Electrolyte for inhibiting transition metal dissolution and lithium ion battery

Abstract

The application discloses an electrolyte for inhibiting transition metal dissolution and a lithium ion battery, and the electrolyte comprises: a primary injection electrolyte and a secondary injection electrolyte, and the mass ratio of the primary injection electrolyte to the secondary injection electrolyte is preferably (1-19):1; the primary injection electrolyte comprises: a first non-aqueous organic solvent, a first lithium salt and a primary additive; the primary additive comprises: a film-forming additive; the secondary injection electrolyte comprises: a second non-aqueous organic solvent, a second lithium salt and a secondary additive; and the secondary additive comprises: a complex transition metal ion additive and a water-removing and acid-removing additive. The electrolyte disclosed by the application can effectively inhibit the dissolution, migration and deposition of transition metals, and can solve problems such as low capacity and cycle attenuation; and the lithium ion battery prepared by using the electrolyte disclosed by the application has high rate and good cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and more specifically, relates to an electrolyte that inhibits the dissolution of transition metals and a lithium-ion battery. Background Technology

[0002] With the development of new energy sources, lithium-ion batteries have become the most popular type of battery and have attracted much attention. Commercially available lithium battery cathode materials mainly include layered lithium cobalt oxide, ternary materials, spinel-structured lithium manganese oxide, and olivine-structured lithium iron phosphate. Transition metal ions are prone to dissolution, especially during storage or cycling under extreme conditions such as high voltage and high temperature. The dissolved transition metals can lead to a sharp decline in battery capacity and even safety issues. Therefore, the research and development of cathode materials and their matching electrolytes is particularly urgent.

[0003] From the perspective of reducing material costs, reducing or even eliminating the content of expensive cobalt is an inevitable trend. With the decrease in cobalt content, the content of inexpensive manganese is significantly increased. Currently, cathode materials with high manganese content include lithium manganese oxide, spinel lithium nickel manganese oxide, layered lithium nickel manganese oxide, and lithium manganese iron phosphate. However, trivalent manganese ions are prone to lattice distortion during battery charging and discharging, leading to manganese dissolution and deposition on the negative electrode surface, damaging the solid electrolyte interphase (SEI) film. Specifically, manganese dissolution on the cathode material surface hinders lithium-ion diffusion during subsequent charging and discharging, increasing battery polarization and reducing capacity. On the negative electrode material surface, divalent manganese ions diffuse to the negative electrode, are reduced to elemental form from the surface to the inner layer, and are then oxidized back to divalent, repeating this cycle. Simultaneously, the increase in low-lithium-intercalated graphite in the negative electrode and the increased disorder on the graphite surface also promote SEI film regeneration. In summary, manganese leaching damages the SEI film on the negative electrode surface. The continuous regeneration and repair of the SEI film consumes a large amount of active lithium, causing problems such as rapid decline in cell lifespan and severe gas generation.

[0004] CN 116845509 A discloses a method for secondary electrolyte injection and its application. This invention first uses a first electrolyte containing ethers to pre-charge and form a thin and uniform SEI film with low polarization, low internal resistance, and high uniformity. Then, it switches to a second electrolyte to maintain the SEI film already formed in the battery cell. This method not only inhibits the decomposition of the second electrolyte and improves its stability, but also reduces manganese ion dissolution due to the uniform, stable, and lower-resistance SEI film. Consequently, the content of transition metals deposited on the negative electrode surface is also reduced, improving the rate capability and cycle performance of the manganese-based positive electrode battery cell system.

[0005] In summary, the secondary electrolyte injection process currently reduces the dissolution of transition metals and improves cell lifespan. Therefore, the development of electrolytes based on secondary electrolyte injection has become a research hotspot. Summary of the Invention

[0006] The purpose of this invention is to provide an electrolyte and a lithium-ion battery that inhibit the dissolution of transition metals. The electrolyte of this invention can effectively inhibit the dissolution, migration and deposition of transition metals, and can solve problems such as low capacity and cycle decay. The lithium-ion battery prepared using the electrolyte of this invention has high rate capability and good cycle performance.

[0007] To achieve the above objectives, one aspect of the present invention provides an electrolyte for inhibiting the dissolution of transition metals, the electrolyte comprising: a primary electrolyte and a secondary electrolyte, wherein the mass ratio of the primary electrolyte to the secondary electrolyte is preferably (1~19):1; The primary electrolyte solution includes: a first non-aqueous organic solvent, a first lithium salt, and a primary additive; the primary additive includes: a film-forming additive. The secondary electrolyte includes: a second non-aqueous organic solvent, a second lithium salt, and a secondary additive; the secondary additive includes: a complexing transition metal ion additive and a dehydrating and acid-suppressing additive.

[0008] According to the present invention, preferably, the complexing transition metal ion additive is a crown ether compound, preferably at least one of the compounds shown in Formulas I-IV; Formula I (4,10,16-triaza-18-crown ether-6); Formula II (4,13-diaza-18-crown ether-6); Formula III (dibenzo-18-crown ether-6); Formula IV (tribenzo-18-crown ether-6).

[0009] According to the present invention, preferably, the dehydrating and acid-suppressing additives include at least two of lithium trimethylsilane phosphate, lithium trimethylsilane borate, trimethylsilyl imidazole, and dimethyldiphenoxysilane.

[0010] According to the present invention, preferably, the film-forming additive comprises: a film-forming additive that inhibits the dissolution of transition metal ions and other film-forming additives; the mass ratio of the film-forming additive that inhibits the dissolution of transition metal ions to other film-forming additives is (1-2):1; The film-forming additive that inhibits the dissolution of transition metal ions includes at least one of lithium difluorooxalate borate, lithium dioxalate borate, and lithium trimethylsilane phosphate. The other film-forming additives include at least one of the following: vinylene carbonate, vinyl sulfate, propylene sulfonate lactone, fluoroethylene carbonate, and lithium difluorophosphate.

[0011] According to the present invention, preferably, the first non-aqueous organic solvent and the second non-aqueous organic solvent are each independently selected from at least one of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, propylene carbonate and diethyl carbonate; The first lithium salt and the second lithium salt are each independently selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate and lithium bisfluorosulfonylimide.

[0012] According to the present invention, preferably, based on the total weight of the primary electrolyte, the content of the first non-aqueous organic solvent is 50-90 wt%, the content of the first lithium salt is 5-20 wt%, and the content of the primary additive is 2-20 wt%; the sum of the weight percentages of all components of the primary electrolyte is 100%.

[0013] According to the present invention, preferably, based on the total weight of the secondary electrolyte, the content of the second non-aqueous organic solvent is 50-90 wt%, the content of the second lithium salt is 5-20 wt%, the content of the complexing transition metal ion additive is 2-20 wt%, and the content of the dehydration and acid-suppressing additive is 2-20 wt%; the sum of the weight percentages of each component of the secondary electrolyte is 100%.

[0014] Another aspect of the present invention provides a lithium-ion battery in which the electrolyte is prepared using a secondary electrolyte injection process, and the electrolyte is the electrolyte described above.

[0015] According to the present invention, preferably, the secondary electrolyte injection process includes the following steps: injecting the battery cell with the primary electrolyte injection solution according to any one of claims 1-7, followed by a first soaking, formation, and aging; injecting the battery cell with the secondary electrolyte injection solution according to any one of claims 1-7 again, and finally, performing a second soaking; Preferably, the temperature of the first immersion is 30~50℃ and the time is 12~36h; the temperature of the second immersion is 20~30℃ and the time is 12~36h.

[0016] According to the present invention, preferably, the positive electrode active material used in the positive electrode of the lithium-ion battery is selected from at least one of lithium manganese oxide, lithium manganese iron phosphate, lithium iron phosphate, lithium nickel cobalt manganese iron phosphate, and sodium nickel iron manganese oxide.

[0017] The technical solution of the present invention has the following beneficial effects: (1) In this invention, a secondary liquid injection method is used to reduce the impedance between the positive and negative electrodes, while suppressing the dissolution, transfer and deposition of transition metal ions, thereby improving the rate and cycle performance of the battery cell system.

[0018] (2) In this invention, the additive for complexing transition metal ions in the secondary electrolyte additive is a novel crown ether compound, which has a strong binding force to form a complex with transition metal ions and inhibits the migration of dissolved transition metal ions in the solution.

[0019] (3) In this invention, the secondary electrolyte additive also contains water-removing and acid-suppressing additives, which are beneficial to reduce the increase of electrolyte acidity and moisture during the cycle, protect the SEI membrane and CEI membrane, and thus inhibit the dissolution of transition metal ions.

[0020] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0021] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0022] The present invention is further illustrated by the following examples: In the following embodiments and comparative examples: The 4,10,16-triaza-18-crown ether-6 used is shown in Formula I, and its specific preparation method is as follows: In a reaction flask equipped with a stirrer, reflux condenser, and dropping funnel, add 1.87 g (0.01 mol) of 1,2-bis(2-chloroethoxy)ethane, 400 mL of anhydrous acetonitrile, 12.5 g of anhydrous sodium carbonate, and 0.15 g of sodium iodide, and heat to a gentle boil with stirring. Dissolve 1.46 g (0.01 mol) of tris(2-aminoethyl)amine in 20 mL of anhydrous acetonitrile and slowly add it dropwise to the reaction solution through a dropping funnel. Control the dropping rate to complete the addition within 5 hours, using a high dilution method to promote single-ring closure. After the addition is complete, maintain reflux for 20 hours until the reaction is complete. After the reaction is complete, cool to room temperature, filter to remove the generated inorganic salt precipitate, and remove the solvent from the filtrate by vacuum distillation. The crude product was dissolved in a boiling mixture of dioxane and acetone (1:1 by volume), cooled, and allowed to stand to precipitate a solid. The resulting white solid was filtered off, dissolved in water, and continuously extracted with chloroform. The extract was dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. Finally, recrystallization was performed using a hexane / ethanol mixture (1:1 by volume) to give a white crystalline product, 4,10,16-triaza-18-crown ether-6.

[0023] The 4,13-diaza-18-crown ether-6 used, as shown in Formula II, was purchased from Aladdin; the dibenzo-18-crown ether-6 used, as shown in Formula III, was purchased from Merck Chemicals.

[0024] Example 1

[0025] The electrolyte for inhibiting the dissolution of transition metals includes: a primary electrolyte and a secondary electrolyte, with a mass ratio of 8:2 between the primary and secondary electrolytes. Preparation of primary electrolyte: A first non-aqueous solvent, a first lithium salt, and primary additives are mixed and stirred evenly to obtain a primary electrolyte. The first non-aqueous solvent is a mixture of ethylene carbonate and ethyl methyl carbonate, with a mass ratio of 3:7. The first lithium salt is lithium hexafluorophosphate. The primary additives include a film-forming additive to inhibit manganese dissolution and other film-forming additives. The film-forming additive to inhibit manganese dissolution is a mixture of lithium trimethylsilane phosphate, lithium dioxalate borate, and lithium difluorooxalate borate, with a mass ratio of 1:1:1. Other film-forming additives are a mixture of fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate, with a mass ratio of 1:1:1. Based on the total weight of the primary electrolyte, the content of the first non-aqueous solvent is 80 wt%, and the content of the first lithium salt is 10 wt%. The content of the film-forming additive that inhibits manganese leaching is 5 wt%, and the content of other film-forming additives is 5 wt%.

[0026] Preparation of secondary injection electrolyte: A second non-aqueous solvent, a second lithium salt, and secondary additives are mixed and stirred evenly to obtain a secondary injection electrolyte; wherein, the second non-aqueous solvent is a mixture of ethylene carbonate and methyl ethyl carbonate, with a mass ratio of ethylene carbonate:methyl ethyl carbonate = 3:7; the second lithium salt is lithium hexafluorophosphate; the secondary additives include crown ether complexed transition metal ion additives and dehydration and acid suppression additives, wherein the crown ether complexed transition metal ion additives are 4,10,16-triaza-18-crown ether-6, 4,13-diaza-18-crown ether-6, and diaza-18-crown ether-6. A mixture of benzo-18-crown ether-6, 4,10,16-triaza-18-crown ether-6:4,13-diaza-18-crown ether-6:dibenzo-18-crown ether-6 = 1:1:1 (mass ratio); the dehydration and acid-suppressing additive is a mixture of lithium trimethylsilane phosphate, lithium trimethylsilane borate, and trimethylsilyl imidazole, lithium trimethylsilane phosphate:lithium trimethylsilane borate:trimethylsilyl imidazole = 1:1:1 (mass ratio); based on the total weight of the secondary electrolyte, the content of the second non-aqueous solvent is 70 wt%, the content of the second lithium salt is 10 wt%, the content of the crown ether complex transition metal ion additive is 10 wt%, and the content of the dehydration and acid-suppressing additive is 10 wt%.

[0027] The fabrication of lithium-ion batteries: The positive electrode active material lithium manganese iron phosphate (LiMn0.5Fe0.5PO4), conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 93:4:3, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain the positive electrode slurry. The positive electrode slurry was then uniformly coated on both sides of an aluminum foil, with an areal density of 200 g / m³ on each side. 2 The compacted density is 2.6 g / cm³. 3 After drying, rolling, and slitting, positive electrode sheets are obtained.

[0028] Artificial graphite, conductive carbon black Super-P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5, and then dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry was coated on both sides of a copper foil, with an areal density of 115 g / m² on each side. 2 The compacted density is 1.6 g / cm³. 3 After drying, rolling, and slitting, the negative electrode sheet is obtained.

[0029] A PE separator with a thickness of 13μm is placed between the positive and negative electrodes. Then, the positive electrode, negative electrode and separator are stacked, with 25 positive electrode sheets and 26 negative electrode sheets. After hot pressing and welding the electrode tabs, they are placed in an aluminum-plastic bag and vacuum baked at 85℃ for 48 hours to obtain the battery cell to be injected with electrolyte.

[0030] Take 32g of the first-injection electrolyte to inject the cell into the cell once, immerse it at 45℃ for 24h, and then age it at 45℃ for 48h after formation. Take 8g of the second-injection electrolyte to inject the cell into the cell a second time, immerse it at 25℃ for 24h after the second injection, and then perform capacity testing to obtain a lithium-ion battery.

[0031] Example 2

[0032] The electrolyte for inhibiting the dissolution of transition metals includes: a primary electrolyte and a secondary electrolyte, with a mass ratio of 8:2 between the primary and secondary electrolytes. Preparation of primary electrolyte: A first non-aqueous solvent, a first lithium salt, and primary additives are mixed and stirred evenly to obtain a primary electrolyte. The first non-aqueous solvent is a mixture of ethylene carbonate and methyl ethyl carbonate, with a mass ratio of 4:6. The first lithium salt is lithium hexafluorophosphate. The primary additives include a film-forming additive to inhibit manganese dissolution and other film-forming additives. The film-forming additive to inhibit manganese dissolution is a mixture of lithium trimethylsilane phosphate, lithium dioxalate borate, and lithium difluorooxalate borate, with a mass ratio of 3:1:2. The other film-forming additives are a mixture of fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate, with a mass ratio of 2:2:1. Based on the total weight of the primary electrolyte, the content of the first non-aqueous solvent is 80 wt%, and the content of the first lithium salt is 10 wt%. The content of the film-forming additive that inhibits manganese leaching is 5 wt%, and the content of other film-forming additives is 5 wt%.

[0033] Preparation of secondary injection electrolyte: A second non-aqueous solvent, a second lithium salt, and secondary additives are mixed and stirred evenly to obtain a secondary injection electrolyte; wherein, the second non-aqueous solvent is a mixture of ethylene carbonate and methyl ethyl carbonate, with a mass ratio of 4:6; the second lithium salt is lithium hexafluorophosphate; the secondary additives include crown ether complexed transition metal ion additives and dehydration and acid suppression additives, wherein the crown ether complexed transition metal ion additives are 4,10,16-triaza-18-crown ether-6, 4,13-diaza-18-crown ether-6, and diaza-18-crown ether-6. A mixture of benzo-18-crown ether-6, 4,10,16-triaza-18-crown ether-6:4,13-diaza-18-crown ether-6:dibenzo-18-crown ether-6 = 3:1:1 (mass ratio); the dehydration and acid-suppressing additive is a mixture of lithium trimethylsilane phosphate, lithium trimethylsilane borate, and trimethylsilyl imidazole, lithium trimethylsilane phosphate:lithium trimethylsilane borate:trimethylsilyl imidazole = 2:2:1 (mass ratio); based on the total weight of the secondary electrolyte, the content of the second non-aqueous solvent is 70 wt%, the content of the second lithium salt is 10 wt%, the content of the crown ether complex transition metal ion additive is 10 wt%, and the content of the dehydration and acid-suppressing additive is 10 wt%.

[0034] The fabrication of lithium-ion batteries: The lithium-ion battery was prepared according to the method of Example 1, except that the primary and secondary electrolytes prepared in Example 1 were replaced with the primary and secondary electrolytes prepared in Example 2.

[0035] Example 3

[0036] The electrolyte for inhibiting the dissolution of transition metals includes: a primary electrolyte and a secondary electrolyte, with a mass ratio of 8:2 between the primary and secondary electrolytes. Preparation of primary electrolyte: A first non-aqueous solvent, a first lithium salt, and primary additives are mixed and stirred evenly to obtain a primary electrolyte. The first non-aqueous solvent is a mixture of ethylene carbonate and ethyl methyl carbonate, with a mass ratio of 3:7. The first lithium salt is lithium hexafluorophosphate. The primary additives include a film-forming additive to inhibit manganese dissolution and other film-forming additives. The film-forming additive to inhibit manganese dissolution is a mixture of lithium trimethylsilane phosphate, lithium dioxalate borate, and lithium difluorooxalate borate, with a mass ratio of 1:1:1. Other film-forming additives are a mixture of fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate, with a mass ratio of 1:1:1. Based on the total weight of the primary electrolyte, the content of the first non-aqueous solvent is 70 wt%, and the content of the first lithium salt is 15 wt%. The content of film-forming additives that inhibit manganese leaching is 7.5 wt%, and the content of other film-forming additives is 7.5 wt%.

[0037] Preparation of secondary injection electrolyte: A second non-aqueous solvent, a second lithium salt, and secondary additives are mixed and stirred evenly to obtain a secondary injection electrolyte; wherein, the second non-aqueous solvent is a mixture of ethylene carbonate and methyl ethyl carbonate, with a mass ratio of ethylene carbonate:methyl ethyl carbonate = 3:7; the second lithium salt is lithium hexafluorophosphate; the secondary additives include crown ether complexed transition metal ion additives and dehydration and acid suppression additives, wherein the crown ether complexed transition metal ion additives are 4,10,16-triaza-18-crown ether-6, 4,13-diaza-18-crown ether-6, and diaza-18-crown ether-6. A mixture of benzo-18-crown ether-6, 4,10,16-triaza-18-crown ether-6:4,13-diaza-18-crown ether-6:dibenzo-18-crown ether-6 = 1:1:1 (mass ratio); the dehydration and acid-suppressing additive is a mixture of lithium trimethylsilane phosphate, lithium trimethylsilane borate, and trimethylsilyl imidazole, lithium trimethylsilane phosphate:lithium trimethylsilane borate:trimethylsilyl imidazole = 1:1:1 (mass ratio); based on the total weight of the secondary electrolyte, the content of the second non-aqueous solvent is 80 wt%, the content of the second lithium salt is 10 wt%, the content of the crown ether complex transition metal ion additive is 5 wt%, and the content of the dehydration and acid-suppressing additive is 5 wt%.

[0038] The fabrication of lithium-ion batteries: The lithium-ion battery was prepared according to the method of Example 1, except that the primary and secondary electrolytes prepared in Example 1 were replaced with the primary and secondary electrolytes prepared in Example 3.

[0039] Example 4

[0040] The electrolyte for inhibiting the dissolution of transition metals includes: a primary electrolyte and a secondary electrolyte, with a mass ratio of 6:4 between the primary and secondary electrolytes. Preparation of primary electrolyte: A first non-aqueous solvent, a first lithium salt, and primary additives are mixed and stirred evenly to obtain a primary electrolyte. The first non-aqueous solvent is a mixture of ethylene carbonate and ethyl methyl carbonate, with a mass ratio of 3:7. The first lithium salt is lithium hexafluorophosphate. The primary additives include a film-forming additive to inhibit manganese dissolution and other film-forming additives. The film-forming additive to inhibit manganese dissolution is a mixture of lithium trimethylsilane phosphate, lithium dioxalate borate, and lithium difluorooxalate borate, with a mass ratio of 1:1:1. Other film-forming additives are a mixture of fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate, with a mass ratio of 1:1:1. Based on the total weight of the primary electrolyte, the content of the first non-aqueous solvent is 80 wt%, and the content of the first lithium salt is 10 wt%. The content of the film-forming additive that inhibits manganese leaching is 5 wt%, and the content of other film-forming additives is 5 wt%.

[0041] Preparation of secondary injection electrolyte: A second non-aqueous solvent, a second lithium salt, and secondary additives are mixed and stirred evenly to obtain a secondary injection electrolyte; wherein, the second non-aqueous solvent is a mixture of ethylene carbonate and methyl ethyl carbonate, with a mass ratio of ethylene carbonate:methyl ethyl carbonate = 3:7; the second lithium salt is lithium hexafluorophosphate; the secondary additives include crown ether complexed transition metal ion additives and dehydration and acid suppression additives, wherein the crown ether complexed transition metal ion additives are 4,10,16-triaza-18-crown ether-6, 4,13-diaza-18-crown ether-6, and diaza-18-crown ether-6. A mixture of benzo-18-crown ether-6, 4,10,16-triaza-18-crown ether-6:4,13-diaza-18-crown ether-6:dibenzo-18-crown ether-6 = 1:1:1 (mass ratio); the dehydration and acid-suppressing additive is a mixture of lithium trimethylsilane phosphate, lithium trimethylsilane borate, and trimethylsilyl imidazole, lithium trimethylsilane phosphate:lithium trimethylsilane borate:trimethylsilyl imidazole = 1:1:1 (mass ratio); based on the total weight of the secondary electrolyte, the content of the second non-aqueous solvent is 70 wt%, the content of the second lithium salt is 10 wt%, the content of the crown ether complexed transition metal ion additive is 10 wt%, and the content of the dehydration and acid-suppressing additive is 10 wt%.

[0042] The fabrication of lithium-ion batteries: The lithium-ion battery was prepared according to the method of Example 1, except that the primary and secondary electrolytes prepared in Example 1 were replaced with the primary and secondary electrolytes prepared in Example 4, and the amount of primary electrolyte was adjusted to 24g and the amount of secondary electrolyte was adjusted to 16g.

[0043] Example 5

[0044] The electrolyte used in this embodiment to suppress the dissolution of transition metals is the same as in Example 1.

[0045] The fabrication of lithium-ion batteries: The lithium-ion battery was prepared according to the method of Example 1, with the only difference being: 32g of the first-fill electrolyte was used to fill the cell once, and it was immersed at 45°C for 48h. After formation, it was aged at 45°C for 24h. 8g of the second-fill electrolyte was used to fill the cell a second time, and after the second filling, it was immersed at 45°C for 24h. Then, the capacity was measured to obtain the lithium-ion battery.

[0046] Comparative Example 1

[0047] The fabrication of lithium-ion batteries: The positive electrode, negative electrode, and the cell to be injected with electrolyte are all the same as in Example 1; 40g of the electrolyte prepared in Example 1 was used to inject the electrolyte into the cell. The cell was immersed at 45°C for 24 hours, and after formation, it was aged at 45°C for 48 hours. Then, the cell was subjected to capacity testing to obtain a lithium-ion battery.

[0048] Comparative Example 2

[0049] The fabrication of lithium-ion batteries: The positive electrode, negative electrode, and the cell to be injected with electrolyte are all the same as in Example 1; 40g of the secondary electrolyte prepared in Example 1 was used to inject the electrolyte into the cell. The cell was immersed at 45°C for 24 hours, and after formation, it was aged at 45°C for 48 hours. Then, the cell was subjected to capacity testing to obtain a lithium-ion battery.

[0050] Comparative Example 3

[0051] The fabrication of lithium-ion batteries: The positive electrode, negative electrode, and the cell to be injected with electrolyte are all the same as in Example 1; 32g of the secondary electrolyte prepared in Example 1 was used to perform a first electrolyte injection on the cell. The cell was immersed at 45°C for 24 hours and then aged at 45°C for 48 hours after formation. 8g of the first electrolyte prepared in Example 1 was used to perform a second electrolyte injection on the cell. After the second electrolyte injection, the cell was immersed at 25°C for 24 hours. After that, the cell was subjected to capacity testing to obtain a lithium-ion battery.

[0052] Comparative Example 4

[0053] The only difference between the electrolyte provided in this comparative example and that in Example 1 is that the secondary injection electrolyte does not contain crown ether complexed transition metal ion additives; that is, in the final prepared secondary injection electrolyte, the content of the second non-aqueous solvent is 70 wt%, the content of the second lithium salt is 10 wt%, and the content of the dehydration and acid suppression additive is 20 wt%, based on the total weight of the secondary injection electrolyte.

[0054] The fabrication of lithium-ion batteries: Lithium-ion batteries were prepared according to the method of Example 1, except that the primary and secondary electrolytes prepared in Example 1 were replaced with the primary and secondary electrolytes prepared in Comparative Example 4.

[0055] Comparative Example 5

[0056] The only difference between the electrolyte provided in this comparative example and that in Example 1 is that the secondary injection electrolyte does not contain dehydration and acid-suppressing additives; that is, in the final prepared secondary injection electrolyte, the content of the second non-aqueous solvent is 70 wt%, the content of the second lithium salt is 10 wt%, and the content of the crown ether complex transition metal ion additive is 20 wt%, based on the total weight of the secondary injection electrolyte.

[0057] The fabrication of lithium-ion batteries: The lithium-ion battery was prepared according to the method of Example 1, except that the primary and secondary electrolytes prepared in Example 1 were replaced with the primary and secondary electrolytes prepared in Comparative Example 5.

[0058] Test case

[0059] The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to performance tests. The specific test methods are as follows, and the specific test results are shown in the table below.

[0060] High-Temperature 1C / 1C Capacity Retention Test: The lithium-ion battery was left to stand at 25±2℃ for 24 hours, then charged at 1C constant current and constant voltage to 4.0V (current dropped to 0.05C and stopped), left to stand for 10 minutes, and then discharged at 1C to 2.5V, recording the initial capacity C0; left to stand at 45℃ for 4 hours, and the cycle of 1C charge → 10 minutes stand → 1C discharge → 10 minutes stand was repeated for a total of 1000 cycles; left to stand at 25±2℃ for 24 hours, and the discharge capacity C was retested. 1000 Capacity retention rate = C 1000 / C0×100%.

[0061] DC internal resistance at room temperature: At an ambient temperature of 25℃±2℃, charge at a constant current and constant voltage of 1C to 4.0V (stop when current drops to 0.05C), discharge at a constant current of 1C to 50% SOC, and let stand for 30 minutes to allow the voltage to stabilize. Apply a constant current pulse discharge of 5C for 10s, record the stable voltage U1 before the pulse discharge, the voltage U2 at the moment of discharge end, and record the discharge current I simultaneously; DC internal resistance R=(U1-U2) / I. Test 5 samples in the same batch and take the arithmetic mean as the final result.

[0062] 2C constant current charge ratio test: A lithium-ion battery in a discharged state, placed at 25±2℃ for 24 hours, was charged at a constant current of 2C to 4.0V, and the capacity during the constant current phase was recorded as Q1. Then, constant voltage charging was continued until the current dropped to 0.05C, and the capacity during the constant voltage phase was recorded as Q2. 2C constant current charge ratio = Q1 / (Q2+Q1)×100%

[0063] Manganese content (ppm) of the negative electrode when capacity decays to 70%: The lithium-ion battery was subjected to the above high-temperature 1C / 1C cycle until the capacity decayed to 70% of the initial capacity, and then discharged to 0V at 0.05C. The negative electrode was then disassembled and removed in an argon glove box (water and oxygen content <1ppm). The sample was microwave digested (concentrated nitric acid, held at 180℃ for 30 min) and then brought to volume. The manganese concentration was determined by ICP-OES.

[0064] Table 1

[0065] The comparison between Example 1 and Example 2 shows that changing the solvent ratio and additive ratio within a small range has little effect on the rate of increase and cycle performance.

[0066] The comparison between Example 1 and Example 3 shows that increasing the content of the primary additive and decreasing the content of the secondary additive results in a lower content of additives that complex manganese ions, and a significant increase in the manganese ion content of the negative electrode.

[0067] The comparison between Example 1 and Example 4 shows that reducing the content of the first electrolyte injection and increasing the content of the second electrolyte injection results in insufficient film-forming additive content, higher film-forming impedance, and higher DC internal resistance.

[0068] The comparison results between Example 1 and Example 5 show that changing the wetting time and temperature after electrolyte injection will affect the wetting and stability of the electrolyte, and thus affect the rate and cycle performance.

[0069] A comparison of the data results from Example 1 and Comparative Example 1 shows that the manganese ion content on the negative electrode side of the electrolyte without secondary injection is significantly increased, and the cycle retention rate is significantly reduced.

[0070] A comparison of the data results from Example 1 and Comparative Example 2 shows that without using a primary electrolyte, the content of film-forming additives is insufficient, resulting in a larger film impedance and a significant deterioration in both cycle and rate performance.

[0071] A comparison of the data results from Example 1 and Comparative Example 3 shows that if a secondary electrolyte is used for the first injection, and then a primary electrolyte is used for the second injection, the electrolyte film will be thicker and have higher impedance, resulting in poorer cycle and rate performance.

[0072] The comparison of data results between Example 1 and Comparative Example 4 shows that the secondary electrolyte does not contain crown ether additives. The dissolved manganese ions cannot be complexed and will continue to migrate to the negative electrode side, thereby damaging the SEI film and causing poor cycle and rate performance.

[0073] A comparison of the data results from Example 1 and Comparative Example 5 shows that the secondary electrolyte does not contain additives for removing water and inhibiting acid, which leads to an increase in water content and acidity during the circulation process, thereby affecting the circulation performance.

[0074] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. An electrolyte for inhibiting the dissolution of transition metals, characterized in that, The electrolyte includes a primary injection electrolyte and a secondary injection electrolyte, wherein the preferred mass ratio of the primary injection electrolyte to the secondary injection electrolyte is (1~19):1; The primary electrolyte solution includes: a first non-aqueous organic solvent, a first lithium salt, and a primary additive; the primary additive includes: a film-forming additive. The secondary electrolyte includes: a second non-aqueous organic solvent, a second lithium salt, and a secondary additive; the secondary additive includes: a complexing transition metal ion additive and a dehydrating and acid-suppressing additive.

2. The electrolyte according to claim 1, wherein, The complexing transition metal ion additive is a crown ether compound, preferably at least one of the compounds shown in Formula I-IV; Formula I; Formula II; Formula III; Formula IV.

3. The electrolyte according to claim 1, wherein, The dehydrating and acid-suppressing additives include at least two of lithium trimethylsilane phosphate, lithium trimethylsilane borate, trimethylsilyl imidazole, and dimethyldiphenoxysilane.

4. The electrolyte according to claim 1, wherein, The film-forming additives include: a film-forming additive that inhibits the dissolution of transition metal ions and other film-forming additives; the mass ratio of the film-forming additive that inhibits the dissolution of transition metal ions to other film-forming additives is (1-2):1; The film-forming additive that inhibits the dissolution of transition metal ions includes at least one of lithium difluorooxalate borate, lithium dioxalate borate, and lithium trimethylsilane phosphate. The other film-forming additives include at least one of vinylene carbonate, vinyl sulfate, propylene sulfonate lactone, fluoroethylene carbonate, and lithium difluorophosphate.

5. The electrolyte according to claim 1, wherein, The first non-aqueous organic solvent and the second non-aqueous organic solvent are each independently selected from at least one of dimethyl carbonate, ethylene carbonate, methyl ethyl carbonate, propylene carbonate, and diethyl carbonate; The first lithium salt and the second lithium salt are each independently selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate and lithium bisfluorosulfonylimide.

6. The electrolyte according to claim 1, wherein, Based on the total weight of the primary electrolyte, the content of the first non-aqueous organic solvent is 50-90 wt%, the content of the first lithium salt is 5-20 wt%, and the content of the primary additive is 2-20 wt%; the sum of the weight percentages of all components of the primary electrolyte is 100%.

7. The electrolyte according to claim 1, wherein, Based on the total weight of the secondary electrolyte, the content of the second non-aqueous organic solvent is 50-90 wt%, the content of the second lithium salt is 5-20 wt%, the content of the complexing transition metal ion additive is 2-20 wt%, and the content of the dehydration and acid suppression additive is 2-20 wt%; the sum of the weight percentages of each component of the secondary electrolyte is 100%.

8. A lithium-ion battery, characterized in that, In the preparation process of this lithium-ion battery, the electrolyte adopts a two-stage electrolyte injection process, and the electrolyte is the electrolyte described in any one of claims 1-7.

9. The lithium-ion battery according to claim 8, wherein, The secondary electrolyte injection process includes the following steps: the battery cell is injected with the primary electrolyte as described in any one of claims 1-7, followed by a first soaking, formation, and aging process; the battery cell is injected with the secondary electrolyte as described in any one of claims 1-7 again, and finally, a second soaking process is performed. Preferably, the temperature of the first immersion is 30~50℃ and the time is 12~36h; the temperature of the second immersion is 20~30℃ and the time is 12~36h.

10. The lithium-ion battery according to claim 8, wherein, The positive electrode active material used in the positive electrode of the lithium-ion battery is selected from at least one of lithium manganese oxide, lithium manganese iron phosphate, lithium iron phosphate, lithium nickel cobalt manganese iron phosphate, and sodium nickel iron manganese oxide.

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