A positive electrode lithium supplementing material, a preparation method and application thereof

Abstract

This application discloses a cathode lithium replenishment material, its preparation method, and its application. The cathode lithium replenishment material includes a lithium-rich core material and a first shell layer. The first shell layer is disposed on the outer surface of the lithium-rich core material, and reinforcing particles are embedded on the surface and / or inside the first shell layer. The cathode lithium replenishment material of this application has a first shell layer containing reinforcing particles covering the lithium-rich core material. The inclusion of reinforcing particles can, on the one hand, improve the stability of the first shell layer, preventing direct contact between the lithium replenishment material and the electrolyte due to easy damage to the coating layer, and on the other hand, improve the ion mobility of the lithium replenishment material.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a positive electrode lithium replenishment material, its preparation method and application. Background Technology

[0002] Lithium-ion batteries have attracted much attention for their application in devices such as mobile phones and electric vehicles due to their long cycle life and high specific energy. However, during the first charge of a lithium-ion battery with graphite as the negative electrode, 10% of the active lithium from the positive electrode is consumed to form a solid electrolyte interphase layer on the surface of the negative electrode, thereby reducing the specific energy of existing lithium-ion batteries. To address this issue, many studies have been conducted to compensate for the loss of active lithium during the first cycle of lithium-ion batteries.

[0003] Lithium sulfide, with its high theoretical capacity of 1166 mAh / g, is a promising cathode lithium supplement material. However, lithium-rich materials, such as lithium sulfide, suffer from low electronic and ionic conductivity, and their large particle size makes internal delithiation difficult. Furthermore, their high sensitivity to water further limits their applications. To address these issues, it is necessary to improve encapsulation technology to promote the application of lithium-rich materials like lithium sulfide as cathode lithium supplement materials. Summary of the Invention

[0004] In view of this, one objective of this application is to provide a positive electrode lithium replenishment material, wherein a first shell containing reinforcing particles is coated on a lithium-rich material core. The reinforcing particles can improve the stability of the first shell and prevent the lithium replenishment material from directly contacting the electrolyte due to the easy damage of the coating layer. On the other hand, by physically confining the material to create a nanoscale lithium-rich core, the ion mobility of the lithium replenishment material can be improved.

[0005] Another objective of this application is to provide a method for preparing a positive electrode lithium replenishment material.

[0006] Another objective of this application is to provide a lithium-rich cathode.

[0007] Another object of this application is to provide a secondary battery.

[0008] To achieve the above objectives, a first aspect of this application provides a positive electrode lithium replenishment material, comprising:

[0009] Lithium-rich core materials;

[0010] A first shell layer is disposed on the outer surface of the lithium-rich core material, and reinforcing particles are embedded on the surface and / or inside the first shell layer.

[0011] In some embodiments of this application, the reinforcing particles are distributed in a tightly packed manner on the first shell in which they reside.

[0012] In some embodiments of this application, the reinforcing particles include one or more of silica nanoparticles and nano-metal oxides.

[0013] In some embodiments of this application, the particle size of the reinforcing particles ranges from 5 to 50 nm.

[0014] In some embodiments of this application, the first shell is a hollow shell.

[0015] In some embodiments of this application, the inner diameter of the first shell is in the range of 50-500 nm, the outer diameter of the first shell is in the range of 70-570 nm, and the difference between the inner diameter and the outer diameter of the first shell does not exceed 100 nm.

[0016] In some embodiments of this application, the lithium-rich core material is a soluble and regenerable lithium-containing compound.

[0017] In some embodiments of this application, the first shell layer is made of carbon material or heteroatom-doped carbon material.

[0018] In some embodiments of this application, the soluble and regenerable lithium-containing compound includes one or more of lithium sulfide, lithium phosphide, lithium bromide, and lithium iodide.

[0019] In some embodiments of this application, the positive electrode lithium replenishment material further includes a second shell layer, which covers the outer surface of the first shell layer and the reinforcing particles.

[0020] In some embodiments of this application, the second shell layer includes at least one of an isolation encapsulation layer, an ion conductor encapsulation layer, and an electronic conductor encapsulation layer.

[0021] In some embodiments of this application, the mass ratio of the lithium-rich core material, all shell materials, and the reinforcing particles is 80:(5-10):(10-15).

[0022] In some embodiments of this application, the diameter of the lithium-rich core material is 50-500 nm.

[0023] In some embodiments of this application, the portion of the lithium-rich core material other than its outer surface constitutes a coating layer, and the thickness of the coating layer is 50-100 nm.

[0024] To achieve the above objectives, a second aspect of this application provides a method for preparing a positive electrode lithium replenishment material, comprising:

[0025] A first-shell framework containing reinforcing particles was prepared using a template sacrificial method.

[0026] A lithium-rich material is formed inside the first shell framework containing reinforcing particles using an impregnation method, followed by sintering to obtain the positive electrode lithium replenishment material.

[0027] In some embodiments of this application, the preparation of the first shell framework containing reinforcing particles using the template sacrificial method includes:

[0028] Using polymer microspheres as templates, the particles are coated with a first shell source material, covalently grafted with reinforcing particles, and then removed by immersion.

[0029] To achieve the above objectives, a third aspect of this application provides a lithium-rich cathode, comprising a cathode active material, wherein the cathode active material comprises the cathode lithium replenishment material of the embodiments of this application or the cathode lithium replenishment material prepared by the preparation method of the cathode lithium replenishment material of the embodiments of this application.

[0030] To achieve the above objectives, a fourth aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is a lithium-rich positive electrode according to the embodiments of this application.

[0031] The beneficial effects of the positive electrode lithium replenishment material in this application embodiment are as follows:

[0032] (1) It has a core-shell structure - a first shell containing reinforcing particles is coated on the core of the lithium-rich material. The reinforcing particles can improve the stability of the first shell and prevent the lithium-replenishing material from directly contacting the electrolyte due to the easy destruction of the coating layer. On the other hand, it can create a nanoscale lithium-rich core through physical confinement and improve the ion mobility of the lithium-replenishing material.

[0033] (2) The core-shell structure can also effectively limit the morphology and size of lithium-rich core material particles, while reducing the direct contact area between the lithium-rich core material and water in the positive electrode lithium replenishment material, thereby reducing the occurrence of side reactions.

[0034] (3) Selecting carbon materials or heteroatom-doped carbon materials as the first shell can enhance the conductivity of the positive electrode lithium replenishment material and improve the battery performance of the positive electrode lithium replenishment material.

[0035] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0036] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0037] Figure 1 This is a schematic diagram of the structure of a positive electrode lithium replenishment material according to an embodiment of this application.

[0038] Figure label:

[0039] 1-Lithium-rich core material; 2-First shell layer; 3-Reinforcing particles; 4-Second shell layer. Detailed Implementation

[0040] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0041] In the application, the disclosure of the numerical range includes all values ​​throughout the range and the disclosure of further subdivisions of the range, including the endpoints and subranges given for these ranges.

[0042] Unless otherwise specified, all raw materials and equipment involved in the application are those that can be manufactured commercially or by known methods; and all methods involved are conventional methods unless otherwise specified.

[0043] An embodiment of the present application for lithium replenishment material is described below with reference to the accompanying drawings.

[0044] Figure 1 This is a schematic diagram of the structure of a positive electrode lithium replenishment material according to an embodiment of this application.

[0045] like Figure 1 As shown, the positive electrode lithium replenishment material of this application embodiment includes a lithium-rich core material 1 and a first shell layer 2. The first shell layer 2 is disposed on the outer surface of the lithium-rich core material 1, and reinforcing particles 3 are embedded on the surface and / or inside of the first shell layer 2.

[0046] The positive electrode lithium replenishment material of this application embodiment has a core-shell structure—a first shell layer containing reinforcing particles is coated on a lithium-rich material core. The reinforcing particles can improve the stability of the first shell layer and prevent the lithium replenishment material from directly contacting the electrolyte due to the easy destruction of the coating layer. On the other hand, they can also create a nanoscale lithium-rich core through physical confinement, thereby improving the ion mobility of the lithium replenishment material.

[0047] In some embodiments of this application, the reinforcing particles are distributed in a closely packed manner on their respective first shell layers. The reason for this close-packed distribution is that the reinforcing particles prepared in the subsequent cathode material fabrication method are nanospheres, which, due to their large specific surface area, spontaneously aggregate to form a close-packed structure. When there are multiple first shell layers, and reinforcing particles are distributed on the surface and / or inside all multiple first shell layers, the packing density of the reinforcing particles on each first shell layer can be the same or different; preferably, when different, the packing density of the reinforcing particles on the innermost first shell layer is the highest.

[0048] In some embodiments of this application, the reinforcing particles include, but are not limited to, one or more of silica nanoparticles and nano-metal oxides. As non-limiting examples, nano-metal oxides include, but are not limited to, one or more of nano-titanium dioxide, nano-zinc oxide, nano-alumina, nano-zirconia, nano-cerium oxide, and nano-iron oxide. Selecting one or more of silica nanoparticles and nano-metal oxides as reinforcing particles can enhance ionic conductivity and suppress cation disorder within the crystal structure by providing active sites for ion diffusion, while simultaneously providing a protective layer to suppress reactions between the positive electrode and the electrolyte.

[0049] In some embodiments of this application, the particle size of the reinforcing particles is, but is not limited to, between 5-50 nm. For example, the upper limit may also be, but is not limited to, 60 nm, 75 nm, 100 nm, or 125 nm, and the lower limit may also be, but is not limited to, 0.5 nm, 1 nm, 2 nm, or 3 nm. When the particle size of the reinforcing particles is within the above range, they can function as a scaffold structure; if the particle size is smaller than the lower limit, the specific surface area is too large, leading to severe agglomeration and increased internal resistance; if the particle size is larger than the upper limit, they detach from the first shell layer and have no reinforcing effect.

[0050] It is understood that the reinforcing particles in this application may be distributed only on the surface or inside the first shell, or simultaneously on both the surface and inside the first shell. When the reinforcing particles are distributed only on the surface of the first shell, they help to enhance the wettability of the electrolyte, but have a weaker effect on structural reinforcement. When the reinforcing particles are distributed only inside the first shell, they have a better effect on structural reinforcement. When the reinforcing particles are distributed simultaneously on both the surface and inside the first shell (for example, the reinforcing particles are embedded in the first shell, with some of the reinforcing particles located inside the first shell and some located outside the surface of the first shell), they are beneficial for both enhancing electrolyte wettability and improving structural stability.

[0051] In some embodiments of this application, the lithium-rich core material includes, but is not limited to, one or more of lithium-rich oxides, lithium nitride, lithium fluoride, lithium carbide, and soluble regenerable lithium-containing compounds. The soluble regenerable lithium-containing compounds include, but are not limited to, one or more of lithium sulfide, lithium phosphide, lithium bromide, and lithium iodide. It should be noted that the term "soluble and regenerable" in the context of soluble and regenerable lithium-containing compounds in this application actually refers to recrystallization, which is equivalent to soluble regeneration. Recrystallization is the process of dissolving a crystal in a solvent or melting it, and then recrystallizing it again from the solution or melt.

[0052] In some embodiments of this application, the first shell is a hollow shell. This structure facilitates the encapsulation of lithium-rich core materials and effectively limits the morphology and size of the core materials, thereby improving their conductivity. Specifically, the inner diameter of the first shell ranges from 50 to 500 nm, thus limiting the size of the lithium-rich core material to within 50-500 nm. It is understood that, especially when using recyclable lithium compounds as lithium-rich core materials, such as lithium sulfide, commercially available lithium sulfide particles are relatively large, typically at the micrometer level, resulting in poor conductivity. This application uses a template sacrificial method to prepare a hollow shell structure, and then uses an impregnation method to allow lithium sulfide to enter the hollow shell to form a lithium-rich core material. This limits the particle size of lithium sulfide to below the nanometer level, thereby improving the conductivity of lithium sulfide as a lithium-rich material. The outer diameter of the first shell ranges from 70 to 570 nm, and the difference between the inner and outer diameters of the first shell does not exceed 100 nm.

[0053] In some embodiments of this application, to further improve the stability of the cathode lithium replenishment material, the number of first shell layers can be two or more, and multiple first shell layers are arranged sequentially from the side closest to the lithium-rich core material to the side furthest from the lithium-rich core material (the later one covers the surface of the previous one). In this case, the surface and / or interior of the innermost first shell layer (closest to the lithium-rich core material) must be distributed with reinforcing particles to prevent the collapse of the entire hollow structure of the first shell layer. The material source of the first shell layer is connected through covalent bonds or hydrogen bonds. The surface and / or interior of the remaining first shell layers may or may not be distributed with reinforcing particles. When the surface and / or interior of the remaining first shell layers are also distributed with reinforcing particles, it may further enhance the stability of the lithium replenishment material. Taking the case where reinforcing particles are embedded in the first shell layer as an example: In some embodiments of this application, when the number of first shell layers is two or more, the reinforcing particles are only embedded in the innermost first shell layer (the conductive coating layer closest to the lithium-rich core material). This can prevent the collapse of the hollow shell structure and connect the material source of the conductive coating layer through covalent bonds or hydrogen bonds. In some embodiments of this application, the reinforcing particles can be embedded in the innermost first shell layer and the first shell layer between the innermost first shell layer and the outermost first shell layer (farthest from the lithium-rich core material). In still other embodiments of this application, the reinforcing particles can be embedded in the innermost first shell layer and the outermost first shell layer. In still other embodiments of this application, the reinforcing particles can be embedded in all the first shell layers. As a possible example, the hollow shell layer of the cathode lithium replenishment material of this application includes only one conductive coating layer, and the reinforcing particles are embedded in this conductive coating layer. It should be noted that when a reinforcing particle is embedded in a certain first shell layer, the first shell layer located outside it and adjacent to it covers the outer surface of the first shell layer and the reinforcing particle embedded therein. In addition, the number of first shell layers should be controlled within a reasonable range, for example, including but not limited to 5 or less. More than 5 will increase the internal resistance of the material and reduce the energy density.

[0054] It should be noted that in this application, the reinforcing particles are selected from one or more of silica nanoparticles and nano-metal oxides. Although they exist only in particle form, they will form doping in the part that comes into contact with the core during the sintering process, which brings beneficial effects.

[0055] In some embodiments of this application, the first shell layer is made of carbon material, including but not limited to one or more of graphite, amorphous carbon, hard carbon, carbon fiber, and carbon nanotubes. In other embodiments, the first shell layer is made of heteroatom-doped carbon material, including but not limited to one or more of nitrogen-doped carbon, sulfur-doped carbon, and phosphorus-doped carbon. Choosing carbon material or heteroatom-doped carbon material for the first shell layer can enhance the conductivity of the positive electrode lithium-filling material and improve its battery performance.

[0056] In some embodiments of this application, to further improve the density and conductivity of the entire coating layer of the lithium-rich core material, the positive electrode lithium replenishment material of this application further includes a second shell layer 4, which covers the outer surfaces of the first shell layer 2 and the reinforcing particles 3. It should be noted that when there are multiple first shell layers, the second shell layer covers the outermost surface of the first shell layer (farthest from the lithium-rich core material), or covers both the outermost surface of the first shell layer (farthest from the lithium-rich core material) and the outer surface of the reinforcing particles. The second shell layer is a conductive encapsulation layer, including but not limited to at least one of an isolation encapsulation layer, an ion conductor encapsulation layer, and an electronic conductor encapsulation layer. The material of the isolation encapsulation layer includes, but is not limited to, one or more of ceramics, polymers, and carbon materials, preferably carbon materials. The material of the electronic conductor encapsulation layer includes, but is not limited to, at least one of carbon materials, conductive polymers, or conductive oxides, preferably carbon materials. The material of the ion conductor encapsulation layer includes, but is not limited to, at least one of perovskite, NASICON, garnet, or polymer solid electrolytes. As a possible example, the second shell is made of carbon material, including but not limited to one or more of graphite, amorphous carbon, hard carbon, carbon nanotubes, and graphene sheets.

[0057] As a possible example, such as Figure 1 As shown, the positive electrode lithium replenishment material of this application includes a lithium-rich core material 1, a first shell layer 2, reinforcing particles 3, and a second shell layer 4. There is one first shell layer 2, which is disposed on the outer surface of the lithium-rich core material 1. The reinforcing particles 3 are embedded in the first shell layer 2. Both the first shell layer 2 and the second shell layer 4 are carbon layers. The second shell layer 4 covers the outer surfaces of the first shell layer 2 and the reinforcing particles 3.

[0058] In some embodiments of this application, the mass ratio of the lithium-rich core material, all shell materials, and all reinforcing particles is 80:(5-10):(10-15). As a non-limiting example, the mass ratio of the lithium-rich core material, all shell materials, and all reinforcing particles includes, but is not limited to, 80:5:10, 80:7.5:10, 80:10:10, 80:5:12.5, 80:5:15, 80:10:12.5, or 80:10:15. A mass ratio of the lithium-rich core material, all shell materials, and all reinforcing particles within the above range can effectively confine the nano-lithium-rich core material; if the mass ratio is less than 80:5:10, the lithium-rich core material cannot be completely coated; if the mass ratio is greater than 80:10:15, the coating layer is too thick, reducing the energy density. It should be noted that, here, all shell materials are referred to as either the first shell material or the second shell material when the positive electrode lithium replenishment material contains only the first shell material; the explanation for reinforcing particles is similar and will not be repeated here.

[0059] In some embodiments of this application, the diameter of the lithium-rich core material is 50-500 nm. As a non-limiting example, the diameter of the lithium-rich core material includes, but is not limited to, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm. A lithium-rich core material diameter within the above range can achieve capacity advantages; smaller than 50 nm affects energy density; and larger than 500 nm reduces capacity.

[0060] In some embodiments of this application, the portion of the lithium-rich core material outside its outer surface in the positive electrode lithium replenishment material constitutes a coating layer, with a thickness of 50-100 nm. As a non-limiting example, the coating layer thickness includes, but is not limited to, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm. A coating layer thickness within the above range can improve the material's conductivity; less than 50 nm allows moisture to easily react with the core; greater than 100 nm increases the resistance to lithium-ion migration. It should be noted that the portion outside the outer surface of the lithium-rich core material here refers to... Figure 1 Taking the structure shown as an example, it is the part between the surface of the first shell 2 adjacent to the lithium-rich core material 1 and the outer surface of the second shell 4.

[0061] It should be noted that in this application, when there are multiple first shell layers and multiple second shell layers, the total thickness of the covering layer is still within the aforementioned range. However, the thickness of each first shell layer can be the same or different, and the thickness of each second shell layer can also be the same or different. Furthermore, the materials of each first shell layer can be the same or different, and the materials of each second shell layer can also be the same or different.

[0062] The method for preparing the positive electrode lithium replenishment material according to the embodiments of this application includes the following steps:

[0063] S101. A first shell framework containing reinforcing particles was prepared using the template sacrificial method.

[0064] The template sacrifice method used in this application is also known as the sacrifice method or template sacrifice encapsulation method.

[0065] In some embodiments of this application, a template-sacrificial method is used to prepare a first shell framework containing reinforcing particles, comprising: using polymer microspheres as templates, coating them with a first shell source material, covalently grafting reinforcing particles, and immersing to remove the template.

[0066] In some embodiments of this application, the polymer microspheres include, but are not limited to, one or more of polymethyl methacrylate (PMMA) microspheres and polystyrene (PS) microspheres. The particle size of the template includes, but is not limited to, 50-500 nm.

[0067] In some embodiments of this application, the first shell source material includes, but is not limited to, one or more of polyethylene oxide, polyaniline, polyacrylonitrile, polyvinyl alcohol, polyvinylpyrrolidone, polypyrrole, sucrose, glucose, phenolic resin, gelatin, melamine, protein, furfural, graphene oxide, graphene, polydopamine, and bacterial cellulose.

[0068] In some embodiments of this application, the mass ratio of the template to the first shell source material is 9-1:1-1. As a non-limiting embodiment, the mass ratio of the template to the first shell source material includes, but is not limited to, 9:1, 7:1, 5:1, or 1:1. Within the above-mentioned range, the template to the first shell source material can provide complete coverage.

[0069] In some embodiments of this application, the reaction conditions for the covalently grafted reinforced particles are: reaction temperature 25-60℃, reaction time 3-10h, and the reaction is carried out under stirring conditions.

[0070] It should be noted that the reaction temperature of the covalently grafted reinforced particles includes, but is not limited to, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, or 60℃. The reaction time of the covalently grafted reinforced particles includes, but is not limited to, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h.

[0071] In some embodiments of this application, the template is removed by soaking in an organic solvent, including but not limited to at least one of acetone, ethyl acetate, dichloroethane, and xylene.

[0072] It should be noted that the first shell framework containing reinforcing particles prepared here is not the final form of the first shell in the cathode lithium replenishment material. Furthermore, during the covalent grafting process, the reinforcing particle source solution is used, including but not limited to tetraethyl orthosilicate ethanol solution, tetrabutyl titanate ethanol solution, and aluminum isopropoxide ethanol solution.

[0073] S102. A lithium-rich material is formed inside the first shell skeleton containing reinforcing particles by impregnation, and then sintered to obtain the positive electrode lithium replenishment material.

[0074] In some embodiments of this application, a lithium-rich material is formed inside a first shell containing reinforcing particles using an impregnation method. This includes: placing the first shell containing reinforcing particles in a glove box, immersing it in a polar solvent solution of a lithium-rich core material, and heating to remove the polar solvent. The polar solvent includes, but is not limited to, one or more of ethanol, glycerol, and propylene glycol. It should be noted that the heating temperature is set to allow the polar solvent to evaporate.

[0075] In some embodiments of this application, the molar concentration of the lithium-rich core material includes, but is not limited to, 0.01-0.1 mol / L. As non-limiting examples, the molar concentration of the lithium-rich core material includes, but is not limited to, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, or 0.1 mol / L.

[0076] In this application, the purpose of sintering here is to transform the first shell skeleton containing reinforcing particles obtained in step S101 into the first shell containing reinforcing particles in the positive electrode lithium replenishment material.

[0077] In some embodiments of this application, sintering is carried out in an inert atmosphere, which includes, but is not limited to, one or more of nitrogen, argon, helium, etc.

[0078] In some embodiments of this application, the sintering temperature is 300-500°C. As a non-limiting example, the sintering temperature includes, but is not limited to, 300°C, 350°C, 400°C, 450°C, or 500°C.

[0079] In some embodiments of this application, the sintering time is 1-3 hours. As a non-limiting example, the sintering time includes, but is not limited to, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours.

[0080] In some embodiments of this application, sintering can be carried out in a tube furnace, rotary furnace, sintering furnace, box furnace, roller kiln, pusher kiln or fluidized bed, etc.

[0081] In some embodiments of this application, when there are two or more first shells, and each first shell contains reinforcing particles, for each additional first shell containing reinforcing particles, step S101 is repeated once before step S102. However, except for the first shell containing reinforcing particles located on the outermost side (farthest from the lithium-rich core material), the process of "soaking to remove template" must be removed when preparing the remaining first shells containing reinforcing particles.

[0082] In some embodiments of this application, when there are two or more first shell layers, and the innermost first shell layer (closest to the lithium-rich core material) contains reinforcing particles, while the remaining first shell layers partially contain reinforcing particles and partially do not, then for each additional first shell layer, before proceeding to step S102:

[0083] When the first shell contains reinforcing particles, repeat step S101 once more, but the "soaking to remove template" process needs to be removed.

[0084] When the first shell does not contain reinforcing particles, repeat step S101 once more, but the process of "covalently grafting reinforcing particles and soaking to remove template" needs to be removed.

[0085] Until the last first shell layer is formed using the above method, regardless of the situation, the template must be removed by soaking.

[0086] In some embodiments of this application, when the positive electrode lithium replenishment material contains a second shell, the preparation method of the positive electrode lithium replenishment material further includes a step of forming the second shell by chemical vapor deposition (CVD) after step S102.

[0087] It should be noted that the method for forming the second shell in this application is not limited to chemical vapor deposition (CVD), but can also employ at least one of sol-gel method, solution method, solid phase method, etc.

[0088] As a possible example, the method for preparing the cathode material according to an embodiment of this application includes the following steps:

[0089] (1) Preparation of the first shell skeleton containing reinforcing particles: Polymethyl methacrylate (PMMA) microspheres with a particle size of 50-500 nm were added to a 0.1-2 mol / L aqueous solution of dopamine hydrochloride, followed by 100-500 mg of ammonium bicarbonate and 5 ml of 0.01 mol / L tetraethyl orthosilicate ethanol solution. The mixture was stirred at 25-60 °C for 3-10 h. After that, the polymethyl methacrylate (PMMA) microspheres were removed by immersion in acetone to obtain a nano-silica microsphere-reinforced coating skeleton shell (i.e., the first shell skeleton containing reinforcing particles).

[0090] (2) Preparation of intermediate product: The first shell skeleton containing reinforcing particles obtained in step (1) is placed in a glove box and immersed in a 0.01-0.1 mol / L lithium sulfide ethanol solution. The ethanol is heated to evaporate and the intermediate product is obtained.

[0091] (3) Preparation of lithium-rich core material with first shell coating containing reinforcing particles: The intermediate product obtained in step (2) is transferred to a tube furnace and sintered at 300-500℃ for 1-3 hours under an inert atmosphere to obtain lithium-rich core material with first shell coating containing reinforcing particles.

[0092] (4) Preparation of the second shell: The lithium-rich core material containing the reinforcing particles obtained in step (3) is sintered at 700°C for 40 min in a methane atmosphere by chemical vapor deposition (CVD) to form a graphite second shell on the outer surface of the lithium-rich core material, which is coated by the first shell of the application, and thus the positive electrode lithium replenishment material of this application is obtained.

[0093] The lithium-rich cathode of this application includes a cathode active material, which includes the cathode lithium replenishment material of this application or the cathode lithium replenishment material prepared by the preparation method of the cathode lithium replenishment material of this application.

[0094] In some embodiments of this application, the content of the positive electrode lithium replenishment material accounts for 0.5-15 wt% of the total positive electrode active material. By way of non-limiting example, the content of the positive electrode lithium replenishment material accounts for 3 wt%, 6 wt%, 9 wt%, 12 wt%, or 15 wt% of the total positive electrode active material.

[0095] In some embodiments of this application, the positive electrode active material may further include at least one of the following: positive electrode active material, positive electrode conductive agent, and positive electrode binder. The positive electrode active material includes, but is not limited to, one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. The positive electrode active material is capable of lithium intercalation and deintercalation, alloying and dealloying, or plating and stripping. The positive electrode conductive agent includes, but is not limited to, one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes. Adding a positive electrode conductive agent to the positive electrode material can enhance the conductivity of the electrode material layer, improve the conductivity of the lithium supplement material, and facilitate electron and ion transport. The positive electrode binder includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), sodium alginate, sodium carboxymethyl cellulose, and polyacrylic acid.

[0096] In some embodiments of this application, the lithium-rich cathode further includes a current collector, which may be selected to contain aluminum or any other suitable conductive metal foil (e.g., solid, mesh, or covered foil), metal grid or screen, or porous metal. In some variations, the surface of the current collector may contain a surface-treated (e.g., carbon-coated and / or etched) metal foil.

[0097] The secondary battery of this application embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is a lithium-rich positive electrode of this application embodiment.

[0098] In some embodiments of this application, the positive electrode, separator, and negative electrode can be processed using a stacking or winding process to form a secondary battery. It should be noted that the secondary batteries in the embodiments of this application include, but are not limited to, lithium-ion batteries.

[0099] The negative electrode, electrolyte, separator, etc. of the secondary battery in this application embodiment are not specifically limited and can be applied to any battery system.

[0100] The secondary battery of this application embodiment can be widely used in new energy vehicles, aerospace, electronic products and other fields.

[0101] The preparation method of the positive electrode lithium replenishment material, the lithium-rich positive electrode, and the secondary battery of the embodiments of this application all have the beneficial effects of the positive electrode lithium replenishment material of the embodiments of this application.

[0102] The following non-limiting embodiments further illustrate certain features of the present technology.

[0103] All raw materials used in the following non-limiting examples and comparative examples are commercially available materials that have not undergone purification and are of analytical grade (AR) reagent level.

[0104] I. Examples and Comparative Examples

[0105] Example 1

[0106] like Figure 1As shown, the positive electrode lithium replenishment material of this embodiment includes a lithium-rich core material 1, a first shell layer 2, reinforcing particles 3, and a second shell layer 4. The lithium-rich core material is lithium sulfide (Li2S). The first shell layer 2 coats the surface of the lithium-rich core material and is made of nitrogen-doped carbon nanotubes. Reinforcing particles 3 are embedded in the first shell layer 2. The reinforcing particles 3 are 20nm silicon dioxide nanoparticles and are distributed in a tightly packed manner within the first shell layer 2. The second shell layer 4 coats the outer surfaces of the first shell layer 2 and the reinforcing particles 3. The second shell layer 4 is made of graphite. There is one second shell layer and one first shell layer 2. The second shell layer 4 and the first shell layer 2 containing the reinforcing particles 3 together constitute the coating layer. The mass ratio of the lithium-rich core material, all shell layers (first and second shell layers), and reinforcing particles is 90:4:6. The diameter of the lithium-rich core material is 100nm, the thickness of the coating layer is 25nm, and the thickness of the first shell layer is 15nm.

[0107] The preparation method of the positive electrode lithium replenishment material in this embodiment includes the following steps:

[0108] (1) Preparation of the first shell skeleton containing reinforcing particles: 1g of polymethyl methacrylate (PMMA) microspheres with a particle size of 100nm were added to 20mL of 0.1mol / L dopamine hydrochloride aqueous solution, followed by 250mg of ammonium bicarbonate and 5ml of 0.01mol / L tetraethyl orthosilicate ethanol solution. The mixture was stirred at 400r / min for 6.5h at 40℃. After that, the polymethyl methacrylate (PMMA) microspheres were removed by immersion in 20ml of acetone to obtain the nano-silica microsphere reinforced coating skeleton shell (i.e., the first shell skeleton containing reinforcing particles).

[0109] (2) Preparation of intermediate product: The first shell skeleton containing reinforcing particles obtained in step (1) is placed in a vacuum glove box, immersed in 25 ml of 2 mol / L lithium sulfide ethanol solution for 30 min, and then heated to 60 °C to evaporate the ethanol to obtain the intermediate product.

[0110] (3) Preparation of lithium-rich core material with first shell coating containing reinforcing particles: The intermediate product obtained in step (2) is transferred to a tube furnace and sintered at 400°C for 2 hours under nitrogen atmosphere to obtain lithium-rich core material with first shell coating containing reinforcing particles.

[0111] (4) Preparation of the second shell: The lithium-rich core material containing the reinforcing particles obtained in step (3) is sintered at 700°C for 40 min in a methane atmosphere by chemical vapor deposition (CVD) to form a graphite second shell on the outer surface of the lithium-rich core material, which is coated by the first shell of the chemical vapor deposition (CVD) method. This is the positive electrode lithium replenishment material of this embodiment.

[0112] The lithium-rich cathode of this embodiment includes a cathode current collector and a cathode active material coated on the surface of the cathode current collector. The cathode current collector is aluminum foil, and the cathode active material includes the following components in parts by weight: 93 parts of lithium iron phosphate cathode active material, 2 parts of cathode lithium supplementation material in this embodiment, 2 parts of cathode conductive agent Super P, and 3 parts of cathode binder polyvinylidene fluoride.

[0113] The secondary battery of this embodiment includes a positive electrode, a negative electrode, a separator stacked between the positive electrode and the negative electrode, and an electrolyte. The positive electrode is a lithium-rich positive electrode of this embodiment. The negative electrode includes a negative electrode current collector and a negative electrode active material coated on the surface of the negative electrode current collector. The negative electrode current collector is copper foil. The negative electrode active material includes the following components in parts by weight: 95 parts graphite (negative electrode active material), 2 parts Super P (negative electrode conductive agent), 0.5 parts carboxymethyl cellulose (CMC) (thickening agent), and 2.5 parts styrene-butadiene rubber (SBR) (negative electrode binder). The separator is a polyethylene (PE) microporous separator. The electrolyte includes ethylene carbonate (EC), ethyl methyl carbonate (DEC), and LiPF6, wherein the volume ratio of ethylene carbonate (EC) to ethyl methyl carbonate (DEC) is 3:7, and the concentration of LiPF6 is 1 mol / L.

[0114] The method for preparing the secondary battery in this embodiment includes the following steps:

[0115] 1) Preparation of positive electrode: N-methylpyrrolidone, lithium iron phosphate, positive electrode lithium supplementation material, positive electrode conductive agent Super P and positive electrode binder polyvinylidene fluoride are mixed in a mass ratio of 100:93:2:2:3 and ball-milled to obtain positive electrode slurry. The ball milling time is 60 min and the speed is 30 Hz. The positive electrode slurry is coated on the surface of aluminum foil, rolled and then vacuum dried at 100℃ overnight to obtain positive electrode sheet.

[0116] 2) Preparation of negative electrode: The negative electrode active material (graphite), negative electrode conductive agent (conductive carbon black, Super P), thickener (carboxymethyl cellulose, CMC), and negative electrode binder (styrene-butadiene rubber, SBR) are mixed evenly in deionized water at a mass ratio of 95:2:0.5:2.5 to prepare a negative electrode slurry. The negative electrode slurry is coated on the surface of the current collector copper foil. After drying-rolling-secondary drying process, the negative electrode sheet is obtained.

[0117] 3) Preparation of electrolyte: Mix ethylene carbonate (EC) and ethyl methyl carbonate (DEC) in a volume ratio of 3:7, and add LiPF6 to form an electrolyte with a concentration of 1 mol / L.

[0118] 4) Assembly of secondary batteries (lithium-ion batteries): Lithium-ion batteries are assembled in a glove box under a nitrogen inert atmosphere according to the assembly sequence of lithium negative electrode-separator-electrolyte-positive electrode.

[0119] Example 2

[0120] This embodiment is basically the same as embodiment 1, except that:

[0121] The positive electrode lithium replenishment material in this embodiment does not include the second shell layer 4.

[0122] The method for preparing the positive electrode lithium replenishment material in this embodiment does not include step (4). The lithium-rich core material containing the first shell layer of reinforcing particles obtained in step (3) is the positive electrode lithium replenishment material in this embodiment.

[0123] Example 3

[0124] This embodiment is basically the same as embodiment 1, except that:

[0125] In the positive electrode lithium replenishment material of this embodiment, the lithium-rich core material is lithium phosphide (Li3P).

[0126] Example 4

[0127] This embodiment is basically the same as embodiment 1, except that:

[0128] In this embodiment, the positive electrode lithium replenishment material has two first shells, which are defined as first shell A and first shell B for ease of description. First shell A and first shell B are arranged sequentially from the side closer to the lithium-rich core material to the side farther away from the lithium-rich core material. Both first shell A and first shell B are embedded with 20nm silica nanoparticles as reinforcement particles, which are distributed in a tightly packed manner in their respective first shells. A second shell layer covers the outer surface of first shell B and its reinforcement particles. The second shell layer and the two first shells containing reinforcement particles together constitute the coating layer. The mass ratio of the lithium-rich core material, all shells (first shell A and first shell B), and all reinforcement particles is 90:4:6. The diameter of the lithium-rich core material is 100nm, and the thickness of the coating layer is 30nm.

[0129] The preparation method of the positive electrode lithium replenishment material in this embodiment includes the following steps:

[0130] (1) Preparation of the first shell A containing reinforcing particles: 1g of polymethyl methacrylate (PMMA) microspheres with a particle size of 100nm were added to 20mL of 0.1mol / L dopamine hydrochloride aqueous solution, followed by 250mg of ammonium bicarbonate and 2.5ml of 0.01mol / L tetraethyl orthosilicate ethanol solution. The mixture was stirred at 400r / min at 40℃ for 6.5h to obtain the first shell A containing reinforcing particles.

[0131] (2) Preparation of the first shell B containing reinforcing particles: The first shell A containing reinforcing particles after filtration and drying was added to 20 mL of 0.1 mol / L dopamine hydrochloride aqueous solution, followed by 250 mg ammonium bicarbonate and 2.5 mL of 0.01 mol / L tetraethyl orthosilicate ethanol solution. The mixture was stirred at 400 r / min for 6.5 h at 40 °C. After that, the polymethyl methacrylate (PMMA) microspheres were removed by immersion in 20 mL of acetone to obtain the first shell B and A containing reinforcing particles.

[0132] (3) Preparation of intermediate product: The first shell skeleton containing reinforcing particles obtained in step (2) is placed in a vacuum glove box, immersed in 25L of 2mol / L lithium sulfide ethanol solution for 30min, and then heated to 60℃ to evaporate the ethanol to obtain the intermediate product.

[0133] (4) Preparation of lithium-rich core material with first shell coating containing reinforcing particles: The intermediate product obtained in step (3) is transferred to a tube furnace and sintered at 400°C for 2 hours under nitrogen atmosphere to obtain lithium-rich core material with first shell coating containing reinforcing particles.

[0134] (5) Preparation of the second shell: The lithium-rich core material containing the reinforcing particles obtained in step (4) is sintered at 700°C for 40 min in a methane atmosphere by chemical vapor deposition (CVD) to form a graphite second shell on the outer surface of the lithium-rich core material, which is coated by the first shell of the reinforcing particles, thus obtaining the positive electrode lithium replenishment material of this embodiment.

[0135] Example 5

[0136] This embodiment is basically the same as embodiment 4, except that:

[0137] In the positive electrode lithium replenishment material of this application, no reinforcing particles are embedded in the first shell layer B, and the mass ratio of the lithium-rich core material, all shell layers (first shell layer A and first shell layer B), and all reinforcing particles is 90:5:5.

[0138] In the preparation method of the positive electrode lithium replenishment material of this application, step (2) is deleted as follows: "and 5 ml of 0.01 mol / L tetraethyl orthosilicate ethanol solution, and stir at 400 r / min for 6.5 h at 40 °C".

[0139] Example 6

[0140] This embodiment is basically the same as embodiment 4, except that:

[0141] In the positive electrode lithium replenishment material of this application, the mass of the reinforcing particles embedded in the first shell layer A and the first shell layer B is halved, and the packing density is half of that in Example 4. The mass ratio of the lithium-rich core material, all shell layers (first shell layer A and first shell layer B), and all reinforcing particles is 90:7:3.

[0142] In the preparation method of the positive electrode lithium replenishment material of this application, the amount of tetraethyl orthosilicate ethanol solution in steps (1) and (2) is halved.

[0143] Comparative Example 1

[0144] This comparative example is basically the same as Example 1, except that:

[0145] The difference between the positive electrode lithium replenishment material in this comparative example and Example 1 is that there are no reinforcing particles in the first shell layer. II. Performance Testing

[0146] 1. Testing Method

[0147] (1) Moisture resistance test of positive electrode lithium replenishment material

[0148] The specific capacity of the lithium-ion batteries of each embodiment and comparative example was tested under different humidity conditions (25%, 20%, 10%) at room temperature for different durations.

[0149] (2) Electrochemical performance

[0150] Electrochemical performance tests, such as the first discharge specific capacity at 0.1C and the first discharge specific capacity at 1C, were conducted on the lithium-ion batteries of each embodiment and comparative example. The test conditions were as follows: the lithium-ion batteries were placed at room temperature for 24 hours before charge and discharge tests were conducted, and the charge and discharge voltage was 2.5-4.2V.

[0151] 2. Test Results

[0152] The performance of the lithium-ion batteries in Examples 1-6 and Comparative Example 1 was tested. The results of the moisture resistance test are shown in Tables 1, 2 and 3, and the results of the electrochemical performance test are shown in Table 4.

[0153] Table 1. Specific capacity of lithium-ion batteries after different storage times under conditions of 15% humidity and 25℃.

[0154]

[0155] Table 2. Specific capacity of lithium-ion batteries after different storage times under conditions of 20% humidity and 25℃.

[0156]

[0157] Table 3. Specific capacity of lithium-ion batteries after different storage times under conditions of 25% humidity and 25℃.

[0158]

[0159] Table 4. Electrochemical performance test results of lithium-ion batteries in Examples 1-6 and Comparative Example 1

[0160]

[0161]

[0162] As shown in Tables 1-4, due to the stability of the metal nanoparticle-enhanced structure and the reduction of contact between the core and moisture by the multilayer carbon coating, the positive electrode lithium replenishment material exhibits excellent charge specific capacity in carbonate-based electrolytes. Example 2 lacks the protection of the outer carbon layer; when stored in air with a certain humidity, the core comes into contact with moisture and immediately reacts to generate hydrogen sulfide, causing capacity decay. Example 3 uses lithium phosphide as the core, with a theoretical capacity of 1550 mAh / g, and ultimately achieves a high charge specific capacity of 880 mAh / g at 0.1C in carbonate-based electrolytes. Examples 4, 5, and 6 change the number of first shell layers and the number of reinforcing particles. Multiple first shell layers can improve the stability of the core in a certain humidity environment, but they also hinder lithium-ion migration to some extent. Comparative Example 1 has no reinforcing particles; when the template is immersed in acetone, the shell structure is unstable and collapses. Subsequent recrystallization of lithium sulfide mostly grows on the shell surface, which readily reacts directly with air moisture, thus resulting in a low final discharge specific capacity.

[0163] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0164] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A positive electrode lithium supplementing material, characterized by, include: A lithium-rich core material, wherein the lithium-rich core material is a soluble and regenerable lithium-containing compound; the soluble and regenerable lithium-containing compound includes one or more of lithium sulfide, lithium phosphide, lithium bromide, and lithium iodide; A first shell layer is disposed on the outer surface of the lithium-rich core material, and reinforcing particles are embedded on the surface and / or inside the first shell layer; the first shell layer is a hollow shell layer; the material of the first shell layer is carbon material or heteroatom-doped carbon material; the reinforcing particles include one or more of silica nanoparticles and nano-metal oxides. A second shell layer covers the outer surface of the first shell layer and the reinforcing particles; the second shell layer includes at least one of an isolation encapsulation layer, an ion conductor encapsulation layer, and an electronic conductor encapsulation layer. 2.The positive-electrode lithium supplementing material of claim 1, characterized in that, The reinforcing particles are distributed in a tightly packed manner on the first shell in which they reside.

3. The positive electrode lithium replenishment material according to claim 1, characterized in that, The particle size range of the reinforcing particles is 5-50 nm.

4. The positive electrode lithium replenishment material according to claim 1, characterized in that, The inner diameter of the first shell ranges from 50 to 500 nm, the outer diameter of the first shell ranges from 70 to 570 nm, and the difference between the inner diameter and the outer diameter of the first shell does not exceed 100 nm.

5. The positive electrode lithium replenishment material according to any one of claims 1 to 4, characterized in that, The mass ratio of the lithium-rich core material, all shell materials, and the reinforcing particles is 80:(5-10):(10-15).

6. The positive electrode lithium replenishment material according to any one of claims 1 to 4, characterized in that, The lithium-rich core material has a diameter of 50-500 nm; And / or, the portion of the lithium-rich core material other than its outer surface constitutes a coating layer, the thickness of which is 50-100 nm.

7. A method for preparing a positive electrode lithium replenishment material, characterized in that, include: A first shell framework containing reinforcing particles was prepared using a template sacrificial method; the reinforcing particles included one or more of silica nanoparticles and nano-metal oxides. The first shell layer is made of carbon material or heteroatom-doped carbon material; the preparation of the first shell layer skeleton containing reinforcing particles by template sacrifice method includes: using polymer microspheres as templates, coating with the first shell layer source material, covalently grafting reinforcing particles, and immersing to remove the template; A lithium-rich material is formed inside the first shell framework containing reinforcing particles using an impregnation method, followed by sintering to obtain the positive electrode lithium replenishment material.

8. A lithium-rich cathode, characterized in that, It includes a positive electrode active material, which includes the positive electrode lithium replenishment material as described in any one of claims 1 to 6, or the positive electrode lithium replenishment material prepared by the preparation method described in claim 7.

9. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The cathode is the lithium-rich cathode as described in claim 8.

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