CN111697216A - Lithium manganate coated high nickel cobalt lithium manganate lithium ion battery positive electrode material and preparation method thereof - Google Patents

Abstract

The invention discloses a lithium manganate coated high nickel nickel cobalt lithium manganate lithium ion battery positive electrode material and a preparation method thereof. The method comprises the following steps: step S1, adding high nickel nickel cobalt lithium manganate into a sodium hydroxide aqueous solution The precursor is stirred in a magnetic stirrer to obtain a uniform alkaline precursor dispersion; in step S2, an aqueous solution containing manganese ions is slowly added dropwise to the alkaline precursor dispersion under stirring conditions to form a manganese oxide package Coated high nickel nickel cobalt lithium manganate precursor dispersion; step S3, after centrifuging and vacuum drying the dispersion, adding lithium hydroxide as a reactant, fully mixing by ball milling, and preparing by high temperature reaction in an oxygen atmosphere Lithium manganate coated nickel cobalt manganate lithium ion battery cathode material. The composite material prepared by the invention has been confirmed through battery assembly and electrochemical performance test that the process improves the cycle stability under the condition of maintaining a high reversible capacity.

Description

A lithium manganate coated high nickel nickel cobalt manganate lithium ion battery cathode material and its preparation backup method

technical field

The invention belongs to the technical field of positive electrode materials for lithium ion batteries, and in particular relates to a positive electrode material for lithium ion batteries coated with high nickel nickel cobalt manganate lithium manganate and a preparation method thereof.

Background technique

With the development of modern society, electric energy has become an indispensable part of people's lives, and almost all modern facilities require the supply of electric energy. Among them, the storage and supply of electric power is an important subject in the electric energy problem. As the most widely used electrical energy storage device, lithium-ion batteries have important applications in all aspects of life. In order to meet the requirements of electric energy storage and use in the future, it is imperative to develop new lithium-ion batteries with high capacity, high cycle stability, and high rate performance. Lithium-ion batteries are mainly composed of four parts: positive electrode, negative electrode, separator and electrolyte. Among them, the cathode and anode materials have a greater impact on the device performance. The battery specific capacity of commercial graphite anodes has exceeded 330mAh/g. The theoretical specific capacity of the lithium battery silicon anode in the laboratory research and development stage has reached 4000mAh/g. In contrast, lithium-ion battery cathode materials have relatively low energy storage capacity. Improving the specific capacity and electrochemical performance of lithium battery cathode materials is one of the most critical factors to improve the performance of lithium ion batteries.

The commonly used cathode material for lithium ion batteries in industrial production is lithium cobalt oxide LiCoO ₂ , but its specific capacity is low, and the price of cobalt increases year by year, which limits the application of lithium cobalt oxide. Another widely used cathode material is lithium iron phosphate LiFePO ₄ . Iron and phosphorus elements are widely present in nature, with low price and little environmental pollution, but their energy density and tap density are very low, and it is difficult to meet high Capacity requirements for lithium-ion batteries. The high nickel nickel cobalt manganese lithium manganate LiNi _x Co _y Mn _z O ₂ ternary cathode material involved in this patent has good specific capacity, voltage platform and tap density, and is a relatively balanced material, which is the next generation of lithium ion New research directions for cathode materials. In this material, the role of nickel ions is to improve the capacity of the battery; the role of cobalt ions is to improve the electrical conductivity to improve the high-current charge-discharge performance; the role of manganese ions shows better cycle stability and thermal stability, thereby improving the battery safety. With the increase of nickel ions, the cathode material faces some serious problems to be solved, namely, the cycling stability and safety performance of the material are reduced. There are many reasons for these problems, including the mixing of cations in the material, the dissolution of the electrode material, the change of the material structure, and the formation of the solid electrolyte interfacial film, thereby deteriorating the performance of the material. Therefore, it is particularly important to improve the electrochemical performance of the ternary cathode material from different perspectives and propose innovations in the structure to improve the performance of the battery.

At present, the patents on the modification of this material mainly focus on element doping and surface coating. These modifications usually have the following problems: (1) The formula is complicated. For example, the modification method disclosed in the invention patent CN 110534731A requires up to 8 solution. Another example is the invention patent CN110504433A, which requires not only pH adjusters such as dilute hydrochloric acid, citric acid, and sodium hydroxide, but also organic solvents such as ethylene glycol and ethanol. (2) The process is complicated. For example, the method for coating a ternary material with lithium manganate disclosed in the invention patent 110034293A requires the preparation of multiple intermediate products, and the time for each reaction is relatively long. (3) The solvent has high toxicity. For example, the preparation method of the invention patent CN110504423A uses N-methylpyrrolidone which is more toxic.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a lithium manganate coated high nickel nickel cobalt lithium manganate lithium ion battery cathode material and a preparation method thereof, to obtain a cathode composite material with better cycle stability, to improve the high nickel nickel cobalt lithium manganate The surface manganese element content of the positive electrode material can improve its cycle stability, thereby ensuring higher specific capacity and improving the service life of the battery. The preparation method uses a simple and environmentally friendly formula, and the preparation process is simple, and can be applied to large-scale production. .

The present invention adopts following technical scheme to realize:

A preparation method of a lithium manganate-coated high-nickel-nickel-cobalt manganate lithium-ion battery positive electrode material, comprising the following steps:

Step S1, adding a high nickel nickel cobalt lithium manganate precursor to the sodium hydroxide aqueous solution, and stirring in a magnetic stirrer to obtain a uniform alkaline precursor dispersion;

Step S2, under stirring, slowly drop an aqueous solution containing manganese ions into the alkaline precursor dispersion to form a manganese oxide-coated high nickel nickel cobalt lithium manganate precursor dispersion;

Step S3, after centrifuging and vacuum drying the dispersion liquid, adding lithium hydroxide as a reactant, fully mixing by ball milling, and reacting at high temperature in an oxygen atmosphere to prepare a lithium manganate-coated nickel-cobalt-manganate lithium-ion battery cathode Material.

A further improvement of the present invention is that the high-nickel-nickel-cobalt lithium manganate precursor in the step S1 can stably exist in an alkaline environment, and the substance is particles of 1-100 microns; wherein the high-nickel-nickel-cobalt lithium manganate precursor is It is obtained by reacting manganese sulfate, cobalt sulfate and nickel sulfate under alkaline conditions; the atomic content ratio of nickel, cobalt and manganese is 8:1:1, 8.5:0.75:0.75 or 8.3:1:0.7, and the atomic content of nickel exceeds that of nickel 75% of cobalt manganese.

A further improvement of the present invention is that in the step S1, the concentration of the aqueous sodium hydroxide solution is 0.01-1.5 mol/L, and the mass ratio of sodium hydroxide to high nickel nickel cobalt lithium manganate precursor is 1: (1-50); After stirring at a rotational speed of 50-500 rpm for 0.1-3 hours, an alkaline high nickel nickel cobalt lithium manganate precursor dispersion liquid is obtained.

A further improvement of the present invention is that in the step S2, the manganese ions come from manganese salts, including manganese sulfate, manganese chloride, manganese nitrate and manganese carbonate, and the concentration of the aqueous solution containing manganese ions is 0.0025-2.5 mol/L. The time should be controlled within 1-120min.

A further improvement of the present invention is that, in the step S2, a continuous stirring speed of 50-500 rpm is used to stir for 1-120 min until the dropwise addition is completed.

A further improvement of the present invention is that in the step S3, the mass ratio of lithium hydroxide to the coating precursor is 1:(1.0-3.5).

A further improvement of the present invention is that in the step S3, the ball milling process is ball-milled at a speed of 100-500rpm for 0.1-6h, the reaction temperature with oxygen is 400-800°C, the reaction time is 5-30 hours, and the temperature is lowered to room temperature to obtain Lithium manganate coated nickel cobalt lithium manganate lithium ion battery cathode material.

A lithium manganate-coated positive electrode material for a high-nickel-nickel-cobalt manganate lithium-ion battery is prepared by using the above-mentioned preparation method.

Compared with the prior art, the present invention at least has the following beneficial technical effects:

The positive electrode material of the high-nickel-nickel-cobalt lithium manganate lithium ion battery covered by the lithium manganate proposed by the invention adopts a simple formula, reacts in an alkaline environment, and avoids the damage of the high-nickel-nickel-cobalt lithium manganate precursor. The coating reaction of manganese oxide is carried out in a water system, which has low requirements on the environment and simple operation. At the same time, the industrial methods of magnetic stirring and ball-milling stirring are simple, which is beneficial to large-scale production. At the same time, in the preparation process of the precursor, the reaction is carried out at normal temperature, and the safety of synthesis is improved while saving energy, which is beneficial to realizing large-scale production.

The lithium manganate-coated high-nickel-nickel-cobalt lithium manganate lithium ion battery positive electrode material prepared by the invention is uniformly coated, and the content of the surface-coated lithium manganate can be more formulated and controlled, and can be used for battery electrode production; The electrode paste made by adding a binder and N-methylpyrrolidone to this material is in common soft materials (such as polyterephthalic acid, polyimide and polydimethylsiloxane) or It has good film formation and forming performance on hard (such as copper, aluminum and silica) substrates. At the same time, it also shows good cycle stability and thermal stability in the test of assembled button battery.

Description of drawings

(a) and (b) in Figure 1 are scanning electron microscope photographs of NCMOH; (c) and (d) in Figure 1 are scanning electron microscope photographs of MO-NCMOH;

Fig. 2 is the X-ray diffraction pattern of LMO-NCM, NCM and LMO;

(a) and (b) in Figure 3 are scanning electron microscope pictures of NCM, and (c) and (d) in Figure 3 are scanning electron microscopy pictures of LMO-NCM;

Fig. 4 is the battery cycle performance test data chart prepared by LMO-NCM in Example 3;

Fig. 5 is the battery rate performance test data chart prepared by LMO-NCM in Example 3;

Fig. 6 is the battery cycle performance test data chart prepared by LMO-NCM in Example 6;

Fig. 7 is the battery rate performance test data chart prepared by LMO-NCM in Example 6;

Fig. 8 is the battery cycle performance test data chart prepared by LMO-NCM in Example 9;

FIG. 9 is the rate performance test data of the battery prepared by LMO-NCM in Example 9. FIG.

Detailed ways

The present invention is further described by the following examples, and does not limit the present invention in any way. On the premise of not departing from the technical solutions of the present invention, any changes or changes made to the present invention that are easily implemented by those of ordinary skill in the art will be fall within the scope of the claims of the present invention.

The present invention provides a method for preparing a lithium manganate-coated positive electrode material for a high-nickel-nickel-cobalt lithium manganate lithium-ion battery, which includes the following specific embodiments:

Example 1

Weigh 2 g of high nickel nickel cobalt lithium manganate precursor (NCMOH) and 340 mg of sodium hydroxide into 20 mL of water, and perform magnetic stirring at a speed of 200 rpm for half an hour, so that the precursors are uniformly mixed in the liquid phase to obtain a precursor dispersion liquid. Dissolve 900 mg of manganese sulfate in water, after dissolving, wet the acid burette with a certain amount of solution, fix the acid burette above the precursor dispersion with a butterfly clip, keep the magnetic stirring of the dispersion at 200 rpm, and slowly add sulfuric acid dropwise The manganese solution is put into the dispersion liquid, and the manganese sulfate solution is added dropwise into the dispersion liquid within 30 minutes to obtain a manganese oxide-coated nickel cobalt lithium manganate precursor dispersion liquid.

Pour the dispersion into a centrifuge tube, centrifuge at 2500 rpm for 3 minutes, pour off the supernatant, then add water and wash it three times. clear liquid. Then, ethanol was added to carry out alcohol washing three times, and the operation was the same as before, centrifugation at 2500 rpm for 3 minutes, and the supernatant was discarded. Finally, it was dried in a vacuum drying oven at 80 degrees Celsius for 10 hours to obtain a manganese oxide-coated high nickel nickel cobalt lithium manganate precursor (MO-NCMOH). Its scanning electron microscope photos are shown in Figures 1(c) and (d), compared with the uncoated high nickel nickel cobalt lithium manganate precursor as shown in Figure 1(a). , (b), whose surface morphologies are completely different, showing a layer of uniformly coated manganese oxide.

Example 2

Weigh 1 g of the dry sample in Example 1, and weigh 450 mg of solid lithium hydroxide, pour the two into a ball-milling jar, and then ball-mill at 150 rpm for 4 hours. Take out the sample after ball milling, put the sample into a tube furnace, pass oxygen atmosphere, react at 750 degrees Celsius for 900 minutes, then cool down to room temperature, take out the sample, and obtain high nickel nickel cobalt coated with lithium manganate Lithium manganate (LMO-NCM) cathode material for lithium-ion batteries. The X-ray diffraction patterns of LMO-NCM, NCM and LMO are shown in Figure 2. The diffraction peak positions of the three materials are the same, indicating that they have the same crystal structure. The scanning electron microscope photos of NCM are shown in Fig. 3(a), (b), and the scanning electron microscope photos of LMO-NCM are shown in Fig. 3(c), (d), both of which have the same surface morphology, It also proves that the crystal structure is the same.

Example 3

Weigh 160 mg of LMO-NCM in Example 2, 20 mg of conductive carbon black and 400 microliters of an NMP solution of PVDF with a concentration of 50 mg/ml. The three were added to the ball milling jar and ball milled at 350 rpm for 30 minutes.

After the ball milling is completed, the slurry mixed uniformly is coated on the current collector, and is kept at 80 degrees for 10 hours for vacuum drying to obtain a positive electrode piece of the battery.

The positive electrode piece was assembled into a half-cell and the performance was tested, and the counter electrode was a metal lithium piece. The constant current charge-discharge cycle test was performed between 2.8V and 4.3V. For the cycle stability test, a current of 0.1C was used in the first cycle, and 0.5C was used for the subsequent cycle. The cycle performance is shown in Figure 4. The capacity retention rate was 87.5% after 200 charge-discharge cycles. For the rate performance test, 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, 4C, 5C and 0.1C were used for five cycles each, and the rate performance is shown in Figure 5.

Example 4

Weigh 1.2g high nickel nickel cobalt lithium manganate precursor (NCMOH) and 1.2g sodium hydroxide into 20mL water, and conduct magnetic stirring at a speed of 500rpm for 3 hours, so that the precursors are uniformly mixed in the liquid phase, and the precursor dispersion is obtained. liquid. Dissolve 540 mg of manganese sulfate in water. After dissolving, wet the acid burette with a certain amount of solution, fix the acid burette above the precursor dispersion with a butterfly clip, keep the magnetic stirring of the dispersion at 500 rpm, and slowly add sulfuric acid dropwise. The manganese solution is put into the dispersion liquid, and the manganese sulfate solution is added dropwise into the dispersion liquid within 60 minutes to obtain a manganese oxide-coated nickel cobalt lithium manganate precursor dispersion liquid.

Pour the dispersion into a centrifuge tube, centrifuge at 3000 rpm for 5 minutes, pour off the supernatant, then add water and wash it three times. clear liquid. Then, ethanol was added to carry out alcohol washing three times. The operation was the same as before, centrifugation at 3000 rpm for 5 minutes, and the supernatant was discarded. Finally, it was dried in a vacuum drying oven at 80 degrees Celsius for 10 hours to obtain a manganese oxide-coated high nickel nickel cobalt lithium manganate precursor (MO-NCMOH).

Example 5

Weigh 1 g of the dry sample in Example 4, and weigh 1.5 g of solid lithium hydroxide, pour the two into a ball-milling jar, and then ball-mill at 300 rpm for 2 hours. After ball milling, take out the sample, put the sample into a tube furnace, pass oxygen atmosphere, react at 800 degrees Celsius for 300 minutes, then cool down to room temperature, take out the sample, and obtain high nickel nickel cobalt coated with lithium manganate Lithium manganate (LMO-NCM) cathode material for lithium-ion batteries.

Example 6

Weigh 160 mg of LMO-NCM from Example 5, 20 mg of conductive carbon black and 400 microliters of an NMP solution of PVDF at a concentration of 50 mg/ml. The three were added to the ball milling jar and ball milled at 350 rpm for 30 minutes.

After the ball milling is completed, the slurry mixed uniformly is coated on the current collector, and is kept at 80 degrees for 10 hours for vacuum drying to obtain a positive electrode piece of the battery.

The positive electrode piece was assembled into a half-cell and the performance was tested, and the counter electrode was a metal lithium piece. The constant current charge-discharge cycle test was performed between 2.8V and 4.3V. For the cycle stability test, a current of 0.1C was used in the first cycle, and 0.5C was used for the subsequent cycle. The cycle performance is shown in Figure 6. The capacity retention rate was 87.5% after 200 charge-discharge cycles. For the rate performance test, 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, 4C, 5C and 0.1C were used for five cycles each, and the rate performance is shown in Figure 7.

Example 7

Weigh 2 g of high nickel nickel cobalt lithium manganate precursor (NCMOH) and 40 mg of sodium hydroxide into 50 mL of water, and perform magnetic stirring at a speed of 50 rpm for 10 minutes, so that the precursors are uniformly mixed in the liquid phase to obtain a precursor dispersion liquid. Dissolve 151 mg of manganese sulfate in water, after dissolving, wet the acid burette with a certain amount of solution, fix the acid burette above the precursor dispersion with a butterfly clip, keep the magnetic stirring of the dispersion at 50 rpm, and slowly add sulfuric acid dropwise The manganese solution was put into the dispersion liquid, and the manganese sulfate solution was added dropwise into the dispersion liquid within 5 minutes to obtain a manganese oxide-coated nickel cobalt lithium manganate precursor dispersion liquid.

Pour the dispersion into a centrifuge tube, centrifuge at 2000 rpm for 10 minutes, discard the supernatant, then add water and wash three times with water. The operation is the same as before, centrifuge at 2000 rpm for 10 minutes, and discard clear liquid. Then, ethanol was added to carry out alcohol washing three times. The operation was the same as before, centrifugation at 2000 rpm for 10 minutes, and the supernatant was discarded. Finally, it was dried in a vacuum drying oven at 80 degrees Celsius for 10 hours to obtain a manganese oxide-coated high nickel nickel cobalt lithium manganate precursor (MO-NCMOH).

Example 8

Weigh 1 g of the dry sample in Example 7, and weigh 600 mg of solid lithium hydroxide, pour the two into a ball-milling jar, and then ball-mill at 100 rpm for 6 hours. Take out the sample after ball milling, put the sample into a tube furnace, pass oxygen atmosphere, react at 400 degrees Celsius for 30 hours, then cool down to room temperature, take out the sample, and obtain high nickel nickel cobalt coated with lithium manganate Lithium manganate (LMO-NCM) cathode material for lithium-ion batteries.

Example 9

160 mg of LMO-NCM from Example 8, 20 mg of conductive carbon black, and 400 microliters of an NMP solution of PVDF at a concentration of 50 mg/ml were weighed. The three were added to the ball milling jar and ball milled at 350 rpm for 30 minutes.

After the ball milling is completed, the slurry mixed uniformly is coated on the current collector, and is kept at 80 degrees for 10 hours for vacuum drying to obtain a positive electrode piece of the battery.

The positive electrode piece was assembled into a half-cell and the performance was tested, and the counter electrode was a metal lithium piece. The constant current charge-discharge cycle test was performed between 2.8V and 4.3V. For the cycle stability test, a current of 0.1C was used in the first cycle, and 0.5C was used for the subsequent cycle. The cycle performance is shown in Figure 8. The capacity retention rate was 87.5% after 200 charge-discharge cycles. For the rate performance test, 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, 4C, 5C and 0.1C were used for five cycles each, and the rate performance is shown in Figure 9.

Claims (8)

1. a preparation method of lithium manganate coating high nickel nickel cobalt lithium manganate lithium ion battery positive electrode material, is characterized in that, comprises the following steps: Step S1, adding a high nickel nickel cobalt lithium manganate precursor to the sodium hydroxide aqueous solution, and stirring in a magnetic stirrer to obtain a uniform alkaline precursor dispersion; Step S2, under stirring, slowly drop an aqueous solution containing manganese ions into the alkaline precursor dispersion to form a manganese oxide-coated high nickel nickel cobalt lithium manganate precursor dispersion; Step S3, after centrifuging and vacuum drying the dispersion liquid, adding lithium hydroxide as a reactant, fully mixing by ball milling, and reacting at high temperature in an oxygen atmosphere to prepare a lithium manganate-coated nickel-cobalt-manganate lithium-ion battery cathode Material. 2. the preparation method of a kind of lithium manganate coating high nickel nickel cobalt manganate lithium ion battery positive electrode material according to claim 1, is characterized in that, the high nickel nickel cobalt lithium manganate precursor in described step S1 It can exist stably in an alkaline environment, and the substance is particles of 1-100 microns; the high nickel nickel cobalt lithium manganate precursor is obtained by reacting manganese sulfate, cobalt sulfate and nickel sulfate under alkaline conditions; nickel cobalt manganese The atomic content ratio is 8:1:1, 8.5:0.75:0.75 or 8.3:1:0.7, and the atomic content of nickel exceeds 75% of nickel, cobalt, and manganese. 3. the preparation method of a kind of lithium manganate coating high nickel nickel cobalt manganate lithium ion battery positive electrode material according to claim 1, is characterized in that, in described step S1, the concentration of sodium hydroxide aqueous solution is 0.01- 1.5mol/L, the mass ratio of sodium hydroxide to high-nickel-nickel-cobalt lithium manganate precursor is 1: (1-50); after stirring at a rotating speed of 50-500rpm for 0.1-3 hours, alkaline high-nickel-nickel-cobalt manganate is obtained Lithium precursor dispersion. 4. the preparation method of a kind of lithium manganate coating high nickel nickel cobalt manganate lithium ion battery positive electrode material according to claim 1, is characterized in that, in described step S2, manganese ion comes from manganese salt, comprises sulfuric acid For manganese, manganese chloride, manganese nitrate and manganese carbonate, the concentration of the aqueous solution containing manganese ions is 0.0025-2.5mol/L, and the dripping time should be controlled within 1-120min. 5. the preparation method of a kind of lithium manganate coating high nickel nickel cobalt lithium manganate lithium ion battery positive electrode material according to claim 1, is characterized in that, in described step S2, use the continuous stirring speed with 50-500rpm Stir for 1-120min until the dropwise addition ends. 6. the preparation method of a kind of lithium manganate coating high nickel nickel cobalt manganate lithium ion battery positive electrode material according to claim 1, is characterized in that, in described step S3, lithium hydroxide and coating precursor are mixed The mass ratio is 1:(1.0-3.5). 7. the preparation method of a kind of lithium manganate coating high nickel nickel cobalt lithium manganate lithium ion battery positive electrode material according to claim 1, is characterized in that, in described step S3, ball milling process is ball milling with the rotating speed of 100-500rpm 0.1-6h, the reaction temperature with oxygen is 400-800°C, and the reaction time is 5-30 hours, and after being lowered to room temperature, a lithium manganate-coated nickel-cobalt manganate lithium-ion battery cathode material is obtained. 8 . A lithium manganate-coated positive electrode material for a high-nickel-nickel-cobalt lithium manganate lithium-ion battery, characterized in that, it is prepared by using the preparation method described in any one of claims 1 to 7 .

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