetric fluorosulfonate compound is in the range of 3.2-4.5D.

2. The electrolyte for lithium iron phosphate batteries according to claim 1, characterized in that, The asymmetric fluorosulfonate compound is 2,2,2-trifluoroethyltrifluoromethane sulfonate and / or 2,2,2-trifluoroethyltrifluoropropane sulfonate.

3. The electrolyte for lithium iron phosphate batteries according to claim 1, characterized in that, The asymmetric fluorosulfonate compound accounts for 5% to 15% of the solvent volume of the electrolyte.

4. The electrolyte for lithium iron phosphate batteries according to claim 1, characterized in that, The non-aqueous solvent also includes a carbonate solvent, which is any one or a mixture of two or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

5. The electrolyte for lithium iron phosphate batteries according to claim 1, characterized in that, The concentration of the lithium salt in the electrolyte is 0.8–1.2 mol / L.

6. The electrolyte for lithium iron phosphate batteries according to any one of claims 1-5, characterized in that, The carbonate additive is at least one of vinylene carbonate, fluoroethylene carbonate, and vinyl ethylene carbonate; the nitrile additive is at least one of adiponitrile, succinic anion, benzonitrile, hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, and ethylene glycol bis(propionitrile) ether; the additive accounts for 0.5% to 5% of the mass percentage of the electrolyte.

7. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte for lithium manganese iron phosphate batteries as described in any one of claims 1-6.

8. The lithium-ion battery according to claim 7, characterized in that, The positive electrode material of the lithium-ion battery is lithium manganese iron phosphate. , where 0.5 < x < 0.

8.

9. The lithium-ion battery according to claim 7 or 8, characterized in that, The negative electrode material of the lithium-ion battery is one of graphite, silicon carbide, silicon suboxide, or metallic lithium.

10. The lithium-ion battery according to claim 7, characterized in that, The lithium-ion battery has an upper limit of operating voltage of 4.3V, a lower limit of discharge voltage of 2.5V, and an operating temperature range of -20~70℃.

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