Lithium-rich composite material, method for preparing the same, and secondary battery

Abstract

The application belongs to the technical field of batteries, and particularly relates to a lithium-rich composite material and a preparation method thereof, and a secondary battery. The lithium-rich composite material comprises a lithium-rich positive electrode inner core and a metal phosphate coating layer in-situ coated on the outer surface of the inner core; the chemical general formula of the lithium-rich positive electrode inner core is Li x M y O z , M is at least one element selected from Ni, Mn, Cu and Co, 0 < x / y < 3, y > 0, and 0 < z < 6; and the metal elements in the metal phosphate coating layer are at least one element selected from Ni, Mn, Cu and Co. The lithium-rich composite material provided by the application is rich in lithium ions, can be used as a positive electrode lithium supplement material and a positive electrode material, can effectively compensate for the active lithium source consumed by the positive electrode material in the first charge-discharge process, and can maintain the capacity and stability of the positive electrode material. Moreover, the lithium-rich composite material has good environmental stability, cycle stability and structural stability, and prolongs the use and storage life of the positive electrode material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of batteries, and particularly relates to a lithium-rich composite material and a preparation method thereof, and a secondary battery. BACKGROUND

[0002] During the first charge-discharge process of a lithium ion secondary battery, a large amount of solid electrolyte interphase (SEI) is generated on the surface of the negative electrode, which consumes the limited lithium ions and electrolyte in the lithium ion battery, causes irreversible capacity loss, and reduces the energy density of the lithium ion secondary battery. In a battery using a graphite negative electrode, about 10% of the active lithium source is consumed during the first cycle. When a high-specific-capacity negative electrode material such as an alloy (silicon, tin, etc.), an oxide (silicon oxide, tin oxide, etc.), and amorphous carbon negative electrode is used, the consumption of the active lithium source will be further intensified. Therefore, a suitable lithium supplement method is particularly important for improving the energy density of the lithium ion secondary battery.

[0003] In view of the above problems, a relatively safe and easy-to-operate positive electrode lithium supplement method has been proposed. For example, Li2Mn 1.5 Ni 0.5 O4, Li2NiO2, Li2MnO2, Li2CuO2, etc. lithium-rich transition metal oxide lithium supplement materials have high specific capacity and simple preparation method, and can better improve the energy density of the lithium ion secondary battery. However, the surface free lithium content of such materials is extremely high, which can easily cause the gelation of the slurry during the slurry preparation process, and seriously affects the processing performance. Moreover, the extremely high free lithium content can greatly deteriorate the high-temperature storage performance of the lithium ion secondary battery, resulting in storage swelling and performance degradation. SUMMARY

[0004] The present application aims to provide a lithium-rich composite material and a preparation method thereof, and a secondary battery, which aims to solve the problem that the lithium source is consumed too much during the cycle process of the existing positive electrode material in the secondary battery, thereby reducing the energy density and cycle life of the secondary battery.

[0005] To achieve the above application purposes, the technical solutions adopted by the present application are as follows:

[0006] In a first aspect, the present application provides a lithium-rich composite material, which comprises a lithium-rich positive electrode inner core and a metal phosphate coating layer coated on the outer surface of the lithium-rich positive electrode inner core; wherein the chemical formula of the lithium-rich positive electrode inner core is Li x M y O zWherein, M is selected from at least one element of Ni, Mn, Cu, Co, 0

[0007] In a second aspect, the application provides a preparation method of the lithium-rich composite material, comprising the following steps:

[0008] Dissolving the phosphorus source and the metal source in water, mixing, to generate a composite material with the metal source as the core and the metal phosphate as the shell; wherein the metal element in the metal source is selected from at least one element of Ni, Mn, Cu, Co;

[0009] Mixing the composite material with a lithium source, and sintering to obtain a lithium-rich composite material coated with a metal phosphate shell in situ, wherein the core of the lithium-rich composite material comprises a chemical formula of Li x M y O z A lithium-rich positive electrode material, wherein M is selected from at least one element of Ni, Mn, Cu, Co, 0

[0010] In a third aspect, the application provides a secondary battery, wherein the positive electrode of the secondary battery comprises the lithium-rich composite material prepared by the above method, or the lithium-rich composite material.

[0011] The lithium-rich composite material provided in the first aspect of the present application comprises a lithium-rich positive electrode inner core and a metal phosphate coating layer in-situ coated on the outer surface of the lithium-rich positive electrode inner core. On the one hand, the lithium-rich positive electrode inner core is rich in lithium ions, so the lithium-rich composite material can be used as a positive electrode lithium supplement material to effectively make up for the active lithium source consumed in the first cycle charging and discharging process of the positive electrode material, thereby maintaining the capacity and cycle stability of the positive electrode material. On the other hand, the lithium-rich composite material has a high capacity and is beneficial to lithium ion intercalation and deintercalation in the charging and discharging process, and can be directly used as a positive electrode material. Moreover, the metal elements in the metal phosphate coating layer in-situ coated on the outer surface of the inner core in the lithium-rich composite material are selected from at least one element of Ni, Mn, Cu and Co. The phosphate formed by these metal elements has hydrophobicity, which can reduce the residual alkali degree on the surface of the lithium-rich positive electrode inner core, avoid the contact reaction between the residual alkali on the surface of the lithium-rich positive electrode inner core and NMP and PVDF, etc. in the mixing process of the lithium-rich composite material for preparing a positive electrode sheet, and improve the paste phenomenon of the lithium-rich composite material. At the same time, the sensitivity of the metal elements in the lithium-rich positive electrode inner core to environmental moisture can be reduced, thereby prolonging the service and storage life of the lithium-rich composite material and improving the energy density of the lithium ion battery. The metal phosphate coating layer also prevents the corrosion of the electrolyte on the internal positive electrode active material, thereby improving the safety and stability of the positive electrode material, and improving the cycle stability and structural stability of the material. In addition, the metal phosphate coating layer is in-situ coated on the outer surface of the inner core, which can improve the combination tightness and stability of the coating layer and the inner core, and will not cause structural changes of the lithium-rich positive electrode inner core. After the lithium-rich composite material as the positive electrode material inner core releases lithium ions, the coating layer can also inhibit the dissolution of metal ions in the lithium-rich positive electrode inner core, reduce the loss of metal ions, avoid the formation of non-active substances and the loss of active substances, and improve the stability and electrochemical performance of the positive electrode material.

[0012] The preparation method of the lithium-rich composite material provided in the second aspect of the present application comprises the following steps: dissolving a phosphorus source and a metal source in water, mixing and processing to form a shell layer of metal phosphate on the surface, to obtain a composite material with the metal source as the inner core and the metal phosphate as the shell layer; then mixing with a lithium source and performing sintering treatment, so that the lithium source reacts with the metal source in the inner core of the composite material to generate a chemical formula Li x M y O z lithium-rich positive electrode material, to obtain a lithium-rich composite material in which the lithium-rich positive electrode inner core is in-situ coated with a metal phosphate shell layer. The preparation process is simple, suitable for industrial large-scale production and application, and the metal phosphate shell layer and the lithium-rich positive electrode inner core in the lithium-rich composite material are both in-situ generated, the coating is more compact and uniform, the combination tightness of the shell layer and the inner core in the lithium-rich composite material is improved, and the lithium-rich composite material has more stable and more excellent electrochemical performance through the synergistic effect of the inner core and the shell layer in the lithium-rich composite material.

[0013] The secondary battery provided in the third aspect of the present application contains the above-mentioned lithium-rich composite material in the positive electrode, the lithium-rich composite material including a lithium-rich positive electrode inner core and a metal phosphate coating layer coated on the outer surface of the lithium-rich positive electrode inner core. Through the synergistic effect of the inner core and the coating layer, the lithium-rich composite material not only contains lithium ions and can be used as a positive electrode lithium supplement material to effectively compensate for the active lithium source consumed by the positive electrode material during the first cycle charging and discharging process, but also can be used directly as a positive electrode material because lithium ions can be cyclically deintercalated, and has a high capacity. Thus, the capacity and cycle stability of the positive electrode material are maintained, the residual alkalinity in the surface of the positive electrode material is reduced, the gelling phenomenon of the positive electrode material is improved, the environmental stability, cycle stability and structural stability of the positive electrode material are improved, and the service and storage life of the positive electrode material is prolonged. Therefore, the energy density, service life, stability and safety of the secondary battery are improved. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0015] Figure 1 is a flowchart of the preparation method of the lithium-rich composite material provided in the embodiments of the present application. DETAILED DESCRIPTION

[0016] In order to make the technical problems, technical solutions and beneficial effects of the present application more clearly understood, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0017] In the present application, the term "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can represent the following cases: A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it.

[0018] In this application, "at least one" means one or more, "multiple" means two or more. "At least one of the following" or the like means any combination of these items, including a single item or any combination of multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0019] It should be understood that the size of the sequence number of the above-mentioned processes in various embodiments of the present application does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of the processes should be determined according to their functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0020] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0021] The weight of the related components mentioned in the specification of the embodiments of the present application can not only refer to the specific content of each component, but also represent the weight ratio relationship between each component, therefore, as long as the content of the related components in the specification of the embodiments of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass in the specification of the embodiments of the present application can be μg, mg, g, kg and other mass units commonly known in the chemical field.

[0022] The terms "first", "second" are only for the purpose of description, used to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be called the second XX, and similarly, the second XX can also be called the first XX. Therefore, the features limited by "first" and "second" can explicitly or implicitly include one or more of the features.

[0023] The first aspect of the embodiments of the present application provides a lithium-rich composite material, which comprises a lithium-rich positive electrode inner core and a metal phosphate coating layer coated on the outer surface of the lithium-rich positive electrode inner core; wherein the chemical formula of the lithium-rich positive electrode inner core is Li x M y O zwherein M is selected from at least one element of Ni, Mn, Cu, and Co, 0 < x / y < 3, y > 0, and 0 < z < 6; and the metal element in the metal phosphate coating layer is selected from at least one element of Ni, Mn, Cu, and Co.

[0024] The lithium-rich composite material provided in the first aspect of the embodiments of the present application comprises a lithium-rich positive electrode inner core and a metal phosphate coating layer in-situ coated on the outer surface of the lithium-rich positive electrode inner core, wherein the chemical formula of the lithium-rich positive electrode inner core is Li x M y O z wherein M is selected from at least one element of Ni, Mn, Cu, and Co, 0 < x / y < 3, y > 0, and 0 < z < 6, the positive electrode material comprising a spinel structure and a layered structure, which not only has a high capacity and is beneficial to the embedding and extraction of lithium ions during the charging and discharging process, so that the lithium-rich composite material can be directly used as a positive electrode material, but also is rich in lithium ions, which can effectively compensate for the active lithium source consumed by the positive electrode material during the first cycle of charging and discharging, thereby maintaining the capacity and cycle stability of the lithium-rich composite material. In addition, the metal element in the metal phosphate coating layer in-situ coated on the outer surface of the lithium-rich positive electrode inner core is selected from at least one element of Ni, Mn, Cu, and Co. The phosphate formed by these metal elements has hydrophobicity, which can reduce the residual alkalinity on the surface of the lithium-rich positive electrode inner core on the one hand, avoid the contact reaction between the residual alkali on the surface of the lithium-rich positive electrode inner core and NMP and PVDF, etc. during the preparation of the positive electrode sheet, and improve the coagulation phenomenon of the lithium-rich composite material. On the other hand, it can reduce the sensitivity of the metal elements in the lithium-rich positive electrode inner core to environmental moisture, thereby prolonging the service and storage life of the lithium-rich composite material and improving the energy density of the lithium ion battery. Moreover, the metal phosphate coating layer also prevents the corrosion of the electrolyte on the internal positive electrode active material, thereby improving the safety and stability of the lithium-rich composite material and improving the cycle stability and structural stability of the material. In addition, the metal phosphate coating layer is in-situ coated on the outer surface of the inner core, which can improve the combination tightness and stability of the coating layer and the inner core, and will not cause the structural change of the lithium-rich positive electrode inner core. After the lithium-rich composite material as the positive electrode material inner core releases lithium ions, the coating layer can also inhibit the dissolution of metal ions in the lithium-rich positive electrode inner core, reduce the loss of metal ions, avoid the formation of non-active substances and the loss of active substances, and improve the stability and electrochemical performance of the positive electrode material.

[0025] In some embodiments, the metal element in the metal phosphate coating layer is the same as the M element in the lithium-rich positive electrode inner core. The same metal element is used in the lithium-rich positive electrode inner core and the metal phosphate coating layer of the lithium-rich composite material of the embodiments of the present application, which is beneficial to improving the electrochemical stability of the lithium-rich composite material; and is beneficial to the in-situ generation of the metal phosphate coating layer, thereby improving the structural stability of the lithium-rich composite material.

[0026] In some embodiments, the chemical formula is Li x M y O z In the lithium-rich positive electrode core of the formula Li

[0027] The particle size of the lithium-rich composite material of the embodiments of the present application affects the compaction density and rate performance of the material. If the particle size of the lithium-rich composite material is too large, the ion transmission path is long, which is not conducive to ion transmission, thereby reducing the rate performance. If the particle size of the lithium-rich composite material is too small, the compaction density of the material is reduced.

[0028] In some embodiments, the particle size D50 of the lithium-rich composite material is 0.1-25 μm, and this particle size range can better balance the rate performance and compaction density of the lithium-rich composite material. In some specific embodiments, the particle size D50 of the lithium-rich composite material includes but is not limited to 0.1-1 μm, 1-2 μm, 2-3 μm, 3-4 μm, 4-5 μm, 5-6 μm, 6-7 μm, 7-8 μm, 8-9 μm, 9-10 μm, 10-13 μm, 13-15 μm, 15-18 μm, 18-20 μm, 20-25 μm, etc. In some preferred embodiments, the particle size D50 of the lithium-rich composite material is 0.1-10 μm.

[0029] In some embodiments, the average particle size of the lithium-rich composite material is 0.5-2 μm, and this particle size range can better balance the rate performance and compaction density of the lithium-rich composite material. In some specific embodiments, the average particle size of the lithium-rich composite material includes but is not limited to 0.5-1 μm, 1-1.5 μm, 1.5-2 μm, etc.

[0030] In some embodiments, the specific surface area of the lithium-rich composite material is not less than 0.5 m 2 / g. The lithium-rich composite material of the embodiments of the present application has a large specific surface area, which is not only conducive to balancing the rate performance and compaction density of the lithium-rich composite material, but also provides a larger reaction surface for lithium ions to be embedded and extracted during the charging and discharging process, thereby improving the charging and discharging activity of the lithium-rich composite material. In some specific embodiments, the specific surface area of the lithium-rich composite material is 0.5-5 m 2 / g, specifically including but not limited to 0.5 m 2 / g, 1 m 2 / g, 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, etc.

[0031] In some embodiments, the mass percentage of the metal phosphate coating layer in the lithium-rich composite material is 1-15%. The mass percentage of the metal phosphate coating layer in the embodiments of the present application can effectively ensure that the coating layer not only reduces the residual alkali degree of the surface of the core of the lithium-rich positive electrode, improves the paste phenomenon of the lithium-rich composite material, but also reduces the sensitivity of the transition metal oxide of the lithium-rich composite material to environmental moisture, thereby prolonging the use and storage life of the lithium-rich composite material, improving the energy density of the lithium ion battery, and the phosphate coating layer also prevents the corrosion of the electrolyte on the internal positive active material, thereby improving the safety and stability of the lithium-rich composite material and improving the cycle stability and structural stability of the material. In some specific embodiments, the mass percentage of the metal phosphate coating layer in the lithium-rich composite material includes but is not limited to 1%, 2%, 3%, 5%, 7%, 9%, 10%, 12%, 13%, 15%, etc.

[0032] In some embodiments, the thickness of the metal phosphate coating layer is 1-500 nm. If the thickness of the metal phosphate coating layer is low, the coating may not be complete, and some areas on the surface may exist or be easily exposed, thereby not conducive to improving the stability of the interface and not conducive to improving the electrochemical performance of the lithium-rich composite material. If the thickness of the metal phosphate coating layer is large, the proportion of the metal phosphate coating layer in the lithium-rich composite material is too high, and the proportion of the lithium-rich positive active ingredient in the core is reduced, thereby reducing the specific capacity of the lithium-rich composite material as a whole. In some specific embodiments, the thickness of the metal phosphate coating layer includes but is not limited to 1 nm, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc. In some preferred embodiments, the thickness of the metal phosphate coating layer is 10-300 nm.

[0033] In some embodiments, the particle size D50 of the lithium-rich positive electrode core in the lithium-rich composite material is 0.1-25 μm, and further, not less than 0.1 μm and less than 25 μm. The lithium-rich positive electrode core with this particle size balances the rate performance and the compaction density of the lithium-rich composite material. In some specific embodiments, the particle size D50 of the lithium-rich positive electrode core in the lithium-rich composite material includes but is not limited to 0.1-1 μm, 1-2 μm, 2-4 μm, 4-6 μm, 6-8 μm, 8-9 μm, 10-15 μm, 15-20 μm, 20-24 μm, etc. In some preferred embodiments, the particle size D50 of the lithium-rich positive electrode core is 1-10 μm.

[0034] In some embodiments, the particle size D50 of the metal phosphate coating layer is 0.1-50 nm, and small particle size is conducive to forming a dense and stable metal phosphate coating layer. In some specific embodiments, the particle size D50 of the metal phosphate coating layer includes but is not limited to 0.1-1 nm, 1-5 nm, 5-10 nm, 10 nm-20 nm, 20-30 nm, 30-40 nm, 40-49 nm, etc. In some preferred embodiments, the particle size D50 of the metal phosphate coating layer is 0.1-10 nm.

[0035] In some embodiments, the lithium-rich positive electrode core is a positive electrode material including a spinel structure and a layered structure.

[0036] The lithium-rich composite material of the embodiments of the present application can be prepared by the following embodiment method.

[0037] As shown in FIG. 1, the second aspect of the embodiments of the present application provides a preparation method of a lithium-rich composite material, including the following steps: Figure 1

[0038] S10. Dissolving the phosphorus source and the metal source in water and mixing to generate a composite material with the metal source as the core and the metal phosphate as the shell; wherein the metal element in the metal source is selected from at least one element of Ni, Mn, Cu, and Co;

[0039] S20. Mixing the composite material with the lithium source and then performing sintering treatment to obtain a lithium-rich composite material coated with a metal phosphate shell in situ, and the core of the lithium-rich composite material includes a chemical formula of Li x M y O z A lithium-rich positive electrode material, wherein M is selected from at least one element of Ni, Mn, Cu, and Co, 0

[0040] The preparation method of the lithium-rich composite material provided in the second aspect of the embodiments of the present application dissolves the phosphorus source and the metal source in water, forms a shell layer of metal phosphate on the surface through mixing treatment, and obtains a composite material with the metal source as the core and the metal phosphate as the shell; then mixes the lithium source and performs sintering treatment, and the lithium source reacts with the metal source in the core of the composite material to generate a chemical formula of Li x M y O z ​The lithium-rich positive electrode material is coated with a metal phosphate shell and a lithium-rich positive electrode core in situ to obtain a lithium-rich composite material. The preparation process is simple and suitable for industrial large-scale production and application. The metal phosphate shell and the lithium-rich positive electrode core in the lithium-rich composite material are generated in situ, the coating layer is more compact and uniform, and the combination of the shell and the core is improved. The lithium-rich composite material prepared by the synergistic effect of the metal phosphate shell and the lithium-rich positive electrode core is rich in lithium ions, which can effectively make up for the active lithium source consumed in the first cycle of the lithium-rich composite material, thereby maintaining the capacity and cycle stability of the lithium-rich composite material. The in-situ generated metal phosphate shell reduces the residual alkali degree on the surface of the lithium-rich composite material, improves the gelation phenomenon of the lithium-rich composite material, improves the environmental stability, cycle stability and structural stability of the lithium-rich composite material, prolongs the service and storage life of the lithium-rich composite material, and improves the energy density of the lithium ion battery.

[0041] In some embodiments, in step S10, the phosphorus source and the metal source are dissolved in water, and the metal phosphate shell is coated on the surface of the metal source by mixing treatment to generate a composite material with the metal source as the core and the metal phosphate as the shell. The metal elements in the metal source are selected from at least one element of Ni, Mn, Cu and Co; and the phosphate formed by the metal elements has hydrophobicity.

[0042] In some embodiments, the phosphorus source is selected from at least one of potassium phosphate, sodium phosphate, ammonium phosphate, phosphoric acid, potassium phosphate and sodium dihydrogen phosphate. In some embodiments, the metal source is selected from at least one of oxides, hydroxides, nitrates and carbonates. The above-mentioned phosphorus source and metal source in the embodiments of the present application can react to generate hydrophobic metal phosphate. The metal source can also react with lithium source to generate lithium-rich positive electrode active material.

[0043] In some embodiments, in step S20, after the composite material is mixed with the lithium source, the sintering treatment conditions include sintering in an inert atmosphere at a temperature of 650-900°C for 5-24 hours. During the sintering process, lithium ions in the lithium source can migrate to the core of the composite material at high temperature, and the lithium ions react with the metal in the core of the composite material to generate a chemical formula of Li x M y O zLi2MPO4. The metal phosphate shell layer has high stability and will not react with lithium source in the sintering process, so as to maintain the metal phosphate shell layer, thereby obtaining the lithium-rich composite material of the lithium-rich positive electrode inner core and the metal phosphate coating layer in-situ coated on the outer surface of the lithium-rich positive electrode inner core. For synthesis of the lithium-rich composite material, due to its high activity, it needs to be in an inert atmosphere such as nitrogen, argon, helium, etc. The reaction temperature of 650-900°C and the reaction time of 5-24 hours can make the reaction more sufficient, and the generated lithium-rich composite material product is more uniform. If the reaction temperature is too high and the reaction time is too long, the crystal grains will become large, reducing the rate performance and the compaction density of the lithium-rich composite material.

[0044] In some embodiments, the metal element in the metal phosphate shell layer is the same as the M element in the inner core, which is beneficial to improve the electrochemical stability of the lithium-rich composite material; and is beneficial to in-situ generation of the metal phosphate coating layer, thereby improving the structural stability of the lithium-rich composite material.

[0045] In some embodiments, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium oxide, lithium acetate, and lithium oxalate. The lithium ion of the lithium source can migrate into the inner core of the composite material to react with the metal ion at a high sintering temperature, thereby generating the lithium-rich positive electrode active material of the chemical formula Li x M y O z in-situ at the inner core position.

[0046] In some embodiments, the mass percentage content of the metal phosphate coating layer in the lithium-rich composite material is 1-15%. The mass percentage content can effectively ensure that the coating layer not only reduces the residual alkali degree of the surface of the lithium-rich positive electrode inner core, but also improves the condensate phenomenon of the lithium-rich composite material, and can reduce the sensitivity of the transition metal oxide of the lithium-rich material to environmental moisture, thereby prolonging the use and storage life of the lithium-rich composite material, improving the energy density of the lithium ion battery, and preventing the electrolyte from corroding the internal positive electrode active material, thereby improving the safety and stability of the lithium-rich composite material and improving the cycle stability and structural stability of the material.

[0047] In some embodiments, the particle size D50 of the lithium-rich composite material is 0.1-25 μm. The particle size range can better balance the rate performance and the compaction density of the lithium-rich composite material.

[0048] In some embodiments, the average particle size of the lithium-rich composite material is 0.5-2 μm. The particle size range can better balance the rate performance and the compaction density of the lithium-rich composite material.

[0049] In some embodiments, the specific surface area of the lithium-rich composite material is not less than 0.5 m 2The lithium-rich composite material has a large specific surface area, which is beneficial to balance the rate performance and the compaction density of the lithium-rich composite material, and the high specific surface area provides a larger reaction surface for lithium ion embedding and de-embedding in the charging and discharging process, thereby improving the charging and discharging activity of the lithium-rich composite material.

[0050] In some embodiments, the thickness of the metal phosphate shell layer is 1-500 nm; if the thickness of the metal phosphate coating layer is low, the coating may not be complete, and some areas on the surface may exist or be easily exposed, thereby being not conducive to improving the interface stability and not conducive to improving the electrochemical performance of the lithium-rich composite material; if the thickness of the metal phosphate coating layer is large, the proportion of the metal phosphate coating layer in the lithium-rich composite material is too high, and the proportion of the lithium-rich positive active ingredient in the core is reduced, thereby reducing the specific capacity of the lithium-rich composite material as a whole.

[0051] In some embodiments, the particle size D50 of the core in the lithium-rich composite material is 0.1-25 μm; the lithium-rich positive core with the particle size balances the rate performance and the compaction density of the lithium-rich composite material.

[0052] In some embodiments, the particle size D50 of the particles in the metal phosphate shell layer is 0.1-50 nm, and small particle size particles are conducive to forming a dense and stable metal phosphate coating layer.

[0053] The third aspect of the embodiments of the present application provides a secondary battery, which contains the lithium-rich composite material prepared by the above method or the lithium-rich composite material described above.

[0054] The secondary battery provided by the third aspect of the embodiments of the present application contains the lithium-rich composite material described above, which includes a lithium-rich positive core and a metal phosphate coating layer in-situ coated on the outer surface of the lithium-rich positive core. Through the synergistic effect of the core and the coating layer, the lithium-rich composite material not only contains lithium ions as a positive electrode lithium supplement material to effectively compensate for the active lithium source consumed in the first cycle charging and discharging process of the positive electrode material, but also can cycle and de-embed lithium ions to be directly used as a positive electrode material with high capacity, thereby maintaining the capacity and cycle stability of the lithium-rich composite material. Moreover, the residual alkali degree on the surface of the lithium-rich composite material is reduced, the gelation phenomenon of the lithium-rich composite material is improved, the environmental stability, cycle stability and structural stability of the lithium-rich composite material are improved, and the service and storage life of the lithium-rich composite material is prolonged. Therefore, the energy density, service life, stability and safety of the secondary battery are improved.

[0055] The negative electrode, the separator, the electrolyte and the like of the secondary battery are not specifically limited in the embodiments of the present application, and appropriate material types can be selected according to actual application requirements.

[0056] For the above-mentioned implementation details and operations of the present application to be clearly understood by those skilled in the art, and the embodiment of the present application, the performance of the lithium-rich composite material and its preparation method, and the secondary battery is significantly improved, the following will be illustrated by multiple embodiments.

[0057] Embodiment 1

[0058] A Li2MnO2 / Mn3(PO4)2 lithium-rich composite material includes a Li2MnO2 lithium-rich positive electrode core and a Mn3(PO4)2 coating layer, and its preparation includes the following steps:

[0059] 1. A certain amount of ammonium phosphate is used to treat MnCO3 in deionized water to generate a Mn3(PO4)2 shell layer from part of the Mn source. After filtration and drying at 60°C, a composite material with MnCO3 as the core and a Mn3(PO4)2 shell layer is obtained, wherein the mass percentage of the Mn3(PO4)2 shell layer is 3.5wt%.

[0060] 2. A certain amount of lithium oxide is added to the composite material of step 1, wherein the molar amount of lithium hydroxide is 0.105 mol, and the molar amount of the MnCO3 core in the composite material is 0.1 mol. After mixing uniformly, sintering at 750°C for 10h under a nitrogen atmosphere, a Li2MnO2 / Mn3(PO4)2 lithium-rich composite material is obtained, with Li2MnO2 as the core and a particle size of 1.35μm, Mn3(PO4)2 as the shell layer, a thickness of 15nm, and a mass percentage of the Mn3(PO4)2 shell layer of 3.5wt%.

[0061] Embodiment 2

[0062] A Li2NiO2 / Ni3(PO4)2 lithium-rich composite material includes a Li2NiO2 lithium-rich positive electrode core and a Ni3(PO4)2 coating layer, and its preparation includes the following steps:

[0063] 1. A certain amount of ammonium phosphate is used to treat NiCO3 in deionized water to generate a Ni3(PO4)2 shell layer from part of the Ni source. After filtration and drying at 60°C, a composite material with NiCO3 as the core and a Ni3(PO4)2 shell layer is obtained, wherein the mass percentage of the Ni3(PO4)2 shell layer is 3.5wt%.

[0064] 2. A certain amount of lithium oxide is added to the composite material of step 1, wherein the molar amount of lithium hydroxide is 0.105 mol, and the molar amount of the NiCO3 core in the composite material is 0.1 mol. After mixing uniformly, the Li2NiO2 / Ni3(PO4)2 lithium-rich composite material is obtained by sintering at 750°C for 10 h under a nitrogen atmosphere, wherein Li2NiO2 is the core with a particle size of 1.45 μm, and Ni3(PO4)2 is the shell layer with a thickness of 17 nm, and the mass percentage of the Ni3(PO4)2 shell layer is 3.5 wt%.

[0065] Example 3

[0066] A Li2CuO2 / Cu3(PO4)2 lithium-rich composite material includes a Li2CuO2 lithium-rich positive electrode core and a Cu3(PO4)2 coating layer, and the preparation thereof includes the following steps:

[0067] 1. A certain amount of ammonium phosphate is used to treat CuCO3 in deionized water to form a Cu3(PO4)2 shell layer from part of the Cu source. After filtration and drying at 60°C, a composite material with CuCO3 as the core and a Cu3(PO4)2 shell layer is obtained, wherein the mass percentage of the Cu3(PO4)2 shell layer is 3.5 wt%.

[0068] 2. A certain amount of lithium oxide is added to the composite material of step 1, wherein the molar amount of lithium hydroxide is 0.105 mol, and the molar amount of the CuCO3 core in the composite material is 0.1 mol. After mixing uniformly, the Li2CuO2 / Cu3(PO4)2 lithium-rich composite material is obtained by sintering at 750°C for 10 h under a nitrogen atmosphere, wherein Li2CuO2 is the core with a particle size of 1.40 μm, and Cu3(PO4)2 is the shell layer with a thickness of 16 nm, and the mass percentage of the Cu3(PO4)2 shell layer is 3.5 wt%.

[0069] Example 4

[0070] A Li2MnO2 / Mn3(PO4)2 lithium-rich composite material includes a Li2MnO2 lithium-rich positive electrode core and a Mn3(PO4)2 coating layer, and the difference from example 1 is that the mass percentage of the Mn3(PO4)2 coating layer in the lithium-rich composite material is 1%.

[0071] Example 5

[0072] A Li2MnO2 / Mn3(PO4)2 lithium-rich composite material includes a Li2MnO2 lithium-rich positive electrode core and a Mn3(PO4)2 coating layer, and the difference from example 1 is that the mass percentage of the Mn3(PO4)2 coating layer in the lithium-rich composite material is 5%.

[0073] Example 6

[0074] A Li2MnO2 / Mn3(PO4)2 lithium-rich composite material, comprising a Li2MnO2 lithium-rich positive electrode inner core and a Mn3(PO4)2 coating layer, which is different from example 1 in that the mass percentage content of the Mn3(PO4)2 coating layer in the lithium-rich composite material is 8%.

[0075] Example 7

[0076] A Li2MnO2 / Mn3(PO4)2 lithium-rich composite material, comprising a Li2MnO2 lithium-rich positive electrode inner core and a Mn3(PO4)2 coating layer, which is different from example 1 in that the mass percentage content of the Mn3(PO4)2 coating layer in the lithium-rich composite material is 10%.

[0077] Example 8

[0078] A Li2MnO2 / Mn3(PO4)2 lithium-rich composite material, comprising a Li2MnO2 lithium-rich positive electrode inner core and a Mn3(PO4)2 coating layer, which is different from example 1 in that the mass percentage content of the Mn3(PO4)2 coating layer in the lithium-rich composite material is 15%.

[0079] Example 9

[0080] A Li2MnO2 / Mn3(PO4)2 lithium-rich composite material, comprising a Li2MnO2 lithium-rich positive electrode inner core and a Mn3(PO4)2 coating layer, which is different from example 1 in that the mass percentage content of the Mn3(PO4)2 coating layer in the lithium-rich composite material is 16%.

[0081] Comparative example 1

[0082] A Li2MnO2 lithium-rich positive electrode material, the preparation of which comprises the steps of: mixing 0.1 mol of MnCO3 with 0.105 mol of lithium oxide, uniformly, and then sintering at 750°C for 10 h under a nitrogen atmosphere, to obtain the Li2MnO2 lithium-rich positive electrode material.

[0083] Comparative example 2

[0084] A Li2MnO2 / Mn3(PO4)2 lithium-rich composite material, comprising a Li2MnO2 lithium-rich positive electrode inner core and a Mn3(PO4)2 coating layer, which is different from other examples 1 in that the Mn3(PO4)2 coating layer is not coated on the inner core material by an in-situ coating method, and the preparation of which comprises the steps of:

[0085] 1. Mixing 0.1 mol of MnCO3 with 0.105 mol of lithium oxide, uniformly, and then sintering at 750°C for 10 h under a nitrogen atmosphere, to obtain the Li2MnO2 lithium-rich positive electrode inner core.

[0086] 2. The Li2MnO2 lithium-rich positive electrode core prepared in step 1 is added with 3.5 wt% of Mn3(PO4)2, and then mixed uniformly. The mixture is sintered at 650°C for 5h under a nitrogen atmosphere to obtain a Li2MnO2 / Mn3(PO4)2 lithium-rich composite material.

[0087] Further, in order to verify the progressiveness of the embodiments of the present application, the embodiments and the comparative examples are subjected to the following performance tests:

[0088] 1. The specific surface area BET of the lithium-rich composite materials prepared in the embodiments and the comparative examples is tested respectively, and the test results are shown in Table 1 below:

[0089] Table 1

[0090]

[0091]

[0092] From the test results in Table 1 above, it can be seen that the specific surface areas of the lithium-rich composite materials prepared in the embodiments and the comparative examples are basically consistent, which indicates that the preparation method of the embodiments of the present application reduces the influencing factors on the electrochemical performance test of the prepared lithium-rich composite materials.

[0093] 2. The lithium-rich composite materials prepared in the embodiments and the comparative examples are applied to lithium ion batteries, and the preparation steps of the lithium ion batteries specifically include:

[0094] ① Preparation of positive electrode sheet: the lithium-rich composite materials prepared in the embodiments and the comparative examples are respectively stirred and mixed uniformly with SP (conductive carbon black), PVDF (polyvinylidene fluoride) and NMP (N-methyl pyrrolidone) in a mass ratio of 93.5:2.5:4:100 by using a ball mill stirrer for 2h to obtain a positive electrode slurry; the prepared positive electrode slurry is added to an aluminum foil, uniformly scraped flat by using a doctor blade, dried at 130°C, and then rolled to obtain a positive electrode sheet.

[0095] ② Battery assembly process: the prepared positive electrode is attached to a positive electrode metal shell by using conductive glue, a lithium sheet is used as a negative electrode, a Celgard 2400 microporous membrane is used as a separator, and a 1.0 mol / L LiPF6 solution is used as an electrolyte, wherein the solvent of the electrolyte is a mixed solution of ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) in a volume ratio of 1:1:1, and a button cell is assembled in a glove box.

[0096] ③ The electrochemical performance of each lithium-ion battery assembled above, including the examples or comparative examples, was tested under the following conditions: constant current and constant voltage charging at 0.055C to 4.2V, with a cutoff current of 0.02C; resting for 10 minutes, followed by constant current discharge at 0.055C to 2.0V. Then, constant current and constant voltage charging at 2C to 4.2V was performed, with a cutoff current of 0.02C; resting for 10 minutes, followed by constant current discharge at 2C to 2.0V, for 100 cycles. The test results are shown in Table 2 below:

[0097] Table 2

[0098]

[0099] As shown in Table 2 above, under the test conditions of 0.055C (25℃, 2.0-4.2V), the electrochemical performance of Example 1 is higher than that of Examples 2-3. This is because although the coating layer has the same content, the core material of the lithium-rich composite material is different. Therefore, the initial charge specific capacity of Example 1 can reach 477.3mAh / g, and the capacity retention rate after 100 cycles can also be maintained at 93%. At the same time, through the comparison between Examples 1 and Examples 4-9, it can be seen that when the shell and core materials of the lithium-rich composite material are the same, that is, when the lithium-rich cathode core is Li2MnO2 and the coating layer is Mn3(PO4)2, if the coating layer content is too high, the proportion of the lithium-rich cathode core will decrease, and the increase in coating layer thickness will also increase the difficulty of lithium ion release in the lithium-rich core material, thereby reducing the capacity, lithium replenishment, and cycle performance of the material to a certain extent. In summary, the specific capacity of the lithium-rich composite material of the present invention is much higher than that of comparative examples 1 and 2. This demonstrates that the core-shell structured lithium-rich composite material prepared by in-situ coating method in the embodiments of this application has good structural stability and cycle stability.

[0100] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a lithium-rich composite material, characterized in that, Includes the following steps: A phosphorus source and a metal source are dissolved in water and mixed to generate a composite material with the metal source as the core and a metal phosphate as the shell; wherein the metal element in the metal source is selected from at least one element selected from Ni, Mn, Cu, and Co. The composite material is mixed with a lithium source and then sintered to obtain a lithium-rich composite material with an in-situ coated metal phosphate shell. The core of the lithium-rich composite material comprises a material with the chemical formula Li. x M y O z The lithium-rich cathode material, wherein M is selected from at least one element selected from Ni, Mn, Cu, and Co, 0 < x / y ≤ 3, y > 0, and 0 < z < 6; the lithium-rich cathode core is a cathode material including spinel structure and layered structure, and the metal element in the metal phosphate shell is the same as the M element in the core.

2. The method for preparing the lithium-rich composite material as described in claim 1, characterized in that, The sintering conditions include sintering in an inert atmosphere at a temperature of 650–900°C for 5–24 hours.

3. The method for preparing the lithium-rich composite material as described in claim 1 or 2, characterized in that, The phosphorus source is selected from at least one of potassium phosphate, sodium phosphate, ammonium phosphate, phosphoric acid, and sodium dihydrogen phosphate. And / or, the metal source is selected from at least one of oxides, hydroxides, nitrates, and carbonates; And / or, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium oxide, lithium acetate, and lithium oxalate.

4. The method for preparing the lithium-rich composite material as described in claim 3, characterized in that, In the lithium-rich composite material, the mass percentage of the metal phosphate shell is 1-15%; And / or, the particle size D50 of the lithium-rich composite material is 0.1–25 μm; And / or, the average particle size of the lithium-rich composite material is 0.5–2 μm; And / or, the specific surface area of ​​the lithium-rich composite material is not less than 0.5 m². 2 / g; And / or, the thickness of the metal phosphate shell is 1–500 nm; And / or, in the lithium-rich composite material, the particle size D50 of the core is 0.1 to 25 μm; And / or, the particle size D50 in the metal phosphate shell is 0.1 to 50 nm.

5. The method for preparing the lithium-rich composite material as described in claim 1, characterized in that, In the lithium-rich cathode core, 1≤x / y≤2, 0<z≤4.

6. A lithium-rich composite material, characterized in that, The lithium-rich composite material is prepared by the method according to any one of claims 1 to 5.

7. A secondary battery, characterized in that, The positive electrode of the secondary battery contains a lithium-rich composite material prepared by any one of claims 1 to 5, or a lithium-rich composite material as described in claim 6.

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