Safe lithium ion battery gel electrolyte as well as preparation method and application thereof

Abstract

The invention provides a safe lithium ion battery gel electrolyte as well as a preparation method and application thereof. The safe lithium ion battery gel electrolyte is prepared from the following raw materials: lithium salt, an organic solvent, a film-forming agent, a thermal initiator and a gel polymer monomer, the gel polymer monomer comprises an acrylic ester compound and a phosphate ester compound. According to the gel electrolyte provided by the invention, through cooperation and compounding of all the components, especially introduction of the phosphate ester compound, the electrolyte has relatively good safety performance; the acrylate compound has an acrylate functional group and plays a role of a cross-linking agent, the phosphate compound plays a flame-retardant role, and through thermal polymerization, phosphate with the flame-retardant role is distributed among battery pole pieces and among active particles of the pole pieces in a three-dimensional network manner along with the acrylate cross-linking agent; thermal runaway among active particles can be uniformly and effectively blocked, so that the safety of the battery can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery electrolytes and relates to a safe lithium ion battery gel electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have become the main power source for portable electronic devices, electric vehicles and energy storage systems due to their high energy density, long cycle life and low self-discharge rate. As the requirements for battery energy density continue to increase, silicon-based materials have become one of the most promising alternatives to graphite anode materials due to their extremely high theoretical specific capacity (about 4200mAh / g).

[0003] However, silicon-based negative electrode materials have the problem of volume expansion during the charging and discharging process. Volume expansion will cause cracks in silicon-based negative electrode materials and even pulverize them, destroying the contact between the electrode material and the current collector, causing the active material to separate from the electrode sheet, and causing the battery capacity to decay rapidly.

[0004] Therefore, it is desirable in the art to develop an electrolyte for use in lithium-ion silicon negative electrode batteries so that the batteries have higher safety. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention aims to provide a safe lithium ion battery gel electrolyte and a preparation method and application thereof.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a safe lithium ion battery gel electrolyte, wherein the raw materials for preparing the safe lithium ion battery gel electrolyte include lithium salt, organic solvent, film-forming agent, thermal initiator and gel polymer monomer;

[0008] The gel polymer monomers include acrylic acid ester compounds and phosphate ester compounds.

[0009] The gel electrolyte provided by the present invention has good safety performance through the synergy and compounding of various components, especially the introduction of phosphate compounds; the acrylate compounds have acrylate functional groups and act as cross-linking agents, and the phosphate compounds act as flame retardants. Through thermal polymerization, the phosphates with flame retardant effects are distributed in a three-dimensional network between the battery pole pieces and between the active particles of the pole pieces along with the acrylate cross-linking agents, which can evenly and effectively block thermal runaway between the active particles, thereby improving the safety of the battery.

[0010] Acrylate compounds can form a polymer matrix with a network structure in the gel electrolyte, which is heat-resistant and resistant to oxidation. It is distributed between the particles of the battery pole piece, which can alleviate the material cracks and powdering problems caused by volume expansion and contraction between the particles. It can also eliminate the battery leakage problem and improve the physical hardness of the soft-pack battery, thereby improving the safety and stability of the battery.

[0011] Phosphate polymers with unsaturated functional groups react with acrylic compounds to form three-dimensional network polymers, wherein the phosphate functional groups have water absorption at high temperatures and form phosphoric acid polymers to play a flame retardant role.

[0012] The composite gel polymer monomers react with each other to generate a three-dimensional network gel electrolyte with flame retardant effect, which is distributed between the battery pole piece and the separator and between the pole piece particles, thereby improving the safety of the battery at high temperature.

[0013] Preferably, the acrylate compound includes any one or a combination of at least two of (ethoxy)bisphenol A diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, (ethoxy)1,6-hexanediol diacrylate, 1,4-butanediol acrylate, neopentyl glycol diacrylate, (propoxy)neopentyl glycol diacrylate, polyethylene glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, (ethoxy)trimethylolpropane triacrylate, (propoxy)trimethylolpropane triacrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol tetraacrylate, (ethoxy)pentaerythritol tetraacrylate, dipentaerythritol tetraacrylate, and (ethoxy)dipentaerythritol tetraacrylate.

[0014] Preferably, the phosphate ester compound includes any one of diethyl allyl phosphate, triallyl phosphite, tripropargyl phosphate, triallyl phosphate, triallyl butyl phosphate, diethyl allyl phosphonate, dipropyl allyl phosphate, triallyl ethyl phosphate, triethyl phosphate, tripropyl phosphate, triallyl phosphate, and tripropargyl phosphate, or a combination of at least two thereof.

[0015] Preferably, the phosphate compound has an unsaturated functional group.

[0016] Preferably, the lithium salt includes any one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(trifluorophosphoryl)imide, lithium bis(oxalatoborate), lithium hexafluorophosphate or lithium tetrafluoroborate, or a combination of at least two thereof.

[0017] Preferably, the lithium salt is, for example, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(trifluorophosphoryl)imide, lithium bis(oxalatoborate), lithium hexafluorophosphate, lithium tetrafluoroborate, a combination of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(trifluorophosphoryl)imide.

[0018] Preferably, the organic solvent includes any one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, ethyl propionate, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, acetone, acetonitrile, methyl acetate, ethyl acetate, methyl propionate, tetrahydrofuran or 2-methyltetrahydrofuran, or a combination of at least two thereof.

[0019] In the present invention, the organic solvent is, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, ethyl propionate, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, acetone, acetonitrile, methyl acetate, ethyl acetate, methyl propionate, tetrahydrofuran, 2-methyltetrahydrofuran, ethylene carbonate and ethyl methyl carbonate, ethylene carbonate and propylene carbonate, dimethyl carbonate and diethyl carbonate, ethyl methyl carbonate and ethyl acetate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, or a combination of ethyl methyl carbonate, ethyl acetate and ethyl propionate.

[0020] Preferably, the organic solvent comprises ethylene carbonate and ethyl methyl carbonate.

[0021] Preferably, the organic solvent comprises ethylene carbonate and ethyl methyl carbonate in a ratio of 3:7.

[0022] Preferably, the film-forming agent includes any one of vinylene carbonate, lithium difluorophosphate or lithium difluorooxalatoborate, or a combination of at least two of them. The film-forming agent can form a stable and uniform solid electrolyte interface (SEI) film on the electrode surface, effectively preventing the solvent molecules and other electrolyte components in the electrolyte from reacting with the electrode material.

[0023] Preferably, the film former is, for example, vinylene carbonate, lithium difluorophosphate, lithium difluorooxalatoborate, vinylene carbonate and lithium difluorophosphate, lithium difluorophosphate and lithium difluorooxalatoborate, or a combination of vinylene carbonate, lithium difluorophosphate and lithium difluorooxalatoborate.

[0024] Preferably, the thermal initiator includes any one of azobisisobutyronitrile, dibenzoyl peroxide, di(4-tert-butylcyclohexyl) peroxydicarbonate, dodecanoyl peroxide or diisopropyl peroxydicarbonate or a combination of at least two thereof. The main function of the thermal initiator in the gel electrolyte of lithium-ion batteries is to start the polymerization reaction, control the polymerization rate and promote the uniformity of the polymerization.

[0025] Preferably, the thermal initiator is, for example, azobisisobutyronitrile, dibenzoyl peroxide, di(4-tert-butylcyclohexyl)peroxydicarbonate, dodecanoyl peroxide, diisopropyl peroxydicarbonate, azobisisobutyronitrile and dibenzoyl peroxide, dibenzoyl peroxide and di(4-tert-butylcyclohexyl)peroxydicarbonate, or a combination of azobisisobutyronitrile, dibenzoyl peroxide and di(4-tert-butylcyclohexyl)peroxydicarbonate.

[0026] Preferably, the raw materials for preparing the safe lithium-ion battery gel electrolyte include the following components by weight percentage:

[0027]

[0028] The rest is organic solvent.

[0029] Preferably, the raw materials for preparing the safe lithium ion battery gel electrolyte are measured by weight percentage, the amount of lithium salt can be 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 45%, etc., the amount of film-forming agent can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., the thermal initiation The dosage of the solvent can be 0.05%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2% and the like; the dosage of the acrylate compound can be 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% and the like; the dosage of the phosphate compound can be 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% and the like; and the rest are organic solvents.

[0030] In a second aspect, the present invention provides a method for preparing the safe lithium ion battery gel electrolyte as described in the first aspect, the preparation method comprising the following steps:

[0031] (1) mixing a lithium salt, a film-forming agent, a thermal initiator, a gel polymer monomer and an organic solvent to obtain a mixed solution;

[0032] (2) Injecting the mixed solution into a battery cell, and after standing for a while, performing heat-pressing to initiate polymerization to form the safe lithium-ion battery gel electrolyte in the battery cell.

[0033] The gel electrolyte provided by the present invention forms a three-dimensional cross-linked flame-retardant gel network in the battery through in-situ polymerization, thereby improving the safety performance of the battery while maintaining the interface stability and mechanical strength of the battery. The three-dimensional cross-linked network is particularly suitable for silicon negative electrode batteries.

[0034] Preferably, the standing time is 40 to 50 h, for example, 40 h, 41 h, 42 h, 43 h, 44 h, 45 h, 46 h, 47 h, 48 h, 49 h or 50 h.

[0035] Preferably, the hot pressing is carried out in a forming cabinet.

[0036] Preferably, the hot pressing temperature is 70-90°C, for example, 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C or 90°C, and the hot pressing time is 0.2-2h, for example, 0.2h, 0.5h, 1h, 1.5h, 2h, etc.

[0037] In a third aspect, the present invention provides a use of the safe lithium ion battery gel electrolyte as described in the first aspect in a lithium ion battery.

[0038] Preferably, the lithium-ion battery comprises a lithium-ion silicon negative electrode battery.

[0039] Preferably, the battery containing the safe lithium ion battery gel electrolyte is placed at room temperature and then subjected to conventional formation, high temperature aging, vacuum pumping and capacity separation, and finally battery packaging to prepare a finished lithium ion battery.

[0040] Preferably, the voltage upper limit of the conventional formation is 3.8V, and the charging current is 0.1C and 0.2C.

[0041] Preferably, the high temperature aging temperature is 40-50°C, for example, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C or 50°C, and the high temperature aging time is 20-30h, for example, 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, 29h or 30h, etc.

[0042] Preferably, the vacuum degree of the vacuum pumping is 70-100 kPa, for example, 70 kPa, 75 kPa, 80 kPa, 85 kPa, 90 kPa, 95 kPa, 100 kPa, etc., and the vacuum pumping time is 3-10 s, for example, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s or 10 s, etc.

[0043] Compared with the prior art, the present invention has at least the following beneficial effects:

[0044] The gel electrolyte provided by the present invention has good safety performance through the synergy and compounding of various components, especially the introduction of phosphate compounds; the acrylate compounds have acrylate functional groups and act as cross-linking agents, and the phosphate compounds act as flame retardants. Through thermal polymerization, the phosphates with flame retardant effects are distributed in a three-dimensional network between the battery pole pieces and between the active particles of the pole pieces along with the acrylate cross-linking agents, which can evenly and effectively block thermal runaway between the active particles, thereby improving the safety of the battery. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0046] Example 1

[0047] In this embodiment, a safe lithium ion battery gel electrolyte is provided. The raw materials for preparing the safe lithium ion battery gel electrolyte include the following components in terms of weight percentage:

[0048]

[0049] The rest is organic solvent;

[0050] Among them, the lithium salt is lithium hexafluorophosphate; the film-forming agent is a mixture of vinylene carbonate, lithium difluorophosphate and lithium difluorooxalatoborate in a mass ratio of 2:1:1; the thermal initiator is azobisisobutyronitrile; the acrylate compound is pentaerythritol tetraacrylate; the phosphate compound is triethyl phosphate; and the organic solvent is a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a mass ratio of 3:7.

[0051] The preparation method comprises the following steps:

[0052] (1) mixing an organic solvent and a lithium salt, and stirring until the lithium salt is completely dissolved; then adding a film-forming agent, an acrylate compound, and a phosphate compound, and stirring thoroughly; finally adding a thermal initiator, and stirring thoroughly to obtain a mixed solution;

[0053] (2) The mixed solution is injected into a battery cell, allowed to stand for 45 hours, and then subjected to hot pressing at 85° C. for 0.5 hours in a formation cabinet to initiate polymerization, thereby forming the safe lithium-ion battery gel electrolyte in the battery cell.

[0054] In this embodiment, a lithium-ion silicon negative electrode battery is also provided, and the preparation method includes the following steps:

[0055] The battery containing the gel electrolyte was placed at room temperature and then subjected to conventional formation, with the upper limit of the formation voltage being 3.8V and the charging current being 0.1C and 0.2C;

[0056] The formed battery is subjected to high temperature aging at 45°C for 24 hours.

[0057] After aging, vacuum pumping is performed with a vacuum degree of 88 kPa and a vacuum pumping time of 5 s. The film formation potential data is checked, the battery quality is checked, and the battery liquid absorption amount is estimated.

[0058] Finally, the battery is divided into different capacities, with the currents being 0.2C and 0.5C respectively. After two weeks of charge and discharge cycles, the battery manufacturing process is completed and a finished lithium-ion silicon negative electrode battery is obtained.

[0059] Embodiment 2-8

[0060] The only difference between Examples 2-8 and Example 1 is that the specific selection and / or dosage (%) of the acrylate compound and the phosphate compound is different, as shown in Table 1. The contents not shown in Table 1 are deemed to be the same as those in Example 1.

[0061] The preparation method is as in Example 1.

[0062] Table 1

[0063]

[0064] Comparative Example 1

[0065] The only difference between this comparative example and Example 1 is that the preparation raw materials do not include phosphate compounds.

[0066] Comparative Example 2

[0067] The only difference between this comparative example and Example 1 is that the preparation raw materials do not include acrylic acid ester compounds, phosphate compounds and thermal initiators.

[0068] The battery cells used in Examples 1 to 8 and Comparative Examples 1 to 2 are: positive electrode material ternary 811 (Rongbai Technology), negative electrode material S420A (B&T), and the separator is a polypropylene separator. It should be noted that the electrolyte provided in the present invention is not only applicable to ternary 811 positive electrode material, but also to other ternary positive electrode materials with different nickel, cobalt and manganese contents; the electrolyte provided in the present invention is not only applicable to S420A negative electrode, but also has the effect of protecting the particle surface in negative electrodes with higher silicon content or graphite negative electrodes.

[0069] The performance test of the batteries provided in the embodiments and comparative examples is carried out in the following manner:

[0070] (1) Thermal shock test: The tested battery is placed steadily in a test cabinet, and the test cabinet is heated to 150°C±2°C at a heating rate of 5°C±2°C and kept warm for 30 min. The passing standard is that the battery does not catch fire or explode. In each embodiment and comparative example, 5 batteries are tested respectively, and the number of batteries that pass the test is recorded. If all 5 batteries pass the test, it is recorded as 5 / 5; if 4 batteries pass the test, it is recorded as 4 / 5, and the same applies to other cases.

[0071] (2) Needle puncture test: A battery to be tested with a 100% SOC is placed in an explosion-proof test cabinet at an ambient temperature of (20±5°C), and a 3mm diameter non-rusting steel needle is used to pierce the center of the largest surface of the battery at a speed of 20mm / s and maintained for 1 minute. Pass standard: the battery does not catch fire or explode. In each embodiment and comparative example, 5 batteries are tested respectively, and the number of batteries that pass the test is recorded. If all 5 batteries pass the test, it is recorded as 5 / 5; if 4 batteries pass the test, it is recorded as 4 / 5, and the same applies to other examples.

[0072] The performance test results are shown in Table 2.

[0073] Table 2

[0074]

[0075]

[0076] It can be seen from Table 2 that the batteries prepared by the gel electrolyte provided by the embodiments of the present invention have relatively high safety performance (the passing rate of the thermal shock test is 100%, and the passing rate of the needle puncture test is 80% to 100%).

[0077] Compared with Example 1, the pass rate of the puncture test of the battery prepared by the gel electrolyte provided in Comparative Example 1 is significantly reduced, and the safety performance of the battery is reduced; the pass rate of the thermal shock test of the battery prepared by the gel electrolyte provided in Comparative Example 2 is reduced, the pass rate of the puncture test is greatly reduced, and the safety performance of the battery is significantly reduced.

[0078] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the safe lithium-ion battery gel electrolyte and its preparation method and application, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A safe lithium ion battery gel electrolyte, characterized in that: The raw materials for preparing the safe lithium ion battery gel electrolyte include lithium salt, organic solvent, film-forming agent, thermal initiator and gel polymer monomer; The gel polymer monomers include acrylic acid ester compounds and phosphate ester compounds.

2. The safe lithium ion battery gel electrolyte according to claim 1, characterized in that: The acrylate compound includes any one of (ethoxy)bisphenol A diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, (ethoxy)1,6-hexanediol diacrylate, 1,4-butanediol acrylate, neopentyl glycol diacrylate, (propoxy)neopentyl glycol diacrylate, polyethylene glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, (ethoxy)trimethylolpropane triacrylate, (propoxy)trimethylolpropane triacrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol tetraacrylate, (ethoxy)pentaerythritol tetraacrylate, dipentaerythritol tetraacrylate, and (ethoxy)dipentaerythritol tetraacrylate, or a combination of at least two thereof.

3. The safe lithium ion battery gel electrolyte according to claim 1 or 2, characterized in that: The phosphate compound includes any one of diethyl allyl phosphate, triallyl phosphite, tripropargyl phosphate, triallyl phosphate, triallyl butyl phosphate, diethyl allylphosphonate, dipropyl allyl phosphate, triallyl ethyl phosphate, triethyl phosphate, tripropyl phosphate, triallyl phosphate, and tripropargyl phosphate, or a combination of at least two thereof; Preferably, the phosphate compound has an unsaturated functional group.

4. The safe lithium ion battery gel electrolyte according to any one of claims 1 to 3, characterized in that: The lithium salt includes any one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(trifluorophosphoryl)imide, lithium bis(oxalatoborate), lithium hexafluorophosphate or lithium tetrafluoroborate, or a combination of at least two thereof; Preferably, the organic solvent comprises any one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, ethyl propionate, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, acetone, acetonitrile, methyl acetate, ethyl acetate, methyl propionate, tetrahydrofuran or 2-methyltetrahydrofuran, or a combination of at least two thereof, preferably a combination of ethylene carbonate and ethyl methyl carbonate.

5. The safe lithium ion battery gel electrolyte according to any one of claims 1 to 4, characterized in that: The film-forming agent includes any one of vinylene carbonate, lithium difluorophosphate or lithium difluorooxalatoborate, or a combination of at least two thereof.

6. The safe lithium ion battery gel electrolyte according to any one of claims 1 to 5, characterized in that: The thermal initiator includes any one of azobisisobutyronitrile, dibenzoyl peroxide, di(4-tert-butylcyclohexyl)peroxydicarbonate, dodecanoyl peroxide or diisopropyl peroxydicarbonate, or a combination of at least two thereof.

7. The safe lithium ion battery gel electrolyte according to any one of claims 1 to 6, characterized in that: The raw materials for preparing the safe lithium ion battery gel electrolyte include the following components by weight percentage: The rest is organic solvent.

8. A method for preparing a safe lithium ion battery gel electrolyte as claimed in any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: (1) mixing a lithium salt, a film-forming agent, a thermal initiator, a gel polymer monomer and an organic solvent to obtain a mixed solution; (2) Injecting the mixed solution into a battery cell, and after standing for a while, performing heat-pressing to initiate polymerization to form the safe lithium-ion battery gel electrolyte in the battery cell.

9. The preparation method according to claim 8, characterized in that: The standing time is 40 to 50 hours; Preferably, the hot pressing is carried out in a forming cabinet; Preferably, the hot pressing temperature is 70-90° C., and the hot pressing time is 0.2-2 h.

10. Use of the safe lithium ion battery gel electrolyte according to any one of claims 1 to 7 in a lithium ion battery; Preferably, the lithium-ion battery comprises a lithium-ion silicon negative electrode battery; Preferably, the battery containing the safe lithium ion battery gel electrolyte is placed at room temperature, and then subjected to conventional formation, high temperature aging, vacuum pumping and capacity separation, and finally battery packaging to prepare a finished lithium ion battery; Preferably, the voltage upper limit of the conventional formation is 3.8V, and the charging current is 0.1C and 0.2C; Preferably, the high temperature aging temperature is 40-50°C, and the high temperature aging time is 20-30h; Preferably, the vacuum degree of the vacuum pumping is 70-100 kPa, and the vacuum pumping time is 3-10 s.

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