Fluorinated alcohol electrolyte, preparation method and application of fluorinated alcohol electrolyte in lithium ion battery

Abstract

The invention provides a fluorinated alcohol electrolyte, a preparation method and application in a lithium ion battery, the electrolyte contains a fluorinated alcohol additive, the structural formula is R-OH, R is CF < x > H < 2-x >, CF < x > H < 3-x > CF < x > H < 2-x >, CF < x > H < 3-x > CHCFF < x > H < 3-x >, and CF < x > H < 3-x > CFCFF < x > H < 3-x >; compared with the prior art, the development of the fluoroalcohol additive is beneficial to exerting the performance of the battery, and fluoroalcohols can quickly react to form a film on a negative electrode to form a protective layer, namely, the fluoroalcohols can effectively gather on the surface of the negative electrode to form a fluorine-containing SEI film. By adopting the electrolyte of the fluorinated alcohol additive, the electrochemical performance of the lithium ion battery is improved. And comparing the performance of the battery containing the fluorinated alcohol additive with the performance of the battery without the fluorinated alcohol additive. Results show that compared with a battery without the additive, the battery containing the additive has the advantages that the capacity exertion and utilization are obviously improved, and the cycle performance is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries and electrolytes, and specifically relates to a fluorinated alcohol electrolyte, a preparation method thereof and application in lithium ion batteries. Background Art

[0002] As market demands increase, the next generation of lithium-ion batteries should have higher energy density and safety. Therefore, the requirements for lithium-ion battery electrolytes are becoming more and more stringent. Electrolytes usually contain organic solvents, lithium salts and additives, which must ensure safe and reliable operation of the battery while taking into account the performance of the battery.

[0003] In order to ensure the safety, reliability and excellent performance of lithium-ion batteries, additives with different functions have been developed in the electrolyte. With the development of lithium-ion batteries, the electrolyte additives are becoming more and more abundant. Such as: film-forming additives, flame retardant additives, acid and water removal additives and overcharge protection additives. In traditional electrolytes, alcohol lithium salts (ROLi) are formed under electrochemical reactions, which intensifies the reaction and eventually forms a SEI film on the electrode surface (Journal of Power Sources.2008.178:409-421). Typical market film-forming additives are vinylene carbonate (VC) and fluoroethylene carbonate (FEC). Their good preferential film-forming properties protect the positive and negative electrodes from direct contact with the electrolyte, resulting in the decomposition of the electrolyte solvent. Although this type of additive has excellent film-forming properties, the continuous development of lithium-ion batteries makes it difficult for them to meet battery needs. Therefore, it is imperative to develop new electrolyte additives.

[0004] The patent with publication number CN117613390A published on February 27, 2024, discloses a method for preparing a wide temperature range electrolyte for lithium-ion batteries, using tetraethoxysilane (TEOS) as an electrolyte additive in a ternary graphite system to obtain good battery performance. However, it does not disclose how to improve the initial efficiency of the battery.

[0005] The patent with publication number CN117638233A published on March 1, 2024, discloses a flame-retardant lithium-rich manganese-based lithium-ion battery high-voltage electrolyte, which uses phosphate esters as electrolyte flame-retardant additives. The battery operates stably at a high voltage of 4.8V and the electrolyte is non-flammable. However, its number of cycles is small and cannot meet the requirements.

[0006] Therefore, there is an urgent need to explore a new type of electrolyte additive that can further improve battery performance, meet current energy needs, and solve battery life anxiety. Summary of the invention

[0007] The object of the present invention is to provide a fluorinated alcohol electrolyte and a preparation method thereof, wherein a fluorinated alcohol additive is added to the electrolyte, and the electrolyte containing the fluorinated alcohol additive effectively improves the formation of the negative electrode SEI film, thereby improving the initial efficiency and cycle performance of the battery.

[0008] Another object of the present invention is to provide an application of a fluorinated alcohol electrolyte in a lithium ion battery, which improves the initial efficiency and cycle performance of the lithium ion battery, with the initial efficiency reaching more than 91%, and the retention rate reaching more than 91% after 1,000 cycles.

[0009] The specific technical solutions of the present invention are as follows:

[0010] A fluorinated alcohol electrolyte, comprising a fluorinated alcohol additive; the fluorinated alcohol additive has a structural formula of R-OH, wherein R is CF x H 2-x CF x H 3-x CF x H 2-x CF x H 3-x CHCF x H 3-x CF x H 3-x CFCF x H 3-x ; x values ​​are 1, 2, 3.

[0011] Preferably, the fluorinated alcohol additive is trifluoroethanol or difluoroethanol. The longer the molecular chain, the larger the molecular weight, which increases the viscosity in the electrolyte and causes a decrease in conductivity. The smaller the molecule, the lower the boiling point and the more difficult it is to achieve high-temperature storage and circulation. Therefore, the present invention preferably uses trifluoroethanol or difluoroethanol.

[0012] The mass proportion of the fluorinated alcohol additive in the fluorinated alcohol electrolyte is 0.1-8%, preferably 1-2%;

[0013] The fluorinated alcohol electrolyte also contains lithium hexafluorophosphate LiPF6, the concentration of which is 1 mol / L;

[0014] The fluorinated alcohol electrolyte also contains vinylene carbonate, the mass concentration of which is 2%;

[0015] The fluorinated alcohol electrolyte further contains ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1-3:1-7; preferably 1:1 or 3:7;

[0016] The present invention provides a method for preparing a fluorinated alcohol electrolyte, which specifically comprises: dissolving LiPF6 and vinylene carbonate (VC) in ethylene carbonate (EC) and ethyl methyl carbonate (EMC), adding a fluorinated alcohol additive, and mixing to obtain the electrolyte.

[0017] Another object of the present invention is to provide an application of a fluorinated alcohol electrolyte in a lithium ion battery.

[0018] The lithium ion battery comprises a positive electrode, a negative electrode and a fluorinated alcohol electrolyte.

[0019] The positive electrode comprises the following raw materials: lithium iron phosphate, a conductive agent and a binder, with a mass ratio of 94:3:3;

[0020] The negative includes the following raw materials: graphite, conductive agent, adhesive SBR and thickener CMC, with a mass ratio of 94:3:2:1.

[0021] The present invention improves the first efficiency and cycle performance of the lithium ion battery, the first efficiency reaches more than 91%, and the retention rate reaches more than 91% after 1000 cycles.

[0022] Compared with the prior art, the development of the fluorinated alcohol additives of the present invention is conducive to the performance of the battery. Fluorinated alcohols can quickly react at the negative electrode to form a protective layer, that is, effectively aggregate on the surface of the negative electrode to form a fluorine-containing SEI film. The present invention uses an electrolyte containing fluorinated alcohol additives to improve the electrochemical performance of lithium-ion batteries. Comparing the performance of batteries containing fluorinated alcohol additives and batteries without fluorinated alcohol additives, the results show that compared with batteries without additives, the capacity and utilization of batteries containing additives are significantly improved, and the cycle performance is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a battery performance test for embodiments and comparative examples. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0026] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0027] The specific steps for making a 2Ah soft pack battery are as follows:

[0028] 1) Add graphite: conductive agent Super P: adhesive SBR: thickener CMC in a ratio of 94%: 3%: 2%: 1% by mass into a stirring tank, use deionized water as a solvent, make the solid content 50%, and then stir and mix to form a negative electrode slurry;

[0029] 2) Prepare the negative electrode slurry described in step 1) at a single surface density of 154 g / m 2 The standard is coated on the copper foil, and then baked at 80℃ with air blowing for 2 hours, 1 meter / minute, and roller pressure of 20KN.

[0030] 3) Add lithium iron phosphate: conductive agent Super P: binder in a ratio of 94%:3%:3% by mass into a stirring tank, use N-methylpyrrolidone as a solvent, make the solid content 65%, and then stir and mix to make a positive electrode slurry;

[0031] 4) Prepare the positive electrode slurry described in step 3) at a single surface density of 173 g / m 2 The standard is coated on aluminum foil, and then baked at 80℃ with air blowing for 2 hours; 1 meter / minute, roller pressure 30KN.

[0032] 5) Wind the positive and negative electrodes and the separator described in step 2) and step 4), package them in a shell, and then bake them at 80°C in vacuum for 24 hours, then inject the electrolyte, and control the amount added to 4.2g / Ah; the electrolyte is 1mol / L LiPF6 and 2% mass fraction of vinylene carbonate (VC) dissolved in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0033] Example 1

[0034] A fluorinated alcohol electrolyte is used in the preparation of lithium-ion batteries. A 2Ah soft-pack battery is prepared using trifluoroethanol as an electrolyte additive. The specific steps are as follows:

[0035] 1) Add graphite: conductive agent Super P: adhesive SBR: thickener CMC in a ratio of 94%: 3%: 2%: 1% by mass into a stirring tank, use deionized water as a solvent, make the solid content 50%, and then stir and mix to form a negative electrode slurry;

[0036] 2) Prepare the negative electrode slurry described in step 1) at a single surface density of 154 g / m 2 The standard is coated on the copper foil, and then baked at 80℃ with air blowing for 2 hours, 1 meter / minute, and roller pressure of 20KN.

[0037] 3) Add lithium iron phosphate: conductive agent Super P: binder in a ratio of 94%:3%:3% by mass into a stirring tank, use N-methylpyrrolidone as a solvent, make the solid content 65%, and then stir and mix to make a positive electrode slurry;

[0038] 4) Prepare the positive electrode slurry described in step 3) at a single surface density of 173 g / m 2 The standard is coated on the aluminum foil, and the insulating glue in step 3 is coated on the blank area of ​​the aluminum foil, and then baked at 80℃ with air blowing for 2 hours; 1 meter / minute, and the rolling pressure is 30KN.

[0039] 5) Wind the positive and negative electrodes and the separator described in steps 2) and 4), put them into a shell and package them, then bake them at 80°C in vacuum for 24 hours, inject the electrolyte, and control the amount added to 4.2g / Ah; the electrolyte is 1mol / L LiPF6 and 2% mass fraction of vinylene carbonate (VC) dissolved in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and then add 1% mass percentage of trifluoroethanol (2,2,2-trifluoroethanol).

[0040] Example 2

[0041] A fluorinated alcohol electrolyte is used in the preparation of lithium-ion batteries. A 2Ah soft-pack battery is prepared using trifluoroethanol as an electrolyte additive. The specific steps are as follows:

[0042] The method is carried out according to Example 1, which means that the amount of trifluoroethanol added is 2% by mass.

[0043] Example 3

[0044] A fluorinated alcohol electrolyte is used in the preparation of lithium-ion batteries. The electrolyte with difluoroethanol as an additive is used to prepare a 2Ah soft-pack battery. The specific steps are as follows:

[0045] 1) Add graphite: conductive agent Super P: adhesive SBR: thickener CMC in a ratio of 94%: 3%: 2%: 1% (% refers to mass percentage) into a stirring tank, use deionized water as a solvent, make the solid content 50%, and then stir and mix to form a negative electrode slurry;

[0046] 2) Prepare the negative electrode slurry described in step 1) at a single surface density of 154 g / m 2 The standard is coated on the copper foil, and then baked at 80℃ with air blowing for 2 hours, 1 meter / minute, and roller pressure of 20KN.

[0047] 3) Add lithium iron phosphate: conductive agent Super P: binder in a ratio of 94%: 3%: 3% (% refers to mass percentage) into a stirring tank, use N-methylpyrrolidone as a solvent, make the solid content 65%, and then stir and mix to make a positive electrode slurry;

[0048] 4) Prepare the positive electrode slurry described in step 3) at a single surface density of 173 g / m 2 The standard is coated on the aluminum foil, and the insulating glue in step 3 is coated on the blank area of ​​the aluminum foil, and then baked at 80℃ with air blowing for 2 hours; 1 meter / minute, and the rolling pressure is 30KN.

[0049] 5) Wind the positive and negative electrodes and the separator described in steps 2) and 4), put them into a shell and package them, then bake them at 80°C in vacuum for 24 hours, and then inject the electrolyte, with the amount added controlled at 4.2g / Ah; the electrolyte is 1mol / L LiPF6 and 2% mass fraction of vinylene carbonate (VC) dissolved in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1, to which 1% mass of difluoroethanol (i.e., 2,2-difluoroethanol) is added.

[0050] Example 4

[0051] A fluorinated alcohol electrolyte is used in the preparation of lithium-ion batteries. The electrolyte with difluoroethanol as an additive is used to prepare a 2Ah soft-pack battery. The specific steps are as follows:

[0052] The process was carried out in accordance with Example 3, except that the amount of difluoroethanol added was 2% by mass.

[0053] The batteries of each embodiment and comparative example were tested at 25° C. at 1C, with a charge and discharge voltage range of 2.5 to 3.65V.

[0054] Table 1 Battery performance with different proportions of additives

[0055] Battery additive First effect (%) Capacity retention after 1000 cycles (mAh) Comparative Example / 89.2 1642.2 Example 1 1% trifluoroethanol 91.2 1653.4 Example 2 2% trifluoroethanol 92.4 1675.8 Example 3 1% difluoroethanol 91.8 1669.6 Example 4 2% difluoroethanol 93.1 1709.4

[0056] Figure 1 The battery performance test of the embodiment and the comparative example was carried out at 25℃ 1C constant current and constant voltage charging and 1C constant current discharge. The first efficiency of the battery with fluorinated alcohol additives was higher than that of the comparative example, and the residual capacity after the cycle was higher than that of the comparative example. The battery containing 2% difluoroethanol had the highest first efficiency and the highest residual capacity.

[0057] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A fluorinated alcohol electrolyte, characterized in that: The fluorinated alcohol electrolyte includes a fluorinated alcohol additive; the fluorinated alcohol additive has a structural formula of R-OH, wherein R is CF x H 2-x CF x H 3-x CF x H 2-x CF x H 3-x CHCF x H 3-x CF x H 3- x CFCF x H 3-x , x takes values ​​of 1, 2, and 3.

2. The fluorinated alcohol electrolyte according to claim 1, characterized in that The mass proportion of the fluorinated alcohol additive in the fluorinated alcohol electrolyte is 0.1-8%.

3. The fluorinated alcohol electrolyte according to claim 1 or 2, characterized in that: The fluorinated alcohol additive is trifluoroethanol.

4. The fluorinated alcohol electrolyte according to claim 1 or 2, characterized in that: The fluorinated alcohol additive is difluoroethanol.

5. The fluorinated alcohol electrolyte according to claim 1 or 2, characterized in that: The fluorinated alcohol electrolyte also contains lithium hexafluorophosphate LiPF6.

6. The fluorinated alcohol electrolyte according to claim 1 or 2, characterized in that: The fluorinated alcohol electrolyte also contains vinylene carbonate.

7. The fluorinated alcohol electrolyte according to claim 1 or 2, characterized in that: The fluorinated alcohol electrolyte also contains ethylene carbonate and ethyl methyl carbonate.

8. A method for preparing the fluorinated alcohol electrolyte according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: dissolving LiPF6 and vinylene carbonate in ethylene carbonate and ethyl methyl carbonate, adding fluorinated alcohol additives, and mixing well to obtain the product.

9. Use of the fluorinated alcohol electrolyte according to any one of claims 1 to 7 in a lithium ion battery.

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