Electrolyte and semi-solid batteries

Abstract

The present invention belongs to the field of batteries, and specifically relates to an electrolyte and a semi-solid-state battery. The electrolyte comprises a lithium salt, a solvent, and an additive; the additive comprises a solvent additive; the solvent additive comprises a low HOMO energy level solvent; preferably, the low HOMO energy level solvent is 2,2,2-trifluoroethanol (TFEA). The electrolyte of the present application, by using a low HOMO energy level solvent additive, can effectively improve the stability of the battery at high voltage, protect the electrolyte-electrode interface, inhibit transition metal dissolution, reduce electrolyte side reactions caused by moisture, free acid, and transition metals, improve the battery's performance in high-temperature storage tests, and simultaneously improve the battery's cycle life and rate performance.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and in particular relates to an electrolyte and a semi-solid battery. Background Art

[0002] Solid-state batteries have attracted much attention due to their higher energy density and stronger thermal stability than traditional liquid lithium-ion batteries. Semi-solid-state batteries, as a phased achievement in the transition from traditional liquid batteries to all-solid-state batteries, combine the advantages of both solid-state batteries and liquid batteries, which has led relevant scientific research institutions to invest a lot of resources in the research and development of semi-solid-state batteries. At the same time, because the manufacturing process of semi-solid-state batteries is similar to that of existing liquid batteries, their production equipment is compatible with existing liquid battery production equipment. Therefore, semi-solid-state battery technology is expected to achieve commercialization in a relatively short period of time, while also being able to take lithium-ion battery performance to a new level.

[0003] Key material technologies for semi-solid-state batteries include the development of cathode materials, anode materials, separator materials, and electrolyte materials. Electrolyte materials, the "blood" of the battery, are responsible for transferring ions between the positive and negative electrodes. Because the electrolyte is in direct contact with the positive and negative electrodes, it must be compatible with both the cathode and negative electrode materials, possess a wide chemical stability window, and be able to form an effective SEI on the surfaces of the positive and negative electrodes. Therefore, the electrolyte needs to be tailored to the electrode materials, battery characteristics, and performance requirements.

[0004] Lithium-rich manganese-based cathode materials are currently attracting significant attention in the field of semi-solid-state batteries due to their exceptional properties. They offer high operating voltages and discharge capacities of up to 300 mAh, significantly improving battery energy density. Lithium-rich manganese materials primarily utilize manganese metal, which is relatively inexpensive compared to cobalt and nickel, reducing battery material costs. However, these materials also face several pressing challenges. First, their extremely high operating voltage hinders their application. The upper cutoff voltage of lithium-rich manganese-based batteries can reach 4.6V, while the stable voltage window of conventional battery electrolytes lies between 2.0 and 4.3V. Excessively high voltages can lead to side reactions such as oxidative decomposition of the electrolyte on the cathode side, resulting in battery gassing and other consequences, seriously impacting battery performance and safety. Second, lithium-rich manganese-based materials are highly alkaline and readily absorb water, placing stringent requirements on battery production site conditions. Excessive moisture can also degrade battery performance. Finally, both lithium-rich manganese-based materials and solid electrolytes suffer from low ionic conductivity, resulting in poor power performance in lithium-rich manganese-based semi-solid-state batteries. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an electrolyte and a semi-solid battery.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] An electrolyte comprises a lithium salt, a solvent and an additive; the additive comprises a solvent additive; the solvent additive comprises a low HOMO energy level solvent; preferably, the low HOMO energy level solvent is 2,2,2-trifluoroethanol (TFEA).

[0008] The low HOMO energy level solvent accounts for 2-8% by mass in the electrolyte, preferably 8%.

[0009] The solvent additives also include acid and water removal additives;

[0010] Preferably, the acid and water removal additive comprises one or a mixture of tris(trimethylsilyl)phosphate TMSP or tris(trimethylsilyl)borate TMSB;

[0011] Preferably, the mass proportion of the acid and water removal additive in the electrolyte is 0.5-0.8%.

[0012] The acid and water removal additive is a mixture of tris(trimethylsilyl)phosphate TMSP and tris(trimethylsilyl)borate TMSB; preferably, the mass ratio of the two is 3:(3-5).

[0013] The solvent additive further comprises a fluorobenzene-based wetting additive; preferably, the fluorobenzene-based wetting additive is fluorobenzene FB;

[0014] Preferably, the mass proportion of the fluorobenzene wetting additive in the electrolyte is 0.5-2%, preferably 1%.

[0015] The additives also include film-forming additives; preferably, the film-forming additive is lithium difluorodioxalate phosphate LiODFP;

[0016] Preferably, the mass proportion of the lithium difluorobis(oxaloyl)phosphate LiODFP in the electrolyte is 0.2-1%, preferably 0.5%.

[0017] The solvent includes one or a mixture of carbonates, sulfates, sulfonates, fluoroesters, fluorosulfates, or fluorosulfonates;

[0018] Preferably, the solvent comprises one of propylene carbonate PC, ethylene carbonate EC, vinylene carbonate VC, ethyl methyl carbonate EMC, dimethyl carbonate DMC, diethyl carbonate DEC, fluoroethylene carbonate FEC, propylene sulfite PS, vinyl sulfate DTD, propenyl-1,3-sultone PST, and methylene methanedisulfonate MMDS, or a mixture thereof;

[0019] Preferably, the solvent is a mixture of propylene carbonate PC, ethyl methyl carbonate EMC, fluoroethylene carbonate FEC, and vinyl sulfate DTD;

[0020] Preferably, the mass ratio of propylene carbonate PC, ethyl methyl carbonate EMC, fluoroethylene carbonate FEC, and vinyl sulfate DTD in the electrolyte is: 6: (61.5-69.8): (5-8): 1.

[0021] The lithium salt is one or a mixture of LiPF6, LiBOB, LiBF4, LiODFB, LiTFSI, LiFSI, LiPO2F2, and LiFOP;

[0022] Preferably, the lithium salt is a mixture of LiPF6, LiFSI and LiPO2F2; preferably, the mass ratio of LiPF6, LiFSI and LiPO2F2 is 10:2:1.2.

[0023] The present invention also includes a semi-solid battery comprising the electrolyte.

[0024] The semi-solid-state battery comprises an electrolyte, a positive electrode sheet, a negative electrode sheet and a separator; the positive electrode active material in the positive electrode sheet is a lithium-rich manganese-based positive electrode material coated with a solid electrolyte.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The electrolyte of the present application, by adopting a solvent additive with a low HOMO energy level and optionally combining functional additives (acid and water removal and additives, fluorobenzene wetting additives, film-forming additives) to form an electrolyte solution, can effectively improve the stability of the battery at high voltage, protect the electrolyte-electrode interface, inhibit the dissolution of transition metals, reduce the electrolyte side reactions caused by moisture, free acid and transition metals, improve the performance of the battery in high-temperature storage tests, and at the same time improve the cycle life and rate performance of the battery.

[0027] 1. Adding solvent additives with low HOMO energy level can improve the antioxidant properties of the electrolyte, thereby improving the performance of the battery at high voltage.

[0028] 2. Adding acid and water removal additives can reduce the water and free acid content in the battery system caused by alkaline residues in the positive electrode, thereby improving the overall performance of the battery. As a preferred form, a mixed solution of TMSP and TMSB is adopted. The two silane additives work together with lithium salts and low HOMO energy level solvent additives to form a high entropy SEI on the negative electrode surface, producing a cocktail effect, which can protect the electrode while reducing the interfacial impedance.

[0029] 3. Introducing a fluorobenzene-based wetting additive. This additive has low surface tension and can effectively reduce electrolyte infiltration time, enhance contact between solid electrolytes and between the solid electrolyte and the electrode, reduce interfacial resistance, and improve battery rate performance. The addition of a fluorobenzene-based wetting additive can also reduce the amount of electrolyte injected into the battery, further increasing the battery's energy density.

[0030] 4. To address the more active nature of lithium-rich manganese-based cathode materials, a film-forming additive, LiODFP, is added. This additive effectively forms a film on the positive and negative electrode surfaces, inhibiting the dissolution and migration of transition metals on the positive electrode side, thereby improving the battery's cycle life and high-temperature storage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 HOMO energy level diagrams of the solvents and solvent additives of the embodiments and comparative examples of the present invention;

[0032] Figure 2 Graph showing rate performance test results for the embodiments of the present invention and the comparative example;

[0033] Figure 3 The graphs are the cycle performance results of the embodiments of the present invention and the comparative examples;

[0034] Figure 4 Graph showing the thickness expansion rate during high temperature storage for the embodiments of the present invention and the comparative example;

[0035] Figure 5 Result diagram of the Mn content of the negative electrode of the embodiment of the present invention and the comparative example. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and the best embodiments.

[0037] Example 1:

[0038] A semi-solid battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte;

[0039] The positive electrode sheet is prepared in the following manner: a solid electrolyte-coated lithium-manganese-rich positive electrode material, a conductive agent SuperP, a binder PVDF and N-methylpyrrolidone (NMP) are uniformly mixed in a mass ratio of 96:2.0:2.0 to form a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode collector with a coating amount of 0.018 g / cm2, dried at 85°C and then cold pressed; after slicing, trimming and striping, the tabs are welded to form a lithium-ion secondary battery positive electrode sheet.

[0040] The negative electrode sheet was prepared by the following method: graphite, SiC, conductive agent SuperP, thickener CMC, binder SBR were uniformly mixed with pure water in a mass ratio of 52.5:44:1.0:1.0:1.5 to form a negative electrode slurry; the negative electrode slurry was evenly coated on the negative electrode collector copper foil with a coating amount of 0.009g / cm2 and dried at 85°C, and then after cold pressing, cutting, slitting, and welding the tabs to form a lithium-ion secondary battery negative electrode sheet.

[0041] The separator is a 16μm solid electrolyte coated polyethylene separator.

[0042] The electrolyte includes a lithium salt, a solvent and an additive; the solvent includes one or a mixture of carbonates, sulfates, sulfonates, fluoroesters, fluorosulfates, or fluorosulfonates;

[0043] Preferably, the solvent includes one of propylene carbonate PC, ethylene carbonate EC, vinylene carbonate VC, ethyl methyl carbonate EMC, dimethyl carbonate DMC, diethyl carbonate DEC, fluoroethylene carbonate FEC, propylene sulfite PS, vinyl sulfate DTD, propenyl-1,3-sultone PST, and methylene methanedisulfonate MMDS, or a mixture thereof; preferably, the solvent is a mixture of propylene carbonate PC, ethyl methyl carbonate EMC, fluoroethylene carbonate FEC, and vinyl sulfate DTD; preferably, the mass ratio of propylene carbonate PC, ethyl methyl carbonate EMC, fluoroethylene carbonate FEC, and vinyl sulfate DTD in the electrolyte is: 6: (61.5-69.8): (5-8): 1. The lithium salt is one or a mixture of LiPF6, LiBOB, LiBF4, LiODFB, LiTFSI, LiFSI, LiPO2F2, and LiFOP; preferably, it is a mixture of LiPF6, LiFSI, and LiPO2F2; preferably, the mass ratio of LiPF6, LiFSI, and LiPO2F2 in the electrolyte is: 10:2:1.2.

[0044] The additives include solvent additives; the solvent additives include low HOMO energy level solvents; EC, PC, DMC, EMC, DEC, FEC, TFEA were tested, and the results were as follows Figure 1 Therefore, 2,2,2-trifluoroethanol (TFEA) was used as a low HOMO energy level solvent. Its addition amount was tested, as shown in Table 1. The addition of a low HOMO energy level solvent improved the antioxidant properties of the electrolyte, thereby improving the performance of the battery at high voltage.

[0045] The solvent additive also includes an acid-removing and water-removing additive; the acid-removing and water-removing additive includes one of tris(trimethylsilyl)phosphate TMSP or tris(trimethylsilyl)borate TMSB or a mixture thereof; preferably, the mass ratio of the acid-removing and water-removing additive in the electrolyte is 0.5-0.8%. The acid-removing and water-removing additive is a mixture of tris(trimethylsilyl)phosphate TMSP and tris(trimethylsilyl)borate TMSB; preferably, the mass ratio of the two is 3:(3-5). Adding the acid-removing and water-removing additive reduces the content of water and free acid in the battery system due to alkaline residues in the positive electrode, thereby improving the overall performance of the battery (Example 4). Since boron-containing compounds can reduce the internal resistance of the battery, we tested a solution of mixing TMSP and TMSB (Examples 5 and 6). The two silane additives work together with the lithium salt and fluorinated solvent to form a high-entropy SEI on the surface of the negative electrode, producing a cocktail effect, which can protect the electrode while reducing the interfacial impedance.

[0046] The solvent additive further includes a fluorobenzene-based wetting additive; preferably, the fluorobenzene-based wetting additive is fluorobenzene FB; preferably, the mass proportion of the fluorobenzene-based wetting additive in the electrolyte is 0.5-2%, preferably 1%.

[0047] The additive has low surface tension, can effectively reduce the electrolyte infiltration time, enhance the contact between solid electrolytes and between solid electrolytes and electrodes, reduce interfacial resistance, and improve battery rate performance (Example 7). Adding FB can also reduce the battery injection volume, further improving the battery energy density.

[0048] To address the more active nature of lithium-rich manganese-based cathode materials, a highly efficient film-forming additive, LiODFP (Example 8), was added. This additive effectively forms a film on the positive and negative electrode surfaces, inhibiting the dissolution and migration of transition metals on the positive electrode side, thereby improving the battery's cycle life and high-temperature storage performance.

[0049] The specific embodiment recipe parameters are shown in Table 1.

[0050] Table 1

[0051]

[0052] The positive electrode sheet, negative electrode sheet and separator are assembled into a 12Ah soft-pack laminated battery, and the electrolyte is added to form a semi-solid-state battery.

[0053] The electrical performance test was carried out on the soft-pack semi-solid-state full battery, and the results are shown in Table 2.

[0054] Table 2

[0055]

[0056] Figure 2 The figure shows the rate performance compared with the discharge capacity under 3C current discharge conditions. The addition of LiODFB and FB can effectively improve the rate performance of the battery.

[0057] Figure 3 The results of the room temperature cycle test at 25°C are shown. The cycle format is 1C constant current charge to 4.6V, then constant voltage charge, and the cut-off current is 0.05C. After charging to 100% SOC and standing for 0.5h, 1C discharge is performed to 2.5V. First, the addition of fluorinated solvents improves the oxidation resistance of the electrolyte, thereby effectively improving the cycle performance of the battery. The cycle performance is further improved after the addition of TMSP and TMSB. The addition of FB has no obvious effect on the cycle performance. Since LiODFB can effectively form a film on both the positive and negative electrodes, it can significantly inhibit the voltage drop during the first 10 cycles of the inhibitory battery, thereby improving the cycle performance of the battery.

[0058] Figure 4 The results of the battery high-temperature storage test at 60°C are shown. The thickness of the battery is tested every 7 days, and the residual capacity of the battery is tested on the 28th day. Since the F element in the fluorinated solvent reacts with the water in the electrolyte to produce HF, thereby promoting the side reaction of the electrolyte, the addition of the fluorinated solvent will cause the battery to produce more gas and increase the thickness. The addition of silane additives reduces the water and free acid in the battery system, thereby further inhibiting the occurrence of electrolyte side reactions. The interfacial film generated by LiODFB passivates the positive and negative electrode surfaces and can also inhibit the occurrence of gas production.

[0059] In addition, the dissolution of transition metals in the positive electrode material after 300 cycles was tested. The battery with 300 cycles was charged to 100% SOC, and the negative electrode sheet was removed after dissection. The negative electrode material powder was scraped and tested by ICP. The Mn element content was as follows: Figure 5 As shown in Figure 3, the addition of fluorinated solvents can improve the electrochemical stability of the battery system, thereby inhibiting transition metal dissolution. Silane additives TMSP and TMSB can further inhibit transition metal dissolution. FB has no significant effect on transition metal dissolution. The addition of the film-forming additive LiODFB also significantly inhibits transition metal dissolution.

[0060] In summary, the electrolyte of the present application, by adopting a solvent additive with a low HOMO energy level and optionally combining functional additives (acid and water removal and additives, fluorobenzene wetting additives, film-forming additives) to form an electrolyte solution, can effectively improve the stability of the battery at high voltage, protect the electrolyte-electrode interface, inhibit the dissolution of transition metals, reduce the electrolyte side reactions caused by moisture, free acid and transition metals, improve the performance of the battery in high-temperature storage tests, and at the same time improve the cycle life and rate performance of the battery.

[0061] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: The invention comprises a lithium salt, a solvent and an additive; the additive comprises a solvent additive; the solvent additive comprises a low HOMO energy level solvent; the low HOMO energy level solvent is 2,2,2-trifluoroethanol TFEA; the mass proportion of the low HOMO energy level solvent in the electrolyte is 2-8%; the solvent additive further comprises an acid-removing and water-removing additive; the acid-removing and water-removing additive comprises one or a mixture of tris(trimethylsilyl) phosphate TMSP or tris(trimethylsilyl) borate TMSB; the solvent additive further comprises a fluorobenzene-based wetting additive; the fluorobenzene-based wetting additive is fluorobenzene FB; the additive further comprises a film-forming additive; the film-forming additive is lithium difluorodioxalatophosphate LiODFP.

2. The electrolyte according to claim 1, characterized in that The mass proportion of the low HOMO energy level solvent in the electrolyte is 8%.

3. The electrolyte according to claim 1, characterized in that The mass proportion of the acid and water removal additive in the electrolyte is 0.5-0.8%.

4. The electrolyte according to claim 1, characterized in that The acid and water removal additive is a mixture of tris(trimethylsilyl)phosphate TMSP and tris(trimethylsilyl)borate TMSB.

5. The electrolyte according to claim 4, characterized in that The mass ratio of (trimethylsilyl) phosphate TMSP to tris(trimethylsilyl) borate TMSB is 3:(3-5).

6. The electrolyte according to claim 1, characterized in that The mass proportion of the fluorobenzene wetting additive in the electrolyte is 0.5-2%.

7. The electrolyte according to claim 6, characterized in that The mass proportion of the fluorobenzene wetting additive in the electrolyte is 1%.

8. The electrolyte according to claim 1, characterized in that The mass proportion of the lithium difluorodioxalatophosphate LiODFP in the electrolyte is 0.2-1%.

9. The electrolyte according to claim 8, characterized in that The mass proportion of the lithium difluorodioxalatophosphate LiODFP in the electrolyte is 0.5%.

10. The electrolyte according to claim 1, characterized in that The solvent includes one or a mixture of carbonates, sulfates, sulfonates, fluoroesters, fluorosulfates, or fluorosulfonates.

11. The electrolyte according to claim 1, characterized in that The solvent includes one of propylene carbonate PC, ethylene carbonate EC, vinylene carbonate VC, ethyl methyl carbonate EMC, dimethyl carbonate DMC, diethyl carbonate DEC, fluoroethylene carbonate FEC, propylene sulfite PS, vinyl sulfate DTD, propenyl-1,3-sultone PST, and methylene methanedisulfonate MMDS, or a mixture thereof.

12. The electrolyte according to claim 1, characterized in that The solvent is a mixture of propylene carbonate PC, ethyl methyl carbonate EMC, fluoroethylene carbonate FEC and vinyl sulfate DTD.

13. The electrolyte according to claim 12, characterized in that The mass proportions of propylene carbonate PC, ethyl methyl carbonate EMC, fluoroethylene carbonate FEC, and vinyl sulfate DTD in the electrolyte are: 6: (61.5-69.8): (5-8):

1.

14. The electrolyte according to claim 1, characterized in that The lithium salt is one or a mixture of LiPF6, LiBOB, LiBF4, LiODFB, LiTFSI, LiFSI, LiPO2F2, and LiFOP.

15. The electrolyte according to claim 14, characterized in that The lithium salt is a mixture of LiPF6, LiFSI and LiPO2F2; the mass ratio of LiPF6, LiFSI and LiPO2F2 is 10:2:1.

2.

16. A semi-solid-state battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 1 to 15.

17. The semi-solid-state battery according to claim 16, characterized in that: It includes an electrolyte, a positive electrode sheet, a negative electrode sheet and a separator; the positive electrode active material in the positive electrode sheet is a lithium-rich manganese-based positive electrode material coated with a solid electrolyte.

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