CN111916712B - Method for modifying surface of lithium cobaltate positive electrode material by phosphorus-containing compound and lithium cobaltate positive electrode material - Google Patents
Method for modifying surface of lithium cobaltate positive electrode material by phosphorus-containing compound and lithium cobaltate positive electrode material Download PDFInfo
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Abstract
The invention provides a method for modifying the surface of a lithium cobaltate positive electrode material by a phosphorus-containing compound and the lithium cobaltate positive electrode material, which comprises the following steps: step 1, taking a lithium cobaltate powder material with a layered structure as a matrix, and carrying out ball milling and mixing with a phosphorus-containing compound according to a certain proportion to obtain a mixed powder material; and 2, heating the mixed powder material in an atmosphere protective environment to obtain the modified lithium cobaltate positive electrode material, wherein the interior of the modified lithium cobaltate positive electrode material is lithium cobaltate, the near surface of the modified lithium cobaltate positive electrode material comprises lithium cobaltate crystal lattices and phosphate radicals which form bonds, and the surface of the modified lithium cobaltate positive electrode material comprises an amorphous coating layer consisting of metal ions and phosphate radicals. The invention adopts the process control and treatment of mixing and heating the phosphorus-containing compound and the lithium cobaltate to modify the surface of lithium cobaltate particles, and enhances the stability of the lithium cobaltate structure by doping phosphate radicals in surface lattices; and the electrode electrolyte interface is effectively protected by containing the amorphous coating layer, so that the side reaction of the interface is reduced, and the rate capability and the cycle performance are improved.
Description
Technical Field
The invention relates to the technical field of lithium cobaltate positive electrode materials, in particular to a method for modifying the surface of a lithium cobaltate positive electrode material by a phosphorus-containing compound and the lithium cobaltate positive electrode material.
Background
The lithium cobaltate anode material is an ideal anode material of a lithium ion battery in the future, improves the working voltage of the lithium cobaltate and can provide higher specific capacity and energy density. However, when the charging voltage is 4.5V or more, lithium cobaltate faces a series of problems such as irreversible reduction of phase transition, c-axis shrinkage of particles by more than 3%, destruction of material structure by release of lattice oxygen, phase transition of interface, dissolution of transition metal, etc., resulting in degradation of cycle stability thereof.
In the prior art, surface coating of lithium cobaltate is the most commonly used modification means, such as MgO, ZnO, Al2O3、 AlPO4The material coating layers play a role in protecting lithium cobaltate and improve the cycle performance of the lithium cobaltate.
However, the current process for manufacturing the coating layer is usually very complicated and difficult to control in process control.
Prior art documents:
patent document 1: CN101859887 transition metal phosphate coated lithium ion battery composite anode material
Patent document 2: CN102054985 lithium manganate material and preparation method thereof
Patent document 3: CN102447106 spinel lithium manganate composite material and preparation method thereof, and lithium ion battery
Disclosure of Invention
The invention aims to provide a method for modifying the surface of a lithium cobaltate positive electrode material by a phosphorus-containing compound, which is different from the prior complex coating means, the method adopts the process control and treatment of mixing and heating the phosphorus-containing compound and the lithium cobaltate to modify the surface of lithium cobaltate particles, and enhances the stability of a lithium cobaltate structure by doping phosphate radicals in surface lattices; and by containing phosphate radical and Na+、Li+、Co3+The amorphous coating layer of the groups or ions effectively protects the interface of the electrode electrolyte and reduces the side reaction of the interface.
In order to achieve the above object, a first aspect of the present invention provides a method for modifying a surface of a lithium cobaltate positive electrode material with a phosphorus-containing compound, comprising ball-milling and mixing a lithium cobaltate powder material and the phosphorus-containing compound uniformly according to a certain proportion, and then heating the mixture at a certain temperature to obtain the phosphorus-containing compound surface-modified lithium cobaltate positive electrode material, wherein lithium cobaltate is arranged in the material, lithium cobaltate crystal lattices near the surface of the material form bonds with phosphate radicals, and the surface of the material is K+、Na+、Li+、Co3+One or more amorphous coatings consisting of phosphate radicals in the plasma.
Tests show that the lithium cobaltate anode material prepared by the invention is modified and coated by simplified process treatment, lithium cobaltate crystal lattices near the surface of the lithium cobaltate anode material are bonded with phosphate radicals, and the surface of the material is K+、Na+、Li+、Co3+One or more amorphous coatings consisting of the plasma and phosphate radicals lead the structure of the lithium cobaltate positive electrode material to be stable in a fully charged state due to the stabilizing effect of strong P-O covalent bonds in the phosphate radicals on O atoms.
Meanwhile, phosphate radical is easily adsorbed by transition metal and oxide thereof, and plays a role in protecting metal materials. Thus, the phosphate radical is in LiCoO2Surface adsorption or bonding, and compensation of dangling bond and unsaturated coordination relation on the surface of the material, thereby being beneficial to stabilizing LiCoO2The O atoms on the surface achieve the effect of stabilizing the surface interface structure of the material. Meanwhile, the phosphate radical can protect the transition metal elements from being corroded, and the effect of inhibiting the dissolution of Co atoms is achieved. Different from the conventional lengthy and complicated surface coating and low-efficiency surface coating modification means, the invention provides a method for introducing phosphate radical into LiCoO in situ, efficiently and controllably by using gas-solid interface reaction2The surface of the LiCoO is modified at a molecular level, and the LiCoO is stabilized by obtaining a P-O covalent bond through a gas-solid reaction or a liquid-solid reaction2O and Co in the surface lattice, realizing lithium cobaltate (LiCoO)2) The long-acting stable circulation of the anode material under the high voltage of 4.5V or even 4.6V improves the voltage, the capacity and the circulation stability of the lithium cobaltate in the lithium ion battery.
On the other hand, the method provided by the invention can obtain the surface modified lithium cobaltate material only by mixing and heating, the process is simple and easy to control, the modification effect is obvious, and the method is suitable for industrial production and application.
In some embodiments, the aforementioned modification treatment comprises the steps of:
step 1, taking a lithium cobaltate powder material with a layered structure as a matrix, and carrying out ball milling and mixing with a phosphorus-containing compound according to a certain proportion to obtain a mixed powder material;
and 2, heating the mixed powder material in an atmosphere protective environment to obtain the modified lithium cobaltate positive electrode material, wherein the interior of the modified lithium cobaltate positive electrode material is lithium cobaltate, the near surface of the modified lithium cobaltate positive electrode material comprises lithium cobaltate crystal lattices and phosphate radicals which form bonds, and the surface of the modified lithium cobaltate positive electrode material comprises an amorphous coating layer consisting of metal ions and phosphate radicals.
The space group of the layered lithium cobaltate is R-3m, Li+And Co3+Orderly and alternately arranged layer by layer in the cubic close packed O2-In the octahedral position constituted, Li+Can be in CoO2In the 2D direction, Li+Has a diffusion coefficient of 10- 11m2 s-1-10-12m2 s-1The theoretical capacity is up to 274mAh g which is higher than that of spinel oxide anode and lithium iron phosphate anode materials-1And has a very high volumetric energy density. During the modification and mixing heat treatment with the phosphate radical in LiCoO2Surface adsorption or bonding, and compensation of dangling bond and unsaturated coordination relation on the surface of the material, thereby being beneficial to stabilizing LiCoO2The O atoms on the surface achieve the effect of stabilizing the surface interface structure of the material. Meanwhile, the phosphate radical can protect the transition metal elements from being corroded, and the effect of inhibiting the dissolution of Co atoms is achieved.
Preferably, in the preparation process, the particle size range of the selected lithium cobaltate powder material is 1-50 microns, and the space group is R-3 m.
Preferably, the phosphorus-containing compound used in the past world is one or more of sodium hypophosphite, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate, phosphoric acid, hypophosphorous acid, diammonium hydrogen phosphate, ammonium hypophosphite, ammonium dihydrogen phosphate and trioctyl phosphate.
In an alternative embodiment, the metal ion comprises K+、Na+、Li+、Co3+At least one of (1).
Preferably, the mass ratio of the phosphorus-containing compound to the lithium cobaltate powder material is (0.005-1): 5. Especially (0.5-1): 5.
In an optional embodiment, the heating temperature is 200-500 ℃ and the heating time is 0.5-6 hours.
In alternative embodiments, the atmospheric protective environment is an air, argon, or nitrogen environment.
In an alternative embodiment, a small amount of alcohol may also be added during ball milling mixing to increase efficiency. When heating is carried out in the later period, the alcohol can be volatilized.
Thus, in combination with the results prepared in the examples, the lithium cobaltate (LiCoO) prepared according to the modification of the present invention2) The positive electrode material comprises a lithium cobaltate matrix, a near-surface interface layer and an amorphous coating wrapping the interface layer, wherein: the near-surface interface layer comprises a lithium cobaltate crystal lattice and phosphate radicals which form bonds, and the amorphous coating is formed by metal ions and the phosphate radicals.
It should be understood that all combinations of the foregoing concepts and additional concepts described in greater detail below can be considered as part of the inventive subject matter of this disclosure unless such concepts are mutually inconsistent. In addition, all combinations of claimed subject matter are considered a part of the presently disclosed subject matter.
The foregoing and other aspects, embodiments and features of the present teachings can be more fully understood from the following description taken in conjunction with the accompanying drawings. Additional aspects of the present invention, such as features and/or advantages of exemplary embodiments, will be apparent from the description which follows, or may be learned by practice of specific embodiments in accordance with the teachings of the present invention.
Drawings
The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Embodiments of various aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
fig. 1 shows X-ray diffraction patterns of modified lithium cobaltate positive electrode materials of examples 1, 3 and 5.
FIG. 2 is a high resolution TEM image of the surface coating of example 3.
FIG. 3 is a phosphorus 2p photoelectron spectrum before and after the removal of the coating layer by washing in example 3.
FIG. 4 shows the initial lithium cobaltate, example 3, example 5 in a half cell with 0.1Ag-1The current charge and discharge cycle performance, and the voltage range is 3.0-4.6V.
FIG. 5 shows the original lithium cobaltate, example 3, example 5 in a half cell with 0.1Ag-1、0.5Ag-1、1Ag-1、1.5A g-1、2Ag-1The multiplying power performance of current charging and discharging is that the voltage range is 3.0-4.6V.
Detailed Description
In order to better understand the technical content of the present invention, specific embodiments are described below with reference to the accompanying drawings.
In this disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. Embodiments of the present disclosure are not necessarily intended to include all aspects of the invention. It should be appreciated that the various concepts and embodiments described above, as well as those described in greater detail below, may be implemented in any of numerous ways, as the disclosed concepts and embodiments are not limited to any one implementation. In addition, some aspects of the present disclosure may be used alone, or in any suitable combination with other aspects of the present disclosure.
According to the embodiment of the invention, the method for modifying the surface of the lithium cobaltate positive electrode material by utilizing the phosphorus-containing compound is provided, the lithium cobaltate powder material and the phosphorus-containing compound are ball-milled and mixed uniformly according to a certain proportion, then the mixture is heated to obtain the surface-modified lithium cobaltate positive electrode material, the interior of the material is a lithium cobaltate positive electrode, lithium cobaltate crystal lattices near the surface of the material form bonds with phosphate radicals, and the surface of the material is K+、Na+、Li+、Co3+When the modified lithium cobaltate is used as the anode material of the lithium ion battery, the modified lithium cobaltate has the advantages of high voltage, high capacity, good cycle stability, good rate capability and the like.
Due to the stabilizing effect of strong P-O covalent bonds in phosphate radicals on O atoms, the lithium cobaltate positive electrode material has a stable structure in a fully charged state. Meanwhile, phosphate radical is easily adsorbed by transition metal and oxide thereof, and plays a role in protecting metal materials. Thus, the phosphate radical is in LiCoO2Surface adsorption or bonding, and compensation of dangling bond and unsaturated coordination relation on the surface of the material, thereby being beneficial to stabilizing LiCoO2The O atoms on the surface achieve the effect of stabilizing the surface interface structure of the material. Meanwhile, the phosphate radical can protect the transition metal elements from being corroded, and the effect of inhibiting the dissolution of Co atoms is achieved.
The modification idea used by the invention is generally different from the conventional long and complicated surface coating and low-efficiency surface coating modification means, and the invention provides the method for efficiently and controllably introducing phosphate radical into LiCoO in situ by using gas-solid interface reaction2The surface of the LiCoO is modified at a molecular level, and the LiCoO is stabilized by obtaining a P-O covalent bond through a gas-solid reaction or a liquid-solid reaction2O and Co in the surface lattice to realize LiCoO2The long-acting stable cycle under the high voltage of 4.5V or even 4.6V improves the voltage, the capacity and the cycle stability of the lithium cobaltate in the lithium ion battery.
In an alternative embodiment, the above-described improvement process includes the following processes:
1) ball-milling and uniformly mixing a lithium cobaltate powder material and a phosphorus-containing compound according to a certain proportion;
2) heating the mixture to obtain the lithium cobaltate crystal lattice and phosphate radical bonds near the surface of the material, wherein the surface of the material is formed by K+、Na+、Li+、Co3+One or more of metal ions and/or phosphate radicals.
Preferably, in the preparation process, the particle size range of the selected lithium cobaltate powder material is 1-50 microns, and the space group is R-3 m.
Preferably, the phosphorus-containing compound used in the past world is one or more of sodium hypophosphite, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate, phosphoric acid, hypophosphorous acid, diammonium hydrogen phosphate, ammonium hypophosphite, ammonium dihydrogen phosphate and trioctyl phosphate.
In an alternative embodiment, the metal ion comprises K+、Na+、Li+、Co3+At least one of (1).
Preferably, the mass ratio of the phosphorus-containing compound to the lithium cobaltate powder material is (0.005-1): 5, especially (0.5-1): 5, the heating temperature is 200-500 ℃, and the heating time is 0.5-6 hours, so that the modification of the lithium cobaltate powder base material is realized, and the high power performance and the cycle performance are improved. .
In alternative embodiments, the atmospheric protective environment is an air, argon, or nitrogen environment.
In an alternative embodiment, a small amount of alcohol may also be added during ball milling mixing to increase efficiency. When heating is carried out in the later period, the alcohol can be volatilized.
Thus, in combination with the results prepared in the examples, the lithium cobaltate (LiCoO) prepared according to the modification of the present invention2) The positive electrode material comprises a lithium cobaltate matrix, a near-surface interface layer and an amorphous coating wrapping the interface layer, wherein: the near-surface interface layer comprises a lithium cobaltate crystal lattice and phosphate radicals which form bonds, and the amorphous coating is formed by metal ions and the phosphate radicals.
Therefore, through the modification treatment which simplifies the operation and optimizes the result, the prepared lithium cobaltate material has high voltage, high capacity, high rate performance and excellent cycle performance when the charging voltage is 4.5V or more, has obvious modification effect and is suitable for industrial production and application.
We will now more specifically exemplify the above-mentioned material proportioning and modification treatment process.
[ example 1 ]
Mixing 0.1g of sodium phosphate and 10g of lithium cobaltate in a ball milling tank, carrying out ball milling for 2 hours, heating for 5-6 hours at 400 ℃ in air, and naturally cooling to obtain the surface modified lithium cobaltate material.
[ example 2 ]
Mixing 0.2g of sodium hypophosphite and 10g of lithium cobaltate, ball-milling for 2 hours, heating for 1 hour at 200 ℃ in argon, and naturally cooling to obtain the surface-modified lithium cobaltate material.
[ example 3 ]
Mixing 0.5g of sodium hypophosphite and 10g of lithium cobaltate, ball-milling for 2 hours, heating for 2 hours at 500 ℃ in air, and naturally cooling to obtain the surface modified lithium cobaltate material.
[ example 4 ]
Mixing 2g of diammonium hydrogen phosphate and 10g of lithium cobaltate, ball-milling for 3 hours, heating for 3 hours at 300 ℃ in argon, and naturally cooling to obtain the surface-modified lithium cobaltate material.
[ example 5 ]
Mixing and ball-milling 0.1g of diammonium hydrogen phosphate and 10g of lithium cobaltate for 2 hours, heating the mixture for 2 hours at 400 ℃ in air, and naturally cooling the mixture to obtain the surface-modified lithium cobaltate material.
[ example 6 ]
Mixing and ball-milling 0.2g of trioctyl phosphate and 10g of lithium cobaltate for 3 hours, heating the mixture for 1 hour at 200 ℃ in air, and naturally cooling the mixture to obtain the surface modified lithium cobaltate material.
[ example 7 ]
Mixing 1g of ammonium hypophosphite and 10g of lithium cobaltate, ball-milling for 2 hours, heating for 3 hours at 200 ℃ in argon, and naturally cooling to obtain the surface-modified lithium cobaltate material.
[ example 8 ]
Mixing 2g of ammonium hypophosphite and 10g of lithium cobaltate, ball-milling for 3 hours, heating for 1 hour at 300 ℃ in argon, and naturally cooling to obtain the surface-modified lithium cobaltate material.
[ description of test results ]
Referring to fig. 1, in the lithium cobaltate positive electrode materials prepared in examples 1, 3 and 5, the modification of the lithium cobaltate matrix by the phosphorus-containing compound was surface modification, and the position and intensity of the X-ray diffraction peak of the material were not changed. Further combining the schematic of the photoelectron spectrum of phosphorus 2p before and after the formation of the coating layer on the surface of the lithium cobaltate material shown in fig. 2 and the washing removal of the coating layer shown in fig. 3, the formed coating layer is an amorphous coating composed of metal ions and phosphate groups. And the surface crystal lattice of the modified material contains phosphate radical, and a photoelectron spectrum signal of phosphorus 2p still exists after the surface coating layer is washed and removed.
The original lithium cobaltate, the positive electrode materials prepared in the examples 3 and 5 are used as electrode materials, the electrode materials are respectively mixed with polyvinylidene fluoride and conductive carbon according to the mass ratio of 8:1:1, N-methyl pyrrolidone is used as a solvent to prepare slurry, the slurry is coated on aluminum foil and dried at 80 ℃, the slurry is cut into pole pieces, the pole pieces and the materials such as lithium pieces, electrolyte, diaphragms, battery cases and the like are assembled into button cells in a glove box for testing, and fig. 4 shows that the original lithium cobaltate is at 25 ℃, the positive electrode materials prepared in the examples 3 and 5 are used for 0.1Ag in a half cell-1The current charging and discharging cycle performance test result shows that the voltage interval is 3.0-4.6V; combining the original lithium cobaltate of fig. 5, example 3, example 5 with 0.1Ag in half-cell-1、0.5Ag-1、1Ag-1、1.5Ag-1、2Ag-1The rate capability of current charging and discharging is 3.0-4.6V, and the voltage interval is 3.0-4.6V, so that the rate capability and the cycle performance of the lithium cobaltate material prepared by the method are remarkably improved when the charging voltage is 4.5V or more, and the specific capacity of the anode material prepared by the method reaches more than 2 times of that of the traditional lithium cobaltate anode material and reaches 0.1-2.0Ag when the anode material is cycled for 50 circles-1The lithium cobaltate material prepared by the invention is obviously superior to the traditional lithium cobaltate anode material when charging and discharging under the current density, and the current density is 1.0Ag-1Above, the specific capacity is superior to more than 50% of that of the traditional anode material.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be determined by the appended claims.
Claims (6)
1. A method for modifying the surface of a lithium cobaltate positive electrode material by a phosphorus-containing compound is characterized by comprising the following steps of:
step 1, taking a lithium cobaltate powder material with a layered structure as a matrix, and carrying out ball milling and mixing with a phosphorus-containing compound according to a certain proportion to obtain a mixed powder material; wherein the phosphorus-containing compound is sodium phosphate, sodium hypophosphite, diammonium hydrogen phosphate, trioctyl phosphate or ammonium hypophosphite;
and 2, heating the mixed powder material at 200-500 ℃ for 0.5-6 hours in an air environment to obtain the modified lithium cobaltate positive electrode material, wherein the interior of the modified lithium cobaltate positive electrode material is lithium cobaltate, the near surface of the modified lithium cobaltate positive electrode material comprises lithium cobaltate crystal lattices and phosphate radicals which form bonds, and the surface of the modified lithium cobaltate positive electrode material comprises an amorphous coating layer consisting of metal ions and phosphate radicals.
2. The method for modifying the surface of the lithium cobaltate cathode material by the phosphorus-containing compound according to claim 1, wherein the particle size range of the lithium cobaltate powder material is 1-50 micrometers, and the space group is R-3 m.
3. The method for modifying the surface of a lithium cobaltate positive electrode material with a phosphorus-containing compound according to claim 1, wherein the metal ions comprise Na+、Li+、Co3+At least one of (1).
4. The method for modifying the surface of the lithium cobaltate positive electrode material by using the phosphorus-containing compound according to any one of claims 1 to 3, wherein the mass ratio of the phosphorus-containing compound to the lithium cobaltate powder material is (0.005-1): 5.
5. The lithium cobaltate positive electrode material prepared by the method for modifying the surface of the lithium cobaltate positive electrode material by using the phosphorus-containing compound according to any one of claims 1 to 4, is characterized by comprising a lithium cobaltate matrix, a near-surface interface layer and an amorphous coating wrapping the interface layer, wherein the near-surface interface layer is formed by bonding lithium cobaltate crystal lattices and phosphate groups, and the amorphous coating is formed by an amorphous coating consisting of metal ions and phosphate groups.
6. The lithium cobaltate positive electrode material according to claim 5, wherein the metal ions comprise Na+、Li+、Co3+At least one of (1).
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| CN110400929A (en) * | 2019-09-02 | 2019-11-01 | 中南大学 | A kind of metal-doped ternary positive electrode active material of Phosphate coating and its preparation and application |
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