Lithium battery electrolyte and lithium ion battery

Abstract

The invention relates to a lithium battery electrolyte and a lithium ion battery, and mainly solves the problems of poor normal-temperature cycle performance, high-temperature shelving gas production and low low-temperature discharge efficiency of the lithium ion battery. The electrolyte 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 compounds shown in a general formula (1), in the general formula (1), # imgabs 0 # R1, R2, R3 and R4 are independently alkyl, fluoroalkyl, alkoxy, fluoroalkoxy, alkenyl, fluoroalkenyl, alkenyloxy, fluoroalkenyloxy, alkynyl, fluoroalkynyl, aryl, aryloxy, cyano, silane, ether silicon group or amido, A represents a structural formula 1: # imgabs 1 # structural formula 2: # imgabs 2 # or a structural formula 3: # imgabs 3 # m > = 0, n > = 0, R5 represents H, F or alkyl, R6 represents O, S or = CxH2x, R7 represents-CxH2x-, and x > = 1. The invention well solves the common problems in the lithium ion battery, and can be used in the industrial production of the lithium battery.

Description

[0001] This application is a divisional application for application number 2020114304510, filing date December 9, 2020, and invention name "A lithium battery electrolyte and a lithium-ion battery." Technical Field

[0002] The present invention belongs to the field of lithium ion batteries, and in particular relates to a lithium battery electrolyte and a lithium ion battery. Background Art

[0003] Lithium-ion batteries have the advantages of high energy density, high operating voltage, no memory effect, fast charge and discharge, and low environmental pollution, so they are widely used. However, with higher requirements for the energy density, safety performance and service life of commercial lithium-ion batteries, the development of lithium-ion batteries with high energy density, good cycle performance and high safety is an urgent need for the development of the industry.

[0004] During the first charge of a lithium-ion battery, the electrolyte reacts with the carbon negative electrode to form a passivation film (SEI film). During the charge and discharge process, lithium ions must pass through the SEI film, so the SEI film has an important impact on the main performance of lithium-ion batteries (such as cycle, high temperature and power performance). The SEI film can prevent the electrolyte from further decomposing and reduce the side reactions on the negative electrode interface. However, as the charge and discharge proceed, the SEI film may dissolve, rupture, decompose, reorganize or thicken, resulting in negative effects such as increased internal resistance or gas production in the battery, thereby affecting the battery's cycle life, capacity and safety performance. These negative effects will be more serious when the battery is stored or cycled at high temperatures. 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 or different amounts of the same additive in the electrolyte will result in different SEI film quality and different membrane impedance. Therefore, it is very necessary to improve the quality of the SEI / CEI film by selecting appropriate additives and electrolyte formulations to achieve high-performance lithium-ion batteries. Summary of the invention

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

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A first aspect of the present invention provides a lithium battery electrolyte, comprising a solvent, a lithium salt and an additive, wherein the additive comprises a phosphorus-containing additive, and the phosphorus-containing additive is one or more compounds represented by the general formula (1), wherein the general formula (1) is:

[0008]

[0009] R1, R2, R3, and R4 are independently alkyl, fluoroalkyl, alkoxy, fluoroalkoxy, alkenyl, fluoroalkenyl, alkenyloxy, fluoroalkenyloxy, alkynyl, fluoroalkynyl, aryl, aryloxy, cyano, silane, ethersilyl, or amine, and A is represented by structural formula 1: Structural formula 2: Or structural formula 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, and R4 are independently alkoxy, fluoroalkoxy, alkenyloxy, fluoroalkenyloxy, aryloxy, or ethersilyl.

[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 an alkylene group wherein x is 1 to 5.

[0015] In the present invention, the alkoxy group, fluoroalkoxy group, alkenyloxy group and fluoroalkenyloxy group preferably have 1 to 5 carbon atoms.

[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% to 5% of the total mass of the lithium-ion battery electrolyte.

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

[0021] Preferably, the solvent is one or more of carbonates, carboxylates and ethers.

[0022] More preferably, the carbonate is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate.

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

[0024] Further preferably, the solvent comprises at least 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 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 0.001-2 mol / L.

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

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

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

[0031] The second aspect of the present invention 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 invention, the positive electrode of the lithium-ion battery is a ternary positive electrode material or a lithium cobalt oxide positive electrode material, and the negative electrode is a graphite material or silicon dioxide.

[0033] The lithium battery electrolyte of the present invention improves the quality of the SEI / CEI film by selecting a phosphorus-containing additive having the general formula (1) and optimizing the formula of the electrolyte, thereby significantly improving the performance of the lithium ion battery. The capacity retention rate of the lithium ion battery of the present invention after 300 cycles at 1.0C at 25°C can reach up to 93%, and the swelling rate after being stored at 60°C for 30 days is as low as 19%, achieving good technical effects.

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

[0035] The lithium battery electrolyte of the present invention can improve the performance of the lithium battery. The lithium ion battery prepared by using the electrolyte of the present invention has the advantages of good room temperature cycle performance, low high temperature shelf expansion rate and high low temperature discharge efficiency, and has great application prospects. DETAILED DESCRIPTION

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

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

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

[0039] Negative electrode: graphite material, positive electrode: 4.2V NCM523 material, the electrolyte, positive electrode, and negative electrode are assembled into a lithium battery according to conventional processes. The battery capacity retention rate of the lithium battery prepared in each embodiment and comparative example after 300 cycles of charge and discharge at 1.0C in the voltage range of 4.2-2.75V at 25°C was tested; the battery swelling rate of the lithium battery prepared in each embodiment and comparative example after being placed at 60°C for 30 days was tested; the discharge efficiency of the lithium battery prepared in each embodiment and comparative example after 0.2C discharge to 2.75V at -20°C was tested, and the results are shown in Table 1.

[0040] 300-cycle capacity retention rate (%) = discharge capacity of lithium battery after 300 cycles / average discharge capacity 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] 0.2C discharge efficiency at -20℃ (%) = 0.2C discharge capacity of lithium battery at -20℃ / 0.2C charging capacity of lithium battery at room temperature*100.

[0043] Table 1

[0044]

[0045]

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

[0047] It can be seen from Table 1 that in the full battery matched with the ternary positive electrode material and the graphite negative electrode, compared with the basic formula (Comparative Example 1), the room temperature cycle performance of the lithium battery with the addition of different phosphorus-containing compounds is improved, and the gas production of the lithium battery is suppressed after being placed at a high temperature of 60°C for 30 days; the phosphorus-containing compounds used in Examples 1 to 32 have better effects on improving the room temperature cycle performance, high temperature gas production performance, and low temperature discharge performance of the lithium battery than the phosphorus-containing compound SS.

[0048] Comparative Example 6 and Examples 33 to 39

[0049] Electrolyte: The solvent is ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and carboxylic acid ester, the lithium salt is lithium hexafluorophosphate, and the additive is the compound shown in structural formula A. The specific composition and dosage of the electrolyte (based on the total mass of the electrolyte) are shown in Table 2.

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

[0051] 300-cycle capacity retention rate (%) = discharge capacity of lithium battery after 300 cycles / average discharge capacity 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] 0.2C discharge efficiency at -20℃ (%) = 0.2C discharge capacity of lithium battery at -20℃ / 0.2C charging capacity of lithium battery 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] As can be seen from Table 2, after adding the phosphorus-containing compound A, compared with the use of chain carbonate alone, the synergistic use of dimethyl carbonate and carboxylic acid ester can improve the room temperature cycle performance of the lithium battery and the discharge efficiency at -20°C, while inhibiting the gas production of the lithium battery after being stored at a high temperature of 60°C for 30 days; the optimal proportion of dimethyl carbonate and carboxylic acid ester is 30% of the total mass of the electrolyte.

[0059] Comparative Example 7 and Examples 40 to 59

[0060] Electrolyte: The solvent is ethylene carbonate:propylene carbonate:dimethyl carbonate:ethyl methyl carbonate:ethyl acetate=5:1:4:5:2 (mass ratio), the lithium salt is 1.2M lithium hexafluorophosphate, and the other components and amounts in the electrolyte (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, the electrolyte, positive electrode, and negative electrode are assembled into a lithium battery according to conventional processes. The battery capacity retention rate of the lithium battery prepared in each embodiment and comparative example after 300 cycles of charge and discharge at 1.0C in the voltage range of 4.4-2.75V at 25°C; the battery swelling rate of the lithium battery prepared in each embodiment and comparative example after being placed at 60°C for 7 days; the discharge efficiency of the lithium battery prepared in each embodiment and comparative example at 0.2C discharge to 2.75V at -20°C; the results are shown in Table 3.

[0062] 300-cycle capacity retention rate (%) = discharge capacity of lithium battery after 300 cycles / average discharge capacity 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] 0.2C discharge efficiency at -20℃ (%) = 0.2C discharge capacity of lithium battery at -20℃ / 0.2C charging capacity of lithium battery at room temperature*100.

[0065] Table 3

[0066]

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

[0068] It can be seen from Table 3 that in the full battery with 4.4V lithium cobalt oxide positive electrode material and silicon monoxide negative electrode, compared with the lithium battery without adding phosphorus-containing compounds, the room temperature cycle performance of the lithium battery with different phosphorus-containing compounds is improved, and the gas production of the lithium battery is suppressed after being placed at 60°C for 7 days; the synergistic use of FEC, LiBF4, LiPO2F2 and phosphorus-containing compounds can further improve the room temperature cycle performance and high temperature gas production performance of the lithium battery.

[0069] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium battery electrolyte, comprising a solvent, a lithium salt and an additive, characterized in that: The additive includes a phosphorus-containing additive, and the phosphorus-containing additive is one or more compounds represented by the general formula (1), wherein the general formula (1) is: R1, R2, R3, and R4 are independently alkoxy, aryloxy, or ether silicon, and R1, R2, R3, and R4 are not alkoxy at the same time, and A represents structural formula 1: Structural formula 2: Or structural formula 3: m≥0, n≥0, R5 represents H or F, R6 represents S or =CH2, R7 represents 1 to 5 alkylene groups, The solvent at least includes 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 ion battery electrolyte.

2. The lithium battery electrolyte according to claim 1, characterized in that: The phosphorus-containing additive is one or more of the following compounds:

3. The lithium battery electrolyte according to claim 1, characterized in that: The phosphorus-containing additive accounts for 1% to 5% of the total mass of the lithium-ion battery electrolyte; And / or, the carbonate is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate, and the carboxylate 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.

4. The lithium battery electrolyte according to claim 1, characterized in that: The additives also include other additives, and the other additives are one or more of fluoroethylene carbonate, lithium tetrafluoroborate, and lithium difluorophosphate.

5. 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 4.

6. The lithium-ion battery according to claim 5, characterized in that: The positive electrode is a ternary positive electrode material or a lithium cobalt oxide positive electrode material, and the negative electrode is a graphite material or silicon monoxide.

7. The lithium-ion battery according to claim 6, characterized in that: The positive electrode is a ternary positive electrode material, the negative electrode is a graphite material, and the phosphorus-containing additive is 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.

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

9. The lithium-ion battery according to claim 6, characterized in that: The positive electrode is a lithium cobalt oxide positive electrode material, the negative electrode is silicon dioxide, and the phosphorus-containing additive is 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, and the other additives include fluoroethylene carbonate, lithium tetrafluoroborate, and lithium difluorophosphate.

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

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