Gaseous flame-retardant electrolyte, battery and electrical equipment

Abstract

The present invention provides a gaseous flame-retardant electrolyte, a battery, and electrical equipment. The gaseous flame-retardant electrolyte comprises an electrolyte salt, an organic solvent, a basic film-forming additive, a primary amine additive, and a nano-metal oxide additive. The primary amine additive has a mass percentage of M1% (0.05 ≤ M1 ≤ 2.8%), and the nano-metal oxide additive has a mass percentage of M2% (0.01 ≤ M2 ≤ 0.08%), with a ratio of 10 ≤ M1 / M2 ≤ 50. This electrolyte achieves a flame-retardant effect while improving its flash point and preventing degradation of the battery's cycling performance.

Description

Technical Field

[0001] The present application relates to the technical field of electrolytes, and in particular to a gaseous flame-retardant electrolyte, a battery, and electrical equipment. Background Art

[0002] Liquid organic electrolytes are widely used in secondary batteries (such as lithium-ion and sodium-ion batteries) due to their excellent ionic conductivity and electrode compatibility. However, their main components, such as carbonate solvents, are often highly flammable, posing a serious safety hazard. This is particularly true when the battery experiences thermal runaway, mechanical abuse, or internal short circuits, where they can easily cause fire or even explosion. To improve battery safety, researchers have developed a variety of flame-retardant electrolyte technologies. The current main strategy involves adding flame-retardant additives such as phosphates (e.g., TPP, TEP, DMMP), fluorophosphates, phosphazenes, and ionic liquids to the electrolyte. However, the introduction of flame retardants often significantly degrades the electrochemical performance of the electrolyte, such as reduced ionic conductivity, increased interfacial impedance, deteriorating the cycling stability and rate performance of electrode materials (especially high-voltage cathode materials), and leading to severe battery capacity decay. Furthermore, some flame retardants have poor compatibility with electrode materials, potentially triggering side reactions or gassing.

[0003] Therefore, how to effectively improve the flame retardant properties of the electrolyte while maximally maintaining or even optimizing the basic electrochemical properties of the battery has become a core problem that needs to be urgently solved in the current development of flame retardant electrolyte technology. Summary of the Invention

[0004] The purpose of this application is to provide a gaseous flame-retardant electrolyte to effectively improve the flame-retardant performance of the electrolyte while maintaining or even optimizing its electrochemical properties such as battery cyclability and electrolyte flash point.

[0005] To achieve the above objectives, this application provides the following technical solutions:

[0006] The present application provides a gaseous flame-retardant electrolyte, which comprises: an electrolyte salt, an organic solvent, a basic film-forming additive, a primary amine additive, and a nano-metal oxide additive, wherein the organic solvent comprises a carbonate solvent;

[0007] Wherein, the mass percentage of the primary amine additive is M1%, 0.05≤M1≤2.8; the mass percentage of the nano metal oxide additive is M2%, 0.01≤M2≤0.08; and 10≤M1 / M2≤50.

[0008] Furthermore, the particle size of the nano metal oxide additive is 20-80 μm.

[0009] Furthermore, based on the mass fraction of the electrolyte being 100%, the mass percentage content of the carbonate solvent is greater than or equal to 55%;

[0010] Furthermore, the carbonate solvent is any one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate or propylene carbonate, or a combination of at least two thereof;

[0011] Furthermore, the organic solvent further comprises any one or more combinations of ethyl acetate, 2,2-difluoroethyl acetate, acetonitrile, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or tetrahydrofuran;

[0012] Furthermore, based on the mass fraction of the electrolyte being 100%, the content of the organic solvent in the electrolyte is 58.5% to 92.7%.

[0013] Furthermore, the temperature at which the primary amine additive and / or nano-metal oxide additive reacts with the carbonate organic solvent to generate CO2 is 75-90°C.

[0014] Furthermore, the primary amine additive is selected from one or more of octadecylamine, coconut oil primary amine, hydrogenated tallow primary amine, soybean oil primary amine, oleic acid primary amine, aniline, methylamine, ethylamine, ethylenediamine, benzylamine or cyclohexylamine.

[0015] Furthermore, the nano metal oxide additive is selected from one or more of ZnO, MgO, SiO2 or CaO.

[0016] Furthermore, the basic film-forming additives include one or more of vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, phthaleinsulfathiazole, and vinyl sulfate;

[0017] Furthermore, based on the mass fraction of the electrolyte being 100%, the content of the basic film-forming additive in the electrolyte is 0.5-5%.

[0018] Furthermore, the electrolyte salt is selected from one or more of XPF6, XClO4, XBF4, XAsF6, XFSI, XTFSI, XBOB, XODFB, XCF3SO3 or XPO2F2; wherein X includes any one of Li, Na or K;

[0019] Furthermore, the concentration of the electrolyte salt in the electrolyte is 0.8-1.2 mol / L.

[0020] The present invention provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the electrolyte is the above-mentioned gaseous flame-retardant electrolyte.

[0021] The present invention provides an electrical device, wherein the battery comprises the above-mentioned gaseous flame-retardant electrolyte.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The gaseous flame-retardant electrolyte provided by the present invention does not use conventional phosphorus-containing compounds as flame retardants. Instead, primary amines and nano-metal oxides are added to an electrolyte mainly containing carbonate compounds as solvents. The primary amines do not react with carbonate compounds at relatively low temperatures but react with carbonate compounds at relatively high temperatures (75-90°C), while the nano-metal oxides can catalyze the simultaneous hydrolysis of carbonate compounds and trace water in the electrolyte at a similar and relatively high temperature (75-90°C) to generate carbon dioxide that can form a flame-retardant layer, thereby achieving a flame-retardant effect. In addition, the primary amines and nano-metal oxides are used in combination in the present application. While providing a sufficient amount to form the flame-retardant layer, the amounts of the primary amines and nano-metal oxides added can be appropriately reduced, thereby avoiding excessive addition of the primary amines, which would result in an excessively low flash point of the electrolyte and a decrease in the cycle performance of the battery. At the same time, lithium plating defects caused by excessive addition of nano-metal oxide particles are avoided. Thus, the flame-retardant effect and safety performance are ensured while the flash point of the electrolyte is improved, the cycle performance of the battery is not degraded, and lithium plating at the negative electrode is not aggravated. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions of this application in conjunction with the embodiments. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0025] The applicant discovered that adding primary amines to an electrolyte containing carbonate compounds as the main organic solvent can cause the electrolyte to produce a large amount of CO2 when the temperature is raised to above 75°C, which can improve the flame retardant properties of the electrolyte. However, it will deteriorate the electrochemical performance of the battery, specifically by reducing ionic conductivity, increasing interfacial impedance, lithium precipitation, deteriorating the cycle stability and rate performance of electrode materials (especially high-voltage positive electrode materials), or causing serious battery capacity decay; in particular, when the addition amount of primary amine is increased to above 2.8%, the deterioration of battery performance is particularly obvious, but reducing the addition amount of primary amine will result in the carbon dioxide generated being insufficient to form a flame retardant layer with good flame retardant effect, and the improvement effect on safety performance is not obvious. Based on this, the applicant proposed a new gaseous flame-retardant electrolyte, which simultaneously adds primary amines and nano-metal oxides to an electrolyte with carbonate compounds as the main organic solvent, and controls the addition amount of primary amines and nano-metal oxides so that the amount of carbon dioxide forming the flame-retardant layer meets the flame-retardant requirements. It can also improve the battery performance degradation problem caused by excessive addition of primary amines or nano-metal oxides, so that the battery has electrochemical properties such as flame retardancy, improved electrolyte lightning, and no degradation of battery cycle performance and capacity retention rate.

[0026] The gaseous flame retardant electrolyte, battery and electrical equipment provided by the present invention are described in detail below:

[0027] The gaseous flame-retardant electrolyte includes: an electrolyte salt, an organic solvent, a basic film-forming additive, a primary amine additive and a nano-metal oxide additive, wherein the organic solvent includes a carbonate solvent; wherein the mass percentage of the primary amine additive is M1%, 0.05≤M1≤2.8; the mass percentage of the nano-metal oxide additive is M2%, 0.01≤M2≤0.08; and 10≤M1 / M2≤50.

[0028] The amino group (-NH2) of the primary amine acts as a nucleophile to attack the carbonyl carbon atom of the carbonate, forming a negatively charged tetrahedral intermediate. This intermediate is unstable, and the CO bond cleaves to form a carbamate (RNHCOOR') and the corresponding alcohol (R'OH). This process is similar to the nucleophilic substitution mechanism of the carbonyl group under alkaline conditions. A six-membered ring transition state forms within the carbamate molecule, lowering the decarboxylation barrier. The lone pair of electrons on the carbamate nitrogen atom conjugates with the carbonyl π* orbital, weakening the C-N bond and accelerating decarboxylation. The resulting CO2 is released as a gas. Excessive addition of primary amines can degrade the battery's cycling performance, while insufficient amounts can reduce CO2 production, making it insufficient for forming a flame-retardant layer. Therefore, the primary amine content is controlled between 0.05% and 2.8%.

[0029] At around 80°C, nanometal oxide additives catalyze the hydrolysis of carbonate solvents and trace water in the electrolyte, generating alcohols and CO2. Nanometal oxide additives can significantly increase the hydrolysis rate at high temperatures, rapidly gathering large amounts of gaseous CO2. The nanoparticles themselves possess a strong flame retardant effect, lowering the flash point of the electrolyte. However, excessive levels of nanometal oxide additives can cause lithium deposition in the battery cell. Due to solubility limitations, excessive levels can be limited, while too little can affect carbon dioxide production and be insufficient to create a flame-retardant layer. Therefore, the content of nanometal oxide additives is controlled at 0.01% to 0.08%.

[0030] By limiting the content ratio of the primary amine additive and the nano-metal oxide additive, the battery can be made flame retardant, the flash point of the electrolyte can be increased, and the degradation of the battery's cycle performance, capacity retention rate and other performance can be reduced.

[0031] In some optional embodiments, the amount of primary amine contained in the gaseous flame retardant electrolyte can be 0.05%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5% or 2.8%, etc., or other values ​​within the range of 0.05% to 2.8%.

[0032] In some optional embodiments, the amount of nano metal oxide contained in the gaseous flame retardant electrolyte may be 0.01%, 0.03%, 0.05% or 0.08%, etc., or may be other values ​​within the range of 0.01% to 0.08%.

[0033] In some preferred embodiments, the particle size of the nano metal oxide additive is 20-80 μm.

[0034] If the particle size of the nano metal oxide additive is higher than 80µm, the catalytic effect will be weakened and it will be easy to agglomerate or settle in the electrolyte; if it is lower than 20µm, the catalytic activity will be too strong, and the battery cell may produce gas at room temperature.

[0035] In some preferred embodiments, the organic solvent includes a carbonate solvent, which is illustratively but not limitatively selected from any one of dimethyl carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC) or propylene carbonate, or a combination of at least two thereof. The mass percentage of the carbonate solvent is preferably greater than or equal to 55%, which provides raw material support for the carbon dioxide forming the flame retardant layer. In addition, since one of the raw materials of the flame retardant layer is derived from the non-aqueous solvent of the battery, it not only does not need to consider the problem of insufficient raw materials, but also reduces the amount of non-aqueous solvent used as fuel in conventional batteries when combustion occurs, thereby improving battery safety.

[0036] In some preferred embodiments, the organic solvent further comprises a combination of any one or more of ethyl acetate, 2,2-difluoroethyl acetate, acetonitrile, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or tetrahydrofuran; and the content of the organic solvent in the electrolyte is 58.5% to 92.7%, based on the mass fraction of the electrolyte being 100%.

[0037] In some preferred embodiments, the temperature at which the primary amine additive and / or the nano-metal oxide additive reacts with the carbonate organic solvent to generate CO2 is 75-90°C.

[0038] In some preferred embodiments, the primary amine additive is selected from one or more of octadecylamine, coconut oil primary amine, hydrogenated tallow primary amine, soybean oil primary amine, oleic acid primary amine, aniline, methylamine, ethylamine, ethylenediamine, benzylamine or cyclohexylamine.

[0039] In some preferred embodiments, the nano metal oxide additive is selected from one or more of ZnO, MgO, SiO2 or CaO.

[0040] In some preferred embodiments, the basic film-forming additive includes one or more of vinylene carbonate (VC), 1,3-propane sultone, fluoroethylene carbonate (FEC), phthaleinsulfathiazole, and dithiothreitol disulfate (DTD). The content of the basic film-forming additive in the electrolyte is 0.5-5%, based on the mass fraction of the electrolyte as 100%.

[0041] In some preferred embodiments, the electrolyte salt is selected from one or more of XPF6 (hexafluorophosphate), XClO4 (perchlorate), XBF4 (tetrafluoroborate), XAsF6 (hexafluoroarsenate), XFSI (hexafluoroarsenate), XTFSI (bisfluorosulfonyl imide salt), XBOB (bisoxalatoborate), XODFB (difluorooxalatoborate), XCF3SO3 (trifluoromethanesulfonate) or XPO2F2 (difluorophosphate); wherein X includes any one of Li, Na or K; and the concentration of the electrolyte salt in the electrolyte is 0.8~1.2 mol / L.

[0042] In addition, the present invention also provides a battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned gaseous flame-retardant electrolyte.

[0043] The present invention also provides an electrical device, wherein the battery used in the electrical device includes the above-mentioned gaseous flame-retardant electrolyte.

[0044] The preparation method of a lithium-ion battery comprises the following steps:

[0045] (1) Preparation of positive electrode sheet: Dissolve polyvinylidene fluoride (PVDF) evenly in N-methylpyrrolidone (NMP), then add the conductive agent Super P, mix thoroughly, and then add the positive electrode active material LiNi 0.92 Co 0.03 Mn 0.03 O2 powder is gradually added (LiNi 0.92 Co 0.03 Mn 0.03 The mass ratio of O2 powder, PVDF and conductive agent Super P is 97.4:1.3:1.3 to obtain positive electrode slurry (the solid content of the positive electrode slurry is 63.1%). The positive electrode slurry is coated on the current collector, and then dried, rolled and slit to obtain positive electrode sheets that can be directly stacked.

[0046] (2) Preparation of negative electrode sheets: artificial graphite, conductive carbon, silicon oxide powder, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of 80.9:2.9:13.2:1.2:1.8 were pre-mixed and stirred at a speed of 250 rpm for 140 min to obtain a negative electrode slurry. The negative electrode slurry was then transferred to deionized water for dispersion. After mixing evenly, the negative electrode slurry was sieved. Finally, the sieved negative electrode slurry was coated on the negative electrode current collector, and then dried, rolled, and slit to obtain a negative electrode sheet that can be laminated.

[0047] (3) Cell production: The positive and negative electrodes and separators after stripping are stacked on a stacking machine. The separator is made of a three-layer material of PP / PE / PP to form a soft-pack cell.

[0048] (4) Liquid injection, formation and aging: After the battery cells are dried at high temperature, the electrolytes of the examples and comparative examples are injected into the soft-pack battery cells. After the electrolyte injection, the lithium battery undergoes the initial packaging and surface cleaning process to complete the preliminary work, and is placed at room temperature for one day. The formation is carried out using a step-by-step formation method. The first step is a formation current of 0.05C, and constant current charging is performed for 2 hours. The second step is a formation current of 0.1C, and constant current charging is performed until the voltage reaches 3.85V. After formation, it is aged at 50℃ for one day, cooled to room temperature, and finally sealed.

[0049] Test method:

[0050] High-temperature storage and safety testing was performed using 4.25V NCM|| graphite soft-pack batteries, and the testing was performed using the Xinwei charge and discharge test system.

[0051] 1. Gas production of battery cells stored at 60℃

[0052] At 25°C, the lithium ion batteries obtained in the examples and comparative examples were charged to 4.25 V at a constant current and constant voltage of 1C. After standing for 5 minutes, the cell volume was measured by the water displacement method to obtain V1. After drying the water, the cells were placed in a 60°C blast oven for 14 days, taken out, and allowed to stand for two hours to return to room temperature. The cell volume was then measured by the water displacement method to obtain V2. The gas production was calculated as follows:

[0053] Gas production of battery cells stored at 60°C high temperature = V2-V1.

[0054] 2. Gas production of battery cells stored at 80℃

[0055] At 25°C, the lithium ion batteries obtained in the examples and comparative examples were charged to 4.25 V at a constant current and constant voltage of 1C. After standing for 5 minutes, the cell volume was measured by the water displacement method to obtain V3. After drying the water, the cells were placed in an 80°C blast oven for 14 days, taken out, and allowed to stand for two hours to return to room temperature. The cell volume was then measured by the water displacement method to obtain V4. The gas production was calculated as follows:

[0056] Gas production of battery cells stored at 80°C high temperature = V4-V3.

[0057] 3. CO2 ratio in gas production of 80℃ high temperature storage cells

[0058] The gas inside the battery cell that has been stored at 80°C is extracted with a needle, and the CO2 content of the obtained gas is measured using GC.

[0059] 4. Acupuncture pass rate

[0060] At 25°C, the lithium-ion batteries obtained in the examples and comparative examples were charged to 4.25 V at a constant current and constant voltage of 1C. After standing for 5 minutes, a φ5mm steel needle was used to penetrate the battery cell at a speed of (25±2)mm / s from a direction perpendicular to the steel plate and remain in the battery cell. If the battery cell caught fire after 10 seconds, it was considered to have failed, and if the battery cell did not catch fire, it was considered to have passed. The needle penetration rate was calculated by the following formula:

[0061] Puncture pass rate = number of cells passing the test / 3×100%.

[0062] 5. Flash point of electrolyte

[0063] Part of the electrolytes of the examples and comparative examples were sent to a third-party agency for flash point testing.

[0064] 6. 25℃ normal temperature cycle capacity retention rate

[0065] At 25°C, the lithium ion batteries obtained in the examples and comparative examples were charged to 4.25 V at a constant current and constant voltage of 1C, allowed to stand for 5 minutes, and then discharged to 2.5 V at a constant current of 1C. The above is one charge / discharge cycle; wherein, the capacity retention rate of the lithium ion battery after 500 cycles is calculated by the following formula:

[0066] Capacity retention rate of lithium-ion battery after 500 cycles (%) = (discharge capacity at the 500th cycle / first discharge capacity) × 100%.

[0067] 7. Lithium deposition test

[0068] At 25°C, the lithium-ion batteries prepared in the Examples and Comparative Examples were fully charged and discharged at 1C for 500 cycles, then fully charged at 1C. The negative electrode sheets were then disassembled and the lithium deposition on the negative electrode sheet surfaces was observed. A lithium deposition area of ​​less than 5% on the negative electrode surface was considered mild, a lithium deposition area of ​​5% to 40% on the negative electrode surface was considered moderate, and a lithium deposition area of ​​more than 40% on the negative electrode surface was considered severe.

[0069] Table 1

[0070]

[0071] Note: The addition amount of each raw material in Table 1 is the mass fraction of each raw material in the electrolyte obtained by taking the mass fraction of the electrolyte as 100%.

[0072] Table 2

[0073]

[0074] As can be seen from Table 2, by comparing Examples 1-11 with Comparative Example 1, the combination of primary amine additives and nano-metal oxide additives can achieve large-scale production of CO2 at 80°C without deteriorating the cycle performance, significantly improve the needle puncture rate, and significantly increase the flash point of the electrolyte.

[0075] From Table 2, it can be seen that the combination of primary amine additives and nano-metal oxide additives has a low gas production at 60°C. The reason is that the energy barrier required for the reaction is not reached. However, at around 80°C, the decarboxylation reaction can be accelerated to quickly gather a large amount of CO2 to achieve the purpose of building a flame retardant layer.

[0076] It can be seen from Table 2 that although excessive primary amine additives can improve safety performance, they will greatly deteriorate electrochemical cycle performance. When the amount is too small, it is not enough to build a flame retardant layer and improve the needle puncture rate. Excessive nano-metal oxide additives will cause severe lithium deposition in the battery cell. When the amount is too small, it is not enough to build a flame retardant layer and improve the needle puncture rate.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A gaseous flame-retardant electrolyte, characterized in that: include: Electrolyte salt, organic solvent, basic film-forming additive, primary amine additive and nano metal oxide additive; the organic solvent includes carbonate solvent; The mass percentage of the primary amine additive is M1%, 0.05≤M1≤2.8; the mass percentage of the nano metal oxide additive is M2%, 0.01≤M2≤0.08; and 10≤M1 / M2≤50.

2. The gaseous flame-retardant electrolyte according to claim 1, characterized in that: The particle size of the nano metal oxide additive is 10-80 μm.

3. The gaseous flame-retardant electrolyte according to claim 1, characterized in that: Based on the mass fraction of the electrolyte being 100%, the mass percentage of the carbonate solvent is greater than or equal to 55%; and / or The carbonate solvent is any one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate or propylene carbonate; and / or The organic solvent further comprises any one or more combinations of ethyl acetate, 2,2-difluoroethyl acetate, acetonitrile, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or tetrahydrofuran; and / or Based on the mass fraction of the electrolyte being 100%, the content of the organic solvent in the electrolyte is 58.5% to 92.7%.

4. The gaseous flame-retardant electrolyte according to claim 1, characterized in that: The temperature for the reaction of the primary amine additive and / or nano metal oxide additive with the carbonate organic solvent to generate CO2 is 75-90°C.

5. The gaseous flame-retardant electrolyte according to claim 1, characterized in that: The primary amine additive is selected from one or more of octadecylamine, coconut oil primary amine, hydrogenated tallow primary amine, soybean oil primary amine, oleic acid primary amine, aniline, methylamine, ethylamine, ethylenediamine, benzylamine or cyclohexylamine.

6. The gaseous flame-retardant electrolyte according to claim 1, characterized in that: The nano metal oxide additive is selected from one or more of ZnO, MgO, SiO2 and CaO.

7. The gaseous flame-retardant electrolyte according to claim 1, characterized in that: The basic film-forming additives include one or more of vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, phthaleinsulfathiazole or vinyl sulfate; and / or Based on the mass fraction of the electrolyte being 100%, the content of the basic film-forming additive in the electrolyte is 0.5-5%.

8. The gaseous flame-retardant electrolyte according to claim 1, characterized in that: The electrolyte salt is selected from one or more of XPF6, XClO4, XBF4, XAsF6, XFSI, XTFSI, XBOB, XODFB, XCF3SO3 or XPO2F2; wherein X includes any one of Li, Na or K; and / or The concentration of the electrolyte salt in the electrolyte solution is 0.8-1.2 mol / L.

9. A battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The electrolyte is the gaseous flame-retardant electrolyte according to any one of claims 1 to 8.

10. An electrical device, characterized in that: A battery comprising the battery of claim 9.

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