Electrolyte additive, electrolyte, lithium ion battery and preparation method and application of lithium ion battery

Abstract

The invention relates to an electrolyte additive, an electrolyte, a lithium ion battery as well as a preparation method and application of the electrolyte additive, belongs to the technical field of lithium ion batteries, and solves the problem that the lithium ion battery with an existing additive cannot have good long cycle performance, flame retardant property and low-temperature effect at the same time. The electrolyte additive disclosed by the invention has a structure as shown in a formula I: # imgabs0 #. The electrolyte additive disclosed by the invention is applied to the field of lithium ion batteries, and the lithium ion battery with good long cycle performance, flame retardant property and low-temperature effect can be obtained at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte additive, an electrolyte, a lithium ion battery, and a preparation method and application thereof. Background Art

[0002] Safe and durable batteries have recently attracted increasing attention for their widespread use in electric vehicles and large-scale power grids. However, battery safety issues caused by dendrite growth, limited operating temperature range, and the risk of thermal runaway (TR) have limited their further development and wider adoption. These issues, in turn, depend on internal battery processes, for which the development of novel chemistries is crucial. A major concern with electrolytes is their side reactions with metal anodes, such as irreversible anode cycling, solid electrolyte interface (SEI) fracture, and metal dendrite formation. Inorganic-based SEIs can optimize electrochemical properties, such as cycling performance, and the introduction of large amounts of elemental fluorine into the electrolyte can significantly enhance battery performance. However, most hydrofluorocarbons (HFCs) have high global warming potentials (GWPs) and ozone depletion potentials (ODPs), which are incompatible with the sustainable development of the battery industry. Therefore, the development of clean fluorine sources is essential.

[0003] For safety reasons, phosphate solvents are used because of their non-flammability. However, they cannot form a stable SEI on the surface of graphite or metal anodes and can only cycle stably when the salt concentration is high. High-concentration electrolytes inevitably increase cost, viscosity and reduce electrode wettability. Recently, it has been proposed to use inert anti-solvents to dilute concentrated electrolytes and form locally concentrated electrolytes (LCEs) to reduce viscosity and solve the above problems to achieve better performance. Through this strategy, LCEs achieve high coulombic efficiency (CE) and better capacity retention, but at the cost of low conductivity (<3mS·cm -1 ). Due to the huge difference in ion solubility between polar solvents and inert diluents, the introduction of diluents may bring new problems such as salting out and phase separation. In addition, for various non-flammable diluents, their low boiling points also hinder their operation at higher temperatures. At the same time, commercial electrolytes based on ethylene carbonate (EC) can only operate in the temperature range of -20 to 50°C. Considering these factors, designing electrolytes with inherently safe physical properties, beneficial SEI chemistry, environmental friendliness and temperature sustainability seems insurmountable. Summary of the Invention

[0004] In view of the above analysis, the present invention aims to provide an electrolyte additive, an electrolyte, a lithium-ion battery, and a preparation method and application thereof, so as to solve the problem that lithium-ion batteries using existing additives cannot achieve good long cycle performance, flame retardant performance and low temperature effect at the same time.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides an electrolyte additive having a structure shown in Formula I:

[0007]

[0008] Wherein R1 is one of the following groups:

[0009]

[0010] Where · is the connection site with the main body.

[0011] In a second aspect, the present invention provides a method for preparing an electrolyte additive, comprising the following steps:

[0012] Step 1: Weigh the reaction raw materials and solvent and place them in a reaction vessel;

[0013] Step 2: heating under inert gas protection, reacting, and post-processing to obtain an electrolyte additive;

[0014] In step 1, the reaction raw materials include tris(trifluoromethylsilyl)phosphate and a reaction monomer, and the reaction monomer includes one of imidazole, diethylamine, dipropylamine and propargyl alcohol.

[0015] Optionally, in step 2, the heating temperature is 45-55° C. and the reaction time is 6-30 h.

[0016] Optionally, the molar ratio of tris(trifluoromethylsilyl)phosphate to the reactive monomer is 1:2.2-2.5.

[0017] In a third aspect, the present invention provides an application of the above-mentioned electrolyte additive or the above-mentioned preparation method in the field of lithium-ion batteries.

[0018] In a fourth aspect, the present invention provides a lithium-ion battery electrolyte comprising a lithium salt, an organic solvent and the above-mentioned electrolyte additive.

[0019] Optionally, the concentration of the lithium salt in the electrolyte is 0.5-2.2M.

[0020] Optionally, the organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl fluorocarbonate, dipropyl carbonate, ethyl methyl carbonate, butyl acetate, methyl propionate, methyl butyrate, ethyl acetate, dimethyl ether and ethyl butyrate.

[0021] In a fifth aspect, the present invention provides a method for preparing a lithium-ion battery electrolyte, comprising the following steps:

[0022] Step i: mixing organic solvents in proportion to obtain a mixed organic solvent;

[0023] Step ii: dissolving the lithium salt in the mixed organic solvent, then adding the electrolyte additive to the mixed organic solvent, completely dissolving and mixing uniformly to obtain a lithium-ion battery electrolyte.

[0024] In a sixth aspect, the present invention provides a method for preparing a lithium ion battery, comprising the following steps:

[0025] (a) preparing an electrolyte by the above-mentioned preparation method;

[0026] (b) Cell preparation;

[0027] (c) Battery cell packaging.

[0028] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0029] (1) The additive of the present invention can change the substituent structure of silicon. On the one hand, it can make the electrolyte more easily oxidatively decompose on the positive electrode surface, thereby forming a positive electrode interface film containing Si-O on the positive electrode surface, thereby effectively improving the cycle stability of the battery. On the other hand, the fluorine element can enhance the strength of the SEI film, effectively improve lithium dendrites, and have excellent flame retardant properties. In addition, the increase in SEI film strength can effectively prevent the co-intercalation of solvent molecules from damaging the electrode, thereby improving the cycle efficiency and reversible capacity of the battery.

[0030] (2) The present invention uses Si-F bonds instead of CF bonds and introduces some highly polar groups to improve the solvent's solvating capacity, thereby increasing the solvent's ion clustering and conductivity, thereby improving the electrochemical properties of the electrolyte, such as conductivity. Specifically, without the addition of the additive, the electrolyte's conductivity was 8.6 mS / cm. After adding the additive of the present invention, the electrolyte's conductivity was 9.5 mS / cm, an increase of 10.5%. The increase in electrolyte conductivity can improve the low-temperature performance of the battery.

[0031] (3) The lithium-ion batteries to which the additive of the present invention is added have good long-cycle performance (the capacity retention rate of the lithium-ion batteries after 800 cycles is above 95%), flame retardancy (there is no open flame or smoke in the batteries during the needle puncture test) and low-temperature effect (the capacity retention rate at -30°C is 48%-52%, and the capacity retention rate at -40°C is 24%-27%).

[0032] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages may become obvious from the description or be understood through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0034] Figure 1 The compound FSPN-1 prepared in Preparation Example 1 1 H-NMR spectrum;

[0035] Figure 2 The capacity retention rate of the lithium-ion battery of the embodiment and the comparative example at 25°C FC / 1C cycle;

[0036] Figure 3 This is a diagram of a needle penetrating the lithium-ion battery prepared in Example 1 of the present invention during a needle penetration test;

[0037] Figure 4 This is a picture of the lithium-ion battery prepared in Example 1 of the present invention being pulled out by a needle during a needle penetration test;

[0038] Figure 5 This is a diagram of a needle penetrating the lithium-ion battery prepared in Example 2 of the present invention during a needle penetration test;

[0039] Figure 6 This is a picture of the lithium-ion battery prepared in Example 2 of the present invention being pulled out by a needle during a needle penetration test;

[0040] Figure 7 This is a diagram of a needle penetrating the lithium-ion battery prepared in Comparative Example 1 in a needle penetration test;

[0041] Figure 8 This is a picture of the lithium-ion battery prepared in Comparative Example 1 catching fire and exploding in the needle penetration test;

[0042] Figure 9 This is a diagram of a needle penetrating the lithium-ion battery prepared in Comparative Example 2 in a needle penetration test;

[0043] Figure 10 This is a picture of the lithium-ion battery prepared in Comparative Example 2 catching fire and exploding in the needle penetration test;

[0044] Figure 11 The figures are the low temperature performance test results of the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0045] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0046] In a first aspect, the present invention provides an electrolyte additive for lithium-ion batteries, which has a structure shown in Formula I:

[0047]

[0048] Wherein R1 is one of the following groups:

[0049]

[0050] Where · is the connection site with the main body.

[0051] Specifically, the electrolyte additive of the present invention is one of the following FSPN1-4 structures:

[0052]

[0053] In a second aspect, the present invention provides a method for preparing an electrolyte additive, which is used to prepare the above-mentioned electrolyte additive, comprising the following steps:

[0054] Step 1: Weigh the reaction raw materials and solvent and place them in a reaction vessel;

[0055] Step 2: Under nitrogen protection, heat to a certain temperature, react, and post-treat to obtain an electrolyte additive.

[0056] Specifically, in step 1, the reaction raw materials include tris(trifluoromethylsilane) phosphate and a reaction monomer (e.g., imidazole, diethylamine, dipropylamine, propargyl alcohol), and the molar (mol) mass (g) ratio of tris(trifluoromethylsilane) phosphate to the solvent is 0.1:(100-150), for example, 0.1:100, 0.1:110, 0.1:120, 0.1:130, 0.1:140, 0.1:150.

[0057] When the prepared compound is FSPN-1, the reaction raw materials are tris(trifluoromethylsilyl)phosphate and imidazole, and the molar ratio of the two is 1:2.2-2.5, for example, 1:2.2, 1:2.3, 1:2.4, 1:2.5. The reaction equation is as follows:

[0058]

[0059] When the prepared compound is FSPN-2, the reaction raw materials are tris(trifluoromethylsilyl)phosphate and diethylamine, and the molar ratio of the two is 1:2.2-2.5, for example, 1:2.2, 1:2.3, 1:2.4, 1:2.5. The reaction equation is as follows:

[0060]

[0061] When the prepared compound is FSPN-3, the reaction raw materials are tris(trifluoromethylsilyl)phosphate and dipropylamine, and the molar ratio of the two is 1:2.2-2.5, for example, 1:2.2, 1:2.3, 1:2.4, 1:2.5. The reaction equation is as follows:

[0062]

[0063] When the compound prepared is FSPN-4, the reaction raw materials are tris(trifluoromethylsilyl)phosphate and propargyl alcohol, and the molar ratio of the two is 1:2.2-2.5, for example, 1:2.2, 1:2.3, 1:2.4, 1:2.5. The reaction equation is as follows:

[0064]

[0065] Specifically, in step 2, the heating temperature is 45-55°C, for example, 45°C, 47°C, 49°C, 50°C, 52°C, 55°C.

[0066] The reaction time is 6-30h, for example, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h. Specifically, when the prepared compound is FSPN-1, the reaction time is 10-24 h, for example, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h; when the prepared compound is FSPN-2, the reaction time is 6-8 h, for example, 6 h, 6.5 h, 7 h, 7.5 h, 8 h; when the prepared compound is FSPN-3, the reaction time is 18-24 h, for example, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h; when the prepared compound is FSPN-4, the reaction time is 20-30 h, for example, 20 h, 22 h, 24 h, 26 h, 28 h, 30 h.

[0067] In addition, in step 1, a strong organic base is also added to remove the proton H on the reaction monomer. Exemplarily, the strong organic base can be sodium ethoxide, and the sodium ethoxide must be in excess. Specifically, the mass ratio of sodium ethoxide to the reaction monomer is 1:3-5, for example, 1:3, 1:3.5, 1:4, 1:4.5, 1:5. If the sodium ethoxide is not in excess, the reaction between tris(trifluoromethylsilyl)phosphate and the reaction monomer will be incomplete, affecting the overall performance of the battery.

[0068] In step 1, the solvent is an organic solvent, for example, at least one of dichloroethane, dichloromethane, chloroform, and carbon tetrachloride.

[0069] Specifically, in step 2, the post-treatment includes filtration and decompression of the filtrate to remove the solvent.

[0070] Thirdly, the present invention provides an application of the above electrolyte additive in the field of lithium-ion batteries.

[0071] In a fourth aspect, the present invention further provides a lithium-ion battery electrolyte comprising a lithium salt, an organic solvent and the above-mentioned electrolyte additive.

[0072] Specifically, the lithium salt is at least one of LiPF6, LiTFSI, and LiFSI. The concentration of the lithium salt in the electrolyte is 0.5 to 2.2 M, for example, 0.5 M, 0.7 M, 0.9 M, 1 M, 1.2 M, 1.5 M, 1.8 M, 2 M, or 2.2 M.

[0073] The organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, fluoromethyl ethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, butyl acetate, methyl propionate, methyl butyrate, ethyl acetate, dimethyl ether and ethyl butyrate, and is preferably at least two of ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, dimethyl ether and butyl acetate. Preferably, the organic solvent is a mixed organic solvent, including ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), and the mass ratio of the three is: (1-5): (5-10): (0.5-2), for example, 1:5:0.5, 2:8:1.5, 3:10:1, 4:9:2, 5:10:1.

[0074] Solvation capacity is a measure of solvent effectiveness. The low polarity of the C-F bond in existing fluorinated solvents generally makes them useful as weak solvents. However, their insufficient solvation leads to poor electrolyte compatibility, ion clustering, and low conductivity, which in turn affects the electrochemical performance of the electrolyte.

[0075] As a preferred technical solution of the present invention, in the electrolyte, the mass fraction of ethylene carbonate (EC) is 20-30%, the mass fraction of ethyl methyl carbonate (EMC) is 20-30%, and the mass fraction of dimethyl carbonate (DMC) is 40-60%, wherein the mass fraction of ethylene carbonate can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%, etc., the mass fraction of ethyl methyl carbonate can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%, etc., and the mass fraction of dimethyl carbonate can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58% or 60%, etc., including but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0076] Moreover, in the electrolyte, the mass ratio of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) is (1-5):(5-10):(0.5-2), for example, 1:5:0.5, 2:8:1.5, 3:10:1, 4:9:2, 5:10:1.

[0077] Specifically, the electrolyte additive accounts for 0.5% to 2% of the total mass of the electrolyte, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2%.

[0078] The above-mentioned lithium-ion battery electrolyte is prepared by the following method:

[0079] Step i: In an argon glove box with a water content of <1 ppm, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed in a certain proportion to obtain a mixed organic solvent;

[0080] Step ii: dissolving the lithium salt in the above-mentioned mixed organic solvent, then adding the electrolyte additive into the mixed organic solvent, completely dissolving it, and mixing it evenly to obtain a lithium-ion battery electrolyte.

[0081] Specifically, in step i, EC needs to be preheated and melted at a temperature of 40-50° C. (eg, 40° C., 45° C., 50° C.).

[0082] In a fifth aspect, the present invention further provides a method for preparing a lithium ion battery, comprising the following steps:

[0083] (a) Electrolyte preparation

[0084] The electrolyte was prepared by the above method.

[0085] (b) Cell preparation

[0086] The battery cell adopts the standard process of Xinyuan Intelligent Storage (number XY)

[0087] (c) Cell packaging

[0088] Liquid injection and primary packaging are carried out in an argon glove box, and the volume is divided after standing for a period of time (24-36 hours, for example, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 36 hours). Secondary packaging is carried out after aging for a period of time (20-24 hours, for example, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours). The secondary packaging machine used is Shenzhen Kejing Vacuum Secondary Packaging Machine.

[0089] The electrolyte additive and preparation method thereof of the present invention are described in detail below with reference to specific preparation examples and embodiments.

[0090] Unless otherwise specified, the reagents, materials, and instruments used in the preparation examples, embodiments, and comparative examples of the present invention are conventional reagents, materials, and instruments and can be purchased. The reagents involved can also be purchased and synthesized by conventional synthesis methods.

[0091] The raw materials used, tris(trifluoromethylsilyl) phosphate and imidazole, were purchased from Anaiji Chemical.

[0092] Preparation Example 1-1 (Preparation of Compound FSPN-1)

[0093] 35 g (0.1 mol) of tris(trifluoromethylsilyl) phosphate, 22.4 g (0.33 mol) of pyrazole, 10.0 g of sodium ethoxide, and 150.0 g of dichloroethane were weighed in sequence into a 500 mL three-necked flask. Under nitrogen protection, the mixture was heated at 45 °C for 20 h. The system changed from a white turbid liquid to a yellow turbid liquid.

[0094] After the reaction was complete, the system was filtered and the filtrate was decompressed to remove the solvent to obtain 46.2 g of a yellow liquid with a gas chromatography purity (GC purity) of 99.88% and a yield of 93.5%.

[0095] Preparation Example 1-2 (Preparation of Compound FSPN-1)

[0096] The reaction was heated at 55°C for 12 h. The rest of the reaction was the same as in Preparation Example 1-1.

[0097] After the reaction was complete, the system was filtered, and the filtrate was decompressed to remove the solvent to obtain 46.3 g of a yellow liquid with a gas chromatography purity (GC purity) of 99.87% and a yield of 93.7%.

[0098] Preparation Example 2-1 (Preparation of Compound FSPN-2)

[0099] 35 g (0.1 mol) of tris(trifluoromethylsilyl) phosphate, 16.2 g (0.23 mol) of diethylamine, 10.0 g of sodium ethoxide, and 150.0 g of dichloroethane were weighed in sequence into a 500 mL three-necked flask. Under nitrogen protection, the mixture was heated at 45 °C for 7 h. The system changed from a white turbid liquid to a light yellow turbid liquid.

[0100] After the reaction was complete, the system was filtered and the filtrate was desolvated under reduced pressure to obtain 40.8 g of a light yellow liquid with a GC purity of 99.12% and a yield of 89.8%.

[0101] Preparation Example 2-2 (Preparation of Compound FSPN-2)

[0102] The reaction was heated at 55°C for 6 h. The rest of the reaction was the same as in Preparation Example 2-1.

[0103] After the reaction of the system was completed, the mixture was filtered and the filtrate was decompressed to remove the solvent to obtain 40.6 g of a yellow liquid with a gas chromatography purity (GC purity) of 99.15% and a yield of 89.4%.

[0104] Preparation Example 3-1 (Preparation of Compound FSPN-3)

[0105] 35 g (0.1 mol) of tris(trifluoromethylsilyl)phosphate, 20.3 g (0.23 mol) of dipropylamine, 10.0 g of sodium ethoxide, and 150.0 g of dichloroethane were weighed in a 500 mL three-necked flask. Under nitrogen protection, the mixture was heated at 55 °C for 22 h. The system changed from a white turbid liquid to a dark yellow turbid liquid.

[0106] After the reaction was complete, the system was filtered and the filtrate was desolvated under reduced pressure to obtain 37.5 g of a dark yellow liquid with a GC purity of 99.45% and a yield of 68.3%.

[0107] Preparation Example 3-2 (Preparation of Compound FSPN-3)

[0108] The reaction was heated at 50°C for 24 hours. The rest of the reaction was the same as in Preparation Example 3-1.

[0109] After the reaction was complete, the system was filtered, and the filtrate was decompressed to remove the solvent to obtain 37.3 g of a yellow liquid with a gas chromatography purity (GC purity) of 99.41% and a yield of 67.9%.

[0110] Preparation Example 4-1 (Preparation of Compound FSPN-4)

[0111] 35 g (0.1 mol) of tris(trifluoromethylsilyl) phosphate, 12.9 g (0.23 mol) of propargyl alcohol, 10.0 g of sodium ethoxide, and 150.0 g of dichloroethane were weighed in a 500 mL three-necked flask. Under nitrogen protection, the mixture was heated at 55 ° C for 30 h. The system changed from a white turbid liquid to a light yellow turbid liquid.

[0112] After the reaction was complete, the system was filtered and the filtrate was desolvated under reduced pressure to obtain 24.6 g of a dark yellow liquid with a GC purity of 97.45% and a yield of 60.5%.

[0113] Preparation Example 4-2 (Preparation of Compound FSPN-4)

[0114] The reaction was heated at 45°C for 30 h. The rest of the reaction was the same as in Preparation Example 4-1.

[0115] After the reaction of the system was completed, the mixture was filtered and the filtrate was desolvated under reduced pressure to obtain 24.5 g of a yellow liquid with a gas chromatography purity (GC purity) of 97.41% and a yield of 60.2%.

[0116] Preparation Example 4-3 (Preparation of Compound FSPN-4)

[0117] The reaction was heated at 55°C for 20 h. The rest of the reaction was the same as in Preparation Example 4-1.

[0118] After the reaction was complete, the system was filtered, and the filtrate was decompressed to remove the solvent to obtain 24.4 g of a yellow liquid with a gas chromatography purity (GC purity) of 97.25% and a yield of 60%.

[0119] Examples 1-4 of the present invention provide a method for preparing a lithium-ion battery, and the formula of the battery electrolyte and the corresponding battery positive electrode material are shown in Table 1. Comparative Examples 1 and 2 use existing commercial additives.

[0120] The preparation method of a lithium-ion battery comprises the following steps:

[0121] (a) Electrolyte preparation

[0122] In an argon glove box with a water content of <1 ppm, organic solvents were mixed in a certain proportion, and lithium salt was dissolved in the above organic solvents. Then, the additives prepared in Preparation Example 1-1, Preparation Example 2-1, Preparation Example 3-1, and Preparation Example 4-1 and commercial additives were added to the organic solvents, completely dissolved, and mixed uniformly to obtain an electrolyte.

[0123] (b) Cell preparation

[0124] The battery cell adopts the standard process of Xinyuan Intelligent Storage (number XY)

[0125] (c) Cell packaging

[0126] Liquid injection and primary packaging are carried out in an argon glove box, and the volume is divided after standing for 24-36 hours. Secondary packaging is carried out after aging for 20-24 hours. The secondary packaging machine used is Shenzhen Kejing Vacuum Secondary Packaging Machine.

[0127] The lithium ion batteries prepared with the electrolytes in the above examples and comparative examples were tested for cycle performance. The test results are shown in Figure 2. Figure 2 shown.

[0128] Table 1 Lithium-ion battery electrolyte formula

[0129]

[0130]

[0131] Depend on Figure 2It can be seen that after 800 cycles, the capacity retention rates of the lithium-ion batteries to which the additives of the present invention are added (Example 1 and Example 2, the curves of the two almost overlap) are all above 95%, while the capacity retention rates of the lithium-ion batteries using commercial electrolytes are 89% (Comparative Example 1) and 83% (Comparative Example 2), respectively. This proves that the addition of the additives of the present invention can effectively improve the cycle stability of the battery. It is expected that the capacity retention rate will decay to below 80% after 4000 cycles, while the capacity retention rate of Comparative Example 2 has been reduced to below 80% when the cycle reaches about 840 cycles. This is because the additives of the present invention can form a layer of positive electrode interface film containing Si-O on the surface of the positive electrode, which helps the CEI film of the positive electrode to effectively improve the cycle stability.

[0132] Figure 3-10 The following is a picture of the puncture test of the lithium-ion batteries prepared in Examples 1-2 and Comparative Examples 1-2 of the present invention. The puncture test is to use a steel needle to pierce the battery to simulate the large-area short circuit phenomenon inside the battery cell to test the safety of the battery. Figure 3 and Figure 4 It can be seen that after the needle was inserted into and pulled out of the lithium ion battery prepared in Example 1 of the present invention, there was no open flame or smoke in the battery, thereby proving that the lithium ion battery added with the electrolyte additive of the present invention has good flame retardant properties, which fully demonstrates the safety of the electrolyte of the present invention.

[0133] Figure 4 and Figure 5 and Figure 3 and Figure 4 Similarly, it was demonstrated that the lithium-ion battery prepared in Example 2 of the present invention did not produce any open flame or smoke during the needle penetration test.

[0134] The puncture test results of the lithium-ion batteries prepared in Examples 3 and 4 of the present invention were similar to those of Examples 1 and 2. In the puncture test, no open flame or smoke was generated in the batteries.

[0135] In summary, the lithium-ion battery using the electrolyte additive of the present invention has good flame retardancy, and the battery does not produce open flames or smoke in the needle penetration test.

[0136] Depend on Figure 7-10 It can be seen that the batteries caught fire and exploded after the needle was inserted into them, which proves that the flame retardant performance of lithium-ion batteries using commercial electrolytes is poor and the electrolyte safety is poor.

[0137] By comparison Figure 3-6 and Figure 7-10 It can be seen that the addition of the additive of the present invention can effectively improve the flame retardancy of the battery. This is because the fluorine element in the additive of the present invention can enhance the strength of the SEI film, effectively improve lithium dendrites and have excellent flame retardancy.

[0138] The inventors have conducted a large number of experimental studies during the research process, and now use some solutions with poor performance as comparative examples.

[0139] Comparative Example 3

[0140] This comparative example is basically the same as Example 1, except that the amount of the additive of the present invention is 3% of the total mass of the electrolyte.

[0141] Comparative Example 4

[0142] This comparative example is basically the same as Example 1, except that the amount of the additive of the present invention is 0.5% of the total mass of the electrolyte.

[0143] Comparative Example 5

[0144] This comparative example is substantially the same as Example 1, except that the mass ratio of the three solvents is EC:EMC:DMC (mass ratio) = 6:14:5.

[0145] In addition, the present invention also conducted low temperature performance tests on the batteries prepared in the examples and comparative examples. The results are shown in Table 1. Figure 11 .

[0146] Depend on Figure 11 It can be seen that the low-temperature capacity retention rate of the lithium-ion battery with the additive of the present invention (Examples 1-4) is 48%-52% at -30°C, for example, 52% (Example 1), 52% (Example 2), 48% (Example 3), 49% (Example 4), and the capacity retention rate at -40°C is 24%-27%, for example, 27% (Example 1), 26% (Example 2), 24% (Example 3), 25% (Example 4), while the low-temperature capacity retention rate of the lithium-ion battery using commercial electrolyte is 39% and 38% at -30°C (much lower than 48%-52% of the present invention), and 13% and 13% at -40°C (much lower than 24%-27% of the present invention). This proves that the low-temperature effect of the battery can be effectively improved after adding the additive of the present invention. This is because at low temperatures, the viscosity of the electrolyte increases, resulting in a decrease in ion mobility. First, this additive can reduce the viscosity of the electrolyte, thereby increasing its electrical conductivity and ion mobility, and improving the performance of the battery at low temperatures; secondly, this additive can enhance the strength of the negative electrode SEI film, effectively preventing the co-insertion of solvent molecules from damaging the electrode, and improving the battery's cycle efficiency and reversible capacity.

[0147] In addition, by Figure 11 It can also be seen that too little additive of the present invention has little effect on improving battery performance (Comparative Example 3), while too much additive increases the viscosity of the electrolyte, affecting the low-temperature performance of the battery (Comparative Example 4).

[0148] By comparison Figure 11 It can be seen from the curve of Comparative Example 5 and the curves of Examples 1-4 that an inappropriate mass ratio of the three solvents EC, EMC and DMC will also affect the low-temperature performance of the battery.

[0149] In summary, the lithium-ion batteries containing the additives of the present invention have good long-cycle performance (the capacity retention rate of the lithium-ion batteries is above 95% after 800 cycles), flame retardancy (no open flame or smoke is generated in the batteries during the needle penetration test), and low-temperature effects (the capacity retention rate at -30°C is 48%-52%, and the capacity retention rate at -40°C is 24%-27%).

[0150] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. An electrolyte additive, characterized in that The additive has a structure shown in Formula I: Wherein R1 is one of the following groups: Where · is the connection site with the main body.

2. A method for preparing an electrolyte additive, characterized in that: The steps include: Step 1: Weigh the reaction raw materials and solvent and place them in a reaction vessel; Step 2: heating under inert gas protection, reacting, and post-processing to obtain an electrolyte additive; In step 1, the reaction raw materials include tris(trifluoromethylsilyl)phosphate and a reaction monomer, and the reaction monomer includes one of imidazole, diethylamine, dipropylamine and propargyl alcohol.

3. The preparation method according to claim 2, characterized in that In step 2, the heating temperature is 45-55° C. and the reaction time is 6-30 h.

4. The preparation method according to claim 2, characterized in that The molar ratio of tris(trifluoromethylsilyl)phosphate to the reactive monomer is 1:2.2-2.

5.

5. Use of the electrolyte additive according to claim 1 or the preparation method according to any one of claims 2 to 4 in the field of lithium-ion batteries.

6. A lithium ion battery electrolyte, characterized in that: The electrolyte comprises a lithium salt, an organic solvent and the electrolyte additive according to claim 1.

7. The electrolyte according to claim 6, characterized in that The concentration of lithium salt in the electrolyte is 0.5 to 2.2 M.

8. The electrolyte according to claim 6, characterized in that The organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl fluorocarbonate, dipropyl carbonate, ethyl methyl carbonate, butyl acetate, methyl propionate, methyl butyrate, ethyl acetate, dimethyl ether and ethyl butyrate.

9. A method for preparing a lithium ion battery electrolyte, characterized in that: The steps include: Step i: mixing organic solvents in proportion to obtain a mixed organic solvent; Step ii: dissolving the lithium salt in the above-mentioned mixed organic solvent, then adding the electrolyte additive according to claim 1 to the mixed organic solvent, completely dissolving it, and mixing it evenly to obtain a lithium-ion battery electrolyte.

10. A method for preparing a lithium ion battery, characterized in that: The steps include: (a) preparing an electrolyte by the preparation method according to claim 9; (b) Cell preparation; (c) Battery cell packaging.

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