Positive electrode active material and preparation method and application thereof

Abstract

The invention relates to a positive electrode active material and a preparation method and application thereof. The positive electrode active material is a layered lithium-rich manganese-based oxide, and comprises a double alkali metal lithium-rich layered structure and an in-situ generated heteroepitaxial structure; wherein the double-alkali metal lithium-rich layered structure is a nano symbiotic structure containing two alkali metal elements, and comprises an R-3m space group structure and a C2 / m space group structure; and the heteroepitaxial structure comprises one or more non-layered space group structures of Fd-3m, Fm-3m and Pbnm. According to the scheme provided by the invention, the positive electrode active material has good mechanical strength and compression resistance, the structural stability and the material compaction density of the positive electrode plate can be improved, the energy density advantage of the lithium-rich manganese-based positive electrode material can be brought into play, the thermal stability of the electrode can be improved, side reactions are reduced, and the service life of the electrode is prolonged. And the electrochemical performance and the energy density of the lithium ion battery are integrally improved.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in consumer electronics such as mobile phones, computers, cameras, electric vehicles, drones, energy storage power stations, and many other fields due to their comprehensive advantages such as high operating voltage, high energy density, long cycle life, low self-discharge, no memory effect, and environmental friendliness. The main components of lithium-ion batteries are positive electrodes, negative electrodes, electrolytes, and diaphragms. The storage and release of energy is achieved in the form of redox reactions of electrode materials, and the positive electrode active material is the most critical core material.

[0003] With the iteration of equipment and facilities such as electric vehicles, electronic products and energy storage devices, the market has put forward higher requirements for the energy density and safety performance of lithium batteries. At present, the common positive active materials are mainly lithium cobalt oxide (LCO), lithium iron phosphate (LFP) and ternary materials (NCM / NCA). Among them, the theoretical capacity of lithium cobalt oxide is about 274mAh / g, but in practical applications it can only reach about 140mAh / g, and its structure is prone to collapse during deep lithium removal, resulting in a decrease in cycle life and thermal runaway; ternary materials are high-nickel materials, which can effectively increase their capacity, but poor thermal stability and structural phase change problems can also easily lead to a decrease in cycle performance; the actual capacity of lithium iron phosphate is close to the theoretical capacity, and there is insufficient room for further optimization. Its energy density can be slightly increased by manganese doping, but the voltage platform is low, the volume energy density is insufficient, and manganese dissolution can also easily lead to a decrease in cycle life. The capacity improvement of these conventional positive active materials has gradually reached a bottleneck, and it is difficult to meet the market demand for lithium metal batteries or solid-state batteries with higher energy density.

[0004] Therefore, how to design, develop and synthesize a new type of positive electrode active material to give full play to its energy density advantages and meet the needs of high energy density lithium-ion batteries. Summary of the invention

[0005] In order to solve or partially solve the problems existing in the related art, the present application provides a positive electrode active material and a preparation method and application thereof. The positive electrode active material has good mechanical strength and compressive resistance, can improve the structural stability and material compaction density of the positive electrode plate, which is not only conducive to the lithium-rich manganese-based positive electrode material to exert its energy density advantage, but also can improve the thermal stability of the electrode, reduce side reactions, and overall improve the electrochemical performance and energy density of lithium-ion batteries.

[0006] In a first aspect, the present application provides a positive electrode active material, which is a layered lithium-rich manganese-based oxide; The positive electrode active material includes a double alkali metal lithium-rich layered structure and an in-situ generated heteroepitaxial structure; wherein the double alkali metal lithium-rich layered structure is a nano-symbiotic structure containing two alkali metal elements, which includes an R-3m space group structure and a C2 / m space group structure; the heteroepitaxial structure includes one or more non-layered space group structures of Fd-3m, Fm-3m, and Pbnm.

[0007] In some embodiments of the present application, the chemical formula of the positive electrode active material is Li[Li x A a Mn y M z N w ]O 2 ; Wherein, A is a metal element of the IA main group except Li, M is one or more metal elements selected from Ni, Co, and Fe, and N is an element other than Li / Mn / M / A; 0<x≤0.35, 0<a≤0.05, 0.4≤y<0.8, 0<z≤0.4, 0<w≤0.08, 1≤y / z≤4, y+z+w=0.8, 1<(1+x) / (y+z+w)≤1.7, 0<w / (y+z+w)<0.1.

[0008] In some preferred embodiments of the present application, N in the positive electrode active material is selected from at least two elements other than Li / Mn / M / A.

[0009] In some preferred embodiments of the present application, N in the positive electrode active material includes B element and at least one element other than Li / Mn / M / A.

[0010] In some preferred embodiments of the present application, N in the positive electrode active material is one or more of B, Mg, Ca, Al, Zr, Y, and La.

[0011] In some embodiments of the present application, the D50 particle size of the positive electrode active material is ≤5 μm.

[0012] In some embodiments of the present application, the specific surface area of ​​the positive electrode active material is ≤1 m² / g.

[0013] In some embodiments of the present application, the residual lithium on the surface of the positive electrode active material is ≤0.18 wt %.

[0014] In some embodiments of the present application, in the X-ray diffraction pattern of the positive electrode active material, the intensity ratio of the (003) to (104) diffraction peaks is greater than 1.2.

[0015] In some embodiments of the present application, the thickness of the heteroepitaxial structure is 1 nm to 30 nm.

[0016] A second aspect of the present application provides a method for preparing a positive electrode active material, which comprises the following steps: 1) dissolving a Li source, a Mn source, an M source, a N source, and an A source in a first solvent to obtain a first solution; 2) adding a second solution to the first solution to react and obtain a precursor solution; the second solution comprises an acid; 3) The precursor solution is subjected to heat treatment to obtain the positive electrode active material including the double alkali metal lithium-rich layered structure and the heteroepitaxial structure.

[0017] In some embodiments of the present application, in step 1), the first solvent includes one or more reagents selected from the group consisting of water, methanol, ethanol, and ethylene glycol.

[0018] In some embodiments of the present application, in the step 1), the concentration of the total solute in the first solution is S1 mol / L, 0.2≤S1≤1.

[0019] In some embodiments of the present application, in step 1), the Li source\Mn source\M source\N source\A source is selected from one or more of halides, hydroxides, nitrates, carbonates, sulfates, acetates, borates, and oxides of the corresponding elements.

[0020] In some embodiments of the present application, in step 2), the acid in the second solution includes one or more of tartaric acid, ascorbic acid, citric acid, acetic acid, oxalic acid, malic acid, and lactic acid.

[0021] In some embodiments of the present application, in the step 2), the concentration of the total solute in the second solution is S2 mol / L, 0.8≤S2≤4.

[0022] In some preferred embodiments of the present application, the concentration of the total solute in the first solution is S1 mol / L, and S1 and S2 satisfy: 1.5≤S2 / S1≤8.

[0023] In some embodiments of the present application, the reaction time in step 2) is 2h~18h.

[0024] In some embodiments of the present application, the step 3) includes: 3.1) drying and grinding the precursor solution to obtain precursor particles; 3.2) heat treating the precursor particles at 200° C. to 1000° C. for 2 h to 10 h to obtain pretreated active particles; 3.3) The pretreated active particles are heat treated at 750° C. to 1050° C. for 15 h to 25 h to obtain positive electrode active particles.

[0025] In some preferred embodiments of the present application, the heat treatment process of step 3.2) is heat treatment at 400°C to 700°C for 4h to 8h; preferably heat treatment at 500°C to 600°C for 5h to 7h; The heat treatment process of step 3.3) is heat treatment at 850°C-1000°C for 18h-23h; preferably heat treatment at 900°C-980°C for 19h-21h.

[0026] A third aspect of the present application provides a positive electrode plate, which includes a positive electrode collector and a positive electrode material layer disposed on the positive electrode collector, wherein the positive electrode material layer includes the above-mentioned positive electrode active material or the positive electrode active material prepared by the above-mentioned preparation method.

[0027] In some embodiments of the present application, the compaction density of the positive electrode sheet is 2.5 g / cm 3 ~ 3.5 g / cm 3 .

[0028] A third aspect of the present application provides a lithium-ion battery, comprising the above-mentioned positive electrode plate.

[0029] A fourth aspect of the present application provides an electrical device or various energy storage systems using batteries as energy storage elements, which include the above-mentioned lithium-ion battery.

[0030] The technical solution provided by this application may have the following beneficial effects: (1) The positive electrode active material of the present application comprises a hexagonal layered structure with a lithium metal ratio of 1:1 and a monoclinic layered structure with a lithium metal ratio greater than 1, as well as a heteroepitaxial surface structure generated in situ thereon. The positive electrode active material with the double alkali metal lithium-rich layered structure as a matrix has dual redox properties of transition metal cations and oxygen anions, can provide a high specific capacity and voltage platform, achieve an energy density of ≥900Wh / kg, and has good mechanical strength and compressive resistance, can alleviate particle breakage during rolling, improve the positive electrode structure stability and compaction density, and enhance the energy density and electrochemical performance of lithium-ion batteries.

[0031] (2) In the positive electrode active material of the present application, the dual alkali metals are simultaneously present at the Li site of the lithium layer, which can expand the lithium layer spacing, improve the lithium ion diffusion rate and kinetic characteristics, and maintain the integrity and stability of the lithium layer structure during the deep delithiation state of the electrochemical reaction, inhibiting the shrinkage and expansion of the unit cell; and the crystal structure is long-range ordered, which can not only alleviate the Li + Uneven embedding and de-embedding behavior avoids stress accumulation caused by lattice distortion, and can effectively reduce structural defect sites, improve the thermal stability of the positive electrode and interface side reactions, comprehensively enhance the energy density and kinetic performance of lithium-ion batteries, reduce the risk of thermal runaway, and improve battery safety.

[0032] (3) The preparation method of the present application uses an acid solution dissociation and complexing ion method to in situ synthesize a micron-sized single crystal double alkali metal lithium-rich manganese-based positive electrode active material having a surface heteroepitaxial structure and a bulk double alkali metal lithium-rich layered structure. The synthesis steps do not require washing, purification, etc., and are simple and easy to operate, which is conducive to large-scale industrial application.

[0033] (4) By strictly controlling the temperature and time conditions of the heat treatment process, the present application makes it easier to form heteroepitaxial structures such as spinel, rock salt phase, olivine, etc. containing elements such as B, Mg, and Al. At the same time, the material can reach the micron level, that is, it has an appropriate particle size, specific surface area, etc., so that it has the characteristics of high energy density, good thermal stability, high structural strength, high compaction density, etc., thereby improving the kinetic performance and cycle performance of the battery.

[0034] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above and other objects, features and advantages of the present application will become more apparent by describing in more detail the exemplary embodiments of the present application in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the present application.

[0036] Figure 1 is the XRD diagram of Example 1 and Comparative Example 1 of the present application; Figure 2 is a SEM image of Example 1 of the present application; Figure 3 is a TEM image of Example 1 of the present application; Figure 4 It is the XPS chart of Example 1 of the present application and the comparative example. DETAILED DESCRIPTION

[0037] To make the present invention easy to understand, the present invention will be described in detail below. However, before describing the present invention in detail, it should be understood that the present invention is not limited to the specific embodiments described. It should also be understood that the terms used herein are only for describing specific embodiments and are not intended to be limiting.

[0038] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0039] Where a numerical range is provided, it is to be understood that each intermediate value between the upper and lower limits of the range and any other provisions or intermediate values ​​in the specified range is encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included in the smaller ranges and are also encompassed within the present invention, subject to any explicitly excluded limits in the specified range. Where a specified range includes one or two limits, the scope excluding any or both of those included limits is also encompassed within the present invention. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically limited.

[0040] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the invention belongs. Although any methods and materials or equivalent methods and materials described herein can also be used in the practice or testing of the present invention, preferred methods and materials are now described.

[0041] With the iteration of equipment and facilities such as electric vehicles, electronic products and energy storage devices, the market has put forward higher demands on the energy density and safety performance of lithium batteries. However, the energy density of traditional lithium-ion batteries is difficult to exceed 400Wh / kg, and the safety risks and raw material costs remain high, which is mainly restricted by the development of positive electrode materials.

[0042] At present, the capacity improvement of conventional positive electrode materials such as lithium cobalt oxide, ternary materials, lithium iron phosphate (manganese), and lithium manganate has gradually reached a bottleneck, and it is difficult to be compatible with high-energy-density lithium metal batteries or solid-state batteries. However, lithium-rich manganese-based positive electrode active materials with dual redox properties of transition metal cations and oxygen anions have good energy density advantages, a specific capacity of more than 250mAh / g, and an operating voltage of 3.6V. The preparation process of lithium-rich manganese-based active positive electrode materials is similar to that of traditional layered positive electrode materials, and the manganese ore required is green, environmentally friendly, and inexpensive. It is expected to become a new generation of positive electrode materials for lithium metal batteries or solid-state batteries.

[0043] Therefore, the key is how to design the element doping ratio and structure of lithium-rich manganese-based positive electrode active materials so that they can achieve good energy density while improving their initial efficiency and cycle life.

[0044] The positive electrode active material provided in the embodiment of the present application is a layered lithium-rich manganese-based oxide, including a double alkali metal lithium-rich layered structure and an in-situ generated heteroepitaxial structure; wherein the double alkali metal lithium-rich layered structure is a nano-symbiotic structure containing two alkali metal elements, including an R-3m space group structure and a C2 / m space group structure; the heteroepitaxial structure includes one or more non-layered space group structures of Fd-3m, Fm-3m, and Pbnm.

[0045] The alkali metals mentioned in this application refer to metal elements in Group IA of the periodic table, which have the characteristics of low density and high reactivity. Their oxides are strongly alkaline when dissolved in water, so they are called "alkali metals", such as lithium, sodium, potassium, rubidium, cesium, and francium.

[0046] The double alkali metal lithium-rich layered structure described in the present application is the bulk structure of the positive electrode active material, that is, the main structure. The lithium metal ratio is the molar ratio between lithium and non-IA group metal elements. The positive electrode active material simultaneously contains a hexagonal layered structure with a lithium metal ratio of 1:1 and a monoclinic layered structure with a lithium metal ratio of >1. The positive electrode active material with the double alkali metal lithium-rich layered structure as the matrix has dual redox characteristics of transition metal cations and oxygen anions, can provide a high specific capacity and voltage platform, and achieve an energy density of ≥900Wh / kg. The double alkali metal is simultaneously present at the Li position of the lithium layer, which can expand the lithium layer spacing, improve the lithium ion diffusion rate and kinetic characteristics, and maintain the integrity and stability of the lithium layer structure when the electrochemical reaction is deeply delithiated, inhibiting the shrinkage and expansion of the unit cell.

[0047] The heteroepitaxial structure described in the present application is the surface part of the positive electrode active material. Among them, the crystal systems stacked in different arrangements such as the spinel phase formed by the Fd-3m space group structure, the rock salt phase formed by the Fm-3m, and the olivine phase formed by the Pbnm can physically isolate the electrolyte and the matrix structure of the positive electrode active material, that is, alleviate the electrolyte from corroding the R-3m space group structure and the C2 / m space group structure of the bulk phase, alleviate the dissolution of transition metal ions and the release of oxygen, improve the structural stability of the positive electrode active material, and thus improve the electrode stability; at the same time, the surface heteroepitaxial structure as a three-dimensional layer can accelerate ion conductivity and electronic conductivity, and provide an appropriate amount of lithium oxygen divacancy on the surface, reduce the lithium ion transition energy barrier and capture the lattice oxygen escaping from the bulk phase, improve the battery cycle stability, and extend the battery cycle life.

[0048] Preferably, the heteroepitaxial structure comprises at least two non-layered space group structures.

[0049] The positive electrode active material in the embodiment of the present application comprises the above-mentioned double alkali metal lithium-rich layered bulk structure and the heteroepitaxial surface structure generated in situ thereon, has good mechanical strength and compressive resistance, can alleviate the particle breakage during the rolling process, improve the positive electrode structure stability and compaction density, and presents a bulk phase long-range ordered crystal structure, which can not only alleviate the Li + Uneven embedding and de-embedding behavior avoids stress accumulation caused by lattice distortion, and can effectively reduce structural defect sites, improve positive electrode thermal stability and interface side reactions, and comprehensively enhance the energy density and electrochemical performance of lithium-ion batteries.

[0050] Furthermore, the heteroepitaxial structure of the positive electrode active material described in the present application is formed by in-situ generation, which can not only reduce the risk of impurity introduction and ensure that it can better exert its advantages of high energy density; but also structurally it is tightly integrated with the double alkali metal lithium-rich layered phase structure, and the elements are evenly distributed, which can alleviate the breakage of the positive electrode active material particles during rolling, improve the stability and compaction density of the positive electrode sheet, thereby effectively reducing the interface impedance, and also has good barrier and ion conduction functions, thereby improving the electrochemical performance of the battery as a whole.

[0051] In some embodiments, the positive electrode active material has the general chemical formula Li[Li x A a Mn y M z N w ]O 2 ; Wherein, A is a metal element of the IA main group except Li, M is one or more metal elements of Ni, Co, and Fe, and N is an element other than Li / Mn / M / A; 0<x≤0.35, 0<a≤0.05, 0.4≤y<0.8, 0<z≤0.4, 0<w≤0.08.

[0052] Specifically, A can be an element such as Na, K, etc.; N can be an element such as B, Mg, Ca, Al, Zr, Y, La, etc.

[0053] In some preferred embodiments, N in the positive electrode active material can be selected from at least two elements other than Li / Mn / M / A; more preferably, it includes B element and at least one element other than Li / Mn / M / A. Specifically, element combinations such as B and Al, B and Mg, B and Ca, and B and Y can be used.

[0054] Furthermore, in the positive electrode active material, Mn element and M element satisfy 1≤y / z≤4, preferably 1.5≤y / z≤3; Li and non-Li elements satisfy 1<(1+x) / (y+z+w)≤1.7, preferably 1.1<(1+x) / (y+z+w)≤1.6, and more preferably 1.15<(1+x) / (y+z+w)≤1.5; Mn, M, and N elements satisfy y+z+w=0.8, and 0<w / (y+z+w)<0.1, preferably 0.001<w / (y+z+w)≤0.03.

[0055] In the embodiment of the present application, by designing the type and stoichiometric ratio of each element in the double alkali metal lithium-rich manganese-based layered positive electrode material, it forms positive electrode active material particles having both a double alkali metal lithium-rich layered bulk phase structure and a heteroepitaxial surface structure, thereby giving full play to the high energy density advantage of the lithium-rich manganese-based positive electrode material.

[0056] In some embodiments, the D50 particle size of the positive electrode active material is ≤5 μm. Further, the positive electrode active material is a micron-sized particle. The D50 particle size refers to the median of the cumulative distribution of 50% of the particle sizes in the sample that is less than or equal to this value.

[0057] In some specific embodiments, the D50 particle size of the positive electrode active material is 0.5-5 μm; 0.9-3 μm; more preferably 1-2.5 μm. For example, the D50 particle size of the positive electrode active material is 5 μm, 4.5 μm, 4 μm, 3.5 μm, 3 μm, 2.5 μm, 2 μm, 1.5 μm, 1 μm, 0.95 μm, etc.

[0058] In the embodiments of the present application, the particle size of the positive electrode active material can reach micrometer level, has good thermal stability, and has good structural strength and compaction density, which can improve the cycle performance of the lithium-ion battery.

[0059] In some embodiments, the specific surface area of ​​the positive electrode active material is ≤1 m² / g; preferably ≤0.9 m² / g; and more preferably 0.2-0.8 m² / g. For example, the specific surface area of ​​the positive electrode active material is 1 m² / g, 0.9 m² / g, 0.8 m² / g, 0.75 m² / g, 0.7 m² / g, 0.65 m² / g, 0.6 m² / g, 0.55 m² / g, 0.5 m² / g, 0.45 m² / g, 0.4 m² / g, 0.35 m² / g, 0.3 m² / g, 0.25 m² / g, 0.2 m² / g, etc.

[0060] In some embodiments, the surface residual lithium of the positive electrode active material is ≤0.18%; preferably ≤0.15%. For example, the surface residual lithium of the positive electrode active material is 0.18%, 0.17%, 0.16%, 0.15%, 0.14%, 0.13%, 0.12%, 0.11%, 0.1%, etc. Among them, the residual lithium refers to the lithium content (mass percentage) attached to the surface of the material particles, mainly in the form of hydroxide and carbonate, which is measured by the hydrochloric acid titration method after mixing with water as specified in GB / T 41704-2022.

[0061] In some embodiments, the thickness of the heteroepitaxial structure is 1 nm to 30 nm. For example, the thickness of the heteroepitaxial structure is 1 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 25 nm, 28 nm, 30 nm, etc.

[0062] In the embodiments of the present application, the particle size, specific surface area, residual lithium and thickness of the heteroepitaxial structure of the positive electrode active material and its surface layer meet the above conditions, and not only have good structural strength, compaction density and rate performance, but also play an auxiliary role in lithium supplementation and improving interface stability, thereby improving battery kinetic performance, improving battery thermal stability, first effect (first coulomb efficiency) and cycle stability, reducing the risk of thermal runaway, and improving battery safety performance.

[0063] In some embodiments, in the X-ray diffraction pattern of the positive electrode active material, the intensity ratio of the (003) to (104) diffraction peaks is greater than 1.2.

[0064] The positive electrode active material of the embodiment of the present application has a highly ordered layered structure, and the diffusion path of lithium ions between layers is unobstructed, which is beneficial to improving the lithium ion transmission efficiency; it can also reduce lattice distortion and irreversible phase change during charging and discharging, inhibit the formation of oxygen vacancies and rock salt phase transition induced by transition metal migration, and evenly distribute stress during high-voltage charging, which can avoid particle cracking and electrolyte side reactions, enhance cycle stability, capacity retention rate, and lithium ion transmission efficiency, improve thermal stability and safety, and reduce the risk of thermal runaway.

[0065] For positive electrode active materials, co-precipitation is usually used for synthesis. The traditional co-precipitation method usually mixes a metal salt solution with a precipitant to generate a precursor, which is then sintered with a lithium salt to obtain a positive electrode active material. However, because lithium-rich manganese-based positive electrode active materials contain a variety of transition metals, it is difficult to synthesize particles with uniform properties using the traditional co-precipitation method. Most of their morphological structures show secondary spherical polycrystalline particles with low thermodynamic stability. The actual compaction density and mechanical strength are low, and the irregular orientation of polycrystalline and the characteristics of polycrystalline boundaries also lead to intercrystalline cracks and intracrystalline cracks caused by volume changes during the electrochemical cycle. These problems are more serious. Therefore, traditional lithium-rich manganese-based positive electrode active materials generally face challenges such as low first-week coulomb efficiency, fast capacity and voltage decay, poor rate performance, and low compaction density, which restricts the development of high energy density and long-life lithium batteries, especially lithium metal batteries or solid-state batteries.

[0066] Therefore, how to quickly synthesize single-crystal lithium-rich manganese-based positive electrode active materials with uniform composition and good crystallographic properties suitable for lithium metal batteries or solid-state batteries is the key to further improving their thermodynamic stability and mechanical strength, thereby increasing the battery's compaction density and upper limit of cycle performance, and bringing out the true energy density advantage of lithium-rich manganese-based positive electrode materials.

[0067] The embodiment of the present application provides a method for preparing a positive electrode active material, which is applicable to the above-mentioned lithium-rich manganese-based positive electrode active material.

[0068] The preparation method comprises the following steps: 1) dissolving a Li source, a Mn source, an M source, a N source, and an A source in a first solvent to obtain a first solution; 2) adding a second solution to the first solution to react and obtain a precursor solution; the second solution comprises an acid; 3) The precursor solution is heat-treated to obtain a positive electrode active material including a double alkali metal lithium-rich layered structure and a heteroepitaxial structure.

[0069] The preparation method of the embodiment of the present application is to in situ synthesize a micron-sized single-crystal double alkali metal lithium-rich manganese-based positive electrode active material having a surface heteroepitaxial structure and a bulk double alkali metal lithium-rich layered structure by a method of acid dissociation and complexing ions. The synthesis steps do not require washing, purification, etc., and are simple and easy to operate, which is conducive to large-scale industrial applications.

[0070] In some embodiments, the Li source, Mn source, M source, N source, and A source mentioned in step 1) can be selected from one or more of halides, hydroxides, nitrates, carbonates, sulfates, acetates, borates, and oxides of the corresponding elements.

[0071] Specifically, the Li source can be selected from Li 2 CO 3 、LiNO 3 , LiAc, LiCl, LiOH or more.

[0072] A in the A source can be a metal element of the IA main group except Li, specifically including Na and K. Further, the A source can be selected from NaCl, KCl, NaNO 3 、KNO 3 、Na 2 CO 3 , K 2 CO 3 , NaAc, KAc, Na 2 B 4 O 7 , K 2 B 4 O 7 One or more compounds in .

[0073] The Mn source can be selected from Mn(NO 3 ) 2 、MnCO 3 、MnCl 2 One or more of .

[0074] In the M source, M can be one or more of Ni, Co, and Fe metal elements. Further, the M source can be selected from Ni(NO 3 ) 2 、Co(NO 3 ) 2、Fe(NO 3 ) 3 、NiCl 2 、CoCl 2 、FeCl 3 One or more of .

[0075] The N in the N source may be other elements other than Li / Mn / M / A. Further, the N source is selected from La(NO 3 ) 3 、Y(NO 3 ) 3 、Zr(NO 3 ) 4 、Al(OH) 3 、Al(NO 3 ) 3 , B 2 O 3 , H 3 BO 3 MgF 2 , CaF 2 One or more of .

[0076] Furthermore, the chemical formula of the synthesized lithium-rich manganese-based positive electrode active material is Li[Li x A a Mn y M z N w ]O 2 Among them, the content of the added Li source satisfies 0<x≤0.35; the content of the added A source satisfies 0<a≤0.05, preferably 0.005<a≤0.02; the content of the added Mn source satisfies 0.4≤y<0.8; the content of the added M source satisfies 0<z≤0.4; and the content of the added N source satisfies 0<w≤0.08. Furthermore, the molar ratio of the added Mn source to the M source is 1≤y / z≤4, preferably 1.5≤y / z≤3; the molar ratio of the added Li source to the non-Li cation is 1<(1+x) / (y+z+w)≤1.7, preferably 1.1<(1+x) / (y+z+w)≤1.6, and more preferably 1.15<(1+x) / (y+z+w)≤1.5; the added Mn source, M source, and N source satisfy the relationship y+z+w=0.8, and 0<w / (y+z+w)≤0.1, preferably 0.001<w / (y+z+w)≤0.03.

[0077] In some embodiments, in step 1), the first solvent includes one or more reagents selected from water, methanol, ethanol, and ethylene glycol; preferably a combination of water and ethanol; more preferably water and ethanol in a volume ratio of 1:2. By adjusting the type and ratio of the first solvent, the degree of ion dissociation will be affected, thereby affecting the dissociation and complexation reaction process and the crystal nucleus growth process, so that the particles synthesized by this method have a long-range ordered layered double alkali metal bulk structure.

[0078] In some embodiments, the concentration of the total solute in the first solution is S1 mol / L, 0.2≤S1≤1, preferably 0.4≤S1≤0.6.

[0079] In some embodiments, the second solution is prepared by dissolving an acid in a first solvent. That is, the second solution comprises an acid and a first solvent, wherein the first solvent comprises one or more reagents selected from water, methanol, ethanol, and ethylene glycol; and the acid comprises one or more selected from tartaric acid, ascorbic acid, citric acid, acetic acid, oxalic acid, malic acid, and lactic acid. Further, in the second solution, the acid concentration is 1 mol / L to 5 mol / L; preferably 1.5 mol / L to 3.5 mol / L. For example, the acid concentration in the second solution may be 1 mol / L, 1.5 mol / L, 1.8 mol / L, 2mol / L, 2.5 mol / L, 3mol / L, 3.5 mol / L, 4 mol / L, 5mol / L, etc.

[0080] In some preferred embodiments, the concentration of the total solute in the second solution is S2 mol / L, and the concentrations of the first solution and the second solution satisfy: 1.5≤S2 / S1≤8, preferably 3≤S2 / S1≤6. The grain formation-growth process is regulated by adjusting the relationship between the concentration of the second solution and the concentration of the first solution, so that the particles synthesized by this method have a long-range ordered layered double alkali metal bulk structure.

[0081] In some embodiments, the reaction time of the first solution and the second solution in step 2) is 2h~18h; preferably 5h~10h. For example, the reaction time of the first solution and the second solution can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 12h, 14h, 15h, 16h, 18h, etc. By adjusting the reaction time, the acid solution dissociates and the complex ions react sufficiently to obtain a lithium-rich manganese-based positive electrode active material that meets the above-mentioned stoichiometric ratio.

[0082] In some embodiments, step 3) specifically includes: 3.1) Drying and grinding the precursor solution to obtain precursor particles; 3.2) heat treating the precursor particles at 200°C to 1000°C for 2h to 10h to obtain pretreated active particles; 3.3) The pretreated active particles are heat treated at 750°C to 1050°C for 15h to 25h to obtain positive electrode active particles.

[0083] In some specific embodiments, the drying in step 3.1) can be performed by evaporation, drying, freeze drying, etc. The D50 particle size of the precursor particles obtained after the grinding treatment is ≤5 μm.

[0084] In some specific embodiments, the heat treatments in steps 3.2) and 3.3) are both performed under air conditions. Preferably, the heat treatment process in step 3.2) is heat treatment at 400°C to 700°C for 4h to 8h; more preferably, heat treatment at 500°C to 600°C for 5h to 7h. Preferably, the heat treatment process in step 3.3) is heat treatment at 850°C to 1000°C for 18h to 23h; more preferably, heat treatment at 900°C to 980°C for 19h to 21h.

[0085] By strictly controlling the temperature and time conditions of the heat treatment process, it is easier to form heteroepitaxial structures such as spinel, rock salt phase, olivine, etc. containing elements such as B, Mg, and Al. At the same time, the material can reach the micron level, that is, it has an appropriate particle size, specific surface area, etc., so that it has high energy density, good thermal stability, high structural strength, high compaction density, etc., and improves the kinetic performance and cycle performance of the battery. If the temperature is too low or the heat treatment time is too short, it is not conducive to the formation of the heteroepitaxial structure of the surface layer; if the temperature is too high or the heat treatment time is too long, the heteroepitaxial structure is obvious, but the particle size is too large, and the electrical properties are poor. The kinetic properties of lithium-rich manganese-based materials are poor, and it is difficult to give full play to the high capacity advantage of lithium-rich manganese-based positive active materials.

[0086] In the embodiment of the present application, the synthesis process of the lithium-rich manganese-based layered positive electrode active material is simple, and no additional washing, purification and other steps are required, which simplifies the preparation process of the traditional single crystal lithium-rich manganese-based positive electrode active material, and the introduced elements are low-cost, reducing pollution and cost, suitable for large-scale production, and have extremely high industrial production application value. In addition, through a reasonable sintering system and temperature system, the problems of poor grain fusion and intercrystalline cracks caused by poor development of single crystals during the synthesis process are alleviated, and micron-sized double alkali metal large single crystal particles with long-range order in the bulk phase and at least one non-layered heteroepitaxial structure on the surface are obtained, which helps to give full play to its real energy density advantage and is conducive to promoting the commercial application of high-performance single crystal lithium-rich materials.

[0087] The positive electrode sheet provided in the embodiment of the present application includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector, wherein the positive electrode material layer includes the positive electrode active material mentioned above or the positive electrode active material prepared by the above preparation method. The positive electrode current collector adopts a conventional metal foil or a composite current collector, such as aluminum foil.

[0088] In some embodiments, the positive electrode material layer is formed by coating the positive electrode slurry on the surface of the positive electrode current collector. The positive electrode slurry includes the above-mentioned positive electrode active material as well as a conductive agent and a binder. The embodiment of the present application does not specifically limit the types of conductive agents and binders, and can be selected according to actual needs. As an example, the conductive agent includes but is not limited to at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; the binder includes but is not limited to polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0089] The positive electrode active material, conductive agent and binder are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to obtain a uniform positive electrode slurry, and then the positive electrode slurry is evenly coated on the positive electrode collector, and the positive electrode sheet is obtained through processes such as drying, rolling and compacting.

[0090] In some embodiments, the compaction density of the positive electrode sheet is 2.5 g / cm 3 ~ 3.5 g / cm 3 Specifically, it can be 2.5 g / cm 3 , 2.6 g / cm 3 , 2.7 g / cm 3 , 2.8 g / cm 3 , 2.9 g / cm 3 、3.0g / cm 3 、3.1 g / cm 3 、3.2g / cm 3 、3.3 g / cm 3 , 3.4 g / cm 3 , 3.5g / cm 3 wait.

[0091] The lithium-ion battery involved in the present application includes the above-mentioned positive electrode plate.

[0092] Lithium-ion batteries also include electrolyte, separator and negative electrode. The negative electrode, separator and positive electrode can be stacked in sequence to form a battery cell through a winding process or a lamination process. The battery cell is loaded into the aluminum-plastic film that has been punched and formed, and the battery cell is baked. Then, the electrolyte is injected into the baked and dried battery cell so that the battery cell is immersed in the electrolyte. Then, vacuum packaging, standing, formation and other processes are performed to complete the preparation of the lithium-ion battery.

[0093] The electrolyte, the isolation membrane and the negative electrode plate can be made of any known materials, and this application does not limit this.

[0094] In some embodiments, the separator described in the present application can be arbitrarily selected from well-known porous structure separators with good chemical stability and mechanical stability. The material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0095] In some embodiments, the electrolyte described in the present application can be selected from electrolytes containing a solvent, an additive, and a lithium salt. Among them, the lithium salt can be selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(oxalate)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)imide, lithium difluoro(oxalato)phosphate, and lithium perchlorate. The concentration of the lithium salt in the electrolyte is 0.9 mol / L to 1.3 mol / L. The solvent can be selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate, and the carboxylic ester solvent can be selected from one or more of ethyl propionate, ethyl acetate, and propyl propionate. The additives can be selected from one or more of ethylene carbonate, vinylene carbonate, ethylene vinyl carbonate, methylene ethylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, and difluoroethylene carbonate. The components can be freely combined, without particular limitation.

[0096] In some embodiments, the negative electrode sheet can be a lithium metal thin sheet. In other embodiments, the negative electrode sheet can also include a negative electrode current collector and a negative electrode material layer provided on the negative electrode current collector. Among them, the negative electrode current collector uses a conventional metal foil or a composite current collector, for example, a copper foil can be used. In some specific embodiments, the negative electrode material layer is formed by coating a negative electrode slurry on the surface of the negative electrode current collector. The negative electrode slurry includes a negative electrode active material, a conductive agent, and a binder. The types of the negative electrode active material, the conductive agent, and the binder are not specifically limited in the embodiments of the present application and can be selected according to actual needs. As an example, the negative electrode active material can be natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO m (0 < m < 2, such as m = 1), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 、spinel-structured lithium titanate Li 4 Ti 5 O 12, Li-Al alloy and metallic lithium; the conductive agent can be one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; the binder can be one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) polyvinyl butyral (PVB), water-based acrylic resin and carboxymethyl cellulose (CMC). The negative electrode sheet can be prepared according to conventional methods in the art. For example, the negative electrode active material, the conductive agent, and the binder are dispersed in a solvent, and the solvent can be N-methylpyrrolidone (NMP) or deionized water to form a uniform negative electrode slurry, and then the negative electrode slurry is coated on the negative electrode current collector, and after drying, rolling, compacting and other processes, the negative electrode sheet is obtained.

[0097] The present application has no particular restrictions on the application fields of lithium-ion batteries, and they can be used in consumer electronics, new energy vehicle-grade energy storage and other fields.

[0098] In order to make the present invention easier to understand, the present invention will be further described in detail below in conjunction with examples, which are merely illustrative and are not intended to limit the scope of application of the present invention. The raw materials or components used in the present invention can be obtained by commercial routes or conventional methods unless otherwise specified.

[0099] Example 1 1) Add 26.4mmol lithium nitrate (LiNO 3 )、Mn source 10.66mmol manganese nitrate (Mn(NO 3 ) 2 )、Source A 0.02 potassium nitrate (KNO 3 )、M source 5.33mmol nickel nitrate (Ni(NO 3 ) 2 ) and N source 0.08mmol aluminum nitrate (Al(NO 3 ) 3 )、0.32mmol boric acid (H 3 BO 3 ) is dissolved in a water / ethanol solvent (volume ratio 1:2) to form a uniformly mixed first solution.

[0100] 2) Dissolve 80mmol of oxalic acid (H 2 C 2 O 4 ) is prepared into a second solution of a uniform mixture of water / ethanol solvent (volume ratio 1:2) with an acid concentration of 2 mol / L.

[0101] 3) The second solution was added dropwise to the first solution, and the mixture was aged for 6 h under magnetic stirring at 500 r / min to obtain a mixed solution.

[0102] 4) Freeze-drying the mixed solution and grinding it thoroughly to obtain precursor particles.

[0103] 5) Sintering the precursor particles in air, heating the temperature from room temperature to 550°C at a rate of 2°C / min and keeping the temperature for 6 hours, then heating the temperature to 950°C at a rate of 1°C / min and keeping the temperature for 20 hours, and then cooling the furnace to room temperature to obtain a micron-sized single crystal lithium-rich manganese-based positive electrode active material with a heteroepitaxial structure.

[0104] Example 2 The preparation method of this embodiment is the same as that of embodiment 1, except that the N source is used. The experimental groups are: Group 2A: Boric acid (H 3 BO 3 ) content was adjusted to 0, and other operations and parameters were the same as those in Example 1; Group 2B: Boric acid (H 3 BO 3 ) content was adjusted to 0.16 mmol, and other operations and parameters were the same as in Example 1; Group 2C: Aluminum nitrate (Al(NO 3 ) 3 ) was removed and 0.08 mmol of yttrium nitrate (Y(NO 3 ) 3 ), other operations and parameters are the same as those in Example 1; Group 2D: Aluminum nitrate (Al(NO 3 ) 3 ) was removed and 0.08 mmol lanthanum nitrate (La(NO 3 ) 3 ), other operations and parameters are the same as in Example 1.

[0105] Example 3 The preparation method of this embodiment is the same as that of embodiment 1, except that the Li source is used. The experimental groups are: Group 3A: Li source is adjusted to lithium nitrate (LiNO 3 ) and lithium carbonate (Li 2 CO 3 ), the molar ratio of the two is 9:0.5, the total content of lithium salt remains unchanged, and other operations and parameters are the same as in Example 1; Group 3B: Li source was adjusted to lithium nitrate (LiNO 3 ) and lithium hydroxide (LiOH), the molar ratio of the two is 9:1, the total content of lithium salt remains unchanged, and other operations and parameters are the same as in Example 1; Group 3C: Li source was adjusted to lithium nitrate (LiNO 3 ) and lithium acetate (LiAc), the molar ratio of the two is 9:1, the total content of lithium salt remains unchanged, and other operations and parameters are the same as in Example 1.

[0106] Example 4 The preparation method of this embodiment is the same as that of embodiment 1, except that the acid component and content in the second solution are different. The experimental groups are: Group 4A: The second solution in step 2) is adjusted to contain oxalic acid (H 2 C 2 O 4 ) is configured into a uniform mixture of water / ethanol (volume ratio 1:2) with a concentration of 1.5 mol / L, and other operations and parameters are the same as those in Example 1; Group 4B: In step 2), the second solution is oxalic acid (H 2 C 2 O 4 ) was adjusted to citric acid (C 6 H 8 O 7 ), other operations and parameters are the same as in Example 1.

[0107] Example 5 The preparation method of this embodiment is the same as that of embodiment 1, except for the type and ratio of solvents in the first solution and the second solution. The experimental groups are: Group 5A: The water / ethanol solvent (volume ratio 1:2) was adjusted to a water / ethanol solvent with a volume ratio of 1:1, and the other operations and parameters were the same as those in Example 1; Group 5B: The water / ethanol solvent (volume ratio 1:2) was adjusted to a water / ethanol / ethylene glycol solvent with a volume ratio of 1:1:1. Other operations and parameters were the same as those in Example 1.

[0108] Example 6 The preparation method of this embodiment is the same as that of embodiment 1, except for the sintering method and temperature regime in step 5). The experimental groups are: Group 6A: the temperature was adjusted from 550°C for 6 hours to 600°C for 8 hours, and the other operations and parameters were the same as those in Example 1; Group 6B: the temperature was adjusted from 550°C for 6 hours to 600°C for 4 hours, and the other operations and parameters were the same as those in Example 1; Group 6C: the temperature at 950°C for 20 h was adjusted to 1000°C for 20 h, and the other operations and parameters were the same as those in Example 1; Group 6D: the temperature at 950° C. for 20 h was adjusted to 900° C. for 20 h, and other operations and parameters were the same as those in Example 1; Group 6E: the temperature was adjusted from 950° C. for 20 h to 950° C. for 25 h. Other operations and parameters were the same as those in Example 1. Group 6F: The temperature was adjusted from 950° C. for 20 h to 950° C. for 15 h. Other operations and parameters were the same as those in Example 1.

[0109] Comparative Example 1 The lithium-rich material precursor (Mn 0.666 Ni 0.334 CO 3 ) and lithium carbonate (Li 2 CO 3 ), potassium nitrate (K 2 CO 3 )、Aluminum hydroxide(Al(OH) 3 ), boric acid (H 3 BO 3 )The solid phase is mixed evenly, wherein the stoichiometric ratio of each element satisfies: Li / (Mn+Ni)=1.5, K / (Mn+Ni)=0.0025, Al / (Mn+Ni)=0.005, B / (Mn+Ni)=0.01. The mixed material is sintered in air, the temperature is raised from room temperature to 510°C at a rate of 2°C / min for 6 hours, and then raised to 910°C at a rate of 1°C / min for 20 hours, and then cooled to room temperature with the furnace to obtain a lithium-rich manganese-based positive electrode active material with the same chemical composition as Example 1. (Conventional coprecipitation-solid phase sintering method without acid treatment) Comparative Example 2 The preparation method of this comparative example is the same as that of comparative example 1, except that potassium nitrate (K 2 CO 3 ).

[0110] Comparative Example 3 The preparation method of this comparative example is the same as that of comparative example 1, except that the boric acid (H 3 BO 3 ).

[0111] Comparative Example 4 The preparation method of this comparative example is the same as that of comparative example 1, except that the aluminum hydroxide (Al(OH) 3 ).

[0112] Physical and chemical properties test The physical and chemical properties of the lithium-rich manganese-based materials prepared in the above examples and comparative examples were tested, and the test results are shown in Table 1.

[0113] 1) Particle size detection: GB / T 19077-2016 (laser diffraction method) 2) Specific Surface Area (SSA) test: GB / T 19587-2017 (gas adsorption method) 3) Residual lithium detection: GB / T 41704-2022 (potentiometric titration method) Table 1

[0114] Combined with the attached analysis: The lithium-rich manganese-based positive electrode active materials of Example 1 and Comparative Example 1 were subjected to X-ray diffraction (XRD) detection, scanning electron microscope (SEM) detection, transmission electron microscope (TEM) detection and X-ray photoelectron spectroscopy (XPS) detection, and the detection results are shown in the accompanying drawings.

[0115] in, Figure 1 The XRD test results of the lithium-rich manganese-based positive electrode active materials of Example 1 and Comparative Example 1 are shown; Figure 2 This is a SEM test result diagram of the lithium-rich manganese-based positive electrode active material of Example 1; Figure 3 This is a TEM test result diagram of the lithium-rich manganese-based positive electrode active material of Example 1; Figure 4 This is a graph showing the XPS test results of the lithium-rich manganese-based positive electrode active materials of Example 1 and Comparative Example 1.

[0116] Combination Figure 1 , indicating that the obtained material shows a composite diffraction peak of lithium-rich material with a hexagonal layered structure of the R-3m space group and a monoclinic layered structure of the C2 / m space group, and (003) / (104)>1.2, and the splitting peaks related to (006) / (102) and (108) / (110) are obvious, indicating that the degree of cation mixing of the material is weak and the layered structure is orderly; combined with Figure 1 , Figure 2 and Figure 3 , indicating that the obtained material is a long-range ordered single crystal material at the micrometer scale, the bulk phase is successfully calibrated as a layered structure, and there is a Fd-3m space group spinel phase heteroepitaxial structure with a thickness of about 10nm on the surface; combined with Figure 4 , indicating that the surface oxygen vacancies of the obtained material increased, the surface residual alkali decreased, and the lattice oxygen redox reversibility and interface side reactions were regulated.

[0117] From the test results of the combined drawings and Table 1, it can be seen that the lithium-rich manganese-based positive electrode active material synthesized by the method of the embodiment of the present application is a large single crystal material of several hundred nanometers to micrometers with a size of ≤5μm, and has a clear and ordered layered structure, a suitable specific surface area (specific surface area is basically ≤1 m² / g) and residual lithium on the surface (residual lithium ≤0.18%), which can give full play to its advantages of high energy density and can regulate electrochemical performance.

[0118] The positive electrode active materials prepared in the above embodiments and comparative examples were made into positive electrode sheets, and lithium ion batteries were made with negative electrode sheets, electrolytes, separators, etc. The electrochemical performance of the lithium ion batteries was tested to observe the effect of the positive electrode active materials on the electrochemical performance of the batteries.

[0119] Application Examples The positive electrode active material prepared by the method of the above embodiment and comparative example is mixed with the conductive agent acetylene black and the binder PVDF (polyvinylidene fluoride) in a mass ratio of 8:1:1, and fully stirred and mixed in N-methylpyrrolidone solvent to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector Al foil, and then cut into positive electrode sheets with a diameter of 12 mm after drying, rolling, compacting and other processes.

[0120] Then, the above positive electrode is matched with a lithium metal sheet as the negative electrode and a microporous single-layer polypropylene PP film as a separator containing 1.2M LiPF 6 EC / EMC / DMC (volume ratio 1:2:2) solution was used as the electrolyte and button cells were assembled in an argon-filled glove box.

[0121] Electrochemical performance test In a (30±2)℃ constant temperature box, the lithium-ion battery was charged at 0.1C constant current and constant voltage to a cut-off voltage of 4.8V, and a cut-off current of 0.05C, and then discharged at 0.1C constant current and constant voltage to a cut-off voltage of 2V, and the first week coulomb efficiency % and reversible specific capacity (charge specific capacity mAh / g, discharge specific capacity mAh / g) of the positive electrode sheet with different compaction densities were tested. The test results are shown in Table 2.

[0122] Table 2

[0123] The test data of the embodiment show that the first-week reversible specific capacity of embodiment 1 is as high as 253.4 mAh / g, which is much higher than 234.9 mAh / g of comparative example 1, and the first-week coulombic efficiency is increased from 78.9% of comparative example 1 to 82.2%. 3 Under the same conditions, the reversible specific capacity of Example 1 is 267.8 mAh / g, and the energy density is nearly 960 Wh / kg; however, after the compaction density of Comparative Example 1 is increased, the battery charging and discharging is abnormal, which may be caused by polarization and other reasons; after the compaction density of Comparative Example 2 is increased, the battery charging and discharging is also abnormal; Comparative Examples 3 and Comparative Examples 4 are increased to 3.0 or 3.5 g / cm 3 It shows abnormal charge and discharge, and cannot withstand higher density compaction. It can be seen that Comparative Examples 1, 2, 3, and 4 cannot achieve the high energy density target of 960Wh / kg, and the compaction density cannot meet the requirements.

[0124] The test data of Example 1, Example 2 and Comparative Examples 1 to 4 show that after adjusting the N source of the lithium-rich manganese-based positive electrode material, the positive electrode active material prepared by the acid solution dissociation and complexation and two-stage high-temperature sintering method of the embodiment of the present application still has a high energy density; especially when the N source contains two or more elements other than Li / Mn / M / A, and one of them is element B, it has a better energy density advantage.

[0125] The test data of Example 1, Example 2, Example 3, Example 4, and Example 5 show that by using the Li source, N source, M source, A source, acid solution, and solvent specified in the embodiments of the present application, a lithium-rich manganese-based layered positive electrode material with a double alkali metal lithium-rich layered structure and a heteroepitaxial structure can be achieved, and the structural stability and compaction density are high, which can give full play to the material's true high energy density advantages and cycle performance.

[0126] The test data of Example 1 and Example 6 show that the sintering method and temperature system defined in the present application are conducive to the formation of bulk double alkali metal lithium-rich layered structure and surface heteroepitaxial structure.

[0127] The micron-sized large single crystal particles prepared by the embodiment of the present application have good mechanical strength and compressive resistance, can alleviate the particle breakage during rolling, improve the structural stability and compaction density, and are conducive to the lithium-rich manganese-based positive electrode material to exert the real energy density advantage and obtain a high-performance lithium-ion battery with high energy density and high electrochemical performance.

[0128] It should be noted that the embodiments described above are only used to explain the present application and do not constitute any limitation to the present application. The present application is described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present application may be modified as specified within the scope of the claims of the present application, and the present application may be revised without departing from the scope and spirit of the present application. Although the present application described therein relates to specific methods, materials and embodiments, it does not mean that the present application is limited to the specific examples disclosed therein. On the contrary, the present application can be extended to all other methods and applications with the same functions.

Claims

1. A positive electrode active material, characterized in that: The positive electrode active material is a layered lithium-rich manganese-based oxide, and the positive electrode active material includes a double alkali metal lithium-rich layered structure and an in-situ generated heteroepitaxial structure; The double alkali metal lithium-rich layered structure is a nano-symbiotic structure containing two alkali metal elements, which includes an R-3m space group structure and a C2 / m space group structure; The heteroepitaxial structure comprises one or more non-layered space group structures of Fd-3m, Fm-3m, and Pbnm.

2. The positive electrode active material according to claim 1, characterized in that The chemical formula of the positive electrode active material is Li[Li x A a Mn y M z N w ]O2; wherein A is a metal element of the IA main group except Li, M is one or more metal elements selected from Ni, Co, and Fe, and N is an element other than Li / Mn / M / A; 0<x≤0.35, 0<a≤0.05, 0.4≤y<0.8, 0<z≤0.4, 0<w≤0.08, 1≤y / z≤4, y+z+w=0.8, 1<(1+x) / (y+z+w)≤1.7, 0<w / (y+z+w)<0.

1.

3. The positive electrode active material according to claim 2, characterized in that The N in the positive electrode active material is selected from at least two elements other than Li / Mn / M / A.

4. The positive electrode active material according to claim 3, characterized in that In the positive electrode active material, N includes B element and at least one element other than Li / Mn / M / A.

5. The positive electrode active material according to claim 2, characterized in that The N in the positive electrode active material is one or more of B, Mg, Ca, Al, Zr, Y, and La.

6. The positive electrode active material according to claim 1, characterized in that The D50 particle size of the positive electrode active material is ≤5 μm; And / or, the specific surface area of ​​the positive electrode active material is ≤1m² / g; And / or, the surface residual lithium of the positive electrode active material is ≤0.18%; and / or, in the X-ray diffraction pattern of the positive electrode active material, the intensity ratio of the (003) to (104) diffraction peaks is greater than 1.2; And / or, the thickness of the heteroepitaxial structure is 1 nm to 30 nm.

7. A method for preparing a positive electrode active material, characterized in that: The method comprises the following steps: 1) dissolving a Li source, a Mn source, an M source, a N source, and an A source in a first solvent to obtain a first solution; 2) adding a second solution to the first solution to react and obtain a precursor solution; the second solution comprises an acid; 3) heat-treating the precursor solution to obtain the positive electrode active material comprising a double alkali metal lithium-rich layered structure and a heteroepitaxial structure as claimed in any one of claims 1 to 6.

8. The preparation method according to claim 7, characterized in that: In the step 1), the first solvent includes one or more reagents selected from water, methanol, ethanol, and ethylene glycol; and / or, the concentration of the total solute in the first solution is S1 mol / L, 0.2≤S1≤1; And / or, the Li source\Mn source\M source\N source\A source is selected from one or more of halides, hydroxides, nitrates, carbonates, sulfates, acetates, borates and oxides of the corresponding elements.

9. The preparation method according to claim 7, characterized in that: In step 2), the acid in the second solution includes one or more of tartaric acid, ascorbic acid, citric acid, acetic acid, oxalic acid, malic acid, and lactic acid; and / or, the concentration of total solute in the second solution is S2 mol / L, 0.8≤S2≤4; And / or, the reaction time in step 2) is 2h~18h.

10. The preparation method according to claim 9, characterized in that: The concentration of total solute in the first solution is S1 mol / L, and S1 and S2 satisfy: 1.5≤S2 / S1≤8.

11. The preparation method according to claim 7, characterized in that: The step 3) comprises: 3.1) drying and grinding the precursor solution to obtain precursor particles; 3.2) heat treating the precursor particles at 200° C. to 1000° C. for 2 h to 10 h to obtain pretreated active particles; 3.3) The pretreated active particles are heat treated at 750° C. to 1050° C. for 15 h to 25 h to obtain positive electrode active particles.

12. The preparation method according to claim 11, characterized in that: The heat treatment process of step 3.2) is heat treatment at 400°C to 700°C for 4h to 8h; The heat treatment process of step 3.3) is heat treatment at 850°C~1000°C for 18h~23h.

13. The preparation method according to claim 12, characterized in that: The heat treatment process of step 3.2) is heat treatment at 500°C to 600°C for 5h to 7h; The heat treatment process of step 3.3) is heat treatment at 900°C~980°C for 19h~21h.

14. A positive electrode sheet, characterized in that: It comprises a positive electrode current collector and a positive electrode material layer arranged on the positive electrode current collector, wherein the positive electrode material layer comprises the positive electrode active material according to any one of claims 1 to 6 or the positive electrode active material prepared by the preparation method according to any one of claims 7 to 13.

15. The positive electrode sheet according to claim 14, characterized in that: The compaction density of the positive electrode sheet is 2.5 g / cm 3 ~ 3.5 g / cm 3 .

16. A lithium ion battery comprising the positive electrode sheet according to claim 14 or 15.

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