Electrolyte for improving safety of lithium ion battery as well as preparation method and application of electrolyte

Abstract

The invention provides an electrolyte for improving the safety of a lithium ion battery as well as a preparation method and application of the electrolyte. The electrolyte comprises a basic electrolyte, a siloxane precursor and a stabilizer, the siloxane precursor is selected from alkoxy silane R-Si (OR ') 3, and the stabilizer is fluorine-containing alkyl modified siloxane. Compared with the prior art, the electrolyte provided by the invention forms a dynamic protection barrier in the lithium ion battery, so that a large amount of heat is absorbed during thermal runaway, high-temperature combustion of the battery is prevented, and the electrolyte is rapidly cured when the battery is damaged to protect the integrity of the battery structure. The electrolyte provided by the invention can be rapidly cured at the initial stage of thermal runaway (80-120 DEG C), cuts off an electron transmission path, and can prevent continuous temperature rise caused by internal short circuit of the lithium ion battery, thereby achieving the purpose of avoiding thermal runaway of the lithium ion battery.

Description

Technical Field

[0001] The invention belongs to the field of batteries, and in particular relates to an electrolyte for improving the safety of lithium-ion batteries and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, with their high energy density, long life and fast charging capabilities, have become an indispensable key technology in modern communications, transportation, energy storage and other fields. However, the chemical characteristics and system composition of lithium-ion batteries determine their potential dangers. Lithium, as an element of the second period and the first main group in the periodic table, has extremely active chemical properties. When a lithium-ion battery undergoes a thermal runaway reaction, a large amount of heat is released, which can easily lead to unsafe behaviors such as fire or explosion. Therefore, the safety of lithium-ion batteries has always been the focus of attention in the industry, and its importance is self-evident.

[0003] Internal short circuits are the most important cause of safety issues for lithium-ion batteries. External short circuits, overcharging, extrusion, mechanical damage, and electrolyte leakage can also cause internal short circuits. Once an internal short circuit occurs, the temperature and pressure inside the battery will rise rapidly, causing thermal runaway and safety accidents.

[0004] At present, the safety protection measures for lithium-ion batteries are mainly concentrated in the battery management system (BMS), thermal management system, battery shell design, etc. Although these measures have improved the safety of batteries to a certain extent, the detection and prevention methods for internal short circuits in batteries are still not perfect. Once a short circuit occurs inside the battery, it is often difficult to detect and deal with it in time, thus causing serious safety accidents.

[0005] Therefore, developing an electrolyte that can solidify rapidly under high temperature conditions of battery thermal runaway is of great significance to improving the overall safety of lithium-ion batteries. Summary of the invention

[0006] The object of the present invention is to provide an electrolyte for improving the safety of lithium-ion batteries and a preparation method thereof, wherein the provided electrolyte comprises a basic electrolyte, a siloxane precursor and a stabilizer, and can improve the safety performance of lithium-ion batteries.

[0007] Another object of the present invention is to provide an application of an electrolyte for improving the safety of lithium-ion batteries, which is used to prepare lithium-ion batteries. The electrolyte maintains normal functions under normal working conditions, but can absorb a large amount of heat to delay or prevent high-temperature combustion of the battery during thermal runaway, and can quickly solidify to stabilize the battery structure when the battery is damaged.

[0008] The specific technical solutions of the present invention are as follows:

[0009] An electrolyte for improving the safety of lithium-ion batteries, comprising a basic electrolyte, a siloxane precursor and a stabilizer;

[0010] The mass proportion of the siloxane precursor is 1-2%;

[0011] The mass proportion of the stabilizer is 0.2-0.6%;

[0012] The basic electrolyte is the balance.

[0013] The siloxane precursor is selected from alkoxysilane R-Si(OR') 3 , R is C1-C6 alkyl, vinyl or phenyl; R' is C1-C4 alkyl; preferably, the siloxane precursor is selected from methyltrimethoxysilane (CH 3 -Si(OCH 3 ) 3 ), vinyltrimethoxysilane (CH 2 =CH-Si(OCH 3 ) 3 ), phenyltrimethoxysilane (C 6 H 5 -Si(OCH 3 ) 3 ).

[0014] The stabilizer is a fluorinated alkyl modified siloxane, preferably trifluoropropyltrimethylsilane, which is used to inhibit the pre-hydrolysis of siloxane in the normal electrolyte and improve the chemical inertness of siloxane in the electrolyte.

[0015] The basic electrolyte comprises lithium salt (LiPF6), organic solvent (carbonate) and conventional additives, and is used to provide normal charging and discharging functions of the lithium-ion battery.

[0016] The invention provides a method for preparing an electrolyte for improving the safety of lithium-ion batteries, which specifically comprises: under nitrogen protection, first adding a stabilizer to a basic electrolyte of a formula amount, mixing it evenly, then adding a siloxane precursor, and stirring evenly.

[0017] The invention provides an application of an electrolyte for improving the safety of a lithium ion battery, which is used for preparing a lithium ion battery.

[0018] The working principle provided by the present invention is as follows: the stabilizer can inhibit the pre-hydrolysis of siloxane in the normal electrolyte, so that the electrolyte can work normally in daily operation. The electrolyte maintains normal function under normal working conditions. When the battery thermal runaway occurs, the LiPF in the electrolyte 6 Decomposition produces HF acid: R-Si(OR') 3 Reacts with HF acid to generate R-Si(OH) 3, the thermal runaway temperature increases, prompting R-Si(OH) 3 Dehydration condensation forms an elastic gel through Si-O-Si bond cross-linking. When the gel is formed, it absorbs heat and prevents the heat from continuing to rise. The gel wraps the electrolyte and inhibits the diffusion of volatile components. The gel has a high heat capacity and slows down heat conduction.

[0019] The electrolyte provided by the present invention forms a dynamic protective barrier inside the lithium-ion battery to absorb a large amount of heat during thermal runaway, prevent the battery from burning at high temperature, and quickly solidify when the battery is damaged to protect the integrity of the battery structure. The electrolyte provided by the present invention can quickly solidify at the early stage of thermal runaway (80-120°C), cut off the electron transmission path, and prevent the temperature from continuing to rise due to internal short circuits in the lithium-ion battery, thereby achieving the purpose of avoiding thermal runaway of the lithium-ion battery.

[0020] Compared with the prior art, the present invention can improve safety: after gelation, a dynamic protective barrier is formed inside the lithium-ion battery, which significantly improves the safety of the battery during thermal runaway. It can delay fire: it absorbs a large amount of heat during the gelation process, effectively delaying or preventing the occurrence of high-temperature combustion of the battery. It can achieve structural protection: after gelation, a protective barrier is formed to prevent further damage to the internal structure of the battery. In addition, the electrolyte of the present invention has good compatibility: the siloxane precursor in the electrolyte does not affect the normal charge and discharge performance of the battery under normal working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Polarization diagram of Example 1 and conventional electrolyte;

[0022] Figure 2 Polarization diagram of Example 2 and conventional electrolyte;

[0023] Figure 3 It is a temperature rise curve diagram of overcharge test of the embodiment and the comparative example;

[0024] Figure 4 It is a graph showing the acupuncture test results of the embodiments and comparative examples;

[0025] Figure 5 This is a picture of the battery after acupuncture in Example 1;

[0026] Figure 6 This is a picture of the battery after acupuncture in comparative example 1;

[0027] Figure 7 This is a picture of the battery after acupuncture in Example 2;

[0028] Figure 8 This is a picture of the battery after puncture in comparative example 2;

[0029] Fig. 9 This is a picture of the battery after puncture in comparative example 3. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0032] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0033] The basic electrolyte used in the following embodiments and comparative examples of the present invention is the same, comprising the following raw materials in mass percentage: 60% EMC ethyl methyl carbonate, 5% VC vinylene carbonate, 5% PC propylene carbonate and 30% EC ethylene carbonate, containing LiPF61M.

[0034] Example 1

[0035] An electrolyte for improving the safety of a lithium-ion battery comprises, by mass percentage, 98% of a basic electrolyte content + 1.5% of methyltrimethoxysilane + 0.5% of trifluoropropyltrimethylsilane.

[0036] The preparation method is as follows: under nitrogen protection, first add a stabilizer to the basic electrolyte in a formula amount, mix well, then add a siloxane precursor, and stir well.

[0037] Electrochemical performance test:

[0038] The prepared electrolyte was used to assemble a lithium-ion battery using a conventional lithium-ion button battery assembly process. The electrochemical properties of the button battery were tested at room temperature.

[0039] Safety Testing:

[0040] The prepared electrolyte is injected into the battery, and the lithium-ion square aluminum shell battery is assembled according to the conventional method.

[0041] The battery is tested for thermal runaway and needle puncture safety. During the test, the occurrence of the battery gel curing reaction is observed and the formation speed and quality of the protective layer are recorded.

[0042] Overcharge test: Overcharge the battery and monitor the battery cell temperature throughout the process. When the battery voltage exceeds the rated voltage at a certain temperature, check whether the temperature continues to rise. After returning to room temperature, disassemble the battery and observe the internal situation.

[0043] Needle penetration test: Place the fully charged battery at room temperature, use a specified steel needle to penetrate the battery from a direction perpendicular to the battery plates, and observe and record the battery condition.

[0044] Example 2

[0045] An electrolyte for improving the safety of a lithium-ion battery comprises, by mass percentage, 98% of a basic electrolyte content + 1.5% of vinyltrimethoxysilane + 0.5% of trifluoropropyltrimethylsilane.

[0046] The electrolyte was prepared in the same manner as in Example 1, and the battery was assembled and tested.

[0047] Comparative Example 1

[0048] An electrolyte, calculated by mass percentage, includes a base electrolyte content of 98.5% + 1.5% vinyltrimethoxysilane.

[0049] The electrolyte was prepared in the same manner as in Example 1, and the battery was assembled and tested.

[0050] Comparative Example 2

[0051] An electrolyte comprises, by mass percentage, 99.5% of a basic electrolyte content and 0.5% of trifluoropropyltrimethylsilane.

[0052] The electrolyte was prepared in the same manner as in Example 1, and the battery was assembled and tested.

[0053] Comparative Example 3 (conventional basic electrolyte)

[0054] An electrolyte comprises 100% of a basic electrolyte content by mass percentage.

[0055] Electrochemical performance test:

[0056] The common electrolyte purchased on the market was used to assemble lithium-ion batteries using conventional lithium-ion button battery assembly processes. The electrochemical properties of the button batteries were tested at room temperature.

[0057] Safety test: The battery was assembled and subjected to the safety test in Example 1.

[0058] The electrochemical performance comparison of button cells assembled with conventional lithium ion electrolytes in Example 1 is shown in Table 1. The electrochemical performance comparison of button cells assembled with conventional lithium ion electrolytes in Example 2 is shown in Table 2.

[0059] Table 1 Performance comparison between Example 1 and Comparative Example 3

[0060]

[0061] Table 2 Performance comparison between Example 2 and Comparative Example 3

[0062]

[0063] Figure 1 Polarization diagram of Example 1 and conventional electrolyte; Figure 2 2 is a polarization diagram of Example 2 and a conventional electrolyte; it can be seen that the polarization and charge-discharge capacity performance of Example 1 and the conventional electrolyte are basically consistent, and the polarization and charge-discharge capacity performance of Example 2 and the conventional electrolyte are also basically consistent. The electrolyte of the present invention does not affect the normal charge-discharge performance of the battery under normal working conditions.

[0064] The temperature rise curves of the overcharge test of the embodiment and the comparative example are shown in FIG. Figure 3 The results are shown in Table 3. Figure 4 , the results are shown in Table 4.

[0065] Table 3 Overcharge test results of various embodiments and comparative examples

[0066] Overcharge test phenomenon Example 1 No burning, no explosion Example 2 No burning, no explosion Comparative Example 1 combustion Comparative Example 2 combustion Comparative Example 3 combustion

[0067] Table 4 Acupuncture test results of each embodiment and comparative example

[0068] Acupuncture test phenomenon Example 1 No burning, no explosion Example 2 No burning, no explosion Comparative Example 1 combustion Comparative Example 2 combustion Comparative Example 3 combustion

[0069] Figure 5-Figure 9 The pictures of the batteries after needle puncture of the embodiment and the comparative example are shown. It can be seen that after adding the electrolyte of the present invention, in the overcharge test, the battery temperature reaches the initial temperature of thermal runaway, and the rising speed slows down significantly. After reaching the battery solidification temperature, the temperature no longer rises; in the needle puncture test, the maximum temperature of the battery does not exceed 100°C, which effectively reduces the probability of battery combustion. The electrolyte can protect the integrity of the battery and effectively prevent the occurrence of internal short circuits.

[0070] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. An electrolyte for improving the safety of a lithium-ion battery, characterized in that: The electrolyte for improving the safety of lithium-ion batteries comprises a basic electrolyte, a siloxane precursor and a stabilizer; the siloxane precursor is selected from alkoxysilane R-Si(OR')3, R is a C1-C6 alkyl, vinyl or phenyl; and R' is a C1-C4 alkyl.

2. The electrolyte for improving the safety of lithium-ion batteries according to claim 1, characterized in that: The siloxane precursor is selected from methyltrimethoxysilane (CH3-Si(OCH3)3), vinyltrimethoxysilane (CH2=CH-Si(OCH3)3) or phenyltrimethoxysilane (C6H5-Si(OCH3)3).

3. The electrolyte for improving the safety of lithium-ion batteries according to claim 1, characterized in that: The stabilizer is a fluorinated alkyl-modified siloxane.

4. The electrolyte for improving the safety of lithium-ion batteries according to claim 1 or 3, characterized in that: The stabilizer is trifluoropropyltrimethylsilane.

5. The electrolyte for improving the safety of lithium-ion batteries according to claim 1 or 2, characterized in that: The mass proportion of the siloxane precursor is 1-2%.

6. The electrolyte for improving the safety of lithium-ion batteries according to claim 1 or 3, characterized in that: The mass proportion of the stabilizer is 0.2-0.6%.

7. The electrolyte for improving the safety of lithium-ion batteries according to claim 1 or 3, characterized in that: The basic electrolyte comprises a lithium salt, an organic solvent and an additive.

8. A method for preparing an electrolyte for improving the safety of a lithium-ion battery according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: under nitrogen protection, first adding a stabilizer to a basic electrolyte of a formula amount, mixing it evenly, then adding a siloxane precursor, and stirring it evenly.

9. An application of the electrolyte for improving the safety of lithium-ion batteries according to any one of claims 1 to 7, characterized in that: Used to prepare lithium-ion batteries.

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