Non-aqueous electrolyte and lithium ion battery

Abstract

The application relates to a non-aqueous electrolyte and a lithium ion battery. The non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive. The mass percentage content of the additive in the non-aqueous electrolyte is 0.001% to 10%, the additive comprises 1,3,6-hexanetricarbonitrile and vinylene carbonate, and the mass ratio of 1,3,6-hexanetricarbonitrile to vinylene carbonate is 1:4 to 19. Through the synergistic effect of 1,3,6-hexanetricarbonitrile and vinylene carbonate, the lithium ion battery prepared by using the non-aqueous electrolyte has better cycle performance and heat resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to a non-aqueous electrolyte and a lithium ion battery. BACKGROUND

[0002] In recent years, the development of battery technology has also improved rapidly, and the broad market has provided more development opportunities; At the same time, it also brings greater challenges. The extensive use leads to higher requirements for the adaptability of battery technology to the battery use environment, and the market needs the battery to maintain good performance in different harsh environments, and a larger temperature range becomes an important issue for battery development. In order to solve this problem, people need to make more progress in battery materials.

[0003] Lithium ion secondary batteries are widely used in electric vehicles and consumer electronics due to their high energy density, high output power, and low environmental pollution. In order to further improve the energy density of lithium ion batteries, on the one hand, the gram capacity of the positive and negative electrode materials is increased, and on the other hand, the compaction density of the negative electrode film is increased. However, when the compaction density of the negative electrode film is increased, the cycle life of the lithium ion battery is reduced. Therefore, it is necessary to improve the performance of the lithium ion battery when the compaction density of the negative electrode film is increased. SUMMARY

[0004] The first object of the present application is to provide a non-aqueous electrolyte, and the second object is to provide a lithium ion battery, so that the cycle performance and heat resistance of the lithium ion battery are effectively improved.

[0005] To solve the above technical problems, the present application adopts the following technical solutions:

[0006] The first aspect of the present application provides a non-aqueous electrolyte, which comprises a lithium salt, an organic solvent and an additive, the additive comprising 1,3,6-hexane trinitrile and vinylene carbonate.

[0007] The mass percentage content of the additive in the non-aqueous electrolyte is 0.001% to 10%, and the mass ratio of the 1,3,6-hexane trinitrile to the vinylene carbonate is 1:4 to 19.

[0008] The compounding, addition amount and ratio of the above-mentioned additive can effectively improve the cycle performance and heat resistance of the prepared lithium ion battery.

[0009] Preferably, the mass percentage content of the additive in the non-aqueous electrolyte is 1% to 5%.

[0010] Further preferably, the mass percentage content of the additive in the non-aqueous electrolyte is 2% to 3.5%.

[0011] Preferably, the additive is 1,3,6-hexanetricarbonitrile and vinylene carbonate, and when only these two additives are used, the lithium ion battery with the non-aqueous electrolyte has better cycle performance and heat resistance.

[0012] Preferably, the organic solvent includes a cyclic carbonate and a chain carbonate, and the mass percentage of the cyclic carbonate in the organic solvent is 30% to 50%. The chain carbonate includes a symmetrical chain carbonate and an asymmetrical chain carbonate, and the mass ratio of the symmetrical chain carbonate to the asymmetrical chain carbonate is 1:2 to 6.

[0013] The combination and ratio of the above-mentioned organic solvent can effectively improve the cycle performance and heat resistance of the prepared lithium ion battery. At the same time, the organic solvent can produce a synergistic effect with the additive, further improving the cycle performance and heat resistance of the lithium ion battery.

[0014] Further preferably, the cyclic carbonate includes one or more of vinylene carbonate and propylene carbonate.

[0015] Still further preferably, the cyclic carbonate is vinylene carbonate.

[0016] Further preferably, the symmetrical chain carbonate includes one or more of dimethyl carbonate and diethyl carbonate, and the asymmetrical chain carbonate includes methyl ethyl carbonate.

[0017] Under the action of the combination and ratio of the above-mentioned cyclic carbonate and chain carbonate, the lithium ion battery can have better cycle performance and heat resistance.

[0018] Preferably, the mass percentage of the lithium salt in the non-aqueous electrolyte is 5% to 20%.

[0019] Further preferably, the mass percentage of the lithium salt in the non-aqueous electrolyte is 10% to 15%.

[0020] Still further preferably, the mass percentage of the lithium salt in the non-aqueous electrolyte is 12% to 14%.

[0021] Preferably, the lithium salt includes a phosphorus-containing compound and a boron-containing compound.

[0022] The phosphorus-containing compound includes one or more of lithium hexafluorophosphate, lithium difluorodioxalate phosphate, lithium difluorophosphate, and lithium tetrafluorophosphate oxalate phosphate.

[0023] The boron-containing compound includes one or more of lithium tetrafluoroborate, lithium dioxalate borate, and lithium difluorophosphate oxalate borate.

[0024] Preferably, the lithium salt includes lithium difluoro(oxalate)borate and lithium hexafluorophosphate, and the mass ratio of the lithium difluoro(oxalate)borate to the lithium hexafluorophosphate is 1:18-29.

[0025] The lithium salt, the organic solvent and the additive can produce a synergistic effect, and thus the cycle performance and heat resistance of the prepared lithium ion battery are optimal.

[0026] The second aspect of the present application provides a lithium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and the non-aqueous electrolyte.

[0027] The positive electrode sheet comprises a layered transition metal oxide, an olivine phosphate compound and a spinel-containing compound.

[0028] Preferably, the active substance in the positive electrode sheet comprises lithium iron phosphate.

[0029] Preferably, the active substance in the negative electrode sheet comprises graphite, and the compaction density of the negative electrode sheet is 1.45-1.60 g / cm 3 .

[0030] Compared with the prior art, the present application has the following advantages:

[0031] The non-aqueous electrolyte and the lithium ion battery provided by the present application have better cycle performance and heat resistance, and the prepared power battery can meet the increasingly high requirements of new energy vehicles and other fields on lithium ion batteries. Therefore, the non-aqueous electrolyte and the lithium ion battery provided by the present application have good market prospects and economic benefits. DETAILED DESCRIPTION

[0032] When the compaction density of the negative electrode sheet is increased to improve the energy density of the lithium ion battery, the cycle life of the lithium ion battery is reduced. The inventors of the present application have repeatedly conducted in-depth research to improve the performance of the lithium ion battery, and found that the lithium ion battery prepared by using the following non-aqueous electrolyte can effectively improve the cycle performance and heat resistance of the lithium ion battery, thereby completing the present application.

[0033] It is found through research that due to the increase of the compaction density of the negative electrode sheet, the wettability of the electrode sheet and the electrolyte is poor, and lithium ions are difficult to diffuse, thereby reducing the cycle life of the lithium ion battery. Therefore, the formula of the electrolyte is improved in the present application. The non-aqueous electrolyte provided by the present application comprises a compound capable of forming a lithium ion solvent and an additive capable of forming a protective film on the surface of the positive electrode and the negative electrode. When the compaction density of the negative electrode sheet is increased, the non-aqueous electrolyte provided by the present application has better wettability with the electrode sheet, which is beneficial to the diffusion of lithium ions, thereby improving the cycle life and high-temperature resistance of the lithium ion battery. The electrolyte provided by the present application further comprises a lithium salt and an organic solvent.

[0034] The additive includes 1,3,6-hexanetricarbonitrile (HTCN) and vinylene carbonate (VC), and the mass percentage of the additive in the non-aqueous electrolyte is 2% to 3.5%. Meanwhile, the mass ratio of 1,3,6-hexanetricarbonitrile and vinylene carbonate is 1:4 to 19.

[0035] The organic solvent includes cyclic carbonate and chain carbonate, the mass percentage of the cyclic carbonate in the organic solvent is 30% to 50%, the chain carbonate includes symmetrical chain carbonate and asymmetrical chain carbonate, and the mass ratio of the symmetrical chain carbonate and the asymmetrical chain carbonate is 1:2 to 6.

[0036] The lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluoro dioxalate phosphate, lithium tetrafluoro oxalate phosphate, lithium tetrafluoroborate, lithium difluoro oxalate borate and lithium difluoro oxalate borate.

[0037] The lithium ion battery provided by the application includes the non-aqueous electrolyte, the positive electrode and the negative electrode capable of absorbing or releasing metal ions. The negative electrode includes a negative active material including graphite particles and metal particles capable of forming an alloy with Li. Under the synergistic effect of the additive, the organic solvent and the lithium salt, the electrolyte has better wettability with the electrode sheet, the diffusion capacity of lithium ions is improved, and therefore, the lithium ion battery has better cycle performance and high-temperature resistance.

[0038] The application will be further described in combination with examples. However, the application is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to different requirements of specific use, and the implementation conditions not mentioned are conventional conditions in the industry. The technical features involved in each embodiment of the application can be combined with each other as long as there is no conflict.

[0039] In the specific embodiments of the application, the raw materials used can be obtained by marketing. In the specific embodiments of the application, lithium iron phosphate batteries are taken as examples. The lithium iron phosphate battery has the characteristics of high cycle life, good safety and low price, and therefore, lithium iron phosphate is one of the most commonly used positive electrode materials of power batteries.

[0040] Preparation of the non-aqueous electrolyte:

[0041] In an argon-filled glove box (H2O content <10 ppm), one or both of dimethyl carbonate (DMC) and diethyl carbonate (DEC), vinylene carbonate (EC) and methyl ethyl carbonate (EMC) are mixed uniformly in different mass ratios, a certain proportion of lithium difluoro oxalate borate (LiODFB) and lithium hexafluorophosphate (LiPF6) are added to the mixed solution to prepare an electrolyte, and different contents of various additives are added to the electrolyte as comparative examples or examples.

[0042] Preparation of lithium ion battery:

[0043] Positive electrode: 95wt% of active material lithium iron phosphate, 3wt% of acetylene black as conductive material, 2wt% of polyvinylidene fluoride (PVDF) as binder material were mixed in N-methyl pyrrolidone solvent using a dispersion mixer to make slurry. After the slurry was uniformly coated on both sides of aluminum foil and dried, the positive electrode was made by pressing, and the compaction density of the positive electrode was 2.3 g / cm 3 .

[0044] Negative electrode: 95wt% of active material artificial graphite, 2wt% of conductive carbon black (SP) as conductive material, 3wt% of sodium carboxymethyl cellulose (CMC) as binder material were mixed using a dispersion mixer to make slurry. After the slurry was uniformly coated on both sides of copper foil and dried, the negative electrode was made by pressing, and the compaction density of the negative electrode was 1.6 g / cm 3 .

[0045] The above-mentioned positive electrode, negative electrode, and polyolefin separator were stacked in the order of positive electrode, separator, and negative electrode, and were coated with an aluminum film to obtain a battery element. After injecting an electrolyte, vacuum sealing was performed to make a non-aqueous electrolyte lithium ion battery.

[0046] Evaluation of non-aqueous electrolyte secondary battery:

[0047] Battery normal temperature test: The positive electrode used lithium iron phosphate, and the assembled battery was first subjected to formation. The formation conditions were: constant current charging to 3.7V at 0.1C, and finally constant voltage charging at 3.7V for 2h, standing for 10min, and then constant current discharging to 2.75V at 0.2C. Under the condition of normal temperature 25℃, constant current charging to 3.75V at 1C, and then constant voltage charging at 3.75V for 2h, standing for 10min, constant current discharging to 2.75V at 1C, and recording the first week discharge capacity as W1, standing for 10min. The cycle number was set to 2000 cycles, and the 2000th week discharge capacity was recorded as W 2000 . The 2000th week capacity retention rate = W 2000 / W1x100%.

[0048] Battery high temperature test: the assembled battery is first subjected to formation, and the formation conditions are as follows: constant current charging at 0.1C to 3.75V, finally constant voltage charging at 3.75V for 2h, standing for 10min, and then constant current discharging at 0.2C to 2.75V. The test conditions of the high temperature cycle performance of the lithium ion battery are as follows: under the condition of high temperature 45℃, constant current charging at 1C to 3.75V, constant voltage charging at 3.75V for 2h, standing for 10min, and then constant current discharging at 1C to 2.75V, and the first week discharge capacity is recorded as W1; the cycle number is set to 1000, and the 1000th week discharge capacity is recorded as W1000. 1000 The 1000th week capacity retention rate = W1000 / W1x100%. 1000

[0049] In each of the examples and the comparative examples, the formula of the nonaqueous electrolyte and the 2000th week capacity retention rate (%) at 25℃ and the 1000th week capacity retention rate (%) at 45℃ are shown in Table 1.

[0050] Table 1

[0051]

[0052] As can be seen from each of the examples and Comparative Examples 1-3, the additive in the electrolyte of the present application uses the complex of HTCN and VC, which can effectively improve the cycle performance and heat resistance of the lithium ion battery. Referring to Comparative Examples 8 and 9, it can be seen that the mass ratio of the additives HTCN and VC also affects the cycle performance and heat resistance of the lithium ion battery. The performance data in each example shows that adjusting the ratio of HTCN and VC can further improve the cycle performance and heat resistance of the lithium ion battery.

[0053] At the same time, referring to each of the examples and Comparative Examples 4-7, it can be seen that the formula of the organic solvent and the lithium salt used in the present application can produce a synergistic effect with the additive, further improving the cycle performance and heat resistance of the lithium ion battery. Among them, when the mass percentage of the lithium salt in the electrolyte is 12.5%, the cycle performance and heat resistance of the lithium ion battery prepared are best.

[0054] The above has described the present application in detail, which is intended to enable those skilled in the art to understand the content of the present application and 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 should be covered within the protection scope of the present application.​

Claims

1. A non-aqueous electrolyte, characterized in that, The non-aqueous electrolyte comprises lithium salt, organic solvent, and additives, wherein the additives include 1,3,6-hexanetrionitrile and vinylene carbonate, and the additives constitute 2.5% to 3.5% by mass in the non-aqueous electrolyte. The mass ratio of the 1,3,6-hexanetrionitrile to the vinylene carbonate is 1:4 to 19; The organic solvent includes cyclic carbonates and chain carbonates. The chain carbonates include symmetrical chain carbonates and asymmetrical chain carbonates. The cyclic carbonates have a mass percentage of 30% to 50% in the organic solvent. The mass ratio of the symmetrical chain carbonates to the asymmetrical chain carbonates is 1:2 to 6. The lithium salt includes lithium difluorooxalate borate and lithium hexafluorophosphate, wherein the mass ratio of lithium difluorooxalate borate to lithium hexafluorophosphate is 1:18 to 29.

2. The non-aqueous electrolyte as described in claim 1, characterized in that, The cyclic carbonates include one or more of ethylene carbonate and propylene carbonate.

3. The non-aqueous electrolyte as described in claim 1, characterized in that, The symmetrical chain carbonates include one or more of dimethyl carbonate and diethyl carbonate, and the asymmetrical chain carbonates include ethyl methyl carbonate.

4. The non-aqueous electrolyte as described in claim 1, characterized in that, The lithium salt has a mass percentage content of 5% to 20% in the non-aqueous electrolyte.

5. The non-aqueous electrolyte as described in claim 4, characterized in that, The lithium salt has a mass percentage content of 10% to 15% in the non-aqueous electrolyte.

6. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte as described in any one of claims 1 to 5.

7. The lithium-ion battery as described in claim 6, characterized in that, The active material in the positive electrode includes lithium iron phosphate.

8. The lithium-ion battery as described in claim 6, characterized in that, The active material in the negative electrode sheet includes graphite, and the compaction density of the negative electrode sheet is 1.45 to 1.60 g / cm 3 .

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