Cobalt-free lithium-rich manganese-based positive electrode material and preparation method therefor

Abstract

Disclosed in the present application is a preparation method for a cobalt-free lithium-rich manganese-based positive electrode material. The preparation method comprises: mixing a nickel manganese hydroxide precursor with a lithium source, adding a zinc additive and a fluorine additive thereto, and uniformly mixing same to obtain a premixed material; and heating the premixed material to a first calcination temperature for calcination in an oxidizing gas atmosphere, then continuously heating the premixed material to a second calcination temperature for calcination, and after naturally cooling same, obtaining a cobalt-free lithium-rich manganese-based positive electrode material. Further disclosed in the present application is a cobalt-free lithium-rich manganese-based positive electrode material obtained by means of the preparation method. In the present application, Zn-ion lithium site and transition metal site double-site doping and F-ion oxygen site doping are used, such that the first coulombic efficiency is improved, lithium ion transport is promoted, and the rate capability and cycle performance of the material are improved; in addition, expensive and harmful cobalt is removed, thereby preparing the cobalt-free lithium-rich manganese-based positive electrode material by means of a simple solid-phase sintering method. The process flow is simple, the production cost is low, and industrialization is easier to achieve.

Description

A cobalt-free lithium-rich manganese-based positive electrode material and its preparation method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on May 29, 2023, with application number 202310617862.8 and invention name “A cobalt-free lithium-rich manganese-based positive electrode material and its preparation method”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This patent application belongs to the field of lithium-ion battery positive electrode materials, and specifically relates to a cobalt-free lithium-rich manganese-based positive electrode material and its preparation method. Background Art

[0004] Layered lithium-rich manganese-based materials (LMR) are expected to become the cathode materials for the next generation of lithium-ion batteries due to their high specific capacity (>250mAh / g) and low cost. Although it has been nearly 30 years since the discovery of this material, it has never been truly commercialized. The main reasons include: During the cycle, Mn 3+ Migration into lithium vacancies causes the layered structure to transform into a spinel structure, resulting in a continuous decrease in the average discharge voltage, causing serious energy loss and posing huge challenges to battery management; the low electronic conductivity of Li2MnO3 makes the LMR material have poor rate performance; the lower electrode density results in a low volume energy density of the material; in addition, LMR materials need to be at high voltage (>4.55V) to exert high capacity, but the electrolyte is easily oxidized and decomposed at high voltage, accompanied by the oxidation of lattice oxygen to O2 escape. The above problems have seriously affected its commercialization process.

[0005] In addition, due to the high price and toxicity of Co, unlike Ni and Mn, which are abundant and inexpensive in my country, the development of low-cobalt and cobalt-free cathode materials has been promoted. Therefore, cobalt-free lithium-rich manganese-based cathode materials have received widespread attention. However, their application is currently limited by many defects such as low initial charge and discharge coulombic efficiency, poor rate performance, and long-cycle voltage decay. In order to improve the defects of cobalt-free lithium-rich manganese-based materials, the process of improving material stability by means of ion doping and surface coating has become relatively mature. Traditional element doping, surface coating, and liquid or gas phase post-treatment all have a certain effect on improving the electrochemical performance of LMR materials, but the improvement effect produced by different modification methods will vary. At present, a single modification method still cannot fundamentally solve the problems faced by LMR materials. Therefore, it is necessary to adopt a combination of multiple modification methods and develop new structures (such as single crystal structure, composite structure, composition regulation and gradient structure, etc.) to solve the problems faced by LMR materials.

[0006] Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O2 lithium-rich layered positive electrode material, the results show that Zn doping is beneficial to improving the structural stability of the material, and at the same time, the lower charge and discharge resistance improves the reaction kinetics, which enables the material to have good cycle performance, but due to the cumbersome process of the co-precipitation method, the industrial production is difficult and it is difficult to achieve industrial application. Chinese patent document CN112701273A discloses a method for preparing a fluorine-doped lithium-rich manganese-based positive electrode material, the preparation method comprising the following steps: using a soluble metal salt, a precipitant, a soluble fluorine-containing compound and water to prepare a fluorine-doped lithium-rich manganese-based precursor by precipitation reaction; the fluorine-doped lithium-rich manganese-based precursor is uniformly mixed with a lithium salt, and a fluorine-doped lithium-rich manganese-based positive electrode material can be obtained by pre-burning and high-temperature sintering. This method performs fluorine doping in the precursor preparation stage, and the doping uniformity is good, which can improve the cycle performance of the lithium-rich layered oxide material to a certain extent, but the first coulomb efficiency is low, which is significantly lower than that of the unmodified sample. Single fluorine doping cannot effectively suppress the loss of irreversible capacity in the first cycle. Chinese patent document CN114420920A discloses a fluorine ion gradient-doped lithium-rich manganese-based cathode material, its preparation method, and application, comprising the following steps: A. preparing the lithium-rich manganese-based cathode material according to existing methods; B. dissolving a fluoride salt in a solvent, then adding the lithium-rich manganese-based cathode material with stirring and ultrasonically dispersing it; C. grinding and evaporating the resulting powder to dryness, and then transferring the resulting powder to a muffle furnace for calcination at a temperature of 250-350°C for 3-4 hours. This application directly performs a secondary treatment on the lithium-rich manganese-based bulk material, coating the particle surface with fluorine to obtain a modified material with a fluorine gradient doping from the particle surface to the interior. However, the gradient doping is achieved only on the surface of the particles, leaving the interior of the particles unmodified. As the charge and discharge cycles proceed, the electrolyte gradually infiltrates the interior, or the particles break, exposing the unmodified interior to the electrolyte. This can cause various complex side reactions, which can affect the electrochemical performance.

[0007] Summary of the Invention

[0008] Therefore, the technical problem to be solved by this application is that the existing technology uses a co-precipitation method to prepare lithium-rich manganese-based positive electrode materials, which requires adjusting conditions such as pH, temperature, reaction rate, etc., and the process is complicated and difficult to industrialize, as well as the defects of using a single element doping in the existing technology, thereby providing a cobalt-free lithium-rich manganese-based positive electrode material and a preparation method thereof.

[0009] In order to solve the above technical problems, the technical solutions adopted in this application are as follows:

[0010] The present application provides a method for preparing a cobalt-free lithium-rich manganese-based positive electrode material, comprising the following steps:

[0011] S1: After mixing the nickel manganese hydroxide precursor with the lithium source, a zinc element additive and a fluorine element additive are added and mixed evenly to obtain a premixed material;

[0012] S2: heating the premixed material to a first calcination temperature in an oxidizing gas atmosphere, then continuing to heat the premixed material to a second calcination temperature, and then naturally cooling the premixed material to obtain the cobalt-free lithium-rich manganese-based positive electrode material.

[0013] Furthermore, in step S2, the specific calcination is to heat the temperature to 450°C to 550°C at a heating rate of 2 to 5°C / min and pre-calcine for 4 to 6 hours, and then heat the temperature to 800°C to 950°C at a heating rate of 2 to 5°C / min and calcine for 8 to 12 hours.

[0014] In step S1, the ratio of the amount of lithium element substance in the lithium source to the sum of the amount of nickel and manganese element substances in the nickel manganese hydroxide precursor is 1.1 to 1.6:1;

[0015] The mass of the zinc element additive is 0.08-1% of the mass of the nickel manganese hydroxide precursor;

[0016] The mass of the fluorine element additive is 0.1-1% of the mass of the nickel manganese hydroxide precursor.

[0017] The nickel manganese hydroxide precursor has a chemical formula of Ni y Mn 1-y (OH)2,0 <y≤0.5。

[0018] Optionally, the specific surface area of ​​the nickel manganese hydroxide precursor is 20m 2 / g~30m 2 / g, tap density is 1.0g / cm 3 ~1.5g / cm 3 , the median particle size D50 is 3~7μm.

[0019] The lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate;

[0020] The zinc element additive includes at least one of zinc oxide, zinc carbonate, and zinc acetate;

[0021] The fluorine element additive includes lithium fluoride.

[0022] The oxidizing gas is air or oxygen.

[0023] The present application also provides a cobalt-free lithium-rich manganese-based positive electrode material, which is prepared by the above preparation method.

[0024] The technical solution of this application has the following advantages:

[0025] (1) The present application adopts dual-site doping of Zn ions at the lithium site and transition metal site and F ion oxygen site, and reduces the release of irreversible oxygen in the first cycle through multi-site doping, thereby improving the first coulombic efficiency; reduces the internal resistance of charge and discharge, promotes lithium ion transmission, and improves the rate performance of the material; inhibits the transformation from layered to spinel to stabilize the lattice structure, improves the voltage attenuation during the cycle, and improves the cycle performance of the material; at the same time, removes expensive and harmful cobalt and prepares a cobalt-free lithium-rich manganese-based positive electrode material by a simple solid-phase sintering method. The process flow is simple, the production cost is low, and it is easier to achieve industrialization.

[0026] (2) This application uses solid phase sintering to 2+ Cation doping into the transition metal layer, due to Zn 2+ radius Greater than Ni 2+ With Mn 4+ radius, the interlayer spacing increases after doping, the unit cell volume increases, and the expansion of the lattice can provide more lattice space for lithium intercalation and deintercalation, promote the insertion and extraction of lithium ions, reduce the Rct of the active electrode, promote the charge transfer reaction in the active electrode, reduce the charge and discharge resistance, and improve the rate performance of the positive electrode material; at the same time, Zn2+ with a large radius does not participate in the valence change reaction, plays a supporting role between the layers, stabilizes the layered structure and improves the structural stability, and the electrochemical performance is manifested as an improvement in the cycle performance; in addition, some Zn 2+ Irreversibly inserted into the lithium site of the lithium-rich manganese-based cathode material, the Li + Zn 2+ Selectively replacing, the formation of Zn-O bonds with stronger bond energy than Li-O bonds can inhibit the formation of Li + and O2 are separated from the Li2MnO3 component, while Zn 2+ Doping does not reduce the reversible capacity of lithium-rich manganese-based cathode materials. During the cycle, Zn 2+ The cation disorder and electrolyte decomposition are reduced, thus improving the cycle stability. 2+ The dual-site doping at the transition metal site and the lithium site works together to improve the rate performance and cycle performance of the lithium-rich positive electrode material.

[0027] F -As a commonly used doping ion in positive electrode materials, it is often used to replace oxygen ions in materials. The chemical bond strength between F and transition metals is much greater than the chemical bond strength formed by other anions and transition metals. After F replaces part of O, it can alleviate the transformation of the layered structure on the surface of the material to the spinel structure, improve the voltage attenuation during the cycle, and improve the cycle performance of the material. At the same time, F doping can form a more stable SEI layer to improve Li + The diffusion rate is increased, the dissolution of transition metals is reduced, and the internal resistance during the cycle is lowered, which significantly improves the cycle stability of lithium-rich manganese-based positive electrode materials.

[0028] It can be seen that the action mechanisms of Zn and F are different. Zn is doped into the lithium site and transition metal site, and F is doped into the oxygen site. The synergistic effect brought about by the doping of the two elements at different sites can jointly improve the electrochemical performance of lithium-rich manganese-based materials. Therefore, the synergistic effect of multi-site doping of Zn and F anions and cations can effectively improve the comprehensive performance of lithium-rich manganese-based positive electrode materials. Zn doping into positive electrode materials mainly replaces lithium ions and transition metal ions, and F doping replaces oxygen ions. Since the bond energy between Zn and anions is significantly greater than the bond energy between Ni and Mn transition metals and anions, and the bond energy between F and transition metals is greater than the bond energy between O and transition metals, and the binding force brought about by the single doping of Zn or F is much smaller than that of Zn and F co-doping, the co-doping of Zn and F has a more obvious effect on stabilizing the structure of the positive electrode material, increasing the interlayer spacing, reducing irreversible oxygen redox, and improving the electrochemical performance.

[0029] (3) When Zn and F are doped at the same time, it will be difficult for Zn and F ions to enter the lattice structure of the material. Therefore, the present application adopts a specific heating rate. During high-temperature solid-phase sintering, Zn and F ions can more effectively attack lithium, transition metal and oxygen sites. At the same time, using an excessively fast heating rate is not conducive to eliminating the thermal stress in the positive electrode material, thereby inducing an increase in intrinsic microstructural defects (such as point defects or even dislocations). The oxygen vacancy concentration in the bulk phase of the lithium-rich manganese-based material will increase, and the loss of lattice oxygen will increase, resulting in a decrease in the orderliness of the material structure. The structural stability of the positive electrode material will deteriorate during the electrochemical deintercalation of lithium, thereby affecting the cycle life of the battery. A too slow heating rate will significantly increase the sintering time, which will also increase the bulk oxygen vacancy concentration and the loss of lattice oxygen, inducing the irreversible transformation of the material from a layered structure to a spinel phase, resulting in a decrease in the crystal structure and cycle life of the lithium-rich manganese-based positive electrode material. In addition, an excessively long sintering time will increase the sintering cost.

[0030] (4) The present application adopts a gradient sintering method to prepare positive electrode materials. The purpose of pre-calcining at a temperature of 450°C to 550°C is to dehydrate and decompose nickel manganese hydroxide and lithium salt to form oxides, so that they can react more fully in the subsequent high-temperature stage to prevent the stability of the crystal structure of the positive electrode material from deteriorating. The calcination temperature is set at 800°C to 950°C. A lower calcination temperature will lead to insufficient reaction, which is not conducive to the formation of a layered structure of the material, while an excessively high sintering temperature will lead to impure phases in the material structure. XRD shows that spinel phase and Mn3O4 impurity phase are generated between 2θ=42° to 44° and between 62° to 65°. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0032] FIG1 is an electron microscope photograph of the cobalt-free lithium-rich manganese-based positive electrode material obtained in Example 2;

[0033] FIG2 is an XRD spectrum of the cobalt-free lithium-rich manganese-based positive electrode materials obtained in Example 2 and Comparative Example 1;

[0034] FIG3 is an XRD spectrum of the cobalt-free lithium-rich manganese-based positive electrode material obtained in Comparative Example 6;

[0035] FIG4 is a graph showing the capacity retention rate of batteries made from the positive electrode materials of Example 2 and Comparative Example 1 after 50 cycles. DETAILED DESCRIPTION

[0036] The following examples are provided to further better understand the present application, but are not limited to the best implementation mode described herein, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the scope of protection of the present application.

[0037] If no specific experimental steps or conditions are specified in the examples, the experiments can be carried out according to the conventional experimental steps or conditions described in the literature in the art.

[0038] Example 1

[0039] This embodiment provides a cobalt-free lithium-rich manganese-based positive electrode material, and the specific preparation method is as follows:

[0040] (1) According to the amount of lithium element in the lithium source and Ni 0.33 Mn0.67 The ratio of the sum of the amounts of nickel and manganese in the (OH)2 precursor is 1.35. 0.33 Mn 0.67 (OH)2 precursor and lithium carbonate, where Ni 0.33 Mn 0.67 The specific surface area of ​​the (OH)2 precursor is 23m 2 / g, and the tap density is 1.35g / cm 3 , the median particle size D50 is 4.2μm, and the mass is weighed as Ni 0.33 Mn 0.67 0.2% of the mass of the (OH)2 precursor ZnO and 0.2% of the mass of the nickel manganese hydroxide precursor LiF are mixed uniformly using a high-speed mixer to obtain a premixed material;

[0041] (2) The premixed material was heated to 450°C in a box furnace at a heating rate of 2°C / min and pre-calcined for 5 h, then heated to 950°C at a heating rate of 5°C / min and calcined at high temperature for 9 h. The sintering atmosphere was compressed air with an air flow rate of 4 L / min. The material was naturally cooled to room temperature and sieved through a 325-mesh sieve to obtain a cobalt-free lithium-rich manganese-based positive electrode material co-doped with zinc and fluorine.

[0042] Example 2

[0043] This embodiment provides a cobalt-free lithium-rich manganese-based positive electrode material, and the specific preparation method is as follows:

[0044] (1) According to the amount of lithium element in the lithium source and Ni 0.33 Mn 0.67 The ratio of the sum of the amounts of nickel and manganese in the (OH)2 precursor is 1.35. 0.33 Mn 0.67 (OH)2 precursor and lithium carbonate, where Ni 0.33 Mn 0.67 The specific surface area of ​​the (OH)2 precursor is 23m 2 / g, and the tap density is 1.35g / cm 3 , the median particle size D50 is 4.2μm, and the mass is weighed as Ni 0.33 Mn 0.67 0.3% of the mass of the (OH)2 precursor ZnO and 0.25% of the mass of the nickel manganese hydroxide precursor LiF are mixed uniformly using a high-speed mixer to obtain a premixed material;

[0045] (2) The premixed material was heated to 500°C in a box furnace at a heating rate of 3°C / min and pre-calcined for 5 h, then heated to 900°C at a heating rate of 2°C / min and calcined at high temperature for 10 h. The sintering atmosphere was compressed air with an air flow rate of 4 L / min. The material was naturally cooled to room temperature and sieved through a 325-mesh sieve to obtain a zinc- and fluorine-co-doped cobalt-free lithium-rich manganese-based positive electrode material.

[0046] As shown in FIG1 , which is an SEM photograph of the cobalt-free lithium-rich manganese-based positive electrode material obtained in Example 2, it can be seen that the prepared lithium-rich manganese-based positive electrode material is a secondary spherical particle formed by stacking primary particles.

[0047] Comparative Example 1

[0048] This comparative example provides a cobalt-free lithium-rich manganese-based positive electrode material, and the specific preparation method is as follows:

[0049] (1) According to the amount of lithium element in the lithium source and Ni 0.33 Mn 0.67 The ratio of the sum of the amounts of nickel and manganese in the (OH)2 precursor is 1.35. 0.33 Mn 0.67 (OH)2 precursor and lithium carbonate, where Ni 0.33 Mn 0.67 The specific surface area of ​​the (OH)2 precursor is 23m 2 / g, and the tap density is 1.35g / cm 3 , the median particle size D50 was 4.2 μm, and a premixed material was obtained;

[0050] (2) The premixed material was heated to 500°C in a box furnace at a heating rate of 3°C / min and pre-calcined for 5 h, then heated to 900°C at a heating rate of 2°C / min and calcined at high temperature for 10 h. The sintering atmosphere was compressed air with an air flow rate of 4 L / min. The material was naturally cooled to room temperature and sieved through a 325-mesh sieve to obtain a cobalt-free lithium-rich manganese-based positive electrode material.

[0051] As shown in Figure 2, the XRD spectra of the positive electrode materials prepared in Example 2 and Comparative Example 1 show a typical lithium-rich manganese-based material structure, with the main phase being an α-NaFeO2 structure, where 2θ = 20-23° corresponds to the diffraction peak of the Li2MnO3 superlattice structure. The peak positions in the XRD spectra of Example 2 are roughly the same as those of Comparative Example 1, indicating that the co-doping of Zn and F does not change the crystal structure of the lithium-rich manganese-based positive electrode material. After doping, the diffraction peak shifts to a lower angle, the interlayer spacing increases, and lithium ions are deintercalated, thereby improving the rate performance of the material. In addition, the peak intensity increases after doping, and the crystallinity is better.

[0052] Comparative Example 2

[0053] This comparative example provides a cobalt-free lithium-rich manganese-based positive electrode material, and the specific preparation method is as follows:

[0054] (1) According to the amount of lithium element in the lithium source and Ni 0.33 Mn 0.67 The ratio of the sum of the amounts of nickel and manganese in the (OH)2 precursor is 1.35. 0.33 Mn 0.67 (OH)2 precursor and lithium carbonate, where Ni 0.33 Mn 0.67 The specific surface area of ​​the (OH)2 precursor is 23m 2 / g, and the tap density is 1.35g / cm 3 , the median particle size D50 is 4.2μm, and the mass is weighed as Ni 0.33 Mn 0.67 0.3% ZnO by mass of (OH)2 precursor, the above raw materials are mixed uniformly using a high-speed mixer to obtain a premixed material;

[0055] (2) The premixed material was heated to 500°C in a box furnace at a heating rate of 3°C / min and pre-calcined for 5 h, then heated to 900°C at a heating rate of 2°C / min and calcined at high temperature for 10 h. The sintering atmosphere was compressed air with an air flow rate of 4 L / min. The material was naturally cooled to room temperature and sieved through a 325-mesh sieve to obtain a zinc-doped cobalt-free lithium-rich manganese-based positive electrode material.

[0056] Comparative Example 3

[0057] This comparative example provides a cobalt-free lithium-rich manganese-based positive electrode material, and the specific preparation method is as follows:

[0058] (1) According to the amount of lithium element in the lithium source and Ni 0.33 Mn 0.67 The ratio of the sum of the amounts of nickel and manganese in the (OH)2 precursor is 1.35. 0.33 Mn 0.67 (OH)2 precursor and lithium carbonate, where Ni 0.33 Mn 0.67 The specific surface area of ​​the (OH)2 precursor is 23m 2 / g, and the tap density is 1.35g / cm 3 , the median particle size D50 is 4.2 μm, and LiF is weighed at a mass of 0.25% of the mass of the nickel manganese hydroxide precursor, and the above raw materials are mixed uniformly using a high-speed mixer to obtain a premixed material;

[0059] (2) The premixed material was heated to 500°C in a box furnace at a heating rate of 3°C / min and pre-calcined for 5 h, then heated to 900°C at a heating rate of 2°C / min and calcined at high temperature for 10 h. The sintering atmosphere was compressed air with an air flow rate of 4 L / min. The material was naturally cooled to room temperature and sieved through a 325-mesh sieve to obtain a fluorine-doped cobalt-free lithium-rich manganese-based positive electrode material.

[0060] Comparative Example 4

[0061] This comparative example provides a cobalt-free lithium-rich manganese-based positive electrode material, and the specific preparation method is as follows:

[0062] (1) An undoped, cobalt-free, lithium-rich manganese-based positive electrode material was prepared according to the method and steps described in Comparative Example 1.

[0063] (2) At room temperature, prepare 250mL of a 0.1mol / L mixed solution containing different compounds of zinc acetate and ammonium fluoride, wherein the molar ratio of zinc acetate to ammonium fluoride is 1:1, take 20g of the lithium-rich manganese-based positive electrode material synthesized in step S1 and disperse it therein, and magnetically stir for 3h to allow the ion adsorption and desorption on the surface of the solid material to reach equilibrium, and the magnetic stirring rate is 400rpm. Then, transfer the obtained suspension to a stainless steel reactor with a volume of 400mL, so that the filling rate of the reactor core is 64.0%, tighten the lid to make it airtight, place the reactor in a forced air drying oven, keep it at 120℃ for 6h, take it out after natural cooling, filter the product obtained after the hydrothermal reaction, wash it three times with distilled water, and place it in a vacuum drying oven at 100℃ for 12h;

[0064] (3) The dried lithium-rich manganese-based positive electrode material is placed in a muffle furnace and heated to 450°C at a heating rate of 5°C / min in air and calcined for 6 hours to further remove moisture from the material. The material is cooled and sieved to obtain a cobalt-free lithium-rich manganese-based positive electrode material doped with zinc and fluorine by a hydrothermal method.

[0065] Comparative Example 5

[0066] This comparative example provides a cobalt-free lithium-rich manganese-based positive electrode material, and the specific preparation method is as follows:

[0067] (1) Nickel sulfate hexahydrate and manganese sulfate monohydrate were weighed in a molar ratio of 33:67 and dissolved in deionized water to prepare a 2 mol / L metal salt solution A; sodium carbonate was dissolved in water to prepare a 2 mol / L precipitant solution B, and then zinc sulfate heptahydrate and ammonium fluoride were added and stirred until completely dissolved to obtain solution C, wherein the molar ratio of zinc sulfate heptahydrate to sodium carbonate was controlled to be 5:100, and the molar ratio of ammonium fluoride to sodium carbonate was controlled to be 5:100; under stirring at 500 rpm / min, solutions A and C were slowly added dropwise to deionized water, the pH value of the reaction system was controlled to be 8, the system temperature was controlled to be 55°C, and after reacting for 20 hours, the obtained precipitate was washed, filtered, and dried to obtain a zinc-fluorine co-doped nickel manganese hydroxide precursor.

[0068] (2) According to the ratio of the amount of lithium element in the lithium source to the sum of the amount of nickel and manganese elements in the zinc and fluorine co-doped nickel manganese hydroxide precursor of 1.35, the zinc and fluorine co-doped lithium-rich manganese-based precursor was weighed and mixed with lithium carbonate. The mixed powder was heated to 500°C at a heating rate of 3°C / min in a box furnace and pre-calcined for 5h. Then, the mixed powder was heated to 900°C at a heating rate of 2°C / min and high-temperature calcined for 10h. The sintering atmosphere was compressed air with an air flow rate of 4L / min. The mixture was naturally cooled to room temperature and sieved through a 325-mesh sieve to obtain a co-precipitation Zn and F co-doped cobalt-free lithium-rich manganese-based positive electrode material.

[0069] Comparative Example 6

[0070] This comparative example provides a cobalt-free lithium-rich manganese-based positive electrode material, and the specific preparation method is as follows:

[0071] (1) According to the amount of lithium element in the lithium source and Ni 0.33 Mn 0.67 The ratio of the sum of the amounts of nickel and manganese in the (OH)2 precursor is 1.35. 0.33 Mn 0.67 (OH)2 precursor and lithium carbonate, where Ni 0.33 Mn 0.67 The specific surface area of ​​the (OH)2 precursor is 23m 2 / g, and the tap density is 1.35g / cm 3 , the median particle size D50 is 4.2μm, and the mass is weighed as Ni 0.33 Mn 0.67 0.3% of the mass of the (OH)2 precursor ZnO and 0.25% of the mass of the nickel manganese hydroxide precursor LiF are mixed uniformly using a high-speed mixer to obtain a premixed material;

[0072] (2) The premixed material was directly heated to 980°C in a box furnace at a heating rate of 5°C / min and calcined for 10 h. The sintering atmosphere was compressed air with an air flow rate of 4 L / min. The material was naturally cooled to room temperature and sieved through a 325-mesh sieve to obtain a zinc- and fluorine-co-doped cobalt-free lithium-rich manganese-based positive electrode material.

[0073] Its XRD spectrum is shown in FIG3 , where spinel phase and Mn3O4 impurity phase are generated between 2θ=42°~44° and 62°~65°.

[0074] Comparative Example 7

[0075] This comparative example provides a cobalt-free lithium-rich manganese-based positive electrode material, and the specific preparation method is as follows:

[0076] (1) According to the amount of lithium element in the lithium source and Ni 0.33 Mn 0.67 The ratio of the sum of the amounts of nickel and manganese in the (OH)2 precursor is 1.35. 0.33 Mn 0.67 (OH)2 precursor and lithium carbonate, where Ni 0.33 Mn 0.67 The specific surface area of ​​the (OH)2 precursor is 23m 2 / g, and the tap density is 1.35g / cm 3 , the median particle size D50 is 4.2μm, and the mass is weighed as Ni 0.33 Mn 0.67 0.3% of the mass of the (OH)2 precursor ZnO and 0.25% of the mass of the nickel manganese hydroxide precursor LiF are mixed uniformly using a high-speed mixer to obtain a premixed material;

[0077] (2) The premixed material was heated to 500°C in a box furnace at a heating rate of 3°C / min and pre-calcined for 5 h, then heated to 900°C at a heating rate of 8°C / min and calcined at high temperature for 10 h. The sintering atmosphere was compressed air with an air flow rate of 4 L / min. The material was naturally cooled to room temperature and sieved through a 325-mesh sieve to obtain a zinc- and fluorine-co-doped cobalt-free lithium-rich manganese-based positive electrode material.

[0078] Comparative Example 8

[0079] This comparative example provides a cobalt-free lithium-rich manganese-based positive electrode material, and the specific preparation method is as follows:

[0080] (1) According to the amount of lithium element in the lithium source and Ni 0.33 Mn 0.67 The ratio of the sum of the amounts of nickel and manganese in the (OH)2 precursor is 1.35. 0.33 Mn 0.67(OH)2 precursor and lithium carbonate, where Ni 0.33 Mn 0.67 The specific surface area of ​​the (OH)2 precursor is 23m 2 / g, and the tap density is 1.35g / cm 3 , the median particle size D50 is 4.2μm, and the mass is weighed as Ni 0.33 Mn 0.67 0.3% of the mass of the (OH)2 precursor ZnO and 0.25% of the mass of the nickel manganese hydroxide precursor LiF are mixed uniformly using a high-speed mixer to obtain a premixed material;

[0081] (2) The premixed material was directly heated to 900°C in a box furnace at a heating rate of 3°C / min and calcined for 10 h. The sintering atmosphere was compressed air with an air flow rate of 4 L / min. The material was naturally cooled to room temperature and sieved through a 325-mesh sieve to obtain a zinc- and fluorine-co-doped cobalt-free lithium-rich manganese-based positive electrode material.

[0082] Test example

[0083] The positive electrode materials obtained in the examples and comparative examples were used to prepare button cells. The specific preparation method was as follows: a slurry was applied at a ratio of 90 (main material): 5 (polyvinylidene fluoride PVDF): 5 (conductive agent acetylene black) to form a pole piece. A metal lithium sheet was used as the counter electrode, the separator model was Celgard 2500, and a 1 mol / L lithium hexafluorophosphate solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC volume ratio was 1:1) was used as the electrolyte. CR2032 button cells were assembled in an argon glove box (where water <0.01 ppm, oxygen <0.01 ppm). Finally, the cells were placed in a blue electric test system for electrical performance testing. The electrical performance test conditions were: charge and discharge voltage range 2.0V-4.8V, test temperature 25°C, 0.1C / 0.1C cycle for 1 week to test the initial charge and discharge performance of the battery, and 1C / 1C cycle for 50 weeks to test the cycling performance of the battery. The results are shown in Table 1 and Figure 4 below.

[0084] Table 1 Performance of button batteries prepared from positive electrode materials obtained in Examples and Comparative Examples

[0085] By comparing the embodiments and comparative examples, it can be seen that the 0.1C first-cycle discharge capacity, first coulomb efficiency and cycle performance of the cobalt-free lithium-rich manganese-based positive electrode material obtained by multi-site doping with Zn and F using the technical solution of the present application are significantly improved. Comparative Example 1 is undoped, and Comparative Examples 2 and 3 are doped with a single element respectively, and their performance is obviously inferior to the embodiments of the present application; Comparative Examples 4 and 5 do not adopt the method of co-sintering for doping, and at the same time, Comparative Examples 4 and 5 do not perform bulk doping, and the Zn and F therein only act alone, and solid-phase sintering is still required after doping, which is not only inferior to the technical solution of the present application, but also has the problem of cumbersome steps. In Comparative Example 6, a higher sintering temperature is used to directly heat the temperature to 980°C for high-temperature calcination for 10 hours, resulting in the production of impure phases. At the same time, the excessively high temperature and excessively fast heating rate affect the final battery performance. In Comparative Example 7, a faster heating rate is used, and the irreversible redox of oxygen increases, which ultimately leads to poor cycle stability. In Comparative Example 8, a slower heating temperature was used to directly raise the temperature to 900° C. and calcined for 10 hours. The sintering time was too long, inducing an irreversible transformation of the material from a layered structure to a spinel structure, ultimately resulting in a decrease in its cyclic stability.

[0086] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt-free lithium-rich manganese-based positive electrode material, characterized in that: The steps include: S1: After mixing the nickel manganese hydroxide precursor with the lithium source, a zinc element additive and a fluorine element additive are added and mixed evenly to obtain a premixed material; S2: heating the premixed material to a first calcination temperature in an oxidizing gas atmosphere, and then continuing to heat the premixed material to a second calcination temperature, and then naturally cooling the premixed material to obtain the cobalt-free lithium-rich manganese-based positive electrode material.

2. The preparation method according to claim 1, characterized in that: In step S2, the specific calcination is to heat the temperature to 450°C-550°C at a heating rate of 2-5°C / min, pre-calcine for 4h-6h, and then heat the temperature to 800°C-950°C at a heating rate of 2-5°C / min and calcine for 8h-12h.

3. The preparation method according to claim 1 or 2, characterized in that: In step S1, the ratio of the amount of lithium element substance in the lithium source to the sum of the amount of nickel and manganese element substances in the nickel manganese hydroxide precursor is 1.1-1.6:1; The mass of the zinc element additive is 0.08-1% of the mass of the nickel manganese hydroxide precursor; The mass of the fluorine element additive is 0.1-1% of the mass of the nickel manganese hydroxide precursor.

4. The preparation method according to any one of claims 1 to 3, characterized in that The nickel manganese hydroxide precursor has a chemical formula of Ni y Mn 1-y (OH)2,0 <y≤0.5。 5. The preparation method according to claim 4, characterized in that: The specific surface area of ​​the nickel manganese hydroxide precursor is 20 m 2 / g~30m 2 / g, tap density is 1.0g / cm 3 ~1.5g / cm 3 , the median particle size D50 is 3 to 7 μm.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The lithium source includes at least one of lithium carbonate, lithium hydroxide and lithium acetate; The zinc element additive includes at least one of zinc oxide, zinc carbonate and zinc acetate; The fluorine element additive includes lithium fluoride.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The oxidizing gas is air or oxygen.

8. A cobalt-free lithium-rich manganese-based positive electrode material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

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