WO2023178900A1 - Lithium nickel manganese cobalt oxide gradient positive electrode material and preparation method therefor - Google Patents

Abstract

Disclosed in the present invention are a lithium nickel manganese cobalt oxide gradient positive electrode material and a preparation method therefor. The preparation method comprises the following steps: obtaining a lithium nickel manganese cobalt oxide gradient positive electrode material precursor, the nickel content in the lithium nickel manganese cobalt oxide gradient positive electrode material precursor decreasing from a core to a shell in a gradient mode, and the cobalt and manganese contents increasing from the core to the shell in a gradient mode; and uniformly mixing the lithium nickel manganese cobalt oxide gradient positive electrode material precursor with a lithium source, and then carrying out gradient calcination, thereby obtaining the lithium nickel manganese cobalt oxide gradient positive electrode material, the gradient calcination process comprising controlling the calcination temperature so that the calcination temperature decreases in a gradient mode. According to the present invention, by means of gradient temperature-based calcination, the core and the shell are in respective optimal sintering conditions, so as to avoid differences in core and shell components and structures in a sintering process, which may cause different degrees of shrinkage and gradual separation of the core and the shell in a cycling process, thereby effectively improving the long-term cycle performance of the material.

Description

A kind of nickel cobalt lithium manganate gradient cathode material and preparation method thereof Technical field

The present invention relates to the technical field of positive electrode materials, and in particular to a nickel cobalt lithium manganate gradient positive electrode material and a preparation method thereof.

Background technique

Lithium nickel cobalt manganate ternary lithium ion battery cathode material is widely used in the field of new energy vehicles due to its high energy density.

High nickel enrichment is generally used to maximize reversible capacity. However, as the nickel content increases, more and more cations are mixed in high-nickel materials, and the cycle and thermal stability gradually decrease, resulting in a reduction in the cycle life of the battery. Therefore, some studies have proposed that by controlling the gradual decrease of nickel from the core to the particle surface, that is, the higher nickel content in the core contributes to a higher discharge capacity, and the higher cobalt and manganese content in the outer layer provides more structural stability, thereby improving the material interface. Stability and battery cycle life. However, the differences in composition and structure between the core and the shell during the sintering process cause the core and shell to shrink to varying degrees during the cycle and gradually separate, thereby inhibiting the diffusion-migration process of ions/electrons between the core and the shell, resulting in Decrease in long-term cyclic performance of materials.

Contents of the invention

The purpose of the present invention is to overcome the above technical deficiencies, propose a lithium nickel cobalt manganate gradient cathode material and a preparation method thereof, and solve the problem of unreasonable sintering processes of nickel cobalt lithium manganate gradient cathode materials with gradient changes in nickel content in the prior art, resulting in material Technical issues that degrade performance.

During the experiment, the inventor found that since the nickel content gradually increased from the outer shell to the core, due to the concentration diffusion mechanism during the sintering process, the nickel in the core part gradually diffused to the surface, and the content of manganese and cobalt on the surface was higher than that in the core, gradually Diffusion to the interior, theoretically the optimal calcination temperature increases step by step from the core to the shell. Therefore, it is hoped that through temperature gradient calcination, the core and shell will be in their respective optimal sintering conditions to avoid core and shell composition and structural differences during the sintering process, which will cause the core and shell to shrink to varying degrees and gradually separate during the cycle, thereby improving the long-term durability of the material. Cycle performance.

Based on this, the first aspect of the present invention provides a method for preparing a lithium nickel cobalt manganate gradient cathode material, which includes the following steps:

Obtain a lithium nickel cobalt manganate gradient cathode material precursor; wherein, the nickel content in the lithium nickel cobalt manganate gradient cathode material precursor decreases from the core to the outer shell, and the cobalt and manganese contents increase from the core to the outer shell;

The lithium nickel cobalt manganate gradient cathode material precursor and the lithium source are mixed evenly and then gradient calcination is performed to obtain the nickel cobalt lithium manganate gradient cathode material; wherein, the gradient calcination process includes: controlling the calcination temperature to decrease the calcination temperature gradient.

A second aspect of the present invention provides a lithium nickel cobalt manganate gradient positive electrode material, which is obtained by the preparation method of a lithium nickel cobalt manganate gradient positive electrode material provided by the first aspect of the present invention.

Compared with the existing technology, the beneficial effects of the present invention include:

The present invention uses temperature gradient calcination to keep the core and shell in their respective optimal sintering conditions to avoid core and shell composition and structural differences during the sintering process, causing the core and shell to shrink to varying degrees and gradually separate during the cycle, thereby effectively improving the long-term durability of the material. Cycle performance.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with examples. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention.

A first aspect of the invention provides a method for preparing a lithium nickel cobalt manganate gradient cathode material, which includes the following steps:

S1. Obtain a lithium nickel cobalt manganate gradient cathode material precursor; wherein, the nickel content in the nickel cobalt lithium manganate gradient cathode material precursor decreases from the core to the outer shell, and the cobalt and manganese contents increase from the core to the outer shell;

S2. Mix the lithium nickel cobalt manganate gradient cathode material precursor and the lithium source evenly and then perform gradient calcination to obtain the nickel cobalt lithium manganate gradient cathode material; wherein, the gradient calcination process includes: controlling the calcination temperature to achieve a calcination temperature gradient decline.

In the present invention, the steps of obtaining the nickel-cobalt lithium manganate gradient cathode material precursor include:

S11. Prepare n groups of mixed salt solutions containing nickel sources, cobalt sources and manganese sources with different nickel contents; where n is a positive integer ≥ 2; in some embodiments of the present invention, n is 3; nickel source It is at least one of nickel sulfate, nickel chloride, nickel nitrate, and nickel acetate. The cobalt source is at least one of cobalt sulfate, cobalt chloride, cobalt nitrate, and cobalt acetate. The manganese source is manganese sulfate, manganese chloride, At least one of manganese nitrate and manganese acetate. In some specific embodiments of the present invention, the nickel source, cobalt source and manganese source are configured into three metal ratios according to the nickel, cobalt and manganese metal molar ratios of 5:2:3, 7:1:2 and 90:5:5 respectively. The mixed salt solutions are respectively counted as A metal salt solution, B metal salt solution, and C metal salt solution; further, in the above mixed salt solution, the total metal ion concentration of nickel, cobalt, and manganese is 1 to 3 mol/L.

S12. Prepare an alkali solution and a complexing agent solution; wherein the alkali is at least one of sodium hydroxide and potassium hydroxide; the concentration of the alkali solution is 2 to 6 mol/L, and further 4 mol/L; the complexing agent is ammonia water , at least one of citric acid; the concentration of the complexing agent solution is 0.5~5mol/L, further 1mol/L.

S13. Mix n groups of mixed salt solutions with different nickel contents in sequence with an alkali solution and a complexing agent solution, and perform a continuous reaction to prepare a nickel cobalt lithium manganate gradient cathode material precursor; the reaction temperature is controlled at 40 to 60°C. The reaction pH is between 10 and 13, and the reaction process is protected by nitrogen.

In step S13 of the present invention, the steps of sequentially mixing n groups of mixed salt solutions with different nickel contents with an alkali solution and a complexing agent solution for continuous reaction include:

S131. Pour the first group of mixed salt solutions, alkali solutions, and complexing agent solutions into the reaction vessel for reaction to obtain the first reaction solution;

S132. Mix and react the i-th reaction solution, the i+1-th group of mixed salt solutions, alkali solutions, and complexing agent solutions to obtain the i+1-th reaction solution;

S133. Repeat step S132 to perform the mixing reaction in sequence until the nth reaction solution is obtained, and undergoes aging, filtration, washing and drying to obtain the nickel cobalt lithium manganate gradient cathode material precursor;

Among them, i is a positive integer, 1≤i<i+1≤n, and the nickel content of the i-th group of mixed salt solutions is greater than the nickel content of the i+1-th group of mixed salt solutions, and the cobalt-manganese content of the i-th group of mixed salt solutions It is less than the cobalt and manganese content of the mixed salt solution of the i+1 group, thereby achieving a gradient decrease in nickel content from the core to the outer shell, and a gradient increase in the cobalt and manganese content from the core to the outer shell.

In some preferred embodiments of the present invention, the mixed salt solution, alkali solution, and complexing agent are all introduced into the reaction system at a certain flow rate.

In some specific embodiments of the present invention, the nickel source, the cobalt source and the manganese source are respectively configured to the total metal ion concentration according to the nickel, cobalt and manganese metal molar ratios of 5:2:3, 7:1:2 and 90:5:5. A mixed salt solution of 1 to 3 mol/L is counted as A metal salt solution, B metal salt solution, and C metal salt solution respectively, and the feed rate of the mixed salt solution, alkali solution, and complexing agent solution is 1 mol/h respectively. , 0.5mol/h and 2mol/h, the reaction times of A metal salt solution, B metal salt solution and C metal salt solution are 4h, 6h and 20h respectively.

In the present invention, the lithium source is lithium hydroxide or lithium carbonate. In some embodiments of the invention, the lithium source is lithium hydroxide monohydrate (LiOH·H ₂ O). Further, the molar ratio of the lithium nickel cobalt manganate gradient cathode material precursor to the lithium source is 1: (1.01 to 1.1). In some embodiments of the invention, the molar ratio of the nickel cobalt lithium manganate gradient cathode material precursor to the lithium source is The molar ratio of sources is 1:1.04.

In the present invention, the calcination temperature is controlled according to the optimal sintering temperature of each layer of the nickel cobalt lithium manganate gradient cathode material precursor to reduce the calcination temperature gradient, so that each layer structure is at its own optimal sintering temperature to avoid occurrences during the sintering process. The differences in the composition and structure of the core and shell cause the core and shell to shrink to varying degrees and gradually separate during the cycle, thus improving the long-term cycle performance of the material. The optimal sintering temperature of each layer of the gradient cathode material precursor of lithium nickel cobalt manganate was obtained by conducting a sintering DOE test on lithium salt and lithium nickel cobalt manganate ternary cathode material precursor of different compositions at different temperatures. Due to time and Due to cost reasons, the fluctuation range of different proportions is ±0.01, and the fluctuation range of different temperatures is generally ±10°C. The nickel cobalt lithium manganate ternary cathode material obtained from the above-mentioned DOE test has been discharged after electrochemical testing. The sintering parameters (temperature, etc.) with the largest specific capacity and best cycle performance are the optimal values. This process is an existing technology and will not be described in detail here. In some specific embodiments of the present invention, through DOE experiments, the optimal sintering temperature of the precursor hydroxide Ni _0.81 Co _0.08 Mn _0.11 (OH) ₂ is 800 to 820°C, and the optimal sintering temperature of the precursor hydroxide Ni _0.5 Co _0.2 Mn The optimal sintering temperature of _0.3 (OH) ₂ is 900~920℃, the optimal sintering temperature of precursor hydroxide Ni _0.7 Co _0.1 Mn _0.2 (OH) ₂ is 840~860℃, and the optimal sintering temperature of precursor hydroxide Ni _0.90 Co The optimal sintering temperature of _0.05 Mn _0.05 (OH) ₂ is 740~760℃. Furthermore, the gradient calcination process was carried out in an oxygen atmosphere.

In some preferred embodiments of the present invention, the sintering time corresponding to the lowest sintering temperature is 6 to 12 hours, and the sintering time corresponding to other sintering temperatures except the lowest sintering temperature is 0.5 to 1.5 hours. Within this time range, the obtained lithium nickel cobalt manganate gradient cathode material has better battery performance.

In some preferred embodiments of the present invention, a flux is also added during the above gradient calcination process. By introducing flux in the gradient calcination process, the present invention can reduce the calcination temperature of the shell part, make the shell material recrystallize at a relatively low temperature, reduce the temperature difference between the outer shell part and the core part, and weaken the occurrence of cores during the sintering process. The differences in composition and structure between the shells cause the core and shell to shrink and separate to varying degrees during the cycle, ultimately improving the cycle performance of the cathode material. However, the amount of flux added should not be too high. Preferably, the molar ratio of the nickel cobalt lithium manganate gradient cathode material precursor to the cosolvent is 1: (0.00001~0.003), and further is 1: (0.00001~0.001); the cosolvent is selected from boron, silicon, magnesium, and calcium. At least one of oxides, hydroxides, carbonates or chlorides.

A second aspect of the present invention provides a lithium nickel cobalt manganate gradient positive electrode material, which is obtained by the preparation method of a lithium nickel cobalt manganate gradient positive electrode material provided by the first aspect of the present invention.

To avoid redundancy, in the following examples and comparative examples of the present invention, the preparation process of the gradient precursor hydroxide with the nickel content gradually decreasing from the core to the shell is as follows:

According to the nickel-cobalt-manganese metal molar ratios of 5:2:3, 7:1:2 and 90:5:5, NiSO ₄ ·6H ₂ O, CoSO ₄ ·7H ₂ O and MnSO ₄ ·H ₂ O are respectively configured into the total A mixed salt solution with a metal ion concentration of 2mol/L of A, B, and C; then prepare a 1mol/L ammonia solution and a 4mol/L sodium hydroxide solution; first add the high-nickel metal salt solution in C, NaOH solution and ammonia solution were simultaneously pumped into the reaction kettle at pump speeds of 1 mol/h, 0.5 mol/h and 2 mol/h. The reaction temperature was controlled between 40-60°C and the reaction pH was between 10-13. The reaction process Use nitrogen as protection; during this process, the metal ions passed into the kettle are complexed by ammonium ions, uniformly forming a large number of nuclei; after the reaction proceeds for 20 hours, C is switched to B metal salt solution and is passed into the kettle to form Intermediate buffer layer; after continuing the reaction for 6 hours, pass the A mixed salt solution into the kettle, and continue the reaction for 4 hours before ending; after aging, filtration, washing and drying, a gradient precursor hydroxide with a gradually decreasing nickel content from the core to the shell is obtained Ni _0.81 Co _0.08 Mn _0.11 (OH) ₂ .

Example 1

Weigh the gradient precursor hydroxide, LiOH monohydrate, and boron oxide according to the molar ratio of 1:1.04:0.001, place them in a ball mill tank and mix them evenly. Place the mixture in an oxygen atmosphere furnace for gradient calcination. The reaction is completed. Finally, the gradient cathode material is obtained after cooling, crushing and sieving. Among them, the specific gradient calcination process is as follows: first, the temperature is raised from room temperature to 900°C at a heating rate of 2°C/min, kept for 1 hour, then lowered to 850°C at a cooling rate of 5°C/min, and kept for 1 hour. Finally, the temperature was lowered to 750°C and kept warm for 10 hours.

Example 2

Weigh the gradient precursor hydroxide and monohydrate LiOH according to the molar ratio of 1:1.04, place them in a ball mill tank and mix them evenly. Place the mixture in an oxygen atmosphere furnace for gradient calcination. After the reaction is completed, cool and Crush and sieve to obtain gradient cathode material. Among them, the specific gradient calcination process is as follows: first, the temperature is raised from room temperature to 920°C at a heating rate of 2°C/min, kept for 1 hour, then lowered to 850°C at a cooling rate of 5°C/min, and kept for 1 hour. Finally, the temperature was lowered to 750°C and kept warm for 10 hours.

Example 3

After weighing the gradient precursor hydroxide, LiOH monohydrate and boron oxide according to the molar ratio of 1:1.04:0.003, place them in a ball mill tank and mix them evenly. Place the mixture in an oxygen atmosphere furnace for gradient calcination. The reaction is completed. Finally, the gradient cathode material is obtained after cooling, crushing and sieving. Among them, the specific gradient calcination process is as follows: first, the temperature is raised from room temperature to 900°C at a heating rate of 2°C/min, kept for 1 hour, then lowered to 850°C at a cooling rate of 5°C/min, and kept for 1 hour. Finally, the temperature was lowered to 750°C and kept for 10 hours.

Example 4

Weigh the gradient precursor hydroxide, LiOH monohydrate and boron oxide according to the molar ratio of 1:1.04:0.005, mix them evenly in a ball mill jar, and place the mixture in an oxygen atmosphere furnace for gradient calcination. The reaction is completed. Finally, the gradient cathode material is obtained after cooling, crushing and sieving. Among them, the specific gradient calcination process is as follows: first, the temperature is raised from room temperature to 900°C at a heating rate of 2°C/min, kept for 1 hour, then lowered to 850°C at a cooling rate of 5°C/min, and kept for 1 hour. Finally, the temperature was lowered to 750°C and kept for 10 hours.

Comparative example 1

Weigh the gradient precursor hydroxide, LiOH monohydrate, and boron oxide according to the molar ratio of 1:1.04:0.001, place them in a ball mill tank and mix them evenly. Place the mixture in an oxygen atmosphere furnace for gradient calcination. The reaction is completed. Finally, the gradient cathode material is obtained after cooling, crushing and sieving. Among them, the specific gradient calcination process is: first, the temperature is raised from room temperature to 750°C at a heating rate of 2°C/min, kept for 10 hours, then the temperature is raised to 850°C, kept for 1 hour, and finally the temperature is raised to 900°C. Keep warm for 1 hour.

Comparative example 2

Weigh the gradient precursor hydroxide, LiOH monohydrate, and boron oxide according to the molar ratio of 1:1.04:0.001, place them in a ball mill tank and mix them evenly. Place the mixture in an oxygen atmosphere furnace for gradient calcination. The reaction is completed. Finally, the gradient cathode material is obtained after cooling, crushing and sieving. Among them, the gradient calcination process is as follows: first, the temperature is raised from room temperature to 900°C at a heating rate of 2°C/min, maintained for 4 hours, and then lowered to 850°C at a cooling rate of 5°C/min, and maintained for 4 hours. Finally, the temperature was lowered to 750°C and kept warm for 4 hours.

Comparative example 3

Weigh the gradient precursor hydroxide and monohydrate LiOH according to the molar ratio of 1:1.04, place them in a ball mill tank and mix them evenly. Place the mixture in an oxygen atmosphere furnace for calcination. After the reaction is completed, it is cooled and crushed. and sieved to obtain gradient cathode materials. Among them, the specific calcination process is: raising the temperature to 820°C and holding it for 12 hours.

Comparative example 4

Weigh the gradient precursor hydroxide, LiOH monohydrate and boron oxide according to the molar ratio of 1:1.04:0.001, place them in a ball mill tank and mix them evenly. Place the mixture in an oxygen atmosphere furnace for calcination. After the reaction is completed , after cooling, crushing and screening, the gradient cathode material is obtained. Among them, the specific calcination process is: raising the temperature to 800°C and holding it for 12 hours.

test group

Mix the prepared positive electrode material with the conductive agent acetylene carbon black and the binder PVDF according to the mass ratio of 92:4:4, add an appropriate amount of 1-methyl-2-pyrrolidone and ball-mill for 1 hour to form a slurry that is evenly coated on aluminum on the sheet, dried and pressed into sheets to make positive electrode sheets. A 2032 button battery is assembled with metal lithium sheets as the negative electrode. The blue battery test system is used for electrical performance testing. The charge and discharge voltage is 2.5~4.25V. The first cycle is charged and discharged at 0.2/0.2C, and then cycled at 0.5C/1C for 50 seconds. lock up. The specific test results are shown in Table 1.

Table 1

It can be seen from Table 1 that the gradient cathode materials obtained in Examples 1 to 4 of the present invention obviously have better cycle performance.

The above-described specific embodiments of the present invention do not limit the scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (10)

A method for preparing a lithium nickel cobalt manganate gradient cathode material, which is characterized by comprising the following steps: Obtain a lithium nickel cobalt manganate gradient cathode material precursor; wherein, the nickel content in the lithium nickel cobalt manganate gradient cathode material precursor decreases from the core to the outer shell, and the cobalt and manganese contents increase from the core to the outer shell; Mix the lithium nickel cobalt manganate gradient cathode material precursor and the lithium source evenly and then perform gradient calcination to obtain the nickel cobalt lithium manganate gradient cathode material; wherein the gradient calcination process includes: controlling the calcination temperature to make the calcination Temperature gradient decreases. The preparation method of lithium nickel cobalt manganate gradient cathode material according to claim 1, characterized in that the step of obtaining the precursor of lithium nickel cobalt manganate gradient cathode material includes: S11. Prepare n groups of mixed salt solutions containing nickel source, cobalt source and manganese source with different nickel contents; S12. Prepare alkali solution and complexing agent solution; S13. Mix n groups of mixed salt solutions with different nickel contents in sequence with an alkali solution and a complexing agent solution, and perform continuous reactions to prepare a nickel cobalt lithium manganate gradient cathode material precursor; Among them, n is a positive integer ≥ 2. The preparation method of lithium nickel cobalt manganate gradient cathode material according to claim 2, characterized in that the step of mixing n groups of mixed salt solutions with different nickel contents with an alkali solution and a complexing agent solution for continuous reaction includes: S131. Pour the first group of mixed salt solutions, alkali solutions, and complexing agent solutions into the reaction vessel for reaction to obtain the first reaction solution; S132. Mix and react the i-th reaction solution, the i+1-th group of mixed salt solutions, alkali solutions, and complexing agent solutions to obtain the i+1-th reaction solution; S133. Repeat step S132 to perform the mixing reaction in sequence until the nth reaction solution is obtained, and undergoes aging, filtration, washing and drying to obtain the nickel cobalt lithium manganate gradient cathode material precursor; Among them, i is a positive integer, 1≤i<i+1≤n, and the nickel content of the i-th group of mixed salt solutions is greater than the nickel content of the i+1-th group of mixed salt solutions, and the cobalt-manganese content of the i-th group of mixed salt solutions Less than the cobalt and manganese content of the mixed salt solution of the i+1 group. The preparation method of lithium nickel cobalt manganate gradient cathode material according to claim 2, characterized in that n is 3, and the preparation of n groups of mixed salt solutions containing nickel source, cobalt source and manganese source with different nickel contents It includes: configuring the nickel source, cobalt source and manganese source into a mixed salt solution with three metal ratios according to the nickel, cobalt and manganese metal molar ratios of 5:2:3, 7:1:2 and 90:5:5 respectively. The preparation method of lithium nickel cobalt manganate gradient cathode material according to claim 2, characterized in that the step of mixing n groups of mixed salt solutions with different nickel contents with an alkali solution and a complexing agent solution in sequence to perform a continuous reaction , the reaction temperature is controlled between 40 and 60°C, the reaction pH is between 10 and 13, and nitrogen is used as protection during the reaction process. The preparation method of lithium nickel cobalt manganate gradient cathode material according to claim 1, characterized in that the calcination temperature is controlled according to the optimal sintering temperature of each layer of the lithium nickel cobalt manganate gradient cathode material precursor to reduce the calcination temperature gradient; The optimal sintering temperature of each layer of the lithium nickel cobalt manganate gradient cathode material precursor was obtained by conducting a sintering DOE test on lithium salts and lithium nickel cobalt manganate ternary cathode material precursors of different compositions at different temperatures. For the lithium nickel cobalt manganate ternary cathode material obtained from the DOE test, after electrochemical testing, the sintering temperature with the largest discharge specific capacity and the best cycle performance is the optimal sintering temperature. The method for preparing a gradient cathode material of lithium nickel cobalt manganate according to claim 1, characterized in that the gradient calcination process is carried out in an oxygen atmosphere. The preparation method of lithium nickel cobalt manganate gradient cathode material according to claim 1, characterized in that the sintering time corresponding to the lowest sintering temperature is 6 to 12 hours, and the sintering time corresponding to other sintering temperatures except the lowest sintering temperature is 0.5 to 1.5 h. The preparation method of lithium nickel cobalt manganate gradient cathode material according to claim 1, characterized in that, during the gradient calcination process, a flux is also added, and the precursor of the lithium nickel cobalt manganate gradient cathode material is mixed with a flux. The molar ratio of the solvent is 1: (0.00001-0.003); the co-solvent is selected from at least one of boron, silicon, magnesium and calcium oxides, hydroxides, carbonates or chlorides. A lithium nickel cobalt manganate gradient cathode material, characterized in that the lithium nickel cobalt manganate gradient cathode material is obtained by the preparation method of the lithium nickel cobalt manganate gradient cathode material described in any one of claims 1 to 9.