High-temperature-resistant lithium ion battery electrolyte and lithium ion battery

Abstract

The application belongs to the technical field of lithium batteries, and relates to a high-temperature-resistant lithium ion battery electrolyte and a lithium ion battery. The high-temperature-resistant lithium ion battery electrolyte comprises an organic solvent and a lithium salt, and the organic solvent comprises a carbonate compound and a nitrile compound containing an ether bond. The lithium ion battery prepared based on the high-temperature-resistant lithium ion battery electrolyte can stably operate at 80 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, and relates to a high-temperature resistant lithium-ion battery electrolyte and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, portable electronic devices, and energy storage due to their advantages such as high operating voltage, high energy density, environmental friendliness, long cycle life, and no memory effect. As the application scope of lithium-ion batteries expands, to meet certain special operating environments, such as military or extreme high-temperature environments, lithium-ion batteries are required to operate in extreme environments exceeding 60°C. This necessitates higher high-temperature cycle resistance for lithium-ion batteries.

[0003] Electrolyte is a crucial component of a battery, responsible for transporting ions between the positive and negative electrodes within the battery. It significantly impacts battery capacity, operating temperature range, cycle performance, and safety. Therefore, the electrolyte is key to achieving high-temperature operation of lithium-ion batteries. Currently, the most widely used electrolyte system is formed by dissolving lithium salts containing LiPF6 in carbonate-based organic solvents. LiPF6 decomposes at 75°C, producing HF and PF5. PF5 is a Lewis acid, which attacks the carbon-oxygen double bonds on the carbonate, causing the carbonate solvent to decompose. Simultaneously, the generated HF dissolves the SEI film on the negative electrode surface, thus reducing battery life. Therefore, there is an urgent need to develop a high-temperature resistant lithium-ion battery electrolyte. Summary of the Invention

[0004] This invention addresses the shortcomings of existing lithium-ion battery electrolytes by providing a high-temperature resistant lithium-ion battery electrolyte and a lithium-ion battery.

[0005] One object of the present invention is to provide a high-temperature resistant lithium-ion battery electrolyte, comprising an organic solvent and a lithium salt, wherein the organic solvent comprises carbonate compounds and nitrile compounds containing ether bonds.

[0006] Preferably, the nitrile compound containing an ether bond has the general formula shown in Formula I:

[0007]

[0008] Where x is an integer from 0 to 50, and R is selected from one or more of the following structures:

[0009] CH3;

[0010] Where y is an integer from 0 to 50;

[0011]

[0012] Where a and b are each an integer from 0 to 50.

[0013] Preferably, the nitrile compound containing an ether bond includes one or more of ethylene glycol bis(propionitrile) ether, 1,2,3-tris(cyanoethoxy)propane and 3-methoxypropionitrile.

[0014] Preferably, the volume ratio of the nitrile compound containing ether bonds to the carbonate compound is 1:4 to 2:3.

[0015] The present invention utilizes cyano groups in nitrile compounds containing ether bonds, which can complex transition metal ions to reduce their oxidizing properties and inhibit dissolution. Simultaneously, nitrile compounds containing ether bonds are abundant in the electrolyte system, which can regulate the solvation structure of the electrolyte. When these compounds enter the solvation sheath, they partially occupy solvation sites of other solvent molecules surrounding the lithium ions and promote the entry of lithium salt anions into the solvation sheath. At this point, the lithium-ion solvation sheath mainly consists of nitrile compounds containing ether bonds, lithium salt anions, and some other solvents (carbonate compounds). This solvation sheath partially decomposes on the positive electrode surface, forming an organic-inorganic composite interface film rich in inorganic components. This suppresses the severe side reactions at the electrode-electrolyte interface at high temperatures, enabling the lithium-ion battery to operate at high temperatures and high pressures.

[0016] Preferably, the carbonate compound is a cyclic carbonate and / or a halogenated cyclic carbonate. The cyclic carbonate and / or the halogenated cyclic carbonate are stable and have high boiling points, which is beneficial for the operation of lithium-ion batteries at high temperatures. Furthermore, cyclic carbonates have high polarity, which allows them to effectively dissolve lithium salts. Additionally, cyclic carbonates can undergo ring-opening on the positive and negative electrode surfaces to form films with nitrile compounds containing ether bonds and lithium salts.

[0017] Preferably, the cyclic carbonate is one or more of ethylene carbonate, propylene carbonate, and butene carbonate.

[0018] Preferably, the halogenated compound of the cyclic carbonate is a fluorinated compound of the cyclic carbonate, such as one or more of fluoroethylene carbonate, trifluoromethyl ethylene carbonate, and difluoroethylene carbonate.

[0019] Preferably, the lithium salt is a high-temperature resistant lithium salt with a thermal decomposition temperature ≥200℃. The electrolyte of this invention uses a high-temperature resistant lithium salt, which has a higher thermal decomposition temperature and better stability in the electrolyte compared to traditional lithium salts, thus benefiting the operation of lithium-ion batteries at high temperatures.

[0020] Preferably, the lithium salt is one or more of the following: bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium dioxalate borate (LiBOB), lithium tetrafluoroborate (LiBF4), and lithium difluorophosphate (LiDFOP).

[0021] Preferably, the lithium salt is a mixture of bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate, wherein the molar ratio of lithium difluorooxalate borate to bis(trifluoromethanesulfonyl)imide is 1:20 to 1:1.

[0022] Preferably, the preparation method of the high-temperature resistant lithium-ion battery electrolyte includes the following steps: mixing an organic solvent and a lithium salt, heating at 40-80°C for 8-20 hours, and then cooling at room temperature.

[0023] A lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is the high-temperature resistant lithium-ion battery electrolyte described above.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The organic solvent of the lithium-ion battery electrolyte of the present invention is a mixture of carbonate compounds and nitrile compounds containing ether bonds. The presence of nitrile compounds containing ether bonds is beneficial to complexing transition metal ions to reduce their oxidizing properties and inhibit dissolution. It also has good compatibility with the positive and negative electrodes and can form a stable interface film on the surface of the positive and negative electrodes.

[0026] (2) The lithium salt in the lithium-ion battery electrolyte of the present invention is preferably a high-temperature resistant lithium salt, which has a higher thermal decomposition temperature and better stability in the electrolyte compared with traditional lithium salts, which is beneficial for the lithium-ion battery to operate at high temperatures.

[0027] (3) The carbonate compound of the organic solvent in the electrolyte of the present invention is preferably a cyclic carbonate and / or a halogenated compound of a cyclic carbonate, which is stable and has a high boiling point, thus improving the high temperature stability of the lithium-ion battery.

[0028] (4) The volume ratio of the nitrile compound containing ether bonds to the carbonate compound of the present invention is 1:4 to 2:3. The nitrile compound containing ether bonds exists in large quantities in the electrolyte system, which can regulate the solvation structure of the electrolyte. It enters the solvation sheath, partially occupies the solvation positions of the remaining solvent molecules around the lithium ions, and promotes the entry of lithium salt anions into the solvation sheath. This solvation sheath partially decomposes on the surface of the positive electrode, forming an organic-inorganic composite interface film rich in inorganic components, thereby suppressing the violent side reactions at the electrode-electrolyte interface at high temperature and realizing the high temperature and high pressure operation of the lithium-ion battery.

[0029] (5) The present invention prepares a high-temperature resistant lithium-ion battery electrolyte in a very simple way, and the lithium-ion battery based on it can achieve stable operation at a high temperature of 80°C. Detailed Implementation

[0030] The technical solution of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the present invention. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0031] Example 1

[0032] Preparation of high-temperature resistant lithium-ion battery electrolyte

[0033] The high-temperature resistant lithium-ion battery electrolyte of this embodiment includes an organic solvent and a lithium salt. The organic solvent is a mixed solution of ethylene glycol bis(propionitrile) ether and ethylene carbonate in a volume ratio of 3:7. The lithium salt is a mixture of lithium difluorooxalate borate and lithium bis(trifluoromethanesulfonyl)imide in a molar ratio of 2:8. The concentration of the lithium salt in the electrolyte is 1 mol / L. Ethylene glycol bis(propionitrile) ether and ethylene carbonate are mixed, and then lithium difluorooxalate borate and lithium bis(trifluoromethanesulfonyl)imide are added. The mixture is heated at 60°C for 12 hours until it is fully dissolved, and then cooled at room temperature to obtain the high-temperature resistant lithium-ion battery electrolyte.

[0034] Preparation of NCM811 lithium-ion batteries

[0035] The positive electrode active material NCM811, the binder polyvinylidene fluoride, and the conductive agent Super- were mixed in a weight ratio of 8:1:1. N-methylpyrrolidone was added and stirred evenly to form a positive electrode slurry. The positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 13 μm. After the aluminum foil was dried at room temperature, it was transferred to an oven at 120°C and dried for 10 hours. Then, it was rolled and cut into sheets to obtain NCM811 positive electrode sheets.

[0036] The positive electrode shell, positive electrode sheet, separator, lithium sheet, and negative electrode shell are stacked in sequence. After injecting the electrolyte from Example 1, the battery is sealed under a pressure of 50 MPa and then kept at a constant temperature of 25°C for more than 12 hours to obtain the NCM811 lithium-ion battery.

[0037] The preparation method of lithium iron phosphate lithium-ion battery is the same as that of NCM811 lithium-ion battery mentioned above, except that the positive electrode active material is lithium iron phosphate.

[0038] The NCM811 lithium-ion battery and lithium iron phosphate lithium-ion battery of Example 1 were subjected to high-temperature cycle performance testing at 80°C: Before the test, the battery was placed in an environment of 80°C and left to stand for 1 hour. When the battery body temperature reached 80°C, a charge-discharge test was performed at a rate of 1C. The results are shown in Table 1.

[0039] Example 2

[0040] Preparation of high-temperature resistant lithium-ion battery electrolyte

[0041] The high-temperature resistant lithium-ion battery electrolyte of this embodiment includes an organic solvent and a lithium salt. The organic solvent is a mixed solution of 1,2,3-tris(cyanoethoxy)propane and ethylene carbonate in a volume ratio of 1:4. The lithium salt is a mixture of lithium difluorooxalate borate and lithium bis(trifluoromethanesulfonyl)imide in a molar ratio of 1:9. The concentration of the lithium salt in the electrolyte is 1 mol / L. 1,2,3-tris(cyanoethoxy)propane and ethylene carbonate are mixed, then lithium difluorooxalate borate and lithium bis(trifluoromethanesulfonyl)imide are added, and the mixture is heated at 65°C for 10 hours until fully dissolved. After cooling to room temperature, the high-temperature resistant lithium-ion battery electrolyte is obtained.

[0042] The method for preparing the NCM811 lithium-ion battery is the same as in Example 1, except that the electrolyte from Example 2 is injected into the battery for encapsulation and then left to stand to obtain the lithium-ion battery.

[0043] The NCM811 lithium-ion battery of Example 2 was subjected to a high-temperature cycling performance test at 80°C, and the results are shown in Table 1.

[0044] Example 3

[0045] Preparation of high-temperature resistant lithium-ion battery electrolyte

[0046] The high-temperature resistant lithium-ion battery electrolyte of this embodiment includes an organic solvent and a lithium salt. The organic solvent is a mixed solution of 3-methoxypropionitrile and propylene carbonate in a volume ratio of 2:3. The lithium salt is a mixture of lithium difluorooxalate borate and lithium bis(trifluoromethanesulfonyl)imide in a molar ratio of 3:7. The concentration of the lithium salt in the electrolyte is 1 mol / L. 3-methoxypropionitrile and propylene carbonate are mixed, then lithium difluorooxalate borate and lithium bis(trifluoromethanesulfonyl)imide are added, and the mixture is heated at 55°C for 12 hours until fully dissolved. After cooling to room temperature, the high-temperature resistant lithium-ion battery electrolyte is obtained.

[0047] The method for preparing the NCM811 lithium-ion battery is the same as in Example 1, except that the electrolyte from Example 3 is injected into the battery for encapsulation and then left to stand to obtain the lithium-ion battery.

[0048] The NCM811 lithium-ion battery of Example 3 was subjected to a high-temperature cycling performance test at 80°C, and the results are shown in Table 1.

[0049] Comparative Example 1

[0050] The lithium-ion battery electrolyte of Comparative Example 1 differs from that of Example 1 in that the organic solvent of Comparative Example 1 is a mixed solution of ethylene glycol bis(propionitrile) ether and ethylene carbonate in a volume ratio of 9:1. Otherwise, the lithium-ion battery electrolyte is prepared in the same manner as in Example 1.

[0051] The method for preparing the NCM811 lithium-ion battery is the same as in Example 1, except that the electrolyte of Comparative Example 1 is injected into the battery for encapsulation and then left to stand to obtain the lithium-ion battery.

[0052] The NCM811 lithium-ion battery of Comparative Example 1 was subjected to high-temperature cycling performance testing at 80℃, and the results are shown in Table 1.

[0053] Comparative Example 2

[0054] The lithium-ion battery electrolyte of Comparative Example 2 differs from that of Example 1 in that the organic solvent of Comparative Example 2 is a mixed solution of ethylene glycol bis(propionitrile) ether and ethylene carbonate in a volume ratio of 8:2. Otherwise, it is the same as that of Example 1, and the lithium-ion battery electrolyte is prepared.

[0055] The method for preparing the NCM811 lithium-ion battery is the same as in Example 1, except that the electrolyte of Comparative Example 2 is added to the battery for encapsulation and then left to stand to obtain the lithium-ion battery.

[0056] The NCM811 lithium-ion battery of Comparative Example 2 was subjected to high-temperature cycling performance testing at 80℃, and the results are shown in Table 1.

[0057] Comparative Example 3

[0058] The lithium-ion battery electrolyte of Comparative Example 3 differs from that of Example 1 in that the organic solvent of Comparative Example 3 is a mixed solution of ethylene glycol bis(propionitrile) ether and ethylene carbonate in a volume ratio of 7:3. Otherwise, it is the same as that of Example 1, and the lithium-ion battery electrolyte is prepared.

[0059] The preparation method of the NCM811 lithium-ion battery is the same as that in Example 1, except that the electrolyte of Comparative Example 3 is injected into the battery for encapsulation and then left to stand to obtain the lithium-ion battery. The NCM811 lithium-ion battery of Comparative Example 3 was subjected to a high-temperature cycle performance test at 80°C, and the results are shown in Table 1.

[0060] Comparative Example 4

[0061] The lithium-ion battery electrolyte of Comparative Example 4 differs from that of Example 1 in that the organic solvent of Comparative Example 4 is a mixed solution of ethylene glycol bis(propionitrile) ether and ethylene carbonate in a volume ratio of 1:9. Otherwise, it is the same as that of Example 1, and the lithium-ion battery electrolyte is prepared.

[0062] The method for preparing NCM811 lithium-ion batteries is the same as in Example 4, except that the electrolyte of Comparative Example 4 is injected into the battery for encapsulation and then left to stand to obtain the lithium-ion battery.

[0063] The NCM811 lithium-ion battery of Comparative Example 4 was subjected to high-temperature cycling performance testing at 80℃, and the results are shown in Table 1.

[0064] Comparative Example 5

[0065] The lithium-ion battery electrolyte of Comparative Example 5 differs from that of Example 1 in that the organic solvent of Comparative Example 5 is a mixed solution of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7, and the lithium salt is LiPF6. The other components are the same as those in Example 1, and the lithium-ion battery electrolyte is prepared accordingly.

[0066] The method for preparing NCM811 lithium-ion batteries is the same as in Example 1, except that the electrolyte of Comparative Example 5 is injected into the battery for encapsulation and then left to stand to obtain the lithium-ion battery.

[0067] The NCM811 lithium-ion battery of Comparative Example 5 was subjected to high-temperature cycling performance testing at 80℃, and the results are shown in Table 1.

[0068] Table 1. Results of 80°C high-temperature cycling performance tests of lithium-ion batteries in Examples 1-3 and Comparative Examples 1-5

[0069]

[0070] As shown in Table 1, the electrolyte of Comparative Example 1 used a mixed solution of ethylene glycol bis(propionitrile) ether and ethylene carbonate at a volume ratio of 9:1 as the organic solvent; the electrolyte of Comparative Example 2 used a mixed solution of ethylene glycol bis(propionitrile) ether and ethylene carbonate at a volume ratio of 8:2 as the organic solvent; the electrolyte of Comparative Example 3 used a mixed solution of ethylene glycol bis(propionitrile) ether and ethylene carbonate at a volume ratio of 7:3 as the organic solvent; and the electrolyte of Comparative Example 4 used a mixed solution of ethylene glycol bis(propionitrile) ether and ethylene carbonate at a volume ratio of 1:9 as the organic solvent. The lithium-ion batteries prepared based on the electrolytes of Comparative Examples 1-4 exhibited very poor capacity retention at 80°C. The electrolyte of Example 1 used a mixed solution of ethylene glycol bis(propionitrile) ether and ethylene carbonate in a volume ratio of 3:7 as the organic solvent, and a mixture of lithium difluorooxalate borate and lithium bis(trifluoromethanesulfonyl)imide in a molar ratio of 2:8 as the lithium salt. The NCM811 lithium-ion battery and lithium iron phosphate lithium-ion battery prepared based on it achieved a capacity retention of over 89% after 100 cycles at 80°C, and can operate stably at high temperatures.

[0071] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0072] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0073] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A high-temperature resistant lithium-ion battery electrolyte, characterized in that, Includes organic solvents and lithium salts, wherein the organic solvents include carbonate compounds and ethylene glycol bis(propionitrile) ether; The carbonate compounds are cyclic carbonates and / or halogenated compounds of cyclic carbonates; The volume ratio of the ethylene glycol bis(propionitrile) ether to the carbonate compound is 1:4 to 2:3; The lithium salt is a mixture of bis(trifluoromethanesulfonyl)imide and lithium difluorooxalate borate, with a molar ratio of lithium difluorooxalate borate to bis(trifluoromethanesulfonyl)imide of 1:20 to 1:

1.

2. The high-temperature resistant lithium-ion battery electrolyte according to claim 1, characterized in that, The cyclic carbonate is one or more of ethylene carbonate, propylene carbonate, and butene carbonate.

3. The high-temperature resistant lithium-ion battery electrolyte according to claim 1, characterized in that, The halogenated compound of the cyclic carbonate is a fluorinated compound of the cyclic carbonate, and the fluorinated compound of the cyclic carbonate is one or more of fluoroethylene carbonate, trifluoromethyl ethylene carbonate, and difluoroethylene carbonate.

4. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is the high-temperature resistant lithium-ion battery electrolyte as described in claim 1.

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