CN118588923A - A magnesium-aluminum-titanium co-doped nickel-cobalt-manganese-oxide positive electrode material and a preparation method thereof - Google Patents

Abstract

A magnesium-aluminum-titanium co-doped nickel-cobalt lithium manganate positive electrode material and a preparation method thereof belong to the field of positive electrodes of lithium ion batteries. Firstly preparing magnesium aluminum titanium hydrotalcite nano-sheets and spherical nickel cobalt manganese hydroxide precursors, then uniformly mixing the magnesium aluminum titanium hydrotalcite nano-sheets, the nickel cobalt manganese hydroxide precursors and lithium compounds through solid-phase ball milling, and roasting at high temperature to obtain a doped finished product material LiMg _xNiCoMnAl_yTi_zO₂, wherein x is more than or equal to 0.007 and less than or equal to 0.018,0.005, y is more than or equal to 0.008,0.001 and z is more than or equal to 0.003. The method has the advantages that the magnesium-aluminum-titanium hydrotalcite is used as a doping source, the three-element co-doping material is synthesized by one-step roasting, the uniform distribution of magnesium, aluminum and titanium in the material is realized, the advantages of improving the stability of magnesium and aluminum elements and improving the discharge specific capacity of titanium elements are combined, and the finished product material with lower lithium-nickel mixed discharge degree and better cycle performance is synthesized.

Description

A magnesium-aluminum-titanium co-doped nickel-cobalt-manganese-oxide positive electrode material and a preparation method thereof

Technical Field

The present invention belongs to the field of lithium ion batteries, and particularly relates to a magnesium-aluminum-titanium co-doped nickel-cobalt-manganese-oxide positive electrode material and a preparation method thereof, that is, using magnesium-aluminum-titanium hydrotalcite nanosheets as a doping source, and one-step calcination to synthesize a ternary co-doped nickel-cobalt-manganese-oxide positive electrode material and a preparation method thereof.

Background Art

Lithium-ion batteries are currently the most widely used and most promising batteries for electric vehicles. Compared with nickel-metal hydride and nickel-cadmium batteries, they have the advantage of higher energy density and do not contain toxic substances, so they have broad application prospects. The performance of the positive electrode material directly determines the overall performance of the battery. The high-nickel ternary positive electrode material lithium nickel cobalt manganese oxide LiNi _1-xy Co _x Mn _y (0.8≤1-xy≤1) has attracted widespread attention due to its higher specific capacity and better rate performance, becoming one of the positive electrode materials with the best application prospects in lithium-ion batteries.

As the nickel content increases, although its energy density is improved, it will also bring about structural instability problems, among which lithium-nickel mixing is the key reason for structural instability. During the charge and discharge process, the degree of lithium-nickel mixing gradually increases with the progress of the charge and discharge process. As lithium ions are released, there are more lithium vacancies on the surface, and the energy barrier for Ni ²⁺ to migrate to the lithium site is reduced, and the lithium-nickel mixing is aggravated, which in turn affects the cycle performance of the material. Therefore, there are many works dedicated to reducing excessive lithium-nickel mixing of materials to achieve the purpose of improving electrochemical performance. Among them, element doping is a more common means, but generally speaking, single-element doping can often only improve a relatively single problem, and even at the same time it will have some negative effects on the electrochemical performance. Therefore, in order to improve the problem more comprehensively, multi-element co-doping has become a new research focus. At present, the following two routes are generally taken for the co-doping process.

One process route is to introduce doping elements when synthesizing precursors by coprecipitation, use sulfate or other forms for coprecipitation, and then lithiation and roast to obtain the modified finished material. In document (1) Chinese invention patent publication number CN116706044 A, Wang Haizhou et al. used cobalt salt, precipitant, aluminum salt, nickel salt, magnesium salt, manganese salt and complexing agent as raw materials, and synthesized nickel-manganese-magnesium-aluminum co-doped lithium cobalt oxide positive electrode materials by multiple coprecipitation methods, and then improved its electronic conductivity by solid electrolyte coating. This method uses multi-element co-doping and synergistic coating to synthesize finished materials with stable structure and good electrochemical performance. However, when doping elements are introduced when synthesizing precursors by the coprecipitation method, it is easy to cause uneven distribution of elements in the precursor material due to uneven precipitation, which in turn affects the finished material and ultimately affects the material performance.

Another process route is to synthesize the precursor by the sol-gel method, and then obtain the modified finished material by lithium calcination. In document (2) China Invention Patent Publication No. CN 115911393A, Wang Pengfeng et al. reacted nickel oxide, cobalt acetate, manganese dioxide, lanthanum acetate with an aqueous solution of an organic acid complexing agent and an aqueous solution of an organic reducing complexing agent, heated them, evaporated and concentrated them to obtain a gel, and then pre-sintered them to obtain a precursor, and then added lithium for a second calcination. During the calcination, magnesium ethanol was added to finally obtain a lanthanum-magnesium co-doped nickel cobalt manganese oxide material. This method can prepare a finished material with relatively uniform doping elements, a low degree of lithium-nickel mixing, and better electrochemical properties. However, the process flow is relatively complicated, and the post-processing of the raw materials is relatively difficult, so it is not suitable for industrial scale-up production. In short, a simple and scalable process is used to obtain a multi-element co-doped material, and the stability and electrochemical properties are improved compared to the unmodified material, which is a work of high value.

Summary of the invention

The first object of the present invention is to provide a magnesium-aluminum-titanium co-doped nickel- _cobalt -manganese-oxide positive electrode material, the chemical composition of the material is _{LiMgxNiCoMnAlyTizO2} , wherein 0.007≤x≤0.018, 0.005≤y≤0.008, _{and 0.001≤z≤0.003} .

Another object of the present invention is to provide a method for preparing a magnesium-aluminum-titanium co-doped nickel-cobalt-manganese-oxide positive electrode material, first preparing magnesium-aluminum-titanium hydrotalcite, then mixing magnesium-aluminum-titanium hydrotalcite nanosheets, nickel-cobalt- _manganese hydroxide precursor and lithium compound uniformly by solid phase ball milling, and then calcining at high temperature to obtain a doped finished material _{LiMgxNiCoMnAlyTizO2} , wherein 0.007≤x≤0.018, 0.005≤y≤0.008, _{and 0.001≤z≤0.003} . The process flow of the preparation method is shown in Figure 1, and the specific process steps are as follows:

(1) Preparation of magnesium-aluminum-titanium hydrotalcite nanosheets: magnesium salt, aluminum salt and titanium salt were weighed according to the ratio of magnesium, aluminum and titanium substances being x:y:z=6:2:2. The magnesium salt and aluminum salt were first dissolved in deionized water to prepare a salt solution A with a total metal ion concentration of 0.8 to 1.2 mol/L. Sodium hydroxide and sodium carbonate were dissolved in deionized water to prepare an alkaline solution B with a sodium hydroxide concentration of 1.6 to 2.4 mol/L and a sodium carbonate concentration of 0.4 to 0.6 mol/L. An equal volume of the salt solution was added. A, alkaline solution B and 0.2-0.3 mol/L of a corresponding amount of liquid titanium salt are simultaneously poured into a colloid mill with a rotation speed of 2500-3500 sodium hydroxide for a mixed reaction for 1-3 minutes, the suspension after the mixed reaction is stirred and aged in a water bath at 90-95° C. for 3-5 hours, then repeatedly washed and filtered with water until the pH value of the filtrate is 7-8, and then repeatedly washed and filtered with ethanol of an equal volume to water, and the washed filter cake is dried at 60-80° C. for 10-12 hours to obtain magnesium aluminum titanium hydrotalcite nanosheets;

The magnesium salt is one or more of magnesium nitrate, magnesium sulfate, magnesium chloride or magnesium acetate, the aluminum salt is one or more of aluminum nitrate, aluminum sulfate, aluminum chloride or aluminum acetate, and the titanium salt is one or more of tetrabutyl titanate and titanium tetrachloride.

(2) Preparation of spherical nickel-cobalt-manganese hydroxide precursor: Before the coprecipitation reaction begins, _N2 is introduced to remove _O2 in the deionized water in the kettle, and the _N2 atmosphere is maintained during the reaction; nickel salt, cobalt salt and manganese salt are weighed according to the ratio of nickel, cobalt and manganese substances of x:y:z=8:1:1, a salt solution with a metal ion concentration of 1.5-2.5 mol/L is prepared, an alkaline solution with a sodium hydroxide concentration of 4.5-7.5 mol/L is prepared, and an ammonia solution with an ammonia concentration of 4-14 g/L is prepared and filled into the overflow reactor as the reaction bottom liquid; the stirring speed of the overflow reactor is set to 300-600 rpm and the speed is maintained unchanged during the entire reaction process, the temperature of the overflow reactor is increased to 50-60°C and the temperature is maintained unchanged during the entire reaction process; A salt solution with a metal ion concentration of 1.5 to 2.5 mol/L is injected into the overflow reactor at a speed of filling the overflow reactor in 20 to 25 hours, and the injection speed of the salt solution is kept constant during the entire reaction process. At the same time, an ammonia solution with a concentration of 2 mol/L is injected to maintain the ammonia concentration of the reaction system at 4 to 14 g/L. A sodium hydroxide solution with a concentration of 4.5 to 7.5 mol/L is injected and its flow rate is controlled to adjust the pH value of the reaction solution in the overflow reactor. At the beginning of the reaction, the flow rate of the sodium hydroxide solution is adjusted so that the pH value of the reaction solution is 11.30 to 11.50. When NiCoMn(OH) 2 When the _particle size D50 reaches 10-12 microns, the liquid feeding can be stopped, and the NiCoMn(OH) ₂ suspension overflowing from the overflow reactor is collected. After a sufficient amount of suspension is collected, the reaction is stopped, and the suspension is repeatedly washed and filtered until the pH value of the filtrate is 7-8. The washed filter cake is dried at 80-120°C for 8-16 hours to obtain spherical nickel cobalt manganese hydroxide with a particle size D50 of 10-12 microns;

The nickel salt is one or more of nickel nitrate, nickel sulfate, nickel chloride or nickel acetate, the cobalt salt is one or more of cobalt nitrate, cobalt sulfate, cobalt chloride or cobalt acetate, and the manganese salt is one or more of manganese nitrate, manganese sulfate, manganese chloride or manganese acetate.

(3) Mixing hydrotalcite, precursor and lithium compound: Weigh the magnesium aluminum titanium hydrotalcite nanosheets prepared in step (1), the nickel cobalt manganese hydroxide precursor prepared in step (2) and the lithium compound respectively, wherein the corresponding amounts are weighed according to the ratio of n(Li):n(Ni+Co+Mn)=1.05:1, m(hydrotalcite):m(precursor)=0.01:1-0.03:1, and mix the three by solid phase ball milling for 2-5 hours to make them uniformly mixed;

The lithium compound is one or more of lithium hydroxide and lithium carbonate.

(4) Preparation of finished materials: The mixed materials are heated to 750-770°C at a rate of 3-8°C/min in an oxygen atmosphere and reacted at a constant temperature for 15-20 hours, then cooled to room temperature along with the furnace, and ground through a 400-mesh sieve to obtain a magnesium-aluminum _- titanium doped positive electrode material: _{LiMgxNiCoMnAlyTizO2} wherein 0.007≤x≤0.018, 0.005≤x≤0.008, _{and 0.001≤x≤0.003} .

The morphology of the samples was characterized by a German Zeiss Supra55 field emission scanning electron microscope. Figure 2 is a scanning electron microscope image of magnesium aluminum titanium hydrotalcite nanosheets. The radial size of the magnesium aluminum titanium hydrotalcite nanosheets is 30 to 50 nm, the particle size is small and the distribution is relatively uniform, and there is no obvious aggregation. The nano-scale modified material is conducive to uniform mixing with the precursor and lithium source during ball milling, and it is easier to form a material with uniform element distribution after calcination. Figure 3 is a scanning electron microscope image of the _{LiMgNiCoMnAlTiO2} sample obtained by lithium calcination of magnesium aluminum titanium hydrotalcite doped with nickel cobalt manganese precursor, and Figure 4 is a scanning electron microscope image of the _LiNiCoMnO2 sample obtained by direct lithium calcination of nickel cobalt manganese hydroxide precursor. Compared with the scanning electron microscope images of the samples before and after doping, there is no obvious change on the surface of the material, indicating that most of the doping elements enter the bulk phase and are not enriched on the surface. Figure 5 is a distribution diagram of different elements in the _{LiMgNiCoMnAlTiO2} sample obtained by lithiation calcination of magnesium-aluminum-titanium hydrotalcite doped with nickel-cobalt-manganese precursor. The elements of the finished material after hydrotalcite modification are evenly distributed.

The structure of the prepared samples was characterized by using a Japanese Rigaku UItima III X-ray diffractometer. The X-ray diffraction analysis results of Example 1 and Comparative Example 1 of the present invention are shown in Figure 6. The XRD diffraction peaks of the finished materials were analyzed, and it was found that they corresponded well to the PDF standard card 89-3601 of the α-LiNiO ₂ phase. Comparing the intensity ratio of the (003) diffraction peak to the (104) diffraction peak, all materials satisfied (003)/(104)＞1.2, (006)/(012) and (018)/(110) showed obvious splitting, indicating that the lithium-nickel mixing degree was low, which met the requirements of the layered material structure. The Li ⁺ /Ni ^{2 +} mixing degree can be obtained by refining the X-ray diffraction data, and these data are listed in Table 1. It can be seen from Table 1 that the introduction of the doping source does not produce obvious changes in the material crystal form. This is because the amount added is small. Compared with the _LiNiCoMnO2 sample prepared in Comparative Example 1, the magnesium-aluminum-titanium hydrotalcite-doped _{LiMgNiCoMnAlTiO2} sample prepared by the method of the present invention has a more regular layered structure and a lower degree of Li ⁺ /Ni2 ⁺ mixing. This shows that the co-doping of the three elements can reduce the lithium-nickel mixing and thus improve the material structure stability.

Table 1. Data list of Li ⁺ /Ni ²⁺ mixing degree calculated from X-ray diffraction data of finished materials prepared in Examples and Comparative Examples

sample The degree of Ni ²⁺ mixing in the Li ⁺ layer Example 1 1.91 Comparative Example 1 3.85

The finished material prepared by the embodiment and comparative example method of the method of the present invention is the positive electrode active material, which is mixed with acetylene black conductive agent and polyvinylidene fluoride binder in a mass ratio of 8:1:1, coated on the surface of aluminum foil current collector, rolled after drying at 110°C, and vacuum dried in a vacuum oven at 120°C for 12h. The electrode sheet with a diameter of 1cm is made by a punching machine as the positive electrode, the metal lithium sheet is used as the negative electrode, the polyethylene film is used as the diaphragm, and 1mol/L _LiPF6 +EC+DMC is used as the electrolyte. The button battery is assembled in the UniLab glove box ( _H2O <1ppm, _O2 <1ppm) of M.Braun. The electrochemical performance test was carried out using Wuhan Blue Electric CT2001A battery tester, with a voltage range of 2.75~4.3V (vs.Li ⁺ /Li), 1C=200mA·g ^-1 . The test results are shown in Figures 7, 8 and Table 2. The magnesium-aluminum-titanium doped lithium nickel-cobalt-manganese oxide _{LiMgNiCoMnAlTiO2} sample prepared by the method of the embodiment of the present invention has the advantage of significantly improving the cycle performance without significantly reducing the first-cycle discharge capacity compared with the undoped sample prepared by the comparative example method.

Table 2. Electrochemical data of finished materials prepared in Examples and Comparative Examples

In summary, the characteristics and advantages of the method of the present invention are: (1) A magnesium, aluminum, and titanium co-doped lithium nickel cobalt manganese oxide positive electrode material is synthesized, which combines the advantages of magnesium and aluminum elements in improving stability and titanium elements in improving discharge specific capacity, has low lithium-nickel mixing, and has good electrochemical cycle performance. (2) Magnesium aluminum titanium hydrotalcite is used as the doping source to achieve three-element co-doping in one step, with uniform element distribution, simple process steps, and is suitable for scale-up production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the process flow of preparing magnesium-aluminum-titanium doped nickel-cobalt-manganese oxide positive electrode material according to the present invention.

FIG. 2 is a scanning electron microscope photograph of the magnesium-aluminum-titanium hydrotalcite nanosheets prepared in Example 1.

FIG. 3 is a scanning electron microscope photograph of LiMgNiCoMnAlTiO ₂ obtained by lithiation and calcination of magnesium-aluminum-titanium hydrotalcite nanosheets and spherical nickel-cobalt-manganese hydroxide precursors in Example 1.

FIG. 4 is a scanning electron microscope photograph of LiNiCoMnO ₂ obtained by lithiation and calcination of a nickel-cobalt-manganese hydroxide precursor in Comparative Example 1.

FIG5 is a distribution diagram of different elements in the _{LiMgNiCoMnAlTiO2} sample obtained by lithiation calcination of magnesium-aluminum-titanium hydrotalcite doped with nickel-cobalt-manganese precursor in Example 1

Figure 6 is an X-ray diffraction spectrum of the finished product materials prepared in the embodiments of the present invention and the comparative examples, wherein the horizontal axis is the diffraction angle 2θ, in degrees (°); the vertical axis is the diffraction peak intensity, in absolute units (a.u.).

Curve a is the X-ray diffraction spectrum of LiMgNiCoMnAlTiO ₂ prepared in Example 1;

Curve b is the X-ray diffraction spectrum of LiNiCoMnO ₂ prepared in Comparative Example 1;

Figure 7 is a charge-discharge curve of the finished material prepared in the embodiment of the present invention and the comparative example at room temperature in the first week, wherein the horizontal axis is the discharge specific capacity, the unit is milliampere hour/gram (mAh/g); the vertical axis is the voltage, the unit is volt (V).

Curve a is the first cycle charge and discharge curve of _{LiMgNiCoMnAlTiO2} prepared in Example 1;

Curve b is the first cycle charge and discharge curve of LiMgNiCoMnAlTiO2 prepared in Example ₂ ;

Curve c is the first cycle charge and discharge curve of _{LiMgNiCoMnAlTiO2} prepared in Example 3;

Curve d is the first-week charge-discharge curve of LiNiCoMnO ₂ prepared in Example 1;

Figure 8 is a room temperature electrochemical cycle performance curve of the finished materials prepared in the embodiments of the present invention and the comparative examples, wherein the horizontal axis is the cycle number, in units of weeks; the vertical axis is the discharge specific capacity, in units of milliampere hours per gram (mAh/g).

Curve a is the electrochemical cycle performance curve of _{LiMgNiCoMnAlTiO2} prepared in Example 1; Curve b is the electrochemical cycle performance curve of LiMgNiCoMnAlTiO2 prepared in Example ₂ ; Curve c is the electrochemical cycle performance curve of _{LiMgNiCoMnAlTiO2} prepared in Example 3; Curve d is the electrochemical cycle performance curve of _LiNiCoMnO2 prepared in Comparative Example 1;

DETAILED DESCRIPTION

In order to further illustrate the technical solution of the present invention, the implementation scheme of the present invention is described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the technical solution of the present invention, rather than limiting the claims of the present invention.

Example 1

(1) Preparation of magnesium aluminum titanium hydrotalcite nanosheets: magnesium sulfate, aluminum sulfate and tetrabutyl titanate were weighed according to the ratio of the amount of Mg, Al and Ti being x:y:z=6:2:2. Magnesium sulfate and aluminum sulfate were first dissolved in deionized water to prepare a salt solution A with a total metal ion concentration of 0.8 mol/L. Sodium hydroxide and sodium carbonate were dissolved in deionized water to prepare an alkaline solution B with a sodium hydroxide concentration of 1.6 mol/L and a sodium carbonate concentration of 0.4 mol/L. Equal volumes of the salt solution A, the alkaline solution B and 0.2 mol/L of tetrabutyl titanate were simultaneously poured into a colloid mill with a rotation speed of 2500 sodium hydroxide for mixing reaction for 1 minute. The suspension after the mixed reaction was stirred and aged in a water bath at 90°C for 3 hours, and then repeatedly washed and filtered with water until the filtrate had a pH of 8, and then repeatedly washed and filtered with an equal volume of ethanol to water. The washed filter cake was dried at 60°C for 12 hours to obtain magnesium aluminum titanium hydrotalcite nanosheets.

(2) Preparation of spherical nickel cobalt manganese hydroxide precursor: Before the coprecipitation reaction begins, _N2 is introduced to remove _O2 in the deionized water in the kettle, and the _N2 atmosphere is maintained during the reaction; nickel nitrate, cobalt nitrate and manganese nitrate are weighed according to the ratio of nickel, cobalt and manganese substances of x:y:z=8:1:1, a salt solution with a metal ion concentration of 2 mol/L is prepared, an alkaline solution with a sodium hydroxide concentration of 6 mol/L is prepared, and an ammonia solution with an ammonia concentration of 10 g/L is prepared and filled into the overflow reactor as the reaction bottom liquid; the stirring speed of the overflow reactor is set to 500 rpm and the speed is maintained unchanged during the entire reaction process, and the temperature of the overflow reactor is increased to 50°C and the temperature is maintained unchanged during the entire reaction process ; Inject a salt solution with a metal ion concentration of 2 mol/L at a speed that fills the overflow reactor in 24 hours and keep the injection speed of the salt solution constant during the entire reaction process, and inject ammonia solution with a concentration of 2 mol/L to maintain the ammonia concentration of the reaction system at 10 g/L, inject a sodium hydroxide solution with a concentration of 6 mol/L and control its flow rate to adjust the pH value of the reaction solution in the overflow reactor; at the beginning of the reaction, adjust the flow rate of the sodium hydroxide solution so that the pH value of the reaction solution is 11.40, and stop feeding the solution when the particle size D50 of the NiCoMn(OH) ₂ particles reaches 11 microns. At this time, start collecting the NiCoMn(OH) ₂ suspension overflowing from the overflow reactor, stop the reaction after collecting a sufficient amount of the suspension, wash and filter the suspension repeatedly until the pH value of the filtrate is 7, and dry the washed filter cake at 100°C for 10 hours to obtain spherical nickel cobalt manganese hydroxide with a particle size D50 of 11 microns;

(3) Mixing hydrotalcite, precursor and lithium compound: Weigh the magnesium aluminum titanium hydrotalcite nanosheets prepared in step (1), the nickel cobalt manganese hydroxide precursor prepared in step (2) and lithium hydroxide respectively, wherein the corresponding amounts are weighed according to the ratio of n(Li):n(Ni+Co+Mn)=1.05:1, m(hydrotalcite):m(precursor)=0.03:1, and mix the three by solid phase ball milling for 3 hours to make them uniformly mixed;

(4) Preparation of finished materials: The mixed materials were heated to 770°C at a rate of 3°C/min in an oxygen atmosphere and reacted at a constant temperature for 20 hours, then cooled to room temperature along with the furnace, and ground through a 400-mesh sieve to obtain a magnesium-aluminum-titanium doped positive electrode material: Li _1.016 Mg _0.018 Ni _0.832 Co _0.105 Mn _0.052 Al _0.008 Ti _0.003 O ₂ .

The scanning electron microscope results of the magnesium aluminum titanium hydrotalcite nanosheets prepared in this embodiment are shown in Figure 2. The radial size of the magnesium aluminum titanium hydrotalcite nanosheets is 30 to 50 nm. Figure 3 is a scanning electron microscope photo of _{LiMgNiCoMnAlTiO2} obtained by lithiation and calcination of magnesium aluminum titanium hydrotalcite nanosheets and spherical nickel cobalt manganese hydroxide precursors. It can be seen that the surface roughness of the material does not change significantly after doping, the synthesized finished material has high sphericity, a particle size of about 10μm, and a relatively uniform particle size distribution. Figure 5 is a distribution diagram of different elements in the _{LiMgNiCoMnAlTiO2} sample obtained by lithiation and calcination of magnesium aluminum titanium hydrotalcite doped with nickel cobalt manganese precursors. The elements of the finished material after hydrotalcite modification are evenly distributed.

The X-ray diffraction analysis results of the magnesium-aluminum-titanium co-doped lithium nickel-cobalt-manganese oxide _{LiMgNiCoMnAlTiO2} sample prepared in this embodiment are shown in curve a in Figure 6, and it is found that it corresponds well to the PDF standard card of the α- _{LiNiO2 phase} , which shows that the prepared magnesium-aluminum-titanium co-doped lithium nickel-cobalt-manganese oxide _{LiMgNiCoMnAlTiO2} sample has a layered structure and good crystallinity. The Li ⁺ /Ni2 ⁺ mixing degree can be obtained by refining the X-ray diffraction data, which is listed in Table 1. The Li ⁺ /Ni2 ⁺ mixing degree of the material is only 1.91%, indicating that its layered structure has good stability.

The magnesium-aluminum-titanium co-doped lithium nickel-cobalt-manganese oxide _{LiMgNiCoMnAlTiO2} sample prepared in this embodiment was assembled into a button cell and the electrochemical performance was tested at room temperature. The results are shown in curve a in Figure 7, curve a in Figure 8 and Table 2. The discharge specific capacity of the material is 200.0 mAh/g, and the capacity retention rate after 150 cycles is 100%.

Example 2

(1) Preparation of magnesium aluminum titanium hydrotalcite nanosheets: magnesium chloride, aluminum chloride and tetrabutyl titanate were weighed according to the ratio of magnesium, aluminum and titanium substances (x:y:z=6:2:2). Magnesium sulfate and aluminum sulfate were first dissolved in deionized water to prepare a salt solution A with a total metal ion concentration of 1.2 mol/L. Sodium hydroxide and sodium carbonate were dissolved in deionized water to prepare an alkaline solution B with a sodium hydroxide concentration of 2.4 mol/L and a sodium carbonate concentration of 0.6 mol/L. Equal volumes of the salt solution A, the alkaline solution B and 0.3 mol/L of tetrabutyl titanate were simultaneously poured into a colloid mill with a rotation speed of 3500 sodium hydroxide for mixing reaction for 3 minutes. The suspension after the mixed reaction was stirred and aged in a water bath at 95°C for 3 hours, and then repeatedly washed and filtered with water until the filtrate pH = 8, and then repeatedly washed and filtered with an equal volume of ethanol to water. The washed filter cake was dried at 80°C for 10 hours to obtain magnesium aluminum titanium hydrotalcite nanosheets.

(2) Preparation of spherical nickel cobalt manganese hydroxide precursor: Before the coprecipitation reaction begins, _N2 is introduced to remove _O2 in the deionized water in the kettle, and the _N2 atmosphere is maintained during the reaction; nickel sulfate, cobalt sulfate and manganese sulfate are weighed according to the ratio of nickel, cobalt and manganese substances of x:y:z=8:1:1, a salt solution with a metal ion concentration of 1.5 mol/L is prepared, an alkaline solution with a sodium hydroxide concentration of 4.5 mol/L is prepared, and an ammonia solution with an ammonia concentration of 4 g/L is prepared and filled into the overflow reactor as the reaction bottom liquid; the stirring speed of the overflow reactor is set to 300 rpm and the speed is maintained unchanged during the entire reaction process, and the temperature of the overflow reactor is increased to 50°C and the temperature is maintained unchanged during the entire reaction process ; Inject a salt solution with a metal ion concentration of 1.5 mol/L at a speed that fills the overflow reactor in 20 hours and keep the injection speed of the salt solution constant during the entire reaction process, inject an ammonia solution with a concentration of 2 mol/L to maintain the ammonia concentration of the reaction system at 4 g/L, inject a sodium hydroxide solution with a concentration of 4.5 mol/L and control its flow rate to adjust the pH value of the reaction solution in the overflow reactor; at the beginning of the reaction, adjust the flow rate of the sodium hydroxide solution to make the pH value of the reaction solution 11.30, and stop feeding the solution when the particle size D50 of the NiCoMn(OH) ₂ particles reaches 10 microns. At this time, start collecting the NiCoMn(OH) ₂ suspension overflowing from the overflow reactor, stop the reaction after collecting a sufficient amount of the suspension, wash and filter the suspension repeatedly until the pH value of the filtrate is 7, and dry the washed filter cake at 80°C for 16 hours to obtain spherical nickel cobalt manganese hydroxide with a particle size D50 of 10 microns;

(3) Mixing hydrotalcite, precursor and lithium compound: Weigh the magnesium aluminum titanium hydrotalcite nanosheets prepared in step (1), the nickel cobalt manganese hydroxide precursor prepared in step (2) and lithium hydroxide respectively, wherein the corresponding amounts are weighed according to the ratio of n(Li):n(Ni+Co+Mn)=1.05:1, m(hydrotalcite):m(precursor)=0.01:1, and mix the three by solid phase ball milling for 2 hours to make them uniformly mixed;

(4) Preparation of finished materials: The mixed materials were heated to 760°C at a rate of 8°C/min in an oxygen atmosphere and reacted at a constant temperature for 18 hours, then cooled to room temperature along with the furnace, and ground through a 400-mesh sieve to obtain a magnesium-aluminum-titanium doped positive electrode material: Li _1.004 Mg _0.007 Ni _0.824 Co _0.109 Mn _0.060 Al _0.005 Ti _0.001 O ₂ .

The magnesium-aluminum-titanium co-doped lithium nickel-cobalt-manganese oxide _{LiMgNiCoMnAlTiO2} sample prepared in this embodiment was assembled into a button cell and the electrochemical performance was tested at room temperature. The results are shown in curve b in FIG. 7 , curve b in FIG. 8 and Table 2. The discharge specific capacity of the material is 199.1 mAh/g, and the 150-cycle capacity retention rate is 96.8%.

Example 3

(1) Preparation of magnesium aluminum titanium hydrotalcite nanosheets: magnesium nitrate, aluminum nitrate and titanium tetrachloride were weighed according to the ratio of magnesium, aluminum and titanium substances (x:y:z=6:2:2). Magnesium sulfate and aluminum sulfate were first dissolved in deionized water to prepare a salt solution A with a total metal ion concentration of 1 mol/L. Sodium hydroxide and sodium carbonate were dissolved in deionized water to prepare an alkaline solution B with a sodium hydroxide concentration of 2 mol/L and a sodium carbonate concentration of 0.5 mol/L. Equal volumes of the salt solution A, the alkaline solution B and 0.25 mol/L of titanium tetrachloride were simultaneously poured into a colloid mill with a sodium hydroxide speed of 3000 for mixing reaction for 2 minutes. The suspension after the mixed reaction was stirred and aged in a water bath at 92°C for 5 hours, and then repeatedly washed and filtered with water until the filtrate pH = 7, and then repeatedly washed and filtered with an equal volume of ethanol to water. The washed filter cake was dried at 70°C for 11 hours to obtain magnesium aluminum titanium hydrotalcite nanosheets.

(2) Preparation of spherical nickel cobalt manganese hydroxide precursor: Before the coprecipitation reaction begins, _N2 is introduced to remove _O2 in the deionized water in the kettle, and the _N2 atmosphere is maintained during the reaction; nickel chloride, cobalt chloride and manganese chloride are weighed according to the ratio of nickel, cobalt and manganese substances of x:y:z=8:1:1, a salt solution with a metal ion concentration of 2.5 mol/L is prepared, an alkaline solution with a sodium hydroxide concentration of 7.5 mol/L is prepared, and an ammonia solution with an ammonia concentration of 14 g/L is prepared and filled into the overflow reactor as the reaction bottom liquid; the stirring speed of the overflow reactor is set to 600 rpm and the speed is maintained unchanged during the entire reaction process, and the temperature of the overflow reactor is increased by 60°C and the temperature is maintained unchanged during the entire reaction process ; Inject a salt solution with a metal ion concentration of 2.5 mol/L at a speed that fills the overflow reactor in 25 hours and keep the injection speed of the salt solution constant during the entire reaction process, and inject ammonia solution with a concentration of 2 mol/L to maintain the ammonia concentration of the reaction system at 14 g/L, inject a sodium hydroxide solution with a concentration of 7.5 mol/L and control its flow rate to adjust the pH value of the reaction solution in the overflow reactor; at the beginning of the reaction, adjust the flow rate of the sodium hydroxide solution to make the pH value of the reaction solution 11.50, and stop feeding the solution when the particle size D50 of the NiCoMn(OH) ₂ particles reaches 12 microns. At this time, start collecting the NiCoMn(OH) ₂ suspension overflowing from the overflow reactor, stop the reaction after collecting a sufficient amount of the suspension, wash and filter the suspension repeatedly until the pH value of the filtrate is 8, and dry the washed filter cake at 120°C for 8 hours to obtain spherical nickel cobalt manganese hydroxide with a particle size D50 of 12 microns;

(3) Mixing hydrotalcite, precursor and lithium compound: Weigh the magnesium aluminum titanium hydrotalcite nanosheets prepared in step (1), the nickel cobalt manganese hydroxide precursor prepared in step (2) and lithium carbonate respectively, wherein the corresponding amounts are weighed according to the ratio of n(Li):n(Ni+Co+Mn)=1.05:1, m(hydrotalcite):m(precursor)=0.03:1, and mix the three by solid phase ball milling for 5 hours to make them uniformly mixed;

(4) Preparation of finished materials: The mixed materials were heated to 750°C at a rate of 5°C/min in an oxygen atmosphere and reacted at a constant temperature for 15 hours, then cooled to room temperature along with the furnace, and ground through a 400-mesh sieve to obtain a magnesium-aluminum-titanium doped positive electrode material: Li _1.016 Mg _0.018 Ni _0.832 Co _0.105 Mn _0.052 Al _0.008 Ti _0.003 O ₂ .

The magnesium-aluminum-titanium co-doped lithium nickel-cobalt-manganese oxide _{LiMgNiCoMnAlTiO2} samples prepared in this embodiment were assembled into button cells for electrochemical performance tests at room temperature. The magnesium-aluminum-titanium co-doped lithium nickel-cobalt-manganese oxide _{LiMgNiCoMnAlTiO2} samples prepared in this embodiment were assembled into button cells for electrochemical performance tests at room temperature. The results are shown in curve c in Figure 7, curve c in Figure 8 and Table 2. The discharge specific capacity of the material is 198.7 mAh/g, and the 150-cycle capacity retention rate is 100%.

Comparative Example 1

Preparation of spherical nickel cobalt manganese hydroxide precursor: Before the coprecipitation reaction begins, _N2 is introduced to remove _O2 in the deionized water in the kettle, and the _N2 atmosphere is maintained during the reaction; nickel acetate, cobalt acetate and manganese acetate are weighed according to the ratio of the amount of nickel, cobalt and manganese substances of x:y:z=8:1:1, a salt solution with a metal ion concentration of 2 mol/L is prepared, an alkaline solution with a sodium hydroxide concentration of 6 mol/L is prepared, and an ammonia solution with an ammonia concentration of 10 g/L is prepared and filled with the overflow reactor as the reaction bottom liquid; the stirring speed of the overflow reactor is set to 500 rpm and the speed is maintained unchanged during the entire reaction process, and the temperature of the overflow reactor is increased to 55°C and the temperature is maintained unchanged during the entire reaction process ; Inject a salt solution with a metal ion concentration of 2 mol/L at a speed that fills the overflow reactor in 24 hours and keep the injection speed of the salt solution constant during the entire reaction process, and inject ammonia solution with a concentration of 2 mol/L to maintain the ammonia concentration of the reaction system at 10 g/L, inject a sodium hydroxide solution with a concentration of 6 mol/L and control its flow rate to adjust the pH value of the reaction solution in the overflow reactor; at the beginning of the reaction, adjust the flow rate of the sodium hydroxide solution so that the pH value of the reaction solution is 11.40, and stop feeding the solution when the particle size D50 of the NiCoMn(OH) ₂ particles reaches 11 microns. At this time, start collecting the NiCoMn(OH) ₂ suspension overflowing from the overflow reactor, stop the reaction after collecting a sufficient amount of the suspension, wash and filter the suspension repeatedly until the pH value of the filtrate is 7, and dry the washed filter cake at 100°C for 10 hours to obtain spherical nickel cobalt manganese hydroxide with a particle size D50 of 11 microns;

(2) Precursor and lithium compound mixing: nickel cobalt manganese hydroxide precursor Ni _0.84 Co _0.10 Mn _0.06 (OH) ₂ and lithium hydroxide are weighed respectively in a ratio of n(Li):n(Ni+Co+Mn)=1.05:1, and the two are mixed by solid phase ball milling for 3 hours to make them uniformly mixed;

(3) Preparation of finished material: The mixed material was heated to 770°C at a rate of 3°C/min in an oxygen atmosphere and reacted at a constant temperature for 20 hours, then cooled to room temperature along with the furnace, and ground through a 400-mesh sieve to obtain the positive electrode material.

The scanning electron microscope photographs of the nickel cobalt lithium manganese oxide sample prepared in this comparative example at low magnification and high magnification are shown in FIG4 , respectively. The particle size of the synthesized finished material is about 10 μm, the surface is smooth, and the sphericity is good.

The X-ray diffraction analysis results of the lithium nickel cobalt manganese oxide sample prepared in this comparative example are shown in curve b in Figure 6, and it is found that it corresponds well to the PDF standard card of the α-LiNiO ₂ phase, which shows that the prepared lithium nickel cobalt manganese oxide sample has a layered structure and good crystallinity. The degree of Li ⁺ /Ni ²⁺ mixing can be obtained by refining the X-ray diffraction data, which is listed in Table 1.

The nickel cobalt lithium manganese oxide sample prepared in this comparative example was assembled into a button cell and the electrochemical performance was tested at room temperature. The results are shown in curve d in FIG. 7 , curve d in FIG. 8 and Table 2. The discharge specific capacity of the material is 203.2 mAh/g, and the capacity retention rate after 150 cycles is 92.4%.

Claims (9)

1. The chemical composition of the magnesium aluminum titanium co-doped nickel cobalt lithium manganate positive electrode material is LiMg _xNiCoMnAl_yTi_zO₂, wherein x is more than or equal to 0.007 and less than or equal to 0.018,0.005, y is more than or equal to 0.008,0.001 and z is more than or equal to 0.003.

2. The preparation method of the magnesium-aluminum-titanium co-doped nickel-cobalt lithium manganate positive electrode material is characterized by comprising the following steps of:

(1) Preparation of magnesium aluminum titanium hydrotalcite nano-sheets: weighing magnesium salt, aluminum salt and titanium salt according to the proportion of the amount of magnesium, aluminum and titanium substances of x:y:z=6:2:2, firstly dissolving the magnesium salt and the aluminum salt in deionized water to prepare a salt solution A with the total concentration of metal ions of 0.8-1.2 mol/L, and dissolving sodium hydroxide and sodium carbonate in the deionized water to prepare an alkaline solution B with the concentration of sodium hydroxide of 1.6-2.4 mol/L and the concentration of sodium carbonate of 0.4-0.6 mol/L; simultaneously pouring the equal volume of salt solution A, alkali solution B and corresponding amount of 0.2-0.3 mol/L of liquid titanium salt into a colloid mill with the rotating speed of 2500-3500 sodium hydroxide for mixed reaction for 1-3 minutes, stirring and ageing the mixed suspension in a water bath with the temperature of 90-95 ℃ for 3-5 hours, repeatedly washing and filtering with water until the pH value of the filtrate is=7-8, repeatedly washing and filtering with ethanol with the same volume as that of water, and drying the washed filter cake at the temperature of 60-80 ℃ for 10-12 hours to obtain magnesium aluminum titanium hydrotalcite nano-sheets;

(2) Preparing a spherical nickel cobalt manganese hydroxide precursor: before the coprecipitation reaction starts, introducing N ₂ to remove O ₂ in deionized water in a kettle, and maintaining N ₂ atmosphere in the reaction process; weighing nickel salt, cobalt salt and manganese salt according to the proportion of the amounts of nickel, cobalt and manganese substances of x:y:z=8:1:1, preparing a salt solution with the metal ion concentration of 1.5-2.5 mol/L, preparing an alkaline solution with the sodium hydroxide concentration of 4.5-7.5 mol/L, preparing an ammonia solution with the ammonia concentration of 4-14 g/L, and filling the overflow reaction kettle as a reaction base solution; setting the stirring rotation speed of the overflow reaction kettle to 300-600 rpm, keeping the rotation speed unchanged in the whole reaction process, and raising the temperature of the overflow reaction kettle to 50-60 ℃ and keeping the temperature unchanged in the whole reaction process; injecting a salt solution with the metal ion concentration of 1.5-2.5 mol/L at the speed of filling the overflow reaction kettle for 20-25 hours, keeping the injection speed of the salt solution constant in the whole reaction process, simultaneously injecting an ammonia solution with the concentration of 2mol/L to keep the ammonia concentration of the reaction system at 4-14 g/L, injecting a sodium hydroxide solution with the concentration of 4.5-7.5 mol/L, and controlling the flow rate of the sodium hydroxide solution to regulate and control the pH value of the reaction solution in the overflow reaction kettle; regulating the flow rate of a sodium hydroxide solution at the beginning of the reaction to enable the pH value of the reaction solution to be 11.30-11.50, stopping feeding the solution when the particle size D50 in NiCoMn (OH) ₂ particles reaches 10-12 microns, at the moment, starting to collect a NiCoMn (OH) ₂ suspension overflowed from an overflow reaction kettle, stopping the reaction after enough suspension is collected, repeatedly washing and filtering the suspension until the pH value of the filtrate is 7-8, and drying the washed filter cake at 80-120 ℃ for 8-16 hours to obtain spherical cobalt manganese nickel hydroxide with the medium particle size D50 of 10-12 microns;

(3) Hydrotalcite, precursor and lithium compound are mixed: respectively weighing the magnesium aluminum titanium hydrotalcite nano-plate prepared in the step (1), the nickel cobalt manganese hydroxide precursor prepared in the step (2) and the lithium compound, wherein the corresponding amount is weighed according to the proportion of n (Li): n (Ni+Co+Mn) =1.05:1, m (hydrotalcite): m (precursor) =0.01:1-0.03:1, and the three are mixed and ball-milled for 2-5 hours to uniformly mix the three;

(4) Preparation of finished material: heating the mixed materials to 750-770 ℃ at a speed of 3-8 ℃/min in an oxygen atmosphere, reacting for 15-20 hours at a constant temperature, then cooling to room temperature along with a furnace, and grinding the materials through a 400-mesh screen to obtain the magnesium-aluminum-titanium doped cathode material: liMg _xNiCoMnAl_yTi_zO₂ wherein 0.007.ltoreq.x.ltoreq. 0.018,0.005 x is less than or equal to 0.008,0.001 and less than or equal to x is less than or equal to 0.003.

3. The method of claim 2, wherein the magnesium salt in step (1) is one or more of magnesium nitrate, magnesium sulfate, magnesium chloride, or magnesium acetate.

4. The method of claim 2, wherein the aluminum salt in step (1) is one or more of aluminum nitrate, aluminum sulfate, aluminum chloride, or aluminum acetate.

5. The method according to claim 2, wherein the titanium salt in the step (1) is one or more of tetrabutyl titanate and titanium tetrachloride.

6. The method of claim 2, wherein the nickel salt in step (2) is one or more of nickel nitrate, nickel sulfate, nickel chloride or nickel acetate.

7. The method of claim 2, wherein the cobalt salt in step (2) is one or more of cobalt nitrate, cobalt sulfate, cobalt chloride or cobalt acetate.

8. The method of claim 2, wherein the manganese salt in step (2) is one or more of manganese nitrate, manganese sulfate, manganese chloride or manganese acetate.

9. The method according to claim 2, wherein the lithium compound in the step (3) is one or more of lithium hydroxide and lithium carbonate.