Additive containing fluorine and sulfur, electrolyte, battery and preparation method

Abstract

The invention relates to the technical field of energy storage batteries, in particular to a fluorine-containing sulfur additive, an electrolyte, a battery and a preparation method. The fluorine-containing sulfur additive is characterized in that the fluorine-containing sulfur additive has a structure as shown in a formula (I), in the # imgabs0 #, R1 is selected from a carbon atom-containing organic group with the carbon atom number of 1-4, R2 is selected from a carbon atom-containing organic group with the carbon atom number of 1-4, the numerical value of n is 1-6, n represents the number of fluorine atoms, and x represents the number of sulfur atoms; preferably, the organic group is an alkyl group or an alkyl substituent group. The electrolyte contains the fluorine-sulfur additive, so that the film-forming impedance of the battery can be improved, and a lithium fluoride compact protective film formed by fluorine atoms protects a positive electrode interface and reduces the oxidation of a high-voltage positive electrode on the electrolyte; meanwhile, the contained sulfur atoms can be reduced on the surface of the negative electrode, the reduction reaction of the electrolyte and negative electrode lithium is inhibited, and the overall cycle performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage batteries, and in particular to a fluorine-sulfur additive, an electrolyte, a battery and a preparation method. Background Art

[0002] As lithium-ion batteries become more and more popular, their applications have evolved from being usable and capable to being easy to use. How to improve battery life is one of the key issues that people are considering. The way to improve specific energy is, on the one hand, to develop new materials with higher specific energy, such as lithium-rich manganese-based materials, silicon negative electrode materials, etc., and on the other hand, to increase the upper limit of the application voltage of battery materials and improve the overall specific capacity of the materials. Among them, increasing the upper limit of the application voltage of materials is an effective means to quickly iterate and improve mature material systems, such as high-voltage nickel-cobalt-manganese ternary materials, high-voltage lithium cobalt oxide materials, etc. After the upper limit voltage of the application of materials is increased, in addition to the advantages of specific capacity, it will also bring some adverse effects, especially the oxidation problem of the electrolyte under high voltage, which will lead to gas production and swelling inside the battery, and a rapid decline in battery electrical performance. In order to solve the problem of electrolyte oxidation in batteries under high voltage, the commonly used method is to add fluorine-containing additives such as fluoroethylene carbonate, and use fluorine atoms to form high-voltage resistant fluorides at high voltage to isolate the direct contact between the positive active material and the electrolyte, thereby reducing the oxidation problem of the electrolyte under high voltage. However, under high voltage, the positive active material usually releases some transition metal cations. These cations can pass through the positive electrode interface protective film and deposit on the negative electrode surface, continuously destroying the negative electrode interface, causing the electrolyte to continue to react at the negative electrode interface, affecting the electrical performance of the battery. In order to solve this problem, people usually add sulfur-containing additives to the high voltage electrolyte system, and use the good film-forming properties of sulfur-based additives at the negative electrode to protect the negative electrode interface and reduce the overall side reactions of the battery. However, this method of using multiple additives to protect the positive electrode interface and the negative electrode interface respectively to achieve stable operation of the battery under high voltage system will greatly increase the internal resistance of the battery as a whole, reduce the charge and discharge speed of the battery, and cannot meet the current demand for fast charge and discharge. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies and defects of the prior art and to provide a fluorine-sulfur additive, an electrolyte, a battery and a preparation method.

[0004] In order to achieve the above objectives, this application adopts the following solutions:

[0005] A fluorine-sulfur additive having the structure of the following formula (I);

[0006]

[0007] Wherein, R1 is selected from an organic group containing carbon atoms having 1-4 carbon atoms, R2 is selected from an organic group containing carbon atoms having 1-4 carbon atoms, the value of n is 1-6, n represents the number of fluorine atoms, and x represents the number of sulfur atoms; preferably, the organic group is an alkyl group or an alkyl substituent.

[0008] The atomic ratio of fluorine to sulfur is (3-6):1.

[0009] The fluorine-sulfur additive is at least one of 1-propanol, 3,3,3-trifluoro-1-[(phenylmethyl)thio]-, 1-acetate (CAS: 201862-01-3, D1), phenyl 1-acetoxy-pentafluoropropyl sulfide (CAS: 129265-02-7, D2), 1,3-oxothiazole-4-propionic acid, and 5-oxo-2,2-bis(trifluoromethyl)-1,1-dimethylethyl ester (CAS: 603960-98-1, D3), wherein the structural formulas of D1, D2, and D3 are as follows.

[0010]

[0011] The present invention also includes an electrolyte, comprising a lithium salt, a solvent and an additive; the additive comprises a conventional additive and the fluorine-sulfur-containing additive.

[0012] The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide;

[0013] Preferably, the solvent comprises at least one of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, diethyl carbonate, propylene carbonate, and ethyl acetate;

[0014] Preferably, the conventional additives include at least one of vinylene carbonate, vinyl sulfate, lithium difluorooxalatoborate, lithium difluorophosphate, and methylene methanedisulfonate.

[0015] The solvent accounts for 80 to 95 parts by weight, the lithium salt accounts for 8 to 15 parts by weight, the fluorine-sulfur additive accounts for 0.5 to 6 parts by weight, and the conventional additive accounts for 0.5 to 10 parts by weight.

[0016] The present invention also includes a battery comprising a positive electrode, a negative electrode, a separator, and the electrolyte according to any one of claims 4 to 6.

[0017] The positive electrode includes a positive electrode active material, a positive electrode conductor and a positive electrode binder; preferably, the positive electrode active material is a ternary positive electrode material; preferably, the positive electrode conductor is a mixture of CNT and carbon black; preferably, the ratio of the two is 1:3; preferably, the positive electrode binder is PVDF; preferably, the mass ratio of the positive electrode active material, the positive electrode conductor and the positive electrode binder is (90-98): (1-5): (1-5); preferably 96:2:2.

[0018] The negative electrode includes a negative electrode active material, a negative electrode conductive agent and a negative electrode binder; preferably, the negative electrode active material is graphite or artificial graphite; preferably, the negative electrode conductive agent is carbon black; preferably, the negative electrode binder is a mixture of CMC and SBR; preferably, the mass ratio of CMC to SBR is 1:1.2; preferably, the mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder is (90-98):(1-5):(1-5); preferably 96:2.2:1.8.

[0019] The present invention also includes a method for preparing the battery, comprising the following steps: combining a positive electrode, a negative electrode and a separator into a battery, placing the battery in an aluminum-plastic film and drying the battery, injecting the electrolyte, forming and exhausting the electrolyte, and packaging the battery to complete the preparation; preferably, the separator is a double-sided ceramic polyethylene separator.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The fluorine-sulfur additives described in this application can improve the film-forming impedance of the battery. The dense lithium fluoride protective film formed by the fluorinated atoms protects the positive electrode interface and reduces oxidation of the electrolyte by the high-voltage positive electrode. The sulfur atoms contained in the additives can also be reduced on the negative electrode surface, inhibiting the reduction reaction between the electrolyte and the negative electrode lithium, thereby improving the overall cycle performance of the battery. As a preferred form, by adding additives with different fluorine-sulfur atomic ratios, the battery's voltage resistance can be improved while also taking into account the battery's power performance, avoiding the impact of increased impedance caused by excessive film-forming additives. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] The fluorine-containing sulfur additives used in this application are 1-propanol, 3,3,3-trifluoro-1-[(phenylmethyl)thio]-, 1-acetate (CAS: 201862-01-3, D1), phenyl 1-acetoxy-pentafluoropropyl sulfide (CAS: 129265-02-7, D2), 1,3-oxothiazole-4-propionic acid, 5-oxo-2,2-bis(trifluoromethyl)-1,1-dimethylethyl ester (CAS: 603960-98-1, D3).

[0024] The structural formulas of D1, D2 and D3 are as follows.

[0025]

[0026]

[0027] Example 1

[0028] Electrolyte, including:

[0029] Solvent: 25g of ethylene carbonate, 30g of ethyl methyl carbonate, 25g of diethyl carbonate;

[0030] Lithium salt: 8g lithium hexafluorophosphate;

[0031] Conventional additives: 0.2g of vinylene carbonate, 0.3g of vinyl sulfate;

[0032] Fluorine-containing sulfur additive: 0.5g D1.

[0033] Example 2

[0034] Electrolyte, including:

[0035] Solvent: 25g of ethylene carbonate, 38g of ethyl methyl carbonate, 25g of diethyl carbonate;

[0036] Lithium salt: 12g lithium hexafluorophosphate;

[0037] Conventional additives: 2g of vinylene carbonate, 3g of vinyl sulfate;

[0038] Fluorine-containing sulfur additive: 3g D1.

[0039] Example 3

[0040] Electrolyte, including:

[0041] Solvent: 30 g of ethylene carbonate, 30 g of ethyl methyl carbonate, 35 g of diethyl carbonate;

[0042] Lithium salt: 15g lithium hexafluorophosphate;

[0043] Conventional additives: 5g vinylene carbonate, 3g vinyl sulfate, 1g lithium difluorooxalatoborate, 1g methylene methanedisulfonate;

[0044] Fluorine-containing sulfur additive: 6g D1.

[0045] Example 4

[0046] Electrolyte, including:

[0047] Solvent: 25g of ethylene carbonate, 35g of ethyl methyl carbonate, 25g of diethyl carbonate;

[0048] Lithium salt: 12g lithium hexafluorophosphate;

[0049] Conventional additives: 0.5 g of vinylene carbonate, 0.8 g of vinyl sulfate, 0.6 g of lithium difluorooxalatoborate, and 0.6 g of methylene methanedisulfonate;

[0050] Fluorine-containing sulfur additive: 1.5g D1.

[0051] Example 5

[0052] Electrolyte, including:

[0053] Solvent: 25g of ethylene carbonate, 35g of ethyl methyl carbonate, 25g of diethyl carbonate;

[0054] Lithium salt: 12g lithium hexafluorophosphate;

[0055] Conventional additives: 0.5 g of vinylene carbonate, 0.8 g of vinyl sulfate, 0.6 g of lithium difluorooxalatoborate, and 0.6 g of methylene methanedisulfonate;

[0056] Fluorine-containing sulfur additive: 1.5g D2.

[0057] Example 6

[0058] Electrolyte, including:

[0059] Solvent: 25g of ethylene carbonate, 35g of ethyl methyl carbonate, 25g of diethyl carbonate;

[0060] Lithium salt: 12g lithium hexafluorophosphate;

[0061] Conventional additives: 0.5 g of vinylene carbonate, 0.8 g of vinyl sulfate, 0.6 g of lithium difluorooxalatoborate, and 0.6 g of methylene methanedisulfonate;

[0062] Fluorine-containing sulfur additive: 1.5g D3.

[0063] Example 7

[0064] Electrolyte, including:

[0065] Solvent: 25g of ethylene carbonate, 35g of ethyl methyl carbonate, 25g of diethyl carbonate;

[0066] Lithium salt: 12g lithium hexafluorophosphate;

[0067] Conventional additives: 0.5 g of vinylene carbonate, 0.8 g of vinyl sulfate, 0.6 g of lithium difluorooxalatoborate, and 0.6 g of methylene methanedisulfonate;

[0068] Fluorine-containing sulfur additives: 0.5g of D1, 0.5g of D2, 0.5g of D3.

[0069] Comparative Example 1

[0070] Electrolyte, including:

[0071] Solvent: 25g of ethylene carbonate, 35g of ethyl methyl carbonate, 25g of diethyl carbonate;

[0072] Lithium salt: 12g lithium hexafluorophosphate;

[0073] Conventional additives: 0.5 g of vinylene carbonate, 0.8 g of vinyl sulfate, 0.6 g of lithium difluorooxalatoborate, and 0.6 g of methylene methanedisulfonate;

[0074] Based on the electrolytes of Examples 1 to 7 and Comparative Example 1, a high-voltage and high-power battery was further prepared. The specific preparation methods were as follows (except for the different electrolyte formulas, all other aspects were the same):

[0075] The ternary positive electrode material, conductive agent CNT, carbon black and binder PVDF are evenly dispersed in NMP solvent at a mass ratio of 96:0.5:1.5:2.0. After stirring for a period of time under vacuum, the solid content of the positive electrode slurry is controlled at 60%. The positive electrode slurry is evenly coated on both surfaces of the aluminum foil, the electrode is dried, and the pressure is adjusted to 3.3g / cm 3 Compact and roll, and finally die-cut into specified sizes.

[0076] Artificial graphite, carbon black, binder CMC and binder SBR are evenly dispersed in deionized water at a mass ratio of 96.0:1.0:1.2:1.8. After thorough stirring in vacuum, a uniformly mixed negative electrode slurry is obtained. The solid content of the negative electrode slurry is controlled at 50%. The negative electrode slurry is evenly coated on both surfaces of the negative electrode current collector copper foil, the electrode is dried, and the negative electrode slurry is heated at 1.6 g / cm 3 Compact and roll the product. Finally, cut it into the required size for later use.

[0077] A 7-micron double-sided ceramic polyethylene diaphragm is used to combine the positive and negative pole pieces and the diaphragm into a battery. After being placed in an aluminum-plastic film and dried, the electrolyte is injected. After the exhaust is generated using a 0.05C charging current, the battery is completed after packaging.

[0078] The performance of the batteries prepared using the electrolytes of Examples 1 to 7 and Comparative Example 1 was tested below.

[0079] High-voltage cycling performance test: At 25°C, the batteries prepared in Examples 1-7 and Comparative Example 1 were charged at a constant current rate of 2C. When the battery voltage reached 4.5V, they were switched to constant voltage charging and continued until the current dropped to 0.05C. After a 10-minute rest period, the batteries were discharged at a constant current rate of 2C until the battery voltage dropped to 2.8V, followed by a 10-minute rest period. This charge and discharge procedure was repeated 500 times, and the battery's cycle capacity retention was recorded.

[0080] 60°C High-Temperature Storage Experiment: Batteries prepared in Examples 1-6 and Comparative Example 1 were charged at a constant current rate of 2C at 25°C. When the battery voltage reached 4.5V, they were switched to constant voltage charging and continued until the current dropped to 0.05C. The fully charged batteries were then placed in a 60°C oven and stored for one month. They were then discharged at a 2C rate at 25°C to determine the residual capacity. They were then charged and discharged again at a 2C rate to determine the recovered capacity after high-temperature storage.

[0081] The test results of the batteries prepared using the electrolytes of Examples 1 to 7 and Comparative Example 1 are shown in Table 1 below.

[0082] Table 1: Test results of the time required for battery immersion in various examples and comparative examples

[0083]

[0084] Table 2 Residual capacity and recovery capacity of batteries of various embodiments and comparative examples after storage at 60°C

[0085]

[0086]

[0087] Table 3 Comparison of internal resistance test of batteries in various embodiments and comparative examples

[0088] DC internal resistance (mΩ) Example 1 20.5 Example 2 24.3 Example 3 24.7 Example 4 23.2 Example 5 22.6 Example 6 26.8 Example 7 27.5 Comparative Example 1 28.8

[0089] The results show that the use of fluorine-sulfur additives significantly improves the battery's overall high-voltage cycle capacity retention and high-temperature storage performance during high-power charge and discharge. In Tables 1-3, the addition of D1 optimizes overall battery performance. However, excessive addition leads to increased deposition of reactants on the negative electrode surface, resulting in excessive surface impedance and affecting overall electrical performance.

[0090] The fluorine-sulfur additives described in this application can improve the film-forming impedance of the battery. The dense lithium fluoride protective film formed by the fluorinated atoms protects the positive electrode interface and reduces oxidation of the electrolyte by the high-voltage positive electrode. The sulfur atoms contained in the additives can also be reduced on the negative electrode surface, inhibiting the reduction reaction between the electrolyte and the negative electrode lithium, thereby improving the overall cycle performance of the battery. As a preferred form, the addition of fluorine-sulfur additives improves the battery's voltage resistance while also taking into account the battery's power performance, avoiding the impact of increased impedance caused by excessive film-forming additives.

[0091] The basic principles, main features and advantages of the present invention are shown and described above. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0092] The embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims rather than the foregoing description, and all changes that come within the meaning and range of equivalents of the claims are therefore intended to be embraced therein.

[0093] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A fluorine-sulfur additive, characterized in that: Having the following structure (I): Wherein, R1 is selected from an organic group containing carbon atoms having 1-4 carbon atoms, R2 is selected from an organic group containing carbon atoms having 1-4 carbon atoms, the value of n is 1-6, n represents the number of fluorine atoms, and x represents the number of sulfur atoms; preferably, the organic group is an alkyl group or an alkyl substituent.

2. The fluorine-containing sulfur additive according to claim 1, characterized in that The atomic ratio of fluorine to sulfur is (3-6):

1.

3. The fluorine-containing sulfur additive according to claim 1, characterized in that The fluorine-sulfur additive is at least one of 1-propanol, 3,3,3-trifluoro-1-[(phenylmethyl)thio]-, 1-acetate, phenyl 1-acetoxy-pentafluoropropyl sulfide, 1,3-oxothiazole-4-propionic acid, and 5-oxo-2,2-bis(trifluoromethyl)-1,1-dimethylethyl ester.

4. An electrolyte, characterized in that The invention comprises a lithium salt, a solvent and an additive; the additive comprises a conventional additive and the fluorine-sulfur-containing additive according to any one of claims 1 to 3.

5. The electrolyte according to claim 4, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide; Preferably, the solvent comprises at least one of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, diethyl carbonate, propylene carbonate, and ethyl acetate; Preferably, the conventional additives include at least one of vinylene carbonate, vinyl sulfate, lithium difluorooxalatoborate, lithium difluorophosphate, and methylene methanedisulfonate.

6. The electrolyte according to claim 4, characterized in that The solvent accounts for 80 to 95 parts by weight, the lithium salt accounts for 8 to 15 parts by weight, the fluorine-sulfur additive accounts for 0.5 to 6 parts by weight, and the conventional additive accounts for 0.5 to 10 parts by weight.

7. A battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 4 to 6.

8. The battery according to claim 7, characterized in that The positive electrode includes a positive electrode active material, a positive electrode conductor and a positive electrode binder; preferably, the positive electrode active material is a ternary positive electrode material; preferably, the positive electrode conductor is a mixture of CNT and carbon black; preferably, the ratio of the two is 1:3; preferably, the positive electrode binder is PVDF; preferably, the mass ratio of the positive electrode active material, the positive electrode conductor and the positive electrode binder is (90-98): (1-5): (1-5); preferably 96:2:

2.

9. The battery according to claim 7, characterized in that The negative electrode includes a negative electrode active material, a negative electrode conductive agent and a negative electrode binder; preferably, the negative electrode active material is graphite or artificial graphite; preferably, the negative electrode conductive agent is carbon black; preferably, the negative electrode binder is a mixture of CMC and SBR; preferably, the mass ratio of CMC to SBR is 1:1.2; preferably, the mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder is (90-98):(1-5):(1-5); preferably 96:2.2:1.

8.

10. A method for preparing a battery according to any one of claims 7 to 8, characterized in that: The method comprises the following steps: combining a positive electrode, a negative electrode and a separator into a battery, placing the battery into an aluminum-plastic film and drying the battery, injecting the electrolyte, forming and exhausting the electrolyte, and packaging the electrolyte to complete the preparation of the battery; preferably, the separator is a double-sided ceramic polyethylene separator.

Images