Coated lithium manganate material, preparation method and application thereof, and lithium ion battery

Abstract

The invention relates to the technical field of battery materials, in particular to a coated lithium manganate material, a preparation method and application thereof and a lithium ion battery, the preparation method comprises the following steps: S1, preparing a porous conductive adhesive: mixing a conductive polymer monomer, a nano conductive filler and a pore-foaming agent, carrying out polymerization reaction, and removing the pore-foaming agent; s2, pretreatment of lithium manganate: cleaning the surface of the lithium manganate, and then adding the lithium manganate into a dispersing agent for dispersing to form a lithium manganate suspension; s3, coating treatment: adding the porous conductive adhesive into the lithium manganate suspension, mixing and stirring, and then removing the dispersing agent; s4, heat treatment; the coated lithium manganate material comprises a core layer and a shell layer coating the outer surface of the core layer, the core layer comprises lithium manganate, and the shell layer comprises a porous conductive adhesive; the coated lithium manganate material is applied to a power battery; the positive electrode material of the lithium ion battery is prepared by mixing a coated lithium manganate material, a conductive agent and a binder. According to the invention, the charge-discharge rate performance, the cycle stability and the safety performance of the battery are obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a coated lithium manganate material, a preparation method and application thereof, and a lithium ion battery. Background Art

[0002] Lithium manganese oxide (LMO) boasts numerous advantages, including abundant resources, low cost, good safety, and excellent rate performance, and holds broad application prospects in power batteries and other fields. However, in practical applications, LMO materials still face some challenges, particularly in extreme conditions such as high temperatures or thermal runaway, where their safety performance faces challenges.

[0003] When a battery experiences thermal runaway, the internal temperature of the battery rises sharply, which may trigger a series of adverse reactions. For lithium manganese oxide positive electrode materials, thermal runaway may lead to excessive deintercalation and intercalation of lithium ions, which in turn causes damage to the material structure and even leads to serious safety accidents such as battery combustion and explosion. In order to solve these problems, the commonly used methods currently used include modifying lithium manganese oxide by means of doping with metal ions and surface coating. However, traditional coating materials often have problems such as insufficient conductivity and the inability to effectively prevent abnormal deintercalation and intercalation of lithium ions under extreme conditions such as thermal runaway. For example, although some inorganic oxide coating layers can reduce the corrosion of lithium manganese oxide by the electrolyte to a certain extent, their own conductivity is poor, which increases the internal resistance of the battery and affects the battery's charge and discharge performance; and some organic coating materials have poor stability at high temperatures and are difficult to play an effective protective role during thermal runaway.

[0004] Therefore, it is of great practical significance to develop a material that can maintain good conductivity under normal working conditions and effectively prevent lithium ion deintercalation during battery thermal runaway, thereby significantly improving the safety performance of lithium manganese oxide. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a coated lithium manganate material, a preparation method and application thereof, and a lithium ion battery.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing a coated lithium manganate material, comprising the following steps: S1. Preparing a porous conductive adhesive: mixing a conductive polymer monomer, a nano-conductive filler, and a porogen, performing a polymerization reaction, and then removing the porogen to obtain a porous conductive adhesive; the mass ratio of the conductive polymer monomer, the nano-conductive filler, and the porogen is (4-7):(0.5-2):(2-5); the porogen comprises at least one of polyvinyl alcohol and polyethylene glycol; the pore size of the porous conductive adhesive is 1 nm to 3 nm; S2. Lithium manganate pretreatment: cleaning the surface of lithium manganate and then adding a dispersant to disperse it to form a lithium manganate suspension; S3. Coating treatment: adding the porous conductive adhesive to the lithium manganate suspension, mixing and stirring, and then removing the dispersant to obtain a preliminary coated product; the mass ratio of the porous conductive adhesive to the lithium manganate is (0.05-0.2):1; S4. Heat treatment: heat-treating the preliminary coated product to obtain a coated lithium manganate material.

[0007] Preferably, the conductive polymer monomer includes at least one of aniline and pyrrole; and / or the nano-conductive filler includes at least one of carbon nanotube and graphene.

[0008] Preferably, in step S1, the conductive polymer monomer is first dissolved in an organic solvent, the initiator is added and mixed evenly, and then the nano-conductive filler is added and ultrasonically dispersed for 25 min-45 min, followed by the addition of a porogen and stirring for 2 h-4 h. The polymerization reaction is carried out at 40°C-60°C for 6 h-9 h, and then the organic solvent and the porogen are removed by solvent volatilization, thermal decomposition or chemical dissolution. The organic solvent is toluene or dichloromethane; and / or the mass ratio of the conductive polymer monomer to the initiator is (8-12):1, and the initiator is ammonium persulfate or ferric chloride.

[0009] Preferably, in step S2, the lithium manganate is ultrasonically dispersed in a dispersant for 20 min-30 min; and / or the dispersant is water or ethanol.

[0010] Preferably, in step S3, the mixing temperature is 40° C.-60° C., and the stirring time is 3 h-5 h; and / or the dispersant is removed by spray drying, freeze drying or vacuum drying.

[0011] Preferably, in step S4, the heat treatment temperature is 200° C.-400° C., and the heat treatment time is 1 h-3 h.

[0012] The present invention also proposes a coated lithium manganate material, which is made using the above-mentioned method for preparing the coated lithium manganate material. The coated lithium manganate material includes a core layer and a shell layer coated on the outer surface of the core layer, the core layer includes lithium manganate, and the shell layer includes a porous conductive glue. The thickness of the shell layer is 200 nm-300 nm.

[0013] The present invention also proposes an application of the above-mentioned coated lithium manganese oxide material in a power battery.

[0014] The present invention also provides a lithium-ion battery, wherein the positive electrode material of the lithium-ion battery is prepared by mixing the above-mentioned coated lithium manganate material, a conductive agent and a binder in a mass ratio of (7-9): (0.5-1.5): (0.5-1.5).

[0015] Preferably, the conductive agent includes at least one of acetylene black, graphene, carbon nanotubes and conductive carbon black, and / or the binder is polyvinylidene fluoride, polyacrylonitrile, polyimide or polytetrafluoroethylene.

[0016] Beneficial effects of the present invention: In the preparation method of the coated lithium manganate material of the present invention, a porous conductive adhesive is prepared using a conductive polymer monomer, a nano-conductive filler, and a porogen. This porous conductive adhesive is then mixed with a lithium manganate suspension and heat-treated to uniformly coat the surface of the lithium manganate with the porous conductive adhesive. The addition of the porogen forms a porous structure in the conductive adhesive. The conductive polymer and nano-conductive filler provide a fast channel for the transmission of lithium ions, improving conductivity. The porous conductive adhesive can effectively improve the safety of lithium manganate in batteries. The appropriate pore size ensures the transmission of lithium ions and the closure of the pores when the temperature rises. The preparation method is simple and feasible.

[0017] The coated lithium manganese oxide material of the present invention has a core-shell structure, in which the lithium manganese oxide is coated with a porous conductive adhesive in the shell layer. The porous conductive adhesive has excellent electrical conductivity, thereby improving the charge and discharge rate performance of the battery. During thermal runaway, the pore structure of the porous conductive adhesive closes, effectively preventing the insertion and removal of lithium ions and improving the safety of the battery. Furthermore, the porous conductive adhesive forms a stable coating structure with the lithium manganese oxide, which can reduce electrolyte corrosion of the lithium manganese oxide during the long-term cycle of the battery, thereby improving the structural stability and cycle life of the lithium manganese oxide material.

[0018] The positive electrode material of the lithium-ion battery of the present invention is made by mixing a coated lithium manganese oxide material, a conductive agent and a binder. Compared with the uncoated lithium manganese oxide material, the use of the coated lithium manganese oxide material of the present invention significantly improves the charge and discharge rate performance, cycle stability and safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which: Figure 1 is an SEM image of the coated lithium manganate material of Example 1 of the present invention; Figure 2 This is an SEM image of the uncoated lithium manganate material of Comparative Example 1; Figure 3 8C rate discharge comparison curve of the batteries of Example 1 and Comparative Example 2 of the present invention; Figure 4 1C rate cycle performance comparison curve of the batteries of Example 1 and Comparative Example 2 of the present invention; Figure 5 1 is a graph showing changes in battery internal resistance versus temperature when the batteries of Example 1 and Comparative Example 2 are overcharged. DETAILED DESCRIPTION

[0020] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the present invention will be further described in detail below with reference to examples. The examples are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0021] The present invention provides a method for preparing a coated lithium manganate material, comprising the following steps: S1. Preparation of a porous conductive adhesive: A conductive polymer monomer, a nano-conductive filler, and a porogen are mixed and polymerized, and the porogen is subsequently removed to obtain a porous conductive adhesive. The mass ratio of the conductive polymer monomer, the nano-conductive filler, and the porogen is (4-7):(0.5-2):(2-5), and this mass ratio can be selected from 5:1:3, 4:1:2, 7:2:4, 6:1.5:5, or 4:0.5:3.

[0022] Porogens are used to form the porous structure of the conductive adhesive. Porogens include at least one of polyvinyl alcohol and polyethylene glycol. The porous structure of porous conductive adhesives offers unique advantages. On the one hand, it significantly increases the specific surface area of ​​the material, providing more active sites for the insertion and extraction of lithium ions, accelerating ion transport rates, and thus improving the battery's charge and discharge performance. On the other hand, the porous structure can effectively buffer the volume changes of the material during charge and discharge, reducing the structural stress caused by volume expansion and contraction, lowering the risk of material rupture, and thus improving the material's safety performance.

[0023] In some embodiments, a conductive polymer and a nano-conductive filler are used to provide conductive properties, wherein the conductive polymer monomer includes at least one of aniline and pyrrole, the conductive polymer includes at least one of polyaniline and polypyrrole, the nano-conductive filler includes at least one of carbon nanotubes and graphene, and the nano-conductive filler has a nanometer size.

[0024] In some embodiments, in step S1, the conductive polymer monomer is first dissolved in an organic solvent, an appropriate amount of initiator is added and mixed evenly, and then a nano-conductive filler is added and ultrasonically dispersed for 25 min-45 min, followed by adding a porogen and stirring for 2 h-4 h. The polymerization reaction is carried out at 40°C-60°C for 6 h-9 h to form a conductive adhesive precursor. Further, the organic solvent and porogen are removed from the conductive adhesive precursor by solvent volatilization, thermal decomposition or chemical dissolution, thereby forming a porous structure in the conductive adhesive to prepare a porous conductive adhesive. It can be understood that the solvent volatilization, thermal decomposition or chemical dissolution method can all use existing technologies, and the specific process steps are not limited here.

[0025] Specifically, the ultrasonic dispersion time can be 25 min, 30 min, 35 min, 40 min or 45 min, etc., the stirring time can be 2 h, 2.5 h, 3 h, 3.5 h or 4 h, etc., the polymerization reaction temperature can be 40°C, 45°C, 50°C, 55°C or 60°C, and the polymerization reaction time can be 6 h, 7 h, 8 h, 8.5 h or 9 h, etc.

[0026] The organic solvent is toluene or dichloromethane, the initiator is ammonium persulfate or ferric chloride, and the mass ratio of the conductive polymer monomer to the initiator is (8-12):1. This mass ratio can be selected from 8:1, 9:1, 10:1, 11:1, or 12:1. The conductive polymer monomer is dissolved in the organic phase, and the initiator acts as an oxidizing phase, initiating polymerization at the interface between the two phases. The conductive polymer monomer undergoes a polymerization reaction to produce the corresponding conductive polymer. The mass concentration of the conductive polymer monomer dissolved in the organic solvent can be 0.05 g / mL to 0.15 g / mL, such as 0.05 g / mL, 0.1 g / mL, or 0.15 g / mL.

[0027] The porous conductive adhesive prepared in step S1 has temperature-sensitive properties. The pore size of the porous conductive adhesive is 1 nm-3 nm. This pore size range can not only ensure that the lithium ions of lithium manganese oxide can be smoothly transmitted through the pores of the porous conductive adhesive under normal working conditions, but also ensure that in the event of thermal runaway, as the temperature rises, the pore structure is effectively closed, thereby preventing the deintercalation of lithium ions.

[0028] It should be noted that the specific process parameters for preparing the porous conductive adhesive can be dynamically adjusted according to the specific production conditions, and this application will not limit them one by one.

[0029] S2. Lithium manganate pretreatment: clean the surface of lithium manganate and then add a dispersant to disperse it to form a lithium manganate suspension.

[0030] The lithium manganese oxide raw material (particles) is first screened and cleaned to remove impurities and dust on its surface. For example, the surface cleaning is performed by washing the lithium manganese oxide with deionized water or ethanol 2-4 times, for example 3 times.

[0031] In some embodiments, in step S2, the dispersant is water or ethanol. The mass concentration of lithium manganate in the dispersant may be 0.1 g / mL to 0.3 g / mL, such as 0.1 g / mL, 0.2 g / mL, or 0.3 g / mL. The lithium manganate is ultrasonically dispersed in the dispersant for 20 min to 30 min, such as 20 min, 25 min, 28 min, or 30 min, or mechanically stirred to form a uniform lithium manganate suspension for subsequent uniform mixing with the porous conductive adhesive.

[0032] It should be noted that the specific process parameters of lithium manganate pretreatment can be dynamically adjusted according to specific production conditions, and this application will not limit them one by one.

[0033] S3. Coating: Add the porous conductive adhesive to the lithium manganate suspension and mix and stir until the porous conductive adhesive is evenly coated on the surface of the lithium manganate. Then, remove the dispersant to obtain a preliminary coated product. The mass ratio of the porous conductive adhesive to the lithium manganate is (0.05-0.2):1. This mass ratio can be selected from 0.05:1, 0.1:1, 0.15:1, or 0.2:1.

[0034] In some embodiments, in step S3, the mixing temperature is 40°C-60°C, and may be 40°C, 45°C, 50°C, 55°C, or 60°C, and the stirring time is 3 hours-5 hours, and may be 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours. The dispersant is removed by spray drying, freeze drying, or vacuum drying. Spray drying, freeze drying, or vacuum drying can all be performed using existing technologies, and the specific process steps are not limited herein.

[0035] It should be noted that the specific process parameters of the coating treatment can be dynamically adjusted according to the specific production conditions, and this application will not limit them one by one.

[0036] S4. Heat treatment: heat-treating the preliminary coated product to obtain a coated lithium manganate material.

[0037] In order to further improve the coating effect of the porous conductive adhesive on lithium manganese oxide, the preliminary coating product obtained in step S3 is heat treated to allow the porous conductive adhesive to chemically bond or physically adsorb to the surface of the lithium manganese oxide, thereby enhancing the bonding force between the porous conductive adhesive and the lithium manganese oxide, and finally obtaining a lithium manganese oxide material coated with a porous conductive adhesive. The thickness of the porous conductive adhesive layer is 200 nm-300 nm.

[0038] In some embodiments, in step S4, the heat treatment temperature is 200°C-400°C, and may be 200°C, 250°C, 300°C, 350°C, or 400°C, etc., and the heat treatment time is 1 h-3 h, and may be 1 h, 1.5 h, 2 h, 2.5 h, or 3 h, etc. It should be noted that the specific process parameters of the heat treatment can be dynamically adjusted according to the specific production conditions, and this application does not limit them one by one.

[0039] The present invention also provides a coated lithium manganate material, produced using the aforementioned method for preparing a coated lithium manganate material. The coated lithium manganate material comprises a core layer and a shell layer coated on the outer surface of the core layer. The core layer comprises lithium manganate, and the shell layer comprises a porous conductive adhesive. The porous conductive adhesive is similar to the porous conductive adhesive in the aforementioned method for preparing a coated lithium manganate material, and is produced using a conductive polymer monomer, a nano-conductive filler, and a porogen. The shell layer has a thickness of 200 nm to 300 nm, such as 200 nm, 250 nm, 280 nm, or 300 nm.

[0040] The present invention also proposes an application of the above-mentioned coated lithium manganese oxide material in a power battery.

[0041] The present invention also provides a lithium-ion battery, wherein the positive electrode material is prepared by mixing the above-mentioned coated lithium manganese oxide material, a conductive agent, and a binder in a mass ratio of (7-9):(0.5-1.5):(0.5-1.5), and the mass ratio may be 7:0.5:0.5, 8:1:1, 9:1:1.5, 8:0.5:1, etc. In some embodiments, the conductive agent includes at least one of acetylene black, graphene, carbon nanotubes (CNTs), and conductive carbon black (SP), and the binder may be polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide (PI), or polytetrafluoroethylene (PTFE).

[0042] In some embodiments, a method for preparing a lithium-ion battery includes the following steps: uniformly mixing a coated lithium manganese oxide material, a conductive agent, and a binder in a certain mass ratio, adding an appropriate amount of an organic solvent (such as N-methylpyrrolidone, NMP), and stirring to form a uniform slurry; coating the slurry on an aluminum foil current collector, and performing processes such as drying and roller pressing to prepare a positive electrode sheet for the lithium-ion battery. Furthermore, the positive electrode sheet is assembled with a negative electrode sheet (such as a graphite negative electrode), a separator, and an electrolyte to form a lithium-ion battery.

[0043] The present invention uses a porous conductive adhesive to coat lithium manganese oxide. When the battery experiences thermal runaway, the pore structure of the porous conductive adhesive closes due to rising temperature. This change in pore structure effectively prevents the deintercalation and deintercalation of lithium ions, preventing further deterioration of thermal runaway caused by abnormal lithium ion behavior, thereby significantly improving battery safety. Under normal operating conditions, the porous conductive adhesive has excellent electrical conductivity. The conductive polymer and nano-conductive filler within it provide a fast channel for lithium ion transmission, reducing the battery's internal resistance and improving the battery's charge and discharge efficiency.

[0044] Furthermore, the porous conductive adhesive forms a stable coating structure with the lithium manganese oxide through chemical bonding or physical adsorption. This structure not only protects against thermal runaway but also reduces electrolyte corrosion of the lithium manganese oxide during long-term battery cycling, inhibiting the dissolution of manganese ions and thus improving the structural stability and cycle life of the lithium manganese oxide material.

[0045] The following is described by specific examples: Example 1 The preparation method of the coated lithium manganate material of this embodiment includes the following steps: S1. Preparation of a porous conductive adhesive: A conductive polymer monomer, a nano-conductive filler, and a porogen are mixed and polymerized, followed by removal of the porogen to obtain a porous conductive adhesive. The mass ratio of the conductive polymer monomer, nano-conductive filler, and porogen is 5:1:3. The conductive polymer monomer is aniline, the nano-conductive filler is carbon nanotubes, and the porogen is polyvinyl alcohol.

[0046] Specifically, the conductive polymer monomer is first dissolved in an organic solvent, an initiator is added, and the mixture is mixed thoroughly. A nano-conductive filler is then added and ultrasonically dispersed for 30 minutes. A porogen is then added and stirred for 2 hours. Polymerization is then carried out at 60°C for 6 hours to form a conductive adhesive precursor. The conductive adhesive precursor is then vacuum-dried at 80°C for 12 hours to remove the organic solvent and porogen, resulting in a porous conductive adhesive. The organic solvent is toluene, the initiator is ammonium persulfate, the weight ratio of the conductive polymer monomer to the initiator is 10:1, and the concentration of the conductive polymer monomer dissolved in the organic solvent is 0.1 g / mL. The pore size of the porous conductive adhesive is 2 nm.

[0047] S2. Lithium manganate pretreatment: Clean the surface of the lithium manganate and then disperse it in a dispersant to form a lithium manganate suspension. Surface cleaning involves rinsing the lithium manganate three times with deionized water. The dispersant is ethanol. The concentration of lithium manganate in the dispersant is 0.2 g / mL. Ultrasonic dispersion of the lithium manganate in the dispersant is performed for 20 minutes.

[0048] S3. Coating Treatment: Add the porous conductive adhesive to the lithium manganese oxide suspension and mix and stir until the porous conductive adhesive is evenly coated on the surface of the lithium manganese oxide. The dispersant is then removed to obtain a preliminary coated product. The mass ratio of porous conductive adhesive to lithium manganese oxide is 0.1:1. The mixing temperature is 50°C and the stirring time is 4 hours. The dispersant is then removed by spray drying.

[0049] S4. Heat Treatment: Heat treat the preliminary coated product to produce a coated lithium manganese oxide material. The heat treatment temperature is 300°C and the heat treatment time is 2 hours. The thickness of the porous conductive adhesive layer coated with the lithium manganese oxide material is 250 nm.

[0050] The coated lithium manganate material of this embodiment is made using the above-mentioned method for preparing the coated lithium manganate material. The coated lithium manganate material includes a core layer and a shell layer coated on the outer surface of the core layer. The core layer includes lithium manganate, and the shell layer includes a porous conductive glue. The thickness of the shell layer is 250 nm.

[0051] The positive electrode material of the lithium-ion battery of this embodiment is prepared by mixing the above-mentioned coated lithium manganate material, a conductive agent and a binder in a mass ratio of 8:1:1, the conductive agent is acetylene black, and the binder is polyvinylidene fluoride.

[0052] Example 2 The preparation method of the coated lithium manganate material of this embodiment includes the following steps: S1. Preparation of a porous conductive adhesive: A conductive polymer monomer, a nano-conductive filler, and a porogen are mixed and polymerized, followed by removal of the porogen to obtain a porous conductive adhesive. The mass ratio of the conductive polymer monomer, nano-conductive filler, and porogen is 6:1.5:4. The conductive polymer monomer is pyrrole, the nano-conductive filler is graphene, and the porogen is polyethylene glycol.

[0053] Specifically, the conductive polymer monomer is first dissolved in an organic solvent, an initiator is added, and the mixture is thoroughly mixed. A nano-conductive filler is then added and ultrasonically dispersed for 40 minutes. A porogen is then added and stirred for 3 hours. Polymerization is then carried out at 50°C for 8 hours to form a conductive adhesive precursor. The porogen is removed with dilute hydrochloric acid to produce a porous conductive adhesive. The organic solvent is dichloromethane, the initiator is ferric chloride, the weight ratio of the conductive polymer monomer to the initiator is 10:1, and the concentration of the conductive polymer monomer dissolved in the organic solvent is 0.1 g / mL. The pore size of the porous conductive adhesive is 1.5 nm.

[0054] S2. Lithium manganate pretreatment: Clean the surface of the lithium manganate and then disperse it in a dispersant to form a lithium manganate suspension. Surface cleaning involves washing the lithium manganate three times with ethanol. The dispersant is water. The concentration of lithium manganate in the dispersant is 0.2 g / mL. Ultrasonic dispersion of the lithium manganate in the dispersant is performed for 25 minutes.

[0055] S3. Coating Treatment: Add the porous conductive adhesive to the lithium manganate suspension and mix and stir until the porous conductive adhesive is evenly coated on the surface of the lithium manganate. The dispersant is then removed to obtain a preliminary coated product. The mass ratio of porous conductive adhesive to lithium manganate is 0.15:1. The mixing temperature is 60°C and the stirring time is 5 hours. The dispersant is then removed by spray drying.

[0056] S4. Heat Treatment: Heat treat the preliminary coated product to produce a coated lithium manganese oxide material. The heat treatment temperature is 350°C and the heat treatment time is 1.5 hours. The thickness of the porous conductive adhesive layer coated with the lithium manganese oxide material is 200 nm.

[0057] The coated lithium manganate material of this embodiment is made using the above-mentioned method for preparing the coated lithium manganate material. The coated lithium manganate material includes a core layer and a shell layer coated on the outer surface of the core layer. The core layer includes lithium manganate, and the shell layer includes a porous conductive glue. The thickness of the shell layer is 200 nm.

[0058] The positive electrode material of the lithium-ion battery of this embodiment is made by mixing the above-mentioned coated lithium manganate material, a conductive agent and a binder in a mass ratio of 9:1:1.5, wherein the conductive agent is acetylene black and the binder is polyvinylidene fluoride.

[0059] Example 3 The preparation method of the coated lithium manganate material of this embodiment includes the following steps: S1. Preparation of a porous conductive adhesive: A conductive polymer monomer, a nano-conductive filler, and a porogen are mixed and polymerized, followed by removal of the porogen to obtain a porous conductive adhesive. The mass ratio of the conductive polymer monomer, nano-conductive filler, and porogen is 4:1:2. The conductive polymer monomers are aniline and pyrrole, the nano-conductive fillers are carbon nanotubes and graphene, and the porogens are polyvinyl alcohol and polyethylene glycol.

[0060] Specifically, the conductive polymer monomer is first dissolved in an organic solvent, an initiator is added, and the mixture is mixed thoroughly. A nano-conductive filler is then added and ultrasonically dispersed for 35 minutes. A porogen is then added and stirred for 4 hours. Polymerization is then carried out at 40°C for 9 hours to form a conductive adhesive precursor. The conductive adhesive precursor is then vacuum-dried at 90°C for 10 hours to remove the organic solvent and porogen, resulting in a porous conductive adhesive. The organic solvent is toluene, the initiator is ferric chloride, the weight ratio of the conductive polymer monomer to the initiator is 9:1, and the concentration of the conductive polymer monomer dissolved in the organic solvent is 0.15 g / mL. The pore size of the porous conductive adhesive is 2.5 nm.

[0061] S2. Lithium manganate pretreatment: Clean the surface of the lithium manganate and then disperse it in a dispersant to form a lithium manganate suspension. Surface cleaning involves rinsing the lithium manganate three times with deionized water. The dispersant is ethanol. The concentration of lithium manganate in the dispersant is 0.25 g / mL. Ultrasonic dispersion of the lithium manganate in the dispersant is performed for 30 minutes.

[0062] S3. Coating Treatment: Add the porous conductive adhesive to the lithium manganate suspension and mix and stir until the porous conductive adhesive is evenly coated on the surface of the lithium manganate. The dispersant is then removed to obtain a preliminary coated product. The mass ratio of porous conductive adhesive to lithium manganate is 0.2:1. The mixing temperature is 40°C and the stirring time is 5 hours. The dispersant is then removed by spray drying.

[0063] S4. Heat Treatment: Heat treat the preliminary coated product to produce a coated lithium manganese oxide material. The heat treatment temperature is 250°C and the heat treatment time is 2.5 hours. The thickness of the porous conductive adhesive layer coated with the lithium manganese oxide material is 300 nm.

[0064] The coated lithium manganate material of this embodiment is made using the above-mentioned method for preparing the coated lithium manganate material. The coated lithium manganate material includes a core layer and a shell layer coated on the outer surface of the core layer. The core layer includes lithium manganate, and the shell layer includes a porous conductive glue. The thickness of the shell layer is 300 nm.

[0065] The positive electrode material of the lithium-ion battery of this embodiment is prepared by mixing the above-mentioned coated lithium manganate material, a conductive agent and a binder in a mass ratio of 8:0.5:1, wherein the conductive agent is CNT and SP, and the binder is PAN.

[0066] Comparative Example 1 The difference between this comparative example and Example 1 is that the lithium manganese oxide material is not coated with a porous conductive adhesive.

[0067] The rest is the same as in Example 1 and will not be described again here.

[0068] Comparative Example 2 The difference between this comparative example and Example 1 is that in the preparation method of the coated lithium manganate material, no porogen is added in step S1, and the conductive adhesive does not have a porous structure. Step S1 is as follows: S1. Preparing a conductive adhesive: Mixing a conductive polymer monomer with a nano-conductive filler and performing a polymerization reaction to obtain a conductive adhesive. The weight ratio of the conductive polymer monomer to the nano-conductive filler is 5:1. The conductive polymer monomer is aniline, and the nano-conductive filler is carbon nanotubes.

[0069] The rest is the same as in Example 1 and will not be described again here.

[0070] Performance testing: The following performance tests were conducted on the coated lithium manganese oxide materials of Examples 1 and 2, the uncoated lithium manganese oxide of Comparative Example 1, and the conductive adhesive-coated lithium manganese oxide material of Comparative Example 2: (1) Observe the surface morphology by scanning electron microscopy (SEM) to determine the coating uniformity of the porous conductive adhesive; (2) Analyze the crystal structure by X-ray diffraction (XRD) to determine whether the coating process has an impact on the crystal structure of lithium manganese oxide; (3) Prepare the lithium manganese oxide material into a positive electrode sheet and assemble it into a lithium-ion battery for electrochemical performance tests, such as cyclic voltammetry (CV), constant current charge and discharge test, etc., perform cycle performance tests at room temperature with a charge and discharge rate of 1C, perform discharge tests at a rate of 8C, and perform simulated thermal runaway tests and battery overcharge tests to evaluate the battery's charge and discharge performance, cycle stability, and safety performance under thermal runaway conditions. The test results are as follows: Figure 1 、 2 shown.

[0071] In the test results of Example 1, Figure 1 The SEM image shows that the porous conductive glue is evenly coated on the surface of the lithium manganese oxide particles, forming a continuous coating layer, and the coating layer is distributed throughout the porous structure. XRD analysis shows that the coating process has no significant effect on the crystal structure of the lithium manganese oxide. The battery performance test results show that the initial discharge capacity of the battery at a charge and discharge rate of 1C is 118mAh / g. Figure 4 It can be seen that after 500 cycles, the battery's capacity retention rate was 82%, indicating good cycle performance. In the simulated thermal runaway test, when the temperature rose to 108°C, the pore structure of the porous conductive glue coating the lithium manganese oxide material began to close, and the battery did not experience obvious thermal runaway, indicating good battery stability and good safety performance.

[0072] In the test results of Example 2, SEM observations showed uniform coating of the porous conductive adhesive, and XRD analysis indicated no significant changes in the crystal structure of the lithium manganese oxide during the coating process. Battery performance tests revealed an initial discharge capacity of 115 mAh / g at a 1C charge / discharge rate, and a capacity retention rate of 83% after 500 cycles, demonstrating good cycling performance. In a simulated thermal runaway test, the pore structure of the porous conductive adhesive coating the lithium manganese oxide material began to close when the temperature rose to 105°C, indicating good battery stability and safety.

[0073] Figure 2 This is an SEM image of the uncoated lithium manganese oxide from Comparative Example 1. This uncoated lithium manganese oxide was used in a lithium-ion battery. Battery performance testing showed that the battery had an initial discharge capacity of 100 mAh / g at a 1C charge / discharge rate. After 400 cycles, the capacity retention rate was only 81%, indicating poor cycling performance. In a simulated thermal runaway experiment, when the temperature rose to 117°C, the battery rapidly experienced thermal runaway and combustion, indicating poor battery safety performance.

[0074] In the test results of Comparative Example 2, SEM observation results show that the conductive adhesive is evenly coated, and XRD analysis shows that the crystal structure of lithium manganese oxide has no obvious change during the coating process. Figure 4 It can be seen that at a charge and discharge rate of 1C, the capacity retention rate of the battery after 450 cycles is only 81%, indicating that the battery's cycle performance is poor.

[0075] according to Figure 3 It can be seen that when the discharge rate is 8C, the battery capacity retention rate of Comparative Example 2 drops to about 94%, while the battery capacity retention rate of Example 1 is still close to 100%, which shows that the battery of the present invention has better durability. Figure 5 It can be seen that when the battery is overcharged and the battery temperature gradually rises to 108°C, the internal resistance of the battery in Example 1 increases rapidly to 230mΩ, while the internal resistance of the battery in Comparative Example 2 only increases slowly. It can be seen that as the temperature rises, the internal resistance of the battery in Example 1 increases rapidly, indicating that the porous conductive adhesive begins to gradually close the pores, preventing further passage of lithium ions, and thus preventing further occurrence of thermal runaway. This shows that the battery safety performance of Example 1 is higher, while the battery safety of Comparative Example 2 is worse.

[0076] Compared to uncoated lithium manganese oxide and lithium manganese oxide coated with conductive adhesive, the porous conductive adhesive-coated lithium manganese oxide material prepared by the present invention significantly improves the charge and discharge rate performance, cycle stability, durability, and safety performance of lithium-ion batteries. The lithium-ion battery using the coated lithium manganese oxide material of the present invention has an initial discharge capacity of 115mAh / g-118mAh / g at a 1C charge and discharge rate, and a capacity retention rate of ≥82% after 500 cycles. When the temperature rises to approximately 108°C, the pore structure of the porous conductive adhesive begins to close, effectively preventing the insertion and extraction of lithium ions. The battery does not experience significant thermal runaway and remains relatively stable.

[0077] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other.

[0078] It can be understood that the above embodiments only express the preferred implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the patent scope of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can be made, all of which fall within the scope of protection of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should fall within the scope of coverage of the claims of the present invention.

Claims

1. A method for preparing a coated lithium manganate material, characterized in that: The following steps are involved: S1. Preparing a porous conductive adhesive: mixing a conductive polymer monomer, a nano-conductive filler, and a porogen, performing a polymerization reaction, and then removing the porogen to obtain a porous conductive adhesive; the mass ratio of the conductive polymer monomer, the nano-conductive filler, and the porogen is (4-7):(0.5-2):(2-5); the porogen comprises at least one of polyvinyl alcohol and polyethylene glycol; the pore size of the porous conductive adhesive is 1 nm to 3 nm; S2. Lithium manganate pretreatment: cleaning the surface of lithium manganate and then adding a dispersant to disperse it to form a lithium manganate suspension; S3, coating treatment: adding the porous conductive adhesive to the lithium manganate suspension, mixing and stirring, and then removing the dispersant to obtain a preliminary coated product; The mass ratio of the porous conductive adhesive to the lithium manganese oxide is (0.05-0.2):1; S4. Heat treatment: heat-treating the preliminary coated product to obtain a coated lithium manganate material.

2. The method for preparing the coated lithium manganate material according to claim 1, wherein: The conductive polymer monomer includes at least one of aniline and pyrrole; and / or, The nano conductive filler includes at least one of carbon nanotubes and graphene.

3. The method for preparing the coated lithium manganate material according to claim 1, wherein: In step S1, the conductive polymer monomer is first dissolved in an organic solvent, an initiator is added and mixed evenly, the nano-conductive filler is then added and ultrasonically dispersed for 25 min-45 min, the porogen is then added and stirred for 2 h-4 h, and a polymerization reaction is carried out at 40° C.-60° C. for 6 h-9 h, and then the organic solvent and the porogen are removed by solvent volatilization, thermal decomposition or chemical dissolution; The organic solvent is toluene or dichloromethane; and / or the mass ratio of the conductive polymer monomer to the initiator is (8-12):1, and the initiator is ammonium persulfate or ferric chloride.

4. The method for preparing the coated lithium manganate material according to claim 1, wherein: In the step S2, the lithium manganate is ultrasonically dispersed in the dispersant for 20 min to 30 min; and / or, The dispersant is water or ethanol.

5. The method for preparing the coated lithium manganate material according to claim 1, wherein: In the step S3, the mixing temperature is 40°C-60°C and the stirring time is 3 h-5 h; and / or, The dispersant is removed by spray drying, freeze drying or vacuum drying.

6. The method for preparing the coated lithium manganate material according to claim 1, wherein: In the step S4, the heat treatment temperature is 200° C.-400° C., and the heat treatment time is 1 h-3 h.

7. A coated lithium manganate material, characterized in that: The coated lithium manganate material is made by the preparation method of any one of claims 1 to 6, wherein the coated lithium manganate material includes a core layer and a shell layer coated on the outer surface of the core layer, the core layer includes lithium manganate, the shell layer includes a porous conductive paste, and the thickness of the shell layer is 200 nm-300 nm.

8. Use of the coated lithium manganate material according to claim 7 in a power battery.

9. A lithium-ion battery, characterized in that: The positive electrode material of the lithium-ion battery is prepared by mixing the coated lithium manganate material according to claim 7, a conductive agent and a binder in a mass ratio of (7-9): (0.5-1.5): (0.5-1.5).

10. The lithium-ion battery according to claim 9, characterized in that The conductive agent includes at least one of acetylene black, graphene, carbon nanotubes and conductive carbon black, and / or the binder is polyvinylidene fluoride, polyacrylonitrile, polyimide or polytetrafluoroethylene.

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