CN112713263B - Preparation method of metaphosphate coated lithium cobaltate material and lithium ion battery comprising metaphosphate coated lithium cobaltate material - Google Patents
Preparation method of metaphosphate coated lithium cobaltate material and lithium ion battery comprising metaphosphate coated lithium cobaltate material Download PDFInfo
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- CN112713263B CN112713263B CN202011466036.0A CN202011466036A CN112713263B CN 112713263 B CN112713263 B CN 112713263B CN 202011466036 A CN202011466036 A CN 202011466036A CN 112713263 B CN112713263 B CN 112713263B
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Abstract
The invention provides a preparation method of a metaphosphate coated lithium cobaltate material, which comprises the following steps: dissolving hydroxide in a phosphoric acid solution, reacting to obtain a dihydrogen phosphate solution, adding cobalt salt, adjusting the pH to 9-13, further reacting, washing the obtained precipitate to be neutral, and drying to obtain a precursor; dissolving the precursor, a lithium source and ethyl cellulose in an organic solvent for ball milling, and drying and calcining the obtained sol mixture to obtain the metaphosphate coated lithium cobaltate material. The metaphosphate coated lithium cobaltate material is obtained by adopting an in-situ polymerization mode, has low cost, is applied to a lithium ion battery, and can improve the performance of the battery.
Description
Technical Field
The invention belongs to the field of functional material preparation, and relates to a preparation method of a metaphosphate coated lithium cobaltate material and a lithium ion battery comprising the same.
Background
The lithium ion battery is a novel secondary energy storage battery developed in the 90 s of the 20 th centuryThe cell has the advantages of high energy, long service life, low consumption, no public hazard, no memory effect, small self-discharge, small internal resistance, high cost performance, less pollution and the like, and is widely applied to the field of electronics. One of the bottlenecks that restrict the industrial popularization of lithium ion batteries is the anode material. Currently, lithium cobaltate (LiCoO) is the main anode material of lithium ion batteries2) Lithium nickelate, lithium manganate, lithium iron phosphate, etc., wherein LiCoO2As the lithium ion battery cathode material which is the earliest to be commercially used, the lithium ion battery cathode material has high voltage and high energy density, and is widely applied to small consumer batteries, in particular to digital products such as smart phones and tablet computers. With the development of 5G and the continuous popularization and upgrading of global digital products, LiCoO2The market demand of (1) is continuously increased, the annual growth rate reaches 10%, but the domestic cobalt resource is in short supply, the cobalt yield is slowly increased, the demand of the domestic market can not be met, the 80% cobalt supply needs to be imported, and the LiCoO is often influenced by the export policy of raw materials such as Africa and the like2The price of (A) is high for a long time. Due to the rapid improvement of the performance of consumer digital products, the requirements on the energy density and the charge and discharge rate of lithium ion batteries are higher and higher, and LiCoO is used2The performance of lithium ion batteries, which are positive electrodes, cannot meet the increasingly higher performance requirements. In summary, how to reduce LiCoO2The cost of the soft package lithium ion battery and the effective improvement of the battery performance (in the aspects of capacity, multiplying power and circulation) have very important research significance,
disclosure of Invention
Aiming at the defects of the existing lithium ion battery anode material, the invention provides a novel method for preparing the metaphosphate coated lithium cobaltate material, the obtained metaphosphate coated lithium cobaltate material has low cost, and the metaphosphate coated lithium cobaltate material can improve the battery performance when being applied to the lithium ion battery.
The first aspect of the invention provides a method for preparing a metaphosphate coated lithium cobaltate material, which comprises the following steps:
dissolving hydroxide in a phosphoric acid solution, reacting to obtain a dihydrogen phosphate solution, adding cobalt salt, adjusting the pH to 9-13, further reacting, washing the obtained precipitate to be neutral, and drying to obtain a precursor;
dissolving the precursor, a lithium source and ethyl cellulose in an organic solvent for ball milling, and drying and calcining the obtained sol mixture to obtain the metaphosphate coated lithium cobaltate material.
Preferably, the hydroxide is one or more of barium hydroxide, calcium hydroxide, lithium hydroxide, lanthanum hydroxide, sodium hydroxide, aluminum hydroxide, yttrium hydroxide, potassium hydroxide, neodymium hydroxide, magnesium hydroxide, zinc hydroxide, niobium hydroxide, and strontium hydroxide.
Preferably, the cobalt salt is one or more of cobalt chloride, cobalt sulfate, cobalt nitrate and cobalt acetate.
Preferably, the molar mass ratio of the hydroxide to the cobalt salt is 1: (20-80).
Preferably, the further reaction temperature is 35-100 ℃ and the reaction time is 30-120 min.
Preferably, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxalate.
Preferably, the amount of the lithium source is calculated such that the molar ratio of Li to Co is (0.9-1.1): 1.
Preferably, the ethyl cellulose accounts for 0.5-5.0 wt% of the total amount of the precursor, the lithium source and the ethyl cellulose.
Preferably, the temperature is raised to 600-900 ℃ at the speed of 1-5 ℃/min for calcination, and the calcination time is 0.5-5 h.
Another aspect of the present invention provides a lithium ion battery, wherein the positive electrode material of the lithium ion battery comprises the metaphosphate coated lithium cobaltate material prepared as described above.
Preferably, the positive electrode material comprises a metaphosphate coated lithium cobaltate material, a conductive agent and a binder, and the mass ratio of the metaphosphate coated lithium cobaltate material to the conductive agent to the binder is 100: (0.1-5.0): (0.1-5.0).
Compared with the prior art, the invention has the beneficial effects that:
(1) the preparation method of co-precipitation of dihydric phosphate and cobalt salt is adopted, so that uniform coating of metaphosphate on lithium cobaltate particles is facilitated;
(2) according to the invention, ethyl cellulose ball mill is added into the precursor and the lithium source, and the ethyl cellulose is added to obtain a more uniform metaphosphate coated lithium cobaltate material;
(3) the metaphosphate coated lithium cobaltate material is obtained by an in-situ polymerization mode, and the adopted preparation method is simple and easy to operate, and can realize large-scale production;
(4) the metaphosphate coated lithium cobaltate material obtained by the method can be used as a positive electrode material of a lithium ion battery, so that the discharge capacity and the cycle stability of the lithium ion battery are greatly improved;
(5) the cost of raw materials for generating metaphosphate is lower than that of the raw materials for generating lithium cobaltate, so that the metaphosphate coated lithium cobaltate material obtained by the method has lower cost than a pure lithium cobaltate material, and the manufacturing cost of the raw materials of the lithium ion battery can be greatly reduced.
Drawings
FIG. 1 is a scanning electron micrograph of a lithium cobaltate material prepared according to comparative example 3 of the present invention;
fig. 2 is a scanning electron microscope image of the aluminum metaphosphate coated lithium cobaltate material prepared in example 1 of the present invention.
Detailed Description
Hereinafter, embodiments will be described in detail with respect to a method of preparing a metaphosphate coated lithium cobaltate material of the present invention and a lithium ion battery including the same, however, these embodiments are exemplary and the present disclosure is not limited thereto.
In some embodiments of the present invention, a method of preparing the metaphosphate coated lithium cobaltate material includes: dissolving hydroxide in a phosphoric acid solution, reacting to obtain a dihydrogen phosphate solution, adding cobalt salt, adjusting the pH to 9-13, further reacting, washing the obtained precipitate to be neutral, and drying to obtain a precursor;
dissolving the precursor, a lithium source and ethyl cellulose in an organic solvent for ball milling, and drying and calcining the obtained sol mixture to obtain the metaphosphate coated lithium cobaltate material.
Controlling reaction conditions to enable the hydroxide to react with phosphoric acid to generate dihydrogen phosphate, enabling the dihydrogen phosphate to react with cobalt salt under an alkaline condition to obtain a precursor, dissolving the precursor, a lithium source and ethyl cellulose in an organic solvent to perform ball milling, drying, calcining the dihydrogen phosphate in the precursor at high temperature to generate metaphosphate, and compounding the cobalt salt and the lithium source in situ to form lithium cobaltate, thereby finally obtaining the lithium cobaltate material coated with the metaphosphate.
The preparation process will be described in detail below:
the hydroxide of the invention is preferably one or more of barium hydroxide, calcium hydroxide, lithium hydroxide, lanthanum hydroxide, sodium hydroxide, aluminum hydroxide, yttrium hydroxide, potassium hydroxide, neodymium hydroxide, magnesium hydroxide, zinc hydroxide, niobium hydroxide and strontium hydroxide, the reaction conditions are controlled so that the hydroxide reacts with phosphoric acid to generate corresponding dihydrogen phosphate, for example, the reaction between aluminum hydroxide and phosphoric acid is carried out, the reaction temperature is controlled to be 120-170 ℃ according to the stoichiometric ratio, and aluminum dihydrogen phosphate is obtained; barium hydroxide, calcium hydroxide, lithium hydroxide, lanthanum hydroxide, sodium hydroxide, aluminum hydroxide, yttrium hydroxide, potassium hydroxide, neodymium hydroxide, magnesium hydroxide, zinc hydroxide, niobium hydroxide, strontium hydroxide and phosphoric acid react to respectively generate barium dihydrogen phosphate, calcium dihydrogen phosphate, lithium dihydrogen phosphate, lanthanum dihydrogen phosphate, sodium dihydrogen phosphate, aluminum dihydrogen phosphate, yttrium dihydrogen phosphate, potassium dihydrogen phosphate, neodymium dihydrogen phosphate, magnesium dihydrogen phosphate, zinc dihydrogen phosphate, niobium dihydrogen phosphate and strontium dihydrogen phosphate.
Adding cobalt salt into the obtained dihydric phosphate solution, wherein the cobalt salt is preferably one or more of cobalt chloride, cobalt sulfate, cobalt nitrate and cobalt acetate, then adding an alkali solution to adjust the pH of the solution to 9-13, the alkali solution is preferably a sodium hydroxide solution and/or an ammonia water solution, and is further preferably a sodium hydroxide solution and an ammonia water solution, and the pH is adjusted more accurately and the reaction intensity is alleviated by jointly adjusting the sodium hydroxide and the ammonia water. Under the alkaline condition, cobalt salt and dihydric phosphate react for 30-120min at 35-100 ℃ to obtain a precipitate, the obtained precipitate is washed to be neutral, and the precipitate is dried at 50-80 ℃ to obtain a precursor. The co-precipitation of the dihydrogen phosphate and the cobalt salt is beneficial to uniformly coating the metaphosphate on the lithium cobaltate particles in the subsequent calcination process.
Dissolving a precursor, a lithium source and ethyl cellulose in an organic solvent for ball milling, wherein the organic solvent can be ethanol, methanol, acetone and the like, the ball milling time is 2-10h, the ethyl cellulose swells in the organic solvent to play a thickening role, the precursor and the lithium source can be mixed more uniformly, the contact and the reaction of the two materials are facilitated, and therefore a uniform metaphosphate coated lithium cobaltate material is generated; in addition, the ethyl cellulose itself is decomposed during heating, and is coated around the material after ball milling, mixing and drying, and the synthesis of the material can be promoted due to the heat release of the combustion of the elements such as C, H and the like during the decomposition process. Drying the sol mixture formed after ball milling at the temperature of 130-160 ℃ for 3-12h, then heating to the temperature of 600-900 ℃ at the speed of 1-5 ℃/min for calcining for 0.5-5h, and obtaining the metaphosphate coated lithium cobaltate material after calcining. The metaphosphate is one or more of barium metaphosphate, calcium metaphosphate, lithium metaphosphate, lanthanum metaphosphate, sodium metaphosphate, aluminum metaphosphate, yttrium metaphosphate, potassium metaphosphate, neodymium metaphosphate, magnesium metaphosphate, zinc metaphosphate, niobium metaphosphate and strontium metaphosphate.
The amount of lithium source, cobalt salt and hydroxide used in the preparation process determines the ratio of metaphosphate to lithium cobaltate in the final metaphosphate-coated lithium cobaltate material. The molar ratio of Li to Co of the lithium source and the cobalt salt is controlled to be (0.9-1.1):1, the lithium source and the cobalt salt are favorably and completely converted into lithium cobaltate as far as possible in the calcining process, the adverse effect of excessive lithium source or cobalt salt on the material performance is avoided, and the molar mass ratio of hydroxide to cobalt salt is controlled to be 1: (20-80), the mole ratio of the hydroxide to the cobalt salt determines the mole ratio of the metaphosphate to the lithium cobaltate in the final metaphosphate-coated lithium cobaltate material, and the proportion of the metaphosphate to the lithium cobaltate has great influence on the performance of the lithium ion battery, and when the content of the metaphosphate is too large or too small, the performance of the lithium ion battery is reduced.
In other embodiments of the present invention, a lithium ion battery is provided, the positive electrode material of which comprises the metaphosphate coated lithium cobaltate material prepared as described above.
The positive electrode material comprises a metaphosphate coated lithium cobaltate material, a conductive agent and a binder; further preferably, the mass ratio of the metaphosphate coated lithium cobaltate material to the conductive agent to the binder is 100: (0.1-5.0): (0.1-5.0).
Mixing a metaphosphate coated lithium cobaltate material, a conductive agent and a binder according to the mass ratio, and then adding an organic solvent N-methyl pyrrolidone (NMP), wherein the mass ratio of the NMP to the phosphate coated lithium cobaltate material is (2-5): and 10, fully stirring to form slurry, coating the slurry on the surface of the current collector, drying, and rolling for multiple times to obtain the battery positive plate.
Hereinafter, the technical solution of the present invention will be further described and illustrated by specific examples. However, these embodiments are exemplary, and the present disclosure is not limited thereto. And the drawings used herein are for the purpose of illustrating the disclosure better and are not intended to limit the scope of the invention. Unless otherwise specified, the raw materials used in the following specific examples of the present invention are those commonly used in the art, and the methods used in the examples are those conventional in the art.
Example 1
Dissolving 0.2mol of aluminum hydroxide in 0.6L of 1mol/L phosphoric acid solution, stirring and reacting at 140 ℃ to obtain aluminum dihydrogen phosphate solution, then adding 4mol of cobalt sulfate, then dropwise adding 4mol/L NaOH solution and 0.5mol/L ammonia water solution to adjust the pH of the solution to 11, further reacting at 60 ℃ for 30min, washing the obtained precipitate to be neutral, and drying at 75 ℃ to obtain a precursor;
mixing the precursor with 4.24mol of lithium nitrate, adding ethyl cellulose, wherein the ethyl cellulose accounts for 1 wt% of the total amount of the precursor, the lithium nitrate and the ethyl cellulose, dissolving the mixture in ethanol, performing ball milling for 8 hours to form a sol mixture, drying the sol mixture at 150 ℃ for 8 hours, heating to 850 ℃ at the speed of 3 ℃/min, calcining for 2 hours, and cooling after sintering to obtain the aluminum metaphosphate coated lithium cobaltate material.
Example 2
Dissolving 0.3mol of lithium hydroxide in 0.5mol/L phosphoric acid solution, adjusting the addition amount of the phosphoric acid solution to ensure that the pH value of the reaction end point is 2.5 to obtain a lithium dihydrogen phosphate solution, then adding 10mol of cobalt nitrate, then dropwise adding 3mol/L NaOH solution and 0.5mol/L ammonia water solution to adjust the pH value of the solution to 10, further reacting for 35min at 50 ℃, washing the obtained precipitate to be neutral, and drying at 80 ℃ to obtain a precursor;
mixing the precursor with 5mol of lithium carbonate, adding ethyl cellulose, wherein the ethyl cellulose accounts for 1.5 wt% of the total amount of the precursor, the lithium carbonate and the ethyl cellulose, dissolving the mixture in ethanol, performing ball milling for 7h to form a sol mixture, drying at 140 ℃ for 8h, heating to 750 ℃ at a speed of 2 ℃/min, calcining for 2.5h, and cooling after sintering to obtain the lithium metaphosphate coated lithium cobaltate material.
Example 3
Dissolving 0.4mol of sodium hydroxide in 0.6mol/L of phosphoric acid solution, adjusting the addition amount of the phosphoric acid solution to ensure that the pH value of the reaction end point is 4.2 to obtain sodium dihydrogen phosphate solution, then adding 10.7mol of cobalt chloride, then dropwise adding 3mol/L of NaOH solution and 0.5mol/L of ammonia water solution to adjust the pH value of the solution to be 10.5, further reacting for 30min at 70 ℃, washing the obtained precipitate to be neutral, and drying at 75 ℃ to obtain a precursor;
mixing the precursor with 10mol of lithium hydroxide, adding ethyl cellulose, wherein the ethyl cellulose accounts for 1.2 wt% of the total amount of the precursor, the lithium hydroxide and the ethyl cellulose, dissolving the mixture in ethanol, performing ball milling for 6.5h to form a sol mixture, drying at 150 ℃ for 6h, heating to 800 ℃ at the speed of 1 ℃/min, calcining for 2h, and cooling after sintering to obtain the sodium metaphosphate coated lithium cobaltate material.
Example 4
Dissolving 0.2mol of aluminum hydroxide in 0.6L of 1mol/L phosphoric acid solution, stirring and reacting at 140 ℃ to obtain aluminum dihydrogen phosphate solution, then adding 2mol of cobalt sulfate, then dropwise adding 4mol/L NaOH solution and 0.5mol/L ammonia water solution to adjust the pH of the solution to 11, further reacting at 60 ℃ for 30min, washing the obtained precipitate to be neutral, and drying at 75 ℃ to obtain a precursor;
mixing the precursor with 2.12mol of lithium nitrate, adding ethyl cellulose, wherein the ethyl cellulose accounts for 1 wt% of the total amount of the precursor, the lithium nitrate and the ethyl cellulose, dissolving the mixture in ethanol, performing ball milling for 8h to form a sol mixture, drying the sol mixture at 150 ℃ for 8h, heating to 850 ℃ at the rate of 3 ℃/min, calcining for 2h, and cooling after sintering to obtain the aluminum metaphosphate coated lithium cobaltate material.
Comparative example 1
Mixing 0.2mol of aluminum dihydrogen phosphate, 4mol of cobalt hydroxide and 4.24mol of lithium nitrate, adding ethyl cellulose, wherein the ethyl cellulose accounts for 1 wt% of the total amount of the aluminum dihydrogen phosphate, the cobalt hydroxide, the lithium nitrate and the ethyl cellulose, dissolving the mixture in ethanol, performing ball milling for 8 hours to form a sol mixture, drying for 8 hours at 150 ℃, heating to 850 ℃ at the speed of 3 ℃/min, calcining for 2 hours, and cooling after sintering to obtain the aluminum metaphosphate coated lithium cobaltate material.
Comparative example 2
Comparative example 2 is different from example 1 in that, in comparative example 2, after mixing the precursor with lithium nitrate, ethylcellulose was not added, and the other steps are the same as example 1.
Comparative example 3
Mixing 4mol of cobalt hydroxide and 4.24mol of lithium nitrate, adding ethyl cellulose, wherein the ethyl cellulose accounts for 1 wt% of the total amount of the cobalt hydroxide, the lithium nitrate and the ethyl cellulose, dissolving the mixture in ethanol, performing ball milling for 8 hours to form a sol mixture, drying for 8 hours at 150 ℃, heating to 850 ℃ at the speed of 3 ℃/min, calcining for 2 hours, and cooling after sintering to obtain the lithium cobaltate material.
Fig. 1 is a scanning electron microscope image of the lithium cobaltate material prepared in comparative example 3, and the surface of the lithium cobaltate particles before coating is uniform and smooth, and no other substances exist. Fig. 2 is a scanning electron microscope image of the aluminum metaphosphate coated lithium cobaltate material prepared in example 1, wherein the aluminum metaphosphate forms a coating structure on the surface of the lithium cobaltate through bonding with metal ions; according to the invention, the surface of the lithium cobaltate is coated with the aluminum metaphosphate, so that on one hand, the conductivity of the lithium cobaltate can be enhanced, and the rate performance of the material can be favorably exerted; on the other hand, the coating layer can effectively maintain the stability of the lithium cobaltate material, reduce the material lattice collapse caused by the insertion and the extraction of lithium ions in the charging and discharging process of the lithium cobaltate, and macroscopically, can enhance the stability of the material in the long-term charging and discharging cycle process.
The aluminum metaphosphate coated lithium cobaltate materials of examples 1 to 4 and comparative examples 1 to 3 are respectively dispersed in an NMP solution with a conductive agent Super P and a binder PVDF according to the mass ratio of 100:1:1, the mass ratio of the NMP to the aluminum metaphosphate coated lithium cobaltate material is 2:5, after sufficient stirring, the slurry is uniformly viscous and coated on an aluminum foil, and then the slurry is dried in vacuum to be punched into a positive plate, and the positive plate, a negative plate prepared from soft carbon and a carbonate electrolyte (1.0 mol/L LiPF dissolved in a mixed solvent of ethyl carbonate and dimethyl carbonate (the volume ratio is 1: 1))6) And the diaphragm material forms the lithium ion battery. Lithium ion batteries prepared from the aluminum metaphosphate coated lithium cobaltate materials of examples 1 to 4 and comparative examples 1 to 3 were respectively numbered as lithium ion batteries nos. 1 to 7.
And testing the discharge capacity of the No. 1-7 lithium ion battery. And (3) testing conditions are as follows: the batteries were charged at a constant current of 0.2C to 4.4V, then charged at a constant voltage of 4.4V to a cut-off current of 0.01C, left for 10 minutes, then discharged at a constant current of 0.2C to 3.0V, and left for 10 minutes, respectively. At this point 0.2C discharge capacity was recorded. The above procedure was repeated, wherein the constant discharge currents were varied to 0.5C, 1.0C and 2.0C, respectively, and the discharge capacities were recorded as 0.5C capacity, 1.0C capacity and 2.0C capacity, respectively. The results are shown in Table 1.
Discharge capacities of lithium ion batteries Nos. 11 to 7 in tables
And (3) carrying out cycle performance test on No. 1-7 lithium ion batteries: charging the batteries to 4.4 volts at 23 ℃ by using 1C current respectively, charging the batteries at constant voltage after the voltage is increased to 4.4 volts, stopping the current at 0.02C, and standing for 10 minutes; the discharge was then discharged to 3.0 volts at 1C current, left for 5 minutes and the first cycle discharge capacity was recorded. Repeating the steps 300, 500 and 800 times to obtain the capacity of the battery which is discharged to 3.0V by 1C current after 300, 500 and 800 cycles, and calculating the capacity maintenance rate before and after the cycles according to the following formula:
the capacity retention rate (nth cycle discharge capacity/first cycle discharge capacity) × 100%, where n is 300, 500, or 800.
The capacity retention rates of lithium ion batteries nos. 1 to 7 are shown in table 2.
TABLE 21-7 Capacity Retention rates for lithium ion batteries
As can be seen from tables 1 and 2, the metaphosphate-coated lithium cobalt oxide materials prepared in examples 1 to 3 as the positive electrode material of the lithium ion battery can impart excellent discharge capacity and cycle performance to the lithium ion battery, relative to the lithium cobalt oxide material of comparative example 3. Comparative example 1 a lithium ion battery was constructed by directly mixing and calcining aluminum dihydrogen phosphate, cobalt hydroxide, lithium nitrate, and ethylcellulose, and the prepared metaphosphate-coated lithium cobaltate material was used as a positive electrode material, and the battery performance was reduced compared to example 1.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (10)
1. A method for preparing a metaphosphate coated lithium cobaltate material is characterized by comprising the following steps:
dissolving hydroxide in a phosphoric acid solution, reacting to obtain a dihydrogen phosphate solution, adding cobalt salt, adjusting the pH to 9-13, further reacting, washing the obtained precipitate to be neutral, and drying to obtain a precursor;
dissolving the precursor, a lithium source and ethyl cellulose in an organic solvent for ball milling, and drying and calcining the obtained sol mixture to obtain the metaphosphate coated lithium cobaltate material.
2. The method of claim 1, wherein the hydroxide is one or more of barium hydroxide, calcium hydroxide, lithium hydroxide, lanthanum hydroxide, sodium hydroxide, aluminum hydroxide, yttrium hydroxide, potassium hydroxide, neodymium hydroxide, magnesium hydroxide, zinc hydroxide, niobium hydroxide, and strontium hydroxide.
3. The method of claim 1, wherein the cobalt salt is one or more of cobalt chloride, cobalt sulfate, cobalt nitrate, and cobalt acetate.
4. The method of preparing a metaphosphate coated lithium cobaltate material according to claim 1, wherein a molar mass ratio of the hydroxide to the cobalt salt is from 1: (20-80).
5. The method of claim 1, wherein the further reaction temperature is 35-100 ℃ and the reaction time is 30-120 min.
6. The method of claim 1, wherein the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium oxalate, and the amount of the lithium source is calculated as the molar ratio of Li to Co (0.9-1.1): 1.
7. The method of claim 1, wherein the ethyl cellulose accounts for 0.5-5.0 wt% of the total amount of the precursor, the lithium source, and the ethyl cellulose.
8. The method for preparing a metaphosphate coated lithium cobaltate material as defined in claim 1, wherein the temperature is raised to 600-900 ℃ at a rate of 1-5 ℃/min for calcination for 0.5-5 h.
9. A lithium ion battery, wherein a positive electrode material of the lithium ion battery comprises the metaphosphate coated lithium cobaltate material prepared in claim 1.
10. The lithium ion battery of claim 9, wherein the positive electrode material comprises a metaphosphate coated lithium cobaltate material, a conductive agent and a binder, and the mass ratio of the metaphosphate coated lithium cobaltate material to the conductive agent to the binder is 100: (0.1-5.0): (0.1-5.0).
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