Lithium ion battery electrolyte and lithium ion battery

Abstract

The invention relates to a lithium ion battery electrolyte and a lithium ion battery. In order to inhibit the corrosion of an electrolyte containing fluorine-containing sulfimide lithium salt to a positive current collector in circulation and improve the normal temperature, high temperature and low temperature performance of a lithium ion battery, the invention provides a lithium ion battery electrolyte which comprises a solvent and lithium salt, and the lithium salt comprises a first lithium salt and a second lithium salt, the first lithium salt is fluorine-containing sulfimide lithium salt, the second lithium salt is one or more of 2-trifluoromethyl-4, 5-dicyanoimidazole acid lithium, lithium perchlorate and lithium hexafluorophosphate, the molar ratio of the first lithium salt to the second lithium salt is (2-10): 1, the solvent comprises a first solvent and a second solvent, the first solvent is a carbonic ester compound, and the second solvent is a non-carbonic ester compound. The carbonic ester compound does not comprise ethylene carbonate, the second solvent is one or more of a lactone compound, a fluorobenzene compound and a fluoroether compound, and the mass ratio of the first solvent to the second solvent is (2-10): 1.

Description

Technical Field

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

[0002] Lithium-ion batteries have advantages such as high energy density, high operating voltage, no memory effect, rapid charging and discharging, and low environmental pollution, and are therefore widely used. However, with increasing demands on the energy density, safety performance, and lifespan 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 industry.

[0003] A lithium-ion battery pack comprises at least a negative electrode (anode), a positive electrode (cathode), a separator, and an electrolyte. The electrolyte typically consists of a lithium salt dissolved in a solvent, usually a mixture of organic carbonates, to achieve a good trade-off between viscosity and dielectric constant. Additives may also be added to improve the stability of the electrolyte salt.

[0004] Batteries, as efficient electrochemical energy storage devices, are crucial for the effective utilization of intermittent renewable energy sources. Currently, society has placed higher demands on the application of lithium-ion batteries. The lithium hexafluorophosphate (LiPF6) electrolyte salt, widely used in lithium-ion batteries, is being replaced due to its poor thermal stability, susceptibility to decomposition in moisture, and pitting corrosion. Lithium bis(fluorosulfonyl)imide (LiFSI), with its excellent water and thermal stability, electrochemical stability, and high conductivity, is poised to become the next-generation lithium salt. However, this lithium salt itself can exacerbate the corrosion of the positive electrode current collector aluminum foil in lithium-ion batteries, thus affecting the overall battery performance. Therefore, inhibiting this corrosion is a bottleneck issue in the application of this type of electrolyte and the development of high-power-density lithium batteries.

[0005] During the charging and discharging process of a lithium hexafluorophosphate (LiPF6) electrolyte, the positive electrode current collector aluminum foil forms a stable and dense AlF3 passivation film, protecting the substrate from corrosion and thus improving the overall safety performance and extending the lifespan of the lithium battery. However, in electrolytes containing fluorosulfonylimide lithium salts (such as lithium difluorosulfonylimide (LiFSI) electrolytes), it has been observed that such a stable and dense passivation film cannot form to protect the substrate after charging and discharging. With the increase of cycle number, varying degrees of voids and cracks appear on the surface of the positive electrode current collector aluminum foil, affecting the lifespan, cycle performance, and safety performance of the lithium-ion battery. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium-ion battery electrolyte that can simultaneously improve the room temperature and low temperature cycling performance of an electrolyte containing fluorosulfonylimide lithium salt and suppress its gas generation during high-temperature storage, as well as a lithium-ion battery using the lithium-ion battery electrolyte.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The first aspect of this invention provides a lithium-ion battery electrolyte, the lithium-ion battery electrolyte comprising a solvent and a lithium salt, the lithium salt comprising a first lithium salt and a second lithium salt, the first lithium salt being a fluorosulfonylimide lithium salt, the second lithium salt being one or more selected from lithium 2-trifluoromethyl-4,5-dicyanimidazolium, lithium perchlorate, and lithium hexafluorophosphate, the molar ratio of the first lithium salt to the second lithium salt being (2-10):1, the solvent comprising a first solvent and a second solvent, the first solvent being a carbonate compound, and the carbonate compound excluding ethylene carbonate, the second solvent being one or more selected from lactone compounds, fluorobenzene compounds, and fluoroether compounds, the mass ratio of the first solvent to the second solvent being (2-10):1.

[0009] Preferably, the first lithium salt is lithium bisfluorosulfonylimide and / or lithium bistrifluoromethanesulfonate imide.

[0010] Preferably, the molar concentration of the lithium salt in the lithium-ion battery electrolyte is 1–5 mol / L, for example, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, etc. l / L, 2.9mol / L, 3.0mol / L, 3.1mol / L, 3.2mol / L, 3.3mol / L, 3.4mol / L, 3.5mol / L, 3.6mol / L, 3.7mol / L, 3.8mol / L, 3.9mol / L, 4.0mol / L, 4.1mol / L, 4.2mol / L, 4.3mol / L, 4.4mol / L, 4.5mol / L, 4.6mol / L, 4.7mol / L, 4.8mol / L, 4.9mol / L, 5.0mol / L.

[0011] Preferably, the molar concentration of the first lithium salt in the lithium-ion battery electrolyte is 0.6 to 1.5 mol / L, for example, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, or 1.5 mol / L.

[0012] Preferably, the molar concentration of the second lithium salt in the lithium-ion battery electrolyte is 0.1 to 0.5 mol / L, for example, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, or 0.5 mol / L.

[0013] Preferably, the lithium salt includes lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonate)imide, lithium 2-trifluoromethyl-4,5-dicyanimidazolium, lithium perchlorate, and lithium hexafluorophosphate.

[0014] More preferably, the molar ratio of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonate)imide, lithium 2-trifluoromethyl-4,5-dicyanoimidazolium acid, lithium perchlorate and lithium hexafluorophosphate is (4-8):(1.5-3):(0.8-1.2):(0.8-1.2):1.

[0015] More preferably, the molar ratio of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonate)imide, lithium 2-trifluoromethyl-4,5-dicyanoimidazolium acid and lithium hexafluorophosphate is (5-7):(1.5-2.5):(0.9-1.1):(0.9-1.1):1.

[0016] Preferably, the first solvent includes one or more of propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0017] Preferably, the second solvent includes one or more of γ-butyrolactone, triphenyl borate, fluorobenzene, and hydrofluoroether.

[0018] Preferably, the second solvent includes at least the fluorobenzene compound.

[0019] More preferably, the fluorobenzene compound accounts for 20% to 30% of the total mass of the solvent, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%.

[0020] Preferably, the solvent includes at least ethyl methyl carbonate, and ethyl methyl carbonate accounts for 50% to 70% of the total mass of the solvent, for example, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, or 70%.

[0021] Preferably, the lithium-ion battery electrolyte further includes isocyanate additives.

[0022] More preferably, the isocyanate additive includes ethyl isocyanate methacrylate and / or hexamethyl diisocyanate.

[0023] More preferably, the isocyanate additive accounts for 0.01% to 2% of the total mass of the lithium-ion battery electrolyte, for example, 0.01%, 0.05%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%. %, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.4%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.46%, 0.47%, 0.48%, 0. 49%, 0.5%, 0.51%, 0.52%, 0.53%, 0.54%, 0.55%, 0.56%, 0.57%, 0.58%, 0.59%, 0.6%, 0.61%, 0.62%, 0.63%, 0.64%, 0.65%, 0.66%, 0.67%, 0.68%, 0.69%, 0.7%, 0.71%, 0.72%, 0.73%, 0.74%, 0.75%, 0.76%, 0.77%, 0.78%, 0.79%, 0.8%, 0.81%, 0.82%, 0.83%, 0.84%, 0.85%, 0.86%, 0.87%, 0.88%, 0.89%, 0.9%, 0.91%, 0.92%, 0.93%, 0.94%, 0.95%, 0.96%, 0.97%, 0.98%, 0.99%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%.

[0024] More preferably, the mass of the isocyanate additive is 0.01% to 1% of the total mass of the lithium-ion battery electrolyte.

[0025] Preferably, the lithium-ion battery electrolyte further includes other additives, which include one or more of fluoroethylene carbonate, lithium difluorophosphate, sulfur-containing compounds, and acid anhydride compounds.

[0026] A second aspect of the present invention also provides a lithium-ion battery, the lithium-ion battery comprising the above-described lithium-ion battery electrolyte.

[0027] Preferably, the positive electrode of the lithium battery comprises a nickel-cobalt-manganese ternary material or a lithium cobalt oxide material; the negative electrode of the lithium battery comprises a graphite or silicon-carbon composite negative electrode material (SiC / graphite composite material or SiOx@C composite material).

[0028] Preferably, the lithium battery operates at a voltage of 4.3V or higher.

[0029] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0030] This invention improves electrolyte performance and protects the positive electrode current collector by using different combinations of lithium salts and different organic solvents. In addition, by combining appropriate amounts of special isocyanate additives, it further suppresses gas generation during high-temperature storage while ensuring cycle performance, thus extending the lifespan of lithium-ion batteries. Through overall formula optimization, a lithium-ion battery with excellent comprehensive performance is obtained. Detailed Implementation

[0031] In order to suppress the corrosion of the positive electrode current collector by the electrolyte containing fluorosulfonylimide lithium salt during cycling and improve the performance of lithium-ion batteries at room temperature, high temperature and low temperature, the inventors of this application have conducted a lot of research and experimental verification on the electrolyte formulation. By using different lithium salts in combination and different organic solvents in combination, the electrolyte performance is improved and the positive electrode current collector is protected. In addition, by combining an appropriate amount of special isocyanate additives, gas generation during high-temperature storage is further suppressed while ensuring cycle performance.

[0032] Specifically, the improved lithium-ion battery electrolyte of the present invention includes a solvent and a lithium salt, wherein the lithium salt includes a first lithium salt and a second lithium salt, the first lithium salt being a fluorosulfonylimide lithium salt, and the second lithium salt being one or more of lithium 2-trifluoromethyl-4,5-dicyanimidazolium, lithium perchlorate, and lithium hexafluorophosphate, wherein the molar ratio of the first lithium salt to the second lithium salt is (2-10):1, and the solvent includes a first solvent and a second solvent, wherein the first solvent is a carbonate compound, and the carbonate compound does not include ethylene carbonate, and the second solvent is one or more of lactone compounds, fluorobenzene compounds, and fluoroether compounds, wherein the mass ratio of the first solvent to the second solvent is (2-10):1.

[0033] Furthermore, the lithium-ion battery electrolyte may also contain appropriate amounts of isocyanate additives, including isocyanate ethyl methacrylate and / or hexamethyl diisocyanate.

[0034] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0035] Unless otherwise specified, the raw materials used in the following examples and comparative examples are all commercially available products.

[0036] The preparation methods of lithium-ion battery electrolytes and the assembly of lithium-ion batteries in the following examples and comparative examples refer to the prior art, and are not specifically discussed in this invention.

[0037] Examples 1-17 and Comparative Examples 1-4

[0038] Prepare the lithium-ion battery electrolyte according to the component dosages in Table 1, and then assemble the lithium-ion battery electrolyte, positive electrode (positive electrode current collector aluminum foil, positive electrode material NCM811), negative electrode (positive electrode current collector copper foil, negative electrode material SiC / graphite), and separator (Celegate 2400) into a lithium-ion battery according to conventional processes.

[0039] Table 1

[0040]

[0041] In Table 1: PC: propylene carbonate; EMC: methyl ethyl carbonate; 3FB: trifluorobenzene; LiFSI: lithium bis(fluorosulfonyl)imide; LiTFSI: lithium bis(trifluoromethanesulfonate)imide; LEA: lithium 2-trifluoromethyl-4,5-dicyanimidazolium acid; LiClO4: lithium perchlorate; LiPF6: lithium hexafluorophosphate; IEM: ethyl isocyanate methacrylate; M represents mol / L.

[0042] The room temperature cycle performance of the lithium-ion batteries in Examples 1-17 and Comparative Examples 1-4 was tested. The test method was as follows: After formation, the lithium-ion batteries were charged to 4.3V at 1C at 25°C, then left to rest for 5 minutes, and then discharged to 2.8V at 1C, left to rest for 5 minutes. This process was repeated 500 times. The capacity retention rate (%) after 500 cycles at 45°C was calculated as: (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%. The discharge capacity was tested using a Shenzhen Xinwei Battery Tester.

[0043] The swelling rate of lithium-ion batteries in Examples 1-17 and Comparative Examples 1-4 after being placed at a high temperature of 60°C for 30 days was tested. The test method was as follows: after the lithium-ion battery was formed, it was charged to 4.3V with a current of 0.2C, and then placed at a high temperature of 60°C for 30 days. The swelling rate (%) = the thickness of the lithium-ion battery after being placed at 60°C for 30 days / the initial thickness of the lithium-ion battery × 100%.

[0044] The low-temperature cycling performance of the lithium-ion batteries in Examples 1-17 and Comparative Examples 1-4 was tested. The test method was as follows: After formation, the lithium-ion batteries were charged to 4.3V at 0.2C at -20℃, then left to rest for 5 minutes, and then discharged to 2.8V at 0.2C, left to rest for 5 minutes. This process was repeated 500 times. The capacity retention rate (%) after 100 cycles at -20℃ was calculated as: (Discharge capacity of the 100th cycle / Discharge capacity of the first cycle) × 100%. The discharge capacity was tested using a Shenzhen Xinwei Battery Tester.

[0045] Table 2 shows the room temperature cycling performance, swelling rate after being stored at 60°C for 30 days, and low temperature cycling performance of the lithium-ion batteries of Examples 1-17 and Comparative Examples 1-4.

[0046] Table 2

[0047]

[0048]

[0049] According to Tables 1 and 2, different combinations of lithium salts can improve the room temperature cycle performance, high temperature storage performance, and low temperature cycle performance of lithium-ion batteries. The appropriate addition of isocyanate additives can further improve the above performance. The electrolyte of the embodiment, through overall formulation optimization, significantly suppresses the corrosion behavior of the positive electrode aluminum current collector in the electrolyte containing lithium bis(fluorosulfonyl)imide (LiFSI), protects the positive electrode current collector during cycling, improves the cycle stability and service life of lithium-ion batteries, and significantly improves the suppression of gas generation after high temperature storage and the improvement of discharge efficiency at low temperature. This allows the lithium-ion battery to simultaneously achieve room temperature cycle performance, high temperature storage performance, and low temperature cycle performance.

[0050] Examples 18-21 and Comparative Example 5

[0051] Prepare the lithium-ion battery electrolyte according to the component dosages in Table 3, and then assemble the lithium-ion battery electrolyte, positive electrode (positive electrode current collector aluminum foil, positive electrode material NCM811), negative electrode (positive electrode current collector copper foil, negative electrode material SiC / graphite), and separator (Celegate 2400) into a lithium-ion battery according to conventional processes.

[0052] Table 3

[0053]

[0054] In Table 3: PC: propylene carbonate; GBL: γ-butyrolactone; EC: ethylene carbonate; EMC: methyl ethyl carbonate; 3FB: trifluorobenzene; FB: fluorobenzene; HFE: hydrofluoroether; LiFSI: lithium bis(fluorosulfonyl)imide; LiTFSI: lithium bis(trifluoromethanesulfonate)imide; LEA: lithium 2-trifluoromethyl-4,5-dicyanimidazolium acid; LiPF6: lithium hexafluorophosphate; IEM: ethyl isocyanate methacrylate; M represents mol / L.

[0055] The room temperature cycling performance, swelling rate after being placed at a high temperature of 60°C for 30 days, and low temperature cycling performance of the lithium-ion batteries of Examples 18-21 and Comparative Example 5 were tested according to the methods described above. The results are summarized in Table 4.

[0056] Table 4

[0057]

[0058] According to Tables 3 and 4, the performance of electrolytes containing lithium bis(fluorosulfonyl)imide (LiFSI) is related to organic solvents. The use of ethylene carbonate affects various properties of the electrolyte. The examples show that by combining various organic solvents with other components in the electrolyte, the cycle stability and high-temperature storage safety of lithium-ion batteries are significantly improved.

[0059] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be included within the scope of protection of the invention.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The lithium-ion battery electrolyte includes a solvent and a lithium salt. The lithium salt includes a first lithium salt and a second lithium salt. The first lithium salt is a fluorosulfonylimide lithium salt, and the second lithium salt is one or more of lithium 2-trifluoromethyl-4,5-dicyanimidazolium, lithium perchlorate, and lithium hexafluorophosphate. The molar ratio of the first lithium salt to the second lithium salt is (2-10):

1. The solvent includes a first solvent and a second solvent. The first solvent is a carbonate compound, and the carbonate compound does not include ethylene carbonate. The second solvent is one or more of lactone compounds, fluorobenzene compounds, and fluoroether compounds. The mass ratio of the first solvent to the second solvent is (2-10):

1.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The first lithium salt is lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonate)imide; And / or, the molar concentration of the lithium salt in the lithium-ion battery electrolyte is 1 to 5 mol / L; And / or, the molar concentration of the first lithium salt in the lithium-ion battery electrolyte is 0.6 to 1.5 mol / L; And / or, the molar concentration of the second lithium salt in the lithium-ion battery electrolyte is 0.1 to 0.5 mol / L.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salts include lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonate)imide, lithium 2-trifluoromethyl-4,5-dicyanimidazolium, lithium perchlorate, and lithium hexafluorophosphate.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that, The molar ratio of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonate)imide, lithium 2-trifluoromethyl-4,5-dicyanoimidazolium acid, lithium perchlorate and lithium hexafluorophosphate is (4-8):(1.5-3):(0.8-1.2):(0.8-1.2):

1.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The first solvent includes one or more of propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate; And / or, the second solvent includes one or more of γ-butyrolactone, triphenyl borate, fluorobenzene, and hydrofluoroether; And / or, the second solvent includes at least the fluorobenzene compound.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The solvent includes at least ethyl methyl carbonate, and ethyl methyl carbonate accounts for 50% to 70% of the total mass of the solvent.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium-ion battery electrolyte also includes isocyanate additives.

8. The lithium-ion battery electrolyte according to claim 7, characterized in that, The isocyanate additives include ethyl isocyanate methacrylate and / or hexamethyl diisocyanate; And / or, the mass of the isocyanate additive is 0.01% to 2% of the total mass of the lithium-ion battery electrolyte.

9. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium-ion battery electrolyte also includes other additives, which include one or more of the following: fluoroethylene carbonate, lithium difluorophosphate, sulfur-containing compounds, and acid anhydride compounds.

10. A lithium-ion battery, characterized in that: The lithium-ion battery includes the lithium-ion battery electrolyte as described in any one of claims 1 to 9.

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