Electrolyte with double protection functions of thermal runaway and battery damage and technology for applying electrolyte to lithium metal battery

Abstract

The invention relates to the field of electrolytes, in particular to an electrolyte with double protection functions of thermal runaway and battery damage and a technology for applying the electrolyte to a lithium metal battery. The electrolyte takes lithium hexafluorophosphate as an electrolyte lithium salt and ethylene carbonate and diethyl carbonate as organic solvents; an organic compound containing a plurality of hydroxyl groups, ether bonds and quaternary ammonium salt structures is added as an electrolyte additive. The molecule can effectively inhibit the thermal runaway phenomenon of the lithium battery under a high-temperature condition by absorbing heat generated by the battery and regulating and controlling internal chemical reaction; a stable solid electrolyte interface film can be formed on the surface of the negative electrode of the battery, so that interface impedance and charge transfer resistance are reduced, the cycle life of the battery is prolonged, and the coulombic efficiency of the battery is improved; and oxygen can be effectively prevented from entering the battery, so that the battery is protected from being damaged to a certain extent. Therefore, the electrolyte prepared by the invention can be applied to assembly of a metal lithium battery, and has a wide application prospect compared with the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes, and in particular to an electrolyte having dual protection functions against thermal runaway and battery damage and a technology for applying the electrolyte to lithium metal batteries. Background Art

[0002] Lithium secondary batteries are high-performance batteries with the highest energy density among currently available secondary batteries. They are widely used in electric vehicles, large-scale energy storage, medical electronics and other fields. With the increasing demand for high-safety and high-energy-density energy storage devices, the development of various industries in recent years 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 very important 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 a solid electrolyte interface (SEI) with various compositions is formed on the lithium electrode according to the combination of the solvent and lithium salt forming the electrolyte, and occurs irreversibly. However, organic solvents (such as carbonates) in the electrolyte are flammable substances, which may cause fire or explosion if not handled properly or the battery is damaged. In addition, the electrolyte may decompose at high temperature or in an overcharged state, releasing gas and increasing pressure, leading to battery rupture or further thermal runaway.

[0004] In the prior art, in order to alleviate the occurrence of thermal runaway spread, patent technical document CN112332013B discloses a battery pack, a vehicle and a control method for alleviating the spread of thermal runaway in a battery pack. In the invention, the battery pack includes a spray pipe to alleviate the spread of thermal runaway, but these spray pipes only target the weak points in the secondary battery, and the structure is relatively complicated and the cost is high.

[0005] Therefore, according to the above-mentioned related technologies, it is urgent to develop an electrolyte with dual protection functions of thermal runaway and battery damage and a technology for applying it to lithium metal batteries. Summary of the invention

[0006] In view of this, the purpose of the present invention is to propose an electrolyte with dual protection functions of thermal runaway and battery damage and a technology for applying it to lithium metal batteries, so as to solve the problem that batteries are prone to thermal runaway and battery damage in the prior art.

[0007] Based on the above objectives, the present invention provides an electrolyte having dual protection functions against thermal runaway and battery damage and a technology for applying the electrolyte to lithium metal batteries.

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

[0009] Electrolyte lithium salt, organic solvent, electrolyte additive;

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

[0011]

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

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

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

[0015] Preferably, the electrolyte lithium salt 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 of the electrolyte additive in the electrolyte is 0.5%-2%.

[0019] Preferably, the method for preparing the electrolyte having dual protection functions of thermal runaway and battery damage comprises the following steps:

[0020] Step S1. In an argon-protected glove box, ethylene carbonate and diethyl carbonate are mixed uniformly to obtain an organic solvent;

[0021] 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 of thermal runaway and battery damage.

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

[0023] Beneficial effects of the present invention:

[0024] The present invention provides an electrolyte with dual protection functions against thermal runaway and battery damage and a technology for applying the electrolyte to a lithium metal battery. The present invention adds an organic compound containing multiple hydroxyl groups, ether bonds and quaternary ammonium salt structures as an electrolyte additive to an electrolyte using lithium hexafluorophosphate as an electrolyte lithium salt and ethylene carbonate and diethyl carbonate as organic solvents. The electrolyte can effectively prevent thermal runaway of lithium batteries in high temperature or damaged states and provide protection when the battery is damaged.

[0025] The electrolyte additive of the present invention can effectively inhibit the thermal runaway phenomenon of the lithium battery under high temperature conditions by absorbing the heat generated by the battery and regulating the internal chemical reaction; the hydroxyl group and the ether bond contained in the molecule have strong polarity and hydrogen bond donor ability, and can form a stable SEI film on the surface of the negative electrode when the battery is charged for the first time by forming hydrogen bonds with ethylene carbonate and diethyl carbonate or interacting with fluorine atoms in lithium hexafluorophosphate through electrostatic attraction, thereby avoiding the side reaction between the electrolyte and the negative electrode material, reducing the interface impedance and the charge transfer resistance, and thus improving the cycle life and the first coulomb efficiency of the battery; the quaternary ammonium salt structure contained in the molecule makes the electrolyte additive have good ion conductivity, which can improve the overall ion transmission 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, further affecting the stability of the battery. The electrolyte additive in the present invention can form a SEI film on the surface of the negative electrode, effectively slowing down the entry of oxygen into the battery, thereby having a certain protective effect on battery damage. Compared with the prior art, it has a wide range of application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0029] Figure 2 The lithium metal symmetric battery prepared in Example 1 of the present invention is -2 , the deposition density is 1 mAh cm -2 Cycle curve diagram of

[0030] Figure 3 The lithium metal symmetric battery prepared in Comparative Example 1 of the present invention has a current density of 1 mA cm -2, the deposition density is 1 mAh cm -2 Cycle curve diagram of

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

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

[0033] Figure 6 This is a comparison diagram of the impedance of a lithium metal symmetrical battery before and after the electrolyte is deteriorated in Example 1 of the present invention;

[0034] Figure 7 is an impedance diagram of a lithium metal symmetrical battery after the temperature is increased in Example 1 of the present invention;

[0035] Figure 8 This is an impedance diagram of a lithium metal symmetrical battery after battery damage in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

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

[0038] Lithium hexafluorophosphate was purchased from Tianci Materials Co., Ltd.; ethylene carbonate was purchased from Qingdao Wanhai Huaye Energy Technology Co., Ltd.; and diethyl carbonate was purchased from Weifang Shuoxin Chemical Co., Ltd.

[0039] Example 1: A method for preparing an electrolyte having dual protection functions of thermal runaway and battery damage, comprising the following steps:

[0040] S1. In an argon-protected glove box, ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1:1 to obtain an organic solvent;

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

[0042] Example 2: A method for preparing an electrolyte having dual protection functions of thermal runaway and battery damage, comprising the following steps:

[0043] S1. In an argon-protected glove box, ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1:1.2 to obtain an organic solvent;

[0044] S2. At room temperature, add electrolyte additives to the organic solvent while 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 against thermal runaway and battery damage.

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

[0046] S1. In an argon-protected glove box, ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1:1.2 to obtain an organic solvent;

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

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

[0049] S1. In an argon-protected glove box, ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1:1.5 to obtain an organic solvent;

[0050] S2. At room temperature, add electrolyte additives to the organic solvent while 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 against thermal runaway and battery damage.

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

[0052] S1. In an argon-protected glove box, ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1:1.5 to obtain an organic solvent;

[0053] S2. At room temperature, add electrolyte additives to the organic solvent while stirring, mix evenly, then add lithium hexafluorophosphate and stir evenly to make the mass percentage of the electrolyte additive in the electrolyte be 2%, and the concentration of lithium hexafluorophosphate in the electrolyte be 2 mol / L, to obtain an electrolyte with dual protection functions against thermal runaway and battery damage.

[0054] Example 6: A method for preparing an electrolyte having dual protection functions of thermal runaway and battery damage, comprising the following steps:

[0055] S1. In an argon-protected glove box, ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1:1.5 to obtain an organic solvent;

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

[0057] Example 7: A method for preparing an electrolyte having dual protection functions of thermal runaway and battery damage, comprising the following steps:

[0058] S1. In an argon-protected glove box, ethylene carbonate and diethyl carbonate were mixed in a volume ratio of 1:1 to obtain an organic solvent;

[0059] S2. At room temperature, add electrolyte additives to the organic solvent while stirring, mix evenly, then add lithium hexafluorophosphate and stir evenly to make the mass percentage of the electrolyte additive in the electrolyte be 1%, and the concentration of lithium hexafluorophosphate in the electrolyte be 2 mol / L, to obtain an electrolyte with dual protection functions against thermal runaway and battery damage.

[0060] Comparative Example 1:

[0061] Compared with Example 1, this comparative example does not add electrolyte additives during the preparation of the electrolyte with dual protection functions of thermal runaway and battery damage. The remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, an electrolyte with dual protection functions of thermal runaway and battery damage is obtained.

[0062] Comparative Example 2:

[0063] Compared with Example 1, this comparative example only replaces "the mass percentage of the electrolyte additive in the electrolyte is 0.5%" with "the mass percentage of the electrolyte additive in the electrolyte is 20%", and the remaining steps and parameters are the same. This comparative example will not be repeated, and finally an electrolyte with dual protection functions of thermal runaway and battery damage is obtained.

[0064] Performance Testing:

[0065] The electrolytes with dual protection functions of thermal runaway and battery damage prepared in Examples 1 to 7 and Comparative Examples 1 to 2 were respectively assembled with negative electrode lithium sheets and positive electrode lithium nickel cobalt manganese oxide into full batteries; the electrolytes with dual protection functions of thermal runaway and battery damage prepared in Examples 1 to 7 and Comparative Examples 1 to 2 were respectively assembled with lithium sheets into lithium metal symmetric batteries;

[0066] Stability performance test:

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

[0068] Thermal runaway performance test:

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

[0070] Cycle performance test:

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

[0072] The lithium metal symmetric batteries assembled from Examples 1 to 7 and Comparative Examples 1 to 2 were respectively subjected to a current density of 1 mA cm -2 , the deposition density is 1 mAh cm -2 The cycle curve is drawn under the condition of Figure 2 , Figure 3 As shown;

[0073] The full batteries assembled from Examples 1 to 7 and Comparative Examples 1 to 2 were placed in a voltage range of 2.8-4.3 V and cycled at a rate of 0.5 C for 100 cycles. The results are as follows: Figure 4 As shown;

[0074] The full batteries assembled from Examples 1 to 7 and Comparative Examples 1 to 2 were placed in a voltage range of 2.8-4.3 V and cycled for 5 cycles at 0.2C, 0.5C, 1C, 2C, 3C, 5C, and 0.2C rates. The results are as follows: Figure 5 shown.

[0075] Table 1

[0076]

[0077] Data Analysis:

[0078] From Table 1, Figure 1-8 It can be seen that the electrolyte with dual protection functions of thermal runaway and battery damage prepared by the present invention has better thermal runaway performance and higher cycle stability, and stably passes the tests of heating at 200°C, 300°C, 400°C and 30 minutes in sequence. This may be because the electrolyte additive in the present invention can effectively inhibit the thermal runaway phenomenon of the lithium battery under high temperature conditions by absorbing the heat generated by the battery and regulating the internal chemical reaction; the hydroxyl group and ether bond contained in its molecule have strong polarity and hydrogen bond donor ability, and can form hydrogen bonds with ethylene carbonate and diethyl carbonate or with ethylene carbonate through electrostatic attraction. The fluorine atoms in lithium hexafluorophosphate interact with each other to form a stable SEI film on the surface of the negative electrode when the battery is charged for the first time, avoiding the side reaction between the electrolyte and the negative electrode material, reducing the interface impedance and charge transfer resistance, thereby improving the cycle life and the first coulomb efficiency of the battery; the quaternary ammonium salt structure contained in its molecules makes the electrolyte additive have good ion conductivity, which can improve the overall ion transmission 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 surface of the negative electrode, effectively slowing down the entry of oxygen into the battery, and thus having a certain protective effect on battery damage;

[0079] In Comparative Example 1, since no electrolyte additive was added during the preparation of the electrolyte with dual protection functions of thermal runaway and battery damage, 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 surface of the negative electrode, avoiding the side reaction between the electrolyte and the negative electrode material, reducing the interface impedance and charge transfer resistance, thereby improving the cycle performance, and can effectively slow down the entry of oxygen into the battery, thereby having a certain protective effect on battery damage; and from Figure 2 and Figure 3It can be seen that the lithium metal symmetrical battery assembled by Comparative Example 1 has poor cycle stability and short life, so the thermal runaway performance and cycle stability exhibited by Comparative Example 1 are worse than those of Example 1; Comparative Example 2 replaces "the mass percentage of the electrolyte additive in the electrolyte is 0.5%" with "the mass percentage of the electrolyte additive in the electrolyte is 20%", and 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 too much content is easy to aggregate in the electrolyte, thereby affecting the comprehensive performance of the electrolyte. Therefore, the thermal runaway performance and cycle stability exhibited by Comparative Example 2 are worse than those of Example 1.

[0080] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative 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 may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0081] The present invention is intended 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 should be included in the scope of protection 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 structural formula of the electrolyte additive is as follows: Wherein, R is any one of a hydroxyl group and a trimethylammonium ion.

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 electrolyte lithium salt is any one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium hexafluoroarsenate.

4. The electrolyte with dual protection functions of thermal runaway and battery damage according to claim 1, characterized in that: The electrolyte lithium salt is lithium hexafluorophosphate.

5. The electrolyte with dual protection functions of thermal runaway and battery damage according to claim 1, characterized in that: The organic solvent is a mixture of ethylene carbonate and diethyl carbonate.

6. 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.

7. The electrolyte with dual protection functions of thermal runaway and battery damage according to claim 1, characterized in that: The mass percentage of the electrolyte additive in the electrolyte is 0.5%-2%.

8. The electrolyte with 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 of thermal runaway and battery damage.

9. An application of the electrolyte having dual protection functions of thermal runaway and battery damage according to claims 1-8, 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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