CN112531155A - Preparation method of positive electrode material precursor and preparation method of positive electrode material - Google Patents
Preparation method of positive electrode material precursor and preparation method of positive electrode material Download PDFInfo
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Abstract
The invention discloses a preparation method of a precursor of a positive electrode material and a preparation method of the positive electrode material, wherein the preparation method of the precursor of the positive electrode material comprises the following steps: (1) preparing required raw materials, dissolving metal salts, and mixing to form a mixed solution; (2) adding a precipitator and the mixed solution into a container under the stirring condition, controlling the pH of a reaction system to be 8-11, and reacting for 1-6 hours; (3) and (3) adding a precipitator and the mixed solution into the mixed solution obtained in the step (2) under the stirring condition, controlling the pH value of the reaction system to be higher than the value of 1-3 in the step (2), and reacting for 1-4 hours to obtain a precursor. The preparation method of the cathode material comprises the following steps: and mixing the precursor of the positive electrode material with a lithium source, and then carrying out heat treatment to obtain the lithium-rich positive electrode material with the core-shell structure. The preparation method has the advantages of simple process, high productivity, high core-shell structure quality of the prepared precursor and the anode material and complete structural form.
Description
Technical Field
The invention belongs to the field of lithium ion batteries, and particularly relates to a preparation method of a precursor of a positive electrode material and a preparation method of the positive electrode material.
Background
Lithium ion batteries have achieved great success and popularity in mobile devices, but in the field of power energy, the current layered oxide materials cannot meet the future energy storage requirements at the battery level, and the energy density of batteries is up to 800Wh/Kg in order to meet the future requirements, which is considered by the U.S. department of energy, whereas the energy density of batteries prepared by the prior art is only 350 Wh/Kg. How to improve the energy density becomes one of the keys for restricting the development and popularization of the lithium ion battery in the field of power energy. The positive electrode material is an important factor for improving the energy density of the lithium ion battery.
The chemical expression is xLi2MnO3·(1-x)LiMO2The lithium-rich cathode material can meet the requirement of high energy density, and unlike the traditional layered oxide, the capacity of the lithium-rich cathode material exceeds the traditional topological mechanical theory. From early Mn-based systematic experimental studies by Thackeray et al, the capacity of lithium-rich positive electrode materials has been steadily increasing at an average of 5mAh/g per year, from 200mAh/g to approximately 350mAh/g (326 mAh/g at 0.1C at room temperature), whereas commercially available positive electrode materials, such as LiNi, have0.8Co0.15Al0.05O2(NCA), which has reached its peak value of 200 mAh/g.
However, the widespread application of lithium-rich cathode materials in the field of lithium batteries is restricted by the problems of low rate performance, high irreversible capacity during first discharge, rapid capacity decay in the cycle process, low discharge voltage plateau and the like. In order to solve the above problems, many research subjects have conductedSuch as coating of the finished product with (Al)2O3) And doping (Mg), which can improve the material properties to some extent, such as the material cycle stability and the material magnification, but cannot improve the material properties to a large extent, and thus the precursor must be used to improve the material properties fundamentally.
Disclosure of Invention
The invention aims to overcome the defects and shortcomings in the background art, and provides a precursor of a positive electrode material with a core-shell structure and a preparation method thereof, and a positive electrode material prepared from the precursor and a preparation method thereof.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a preparation method of a precursor of a positive electrode material comprises the following steps:
(1) preparing required raw materials, dissolving metal salts, and mixing to form a mixed solution;
(2) adding a precipitator and the mixed solution into a container under the stirring condition, controlling the pH of a reaction system to be 8-11, and reacting for 1-6 hours;
(3) and (3) adding a precipitator and the mixed solution into the mixed solution obtained in the step (2) under the stirring condition, controlling the pH value of a reaction system to be higher than the value of 1-3 in the step (2), and reacting for 1-4 hours to obtain a precursor.
The design idea of the technical scheme is that the pH value of the reaction system in the step (2) is controlled to be lower than that of the reaction system in the step (3), so that the precipitation reaction is slowly carried out in the step (2) to generate a compact, stable and uniform inner core, after the pH value is increased in the step (3), the precipitation reaction can be promoted to be carried out, and a fluffy shell structure can be quickly formed.
Preferably, the precipitant in step (2) is less basic than the precipitant in step (3). The design aims at selecting substances with different alkalities as precipitating agents of two steps to be respectively added into a reaction system, is one of means for controlling the difference of the pH value of the reaction system of the two steps, selects the precipitating agent to control the pH value of the reaction system, does not need to introduce other substances into the reaction system, does not need to add other equipment, and is simple and convenient to operate and easy to realize.
In the above technical means, the precipitant in the step (2) is preferably ammonium bicarbonate or ammonium oxalate solution with a molar concentration of 0.01mol/L to 5.0mol/L, and the precipitant in the step (3) is preferably sodium carbonate with a molar concentration of 0.01mol/L to 5.0 mol/L. Selecting ammonium bicarbonate or ammonium oxalate as a precipitator in the step (2) so as to ensure that metal ions are precipitated due to the existence of carbonate ions or oxalate ions, and obtain a precipitated precursor; meanwhile, ammonium ions can play a complexing role, so that the growth speed of the kernel in the step (2) is reduced, and a uniform and stable kernel structure is formed conveniently. The sodium carbonate is selected as the precipitator in the step (3), so that the sodium carbonate can improve the pH value of the system, interference ions are not introduced, the existence of carbonate can ensure the precipitation of metal ions, and the precursor is favorably obtained.
Preferably, in the step (2), the stirring speed is 600rmp/min, and in the step (3), the stirring speed is 200 to 400rmp/min lower than the stirring speed in the step (2).
Preferably, the feeding rate of the precipitant and the mixed solution in the step (2) is 20ml/min, and the feeding rate of the precipitant and the mixed solution in the step (3) is 15ml/min lower than the feeding rate in the step (2).
The technical scheme aims to design two precipitation reaction steps (2) and (3) with different conditions, so that the step (2) reacts at a higher stirring speed and a higher feeding speed, the violent and unshaped growth of a precursor core structure is inhibited, the precursor core structure uniformly grows at a slower speed to form a uniform and stable core structure, when the core grows to a certain degree, the stirring speed and the feeding speed are reduced in the step (3), the shell can be ensured to grow fluffily at a higher speed, and thus the core and the shell which are obviously different in structure are formed, the separation of the core and the shell in subsequent treatment is facilitated, and the integrity of the core-shell structure is ensured. Meanwhile, the stirring speed in the step (2) is set to 600rmp/min, so that the phenomenon that the inner core cannot be formed due to too high stirring rotating speed is avoided, the inner core cannot rapidly grow in an amorphous manner at the lowest stirring rotating speed is ensured, and the formation of a uniform and stable inner core structure is facilitated; the feeding speed in the step (2) is set to be 20ml/min, so that the phenomenon that the core cannot be formed due to too high feeding speed is avoided, the core cannot rapidly grow in an amorphous manner at the lowest feeding speed is ensured, and the formation of a uniform and stable core structure is facilitated.
Preferably, the reaction system in the step (3) further comprises a complexing agent, and the complexing agent is an ammonia water solution or an ammonium sulfate solution. The solubility product of the precipitation reaction is small, the supersaturation degree of the solution is large, the nucleation rate is too large, flocculent solids are easily formed, the complexing agent is added in the reaction process, the supersaturation degree and the nucleation rate can be reduced to a certain extent, so that the nucleation rate and the crystal growth rate are dynamically balanced, the purpose of improving the crystal morphology is further achieved, and the completeness and the high quality of a shell structure are guaranteed to be formed.
Preferably, after the reaction in the step (3) is completed, the method further comprises an aging treatment operation, wherein the aging treatment time is 5-15 hours. The aging treatment is added, and the aging treatment time is limited to be 5-15 hours, so that sufficient time for reaction growth of a shell structure can be ensured, the grain size of the crystal is increased, the grain size distribution of the crystal is uniform, the grain size of a final product can be limited to a certain degree, and the condition that a precursor is unstable due to overlarge grain size can be avoided.
Preferably, the metal salt includes at least one of a nickel salt, a cobalt salt, and a manganese salt; the nickel salt is selected from at least one of nickel nitrate, nickel acetate, nickel chloride or nickel sulfate; the cobalt salt is at least one selected from cobalt nitrate, cobalt acetate, cobalt chloride or cobalt sulfate; the manganese salt is selected from at least one of manganese nitrate, manganese acetate, manganese chloride and manganese sulfate.
In the above aspect, the molar concentration of the metal ion in the mixed solution is preferably 0.01mol/L to 5.0 mol/L.
Preferably, the temperature of the reaction system in the step (2) and the step (3) is 30-80 ℃.
Preferably, after the step (3), the method further comprises a washing and drying operation, and specifically comprises the following steps: washing with low-concentration NaOH solution, washing with deionized water for more than one time, filtering, drying the obtained suspension for more than 12 hours, and sieving with a 300-mesh sieve.
A preparation method of a lithium-rich cathode material with a core-shell structure comprises the following steps: preparing a core-shell structure positive electrode material precursor, mixing the core-shell structure positive electrode material precursor with a lithium source, and then carrying out heat treatment to obtain a core-shell structure lithium-rich positive electrode material; the precursor of the core-shell structure cathode material is prepared by the method provided by any one of the technical schemes.
Preferably, the molar ratio of the metal element in the precursor to the lithium element in the lithium compound is (1: 1.2) to (1: 1.7).
Preferably, the heat treatment temperature is 700 to 950 ℃, and the heat treatment time is 10 to 20 hours. The heat treatment process under the condition can lead carbonate in the precursor to be heated and decomposed to generate carbon dioxide, thus leading the core structure and the shell structure to be well separated, strengthening the combination of lithium metal and the precursor and ensuring the stable formation of the lithium-rich cathode material.
Compared with the prior art, the invention has the advantages that:
(1) the preparation method of the precursor can ensure that the core of the precursor grows stably and uniformly, the shell grows rapidly and fluffily, the core and the shell are easy to separate in the subsequent steps, and the prepared cathode material has high core-shell structure quality and complete structural form.
(2) According to the anode material prepared by the invention, the material expands and contracts due to stress generated among crystal grains in the charging and discharging processes, and the core-shell structure can effectively provide an expansion and contraction space for the material, so that the internal structure of the material can be protected, the stability of the material is improved, and the material has good cycle performance.
(3) The preparation method of the precursor and the anode material has simple process and high productivity, and is suitable for large-scale industrial production.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a field emission electron micrograph (FEI-SEM) of a precursor synthesized in example 1 of the present invention;
FIG. 2 is an emission electron micrograph (FEI-SEM) of each of the final products of examples and comparative examples, wherein FIGS. 2a and 2b are field emission electron micrographs (FEI-SEM) of the final product of example 1 of the present invention, FIG. 2c is a field emission electron micrograph (FEI-SEM) of the final product of comparative example 1 of the present invention, and FIG. 2d is a field emission electron micrograph (FEI-SEM) of the final product of comparative example 2;
FIG. 3 is a graph of the cycle performance of the final product of example 1 of the present invention;
FIG. 4 is an X-ray diffraction pattern (XRD) of the final product of example 1 of the present invention.
Detailed Description
In order to facilitate an understanding of the invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.
It should be particularly noted that when an element is referred to as being "fixed to, connected to or communicated with" another element, it can be directly fixed to, connected to or communicated with the other element or indirectly fixed to, connected to or communicated with the other element through other intermediate connecting components.
Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
Example 1:
a preparation method of a precursor of a positive electrode material comprises the following steps:
(1) MnSO is added according to the stoichiometric ratio of Mn, Ni and Co to be 4:1:14·H2O、NiSO46H2O and CoSO4·7H2Dissolving O in deionized water to prepare a mixed solution with the total ion concentration of 2 mol/L.
(2) And simultaneously adding the mixed solution and 2mol/L ammonium bicarbonate aqueous solution into a reaction kettle, controlling the temperature in the reaction kettle to be 60 ℃, controlling the pH to be 9, controlling the adding flow rate of the mixed solution and the ammonium bicarbonate aqueous solution to be 20mL/min, controlling the stirring speed to be 600rmp/min, and reacting for 4 h.
(3) And (3) adding the mixed solution, 2mol/L sodium carbonate aqueous solution and 0.6mol/L ammonia aqueous solution into the mixed solution obtained in the step (2), reducing the adding flow rate to 5ml/min, changing the stirring speed to 400rmp/min, adjusting the pH value to 11, stopping the reaction after 2 hours of reaction, aging the mixed solution for 10 hours, washing the mixed solution by using low-concentration NaOH solution, then washing the mixed solution for 3 times by using deionized water, performing suction filtration, drying the obtained solid in an oven at 80 ℃ for 12 hours, and sieving the solid by using a 300-mesh sieve to obtain the carbonate precursor.
A preparation method of a positive electrode material comprises the following steps:
and (2) putting the precursor prepared by the preparation method of the precursor of the positive electrode material and lithium carbonate into a ball milling tank according to the quantitative proportion of the chemical formula substances for ball milling, wherein the ball milling process comprises the following steps: the ball milling tank is 250mL, the diameter of ball milling beads is 5mm, the ball-material ratio is 1:5, the ball milling rotating speed is 200r/min, and the ball milling time is 10 h. Spreading the ball-milled solid material in a corundum burning bowl, placing in a bell jar furnace, introducing air, heating to 500 deg.C at 5 deg.C/min, keeping the temperature for 6h, heating at 2 deg.C/min, and heatingSintering at 850 deg.C for 12 hr, naturally cooling to room temperature, and sieving to obtain lithium-rich cathode material with core-shell structure and molecular formula of 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2。
The FEI-SEM image of the lithium-rich cathode material carbonate precursor in the preparation process of this example is shown in fig. 1, and it is easy to see that the surface of the carbonate precursor prepared in this example is different from that of the common precursor, and it can be clearly seen that the growth orientation of the precursor is unique, the shell is more fluffy, and the surface structure is also different.
FEI-SEM images of the final product of the lithium-rich cathode material prepared in this embodiment are shown in fig. 2a and fig. 2b, which can clearly show that the core-shell structure of the lithium-rich manganese-based cathode material obtained in this embodiment is separated clearly, and the core-shell structure is complete in shape.
The XRD spectrum of the lithium-rich cathode material synthesized in the example is shown in FIG. 4, and obvious Li can be found in the spectrum2MnO3Characteristic peak, the layered structure LiNi of the material can be deduced from the ratio of I (003)/I (104)1/3Co1/3Mn1/3O2The crystallinity of (2) is high.
Example 2:
a preparation method of a precursor of a positive electrode material comprises the following steps:
(1) MnSO is added according to the stoichiometric ratio of Mn, Ni and Co to be 4:1:14·H2O、NiSO4·6H2O and CoSO4·7H2Dissolving O in deionized water to prepare a mixed solution with the total ion concentration of 2 mol/L.
(2) And simultaneously adding the mixed solution and 2mol/L ammonium bicarbonate aqueous solution into a reaction kettle, controlling the temperature in the reaction kettle to be 40 ℃, controlling the pH to be 10, controlling the adding flow rate of the mixed solution, the ammonium bicarbonate aqueous solution and the ammonia aqueous solution to be 20mL/min, controlling the stirring rotation speed to be 600rmp/min, and reacting for 2 h.
(3) And (3) adding the mixed solution, 2mol/L sodium carbonate aqueous solution and 0.6mol/L ammonia aqueous solution into the mixed solution obtained in the step (2), reducing the adding flow rate to 10ml/min, stirring at the rotating speed of 200rmp/min, adjusting the pH value to 13, stopping the reaction after 1 hour of reaction, aging the mixed solution for 6 hours, washing with low-concentration NaOH solution, washing with deionized water for 3 times, performing suction filtration, drying the obtained solid in an oven at 80 ℃ for 12 hours, and sieving with a 300-mesh sieve to obtain a carbonate precursor.
A preparation method of a positive electrode material comprises the following steps:
and (2) putting the precursor prepared by the preparation method of the precursor of the positive electrode material and lithium carbonate into a ball milling tank according to the quantitative proportion of the chemical formula substances for ball milling, wherein the ball milling process comprises the following steps: the ball milling tank is 250mL, the diameter of ball milling beads is 5mm, the ball-material ratio is 1:5, the ball milling rotating speed is 500r/min, and the ball milling time is 2 h. Spreading the ball-milled solid material in a corundum burning bowl, putting the corundum burning bowl into a bell jar furnace, introducing air, heating to 500 ℃ at the speed of 5 ℃/min, keeping the temperature for 6 hours, then heating to 700 ℃, sintering for 18 hours, naturally cooling to room temperature, and finally sieving and separating to obtain the lithium-rich cathode material with the core-shell structure, wherein the molecular formula of the lithium-rich cathode material is 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2。
Comparative example 1:
this comparative example provides a method for synthesizing a precursor of a positive electrode material different from those of examples 1 and 2, comprising the steps of:
(1) MnSO is added according to the stoichiometric ratio of Mn, Ni and Co to be 4:1:14·H2O、NiSO46H2O and CoSO4·7H2Dissolving O in deionized water to prepare a mixed solution with the total ion concentration of 2 mol/L.
(2) And simultaneously adding the mixed solution, 2mol/L ammonium bicarbonate aqueous solution and 0.6mol/L ammonia aqueous solution (complexing agent) into a reaction kettle, controlling the temperature in the reaction kettle to be 60 ℃ and the pH to be 9, controlling the adding flow rate of the mixed solution, the ammonium bicarbonate aqueous solution and the ammonia aqueous solution to be 20mL/min, and controlling the stirring speed to be 600rmp/min for reacting for 6 hours.
(3) And aging the mixed solution for 10h, washing by using a low-concentration NaOH solution, washing by using deionized water for 3 times, then carrying out suction filtration, drying the obtained solid in an oven at 80 ℃ for 12h, and sieving by using a 300-mesh sieve to obtain the carbonate precursor.
This comparative example also provides a method of synthesizing a cathode material different from examples 1 and 2, comprising the steps of:
and (2) putting the precursor prepared by the preparation method of the precursor of the positive electrode material and lithium carbonate into a ball milling tank according to the quantitative proportion of the substances in the chemical formula for ball milling, wherein the ball milling process comprises the following steps: the ball milling tank is 250mL, the diameter of ball milling beads is 5mm, the ball-material ratio is 1:5, the ball milling rotating speed is 200r/min, and the ball milling time is 10 h. Spreading the ball-milled solid material in a corundum burning bowl, putting the corundum burning bowl into a bell jar furnace, introducing air, heating to 500 ℃ at the speed of 5 ℃/min, keeping the temperature for 6 hours, then heating to 850 ℃ at the speed of 2 ℃/min, sintering for 12 hours, naturally cooling to room temperature, and finally sieving and separating to obtain the common lithium-rich cathode material.
The FEI-SEM image of the final product of the cathode material prepared in this comparative example is shown in fig. 2 c.
Comparative example 2:
this comparative example provides a method for synthesizing a precursor of a positive electrode material, different from examples 1, 2 and 2, comprising the steps of:
(1) MnSO4 & H2O, NiSO4 & 6H2O and CoSO4 & 7H2O are dissolved in deionized water according to the stoichiometric ratio of Mn to Ni to Co being 4:1:1 to prepare a mixed solution with the total ion concentration of 2 mol/L.
(2) And simultaneously adding the mixed solution, 2mol/L sodium carbonate aqueous solution and 0.6mol/L ammonia aqueous solution into a reaction kettle, controlling the temperature in the reaction kettle to be 60 ℃, controlling the pH to be 9, controlling the adding flow rate of the mixed solution, the ammonium bicarbonate aqueous solution and the ammonia aqueous solution to be 20mL/min, controlling the stirring rotation speed to be 600rmp/min, and reacting for 6 hours.
(3) And aging the mixed solution for 10h, washing by using a low-concentration NaOH solution, washing by using deionized water for 3 times, then carrying out suction filtration, drying the obtained solid in an oven at 80 ℃ for 12h, and sieving by using a 300-mesh sieve to obtain the carbonate precursor.
This comparative example also provides a method for synthesizing a positive electrode material different from examples 1, 2 and 1, comprising the steps of:
and (2) putting the precursor prepared by the preparation method of the precursor of the positive electrode material and lithium carbonate into a ball milling tank according to the quantitative proportion of the chemical formula substances for ball milling, wherein the ball milling process comprises the following steps: the ball milling tank is 250mL, the diameter of ball milling beads is 5mm, the ball-material ratio is 1:5, the ball milling rotating speed is 200r/min, and the ball milling time is 10 h. Spreading the ball-milled solid material in a corundum burning bowl, putting the corundum burning bowl into a bell jar furnace, introducing air, heating to 500 ℃ at the speed of 5 ℃/min, keeping the temperature for 6 hours, then heating to 850 ℃ at the speed of 2 ℃/min, sintering for 12 hours, naturally cooling to room temperature, and finally sieving and separating to obtain the common lithium-rich cathode material.
The FEI-SEM image of the final product of the cathode material prepared in this comparative example is shown in fig. 2 d.
As is apparent from fig. 2a and 2b, the cathode material obtained in example 1 has a core-shell structure, while the lithium-rich cathode materials synthesized in comparative example 1 (fig. 2c) and comparative example 2 (fig. 2d) are solid, and the core-shell materials are not separated and are not obviously different from the common cathode materials.
The lithium-rich positive electrode material obtained in the example 1, the comparative example 1 and the comparative example 2 is uniformly mixed with carbon black conductive agent SP and binder PVDF according to the mass ratio of 80:10:10, NMP is added to prepare slurry, the slurry is uniformly coated on an aluminum foil current collector, the slurry is dried at 120 ℃ and pressed into sheets, then a button cell is assembled in a glove box by taking metal lithium as a negative electrode, and finally a charge-discharge cycle test is carried out, wherein the test temperature is 25 ℃, the voltage range is 2.0-4.6V, and the cycle performance is shown in figure 3. As can be seen from fig. 3, the positive electrode material synthesized in example 1 had a high capacity retention rate of 85% or more after 200 cycles of charge and discharge cycles at 0.2C. The lithium-rich cathode material with the core-shell structure synthesized in the embodiment 1 is beneficial to inhibiting the phase change of the material structure and protecting the internal structure, thereby improving the cycle performance.
Claims (10)
1. A preparation method of a precursor of a positive electrode material is characterized by comprising the following steps:
(1) preparing required raw materials, dissolving metal salts, and mixing to form a mixed solution;
(2) adding a precipitator and the mixed solution into a container under the stirring condition, controlling the pH of a reaction system to be 8-11, and reacting for 1-6 hours;
(3) and (3) adding a precipitator and the mixed solution into the mixed solution obtained in the step (2) under the stirring condition, controlling the pH value of a reaction system to be higher than the value of 1-3 in the step (2), and reacting for 1-4 hours to obtain a precursor.
2. The method of claim 1, wherein the precipitant of step (2) is less basic than the precipitant of step (3).
3. The method according to claim 1, wherein the precipitant in step (2) is ammonium bicarbonate or ammonium oxalate solution with a molarity of 0.01-5.0 mol/L, and the precipitant in step (3) is sodium carbonate solution with a molarity of 0.01-5.0 mol/L.
4. The method according to claim 1, wherein the stirring speed in the step (2) is 600rmp/min, and the stirring speed in the step (3) is 200 to 400rmp/min lower than the stirring speed in the step (2).
5. The method according to claim 1, wherein the feeding rate of the precipitant and the mixed solution in the step (2) is 20ml/min, and the feeding rate of the precipitant and the mixed solution in the step (3) is 10 to 15ml/min lower than the feeding rate in the step (2).
6. The preparation method according to claim 1, wherein a complexing agent is further added to the reaction system in the step (3), and the complexing agent is an aqueous ammonia solution or an ammonium sulfate solution.
7. The method according to any one of claims 1 to 6, wherein the reaction of step (3) is completed and then an aging treatment is further performed, and the aging treatment time is 5 to 15 hours.
8. A preparation method of a positive electrode material comprises the following steps:
preparing a core-shell structure positive electrode material precursor by adopting the preparation method of any one of claims 1 to 7, mixing the core-shell structure positive electrode material precursor with a lithium source, and then carrying out heat treatment to obtain the core-shell structure lithium-rich positive electrode material.
9. The method according to claim 8, wherein a molar ratio of the metal element in the precursor to the lithium element in the lithium source is (1: 1.2) to (1: 1.7).
10. The method according to claim 8 or 9, wherein the heat treatment temperature is 700 to 950 ℃ and the heat treatment time is 10 to 20 hours.
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