Lithium battery electrolyte and lithium ion battery

Abstract

The present application relates to a kind of lithium battery electrolyte and lithium ion battery, mainly solve the poor lithium ion battery normal temperature cycle performance, high temperature storage gas production and low temperature discharge efficiency problem.The electrolyte of the present application includes solvent, lithium salt and additive, additive includes phosphorus-containing additive, phosphorus-containing additive is one or more of the compound shown in general formula (1), general formula (1) is: R1, R2, R3, R4 independently be alkyl, fluoroalkyl, alkoxy, fluoroalkoxy, alkenyl, fluoroalkenyl, alkenyloxy, fluoroalkenyloxy, alkynyl, fluoroalkynyl, aryl, aryloxy, cyano, silane, ether silane group or amine group, A indicates structure formula 1: Structure formula 2: Or structure formula 3: m≥0, n≥0, R5 indicates H, F or alkyl, R6 indicates O, S or =C x H 2x , R7 indicates -C x H 2x - x≥1.The present application very good solution to the above-mentioned problems commonly encountered in lithium ion battery, can be used in the industrial production of lithium battery.

Description

[0001] This application is a divisional application of application No. 2020114304510, with the application date of December 9, 2020, and the invention name of a lithium battery electrolyte and a lithium ion battery. TECHNICAL FIELD

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

[0003] Lithium ion batteries have the advantages of high energy density, high working voltage, no memory effect, fast charge and discharge, and small environmental pollution, and thus are widely used. However, as higher requirements are put forward for the energy density, safety performance and service life of commercial lithium ion batteries, it is an urgent need for the industry development to develop lithium ion batteries with high energy density, good cycle performance and high safety.

[0004] During the first charging process of a lithium ion battery, the electrolyte will react with the carbon negative electrode to form a passivation film (SEI film). During the charging and discharging process, lithium ions must pass through the SEI film, so the SEI film has an important influence on the main performance of the lithium ion battery (such as cycle, high temperature and power performance, etc.). The SEI film can prevent further decomposition of the electrolyte and reduce the side reaction at the negative electrode interface, but as the charging and discharging proceed, the SEI film may dissolve, break, decompose, recombine or thicken, etc., resulting in negative effects such as increased internal resistance or gas production of the battery, thereby affecting the cycle life, capacity development and safety performance of the battery. These negative effects will be more serious when the battery is subjected to high-temperature storage or high-temperature cycling. In addition, as the voltage of the lithium ion battery increases, a good passivation film (CEI film) also needs to be formed on the positive electrode side during the cycle. Different additives in the electrolyte or different amounts of the same additive will result in different qualities of the formed SEI film and different film impedances. Therefore, it is necessary to select appropriate additives and electrolyte formulations to improve the quality of the SEI / CEI film in order to achieve high-performance lithium ion batteries. SUMMARY

[0005] The purpose of the present application is to provide a lithium battery electrolyte and a lithium ion battery. The lithium ion battery prepared by using the electrolyte in the present application has the advantages of good room temperature cycle performance, low high-temperature storage expansion rate and high low-temperature discharge efficiency.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] The present application provides a lithium battery electrolyte in the first aspect, which comprises a solvent, a lithium salt and an additive. The additive comprises a phosphorus-containing additive, and the phosphorus-containing additive is one or more of the compounds represented by the general formula (1). The general formula (1) is as follows:

[0008]

[0009] R1, R2, R3, R4 are independently alkyl, fluoroalkyl, alkoxy, fluoroalkoxy, alkenyl, fluoroalkenyl, alkenyloxy, fluoroalkenyloxy, alkynyl, fluoroalkynyl, aryl, aryloxy, cyano, silane, ether silane, or amine, A is represented by structure 1: structure 2: or structure 3:

[0010] m≥0, n≥0, R5 represents H, F, or alkyl, R6 represents O, S, or =C x H 2x , R7 represents -C x H 2x -, x≥1.

[0011] Preferably, R1, R2, R3, R4 are independently alkoxy, fluoroalkoxy, alkenyloxy, fluoroalkenyloxy, aryloxy or ether silane.

[0012] In the present invention, R5 is preferably H.

[0013] In the present invention, R6 is preferably O, S, or =CH2.

[0014] In the present invention, R7 is preferably x is an alkylene group of 1-5.

[0015] In the present invention, the number of carbon atoms of alkoxy, fluoroalkoxy, alkenyloxy, fluoroalkenyloxy is preferably 1-5.

[0016] Preferably, the phosphorus-containing additive is one or more of the following compounds:

[0017]

[0018]

[0019] Preferably, the phosphorus-containing additive accounts for 1-5% of the total mass of the lithium ion battery electrolyte.

[0020] Further preferably, the phosphorus-containing additive accounts for 1.5-3%, further preferably 1.8-2.2%, of the total mass of the lithium ion battery electrolyte.

[0021] Preferably, the solvent is one or more of carbonates, carboxylic acid esters, ethers.

[0022] Further preferably, the carbonates are one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate.

[0023] Further preferably, the carboxylic acid ester is one or more of propyl propionate, ethyl acetate, ethyl butyrate, methyl propionate.

[0024] Further preferably, the solvent comprises at least dimethyl carbonate and a carboxylic acid ester, and the sum of the mass of the dimethyl carbonate and the carboxylic acid ester accounts for 10% to 40% of the total mass of the lithium ion battery electrolyte.

[0025] More preferably, the sum of the mass of the dimethyl carbonate and the carboxylic acid ester accounts for 25% to 35% of the total mass of the lithium ion battery electrolyte.

[0026] Preferably, the lithium salt is one or more of LiClO4, LiPF6, LiTFSI, and LiFSI.

[0027] Preferably, the molar concentration of the lithium salt in the lithium battery electrolyte is 0.001 to 2 mol / L.

[0028] Further preferably, the molar concentration of the lithium salt in the lithium battery electrolyte is 0.1 to 2 mol / L, and more preferably 1 to 1.5 mol / L.

[0029] Preferably, the additive further comprises other additives, and the other additives are one or more of fluoroethylene carbonate, lithium tetrafluoroborate, and lithium difluorophosphate.

[0030] In the present application, preferably, the other additives account for 3% to 15% of the total mass of the lithium ion battery electrolyte, and further preferably 5% to 10%.

[0031] The second aspect of the present application provides a lithium ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is the lithium battery electrolyte.

[0032] In the present application, the positive electrode of the lithium ion battery is a ternary positive electrode material or a lithium cobaltate positive electrode material, and the negative electrode is a graphite material or silicon monoxide.

[0033] In the present application, the lithium battery electrolyte improves the quality of the SEI / CEI film by selecting a phosphorus-containing additive with general formula (1) and optimizing the formula of the electrolyte, so that the performance of the lithium ion battery is significantly improved. The capacity retention rate of the lithium ion battery of the present application after 1.0C cycle for 300 times at 25℃ can reach up to 93%, and the swelling rate after 30 days of storage at 60℃ is as low as 19%, achieving good technical effects.

[0034] Due to the use of the above technical solution, the present application has the following advantages compared with the prior art:

[0035] The lithium battery electrolyte can improve the performance of the lithium battery, the lithium ion battery prepared by using the electrolyte has the advantages of good normal temperature cycle performance, low high temperature storage expansion rate and high low temperature discharge efficiency, and has a wide application prospect. DETAILED DESCRIPTION

[0036] The application will be further described below in conjunction with examples, but the application is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to different specific requirements, and the implementation conditions not marked are conventional conditions in the industry.

[0037] Comparative examples 1 to 5 and examples 1 to 32

[0038] The electrolyte: the solvent is ethylene carbonate: propylene carbonate: dimethyl carbonate: methyl ethyl carbonate: ethyl acetate = 5:1:4:5:2 (mass ratio), the lithium salt is 1.2M lithium hexafluorophosphate, and the other components and the amount (based on the total mass of the electrolyte) in the electrolyte are shown in Table 1.

[0039] The negative electrode: graphite material, the positive electrode: 4.2V NCM523 material, the electrolyte, the positive electrode and the negative electrode are assembled into a lithium battery according to a conventional process. The capacity retention rate of the lithium battery prepared in each example and comparative example after 300 cycles of charging and discharging at 25℃ under 1.0C in the voltage range of 4.2-2.75V is tested; the swelling rate of the lithium battery prepared in each example and comparative example after 30 days of storage at 60℃ is tested; the discharge efficiency of the lithium battery prepared in each example and comparative example at-20℃ under 0.2C discharge to 2.75V is tested, and the results are shown in Table 1.

[0040] 300 cycle capacity retention rate (%) = discharge capacity of lithium battery after 300 cycles / discharge capacity average value of lithium battery before 5 cycles * 100;

[0041] Swelling rate (%) = (thickness of lithium battery after 30 days of storage-thickness of lithium battery before storage) / thickness of lithium battery before storage * 100;

[0042] -20℃ under 0.2C discharge efficiency (%) = discharge capacity of lithium battery at-20℃ under 0.2C / charge capacity of lithium battery at normal temperature under 0.2C * 100.

[0043] Table 1

[0044]

[0045]

[0046] The structural formula of the phosphorus-containing additive used in comparative examples 2 to 5 is:

[0047] As can be seen from Table 1, in the full battery matched by the ternary positive electrode material and the graphite negative electrode, the lithium battery with different phosphorus-containing compounds added has improved room temperature cycle performance compared with the relative comparison base formula (Comparative Example 1), and the gas production of the lithium battery after 30 days of high-temperature storage at 60°C is inhibited; the phosphorus-containing compounds used in Examples 1 to 32 are all better than the phosphorus-containing compound SS in improving the room temperature cycle performance, high-temperature gas production performance and low-temperature discharge performance of the lithium battery.

[0048] Comparative Example 6 and Examples 33 to 39

[0049] The electrolyte is prepared by using vinyl carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate and carboxylic acid ester as the solvent, lithium hexafluorophosphate as the lithium salt and the compound shown in structural formula A as the additive. The specific components and amounts of the electrolyte (based on the total mass of the electrolyte) are shown in Table 2.

[0050] The negative electrode is a graphite material, the positive electrode is a 4.2V NCM523 material, and the electrolyte, the positive electrode and the negative electrode are assembled into a lithium battery according to a conventional process. The lithium battery prepared in each example and comparative example is tested for the battery capacity retention rate after 300 cycles of charge and discharge at 1.0C in the voltage range of 4.2-2.75V at 25°C; the lithium battery prepared in each example and comparative example is tested for the battery swelling rate after 30 days of storage at 60°C; and the lithium battery prepared in each example and comparative example is tested for the discharge efficiency at -20°C under 0.2C discharge to 2.75V, and the results are shown in Table 2.

[0051] 300 cycle capacity retention rate (%) = discharge capacity of lithium battery after 300 cycles / discharge capacity average value of lithium battery before 5 cycles * 100;

[0052] Swelling rate (%) = (thickness of lithium battery after 30 days of storage-thickness of lithium battery before storage) / thickness of lithium battery before storage * 100;

[0053] -20°C 0.2C discharge efficiency (%) = discharge capacity of lithium battery at 0.2C at -20°C / charge capacity of lithium battery at 0.2C at room temperature * 100.

[0054] Table 2

[0055]

[0056]

[0057] EC: ethylene carbonate; PC: propylene carbonate, DMC: dimethyl carbonate; EMC: ethyl methyl carbonate; PP: propyl propionate; EA: ethyl acetate; EB: ethyl butyrate; MP: methyl propionate;

[0058] From Table 2, after adding phosphorus-containing compound A, compared with the use of chain carbonate alone, the use of dimethyl carbonate and carboxylic acid ester in combination can improve the room temperature cycle performance of lithium battery, the discharge efficiency at -20℃, and inhibit the gas production of lithium battery after 30 days of high temperature storage at 60℃; the optimal proportion of dimethyl carbonate and carboxylic acid ester is 30% of the total mass of electrolyte.

[0059] Comparative Example 7 and Examples 40 to 59

[0060] Electrolyte: the solvents are vinyl carbonate: propylene carbonate: dimethyl carbonate: methyl ethyl carbonate: ethyl acetate = 5:1:4:5:2 (mass ratio), the lithium salt is 1.2M lithium hexafluorophosphate, and other components in the electrolyte and the amount (based on the total mass of the electrolyte) are shown in Table 3.

[0061] Negative electrode: SiO X @C material, positive electrode: 4.4V lithium cobalt oxide material, and the electrolyte, positive electrode and negative electrode are assembled into lithium batteries according to a conventional process. The capacity retention rate of the lithium batteries prepared in each example and comparative example after 300 cycles of charging and discharging at 1.0C in the voltage range of 4.4-2.75V at 25℃; the swelling rate of the lithium batteries prepared in each example and comparative example after 7 days of storage at 60℃ is tested; the discharge efficiency of the lithium batteries prepared in each example and comparative example at 0.2C discharge to 2.75V at -20℃ is tested; and the results are shown in Table 3.

[0062] 300 cycle capacity retention rate (%) = discharge capacity of lithium battery after 300 cycles / discharge capacity average value of lithium battery before 5 cycles * 100;

[0063] Swelling rate (%) = (thickness of lithium battery after 7 days of storage-thickness of lithium battery before storage) / thickness of lithium battery before storage * 100;

[0064] -20℃ 0.2C discharge efficiency (%) = 0.2C discharge capacity of lithium battery at -20℃ / 0.2C charge capacity of lithium battery at room temperature * 100.

[0065] Table 3

[0066]

[0067] FEC: fluoroethylene carbonate; LiBF4: lithium tetrafluoroborate; LiPO2F2: lithium difluorophosphate.

[0068] As shown in Table 3, in the full battery matched by the lithium cobaltate positive electrode material at 4.4 V and the silicon monoxide negative electrode, the lithium battery with different phosphorus-containing compounds added has improved room temperature cycle performance compared with the lithium battery without the phosphorus-containing compound added, and the gas production of the lithium battery after being left at high temperature of 60 DEG C for 7 days is inhibited; the FEC, LiBF4 and LiPO2F2 used in cooperation with the phosphorus-containing compound can further improve the room temperature cycle performance and high temperature gas production performance of the lithium battery.

[0069] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and principle of the present application shall be covered within the protection scope of the present application.

Claims

1. A lithium battery electrolyte comprising a solvent, a lithium salt and an additive, characterized in that: The additive comprises a phosphorus-containing additive, The phosphorus-containing additive is one or more of the following compounds: 、 、 、 ， The solvent at least comprises dimethyl carbonate and carboxylic acid ester, and the sum of the mass of the dimethyl carbonate and the carboxylic acid ester accounts for 10% to 40% of the total mass of the lithium battery electrolyte.

2. The lithium battery electrolyte of claim 1, wherein: The phosphorus-containing additive accounts for 1% to 5% of the total mass of the lithium battery electrolyte. And / or, the carboxylic acid ester is one or more of propyl propionate, ethyl acetate, ethyl butyrate, and methyl propionate. And / or, the lithium salt is one or more of LiClO4, LiPF6, LiTFSI, and LiFSI. And / or, the molar concentration of the lithium salt in the lithium battery electrolyte is 1 to 1.5 mol / L.

3. The lithium battery electrolyte of claim 1, wherein: The additive further comprises other additives, which are one or more of fluoroethylene carbonate, lithium tetrafluoroborate, and lithium difluorophosphate.

4. A lithium ion battery comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The electrolyte is the lithium battery electrolyte according to any one of claims 1 to 3.

5. The lithium-ion battery of claim 4, wherein: The positive electrode is a ternary positive electrode material or a lithium cobaltate positive electrode material, and the negative electrode is a graphite material or silicon monoxide.

6. The lithium-ion battery of claim 5, wherein: The positive electrode is a ternary positive electrode material, the negative electrode is a graphite material, and the sum of the mass of the dimethyl carbonate and the carboxylic acid ester accounts for 25% to 35% of the total mass of the lithium battery electrolyte.

7. The lithium-ion battery of claim 6, wherein: The phosphorus-containing additive accounts for 1.5% to 3% of the total mass of the lithium battery electrolyte, the molar concentration of the lithium salt in the lithium battery electrolyte is 1.2 to 1.5 mol / L, and the solvent is a mixture of vinyl carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and ethyl acetate in a mass ratio of (4 to 6):1:(3 to 5):(4 to 6):(1 to 3).

8. The lithium-ion battery of claim 5, wherein: The positive electrode is a lithium cobaltate positive electrode material, the negative electrode is silicon monoxide, the phosphorus-containing additive is , The sum of the mass of the dimethyl carbonate and the carboxylate accounts for 25% to 35% of the total mass of the lithium battery electrolyte, the additive further comprises other additives, and the other additives comprise fluoroethylene carbonate, lithium tetrafluoroborate, and lithium difluorophosphate.

9. The lithium-ion battery of claim 8, wherein: The phosphorus-containing additive accounts for 1.5% to 3% of the total mass of the lithium battery electrolyte, the other additive accounts for 5% to 10% of the total mass of the lithium battery electrolyte, the molar concentration of the lithium salt in the lithium battery electrolyte is 1.2 to 1.5 mol / L, and the solvent is a mixture of vinyl carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and ethyl acetate in a mass ratio of (4 to 6):1:(3 to 5):(4 to 6):(1 to 3).

Images