Electrolyte for lithium-rich manganese-based lithium-ion batteries

Abstract

The present application relates to a kind of electrolyte for lithium-rich manganese-based lithium ion battery, to solve the problem of lithium ion battery electrolyte and lithium ion battery voltage drop and cycle attenuation too fast, the present application uses a kind of lithium-rich manganese-based lithium ion battery for high-pressure electrolyte, including electrolyte lithium salt, non-aqueous organic solvent and additive, wherein non-aqueous organic solvent is the mixture of carbonate, fluorinated carbonate and fluorine ether, additive includes the lithium salt derivative of lithium-containing vinyl malonic acid borate and lithium tetrafluorophosphate oxalate phosphate.This lithium ion battery electrolyte can inhibit the voltage drop of lithium-rich manganese battery under high voltage, improve the cycle life of battery, reduce the thickness expansion of battery, the development of the present application provides the basis for commercial application of lithium-rich manganese battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-rich manganese-based lithium-ion battery technology, and specifically relates to an electrolyte for lithium-rich manganese-based lithium-ion batteries. Background Technology

[0002] The continuous innovation of new energy technologies has provided a powerful impetus for sustainable economic development. Among them, lithium-ion batteries have become a representative of new energy technologies due to their advantages such as high energy density, good cycle performance, high safety and reliability, and strong environmental adaptability. They are widely used in various mobile tools, automobiles, equipment drives, and energy storage.

[0003] Lithium-rich manganese cathode material (LMCM) is known for its high specific capacity (>250 mAh·g). -1 With its advantages such as high efficiency and low cost, lithium-rich manganese-based cathode material is considered the most promising next-generation lithium-ion battery cathode material. However, this cathode material suffers from irreversible structural transformation, reactive oxygen evolution, and electrolyte oxidative decomposition under high voltage during cycling with existing conventional electrolytes. This results in high initial irreversible capacity loss, poor rate performance, energy decay, and voltage decay, hindering the development and further commercial application of lithium-rich manganese-based lithium-ion batteries. Therefore, it is necessary to develop electrolytes that are beneficial to the performance of lithium-rich manganese-based lithium-ion batteries for lithium-rich manganese cathode materials. Summary of the Invention

[0004] The purpose of this invention is to provide an electrolyte for lithium-rich manganese-based lithium-ion batteries, so as to improve the electrochemical performance and service life of lithium-rich manganese-based lithium-ion batteries.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] An electrolyte for lithium-rich manganese-based lithium-ion batteries comprises an electrolyte lithium salt, a non-aqueous organic solvent, and additives. The non-aqueous organic solvent is a mixture of carbonates, fluorocarbonates, and fluoroethers. The additives include a vinyl-containing lithium malonate borate derivative and lithium tetrafluorooxalate phosphate. The structure of the vinyl-containing lithium malonate borate derivative is shown in general formulas A and / or B.

[0007]

[0008] R1, R2, R3, R4, and R5 are independently selected from H, halogen atoms, alkyl groups with 1-3 carbon atoms that are not substituted or substituted with fluorine atoms, alkoxy groups with 1-3 carbon atoms, or cyano groups.

[0009] Preferably, the volume ratio of the carbonates, fluorocarbonates and fluoroethers is (2.5-8):1:(1.5-5).

[0010] More preferably, the volume ratio of the carbonates, fluorocarbonates and fluoroethers is (4-8):1:(2-4).

[0011] More preferably, the volume ratio of the carbonates, fluorocarbonates and fluoroethers is (5-8):1:(2-3).

[0012] Preferably, the carbonate is one or more of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0013] Preferably, the fluorocarbonate is one or more of fluoroethylene carbonate, difluoroethylene carbonate, and tetrafluoroethylene carbonate.

[0014] Preferably, the fluoroether is one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, or 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0015] According to some specific embodiments, the non-aqueous organic solvent is dimethyl carbonate, fluoroethylene carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a volume ratio of (4-8):1:(1-4).

[0016] Preferably, the mass of the vinyl-containing lithium malonate borate derivative is 0.1% to 8% of the total mass of the electrolyte.

[0017] More preferably, the mass of the vinyl-containing lithium malonate borate derivative accounts for 0.1% to 5% of the total mass of the electrolyte.

[0018] More preferably, the mass of the vinyl-containing lithium malonate borate derivative is 0.1% to 3% of the total mass of the electrolyte.

[0019] More preferably, the mass of the vinyl-containing lithium malonate borate derivative accounts for 1% to 2% of the total mass of the electrolyte.

[0020] Preferably, the mass of the lithium tetrafluorooxalate phosphate is 0.5% to 5% of the total mass of the electrolyte.

[0021] More preferably, the mass of the lithium tetrafluorooxalate phosphate accounts for 0.5% to 2% of the total mass of the electrolyte.

[0022] More preferably, the lithium tetrafluorooxalate phosphate is fed into the electrolyte at a mass of 1% to 2% of the total mass.

[0023] Preferably, the mass ratio of the vinyl-containing lithium malonate borate derivative to lithium tetrafluorooxalate phosphate is 1:(0.3-5).

[0024] More preferably, the mass ratio of the vinyl-containing lithium malonate borate derivative to lithium tetrafluorooxalate phosphate is 1:(0.3-4).

[0025] More preferably, the mass ratio of the vinyl-containing lithium malonate borate derivative to lithium tetrafluorooxalate phosphate is 1:(0.5-2).

[0026] Preferably, the lithium salt is LiPF6 and other lithium salts, wherein the other lithium salts are at least one of LiBF4, LiClO4, LiTFSI, and LiFSI.

[0027] Preferably, the concentration of the lithium salt in the electrolyte is 1 to 3 mol / L, for example, 1 mol / L, 1.5 mol / L, 21 mol / L, 2.5 mol / L, or 3 mol / L.

[0028] Preferably, the concentration ratio of LiPF6 to other lithium salts is (2-8):1.

[0029] More preferably, the concentration ratio of LiPF6 to other lithium salts is (3-5):1.

[0030] More preferably, the concentration ratio of LiPF6 to other lithium salts is (4-5):1.

[0031] According to some specific and preferred embodiments, the other lithium salt is LiTFSI and / or LiFSI.

[0032] Preferably, the additive further includes other additives, which are one or more of the following: succinate, adiponitrile, 1,3-propanesulfonate lactone, vinyl sulfate, methylene disulfonate, propylene sulfate, tris(trimethylsilane)borate, tris(trimethylsilyl)phosphite, tris(trimethylsilyl)phosphate, ethylene carbonate, maleic anhydride, and glutaric anhydride.

[0033] More preferably, the other additives are added at a mass of 0.01% to 5% of the total mass of the electrolyte, for example, 0.01%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 0.5%.

[0034] According to some embodiments, the other additive is a combination of trimethylsilyl phosphate and any one or more of glutaric anhydride, vinylene carbonate, and lithium bis(oxalato)fluorophosphate.

[0035] A second aspect of the present invention further provides a lithium-rich manganese-based lithium-ion battery, including a positive electrode, a separator, a negative electrode, and an electrolyte. The electrolyte is the electrolyte for the lithium-rich manganese-based lithium-ion battery described above.

[0036] Preferably, the positive electrode includes a positive electrode active material, and the positive electrode active material is xLi2MnO3·(1-x)LiMO2, where 0 < x < 1, and M = Ni, Co, Mn, and combinations thereof. The negative electrode includes a negative electrode active material, and the negative electrode active material is graphite and / or silicon, silicon oxide materials.

[0037] In the present invention, the method of manufacturing the lithium-ion battery cell is winding or stacking.

[0038] According to a specific embodiment, the lithium-ion battery is a lithium-rich manganese-based positive electrode and graphite negative electrode battery.

[0039] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0040] The electrolyte for the lithium-rich manganese-based lithium-ion battery of the present invention has excellent high-temperature resistance performance, can inhibit the voltage drop of the lithium-rich manganese battery under high voltage, improve the cycle life of the lithium-rich manganese battery, reduce the thickness expansion of the lithium-rich manganese battery, provide a basis for the commercial application of the lithium-rich manganese battery, and has broad application prospects. Specific Embodiments

[0041] Although the lithium-rich manganese positive electrode material has the advantages of high specific capacity and low cost, due to some intractable problems of the lithium-rich manganese positive electrode material itself, the lithium-rich manganese battery using the existing conventional electrolyte has a voltage drop under high voltage and too fast cycle attenuation, a short service life, and thus the commercial application process of the current lithium-rich manganese battery is slow. To solve the above problems, the present invention obtains an electrolyte that can inhibit the voltage drop of the lithium-rich manganese battery under high voltage, improve the cycle life of the battery, and reduce the thickness expansion of the battery by optimizing the selected solvents, additives, and lithium salts with appropriate dosage adjustments. The solution of the present invention is as follows:

[0042] The solvent used in the present invention is a mixture of carbonate esters, fluorinated carbonate esters, and fluoroethers in a certain volume ratio, which can improve the oxidation resistance of the electrolyte under high voltage, avoid the occurrence of excessive side reactions, reduce flammability, improve the safety performance of the battery, and at the same time reduce the overall viscosity of the electrolyte, improve the wetting of the electrode sheet, and increase the conductivity of the electrolyte.

[0043] The vinyl-containing lithium malonate borate derivatives used in this invention (lithium bis(vinylmalonic acid)borate and lithium 2-vinylmalonic acid difluoroborate) not only possess similar properties to lithium oxalate borate, namely similar conductivity and reduction potential, but also contain carbon-carbon double bonds in their structure. This allows them to cross-link during redox reactions at both the positive and negative electrodes, forming a denser and more ductile SEI film, thereby reducing the dissolution of metal ions from lithium-rich manganese materials. Alkenyl-substituted lithium malonate borate has a higher HOMO orbital density than lithium malonate borate, making it easier to bind oxygen released from lithium-rich manganese materials, reducing its oxidative decomposition of the electrolyte and ensuring stable battery cycling. Lithium tetrafluorooxalate phosphate (LiTFOP) can synergistically work with lithium bis(vinylmalonic acid)borate and / or lithium 2-vinylmalonic acid difluoroborate in the electrolyte to form a more stable SEI. It also improves battery shelf performance, reduces gas generation, and lowers impedance.

[0044] The composite lithium salt used in this invention can form a solid interface film rich in inorganic components such as LiF on the electrode surface, increasing the stability of the interface film. On the other hand, these two lithium salts have a high donor number and are easy to dissociate in the electrolyte, releasing more free lithium ions. Therefore, the conductivity of the electrolyte can be improved, avoiding excessive capacity loss of the battery when the current increases from small to large, which helps to improve the battery dynamic performance.

[0045] In the electrolyte of the present invention, the solvent components, additive components, composite lithium salt and the additives, after being appropriately proportioned, can exert their respective advantages and suppress their respective disadvantages. Through their synergistic effect, the lithium-rich manganese-based lithium-ion battery containing the electrolyte of the present invention has excellent cycle performance, thus having good application prospects.

[0046] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0047] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are conventional methods; the experimental materials used, unless otherwise specified, were purchased from conventional biochemical reagent manufacturers.

[0048] Example 1:

[0049] In a glove box filled with argon (water and oxygen content both less than 0.1 ppm), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were mixed in a volume ratio of 6:1:3. 0.9 M lithium hexafluorophosphate (LiPF6) and 0.2 M lithium bis(fluorosulfonyl)imide (LiFSi) were added to the mixed solution, and the mixture was stirred until homogeneous. Then, 1% (by mass) of lithium bis(vinylmalonic acid)borate (LiBMB-A), 2% (by mass) of lithium tetrafluoro(oxalate)phosphate (LiTFOP), 1% (by mass) of trimethylsilyl phosphate (TMSP), and 0.8% (by mass) of glutaric anhydride (GA) were added to obtain the electrolyte of Example 1.

[0050] The positive electrode, separator, and negative electrode are wound or stacked to form a battery cell, which is then installed in a battery casing. The lithium-ion battery electrolyte used in this embodiment is injected, and then formation, degassing, secondary sealing, and volume adjustment are performed according to conventional procedures to obtain the final lithium-ion battery. The positive electrode is Li... 1.13 Mn 0.517 Ni 0.256 Co 0.097 The O2 negative electrode is artificial graphite, the separator is a double-layer composite separator of polyethylene (PE) and polypropylene (PP), and the cell design capacity is 1000mAh.

[0051] Examples 2-16 and Comparative Examples 1-16:

[0052] In Examples 2-16 and Comparative Examples 1-16, the electrolyte solvent, electrolyte lithium salt and additive components were added in the proportions shown in Table 1, and all other components were the same as in Example 1.

[0053] Table 1

[0054]

[0055]

[0056] In Table 1, "%" represents mass percentage, and " / " indicates that it is not used.

[0057] DMC: Dimethyl carbonate; FEC: Fluorinated vinyl carbonate; HFE: 1,1,2,2-Tetrafluoroethyl-2,2,3,3-Tetrafluoropropyl ether; LiPF6: Lithium hexafluorophosphate; LiFSi: Lithium difluorosulfonylimide; LiBMB-A: Lithium bis(vinylmalonic acid)borate; LiBMB-B: Lithium difluoroborate of 2-vinylmalonic acid; LiBOB: Lithium dioxalate borate; LiTFOP: Lithium tetrafluoro(oxalate)phosphate; LiDFOP: Lithium difluorobis(oxalate)phosphate; TMSP: Trimethylsilyl phosphate; GA: Glutaric anhydride; DTD: Ethylene sulfate.

[0058] The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to performance tests. The test items and methods are as follows:

[0059] 400-cycle performance test at room temperature: Under room temperature conditions, charge at a rate of 0.5C, cut-off current of 0.02C, discharge at a rate of 0.5C, voltage range of 2.0-4.8V, cycle for 5 cycles, and record the battery thickness as T1. Then cycle for 400 cycles under the above conditions and record the battery thickness as T2.

[0060] Room temperature cycle capacity retention rate = discharge capacity at 400 cycles at room temperature / discharge capacity at the first cycle at room temperature × 100%.

[0061] Thickness expansion rate = (T2-T1) / T1×100%.

[0062] Voltage drop test: At room temperature, charge at a rate of 0.5C with a cutoff current of 0.02C, discharge at a rate of 0.5C with a voltage range of 2.0-4.8V, cycle under these conditions for 5 weeks, then charge at a rate of 0.5C to 4.8V with a cutoff current of 0.02C, and leave at room temperature for 48 hours. Then test the battery voltage and record it as V1.

[0063] Voltage drop = 4.8 - V1, in volts.

[0064] The relevant test results are shown in Table 2:

[0065] Table 2

[0066]

[0067]

[0068] The data in the table above shows that, for the lithium-rich manganese-based high-voltage 4.8V battery system combined with graphite, compared to the traditional carbonate electrolyte (Comparative Example 1), the solvent system in this embodiment shows better compatibility between the electrolyte and the high-voltage cathode material, significantly reducing gas generation behavior. The solvent system in this embodiment also exhibits better high-voltage tolerance, effectively suppressing electrolyte side reactions, particularly inhibiting the increase in battery thickness caused by the oxidative decomposition of solvents such as EC leading to an increase in SEI film thickness. Furthermore, it significantly helps reduce the full-charge voltage drop and improve cycle performance. Further, the combination and ratio of solvents in this invention have a significant impact on battery performance. As can be seen from Examples and Comparative Examples 7-14, batteries with DMC / FEC and TTE / FEC solvent combinations exhibit poor cycle performance and expansion. In addition, this invention has also optimized the solvent system formulation in detail, with results showing that the battery cycle performance is optimal when the ratio of DMC, FEC, and HFE is 6:1:3. Simulation calculations of the radial distribution function of the electrolytes show that the total coordination number of lithium ions in the solvated structures of Comparative Examples 2 to 4 is approximately 5. However, at a ratio of 6:1:3, the solvated structure contains a significant amount of PF6. - The anion concentration is approximately 0.7, while in other solvated structures it is only 0.4, indicating a higher concentration of PF6. - Entering the solvation shell can greatly improve the stability of the electrolyte.

[0069] In this invention, LiPF6 and LiFSi are added together as electrolyte lithium salts in the electrolyte, which can improve the kinetic performance of the electrolyte and alleviate, to some extent, the irreversible capacity loss caused by the poor rate performance of lithium-rich manganese-based materials.

[0070] The lithium bis(vinylmalonic acid)borate (LiBMB-A) and lithium 2-vinylmalonic acid difluoroborate (LiBMB-B) used in this invention not only possess properties similar to lithium borate oxalate, namely similar conductivity and reduction potential, but also contain carbon-carbon double bonds in their structure. This allows them to cross-link during redox reactions at both the positive and negative electrodes, forming a denser and more ductile SEI film, thereby reducing the dissolution of metal ions in lithium-rich manganese materials. Furthermore, the alkenyl-substituted lithium malonate borate, compared to lithium oxalate... Lithium borate has higher HOMO orbitals, making it easier to bind oxygen released from lithium-rich manganese materials, reducing its oxidative decomposition on the electrolyte and ensuring stable battery cycling. Lithium tetrafluorooxalate phosphate (LiTFOP) can synergistically work with lithium bis(vinylmalonic acid)borate (LiBMB-A) and / or lithium difluoroborate 2-vinylmalonic acid (LiBMB-B) in the electrolyte to form a more stable SEI. At the same time, it also improves the battery's shelf life, reduces gas generation, and lowers impedance.

[0071] As can be seen from Examples 1-16, the electrolyte performance is better when the mass ratio of LiBMB-A or LiBMB-B to LiTFOP is 1:0.3 to 1:4, and the mass percentage of LiBMB-A or LiBMB-B is in the range of 0.5% to 3%, while the mass percentage of LiTFOP is in the range of 0.5% to 2%. If the amount added is too small, the additive's performance cannot be fully realized; if the amount added is too large, it will increase the battery impedance, thus causing a decrease in cycle performance. Therefore, there is an optimal value for the amount of additive added. The most preferred amounts of LiBMB-A and LiTFOP, and LiBMB-B and LiTFOP, are 1% and 2%, and 1% and 1%, respectively.

[0072] This invention also explores the combination of other additives, such as the simultaneous addition of TMSP and GA, LiDFOP and any one of DTD. The results show that, based on the electrolyte of this invention, the combination of other additives also enables the battery to have good performance.

[0073] Through the above embodiments and comparative experiments, it can be found that the battery using the lithium-rich manganese-based cathode material with the electrolyte of the present invention can operate normally in a high-voltage system, and suppresses the amount of gas generated by the battery during cycling, effectively reducing the degree of battery expansion, and also has a good effect on improving the voltage drop of the battery.

[0074] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes made in accordance with the spirit and essence of the present invention are excluded.

Claims

1. An electrolyte for a lithium-rich manganese-based lithium-ion battery, comprising an electrolyte lithium salt, a non-aqueous organic solvent and an additive, characterized in that: The non-aqueous organic solvent is a mixture of carbonates, fluorinated carbonates and fluorinated ethers, the additive includes a lithium salt derivative of a vinyl-containing malonic acid borate and lithium tetrafluoro oxalate phosphate, the lithium salt derivative of the vinyl-containing malonic acid borate has a structure as shown in general formula A and / or B: ， wherein R1, R2, R3, R4, R5 are independently selected from H, a halogen atom, an alkyl group with 1-3 carbon atoms which is unsubstituted or substituted by a fluorine atom, an alkoxy group with 1-3 carbon atoms, or a cyano group, The volume ratio of the carbonates, fluorinated carbonates and fluorinated ethers is (2.5-8):1:(1.5-5).

2. The electrolyte for a lithium-rich manganese-based lithium-ion battery according to claim 1, characterized in that: The carbonates are one or more of vinyl carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, the fluorinated carbonates are one or more of vinyl fluoride carbonate, difluorovinyl carbonate, tetrafluorovinyl carbonate, and the fluorinated ethers are one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

3. The electrolyte for a lithium-rich manganese-based lithium-ion battery according to claim 1, characterized in that: The feeding mass of the lithium salt derivative of the vinyl-containing malonic acid borate accounts for 0.1%-8% of the total mass of the electrolyte, and the feeding mass of the lithium tetrafluoro oxalate phosphate accounts for 0.5%-5% of the total mass of the electrolyte.

4. The electrolyte for a lithium-rich manganese-based lithium-ion battery according to claim 3, characterized in that: The feeding mass ratio of the lithium salt derivative of the vinyl-containing malonic acid borate to the lithium tetrafluoro oxalate phosphate is 1:(0.3-5).

5. The electrolyte for a lithium-rich manganese-based lithium-ion battery according to claim 1, characterized in that: The lithium salt is LiPF6 and other lithium salts, the other lithium salts are at least one of LiBF4, LiClO4, LiTFSI, and LiFSI; and / or, the concentration of the lithium salt in the electrolyte is 1-3 mol / L; and / or the concentration ratio of the LiPF6 and other lithium salts is (2-8):

1.

6. The electrolyte for a lithium-rich manganese-based lithium-ion battery according to claim 5, characterized in that: The other lithium salts are LiTFSI and / or LiFSI.

7. The electrolyte for a lithium-rich manganese-based lithium-ion battery according to claim 1, characterized in that: The additive further includes other additives, the other additives are one or more of butanedinitrile, hexanedinitrile, 1,3-propanesultone, ethylene sulfate, methyl bisulfonate methylene ester, propylene sulfate, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, vinyl ethylene carbonate, maleic anhydride, and glutaric anhydride; and / or, the feeding mass of the other additives accounts for 0.01%-5% of the total mass of the electrolyte.

8. A lithium-rich manganese-based lithium-ion battery comprising a positive electrode, a separator, a negative electrode, and an electrolyte, characterized in that, The electrolyte is the electrolyte for a lithium-rich manganese-based lithium ion battery according to any one of claims 1-7.

9. The lithium-rich manganese-based lithium-ion battery of claim 8, wherein, The positive electrode includes a positive electrode active material, the positive electrode active material is xLi2MnO3·(1-x)LiMO2, wherein 0 The negative electrode includes a negative electrode active material, the negative electrode active material is graphite.

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