Positive electrode additive and preparation method and application thereof

Abstract

The invention relates to a positive electrode additive as well as a preparation method and application thereof. The positive electrode additive is a composite material formed by coating the surface of a heat-conducting ceramic matrix with a conductive polymer, and the mass ratio of the conductive polymer to the heat-conducting ceramic matrix is (0.005-0.3): 1. In the scheme provided by the invention, the anode additive can improve the uniformity of anode heat distribution and improve the heat dissipation capability of the battery, so that the safety performance of the battery under an overheating condition is improved, meanwhile, the internal resistance of a diaphragm of the anode can be reduced, and the electrochemical performance of the battery is improved; the requirements of products in the fields of consumer electronics, new energy automobile power batteries, energy storage equipment and the like are met.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a positive electrode additive and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, thanks to their high energy density, long cycle life, low self-discharge rate, and environmentally friendly properties, have found widespread application in consumer electronics, electric vehicles and transportation, and energy storage systems. In recent years, the widespread use of lithium-ion batteries in portable electronics and their accelerated development into power batteries and medium- and large-sized batteries has led to higher demands on their cycle life, service life, production cost, and safety. Improving battery performance while ensuring safety has become a pressing technical challenge of significant practical significance.

[0003] Most safety issues with lithium-ion batteries are primarily attributed to thermal runaway caused by elevated internal battery temperatures. The positive electrode material, typically a transition metal oxide, is highly oxidizing when charged. At high temperatures, it readily decomposes and releases oxygen, which reacts with the electrolyte and releases significant amounts of heat. Furthermore, when the Joule heat generated by the current and the heat from side reactions at the positive and negative electrodes cannot dissipate promptly, localized heat within the confined space can cause the battery's operating temperature to continuously rise, leading to uneven temperature distribution within the electrodes and deteriorating battery performance. Especially under overheating conditions, this uneven heat distribution can exacerbate side reactions within the battery, generating localized high temperatures and flammable gases, leading to battery bulging and gas leakage, which can in turn trigger safety incidents such as fires and explosions.

[0004] Therefore, in order to improve the thermal stability of batteries and reduce the occurrence of battery safety accidents, it is necessary to design and provide a method that can promote faster heat dissipation of electrodes and more uniform temperature distribution in electrodes. Summary of the Invention

[0005] In order to solve or partially solve the problems existing in the related technology, the present application provides a positive electrode additive and its preparation method and application. The positive electrode additive can improve the uniformity of the heat distribution of the positive electrode, improve the heat dissipation capacity of the battery, thereby improving the safety performance of the battery under overheating conditions. At the same time, it can also reduce the internal resistance of the positive electrode diaphragm and improve the electrochemical performance of the battery, so that it can meet the needs of products in the fields of consumer electronics, new energy vehicle power batteries, energy storage equipment, etc.

[0006] In a first aspect, the present application provides a positive electrode additive, which is a composite material formed by coating a conductive polymer on the surface of a thermally conductive ceramic substrate; the mass ratio of the conductive polymer to the thermally conductive ceramic substrate is (0.005-0.3):1.

[0007] In some embodiments, the thermally conductive ceramic matrix is ​​selected from at least one of silicon carbide, silicon nitride, aluminum nitride, boron nitride, titanium nitride, titanium carbide, or beryllium oxide.

[0008] In some embodiments, the thermally conductive ceramic matrix includes aluminum nitride.

[0009] In some embodiments, the thermally conductive ceramic matrix is ​​preferably aluminum nitride and silicon carbide.

[0010] In some embodiments, the thermally conductive ceramic matrix is ​​more preferably aluminum nitride and silicon carbide in a mass ratio of (8:2) to (9:1).

[0011] In some embodiments, the thermal conductivity of the thermally conductive ceramic matrix is ​​≥40 W / (mK).

[0012] In some embodiments, the conductive polymer is selected from at least one of polypyrrole, polyaniline, poly(3,4-ethylenedioxythiophene), polythiophene, polyacetylene, polyphenylene, and polyphenylenevinylene.

[0013] The second aspect of the present application provides a method for preparing the above-mentioned positive electrode additive, comprising: mixing a thermally conductive ceramic matrix with a conductive polymer solution, grinding and drying, and then heat-treating to obtain the positive electrode additive.

[0014] In some embodiments, the content of the conductive polymer in the conductive polymer solution is 1 wt% to 5 wt%.

[0015] In some embodiments, the grinding treatment time is 0.1 h to 2 h.

[0016] In some embodiments, the D50 particle size of the thermally conductive ceramic matrix after ball milling is less than 1 μm.

[0017] In some embodiments, the drying is vacuum drying, and the drying temperature is 50°C to 100°C.

[0018] In some embodiments, the heat treatment temperature is 200° C. to 500° C., the heat treatment time is 0.5 h to 8 h, and the heat treatment atmosphere is an argon atmosphere or a nitrogen atmosphere.

[0019] In some embodiments, the heat treatment includes a first heat treatment and a second heat treatment; Wherein, the first heat treatment temperature is 200°C to 400°C, the treatment time is 0.5 to 5.5 hours, and the heat treatment atmosphere is argon atmosphere or nitrogen atmosphere; The second heat treatment temperature is 350° C. to 500° C., the treatment time is 0.5 to 1.5 hours, and the heat treatment atmosphere is an argon atmosphere or a nitrogen atmosphere.

[0020] A third aspect of the present application provides a positive electrode slurry comprising the above-mentioned positive electrode additive.

[0021] In some embodiments, the positive electrode slurry includes a solvent, positive electrode powder and the positive electrode additive, and the added mass of the positive electrode additive is 0.1% to 10% of the total mass of the positive electrode powder; the positive electrode powder includes a positive electrode active material, a positive electrode conductor and a positive electrode binder.

[0022] The fourth aspect of the present application provides a positive electrode plate, including a positive electrode current collector and a positive electrode material layer provided on the positive electrode current collector; the positive electrode material layer includes a positive electrode active material, a positive electrode conductor, a positive electrode binder, and the above-mentioned positive electrode additives.

[0023] In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, the binder, and the positive electrode additive is (0.90-0.99):(0.005-0.05):(0.005-0.05):(0.001-0.1).

[0024] In some embodiments, the positive electrode active material is selected from at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and lithium vanadium phosphate.

[0025] In some embodiments, the positive electrode conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, natural graphite, artificial graphite, graphene, carbon fiber, and carbon nanotubes.

[0026] In some preferred embodiments, the positive electrode conductive agent is a mixture of conductive carbon black and carbon nanotubes; more preferably, the mass ratio of the conductive carbon black to the carbon nanotubes is 1:(0.1~0.5).

[0027] In some preferred embodiments, the mass ratio of the carbon nanotubes to the positive electrode additive is (1-30):1.

[0028] In some embodiments, the positive electrode binder is selected from at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, and polyacrylic acid.

[0029] A fifth aspect of the present application provides a lithium-ion battery comprising the positive electrode sheet as claimed in the claim above.

[0030] The technical solution provided by this application may include the following beneficial results: The use of the positive electrode additive described herein can improve the uniformity of heat distribution within the positive electrode sheet, thereby enhancing the heat dissipation capacity of the battery and improving the battery's safety performance under overheating conditions. Furthermore, the composite positive electrode additive formed by coating the surface of a thermally conductive ceramic substrate with a conductive polymer as described herein can reduce the internal resistance of the positive electrode diaphragm and improve the conductivity and dispersibility of the positive electrode additive, thereby improving battery safety without degrading and enhancing the battery's electrochemical performance.

[0031] Furthermore, the material used in the positive electrode additive described in the present application is low in cost, the preparation method is simple, and the positive electrode additive can be evenly dispersed in the positive electrode slurry, which is conducive to its large-scale application in the positive electrode slurry.

[0032] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and other objects, features and advantages of the present application will become more apparent by describing in more detail exemplary embodiments of the present application in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the present application.

[0034] Figure 1 This is a schematic structural diagram of the positive electrode sheet shown in Example 1 of the present application. DETAILED DESCRIPTION

[0035] The embodiments of the present application will be described in more detail below. It should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0036] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit the application. Unless otherwise defined, all terms used herein have the same meaning as those generally understood by those of ordinary skill in the art to which the present invention belongs. Although any methods and materials equivalent to the methods and materials described herein can also be used in the implementation or testing of the present invention, preferred methods and materials are now described.

[0037] It should be understood that although the terms "first", "second", "third", etc. may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. Features defined as "first" or "second" may explicitly or implicitly include one or more of these features. The singular forms "a", "said", and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0038] Where a numerical range is provided, it is understood that each intervening value between the upper and lower limits of the range and any other specified or intervening values ​​in the specified range is encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included in the smaller range and are also encompassed within the present invention, subject to any explicitly excluded limits in the specified range. Where a specified range includes one or two limits, ranges excluding either or both of those included limits are also encompassed within the present invention. In the description of this application, the meaning of "multiple" is two or more, unless otherwise specifically defined.

[0039] During the large-scale manufacturing process of cylindrical or soft-pack lithium-ion batteries, macroscopic differences in the distribution of active materials, slurry density, and compaction density of the electrodes are inevitable. These macroscopic differences inevitably lead to differences in internal resistance, operating current, and heat distribution in the electrodes. At the same time, due to the insufficient thermal conductivity inside the battery, if the generated heat cannot be dissipated in time, the localized heat in the limited space will cause the battery operating temperature to continue to rise, accelerating the uneven temperature distribution in the electrodes and deteriorating battery performance. Especially under overheating conditions, this uneven heat distribution will exacerbate side reactions within the battery, generate localized high temperatures and generate flammable gases, causing battery bulging and gas leakage, which in turn can induce safety accidents such as battery fires and explosions. Therefore, promoting faster heat dissipation and achieving uniform temperature distribution in the electrodes are considered to be effective methods to improve battery thermal stability and reduce battery safety accidents.

[0040] In response to the above problems, the embodiments of the present application provide a positive electrode additive and a preparation method thereof, as well as the application of the positive electrode additive in a positive electrode plate and a lithium-ion battery. The positive electrode additive can improve the uniformity of heat distribution in the positive electrode plate by introducing a high thermal conductivity ceramic material, thereby improving the heat dissipation capacity of the battery. At the same time, by introducing a conductive polymer coating, the prepared positive electrode additive has excellent electrical and thermal conductivity properties, thereby improving the battery safety while taking into account the electrochemical performance of the battery.

[0041] The positive electrode additive provided in the embodiment of the present application is a composite material formed by coating a conductive polymer on the surface of a thermally conductive ceramic matrix. The mass ratio of the conductive polymer to the thermally conductive ceramic matrix in the composite material is (0.005-0.3):1.

[0042] In the embodiment of the present application, the thermally conductive ceramic matrix is ​​introduced into the positive electrode slurry formula, which can improve the safety performance of the lithium-ion battery under overheating conditions; and the positive electrode additive obtained by coating the thermally conductive ceramic matrix with a conductive polymer has good heat dissipation capability while also being able to improve the problem of increased internal resistance of the battery. It has both good thermal and electrical conductivity properties, which can solve the battery safety problem while also improving the electrochemical performance of the battery.

[0043] Furthermore, by limiting the mass of the conductive polymer and thermally conductive ceramic matrix in the positive electrode plate, the main component of the positive electrode additive remains thermally conductive ceramic, meeting the requirements for improving battery safety performance. However, if the thermally conductive ceramic is too much, it can easily lead to an increase in the internal resistance of the membrane and deteriorate the electrochemical performance. If the conductive polymer is too much and the coating layer is too thick, it will not effectively improve the thermal conductivity, and the battery's thermal shock performance under overheating conditions will not be effectively improved, which will not improve the battery's safety performance. Furthermore, the positive electrode additive obtained by coating under the above mass ratio conditions can also reduce its surface energy and prevent particle agglomeration, which is beneficial for improving the dispersion of the positive electrode additive in the positive electrode slurry and the establishment of a thermal conductive network, significantly improving the heat dissipation performance, heat dissipation uniformity, and heat stability of the positive electrode plate using this positive electrode additive.

[0044] In the positive electrode additive described in the present application, the mass ratio of the conductive polymer to the thermally conductive ceramic matrix can be 0.005, 0.008, 0.01, 0.02, 0.03, 0.04, 0.05, 0.08, 0.1, 0.3, etc., or any value within the above range.

[0045] In some specific embodiments, the thermally conductive ceramic matrix is ​​selected from at least one of silicon carbide (SiC), silicon nitride (Si3N4), aluminum nitride (AlN), boron nitride (BN), titanium nitride (TiN), titanium carbide (TiC), or beryllium oxide (BeO). These thermally conductive ceramic matrices have excellent thermal conductivity and can meet the requirements for improved thermal conductivity of positive electrode additives.

[0046] It is understandable that the thermally conductive ceramic matrix can be selected from any one of the above-mentioned nitride ceramics, carbide ceramics or oxide ceramics, or a combination of two of the above-mentioned thermally conductive ceramic matrices.

[0047] In some preferred embodiments, the thermally conductive ceramic matrix is ​​selected from aluminum nitride. Aluminum nitride has a theoretical thermal conductivity of up to 320 W / (m·K), significantly improving the heat dissipation performance of the positive electrode plate. It is non-toxic, low-cost, and easy to process. Furthermore, aluminum nitride can significantly reduce interfacial cracking or failure caused by thermal stress during temperature cycling, exhibits excellent thermal stability and mechanical strength, and exhibits good dispersion in the positive electrode slurry, significantly improving the heat dissipation and thermal stability of the positive electrode plate.

[0048] In some preferred embodiments, the thermally conductive ceramic matrix is ​​selected from a combination of at least two of nitride ceramics, carbide ceramics, and oxide ceramics, one of which is a nitride ceramic, wherein the nitride ceramic is preferably aluminum nitride.

[0049] Specifically, the thermally conductive ceramic matrix is ​​preferably composed of aluminum nitride and silicon carbide; more preferably, the aluminum nitride and silicon carbide are in a mass ratio of (8:2) to (9:1). For example, the mass ratio of aluminum nitride to silicon carbide can be 8:2, 8.5:1.5, 9:1, or any value within the aforementioned range. The combined use of aluminum nitride and silicon carbide not only significantly improves the heat dissipation and thermal stability of the positive electrode sheet, but also further enhances the structural stability and conductivity of the positive electrode sheet, thereby improving the battery's cycle life and electrochemical performance.

[0050] In some specific embodiments, the thermal conductivity of the thermally conductive ceramic substrate is ≥40 W / (m·K). Selecting a material with a thermal conductivity of ≥40 W / (m·K) for the thermally conductive ceramic substrate can provide good thermal conductivity to meet the requirements of lithium-ion batteries used in higher temperature conditions.

[0051] In some specific embodiments, the D50 particle size of the thermally conductive ceramic matrix is ​​less than 1 μm. The nano-scale particle size of the thermally conductive ceramic matrix has good dispersibility in the positive electrode slurry and can be evenly dispersed between the conductive agent and the positive electrode active material, forming a uniform heat dissipation network and achieving good heat dissipation effect.

[0052] In some embodiments, the conductive polymer is selected from at least one of polypyrrole (PPy), polyaniline (PANI), poly(3,4-ethylenedioxythiophene) (PEDOT), polythiophene (PT), polyacetylene (PA), polyphenylene (PPP), or polyphenylenevinylene (PPV). The backbone of each of these conductive polymers contains alternating single and double bonds, capable of forming conductive pathways through a π-conjugated system. When coated on the surface of a thermally conductive ceramic substrate, these polymers form a positive electrode additive with both thermal and electrical conductivity.

[0053] In particular, when the thermal conductive ceramic itself is an electronically inert conductor (insulator) or has poor conductivity, adding it to the positive electrode slurry alone will lead to an increase in the membrane resistance and deteriorate the electrochemical performance of the battery. After being coated with a conductive polymer, it can form conductive active groups on its surface, so that the positive electrode additive improves the battery safety without deteriorating and enhancing the electrochemical performance of the battery. At the same time, it can also reduce the surface energy of the thermal conductive ceramic, avoid the formation of agglomerates of thermal conductive ceramics and deposit in the positive electrode slurry, which is beneficial to the dispersion and uniformity of the positive electrode additive in the positive electrode slurry, and is beneficial to the establishment of a thermal conductive network in the positive electrode sheet, further improving the heat dissipation and thermal conductivity uniformity of the electrode, improving the safety performance of the battery and improving the electrochemical performance of the battery.

[0054] The present application also provides a method for preparing the positive electrode additive, which comprises mixing a thermally conductive ceramic matrix with a conductive polymer solution, grinding the mixture, drying the mixture, and then heat treating the mixture to obtain the positive electrode additive.

[0055] The preparation method of the above-mentioned positive electrode additive provided in the embodiment of the present application mainly includes coating a conductive polymer on the surface of a thermally conductive ceramic substrate to form a composite material, so that it has both thermal conductivity and electrical conductivity, thereby improving the battery safety performance without deteriorating and improving the electrochemical performance of the battery.

[0056] Specifically, the above preparation method includes: 1) Mixing the thermally conductive ceramic matrix and the conductive polymer solution, and stirring them evenly to obtain a mixed solution; 2) Grinding the mixed liquid and drying it to obtain a preformed additive; 3) heat-treating the preformed additive to obtain a positive electrode additive.

[0057] The conductive polymer solution in step 1) is an aqueous solution or an organic solution containing a conductive polymer. The solvent in the organic solution can be ethanol, chloroform, N-methylpyrrolidone, toluene or the like.

[0058] The conductive polymer content in the conductive polymer solution described in step 1) is 1 wt% to 5 wt%, for example, 1 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, or any other value within this range. A conductive polymer content within this range ensures stability in the conductive polymer solution, preventing the formation of aggregates that could affect the coating effect, while effectively coating the thermally conductive ceramic substrate.

[0059] It can be understood that the content of the above conductive polymer in the conductive polymer solution is the mass content ratio.

[0060] The grinding process described in step 2) above is ball milling. Preferably, the ball milling process is performed for 0.1 to 2 hours, for example, 0.1, 0.5, 0.8, 1, 1.2, 1.5, 1.8, or 2 hours. More preferably, the ball milling process is performed using ceramic balls, agate balls, steel balls, or the like, with the ball milling speed being between 650 and 1200 rpm. The grinding time and ball milling speed can be adjusted based on the original particle size of the thermally conductive ceramic substrate and the amount of additive.

[0061] By ball milling the mixed solution of the conductive polymer and the thermally conductive ceramic matrix, the agglomeration of the conductive polymer and the thermally conductive ceramic matrix can be broken, the dispersion of the conductive polymer and the thermally conductive ceramic matrix can be improved, the two can be in uniform contact, and sufficient and appropriate mechanical force can be provided to make the composite effect of the two better and enhance the coating effect.

[0062] The D50 particle size of the thermally conductive ceramic matrix obtained by ball milling is less than 1 μm, that is, it reaches a nano-scale particle size, so that it can be more evenly dispersed between the positive electrode active material and the conductive agent, which is conducive to the establishment of a thermal conductive network.

[0063] The drying process in step 2) is performed by vacuum drying at a temperature of 50°C to 100°C; for example, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, or any other value within this range. The drying time and temperature can be adjusted based on the amount of the mixed solution, but the drying temperature should be neither too high nor too low. A too low temperature will result in prolonged drying time and poor drying results, leading to residual aqueous or organic solvents, which can affect the shape and structure of the resulting cathode additive product during subsequent heat treatment. A too high temperature may lead to rapid water loss during the drying process, resulting in pores in the resulting cathode additive product or affecting surface roughness, thereby impairing its thermal and electrical conductivity.

[0064] The heat treatment in step 3) is performed under an argon or nitrogen atmosphere at a temperature of 200°C to 500°C for a time of 0.5 to 8 hours. Specifically, the heat treatment temperature can be, for example, 200°C, 250°C, 280°C, 300°C, 350°C, 380°C, 400°C, 450°C, 480°C, 500°C, or any value within the aforementioned range. The heat treatment time can be, for example, 0.5 hour, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, or any value within the aforementioned range. The heat treatment temperature and time can be adjusted depending on the amount of preform additive.

[0065] In the embodiment of the present application, a uniform conductive polymer coating can be formed on the surface of the thermally conductive ceramic substrate by mixing evenly and then performing heat treatment, which helps to form a uniform conductive network during the battery use stage, so that the conductive network and the thermal conductive network are evenly distributed on the electrode piece, so that the electrode has excellent thermal conductivity and electrical conductivity, which helps to quickly dissipate heat and improve battery safety performance without deteriorating and improving the electrochemical performance of the battery.

[0066] In some preferred embodiments, the above step 3) includes: 3.1) subjecting the preformed additive to a first heat treatment at a temperature of 200°C to 400°C for 0.5h to 5.5h in an argon or nitrogen atmosphere; 3.2) The preformed additive that has undergone the first heat treatment is subjected to a second heat treatment at a temperature of 350° C. to 500° C. for 0.5 h to 1.5 h in an argon or nitrogen atmosphere.

[0067] In the embodiment of the present application, through the above-mentioned step-by-step heat treatment process, a conductive polymer coating layer can be formed on the surface of the thermally conductive ceramic substrate under the first heat treatment condition, so that the positive electrode additive has both good thermal conductivity and electrical conductivity; under the second heat treatment condition, part of the conductive polymer coating layer can be carbonized to form a carbon coating layer, thereby further enhancing the conductivity, significantly reducing the electrode polarization phenomenon during charging and discharging, and at the same time, buffering volume stress and acting as a physical barrier, thereby improving the cycle stability and safety of the battery and extending the cycle life.

[0068] The embodiment of the present application also provides a positive electrode slurry, to which the above-mentioned positive electrode additive is added.

[0069] In addition to the positive electrode additive, the positive electrode slurry also includes a solvent and a positive electrode powder, wherein the positive electrode powder includes a positive electrode active material, a conductive agent, a binder, etc. The added mass of the positive electrode additive is 0.1% to 10% of the total mass of the positive electrode powder, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 7%, 8%, 9%, 10%, etc., or any value within the above range. If the amount of the positive electrode additive is too low, it will not play a good role in improving the safety performance of the battery. If the amount of the positive electrode additive is too high, the amount of the positive electrode active material and the conductive agent will be reduced accordingly, which will deteriorate the energy density of the battery.

[0070] An embodiment of the present application also provides a positive electrode plate, which includes a positive electrode current collector and a positive electrode material layer (or positive electrode active coating) located on the surface of the positive electrode current collector. The positive electrode material layer is formed by coating the above-mentioned positive electrode slurry on the surface of the positive electrode current collector.

[0071] The positive electrode current collector mentioned in the embodiments of this application is not particularly limited, as long as it is conductive and does not cause adverse chemical changes in the battery. It can be any material known to be suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector can be a metal material such as aluminum, stainless steel, nickel plating, titanium, tantalum, or a carbon material such as carbon cloth or carbon paper; preferably, aluminum foil.

[0072] The positive electrode active material in the positive electrode sheet is mainly a source of lithium ions, and can be selected from lithium cobalt oxide LCO, lithium nickel cobalt manganese oxide NCM, lithium iron phosphate LFP, lithium nickel cobalt aluminum oxide NCA, lithium manganese iron phosphate LMFP, lithium manganese oxide LMO, lithium vanadium phosphate LVP, etc.; preferably at least one of lithium cobalt oxide LCO, lithium nickel cobalt manganese oxide NCM, and lithium iron phosphate LFP.

[0073] The conductive agent in the positive electrode plate can improve the conductivity of the electrode and can be selected from conductive carbon black, acetylene black, Ketjen black, natural graphite, artificial graphite, graphene, carbon fiber, carbon nanotubes CNT, etc.; preferably, it is a mixture of conductive carbon black and carbon nanotubes.

[0074] When the conductive agent is a mixture of conductive carbon black and carbon nanotubes, the mass ratio of the conductive carbon black to the carbon nanotubes is preferably 1:(0.1-0.5); further, the mass ratio of the carbon nanotubes to the positive electrode additive is (1-30):1; preferably (3-25):1.

[0075] When this cathode additive is used with a carbon nanotube conductive agent, the carbon nanotubes participate in the construction of a long-range thermal conductivity network. Therefore, generally speaking, the more carbon nanotubes there are, the better the thermal and electrical conductivity. However, this is due to high costs and difficulty in dispersion, which hinders the uniform dispersion of the carbon nanotubes, the cathode active material, and the cathode additive. When the carbon nanotube content is too high, or when it is excessive relative to other conductive agents such as conductive carbon black and the cathode additive, it can worsen the battery's thermal and electrical conductivity. Furthermore, an excessive amount of conductive agent can also deteriorate the battery's energy density and shorten its service life.

[0076] The positive electrode binder is selected from polyvinylidene fluoride binders. The binder in the positive electrode sheet is a substance that firmly binds the particles of the positive electrode active material, conductive agent, positive electrode additive, etc. together and tightly adheres them to the surface of the positive electrode current collector. It can be polyvinylidene fluoride, sodium carboxymethyl cellulose, polyacrylic acid, etc., preferably polyvinylidene fluoride.

[0077] In the positive electrode sheet, the mass ratio of the positive electrode active material, the conductive agent, the binder and the positive electrode additive can be (0.90~0.99):(0.005~0.05):(0.005~0.05):(0.001~0.1).

[0078] The solvent of the positive electrode slurry may be selected from N-methylpyrrolidone (NMP) or water, so as to obtain a desired viscosity after the positive electrode material and the optional binder and conductive agent are mixed.

[0079] The present invention also provides a lithium-ion battery comprising the aforementioned positive electrode sheet, electrolyte, negative electrode sheet, and separator. The electrolyte, negative electrode sheet, and separator mentioned in the present invention are not particularly limited, as long as they can provide their corresponding functions, and can be any known material suitable for lithium-ion batteries.

[0080] In the lithium-ion battery described herein, a separator is disposed between the positive and negative electrodes to prevent short circuits. The battery preparation process may include the following steps: overlapping the positive and negative electrode sheets via the separator, winding and folding them as needed, and then placing them within a housing; injecting an electrolyte into the housing and encapsulating the housing. Furthermore, overcurrent protection elements, guide plates, and the like may be placed within the housing as needed to prevent pressure buildup and overcharging and discharging within the electrochemical device.

[0081] The application fields of the lithium-ion batteries of the embodiments of the present application are not particularly limited, and can be used in consumer electronics, new energy vehicles, energy storage and other fields.

[0082] To make the present invention easier to understand, the present invention will be further described in detail below with reference to the following examples. These examples are merely illustrative and do not limit the scope of application of the present invention. Unless otherwise specified, the raw materials or components used in the present invention can be obtained through commercial channels or conventional methods.

[0083] Example 1 (1) Preparation of positive electrode additives Aluminum nitride (AlN) ceramic powder was dispersed in a 3 wt% polyaniline (PANI) aqueous solution to form a mixed solution, wherein the mass ratio of polyaniline (PANI) to aluminum nitride (AlN) was 5:100. The mixed solution was then ground in agate mortar for 0.5 h, vacuum dried at 80°C for 8 h, and finally heat treated at 300°C under nitrogen (or argon) protection at a heating rate of 3°C / min for 4 h to obtain the conductive polymer-coated thermally conductive ceramic additive AlN@PANI, which is the positive electrode additive of Example 1.

[0084] (2) Cathode slurry According to the mass percentage, 97.7% lithium cobalt oxide, 0.3% carbon nanotubes, 0.8% conductive carbon black and 1.2% polyvinylidene fluoride were mixed as positive electrode powder and added to N-methylpyrrolidone solvent. The mixture was evenly mixed to form a glue solution. Then, 3% of the total mass of the positive electrode powder was added to the above-mentioned positive electrode additive AlN@PANI and mixed evenly to form a positive electrode slurry.

[0085] (3) Positive electrode The above positive electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and then cut into positive electrode sheets after drying, rolling, compacting and other processes. Figure 1 shown.

[0086] (4) Lithium-ion batteries The negative electrode active material, graphite, is mixed with a binder (SBR-CMC) and a conductive agent (carbon black) in a weight ratio of 95:3.5:1.5 and added to water as a solvent to prepare the negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector copper foil and, after drying, roller pressing, and compaction, cut into negative electrode sheets.

[0087] In an argon-filled glove box with a water content of <10 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a 1:1 volume ratio to prepare a solvent. The electrolyte was then added with lithium hexafluorophosphate (LiPF) and the additive fluoroethylene carbonate (EFC) according to the required concentrations and mixed thoroughly. The concentration of LiPF was 1.2 M and that of EFC was 0.2 M.

[0088] A polyolefin porous membrane is used as the separator.

[0089] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The stacked electrode sheets and separator are then wound to form a battery cell. The cell is placed in a battery case, electrolyte is injected, and the packaged battery undergoes formation (0.1C charging to 4.6V) and aging to obtain a finished lithium-ion battery.

[0090] Example 2 The difference from Example 1 is that the conductive polymer used is polypyrrole (PPy), and the other operations and parameters are the same as Example 1.

[0091] Example 3 The difference from Example 1 is that the conductive polymer used is poly(3,4-ethylenedioxythiophene) (PEDOT), and the other operations and parameters are the same as Example 1.

[0092] Example 4 The difference from Example 1 is that the conductive polymers used are polyaniline and polythiophene in a mass ratio of 1:1. Other operations and parameters are the same as in Example 1.

[0093] Example 5 The difference from Example 1 is that the conductive polymers used are polyaniline, polyacetylene and polyphenylene vinylene in a mass ratio of 1:1:1. Other operations and parameters are the same as those in Example 1.

[0094] Example 6 The difference from Example 1 is that the thermal conductive ceramic used is boron nitride (BN), and the other operations and parameters are the same as Example 1.

[0095] Example 7 The difference from Example 1 is that the thermal conductive ceramic used is titanium nitride (TiN), and the other operations and parameters are the same as Example 1.

[0096] Example 8 The difference from Example 1 is that the thermal conductive ceramic used is silicon carbide, and the other operations and parameters are the same as Example 1.

[0097] Example 9 The difference from Example 1 is that the thermal conductive ceramic used is beryllium oxide, and the other operations and parameters are the same as Example 1.

[0098] Example 10 The difference from Example 1 is that the thermal conductive ceramics used are aluminum nitride and silicon carbide in a mass ratio of 8:2, and other operations and parameters are the same as Example 1.

[0099] Example 11 The difference from Example 1 is that the thermal conductive ceramics used are aluminum nitride and silicon carbide with a mass ratio of 9:1, and other operations and parameters are the same as Example 1.

[0100] Example 12 The difference from Example 1 is that the thermal conductive ceramics used are aluminum nitride and silicon carbide in a mass ratio of 7:3, and the other operations and parameters are the same as Example 1.

[0101] Example 13 The difference from Example 1 is that, in the preparation method of the positive electrode additive, the mass ratio of polyaniline (PANI) to aluminum nitride (AlN) is 0.5:100, and other operations and parameters are the same as Example 1.

[0102] Example 14 The difference from Example 1 is that, in the preparation method of the positive electrode additive, the mass ratio of polyaniline (PANI) to aluminum nitride (AlN) is 3:100, and other operations and parameters are the same as Example 1.

[0103] Example 15 The difference from Example 1 is that, in the preparation method of the positive electrode additive, the mass ratio of polyaniline (PANI) to aluminum nitride (AlN) is 10:100, and other operations and parameters are the same as Example 1.

[0104] Example 16 The difference from Example 1 is that, in the preparation method of the positive electrode additive, the mass ratio of polyaniline (PANI) to aluminum nitride (AlN) is 30:100, and other operations and parameters are the same as Example 1.

[0105] Example 17 The difference from Example 1 is that, in the preparation method of the positive electrode additive, the heat treatment temperature is 200° C., and the other operations and parameters are the same as in Example 1.

[0106] Example 18 The difference from Example 1 is that, in the preparation method of the positive electrode additive, the heat treatment temperature is 400° C., and the other operations and parameters are the same as in Example 1.

[0107] Example 19 The difference from Example 1 is that, in the preparation method of the positive electrode additive, the heat treatment temperature is 500° C., and the other operations and parameters are the same as in Example 1.

[0108] Example 20 The difference from Example 1 is that, in the preparation method of the positive electrode additive, a first heat treatment is performed at 300° C. for 4 h; and then a heat treatment is performed at 500° C. for 0.5 h. Other operations and parameters are the same as in Example 1.

[0109] Example 21 The difference from Example 1 is that, in the preparation method of the positive electrode additive, a first heat treatment is performed at 300° C. for 4 h; and then a heat treatment is performed at 350° C. for 1.5 h. Other operations and parameters are the same as in Example 1.

[0110] Example 22 The difference from Example 10 is that, in the preparation method of the positive electrode additive, a first heat treatment is performed at 300° C. for 4 h; and then a heat treatment is performed at 500° C. for 0.5 h. Other operations and parameters are the same as Example 10.

[0111] Comparative Example 1 Compared with Example 1, the only difference is that no positive electrode additive is introduced into the positive electrode slurry, and other operations and parameters are the same as Example 1.

[0112] Comparative Example 2 Compared with Example 1, the only difference is that no positive electrode additive is prepared, that is, the surface of the thermal conductive ceramic is not coated with a conductive polymer, and aluminum nitride (AlN) is directly introduced into the positive electrode slurry formula as a safety additive. Other operations and parameters are the same as Example 1.

[0113] Comparative Example 3 Compared with Example 1, the only difference is that no positive electrode additive is prepared, that is, the surface of the thermal conductive ceramic is not coated with a conductive polymer, and aluminum nitride (AlN) and the conductive polymer are directly introduced into the positive electrode slurry formula. Other operations and parameters are the same as Example 1.

[0114] Performance Testing (1) Pole sheet diaphragm resistance test: The diaphragm resistance (Ω*cm, ohm centimeter) of the positive electrode sheet can be tested on the positive electrode sheet after rolling using a resistance meter to obtain the diaphragm resistance of the positive electrode sheet; the smaller the diaphragm resistance value, the better the conductivity of the electrode sheet.

[0115] (2) Thermal shock test of soft-pack lithium-ion batteries: At 25°C, charge the soft-pack cells at a constant current of 0.7C to reach the termination voltage, then charge at a constant voltage until the current rate drops to 0.05C and let it stand for 1 hour; then place the cells in a gravity convection or circulating air oven for heating, and increase the oven temperature to 135°C, 140°C and 145°C at a rate of 5°C / min, respectively, and keep them warm for 1 hour. Monitor the state changes of the soft-pack cells during this process. If the battery does not smoke, catch fire or explode, it passes the test, otherwise it fails. The higher the pass rate and pass temperature of the thermal shock test, the better the thermal safety of the cell.

[0116] Table 1

[0117] By comparing the changes in the positive electrode sheet diaphragm resistance and the thermal shock performance of the battery in the above-mentioned embodiments and comparative examples, it can be found that after adopting the positive electrode additive described in the present application, the increase in diaphragm resistance is significantly reduced, the thermal shock performance is significantly improved, and the battery has both excellent safety performance and good electrochemical performance.

[0118] According to the comparison between Example 1, Comparative Example 1 and Comparative Example 2, it can be found that when the thermally conductive ceramic material is introduced alone into the positive electrode sheet (Comparative Example 2), the thermal shock performance can be improved compared with Comparative Example 1 (no thermally conductive ceramic material), but at the same time the internal resistance of the diaphragm is deteriorated, and the diaphragm resistance suddenly increases from 61Ω*cm to 94Ω*cm; compared with Example 1, due to the high specific surface energy of the nano-ceramic material, it is easy to agglomerate, resulting in poor dispersion, which is not conducive to the construction of a uniform thermal conductive network. The thermal shock performance is still lower than that of the positive electrode sheet in Example 1.

[0119] According to the comparison of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3, it can be found that even if the thermally conductive ceramic material and the conductive polymer material are introduced into the positive electrode sheet at the same time (Comparative Example 3), the deterioration of the diaphragm internal resistance is improved compared with the introduction of the thermally conductive ceramic material alone (Comparative Example 2) when the two materials are used simultaneously without coating process. However, at the same time, the thermal shock performance is reduced, and it still fails to achieve a good effect of improving the thermal shock performance of the battery and reducing the internal resistance of the diaphragm.

[0120] According to the comparison of Examples 1-5, it can be found that the positive electrode additives prepared using the conductive polymer described in this application all have excellent thermal shock resistance and the advantage of reducing the increase in diaphragm internal resistance, and have good high temperature resistance of 140°C.

[0121] According to Examples 1 and 6-12, it was found that a combination of aluminum nitride and silicon carbide (SiC) in a thermally conductive ceramic matrix, particularly one with a mass ratio of 8:2 to 9:1, exhibited improved thermal shock resistance and reduced diaphragm internal resistance. Increasing the amount of SiC added degraded the battery's thermal shock resistance and diaphragm internal resistance.

[0122] According to Examples 1 and 13-16, it was found that using different mass ratios of conductive polymer and thermally conductive ceramic substrate to form positive electrode additives resulted in different improvements in battery thermal shock performance. The greater the amount of conductive polymer coating, the lower the sheet resistance, but this gradually approaches the threshold. Further increases in coating beyond 5% yield little benefit in reducing sheet resistance. Furthermore, increasing the amount of conductive polymer coating decreases the thermal conductivity of the ceramic and reduces thermal shock performance. Therefore, the mass ratio of conductive polymer to thermally conductive ceramic substrate is preferably between 0.05 and 0.1.

[0123] According to Examples 1 and 17-22, different heat treatment processes have different effects on improving the battery's thermal shock performance and membrane resistance. A heat treatment temperature that is too low is not conducive to stable coating, while a temperature that is too high can easily lead to carbonization and decomposition of the polymer. Excessive carbonization and decomposition can expose the surface of the thermally conductive ceramic material, which in turn deteriorates conductivity. Therefore, using appropriate temperatures and times, along with a step-by-step heat treatment approach, can form an inner polymer coating, while the outer layer partially carbonizes and decomposes to form a carbon coating, which further improves conductivity and establishes a thermal network.

[0124] The lithium-ion battery preparation method of Example 1 is used below to explore the effect of the relationship between the positive electrode additive and other positive electrode powders in the positive electrode sheet on the battery.

[0125] Example 23 The difference from Example 1 is that in the positive electrode slurry, the conductive agent is 1.1% conductive carbon black and does not contain carbon nanotubes. Other operations and parameters are the same as Example 1.

[0126] Example 24 The difference from Example 1 is that, in the preparation method of the positive electrode slurry, the addition amount of the positive electrode additive is 0.1% of the total weight of the positive electrode powder, and the other operations and parameters are the same as Example 1.

[0127] Example 25 The difference from Example 1 is that, in the preparation method of the positive electrode slurry, the addition amount of the positive electrode additive is 1% of the total weight of the positive electrode powder, and the other operations and parameters are the same as in Example 1.

[0128] Example 26 The difference from Example 1 is that, in the preparation method of the positive electrode slurry, the amount of the positive electrode additive added is 5% of the total weight of the positive electrode powder, and the other operations and parameters are the same as in Example 1.

[0129] Example 27 The difference from Example 1 is that, in the preparation method of the positive electrode slurry, the amount of the positive electrode additive added is 10% of the total weight of the positive electrode powder, and the other operations and parameters are the same as in Example 1.

[0130] Example 28 The difference from Example 1 is that in the positive electrode slurry, the positive electrode powder is 97.15% lithium cobalt oxide, 0.15% carbon nanotubes, 1.5% conductive carbon black and 1.2% polyvinylidene fluoride in terms of mass percentage. Other operations and parameters are the same as in Example 1.

[0131] Example 29 The difference from Example 1 is that in the positive electrode slurry, the positive electrode powder is 96.8% lithium cobalt oxide, 0.5% carbon nanotubes, 1.5% conductive carbon black and 1.2% polyvinylidene fluoride in terms of mass percentage. Other operations and parameters are the same as in Example 1.

[0132] Example 30 The difference from Example 1 is that in the positive electrode slurry, the positive electrode powder is 96.8% lithium cobalt oxide, 0.5% carbon nanotubes, 1.5% conductive carbon black and 1.2% polyvinylidene fluoride in terms of mass percentage. Other operations and parameters are the same as in Example 1.

[0133] Table 2

[0134] According to Example 1 and Example 23, it can be found that when the positive electrode conductive agent is a mixture of conductive carbon black and carbon nanotubes, the effect of improving the internal resistance of the positive electrode film is better and the thermal shock performance is better.

[0135] According to Examples 1 and 24-30, it was found that different amounts of positive electrode additives, carbon nanotubes, and conductive carbon black added to the positive electrode sheet had different effects on improving the battery's thermal shock performance. Increasing the amount of positive electrode additives decreased the membrane resistance, but when the addition reached 10%, the membrane resistance slightly increased due to nanoparticle dispersion issues. Furthermore, increasing the amount of positive electrode additives improved the thermal shock performance, but excessive additions would crowd out the active material content and reduce the battery's energy density. Therefore, the amount of positive electrode additives added relative to the positive electrode powder is preferably 3% to 5%. Increasing the amount of carbon nanotubes and conductive carbon black added to the positive electrode sheet increases the mass of carbon nanotubes relative to conductive carbon black, resulting in improved thermal and electrical conductivity. However, this is costly and difficult to disperse. Excessive relative mass of carbon nanotubes can worsen electrical and thermal conductivity. Since carbon nanotubes can assist the use of positive electrode additives, that is, the two work together to build a long-range thermal conductivity network, when the mass ratio of carbon nanotubes to positive electrode additives is (3~25):1, the battery has better thermal conductivity and can significantly improve the safety performance of the battery.

[0136] The embodiments of the present application have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to the technology in the market, or to enable other persons skilled in the art to understand the embodiments disclosed herein.

Claims

1. A positive electrode additive, characterized in that: The positive electrode additive is a composite material formed by coating a conductive polymer on the surface of a thermally conductive ceramic matrix; the mass ratio of the conductive polymer to the thermally conductive ceramic matrix is ​​(0.005-0.3):

1.

2. The positive electrode additive according to claim 1, characterized in that: The thermally conductive ceramic matrix is ​​selected from at least one of silicon carbide, silicon nitride, aluminum nitride, boron nitride, titanium nitride, titanium carbide or beryllium oxide.

3. The positive electrode additive according to claim 2, characterized in that: The thermally conductive ceramic matrix comprises aluminum nitride; preferably aluminum nitride and silicon carbide; more preferably aluminum nitride and silicon carbide in a mass ratio of (8:2) to (9:1).

4. The positive electrode additive according to claim 1, characterized in that: The thermal conductivity of the thermally conductive ceramic matrix is ​​≥40 W / (m·K).

5. The positive electrode additive according to claim 1, characterized in that: The conductive polymer is selected from at least one of polypyrrole, polyaniline, poly(3,4-ethylenedioxythiophene), polythiophene, polyacetylene, polyphenylene or polyphenylenevinylene.

6. A method for preparing a cathode additive according to any one of claims 1 to 5, characterized in that: include: The heat-conducting ceramic matrix is ​​mixed with a conductive polymer solution, ground and dried, and then heat-treated to obtain the positive electrode additive.

7. The preparation method according to claim 6, characterized in that: The content of the conductive polymer in the conductive polymer solution is 1 wt% to 5 wt%; And / or, the grinding treatment time is 0.1h to 2h; And / or, the D50 particle size of the thermally conductive ceramic matrix after ball milling is less than 1 μm; And / or, the drying is vacuum drying, and the drying temperature is 50° C. to 100° C.; And / or, the heat treatment temperature is 200° C. to 500° C., the heat treatment time is 0.5 h to 8 h, and the heat treatment atmosphere is an argon atmosphere or a nitrogen atmosphere.

8. The preparation method according to claim 6, characterized in that: The heat treatment includes a first heat treatment and a second heat treatment; Wherein, the first heat treatment temperature is 200°C to 400°C, the treatment time is 0.5 to 5.5 hours, and the heat treatment atmosphere is argon atmosphere or nitrogen atmosphere; The second heat treatment temperature is 350° C. to 500° C., the treatment time is 0.5 to 1.5 hours, and the heat treatment atmosphere is an argon atmosphere or a nitrogen atmosphere.

9. A positive electrode slurry, characterized in that: The positive electrode additive comprises the positive electrode additive according to any one of claims 1 to 5 or the positive electrode additive prepared by the preparation method according to any one of claims 6 to 8.

10. The positive electrode slurry according to claim 9, characterized in that: The positive electrode slurry includes a solvent, positive electrode powder and the positive electrode additive, wherein the added mass of the positive electrode additive is 0.1% to 10% of the total mass of the positive electrode powder; the positive electrode powder includes a positive electrode active material, a positive electrode conductive agent and a positive electrode binder.

11. A positive electrode plate, characterized in that: It includes a positive electrode current collector and a positive electrode material layer provided on the positive electrode current collector; The positive electrode material layer includes a positive electrode active material, a positive electrode conductor, a positive electrode binder, and the positive electrode additive according to any one of claims 1 to 5 or the positive electrode additive prepared by the preparation method according to any one of claims 6 to 8.

12. The positive electrode sheet according to claim 11, wherein: The mass ratio of the positive electrode active material, the conductive agent, the binder and the positive electrode additive is (0.90-0.99):(0.005-0.05):(0.005-0.05):(0.001-0.1); and / or, The positive electrode active material is selected from at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and lithium vanadium phosphate; and / or The positive electrode conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, natural graphite, artificial graphite, graphene, carbon fiber, and carbon nanotubes; preferably, it is a mixture of conductive carbon black and carbon nanotubes; more preferably, the mass ratio of the conductive carbon black to the carbon nanotubes is 1:(0.1-0.5); further preferably, the mass ratio of the carbon nanotubes to the positive electrode additive is (1-30):1; and / or, The positive electrode binder is selected from at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, and polyacrylic acid.

13. A lithium ion battery, characterized in that: Including the positive electrode sheet according to claim 11 or 12.

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