CN109713250B

CN109713250B - Preparation method of core-shell structure precursor of lithium battery positive electrode material

Info

Publication number: CN109713250B
Application number: CN201811376242.5A
Authority: CN
Inventors: 李淼; 武斌; 李钊华; 张继泉; 周恒辉; 杨新河
Original assignee: Pulead Technology Industry Co ltd; Beijing Taifeng Xianxing New Energy Technology Co ltd
Current assignee: Pulead Technology Industry Co ltd; Beijing Taifeng Xianxing New Energy Technology Co ltd
Priority date: 2018-11-19
Filing date: 2018-11-19
Publication date: 2021-05-25
Anticipated expiration: 2038-11-19
Also published as: CN109713250A

Abstract

The invention discloses a preparation method of a precursor with a core-shell structure of a lithium battery anode material, belonging to the field of lithium battery electrode materials. The preparation method adopted by the invention has low requirements on equipment, the operation method is simple, and the prepared precursor with the core-shell structure has a uniform and controllable shell layer. Under the voltage of 4.50V and higher, compared with the anode material prepared by the conventional precursor, the anode material prepared by the precursor with the core-shell structure has better cycle performance.

Description

Preparation method of core-shell structure precursor of lithium battery positive electrode material

Technical Field

The invention belongs to the field of lithium battery electrode materials, and relates to a preparation method of a core-shell structure precursor of a lithium battery anode material.

Background

The lithium battery anode material with a layered structure is the most fully researched and widely applied consumer lithium battery anode material at present, such as LiCoO₂、LiNi_0.5Co_0.2Mn_0.3O₂. In recent years, the operating voltage of consumer lithium batteries is higher and higher, and the requirements on the mass energy density, safety performance and the like of the cathode material are also higher and higher. Core-shell with core of laminated structureThe core part of the structural anode material can ensure the mass energy density, and the shell part of the structural anode material has better high-temperature stability and can simultaneously meet the requirements of high energy density and high safety performance.

Such positive electrode materials are being increasingly widely used in lithium ion battery products. For example, the Jens Martin Paulsen patent (US20120134914A1) mixes LiCoO by dry process₂、Li₂CO₃And preparing LiNi from Ni/MnOOH_0.5Mn_0.5O₂Island-coated layered LiCoO₂(ii) a The King Seong-Bae patent (WO2009057834A1) prepares a core-shell structure material with an olivine structure coating layered structure in a dry mixing mode; however, these two methods do not ensure uniform distribution of the shell. In the patent of HAO Jianjun (EP2973794B1), it is described that a shell material is prepared by precipitation and then coated with laminar LiCo by wet coating_0.2Ni_0.8O₂On the surface, the shell prepared by the precipitation method is uniformly distributed, but the process is complex. The above methods are common methods for preparing core-shell structure materials. In addition, SUN Yang Kook (EP2102927B1) prepares a precursor with a core-shell structure by a coprecipitation method, and then prepares LiMn_1-xM_xO_yA core-shell material. The method puts the emphasis on providing qualified precursors with core-shell structures, and the adopted coprecipitation method has complex process.

The above methods have problems of uneven distribution of the shell layer or complicated process.

Disclosure of Invention

The invention aims to provide a preparation method of a precursor of a lithium battery anode material with a core-shell structure. The precursor with the core-shell structure is prepared by adopting a supersaturated solution precipitation method, and the method can ensure that metal salt in the solution is gradually precipitated and coated on the surface of the conventional precursor in a longer heating and stirring process to form a uniform shell layer. The precursor with the core-shell structure prepared by the invention has uniformly distributed shell layers and a simple preparation process. The lithium battery anode material prepared by the precursor with the core-shell structure has higher capacity and good safety performance under the voltage of 4.5V or even higher.

A preparation method of a precursor of a core-shell structure of a lithium battery anode material comprises the following steps:

weighing metal salt and a solvent, wherein the metal salt contains metal elements required by a shell layer to be prepared and is prepared into a metal salt solution;

weighing a conventional precursor composed of at least one of cobaltosic oxide and nickel-cobalt-manganese hydroxide, slowly adding the conventional precursor into the metal salt solution, heating and stirring until the solution is supersaturated, and volatilizing the solvent completely to obtain a mixture;

and (3) placing the mixture into an oven for standing and drying, and covering a uniform shell layer on the surface of the conventional precursor after completely drying to obtain the precursor with the core-shell structure.

Further, the concentration of the metal element in the metal salt solution is more than 0 and less than or equal to the saturation concentration.

Further, the volume of the metal salt solution is calculated by the following formula:

V＝W×m×10^-6/ρ (1)

wherein V is the volume of the metal salt solution (unit is mL), W is the mass of the conventional precursor (unit is g), m is the mass of the metal element (unit is ppm) required for preparing the shell when the conventional precursor is 1g, rho is the concentration of the metal element (unit is g/mL) required for preparing the shell in the solution, and 0< rho is less than or equal to the saturation concentration of the metal element in the metal salt solution.

Furthermore, the metal elements contained in the shell layer are one or more of Na, Mg, Ca, Al, Ga, V, Cr, Fe, Ni, Co, Mn, Ti, Zr, Si and Ge.

Further, m (Na) ≦ 6.0wt.%, m (Mg) ≦ 1.0wt.%, m (Al) ≦ 1.0wt.%, m (Ti) ≦ 1.0wt.%, m (Zr) ≦ 1.0wt.%, m (Ni) ≦ 3.0wt.%, m (Mn) ≦ 3.0 wt.%.

Further, rho is less than or equal to 0.10 g/mL.

Further, weighing metal salt according to the concentration of the metal salt solution, putting the metal salt into a volumetric flask, and adding a solvent to a constant volume.

Further, the metal salt solution is measured by a measuring cylinder, and is poured into a beaker together with the conventional precursor to be heated and stirred.

Further, the temperature of the oven was 100 ℃.

Further, the solvent is one of deionized water, industrial alcohol with a purity of 95vol.% and absolute ethyl alcohol.

Furthermore, the metal salt can be decomposed at high temperature and is one or more of acetate, nitrate, meta-aluminate and organic metal salt, and the metal elements required by the contained shell layer are one or more of Na, Mg, Ca, Al, Ga, V, Cr, Fe, Ni, Co, Mn, Ti, Zr, Si and Ge.

Further, the organic metal salt includes tetrabutyl titanate, aluminum isopropoxide.

Further, the temperature during heating and stirring is 50-100 ℃.

The supersaturated solution precipitation method adopted by the invention can ensure that the metal salt in the solution is gradually precipitated and coated on the surface of the conventional precursor in a longer heating and stirring process to form a uniform shell layer. The surface of the precursor of the lithium battery anode material is generally provided with pores, and the metal salt solution fully infiltrates the precursor, so that the precursor can be coated and can also be immersed into the precursor to a certain depth. The invention utilizes the morphological characteristics of the conventional precursor and adopts a supersaturated solution precipitation method to prepare the precursor with the core-shell structure. The metal elements contained in the shell layer prepared by the method are not only distributed on the surface of the conventional precursor, but also partially enter the pores of the conventional precursor to form gradient distribution. By adopting the preparation method, the thickness of the shell layer is mainly determined by the concentration and the volume of the metal salt solution, the gradient distribution is mainly determined by the appearance of the conventional precursor and the wettability of the metal salt solution, and the components of the shell layer are determined by the components, the concentration and the volume of the metal salt solution. The thickness and composition of the shell layer can be adjusted by selecting conventional precursors and metal salt solutions.

The supersaturated solution precipitation method provided by the invention can obtain the precursor with the core-shell structure, the process operation is simple, the requirement on production equipment is low, and the cycle performance and the safety performance of the lithium battery anode material prepared by the precursor with the core-shell structure are obviously superior to those of the lithium battery anode material prepared by the conventional precursor.

Drawings

FIGS. 1A-1B are SEM images of the morphology of conventional nickel cobalt manganese hydroxide in comparative example 1 and examples 1-3, wherein FIG. 1A is at a magnification of 1K and FIG. 1B is at a magnification of 10K.

FIG. 2 is a SEM image of the core-shell structure of Ni-Co-Mn hydroxide in example 3.

Fig. 3A to 3B are electrical property diagrams of the cathode material prepared from the core-shell structure nickel-cobalt-manganese hydroxide in example 3, in which fig. 3A is a charge-discharge curve diagram, and fig. 3B is a cycle capacity retention ratio diagram.

Fig. 4A to 4C are SEM images of the morphology of conventional cobaltosic oxide in comparative example 2 and examples 4 to 9, in which fig. 4A is magnified at 1K, fig. 4B is magnified at 5K, and fig. 4C is a cross-sectional morphology.

Fig. 5A is a SEM image of the morphology of the core-shell structure cobaltosic oxide in example 4, and fig. 5B is a distribution diagram of its Al element.

Fig. 6A is a SEM image of the morphology of the core-shell structure cobaltosic oxide in example 5, and fig. 6B is a distribution diagram of its Al element.

Fig. 7A is a SEM image of the morphology of the core-shell structure cobaltosic oxide in example 6, and fig. 7B is a distribution diagram of its Al element.

Fig. 8A to 8B are graphs of electrical properties of the cathode material prepared from the core-shell structure cobaltosic oxide in example 6, in which fig. 8A is a charge-discharge graph and fig. 8B is a graph of the cycle capacity retention rate.

Fig. 9A is a SEM image of the morphology of the core-shell structure cobaltosic oxide in example 7, fig. 9B is a Ni element distribution diagram thereof, and fig. 9C is a Mn element distribution diagram thereof.

Fig. 10A is a SEM image of the morphology of the core-shell structure cobaltosic oxide in example 8, fig. 10B is a Ni element distribution diagram thereof, and fig. 10C is a Mn element distribution diagram thereof.

Fig. 11A is a SEM image of the morphology of the core-shell structure cobaltosic oxide in example 9, fig. 11B is a Ni element distribution diagram thereof, and fig. 11C is a Mn element distribution diagram thereof.

Fig. 12A to 12B are graphs of electrical properties of the positive electrode material prepared from the cobaltosic oxide with the core-shell structure in example 9, in which fig. 12A is a charge-discharge graph, and fig. 12B is a graph of the cycle capacity retention rate.

Fig. 13A-13B are SEM images of the morphology of conventional cobaltosic oxide in comparative example 3 and example 10, where fig. 13A is at a magnification of 1K and fig. 13B is at a magnification of 5K.

Fig. 14A-14B are SEM images of the morphology of the conventional nickel cobalt manganese hydroxide in comparative example 3 and example 10, where fig. 14A is at a magnification of 1K and fig. 14B is at a magnification of 5K.

Fig. 15 is a SEM image of the morphology of the mixed precursors in comparative example 3 and example 10, at a magnification of 5K.

Fig. 16A is a SEM image of the morphology of the core-shell structured mixed precursor in example 10, fig. 16B is an Al element distribution diagram thereof, and fig. 16C is a Zr element distribution diagram thereof.

Fig. 17A to 17B are graphs of electrical properties of the cathode material prepared from the core-shell structure mixed precursor in example 10, in which fig. 17A is a charge-discharge curve, and fig. 17B is a graph of cycle capacity retention rate.

Fig. 18A to 18B are SEM images of the morphology of conventional cobaltosic oxide in comparative example 4 and example 11, in which fig. 18A is at a magnification of 1K and fig. 18B is at a magnification of 5K.

Fig. 19A-19B are SEM images of the morphology of the conventional nickel cobalt manganese hydroxide in comparative example 4 and example 11, where fig. 19A is at a magnification of 1K and fig. 19B is at a magnification of 5K.

Fig. 20 is a SEM image of the morphology of the mixed precursor in comparative example 4 and example 11, at a magnification of 1K.

Fig. 21A is a SEM image of the morphology of the core-shell structured mixed precursor in example 11, fig. 21B is an Al element distribution diagram thereof, and fig. 21C is a Zr element distribution diagram thereof.

Fig. 22A to 22B are electrical property diagrams of the cathode material prepared from the core-shell structure mixed precursor in example 11, in which fig. 22A is a charge-discharge curve diagram and fig. 22B is a cycle capacity retention ratio diagram.

Detailed Description

The present invention is illustrated by way of example, but is not limited thereto.

Comparative example 1

Mixing conventional nickel cobalt manganese hydroxide (Ni: Co: Mn ═ 5:2:3) with lithium carbonate in a certain proportion, sintering at 950 ℃ for 10 hours, crushing and sieving to obtain the conventional ternary material. The electrical properties of this positive electrode material are shown in fig. 3A-3B.

Example 1

The morphology and pore distribution of conventional nickel cobalt manganese hydroxide (Ni: Co: Mn ═ 5:2:3) are shown in fig. 1A-1B and table 1, based on which core-shell structure precursors were prepared with Ti ═ 2000 ppm. Tetrabutyl titanate is selected as a solute, absolute ethyl alcohol is selected as a solvent, and 100mL of solution with the Ti concentration of 0.01g/mL is prepared. 20g of nickel cobalt manganese hydroxide was weighed, and 4.0mL of tetrabutyl titanate solution required for shell layer was calculated according to formula (1). Measuring 4.0mL of tetrabutyl titanate solution, stirring at the room temperature at the speed of 400r/min, then slowly pouring nickel-cobalt-manganese hydroxide, heating to 50 ℃, and still stirring at the speed of 400r/min until the absolute ethyl alcohol is completely volatilized. And (3) placing the mixture into an oven at 100 ℃, standing and drying for 2h to obtain a precursor with a core-shell structure.

TABLE 1 pore distribution of conventional nickel cobalt manganese hydroxides

Characteristics of precursor	BET(m²/g)	Total pore volume (cm)³/g)	Average pore diameter (nm)
				Conventional nickel cobalt manganese hydroxide	119.9	0.153	4.523

Example 2

The pore distribution of conventional nickel cobalt manganese hydroxide (Ni: Co: Mn ═ 5:2:3) was as shown in fig. 1A-1B and table 1, based on which core-shell structure precursors were prepared with Ti ═ 2000 ppm. Tetrabutyl titanate is selected as a solute, absolute ethyl alcohol is selected as a solvent, and 100mL of solution with the Ti concentration of 0.001g/mL is prepared. 20g of nickel cobalt manganese hydroxide was weighed, and 40mL of tetrabutyl titanate solution required for shell layer was calculated according to the formula (1). Measuring 40mL of tetrabutyl titanate solution, stirring at room temperature at the speed of 200r/min, then slowly pouring nickel-cobalt-manganese hydroxide, heating to 100 ℃, and still stirring at the speed of 200r/min until the absolute ethyl alcohol is completely volatilized. And (3) placing the mixture into an oven at 100 ℃, standing and drying for 2h to obtain a precursor with a core-shell structure.

Example 3

The pore distribution of conventional nickel cobalt manganese hydroxide (Ni: Co: Mn ═ 5:2:3) was as shown in fig. 1A-1B and table 1, based on which core-shell structure precursors were prepared with Ti ═ 2000 ppm. Tetrabutyl titanate is selected as a solute, absolute ethyl alcohol is selected as a solvent, and 100mL of solution with the Ti concentration of 0.001g/mL is prepared. 20g of nickel cobalt manganese hydroxide was weighed, and 40mL of tetrabutyl titanate solution required for shell layer was calculated according to the formula (1). Measuring 40mL of tetrabutyl titanate solution, stirring at room temperature at the speed of 300r/min, then slowly pouring nickel-cobalt-manganese hydroxide, heating to 70 ℃, and still stirring at the speed of 300r/min until the absolute ethyl alcohol is completely volatilized. And (3) placing the mixture into a baking oven at 100 ℃, standing and drying for 2h to obtain a core-shell precursor with the morphology shown in figure 2, wherein the EDS result shows that the surface of the nickel-cobalt-manganese hydroxide is rich in Ti. And mixing the precursor with the core-shell structure with lithium carbonate in a certain proportion, sintering at 950 ℃ for 10h, and crushing and sieving to obtain the ternary material with the core-shell structure. The electrical properties of this positive electrode material are shown in fig. 3A-3B.

The Ti content of the core-shell structure precursor in examples 1, 2, and 3 is shown in table 2, and the actual Ti content detected by ICP (inductively coupled plasma spectrometer) was close to the designed Ti content, and almost no Ti was lost.

TABLE 2 Ti content of core-shell structured Ni-Co-Mn hydroxide

Ti content	Design value (ppm)	Measured value (ppm)
			Core-shell structure nickel-cobalt-manganese hydroxide in example 1	2000	1967
Core-shell structure nickel-cobalt-manganese hydroxide in example 2	2000	1950
			Core-shell structure nickel-cobalt-manganese hydroxide in example 3	2000	1974

Comparative example 2

Mixing conventional cobaltosic oxide with lithium carbonate in a certain proportion, sintering at 1000 ℃ for 10h, crushing and sieving to obtain the conventional lithium cobaltate material. The electrical properties of this positive electrode material are shown in fig. 8A-8B and fig. 12A-12B.

Example 4

The pore distribution of conventional cobaltosic oxide is shown in fig. 4A-4C and table 3, on the basis of which a core-shell precursor having Al of 5000ppm was prepared. 100mL of solution with the Al concentration of 0.05g/mL is prepared by selecting aluminum nitrate nonahydrate as a solute and deionized water as a solvent. 100g of cobaltosic oxide was weighed, and 10mL of an aluminum nitrate solution was calculated according to the formula (1) as required for preparation of a shell layer. 10mL of aluminum nitrate solution is measured and stirred at the speed of 400r/min at room temperature, then cobaltosic oxide is slowly poured in, heated to 70 ℃, and stirred at the speed of 400r/min until the deionized water is completely volatilized. And (3) placing the mixture into an oven at 100 ℃, standing and drying for 4h to obtain a precursor with a core-shell structure, wherein the morphology of the precursor is shown in figures 5A-5B, and the EDS result shows that small particles containing Al are uniformly distributed on the surface of cobaltosic oxide.

TABLE 3 pore distribution of conventional Cobaltosic tetroxide

Characteristics of precursor	BET(m²/g)	Total pore volume (cm)³/g)	Average pore diameter (nm)
				Conventional cobaltosic oxide	4.191	0.021	23.753

Example 5

The pore distribution of conventional cobaltosic oxide is shown in fig. 4A-4C and table 3, on the basis of which a core-shell precursor having Al of 5000ppm was prepared. Aluminum isopropoxide is selected as a solute, absolute ethyl alcohol is selected as a solvent, and 100mL of solution with the Al concentration of 0.05g/mL is prepared. Weighing 100g of cobaltosic oxide, and calculating 10mL of aluminum isopropoxide solution required for preparing a shell layer according to a formula (1). 10mL of aluminum isopropoxide solution is measured, stirred at the speed of 400r/min at room temperature, then cobaltosic oxide is slowly poured in, heated to 70 ℃, and stirred at the speed of 400r/min until the absolute ethyl alcohol is completely volatilized. And (3) placing the mixture into an oven at 100 ℃, standing and drying for 4h to obtain a precursor with a core-shell structure, wherein the morphology of the precursor is shown in FIGS. 6A-6B, and EDS results show that small particles containing Al are mainly distributed on the surface of cobaltosic oxide and an Al-enriched area is arranged on the part of the precursor.

Example 6

The pore distribution of conventional cobaltosic oxide is shown in fig. 6A-6B and table 3, on the basis of which a core-shell precursor having Al of 5000ppm was prepared. 100mL of solution with the Al concentration of 0.05g/mL is prepared by selecting sodium metaaluminate as a solute and deionized water as a solvent. Weighing 100g of cobaltosic oxide, and calculating 10mL of sodium metaaluminate solution required for preparing a shell layer according to a formula (1). 10mL of sodium metaaluminate solution is measured and stirred at the speed of 400r/min at room temperature, then cobaltosic oxide is slowly poured in, heated to 70 ℃, and stirred at the speed of 400r/min until the deionized water is completely volatilized. And (3) placing the mixture into an oven at 100 ℃, standing and drying for 4h to obtain a precursor with a core-shell structure, wherein the morphology of the precursor is shown in FIGS. 7A-7B, and the EDS result shows that small particles containing Al are uniformly distributed on the surface of cobaltosic oxide. The cobaltosic oxide with the core-shell structure is mixed with lithium carbonate in a certain proportion, sintered for 10 hours at 1000 ℃, and crushed and sieved to obtain the lithium cobaltate material with the core-shell structure. The electrical properties of this positive electrode material are shown in fig. 8A-8B.

The Al content of the core-shell structure precursor is shown in table 4, and the actual Al content detected by ICP is close to the designed Al content, with almost no loss of Al.

TABLE 4 Al content of Cobaltosic oxide in core-shell structure

Al content	Design value (ppm)	Measured value (ppm)
			In example 4Cobaltosic oxide with core-shell structure	5000	4793
Cobaltosic oxide of core-shell structure in example 5	5000	4832
			Cobaltosic oxide of core-shell structure in example 6	5000	4811

Example 7

The pore distribution of conventional cobaltosic oxide is shown in fig. 6A-6B and table 3, and on the basis of this, a core-shell structure precursor having Ni of 4000ppm and Mn of 4000ppm was prepared. Nickel acetate tetrahydrate and manganese acetate tetrahydrate are selected as solutes, industrial alcohol with the purity of 95vol.% is selected as a solvent, and 100mL of solution with the total concentration of Ni/Mn of 0.01g/mL is prepared. 50g of cobaltosic oxide is weighed, and 40mL of nickel/manganese solution required for preparing a shell layer is calculated according to the formula (1). 40mL of nickel/manganese solution is measured, stirred at the speed of 300r/min at room temperature, then cobaltosic oxide is slowly poured into the solution, the solution is heated to 80 ℃, and the solution is still stirred at the speed of 300r/min until the deionized water is completely volatilized. And (3) placing the mixture into an oven at 100 ℃, standing and drying for 8h to obtain a precursor with a core-shell structure, wherein the morphology of the precursor is shown in FIGS. 9A-9C, and the EDS result shows that Ni and Mn are uniformly distributed on the surface of cobaltosic oxide.

Example 8

The pore distribution of conventional cobaltosic oxide is shown in fig. 6A-6B and table 3, and on the basis of this, a core-shell structure precursor having Ni of 4000ppm and Mn of 4000ppm was prepared. Nickel acetate tetrahydrate and manganese acetate tetrahydrate are selected as solutes, deionized water is selected as a solvent, and 100mL of solution with the total concentration of Ni/Mn of 0.01g/mL is prepared. 50g of cobaltosic oxide is weighed, and 40mL of nickel/manganese solution required for preparing a shell layer is calculated according to the formula (1). 40mL of nickel/manganese solution is measured, stirred at the speed of 300r/min at room temperature, then cobaltosic oxide is slowly poured in, heated to 80 ℃, and stirred at the speed of 300r/min until the absolute ethyl alcohol is completely volatilized. And (3) placing the mixture into an oven at 100 ℃, standing and drying for 8h to obtain a precursor with a core-shell structure, wherein the morphology of the precursor is shown in figures 10A-10C, and the EDS result shows that Ni and Mn are uniformly distributed on the surface of cobaltosic oxide.

Example 9

The pore distribution of conventional cobaltosic oxide is shown in fig. 6A-6B and table 3, and on the basis of this, a core-shell structure precursor having Ni of 4000ppm and Mn of 4000ppm was prepared. Nickel nitrate hexahydrate and manganese nitrate tetrahydrate are selected as solutes, industrial alcohol with the purity of 95vol.% is selected as a solvent, and 100mL of solution with the total concentration of Ni/Mn of 0.01g/mL is prepared. 50g of cobaltosic oxide is weighed, and 40mL of nickel/manganese solution required for preparing a shell layer is calculated according to the formula (1). 40mL of nickel/manganese solution is measured, stirred at the speed of 300r/min at room temperature, then cobaltosic oxide is slowly poured into the solution, the solution is heated to 80 ℃, and the solution is still stirred at the speed of 300r/min until the deionized water is completely volatilized. And (3) placing the mixture into an oven at 100 ℃, standing and drying for 8h to obtain a precursor with a core-shell structure, wherein the morphology of the precursor is shown in FIGS. 11A-11C, and the EDS result shows that Ni and Mn are uniformly distributed on the surface of cobaltosic oxide. The cobaltosic oxide with the core-shell structure is mixed with lithium carbonate in a certain proportion, sintered for 10 hours at 1000 ℃, and crushed and sieved to obtain the lithium cobaltate material with the core-shell structure. The electrical properties of this positive electrode material are shown in fig. 12A-12B.

The contents of Ni and Mn in the core-shell structure precursor are shown in Table 5, the actual contents of Ni and Mn detected by ICP are close to the designed contents of Ni and Mn, and Ni and Mn are hardly lost.

TABLE 5 Ni and Mn contents of Cobaltosic oxide of core-shell structure

Comparative example 3

The pore distribution of the conventional cobalt oxide is shown in fig. 13A to 13B and table 6, and the pore distribution of the conventional nickel cobalt manganese hydroxide (Ni: Co: Mn: 8:1:1) is shown in fig. 14A to 14B and table 6. Conventional cobaltosic oxide and conventional nickel-cobalt-manganese hydroxide are mixed according to the mass ratio of 1:1 to prepare a uniform mixed precursor, and the morphology of the uniform mixed precursor is shown in fig. 15. And mixing the mixture of cobaltosic oxide and nickel-cobalt-manganese hydroxide with lithium carbonate in a certain proportion, sintering at 850 ℃ for 10h, crushing and sieving to obtain the lithium cobaltate and ternary element mixed material. The electrical properties of this positive electrode material are shown in fig. 17A-17B.

TABLE 6 pore distribution of conventional precursors

Characteristics of precursor	BET(m²/g)	Total pore volume (cm)³/g)	Average pore diameter (nm)
				Conventional cobaltosic oxide	2.35	0.0033	18.314
Conventional nickel cobalt manganese hydroxide	83.4	0.109	4.632

Example 10

The pore distribution of the conventional cobalt oxide is shown in fig. 13A to 13B and table 6, and the pore distribution of the conventional nickel cobalt manganese hydroxide (Ni: Co: Mn: 8:1:1) is shown in fig. 14A to 14B and table 6. Conventional cobaltosic oxide and conventional nickel-cobalt-manganese hydroxide are mixed according to the mass ratio of 1:1 to prepare a uniform mixed precursor, and the morphology of the uniform mixed precursor is shown in fig. 15. On the basis of the above, a core-shell structure mixed precursor of which Al is 2000ppm/Zr is 1000ppm was prepared. Aluminum isopropoxide and tetrabutyl zirconate are selected as solutes, absolute ethyl alcohol is selected as a solvent, and 100mL of solution with the Al concentration of 0.010g/mL and the Zr concentration of 0.005g/mL is prepared. Weighing 100g of mixed precursor, and calculating 20.0mL of Al/Zr solution required by the shell layer according to the formula (1). 20.0ml of LAl/Zr solution is measured and stirred at the speed of 300r/min at room temperature, then the mixture of cobaltosic oxide and nickel-cobalt-manganese hydroxide is slowly poured in, heated to 60 ℃, and then stirred at the speed of 400r/min until the absolute ethyl alcohol is completely volatilized. And (3) placing the mixture into an oven at 100 ℃ for standing and drying for 2h to obtain the precursor with the core-shell structure, wherein the shape of the precursor is shown in FIGS. 16A-16C, and EDS results show that Al and Zr are uniformly distributed on the surface of the mixed precursor.

The Al and Zr contents of the core-shell structure mixed precursor are shown in table 7, and the actual Al and Zr contents detected by ICP are close to the designed Al and Zr contents, with almost no loss of Al and Zr.

TABLE 7 Al and Zr contents of core-shell structured hybrid precursors

And mixing the mixed precursor with the core-shell structure with lithium carbonate in a certain proportion, sintering at 850 ℃ for 10h, crushing and sieving to obtain the lithium cobaltate and ternary element mixed material with the core-shell structure. The electrical properties of this positive electrode material are shown in fig. 17A-17B.

Comparative example 4

The pore distribution of the conventional cobalt oxide is shown in fig. 18A to 18B and table 8, and the pore distribution of the conventional nickel cobalt manganese hydroxide (Ni: Co: Mn: 8:1:1) is shown in fig. 19A to 19B and table 8. Conventional cobaltosic oxide and conventional nickel-cobalt-manganese hydroxide are mixed according to the mass ratio of 1:1 to prepare a uniform mixed precursor, and the morphology of the uniform mixed precursor is shown in fig. 20. And mixing the mixture of cobaltosic oxide and nickel-cobalt-manganese hydroxide with lithium carbonate in a certain proportion, sintering at 850 ℃ for 10h, crushing and sieving to obtain the lithium cobaltate and ternary element mixed material. The electrical properties of this positive electrode material are shown in fig. 22A-22B.

TABLE 8 pore distribution of conventional precursors

Characteristics of precursor	BET(m²/g)	Total pore volume (cm)³/g)	Average pore diameter (nm)
				Conventional cobaltosic oxide	4.128	0.0032	17.164
Conventional nickel cobalt manganese hydroxide	10.675	0.0961	5.724

Example 11

The pore distribution of the conventional cobalt oxide is shown in fig. 18A to 18B and table 8, and the pore distribution of the conventional nickel cobalt manganese hydroxide (Ni: Co: Mn: 8:1:1) is shown in fig. 19A to 19B and table 8. Conventional cobaltosic oxide and conventional nickel-cobalt-manganese hydroxide are mixed according to the mass ratio of 1:1 to prepare a uniform mixed precursor, and the morphology of the uniform mixed precursor is shown in fig. 20. On the basis of the above, a core-shell structure mixed precursor with 1000ppm of Al/2000 ppm of Zr was prepared. Aluminum isopropoxide and tetrabutyl zirconate are selected as solutes, absolute ethyl alcohol is selected as a solvent, and 100mL of solution with the Al concentration of 0.005g/mL and the Zr concentration of 0.010g/mL is prepared. Weighing 100g of mixed precursor, and calculating 20.0mL of Al/Zr solution required by the shell layer according to the formula (1). 20.0ml of LAl/Zr solution is measured and stirred at the speed of 300r/min at room temperature, then the mixture of cobaltosic oxide and nickel-cobalt-manganese hydroxide is slowly poured in, heated to 60 ℃, and then stirred at the speed of 400r/min until the absolute ethyl alcohol is completely volatilized. And (3) placing the mixture into an oven at 100 ℃ for standing and drying for 2h to obtain the precursor with the core-shell structure, wherein the morphology of the precursor is shown in figures 21A-21C, and EDS results show that Al and Zr are uniformly distributed on the surface of the mixed precursor.

The Al and Zr contents of the core-shell structure mixed precursor are shown in table 9, and the actual Al and Zr contents detected by ICP are close to the designed Al and Zr contents, with almost no loss of Al and Zr.

TABLE 9 Al and Zr contents of core-shell structured hybrid precursors

And mixing the mixed precursor with the core-shell structure with lithium carbonate in a certain proportion, sintering at 850 ℃ for 10h, crushing and sieving to obtain the lithium cobaltate and ternary element mixed material with the core-shell structure. The electrical properties of this positive electrode material are shown in fig. 22A-22B.

The evaluation method for the core-shell structure precursor used in the invention is as follows:

and observing the surface morphology of the precursor of the core-shell structure by using a scanning electron microscope (JEOL, JSM-7500F).

And mixing the core-shell structure precursor, a conductive carbon material and a binding agent polyvinylidene chloride according to a mass ratio of 90:5:5, dripping N-methyl pyrrolidone, grinding into paste, coating the paste on the surface of copper foil, and drying at 120 ℃ to obtain the test pole piece. And (3) grinding the section of the pole piece by using a cross section polishing machine (JEOL, IB-19510CP), and observing the section morphology of the precursor of the core-shell structure by using a scanning electron microscope (JEOL, JSM-7500F).

And detecting the content of the shell layer elements in the precursor of the core-shell structure by using an inductively coupled plasma emission spectrometer (ICAP 6300).

And mixing the precursor with the core-shell structure with lithium carbonate, and sintering in a Kejing furnace (KSL-1200X) to prepare the cathode material with the core-shell structure.

And mixing the positive electrode material, a conductive carbon material and a binding agent polyvinylidene chloride according to the mass ratio of 90:5:5, dripping N-methyl pyrrolidone, grinding into paste, coating the paste on the surface of an aluminum foil, and drying at 120 ℃ to obtain the positive electrode test electrode. The counter electrode (reference electrode) of the experimental battery is a metal lithium sheet, the experimental battery is assembled by a CR2032 type battery assembly, and the experimental battery is placed in a constant temperature box and connected with a charge and discharge tester for charge and discharge tests.

In the ternary material prepared from the precursor with the core-shell structure in the embodiment 3, a specific capacity-voltage curve obtained by a 0.1C/0.1C charge-discharge test at 3.0-4.25V in a half-cell and a capacity retention rate-cycle number curve obtained by a 1C/1C charge-discharge rate at 4.25V are shown in FIGS. 4A-4C, and the discharge specific capacity of the ternary material reaches 163mAh/g, which is equivalent to that of the comparative example 1, and the capacity retention rate after 100 cycles reaches 88.5%, which is higher than that of the comparative example 1.

In the lithium cobaltate material prepared from the core-shell precursor with the shell layer rich in Al in the embodiment 6, a specific capacity-voltage curve obtained by a 0.2C/0.2C charge-discharge test at 3.0-4.5V in a half-cell and a capacity retention rate-cycle number curve obtained by a 0.7C/0.7C charge-discharge rate at 4.6V are shown in fig. 8A-8B, and the discharge specific capacity of the material reaches 186mAh/g, which is lower than the comparative example 2 by 4mAh/g, but the capacity retention rate after 50 cycles at 4.6V reaches 92%, which is higher than the comparative example 2.

In the lithium cobaltate material prepared from the core-shell precursor with the shell layer rich in Ni/Mn in example 9, a specific capacity-voltage curve obtained by a 0.2C/0.2C charge and discharge test at 3.0-4.5V in a half-cell and a capacity retention rate-cycle number curve obtained at 4.6V with a charge and discharge rate of 0.7C/0.7C are shown in fig. 12A-12B, and the specific discharge capacity of the material is equivalent to that of comparative example 2, but the capacity retention rate after 50 cycles at 4.6V reaches 90%, which is higher than that of comparative example 2.

In the lithium cobaltate material prepared from the core-shell precursor with the shell layer rich in Al/Zr in the embodiment 10, a specific capacity-voltage curve obtained by a 0.1C/0.1C charge and discharge test at 3.0-4.25V in a half-cell and a capacity retention rate-cycle number curve obtained by a 0.5C/0.5C charge and discharge rate at 4.25V are shown in fig. 17A-17B, and the specific discharge capacity of the material is equivalent to that of the comparative example 3, but the capacity retention rate after 100 cycles at 4.25V reaches 90%, which is higher than that of the comparative example 3.

In the lithium cobaltate material prepared from the core-shell precursor with the shell layer rich in Al/Zr in the embodiment 11, a specific capacity-voltage curve obtained by a 0.1C/0.1C charge and discharge test at 3.0-4.25V in a half-cell and a capacity retention rate-cycle number curve obtained by a 0.5C/0.5C charge and discharge rate at 4.25V are shown in fig. 22A-22B, and the specific discharge capacity of the material is lower than that of the comparative example 4 by about 2mAh/g, but the capacity retention rate after 100 cycles at 4.25V reaches 93%, which is higher than that of the comparative example 4.

The above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and a person skilled in the art can modify the technical solution of the present invention or substitute the same without departing from the spirit and scope of the present invention, and the scope of the present invention should be determined by the claims.

Claims

1. A preparation method of a precursor of a lithium battery anode material with a core-shell structure comprises the following steps:

weighing metal salt and a solvent, wherein the metal salt contains metal elements required by a shell layer to be prepared, the metal elements are one or more of Na, Mg, Ca, Al, Ga, V, Cr, Fe, Ni, Co, Mn, Ti, Zr, Si and Ge, and the metal salt is prepared into a metal salt solution;

weighing at least one of cobaltosic oxide and nickel-cobalt-manganese hydroxide as a conventional precursor, slowly adding the conventional precursor with pores on the surface into the metal salt solution, heating and stirring until the solution is supersaturated, and volatilizing the solvent completely to obtain a mixture;

and (3) placing the mixture into an oven for standing and drying, and coating a shell layer on the surface of the conventional precursor after completely drying to obtain the precursor with the core-shell structure.

2. The method of claim 1, wherein the metal salt is decomposable at high temperature to one or more of acetate, nitrate, meta-aluminate, and organometallic salts.

3. The method of claim 2, wherein the organometallic salt comprises tetrabutyl titanate, aluminum isopropoxide.

4. The method of claim 1, wherein the solvent is one of deionized water, 95vol.% pure industrial alcohol, and absolute ethanol.

5. The method of claim 1, wherein the concentration of the metallic element in the metallic salt solution is greater than 0 and less than or equal to its saturation concentration.

6. The method of claim 1, wherein the volume of the metal salt solution is calculated by the following equation:

V=W×m/ρ；

wherein V is the volume of the metal salt solution in mL; w is the mass of the conventional precursor in g; m is the mass of metal elements required for preparing the shell when the conventional precursor is 1g, and the unit is ppm; ρ is the concentration of the metal element required for preparing the shell in the solution in g/mL.

7. The method of claim 6, wherein m (Na) ≦ 6.0wt.%, m (Mg) ≦ 1.0wt.%, m (Al) ≦ 1.0wt.%, m (Ti) ≦ 1.0wt.%, m (Zr) ≦ 1.0wt.%, m (Ni) ≦ 3.0wt.%, m (Mn) ≦ 3.0 wt.%.

8. The method of claim 6, wherein ρ ≦ 0.10 g/mL.

9. The method of claim 1, wherein the metal salt is weighed according to the concentration of the metal salt solution, the metal salt is put into a volumetric flask, and then the solvent is added for constant volume; and measuring the metal salt solution by using a measuring cylinder, and pouring the metal salt solution and the conventional precursor into a beaker together for heating and stirring.

10. The method according to claim 1, wherein the temperature of the oven is 100 ℃ and the temperature during heating and stirring is 50-100 ℃.