CN116936763A - Lithium-rich positive electrode material, preparation method thereof, positive electrode plate and secondary battery - Google Patents

Lithium-rich positive electrode material, preparation method thereof, positive electrode plate and secondary battery Download PDF

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Publication number
CN116936763A
CN116936763A CN202310950635.7A CN202310950635A CN116936763A CN 116936763 A CN116936763 A CN 116936763A CN 202310950635 A CN202310950635 A CN 202310950635A CN 116936763 A CN116936763 A CN 116936763A
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lithium
rich
positive electrode
compound particles
coating
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蒋鑫
万远鑫
孔令涌
裴现一男
陈心怡
张莉
张顺心
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Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
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Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Composite Materials (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

A lithium-rich positive electrode material, a preparation method thereof, a positive electrode plate and a secondary battery are provided, wherein the lithium-rich positive electrode material comprises lithium-rich compound particles and a coating material; and the coating material is arranged on the outer surface of the lithium-rich compound particles, and comprises aluminum lithium borate. The lithium-rich positive electrode material provided by the application is beneficial to the conversion of lithium ions from inactive lithium to active lithium in the electrochemical process, so that the capacity retention rate of the material is improved, and the cycle life is prolonged. Meanwhile, the coating material combined on the outer surface of the lithium-rich compound particle can also effectively provide enough protection for the lithium-rich compound particle, and side reaction of electrolyte on the outer surface of the lithium-rich compound particle is reduced, so that interface passivation phenomenon generated on the surface of the lithium-rich compound particle is prevented, and the rate capability and the cycle performance of the lithium-rich positive electrode material are improved while polarization is reduced.

Description

Lithium-rich positive electrode material, preparation method thereof, positive electrode plate and secondary battery
Technical Field
The application relates to the technical field of secondary batteries, in particular to a lithium-rich positive electrode material, a preparation method thereof, a positive electrode plate and a secondary battery.
Background
The lithium ion battery is used as a representative of high-efficiency clean energy technology, has the advantages of high voltage, high energy density, good circularity, no memory effect and the like, and has been widely applied to various fields of national economy such as portable electronic equipment, electric automobiles, large-scale energy storage and the like.
Among positive electrode materials of lithium ion batteries, lithium-rich positive electrode materials are attracting attention because of their high charge capacity characteristics, but the current lithium-rich positive electrode materials still have unsatisfactory rate performance and cycle capacity retention rate, mainly because of irreversible transformation of the structure and transition metal dissolution phenomena during charge and discharge of the materials, resulting in unstable structures that hinder diffusion of lithium ions. In addition, the electrolyte is decomposed in the electrochemical process to accelerate the interface passivation of the material, so that the high-resistance behavior is caused, and the multiplying power and the cycle performance of the material are limited.
Disclosure of Invention
The application aims to provide a lithium-rich positive electrode material, a preparation method thereof, a positive electrode plate and a secondary battery.
The application provides the following technical scheme:
in a first aspect, the present application provides a lithium-rich cathode material comprising lithium-rich compound particles and a coating material; a coating material is at least partially bonded to an outer surface of the lithium-rich compound particles, the coating material comprising lithium aluminum borate.
According to the application, the coating material is arranged on the outer surface of the lithium-rich compound particles, so that the conversion of lithium ions from inactive lithium to active lithium in the electrochemical process is facilitated, the capacity retention rate of the material is improved, and the cycle life is prolonged. Meanwhile, the coating material combined on the outer surface of the lithium-rich compound particle can also effectively provide enough protection for the lithium-rich compound particle, and side reaction of electrolyte on the outer surface of the lithium-rich compound particle is reduced, so that interface passivation phenomenon generated on the surface of the lithium-rich compound particle is prevented, and the rate capability and the cycle performance of the lithium-rich positive electrode material are improved while polarization is reduced. In addition, compared with other coating materials, the lithium aluminum borate can provide higher conductivity, and lithium elements in the lithium aluminum borate can be matched with the deintercalation of lithium ions to form a fast ion channel, so that the deintercalation efficiency of the lithium ions is accelerated, the charge and discharge speed is improved, and more possibilities are provided for the current fast charge technology.
In one embodiment, the lithium aluminum borate is generated from residual alkali on the surface of the lithium-rich compound particles by in-situ reaction. The application prepares the lithium-rich compound particles with coating materials by carrying out high-temperature sintering reaction on boric acid, aluminum hydroxide and lithium-rich compound particles; on one hand, the surface residual alkali can be converted into aluminum lithium borate by the reaction of boric acid and aluminum hydroxide with the surface residual alkali of lithium-rich compound particles, so that the content of the surface residual alkali is effectively reduced, the capacity loss of a secondary battery caused by the residual alkali is avoided, the gas expansion phenomenon of the lithium-rich positive electrode material in the secondary battery process can be effectively reduced, and the electrochemical performance and the processing performance of the lithium-rich positive electrode material are improved; on the other hand, compared with the existing material coating mode, the method for arranging the lithium aluminum borate on the outer surface of the lithium-rich compound particles in an in-situ reaction mode can also reduce the process steps and raw materials, lithium elements in the coating material are provided by the lithium-rich compound particles, no additional lithium source is needed to be added, the synthesis process and the combination process of the lithium aluminum borate occur simultaneously, and finally, the preparation cost of the lithium-rich positive electrode material can be reduced, so that the lithium-rich positive electrode material has extremely high commercial value.
In one embodiment, the outer surface of the lithium-rich compound particle further has concave holes, and part of the lithium aluminum borate is accommodated in the holes. Specifically, the pores on the outer surface of the lithium-rich compound particle may be formed after the boric acid is corroded. When the precursor added first is boric acid, the boric acid reacts with metal elements (such as lithium elements or other transition metal elements) on the outer surfaces of the lithium-rich compound particles, so that the outer surfaces of the lithium-rich compound particles are corroded to form rich pore structures. The holes provide good attachment sites and reaction sites for the subsequently formed lithium aluminum borate, so that a coating material firmly combined with lithium-rich compound particles can be formed.
In one embodiment, the coating material has a neutral ph. Based on the embodiment, the reaction mode of adding boric acid and then adding aluminum hydroxide can lead the lithium aluminum borate in the coating material to be neutral. The formed coating material is neutral, so that lithium ions in the lithium-rich anode material are converted from inactive lithium to active lithium in the electrochemical process, and the capacity retention rate of the material is improved, and the cycle life is prolonged.
In one embodiment, the coating material is a coating with uniform thickness, and the thickness ratio of any two points of the coating material is 0.98-1.02. Specifically, a coating material satisfying the above range can have good uniformity. The coating material with good uniformity has the advantages of effectively providing enough protection for the lithium-rich positive electrode material of the inner core, inhibiting the decomposition of electrolyte at the material interface, further preventing the passivation of the material interface, reducing polarization and improving the multiplying power and the cycle performance of the material.
In one embodiment, the coating material is produced by a liquid phase reaction, and the coating material is a dense and continuous coating of the surface of the lithium-rich compound particles. Specifically, the coating material is formed by using a boric acid solution and an aluminum hydroxide solution to react together. I.e. lithium-rich compound particles are arranged in the mixed solution of the above solutions. The coating material obtained by the method not only can be uniformly coated on the outer surface of the lithium-rich compound particles, but also has the characteristics of continuity and compactness.
In one embodiment, the cladding material further comprises aluminum borate. The aluminum borate is arranged on the outer surface of the lithium-rich compound particles, so that moisture and oxygen can be effectively isolated, stability of the lithium-rich positive electrode material is improved, a supporting structure is formed, and structural collapse of the lithium-rich positive electrode material is prevented. And aluminum borate has stronger thermal stability, and can prevent electrolyte from penetrating into lithium-rich compound particles to react with the lithium-rich compound particles in an environment with higher temperature, thereby preventing the phenomenon of thermal runaway of the lithium-rich positive electrode material.
In one embodiment, the aluminum borate content gradually decreases and the aluminum lithium borate content gradually increases along the direction of the outer surface of the lithium-rich compound particle toward the core.
In one embodiment, the lithium-rich compound particles include secondary particles composed of primary particles, with particle gaps formed between adjacent primary particles, and at least a portion of the coating material fills the gaps of the primary particles.
In one embodiment, the thickness of the coating material is 10nm to 100nm.
In one embodiment, the mass fraction of the coating material in the lithium-rich positive electrode material is 3% -10%.
In one embodiment, the specific surface area of the lithium-rich cathode material is 1.0m 2 /g～2.0m 2 /g。
In one embodiment, the lithium-rich compound particles have a porosity of 40% to 52%.
In one embodiment, the residual alkali content of the lithium-rich positive electrode material is lower than 0.3%, and the water absorption rate of the lithium-rich positive electrode material in air with relative humidity of 30% -35% at 25 ℃ is 0.5ppm/s-5ppm/s.
In one embodiment, the electrochemical impedance of the lithium-rich positive electrode material is 30 Ω to 85 Ω.
In a second aspect, the present application provides a method for preparing a lithium-rich cathode material, comprising:
providing lithium-rich compound particles; and mixing the lithium-rich compound particles, boric acid and aluminum hydroxide together, heating and drying to obtain mixed powder, and sintering the mixed powder at high temperature to obtain the lithium-rich positive electrode material.
In a third aspect, the present application further provides a positive electrode sheet, where the positive electrode sheet includes a current collector and an active material layer disposed on the current collector, where the active material layer includes a positive electrode material and a lithium-rich positive electrode material according to any one of the embodiments of the first aspect, or where the active material layer includes a positive electrode material and a lithium-rich positive electrode material obtained by a method for preparing a lithium-rich positive electrode material according to any one of the embodiments of the second aspect.
In a fourth aspect, the present application also provides a secondary battery, which includes a negative electrode tab, a separator, and the positive electrode tab according to the third aspect.
Drawings
In order to more clearly illustrate the embodiments of the application or the technical solutions in the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the description below are only some embodiments of the application, and that other drawings can be obtained from them without inventive effort for a person skilled in the art.
FIG. 1 is a schematic cross-sectional view of a lithium-rich cathode material in one embodiment;
FIG. 2 is a schematic cross-sectional view of a lithium-rich cathode material in another embodiment;
FIG. 3 is a flow chart of a method of preparing a lithium-rich positive electrode material in one embodiment;
FIG. 4 is a flow chart of a method of preparing a blended powder in an embodiment;
fig. 5 is a flow chart of a method of preparing a blended powder in another embodiment.
Detailed Description
The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present application without making any inventive effort, are intended to fall within the scope of the present application.
It will be understood that when an element is referred to as being "fixed to" another element, it can be directly on the other element or intervening elements may also be present. When a component is considered to be "connected" to another component, it can be directly connected to the other component or intervening components may also be present.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
Some embodiments of the present application are described in detail below with reference to the accompanying drawings. The following embodiments and features of the embodiments may be combined with each other without conflict.
Referring to fig. 1, the lithium-rich cathode material includes lithium-rich compound particles 10 and a coating material 20; the coating material 20 is at least partially bonded to the outer surface of the lithium-rich compound particles, and the coating material comprises lithium aluminum borate.
Specifically, the lithium-rich oxide particles may be mainly composed of a lithium-rich oxide, which is a core of the lithium-rich positive electrode material providing lithium ions, and the structural formula of the lithium-rich oxide is not particularly limited. Alternatively, the shape of the lithium-rich compound particles may be spherical or spheroid in structure or other irregular shape.
Optionally, the lithium-rich compound particles may also be lithium-supplementing materials, as "sacrificial agents" for supplementing the lithium source, thereby ensuring primary charging efficiency.
Alternatively, the lithium-rich oxide has the structural formula Li 2+x M y O z Wherein M is at least one element in W, ti, al, ni, fe, mn, co, cr, V, mo, nb, zr, cu, mg, K, x is more than or equal to 0.2 and less than or equal to 0.2, y is more than 0 and less than 1, and z is more than 0 and less than 12. In the specific embodimentIn the lithium-rich oxide may be Li 5 FeO 4 、Li 6 MnO 4 、Li 6 CoO 4 、Li 6 ZnO 4 、Li 2 NiO 2 、Li 2 CuO 2 、Li 2 CoO 2 、Li 2 MnO 2 、Li 2 Ni 0.5 Mn 1.5 O 4 、Li 2 Ni 0.5 Cu 0.5 O 2 At least one of the following. It should be noted that some of the above-mentioned first lithium-rich oxides can be directly used as lithium-rich positive electrode materials, such as Li 2 NiO 2 、Li 2 CuO 2 、Li 2 CoO 2 、Li 2 MnO 2 、Li 2 Ni 0.5 Mn 1.5 O 4 。
Optionally, the coating material includes lithium aluminum borate, and the lithium aluminum borate is different from the existing aluminum borate and also contains lithium element in the structure of the lithium aluminum borate. The lithium aluminum borate can be combined with the outer surface of the lithium-rich compound particles in a sintering mode after being synthesized in advance, and can be manufactured on the outer surface of the lithium-rich compound particles in an in-situ reaction mode.
It will be appreciated that the pre-synthesized lithium aluminum borate requires the provision of a boron source, an aluminum source and a lithium source, and then the reaction to obtain lithium aluminum borate, and then the co-sintering of the provided lithium-rich compound particles with lithium aluminum borate, so that the lithium aluminum borate is bonded to the outer surface of the lithium-rich compound particles.
According to the application, the coating material is arranged on the outer surface of the lithium-rich compound particles, so that the conversion of lithium ions from inactive lithium to active lithium in the electrochemical process is facilitated, the capacity retention rate of the material is improved, and the cycle life is prolonged. Meanwhile, the coating material combined on the outer surface of the lithium-rich compound particle can also effectively provide enough protection for the lithium-rich compound particle, and side reaction of electrolyte on the outer surface of the lithium-rich compound particle is reduced, so that interface passivation phenomenon generated on the surface of the lithium-rich compound particle is prevented, and the rate capability and the cycle performance of the lithium-rich positive electrode material are improved while polarization is reduced. In addition, compared with other coating materials, the lithium aluminum borate can provide higher conductivity, and lithium elements in the lithium aluminum borate can be matched with the deintercalation of lithium ions to form a fast ion channel, so that the deintercalation efficiency of the lithium ions is accelerated, the charge and discharge speed is improved, and more possibilities are provided for the current fast charge technology.
In one embodiment, the lithium aluminum borate is formed from the in situ reaction of residual alkali on the surface of the lithium-rich compound particles. Specifically, on the basis of the above embodiment, lithium aluminum borate may also be directly generated on the outer surface of the lithium-rich compound particles by the way of co-reacting the precursor and the lithium-rich compound particles.
It will be appreciated that the coating material may be prepared by mixing lithium-rich compound particles with a precursor. The lithium aluminum borate in the coating material can be a product generated after the precursor reacts with residual alkali on the surfaces of the lithium-rich compound particles. Thereby reducing the residual alkalinity of the outer surface of the lithium-rich compound particles.
Alternatively, the precursors of the coating material may be boric acid and aluminum hydroxide. After boric acid and aluminum hydroxide are disposed on the outer surface of the lithium-rich compound particles, residual alkali on the surfaces of the boric acid and aluminum hydroxide and lithium-rich compound particles form lithium aluminum borate (Li) 6 Al 2 B 4 O 12 ). It should be noted that the lithium aluminum borate may be a solid solution formed by combining a plurality of compounds by chemical action (calcination), and may be specifically Li 2 O-LiAlO 2 -LiBO 2 Solid solutions.
Alternatively, the lithium-rich compound particles and the precursor may be reacted by a solid phase reaction or a liquid phase reaction. Alternatively, the coating material may be coated on a part of the outer surface of the lithium-rich compound particle, or coated on the whole outer surface of the lithium-rich compound particle. It will be appreciated that the solid phase reaction may result in insufficient contact between the lithium-rich particles and the precursor, and thus in coating of the coating material on a portion of the outer surface of the lithium-rich particles. The liquid phase reaction has better uniformity, so the liquid phase reaction is coated on the whole outer surface of the lithium-rich compound particles.
The application prepares the lithium-rich compound particles with coating materials by carrying out high-temperature sintering reaction on boric acid, aluminum hydroxide and lithium-rich compound particles; on one hand, the surface residual alkali can be converted into aluminum lithium borate by the reaction of boric acid and aluminum hydroxide with the surface residual alkali of the lithium-rich compound particles, so that the content of the surface residual alkali can be effectively reduced, the gas expansion phenomenon of the lithium-rich positive electrode material in the secondary battery process can be effectively reduced, and the electrochemical performance and the processing performance of the lithium-rich positive electrode material are improved; on the other hand, compared with the existing material coating mode, the method for arranging the lithium aluminum borate on the outer surface of the lithium-rich compound particles in an in-situ reaction mode can also reduce the process steps and raw materials, lithium elements in the coating material are provided by the lithium-rich compound particles, no additional lithium source is needed to be added, the synthesis process and the combination process of the lithium aluminum borate occur simultaneously, and finally, the preparation cost of the lithium-rich positive electrode material can be reduced, so that the lithium-rich positive electrode material has extremely high commercial value.
In one embodiment, the coating material may further include a product formed by reacting another transition metal with the precursor. Such as nickel oxide and the promising reactions. Therefore, by means of co-sintering the precursor (boric acid and aluminum hydroxide) and the lithium-rich compound particles, not only lithium-containing residual alkali on the surfaces of the lithium-rich compound particles can be reduced, but also adverse phases (such as transition metal oxides) in the lithium-rich positive electrode material can be digested, so that the overall specific capacity of the material is improved, and the polarizability is reduced.
In one embodiment, referring to fig. 2, the outer surface of the lithium-rich compound particle 10 further has concave holes 11, and at least part of the lithium aluminum borate is accommodated in the holes 11.
Specifically, the pores on the outer surface of the lithium-rich compound particle may be formed after the boric acid is corroded. For example, since the precursors of the coating material include boric acid and aluminum hydroxide. Therefore, by controlling the addition sequence of boric acid and aluminum hydroxide, pore formation can be performed on the outer surface of the lithium-rich compound particles.
When the precursor added first is boric acid, the boric acid reacts with metal elements (such as lithium elements or other transition metal elements) on the outer surfaces of the lithium-rich compound particles, so that the outer surfaces of the lithium-rich compound particles are corroded to form rich pore structures. The holes provide good attachment sites and reaction sites for the subsequently formed lithium aluminum borate, so that a coating material firmly combined with lithium-rich compound particles can be formed.
In one embodiment, the coating material is neutral. It should be explained that, based on the above embodiment, the reaction mode of adding boric acid first and then adding aluminum hydroxide can make lithium aluminum borate in the coating material appear neutral.
The formed coating material is neutral, so that lithium ions in the lithium-rich anode material are converted from inactive lithium to active lithium in the electrochemical process, and the capacity retention rate of the material is improved, and the cycle life is prolonged.
In one embodiment, the coating material is a uniform coating, and the thickness ratio of any two points of the coating is 0.98-1.02. Specifically, a coating material satisfying the above range can have good uniformity. The coating material with good uniformity has the advantages of effectively providing enough protection for the lithium-rich positive electrode material of the inner core, inhibiting the decomposition of electrolyte at the material interface, further preventing the passivation of the material interface, reducing polarization and improving the multiplying power and the cycle performance of the material.
It should be noted that when the outer surface of the lithium-rich compound particle has no holes, the coating may have a structure with a uniform thickness, as shown in fig. 1, so that the thicknesses at any two points of the coating are similar. And satisfying the above thickness ratio, it can be explained that the coating thickness has uniform characteristics. When the thickness ratio exceeds the above range, the uniformity of the coating thickness is poor, which is unfavorable for reducing the residual alkali amount on the surface of the lithium-rich compound particles, and the coating effect is poor.
In other embodiments, when the outer surface of the lithium-rich compound particle has pores, it may be that the thickness of the coating is uniform at non-pores. Also, it will be appreciated that the thickness of the coating at the holes must be greater than the thickness at the non-holes.
Alternatively, the coating layer may cover the outer surface of the lithium-rich compound particle completely, or may cover part of the outer surface of the lithium-rich compound particle partially.
In one embodiment, the coating material is produced by a liquid phase reaction, and the coating material is a dense and continuous coating of the surface of the lithium-rich compound particles. Specifically, the coating material is formed by using a boric acid solution and an aluminum hydroxide solution to react together. I.e. lithium-rich compound particles are arranged in the mixed solution of the above solutions. The coating material obtained by the method not only can be uniformly coated on the outer surface of the lithium-rich compound particles, but also has the characteristics of continuity and compactness.
In one embodiment, the cladding material further comprises aluminum borate. Specifically, in addition to the above embodiments, there may be two types of aluminum borate bonding methods. Firstly, aluminum borate is prepared in advance, and then the aluminum borate and the lithium-rich compound particles are sintered together, so that the aluminum borate and the lithium aluminum borate are mixed and coated on the outer surfaces of the lithium-rich compound particles. Alternatively, aluminum borate is formed in situ on the outer surface of the lithium-rich compound particles.
It will be appreciated that after coating the lithium-rich particles with the precursor, the precursor in contact with the lithium-rich particles will react with the residual base first to form lithium aluminum borate, whereas the precursor further from the lithium-rich particles will be more difficult to react with the residual base. Therefore, the precursor is pre-coated on the outer surface of the lithium-rich compound particles after reacting with residual alkali, and part of boric acid only reacts with aluminum hydroxide to generate aluminum borate.
The lithium borate is arranged on the outer surface of the lithium-rich compound particles, so that moisture and oxygen can be effectively isolated, the stability of the lithium-rich positive electrode material is improved, a supporting structure is formed, and the collapse of the structure of the lithium-rich positive electrode material is prevented. In addition, lithium borate is a fast ion conductor, and can increase the first discharge capacity and reduce the impedance. And aluminum borate has stronger thermal stability, and can prevent electrolyte from penetrating into lithium-rich compound particles to react with the lithium-rich compound particles in an environment with higher temperature, thereby preventing the phenomenon of thermal runaway of the lithium-rich positive electrode material.
In one embodiment, the aluminum borate content gradually decreases and the lithium aluminum borate content gradually increases along the direction of the outer surface of the lithium-rich compound particles toward the core.
Specifically, the coating material is bonded to the outer surface of the lithium-rich compound particles, and an encapsulation layer and a conversion layer may be formed. Wherein the conversion layer is aluminum lithium borate, and the packaging layer is aluminum borate. Preferably, the encapsulation layer is coated on the outer surface of the conversion layer.
It will be appreciated that the lithium aluminum borate formed by the precursor pre-reaction with the residual base should be a conversion layer adjacent to the welfare compound particles, with the encapsulation layer being located outside the conversion layer.
Further, when the residual alkali on the surface of the lithium-rich compound particle is more, the thickness of the conversion layer should be thicker, the thickness of the encapsulation layer should be thinner, and the presence of the encapsulation layer is less noticeable. When the residual alkali on the surface of the lithium-rich compound particles is smaller, the thickness of the conversion layer should be thinner, the thickness of the encapsulation layer should be thicker, and the presence of the encapsulation layer is more remarkable.
Furthermore, it should be noted that the conversion layer and the encapsulation layer are not clearly distinguished by an interface therebetween. And the precursor reacts with the residual alkali on the surface of the lithium-rich compound particles, so that the formed aluminum lithium borate is concentrated in a large amount in the interface between the lithium-rich compound particles and the coating material, and then the content of the aluminum lithium borate gradually decreases along with the thickening of the coating material. Conversely, the aluminum borate content gradually increases.
In one embodiment, the lithium-rich compound particles include secondary particles composed of primary particles, with particle gaps formed between adjacent primary particles, and at least a portion of the coating material fills the gaps of the primary particles.
Specifically, after primary particles of lithium-rich compound particles and a precursor are mixed in proportion and dried, the materials are mixed by a high-speed mixer and sintered, so that secondary-particle lithium-rich compound particles can be obtained, and aluminum lithium borate can be filled in gaps of the primary particles.
In one embodiment, the thickness of the coating material is 10nm to 100nm. In particular, the thickness of the cladding material may be, but is not limited to, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm. The thickness of the coating material is controlled within the range, so that the particle size of the lithium-rich positive electrode material can be adjusted, and the specific capacity and the electron conducting environment of the lithium-rich positive electrode material can be ensured.
When the thickness of the coating material is smaller than the above range, the coating material does not completely coat the lithium-rich compound particles, the exposure of the lithium-rich compound particles is easy to occur, and the incomplete residual alkali reaction is extremely easy to occur; when the thickness of the coating material is greater than the above range, the particle diameter of the lithium-rich cathode material may be excessively large, and the overall gram-capacity of the lithium-rich cathode material may be reduced since the coating material does not contribute lithium ions.
In one embodiment, the mass fraction of the coating material in the lithium-rich positive electrode material is 3% -10%. Specifically, the mass fraction of the coating material in the cathode material may be, but is not limited to, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%. The mass ratio of the coating material in the lithium-rich positive electrode material is controlled within the range, so that the coating thickness of the coating material can be adjusted more favorably, and the effective protection of the coating material on the lithium-rich compound particles can be realized; and enables lithium ions in the lithium-rich compound particles to have a moderate extraction rate.
In one embodiment, the specific surface area of the borated lithium-rich compound particles is 3m 2 /g～6m 2 Per gram, the specific surface area of the lithium-rich positive electrode material coated by the aluminum lithium borate is 1.0m 2 /g～2.0m 2 /g。
Specifically, the specific surface area of the lithium-rich compound particles after boric acid treatment may be, but is not limited to, 3m 2 /g、3.5m 2 /g、4m 2 /g、4.5m 2 /g、5m 2 /g、5.5m 2 /g、6m 2 And/g. The specific surface area of the lithium-rich positive electrode material coated by the aluminum lithium borate can be, but is not limited to, 1m 2 /g、1.2m 2 /g、1.3m 2 /g、1.4m 2 /g、1.5m 2 /g、2.0m 2 And/g. The lithium-rich positive electrode material after boric acid treatment, namely the structure of the lithium-rich compound particles in the embodiment, is corroded to form holes by adding boric acid. It will be appreciated that the surface of the lithium-rich particles after corrosion by boric acid may be due to adverse phase metal oxides (e.g., niO and Li 2 O) is etched away to form holes. The lithium-rich compound particles after boric acid treatment have a larger specific surface area (3 m 2 /g～6m 2 /g). Thereby providing more attachment sites for subsequent formation of lithium aluminum borate.
Further, after adding aluminum hydroxide, the outer surface of the lithium-rich compound particle forms a coating layer of aluminum lithium borate, and the aluminum lithium borate is generated on the outer surface of the lithium-rich compound particle by in-situ reaction and is also partially accommodated in the corroded holes. The connection between the lithium aluminum borate and the lithium-rich compound particles is firmer. And because the aluminum lithium borate is accommodated in the holes, the specific surface area of the lithium-rich positive electrode material coated by the aluminum lithium borate is smaller than that before coating.
In one embodiment, the lithium-rich compound particles have a porosity of 40% to 52%. The porosity of the lithium-rich compound particles refers to the percentage of the pore volume in the lithium-rich material to the total volume of the lithium-rich material in a natural state, and the smaller the porosity, the smaller the pores, and conversely the more the pores. It can be understood that the voids of the lithium-rich compound particles are actually the corroded holes, and the porosity is controlled within the above range, so that the richness of the holes can be effectively controlled, and the structural stability of the lithium-rich positive electrode material can be ensured.
In one embodiment, the residual alkali content of the lithium-rich positive electrode material is lower than 0.3%, and the water absorption rate of the lithium-rich positive electrode material in air with relative humidity of 30-35% at 25 ℃ is 0.5-5 ppm/s.
It can be understood that the residual alkali content and the water absorption rate of the lithium-rich cathode material are positively correlated, and when the residual alkali content is higher, the residual alkali is more likely to react with water vapor in the air (i.e., the water absorption is faster), so that the slurry is more likely to gel during the coating process. Therefore, on the basis of the above embodiment, the residual alkali on the surface of the lithium-rich compound particles is reduced by the precursor (boric acid and aluminum hydroxide) so that the residual alkali content of the lithium-rich positive electrode material is lower than the above range, whereby the water absorption rate can be reduced so that the water absorption rate is within the above range.
In one embodiment, the lithium-rich positive electrode sheet coated with lithium aluminum borate has similar conductivity to uncoated lithium-rich compound particles. This is because the conductivity of lithium aluminum borate is good, and the conductivity of the lithium-rich cathode material is not lowered. Moreover, the adverse phase (poor electric conductivity) on the surface of the lithium-rich particles is eliminated, so that the electric conductivity of the lithium-rich positive electrode material is improved.
In an embodiment, the present application further provides a method for preparing a lithium-rich cathode material, please refer to fig. 3, which is specifically used for preparing the lithium-rich cathode material in the above embodiment. The preparation method comprises the following steps:
step S10, providing lithium-rich compound particles.
And step S20, mixing the lithium-rich compound particles, boric acid and aluminum hydroxide, heating and drying to obtain mixed powder, and sintering the mixed powder at high temperature to obtain the lithium-rich cathode material.
Specifically, in step S10, the chemical formula of the provided lithium-rich compound particles may be as provided in the first aspect.
Alternatively, the preparation method of the lithium-rich compound particles can be as follows: mixing and sintering an M source and a Li source according to a molar ratio, and obtaining lithium-rich compound particles after material taking, crushing and sieving.
Alternatively, the M source may be, but is not limited to being, one or more of an oxide, hydroxide, carbonate, nitrate, sulfate, acetate. The Li source may be, but is not limited to, one or more of lithium hydroxide, lithium oxide, lithium carbonate, lithium sulfate, lithium oxalate.
Optionally, the co-sintering temperature of the M source and the Li source can be 500-900 ℃, and the temperature is kept for 1-24 h.
Further, referring to fig. 4, in step S20, the mixing process of the lithium-rich compound particles, boric acid and aluminum hydroxide may be:
and S21, adding the lithium-rich compound particles into a mixed solution of an organic solvent and water, and stirring by ultrasonic waves to obtain a solution A.
And S22, respectively adding the boric acid solution and the aluminum hydroxide into water, and obtaining a solution B after sufficient ultrasonic stirring.
In step S23, the solution B is slowly added into the solution A, and the suspension C is obtained after ultrasonic treatment.
In step S24, suspension C is heated in a water bath, and then filtered and dried to obtain a mixed powder.
Optionally, the organic solvent in step S21 is at least one of ethanol, methanol, propanol, propylene glycol, ethyl acetate, and the like.
Optionally, the volume ratio of the organic solution to the water in step S21 is in the range of 2-5:1.
optionally, the ultrasonic treatment time in the step is 5-15 min.
Optionally, the water bath temperature in the step S24 is 30-60 ℃, and the heating time is 5-20 min.
Optionally, the drying temperature in the step S24 is 80-120 ℃ and the drying time is 1-15 h.
In other embodiments, referring to fig. 5, the mixing process of the lithium-rich compound particles, boric acid and aluminum hydroxide may be:
and step S21', adding the lithium-rich compound particles into a mixed solution of an organic solvent and water, and stirring by ultrasonic waves to obtain a solution A.
And step S22', respectively adding aluminum hydroxide into water, and obtaining an aluminum hydroxide solution after sufficient ultrasonic stirring.
In step S23', the boric acid solution is slowly added to the solution a, and then the aluminum hydroxide solution is added to the solution a having boric acid, and the suspension C is obtained after ultrasonic treatment.
In step S24', the suspension C is heated in a water bath, and then filtered and dried to obtain a mixed powder.
The embodiment has the advantages that holes can be formed on the surfaces of the lithium-rich compound particles through corrosion of boric acid in advance, good adhesion sites and reaction sites are provided for aluminum lithium borate formed later, and then a coating material firmly combined with the lithium-rich compound particles can be formed. The resulting coating material may also be neutral.
Preferably, in step S20, the purity of boric acid and aluminum hydroxide must be greater than 98%.
Optionally, in step S20, the sintering temperature of the mixed powder is 500 ℃ to 700 ℃.
Optionally, in steps S10 and S20, the number of the upper sieves is 200 mesh.
Optionally, in steps S10 and S20, the inert gas is at least one of nitrogen, argon, helium, and neon.
In one embodiment, the present application also provides a positive electrode sheet comprising a current collector and an active material layer disposed on the current collector, the active material layer comprising the positive electrode material of any one of the second aspects. The positive electrode material can be used as a lithium supplementing additive to supplement active lithium consumed by forming an SEI film when a battery is charged for the first time, can also be used as a positive electrode active material to participate in circulation, and has good application prospect.
In one embodiment, the positive electrode plate comprises a positive electrode current collector, the positive electrode current collector is provided with a positive electrode active layer, the positive electrode active layer comprises components such as a lithium-rich positive electrode material, a conductive agent, a binder and the like, the materials are not particularly limited, and proper materials can be selected according to practical application requirements. The positive electrode current collector includes, but is not limited to, any one of copper foil and aluminum foil. The conductive agent comprises one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nano tube, and the content of the conductive agent in the positive electrode active layer is 3-5 wt%. The binder comprises one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives, and the content of the binder in the positive electrode active layer is 2-4wt%.
In a fourth aspect, the application also provides a secondary battery, which comprises a negative electrode plate, a diaphragm and the positive electrode plate. The positive electrode plate comprises the lithium-rich positive electrode material.
The technical scheme of the application is described in detail by specific examples.
Example 1
The embodiment provides a lithium-rich positive electrode material and a preparation method thereof. The lithium-rich compound particles are lithium nickelate, and the compact coating consists of lithium aluminum borate. The thickness of the compact coating is 50nm, and the compact coating is rich in theThe mass ratio of the lithium positive electrode material is 5%, and the specific surface area of the lithium-rich positive electrode material is 1.3m 2 /g。
The preparation method of the lithium-rich positive electrode material comprises the following steps:
and step 1, uniformly mixing a lithium source and a nickel source according to a molar ratio, sintering for a period of time in an inert atmosphere, and taking, crushing and sieving after a tube furnace is cooled to obtain a precursor of the lithium-rich anode material.
And 2, respectively adding a small amount of high-purity boric acid and a proper amount of aluminum hydroxide into the precursor of the lithium-rich cathode material obtained in the step 1, mixing and carrying out ultrasonic treatment in an organic/water mixed solution, heating in a water bath for a proper time, and then filtering and drying to obtain green powder. And then sintering the obtained green powder at high temperature for several hours in an inert atmosphere to finally obtain the lithium-rich anode material uniformly coated with aluminum lithium borate.
Example 2
The embodiment provides a lithium-rich positive electrode material and a preparation method thereof. The lithium-rich compound particles are lithium nickelate, and the compact coating consists of lithium aluminum borate and aluminum borate. The thickness of the compact coating is 90nm, the mass ratio of the compact coating on the lithium-rich positive electrode material is 10%, and the specific surface area of the lithium-rich positive electrode material is 1.5m 2 /g。
The specific experimental procedure differs from example 1 in that in step 2, the boric acid and aluminum hydroxide added are in excess.
Example 3
The embodiment provides a lithium-rich positive electrode material and a preparation method thereof. The lithium-rich compound particles are lithium-rich nickel lithium manganate, and the compact coating consists of aluminum lithium borate. The thickness of the compact coating is 50nm, the mass ratio of the compact coating on the lithium-rich positive electrode material is 5%, and the specific surface area of the lithium-rich positive electrode material is 1.3m 2 /g。
The specific implementation procedure was as in example 1.
Example 4
The embodiment provides a lithium-rich positive electrode material and a preparation method thereof. The lithium-rich compound particles are lithium nickelate, and the compact coating consists of lithium aluminum borate. The thickness of the compact coating is 10nm, the mass ratio of the compact coating on the lithium-rich positive electrode material is 3%, and the specific surface area of the lithium-rich positive electrode material is 1.5m 2 /g。
The specific implementation procedure was as in example 1.
Example 5
The embodiment provides a lithium-rich positive electrode material and a preparation method thereof. The lithium-rich compound particles are lithium nickelate, and the compact coating consists of lithium aluminum borate. The thickness of the compact coating is 100nm, the mass ratio of the compact coating on the lithium-rich positive electrode material is 9%, and the specific surface area of the lithium-rich positive electrode material is 1.2m 2 /g。
The specific implementation procedure was as in example 1.
Comparative example 1
The comparative example was lithium nickelate, without any coating on the surface.
Comparative example 2
The comparative example is lithium nickel manganese oxide, and the surface of the comparative example is free of any coating layer.
The lithium-rich cathode materials provided in examples 1-5 above and the lithium-rich cathode materials provided in comparative examples 1-2 were assembled into a cathode and a lithium ion battery, respectively, according to the following methods:
and (3) a positive electrode: lithium-rich cathode material, SP and PVDF were mixed according to 90:4: mixing the homogenized positive electrode slurry according to the mass ratio of 6, coating the positive electrode slurry on the surface of an aluminum foil, vacuum drying overnight at 110 ℃, and rolling to obtain a positive electrode plate;
and (3) a negative electrode: a lithium sheet;
electrolyte solution: mixing ethylene carbonate and ethylmethyl carbonate in a volume ratio of 3:7, and adding LiPF 6 Electrolyte is formed, liPF 6 The concentration of (2) is 1mol/L;
a diaphragm: a polypropylene microporous separator;
and (3) assembling a lithium ion battery: and assembling the button type lithium ion full battery in an inert atmosphere glove box according to the assembling sequence of the graphite negative electrode plate, the diaphragm, the electrolyte and the positive electrode plate.
Each lithium ion battery assembled in the above lithium ion battery example was subjected to electrochemical performance test under the following conditions:
constant-current constant-voltage charging, first-turn charging and discharging voltage is 2.5-4.3V, current is 0.1C, and cut-off current is 0.01C.
The first-circle gas production test is to assemble a lithium ion battery by using a die battery, then charge the lithium ion battery under constant current and constant voltage, wherein the first-circle charge and discharge voltage is 2.5-4.3V, the current is 0.1C, and the cut-off current is 0.01C. The gas in the die cell was introduced into a differential electrochemical mass spectrometer for testing.
In addition, moisture resistance tests are carried out on the lithium-rich cathode materials of the examples and the comparative examples, and the water absorption rate is used as a characterization parameter, and the test method is as follows:
and under the environment condition of 30% humidity, measuring and recording the quality change of the product, and obtaining the water absorption rate of the lithium-rich positive electrode material by carrying out statistical calculation on the quality change in five time points.
The test results of the above lithium-rich cathode material and lithium ion battery are shown in table 1 below
TABLE 1 Performance test results
From the results of the performance tests of examples 1 to 5 and comparative examples 1 to 2, it was found that the lithium aluminum borate as the clad coating of the lithium-rich compound particles had a good performance improving effect. In addition, the water absorption rate of the materials in examples 1-5 is obviously lower than that of comparative examples 1-2, because the coating layer can better isolate the lithium-rich compound particles from contact with the external environment, and effectively reduce residual alkali on the surfaces of the lithium-rich compound particles, thereby reducing the water absorption rate of the lithium-rich cathode material.
Specifically, as shown by the performance test results of comparative examples 1, 4 and 5 and comparative example 1, the aluminum lithium borate coating can not only remarkably reduce residual alkali on the surface of the lithium-rich core material, but also reduce the water absorption rate (wherein the water absorption rate in example 1 reaches 0.52 ppm/s), so that the material has better processing and storage performances. Meanwhile, the lithium aluminum borate coating can obviously improve the discharge specific capacity of the material, mainly because the transition metal oxide phase remained on the surface of the material is corroded in the process of forming the lithium aluminum borate coating, the whole specific capacity of the material is improved, the polarization rate is reduced, and the capacity retention rate of the material is obviously improved. On the other hand, the lithium aluminum borate is used as a good fast ion conductor, the formed neutral coating layer can maximally transmit lithium ions in the electrochemical process and reduce inactive lithium.
Moreover, as can be seen from the performance test results of examples 1, 4 and 5, the lithium aluminum borate coating with moderate thickness can exhibit optimal electrochemical performance, mainly because the too thin coating layer cannot achieve sufficient protection effect, and is easy to fall off during the circulation process, resulting in poor circulation performance. While excessive thickness of the over-coating can affect the energy density of the material as a whole. It is necessary to set the thickness of the over-coating layer within a proper range.
As is clear from the results of the performance tests of examples 1 and 2 and comparative example 1, the initial charge-discharge specific capacity in example 2 was lower than that in example 1. This is because the addition of excess boric acid and aluminum hydroxide during the formation of lithium aluminum borate can further erode the active material of the core, resulting in a slight decrease in electrochemical performance. However, the lithium-rich cathode material provided in example 2 still maintains a low water absorption rate, so the solution provided in example 2 can be applied to electrode materials that require long-term storage or transportation.
As is evident from the performance test results of examples 1 and 3 and comparative examples 1 and 2, the aluminum lithium borate is universal as a surface modification interface of the lithium-rich cathode material, and can be used for lithium-rich nickel lithium, and can also act on lithium-rich nickel lithium manganate, and the electrochemical performance of the aluminum lithium borate is higher than that of the unmodified lithium-rich cathode material. In addition, the effect of the aluminum lithium borate is remarkable in reducing residual alkali, and the water absorption rate is far smaller than that of the unmodified lithium-rich positive electrode material.
In the description of the embodiments of the present application, it should be noted that, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," and the like refer to the orientation or positional relationship based on the drawings, which are merely for convenience of description and to simplify the description, and do not indicate or imply that the apparatus or element to be referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application.
The above disclosure is only a preferred embodiment of the present application, and it should be understood that the scope of the application is not limited thereto, but all or part of the procedures for implementing the above embodiments can be modified by one skilled in the art according to the scope of the appended claims.

Claims (11)

1. A lithium-rich cathode material, comprising:
lithium-rich compound particles;
a coating material, at least a portion of the coating material being bonded to an outer surface of the lithium-rich carbide particles, the coating material comprising lithium aluminum borate.
2. The lithium-rich cathode material of claim 1, wherein the lithium aluminum borate is generated by in situ reaction of residual alkali on the surface of the lithium-rich compound particles; and/or, the outer surface of the lithium-rich compound particle is also provided with concave holes, and at least part of the aluminum lithium borate is accommodated in the holes.
3. The lithium-rich cathode material according to claim 1, wherein,
the pH value of the coating material is neutral;
and/or, the coating material forms a coating with uniform thickness;
and/or the coating material forms a dense and continuous coating.
4. The lithium-rich cathode material of claim 1, wherein the coating material further comprises aluminum borate.
5. The lithium-rich cathode material according to claim 4, wherein the content of aluminum borate gradually decreases and the content of aluminum lithium borate gradually increases in a direction from the outer surface to the core of the lithium-rich compound particles.
6. The lithium-rich cathode material according to claim 1, wherein the lithium-rich compound particles include secondary particles composed of primary particles, gaps between adjacent primary particles are formed, and a part of the coating material is filled in the gaps of the primary particles.
7. The lithium-rich cathode material according to claim 2, wherein the thickness of the coating material is 10nm to 100nm; and/or the mass ratio of the coating material in the lithium-rich positive electrode material is 3-10%; and/or the specific surface area of the lithium-rich positive electrode material is 1.0m 2 /g～2.0m 2 /g; the porosity of the lithium-rich compound particles is 40% -52%.
8. The lithium-rich cathode material of claim 1, wherein the residual alkali content of the lithium-rich cathode material is less than 0.3%; and/or the water absorption rate of the lithium-rich positive electrode material in air with relative humidity of 30-35% at 25 ℃ is 0.5ppm/s-5ppm/s.
9. The preparation method of the lithium-rich cathode material is characterized by comprising the following steps of:
providing lithium-rich compound particles;
and mixing the lithium-rich compound particles, boric acid and aluminum hydroxide, heating and drying to obtain mixed powder, and sintering the mixed powder at high temperature to obtain the lithium-rich positive electrode material.
10. A positive electrode sheet, characterized in that the positive electrode sheet comprises a current collector and an active material layer disposed on the current collector, the active material layer comprising the lithium-rich positive electrode material according to any one of claims 1 to 8; or, the active material layer comprises the lithium-rich cathode material obtained by the preparation method of the lithium-rich cathode material according to claim 9.
11. A secondary battery comprising a negative electrode tab, a separator, and the positive electrode tab of claim 10.
CN202310950635.7A 2023-07-28 2023-07-28 Lithium-rich positive electrode material, preparation method thereof, positive electrode plate and secondary battery Pending CN116936763A (en)

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