Lithium-ion battery

Abstract

A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte solution. The positive electrode comprises a positive electrode active material and a lithium supplementing agent, the lithium supplementing agent comprising LiaMnOc, wherein 2≤a≤6, 1≤c≤4, n is 0 or 1, and M comprises one or more of Fe, Ni, and Co; and the molar content ratio of oxygen in LiaMnOc satisfies y=c / (a+c+n), where 0.2≤y≤0.6. The electrolyte solution comprises a solvent, a lithium salt and an additive. The ratio of the content of Li+ in the electrolyte solution to the content of Li+ in the positive electrode is x, and 0.1≤x≤0.2.

Description

A lithium ion battery

[0001] The present application claims priority to the Chinese patent application No. 202410838932.7, filed on June 26, 2024, and entitled "A lithium ion battery", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application belongs to the technical field of batteries, and specifically relates to a lithium ion battery. BACKGROUND

[0003] Lithium ion batteries are widely used in the energy storage field due to their high safety, long cycle life, and green environmental protection. However, during the first charging process, a large amount of lithium ions are irreversibly consumed from the positive electrode to form an SEI film on the surface of the negative electrode, resulting in a sharp decrease in the number of active lithium ions during the cycle process, which reduces the initial capacity of the battery and affects the storage life of the battery. In order to solve the problem of active lithium loss, lithium supplement technology needs to be developed. Currently, the lithium supplement technology route includes positive electrode lithium supplement and negative electrode lithium supplement. Compared with negative electrode lithium supplement, positive electrode lithium supplement has simple process and good safety. However, common lithium supplement agents will react with electrolyte components, especially with highly active solvents such as ethylene carbonate, during the storage process of the battery, producing gas and reducing the service life of the battery. More seriously, the gas causes the battery to bulge, which is not conducive to the safety performance of the battery.

[0004] SUMMARY

[0005] In view of the problem of gas production at high temperature during storage of the existing lithium supplement agent in the lithium ion battery, the present application provides a lithium ion battery.

[0006] The technical solution adopted by the present application to solve the above technical problems is as follows:

[0007] The present application provides a lithium ion battery, which comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode comprises a positive electrode active material and a lithium supplement agent, the lithium supplement agent comprises Li a M n O c , wherein 2≤a≤6, 1≤c≤4, n is 0 or 1, M comprises one or more of Li, Fe, Ni and Co; the molar content ratio y of oxygen in Li a M n O c is c / (a+c+n), and 0.2≤y≤0.6;

[0008] The electrolyte comprises a solvent, a lithium salt and an additive, and the content of Li + in the electrolyte is less than the content of Li +The ratio of the content of the additive to the content of the solvent is x, 0.1≤x≤0.2.

[0009] Optionally, the additive comprises a sulfate compound, and the solvent comprises a main solvent and an auxiliary solvent.

[0010] The main solvent is ethylene carbonate, and the auxiliary solvent is selected from one or more of a carbonate solvent, an ether solvent, and a carboxylic acid ester solvent.

[0011] The mass ratio of the sulfate compound to the main solvent is z, 2≤100z≤50.

[0012] Optionally, the lithium ion battery satisfies the following condition: 1.5≤y / x≤5; 2≤y / z≤18.

[0013] Optionally, the mass percentage content of the ethylene carbonate in the electrolyte is 5%-35%, and the mass percentage content of the sulfate compound in the electrolyte is 0.5%-5%.

[0014] Optionally, the carbonate solvent comprises one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0015] The ether solvent comprises one or more of 1,3-dioxolane (DOL), 1,4-dioxane (DX), a crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF).

[0016] The carboxylic acid ester solvent comprises one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0017] The sulfate compound comprises one or more of vinyl sulfate, methyl vinyl sulfate, propylene sulfate, diethyl sulfate, diisopropyl sulfate, and bis(2-methylpropyl) sulfate.

[0018] Optionally, the additive further comprises a lithium salt compound, and the lithium salt compound comprises one or more of lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB).

[0019] Optionally, the lithium salt comprises one or more of LiPF6, LiPO2F2, LiBF4, LiBOB, LiClO4, LiCF3SO3, LiDFOB, LiN(SO2CF3)2, and LiN(SO2F)2, and the concentration of the lithium salt is 0.8M-1.5M.

[0020] Optionally, the mass percentage content of the lithium supplementing agent in the positive electrode is 0.1%-10%.

[0021] Optionally, the Li a M n O c One or more of Li2O, Li5FeO4, Li2NiO2, Li6CoO4.

[0022] Optionally, the positive active material includes one or more of lithium iron phosphate, lithium iron manganese phosphate, ternary material, layered transition metal oxide.

[0023] The negative electrode includes one or more of graphite, silicon-based material, hard carbon.

[0024] The separator includes one or more of polymer separator, non-woven fabric.

[0025] In the present application, a positive electrode lithium supplement agent is added, the oxygen of the lithium supplement agent has an oxidizing gas production effect on the electrolyte, at the same time, the content of Li + in the positive electrode is correspondingly increased, the balance of lithium in the positive electrode and the electrolyte is broken, more high-activity lithium compounds are formed on the negative electrode side, and the decomposition of the electrolyte is promoted. The above factors collectively promote the increase of gas production during the storage stage of the battery, threatening the safety performance of the battery.

[0026] The present application adjusts the ratio of the content of Li + in the positive electrode to the content of Li + in the electrolyte, so that the process of Li + forming SEI in the negative electrode is changed, the proportion of the interface film of the high-activity lithium compound is reduced, the reaction with the electrolyte is weakened, and the storage gas production is reduced. By adjusting the oxygen content ratio of the lithium supplement agent, the residual oxygen in the battery after formation is reduced, the oxidizing gas production effect of the residual oxygen on the electrolyte during the storage stage is weakened, the gas production is effectively reduced, and the purpose of improving the high-temperature storage gas production of the lithium ion battery is achieved. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and beneficial effects of the present application clearer and more apparent, the present application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0028] An embodiment of the present application provides a lithium ion battery, which includes a positive electrode, a negative electrode, a separator and an electrolyte, the positive electrode includes a positive active material and a lithium supplement agent, the lithium supplement agent includes Li a M n O c , wherein 2≤a≤6, 1≤c≤4, n is 0 or 1, M includes one or more of Li, Fe, Ni, Co; the Li a M n Oc The molar content ratio y of oxygen is c / (a+c+n), and 0.2≤y≤0.6.

[0029] The electrolyte includes a solvent, a lithium salt, and an additive, and the content of Li + The content of Li + The ratio of the content of Li

[0030] In the present application, the positive electrode is supplemented with a lithium supplement, the oxygen in the lithium supplement has an oxidizing and gas-producing effect on the electrolyte, and the content of Li in the positive electrode is correspondingly increased, which breaks the balance of lithium in the positive electrode and the electrolyte, forms more high-activity lithium compounds on the negative electrode side, and promotes the decomposition of the electrolyte. The above factors collectively promote the increase in gas production during the storage stage of the battery, threatening the safety performance of the battery.

[0031] The present application controls the ratio of the content of Li + The content of Li + The content of Li + The process of forming SEI on the negative electrode is changed, the proportion of the interface film of high-activity lithium compounds is reduced, the reaction with the electrolyte is weakened, the storage gas production is reduced, and the lithium supplement is achieved while the gas production is controlled. By controlling the oxygen content ratio of the lithium supplement, the residual oxygen in the battery after formation is reduced, the oxidizing and gas-producing effect of the residual oxygen on the electrolyte during the storage stage is weakened, the gas production is effectively reduced, and the purpose of improving the high-temperature storage gas production of the lithium ion battery is achieved.

[0032] Specifically, a is 2, 3, 4, 5, or 6. c is 1, 2, 3, or 4, and y is 0.2, 0.3, 0.4, 0.5, or 0.6. x is 5, 5.4, 6, 6.4, 7, 7.4, 8, 8.4, 9, 9.4, or 10.

[0033] In an embodiment, the additive includes a sulfate compound, and the solvent includes a main solvent and an auxiliary solvent.

[0034] The main solvent is ethylene carbonate, and the auxiliary solvent is selected from one or more of a carbonate solvent, an ether solvent, and a carboxylic acid ester solvent.

[0035] The mass ratio of the sulfate compound to the main solvent is z, and 2≤100z≤50.

[0036] The decomposition of ethylene carbonate is effectively inhibited by the sulfate compound, and by selecting a suitable mass ratio of the sulfate compound to ethylene carbonate, the gas production can be reduced while ensuring the storage performance of the battery.

[0037] In a preferred embodiment, 3≤100z≤30.

[0038] In some embodiments, the lithium ion battery satisfies the following conditions: 1.5≤y / x≤5; 2≤y / z≤18. The content of Li + The ratio of the content of Li + The ratio of the content of Li

[0039] For ethylene carbonate, the oxygen content y in the lithium supplement agent and the sulfate compound jointly affect the decomposition of ethylene carbonate. The higher the value of y, the more gas is produced. Appropriately increasing the value of z can effectively control the amount of gas produced. When y / z<2, the storage capacity retention rate is deteriorated. When y / z>18, the amount of gas produced increases significantly, deteriorating the safety performance of the battery.

[0040] In some embodiments, the mass percentage content of ethylene carbonate in the electrolyte is 5% to 35%, and the mass percentage content of the sulfate compound in the electrolyte is 0.5% to 5%.

[0041] Specifically, the mass percentage content of ethylene carbonate in the electrolyte is 5%, 11%, 15%, 17%, 20%, 23%, 25%, 29%, 30%, or 35%. The mass percentage content of the sulfate compound in the electrolyte is 0.5%, 1%, 1.5%, 1.7%, 2%, 2.3%, 2.7%, 3.3%, 3.7%, 4.3%, 4.7%, or 5%.

[0042] In a preferred embodiment, the mass percentage content of ethylene carbonate in the electrolyte is 15% to 30%, and the mass percentage content of the sulfate compound in the electrolyte is 1% to 3%.

[0043] In some embodiments, the carbonate solvent includes one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0044] The ether solvent includes one or more of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF).

[0045] The carboxylic acid ester solvent includes one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0046] The sulfate compound includes one or more of vinyl sulfate, methyl vinyl sulfate, propylene sulfate, diethyl sulfate, diisopropyl sulfate, bis(2-methylpropyl) sulfate.

[0047] In some embodiments, the additive further includes a lithium salt compound, the lithium salt compound including one or more of lithium difluoro(oxalato)borate, lithium bis(oxalato)borate.

[0048] In some embodiments, the lithium salt includes one or more of LiPF6, LiPO2F2, LiBF4, LiBOB, LiClO4, LiCF3SO3, LiDFOB, LiN(SO2CF3)2, and LiN(SO2F)2; the concentration of the lithium salt is 0.8M-1.5M.

[0049] In a preferred embodiment, the concentration of the lithium salt is 0.8M-1.2M.

[0050] In some embodiments, the mass percentage of the lithium supplement agent in the positive electrode is 0.1%-10%.

[0051] Specifically, the mass percentage of the lithium supplement agent in the positive electrode is 0.1%, 0.3%, 0.5%, 0.7%, 1%, 1.5%, 1.7%, 2%, 2.3%, 2.7%, 3.3%, 3.7%, 4.3%, 4.7%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0052] In some embodiments, the Li a M n O c includes one or more of Li2O, Li5FeO4, Li2NiO2, Li6CoO4.

[0053] In a preferred embodiment, the Li a M n O c is selected from Li5FeO4, Li2NiO2.

[0054] In some embodiments, the positive electrode active material includes one or more of lithium iron phosphate, lithium iron manganese phosphate, a ternary material, a layered transition metal oxide;

[0055] The negative electrode includes one or more of graphite, a silicon-based material, hard carbon;

[0056] The separator comprises one or more of a polymer separator, a non-woven fabric. The polymer separator comprises, but is not limited to, a single layer PP (polypropylene), a single layer PE (polyethylene), a double layer PP / PE, a double layer PP / PP, and a triple layer PP / PE / PP separator.

[0057] The application is further illustrated by the following examples.

[0058] Example 1

[0059] This example is used to illustrate the lithium ion battery disclosed in the application, comprising the following operation steps:

[0060] Electrolyte: ethylene carbonate (EC) and methyl ethyl carbonate (EMC) are mixed in a mass ratio of EC: EMC = 3:7, then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and then 3% vinylene carbonate (VC) and 1% vinyl sulfate (DTD) based on the total mass of the electrolyte are added.

[0061] Preparation of the positive electrode sheet

[0062] The positive electrode active material LiFePO4, the positive electrode lithium supplement, the conductive carbon black Super-P, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 93.5:2.5:2:2, and then they are dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil, dried, calendered, and vacuum dried, and then an aluminum lead wire is welded on using an ultrasonic welding machine to obtain the positive electrode sheet.

[0063] Preparation of the negative electrode sheet

[0064] The negative electrode active material artificial graphite, the conductive carbon black Super-P, the binder styrene-butadiene rubber (SBR), and the carboxymethyl cellulose (CMC) are mixed in a mass ratio of 94:1:2.5:2.5, and then they are dispersed in deionized water to obtain a negative electrode slurry. The slurry is coated on both sides of a copper foil, dried, calendered, and vacuum dried, and then a nickel lead wire is welded on using an ultrasonic welding machine to obtain the negative electrode sheet.

[0065] Preparation of the battery cell

[0066] Three layers of the separator are placed between the positive electrode sheet and the negative electrode sheet, and then the sandwich structure composed of the positive electrode sheet, the negative electrode sheet, and the separator is wound, and then the wound body is flattened and placed in an aluminum foil packaging bag, vacuum baked at 75°C for 48h to obtain a battery cell to be injected with electrolyte.

[0067] Injection of electrolyte and formation of the battery cell

[0068] The electrolyte prepared above is injected into the battery cell in a glove box with the dew point controlled below -40°C, vacuum packaged, and left for 24h.

[0069] Then formation was carried out as follows: 0.1C constant current constant voltage charging to 4.3V, 0.1C constant current discharging to 2.5V.

[0070] Practical application voltage range: charge cut-off voltage 3.65V, discharge cut-off voltage 2.5V.

[0071] Examples 2-20

[0072] The examples are used to illustrate the lithium ion battery disclosed in the present application, including most of the operation steps in the above examples, the difference is that the formula in Table 1 is used.

[0073] Comparative examples 1-10

[0074] The comparative examples are used to compare the lithium ion battery disclosed in the present application, including most of the operation steps in Example 1, the difference is that the formula in Table 1 is used.

[0075] Table 1

[0076] Performance test

[0077] I. The batteries prepared in the above examples and comparative examples were subjected to the following performance tests:

[0078] High temperature storage performance test:

[0079] The battery was placed at room temperature, charged to 3.65V at 0.5C constant current constant voltage, discharged to 2.5V at 0.5C constant current, and the capacity C0 was recorded. 0.5C constant current constant voltage charging to 3.65V. Stand for 2h, test volume V0.

[0080] Transfer to 60℃, store for 7d, stand at room temperature for 2h, test volume V1.

[0081] 60℃ continuous storage for 30d, stand at room temperature for 2h, test volume V2; discharge the battery to 2.5V at 0.5C constant current, record the discharge capacity C1, 0.5C constant current constant voltage charging to 3.65V.

[0082] High temperature storage for 7d gas generation rate = (V1-V0) / V0*100%.

[0083] High temperature storage for 30d gas generation rate = (V2-V0) / V0*100%.

[0084] High temperature storage for 30d capacity retention rate = C1 / C0*100%.

[0085] The test results are shown in Table 2.

[0086] Table 2

[0087] From the test results of Example 1, Examples 15-19 and Comparative Example 3, by adding an appropriate amount of lithium supplementing agent, regulating the ratio of Li + content in the electrolyte, the process of SEI formation in the negative electrode changes, the proportion of the interface film of the high-activity lithium compound decreases, the reaction with the electrolyte weakens, the storage gas generation decreases, the lithium supplementing and the control of the gas generation amount are achieved at the same time, and the 30d storage capacity retention of the battery is further improved. + +

[0088] From the test results of Examples 1-4, Comparative Example 1 and Comparative Example 2, when y / x < 1.5, the expected lithium supplementing effect is not achieved, and the 30d storage capacity retention decreases. When y / x > 5, the lithium supplementing agent is excessive, the electrolyte decomposition is promoted, and the storage gas generation is deteriorated. Therefore, by controlling the ratio of Li + content in the electrolyte and Li + content in the positive electrode, and the value of y / x, the control of the gas generation amount and the lithium supplementing effect are achieved.

[0089] From Examples 5-14 and Example 20, the higher the oxygen content y value in the lithium supplementing agent, the more the gas generation, and appropriately increasing the mass ratio of the sulfuric acid ester compound to the main solvent, i.e. the z value, can effectively control the gas generation amount; when y / z < 2, the storage capacity is deteriorated. When y / z > 18, the gas generation increases substantially, and the battery safety performance is deteriorated.

[0090] In summary, the present application regulates the ratio of Li + content in the electrolyte and Li + content in the positive electrode, the mass ratio of the sulfuric acid ester compound to the ethylene carbonate, and the molar content ratio of oxygen in the lithium supplementing agent, so that the use of such electrolyte can ensure high cycle performance and storage performance, while reducing the high-temperature storage gas generation.

[0091] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.​​

Claims

1. A lithium-ion battery, characterized by, The lithium supplement agent comprises Li a M n O c wherein 2≤a≤6, 1≤c≤4, n is 0 or 1, M comprises one or more of Fe, Ni and Co; the Li a M n O c The molar content ratio y of oxygen in the formula is c / (a+c+n), and 0.2≤y≤0.

6. The electrolyte includes a solvent, a lithium salt, and an additive, and a ratio of a content of Li + in the electrolyte to a content of Li + in the positive electrode is x, 0.1≤x≤0.

2.

2. The lithium-ion battery of claim 1, wherein, The additive comprises a sulfate compound, and the solvent comprises a main solvent and an auxiliary solvent. The main solvent is ethylene carbonate, and the auxiliary solvent is selected from one or more of a carbonate solvent, an ether solvent, and a carboxylic acid ester solvent. The mass ratio of the sulfate compound to the main solvent is z, and 2≤100z≤50.

3. The lithium-ion battery of claim 2, wherein, The lithium ion battery satisfies the following conditions: 1.5≤y / x≤5 and 2≤y / z≤18.

4. The lithium-ion battery of claim 2, wherein, The mass percentage of the ethylene carbonate in the electrolyte is 5% to 35%, and the mass percentage of the sulfate compound in the electrolyte is 0.5% to 5%.

5. The lithium-ion battery of claim 2, wherein, The carbonate solvent comprises one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. The ether solvent comprises one or more of 1,3-dioxolane, 1,4-dioxane, a crown ether, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran. The carboxylic acid ester solvent comprises one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The sulfate compound comprises one or more of ethylene sulfate, methyl ethylene sulfate, propylene sulfate, diethyl sulfate, diisopropyl sulfate, and bis(2-methylpropyl) sulfate.

6. The lithium-ion battery of claim 2, wherein, The additive further comprises a lithium salt compound, and the lithium salt compound comprises one or more of lithium difluoro(oxalato)borate and lithium bis(oxalato)borate.

7. The lithium-ion battery of claim 1, wherein, The lithium salt comprises one or more of LiPF6, LiPO2F2, LiBF4, LiBOB, LiClO4, LiCF3SO3, LiDFOB, LiN(SO2CF3)2, and LiN(SO2F)2, and the concentration of the lithium salt is 0.8M to 1.5M.

8. The lithium-ion battery of claim 1, wherein, The mass percentage of the lithium supplementing agent in the positive electrode is 0.1% to 10%.

9. The lithium-ion battery of claim 1, wherein, The Li a M n O c one or more of Li2O, Li5FeO4, Li2NiO2, Li6CoO4.

10. The lithium-ion battery of claim 1, wherein, The positive electrode active material comprises one or more of lithium iron phosphate, lithium iron manganese phosphate, a ternary material, and a layered transition metal oxide. The negative electrode comprises one or more of graphite, a silicon-based material, and hard carbon. The separator comprises one or more of a polymer separator and a non-woven fabric.

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