Electrolyte for lithium ion battery and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses an electrolyte for a lithium ion battery and the lithium ion battery, the electrolyte comprises 8-15 parts of a lithium salt, 70-92 parts of a solvent, 0.1-10 parts of a first additive and 0.1-5 parts of a second additive, by adding the unique additives into the electrolyte, the cycling stability of the battery in a high-temperature environment can be improved, and the service life of the battery is prolonged. And a stable electrode interface film is constructed under high voltage, and positive and negative electrode side reactions are synchronously inhibited, so that the good performance of the battery is kept.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to an electrolyte for lithium-ion batteries and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, as efficient and clean energy storage devices, have been widely used in new energy vehicles, portable electronic devices, and energy storage power stations. However, as application scenarios place increasingly higher demands on battery energy density, cycle life, and safety performance, traditional electrolyte systems have revealed many limitations. For example, traditional carbonate-based electrolytes are prone to oxidative decomposition under high voltage (≥4.5V) conditions, leading to decreased electrode interface stability. Further exothermic reactions may trigger a chain reaction such as separator melting and internal short circuits, resulting in capacity decay and thermal runaway risks.

[0003] To improve interfacial stability, additive modification strategies are widely adopted. Fluorinated ethylene carbonate and ethylene sulfate can enhance the ionic conductivity and mechanical strength of the solid electrolyte interphase (SEI / CEI) membrane; however, a single additive is difficult to synergistically address the requirements of both the positive and negative electrode interfaces, and it is prone to decomposition and gasification under high pressure. Furthermore, lithium hexafluorophosphate in the electrolyte is easily hydrolyzed to produce HF, which corrodes the electrodes and catalyzes the dissolution of transition metals, further compromising interfacial integrity.

[0004] In terms of safety, traditional electrolytes suffer from high flammability and poor thermal stability. While flame-retardant additives containing phosphorus and halogens (such as organophosphates) can inhibit combustion chain reactions, they often worsen electrode compatibility, increase electrolyte viscosity, and reduce conductivity and rate performance. Although some fluorinated solvents are flame-retardant, they are difficult to form an effective positive electrode protective layer under high voltage. Summary of the Invention

[0005] In order to solve the problems mentioned in the background art, the present invention aims to provide an electrolyte for lithium-ion batteries and a lithium-ion battery.

[0006] The objective of this invention can be achieved through the following technical solutions: An electrolyte for lithium-ion batteries, comprising the following raw materials measured in percentage by mass: 8-15 parts lithium salt, 70-92 parts solvent, 0.1-10 parts first additive, and 0.1-5 parts second additive.

[0007] As a further aspect of the present invention, the lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, or lithium difluorooxalate borate.

[0008] As a further aspect of the present invention, the solvent is at least one of organic esters, alkyl ethers, cyclic ethers, sulfones, dinitriles, and ionic liquids.

[0009] As a further embodiment of the present invention, the first additive is at least one of fluoroethylene carbonate, ethylene sulfate, methanedisulfonate, ethylene carbonate, 1,3-propanesulfonate lactone, or p-toluenesulfonyl isocyanate.

[0010] As a further embodiment of the present invention, the second additive is any one of 2-(thiophene methyl)phosphonate diethyl ester, ((2-chlorothiazol-5-yl)methyl)phosphonate diethyl ester, phenylphosphonate diethyl ester, o-phenylenediamine methyl phosphate diethyl ester, or diethyl-2-methylthiazol-4-ylmethylphosphonate.

[0011] As a further aspect of the present invention, the method for preparing the electrolyte includes the following steps: Step 1: Add lithium salt to solvent and stir at room temperature until completely dissolved to form precursor solution; Step 2: Add the first and second additives to the precursor solution, continue stirring at room temperature for 3-5 hours, and then discharge the material.

[0012] A lithium-ion battery, comprising the electrolyte for lithium-ion batteries described above.

[0013] The beneficial effects of this invention are: This invention improves the cycle stability of the battery under high temperature conditions and builds a stable electrode interface film under high voltage by adding unique additives to the electrolyte, thereby suppressing the positive and negative electrode side reactions and maintaining good battery performance.

[0014] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0015] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1 An electrolyte for lithium-ion batteries comprises the following raw materials: 12g lithium salt, 90g solvent, 6g fluoroethylene carbonate, 3g diethyl 2-(thiophenemethyl)phosphonate.

[0017] The method for preparing the electrolyte includes the following steps: Step 1: Add lithium salt to solvent and stir at room temperature until completely dissolved to form precursor solution; Step 2: Add fluoroethylene carbonate and diethyl 2-(thiophenemethyl)phosphonate to the precursor solution, and continue stirring at room temperature for 3-5 hours before discharging.

[0018] The lithium salt is a mixture of lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide in a mass ratio of 5:1; the solvent is a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 3:5:2.

[0019] Example 2 An electrolyte for lithium-ion batteries differs from Example 1 in that 2-(thiophenemethyl)phosphonate diethyl ester is replaced with ((2-chlorothiazol-5-yl)methyl)phosphonate diethyl ester, while all other aspects remain the same.

[0020] Example 3 An electrolyte for lithium-ion batteries differs from Example 1 in that 2-(thiophenemethyl)phosphonate diethyl ester is replaced with phenylphosphonate diethyl ester, while the rest are the same.

[0021] Example 4 An electrolyte for lithium-ion batteries differs from Example 1 in that 2-(thiophene methyl)phosphonate diethyl ester is replaced with o-phenylenediamine methyl phosphate diethyl ester, while the rest are the same.

[0022] Example 5 An electrolyte for lithium-ion batteries differs from Example 1 in that 2-(thiophenemethyl)phosphonate diethyl ester is replaced with diethyl-2-methylthiazol-4-ylmethylphosphonate, while the rest are the same.

[0023] Example 6 An electrolyte for lithium-ion batteries differs from Example 1 in that 1g of diethyl phenylphosphonate is added, while the rest are the same.

[0024] Example 7 An electrolyte for lithium-ion batteries differs from Example 1 in that 2g of diethyl phenylphosphonate is added, while the rest are the same.

[0025] Example 8 An electrolyte for lithium-ion batteries differs from Example 1 in that 3g of diethyl 2-(thiophenemethyl)phosphonate is replaced with a mixture of 2g of diethyl 2-(thiophenemethyl)phosphonate and 3g of diethyl phenylphosphonate, while the rest are the same.

[0026] Example 9 An electrolyte for lithium-ion batteries differs from Example 1 in that the amount of diethyl 2-(thiophenemethyl)phosphonate is modified to 5g, while the rest are the same.

[0027] Example 10 An electrolyte for lithium-ion batteries differs from Example 1 in that 3g of diethyl 2-(thiophenemethyl)phosphonate is replaced with 5g of diethyl phenylphosphonate, while the rest are the same.

[0028] Example 11 An electrolyte for lithium-ion batteries differs from Example 1 in that 3g of diethyl 2-(thiophenemethyl)phosphonate is replaced with a mixture of 2.5g of diethyl 2-(thiophenemethyl)phosphonate and 2.5g of diethyl phenylphosphonate, while the rest are the same.

[0029] Comparative Example 1 An electrolyte for lithium-ion batteries differs from that of Example 1 in that it does not contain diethyl 2-(thiophenemethyl)phosphonate, but is otherwise identical.

[0030] Test case Lithium nickel cobalt manganese oxide (LCM), carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) were mixed in a mass ratio of 95:3:2. N-methylpyrrolidone (NMP) was then added to prepare a slurry. The slurry was stirred using a vacuum mixer and then uniformly coated onto a 12 μm thick aluminum foil using a coating machine. After drying, rolling, and cutting, the positive electrode sheet was obtained. Before use, the positive electrode sheet was baked in an oven until the moisture content was below 200 ppm. Graphite, styrene-butadiene rubber (SBR), and carbon black (conductive agent) were mixed in a mass ratio of 95:2:3. [The remaining text appears to be incomplete and requires further context.] Deionized water was used to prepare a negative electrode slurry, which was stirred using a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was then uniformly coated onto an 8μm thick copper foil using a coating machine. After drying, rolling, and cutting, a negative electrode sheet was obtained. Before use, the obtained negative electrode sheet was baked in an oven until the moisture content was below 200ppm. The positive electrode sheet, negative electrode sheet, and polypropylene separator were wound together to form a battery cell, which was then wrapped in an aluminum-plastic film and baked in an oven at 45℃ for 24 hours. Electrolyte was then injected and the cell was sealed. After standing for 72 hours, the lithium-ion battery was obtained and the following performance tests were performed: (1) Cyclic test of battery cell at room temperature of 4.3V: The battery cell was placed in a constant temperature test chamber at 25℃ and charged and discharged at a rate of 0.5C. The charge and discharge range was 2.8V to 4.3V. Cyclic test was performed. (2) Cyclic test of battery cell at room temperature of 4.4V: The battery cell was placed in a constant temperature test chamber at 25℃ and charged and discharged at a rate of 0.5C. The charge and discharge range was 2.8V to 4.4V, and a cyclic test was performed. (3) Cyclic test of battery cell at room temperature of 4.5V: Place the battery cell in a constant temperature test chamber at 25℃ and charge and discharge it at a rate of 0.5C. The charge and discharge range is 2.8V to 4.5V. Cyclic test is performed. (4) High temperature 45℃, 4.3V cycle test of battery cell: Place the battery cell in a 45℃ constant temperature test cabinet and charge and discharge at a rate of 0.5C, with a charge and discharge range of 2.8V to 4.3V, and perform cycle test; (5) High temperature 60℃, 4.3V cycle test of battery cell: Place the battery cell in a 60℃ constant temperature test cabinet and charge and discharge at a rate of 0.5C. The charge and discharge range is 2.8V to 4.3V. Cyclic test is performed.

[0031] The test results are recorded in Table 1: Table 1

[0032] As shown in Table 1, compared to Comparative Example 1 without the second additive, the battery containing the second additive exhibits significantly improved high-voltage and high-temperature cycle performance. This is mainly related to the phosphate ester and heterocyclic group structure of the second additive. In particular, the example containing diethyl 2-(thiophenemethyl)phosphonate shows the best high-voltage and high-temperature resistance. This is primarily due to the fact that its thiophene group can polymerize at the positive electrode to form a stable CEI film, and the phosphonate group can neutralize harmful substances (such as HF and PF5), stabilize lithium salts, and contribute to the formation of a stable interfacial film, thus improving cycle performance. Simultaneously, the effects of different proportions and contents of diethyl 2-(thiophenemethyl)phosphonate and diethyl phenylphosphonate additives were tested, and the assembled batteries exhibited different performance characteristics. Comparison of the data from Examples 1, 3, 6-8, and Examples 9-11 shows that Example 7 exhibits the best overall performance in terms of high-voltage and high-temperature resistance.

[0033] (6) Electrolyte storage test: The prepared electrolyte was dispensed into aluminum bottles and sealed and stored in an environment of 45°C. The moisture, acidity and color were tested every once in a while. The test results are recorded in Table 2.

[0034] Table 2

[0035] As shown in Table 2, comparing the high-temperature storage data of Examples 1-11 and Comparative Example 1, it can be seen that all the second additives exhibited excellent acid-suppressing effects, with diethyl phthalimide methyl phosphate showing the most significant acid-suppressing effect; none of the second additives showed significant water-removing effects. This is mainly due to the oxygen atom in the phosphonate group of the molecule, which, as a Lewis base, can undergo a coordination reaction with acidic substances (HF, PF5, etc.) in the electrolyte, deactivating them and thus removing the acidic substances; although these second additives cannot directly remove water, by eliminating HF, they can break the chain of a series of harmful side reactions initiated by water, indirectly reducing the harm of water in lithium-ion batteries.

[0036] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte for lithium-ion batteries, characterized in that, Including the following raw materials measured as a percentage by weight: 8-15 parts lithium salt, 70-92 parts solvent, 0.1-10 parts first additive, and 0.1-5 parts second additive.

2. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, or lithium difluorooxalate borate.

3. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The solvent is at least one of organic esters, alkyl ethers, cyclic ethers, sulfones, dinitriles, and ionic liquids.

4. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The first additive is at least one of fluoroethylene carbonate, ethylene sulfate, methylene disulfonate, ethylene carbonate, 1,3-propanesulfonate lactone, or p-toluenesulfonyl isocyanate.

5. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The second additive is any one of 2-(thiophene methyl)phosphonate diethyl ester, ((2-chlorothiazol-5-yl)methyl)phosphonate diethyl ester, phenylphosphonate diethyl ester, o-phenylenediamine methyl phosphate diethyl ester, or diethyl-2-methylthiazol-4-ylmethylphosphonate.

6. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The preparation method of the electrolyte includes the following steps: Step 1: Add lithium salt to solvent and stir at room temperature until completely dissolved to form precursor solution; Step 2: Add the first and second additives to the precursor solution, continue stirring at room temperature for 3-5 hours, and then discharge the material.

7. A lithium-ion battery, characterized in that, Includes the electrolyte for lithium-ion batteries as described in claim 1.

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