Liquid injection method for improving cycle life and stability of semi-solid lithium battery

Abstract

The invention provides a liquid injection method for improving the cycle life and stability of a semi-solid-state battery, and belongs to the technical field of semi-solid-state batteries. According to the method, a three-time liquid injection process is adopted, one-time injection and two-time injection are performed according to a conventional long-circulation VC gradient two-time injection scheme, sufficient infiltration and high VC are ensured, and the electrolyte containing the monomer and the electrolyte containing the initiator are separately subjected to sample preparation and do not contain lithium salt and additives; during third injection, the electrolyte containing the monomer and the electrolyte containing the initiator are injected into the battery together, and the monomer and the initiator are added after formation, so that the SEI film is more stable to form. By adding the monomer and the initiator, the liquid electrolyte is converted into the gelatinous (semi-solid) electrolyte, so that the mechanical strength and the stability of the battery are enhanced while the high ionic conductivity of the liquid electrolyte is maintained, the problem of insufficient stability of the liquid electrolyte in some application scenes is solved, and the service life of the battery is prolonged. And the overall performance and the safety of the battery are improved.

Description

Technical Field

[0001] The invention relates to the technical field of semi-solid batteries, and in particular to a liquid injection method for improving the cycle life and stability of a semi-solid lithium battery. Background Art

[0002] With the progress of scientific and technological innovation, the energy storage market has developed rapidly in recent years, and the market's requirements for energy storage batteries have become increasingly higher. Its core technical indicators include long cycle, low cost and certain power performance. The number of cycles of existing lithium-ion batteries for energy storage generally does not exceed 10,000 times. At the same time, at the end of the life span, the battery often has undesirable phenomena such as increased capacity attenuation, high heat generation, and increased thickness. Therefore, existing technologies often improve the cycle performance of energy storage batteries in terms of materials and processes.

[0003] Some researchers have proposed using a semi-solid solution to solve the safety problem. Common solutions include: 1. The electrolyte containing monomers and initiators is injected into the battery cell before formation. This process has two problems. The first is that large-capacity batteries are difficult to infiltrate, and the electrolyte containing monomers and initiators will make infiltration more difficult; the second is that the electrolyte containing monomers and initiators will polymerize during transportation, especially in summer; 2. The electrolyte containing monomers is injected into the battery cell before formation, and the electrolyte containing initiators is injected into the battery cell after formation. The problem with this process is that the initiator will self-polymerize when the amount of vinylene carbonate VC exceeds 3%. Therefore, how to take into account the safety performance and electrochemical performance of lithium-ion batteries at the same time and further reduce the preparation cost has become the focus of current research.

[0004] Based on this, the present invention proposes a liquid injection method for improving the cycle life and stability of a semi-solid lithium battery. Summary of the invention

[0005] The present invention provides a liquid injection method for improving the cycle life and stability of a semi-solid lithium battery, the purpose of which is to solve the above-mentioned problems existing in the background technology.

[0006] In order to achieve the above-mentioned purpose, the embodiment of the present invention provides a method for injecting liquid to improve the cycle life and stability of a semi-solid lithium battery. The present invention adopts a three-time injection process. The first and second injections are performed according to the conventional long-cycle VC gradient two-injection scheme to ensure sufficient infiltration and high VC. The electrolyte containing the monomer and the electrolyte containing the initiator are separately prepared, and both do not contain lithium salts and additives. During the third injection, the electrolyte containing the monomer and the electrolyte containing the initiator are injected into the battery together to promote infiltration and ensure polymerization uniformity. The present invention can form a long-life and highly safe semi-solid energy storage battery through the electrolyte formulation and injection process.

[0007] The purpose of the embodiment of the present invention is to provide a liquid injection method for improving the cycle life and stability of a semi-solid lithium battery, comprising the following steps:

[0008] S1: injecting electrolyte A into the baked battery cell for high temperature activation and high temperature formation;

[0009] S2: injecting the formed battery into electrolyte B for high temperature aging;

[0010] S3: inject electrolyte C and electrolyte D into the aged battery cell and seal it, and let it stand at room temperature;

[0011] S4: Perform high temperature polymerization and separate the contents to obtain.

[0012] According to one aspect of the embodiment of the present invention, in step S1, the temperature of high temperature activation is 45-50° C. and the time is 72-96 hours.

[0013] According to one aspect of an embodiment of the present invention, in step S2, the high temperature aging temperature is 45-50° C. and the time is 72-96 hours.

[0014] According to one aspect of an embodiment of the present invention, in step S3, the standing time at room temperature is 24 to 72 hours.

[0015] According to one aspect of the embodiment of the present invention, in step S4, the temperature of the high temperature polymerization is 45 to 80° C., and the time is 2 to 24 hours.

[0016] According to one aspect of an embodiment of the present invention, the electrolyte A includes 5% to 14% additives, 70% to 75% solvents and 16% to 20% lithium salts; the lithium salts are LiPF6 and LiFSI; the solvent is vinyl carbonate EC, dimethyl carbonate DMC or ethyl methyl carbonate EMC; the additive is at least one of fluoroethylene carbonate FEC containing vinylene carbonate VC, LiODFP, vinylene sulfate DTD, tris(trimethylsilyl) phosphate TMSP, methylene disulfonate MMDS, and LiPO2F2.

[0017] According to one aspect of an embodiment of the present invention, the electrolyte B includes 62% to 76% solvent, 16% to 20% lithium salt and 8% to 18% additive; the lithium salt is LiPF6 and LiFSI; the additive is vinylene carbonate VC; the solvent is vinyl carbonate EC, dimethyl carbonate DMC or ethyl methyl carbonate EMC.

[0018] According to one aspect of an embodiment of the present invention, the electrolyte C includes 0.03% to 0.10% initiator and 99.90% to 99.97% solvent; the solvent is ethylene carbonate EC, dimethyl carbonate DMC or ethyl methyl carbonate EMC; the initiator includes at least one of azobisisobutyronitrile AIBN, dimethyl azobisisobutyrate AIBME, and benzoyl peroxide BPO.

[0019] According to one aspect of an embodiment of the present invention, the electrolyte D includes 5% to 10% monomers and 90% to 95% solvents; the solvent is ethylene carbonate EC, dimethyl carbonate DMC or ethyl methyl carbonate EMC; the monomer includes at least one of polyethylene glycol methyl ether acrylate PEGMEA, tetraethylene glycol diacrylate TEGDA, pentaerythritol triacrylate PETA, polyethylene glycol diacrylate PEGDA, polymethyl methacrylate PMMA, methyl methacrylate MMA, triethylene glycol dimethacrylate TEGDMA, ethylene glycol dimethacrylate EGDMA, methyl methacrylate MMA, 4,4-bismaleimidodiphenylmethane, pentaerythritol tetraacrylate PET4A, and pentaerythritol triacrylate PETA.

[0020] The above scheme of the present invention has the following beneficial effects:

[0021] (1) The present invention adopts a three-time injection process. The first and second injections are performed according to the conventional long-cycle VC gradient two-injection scheme to ensure sufficient infiltration and high VC. The electrolyte containing the monomer and the electrolyte containing the initiator are separately prepared and do not contain lithium salts and additives. In the third injection, the electrolyte containing the monomer and the electrolyte containing the initiator are injected into the battery together; wherein the monomer and the initiator are added after formation in order to make the SEI film formation more stable. Conventional electrolytes are liquids and do not require monomers and initiators; the role of monomers and initiators is to change the liquid electrolyte into a gel state (semi-solid electrolyte), thereby improving the cycle life and stability of semi-solid batteries.

[0022] (2) The present invention converts the liquid electrolyte into a gel-like (semi-solid) electrolyte by adding monomers and initiators. While maintaining the high ionic conductivity of the liquid electrolyte, it enhances the mechanical strength and stability of the battery, helps to inhibit the formation of lithium dendrites, and reduces side reactions at the negative electrode-electrolyte interface. This not only solves the problem of insufficient stability of the liquid electrolyte in certain application scenarios, but also improves the overall performance and safety of the battery. DETAILED DESCRIPTION

[0023] In order to make the technical problems to be solved, technical solutions and advantages of the present invention more clear, they are described in detail below in conjunction with specific embodiments.

[0024] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0025] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0026] The specific deficiencies of the existing semi-solid battery improvement process include: 1. The electrolyte containing monomers and initiators is injected into the battery cell before formation. This process has two problems. The first is that large-capacity batteries are difficult to infiltrate, and the electrolyte containing monomers and initiators will make infiltration more difficult; the second is that the electrolyte containing monomers and initiators will polymerize during transportation, especially in summer; 2. The electrolyte containing monomers is injected into the battery cell before formation, and the electrolyte containing initiators is injected into the battery cell after formation. The problem of this process is that the initiator will self-polymerize when the amount of vinylene carbonate VC exceeds 3%. Therefore, how to take into account the safety performance and electrochemical performance of lithium-ion batteries at the same time and further reduce the preparation cost has become the focus of current research.

[0027] An embodiment of the present invention provides a method for injecting liquid to improve the cycle life and stability of a semi-solid lithium battery, comprising the following steps:

[0028] S1: injecting electrolyte A into the baked battery cell for high temperature activation and high temperature formation;

[0029] S2: injecting the formed battery into electrolyte B for high temperature aging;

[0030] S3: inject electrolyte C and electrolyte D into the aged battery cell and seal it, and let it stand at room temperature;

[0031] S4: Perform high temperature polymerization and separate the contents to obtain.

[0032] According to one aspect of the embodiment of the present invention, in step S1, the temperature of high temperature activation is 45-50° C. and the time is 72-96 hours.

[0033] According to one aspect of an embodiment of the present invention, in step S2, the high temperature aging temperature is 45-50° C. and the time is 72-96 hours.

[0034] According to one aspect of an embodiment of the present invention, in step S3, the standing time at room temperature is 24 to 72 hours.

[0035] According to one aspect of the embodiment of the present invention, in step S4, the temperature of the high temperature polymerization is 45 to 80° C., and the time is 2 to 24 hours.

[0036] According to one aspect of an embodiment of the present invention, the electrolyte A includes 5% to 14% additives, 70% to 75% solvents and 16% to 20% lithium salts; the lithium salts are LiPF6 and LiFSI; the solvent is vinyl carbonate EC, dimethyl carbonate DMC or ethyl methyl carbonate EMC; the additive is at least one of fluoroethylene carbonate FEC containing vinylene carbonate VC, LiODFP, vinylene sulfate DTD, tris(trimethylsilyl) phosphate TMSP, methylene disulfonate MMDS, and LiPO2F2.

[0037] According to one aspect of an embodiment of the present invention, the electrolyte B includes 62% to 76% solvent, 16% to 20% lithium salt and 8% to 18% additive; the lithium salt is LiPF6 and LiFSI; the additive is vinylene carbonate VC; the solvent is vinyl carbonate EC, dimethyl carbonate DMC or ethyl methyl carbonate EMC.

[0038] According to one aspect of an embodiment of the present invention, the electrolyte C includes 0.03% to 0.10% initiator and 99.90% to 99.97% solvent; the solvent is ethylene carbonate EC, dimethyl carbonate DMC or ethyl methyl carbonate EMC; the initiator includes at least one of azobisisobutyronitrile AIBN, dimethyl azobisisobutyrate AIBME, and benzoyl peroxide BPO.

[0039] According to one aspect of an embodiment of the present invention, the electrolyte D includes 5% to 10% monomers and 90% to 95% solvents; the solvent is ethylene carbonate EC, dimethyl carbonate DMC or ethyl methyl carbonate EMC; the monomer includes at least one of polyethylene glycol methyl ether acrylate PEGMEA, tetraethylene glycol diacrylate TEGDA, pentaerythritol triacrylate PETA, polyethylene glycol diacrylate PEGDA, polymethyl methacrylate PMMA, methyl methacrylate MMA, triethylene glycol dimethacrylate TEGDMA, ethylene glycol dimethacrylate EGDMA, methyl methacrylate MMA, 4,4-bismaleimidodiphenylmethane, pentaerythritol tetraacrylate PET4A, and pentaerythritol triacrylate PETA.

[0040] The technical solution of the present invention has the following advantages:

[0041] The present invention adopts a three-time injection process, and the first and second injections are injected according to the conventional long-cycle VC gradient two-injection scheme to ensure sufficient infiltration and high VC, and the electrolyte containing the monomer and the electrolyte containing the initiator are separately prepared, and both do not contain lithium salts and additives. During the three injections, the electrolyte containing the monomer and the electrolyte containing the initiator are injected into the battery together, and the monomer and the initiator are added after formation, so that the SEI film is more stable. The present invention converts the liquid electrolyte into a gel-like (semi-solid) electrolyte by adding monomers and initiators, while maintaining the high ionic conductivity of the liquid electrolyte, the mechanical strength and stability of the battery are enhanced, it is helpful to inhibit the formation of lithium dendrites, and reduce the side reactions at the negative electrode-electrolyte interface, which not only solves the problem of insufficient stability of the liquid electrolyte in certain application scenarios, but also improves the overall performance and safety of the battery.

[0042] The following is a detailed description through specific embodiments.

[0043] Example 1

[0044] A method for injecting liquid to improve the cycle life and stability of a semi-solid lithium battery comprises the following steps:

[0045] S1: inject the baked battery into electrolyte A (composition includes: solvent is 21.5% EC / 21.5% DMC / 29% EMC, lithium salt is 18.5% LiPF6+LiFSI, additive is 5% VC+3% FEC), activate at 45°C for 96h, and form;

[0046] S2: Inject the formed battery into electrolyte B (composition includes: solvent is 20% EC / 20% DMC / 27.5% EMC, lithium salt is 16.5% LiPF6+LiFSI, additive is 14% VC), and age at 45°C for 96h;

[0047] S3: The aged battery cell is injected with electrolyte C (composition includes: initiator is 0.08% AIBN, solvent is 30% EC / 30% DMC / 39.92% EMC) and electrolyte D (composition includes: monomer is 5% PEGMEA, solvent is 28.5% EC / 28.5% DMC / 38% EMC) and sealed, and left at room temperature for 72h;

[0048] S4: Polymerize at 45℃ for 24h, separate the contents to obtain the product.

[0049] Example 2

[0050] The difference from Example 1 is that the monomer in the electrolyte D is TEGDA, and the other steps and parameters are the same as those in Example 1.

[0051] Example 3

[0052] The difference from Example 1 is that the initiator in electrolyte C is BPO, and the other steps and parameters are the same as those in Example 1.

[0053] Comparative Example 1

[0054] A method for injecting liquid into a semi-solid lithium battery comprises the following steps:

[0055] (1) After the baked battery cell is injected with electrolyte (composition includes: monomer is 5% PEGMEA, solvent is 22% EC / 22% DMC / 35.44% EMC, lithium salt is 12.5% ​​LiPF6+LiFSI, additive is 2% VC+1% FEC, initiator is 0.06% AIBN), directly stand at room temperature for 96 hours, and polymerize at 80°C for 2 hours;

[0056] (2) Heat at 45℃ for 96h; separate the volume to obtain the product.

[0057] In this comparative example, since the electrolyte including monomers and initiators causes wetting difficulties, the gel obtained by high-temperature polymerization is uneven. Although the safety performance is improved to a certain extent, the battery life is reduced.

[0058] Comparative Example 2

[0059] A method for injecting liquid into a semi-solid lithium battery comprises the following steps:

[0060] (1) injecting the electrolyte (composition includes: monomer is 5% PEGMEA, solvent is 20.5% EC / 20.5% DMC / 27.5% EMC, lithium salt is 18.5% LiPF6+LiFSI, additive is 5% VC+3% FEC) into the baked battery cell, high temperature activation at 45°C for 96h, and high temperature formation;

[0061] (2) injecting the electrolyte (composition includes: initiator is 0.06% AIBN, solvent is 20% EC / 20% DMC / 29.44% EMC, lithium salt is 16.5% LiPF6+LiFSI, additive is 14% VC) into the formed battery cell and sealing it;

[0062] (3) Aging at 45°C for 96 hours, and then separating the contents to obtain the product.

[0063] In this comparative example, since the initiator and VC have polymerized before injection, the electrolyte B is milky white and viscous, which makes injection difficult, and it can hardly polymerize with the monomer to form a gel electrolyte after being injected into the battery, which affects the lithium ion transmission and causes rapid life decay.

[0064] Comparative Example 3

[0065] The difference from Example 1 is that the monomer in the electrolyte D is 1% PETA, and the other steps and parameters are the same as those in Example 1.

[0066] The semi-solid batteries prepared in the above-mentioned embodiments and comparative examples were tested, and the results are shown in Table 1 below.

[0067] Table 1

[0068]

[0069] It can be seen from Table 1 that the semi-solid energy storage battery prepared by the present invention has a high capacity retention rate after 1000 cycles of 1p charging, and no puncture or overcharge occurs, and has the advantages of long service life and high safety performance.

[0070] The above is 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 the scope of protection of the present invention.

Claims

1. A method for improving the cycle life and stability of a semi-solid battery, characterized in that: The steps include: S1: injecting electrolyte A into the baked battery cell for high temperature activation and high temperature formation; S2: injecting the formed battery into electrolyte B for high temperature aging; S3: inject electrolyte C and electrolyte D into the aged battery cell and seal it, and let it stand at room temperature; S4: Perform high temperature polymerization and separate the contents to obtain.

2. A method for injecting liquid to improve the cycle life and stability of a semi-solid battery according to claim 1, characterized in that: In step S1, the temperature of high temperature activation is 45-50° C. and the time is 72-96 hours.

3. A method for injecting liquid to improve the cycle life and stability of a semi-solid battery according to claim 1, characterized in that: In step S2, the high temperature aging temperature is 45-50°C and the time is 72-96 hours.

4. The method for injecting liquid to improve the cycle life and stability of a semi-solid battery according to claim 1, characterized in that: In step S3, the standing time at room temperature is 24 to 72 hours.

5. The method for injecting liquid to improve the cycle life and stability of a semi-solid battery according to claim 1, characterized in that: In step S4, the temperature of high temperature polymerization is 45 to 80° C., and the time is 2 to 24 hours.

6. The method for injecting liquid to improve the cycle life and stability of a semi-solid battery according to claim 1, characterized in that: The electrolyte A includes 5% to 14% additives, 70% to 75% solvents and 16% to 20% lithium salts; the lithium salts are LiPF6 and LiFSI; the solvents are ethylene carbonate, dimethyl carbonate or ethyl methyl carbonate; the additives are at least one of fluoroethylene carbonate containing vinylene carbonate, LiODFP, vinylene sulfate, tris(trimethylsilyl)phosphate, methylene disulfonate, and LiPO2F2.

7. A method for injecting liquid to improve the cycle life and stability of a semi-solid battery according to claim 1, characterized in that: The electrolyte B includes 62% to 76% solvent, 16% to 20% lithium salt and 8% to 18% additive; the lithium salt is LiPF6 and LiFSI; the additive is vinylene carbonate; the solvent is vinyl carbonate, dimethyl carbonate or ethyl methyl carbonate.

8. The method for injecting liquid to improve the cycle life and stability of a semi-solid battery according to claim 1, characterized in that: The electrolyte C comprises 0.03% to 0.10% of an initiator and 99.90% to 99.97% of a solvent; the solvent is ethylene carbonate, dimethyl carbonate or ethyl methyl carbonate; the initiator comprises at least one of azobisisobutyronitrile, dimethyl azobisisobutyrate and benzoyl peroxide.

9. The method for injecting liquid to improve the cycle life and stability of a semi-solid battery according to claim 1, characterized in that: The electrolyte D includes 5% to 10% monomers and 90% to 95% solvents; the solvent is ethylene carbonate EC, dimethyl carbonate DMC or ethyl methyl carbonate EMC; the monomer includes at least one of polyethylene glycol methyl ether acrylate PEGMEA, tetraethylene glycol diacrylate TEGDA, pentaerythritol triacrylate PETA, polyethylene glycol diacrylate PEGDA, polymethyl methacrylate PMMA, methyl methacrylate MMA, triethylene glycol dimethacrylate TEGDMA, ethylene glycol dimethacrylate EGDMA, methyl methacrylate MMA, 4,4-bismaleimidodiphenylmethane, pentaerythritol tetraacrylate PET4A, and pentaerythritol triacrylate PETA.

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