Metal electrolyte and preparation method thereof

Abstract

The invention provides a metal electrolyte preparation method which comprises the following steps: S1, performing molecular sieve dewatering on organic solvents, mixing the organic solvents, and performing magnetic stirring; s2, dissolving a lithium salt in an organic solvent, and stirring until the lithium salt is dissolved to obtain a mixed solution; s3, adding an additive and nitrogen diisobutyronitrile into the mixed solution, carrying out magnetic stirring, and standing to obtain a target electrolyte; according to the invention, the molten salt is utilized to construct an ion co-melt on the surfaces of the positive electrode particles, so that various ions can be uniformly and stably distributed on the surface of the positive electrode material, the generation of a subsequent uniform fluorinated layer is promoted, the irreversible phase change and the dissolution of transition metal ions can be better inhibited, and the cycle performance and the thermal stability of the material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and more specifically, to a metal electrolyte and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used in various electronic devices due to their advantages of high operating voltage, high energy density and long cycle life. With the advent of the battery era, the energy density requirements for positive electrode materials are getting higher and higher. Therefore, the application of high-nickel ternary positive electrode materials based on lithium nickel cobalt manganese oxide in new energy vehicles is becoming more and more urgent. High-nickel ternary positive electrode materials have the advantages of high specific capacity and low price. However, as energy storage equipment for new energy vehicles, the energy density and cycle life of high-nickel ternary positive electrode materials still need to be improved.

[0003] A Chinese patent publication number CN113764634A disclosed a method for preparing a lithium fluoride in-situ coated high-nickel ternary positive electrode material, which specifically disclosed the following steps: adding a lithium fluoride source to an anhydrous organic solvent, heating and stirring to obtain a solution a; adding the high-nickel ternary positive electrode material to the solution a and stirring to obtain a black suspension b; heating and stirring the suspension b, evaporating the solvent to obtain a high-nickel ternary powder c coated with the lithium fluoride source; heating and keeping the powder c warm to decompose the lithium fluoride source into lithium fluoride in-situ on the surface of the high-nickel ternary positive electrode, to obtain a lithium fluoride in-situ coated high-nickel ternary positive electrode material.

[0004] However, the existing technology requires dissolving the fluorine source in an anhydrous organic solvent, then drying it, and using a solid phase method to generate a uniform fluorinated layer. The operation process is cumbersome, not conducive to industrialization, and has high production costs.

[0005] Therefore, the present application provides a metal electrolyte and a preparation method thereof to solve the problems existing in the prior art. Summary of the invention

[0006] The purpose and effect of the present invention are achieved by the following specific technical means: a metal electrolyte and a preparation method thereof, comprising the following steps: Step 1: Weigh the ammonium fluoride solid material and the high-nickel ternary positive electrode solid material, put them into a fusion mixer under an inert gas protective atmosphere for low-speed mixing; Step 2: Adjust the speed of the fusion mixer to high-speed mixing, and make the ammonium fluoride evenly distributed on the surface of the high-nickel ternary positive electrode material through high-speed rotation and vibration to obtain a mixed material A for constructing an ion eutectic coating layer, and the inert gas is the protective atmosphere; Step 3: Add the mixed material A in step 2 into a sintering box for heat treatment. The heat treatment process is divided into two stages to obtain a high-nickel ternary positive electrode material wrapped with a fluoride layer, and the mass percentage of lithium fluoride is 0.01~1.0%.

[0007] Preferably, in step 1, the mass ratio of ammonium fluoride to the high-nickel ternary positive electrode material is 1:20-1:200.

[0008] Preferably, the low-speed mixing speed of the fusion mixer in step 1 is 500-800 rpm.

[0009] Preferably, the low speed mixing time in step 1 is 60 to 180 seconds.

[0010] Preferably, the inert gas used in the mixing step 1 is a mixture of one or more of nitrogen, argon and neon.

[0011] Preferably, the high-speed mixing speed of the fusion mixer in step 2 is 2500-3000 rpm.

[0012] Preferably, the high-speed mixing time in step 2 is 60 to 180 seconds.

[0013] Preferably, the inert atmosphere in step 2 is a combination of one or more of nitrogen, argon and neon.

[0014] Preferably, in step three, the temperature of the first heat treatment is 400-500°C, the heating rate of the first heat treatment is 5-10°C / min, the time of the first heat treatment is 10-30min, and the gas flow rate of the inert atmosphere in the first heat treatment is 2-5L / min.

[0015] Preferably, in the step three, the second heat treatment temperature is 150-300° C., the second heat treatment time is 60-180 min, and the gas flow rate of the inert atmosphere in the second heat treatment is 0.5-2 L / min.

[0016] Beneficial effects of the present invention: (1) The present invention directly adopts a solid phase method to generate a uniform fluorinated layer, which greatly simplifies the process flow and reduces costs compared to wet coating.

[0017] (2) The present invention utilizes molten salt to construct an ion eutectic on the surface of the positive electrode particles, so that various ions can be evenly and stably distributed on the surface of the positive electrode material, promoting the subsequent formation of a uniform fluoride layer, thereby better inhibiting irreversible phase change and the dissolution of transition metal ions, and improving the material's cycle performance and thermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a comparison chart of the cycle performance of the embodiment and the comparative example. DETAILED DESCRIPTION

[0019] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail in the specific embodiments. The following embodiments are only examples of implementing the present invention. It must be pointed out that the disclosed embodiments do not limit the scope of the present invention. On the contrary, changes and modifications made without departing from the scope of the present invention are all within the scope of patent protection of the present invention.

[0020] The present invention adopts a conventional button cell preparation method, wherein the positive electrode sheet adopts a nickel cobalt manganese oxide material and the negative electrode adopts a metal lithium sheet. Specifically, the positive electrode sheet is first prepared, the positive electrode active material nickel cobalt manganese oxide, conductive carbon black, and polytetrafluoroethylene are mixed in a mass ratio of 96:2:2, and after the mixing is completed, N-methyl pyrrolidone is added, and the positive electrode slurry is fully stirred and mixed to obtain a positive electrode slurry, which is evenly coated on an aluminum foil, and the positive electrode sheet is obtained after drying, and the electrode sheet is punched into an electrode sheet with a diameter of 14 mm on a sheet punching machine after rolling.

[0021] Preparation of electrolyte: Add diisobutyronitrile to the base electrolyte at a ratio of 0.1-1.0wt%. Comparative Example 1: In an argon atmosphere glove box, after all solvents to be used are dehydrated by molecular sieves, ethylene carbonate (EC), diethyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed in a mass ratio of EC:EMC:DMC=1:1:1 to obtain an organic solvent, and then lithium hexafluorophosphate (LiPF6) is added to the organic solvent. After the lithium hexafluorophosphate is completely dissolved, an electrolyte of 1MLiPF6 EC / EMC / DMC (1:1:1) is obtained, and then 2wt% vinylene carbonate (VC) is added to mix to obtain a basic electrolyte. CR2430 button cells are assembled in an argon glove box, and Li / NCM full cells are assembled in the glove box in the order of positive electrode shell, NCM622 positive electrode, diaphragm, electrolyte, negative electrode metal lithium sheet (18mm), gasket, spring sheet, and negative electrode stainless steel shell.

[0022] Example 1: In an argon atmosphere glove box, after all solvents to be used are dehydrated through molecular sieves, ethylene carbonate (EC), diethyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed at a mass ratio of EC:EMC:DMC=1:1:1 to obtain an organic solvent, and lithium hexafluorophosphate (LiPF6) is added to the organic solvent. After the lithium hexafluorophosphate is completely dissolved, an electrolyte of 1MLiPF6 EC / EMC / DMC (1:1:1) is obtained, and then 2wt% of vinylene carbonate (VC) is added and mixed to obtain a mixed electrolyte. On the basis of this electrolyte, 0.1wt% AIBN was added and mixed evenly to obtain the target electrolyte. CR2430 button cells were assembled in an argon glove box. The Li / NCM full battery was assembled in the glove box in the order of positive electrode shell, NCM622 positive electrode, diaphragm, electrolyte, negative electrode metal lithium sheet (18mm), gasket, spring sheet, and negative electrode stainless steel shell, and placed in a constant temperature blast drying oven at 60°C for 12h. Example 2: In an argon atmosphere glove box, after all solvents to be used are dehydrated through molecular sieves, ethylene carbonate (EC), diethyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed at a mass ratio of EC:EMC:DMC=1:1:1 to obtain an organic solvent, and lithium hexafluorophosphate (LiPF6) is added to the organic solvent. After the lithium hexafluorophosphate is completely dissolved, an electrolyte of 1MLiPF6 EC / EMC / DMC (1:1:1) is obtained, and then 2wt% of vinylene carbonate (VC) is added and mixed to obtain a mixed electrolyte. On the basis of this electrolyte, 0.5wt% AIBN was added and mixed evenly to obtain the target electrolyte. CR2430 button cells were assembled in an argon glove box. The Li / NCM full battery was assembled in the glove box in the order of positive electrode shell, NCM622 positive electrode, diaphragm, electrolyte, negative electrode metal lithium sheet (18mm), gasket, spring sheet, and negative electrode stainless steel shell, and placed in a constant temperature blast drying oven at 60°C for 12h. Example 3: In an argon atmosphere glove box, after all solvents to be used are dehydrated through molecular sieves, ethylene carbonate (EC), diethyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed in a mass ratio of EC:EMC:DMC=1:1:1 to obtain an organic solvent, and lithium hexafluorophosphate (LiPF6) is added to the organic solvent. After the lithium hexafluorophosphate is completely dissolved, an electrolyte of 1MLiPF6 EC / EMC / DMC (1:1:1) is obtained, and then 2wt% of vinylene carbonate (VC) is added and mixed to obtain a mixed electrolyte. On the basis of this electrolyte, 1 wt% AIBN was added and mixed evenly to obtain the target electrolyte. CR2430 button cells were assembled in an argon glove box. The Li / NCM full battery was assembled in the glove box in the order of positive electrode shell, NCM622 positive electrode, diaphragm, electrolyte, negative electrode metal lithium sheet (18 mm), gasket, spring sheet, and negative electrode stainless steel shell, and placed in a constant temperature blast drying oven at 60 °C for 12 h. Table 1 Electrolyte composition and battery performance of Examples 1-3 and Comparative Examples: Group Electrolyte composition <![CDATA[Additive C1]]> <![CDATA[C2 Additive]]> Average Coulombic efficiency Cycle retention rate Example 1 1MLiPF6EC / EMC / DMC (1:1:1) 2%VC 0.1% 98.64% 41% Example 2 1MLiPF6 EC / EMC / DMC (1:1:1) 2%VC 0.5% 99.20% 50% Example 3 1MLiPF6 EC / EMC / DMC (1:1:1) 2%VC 1% 99.56% 70% Comparative Example 1 1MLiPF6 EC / EMC / DMC (1:1:1) 2%VC 0% 99.68% 88% Electrochemical performance test: At 25°C, the battery was activated for 2 cycles at a current density of 0.1C, and then cycled at a rate of 0.33C / 0.33C. The charge and discharge voltage range was 3 to 4.3V.

[0023] from Figure 1 It can be seen from the cycle performance diagram that the lithium metal battery in the comparative example shows obvious capacity decay after about 40 cycles; on the contrary, the discharge capacity of the lithium metal battery to which different amounts of AIBN are added in the embodiment remains basically unchanged after 40 cycles, which is significantly improved compared with the full battery without addition. In particular, the effect is better when the addition amount is higher than 0.5%. Based on the above embodiments and comparative examples, the lithium metal battery electrolyte additive added by the present invention can form a stable inorganic SEI layer and improve the battery cycle life of the lithium metal battery.

[0024] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for preparing a metal electrolyte, characterized in that: The following steps are involved: S1: After removing water from the organic solvent by molecular sieving, the organic solvent is mixed and magnetically stirred; S2: dissolving the lithium salt in an organic solvent, stirring until dissolved, to obtain a mixed solution; S3: Adding additives and diisobutyronitrile to the mixed solution, stirring the solution magnetically, and then allowing the solution to stand to obtain a target electrolyte.

2. The method for preparing a metal electrolyte according to claim 1, characterized in that: The magnetic stirring time in step S1 is 1-2 hours, and the stirring rate is 100 rpm-300 rpm.

3. The method for preparing a metal electrolyte according to claim 1, characterized in that: The magnetic stirring time in step S2 is 4-8 hours, and the stirring rate is 200 rpm-600 rpm.

4. The method for preparing a metal electrolyte according to claim 1, characterized in that: The magnetic stirring time in step S3 is 24 hours, the stirring rate is 200 rpm-600 rpm, and the standing temperature is room temperature.

5. A metal electrolyte prepared by the preparation method according to any one of claims 1 to 4, characterized in that: It includes an organic solvent A, a lithium salt B, additives C1 and C2, wherein the additive C2 is diisobutyronitrile, the addition amount of diisobutyronitrile is 0.1wt%-1.0wt% of the total weight of the electrolyte, the mass fraction of the solvent A is 80wt%-85wt%, the mass fraction of the lithium salt B is 10wt%-15wt%, and the mass fraction of the additive C1 is 1-5wt%.

6. A metal electrolyte and a preparation method thereof according to claim 5, characterized in that: The organic solvent A is one or a mixture of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and ethyl methyl carbonate.

7. A metal electrolyte according to claim 5, characterized in that: The lithium salt B is one or a mixture of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalatoborate and lithium nitrate.

8. A metal electrolyte according to claim 5, characterized in that: The additive C1 is one or a mixture of vinylene carbonate, vinyl sulfate, propylene sulfite, 1-3-propylene sultone, and methylene methane disulfonate.

Images