Flame-retardant material for battery electrode, electrode and preparation method thereof, and lithium secondary battery

Abstract

The present application provides a battery electrode flame retardant material, an electrode and a preparation method thereof and a lithium secondary battery. The battery electrode flame retardant material comprises a flame retardant material substrate and a coating; the coating is coated on the surface of the flame retardant material substrate; the material of the coating comprises a hydroxyl stannate. The present application also provides an electrode with a flame retardant layer on the surface made of the above battery electrode flame retardant material. The present application also provides a lithium secondary battery comprising the above electrode. The surface of the battery electrode flame retardant material provided by the present application has a coating containing a hydroxyl stannate, which can be used as a flame retardant layer of an electrode. When thermal runaway occurs, the coating in the battery electrode flame retardant material can decompose and absorb heat, thereby controlling the intensity of thermal runaway.

Description

[0001] Cross-reference information

[0002] This invention claims priority to Chinese Patent Application No. 202510024981.1, filed in China on January 7, 2025, the disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to a flame-retardant material for battery electrodes, electrodes and their preparation methods, and lithium secondary batteries, belonging to the field of lithium battery technology. Background Technology

[0004] Lithium-ion batteries are playing an increasingly important role in the electronics, automotive, and energy storage fields. People's requirements for lithium-ion batteries are reflected in two aspects: performance and safety.

[0005] The safety issues of lithium secondary batteries manifest in the phenomenon of thermal runaway. Under conditions of thermal abuse, mechanical damage, or failure of internal material systems, the possibility of thermal runaway will increase significantly.

[0006] The energy storage mechanism of lithium-ion batteries is a redox reaction, containing both highly reactive oxidants and reductants. During thermal runaway, the contact between these oxidants and reductants releases a large amount of heat, and the reaction rate increases further with rising temperature, creating a vicious cycle that makes thermal runaway difficult to suppress. Furthermore, battery thermal runaway is accompanied by intense heat and gas generation, leading to heat conduction and explosion. Therefore, suppressing the continued heat and gas generation after thermal runaway, as well as subsequent combustion and explosion, is a key aspect of battery safety research. Suppressing reaction-promoting factors during thermal runaway, such as reducing heat generation, lowering reactant concentrations, reducing reactant contact, and minimizing electron competition, are the main methods to reduce the severity of thermal runaway.

[0007] Adding flame retardants to the material system of lithium secondary batteries allows them to absorb the heat generated by the reaction and dilute or isolate the reactants in the event of thermal runaway. This is currently a relatively mature solution.

[0008] Currently used flame retardants include halogenated flame retardants and inorganic flame retardants. Halogenated flame retardants are mainly halogenated polymers, while inorganic flame retardants mainly include aluminum hydroxide, magnesium hydroxide, and their mixtures. These flame retardants each have the following problems: halogenated polymers have high strength and are not easily incorporated into the main materials of lithium-ion batteries; inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide have poor dispersibility, making them difficult to use in low-cost processes such as coating, and they have poor affinity for lipophilic molecules in electrolytes, leading to a tendency for secondary aggregation and poor compatibility. Summary of the Invention

[0009] In order to solve the above-mentioned technical problems, the present invention aims to provide a flame retardant material for battery electrodes. This flame retardant material for battery electrodes has good flame retardant properties. When coated on the surface of the electrode, it can control the intensity of thermal runaway by decomposition and heat absorption in the event of thermal runaway.

[0010] The present invention also aims to provide an electrode made of the above-mentioned flame-retardant material for battery electrodes, a method for preparing the same, and a lithium secondary battery containing the electrode.

[0011] To achieve the above objectives, the present invention first provides a flame-retardant material for battery electrodes, comprising a flame-retardant substrate and a coating;

[0012] The coating is applied to the surface of the flame-retardant substrate.

[0013] The coating contains hydroxystannate.

[0014] According to a specific embodiment of the present invention, preferably, in the flame retardant material for the battery electrode, the hydroxystannate includes one or more of zinc hydroxystannate, calcium hydroxystannate, magnesium hydroxystannate, aluminum hydroxystannate, etc.

[0015] According to a specific embodiment of the present invention, preferably, in the flame-retardant material for the battery electrode, the thickness of the coating is 20-200 nm.

[0016] According to a specific embodiment of the present invention, preferably, in the flame-retardant material for the battery electrode, the flame-retardant substrate includes an inorganic flame-retardant substrate.

[0017] According to a specific embodiment of the present invention, preferably, in the flame retardant material for the battery electrode, the inorganic flame retardant substrate includes one or more of aluminum hydroxide, magnesium hydroxide, aluminum oxide, and magnesium oxide.

[0018] According to a specific embodiment of the present invention, preferably, the flame retardant material for the battery electrode is granular, that is, the flame retardant material for the battery electrode can be in the form of flame retardant particles; more preferably, the particle size (i.e., flame retardant particles) is 100nm-500nm.

[0019] According to a specific embodiment of the present invention, preferably, the preparation method of the flame-retardant material for the battery electrode includes the following steps:

[0020] The flame-retardant substrate, tin source, metal source, and alkaline solution are mixed, and then heated, separated, washed, and dried to obtain the flame-retardant material for the battery electrode; the metal in the metal source is a metal other than tin in hydroxystannate.

[0021] According to a specific embodiment of the present invention, preferably, the heating temperature is 120℃-180℃.

[0022] According to a specific embodiment of the present invention, preferably, the flame retardant substrate is added in the form of an emulsion, the emulsion comprising the flame retardant substrate, surfactant, and water in a mass ratio of 3-15:30-60:180-360.

[0023] According to a specific embodiment of the present invention, preferably, the tin source includes one or a combination of two or more of tin dioxide, tin tetrachloride, stannous nitrate and stannous sulfate.

[0024] According to a specific embodiment of the present invention, preferably, the metal source includes one or more combinations of oxides, chlorides, nitrates, and sulfates of the metal. More preferably, the metal source is a zinc source, and the zinc source includes one or more combinations of zinc oxide, zinc nitrate, zinc chloride, and zinc sulfate.

[0025] According to a specific embodiment of the present invention, preferably, the alkaline solution comprises one or a combination of two or more of sodium hydroxide solution, potassium hydroxide solution, and ammonia solution, wherein the mass percentage concentration of the ammonia solution is 18%-28%. When ammonia solution is used, its molar amount is expressed as ammonium ions (NH4+). 4+ ( ) molarity meter.

[0026] According to a specific embodiment of the present invention, preferably, in the emulsion of the flame retardant substrate, the surfactant includes a cationic surfactant; more preferably, the cationic surfactant includes one or a combination of two or more of hexadecyltrimethyl quaternary ammonium bromide and octadecyldimethylbenzyl quaternary ammonium chloride.

[0027] According to a specific embodiment of the present invention, preferably, the molar ratio of the tin source to the metal source is 1:2-4:1, the molar ratio of the tin source to the alkaline solution is 1:10-1:1, the molar amount of the tin source is measured in molar amounts of tin, the molar amount of the metal source is measured in molar amounts of metal, and the molar amount of the alkaline solution is measured in molar amounts of alkali.

[0028] According to a specific embodiment of the present invention, preferably, the molar ratio of the tin source to the flame retardant substrate is 1:10-1:1, the molar ratio of the tin source to the surfactant is 1:20-2:1, and the molar amount of the tin source is expressed as the molar amount of tin. In calculations, the molar amount of the flame retardant substrate is expressed as the molar amount of the metal or metal compound it contains; for example, when aluminum hydroxide is used, it can be expressed as the molar amount of aluminum or aluminum hydroxide.

[0029] The present invention also provides an electrode having a flame-retardant layer on its surface, the flame-retardant layer comprising the flame-retardant material for battery electrodes provided by the present invention, wherein the coating amount of the flame-retardant layer is 0.2 mg / cm², based on the area of ​​the electrode surface covered by the flame-retardant layer. 2 -1.5mg / cm 2 The content of the flame-retardant material for the battery electrode is 75%-95% based on 100% by mass of the flame-retardant layer. This coating amount is based on the area of ​​the electrode surface covered by the flame-retardant layer.

[0030] According to a specific embodiment of the present invention, preferably, the electrode is a positive electrode.

[0031] According to a specific embodiment of the present invention, preferably, the flame-retardant layer in the electrode further contains 5%-25% binder.

[0032] According to a specific embodiment of the present invention, preferably, in the flame-retardant layer, the adhesive includes one or a combination of two of polyvinylidene fluoride (PVDF), polyacrylic acid, etc.

[0033] According to a specific embodiment of the present invention, preferably, the thickness of the flame-retardant layer in the electrode is 3μm-10μm.

[0034] According to a specific embodiment of the present invention, preferably, the electrode further includes a current collector and an active layer; the active layer is located on the surface of the current collector, and the flame-retardant layer is located on the outer surface of the active layer.

[0035] According to a specific embodiment of the present invention, preferably, the thickness of the current collector in the electrode is 6μm-12μm.

[0036] According to a specific embodiment of the present invention, preferably, the thickness of the active layer in the electrode is 80μm-120μm.

[0037] The present invention also provides a method for preparing the above-mentioned electrode, wherein the method includes the following steps:

[0038] An active layer is formed on the current collector surface of the electrode;

[0039] A mixed slurry containing flame-retardant materials for battery electrodes is coated on the surface of the active layer, and then dried and rolled to form a flame-retardant layer, thereby obtaining the electrode with the flame-retardant layer.

[0040] The solid content of the mixed slurry containing flame-retardant materials for battery electrodes is 5%-35%.

[0041] According to a specific embodiment of the present invention, preferably, in the method for preparing the electrode, the mixed slurry containing the flame-retardant material for battery electrodes is composed of the flame-retardant material for battery electrodes, a binder, and a solvent.

[0042] According to a specific embodiment of the present invention, preferably, in the electrode preparation method, the coating thickness of the mixed slurry containing flame-retardant material for battery electrodes when coating the surface of the active layer is 5μm-70μm.

[0043] The present invention also provides a lithium secondary battery, wherein the lithium secondary battery includes the electrode provided by the present invention, namely, the electrode including a flame-retardant layer.

[0044] The flame-retardant material for battery electrodes provided by the present invention is a coating containing hydroxystannate. This flame-retardant material for battery electrodes can serve as a flame-retardant layer for electrodes. When thermal runaway occurs, the coating in the flame-retardant material for battery electrodes can decompose and absorb heat, thereby controlling the intensity of thermal runaway. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of a specific structure of an electrode containing a flame-retardant layer provided by the present invention.

[0046] Explanation of main icon numbers:

[0047] 1. Current collector; 2. Active layer; 3. Flame retardant layer. Detailed Implementation

[0048] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0049] However, it should be understood that the present invention is not limited to the specific embodiments, and includes all modifications, equivalents or substitutions within the spirit and technical scope of the present invention.

[0050] In this invention:

[0051] The terms “comprising,” “including,” and “having” are used herein to indicate the presence of a feature, number, step, action, component, or element, or combination thereof, as described in the specification, and it should be understood that the possibility of the presence or addition of one or more other features, numbers, steps, actions, components, elements, or combinations thereof is not excluded in advance.

[0052] A first aspect of the present invention provides a flame-retardant material for battery electrodes, comprising a flame-retardant substrate and a coating;

[0053] The coating is applied to the surface of the flame-retardant substrate.

[0054] The coating contains hydroxystannate.

[0055] According to the flame-retardant material for battery electrodes of the first aspect, preferably, the flame-retardant material for battery electrodes is a flame-retardant substrate with a coating on its surface, the coating containing hydroxystannate, thereby obtaining flame-retardant properties. The hydroxystannates used in this invention include, but are not limited to, one or a combination of two or more of zinc hydroxystannate, calcium hydroxystannate, magnesium hydroxystannate, and aluminum hydroxystannate. The hydroxystannates used in this invention have moderate oleophilicity, allowing compatibility with electrolytes in lithium secondary batteries, and will not adversely affect the lithium secondary battery. Furthermore, the thermal decomposition temperature of the hydroxystannates used in this invention is below 400°C. A coating made of hydroxystannate is applied to the surface of the flame-retardant substrate to obtain the flame-retardant material for battery electrodes, and then the flame-retardant material is coated onto the surface of the electrode to form a flame-retardant layer. When a lithium secondary battery containing this electrode experiences thermal runaway, the hydroxystannate in the coating can begin to decompose and absorb heat in the early stages of thermal runaway at relatively low temperatures, thereby suppressing heat generation during thermal runaway and controlling the degree of thermal runaway. Furthermore, the decomposition of the hydroxystannate in the coating exposes the internal flame-retardant substrate, thus enabling it to exert its flame-retardant effect. Preferably, zinc hydroxystannate provides a decomposition temperature of approximately 180°C.

[0056] According to the flame-retardant material for battery electrodes in the first aspect, preferably, the coating is applied to the surface of the flame-retardant substrate in the form of a coating or the like. The coating can be a coating layer with a uniform thickness or it can be non-uniform, as long as it can coat the flame-retardant substrate and provide suitable flame-retardant properties.

[0057] According to the flame-retardant material for battery electrodes of the first aspect, preferably, the thickness of the coating can be 20-200 nm. In this invention, the thickness of the coating can be determined by: performing focused ion beam (FIB) testing on the flame-retardant material for battery electrodes and measuring based on the cross-sectional images obtained from the test; for a single flame-retardant material for battery electrodes, the thickness of the coating layer at multiple locations can be tested, and then the average of these test values ​​is taken as the thickness value of the coating layer of the individual flame-retardant material for battery electrodes; the number of test locations can be selected according to the uniformity of the coating layer, generally 3-10 locations can be selected. When the thickness of the coating layer is lower than the above range, the amount of flame-retardant material for battery electrodes contained is less, which may not provide sufficient flame-retardant performance; when the thickness of the coating layer is higher than the above range, the size of the flame-retardant material for battery electrodes is larger (for example, the particle size of granular flame-retardant material for battery electrodes may be large), and the flame-retardant layer formed on the electrode surface may also be relatively thick, thereby affecting the performance of the electrode; it may also form a single phase of the coating material, making it difficult to make a slurry that can be used for coating. By controlling the thickness of the coating layer within the aforementioned range, good flame-retardant properties can be provided while avoiding adverse effects on electrode performance. Specifically, the thickness of the coating can be 40-180 nm, 60-160 nm, 80-140 nm, or 100-120 nm.

[0058] According to the flame-retardant material for battery electrodes in the first aspect, the flame-retardant substrate used in this invention can be a material that provides flame-retardant properties, preferably an inorganic flame-retardant substrate, etc.; more preferably, the inorganic flame-retardant substrate includes one or more combinations of aluminum hydroxide, magnesium hydroxide, aluminum oxide, magnesium oxide, etc. Since inorganic flame-retardant substrates have poor oleophilicity, using an inorganic flame-retardant substrate alone as a flame retardant will result in incompatibility with the electrolyte. This invention solves the compatibility problem between the inorganic flame-retardant substrate and the electrolyte by coating the surface of the inorganic flame-retardant substrate with hydroxystannate as a coating material, utilizing the oleophilicity of hydroxystannate. Moreover, hydroxystannate itself has good flame-retardant properties. Thus, this invention unexpectedly achieves good flame-retardant properties while also solving the problems of dispersibility and compatibility of inorganic flame-retardant substrates through the combination of two flame-retardant materials. The preferred technical solution provided by the present invention uses hydroxystannate as a coating agent to coat the surface of an inorganic flame retardant substrate, which can improve its dispersibility and provide good coating performance during the preparation of the flame retardant layer; in addition, by using hydroxystannate as a coating agent, the compatibility between the inorganic flame retardant substrate and oleophilic molecules in electrolytes and the like can also be improved.

[0059] According to the flame-retardant material for battery electrodes of the first aspect, preferably, the flame-retardant material for battery electrodes is granular, that is, the flame-retardant material for battery electrodes of the present invention can be in the form of flame-retardant particles; more preferably, the particle size (i.e., flame-retardant particles) is 100nm-500nm, specifically 150nm-450nm or 200nm-400nm.

[0060] According to the flame-retardant material for battery electrodes of the first aspect, preferably, the method for preparing the flame-retardant material for battery electrodes includes the following steps:

[0061] The flame-retardant substrate, tin source, metal source, and alkaline solution are mixed, and then heated, separated, washed, and dried to obtain the flame-retardant material for the battery electrode; the metal in the metal source is a metal other than tin in hydroxystannate.

[0062] According to the flame-retardant material for battery electrodes of the first aspect, preferably, the heating temperature during the preparation of the flame-retardant material for battery electrodes is 120℃-180℃. During the heating process, by controlling the heating temperature within the above range, atoms inside the flame-retardant substrate can escape during heating, forming a hollow structure, which is beneficial for the formation of the coating layer. When the temperature is below the above range, the raw materials for the coating layer may not be able to complete the reaction, affecting the flame-retardant properties of the coating layer; when the temperature is above the above range, the hydroxystannate in the synthesized coating layer may decompose, which may also affect the integrity and flame-retardant properties of the coating layer. More preferably, the heating temperature is 130℃-170℃ or 140-160℃.

[0063] According to the flame retardant material for battery electrodes of the first aspect, preferably, by using the above-described method, a hydroxystannate with a hierarchical structure can be formed on the surface of the flame retardant substrate, which can give the flame retardant material for battery electrodes good dispersibility.

[0064] According to the flame-retardant material for battery electrodes of the first aspect, preferably, in the process of preparing the flame-retardant material for battery electrodes, the flame-retardant substrate (especially an inorganic flame-retardant substrate) is added in the form of an emulsion, the emulsion comprising the flame-retardant substrate (especially an inorganic flame-retardant substrate), a surfactant, and water in a mass ratio of 3-15:30-60:180-360. When the mass ratio of the flame-retardant substrate, the surfactant, and water is controlled within the above range, the flame-retardant substrate (especially an inorganic flame-retardant substrate) can be well dispersed in the emulsion, providing a good foundation for subsequent coating with hydroxystannate. If the mass ratio of flame retardant substrate (especially inorganic flame retardant substrate), surfactant, and water is lower than the above range, i.e., the amount of flame retardant substrate (especially inorganic flame retardant substrate) decreases and the amount of surfactant increases, excess surfactant may form independent micelles. Tin source, metal source, and alkaline solution tend to cause soft template growth on the micelles. This soft template growth will compete with the coating reaction on the flame retardant surface for tin source, metal source, and alkaline solution, inhibiting the coating reaction. If the mass ratio of flame retardant substrate (especially inorganic flame retardant substrate), surfactant, and water is lower than the above range, i.e., the amount of flame retardant substrate (especially inorganic flame retardant substrate), surfactant, and water increases, excess surfactant may form independent micelles. Tin source, metal source, and alkaline solution are more likely to form soft template growth on the micelles. This soft template growth will compete with the coating reaction on the flame retardant surface for tin source, metal source, and alkaline solution, inhibiting the coating reaction. If the mass ratio of surfactant to water exceeds the aforementioned range, i.e., the amount of flame-retardant substrate (especially inorganic flame-retardant substrate) increases while the amount of surfactant decreases, it may not be possible to achieve a good dispersion effect of the flame-retardant substrate (especially inorganic flame-retardant substrate). For example, the flame-retardant substrate (especially inorganic flame-retardant substrate) may aggregate, which may result in larger flame-retardant particles when coating with hydroxystannate. When using such flame-retardant particles to prepare the flame-retardant layer, it will affect the uniformity of the flame-retardant layer, and thus affect the flame-retardant effect of the flame-retardant layer in the event of thermal runaway. More preferably, the mass ratio of flame-retardant substrate (especially inorganic flame-retardant substrate), surfactant, and water is 5-15:30-60:180-360, 10-15:30-60:180-360, or 10-12:40-60:240-360.

[0065] According to the first aspect of the flame retardant material for battery electrodes, preferably, in the process of preparing the flame retardant material for battery electrodes, the tin source includes one or more combinations of tin dioxide, tin tetrachloride, stannous nitrate and stannous sulfate.

[0066] According to the flame-retardant material for battery electrodes of the first aspect, preferably, in the process of preparing the flame-retardant material for battery electrodes, the metal source includes one or more combinations of oxides, chlorides, nitrates, and sulfates of the metal. Different metal sources can be used when preparing different hydroxystannates. For example, when preparing zinc hydroxystannate, the metal source is a zinc source, which includes one or more combinations of zinc oxide, zinc nitrate, zinc chloride, and zinc sulfate; when preparing calcium hydroxystannate, magnesium hydroxystannate, and aluminum hydroxystannate, the metal source used can be a calcium source, a magnesium source, and an aluminum source, respectively, specifically oxides, nitrates, chlorides, and sulfates of calcium, magnesium, and aluminum.

[0067] According to the flame-retardant material for battery electrodes of the first aspect, preferably, in the process of preparing the flame-retardant material for battery electrodes, the alkaline solution includes one or more combinations of sodium hydroxide solution, potassium hydroxide solution, and ammonia. When ammonia is used, its molar amount is expressed as ammonium ions (NH4+). 4+ The ammonia concentration used in this invention is measured in molar amounts. More preferably, the mass percentage concentration of the ammonia water is 18%-28%, and even more preferably 20%-28%.

[0068] According to the first aspect of the flame-retardant material for battery electrodes, preferably, in the process of preparing the flame-retardant material for battery electrodes, the surfactant in the emulsion of the flame-retardant substrate includes a cationic surfactant; more preferably, the cationic surfactant includes one or a combination of two of the following: trimethyl quaternary ammonium chloride having 12 to 18 alkyl groups, trimethyl quaternary ammonium bromide having 12 to 18 alkyl groups, dimethyl quaternary ammonium chloride having two alkyl groups, dimethyl quaternary ammonium bromide having two alkyl groups, dimethyl ethyl quaternary ammonium chloride having 12 to 18 alkyl groups, dimethyl ethyl quaternary ammonium bromide having 12 to 18 alkyl groups, dimethyl benzyl quaternary ammonium chloride having 12 to 18 alkyl groups, and dimethyl benzyl quaternary ammonium bromide having 12 to 18 alkyl groups. Adding surfactants can improve the dispersibility of flame-retardant substrates (especially inorganic flame-retardant substrates) in emulsions, thereby allowing hydroxystannate to be more uniformly coated on the surface of the flame-retardant substrate (especially inorganic flame-retardant substrates). Without surfactants, the flame-retardant substrates (especially inorganic flame-retardant substrates) may stick together.As exemplary examples, trimethyl quaternary ammonium chlorides having alkyl groups having 12 to 18 carbon atoms include dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, etc.; trimethyl quaternary ammonium bromides having alkyl groups having 12 to 18 carbon atoms include dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, etc.; dimethyl quaternary ammonium chlorides having two alkyl groups having 12 to 18 carbon atoms include didodecyldimethylammonium chloride, ditetradecyldimethylammonium chloride, dihexadecyldimethylammonium chloride, dioctadecyldimethylammonium chloride, etc.; dimethyl quaternary ammonium bromides having two alkyl groups having 12 to 18 carbon atoms include didodecyldimethylammonium bromide, ditetradecyldimethylammonium bromide, dihexadecyldimethylammonium bromide, dioctadecyldimethylammonium bromide, etc.; trimethyl quaternary ammonium chlorides having ... bromides having alkyl groups having 12 to 1 Alkyl dimethyl ethyl quaternary ammonium chlorides include dodecyl dimethyl ethyl ammonium chloride, tetradecyl dimethyl ethyl ammonium chloride, hexadecyl dimethyl ethyl ammonium chloride, octadecyl dimethyl ethyl ammonium chloride, etc.; alkyl dimethyl ethyl quaternary ammonium bromides having 12 to 18 carbon atoms include dodecyl dimethyl ethyl ammonium bromide, tetradecyl dimethyl ethyl ammonium bromide, hexadecyl dimethyl ethyl ammonium bromide, octadecyl dimethyl ethyl ammonium bromide, etc.; alkyl dimethyl benzyl quaternary ammonium chlorides having 12 to 18 carbon atoms include dodecyl dimethyl benzyl ammonium chloride, tetradecyl dimethyl benzyl ammonium chloride, hexadecyl dimethyl benzyl ammonium chloride, octadecyl dimethyl benzyl ammonium chloride, etc.; alkyl dimethyl benzyl quaternary ammonium bromides having 12 to 18 carbon atoms include dodecyl dimethyl benzyl ammonium bromide, tetradecyl dimethyl benzyl ammonium bromide, hexadecyl dimethyl benzyl ammonium bromide, octadecyl dimethyl benzyl ammonium bromide, etc.

[0069] According to the flame-retardant material for battery electrodes of the first aspect, preferably, in the process of preparing the flame-retardant material for battery electrodes, the molar ratio of the tin source to the metal source is 1:2-4:1, the molar ratio of the tin source to the alkaline solution is 1:10-1:1, the molar amount of the tin source is expressed as the molar amount of tin, the molar amount of the metal source is expressed as the molar amount of metal, and the molar amount of the alkaline solution is expressed as the molar amount of alkali. More preferably, the molar ratio of the tin source to the metal source is 1:2-3.5:1, 1:2-2:1, 1:1.5-2:1, or 1:1-2:1; the molar ratio of the tin source to the alkaline solution is 1:10-1:2, 1:10-1:5, or 1:10-1:8.

[0070] According to the flame-retardant material for battery electrodes of the first aspect, preferably, in the process of preparing the flame-retardant material for battery electrodes, the molar ratio of the tin source to the flame-retardant substrate is 1:10-1:1, the molar ratio of the tin source to the surfactant is 1:20-2:1, and the molar amount of the tin source is expressed as the molar amount of tin. More preferably, the molar ratio of the tin source to the flame-retardant substrate is 1:8-1:1.5, 1:10-1:2, 1:8-1:2, or 1:4-1:2; and the molar ratio of the tin source to the surfactant is 1:15-1:1, 1:10-1:1, or 1:8-1:2. In calculations, the molar amount of the flame-retardant substrate is expressed as the molar amount of the metal or metal compound it contains; for example, when aluminum hydroxide is used, it can be expressed as the molar amount of aluminum or aluminum hydroxide.

[0071] A second aspect of the present invention provides an electrode having a flame-retardant layer on its surface, the flame-retardant layer comprising the flame-retardant material for battery electrodes provided by the present invention, wherein the coating amount of the flame-retardant layer is 0.2 mg / cm², based on the area of ​​the electrode surface covered by the flame-retardant layer. 2 -1.5mg / cm 2 The flame-retardant material content of the battery electrode is 75%-95% based on 100% by mass of the flame-retardant layer. When the coating amount of the flame-retardant layer is controlled within the above range, good flame-retardant properties can be provided on the electrode surface. When the coating amount of the flame-retardant layer is lower than the above range, the flame-retardant layer on the electrode surface may be relatively thin, and in the event of thermal runaway, the flame-retardant layer may not provide sufficient flame-retardant properties. When the coating amount of the flame-retardant layer is higher than the above range, the flame-retardant layer on the electrode surface may be relatively thick, thereby affecting the electrode performance. Preferably, the coating amount of the flame-retardant layer is 0.22 mg / cm³. 2 -1.45mg / cm 2 0.25 mg / cm 2 -1.44mg / cm 2 Or 0.3 mg / cm 2 -0.8mg / cm 2 More preferably 0.31 mg / cm³ 2 -0.66mg / cm 2 The electrode surface covered by the flame retardant layer refers to the area covered when the material forming the flame retardant layer is coated. Generally, the flame retardant layer will cover the entire surface of the electrode.

[0072] According to the electrode of the second aspect, preferably, the electrode is a positive electrode. The electrode of the present invention is preferably a positive electrode sheet.

[0073] According to the electrode of the second aspect, the content of the flame-retardant material for the battery electrode is 75%-95% based on 100% by mass of the flame-retardant layer. With the same coating amount of the flame-retardant layer, good flame-retardant performance can be provided when the content of the flame-retardant material for the battery electrode is within the above range. When the content of the flame-retardant material for the battery electrode is lower than the above range, the content of the flame-retardant material for the battery electrode in the flame-retardant layer is low, and the flame-retardant layer may not provide sufficient flame-retardant performance in the event of thermal runaway. When the content of the flame-retardant material for the battery electrode is higher than the above range, the content of the flame-retardant material for the battery electrode in the flame-retardant layer is high, which may affect the performance of the electrode. More preferably, the content of the flame-retardant material for the battery electrode is 80%-90% based on 100% by mass of the flame-retardant layer.

[0074] According to the electrode of the second aspect, preferably, the flame-retardant layer further contains 5%-25% binder, more preferably 10%-20%. With the same coating amount of the flame-retardant layer, when the binder content is within the above range, the flame-retardant material for the battery electrode can achieve good adhesion without affecting its flame-retardant function. When the binder content is below the above range, the flame-retardant material for the battery electrode in the flame-retardant layer may not achieve good adhesion, potentially resulting in weak adhesion and detachment during use. This would prevent the flame-retardant layer from maintaining its integrity, and in the event of thermal runaway, the flame-retardant layer may not provide sufficient flame-retardant performance. When the binder content exceeds the above range, excessive binder in the flame-retardant layer may result in larger gaps between the flame-retardant materials for the battery electrodes, preventing proper coverage. In the event of thermal runaway, this may affect the decomposition endothermic effect of the flame-retardant materials for the battery electrodes. Furthermore, a higher binder content means a lower content of flame-retardant materials for the battery electrodes in the flame-retardant layer. In the event of thermal runaway, insufficient flame-retardant materials for the battery electrodes may also lead to poor flame-retardant performance.

[0075] According to the electrode of the second aspect, preferably, the adhesive includes one or a combination of two of the following: polyvinylidene fluoride, polyacrylic acid, polyacrylate, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylonitrile, polyvinyl alcohol, polytetrafluoroethylene, polyolefin, fluorinated rubber, polyimide, perfluorosulfonic acid ionomer, etc.

[0076] According to the electrode of the second aspect, preferably, the thickness of the flame-retardant layer is 3μm-10μm, more preferably 5μm-8μm. When the electrode is sheet-like and has flame-retardant layers on both sides, the thickness of the flame-retardant layer refers to the thickness of the flame-retardant layer on one side. The thickness of the flame-retardant layer is determined as follows: obtaining a scanning electron microscope image of the cross-section of the electrode with the flame-retardant layer, and then measuring the thickness of the flame-retardant layer at several locations (e.g., 3-10), and taking the average of these measurements as the thickness value of the flame-retardant layer. When the thickness of the flame-retardant layer is controlled within the above range, good flame-retardant performance can be provided on the surface of the electrode. When the thickness of the flame-retardant layer is lower than the above range, the flame-retardant layer on the electrode surface may be relatively thin, and when thermal runaway occurs, the flame-retardant layer may not provide sufficient flame-retardant performance. When the thickness of the flame-retardant layer is higher than the above range, the flame-retardant layer on the electrode surface may be relatively thick, thereby affecting the performance of the electrode.

[0077] According to the electrode of the second aspect, preferably, the positive electrode further includes a current collector and a positive electrode active layer; the positive electrode active layer is located on the surface of the current collector, and the flame retardant layer is located on the outer surface of the positive electrode active layer.

[0078] As a typical example, the structure of the electrode including the flame-retardant layer provided by the present invention can be as follows: Figure 1 As shown, it includes a current collector 1, an active layer 2, and a flame-retardant layer 3. The two active layers 2 are located on opposite sides of the current collector 1, and the two flame-retardant layers 3 are located on the outer surfaces of the two active layers 2, i.e., the surfaces furthest from the current collector 1. It should be noted that the specific structure of this electrode is not limited to... Figure 1 The structure shown.

[0079] According to the electrode of the second aspect, preferably, the current collector used for the positive electrode is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon (sintered carbon), or surface-treated aluminum or stainless steel (treated materials include carbon, nickel, titanium, silver, etc.) can be used as the current collector.

[0080] According to the electrode of the second aspect, preferably, the thickness of the current collector can be between 6 μm and 12 μm, more preferably between 8 μm and 10 μm, but is not limited thereto. Furthermore, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the active layer.

[0081] Specifically, the current collector can be wholly or partially coated with a conductive primer to reduce surface resistance and improve adhesion. In this case, the conductive primer can contain conductive materials and adhesives. The conductive materials are not limited, as long as they are conductive; for example, they can be carbon-based materials. The adhesives can include fluoropolymer adhesives (including PVDF and PVDF copolymers), acrylic adhesives, and water-based adhesives, all of which are soluble in solvents.

[0082] For the electrode according to the second aspect, preferably, the thickness of the positive electrode active layer is 80 μm - 120 μm, preferably between 90 μm and 110 μm, but is not limited thereto. The positive electrode active material for preparing the positive electrode active layer is not particularly limited as long as it is a commonly used positive electrode active material, and the surface of the positive electrode active material may have a conductive coating, such as a carbon coating.

[0083] For the electrode according to the second aspect, preferably, the positive electrode active material used is a compound capable of reversibly inserting and extracting lithium, and preferably may include a lithium transition metal compound containing one or more selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe).

[0084] More specifically, the positive electrode active material may include a lithium metal oxide containing lithium and one or more metals (such as cobalt, manganese, nickel, and aluminum). More specifically, the lithium metal oxide may be a lithium manganese-based oxide (for example, LiMnO2, LiMn2O4, etc.), a lithium cobalt-based oxide (for example, LiCoO2, etc.), a lithium nickel-based oxide (for example, LiNiO2, etc.), a lithium nickel manganese-based oxide (for example, LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), a lithium nickel cobalt-based oxide (for example, LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium manganese cobalt-based oxide (for example, LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium nickel manganese cobalt-based oxide (for example, Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, and p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, and p1 + q1 + r1 = 2), etc.), or a lithium nickel cobalt transition metal (M) oxide (for example, Li(Ni p2 Co q2 Mn r2 M s2O2 (where M is selected from the group composed of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, p2, q2, r2 and s2 are the atomic fractions of each independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), and any one, two or more of the above compounds.

[0085] In particular, lithium metal oxides can be LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxides (e.g., Li(Ni)O2) to improve battery capacity and stability. 1 / 3 Mn 1 / 3 Co 1 / 3 O2, Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 O2, Li(Ni) 0.7 Mn 0.15 Co 0.15 O2, Li(Ni) 0.8 Mn 0.1 Co 0.1 O2, etc.), lithium nickel cobalt aluminum oxides (e.g., Li(Ni) 0.8 Co 0.15 Al 0.05 O2, etc., or lithium nickel manganese cobalt aluminum oxides (e.g., Li(Ni) 0.86 Co 0.05 Mn 0.07 Al 0.02 Compounds such as O2, lithium iron phosphate (e.g., LiFePO4), and any one, two, or more of the above.

[0086] A third aspect of the present invention provides a method for preparing the electrode described in the second aspect, wherein the method includes the following steps:

[0087] An active layer is formed on the current collector surface of the electrode;

[0088] A mixed slurry containing flame-retardant materials for battery electrodes is coated on the surface of the active layer, and then dried and rolled to form a flame-retardant layer, thereby obtaining the electrode with the flame-retardant layer.

[0089] The solid content of the mixed slurry containing flame-retardant materials for battery electrodes is 5%-35%.

[0090] According to the preparation method of the third aspect of the present invention, preferably, the mixed slurry containing the flame retardant material for battery electrodes is composed of the flame retardant material for battery electrodes, a binder and a solvent.

[0091] According to the preparation method of the third aspect of the present invention, preferably, the mixed slurry is prepared by the following process: mixing a flame retardant material for battery electrodes with a binder, adding a solvent to dilute to a predetermined solid content, and then stirring to obtain a uniform suspension, i.e., the mixed slurry.

[0092] According to the preparation method of the third aspect of the present invention, when the solid content of the mixed slurry exceeds the above-mentioned range, the mixed slurry may be too viscous to achieve coating; when the solid content of the mixed slurry is below the above-mentioned range, coating is relatively easy to achieve, but the coating amount of the flame-retardant layer obtained after coating the mixed slurry may be relatively low, failing to provide sufficient flame-retardant performance; if the thickness of the flame-retardant layer is increased to increase the coating amount, the resulting flame-retardant layer may exhibit delamination. Controlling the solid content of the mixed slurry within the above-mentioned range provided by the present invention can yield a uniform flame-retardant layer with a suitable coating amount. Preferably, the solid content of the mixed slurry is 6-30%, 10-27%, or 12-25%.

[0093] According to the preparation method of the third aspect of the present invention, preferably, the stirring is carried out at a rotation speed of 500 r / s-1500 r / s for a stirring time of 240 min-360 min, more preferably at a rotation speed of 800 r / s-1200 r / s for a stirring time of 270 min-330 min. When the stirring is carried out within the above-mentioned rotation speed and time range, good dispersion of the flame retardant material can be achieved. If the rotation speed or time is lower than the above-mentioned range, uniform dispersion may not be achieved. The stirring operation can be carried out using equipment and apparatus commonly used in the art.

[0094] According to the preparation method of the third aspect of the present invention, the solvent used in preparing the mixed slurry can be a solvent commonly used in the art. The solvent may include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP) or acetone, and any one or a mixture of two or more of them may be used.

[0095] According to the preparation method of the third aspect of the present invention, preferably, the coating thickness when coating the surface of the active layer with a mixed slurry containing a flame-retardant material for battery electrodes is 5 μm-70 μm. When the solid content of the mixed slurry containing the flame-retardant material for battery electrodes is high, a lower coating thickness can be selected to ensure that the prepared flame-retardant layer has an appropriate coating amount; while when the solid content of the mixed slurry containing the flame-retardant material for battery electrodes is low, a higher coating thickness is required to ensure that the prepared flame-retardant layer has an appropriate coating amount. More preferably, the coating thickness is 5 μm-60 μm or 8 μm-60 μm, and even more preferably 10 μm-25 μm.

[0096] According to the preparation method of the third aspect of the present invention, the positive electrode of the present invention may be formed by coating a flame retardant layer onto the surface of the positive electrode active layer of at least one side of the current collector.

[0097] According to the preparation method of the third aspect of the present invention, preferably, the coating process further includes a pressing operation, wherein the pressing can be performed by pressing such as roller pressing to attach the flame-retardant material of the battery electrode to the positive electrode active layer of the current collector, thereby forming a flame-retardant layer. Roll pressing can be performed by using a roller pressing method, and in this case, the roller can be maintained at a temperature between room temperature (20°C) and 200°C, but is not limited thereto.

[0098] According to the preparation method of the third aspect of the present invention, preferably, the positive electrode active layer is formed by coating a positive electrode material onto at least one side surface of the current collector.

[0099] According to the preparation method of the third aspect of the present invention, preferably, the coating process further includes a pressing operation, wherein the positive electrode active layer can be attached to at least one side surface of the current collector by pressing method such as rolling. Rolling can be performed by using a pressure roller, and in this case, the pressure roller can be maintained at a temperature between room temperature (20°C) and 200°C, but is not limited thereto.

[0100] A fourth aspect of the present invention provides a lithium secondary battery, wherein the lithium secondary battery includes the electrode provided by the present invention, namely, an electrode containing a flame-retardant layer, which is the positive electrode of the lithium secondary battery.

[0101] The lithium secondary battery of the present invention can be a secondary battery containing a liquid electrolyte or a solid battery containing a solid electrolyte.

[0102] According to the fourth aspect of the present invention, the lithium secondary battery is preferably an all-solid-state battery or a semi-solid-state battery.

[0103] According to a fourth aspect of the present invention, the lithium secondary battery further comprises a corresponding negative electrode. The negative electrode may include a current collector and a negative electrode active layer.

[0104] According to a fourth aspect of the present invention, in a lithium secondary battery, preferably, the active layer of the negative electrode is formed by coating a negative electrode active material onto at least one side surface of the current collector.

[0105] According to the lithium secondary battery of the fourth aspect of the present invention, preferably, the coating process further includes a pressing operation, wherein the active layer of the negative electrode is attached to at least one side surface of the current collector by pressing such as rolling. Rolling can be performed by using a pressing roller, and in this case, the pressing roller can be maintained at a temperature between room temperature (20°C) and 200°C, but is not limited thereto.

[0106] According to the fourth aspect of the lithium secondary battery of the present invention, preferably, the thickness of the active layer of the negative electrode is 80 μm-120 μm, more preferably between 90 μm and 110 μm, but not limited thereto. The negative electrode active material used to prepare the active layer is not particularly limited, as long as it is a commonly used negative electrode active material, and the surface of the negative electrode active material may have a conductive coating, such as a carbon coating.

[0107] According to the fourth aspect of the present invention, the negative electrode active material may include one or more combinations of the group consisting of lithium metal, carbon materials capable of reversibly inserting / deintercalating lithium ions, metals or alloys of these metals with lithium, metal composite oxides, materials that may be doped or undoped with lithium, and transition metal oxides.

[0108] As a carbon material capable of reversibly inserting / deintercalating lithium ions, carbon-based anode active materials commonly used in lithium secondary batteries can be used without particular limitations. Typical examples include crystalline carbon, amorphous carbon, or both. Examples of crystalline carbon can be graphite, such as irregular, planar, flake, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon can be soft carbon (low-temperature sintered carbon) or hard carbon, mesophase pitch carbides, and calcined coke.

[0109] As a metal or an alloy of these metals with lithium, a metal selected from the group consisting of: Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of lithium with the selected metal, may be used.

[0110] As metal composite oxides, one of the following can be used: PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, LixFe2O3 (0≤x≤1), LixWO2 (0≤x≤1), and Sn. x Me 1-x Me' y O z (Me is selected from Mn, Fe, Pb, Ge; Me' is selected from Al, B, P, Si, elements in groups I, II, and III of the periodic table, or halogens; 0 <x≤1;1≤y≤3;1≤z≤8)。

[0111] Materials that can be doped or undoped with lithium can include Si, SiO x(0 < x ≤ 2), an Si-Y alloy (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO₂, and Sn-Y (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and a mixture of SiO₂ and at least one material. The Y element may be selected from the group consisting of: Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0112] The transition metal oxide may include a lithium-containing titanium composite oxide (LTO), a vanadium oxide, and a lithium vanadium oxide.

[0113] In the lithium secondary battery according to the fourth aspect of the present invention, preferably, a conductive material may also be contained in the negative electrode active layer. The conductive material used is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, the following conductive materials may be used: carbon black (such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black); carbon fluoride powder; graphite materials (such as natural graphite or artificial graphite having a good crystal structure); fibrous carbon materials (such as carbon fiber, carbon nanotube, or carbon nanofiber), metal fiber; conductive powders (such as aluminum powder and nickel powder); conductive whiskers (such as potassium titanate whiskers); conductive metal oxides (such as titanium oxide); conductive polymers (such as polystyrene derivatives), etc. Graphite materials, carbon black, and carbon nanotubes (CNT) are preferably used to achieve uniform mixing of the conductive material and improve conductivity.

[0114] In the lithium secondary battery according to the fourth aspect of the present invention, preferably, an appropriate amount of binder may also be contained in the negative electrode active layer. The binder used is not particularly limited. For example, it may be polyvinylidene fluoride (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof.

[0115] According to the fourth aspect of the present invention, the current collector used for the negative electrode is preferably not particularly limited, as long as it has high conductivity without causing changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon (sintered carbon), or surface-treated copper or stainless steel (the treatment materials include carbon, nickel, titanium, silver, etc.) can be used, as well as aluminum-cadmium alloys, etc.

[0116] According to the fourth aspect of the lithium secondary battery of the present invention, preferably, the thickness of the current collector used for the negative electrode can be between 6 μm and 12 μm, more preferably between 8 μm and 10 μm, but is not limited thereto. Furthermore, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the active layer.

[0117] Specifically, the current collector can be wholly or partially coated with a conductive primer to reduce surface resistance and improve adhesion. In this case, the conductive primer may contain conductive materials and adhesives. The conductive materials are not limited, as long as they are conductive; for example, they can be carbon-based materials. The adhesives may include fluoropolymer adhesives (including PVDF and PVDF copolymers), acrylic adhesives, and water-based adhesives, all of which are soluble in solvents.

[0118] According to a fourth aspect of the present invention, when the lithium secondary battery is a secondary battery comprising a liquid electrolyte, a separator can be disposed between multiple electrodes. This separator separates the negative and positive electrodes and provides a pathway for lithium ion movement. Any separator commonly used in lithium secondary batteries can be used, with a particular preference for separators having a high capacity to retain electrolyte moisture and a low resistance to electrolyte ion movement. Specifically, a porous polymer membrane can be used, for example, a porous polymer membrane prepared from polyolefin-based polymers (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or a laminated structure having two or more layers. Furthermore, conventional porous nonwoven fabrics can be used, for example, nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers, but the invention is not limited thereto. In addition, coated separators containing ceramic components or polymer materials can be used to ensure thermal stability or mechanical strength, and single-layer or multi-layer separators can be selectively used. Furthermore, at least one surface of the diaphragm may be coated with an inorganic material, specifically boehmite and / or alumina, with a thickness that can be controlled to be 1-5 μm.

[0119] Furthermore, when the lithium secondary battery is an all-solid-state battery, the solid electrolyte layer can be designed to perform the function of a separator.

[0120] The electrolyte used in this invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, an inorganic solid electrolyte, an inorganic molten electrolyte, etc. All of these can be used to manufacture lithium secondary batteries, but are not limited to these.

[0121] Specifically, the electrolyte can contain organic solvents and lithium salts. Any organic solvent that can serve as a medium for the movement of ions participating in the electrochemical reaction in the battery can be used, without specific restrictions. Specifically, organic solvents that can be used include ester solvents (such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone); ether solvents (such as dibutyl ether or tetrahydrofuran); ketone solvents (such as cyclohexanone); aromatic hydrocarbon solvents (such as benzene and fluorobenzene); carbonate solvents (such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC)); alcohol solvents (such as ethanol and isopropanol); nitriles (such as R-CN, where R is a linear, branched, or cyclic C2 to C20 hydrocarbon group, which may contain double bonds, aromatic rings, or ether bonds); amides (such as dimethylformamide); dioxanes (such as 1,3-dioxane); or sulfoxide solvents, etc. Among these solvents, carbonate solvents are preferred, especially mixtures containing cyclic carbonates (such as ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate), which can improve the charge and discharge performance of the battery.

[0122] Any compound can be used as a lithium salt, as long as it can provide lithium ions and be used in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from at least one of the following groups: F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN -and (CF3CF2SO2)2N - Examples of lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration range of the lithium salt can be from 0.1M to 4.0M, preferably from 0.5M to 3.0M, and more preferably from 1.0M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte exhibits suitable conductivity and viscosity, thus demonstrating excellent performance, and lithium ions can move effectively.

[0123] In addition to the electrolyte components mentioned above, the electrolyte may further contain one or more types of additives, such as compounds based on fluoroolefin carbonates (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-ethylene glycol dimethyl ether (glyme), triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, and aluminum chloride, to enhance battery life, suppress battery capacity decline, and improve battery discharge capability. In this case, the additives may be added in an amount from 0.1 wt% to 10.0 wt% relative to the total weight of the electrolyte.

[0124] The detailed structure of a secondary battery is well known and will not be described in detail here.

[0125] In addition, the aforementioned lithium secondary batteries can be used in mobile devices such as mobile phones, laptops and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0126] The present disclosure will be described in more detail below by way of examples, but the following examples are provided to illustrate the invention by way of description, and the scope of the invention is not limited thereto.

[0127] Example 1

[0128] This embodiment provides a lithium secondary battery, wherein:

[0129] Step 1: Preparation of flame-retardant materials for battery electrodes using zinc hydroxystannate (ZnSn(OH)6) as a surface coating:

[0130] Mix 10 parts by weight of aluminum hydroxide, 60 parts by weight of hexadecyltrimethylammonium bromide, and 360 parts by weight of water, and stir at 60 r / s for 30 min to prepare an inorganic material emulsion.

[0131] Mix 2 parts by mass of zinc oxide, 10 parts by mass of tin tetrachloride, and 30 parts by mass of ammonia (20% by mass percentage). Add an inorganic material emulsion until the pH value is between 8 and 9. Stir at 60 r / s for 30 min to obtain a mixed solution.

[0132] The mixed solution was transferred to a reaction vessel with a polytetrafluoroethylene liner, heated to 180°C and reacted for 12 hours. After washing, the mixture was separated using a centrifuge to obtain a white precipitate, namely zinc hydroxystannate (ZnSn(OH)6), which is used as a flame-retardant material for battery electrodes as a surface coating.

[0133] Step 2: Preparation of a mixed slurry of flame-retardant materials for battery electrodes using zinc hydroxystannate (ZnSn(OH)6) as a surface coating:

[0134] 80 parts by weight of zinc hydroxystannate (ZnSn(OH)6) as a surface coating for battery electrodes were mixed with 20 parts by weight of polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) was added to dilute the mixture to a solid content of 25%. The mixture was stirred at 1000 r / s for 300 min to obtain a uniform suspension, i.e., a mixed slurry.

[0135] Step 3: Preparation of the positive electrode sheet:

[0136] Lithium nickel cobalt manganese oxide (Li(Ni) 0.8 Mn 0.1 Co 0.1 O2), polyvinylidene fluoride (PVDF), and conductive carbon (CNT) are dissolved in N-methylpyrrolidone (NMP) solvent at a mass ratio of 96:2:2 and stirred evenly to prepare a positive electrode slurry;

[0137] The positive electrode slurry is uniformly coated on both sides of the aluminum foil that serves as the positive electrode current collector. After drying and rolling, the positive electrode sheet is formed, and the thickness of the rolled positive electrode sheet is 180μm.

[0138] Step 4: Flame retardant coating:

[0139] The mixed slurry obtained in the second step is uniformly coated on both sides of the positive electrode sheet obtained in the third step using a double-sided coating method. After drying, rolling, and slitting, a positive electrode sheet with a flame-retardant layer is produced, wherein the coating thickness is 10 μm and the coating amount is 0.31 mg / cm³. 2 The thickness of the flame-retardant layer on each side after roll forming is 3μm.

[0140] Step 5: Negative electrode preparation:

[0141] Artificial graphite, conductive carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed evenly in a mass ratio of 96:0.5:1.5:2, deionized water was added and stirred evenly to prepare a negative electrode slurry.

[0142] The negative electrode slurry is evenly coated onto the negative electrode current collector copper foil, and then dried, rolled, and slit to form a negative electrode sheet.

[0143] Step 6: Battery Assembly

[0144] The positive electrode sheet with a flame-retardant layer obtained in step four, the negative electrode sheet obtained in step five, and the separator (polyethylene film, 9 μm thick, with a boehmite coating, 3 μm thick) are wound together to form a core. The core is packaged in aluminum-plastic film, baked to remove moisture, and then injected with electrolyte (a mixture of ethylene carbonate and methyl ethyl carbonate in a mass ratio of 3:7, containing 1 mol / L of lithium hexafluorophosphate). The battery is then formed using a hot-pressing process.

[0145] The hot-pressing formation process is carried out as follows: the assembled battery is hot-pressed at 80°C for 12 hours at a pressure of 1.5 MPa. Then it is charged at a current of 0.01C for 3 hours and then charged at a current of 0.1C for 1 hour to complete the formation of the battery.

[0146] Example 2

[0147] The preparation method of the lithium secondary battery in this embodiment is basically the same as that in Example 1, except that in the fourth step, the coating thickness is 20 μm and the coating amount is 0.66 mg / cm³. 2 The thickness of the flame-retardant layer on each side after roll forming is 5.2 μm.

[0148] Example 3

[0149] The preparation method of the lithium secondary battery in this embodiment is basically the same as that in Example 1, except that in the fourth step, the coating thickness is 50 μm and the coating amount is 1.43 mg / cm³. 2 The thickness of the flame-retardant layer on each side after roll forming is 7.5 μm.

[0150] Example 4

[0151] The preparation method of the lithium secondary battery in this embodiment is basically the same as that in Example 1, except that: in the second step, the solid content is 6%, and in the fourth step, the coating thickness is 50 μm and the coating amount is 0.28 mg / cm³. 2 The thickness of the flame-retardant layer on each side after roll forming is 3μm.

[0152] Example 5: The preparation method of the lithium secondary battery in this example is basically the same as that in Example 1, except that the mass fraction of ammonia in the first step is changed to 10.

[0153] Example 6: The preparation method of the lithium secondary battery in this example is basically the same as that in Example 1, except that the mass fraction of tin tetrachloride in the first step is changed to 20.

[0154] Example 7: The preparation method of the lithium secondary battery in this example is basically the same as that in Example 1, except that the mass fraction of aluminum hydroxide in the first step is changed to 5.

[0155] Example 8: The preparation method of the lithium secondary battery in this example is basically the same as that in Example 2, except that: the solid content in the second step is changed to 12%, and in the fourth step, the coating thickness is 20 μm and the coating amount is 0.23 mg / cm³. 2 The thickness of the flame-retardant layer on each side after roll forming is 3μm.

[0156] Example 9: The preparation method of the lithium secondary battery in this example is basically the same as that in Example 2, except that: the solid content in the second step is changed to 18%, and in the fourth step, the coating thickness is 20 μm and the coating amount is 0.34 mg / cm³. 2 The thickness of the flame-retardant layer on each side after roll forming is 5μm.

[0157] Comparative Example 1

[0158] The preparation method of the lithium secondary battery in this comparative example is basically the same as that in Example 1, except that: in the second step, the solid content is 6%, and in the fourth step, the coating thickness is 10 μm and the coating amount is 0.042 mg / cm³. 2 The thickness of the flame-retardant layer on each side after compaction is 1 μm.

[0159] Comparative Example 2

[0160] The preparation method of the lithium secondary battery in this comparative example is basically the same as that in Comparative Example 1, except that in step four, the coating thickness is 20 μm and the coating amount is 0.10 mg / cm³. 2 The thickness of the flame-retardant layer on each side after roll forming is 1.5 μm.

[0161] Comparative Example 3

[0162] The preparation method of the lithium secondary battery in this comparative example is basically the same as that in Example 1, except that the fourth step of coating the flame retardant layer is not performed.

[0163] Comparative Example 4

[0164] The preparation method of the lithium secondary battery in this comparative example is basically the same as that in Example 1, except that the first step is omitted, and in the second step, the battery electrode with zinc hydroxystannate ZnSn(OH)6 as the surface coating is replaced with aluminum hydroxide as the flame retardant material.

[0165] Comparative Example 5

[0166] The method for preparing the lithium secondary battery in this comparative example uses pure zinc hydroxystannate as the flame retardant material, replacing the zinc hydroxystannate ZnSn(OH)6 used in Example 1 as the flame retardant material for the battery electrode surface coating. A mixed slurry is prepared according to the second step of Example 1. The viscosity of the prepared mixed slurry is too high to be coated onto the surface of the electrode sheet prepared according to the third step of Example 1, i.e., a positive electrode sheet cannot be prepared.

[0167] According to Comparative Example 5, it is difficult to prepare a suitable slurry from zinc hydroxystannate. The slurry has a relatively high viscosity, and zinc hydroxystannate will agglomerate and form relatively large particles. Moreover, according to observation, the uniformity and dispersibility of the prepared slurry are relatively poor.

[0168] Comparative Example 6: The preparation method of the lithium secondary battery in this comparative example is basically the same as that in Example 1, except that the solid content in the second step is changed to 2.5%.

[0169] Comparative Example 7: The preparation method of the lithium secondary battery in this comparative example is basically the same as that in Example 1, except that the solid content in the second step is changed to 50%.

[0170] Experimental example:

[0171] 1. Macroscopic observation of the flame-retardant layer:

[0172] Observation revealed that the flame-retardant layer obtained in Example 1 completely covered the entire surface of the active layer, and the entire surface of the flame-retardant layer showed a relatively uniform color, indicating that the thickness of each part of the flame-retardant layer was relatively consistent and the uniformity of the flame-retardant layer was high.

[0173] While the flame-retardant layer obtained in Comparative Example 1 can also cover the entire surface of the active layer, the color of the entire surface of the flame-retardant layer is not uniform enough, and the color difference between different areas is large. This indicates that the thickness of each part of the flame-retardant layer is not consistent, and the uniformity of the flame-retardant layer is relatively poor.

[0174] 2. Hot box test:

[0175] The lithium secondary batteries obtained in the above embodiments and comparative examples were subjected to hot box testing. The specific testing process was carried out in accordance with the provisions of GB38031(2020)8.1.5, including:

[0176] At room temperature, the lithium secondary batteries were charged to 4.2V at a rate of 0.33C under constant current constant voltage (CC-CV) charging conditions, and then the current was cut off at 0.05C. After charging, the batteries were left to stand for 2 hours.

[0177] Place the settled lithium secondary battery in a hot box and raise the temperature to the set temperature of 130℃ at a heating rate of 5±2℃ / min, then maintain the temperature for 30 minutes. If the lithium secondary battery does not catch fire or explode, raise the temperature to the set temperature of 140℃ at a heating rate of 5±2℃ / min, and so on, until the lithium secondary battery catches fire, explodes, or the voltage drops below 2.8V.

[0178] During the test, the surface temperature of the lithium secondary battery and the ambient temperature were collected. The temperature point where the lithium secondary battery surface temperature was higher than the ambient temperature was recorded as T1; the temperature point where the lithium secondary battery caught fire, exploded, or its voltage dropped below 2.8V was recorded as T2; and the highest temperature of the lithium secondary battery was recorded as T3. The test results are shown in Table 1. Temperature data was collected using a Keysight data acquisition unit (model DAQ970A).

[0179] Table 1

[0180] T1 T2 T3 Is there a fire? Example 1 160 180 182 No fire Example 2 160 180 182 No fire Example 3 160 180 183 No fire Example 4 160 180 182 No fire Example 5 160 180 183 No fire Example 6 160 180 183 No fire Example 7 160 180 183 No fire Example 8 160 180 182 No fire Example 9 160 180 182 No fire Comparative Example 1 160 170 1683 fire Comparative Example 2 160 170 1682 fire Comparative Example 3 160 170 1682 fire Comparative Example 4 160 170 1682 fire

[0181] It should be noted that due to the limitation of the temperature measurement range of the temperature acquisition instrument, the highest temperature that can be acquired is about 1682℃-1683℃. In actual situations, T3 in Comparative Examples 1-4 may be higher than 1682℃-1683℃.

[0182] As can be seen from the experimental results recorded in Table 1, compared with Comparative Examples 1-4, the lithium secondary batteries of Examples 1-9 have higher thermal runaway temperatures and lower thermal runaway intensity.

[0183] Therefore, it can be seen that the flame-retardant layer made of flame-retardant material for battery electrodes provided by the present invention can effectively reduce the reaction between the electrolyte and the positive electrode, and can suppress battery fire.

[0184] The lithium secondary batteries used in Comparative Examples 1 and 2 had a low solid content in the slurry, resulting in a low coating amount of flame-retardant material on the positive electrode surface. During the test, both Comparative Examples 1 and 2 exhibited ignition, indicating that the coating amount of flame-retardant material in the flame-retardant layer was greater than 1.4 mg / cm³. 2 Only then can it play a sufficient role in flame retardancy.

[0185] The viscosity of the mixed slurry prepared in Comparative Example 6 was too low. During the coating process, the mixed slurry flowed continuously and could not be coated onto the surface of the electrode sheet prepared in the third step of Example 1. In other words, it was impossible to prepare a positive electrode sheet coated with a flame-retardant layer.

[0186] The viscosity of the mixed slurry prepared in Comparative Example 7 was too high to be coated onto the surface of the electrode sheet prepared in the third step of Example 1, that is, a positive electrode sheet coated with a flame-retardant layer could not be prepared.

[0187] The lithium secondary batteries obtained in Example 1 and Comparative Example 3 were subjected to explosion pressure tests, which were carried out according to the following steps:

[0188] At room temperature, the lithium secondary batteries were charged to 4.2V at a rate of 0.33C under constant current constant voltage (CC-CV) charging conditions, and then the current was cut off at 0.05C. After charging, the batteries were left to stand for 2 hours.

[0189] The lithium secondary battery, after being left to stand, is placed in an explosion pressure test chamber and heated with 200W of power until the lithium secondary battery catches fire, explodes, or the voltage drops below 2.8V.

[0190] During the test, the explosion pressure, explosion duration, lithium secondary battery surface temperature, and ambient temperature inside the chamber were collected. The test results are shown in Table 2. Among them, the explosion duration and temperature were collected using a Modis explosion pressure chamber (20L). The explosion duration is defined as the time it takes for the pressure inside the explosion pressure chamber to rise rapidly from the beginning to reach its peak.

[0191] Table 2

[0192] Explosion pressure (kPa) Explosion duration (s) Maximum ambient temperature Tmax (°C) Example 1 60.18 2.6 92.1 Comparative Example 3 72.24 2.4 104.4

[0193] In both Example 1 and Comparative Example 3, the surface temperature of the lithium secondary batteries reached over 900°C.

[0194] As shown in Table 2, compared with Comparative Example 3, the lithium secondary battery prepared in Example 1 has a lower explosion pressure and a lower maximum ambient temperature. This indicates that the intensity of the explosion of the lithium secondary battery prepared in Example 1 is lower than that of the lithium secondary battery in Comparative Example 3. Moreover, the explosion time of Example 1 is longer than that of Comparative Example 3, indicating that the interval between ignition and explosion of the lithium secondary battery in Example 1 is longer. This also reflects that Example 1 can provide a good flame-retardant effect by setting a flame-retardant layer on the surface of the electrode active layer.

Claims

1. A flame-retardant material for battery electrodes, comprising a flame-retardant substrate and a coating; The coating is applied to the surface of the flame-retardant substrate. The coating contains hydroxystannate.

2. The flame-retardant material for battery electrodes according to claim 1, wherein, The hydroxystannate includes one or more of zinc hydroxystannate, calcium hydroxystannate, magnesium hydroxystannate, and aluminum hydroxystannate.

3. The flame-retardant material for battery electrodes according to claim 1, wherein, The thickness of the coating is 20-200 nm.

4. The flame-retardant material for battery electrodes according to claim 1, wherein, The flame-retardant substrate is an inorganic flame-retardant substrate.

5. The flame-retardant material for battery electrodes according to claim 4, wherein, The inorganic flame retardant substrate includes one or more of aluminum hydroxide, magnesium hydroxide, aluminum oxide, and magnesium oxide.

6. The flame-retardant material for battery electrodes according to claim 1, wherein, The flame-retardant material used for the battery electrodes is granular.

7. The flame-retardant material for battery electrodes according to claim 6, wherein, The particle size is 100nm-500nm.

8. The flame-retardant material for battery electrodes according to claim 1, wherein, The preparation method of the flame-retardant material for the battery electrode includes the following steps: The flame-retardant substrate, tin source, metal source, and alkaline solution are mixed, and then heated, separated, washed, and dried to obtain the flame-retardant material for the battery electrode. The metal in the metal source is a metal other than tin in hydroxystannate.

9. The flame-retardant material for battery electrodes according to claim 8, wherein, The heating temperature is 120℃-180℃.

10. The flame-retardant material for battery electrodes according to claim 8, wherein, The flame retardant substrate is added in the form of an emulsion, the emulsion containing flame retardant substrate, surfactant, and water in a mass ratio of 3-15:30-60:180-360.

11. The flame-retardant material for battery electrodes according to claim 8, wherein, The tin source includes one or more of tin dioxide, tin tetrachloride, stannous nitrate, and stannous sulfate.

12. The flame-retardant material for battery electrodes according to claim 8, wherein, The metal source includes one or more of the following: oxides, chlorides, nitrates, and sulfates of the metal.

13. The flame-retardant material for battery electrodes according to claim 12, wherein, The metal source is a zinc source, which includes one or more of zinc oxide, zinc nitrate, zinc chloride, and zinc sulfate.

14. The flame-retardant material for battery electrodes according to claim 8, wherein, The molar ratio of the tin source to the metal source is 1:2-4:1, the molar ratio of the tin source to the alkaline solution is 1:10-1:1, the molar amount of the tin source is in the molar amount of tin, the molar amount of the metal source is in the molar amount of metal, and the molar amount of the alkaline solution is in the molar amount of alkali.

15. The flame-retardant material for battery electrodes according to claim 10, wherein, The molar ratio of the tin source to the flame retardant substrate is 1:10-1:1, the molar ratio of the tin source to the surfactant is 1:20-2:1, and the molar amount of the tin source is expressed as the molar amount of tin.

16. An electrode having a flame-retardant layer on its surface, said flame-retardant layer comprising the flame-retardant material for a battery electrode according to any one of claims 1-15, wherein, Based on the area of ​​the electrode surface covered by the flame-retardant layer, the coating amount of the flame-retardant layer is 0.2 mg / cm². 2 -1.5mg / cm 2 ; Based on the mass of the flame-retardant layer being 100%, the content of the flame-retardant material for the battery electrode is 75%-95%.

17. The electrode according to claim 16, wherein, The electrode is a positive electrode.

18. The electrode according to claim 16, wherein, The flame-retardant layer also contains 5%-25% binder.

19. The electrode according to claim 16, wherein, The thickness of the flame-retardant layer is 3μm-10μm.

20. The electrode according to claim 16, wherein, The electrode also includes a current collector and an active layer; The active layer is located on the surface of the current collector, and the flame retardant layer is located on the outer surface of the active layer.

21. The electrode according to claim 20, wherein, The thickness of the current collector is 6μm-12μm.

22. The electrode according to claim 20, wherein, The thickness of the active layer is 80μm-120μm.

23. A method for preparing the electrode according to any one of claims 16-22, wherein, The method includes the following steps: An active layer is formed on the current collector surface of the electrode; A mixed slurry containing flame-retardant materials for battery electrodes is coated on the surface of the active layer, and then dried and rolled to form a flame-retardant layer, thereby obtaining the electrode with the flame-retardant layer. The solid content of the mixed slurry containing flame-retardant materials for battery electrodes is 5%-35%.

24. The method according to claim 23, wherein, The mixed slurry containing flame-retardant material for battery electrodes is composed of flame-retardant material for battery electrodes, binder and solvent.

25. The method according to claim 23, wherein, The coating thickness is 5μm-70μm when a mixed slurry containing flame-retardant materials for battery electrodes is applied to the surface of the active layer.

26. A lithium secondary battery, wherein, The lithium secondary battery comprises the electrode as described in any one of claims 16-22.

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