Method for improving high-rate low-temperature cycle performance of ternary lithium battery by using N-trimethylsilyl diethylamine as electrolyte additive

Abstract

The invention provides a method for improving the high-rate and low-temperature cycle performance of a ternary nickel cobalt lithium manganate battery by using N-trimethylsilyl diethylamine as an electrolyte additive, belongs to the field of electrolyte additive application, and aims to improve the rapid charging performance and the cycle life of the battery under a low-temperature condition. According to the main scheme, 0.2-5 wt% of N-trimethylsilyl diethylamine is added into a substrate electrolyte of 1M LiPF6-EC / DEC to serve as an electrolyte additive, wherein the volume ratio of EC to DEC is 1: 1. After the N-trimethylsilyl diethylamine is added, the capacity retention ratio of the Li / nickel cobalt lithium manganate NCM811 half battery can still be kept at 65.32% after 300 cycles at the current density of 5C, which is improved by 23.70% compared with 41.62% of the traditional electrolyte system, and meanwhile, the cycling stability and the specific capacity of the whole battery (lithium titanate / nickel cobalt lithium manganate) can be remarkably improved. Therefore, the customized N-trimethylsilyl diethylamine additive can realize the quick charging performance at the ultralow temperature.

Description

Technical Field

[0001] The invention relates to the field of electrolyte additives, and in particular to a method for improving the high-rate and low-temperature cycle performance of a ternary nickel-cobalt-manganese-oxide lithium battery by using N-trimethylsilyl diethylamine as an electrolyte additive. Background Art

[0002] With the progress of science and technology and the rapid development of human society, the demand for energy is increasing day by day. Fossil energy such as coal, oil, and natural gas are gradually depleted and can no longer meet people's living needs. The development of new energy has become a major problem that people need to solve urgently. Compared with traditional fossil energy, new energy is not only renewable energy, but also has the excellent characteristics of green environmental protection and no pollution. However, new energy power generation technologies such as wind power and solar energy have great randomness and uncertainty, so the development of energy storage technology has become crucial. In addition, energy storage also plays an important role in regulating the power system, balancing loads, peak load regulation, frequency regulation, mitigating energy fluctuations, and improving power quality and reliability. At present, energy storage technology is favored by various countries and has become an indispensable part of today's society.

[0003] Lithium-ion batteries have attracted much attention in the field of energy storage because of their high energy density, long cycle life, low cost and good safety performance. In recent years, with the vigorous development of large-scale energy storage power stations, new energy vehicles and various electronic products, the demand for lithium-ion batteries in various fields has also increased day by day. In response to the current supply and demand relationship of lithium-ion batteries, developing lithium-ion batteries with better performance has become an important research task at present and an important strategic deployment of countries around the world. The application research of lithium-ion batteries has unlimited prospects and is of great significance.

[0004] The electrolyte used in lithium-ion batteries is an ionic conductor in which electrolyte lithium salt is dissolved in an organic solvent. Although there are many types of organic solvents and lithium salts, only a limited number can actually be used in lithium-ion batteries. In order to ensure the dissolution and ion conduction of lithium salts, the solvent is required to have a sufficiently large polarity. Generally, it contains polar groups such as vouchers (C=O), nitriles (C=N), sulfonyl groups (S=O> and ether bonds (-O-), but the current electrolyte system cannot meet people's needs for high-rate charging and discharging and low-temperature charging of lithium-ion batteries. Summary of the invention

[0005] In view of the current difficulties of existing lithium batteries, the present invention provides a new method for improving the high-rate and low-temperature cycle performance of ternary nickel-cobalt-manganese-oxide lithium batteries by using N-trimethylsilyldiethylamine (TMSDEA) as an electrolyte additive. The introduction of amine groups in the additive helps to capture free hydrogen fluoride and free water in the electrolyte, thereby improving the stability of the electrolyte and reducing the dissolution of transition ions on the positive electrode surface. At the same time, the acidic products formed help to inhibit many possible irreversible side reactions, thereby improving the increase in the internal resistance of the battery and improving its cycle stability and rate characteristics.

[0006] To achieve the above purpose, the present invention adopts the following technical means:

[0007] The invention provides an electrolyte containing N-trimethylsilyldiethylamine, comprising: adding 0.2-5wt% of N-trimethylsilyldiethylamine as an electrolyte additive to a base electrolyte, wherein the base electrolyte is 1MLiPF6-EC / DEC, wherein the volume ratio of EC to DEC is 1:1.

[0008] The present invention also provides a method for preparing an electrolyte containing N-trimethylsilyldiethylamine, comprising the following steps:

[0009] Step 1: First, in a glove box, under the condition that the oxygen content is less than 0.1 ppm and the water content is less than 0.1 ppm, a base electrolyte is prepared, wherein the electrolyte mainly consists of 1 M LiPF6 and a 1:1 EC / DEC mixed solvent;

[0010] The specific steps are to take equal volumes of EC and DEC and stir them magnetically until they are uniform and EC is completely dissolved. After stirring, let the EC / DEC solution stand to completely cool down. After cooling, add 1M LiPF6 in several times, and then continue to stir at a low speed of 100-1200rpm to make it uniform:

[0011] Step 2: On the basis of the prepared base electrolyte, 0.2-5wt% N-trimethylsilyldiethylamine is added dropwise to the base electrolyte, followed by magnetic stirring to make it uniform. After stirring, 1g of 4A molecular sieve and fresh metal lithium sheet are added thereto and allowed to stand to obtain an electrolyte with 0.2-5wt% N-trimethylsilyldiethylamine.

[0012] In the above scheme, after the stirring in step (1) is completed, the EC / DEC solution is allowed to stand for 3 hours to completely cool down, and the standing time in step (2) is 1 week.

[0013] In the above scheme, the magnetic stirring time is 10 h.

[0014] The invention provides a ternary lithium battery, wherein the battery assembly sequence is: a positive electrode shell, a nickel cobalt lithium manganese oxide positive electrode sheet, a PP diaphragm, an electrolyte solution with 0.2-5wt% of N-trimethylsilyl diethylamine added dropwise, a negative electrode sheet, and a negative electrode shell.

[0015] The present invention provides a method for improving the high-rate and low-temperature cycle performance of a ternary lithium battery by using N-trimethylsilyldiethylamine as an electrolyte additive. The method is characterized in that 0.2-5wt% of N-trimethylsilyldiethylamine is added to a base electrolyte as an electrolyte additive, and the base electrolyte is 1M LiPF6-EC / DEC, wherein the volume ratio of EC to DEC is 1:1.

[0016] The beneficial results of the present invention are:

[0017] (1) The invention effectively utilizes N-trimethylsilyldiethylamine as an electrolyte additive to improve the high-rate cycling performance of the ternary nickel-cobalt-manganese-oxide lithium battery system. Compared with the traditional electrolyte, the capacity retention rate after 300 cycles is increased by nearly 28.71%;

[0018] (2) The invention uses N-trimethylsilyl diethylamine as an electrolyte additive for low temperature (-

[0019] The cycling performance at 20°C and high rate (5C) is also obvious. Compared with traditional electrolytes, the capacity retention rate after 120 cycles is improved by nearly 36%.

[0020] (3) The electrolyte additive provided by the present invention can be directly applied to the Li-nickel cobalt manganese oxide NCM811 battery system. After adding N-trimethylsilyl diethylamine, the capacity retention rate of the Li / nickel cobalt manganese oxide NCM811 half-cell can still be maintained at 65.32% after 300 cycles at a current density of 5C, which is 23.70% higher than the 41.62% of the traditional electrolyte system. In addition, it has also been proven that N-trimethylsilyl diethylamine has good compatibility with lithium titanate negative electrodes. At the same time, N-trimethylsilyl diethylamine also has a good improvement effect in the full battery system (lithium titanate LTO / nickel cobalt manganese oxide NCM811), with a capacity retention rate of 69.46% after 300 cycles at a current density of 5C, which is 28.71% higher than the 40.75% of the traditional electrolyte system. Finally, the full battery performance of the added N-trimethylsilyl diethylamine and the traditional electrolyte system at a current density of 5C was tested at -20°C. It was found that the capacity retention rate after 120 cycles with the addition of N-trimethylsilyldiethylamine was 44%, while the retention rate of traditional electrolyte was only 8%. Therefore, the custom-designed N-trimethylsilyldiethylamine additive can achieve fast charging performance at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1Comparison of the cycle stability (5C, 300 cycles) of the Li / NCM811 half-cell tested in Example 1 in different electrolyte systems (conventional electrolyte, containing 0.5wt%, 1wt%, 2wt%, and 5wt% N-trimethylsilyldiethylamine, respectively).

[0022] Figure 2 The rate performance comparison of the Li / nickel cobalt manganese oxide NCM811 half-cell tested in Example 2 in a traditional electrolyte and an electrolyte containing 0.5 wt % N-trimethylsilyl diethylamine.

[0023] Figure 3 The cycling performance (5C, 300 cycles) of the lithium titanate LTO / nickel cobalt manganese oxide NCM811 full battery tested in Example 3 in a traditional electrolyte and an electrolyte containing 0.5 wt% N-trimethylsilyldiethylamine.

[0024] Figure 4 The cycling performance of the traditional electrolyte and the electrolyte containing 0.5 wt% N-trimethylsilyldiethylamine at -20°C and 5C tested in Example 4. Specific embodiments

[0025] Example 1

[0026] When studying the effect of TMSDEA, the cycling performance of NCM811 / Li half-cell was given priority. Therefore, the cycling performance at high rate (5C) was discussed in detail, and the optimal additive ratio was determined. Based on the base electrolyte, a discussion on the addition of TMSDEA in multiple proportions was conducted, including 0.5wt%, 1wt%, 2wt%, and 5wt%. At the beginning of the cycle, the capacities of Baseline, 0.5wt% TMSDEA, 1wt% TMSDEA, 2wt% TMSDEA, and 5wt% TMSDEA were 113.04mAh / g, 157.06mAh / g, 157.93mAh / g, 151.16mAh / g, and 161.616mAh / g, respectively. Therefore, it can be seen that the cycling performance of 5% TMSDEA addition is the best in the initial stage. After 150 cycles, the capacities were 70.36mAh / g, 116.00mAh / g, 114.89mAh / g, 126.09mAh / g, and 122.68mAh / g, respectively. After 300 cycles, the capacities were 47.05mAh / g, 68.37mAh / g, 83.93mAh / g, 98.74mAh / g, and 86.78mAh / g, respectively. Therefore, the capacity retention rates after 300 cycles were 41.62%, 43.53%, 53.14%, 65.32%, and 53.69%, respectively. Therefore, it can be seen that the performance of adding 2wt% TMSDEA is the best, while the performance of adding 1% and 5% is second, and after adding 0.5wt%, it is basically close to the performance without addition. Therefore, it can be concluded that when only 0.5wt% TMSDEA is added, due to the small amount of TMSDEA added, it cannot help the positive electrode form a stable and dense CEI protective film. With the increase of additive content, TMSDEA truly and effectively plays the role of regulating and protecting CEI, but with the excessive addition of TMSDEA (5wt%), it has a negative effect on CEI and forms a relatively thick CEI film.

[0027] Example 2

[0028] Next, the rate performance of the NCM811 / Li half-cell after adding baseline and 2wt% TMSDEA was compared. At a rate of 0.5C, the capacity of the baseline was 181.35mAh / g, while the capacity after adding 2wt% TMSDEA was 201.85mAh / g, which was 20.50mAh / g higher. As the current density continued to increase, at 1C, the capacity of 2wt% TMSDEA could still be maintained at 187.73mAh / g, while the baseline was only 165.56mAh / g. At high current densities of 2C, 5C, and 10C, the capacity of 2wt% TMSDEA was 28.79mAh / g, 27.52mAh / g, and 33.24mAh / g higher than the baseline, respectively. Therefore, it can be found that as the current density increases, the rate performance difference between the two systems becomes greater. After returning to the current density of 0.5C, 2wt% TMSDEA can still return to 188.69mAh / g after addition. Therefore, adding 2wt% TMSDEA has better electrochemical rate performance not only at low current density but also at high current density. Especially at the extreme high current density, it shows more advantageous capacity output.

[0029] Example 3

[0030] Based on the excellent compatibility of TMSDEA with LTO, the LTO / NCM811 full battery was assembled next to explore the effect of TMSDEA on the full battery. Cycled 300 times at a high current density of 5C. First, at the beginning of the cycle, the cycle capacity of the baseline was 144.43mAh / g, while the initial cycle capacity of 2wt% TMSDEA was 166.84mAh / g, which was 22.41mAh / g higher than the capacity of the baseline. After 300 cycles, the effect of TMSDEA addition gradually became prominent, with a capacity of 115.89mAh / g, and a capacity retention rate of 69.46% after 300 cycles at 5C. Compared with 0.5wt% TMSDEA, the capacity of the baseline is only 58.867mAh / g, and the capacity retention rate is 40.75%.

[0031] Example 4

[0032] To investigate whether TMSDEA molecules can improve the performance of full batteries (LTO / NCM811) at low temperatures (-

[0033] The cycling performance of the battery at 20℃ and fast charge / discharge rate (5C) was investigated. It was found that the capacity of baseline and TMSDEA were 39.20mAh / g and 49.71mAh / g respectively at the beginning of the cycle. After 120 cycles, the capacity retention rates of baseline and TMSDEA were 8% and 44% respectively.

Claims

1. An electrolyte containing N-trimethylsilyldiethylamine, characterized in that: include: 0.2-5wt% of N-trimethylsilyldiethylamine is added to the base electrolyte as an electrolyte additive, and the base electrolyte is 1M LiPF6-EC / DEC, wherein the volume ratio of EC to DEC is 1:

1.

2. The electrolyte containing N-trimethylsilyldiethylamine according to claim 1, characterized in that: include: 5 wt % of N-trimethylsilyldiethylamine was added as an electrolyte additive.

3. A method for preparing an electrolyte containing N-trimethylsilyldiethylamine as claimed in claim 1, characterized in that: The steps include: Step 1: First, in a glove box, under the condition that the oxygen content is less than 0.01 ppm and the water content is less than 0.01 ppm, a base electrolyte is prepared, wherein the electrolyte mainly consists of 1M LiPF6 and a 1:1 EC / DEC mixed solvent; The specific steps are to take equal volumes of EC and DEC and stir them magnetically until they are uniform and EC is completely dissolved. After stirring, let the EC / DEC solution stand to completely cool down. After cooling, add 1M LiPF6 in several times, and then continue to stir at a low speed of 100-1200rpm to make it uniform: Step 2: On the basis of the prepared base electrolyte, 0.2-5wt% N-trimethylsilyldiethylamine is added dropwise to the base electrolyte, followed by magnetic stirring to make it uniform. After stirring, 1g of 4A molecular sieve and fresh metal lithium sheet are added thereto and allowed to stand to obtain an electrolyte with 0.2-5wt% N-trimethylsilyldiethylamine.

4. The method for preparing an electrolyte containing N-trimethylsilyldiethylamine according to claim 3, characterized in that: After the stirring in step (1) is completed, the EC / DEC solution is allowed to stand for 3 hours to allow it to cool completely. The standing time in step (2) is 1 week.

5. The method for preparing an electrolyte containing tris(trimethylsilyl)phosphate according to claim 3, characterized in that: The magnetic stirring time is 1-10h.

6. A ternary lithium battery, characterized in that: The battery assembly sequence is: positive electrode shell, positive electrode sheet, PP diaphragm, electrolyte with 0.2-5wt% N-trimethylsilyldiethylamine added, PP diaphragm, lithium sheet, negative electrode shell.

7. A ternary lithium battery according to claim 6, characterized in that: The electrolyte drop amount of 0.2-5wt% N-trimethylsilyldiethylamine electrolyte is 20-350ul.

8. A method for improving the high-rate and low-temperature cycle performance of a ternary lithium battery by using N-trimethylsilyl diethylamine as an electrolyte additive, characterized in that: 0.2-5wt% of N-trimethylsilyldiethylamine is added to the base electrolyte as an electrolyte additive, and the base electrolyte is 1M LiPF6-EC / DEC, wherein the volume ratio of EC to DEC is 1:1.

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