Contains LiPF 6 Gel electrolyte of DOL and its preparation method and application

Abstract

The present invention provides a gel electrolyte containing LiPF6 and DOL, a preparation method and application thereof, and relates to the technical field of lithium ion batteries. The raw materials for preparing the gel electrolyte of the present invention include LiPF6, a carbonate solvent, DOL and an organic weak base, and the gelation process of the LiPF6-DOL system is coordinated and controlled by screening a specific organic weak base, while ensuring or even improving the cycle performance and safety performance of a lithium ion battery using the gel electrolyte containing LiPF6 and DOL.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a gel electrolyte containing LiPF6 and DOL, and a preparation method and application thereof. Background Art

[0002] Compared with liquid electrolytes, solid electrolytes have higher safety, among which gel electrolytes are gaining more and more attention.

[0003] At present, the research on gel electrolytes is mainly focused on lithium bis(trifluoromethylsulfonyl)imide, and the gel electrolyte is prepared by Lewis acid-catalyzed 1,3-dioxolane (DOL) cationic ring-opening polymerization. This is because lithium hexafluorophosphate (LiPF6), commonly used in liquid electrolytes, decomposes to produce phosphorus pentafluoride, which is a strong Lewis acid that quickly triggers the rapid polymerization of 1,3-dioxolane (DOL), which is not conducive to operation and production. Summary of the invention

[0004] Based on this, it is necessary to provide a gel electrolyte containing LiPF6 and DOL and a preparation method and application thereof. The gel electrolyte containing LiPF6 and DOL of the present invention achieves coordinated control of the gel process by screening a specific organic weak base, while ensuring or even improving the cycle performance and safety performance of the battery containing the gel electrolyte of LiPF6 and DOL.

[0005] The present invention adopts the following technical solution:

[0006] The present invention provides a gel electrolyte containing LiPF6 and DOL. The raw materials for preparing the gel electrolyte include LiPF6, a carbonate solvent, DOL and an organic weak base. The organic weak base is selected from at least one of triethylamine, aniline, n-butylamine, diethylenetriamine, pyridine, 4-dimethylaminopyridine, 2-methoxypyridine and 2-fluoropyridine.

[0007] Preferably, the organic weak base is selected from at least one of pyridine and triethylamine, which can further achieve a discharge capacity of 140 mAh / g or more at 160 cycles, and a capacity retention rate of more than 95%.

[0008] Preferably, the carbonate solvent is selected from a mixture of propylene carbonate and ethylene carbonate, and the volume ratio thereof is preferably 1:1.

[0009] The present invention also provides a method for preparing a gel electrolyte containing LiPF6 and DOL, comprising the following steps: using a carbonate solvent to dissolve LiPF6 to prepare a lithium salt solution containing LiPF6; dissolving an organic weak base in DOL to prepare an organic weak base DOL solution; mixing the lithium salt solution containing LiPF6 and the organic weak base DOL solution in a preset ratio to obtain a precursor solution; and allowing the precursor solution to stand to obtain.

[0010] In some embodiments, the concentration of LiPF6 in the lithium salt solution is 1moL / L to 3moL / L, and the content of the organic weak base in the organic weak base DOL solution is 0.01 to 0.20mmoL. Preferably, the concentration of LiPF6 in the lithium salt solution is 2moL / L, and the content of the organic weak base in the organic weak base DOL solution is 0.04 to 0.15mmoL.

[0011] Preferably, in the precursor solution, the volume ratio of the lithium salt solution containing LiPF6 to the organic weak base DOL solution is (1-3): 1. The conditions for standing gelation are: 25-35°C, and the standing time is 40-80h, more preferably 48-72h.

[0012] The present invention also provides the use of the gel electrolyte containing LiPF6 and DOL or the preparation method thereof in the preparation of lithium ion batteries.

[0013] The present invention can also provide a lithium ion battery, comprising the above-mentioned gel electrolyte containing LiPF6 and DOL or the gel electrolyte containing LiPF6 and DOL prepared by the above-mentioned preparation method.

[0014] The lithium-ion battery also includes a positive electrode, a negative electrode and a separator; the positive electrode material is selected from at least one of lithium iron phosphate, high-nickel ternary positive electrode material, lithium nickel cobalt manganese oxide, and lithium titanate, preferably lithium iron phosphate; and / or the negative electrode material is selected from at least one of metallic lithium, silicon-carbon negative electrode, graphite, and carbon nanotubes, preferably metallic lithium; and / or the separator is selected from at least one of polyolefin separators, PP-PE-PP films, cellulose films, and glass cellulose films, preferably polyolefin separators.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention provides a gel electrolyte containing LiPF6 and DOL, and coordinates and controls the gel process by selecting a specific organic weak base, while ensuring or even improving the cycle performance and safety performance of the battery containing the gel electrolyte containing LiPF6 and DOL. The present invention has the advantages of at least the following aspects:

[0017] 1) Compared with the conventional method of preparing gel electrolyte using dual lithium salt, the present invention only needs to use cheaper lithium hexafluorophosphate salt, which is more economical.

[0018] 2) The present invention controls the polymerization speed of the gel electrolyte preparation system by introducing an organic weak base, which is beneficial to industrial production.

[0019] 3) The present invention adopts in-situ polymerization, which can be polymerized at room temperature without heating, and is also beneficial to improving the performance of the battery; by dripping the precursor solution into the diaphragm, it can have good interface compatibility with the positive and negative electrodes, thereby reducing the interface impedance.

[0020] 4) The present invention uses carbonates and DOL to synergistically improve the problems of low boiling point and narrow electrochemical window of organic ether solvents, thereby achieving a better electrochemical window.

[0021] 5) The gel electrolyte prepared by the present invention can solve the safety problem and lithium dendrite problem of organic liquid electrolytes, and has a high capacity retention rate and a high specific capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is an electrochemical window diagram of the gel electrolyte battery prepared in Example 1 of the present invention.

[0023] Figure 2 This is a long cycle diagram of the gel electrolyte battery prepared in Example 2 of the present invention.

[0024] Figure 3 This is a long cycle diagram of the gel electrolyte battery prepared in Example 3 of the present invention.

[0025] Figure 4 This is a sequential cycle diagram of the gel electrolyte battery prepared in Example 4 of the present invention.

[0026] Figure 5 This is an optical photograph of the gel electrolyte prepared in Example 5 of the present invention.

[0027] Figure 6 This is a sequential cycle diagram of the gel electrolyte battery prepared in Example 7 of the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can understand the present invention more clearly.

[0029] The following embodiments are only used to illustrate the present invention, but are not limited to the scope of the present invention. Based on the specific embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work belong to the protection scope of the present invention.

[0030] In the examples of the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art; in the examples of the present invention, unless otherwise specified, the technical means used are conventional means well known to those skilled in the art.

[0031] The technical concept of the present invention is to provide a gel electrolyte containing LiPF6 and DOL, and to coordinate and control the gel process of the LiPF6-DOL electrolyte system by screening specific organic weak bases, while ensuring or even improving the cycle performance of lithium-ion batteries using the gel electrolyte containing LiPF6 and DOL.

[0032] Here are some examples:

[0033] The assembly order of the button cell used in the following experiment is the negative electrode shell, spring sheet, steel sheet, negative electrode material, precursor solution, diaphragm, precursor solution, positive electrode material and positive electrode shell. The assembly of the button cell can be completed by sealing it with a packaging machine.

[0034] Example 1

[0035] This embodiment provides a gel electrolyte containing LiPF6 and DOL, and the preparation method thereof comprises the following steps:

[0036] S1. In a glove box filled with high-purity argon (H2O≤0.1ppm, O2≤0.1ppm), first dissolve lithium hexafluorophosphate (LiPF6) in a mixed solution of propylene carbonate and ethylene carbonate in a volume ratio of 1:1, mix thoroughly, and obtain a 2 mol / L LiPF6 solution.

[0037] Dissolve 0.1 mmol of triethylamine in 0.5 mL of 1,3-dioxolane (DOL) and mix well to obtain a clear solution of triethylamine DOL.

[0038] S2, respectively, mixing the LiPF6 solution and the triethylamine DOL clarified solution in a volume ratio of 1:1 to obtain a precursor solution.

[0039] The precursor solution in this example (containing 1 mL each of LiPF6 solution and triethylamine DOL clear solution) is allowed to stand for about 72 hours to obtain a gel electrolyte.

[0040] Take 50 μL of the above precursor solution to assemble the Li||steel sheet battery. After the gel is complete, perform linear sweep voltammetry test on the Chenhua instrument at a scan rate of 5 mv / s.

[0041] Linear sweep voltammetry test: The steps are to measure the open circuit voltage first, then use the open circuit voltage as the starting voltage, the ending voltage is 5.5v, and the scan rate is 5mv / s. After the settings are completed, the electrochemical window diagram can be obtained. Figure 1 shown.

[0042] Depend on Figure 1It can be seen that within the potential range of 2.5-5V, the line is relatively stable, indicating that within this potential range, the gel electrolyte of this embodiment does not react and exists stably. Therefore, in subsequent cycle tests, the voltage setting should be ensured to be within the electrochemical window of the selected electrolyte to avoid negative effects.

[0043] Example 2

[0044] This embodiment provides a gel electrolyte containing LiPF6 and DOL, and the preparation method thereof comprises the following steps:

[0045] S1. In a glove box filled with high-purity argon (H2O≤0.1ppm, O2≤0.1ppm), first dissolve lithium hexafluorophosphate (LiPF6) in a mixed solution of propylene carbonate and ethylene carbonate in a volume ratio of 1:1, mix thoroughly, and obtain a 2 mol / L LiPF6 solution.

[0046] Dissolve 0.08 mmol of pyridine in 0.5 mL of 1,3-dioxolane (DOL) and mix well to obtain a clear pyridine DOL solution.

[0047] S2, respectively, mixing the LiPF6 solution and the pyridine DOL clarified solution in a volume ratio of 1:1 to obtain a precursor solution.

[0048] The precursor solution in this example (containing 1 mL each of LiPF6 solution and pyridine DOL clear solution) is allowed to stand for about 48 hours to obtain a gel electrolyte.

[0049] Take 75μL of the above precursor solution to assemble a Li||LiFePO4 battery, and then test it in the Blue Electric Battery Test System. The procedure is: first stand to ensure that the gel is complete, then charge to 4.2v at a constant current rate of 0.1C, then discharge to 2.5v at a constant current rate of 0.1C, cycle 10 times, the purpose is to activate the battery, and finally charge to 4.2v at a constant current rate of 0.5C, then discharge to 2.5v at a constant current rate of 0.5C for a long cycle. The long cycle test results are as follows: Figure 2 shown.

[0050] Depend on Figure 2 It can be seen that the battery assembled with the gel electrolyte prepared in this embodiment has a discharge capacity of 140 mAh / g or more when cycled 160 times at 0.5C, and a capacity retention rate of more than 95%, indicating that it has excellent electrochemical performance.

[0051] Example 3

[0052] This embodiment provides a gel electrolyte containing LiPF6 and DOL, and its preparation method is basically the same as that of Example 2, except that 0.04 mmol of 4-dimethylaminopyridine is used instead of 0.08 mmol of pyridine to form a 4-dimethylaminopyridine DOL clear solution.

[0053] The long cycle test results of this embodiment are as follows Figure 3 shown.

[0054] Depend on Figure 3 It can be seen that the battery assembled with the gel electrolyte prepared in this embodiment has a discharge specific capacity of 140 mAh / g or more when cycled 160 times at 0.5C, and a capacity retention rate of more than 93%, indicating that it has excellent electrochemical performance.

[0055] Example 4

[0056] This embodiment provides a gel electrolyte containing LiPF6 and DOL, and the preparation method thereof comprises the following steps:

[0057] S1. In a glove box filled with high-purity argon (H2O≤0.1ppm, O2≤0.1ppm), first dissolve lithium hexafluorophosphate (LiPF6) in a mixed solution of propylene carbonate and ethylene carbonate in a volume ratio of 1:1, mix thoroughly, and obtain a 2 mol / L LiPF6 solution.

[0058] Dissolve 0.15 mmoL of aniline in 0.5 mL of 1,3-dioxolane (DOL), mix well, and obtain a clear aniline DOL solution.

[0059] S2, respectively, mixing the LiPF6 solution and the aniline DOL clarified solution in a volume ratio of 3:1 to obtain a precursor solution.

[0060] The precursor solution in this example (containing 3 mL of LiPF6 solution and 1 mL of pyridine DOL clear solution) is allowed to stand for about 50 hours to obtain a gel electrolyte.

[0061] Take the above 75μL precursor solution to assemble Li||LiFePO4 battery, and then test it in the blue battery test system. The procedure is: first stand to ensure that the gel is complete, then charge to 4.2v at a constant current rate of 0.1C, and then discharge to 2.5v at a constant current rate of 0.1C, and cycle 10 times; change different rates to repeat the above constant current charge and discharge process, the charge and discharge rate is from low to high (0.1C, 0.2C, 0.5C, 1C, 2C, 5C), and the same rate is 10 cycles of charge and discharge. The test results are as follows: Figure 4 shown.

[0062] Depend on Figure 4It can be seen that: the battery performance of the battery assembled with the gel electrolyte prepared in this embodiment has been investigated after experiencing a low rate to a high rate. It can be seen from the figure that at 0.1C and 0.2C, the discharge specific capacity has not decreased compared with the initial state, and even has a small increase, indicating that there is a process of forming an SEI interface film at this stage. Under 1C cycle, it still has a discharge specific capacity of more than 130mAh / g, and the coulombic efficiency is more than 99%.

[0063] Example 5

[0064] This embodiment provides a gel electrolyte containing LiPF6 and DOL, and its preparation method is basically the same as that of Example 4, except that 0.12 mmol of n-butylamine is used to replace 0.15 mmol of aniline to form a clear n-butylamine DOL solution.

[0065] The precursor solution in this example (containing 3 mL of LiPF6 solution and 1 mL of n-butylamine DOL clear solution) was left to stand for about 50 hours to obtain a gel electrolyte. Figure 5 shown.

[0066] Depend on Figure 5 It can be seen that the electrolyte prepared in this embodiment is not easy to flow when inverted, has the physical properties of a gel electrolyte, is not easy to leak in the battery, and reduces the risk of danger.

[0067] Example 6

[0068] This embodiment provides a gel electrolyte containing LiPF6 and DOL, and its preparation method is basically the same as that of Example 4, except that 0.08 mmol of 2-methoxypyridine is used to replace 0.15 mmol of aniline to form a 2-methoxypyridine DOL clear solution.

[0069] Example 7

[0070] This embodiment provides a gel electrolyte containing LiPF6 and DOL, and the preparation method thereof comprises the following steps:

[0071] S1. In a glove box filled with high-purity argon (H2O≤0.1ppm, O2≤0.1ppm), first dissolve lithium hexafluorophosphate (LiPF6) in a mixed solution of propylene carbonate and ethylene carbonate, mix thoroughly, and obtain a 2 mol / L LiPF6 solution.

[0072] Dissolve 0.08 mmol of diethylenetriamine in 0.5 mL of 1,3-dioxolane (DOL), mix well, and obtain a clear solution of diethylenetriamine DOL.

[0073] S2, respectively, mixing the LiPF6 solution and the diethylenetriamine DOL clarified solution in a volume ratio of 2:1 to obtain a precursor solution.

[0074] The precursor solution in this example (containing 2 mL of LiPF6 solution and 1 mL of diethylenetriamine DOL clear solution) is allowed to stand for about 62 hours to obtain a gel electrolyte.

[0075] Take the above 75μL precursor solution to assemble Li||LiFePO4 battery, and then test it in the blue battery test system. The procedure is: first stand to ensure that the gel is complete, then charge to 4.2v at a constant current rate of 0.1C, and then discharge to 2.5v at a constant current rate of 0.1C, and cycle 10 times; change different rates to repeat the above constant current charge and discharge process, the charge and discharge rate is from low to high (0.1C, 0.2C, 0.5C, 1C, 2C, 5C), and the same rate is 10 cycles of charge and discharge. The test results are as follows: Figure 6 shown.

[0076] Depend on Figure 6 It can be seen that: the battery performance of the battery assembled with the prepared gel electrolyte has been investigated after experiencing low rate to high rate. From the figure, it can be seen that at 0.1C and 0.2C, the discharge specific capacity has not decreased compared with the initial rate, and even has a small increase, indicating that there is a process of forming a SEI interface film at this stage. Under 1C cycle, it still has a discharge specific capacity of more than 135mAh / g, and the coulombic efficiency is above 99%.

[0077] Example 8

[0078] This embodiment provides a gel electrolyte containing LiPF6 and DOL, and its preparation method is basically the same as that of Example 7, except that 0.06 mmol of 2-fluoropyridine is used to replace 0.08 mmol of diethylenetriamine to form a 2-fluoropyridine DOL clear solution.

[0079] Comparative Example 1

[0080] This comparative example provides a gel electrolyte containing LiPF6 and DOL, and its preparation method comprises the following steps:

[0081] S1. In a glove box filled with high-purity argon (H2O≤0.1ppm, O2≤0.1ppm), first dissolve lithium hexafluorophosphate (LiPF6) in a mixed solution of propylene carbonate and ethylene carbonate in a volume ratio of 1:1, mix thoroughly, and obtain a 2 mol / L LiPF6 solution.

[0082] S2, directly mix the LiPF6 solution with 1 mL of 1,3-dioxolane (DOL) in a volume ratio of 1:1 to obtain a precursor solution.

[0083] The precursor solution in this embodiment (containing 1 mL of LiPF6 solution and 1 mL of DOL) is allowed to stand for about 0.5 h to obtain a gel electrolyte.

[0084] Comparative Example 2

[0085] This comparative example provides a gel electrolyte containing lithium bis(trifluoromethylsulfonyl)imide and DOL, and the preparation method thereof comprises the following steps:

[0086] S1. In a glove box filled with high-purity argon (H2O≤0.1ppm, O2≤0.1ppm), first dissolve 1mmoL of lithium bis(trifluoromethylsulfonyl)imide in DOL and mix thoroughly to prepare a 1mol / L solution.

[0087] S2, add 1 mmol aluminum trifluoromethanesulfonate to the above solution and mix well to obtain a precursor solution. Let stand for about 24 hours to obtain a gel electrolyte.

[0088] Comparative Example 3

[0089] This comparative example provides a liquid electrolyte containing LiPF6, and its preparation method comprises the following steps:

[0090] In a glove box filled with high-purity argon (H2O≤0.1ppm, O2≤0.1ppm), lithium hexafluorophosphate (LiPF6) is dissolved in a mixed solution of propylene carbonate and ethylene carbonate in a volume ratio of 1:1, and mixed thoroughly to obtain a 1 mol / L LiPF6 solution, which is a liquid electrolyte.

[0091] The performance of the gel electrolyte containing LiPF6 and DOL prepared in the above test examples was further tested and summarized, and the statistical results are shown in the following table:

[0092]

[0093] As can be seen from the table above, compared with Comparative Example 1, the battery assembled with the gel electrolyte of Examples 1-8 still has excellent capacity retention after 160 cycles, indicating that the addition of organic weak base can effectively slow down the gel speed, control the gel process and thus improve the cycle performance. This is because lithium hexafluorophosphate (LiPF6) decomposes to produce phosphorus pentafluoride, which is a strong Lewis acid that triggers 1,3-dioxolane (DOL) to explode, resulting in a capacity retention rate of only 82.6% after 160 cycles.

[0094] Compared with Comparative Example 2, the lithium salt used in the gel electrolyte of Examples 1-8 is lithium hexafluorophosphate, while lithium bis(trifluoromethylsulfonyl)imide is used in Comparative Example 2. Lithium bis(trifluoromethylsulfonyl)imide has high cost, is not suitable for commercial use, and requires an external catalyst to control the gelation process.

[0095] Compared with Comparative Example 3, the electrolytes prepared in Examples 1-8 are in gel state, while the electrolytes prepared in Comparative Example 3 are in liquid state. From the perspective of morphology, the examples are not easy to leak, and the risk of explosion is relatively small.

[0096] In addition, in fact, the inventor team has shown through extensive research that:

[0097] 1) The concentration of LiPF6 in the lithium salt solution of the gel electrolyte containing LiPF6 and DOL of the present invention is preferably controlled at 1-3 mol / L, the content of the organic weak base in the clarified solution of the organic weak base DOL is preferably controlled at 0.01-0.20 mmoL, and the volume ratio of the lithium salt solution containing LiPF6 and the clarified solution of the organic weak base DOL in the precursor solution is controlled at (1-3):1. On the whole, the time for standing the gel at room temperature can be controlled at 48-72 hours, and the discharge specific capacity can be guaranteed to reach about 130 mAh / g at 160 cycles, and the capacity retention rate can reach more than 87%.

[0098] 2) The preparation process of the present invention is simple and inexpensive, and more practical. Compared with lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluorophosphate is inexpensive, which greatly reduces the cost. At the same time, when using lithium bis(trifluoromethylsulfonyl)imide, a catalyst synergy is required. For example, aluminum trifluoromethanesulfonate catalyst is hygroscopic, not easy to weigh, and prone to explosion; for example, tin fluoride catalyst has poor solubility and too long stirring time. These problems increase the difficulty of the process to a certain extent, while the above-mentioned organic weak base basically does not have the problem of hygroscopicity and poor solubility, and the process operation is simpler.

[0099] 3) The gelation process of lithium hexafluorophosphate and DOL can be controlled by selecting the type of organic weak base and adjusting its dosage.

[0100] It is necessary to point out that the above embodiments are limited to further elaboration and explanation of the technical solution of the present invention, and are not further limitations of the technical solution of the present invention. The method of the present invention is only a preferred implementation scheme, and is not used to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A gel electrolyte containing LiPF6 and DOL, characterized in that: The raw materials for preparing the gel electrolyte include LiPF6, a carbonate solvent, DOL and an organic weak base, wherein the organic weak base is selected from at least one of triethylamine, aniline, diethylenetriamine, pyridine and 4-dimethylaminopyridine; the carbonate solvent is a mixture of propylene carbonate and ethylene carbonate in a volume ratio of 1:1; the preparation method of the gel electrolyte containing LiPF6 and DOL comprises the following steps: dissolving LiPF6 in a carbonate solvent to prepare a lithium salt solution containing LiPF6; dissolving an organic weak base in DOL to prepare an organic weak base DOL solution; The lithium salt solution containing LiPF6 and the organic weak base DOL solution are mixed in a preset ratio to obtain a precursor solution; the precursor solution is allowed to stand to gel; the standing conditions are: 25-35°C, and the standing time is 40-80h; in the precursor solution, the volume ratio of the lithium salt solution containing LiPF6 and the organic weak base DOL solution is (1-3):1; the concentration of LiPF6 in the lithium salt solution is 1mol / L-3mol / L, and the content of the organic weak base in the organic weak base DOL solution is 0.01-0.20mmoL.

2. The gel electrolyte containing LiPF6 and DOL according to claim 1, characterized in that: The organic weak base is selected from at least one of pyridine and triethylamine.

3. Use of the gel electrolyte containing LiPF6 and DOL as claimed in claim 1 or 2 in the preparation of lithium ion batteries.

4. A lithium ion battery, characterized in that: A gel electrolyte comprising LiPF6 and DOL as claimed in claim 1 or 2.

5. The lithium-ion battery according to claim 4, characterized in that: The lithium-ion battery also includes a positive electrode, a negative electrode and a separator; the positive electrode material is selected from at least one of lithium iron phosphate, high-nickel ternary positive electrode material, lithium nickel cobalt manganese oxide, and lithium titanate; and / or the negative electrode material is selected from at least one of metallic lithium, silicon-carbon negative electrode, graphite, and carbon nanotubes; and / or the separator is selected from at least one of a polyolefin separator, a PP-PE-PP film, a cellulose film, and a glass cellulose film.

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