Low-temperature-resistant non-combustible polymer lithium battery electrolyte and preparation method thereof

Abstract

The invention discloses a low-temperature-resistant non-combustible polymer lithium battery electrolyte and a preparation method thereof, the low-temperature-resistant non-combustible polymer lithium battery electrolyte comprises the following components in percentage by mass: 9-9.5% of lithium salt, 75-79.4% of polymer, 9.7-10.2% of organic cosolvent and 1-5.7% of filler; and preparing the composite solid electrolyte by adopting a solution pouring method. The prepared electrolyte has high ionic conductivity (the conductivity reaches up to 2.544 mS / cm), excellent electrode interface stability (the LiLi symmetric battery can stably circulate for more than 400 hours) and non-combustible characteristic. The high-nickel solid-state lithium metal battery assembled by the polymer electrolyte still has excellent capacity retention ratio at-20 DEG C. According to the electrolyte, the low-temperature performance of the lithium battery is effectively improved, and the safety of the lithium battery is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium batteries, and in particular relates to a low-temperature-resistant and non-flammable polymer lithium battery electrolyte and a preparation method thereof. Background Art

[0002] With the rapid development of energy storage technology, lithium batteries have become a hot research topic in the field of electrochemical energy storage due to their high energy density. However, the performance of these batteries depends largely on the selection and design of electrolytes.

[0003] Traditional non-aqueous liquid electrolytes are usually composed of lithium salts, high dielectric constant solvents and a small amount of additives. Such electrolytes often have high viscosity under low temperature conditions, which hinders the effective transmission of ions. In addition, their volatility and possible leakage risks also increase the safety risks of batteries, limiting their application in high energy density batteries. Although inorganic solid electrolytes can significantly improve the safety of batteries, their large rigidity leads to poor interfacial contact with electrodes, affecting the stability of the solid-solid interface and thus affecting the overall performance of the battery. Polymer electrolytes are considered to be an ideal electrolyte material due to their good interfacial contact and safety. However, traditional polymer electrolytes still have some problems, such as low ionic conductivity, poor stability of lithium negative electrodes and severe lithium dendrite growth. These problems limit the application of polymer electrolytes in high energy density batteries. Researchers have alleviated the above problems through methods such as modification of the polymer body (the ionic conductivity of the polymer matrix can be improved through copolymerization, blending, cross-linking, branching and grafting), modification of the electrolyte salt (lithium salts with low dissociation energy have a higher degree of dissociation in the polymer and can provide more freely mobile lithium ions), addition of inorganic nanofillers (fillers can inhibit the crystallization of the polymer, reduce the glass transition temperature, and at the same time improve the mechanical strength and ionic conductivity of the electrolyte), surface coating, and introduction of additives.

[0004] In recent years, researchers have introduced high-energy-density lithium metal negative electrodes and high-voltage positive electrode materials in order to improve the energy density of batteries. However, these materials place higher demands on electrolytes, especially stability under high-voltage conditions. Currently, there are few patents related to composite polymer solid electrolytes that are both low-temperature, non-flammable, and compatible with high-voltage positive electrodes. Therefore, the development of a polymer electrolyte that is compatible with high-voltage positive electrodes and can remain stable at low temperatures has become an urgent need for current research. Summary of the invention

[0005] The purpose of this section is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this section, the abstract, and the title. However, such simplifications or omissions shall not be used to limit the scope of the present invention.

[0006] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0007] Therefore, an object of the present invention is to overcome the deficiencies in the prior art and provide a low-temperature resistant and non-combustible electrolyte.

[0008] To solve the above technical problems, the present invention provides the following technical solution: a low-temperature resistant and non-combustible electrolyte, characterized in that it includes a lithium salt, a polymer, an organic co-solvent, and a filler. By mass fraction of the electrolyte, the lithium salt is 9-9.5%, the polymer is 75-79.4%, the organic co-solvent is 9.7-10.2%, and the filler is 1-5.7%.

[0009] Among them, the polymer is polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene, the organic co-solvent includes one or more of trimethyl phosphate, triethyl phosphate, triethyl phosphite, tributyl phosphate, triphenyl phosphate, xylenyl phosphate, tolyl xylenyl phosphate, and tricresyl phosphate, and the filler includes one or more of alumina, silica, titanium oxide, barium titanate, lithium lanthanum zirconium oxide LLZO, lithium lanthanum zirconium tantalum oxide LLZTO, and covalent organic framework COF.

[0010] As a preferred embodiment of the preparation method of the present invention, among them: the lithium salt includes one or several of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, and lithium nitrate.

[0011] Another object of the present invention is to overcome the deficiencies in the prior art and provide a preparation method for a low-temperature resistant and non-combustible electrolyte.

[0012] As a preferred embodiment of the preparation method of the present invention, among them: the lithium salt, the polymer, the filler, and the organic co-solvent are blended and stirred to obtain an electrolyte precursor.

[0013] After the electrolyte precursor is defoamed under vacuum, an electrolyte membrane is prepared by a solution casting method, and after drying, it is vacuum dried to obtain the low-temperature resistant and non-combustible electrolyte.

[0014] As a preferred embodiment of the preparation method of the present invention, among them: the temperature of the blending and stirring is 30-80°C, the time is 2-24 h, and the rotation speed is 500-1500 rpm.

[0015] As a preferred embodiment of the preparation method of the present invention, wherein: the vacuum defoaming time is 2 to 4 h, and the temperature is 25 to 40 °C.

[0016] As a preferred embodiment of the preparation method of the present invention, wherein: the coating thickness of the solution casting method is 0.5 to 1.0 mm.

[0017] Another object of the present invention is to overcome the deficiencies in the prior art and provide a lithium-ion battery, which is characterized in that it includes a positive electrode, a lithium counter electrode, an additive, and the low-temperature non-flammable electrolyte described in claim 1, wherein the positive electrode active material includes NCM811, lithium iron manganese phosphate, and lithium iron phosphate.

[0018] As a preferred embodiment of the lithium-ion battery of the present invention, wherein: the additive includes one or more of fluoroethylene carbonate, trifluoropropylene carbonate, difluoroethylene carbonate, methyltrifluoroethyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, and tris(trimethylsilyl) phosphate.

[0019] As a preferred embodiment of the lithium-ion battery of the present invention, wherein: the addition amount of the additive is 5 to 20% of the low-temperature non-flammable electrolyte.

[0020] As a preferred embodiment of the lithium-ion battery of the present invention, wherein: the lithium-ion battery includes Li|NCM811, Li|LMFP, Li|LFP, SS|SS, Li|SS, and Li|Li batteries.

[0021] Advantages of the present invention:

[0022] From the perspective of the interaction between the components of the electrolyte engineering, the present invention understands that the synergistic effect between the lithium salt and the filler can promote the dissociation of the lithium salt and improve the ionic conductivity of the electrolyte. The lithium salt ions adsorbed and dissociated on the surface of the filler can promote the effective dispersion of the filler in the electrolyte due to electrostatic interaction and avoid agglomeration. The selected solvent has non-flammable characteristics, so the prepared electrolyte also has non-flammable properties, which greatly improves the safety of the battery under extreme conditions. Moreover, the preparation method is simple. Only by adding the materials into the solvent and obtaining the target electrolyte through stirring, casting, and drying. Description of the drawings

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings. Among them:

[0024] Figure 1 It is the ignition experimental diagram of the composite polymer electrolyte of the embodiment of the present invention.

[0025] Figure 2 Linear sweep voltammograms of Examples 4 and 7 of the present invention.

[0026] Figure 3 It is the impedance diagram of Examples 5 and 8 of the present invention.

[0027] Figure 4 It is the 1.0C cycling performance diagram of Li|NCM811 of Examples 1 and 2 of the present invention at room temperature.

[0028] Figure 5 It is the 0.3C cycling performance diagram of Li|NCM811 of Examples 1 and 2 of the present invention at -20°C.

[0029] Figure 6 It is for the Li|Li symmetric battery of Examples 3 and 6 of the present invention at 0.25 mA / cm 2 , 0.5 mAh / cm 2 Condition constant current charge and discharge curve diagram. Specific embodiments

[0030] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the specific embodiments of the present invention in detail in combination with the embodiments of the specification.

[0031] In the following description, many specific details are set forth to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0032] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation manner of the present invention. The "in one embodiment" that appears in different places in this specification does not all refer to the same embodiment, nor is it a separate or selectively exclusive embodiment from other embodiments.

[0033] The raw materials used in the embodiments of the present invention are all commercially available unless otherwise specified. Details are shown in Table 1.

[0034] Table 1

[0035] Name Commercial sales channel Article number NCM811 Duoduo Chemical Reagent Network NE-000198 Lithium sheet Tianjin Zhongneng Lithium Industry / Binder PVDF Colude MA-EN-BI-0008 Lithium bis(fluorosulfonyl)imide Duoduo Chemical Reagent Network NE-000027 Lithium difluoro(oxalato)borate Duoduo Chemical Reagent Network NE-000025 Poly(vinylidene fluoride - hexafluoropropylene) Sigma-Aldrich 427187-100G Triethyl phosphate Rhawn Reagent R002324 Aluminum oxide Rhawn Reagent R096375 Lithium lanthanum zirconium tantalum oxide Duoduo Chemical Reagent Network NE-000250

[0036] The specific performance test conditions for the electrolytes prepared in the examples and comparative examples of the present invention are as follows:

[0037] Ignition experiment test:

[0038] Use the composite solid polymer electrolyte CPE-A obtained in Example 1 for the ignition experiment test. Cut the prepared composite solid polymer electrolyte CPE-A to the size of the coin cell case, place it in the positive electrode case of the coin cell case, and use a high-temperature blowtorch (mainly composed of butane, with a flame temperature of 1300 - 1500 °C) to burn the composite solid polymer electrolyte CPE-A for 1 s. Observe whether it continues to burn after burning, and record it by video during the period.

[0039] Linear sweep voltammetry test: Use a DH7000 electrochemical workstation to perform a linear sweep voltammetry test. First, put the working electrode SS, the electrolyte membrane, and the reference electrode lithium sheet into the coin cell case, add 10 μL of the additive and seal it; then connect the battery to the electrochemical workstation, set the starting potential to 3 V, the ending potential to 6 V, and the scanning rate to 10 mV / s; then start scanning, record the data of the current changing with the potential, and generate a voltammogram; finally, analyze the voltammogram to evaluate the electrochemical performance of the battery.

[0040] Lithium ion conductivity test: Use a DH7000 electrochemical workstation to perform a lithium ion conductivity test. First, put the electrode SS, the electrolyte membrane, and the electrode SS into the coin cell case, add 10 μL of the additive and seal it; then connect the battery to the electrochemical workstation, set the alternating current impedance test parameters, with an alternating voltage perturbation of 10 mV and a frequency range of 100000 - 0.1 Hz, perform the test and record the impedance data; calculate the conductivity of the electrolyte according to the impedance data, and the formula (1) is:

[0041]

[0042] Where L is the thickness of the electrolyte membrane, R is the impedance value, and S is the electrode area.

[0043] Room temperature charge and discharge cycle test: Use a Neware battery tester to perform a room temperature charge and discharge cycle test. First, put the positive electrode NCM811, the electrolyte membrane, and the negative electrode lithium sheet into the coin cell case, add 10 μL of the additive and seal it; then set the charge and discharge test steps: the charging cut-off voltage is 4.5 V (vs. Li / Li +) The discharge cut-off voltage is 2.8 V. The battery is activated by constant current charge and discharge at 0.1 C (1 C = 220 mAh / g) for 2 cycles, at 0.3 C constant current charge / 0.3 C constant current discharge for 2 cycles, and at 0.5 C constant current charge / 0.5 C constant current discharge for 2 cycles. Subsequently, all long cycles are carried out with constant current and constant voltage charge at 1.0 C / constant current discharge at 1.0 C. Finally, corresponding data such as time, voltage, current, and capacity are recorded. Among them, the capacity retention rate (%) of the Nth cycle of the battery = specific discharge capacity of the Nth cycle / specific discharge capacity of the first cycle at 1.0 C × 100%.

[0044] Low-temperature charge and discharge cycle test: The low-temperature charge and discharge cycle test is carried out using a Neware battery tester and a Shanghai Yiheng high and low temperature test chamber. First, the positive electrode NCM811, the electrolyte membrane, and the negative electrode lithium sheet are placed into a button battery case, 10 μL of additive is added and sealed; then the charge and discharge test steps are set: the charge cut-off voltage is 4.5 V (vs. Li / Li + ) The discharge cut-off voltage is 2.8 V. At room temperature, the battery is activated by constant current charge and discharge at 0.1 C (1 C = 220 mAh / g) for 2 cycles and at 0.3 C constant current charge / 0.3 C constant current discharge for 2 cycles. Subsequently, in a low-temperature chamber at -20 °C, it is charged at 0.1 C constant current / discharged at 0.1 C constant current for 2 cycles, and all long cycles are carried out with constant current and constant voltage charge at 0.3 C / constant current discharge at 0.3 C. Finally, corresponding data such as time, voltage, current, and capacity are recorded.

[0045] Constant current charge and discharge test: The constant current charge and discharge test is a test method for evaluating the performance of a battery. The battery is charged with a set constant current (such as 1.0 C) until a preset voltage is reached; after charging is completed, the battery is allowed to stand for a period of time; the battery is then discharged with a set constant current (such as 1.0 C) until the voltage drops to the preset value.

[0046] Example 1

[0047] (1) Weigh 0.3741 g of lithium bis(fluorosulfonyl)imide, 0.1438 g of lithium difluoro(oxalato)borate, 0.5612 g of poly(vinylidene fluoride - hexafluoropropylene), 0.1635 g of LLZTO, and 4.3717 g of triethyl phosphate. Blend them in a brown glass bottle, add a magnetic stirrer, and stir at 80 °C and 500 rpm for 2 h, then stir at 30 °C and 500 rpm for 10 h to obtain electrolyte precursor A.

[0048] (2) After the electrolyte precursor A is defoamed in vacuum at 30 °C for 2 h, it is coated on a clean and dry glass plate using the solution casting method (coating thickness 0.75 mm) to prepare an electrolyte membrane, and then dried in an 80 °C oven for 2 h. After that, it is transferred to a vacuum oven and dried for 12 h to obtain the target product, the composite solid polymer electrolyte CPE - A.

[0049] (3) Prepare the positive electrode sheet by using NCM811 as the active material, in combination with conductive carbon and binder PVDF (homogenize according to the mass ratio of active material: conductive carbon: binder of 90:5:5, and the areal capacity density is ~1.031 mAh / cm 2 ), use a lithium sheet as the negative electrode, use CPE-A as the electrolyte, add 10 μL of additive (a mixed solution of fluoroethylene carbonate and ethylene glycol dimethyl ether with a mass ratio of 3 / 7) to assemble a Li|NCM811 coin cell for cyclic performance testing.

[0050] Example 2

[0051] (1) Weigh 0.3741 g of lithium bis(fluorosulfonyl)imide, 0.1438 g of lithium difluoro(oxalato)borate, 0.5612 g of poly(vinylidene fluoride - hexafluoropropylene), 0.1635 g of alumina, and 4.3717 g of triethyl phosphate. Blend them in a brown glass bottle, add a magnetic stir bar, stir at 80 °C and 500 rpm for 2 h, and then stir at 30 °C and 500 rpm for 10 h to obtain the electrolyte precursor B.

[0052] (2) After the electrolyte precursor B is degassed under vacuum at 30 °C for 2 h, use the solution casting method (coating thickness 0.75 mm) to coat it on a clean and dry glass plate to prepare the electrolyte membrane. Then dry it in an oven at 80 °C for 2 h, and then transfer it to a vacuum oven to dry for 12 h to obtain the target product, the composite solid polymer electrolyte CPE-B.

[0053] (3) Prepare the positive electrode sheet by using NCM811 as the active material, in combination with conductive carbon and binder PVDF (homogenize according to the mass ratio of active material: conductive carbon: binder of 90:5:5, and the areal capacity density is ~1.031 mAh / cm 2 ), use a lithium sheet as the negative electrode, use CPE-B as the electrolyte, add 10 μL of additive (a mixed solution of fluoroethylene carbonate and ethylene glycol dimethyl ether with a mass ratio of 3 / 7) to assemble a Li|NCM811 coin cell for cyclic performance testing.

[0054] Example 3

[0055] The difference from Example 1 is that in step (3), a lithium sheet is used as the battery positive electrode, a lithium sheet is used as the negative electrode, CPE-A is used as the electrolyte, and 10 μL of additive (a mixed solution of fluoroethylene carbonate and ethylene glycol dimethyl ether with a mass ratio of 3 / 7) is added to assemble a Li|Li coin cell.

[0056] Example 4

[0057] The difference from Example 1 is that in step (3), SS is used as the positive electrode, a lithium sheet is used as the negative electrode, CPE-A is used as the electrolyte, and 10 μL of an additive (a mixed solution of fluoroethylene carbonate and dimethoxyethane with a mass ratio of 3 / 7) is added to assemble a Li|SS button cell.

[0058] Example 5

[0059] The difference from Example 1 is that in step (3), SS is used as the positive electrode, SS is used as the negative electrode, CPE-A is used as the electrolyte, and 10 μL of an additive (a mixed solution of fluoroethylene carbonate and dimethoxyethane with a mass ratio of 3 / 7) is added to assemble an SS|SS button cell.

[0060] Example 6

[0061] The difference from Example 2 is that in step (3), a lithium sheet is used as the battery positive electrode, a lithium sheet is used as the negative electrode, CPE-B is used as the electrolyte, and 10 μL of an additive (a mixed solution of fluoroethylene carbonate and dimethoxyethane with a mass ratio of 3 / 7) is added to assemble a Li|Li button cell.

[0062] Example 7

[0063] The difference from Example 2 is that in step (3), SS is used as the positive electrode, a lithium sheet is used as the negative electrode, CPE-B is used as the electrolyte, and 10 μL of an additive (a mixed solution of fluoroethylene carbonate and dimethoxyethane with a mass ratio of 3 / 7) is added to assemble a Li|SS button cell.

[0064] Example 8

[0065] The difference from Example 2 is that in step (3), SS is used as the positive electrode, SS is used as the negative electrode, CPE-B is used as the electrolyte, and 10 μL of an additive (a mixed solution of fluoroethylene carbonate and dimethoxyethane with a mass ratio of 3 / 7) is added to assemble an SS|SS button cell.

[0066] Ignition experiment test:

[0067] The ignition experiment test was carried out using the composite solid polymer electrolyte CPE-A obtained in Example 1. The results are as Figure 1 shown. The designed composite solid polymer electrolyte CPE-A does not burn after being burned by a high-temperature blowtorch for 1 s. Therefore, the designed composite solid polymer electrolyte CPE-A greatly improves the safety of the battery.

[0068] Linear sweep voltammetry test:

[0069] The Li|SS batteries obtained in Example 4 and Example 7 were used for linear sweep voltammetry test at room temperature, with a scanning range of 3 - 6 V and a scanning speed of 10 mV / s. As Figure 2As shown, adding LLZTO further broadens the electrochemical window of the lithium battery (from 4.58 V to 4.72 V), enabling it to better match high-voltage and high-nickel cathode materials.

[0070] Lithium-ion conductivity test:

[0071] The SS|SS batteries obtained from Example 5 and Example 8 were used for impedance testing at room temperature. According to parameters such as electrochemical impedance, the thickness of the sample, and the area of the electrode, the ionic conductivity of the sample was calculated. As Figure 3 shown, the conductivity of the sample in Example 5 was 2.544 mS / cm, and the conductivity of the sample in Example 8 was 2.190 mS / cm. Adding LLZTO can provide a fast lithium-ion transport channel, further improving the lithium-ion transport rate in the lithium battery.

[0072] Room temperature charge-discharge cycle test:

[0073] The Li|NCM811 batteries obtained from Example 1 and Example 2 were used for cycle performance testing at room temperature. The charge cut-off voltage was 4.5 V (vs. Li / Li + ), the discharge cut-off voltage was 2.8 V. The battery was first activated by constant current charge-discharge at 0.1 C (1 C = 220 mAh / g) for 2 times, 0.3 C constant current charge / 0.3 C constant current discharge for 2 times, and 0.5 C constant current charge / 0.5 C constant current discharge for 2 times. Subsequently, the long-term cycle was carried out at 1.0 C constant current and constant voltage charge / 1.0 C constant current discharge. As Figure 4 shown, the discharge specific capacity of Example 1 at 1.0 C was 188.69 mAh / g, and the capacity retention rate after 150 cycles was 77.23%. The discharge specific capacity of Example 2 at 1.0 C was 185.82 mAh / g, and the capacity retention rate after 150 cycles was 69.63%. Among them, the capacity retention rate (%) of the Nth cycle of the battery = the discharge specific capacity of the Nth cycle / the discharge specific capacity of the first cycle at 1.0 C × 100%. As shown in Table 2, the lithium battery with added LLZTO has a higher discharge specific capacity and capacity retention rate.

[0074] Table 2 Room temperature charge-discharge cycle test results

[0075]

[0076] Low temperature charge-discharge cycle test

[0077] The Li|NCM811 batteries obtained from Example 1 and Example 2 were used for cycle performance testing at -20 °C. The charge cut-off voltage was 4.5 V (vs. Li / Li + ), the discharge cut-off voltage was 2.8 V. After room temperature activation cycling, the low temperature long-term cycle test was carried out at a constant current and constant voltage charge / discharge rate of 0.3 C. As Figure 5As shown, the discharge specific capacity of Example 1 at 0.3C is 125.48 mAh / g, and the capacity retention rate after 100 cycles is 90.48%. The discharge specific capacity of Example 2 at 0.3C is 90.41 mAh / g, and the capacity retention rate after 100 cycles is 53.60%. As shown in Table 3, the lithium battery with LLZTO added has higher discharge specific capacity and capacity retention rate at -20°C.

[0078] Table 3 Charge-discharge cycle test results at -20°C

[0079]

[0080] Constant current charge-discharge test:

[0081] The Li|Li battery obtained from Example 3 and Example 6 was tested at room temperature at a current density of 0.25 mA / cm 2 , and the test results are as Figure 6 shown. Example 6 could only cycle for 250 h before short circuit occurred, while Example 3 could stably cycle for more than 400 h.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that triethyl phosphate is not added in step 1, and an equal amount of N,N-dimethylformamide is added. Other conditions are the same as those in Example 1, and the composite solid polymer electrolyte CPE-A1 is obtained. Using NCM811 as the active material, conductive carbon, and binder PVDF to prepare the positive electrode sheet (homogenized according to the mass ratio of active material: conductive carbon: binder of 90:5:5), using a lithium sheet as the negative electrode, using CPE-A1 as the electrolyte, adding 10 μL of additive (a mixed solution of fluoroethylene carbonate and ethylene glycol dimethyl ether with a mass ratio of 3 / 7) to assemble a Li|NCM811 coin cell for cycle performance testing and conduct an ignition experiment on the solid polymer electrolyte.

[0084] Comparative Example 2

[0085] The difference between this comparative example and Example 1 is that triethyl phosphate is not added in step 1, and an equal amount of N-methylpyrrolidone is added. Other conditions are the same as those in Example 1, and the composite solid polymer electrolyte CPE-A2 is obtained. Using NCM811 as the active material, conductive carbon, and binder PVDF to prepare the positive electrode sheet (homogenized according to the mass ratio of active material: conductive carbon: binder of 90:5:5), using a lithium sheet as the negative electrode, using CPE-A2 as the electrolyte, adding 10 μL of additive (a mixed solution of fluoroethylene carbonate and ethylene glycol dimethyl ether with a mass ratio of 3 / 7) to assemble a Li|NCM811 coin cell for cycle performance testing and conduct an ignition experiment on the solid polymer electrolyte.

[0086] Comparative Example 3

[0087] The difference between this comparative example and Example 1 is that in Step 1, lithium bis(fluorosulfonyl)imide and lithium difluoro(oxalato)borate are not added, and 0.5742 g of lithium bis(trifluoromethanesulfonyl)imide is added. The rest is the same as in Example 1, and the composite solid polymer electrolyte CPE-A3 is obtained. Using NCM811 as the active material, conductive carbon, and binder PVDF, a positive electrode sheet is prepared (slurry is made according to the mass ratio of active material:conductive carbon:binder of 90:5:5). Using a lithium sheet as the negative electrode, using CPE-A3 as the electrolyte, adding 10 μL of additive (a mixed solution of fluoroethylene carbonate and ethylene glycol dimethyl ether with a mass ratio of 3 / 7), assembling a Li|NCM811 coin cell for cyclic performance testing and conducting an ignition experiment on the solid polymer electrolyte.

[0088] Comparative Example 4

[0089] The difference between this comparative example and Example 1 is that in Step 1, LLZTO is not added. The rest is the same as in Example 1, and the solid polymer electrolyte CPE-A4 is obtained. Using NCM811 as the active material, conductive carbon, and binder PVDF, a positive electrode sheet is prepared (slurry is made according to the mass ratio of active material:conductive carbon:binder of 90:5:5). Using a lithium sheet as the negative electrode, using CPE-A4 as the electrolyte, adding 10 μL of additive (a mixed solution of fluoroethylene carbonate and ethylene glycol dimethyl ether with a mass ratio of 3 / 7), assembling a Li|NCM811 coin cell for cyclic performance testing and conducting an ignition experiment on the solid polymer electrolyte.

[0090] Comparative Example 5

[0091] The difference between this comparative example and Example 1 is that in Step 2, drying is carried out in a vacuum oven for 24 h. The rest is the same as in Example 1, and the composite solid polymer electrolyte CPE-A5 is obtained. Using NCM811 as the active material, conductive carbon, and binder PVDF, a positive electrode sheet is prepared (slurry is made according to the mass ratio of active material:conductive carbon:binder of 90:5:5). Using a lithium sheet as the negative electrode, using CPE-A5 as the electrolyte, adding 10 μL of additive (a mixed solution of fluoroethylene carbonate and ethylene glycol dimethyl ether with a mass ratio of 3 / 7), assembling a Li|NCM811 coin cell for cyclic performance testing and conducting an ignition experiment on the solid polymer electrolyte.

[0092] Table 4

[0093]

[0094]

[0095] As can be seen from Table 4, the synergistic effect between the lithium salt and the filler in the embodiments of the present invention can promote the dissociation of the lithium salt, improve the ionic conductivity of the electrolyte, and the cyclic performance of the prepared electrolyte at room temperature is significantly better than that of the comparative examples, indicating that the electrolyte of the present invention has outstanding advantages.

[0096] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the present invention.

Claims

1. A low temperature resistant non-flammable electrolyte, characterized in that: It includes lithium salt, polymer, organic co-solvent and filler, wherein, based on the mass fraction of the electrolyte, the lithium salt is 9-9.5%, the polymer is 75-79.4%, the organic co-solvent is 9.7-10.2%, and the filler is 1-5.7%; Wherein, the polymer is polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene, the organic co-solvent includes one or more of trimethyl phosphate, triethyl phosphate, triethyl phosphite, tributyl phosphate, triphenyl phosphate, ditolyl phosphate, toluene dimethyl phosphate, and tricresyl phosphate, and the filler includes one or more of aluminum oxide, silicon oxide, titanium oxide, barium titanate, lithium lanthanum zirconium oxide LLZO, lithium lanthanum zirconium tantalum oxide LLZTO, and covalent organic compound COF.

2. The low temperature resistant non-flammable electrolyte according to claim 1, characterized in that: The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate and lithium nitrate.

3. The method for preparing the low temperature resistant non-flammable electrolyte according to claims 1 to 2, characterized in that: include, The lithium salt, the polymer, the filler and the organic co-solvent are mixed and stirred to obtain an electrolyte precursor; The electrolyte precursor is vacuum defoamed and then the electrolyte membrane is prepared by solution casting method, and then vacuum dried to obtain the low-temperature resistant and non-flammable electrolyte.

4. The preparation method according to claim 3, characterized in that: The blending and stirring temperature is 30-80° C., the time is 2-24 hours, and the rotation speed is 500-1500 rpm.

5. The preparation method according to claim 3, characterized in that: The vacuum defoaming time is 2 to 4 hours, and the temperature is 25 to 40°C.

6. The preparation method according to claim 3, characterized in that: The coating thickness of the solution casting method is 0.5 to 1.0 mm.

7. A lithium ion battery, characterized in that: It comprises a positive electrode, a lithium counter electrode, an additive, and the low-temperature resistant non-flammable electrolyte according to claim 1, wherein the positive electrode active material comprises NCM811, lithium iron manganese phosphate and lithium iron phosphate.

8. The lithium-ion battery according to claim 7, wherein: The additive includes one or more of fluoroethylene carbonate, trifluoropropylene carbonate, bisfluoroethylene carbonate, methyl trifluoroethyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and bis(2,2,2-trifluoroethyl) ether tris(trimethylsilyl) phosphate.

9. The lithium-ion battery according to claim 8, characterized in that: The additive is added in an amount of 5-20% of the low-temperature resistant non-flammable electrolyte.

10. The lithium ion battery according to claim 7, wherein: The lithium-ion batteries include Li NCM811, Li|LMFP, Li|LFP, SS|SS, Li|SS, and Li|Li batteries.

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