An electrolyte for improving battery safety and its preparation method and application

Abstract

The present invention belongs to the technical field of battery materials, and discloses an electrolyte for improving battery safety, a preparation method and an application thereof. An electrolyte comprises an ion plastic, a polyfluoride and a lithium salt; the polyfluoride does not include a fluorinated polyoxyethylene ether. The electrolyte of the present invention is non-flammable, highly safe, and has good lithium conductivity. When applied to a battery, the first coulomb efficiency and cycle performance of the battery can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to an electrolyte for improving battery safety, and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have been widely used in portable electronic products, electric vehicles, aerospace, and energy storage systems due to their high energy density, good cycle stability, environmental friendliness, and wide operating temperature range. However, the carbonate electrolytes currently used in lithium-ion batteries have safety issues such as volatility and flammability. Thermal runaway of the battery will further increase safety risks. At the same time, during the battery cycle, the uneven deposition of lithium will also lead to dendrite growth, which will pierce the diaphragm and cause a short circuit in the battery in severe cases, posing a major safety hazard. In addition, dendrite growth will expose a larger specific surface area, accelerate side reactions with the electrolyte, and cause the electrolyte to catch fire.

[0003] In the prior art, although some electrolytes have good flame retardant effects, when they are applied to batteries, their corresponding first coulombic efficiency and cycle performance are poor.

[0004] Therefore, the development of non-flammable, highly safe and electrochemically sound electrolytes has become the current research focus. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides an electrolyte for improving battery safety and a preparation method and application thereof. The electrolyte of the present invention is non-flammable, highly safe, and has good lithium conductivity. When applied to a battery, the first coulombic efficiency and cycle performance of the battery can be improved.

[0006] A first aspect of the present invention provides an electrolyte for improving battery safety.

[0007] Specifically, an electrolyte for improving battery safety includes ion plasticizer, polyfluoride and lithium salt;

[0008] The polyfluoride is selected from at least one of 1,1,2,2-tetrafluoroethyl ethyl ether, 2,3-difluorophenylpropyl ether, methyl 2,2,3,3,3-pentafluoropropyl ether, methyl nonafluorobutyl ether, bis(2,2,2-trifluoroethyl) ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, pentafluorobenzene, hexafluorobenzene, methyl trifluoroethyl carbonate, and bis(2,2,2-trifluoroethyl) carbonate.

[0009] Preferably, the ionic crystal is composed of anions and cations, the anions are selected from at least one of bis(fluorosulfonyl)imide ions and bis(trifluoromethylsulfonyl)imide ions, and the cations are selected from at least one of N,N-diethylpyrrolidinium, N-ethyl-N-methylpyrrolidinium, N,N-dimethylpyrrolidinium, N-methylpyridinium, N-ethyl-N-methylpiperidinium, 3,3-dimethyloxazolidinium, 4-ethyl-4-methylmorpholinium, 4-isobutyl-4-methylmorpholinium, tetramethylammonium, tetraethylammonium, tetrabutylammonium, tetramethylphosphine, tetraethylphosphine and tetrabutylphosphine.

[0010] Further preferably, the cation in the ionic plasticizer is one of N-ethyl-N-methylpiperidinium, N-ethyl-N-methylpyrrolidinium, and N,N-dimethylpyrrolidinium.

[0011] Preferably, the molar ratio of anions to cations in the ionic plastic crystal is 1:1.

[0012] The above-mentioned ion plastic crystal has certain plasticity and lithium conductivity.

[0013] Preferably, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate and lithium bis(fluorosulfonyl)imide salts.

[0014] Preferably, in the electrolyte, the weight ratio of ion plasticizer, polyfluoride and lithium salt is (1-4):1:(4-8), more preferably (2-3):1:(5-6), and more preferably 3:1:6.

[0015] A second aspect of the present invention provides a method for preparing an electrolyte for improving battery safety.

[0016] Specifically, a method for preparing an electrolyte for improving battery safety comprises the following steps:

[0017] The components are mixed to obtain the electrolyte.

[0018] A third aspect of the present invention provides an application of an electrolyte for improving battery safety.

[0019] A battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and the above-mentioned electrolyte.

[0020] Preferably, the positive electrode sheet contains positive electrode active material, and the positive electrode active material includes at least one of lithium iron phosphate and nickel cobalt manganese salt.

[0021] Preferably, the positive electrode sheet also includes a conductive agent and a binder.

[0022] Preferably, the negative electrode sheet is a single-element lithium metal sheet or a lithium alloy metal sheet.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] The electrolyte of the present invention contains ion plastic crystals, specific polyfluoride and lithium salt, so that the electrolyte is non-flammable, highly safe and has good lithium conductivity. When applied to batteries, the first coulomb efficiency and cycle performance of the batteries can be improved. That is, the electrolyte of the present invention has both good flame retardancy and electrochemical properties. DETAILED DESCRIPTION

[0025] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0026] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0027] Example 1

[0028] An electrolyte for improving battery safety, including ion plasticizer, polyfluoride and lithium salt;

[0029] The cation in the ionic plastic is N-ethyl-N-methylpiperidinium, the anion is bis(fluorosulfonyl)imide, the polyfluoride is pentafluorobenzene, and the lithium salt is LiPF 6 ;

[0030] The weight ratio of the ion plasticizer, polyfluoride and lithium salt is 3:1:6.

[0031] A method for preparing an electrolyte for improving battery safety comprises the following steps:

[0032] The components are mixed to obtain the electrolyte.

[0033] Example 2

[0034] An electrolyte for improving battery safety, including ion plasticizer, polyfluoride and lithium salt;

[0035] The cation in the ion plasticizer is N-ethyl-N-methylpyrrolidinium, the anion is bis(fluorosulfonyl)imide, the anion is pentafluorobenzene, and the lithium salt is LiPF 6 ;

[0036] The weight ratio of the ion plasticizer, polyfluoride and lithium salt is 3:1:6.

[0037] A method for preparing an electrolyte for improving battery safety comprises the following steps:

[0038] The components are mixed to obtain the electrolyte.

[0039] Example 3

[0040] An electrolyte for improving battery safety, including ion plasticizer, polyfluoride and lithium salt;

[0041] The cation in the ion plasticizer is N,N-dimethylpyrrolidinium, the anion is bis(fluorosulfonyl)imide, the polyfluoride is pentafluorobenzene, and the lithium salt is LiPF 6 ;

[0042] The weight ratio of the ion plasticizer, polyfluoride and lithium salt is 3:1:6.

[0043] A method for preparing an electrolyte for improving battery safety comprises the following steps:

[0044] The components are mixed to obtain the electrolyte.

[0045] Example 4

[0046] An electrolyte for improving battery safety, including ion plasticizer, polyfluoride and lithium salt;

[0047] The cation in the ionic plasticizer is N-ethyl-N-methylpiperidinium, the anion is bis(fluorosulfonyl)imide, the polyfluoride is bis(2,2,2-trifluoroethyl) carbonate, and the lithium salt is LiPF 6 ;

[0048] The weight ratio of the ion plasticizer, polyfluoride and lithium salt is 3:1:6.

[0049] A method for preparing an electrolyte for improving battery safety comprises the following steps:

[0050] The components are mixed to obtain the electrolyte.

[0051] Example 5

[0052] An electrolyte for improving battery safety, including ion plasticizer, polyfluoride and lithium salt;

[0053] The cation in the ionic plastic is N-ethyl-N-methylpiperidinium, the anion is bis(fluorosulfonyl)imide, the polyfluoride is 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, and the lithium salt is LiPF 6 ;

[0054] The weight ratio of the ion plasticizer, polyfluoride and lithium salt is 3:1:6.

[0055] A method for preparing an electrolyte for improving battery safety comprises the following steps:

[0056] The components are mixed to obtain the electrolyte.

[0057] Comparative Example 1

[0058] Comparative Example 1 is a commercial electrolyte, and the electrolyte composition is: 1.0M LiPF 6 The volume ratio of EC (ethylene carbonate), DEC (diethyl carbonate), and DMC (dimethyl carbonate) is 1:1:1, and it also contains 5wt.% FEC (fluoroethylene carbonate) and 2wt.% VC (vinylene carbonate).

[0059] Comparative Example 2

[0060] Compared with Example 1, the difference of Comparative Example 2 is that no ion plasticizer is added, and other components and processes are the same as Example 1.

[0061] Comparative Example 3

[0062] Compared with Example 1, the difference of Comparative Example 3 is that no polyfluoride is added, and other components and processes are the same as those of Example 1.

[0063] Comparative Example 4

[0064] Compared with Example 5, the difference of Comparative Example 4 is that the 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether in Example 5 is replaced by an equal amount of fluoropolyoxyethylene ether, and the other components and processes are the same as those in Example 5.

[0065] Comparative Example 5

[0066] Compared with Example 5, the difference of Comparative Example 5 is that an equal amount of trimethylacetic acid molecular crystal shaping is used to replace the ionic crystal shaping in Example 5, and other components and processes are the same as Example 5.

[0067] Product effect testing

[0068] The electrolytes prepared in the above examples and comparative examples were applied to batteries.

[0069] Battery assembly:

[0070] Preparation of positive electrode sheet: After dissolving the binder PVDF (polyvinylidene fluoride) in NMP (N-methylpyrrolidone), add it to the mixture of lithium iron phosphate and conductive agent (conductive carbon black), wherein the mass ratio of lithium iron phosphate, conductive agent and binder is 97:1.5:1.5;

[0071] Preparation of liquid electrolyte: weigh the electrolyte prepared in the above examples and comparative examples;

[0072] Preparation of negative electrode sheet: The negative electrode is a lithium metal electrode sheet, and a 50 μm thick metal lithium strip is die-cut to obtain the negative electrode sheet;

[0073] Battery assembly: stack the positive electrode shell, positive electrode sheet, diaphragm (polyethylene diaphragm), negative electrode sheet, gasket and spring in sequence and inject electrolyte to assemble into a button battery. The battery assembly process belongs to conventional operations in this field.

[0074] Test method:

[0075] Electrolyte Self-Extinguishing Time (SET) Test: Take a 5mm glass fiber ball and soak it to absorb 0.2g electrolyte, and ignite it with a butane lighter. After removing the flame, record the time required for the flame to extinguish. Repeat three times and take the average extinguishing time. It is generally believed that if SET < 6s g -1 , the electrolyte is considered "non-flammable"; if 6s g -1 ≤SET≤20s g -1 , it is considered "flame retardant"; if SET>20s g -1 , it is considered "flammable".

[0076] First coulombic efficiency: The battery is charged and discharged at a rate of 0.1C. The first coulombic efficiency = first discharge capacity / first charge capacity × 100%;

[0077] Cycle performance: At room temperature, the battery is charged and discharged for 100 cycles at 0.1C. The battery life ends when the discharge capacity is less than 80% of the initial discharge capacity.

[0078] The above test results are shown in Table 1.

[0079] Table 1

[0080]

[0081]

[0082] As can be seen from Table 1, from Examples 1-5 and Comparative Example 1, it can be seen that the electrolyte of the present invention has good flame retardant effect and high safety. From Examples 1-5 and Comparative Examples 2-5, it can be seen that when the electrolyte of the present invention is applied to a battery, it corresponds to good first coulomb efficiency and cycle stability. It can be seen that only the electrolyte of the present invention can have good flame retardancy and electrochemical properties at the same time.

Claims

1. An electrolyte, characterized in that: It includes ionic plasticizers, polyfluorides and lithium salts; the polyfluorides do not include fluorinated polyoxyethylene ethers.

2. The electrolyte according to claim 1, characterized in that The polyfluoride is selected from at least one of 1,1,2,2-tetrafluoroethyl ethyl ether, 2,3-difluorophenylpropyl ether, methyl 2,2,3,3,3-pentafluoropropyl ether, methyl nonafluorobutyl ether, bis(2,2,2-trifluoroethyl) ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, pentafluorobenzene, hexafluorobenzene, methyl trifluoroethyl carbonate, and bis(2,2,2-trifluoroethyl) carbonate.

3. The electrolyte according to claim 1, characterized in that The ionic crystal is composed of anions and cations, wherein the anions are selected from at least one of bis(fluorosulfonyl)imide ions and bis(trifluoromethylsulfonyl)imide ions, and the cations are selected from at least one of N,N-diethylpyrrolidinium, N-ethyl-N-methylpyrrolidinium, N,N-dimethylpyrrolidinium, N-methylpyridinium, N-ethyl-N-methylpiperidinium, 3,3-dimethyloxazolidinium, 4-ethyl-4-methylmorpholinium, 4-isobutyl-4-methylmorpholinium, tetramethylammonium, tetraethylammonium, tetrabutylammonium, tetramethylphosphine, tetraethylphosphine and tetrabutylphosphine.

4. The electrolyte according to claim 3, characterized in that The cation in the ionic plastic crystal is one of N-ethyl-N-methylpiperidinium, N-ethyl-N-methylpyrrolidinium, and N,N-dimethylpyrrolidinium.

5. The electrolyte according to claim 1, characterized in that The lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), and lithium difluorooxalatoborate bis(fluorosulfonyl)imide.

6. The electrolyte according to any one of claims 1 to 5, characterized in that: In the electrolyte, the weight ratio of ion plasticizer, polyfluoride and lithium salt is (1-4):1:(4-8).

7. The method for preparing the electrolyte according to any one of claims 1 to 6, characterized in that: The following steps are involved: The components are mixed to obtain the electrolyte.

8. A battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte according to any one of claims 1 to 5.

9. The battery according to claim 7, characterized in that: The positive electrode sheet contains positive electrode active material, and the positive electrode active material includes at least one of lithium iron phosphate and nickel cobalt manganese salt.

10. The battery according to claim 7, characterized in that: The negative electrode sheet is a single-element lithium metal sheet or a lithium alloy metal sheet.

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