A non-aqueous electrolyte, its application and lithium ion battery

Abstract

The present invention relates to the technical field of batteries, and specifically to a non-aqueous electrolyte, its application and a lithium ion battery, a non-aqueous electrolyte, comprising a lithium salt, an organic solvent and an additive, wherein the additive comprises at least tetravinylsilane and glycerol trinitrile, and the lithium salt is selected from at least one of an organic lithium salt or an inorganic lithium salt. In the non-aqueous electrolyte of the present invention, the electrolyte can improve the high-temperature storage performance of the battery and reduce the high-temperature flatulence of the battery. At the same time, because it can increase the number of lithium ion migrations, the electrolyte has good low-temperature performance. The film-forming stability is enhanced, and the thermal stability, low-temperature discharge efficiency and safety performance of the battery can be improved. The lithium ion battery of the present invention has better high-temperature storage performance, cycle performance and low-temperature charge and discharge performance through the following effects of tetravinylsilane and glycerol trinitrile in the electrolyte.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a non-aqueous electrolyte, its application and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in 3C digital, power tools, aerospace, energy storage, power vehicles and other fields due to their advantages such as high operating voltage, high volume density, long cycle life, light weight, customizable shape and good safety factor. With the rapid development of electronic equipment, the performance requirements for batteries are getting higher and higher. Although the current battery technology has made breakthroughs in energy density, charge and discharge rate, etc., there is still room for improvement in battery life, safety and high and low temperature performance. Lithium-ion batteries have performance deterioration problems under high temperature conditions. Decomposition of electrolyte at high temperature. The electrolyte of lithium batteries is usually composed of lithium salts and organic solvents. During the charge and discharge process, the electrolyte will undergo chemical reactions to produce gas. Especially in the case of high temperature or overcharge, the decomposition reaction of the electrolyte is more intense and a large amount of gas will be produced. Electrode corrosion. The positive electrode of lithium-ion batteries is composed of lithium compounds. During the charge and discharge process, oxidation reactions will occur at the positive electrode, and some of these reactions may produce gas. Especially in the case of overcharge or overdischarge, the chemical reaction on the electrode will intensify, resulting in more gas production.

[0003] The electrolyte is a key component of the battery, and its performance has an important impact on the performance of the battery. However, existing electrolytes often have some problems, such as unstable high-temperature performance, low cycle efficiency, and low low-temperature discharge efficiency. Therefore, finding new electrolyte additives to improve the high and low temperature, cycle performance and safety of the battery is an important direction for the development of current battery technology. Summary of the invention

[0004] One of the purposes of the present invention is to provide a non-aqueous electrolyte. The glycerol trinitrile compound can help the positive electrode film formation under the condition of a small addition amount, which is beneficial to high-temperature storage and reduces high-temperature flatulence. The addition of tetravinylsilane (TVSi) can effectively improve the low-temperature discharge performance and has a good combined effect in high-voltage electrolytes.

[0005] A second object of the present invention is to provide an application of a non-aqueous electrolyte.

[0006] The third object of the present invention is to provide a lithium-ion battery with good high-temperature storage performance, reduce high-temperature expansion of the battery, and make the electrolyte have good low-temperature performance.

[0007] The solution adopted by the present invention to achieve one of the purposes is: a non-aqueous electrolyte, including a lithium salt, an organic solvent and an additive, the additive at least includes tetravinylsilane and glycerol trinitrile, and the lithium salt is selected from at least one of an organic lithium salt or an inorganic lithium salt.

[0008] Preferably, the content of tetravinylsilane accounts for 0.5% to 5% of the total weight of the non-aqueous electrolyte, and the content of glycerol trinitrile accounts for 0.5% to 5% of the total weight of the non-aqueous electrolyte.

[0009] Preferably, the weight ratio of tetravinylsilane to glycerol trinitrile is 1:1.

[0010] Preferably, the lithium salt is selected from at least one of an organic lithium salt or an inorganic lithium salt, and the concentration of the lithium salt in the non-aqueous electrolyte is 0.5M to 1.5M.

[0011] Preferably, the lithium salt is selected from at least one of compounds containing fluorine and lithium.

[0012] Preferably, the lithium salt is selected from at least one of hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, lithium dichlorooxalatoborate, and lithium bis(trifluoromethylsulfonyl)imide.

[0013] Preferably, the organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate and tetrahydrofuran.

[0014] The solution adopted by the present invention to achieve the second purpose is: an application of the non-aqueous electrolyte, applying the non-aqueous electrolyte to a battery system of 4.5V and above.

[0015] The solution adopted by the present invention to achieve the third purpose is: a lithium ion battery, the lithium ion battery includes the non-aqueous electrolyte.

[0016] Preferably, it also includes a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material and a separator, wherein the positive electrode active material is a lithium cobalt oxide material, and the negative electrode active material is graphite.

[0017] The structural formula of tetravinylsilane is as follows:

[0018]

[0019] The structural formula of glycerol trinitrile is as follows:

[0020]

[0021] The glycerol trinitrile compound of the present invention can help positive electrode film formation under the condition of a very small addition amount (0.5wt% to 5wt%), which is beneficial to high-temperature storage and reduces high-temperature flatulence. It improves high-temperature capacity retention and high-temperature cycling. The disadvantage is that it will increase film formation impedance and affect low-temperature discharge performance. Adding TVSi can effectively improve low-temperature discharge performance and has a good combined effect in high-voltage electrolytes.

[0022] Tetravinylsilane (TVSi) additives and glycerol trinitrile additives are used in new electrolytes for battery systems with voltages of 4.5V and above, which improve the high-temperature storage performance of the battery and reduce the high-temperature flatulence of the battery. At the same time, because they can increase the number of lithium ion migration, the electrolyte also has good low-temperature performance. The film formation stability is enhanced, which can improve the thermal stability and safety performance of the battery.

[0023] The present invention has the following advantages and beneficial effects:

[0024] In the non-aqueous electrolyte of the present invention, the electrolyte can improve the high-temperature storage performance of the battery, reduce the high-temperature flatulence of the battery, and at the same time, because it can increase the number of lithium ion migration, the electrolyte also has good low-temperature performance. The film formation stability is enhanced, and the thermal stability, low-temperature discharge efficiency and safety performance of the battery can be improved.

[0025] The lithium ion battery of the present invention has excellent high-temperature storage performance, cycle performance and low-temperature charge and discharge performance through the following effects of tetravinylsilane and glycerol trinitrile in the electrolyte. DETAILED DESCRIPTION

[0026] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0027] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0028] The non-aqueous electrolyte of the present invention comprises a lithium salt, an organic solvent and an additive, wherein the additive comprises at least tetravinylsilane and glycerol trinitrile, and the lithium salt is selected from at least one of an organic lithium salt and an inorganic lithium salt.

[0029] The content of tetraethylene silane accounts for 0.5% to 5% of the total weight of the non-aqueous electrolyte, and the content of glycerol trinitrile accounts for 0.5% to 5% of the total weight of the non-aqueous electrolyte.

[0030] The lithium salt is selected from at least one of hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, lithium dichlorooxalatoborate, and lithium bis(trifluoromethylsulfonyl)imide.

[0031] The organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0032] The specific organic solvent generally used is a mixed organic solvent in a mass ratio of EC / EMC / PC=1 / 1 / 1.

[0033] Comparative Examples 1-7 and Examples 1-5

[0034] According to the raw material ratios in the table, electrolytes L1#-L7# were prepared from comparative examples 1-7, and electrolytes L8#-L12# were prepared from examples 1-5.

[0035] The preparation steps of the electrolyte are as follows: EC / EMC / PC=1 / 1 / 1 mass ratio is mixed as an organic solvent. Add additives (as shown in Table 1) to the organic solvent, mix well, and then add LiPF6 to obtain a mixed solution with a LiPF6 concentration of 1.12 mol / L, which is the electrolyte L1#-L10#. Change the type and (or) ratio of raw materials in the electrolyte. The relationship between the number of the obtained electrolyte sample and the composition of the electrolyte is shown in Table 1. EC is ethylene carbonate, PC is propylene carbonate, EMC is ethyl methyl carbonate, FEC is fluoroethylene carbonate, and DTD is vinyl sulfate.

[0036] Table 1 Proportions of raw materials of electrolytes of Examples 1-5 and Comparative Examples 1-7

[0037]

[0038] Example 6

[0039] Preparation of positive electrode:

[0040] The positive electrode active material lithium cobalt oxide material LCO, conductive carbon black SP, and binder polyvinylidene fluoride are fully stirred and mixed in N-methylpyrrolidone solvent at a weight ratio of 97:1.4:1.6 to form a uniform positive electrode slurry. The slurry is coated on the positive electrode current collector Al foil, dried, and cold pressed to obtain a positive electrode sheet.

[0041] Preparation of negative electrode:

[0042] The negative electrode active material graphite, the binder styrene butadiene rubber, and the thickener carboxymethyl cellulose lithium are fully stirred and mixed in a proper amount of deionized water solvent at a mass ratio of 97.7:1.3:1.0 to form a uniform negative electrode slurry. The slurry is coated on the negative electrode current collector Cu foil, dried, and cold pressed to obtain a negative electrode sheet.

[0043] Preparation of electrolyte:

[0044] Electrolytes L1# to L12# were obtained according to the methods of Comparative Examples 1-7 and Examples 1-5.

[0045] The isolation membrane is prepared by using a 5 μm thick polyethylene isolation membrane (provided by Asahi Kasei Corporation) coated with a 3 μm thick alumina ceramic.

[0046] Preparation of secondary batteries:

[0047] The positive electrode sheet, separator and negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrodes to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging bag, and the electrolytes L1#-L12# in Table 1 are respectively injected into the dried battery. After vacuum packaging, standing, formation, shaping and other processes, the preparation of lithium-ion batteries is completed, and batteries C1~C12 are obtained in turn.

[0048] Example 7

[0049] High temperature cycle test of batteries:

[0050] Test method: Place the battery in an environment of 45±2℃, and perform standard charge and discharge cycles, with a cycle rate of 1C and a charging voltage of 3.0-4.5V, to calculate the capacity retention rate of the battery after the cycle. The calculation formula is as follows:

[0051] The nth cycle capacity retention rate (%) = (nth cycle discharge capacity) / (first cycle discharge capacity)*100%.

[0052] Low temperature test of battery:

[0053] Test method: Fully charge the divided battery cells at room temperature, place the fully charged battery in a 0 degree environment for 4 hours, then discharge it at 0.2C discharge capacity to 3.0V, and record the capacity before and after low temperature discharge.

[0054] The battery test results are shown in Table 2:

[0055] Table 2 Battery Tests Prepared by Electrolytes of Comparative Examples 1-7 and Examples 1-5

[0056] Electrolyte No. High temperature 500-week capacity retention rate / % Low temperature discharge capacity retention rate Comparative Example 1L1# 65.12％ 68.26％ Comparative Example 2L2# 72.53％ 75.48％ Comparative Example 3L3# 73.96％ 74.33％ Comparative Example 4L4# 80.76％ 66.51％ Comparative Example 5L5# 71.16％ 83.11％ Comparative Example 6L6# 75.22％ 78.43％ Comparative Example 7L7# 68.25％ 64.58％ Example 1L8# 86.95％ 88.36％ Example 2L9# 84.33％ 84.83％ Example 3L10# 86.79％ 85.51％ Example 4L11# 73.44％ 78.93％ Example 5L12# 75.36％ 73.47％

[0057] From the data in Table 2, it can be seen that by comparing the high-temperature cycle performance and low-temperature performance of the battery prepared with L1#~L12# as the electrolyte, it can be seen that DTD and glycerol trinitrile can improve the high-temperature performance, among which glycerol trinitrile has the best improvement effect, but the addition of glycerol trinitrile has a greater negative impact on the low-temperature discharge performance; FEC and TVSI can improve the low-temperature effect, but the high-temperature performance is poor. By comparing L4# / L5# and L8#~L12#, it can be seen that the combination of glycerol trinitrile and tetravinylsilane has the most balanced high and low temperature performance, which can ensure the cycle efficiency at high temperature while taking into account good low-temperature performance. By comparing L8#~L12#, it can be seen that when the weight ratio of glycerol trinitrile and tetravinylsilane is 1:1, the combined effect is the best, and with the increase in the amount of glycerol trinitrile and tetravinylsilane, the low-temperature discharge and high-temperature cycle performance are not further improved. Considering comprehensively, the optimal addition amount is 0.5%.

[0058] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that: It comprises a lithium salt, an organic solvent and an additive, wherein the additive comprises at least tetravinylsilane and glycerol trinitrile; the content of tetravinylsilane accounts for 0.5% of the total weight of the non-aqueous electrolyte, the content of glycerol trinitrile accounts for 0.5% of the total weight of the non-aqueous electrolyte, and the weight ratio of tetravinylsilane to glycerol trinitrile is 1:1; the lithium salt is LiPF6, the concentration of lithium salt in the non-aqueous electrolyte is 0.5-1.5M, and the organic solvent is an organic solvent mixed with EC, EMC and PC in a mass ratio of 1:1:1; the non-aqueous electrolyte is applied to a battery system with a voltage of 4.5V or above.

2. A lithium ion battery, characterized in that: The lithium ion battery comprises the nonaqueous electrolyte according to claim 1.

3. The lithium-ion battery according to claim 2, characterized in that: It also includes a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, and a separator, wherein the positive electrode active material is a lithium cobalt oxide material, and the negative electrode active material is graphite.

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