An electrolyte with dual protection functions against thermal runaway and battery breakage and its application

Abstract

The present invention relates to the field of electrolytes, and specifically relates to an electrolyte with dual protection functions against thermal runaway and battery damage and its application. In the electrolyte with lithium hexafluorophosphate as the electrolyte lithium salt, ethylene carbonate and diethyl carbonate as organic solvents, an organic compound containing multiple hydroxyl groups, ether bonds and quaternary ammonium salt structures is added as an electrolyte additive. This molecule can effectively inhibit the thermal runaway phenomenon of lithium batteries under high-temperature conditions by absorbing the heat generated by the battery and regulating internal chemical reactions; and can form a stable solid electrolyte interface film on the surface of the battery negative electrode, reducing the interfacial impedance and charge transfer resistance, improving the cycle life and Coulomb efficiency of the battery; and can effectively slow down the entry of oxygen into the battery, thus having a certain protective effect on battery damage. Therefore, the electrolyte prepared by the present invention can be applied to the assembly of metal lithium batteries and has broad application prospects compared with the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes, and particularly to an electrolyte with dual protection functions against thermal runaway and battery breakage and its application. Background Art

[0002] Lithium secondary batteries are high-performance batteries with the highest energy density among currently available secondary batteries, and are widely used in fields such as electric vehicles, large-scale energy storage, and medical electronics. With the increasing demand for high-safety and high-energy-density energy storage devices, in recent years, the development of various industries has put forward higher requirements for battery life, energy density, operating temperature range, rate performance, and safety. As a bridge connecting the positive and negative electrode materials in the battery system, the role of the electrolyte is self-evident. In order to further improve the performance of the battery, it is crucial to select a matching electrolyte.

[0003] Generally, in secondary batteries, during the operation of lithium metal batteries using lithium metal as the negative electrode, lithium ions are reduced on the surface of the lithium electrode, and depending on the combination of the solvent and lithium salt forming the electrolyte, solid electrolyte interfaces (SEIs) with various compositions are formed on the lithium electrode and occur irreversibly. However, organic solvents (such as carbonates) in the electrolyte are flammable substances, and if handled improperly or the battery is damaged, it may cause fire or explosion. In addition, the electrolyte may decompose under high temperature or overcharged conditions, releasing gases and increasing pressure, resulting in battery rupture or further thermal runaway.

[0004] In the prior art, in order to alleviate the occurrence of thermal runaway spread, for example, the patent technical document CN112332013B discloses a battery pack, a vehicle, and a control method for alleviating the thermal runaway spread of the battery pack. In this invention, the battery pack includes a spray pipeline to alleviate the thermal runaway spread, but these spray pipelines only target the weak parts in secondary batteries, with a relatively complex structure and high cost.

[0005] Therefore, according to the above related technologies, it is urgent to develop an electrolyte with dual protection functions against thermal runaway and battery breakage and its application. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide an electrolyte with dual protection functions against thermal runaway and battery breakage and its application to solve the problems of easy thermal runaway and battery breakage in the prior art.

[0007] Based on the above purpose, the present invention provides an electrolyte with dual protection functions against thermal runaway and battery breakage and its application.

[0008] An electrolyte with dual protection functions against thermal runaway and battery breakage is prepared from the following raw materials:

[0009] Lithium salt of electrolyte, organic solvent, electrolyte additive;

[0010] The structural formula of the electrolyte additive is as follows:

[0011]

[0012] Among them, R is any one of a hydroxyl group and a trimethylammonium ion.

[0013] Preferably, the concentration of the lithium salt of electrolyte in the electrolyte is 1-2 mol / L.

[0014] Preferably, the lithium salt of electrolyte is any one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium hexafluoroarsenate.

[0015] Preferably, the lithium salt of electrolyte is lithium hexafluorophosphate.

[0016] Preferably, the organic solvent is a mixture of ethylene carbonate and diethyl carbonate.

[0017] Preferably, the volume ratio of ethylene carbonate to diethyl carbonate in the organic solvent is 1:1-1.5.

[0018] Preferably, the mass percentage content of the electrolyte additive in the electrolyte is 0.5%-2%.

[0019] Preferably, the preparation method of the electrolyte with dual protection functions of thermal runaway and battery breakage includes the following steps:

[0020] Step S1. In a glove box under argon protection, mix ethylene carbonate and diethyl carbonate evenly to obtain an organic solvent;

[0021] Step S2. Under room temperature conditions, add the electrolyte additive to the organic solvent while stirring, mix evenly, and then add the lithium salt of electrolyte and stir evenly to obtain an electrolyte with dual protection functions of thermal runaway and battery breakage.

[0022] An application of an electrolyte with dual protection functions of thermal runaway and battery breakage, and the electrolyte with dual protection functions of thermal runaway and battery breakage is used for assembling a metal lithium battery.

[0023] The beneficial effects of the present invention:

[0024] The present invention provides an electrolyte with dual protection functions against thermal runaway and battery damage, and its application. In the electrolyte with lithium hexafluorophosphate as the electrolyte lithium salt, ethylene carbonate and diethyl carbonate as organic solvents, an organic compound containing multiple hydroxyl groups, ether bonds and quaternary ammonium salt structures is added as an electrolyte additive, which can effectively prevent the thermal runaway phenomenon of lithium batteries under high temperature or damaged conditions and provide protection when the battery is damaged.

[0025] In the present invention, the electrolyte additive can effectively inhibit the thermal runaway phenomenon of lithium batteries under high temperature conditions by absorbing the heat generated by the battery and regulating the internal chemical reactions; the hydroxyl groups and ether bonds contained in its molecules have strong polarity and hydrogen bond donor ability, and can form hydrogen bonds with ethylene carbonate and diethyl carbonate or interact with the fluorine atoms in lithium hexafluorophosphate through electrostatic attraction to form a stable SEI film on the negative electrode surface during the first charging of the battery, avoiding the side reactions between the electrolyte and the negative electrode material, reducing the interfacial impedance and charge transfer resistance, thereby improving the cycle life and first Coulomb efficiency of the battery; the quaternary ammonium salt structure contained in its molecules makes the electrolyte additive have good ionic conductivity, which can improve the overall ionic transport efficiency of the electrolyte, thereby improving the charge and discharge performance of the battery;

[0026] When the battery shell is damaged, oxygen in the air may enter the battery interior, further affecting the battery stability. The electrolyte additive in the present invention can form an SEI film on the negative electrode surface, effectively slowing down the entry of oxygen into the battery, and thus having a certain protective effect on battery damage. Compared with the prior art, it has a wide application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only those of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 is the infrared spectrum comparison diagram of the electrolyte before and after deterioration in Example 1 of the present invention;

[0029] Figure 2 is the cyclic voltammetry curve of the lithium metal symmetric battery prepared from Example 1 of the present invention at a current density of 1 mA cm -2 , with a deposition density of 1 mAh cm -2 ;

[0030] Figure 3 is the cyclic voltammetry curve of the lithium metal symmetric battery prepared from Comparative Example 1 of the present invention at a current density of 1 mA cm -2, the deposition density is 1 mAh cm -2 Cycling curve graph;

[0031] Figure 4 is a performance comparison graph of lithium metal full cells prepared in Example 1 and Comparative Example 1 of the present invention after 100 cycles at a rate of 0.5C in the voltage range of 2.8 - 4.3V;

[0032] Figure 5 is a rate performance comparison graph of lithium metal full cells prepared in Example 1 and Comparative Example 1 of the present invention after 5 cycles at different rates in the voltage range of 2.8 - 4.3V;

[0033] Figure 6 is an impedance comparison graph of lithium metal symmetric cells before and after the electrolyte deterioration in Example 1 of the present invention;

[0034] Figure 7 is an impedance graph of lithium metal symmetric cells after the temperature increase in Example 1 of the present invention;

[0035] Figure 8 is an impedance graph of lithium metal symmetric cells after the battery damage in Example 1 of the present invention. Detailed implementation manners

[0036] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with specific embodiments.

[0037] The sources and properties of some raw materials used in the present invention are as follows:

[0038] Lithium hexafluorophosphate is purchased from Tianci Materials Co., Ltd.; ethylene carbonate is purchased from Qingdao Wanhaihuaye Energy Technology Co., Ltd.; diethyl carbonate is purchased from Weifang Shuoxin Chemical Industry Co., Ltd.

[0039] Example 1: A preparation method of an electrolyte with dual protection functions of thermal runaway and battery damage, including the following steps:

[0040] S1. In a glove box under argon protection, mix ethylene carbonate and diethyl carbonate evenly according to a volume ratio of 1:1 to obtain an organic solvent;

[0041] S2. Under room temperature conditions, add electrolyte additives to the organic solvent while stirring, mix evenly, and then add lithium hexafluorophosphate and stir evenly, so that the mass percentage content of the electrolyte additive in the electrolyte is 0.5%, and the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L, to obtain an electrolyte with dual protection functions of thermal runaway and battery damage.

[0042] Example 2: A preparation method of an electrolyte with dual protection functions of thermal runaway and battery damage, including the following steps:

[0043] S1. In a glove box protected by argon, mix ethylene carbonate and diethyl carbonate evenly at a volume ratio of 1:1.2 to obtain an organic solvent;

[0044] S2. At room temperature, add an electrolyte additive to the organic solvent with stirring, mix evenly, then add lithium hexafluorophosphate and stir evenly, so that the mass percentage of the electrolyte additive in the electrolyte is 1%, and the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L, to obtain an electrolyte with dual protection functions of thermal runaway and battery breakage.

[0045] Example 3: A method for preparing an electrolyte with dual protection functions of thermal runaway and battery breakage, comprising the following steps:

[0046] S1. In a glove box protected by argon, mix ethylene carbonate and diethyl carbonate evenly at a volume ratio of 1:1.2 to obtain an organic solvent;

[0047] S2. At room temperature, add an electrolyte additive to the organic solvent with stirring, mix evenly, then add lithium hexafluorophosphate and stir evenly, so that the mass percentage of the electrolyte additive in the electrolyte is 1%, and the concentration of lithium hexafluorophosphate in the electrolyte is 1.5 mol / L, to obtain an electrolyte with dual protection functions of thermal runaway and battery breakage.

[0048] Example 4: A method for preparing an electrolyte with dual protection functions of thermal runaway and battery breakage, comprising the following steps:

[0049] S1. In a glove box protected by argon, mix ethylene carbonate and diethyl carbonate evenly at a volume ratio of 1:1.5 to obtain an organic solvent;

[0050] S2. At room temperature, add an electrolyte additive to the organic solvent with stirring, mix evenly, then add lithium hexafluorophosphate and stir evenly, so that the mass percentage of the electrolyte additive in the electrolyte is 1.5%, and the concentration of lithium hexafluorophosphate in the electrolyte is 2 mol / L, to obtain an electrolyte with dual protection functions of thermal runaway and battery breakage.

[0051] Example 5: A method for preparing an electrolyte with dual protection functions of thermal runaway and battery breakage, comprising the following steps:

[0052] S1. In a glove box protected by argon, mix ethylene carbonate and diethyl carbonate evenly at a volume ratio of 1:1.5 to obtain an organic solvent;

[0053] S2. Under room temperature conditions, add the electrolyte additive to the organic solvent with stirring, mix evenly, then add lithium hexafluorophosphate and stir evenly, so that the mass percentage content of the electrolyte additive in the electrolyte is 2%, and the concentration of lithium hexafluorophosphate in the electrolyte is 2 mol / L, obtaining an electrolyte with dual protection functions of thermal runaway and battery breakage.

[0054] Example 6: A preparation method of an electrolyte with dual protection functions of thermal runaway and battery breakage, comprising the following steps:

[0055] S1. In a glove box protected by argon, mix ethylene carbonate and diethyl carbonate evenly according to a volume ratio of 1:1.5 to obtain an organic solvent;

[0056] S2. Under room temperature conditions, add the electrolyte additive to the organic solvent with stirring, mix evenly, then add lithium hexafluorophosphate and stir evenly, so that the mass percentage content of the electrolyte additive in the electrolyte is 2%, and the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L, obtaining an electrolyte with dual protection functions of thermal runaway and battery breakage.

[0057] Example 7: A preparation method of an electrolyte with dual protection functions of thermal runaway and battery breakage, comprising the following steps:

[0058] S1. In a glove box protected by argon, mix ethylene carbonate and diethyl carbonate evenly according to a volume ratio of 1:1 to obtain an organic solvent;

[0059] S2. Under room temperature conditions, add the electrolyte additive to the organic solvent with stirring, mix evenly, then add lithium hexafluorophosphate and stir evenly, so that the mass percentage content of the electrolyte additive in the electrolyte is 1%, and the concentration of lithium hexafluorophosphate in the electrolyte is 2 mol / L, obtaining an electrolyte with dual protection functions of thermal runaway and battery breakage.

[0060] Comparative Example 1:

[0061] In this comparative example, compared with Example 1, the electrolyte additive was not added during the preparation of the electrolyte with dual protection functions of thermal runaway and battery breakage, and the remaining steps and parameters were the same. This comparative example will not be repeated here, and finally an electrolyte with dual protection functions of thermal runaway and battery breakage was obtained.

[0062] Comparative Example 2:

[0063] This comparative example is the same as Example 1 except that "the mass percentage content of the electrolyte additive in the electrolyte is 0.5%" is replaced with "the mass percentage content of the electrolyte additive in the electrolyte is 20%". The remaining steps and parameters are the same, so this comparative example will not be repeated here. Finally, an electrolyte with dual protection functions against thermal runaway and battery breakage is obtained.

[0064] Performance test:

[0065] The electrolytes with dual protection functions against thermal runaway and battery breakage prepared in Examples 1 - 7 and Comparative Examples 1 - 2 are respectively assembled with negative lithium sheets and positive nickel cobalt manganese oxide cathodes into full cells; the electrolytes with dual protection functions against thermal runaway and battery breakage prepared in Examples 1 - 7 and Comparative Examples 1 - 2 are respectively assembled with lithium sheets into lithium metal symmetric cells.

[0066] Stability performance test:

[0067] The electrolytes with dual protection functions against thermal runaway and battery breakage prepared in Examples 1 - 7 and Comparative Examples 1 - 2 and the deteriorated electrolytes are respectively tested using a Fourier transform infrared spectrometer (FTIR). The results are as Figure 1 shown;

[0068] Thermal runaway performance test:

[0069] The full cells assembled from Examples 1 - 7 and Comparative Examples 1 - 2 are respectively placed in an oven and then heated at 200 °C, 300 °C, and 400 °C for 30 min to test the thermal runaway performance of the electrolyte.

[0070] Cycling performance test:

[0071] The full cells assembled from Examples 1 - 7 and Comparative Examples 1 - 2 are respectively cycled 100 times at a rate of 0.5C in the voltage range of 2.8 - 4.3V to test the capacity retention rate after 100 cycles of the battery.

[0072] The lithium metal symmetric cells assembled from Examples 1 - 7 and Comparative Examples 1 - 2 are respectively plotted with cycling curves under the conditions of a current density of 1 mA cm -2 , and a deposition density of 1 mAh cm -2 . The results are as Figure 2 , Figure 3 shown;

[0073] The full cells assembled from Examples 1 - 7 and Comparative Examples 1 - 2 are respectively cycled 100 times at a rate of 0.5C in the voltage range of 2.8 - 4.3V. The results are as Figure 4 shown;

[0074] The full cells assembled from Examples 1 - 7 and Comparative Examples 1 - 2 were placed in the voltage range of 2.8 - 4.3 V and cycled 5 times at rates of 0.2C, 0.5C, 1C, 2C, 3C, 5C, and 0.2C, and the results are as Figure 5 shown.

[0075] Table 1

[0076]

[0077]

[0078] Data analysis:

[0079] As can be seen from Table 1, Figures 1-8 the electrolyte prepared in the present invention with the dual protection functions of thermal runaway and battery breakage has better thermal runaway performance and higher cycle stability, and stably passes the tests of heating at 200 °C, 300 °C, and 400 °C for 30 min in sequence. This may be because the electrolyte additive in the present invention can effectively inhibit the thermal runaway phenomenon of lithium batteries under high-temperature conditions by absorbing the heat generated by the battery and regulating internal chemical reactions; the hydroxyl groups and ether bonds contained in its molecules have strong polarity and hydrogen bond donor ability, and can form hydrogen bonds with ethylene carbonate and diethyl carbonate or interact with fluorine atoms in lithium hexafluorophosphate through electrostatic attraction to form a stable SEI film on the negative electrode surface during the first charge of the battery, avoiding side reactions between the electrolyte and the negative electrode material, reducing the interfacial impedance and charge transfer resistance, thereby improving the cycle life and first Coulomb efficiency of the battery; the quaternary ammonium salt structure contained in its molecules makes the electrolyte additive have good ionic conductivity, which can improve the overall ionic transport efficiency of the electrolyte, thereby improving the charge and discharge performance of the battery; and the electrolyte additive in the present invention can form an SEI film on the negative electrode surface, effectively slowing down the entry of oxygen into the battery, and thus having a certain protective effect on battery breakage;

[0080] In Comparative Example 1, since the electrolyte additive was not added during the preparation of the electrolyte with the dual protection functions of thermal runaway and battery breakage, it can be seen from Table 1 that its thermal runaway performance and cycle stability are poor. This may be because the electrolyte additive can form a stable SEI film on the negative electrode surface, avoiding side reactions between the electrolyte and the negative electrode material, reducing the interfacial impedance and charge transfer resistance, thereby improving the cycle performance, and can effectively slow down the entry of oxygen into the battery, and thus having a certain protective effect on battery breakage; and from Figure 2 and Figure 3It can be seen that the lithium metal symmetric battery assembled in Comparative Example 1 has poor cycle stability and a short lifespan. Therefore, the thermal runaway performance and cycle stability shown by Comparative Example 1 are worse than those of Example 1. In Comparative Example 2, since "the mass percentage content of the electrolyte additive in the electrolyte is 0.5%" was replaced with "the mass percentage content of the electrolyte additive in the electrolyte is 20%", it can be seen from Table 1 that its thermal runaway performance and cycle stability are poor. The battery exploded and burned under the conditions of 300°C and heating for 30 minutes. This may be because too much electrolyte additive will react with the electrolyte lithium salt and organic solvent in the electrolyte, or it is easy to aggregate in the electrolyte due to excessive content, thereby affecting the comprehensive performance of the electrolyte. Therefore, the thermal runaway performance and cycle stability shown by Comparative Example 2 are worse than those of Example 1.

[0081] Those of ordinary skill in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

[0082] The present invention aims to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An electrolyte with dual protection functions of thermal runaway and battery damage, characterized in that: Prepared from the following raw materials: Electrolyte lithium salt, organic solvent, electrolyte additive; The electrolyte lithium salt is lithium hexafluorophosphate; The organic solvent is a mixture of ethylene carbonate and diethyl carbonate; The structural formula of the electrolyte additive is as follows: Wherein, R is any one of a hydroxyl group and a trimethylammonium ion; The mass percentage of the electrolyte additive in the electrolyte is 0.5%-2%.

2. The electrolyte having dual protection functions of thermal runaway and battery damage according to claim 1, characterized in that: The concentration of the electrolyte lithium salt in the electrolyte is 1-2 mol / L.

3. The electrolyte with dual protection functions of thermal runaway and battery damage according to claim 1, characterized in that: The volume ratio of ethylene carbonate to diethyl carbonate in the organic solvent is 1:1-1.

5.

4. The electrolyte having dual protection functions of thermal runaway and battery damage according to claim 1, characterized in that: The method for preparing the electrolyte having dual protection functions of thermal runaway and battery damage comprises the following steps: Step S1. In an argon-protected glove box, ethylene carbonate and diethyl carbonate are mixed uniformly to obtain an organic solvent; Step S2. Under room temperature, add electrolyte additives to the organic solvent while stirring, mix evenly, then add electrolyte lithium salt, stir evenly, and obtain an electrolyte with dual protection functions against thermal runaway and battery damage.

5. An application of an electrolyte having dual protection functions of thermal runaway and battery damage according to any one of claims 1 to 4, characterized in that: The electrolyte having dual protection functions of thermal runaway and battery damage is used for assembling metal lithium batteries.

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