WO2025001087A1 - 电解液和储能装置 - Google Patents

电解液和储能装置 Download PDF

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WO2025001087A1
WO2025001087A1 PCT/CN2024/073027 CN2024073027W WO2025001087A1 WO 2025001087 A1 WO2025001087 A1 WO 2025001087A1 CN 2024073027 W CN2024073027 W CN 2024073027W WO 2025001087 A1 WO2025001087 A1 WO 2025001087A1
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electrolyte
energy storage
storage device
positive electrode
lithium
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French (fr)
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邹伟
徐坤
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Xiamen Hithium Energy Storage Technology Co Ltd
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Xiamen Hithium Energy Storage Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0034—Fluorinated solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of energy storage devices, and in particular to an electrolyte and an energy storage device.
  • the purpose of the embodiments of the present application is to provide an electrolyte and an energy storage device.
  • the energy storage device made using the electrolyte can ensure good overcharge safety performance when having a large single cell capacity.
  • An embodiment of the present application provides an electrolyte, which includes, based on the mass of the electrolyte, a fluorinated solvent with a mass percentage of a, a cyclic carbonate with a mass percentage of b, and lithium hexafluorophosphate with a mass percentage of c, wherein 1% ⁇ a ⁇ 30%, 25% ⁇ b ⁇ 45%, and 7% ⁇ c ⁇ 10%.
  • the embodiment of the present application provides an electrolyte, which introduces a fluorinated solvent into the electrolyte to improve the oxidation resistance of the electrolyte and reduce the heat generated by the oxidation reaction of the electrolyte during overcharging.
  • the embodiment of the present application adjusts and reduces the content of lithium hexafluorophosphate in the electrolyte, while ensuring that the electrolyte has sufficient lithium ion conductivity, and can reduce the content of Lewis acid formed by the reaction of lithium hexafluorophosphate in the electrolyte with water in the electrolyte, so that the solid electrolyte interface film (SEI film) formed on the surface of the negative electrode plate and the positive electrode surface passivation film (CEI film) formed on the surface of the positive electrode plate are less corroded, and at the same time, the Lewis acid captures F on the fluorinated solvent, reduces the defluorination effect of the fluorinated solvent, and allows the fluorinated solvent to play a better role in the overcharging process.
  • SEI film solid electrolyte interface film
  • CEI film positive electrode surface passivation film
  • An embodiment of the present application also provides an energy storage device, including a positive electrode plate and the electrolyte as described above.
  • the present application provides an energy storage device, which includes a housing, a battery cell, and an electrolyte. Installed on the inner side of the shell, the electrolyte is injected into the inner side of the shell and soaks the battery core.
  • the overall capacity of the energy storage device is not less than 280Ah (Ampere-Hour).
  • the energy storage device can be a lithium-ion battery.
  • the battery cell includes a positive electrode sheet, a separator, a negative electrode sheet, a positive electrode ear and a negative electrode ear.
  • the separator is located between the positive electrode sheet and the negative electrode sheet, the positive electrode ear is electrically connected to the positive electrode sheet, and the negative electrode ear is electrically connected to the negative electrode sheet.
  • the positive electrode sheet, the separator, and the negative electrode sheet can be stacked in sequence, wound to form a bare battery cell, and then the positive electrode ear and the negative electrode ear are welded to prepare the battery cell.
  • the positive electrode plate includes a positive electrode current collector and a positive electrode active layer coated on the surface of the positive electrode current collector.
  • the coating density of the positive electrode active layer is t g/1540.25 mm2, which satisfies 0.25 ⁇ t ⁇ 0.4.
  • t represents the coating weight of the positive electrode material layer.
  • the positive electrode current collector is aluminum foil.
  • the positive electrode material layer includes materials such as positive electrode active materials and additives.
  • the positive electrode active material is lithium iron phosphate.
  • the additives in the positive electrode material layer include adhesives and conductive agents, etc.
  • the adhesive is polyvinylidene fluoride (PVDF) and the conductive agent is conductive carbon black SP (Super P).
  • the coating weight t of the positive electrode active layer can be 0.25, 0.3, 0.4, and any value between the above values.
  • the smaller the coating weight t of the positive electrode active layer the smaller the energy density of the obtained energy storage device will be.
  • more battery core materials will be consumed, such as current collectors, shells, etc., which will increase the cost of energy storage.
  • the larger the coating weight t of the positive electrode active layer the lower the cost of energy storage will be.
  • t is too large and exceeds the range value, it will cause problems with the wetting of the material, leading to the occurrence of lithium precipitation and gas production, which will affect the overcharge safety performance and charge and discharge cycle performance of the energy storage device.
  • the diaphragm may be an existing battery diaphragm, and illustratively, the diaphragm is a polyethylene film.
  • the negative electrode plate includes a negative electrode current collector and a negative electrode active layer covering the surface of the negative electrode current collector. illustratively, the negative electrode current collector is aluminum foil.
  • the negative electrode active layer includes materials such as negative electrode active materials and additives. illustratively, the negative electrode active material is graphite.
  • the additives in the negative electrode active layer include materials such as thickeners, adhesives, and conductive agents.
  • the adhesive is Polymerized Styrene Butadiene Rubber (SBR), and the conductive agent is conductive carbon black SP (Super P).
  • the electrolyte includes a solvent and a lithium salt.
  • the solvent includes a fluorinated solvent and a cyclic carbonate
  • the lithium salt includes lithium hexafluorophosphate (LiPF6).
  • the mass percentage of the fluorinated solvent is a, 1% ⁇ a ⁇ 30%
  • the mass percentage of the cyclic carbonate is b, 25% ⁇ b ⁇ 45%
  • the mass percentage of lithium hexafluorophosphate is c, 7% ⁇ c ⁇ 10%. In some embodiments, 3% ⁇ a ⁇ 15%.
  • conventional electrolyte solvents such as dimethyl carbonate, ethyl methyl carbonate, etc. can also be added to the electrolyte.
  • additives such as vinyl sulfate (1,3,2-dioxathiolane 2,2-dioxide, DTD) can also be added to the electrolyte.
  • the mass percentage content a of the fluorinated solvent can be 1%, 3%, 5%, 10%, 15%, 30%, and any value between the above values. Too little content a of the fluorinated solvent will not sufficiently improve the overcharge safety performance of the formed energy storage device. Too much content a of the fluorinated solvent will affect the viscosity and conductivity of the electrolyte, thereby deteriorating the charge and discharge cycle performance. By controlling the content a of the fluorinated solvent to meet 1% ⁇ a ⁇ 30%, it is beneficial to ensure that the formed energy storage device has both good overcharge safety performance and charge and discharge cycle performance.
  • the mass percentage of cyclic carbonate b can be 25%, 27%, 35%, 40%, 45%, and any other values between the above values.
  • the main function of cyclic carbonate is to form a film on both the positive and negative electrodes.
  • the content b of cyclic carbonate is too little, it cannot protect the positive and negative electrodes, which will have an adverse effect on overcharge safety performance and charge and discharge cycle performance.
  • the content b of cyclic carbonate is too much, the negative electrode film may be too thick. Too thick film formation may cause problems at the negative electrode interface. Once the interface has problems, the overcharge safety performance and charge and discharge cycle performance will deteriorate.
  • the mass percentage of lithium hexafluorophosphate c can be 7%, 7.5%, 8%, 9%, 10%, and any value between the above values.
  • the main effect is the conductivity of the electrolyte, and ion transmission will be problematic, thereby deteriorating the charge and discharge cycle performance of the formed energy storage device.
  • the lithium hexafluorophosphate content c is too much, the viscosity of the electrolyte will increase, which is not good for conductivity, and more acidic substances such as PF5 and POF3 will be produced, which will damage SEI and CEI, thereby affecting the charge and discharge cycle performance of the formed energy storage device.
  • By controlling the lithium hexafluorophosphate content c to meet 7% ⁇ c ⁇ 10%, it is beneficial to ensure that the formed energy storage device has both good overcharge safety performance and charge and discharge cycle performance.
  • the fluorinated solvent includes at least one of fluorinated carbonate, fluorinated carboxylate and fluorinated ether.
  • the fluorinated carbonate is selected from at least one of chemical formula (I-1) to chemical formula (I-7):
  • the fluorocarboxylate is selected from at least one of Formula (I-8) to Formula (I-17):
  • the fluoroether is selected from at least one of the chemical formulas (I-18) to (I-21):
  • the cyclic carbonate is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), di-fluoroethylene carbonate (DFEC) and vinylene carbonate (VC).
  • EC ethylene carbonate
  • PC propylene carbonate
  • FEC fluoroethylene carbonate
  • DFEC di-fluoroethylene carbonate
  • VC vinylene carbonate
  • the lithium salt can also include at least one of lithium difluorophosphate (LiDFP), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), lithium difluorooxalyldifluoroborate (LiODFB), lithium bis(oxalate)borate (LiBOB), and lithium tetrafluoroborate (LiBF4).
  • LiDFP lithium difluorophosphate
  • LiFSI lithium bis(fluorosulfonyl)imide
  • LiTFSI lithium bistrifluoromethanesulfonimide
  • LiODFB lithium difluorooxalyldifluoroborate
  • LiBOB lithium bis(oxalate)borate
  • LiBF4 lithium tetrafluoroborate
  • the coating weight t of the positive electrode active layer and making large-capacity batteries have the benefit of increasing the overall energy density of the battery cell and reducing the cost of the battery cell, but it also brings challenges to the safety performance of the battery cell.
  • the high coating weight of the positive electrode active layer brings a greater electrode ohmic impedance to the battery cell.
  • the increase in battery cell impedance causes the battery cell to generate more Joule heat during the charging process.
  • the capacity of the manufactured single battery cell is above 280Ah, and the large-capacity battery cell has further advantages over the small-capacity battery cell in terms of cost and energy density.
  • due to the poor heat dissipation of large-capacity batteries heat is easily accumulated in the battery cell during the charging process. The heat accumulation can easily cause a chain chemical reaction inside the battery cell, resulting in safety problems such as battery cell failure and fire.
  • the voltage will rise to the maximum voltage of 1.5V during the continuous charging process.
  • the voltage of the battery cell increases during the continuous charging process, and the electrolyte undergoes an oxidation reaction at the positive electrode.
  • the reaction heat generated by the reaction accumulates in the battery cell.
  • the heat reaches a certain level, under the action of high temperature, the reaction between the electrolyte and the positive electrode plate is further intensified.
  • the SEI film Solid Electrolyte Interphase
  • the fully charged negative electrode directly contacts the electrolyte, and the electrolyte undergoes a reduction reaction at the negative electrode, further releasing heat and accumulating heat.
  • the diaphragm in the battery cell melts and ruptures, resulting in contact between the positive and negative electrodes.
  • the battery cell may catch fire or explode, thereby affecting the safety performance of the battery cell.
  • the present application embodiment provides an electrolyte, including 1% to 30% by mass of a fluorinated solvent, 25% to 45% by mass of a cyclic carbonate, and 7% to 10% by mass of lithium hexafluorophosphate.
  • the embodiments of the present application adjust and reduce the content of lithium hexafluorophosphate in the electrolyte.
  • the coating weight t of the positive electrode active layer, the mass percentage a of the fluorinated solvent, the mass percentage b of the cyclic carbonate and the mass percentage c of the lithium salt satisfy the following relationship: 0.07 ⁇ (1-a-b)*c/t ⁇ 0.288.
  • "*" represents a multiplication sign.
  • (1-a-b)*c/t can be 0.07, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.27, 0.288 and any value between the above values.
  • lithium precipitation may occur in the pores or on the negative electrode layer, causing a large number of reactions between the dendrites precipitated from the negative electrode and the electrolyte during overcharging, generating a large amount of reaction heat, resulting in unsatisfactory overcharge test results.
  • dead lithium is produced, causing irreversible loss of capacity.
  • due to the reaction between the precipitated lithium and the electrolyte by-products, gas generation and other interface problems are caused, resulting in unsatisfactory cycle performance of the energy storage device.
  • the prepared energy storage device can be guided to have a large-capacity single cell while ensuring that the cell overcharge safety test performance rating meets the standard and has good charge and discharge cycle performance, thereby guiding the preparation of an energy storage device with good overcharge safety performance and good charge and discharge cycle performance.
  • Examples 1-23 and Comparative Examples 1-12 each provide an energy storage device, and the energy storage device is exemplified by a lithium-ion battery, which is specifically prepared according to the following steps:
  • the positive electrode active material lithium iron phosphate, conductive carbon black SP, and adhesive PVDF are dispersed in a solvent NMP (N-Methylpyrrolidone) at a mass ratio of 97:0.7:2.3 and mixed evenly to obtain positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and after drying, cold pressing, slitting, and cutting, the positive electrode sheet is obtained.
  • the positive electrode slurry is coated to form a positive electrode active layer, and the coating density of the positive electrode active layer is t g/1540.25 mm 2 , where t represents the coating mass of the positive electrode active layer.
  • negative electrode sheet artificial graphite, conductive carbon SP, thickener CMC and binder SBR are dispersed in deionized water according to the mass ratio of 96.5:0.5:1:2 and mixed evenly to obtain negative electrode slurry, which is then coated on the negative electrode current collector aluminum foil, and then dried, cold pressed, slit and cut to obtain negative electrode sheet.
  • the negative electrode slurry coating forms the negative electrode active layer.
  • Preparation of electrolyte In an argon atmosphere glove box with a moisture content of ⁇ 1ppm, solvent A, dimethyl carbonate, The methyl ester and the ethyl ester are mixed in a mass ratio of 1:1:1, and then the dried electrolyte lithium hexafluorophosphate (LiPF6) is dissolved in the solvent, stirred until completely dissolved and uniformly dissolved, and the solvent A is added and mixed uniformly to obtain an electrolyte.
  • the solvent A includes a fluorinated solvent and a cyclic carbonate.
  • diaphragm 16um polyethylene film is used as diaphragm.
  • Preparation of lithium-ion batteries stack the prepared positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is in the middle of the positive electrode sheet and the positive and negative electrode sheets to separate the positive electrode sheet from the positive and negative electrode sheets, and then wind them to obtain a bare cell, and then weld the positive and negative ears to obtain a cell. Assemble the cell into the shell, inject the prepared electrolyte, and then package, stand, form, shape, and perform capacity testing on the cell to finally prepare a lithium-ion battery.
  • the capacity of the single cell, the coating weight t of the positive electrode active layer, the content of solvent A and the lithium salt LiPF6 are shown in Table 1.
  • the energy storage devices of Examples 1-23 and Comparative Examples 1-12 were subjected to charge and discharge cycle performance tests and safety overcharge tests, and the results are shown in Table 1.
  • the process of the charge-discharge cycle performance test is as follows: the energy storage device is subjected to a charge-discharge cycle test on a charge-discharge instrument, the test temperature is 25°C, the cycle rate is 1C (i.e., both the charge rate and the discharge rate are 1C), the charging voltage is 2.5V to 3.65V, and the capacity retention rate after the cycle is calculated.
  • the process of the safety overcharge test is: test the energy storage device on the charging and discharging instrument, let it stand for 5 hours at (25 ⁇ 2)°C; discharge to 2.5V at 1C, charge to 3.65V at 1C and let it stand for 10 minutes. Then transfer it to the overcharge test instrument for testing, charge at a constant current of 1C, make the voltage of the device reach 5.475V or the charging time reach 1h, observe for 1h, and record whether there is expansion, leakage, smoke, fire, or explosion.
  • the battery cell does not leak, it is the first level of compliance; if the battery cell leaks but does not smoke, it is the second level of compliance; if the battery cell leaks and smokes, but does not catch fire or explode, it is the third level of compliance; if the battery cell catches fire or explodes, it is the fourth level, which means it does not meet the standard.
  • the energy storage devices of Examples 1 to 6 have the same capacity of the single cells and the same coating amount t of the positive electrode active layer, and different fluorinated solvents are added to the electrolyte of the energy storage device, which can improve the overcharge safety performance of the energy storage device.
  • the fluorinated solvents added in Examples 2 to 6 have better effects than the fluorinated solvent added in Example 1.
  • fluorinated solvents are added to the electrolytes of the energy storage devices of Examples 7 to 9, and as the content a of the fluorinated solvent gradually increases, the overcharge safety performance of the energy storage device is significantly improved.
  • the experimental results show that on the basis of adding cyclic carbonates to the electrolyte, the addition of fluorinated solvents and increasing the content of fluorinated solvents in the electrolyte can improve the overcharge safety performance of the energy storage device. This may be due to the fact that fluorinated solvents have antioxidant properties, which can greatly improve the oxidation resistance of the electrolyte.
  • the oxidation reaction of the electrolyte on the positive electrode is reduced, that is, the amount of oxidation reaction of the electrolyte with the positive electrode during the overcharging process is greatly reduced, and the reaction heat generated by the oxidation reaction is reduced, so that the battery cell accumulates less heat at the beginning.
  • the reduction in heat accumulation can reduce the possibility of decomposition of the solid electrolyte interface film (SEI film) on the negative electrode side, thereby prompting the energy storage device to maintain a healthier state during overcharging, thereby improving the performance of the energy storage device in the overcharge safety test.
  • the mass fraction a of the fluorinated solvent in the electrolyte is 1% to 30%.
  • the mass fraction a of the fluorinated solvent in the electrolyte is 3% to 15%.
  • the Lewis acid may not only attack the solid electrolyte interface film (SEI film) on the negative electrode side and the positive electrode surface passivation film (CEI film), resulting in direct contact and reaction between the electrolyte and the positive electrode plate or the negative electrode plate, but also may have the possibility of capturing fluoride ions in the fluorinated solvent. Therefore, when the electrolyte contains less LiPF6, less Lewis acids such as PF5 are produced in the electrolyte, which reduces the attack of the acid on the positive electrode CEI film and the negative electrode SEI film, making the SEI film formed on the surface of the negative electrode plate and the CEI film formed on the surface of the positive electrode plate less corroded.
  • SEI film solid electrolyte interface film
  • CEI film positive electrode surface passivation film
  • the Lewis acid captures F on the fluorinated solvent, which protects the fluorinated solvent from damage and allows the fluorinated solvent to play a role in the overcharging process of the energy storage device, thereby further improving the overcharging safety performance of the energy storage device.
  • Examples 7 to 9 although the addition of fluorinated solvents within a certain content range improves the overcharge safety performance of the energy storage device in Examples 7 to 10, as the content of fluorinated solvents increases, the capacity retention rate of the energy storage device after 1000 cycles at 25°C gradually decreases. This may be due to the competition between the fluorinated solvents and the cyclic carbonates for film formation on the negative electrode side.
  • Examples 10 to 14 although reducing the content of lithium salt LiPF6 in the electrolyte can improve the overcharge safety performance of Examples 10 to 14, the capacity retention rate of the energy storage device after 1000 cycles at 25°C gradually decreases. It can be seen that the overcharge safety performance of the energy storage device may be improved by adding fluorinated solvents within a certain content range and reducing the content of lithium salt LiPF6, but this strategy may have the possibility of a vicious cycle.
  • the electrolytes of the energy storage devices of Examples 15 to 18 all contain fluorinated solvents and cyclic carbonates.
  • the energy storage device maintains good overcharge safety performance while the capacity retention rate after 1000 cycles at 25°C gradually increases.
  • the experimental results show that by increasing the content of the cyclic carbonate solvent in the electrolyte, it is possible to solve the overcharge safety performance problem of the energy storage device while ensuring the charge and discharge cycle performance of the energy storage device. This is because the fluorinated solvent has not yet formed a dense SEI on the negative electrode side.
  • the fluorinated solvent is easily reduced on the negative electrode side, and the SEI membrane formed by the reduction product is not dense enough, which may lead to a decrease in the electrical performance of the energy storage device.
  • the cyclic carbonate can be ring-opened and polymerized at the negative electrode to form a dense SEI membrane, solving the problem of poor film formation caused by the introduction of fluorinated solvents into the electrolyte.
  • the high concentration of cyclic carbonate can also prevent the consumption and oxidation of fluorinated solvents on the negative electrode side, stabilize the content of fluorinated solvents in the electrolyte, and thus indirectly improve the oxidation resistance of the electrolyte, thereby solving the overcharge safety performance of the energy storage device and improving the charge and discharge cycle performance of the energy storage device.
  • the content a of the fluorinated solvent in the electrolyte of the energy storage device of Comparative Example 10 exceeds 30%, and the charge-discharge cycle performance of the obtained energy storage device is very poor.
  • the content c of the lithium salt LiPF6 in the electrolyte of the energy storage device of Comparative Example 11 is less than 7%, and the charge-discharge cycle performance of the obtained energy storage device is very poor.
  • the content b of cyclic carbonate in the electrolyte of the energy storage device of comparative example 12 exceeds 45%, and the obtained energy storage device has poor overcharge safety performance.
  • the electrolyte of the energy storage device of Examples 1 to 23 by adding fluorinated solvent, cyclic carbonate and lithium salt LiPF6, and controlling the content a of fluorinated solvent in the electrolyte to satisfy 1% ⁇ a ⁇ 30%, the content b of cyclic carbonate to satisfy 25% ⁇ b ⁇ 45%, and the content c of lithium salt LiPF6 to satisfy 7% ⁇ c ⁇ 10%, the overcharge safety performance of the energy storage device can be guaranteed, or the capacity retention rate after 1000 cycles at 25°C can be guaranteed, thereby ensuring the charge and discharge cycle performance of the energy storage device.
  • the relationship is satisfied: 0.07 ⁇ (1-a-b)*c/t ⁇ 0.288.
  • the prepared energy storage device has a large single cell capacity while the overcharge safety performance level reaches level two or level one, and the overcharge safety performance is very good.

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Abstract

一种电解液和储能装置，以电解液的质量计，电解液包括质量百分含量为a的氟代溶剂、质量百分含量为b的环状碳酸酯和质量百分含量为c的六氟磷酸锂，其中，1％≤a≤30％，25％≤b≤45％，7％≤c≤10％。利用该电解液制得的储能装置在具有较大单体电芯容量时，能够保证具有较好的过充安全性能。

Description

电解液和储能装置
本申请要求于2023年06月30日提交中国专利局、申请号为2023107991733、申请名称为“电解液和储能装置”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及储能装置技术领域，尤其涉及一种电解液和储能装置。
背景技术
现有储能装置中，大容量的电芯相对小容量电芯，在成本上和能量密度上进一步取得优势。但是由于大容量电芯的散热差，大容量电芯在过充安全测试过程中，热量极易累积在电芯中。热量累积容易造成电芯内部发生连锁化学反应，从而造成电芯失效、着火等安全问题，进而影响储能装置的过充安全性能。
发明内容
本申请实施例的目的是提供一种电解液和储能装置，利用该电解液制得的储能装置在具有较大单体电芯容量时，能够保证具有较好的过充安全性能。
本申请实施例提供一种电解液，以电解液的质量计，电解液包括质量百分含量为a的氟代溶剂、质量百分含量为b的环状碳酸酯和质量百分含量为c的六氟磷酸锂，其中，1％≤a≤30％，25％≤b≤45％，7％≤c≤10％。
本申请实施例提供一种电解液，通过在电解液中引入氟代溶剂，以提升电解液的耐氧化能力，减少过充过程中电解液发生氧化反应而产生的热量。同时，在引入氟代溶剂的同时，为了解决氟代溶剂容易在负极发生还原反应的问题，本申请实施例通过调整降低电解液中六氟磷酸锂的含量，在保证电解液中具有足够的锂离子导电的同时，能够降低电解液中六氟磷酸锂与电解液中的水分反应形成的路易斯酸的含量，从而使得负极极片表面形成的固体电解质界面膜(SEI膜)及正极极片表面形成的正极表面钝化膜(CEI膜)更少地发生腐蚀，同时减少了路易斯酸对氟代溶剂上F的夺取，减少了氟代溶剂的脱氟效应，使得氟代溶剂更好地在过充过程中发挥作用。此外，通过提高电解液中环状碳酸酯的含量，利用环状碳酸酯可以在负极开环聚合，形成致密的SEI膜的特性，解决了氟代溶剂引入电解液中竞争成膜不良的问题，同时高浓度的环状碳酸酯在稳定负极的同时，还能够阻止氟代溶剂在负极侧的消耗与氧化，稳定氟代溶剂在电解液中的含量，从而间接提高电解液的耐氧化性，进而在解决储能装置的过充安全性能的同时，利于提升储能装置的充放电循环性能。
本申请实施例还提供一种储能装置，包括正极极片和如上述的电解液。
具体实施方式
下面将对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
本申请实施例提供一种储能装置，储能装置包括外壳、电芯和电解液。具体的，电芯安 装于外壳的内侧，电解液注入于外壳的内侧，且浸润电芯。示例性的，储能装置的整体容量不小于280Ah(Ampere-Hour，安培小时)。示例性的，储能装置可为锂离子电池。
电芯包括正极极片、隔膜、负极极片、正极耳和负极耳。隔膜位于正极极片与负极极片之间，正极耳与正极极片电连接，负极耳与负极极片电连接。示例性的，可将正极极片、隔膜、负极极片依次叠放，卷绕形成裸电芯，然后焊接正极耳和负极耳制备得到电芯。
其中，正极极片包括正极集流体和覆于正极集流体的表面的正极活性层。正极极片中，正极活性层的涂布密度为t g/1540.25mm2，其满足0.25≤t≤0.4。其中，t表示正极材料层的涂布重量。示例性的，正极集流体为铝箔。正极材料层包括正极活性材料和添加剂等材料。示例性的，正极活性材料为磷酸铁锂。其中，正极材料层中的添加剂包括粘接剂和导电剂等。示例性的，粘接剂为聚偏二氟乙烯(Polyvinylidene Difluoride，PVDF)，导电剂为导电炭黑SP(Super P)。
具体的，正极活性层的涂布重量t可以为0.25、0.3、0.4等数值，以及上述数值之间的任意数值。正极活性层的涂布重量t越小的话，得到的储能装置的能量密度会比较小，同时，会耗费更多的电芯材料，比如集流体、壳体等，使储能的成本变高。正极活性层的涂布重量t越大的话，储能的成本会随之下降，但是t的过大，超过范围值，会使得材料的浸润出现问题，进而导致析锂、产气能情况的出现，从而会影响储能装置的过充安全性能和充放电循环性能。
隔膜可采用现有的电池隔膜，示例性的，隔膜为聚乙烯膜。负极极片包括负极集流体和覆于负极集流体的表面的负极活性层。示例性的，负极集流体为铝箔。负极活性层包括负极活性材料和添加剂等材料。示例性的，负极活性材料为石墨。其中，负极活性层中的添加剂包括增稠剂、粘接剂、导电剂等材料。示例性的，粘接剂为丁苯橡胶(Polymerized Styrene Butadiene Rubber，SBR)，导电剂为导电炭黑SP(Super P)。
电解液包括溶剂和锂盐。溶剂包括氟代溶剂和环状碳酸酯，锂盐包括六氟磷酸锂(Lithium Hexafluorophosphate，LiPF6)。示例性的，以电解液的质量计，氟代溶剂的质量百分含量为a，1％≤a≤30％，环状碳酸酯的质量百分含量为b，25％≤b≤45％，六氟磷酸锂的质量百分含量为c，7％≤c≤10％。在一些实施例中，3％≤a≤15％。需要理解的是，电解液中还可以加入常规电解液溶剂，如碳酸二甲酯、碳酸甲乙酯等。可以理解的是，电解液中还可以加入添加剂，如硫酸乙烯酯(1,3,2-dioxathiolane 2,2-dioxide，DTD)。
具体的，氟代溶剂的质量百分含量为a可以为1％、3％、5％、10％、15％、30％等数值，以及上述数值之间的任意数值。氟代溶剂的含量a过少对形成的储能装置的过充安全性能的改善会不够。氟代溶剂的含量a过多会影响电解液的粘度以及电导率，从而会对充放电循环性能产生恶化影响，通过控制氟代溶剂的含量a满足1％≤a≤30％，利于确保形成的储能装置同时具有较好的过充安全性能和充放电循环性能。
环状碳酸酯的质量百分含量为b可以为25％、27％、35％、40％、45％等数值，以及上述数值之间的任意数值。环状碳酸酯的主要作用是在正负极都会成膜，环状碳酸酯的含量b过少时无法保护正极和负极，对过充安全性能和充放电循环性能都会产生不利的影响。环状碳酸酯的含量b过多的情况下，可能会产生负极成膜过厚的情况，成膜过厚有可能导致负极界面出现问题，界面一旦出问题，过充安全性能和充放电循环性能都会恶化。通过控制环状碳酸酯的含量b满足25％≤b≤45％，利于确保形成的储能装置同时具有较好的过充安全性能和充放电循环性能。
六氟磷酸锂的质量百分含量为c可以为7％、7.5％、8％、9％、10％等数值，以及上述数值之间的任意数值。六氟磷酸锂含量c过少的情况下，主要影响的是电解液的电导率，离子传输会出问题，从而恶化形成的储能装置的充放电循环性能，六氟磷酸锂含量c过多的情况下，会增大电解液粘度，对电导率也不好，还会产生更多PF5、POF3等酸性物质，对SEI、CEI造成破坏，从而影响形成的储能装置的充放电循环性能。通过控制六氟磷酸锂含量c满足7％≤c≤10％，利于确保形成的储能装置同时具有较好的过充安全性能和充放电循环性能。
其中，氟代溶剂包括氟代碳酸酯、氟代羧酸酯和氟代醚中的至少一种。示例性的，氟代碳酸酯选自化学式(I-1)至化学式(I-7)中的至少一种：
示例性的，氟代羧酸酯选自化学式(I-8)至化学式(I-17)中的至少一种：

氟代醚选自化学式(I-18)至化学式(I-21)中的至少一种：
其中，环状碳酸酯选自碳酸乙烯酯(Ethylene carbonate，EC)、碳酸丙烯酯(Propylene Carbonate，PC)、氟代碳酸乙烯酯(Fluoroethylene carbonate，FEC)、双氟代碳酸乙烯酯(Di-Fluoro Ethylene Carbonate，DFEC)、碳酸亚乙烯酯(Vinylene Carbonate，VC)中的至少一种。
其中，锂盐还可以包括二氟磷酸锂(Lithium Difluorophosphate，LiDFP)、双氟磺酰亚胺锂(Lithium Bis(fluorosulfonyl)imide，LiFSI)、双三氟甲磺酰亚胺锂(Bistrifluoromethanesulfonimide Lithium Salt，LiTFSI)、二氟草酸硼酸锂(Lithium Oxalyldifluoro Borate，LiODFB)、二草酸硼酸锂(Lithium Bis(Oxalate)Borate，LiBOB)、四氟硼酸锂(Lithium Tetrafluoroborate，LiBF4)中的至少一种。
储能装置中，提高正极活性层的涂布重量t以及制作大容量的电芯，带来的好处是电芯整体的能量密度升高，电芯成本随之降低，但是也对电芯的安全性能带来了挑战。一方面，正极活性层的高涂布重量给电芯带来更大的电极欧姆阻抗，电芯阻抗的增加导致电芯在充电过程中将产生更多的焦耳热。另一方面，制作的单体电芯容量在280Ah以上，大容量电芯相对小容量电芯，在成本上和能量密度上进一步取得优势。但是由于大容量电芯的散热差，大容量电芯在充电过程中，热量极易累积在电芯中，热量累积容易造成电芯内部发生连锁化学反应，从而造成电芯失效、着火等安全问题。
储能装置的电芯在过充安全测试中，连续充电过程中电压会升至最大电压1.5V，此时电芯在持续充电过程中，电压升高，电解液在正极发生氧化反应，反应产生的反应热累积在电芯中，当热量达到一定程度时，在高温的作用下，电解液与正极极片的反应进一步加剧，同时此时负极极片上形成的SEI膜(Solid Electrolyte Interphase，固体电解质界面膜)因为高温的原因开始分解，SEI膜的分解反应带来反应热，同时因为SEI膜在高温下的分解，导致满充态的负极直接和电解液接触，电解液在负极发生还原反应，进一步放热累积热量。在这种热量带来的高温影响下，电芯中的隔膜发生熔融、破裂，导致正负极接触，此时电芯极可能发生着火、爆炸，从而影响电芯的安全性能。
为了解决大容量电芯的热量累积造成电芯内部发生连锁化学反应而引起电芯失效、着火等的安全问题，本申请实施例提供了一种电解液，包括质量分数1％～30％的氟代溶剂、质量分数25％～45％的环状碳酸酯和质量分数7％～10％的六氟磷酸锂。通过在电解液中引入氟代溶剂，以提升电解液的耐氧化能力，减少过充过程中电解液发生氧化反应而产生的热量。同时，在引入氟代溶剂的同时，为了解决氟代溶剂容易在负极发生还原反应的问题，本申请实施例通过调整降低电解液中六氟磷酸锂的含量，在保证电解液中具有足够的锂离子导电的同时，能够降低电解液中六氟磷酸锂与电解液中的水分反应形成的路易斯酸的含量，从而使得负极极片表面形成的固体电解质界面膜(SEI膜)及正极极片表面形成的正极表面钝化膜(CEI膜)更少地发生腐蚀，同时减少了路易斯酸对氟代溶剂上F的夺取，减少了氟代溶剂的脱氟效应，使得氟代溶剂更好地在过充过程中发挥作用。此外，通过提高电解液中环状碳酸酯的含量，利用环状碳酸酯可以在负极开环聚合，形成致密的SEI膜的特性，解决了氟代溶剂引入电解液中竞争成膜不良的问题，同时高浓度的环状碳酸酯在稳定负极的同时，还能够阻止氟代溶剂在负极侧的消耗与氧化，稳定氟代溶剂在电解液中的含量，从而间接提高电解液的耐氧化性，进而在解决储能装置的过充安全性能的同时，利于提升储能装置的充放电循环性能。
此外，正极活性层的涂布重量t、氟代溶剂的质量百分含量a、环状碳酸酯的质量百分含量b和锂盐的质量百分含量c，满足如下关系式：0.07≤(1-a-b)*c/t≤0.288。其中，“*”表示乘号。具体的，(1-a-b)*c/t可以为0.07、0.15、0.16、0.17、0.18、0.19、0.20、0.21、0.27、0.288等数值，以及上述数值之间的任意数值。(1-a-b)*c/t小于0.07时，由于几个因素的综合作用，可能会出现在孔隙中或者在负极层上出现析锂的现象，引起过充过程中负极析出的枝晶和电解液产生大量反应，产生大量反应热，导致过充测试效果不理想的情况，同时循环过程中，由于析锂的出现，一方面产生死锂，对容量造成不可逆损失，同时由于析出的锂和电解液的反应，造成副产物、产气等界面问题，从而导致储能装置的循环性能不理想的情况出现。当(1-a-b)*c/t＞0.288时，可能存在电解液耐氧化性不足以及电解液对正负极的钝化保护不足的情况，此时电解液无法起到对过充性能的改善作用。通过控制满足0.07≤(1-a-b)*c/t≤0.288，能够指导制备得到的储能装置在具有大容量的单体电芯的同时，保证电芯过充安全测试性能评级达标并具有良好的充放电循环性能，从而能够实现指导制备具有较好的过充安全性能以及良好的充放电循环性能的储能装置。
以下通过具体实施例进行实验证明。其中，实施例1-23和对比例1-12均提供一种储能装置，储能装置以锂离子电池进行示例，具体按照以下步骤制备：
正极极片的制备：将正极活性材料磷酸铁锂、导电炭黑SP、粘接剂PVDF按照质量比97：0.7：2.3分散至溶剂NMP(N-Methylpyrrolidone，N-甲基吡咯烷酮)中进行混合均匀得到正极浆料；将正极浆料涂布于正极集流体铝箔上，经过烘干、冷压、分条、裁片后，得到正极极片。其中，正极浆料涂布形成了正极活性层，正极活性层的涂布密度为t g/1540.25mm2，t表示正极活性层的涂布质量。
负极极片的制备：将取负极活性材料人造石墨、导电炭SP、增稠剂CMC及粘结剂SBR按照质量比96.5：0.5：1：2分散于去离子水中进行混合均匀得到负极浆料，将负极浆料涂布于负极集流体铝箔上，经过烘干、冷压、分条、裁片后，得到负极极片。其中，负极浆料涂布形成了负极活性层。
电解液的制备：在水分含量≤1ppm的氩气气氛手套箱中，将溶剂A、碳酸二甲酯、碳酸 甲乙酯按照质量比1：1：1进行混合，之后将干燥的电解质六氟磷酸锂(LiPF6)溶解到溶剂中，搅拌至完全溶解均匀，加入溶剂A混合均匀后获得电解液。其中，溶剂A包括氟代溶剂和环状碳酸酯。
隔膜的制备：以16um的聚乙烯薄膜为隔膜。
锂离子电池的制备：将制备得到的正极极片、隔膜、负极极片按照顺序叠好，使得隔膜处于正极极片与正负极极片的中间，以隔开正极极片与正负极极片，卷绕之后得到裸电芯，焊接正极耳和负极耳后得到电芯。将电芯装配到外壳中，注入制备得到的电解液后，对电芯进行封装、静置、化成、整形、容量测试等，最终制备得到锂离子电池。
其中，实施例1-23和对比例1-12提供的储能装置中，单体电芯的容量、正极活性层的涂布重量t、溶剂A及锂盐LiPF6的含量如表1所示。取实施例1-23和对比例1-12的储能装置进行充放电循环性能测试及安全过充测试，结果如表1所示。
其中，充放电循环性能测试的过程为：将储能装置在充放电仪上进行充放电循环测试，测试温度为25℃，循环倍率为1C(即充电倍率与放电倍率均为1C)，充电电压为2.5V到3.65V，计算循环后的容量保持率。25℃循环的容量保持率计算公式为：第n次循环后的容量保持率＝(第n次循环后的放电容量/循环第一圈的放电容量)*100％。
安全过充测试的过程为：将储能装置在充放电仪上进行测试，在(25±2)℃下静置5h；1C放电至2.5V，1充电至至3.65V静置10min。后转移至过充测试仪器上进行测试，以1C的恒电流充电，使装置的电压达到5.475V或充电时间达到1h，观察1h，记录是否有膨胀、漏液、冒烟、起火、爆炸现象。评级：电芯未出现漏液为一级达标；电芯出现漏液但是未出现冒烟为二级达标；电芯出现漏液、冒烟，但是未起火、未爆炸，为三级达标；电芯出现起火或爆炸，为四级，即不达标。
表1实施例1-23和对比例1-12的储能装置的组成及性能


从表1可以看出，通过比较对比例1至对比例4，对比例1至对比例4的储能装置中电解液均未添加氟代溶剂，随着单体电芯的容量的提升，储能装置在安全过充测试中的评级逐渐升高，储能装置的过充安全性能评级逐渐不达标，在单体电芯的容量为280Ah时，储能装置的过充安全性能评级低至四级，过充安全性能不达标。同时，随着单体电芯的容量的提升，储能装置在25℃循环1000次后的容量保持率逐渐降低。而实施例1至实施例23中，储能装置的电解液中均同时添加了氟代溶剂和环状碳酸酯，单体电芯的容量可达280Ah以上，同时，储能装置的过充安全性能评级均达标。实验结果表明，储能装置中电解液未添加氟代溶剂时，随着单体电芯的容量的提升，会导致过充安全性能和充放电循环性能均变差。
通过比较对比例4至对比例7，对比例4至对比例7的储能装置中电解液未添加氟代溶剂，在单体电芯的容量为大容量280Ah时，随着正极活性层的涂布量t的增加，储能装置的过充安全性能依然较差，过充安全性能基本上都不达标。同时，25℃循环1000次后的容量保持率逐渐降低。实验结果表明，储能装置中未添加氟代溶剂时，储能装置在具有较大的单体电芯容量时，过充安全性能基本不达标，同时正极活成层的涂布量t的增加会导致储能装置的充放电循环性能变差。
通过比较对比例4和实施例1至实施例20，在储能装置的单体电芯的容量相同以及正极活性层的涂布量t相同的情况下，本申请实施例1至20的电解液中通过添加氟代溶剂和环状碳酸酯，能够改善储能装置的过充安全性能，或者改善25℃循环1000次后的容量保持率。 实验结果表明，电解液中同时添加氟代溶剂和环状碳酸酯利于提升储能装置的过充安全性能，或者利于提升储能装置的充放电循环性能，从而利于提升储能装置的综合性能。
具体的，通过比较实施例1至实施例6，实施例1至实施例6的储能装置的单体电芯的容量相同以及正极活性层的涂布量t相同，储能装置的电解液中添加了不同的氟代溶剂，均能改善储能装置的过充安全性能。其中，实施例2至实施例6中添加的氟代溶剂较实施例1中添加的氟代溶剂的效果更好。
通过比较实施例7至实施例9，实施例7至实施例9的储能装置的电解液中均加入了氟代溶剂，并且随着氟代溶剂的含量a逐渐增多，储能装置的过充安全性能出现明显的改善。实验结果表明，在电解液添加环状碳酸酯的基础上，氟代溶剂的加入以及提升氟代溶剂在电解液中的含量能够提升储能装置的过充安全性能。这可能是由于氟代溶剂具有抗氧化的能力，可以极大提高电解液的耐氧化能力，在过充的高电压过程中，减少了电解液在正极上发生的氧化反应，即极大减少了电解液在过充过程中与正极发生氧化的反应量，降低氧化反应带来的反应产热，使得电芯在一开始就累积更少的热量，此时热量累积的减少可以降低负极侧固体电解质界面膜(SEI膜)发生分解的可能性，从而促使储能装置在过充中保持更为健康的状态，进而改善储能装置在过充安全测试中的性能表现。示例性的，电解液中氟代溶剂的质量分数a为1％～30％，优选地，电解液中氟代溶剂的质量分数a为3％～15％。
通过比较实施例10至实施例14，实施例10至实施例14的储能装置的电解液中均添加了氟代溶剂和环状碳酸酯，同时随着电解液中锂盐LiPF6(六氟磷酸锂)的含量逐渐降低，实施例10至实施例14的储能装置的过充安全性能等级逐渐提升至一级。实验结果表明，降低锂盐LiPF6在电解液中的含量，能够进一步改善储能装置的过充安全性能。这可能是由于电解液的锂盐中LiPF6在电解液存在水分的情况下，容易分解生成PF5(五氟化磷)等路易斯酸，该路易斯酸不但可能攻击负极侧的固体电解质界面膜(SEI膜)及正极表面钝化膜(CEI膜)，导致电解液和正极极片或负极极片直接接触发生反应，并且可能存在会夺取氟代溶剂中氟离子的可能性。因此，当电解液中含有更少量的LiPF6时，电解液中产生更少的PF5等路易斯酸，即减少了酸对正极CEI膜及负极SEI膜的攻击，使得负极极片表面形成的SEI膜和正极极片表面形成的CEI膜更少地发生腐蚀，同时减少了路易斯酸对氟代溶剂上F的夺取，使得氟代溶剂免受破坏，使得氟代溶剂在储能装置过充的过程中发挥出作用，从而利于进一步改善储能装置的过充安全性能。
继续观察实施例7至实施例9，在一定含量范围内加入氟代溶剂虽然改善了实施例7至实施例10中储能装置的过充安全性能，但随着氟代溶剂含量的增加，储能装置在25℃循环1000次后的容量保持率却逐渐降低，这可能是由于氟代溶剂在负极侧与环状碳酸酯发生竞争成膜的缘故。继续观察实施例10至实施例14，降低锂盐LiPF6在电解液中的含量虽然能够改善实施例10至实施例14的过充安全性能，但储能装置在25℃循环1000次后的容量保持率却逐渐降低。可见，通过在一定含量范围内加入氟代溶剂，以及降低锂盐LiPF6的含量可能改善储能装置的过充安全性能，但该策略存在恶性循环的可能。
而通过比较实施例15至实施例18，实施例15至实施例18的储能装置的电解液中均含有氟代溶剂和环状碳酸酯，随着储能装置的电解液中环状碳酸酯溶剂的含量的增加，储能装置在保持较好的过充安全性能的同时，25℃循环1000次后的容量保持率逐渐升高。实验结果表明，通过提高环状碳酸酯溶剂在电解液中的含量，能够在解决储能装置的过充安全性能问题的同时，保证储能装置的充放电循环性能。这是因为氟代溶剂在负极侧还没形成致密SEI 膜之前，氟代溶剂容易在负极侧发生还原，还原产物形成的SEI膜不够致密，可能导致储能装置的电性能下降，通过在电解液中加入高浓度的环状碳酸酯，环状碳酸酯可以在负极开环聚合，形成致密的SEI膜，解决了氟代溶剂引入电解液中竞争成膜不良的问题。同时，高浓度的环状碳酸酯在稳定负极的同时，还能够阻止氟代溶剂在负极侧的消耗与氧化，稳定氟代溶剂在电解液中的含量，从而间接提高电解液的耐氧化性，进而在解决储能装置的过充安全性能的同时，利于提升储能装置的充放电循环性能。
通过比较对比例8至对比例12和实施例1至实施例23，对比例8的储能装置的电解液中虽然添加了氟代溶剂、环状碳酸酯和锂盐LiPF6，但氟代溶剂的含量a低于1％、环状碳酸酯的含量b低于25％，锂盐LiPF6的含量c超出了10％，得到的储能装置的过充安全性能不达标，同时充放电循环性能较差。对比例9的储能装置的电解液中未加入氟代溶剂，环状碳酸酯的含量b低于25％，得到的储能装置的过充安全性能较差。对比例10的储能装置的电解液中氟代溶剂的含量a超出了30％，得到的储能装置充放电循环性能非常差。对比例11的储能装置的电解液中锂盐LiPF6的含量c低于7％，得到的储能装置充放电循环性能非常差。对比例12的储能装置的电解液中环状碳酸酯的含量b超出了45％，得到的储能装置过充安全性能较差。而实施例1至实施例23的储能装置的电解液中，通过添加氟代溶剂、环状碳酸酯和锂盐LiPF6，并且控制电解液中氟代溶剂的含量a满足1％≤a≤30％，环状碳酸酯的含量b满足25％≤b≤45％，锂盐LiPF6的含量c满足7％≤c≤10％，能够保证储能装置的过充安全性能，或者保证25℃循环1000次后的容量保持率，从而保证了储能装置的充放电循环性能。
此外，通过比较实施例7、实施例22与其他实施例(实施例1至6、实施例8至21、实施例23)，实施例7中储能装置的电芯容量为280Ah，为大容量，(1-a-b)*c/t＝0.31＞0.288，储能装置具有较好的充放电循环性能，但过充安全性能等级为四级，过充安全性能不达标。实施例22中储能装置的电芯容量为280Ah，为大容量，(1-a-b)*c/t＝0.056＜0.288，过充安全性能等级为三级，过充安全性能刚好达标。而其他实施例的储能装置中，满足关系式：0.07≤(1-a-b)*c/t≤0.288，制得的储能装置在具有较大单体电芯容量的同时，过充安全性能等级达到二级或一级，过充安全性能非常好。实验结果显示，本申请实施例通过控制正极活性层的涂布重量t、氟代溶剂的质量百分含量a、环状碳酸酯的质量百分含量b和锂盐LiPF6的质量百分含量c，满足如下关系式：0.07≤(1-a-b)*c/t≤0.288时，制得的储能装置在具有较大单体电芯容量的同时，过充安全测试性能评级达标，具有较好的过充安全性能。
以上所揭露的仅为本申请较佳实施例而已，当然不能以此来限定本申请之权利范围，本领域普通技术人员可以理解实现上述实施例的全部或部分流程，并依本申请权利要求所作的等同变化，仍属于本申请所涵盖的范围。

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  1. 一种电解液，其特征在于，以所述电解液的质量计，所述电解液包括质量百分含量为a的氟代溶剂、质量百分含量为b的环状碳酸酯和质量百分含量为c的六氟磷酸锂，其中，1％≤a≤30％，25％≤b≤45％，7％≤c≤10％。
  2. 根据权利要求1所述的电解液，其特征在于，所述环状碳酸酯选自碳酸乙烯酯、碳酸丙烯酯、氟代碳酸乙烯酯、双氟代碳酸乙烯酯、碳酸亚乙烯酯中的至少一种。
  3. 根据权利要求1所述的电解液，其特征在于，所述氟代溶剂包括氟代碳酸酯、氟代羧酸酯和氟代醚中的至少一种。
  4. 根据权利要求3所述的电解液，其特征在于，所述氟代碳酸酯选自化学式(I-1)至化学式(I-7)中的至少一种：
    所述氟代羧酸酯选自化学式(I-8)至化学式(I-17)中的至少一种：

    所述氟代醚选自化学式(I-18)至化学式(I-21)中的至少一种：
  5. 根据权利要求1至4任一项所述的电解液，其特征在于，所述电解液包括锂盐，所述锂盐包括所述六氟磷酸锂，所述锂盐还包括二氟磷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、二氟草酸硼酸锂、二草酸硼酸锂、四氟硼酸锂中的至少一种。
  6. 一种储能装置，其特征在于，包括正极极片和如权利要求1至5任一项所述的电解液。
  7. 根据权利要求6所述的储能装置，其特征在于，所述正极极片包括集流体和覆于所述正极集流体表面的正极活性层，所述正极极片中，所述正极活性层的涂布密度为t g/1540.25mm2，且满足如下关系式：0.07≤(1-a-b)*c/t≤0.288。
  8. 根据权利要求7所述的储能装置，其特征在于，0.25≤t≤0.4。
  9. 根据权利要求7所述的储能装置，其特征在于，所述正极活性层中的材料包括磷酸铁锂。
  10. 根据权利要求6至9任一项所述的储能装置，其特征在于，所述储能装置的容量不小于280Ah。
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CN116154300A (zh) * 2023-02-28 2023-05-23 珠海冠宇电池股份有限公司 电解液和电池
CN116646605A (zh) * 2023-06-30 2023-08-25 厦门海辰储能科技股份有限公司 电解液和储能装置

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