High-rate-performance electrolyte for lithium-rich manganese and preparation method and application of high-rate-performance electrolyte

Abstract

The invention discloses a lithium-manganese-rich high-rate-performance electrolyte and a preparation method and application thereof. The lithium-manganese-rich high-rate-performance electrolyte comprises a lithium salt, an organic solvent and an additive, the additive is 2, 3-bis (trifluoromethyl) propynyl sulfate. According to the electrolyte disclosed by the invention, a compact and uniform CEI film is formed on the surface of a positive electrode, electrolyte oxidation and metal ion dissolution are inhibited, the cycle stability of the battery is improved, the overall oxidation resistance is improved, three-dimensional positive and negative electrode film layers are formed during film forming, and the mechanical strength is improved; the first discharge efficiency and discharge capacity of the lithium ion battery can be obviously improved, the high-temperature cycle performance is also obviously improved, side reactions are prevented, dissolution of transition metal ions is inhibited, and the cycle stability is improved. According to the invention, the growth of lithium dendrites can be effectively inhibited, the battery safety is improved, the electrolyte impedance is reduced, the battery rate and high-low temperature performance are improved, the side reaction with the electrolyte is reduced, the dissolution of transition metal ions at the positive electrode side is inhibited, the gas production rate of the system is reduced, and the cycle life is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology and relates to lithium-ion battery electrolytes, specifically a high-rate performance electrolyte for lithium-manganese-rich batteries, its preparation method, and its application. Background Technology

[0002] With the continuous development of new energy technologies, lithium-ion batteries, as a highly efficient and rechargeable energy storage device, have been widely used in many fields such as portable electronic devices, electric vehicles, and large-scale energy storage systems. Among the many cathode materials for lithium-ion batteries, lithium-rich manganese-based cathode materials have attracted much attention due to their numerous significant advantages. They possess a theoretical specific capacity as high as 250-300 mAh / g, far exceeding traditional cathode materials such as lithium cobalt oxide (theoretical specific capacity of approximately 170 mAh / g) and lithium iron phosphate (theoretical specific capacity of approximately 170 mAh / g). This means that batteries using lithium-rich manganese-based cathode materials can store more electrical energy, thereby providing longer-lasting power support for various high-energy-consuming devices and meeting people's demand for long-range driving capabilities.

[0003] However, lithium-rich manganese-based cathode materials have also revealed some problems that urgently need to be solved in practical applications, among which poor rate performance is particularly prominent. Under high-current charge and discharge conditions, their capacity is severely limited, and they cannot maintain a relatively high capacity level at high rates like some traditional cathode materials. This is mainly due to the following reasons: On the one hand, from the perspective of the intrinsic properties of materials, lithium-rich manganese-based cathode materials have a relatively complex crystal structure. During the charging and discharging process, the insertion and extraction of lithium ions requires a long diffusion path. This makes it difficult for lithium ions to be transported quickly inside the cathode material during high current and high rate charging and discharging, which greatly reduces the overall rate performance of the battery. On the other hand, the interaction between the electrolyte and the lithium-rich manganese-based cathode material also has a significant impact on rate performance. Under high voltage, traditional electrolytes use high-fluorine or perfluorinated solvents, resulting in low overall conductivity. At the same time, in order to ensure that the electrolyte system can withstand high voltage, traditional film-forming additives (such as TPP and PS types) have high film-forming impedance, which further affects the rate performance and cycle stability of the battery.

[0004] Currently, although some research is dedicated to improving the rate performance of lithium-rich manganese-based cathode materials, such as by optimizing the structure of the material itself and surface coating, these methods often have problems such as complex processes, high costs, and limited improvement in material performance. Summary of the Invention

[0005] From an electrolyte perspective, developing an electrolyte that is well-suited to lithium-rich manganese-based cathode materials and can significantly improve their rate performance is of great practical significance for promoting the development of lithium-rich manganese-based lithium-ion batteries in high-performance applications. Based on this market demand and industry background, this invention proposes an electrolyte solution specifically designed for lithium-rich manganese-based cathode materials that can effectively improve their rate performance.

[0006] The present invention adopts the following technical solution:

[0007] A high-rate performance electrolyte for lithium-rich manganese comprises a lithium salt, an organic solvent, and an additive; the additive is 2,3-bis(trifluoromethyl)propynyl sulfate.

[0008] The above-mentioned method for preparing a high-rate performance electrolyte for lithium-rich manganese includes the following steps: mixing components including lithium salt, organic solvent and additives to obtain a high-rate performance electrolyte for lithium-rich manganese.

[0009] Preferably, lithium salt, organic solvent and additives are mixed to obtain a high-rate performance electrolyte for lithium-rich manganese; that is, the high-rate performance electrolyte for lithium-rich manganese of the present invention is composed of lithium salt, organic solvent and additives.

[0010] In this invention, lithium salts include LiPF6, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, and Li2B. 10 Cl 10 At least one of lithium chloroborane, lithium tetrafluorooxalate phosphate, and lithium trioxalate phosphate; preferably, the lithium salt is LiPF6.

[0011] In this invention, the organic solvent includes one or more of chain carbonates, carboxylic acid ester solvents, and ether solvents; in some embodiments, the chain carbonate may specifically be, but is not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), and ethylene carbonate (EC); in some embodiments, the carboxylic acid ester solvent includes cyclic carboxylic acid esters and / or chain carbonates. Examples of cyclic carboxylic acid esters include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone, and examples of chain carbonates include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0012] In some embodiments, chain carbonates having fluorine atoms may also be used. There is no particular limitation on the number of fluorine atoms, as long as there is one or more, such as four or less. These fluorine atoms can be bonded to the same carbon atom or to different carbon atoms. Examples of fluorinated chain carbonates include dimethyl fluoride derivatives, methyl ethyl fluoride derivatives, and diethyl fluoride derivatives.

[0013] Preferably, the organic solvent of the present invention is fluorine-free.

[0014] Preferably, the lithium salt of the present invention is lithium hexafluorophosphate, and the organic solvent is a mixture of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethylene carbonate (EC).

[0015] In this invention, the total mass of lithium salt, organic solvent and additives is 100%, wherein the mass percentage of lithium salt is 10-15%, the mass percentage of additives is 0.3-5%, and the balance is organic solvent.

[0016] Preferably, the total mass of lithium salt, organic solvent, and additives is 100%, wherein the mass percentage of lithium salt is 11-14%, the mass percentage of additives is 1-4%, and the balance is organic solvent. As an example, the mass percentage of additives is 1.5%, 1.8%, 2%, 2.5%, 2.8%, 3%, 3.5%, 3.8%, or any percentage within that range.

[0017] This invention discloses a lithium-ion battery comprising the above-mentioned high-rate performance electrolyte for lithium-rich manganese.

[0018] This invention discloses the application of the above-mentioned high-rate performance electrolyte for lithium-manganese enrichment in the preparation of lithium-ion batteries.

[0019] This invention discloses the application of the above-mentioned high-rate performance electrolyte for lithium-rich manganese in improving the rate cycle performance of lithium-rich manganese-based cathode materials.

[0020] This invention discloses the application of 2,3-bis(trifluoromethyl)propynyl sulfate in the preparation of lithium-ion battery electrolytes.

[0021] In this invention, the lithium-ion battery includes a lithium-rich manganese-based cathode material, which is a conventional product.

[0022] Existing high-voltage lithium-rich manganese electrolytes typically employ a high proportion of fluorinated solvents with a small amount of high-voltage additives. High-proportion fluorinated solvents are costly and may decompose into HF at high temperatures. HF damages the CEI film, leading to the dissolution of metal ions from the positive electrode, resulting in increased self-discharge and poor high-temperature performance. Conventional TPP / PS type additives contain sulfur-containing additives, and benzene rings and methane sulfonates exhibit high film-forming resistance at the positive electrode. Meanwhile, DTD type salts containing sulfates are difficult to synthesize with high purity, resulting in poor storage performance. The electrolyte disclosed in this invention forms a dense and uniform CEI film on the positive electrode surface, inhibiting electrolyte oxidation and metal ion dissolution, improving battery cycle stability, and enhancing overall oxidation resistance. During film formation, it creates three-dimensional positive and negative electrode layers, improving mechanical strength. It can also form a Li2S-rich SEI film on the negative electrode side, improving ionic conductivity and interfacial stability. This significantly improves the initial discharge efficiency and discharge capacity of lithium-ion batteries, and also significantly improves high-temperature cycle performance, preventing side reactions and inhibiting transition metal ion dissolution, thus enhancing cycle stability. Film formation at both positive and negative electrodes: preferential reduction and decomposition on the negative electrode surface to form a LiF-rich SEI film, which can effectively inhibit lithium dendrite growth, improve battery safety, reduce electrolyte resistance, and improve battery rate and high and low temperature performance; a fluorine-rich positive electrode interface can also be formed on the positive electrode side, reducing side reactions with the electrolyte, inhibiting the dissolution of transition metal ions on the positive electrode side, reducing gas production in the system, and increasing cycle life. Detailed Implementation

[0023] This invention discloses a high-rate electrolyte for lithium-rich manganese-based cathode materials, comprising a lithium salt, an organic solvent, and additives. The lithium salt is lithium hexafluorophosphate, with a mass ratio of 10-15%. The organic solvent is a mixture of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethylene carbonate (EC) in a specific volume ratio. The additives include a novel functional group additive at a mass ratio of 0.5-4%, specifically 2,3-bis(trifluoromethyl)propynyl sulfate, with the following structural formula:

[0024] The following specific experiments illustrate the technological advancements of this invention. The raw materials used are existing products, and the specific preparation operations and performance testing are conventional techniques. The lithium-rich manganese is LR-7M2-B, sourced from DangSheng Technology; the 2,3-bis(trifluoromethyl)propynyl sulfate is from Suzhou QiTian New Materials. Example 1

[0025] A high-rate performance electrolyte for lithium-rich manganese is composed of lithium salt, organic solvent and additive; the additive is 2,3-bis(trifluoromethyl)propynyl sulfate.

[0026] According to the composition in Table 1, lithium hexafluorophosphate, 2,3-bis(trifluoromethyl)propynyl sulfate, and organic solvent were mixed to obtain the electrolyte. Example 2

[0027] The conventional method for battery fabrication is briefly described below: (1) Preparation of positive electrode A positive electrode slurry (68% solid content) was prepared by stirring and dispersing 1.5 wt% conductive carbon, 0.7 wt% KS-6, 1.5 wt% polyvinylidene fluoride, and the balance lithium-rich manganese (the sum of the mass percentages of the four components being 100%) in N-methylpyrrolidone. This slurry was coated onto a 15 μm aluminum foil current collector, and then cold-pressed, slit, and cut to obtain the positive electrode sheet. The coating density was 15 g / cm³ on one side of the positive electrode. 2 .

[0028] (2) Preparation of negative electrode sheet A negative electrode slurry (60% solid content) was prepared by mixing 1.5 wt% conductive carbon black, 1.0 wt% carboxymethyl cellulose, 1.5 wt% styrene-butadiene rubber, and the balance graphite (the sum of the mass percentages of the four components is 100%) with deionized water. This slurry was coated onto an 8 μm copper foil current collector, and after cold pressing, slitting, and cutting, the negative electrode sheet was obtained. The coating density was 7 g / cm³ on one side of the negative electrode. 2 .

[0029] (3) Electrolyte preparation According to Table 1, lithium salt LiPF6 and additive 2,3-bis(trifluoromethyl)propynyl sulfate were added to the mixed solvent and stirred normally to obtain the electrolyte.

[0030] (4) A 16μm thick polyethylene microporous membrane coated with an alumina coating is selected, which is a conventional product.

[0031] (5) Preparation of lithium-ion batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The stacked electrodes form a bare cell, which is then inserted into the cell casing. The lithium-ion battery is obtained through existing processes such as baking, electrolyte injection, formation, and sealing.

[0032] This invention discloses a high-rate-performance electrolyte for lithium-rich manganese used in a 4.6V lithium-rich manganese battery system. A pouch lithium battery was prepared using this high-rate-performance electrolyte. The lithium battery was subjected to rate performance and EIS testing after formation and capacity testing. A control group was prepared using a scheme without the addition of 2,3-bis(trifluoromethyl)propynyl sulfate and existing conventional fluorinated systems.

[0033] Rate performance test: The battery is fully charged to 4.6V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C; then discharged to 2.5V at a current of 0.5 / 1 / 1.5C; the discharge capacity is recorded.

[0034] Loop testing: Performance test at room temperature (25℃): In a constant temperature test chamber, the test temperature is 25℃. Charge to 4.6V with constant current and constant voltage at 0.5C, with the current less than 0.05C. After resting for 5 minutes, discharge to 2.5V with constant current at 0.5C. Cycle 100 times. Record the discharge capacity C1 of the first 1C cycle and the discharge capacity C2 of the 100th cycle in steps. Calculate the capacity retention rate at room temperature cycle = C2 / C1*100%.

[0035] High temperature (45℃) performance test: In a constant temperature test chamber, the test temperature is 45℃. Charge to 4.6V with constant current and constant voltage at 0.5C, and the current is less than 0.05C. After resting for 5 minutes, discharge to 2.5V with constant current at 0.5C. Cycle 100 times. Record the discharge capacity C3 of the first 1C cycle and the discharge capacity C4 of the 100th cycle in steps. The capacity retention rate at 55℃ cycle = C4 / C3*100%.

[0036] EIS test Charge the battery to 4.4V at a constant current and constant voltage of 0.5C, with the current being less than 0.05C.

[0037] Set the parameters of the Zahner electrochemical workstation and scan the battery EIS. Then export the scanned data, import it into the Zview device for fitting, and export the electrochemical impedance spectroscopy.

[0038] Test results: After testing the performance of the electrolyte of this invention, the rate capability was significantly improved, the impedance was significantly reduced, and the cycle life was improved.

[0039] Table 1. Effects of different contents of novel additive components on battery cycle and storage performance.

[0040] Vinyl sulfate (DTD), tripropynyl phosphate (TPP), and tetravinylsilane (TVSi) are existing products.

[0041] Table 2. EIS electrochemical impedance data of all-electric cells

[0042] Table 3. Cyclic Retention Rate at Normal (25℃) / High (45℃) Temperature

[0043] Comparative Example 4 The electrolyte consists of 13 wt% lithium hexafluorophosphate, 84 wt% organic solvent and 3 wt% fluoroethylene carbonate (FEC). The organic solvent is composed of DEC:EMC:EC in a volume ratio of 6:2:2. A soft-pack lithium battery was prepared according to Example 2, and the high-temperature cycling retention rate (100 cycles) was 32.7%.

[0044] Comparative Example 5 The electrolyte consists of 13 wt% lithium hexafluorophosphate and 87 wt% organic solvent, which is composed of DEC:EMC:EC in a volume ratio of 6:2:2. The soft-pack lithium battery prepared according to Example 2 has poor performance and is significantly inferior to Comparative Example 1.

[0045] Comparison Example The mainstream lithium-rich manganese soft-pack lithium batteries with the largest market share mainly use lithium hexafluorophosphate and organic solvents as electrolytes. In actual tests, the high-temperature cycle retention rate (100 cycles) is between 53% and 60%, and the 1.5C / 0.5C retention rate is between 91% and 92.5%.

[0046] From an electrolyte perspective, developing an electrolyte that is well-suited to lithium-rich manganese-based cathode materials and can significantly improve their rate performance is of great practical significance for promoting the development of lithium-rich manganese-based lithium-ion batteries in high-performance applications. Based on this market demand and industry background, this invention proposes an electrolyte solution specifically designed for lithium-rich manganese-based cathode materials that can effectively improve their rate performance.

Claims

1. A high-rate performance electrolyte for lithium-rich manganese, characterized in that, It includes lithium salt, organic solvent and additive; the additive is 2,3-bis(trifluoromethyl)propynyl sulfate.

2. The high-rate performance electrolyte for lithium-rich manganese according to claim 1, characterized in that, Lithium salts include LiPF6, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, and Li2B. 10 Cl 10 At least one of lithium chloroborane, lithium tetrafluorooxalate phosphate, and lithium trioxalate phosphate; the organic solvent includes one or more of chain carbonates, carboxylic acid ester solvents, and ether solvents.

3. The high-rate performance electrolyte for lithium-rich manganese according to claim 1, characterized in that, The total mass of lithium salt, organic solvent, and additives is 100%, of which lithium salt accounts for 10-15% by mass, additives account for 0.3-5% by mass, and the balance is organic solvent.

4. The method for preparing the high-rate performance electrolyte for lithium-rich manganese as described in claim 1, characterized in that, The components, including lithium salt, organic solvent and additives, are mixed to obtain a high-rate performance electrolyte for lithium-rich manganese.

5. The method for preparing the high-rate performance electrolyte for lithium-rich manganese according to claim 4, characterized in that, A high-rate performance electrolyte for lithium-rich manganese is obtained by mixing lithium salt, organic solvent and additives.

6. A lithium-ion battery, characterized in that, Includes the high-rate performance electrolyte for lithium-rich manganese as described in claim 1.

7. The lithium-ion battery according to claim 6, characterized in that, Lithium-ion batteries include lithium-rich manganese-based cathode materials.

8. The application of the lithium-rich manganese high-rate electrolyte of claim 1 in the preparation of lithium-ion batteries.

9. The application of the high-rate performance electrolyte for lithium-rich manganese as described in claim 1 in improving the rate cycle performance of lithium-rich manganese-based cathode materials.

10. Application of 2,3-bis(trifluoromethyl)propynyl sulfate in the preparation of lithium-ion battery electrolytes.

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