Application of trimethylsilane-containing cyclic amine compound in electrolyte

Abstract

According to the application of the trimethylsilane-containing cyclic amine compound in the electrolyte provided by the invention, the trimethylsilane-containing cyclic amine compound is added into the non-aqueous electrolyte of a lithium ion battery, and residual moisture and HF of the electrolyte are captured due to the fact that an N-Si bond is easily subjected to reaction breakage with H2O and HF, so that the moisture and acid content in the electrolyte is reduced, and the service life of the electrolyte is prolonged. And acidic substances generated in the battery circulation process are eliminated. Besides, the cyclic amine can form coordination with Lewis acid PF5 to stabilize an intermediate PF5 of a hydrolysis reaction of LiPF6, so that the hydrolysis reaction of LiPF6 in the electrolyte is inhibited, and the service life and the storage life of the electrolyte are prolonged. And finally, the trimethylsilane-containing cyclic amine molecules can be subjected to oxidation reaction on the surface of the positive electrode to form a passivation layer, so that the cycle life of the battery is prolonged, and meanwhile, the transition metal dissolution phenomenon of the positive electrode material in the cycle process is inhibited. While the moisture and acidity of the electrolyte are reduced, the cycle performance of the battery is improved, and the cycle life of the battery is prolonged.

Description

Technical Field

[0001] The invention provides application of a cyclic amine compound containing trimethylsilane in an electrolyte, belonging to the technical field of lithium battery electrolytes. Background Art

[0002] At present, there are many kinds of electrolyte additives for lithium-ion batteries, most of which have a single function. In addition, the electrolyte is easy to hydrolyze and deteriorate, which affects the storage, service life and performance.

[0003] The current booming development of the new energy vehicle industry has led to higher and higher requirements for its core component, lithium-ion power batteries. The pursuit of energy density and safety performance by lithium-ion batteries has led to a clear trend of high nickel content in lithium battery positive electrode materials. High nickel materials are sensitive to moisture and have higher surface activity, which poses a huge challenge to the performance of high-performance electrolytes. The corresponding high-performance electrolyte requires strict control of the moisture and acidity in the electrolyte. Usually, dehydration / acid additives are added in combination with various functional additives to reduce moisture and acidity while improving the cycle performance and safety performance of the electrolyte. At present, dehydration / acid additives are mainly amine compounds, but such additives have a single function and usually affect the cycle performance of the electrolyte, generating HF to damage the electrode; in addition, existing water and HF inhibitors usually reduce the moisture and acidity of the electrolyte while reducing the cycle performance of the battery. It needs to be used in conjunction with various functional additives, but various additives will also affect each other's performance, and also increase production costs. Summary of the invention

[0004] In view of the above technical problems, the technical solution adopted by the present invention is:

[0005] Application of cyclic amine compounds containing trimethylsilane in electrolyte, the structural formula of the cyclic amine compound containing trimethylsilane TMSPL is:

[0006]

[0007] By adding trimethylsilane-containing cyclic amine compounds as additives to the non-aqueous electrolyte of lithium-ion batteries, the N-Si bond is easily broken by reacting with H2O and HF to capture the residual water and HF in the electrolyte, thereby reducing the water and acid content in the electrolyte and eliminating the acidic substances generated during the battery cycle. In addition, the cyclic amine can form a coordination with the Lewis acid PF5 to stabilize the intermediate PF5 of the LiPF6 hydrolysis reaction, thereby inhibiting the hydrolysis reaction of LiPF6 in the electrolyte and extending the use and storage life of the electrolyte. Finally, the cyclic amine molecules containing trimethylsilane can also undergo an oxidation reaction on the surface of the positive electrode to form a passivation layer, thereby improving the cycle life of the battery and inhibiting the dissolution of transition metals in the positive electrode material during the cycle.

[0008] The present invention also provides an electrolyte, comprising a cyclic amine compound TMSPL of trimethylsilane. The electrolyte comprises 1.2M LiPF6 in EC / EMC, 3 / 7-4 / 6wt / wt; 0.2-1.2vol% TMSPL; positive and negative electrodes of the buckle: NMC811 or NMC622 / / Gr.

[0009] The present invention adds a trimethylsilane-containing cyclic amine compound as an additive in a certain proportion to a comparative electrolyte formula to reduce the water content and acidity of the electrolyte while improving the cycle performance of the battery. Among them, amine compounds are commonly used electrolyte dehydration / acid additives. By introducing trimethylsilane into amine molecules, the additive molecules can more easily capture residual water and acid in the electrolyte, inhibit the hydrolysis reaction of the electrolyte, and extend the use and storage life of the electrolyte. At the same time, during the cycle process, it can be oxidized to form a passivation film on the surface of the positive electrode, inhibiting the oxidative decomposition reaction of the electrolyte during the cycle process, thereby improving the cycle life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a photo of the hydrolysis experiment of the electrolyte of the embodiment;

[0011] Figure 2 The discharge capacity retention rate change of the embodiment of the power-off cycle;

[0012] Figure 3 The DC discharge resistance change of the embodiment during the power-on cycle;

[0013] Figure 4 It is the transition metal content of the negative electrode after the recycling cycle of the embodiment. DETAILED DESCRIPTION

[0014] The specific technical solution of the present invention is explained in conjunction with embodiments.

[0015] Comparative sample 1: electrolyte: 1.2M LiPF6 in EC / EMC (3 / 7wt / wt); positive and negative electrodes: NMC811 / / Gr;

[0016] Comparative sample 2: electrolyte: 1.2M LiPF6 in EC / EMC (4 / 6wt / wt); positive and negative electrodes: NMC622 / / Gr;

[0017] Example 1: Electrolyte: 1.2M LiPF6 in EC / EMC (3 / 7wt / wt) + 0.2vol% TMSPL; Positive and negative electrodes: NMC811 / / Gr;

[0018] Example 2: Electrolyte: 1.2M LiPF6 in EC / EMC (3 / 7wt / wt) + 1.2vol% TMSPL; Positive and negative electrodes: NMC811 / / Gr;

[0019] Example 3: Electrolyte: 1.2M LiPF6 in EC / EMC (3 / 7wt / wt) + 2.4vol% TMSPL; Positive and negative electrodes: NMC811 / / Gr;

[0020] Example 4: Electrolyte: 1.2M LiPF6 in EC / EMC (4 / 6wt / wt) + 1.2vol% TMSPL; positive and negative electrodes: NMC622 / / Gr.

[0021] 1. Hydrolysis experiment

[0022] In an argon atmosphere glove box, take 2 mL of the prepared electrolyte solution and add it to a 4 mL transparent glass sample bottle and transfer it to a fume hood. After adding 100 μL of deionized water to each sample bottle, seal the sample bottle and observe and take pictures regularly, such as Figure 1 .

[0023] In Comparative Example 1, due to the addition of water, the lithium hexafluorophosphate in the electrolyte is hydrolyzed to produce low-solubility lithium salts and highly corrosive hydrofluoric acid. The low-solubility lithium salts make the electrolyte turbid, while the highly corrosive hydrofluoric acid corrodes the glass sample bottle. The electrolyte of Example 1 remains in a clear liquid state after being placed for one month, and there is no obvious corrosion to the glass sample bottle, showing that TMSPL has good water removal and acid inhibition functions, indicating that the amine compound can combine with the hydrofluoric acid already present in the electrolyte to form ammonium fluoride salts, thereby achieving the purpose of removing free hydrofluoric acid. At the same time, its Lewis base characteristics enable it to stabilize lithium hexafluorophosphate, inhibit its hydrolysis, and extend the storage life of the electrolyte.

[0024] 2. Electrochemical test

[0025] Button electrochemical performance: The prepared lithium-ion battery electrolytes were added to button batteries with a positive electrode of ternary material (NMC811 or NMC622), a negative electrode of graphite (Gr), and a separator of Celgard2325. The rated capacity of the battery was about 2mAh, and the battery was tested for cycle performance. The battery was placed in a constant temperature incubator at 30°C, charged to 4.35V at a constant current and voltage of 0.1C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.1C, and cycled for 4 cycles. Starting from the 5th cycle, the battery was charged to 4.35V at a constant current and voltage of 0.5C, and discharged to 3.0V at a constant current of 0.5C, and cycled to 104 cycles. The discharge capacity of the 5th cycle was taken as the starting discharge capacity, and the capacity retention rate was calculated as follows.

[0026] The nth cycle capacity retention rate (%) = (nth cycle discharge specific capacity / 5th cycle discharge specific capacity) × 100%

[0027] like Figure 2 and Figure 3 It can be seen from Comparative Sample 1 and Examples 1-3 that adding an appropriate amount of TMSPL can improve the cycle performance of the battery, among which 1.2 vol% is the optimal ratio. It can be seen from Comparative Example 2 and Example 4 that TMSPL can be used in electrolyte systems (EC / EMC, 4 / 6) and positive electrode material systems (NMC622) with different ratios to also improve the cycle performance of the electrolyte, indicating the wide applicability of TMSPL. The increase in DC resistance during the power-on cycle is usually due to the oxidative decomposition of the electrolyte during the cycle. By recording the changes in the DC discharge resistance during the power-on cycle, it can be inferred that TMSPL can form an effective passivation film on the positive electrode surface during the formation process, which can inhibit the oxidative decomposition of the electrolyte during the cycle, thereby extending the cycle life of the battery.

[0028] 3. Transition metal dissolution test of negative electrode after recycling

[0029] The negative electrode materials after recycling are used for ICP-AES analysis, and it can be found that the negative electrode recycled from the battery using the electrolyte containing TMSPL has less transition metal content, such as Figure 4 , indicating that TMSPL can inhibit the dissolution of transition metals in the positive electrode material during the cycle process, proving that the use of additives can improve the cycle life of the battery.

Claims

1. The use of a cyclic amine compound containing trimethylsilane in an electrolyte, characterized in that: The trimethylsilane-containing cyclic amine compound TMSPL has the structural formula: By adding trimethylsilane-containing cyclic amine compounds as additives into the non-aqueous electrolyte of lithium-ion batteries, the N-Si bond reacts with H2O and HF to break, capturing the residual water and HF in the electrolyte, thereby reducing the water and acid content in the electrolyte and eliminating the acidic substances generated during the battery cycle; Cyclic amines can form coordination with Lewis acid PF5 to stabilize the intermediate PF5 of LiPF6 hydrolysis reaction, thereby inhibiting the hydrolysis reaction of LiPF6 in the electrolyte; cyclic amine molecules containing trimethylsilane undergo oxidation reaction on the positive electrode surface to form a passivation layer, thereby improving the cycle life of the battery and inhibiting the dissolution of transition metals in the positive electrode material during the cycle process.

2. An electrolyte, characterized in that: A cyclic amine compound TMSPL including trimethylsilane.

3. An electrolyte according to claim 2, characterized in that: The electrolyte includes 1.2M LiPF6 in EC / EMC, 3 / 7~4 / 6wt / wt; 0.2~1.2vol% TMSPL; positive and negative electrodes: NMC811 or NMC622 / / Gr.

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