Modified positive electrode lithium supplement material and preparation method and application thereof

Abstract

The preparation method comprises the following steps: preparing a nickel salt solution, aluminum alkali solutions with two concentrations, a precipitant and a complexing agent, carrying out a co-precipitation reaction, and strictly controlling the pH value of different stages, the concentration of the complexing agent and the concentration of the aluminum alkali solution to obtain a composite hydroxide precursor with a core-shell structure; the preparation method comprises the following steps: preparing a composite hydroxide precursor, pre-sintering the composite hydroxide precursor for the first time to obtain an aluminum-doped oxide precursor, uniformly mixing the oxide precursor with a lithium salt, carrying out secondary sintering, and crushing, crushing and sieving a product obtained after the secondary sintering to obtain the modified lithium supplement agent of which the interior is doped with aluminum and the surface is coated with an aluminum compound. The modified lithium supplement material prepared by the method has relatively high purity, relatively low surface residual lithium and a stable structure, and the rate capability and the cycle performance of the battery can be remarkably improved by adding the lithium supplement material prepared by the method into a positive electrode active material of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a modified positive electrode lithium replenishing agent material, its preparation method, and its application. Background Technology

[0002] In recent years, with the increasing demand for new energy vehicles and the development of energy storage technology, the demand for lithium-ion batteries has been increasing year by year. However, during the first charge and discharge process, a large amount of solid electrolyte interface film is generated on the surface of the negative electrode of the lithium-ion battery, consuming the limited lithium ions and electrolyte in the battery, causing irreversible capacity loss, reducing the energy density of lithium-ion secondary batteries and the charge and discharge efficiency of electrode materials, thus limiting the application of lithium-ion batteries. Among existing technologies, positive electrode lithium replenishment has gradually attracted attention due to its relatively stable nature, ease of synthesis, low price, and high lithium replenishment capacity. By adding lithium replenishment materials to the positive electrode material, the initial irreversible capacity loss of lithium batteries can be effectively compensated, improving the initial coulombic efficiency and cycle performance.

[0003] Li2NiO2 is a commonly used lithium replenishing agent material in lithium-ion batteries. However, existing lithium replenishing technology using Li2NiO2 still has technical problems such as unstable surface interface, high residual alkali, easy gelation of the prepared slurry when mixed with conventional lithium battery cathode materials, and poor battery rate and cycle performance.

[0004] Chinese invention patent CN114242939A discloses a method for preparing a lithium replenishing agent, Li2NiO2. This method involves mixing the positive electrode lithium replenishing agent Li2NiO2 with an Al dopant to obtain a mixed material. The mixed material is then sintered at high temperature to obtain a sintered material. Finally, the sintered material is coated under a carbon source gas atmosphere to obtain a modified positive electrode material. This modified material improves its stability and conductivity through Al surface doping and carbon coating. However, this method is relatively cumbersome because the positive electrode lithium replenishing agent Li2NiO2 itself has a high residual lithium content on its surface. Re-mixing it with the dopant increases the contact time with air, which can further increase the residual lithium content. Furthermore, it cannot ensure that Al is incorporated into the material. Additionally, the carbon source atmosphere cannot effectively guarantee uniform coating and can easily lead to an increase in the Li2CO3 content of the material, resulting in increased gas production when applied to a battery system.

[0005] Chinese invention patent CN116364905A discloses a method for preparing lithium supplementing agent Li2NiO2. This method involves a co-precipitation reaction between nickel hydroxide or nickel oxide and a metal element solution, followed by mixing the precipitate with a lithium source and sintering at high temperature to obtain a composite lithium supplementing agent material with an internally doped metal element and an externally coated lithium-ion conductor, thereby improving the conductivity and stability of the lithium supplementing agent. However, this method uses a cumbersome wet coating process for the metal element, resulting in high costs and hindering industrial-scale production. Summary of the Invention

[0006] To overcome the problems mentioned in the background section regarding the cumbersome and costly preparation steps of lithium replenishing agent doping and coating, this invention provides a modified cathode lithium replenishing agent material and its preparation method. This lithium replenishing agent material exhibits high purity, low surface residual lithium, and a stable structure. Adding the lithium replenishing agent material prepared according to this invention to the cathode active material of lithium-ion batteries can significantly improve the rate performance and cycle performance of the battery.

[0007] This invention provides a method for preparing a modified cathode lithium replenishing agent material, wherein the lithium replenishing agent material is internally doped with aluminum and its surface is coated with aluminum, and its general chemical formula is Li₂NiaAl. b O2, where 0.990 < a < 0.999, 0.001 < b < 0.010. Specifically, the following steps are included:

[0008] (1) Preparation of composite hydroxide precursor: Nickel salt solution, two different concentrations of aluminum alkali solution, precipitant and complexing agent were prepared and co-precipitated. Pure water, precipitant and complexing agent were added to the reactor to prepare a mixed solution as the bottom liquid. Then, nickel salt solution, low concentration aluminum alkali solution, precipitant and complexing agent were pumped into the reactor at the same time. The flow rate of precipitant and complexing agent was adjusted, pH was controlled at 11.0-12.5, and complexing agent content was 3-8 g / L. When the particle size D150 grew to 3.0-4.0 μm, the low concentration aluminum alkali solution was replaced with a high concentration aluminum alkali solution. At the same time, the flow rate of precipitant was reduced and the flow rate of complexing agent was increased. The pH was controlled at 10.5-12.0 and complexing agent content was 5-10 g / L. When the particle size D250 grew to the target value, the reaction was stopped. After the reaction, the material obtained from the reaction was subjected to solid-liquid separation, washing, drying and sieving to obtain core-shell structured composite hydroxide precursor.

[0009] (2) Preparation of oxide precursor: The above-obtained composite hydroxide precursor is pre-sintered once, held at 300-560℃ for 2-8h, with a heating rate of 1-5℃ / min, and the sintering atmosphere is nitrogen or argon. After cooling, aluminum-doped oxide precursor is obtained.

[0010] (3) Mixed sintering: The aluminum-doped oxide precursor obtained above is uniformly mixed with lithium salt and then sintered at high temperature. The temperature is maintained at 650-820℃ for 6-20h, the heating rate is 1-3℃ / min, and the sintering atmosphere is nitrogen or argon. After cooling, it is crushed, pulverized and sieved to obtain a modified positive electrode lithium replenishing agent material with aluminum doping inside and aluminum coating on the surface.

[0011] Furthermore, in step (1), the nickel salt is any one or more of nickel sulfate, nickel chloride, or nickel nitrate, the aluminum salt is any one or more of aluminum sulfate, aluminum chloride, aluminum nitrate, or sodium aluminate, the precipitant is any one or two of sodium hydroxide or potassium hydroxide, and the complexing agent is any one or more of ammonia, sodium citrate, ammonium sulfate, or EDTA. The aluminum alkali solution is prepared by dissolving the aluminum salt in sodium hydroxide solution or potassium hydroxide solution.

[0012] Furthermore, in step (1), the pH of the bottom liquid is controlled at 11.0-12.5, the metal ion concentration of the nickel salt solution is 1.0-2.5 mol / L, and the flow rate is 50-150 mL / min; the metal ion concentration of the low-concentration aluminum alkali solution is 0.05-2.00 mol / L, the metal ion concentration of the high-concentration aluminum alkali solution is 2.00-4.5 mol / L, and the flow rate is 10-120 mL / min; the concentration of the precipitant is 1-8 mol / L, and the flow rate is 20-150 mL / min; the concentration of the complexing agent is 2-10 mol / L, and the flow rate is 0.5-100 mL / min; the reaction temperature is controlled at 40-80℃, and the rotation speed is controlled at 300-850 rpm.

[0013] Furthermore, in step (1), the shell thickness of the composite hydroxide precursor is controlled within a certain range of 0.15-0.50 μm, and the particle size D250-D150 is controlled within 0.3-1.0 μm.

[0014] Furthermore, the oxygen content of the sintering atmosphere in steps (2) and (3) is <100ppm.

[0015] Furthermore, the lithium salt in step (3) is a mixture of two lithium salts, including Li2O and LiOH, wherein the mass ratio of Li2O to LiOH is (8.0-9.5):1, and the molar ratio of the total Li in the two lithium salts to the Ni in the aluminum-doped oxide precursor is (2.00-2.25):1.

[0016] Furthermore, the prepared lithium replenishing agent material has a purity >96.0%, a total residual lithium content <2.9%, an initial charge specific capacity >425mAh / g, and an irreversible specific capacity of 285-318mAh / g.

[0017] This invention provides a lithium-ion battery that uses the aforementioned modified positive electrode lithium replenishing agent material.

[0018] The present invention also provides an application of a modified positive electrode lithium replenishing agent material.

[0019] Beneficial effects:

[0020] (1) This invention introduces aluminum into the precursor preparation process to prepare a core-shell structured hydroxide precursor. After pre-sintering, an aluminum-doped oxide precursor can be obtained. When mixed with lithium salt to prepare a lithium replenishing agent, a modified lithium replenishing agent with an internally doped aluminum and an aluminum-coated surface can be obtained. After the first charge, the structure of the lithium replenishing agent material Li2NiO2 will irreversibly change from an orthorhombic crystal structure to a layered structure LiNiO2. The Ni content in LiNiO2 is very high. After charging and discharging, it is easy to generate a rock salt phase NiO2 with no electrochemical activity and strong anisotropy, which leads to intensified polarization and increased battery impedance. The lithium replenishing agent material prepared by this invention, with the addition of the doping element aluminum, can stabilize the structure of the lithium replenishing agent material and suppress phase transition. When added to the lithium-ion cathode material, it exhibits better rate performance and cycle performance.

[0021] (2) The aluminum metal element with a high shell concentration in the oxide precursor will partially react with lithium salt to form Li-Al-O lithium-ion conductor during high-temperature sintering, forming a coating layer, which can reduce the residual lithium on the surface. Compared with conventional lithium replenishing agent material Li2NiO2, when added to lithium-ion cathode material, it can improve the slurry gelation phenomenon, reduce side reactions, and significantly improve the rate performance and cycle performance of the battery. Attached Figure Description

[0022] Figure 1 This is a comparison chart of the high-temperature cycle retention rate of button batteries in the test examples of this invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the embodiments.

[0024] Example 1

[0025] Nickel salt solution (2.0 mol / L), aluminum alkali solution (0.2 mol / L), and aluminum alkali solution (2.0 mol / L) were prepared separately using pure water. Pure water, ammonia, and sodium hydroxide solution were added to a reaction vessel to obtain a mixture used as the bottom solution. The pH of this bottom solution was 11.8, and the ammonia concentration was 4.5 g / L. The stirring speed of the reaction vessel was set to 400 rpm, and the temperature inside the reaction vessel was controlled at 50℃. Simultaneously, nickel salt solution (95 mL / min), aluminum alkali solution (25 mL / min, 0.2 mol / L), sodium hydroxide solution (80 mL / min, 4.0 mol / L), and ammonia solution (25 mL / min, 3.5 mol / L) were continuously introduced into the reaction vessel. The pH of the reaction system was controlled at 11.8. The complexing agent concentration was 4.5 g / L. When the particle size D150 grew to 3.5 μm, the aluminum alkali solution was replaced with a 2.0 mol / L solution. Simultaneously, the flow rate of the sodium hydroxide solution was reduced to 45 mL / min, and the flow rate of the ammonia solution was increased to 55 mL / min. Other conditions remained unchanged, with the pH of the reaction system controlled at 11.2 and the complexing agent concentration at 7.6 g / L, until the particle size D250 reached 3.9 μm. Feeding into the reactor was then stopped, yielding a hydroxide precursor slurry. The obtained slurry underwent solid-liquid separation, washing, drying, and sieving to obtain a core-shell structured composite hydroxide precursor. The obtained composite hydroxide precursor was pre-sintered in an atmosphere furnace under a nitrogen protective atmosphere with an initial oxygen content of 20 ppm. The temperature was increased to 380℃ at a rate of 5℃ / min and held for 10 h. After cooling, the oxide precursor was obtained.

[0026] The obtained oxide precursor was mixed with Li₂O and LiOH at a Li:Ni molar ratio of 2.1:1, with a Li:Ni mass ratio of 9.2:1. After uniform mixing, a second sintering was performed in a nitrogen-protected furnace with an initial oxygen content of 20 ppm. The temperature was increased to 720℃ at a rate of 2℃ / min, held for 10 hours, and then allowed to cool naturally to room temperature. After crushing, pulverizing, and sieving, a composite lithium supplement material, Li₂Ni, with internal Al doping and a surface coating of Li-Al-O compounds, was obtained. 0.996 Al 0.004 O2.

[0027] Example 2

[0028] Nickel salt solution (2.0 mol / L), aluminum alkali solution (0.2 mol / L), and aluminum alkali solution (2.0 mol / L) were prepared separately using pure water. Pure water, ammonia, and sodium hydroxide solution were added to a reaction vessel to obtain a mixture used as the bottom solution. The pH of this bottom solution was 11.8, and the ammonia concentration was 4.5 g / L. The stirring speed of the reaction vessel was set to 400 rpm, and the temperature inside the reaction vessel was controlled at 50℃. Simultaneously, nickel salt solution (95 mL / min), aluminum alkali solution (25 mL / min, 0.2 mol / L), sodium hydroxide solution (80 mL / min, 4.0 mol / L), and ammonia solution (25 mL / min, 3.5 mol / L) were continuously introduced into the reaction vessel to maintain the pH of the reaction system at 11.8, thus achieving complexation. The concentration of the complexing agent was 4.5 g / L. When the particle size D150 grew to 3.5 μm, the aluminum alkali solution was replaced with a 2.0 mol / L solution. Simultaneously, the flow rate of the sodium hydroxide solution was reduced to 45 mL / min, and the flow rate of the ammonia solution was increased to 55 mL / min. Other conditions remained unchanged, with the pH of the reaction system controlled at 11.2 and the complexing agent concentration at 7.6 g / L, until the particle size D250 reached 4.3 μm. Feeding into the reactor was then stopped, yielding a hydroxide precursor slurry. The obtained slurry underwent solid-liquid separation, washing, drying, and sieving to obtain a core-shell structured composite hydroxide precursor. The obtained composite hydroxide precursor was pre-sintered in an atmosphere furnace under a nitrogen protective atmosphere with an initial oxygen content of 20 ppm. The temperature was increased to 380℃ at a rate of 5℃ / min and held for 10 h. After cooling, the oxide precursor was obtained.

[0029] The obtained oxide precursor was mixed with Li₂O and LiOH at a Li:Ni molar ratio of 2.1:1, with a Li:Ni mass ratio of 9.2:1. After uniform mixing, a second sintering was performed in a nitrogen-protected furnace with an initial oxygen content of 20 ppm. The temperature was increased to 720℃ at a rate of 2℃ / min, held for 10 hours, and then allowed to cool naturally to room temperature. After crushing, pulverizing, and sieving, a composite lithium supplement material, Li₂Ni, with internal Al doping and a surface coating of Li-Al-O compounds, was obtained. 0.992 Al 0.008 O2.

[0030] Comparative Example 1

[0031] Nickel salt solution (2.0 mol / L), aluminum alkali solution (0.2 mol / L), and aluminum alkali solution (2.0 mol / L) were prepared separately using pure water. Pure water, ammonia, and sodium hydroxide solution were added to a reactor to obtain a mixture used as the bottom solution. The pH of this bottom solution was 11.8, and the ammonia concentration was 4.5 g / L. The stirring speed of the reactor was set to 400 rpm, and the temperature inside the reactor was controlled at 50℃. Simultaneously, the following solutions were continuously introduced into the reactor: nickel salt solution at a flow rate of 95 mL / min, aluminum alkali solution at a flow rate of 25 mL / min and a concentration of 0.2 mol / L, sodium hydroxide solution at a flow rate of 80 mL / min and a concentration of 4.0 mol / L, and ammonia solution at a flow rate of 25 mL / min and a concentration of 3.5 mol / L. The pH of the reaction system was controlled at 11.8, and the complexing agent concentration was 4.5 g / L, until the particle size D150 grew to 3... At a particle size of 0.5 μm, the aluminum alkali solution was replaced with a 2.0 mol / L solution, while the flow rate of the sodium hydroxide solution was reduced to 45 mL / min and the flow rate of the ammonia solution was increased to 55 mL / min. Other conditions remained unchanged, and the pH of the reaction system was controlled at 11.2, and the complexing agent concentration at 7.6 g / L, until the particle size D250 reached 3.7 μm. Feeding into the reactor was then stopped, yielding a hydroxide precursor slurry. The obtained slurry underwent solid-liquid separation, washing, drying, and sieving to obtain a core-shell structured composite hydroxide precursor. The obtained composite hydroxide precursor was then subjected to a pre-sintering process in an atmosphere furnace under a nitrogen protective atmosphere with an initial oxygen content of 20 ppm. The temperature was increased to 380 °C at a rate of 5 °C / min and held for 10 h. After cooling, an oxide precursor was obtained.

[0032] The obtained oxide precursor was mixed with Li₂O and LiOH at a Li:Ni molar ratio of 2.1:1, with a Li:Ni mass ratio of 9.2:1. After uniform mixing, a second sintering was performed in a nitrogen-protected furnace with an initial oxygen content of 20 ppm. The temperature was increased to 720℃ at a rate of 2℃ / min, held for 10 hours, and then allowed to cool naturally to room temperature. After crushing, pulverizing, and sieving, a composite lithium supplement material, Li₂Ni, with internal Al doping and a surface coating of Li-Al-O compounds, was obtained. 0.9993 Al 0.0007 O2.

[0033] Comparative Example 2

[0034] Nickel salt solution (2.0 mol / L), aluminum alkali solution (0.2 mol / L), and aluminum alkali solution (2.0 mol / L) were prepared separately using pure water. Pure water, ammonia, and sodium hydroxide solution were added to a reactor to obtain a mixture used as the bottom solution. The pH of this bottom solution was 11.8, and the ammonia concentration was 4.5 g / L. The stirring speed of the reactor was set to 400 rpm, and the temperature inside the reactor was controlled at 50℃. Simultaneously, the following solutions were continuously introduced into the reactor: nickel salt solution at a flow rate of 95 mL / min, aluminum alkali solution at a flow rate of 25 mL / min and a concentration of 0.2 mol / L, sodium hydroxide solution at a flow rate of 80 mL / min and a concentration of 4.0 mol / L, and ammonia solution at a flow rate of 25 mL / min and a concentration of 3.5 mol / L. The pH of the reaction system was controlled at 11.8, and the complexing agent concentration was 4.5 g / L, until the particle size D150 grew to 3... At a particle size of 0.5 μm, the aluminum alkali solution was replaced with a 2.0 mol / L solution, while the flow rate of the sodium hydroxide solution was reduced to 45 mL / min and the flow rate of the ammonia solution was increased to 55 mL / min. Other conditions remained unchanged, and the pH of the reaction system was controlled at 11.2, and the complexing agent concentration at 7.6 g / L, until the particle size D250 reached 4.7 μm. Feeding into the reactor was then stopped, yielding a hydroxide precursor slurry. The obtained slurry underwent solid-liquid separation, washing, drying, and sieving to obtain a core-shell structured composite hydroxide precursor. The obtained composite hydroxide precursor was then subjected to a pre-sintering process in an atmosphere furnace under a nitrogen protective atmosphere with an initial oxygen content of 20 ppm. The temperature was increased to 380 °C at a rate of 5 °C / min and held for 10 h. After cooling, the oxide precursor was obtained.

[0035] The obtained oxide precursor was mixed with Li₂O and LiOH at a Li:Ni molar ratio of 2.1:1, with a Li:Ni mass ratio of 9.2:1. After uniform mixing, a second sintering was performed in a nitrogen-protected furnace with an initial oxygen content of 20 ppm. The temperature was increased to 720℃ at a rate of 2℃ / min, held for 10 hours, and then allowed to cool naturally to room temperature. After crushing, pulverizing, and sieving, a composite lithium supplement material, Li₂Ni, with internal Al doping and a surface coating of Li-Al-O compounds, was obtained. 0.985 Al 0.015 O2.

[0036] Comparative Example 3

[0037] Nickel salt solutions with a metal ion concentration of 2.0 mol / L and aluminum alkali solutions with a metal ion concentration of 2.0 mol / L were prepared using pure water, nickel sulfate, aluminum sulfate, and sodium hydroxide solutions respectively. Pure water, ammonia, and sodium hydroxide solution were added to a reaction vessel to obtain a mixed solution, which served as the bottom solution. The pH of this bottom solution was 11.8, and the ammonia concentration was 4.5 g / L. The stirring speed of the reactor was set to 400 rpm, and the temperature inside the reactor was controlled at 50℃. Simultaneously, a nickel salt solution, a sodium hydroxide solution with a concentration of 4.0 mol / L and a flow rate of 95 mL / min, and ammonia water with a concentration of 3.5 mol / L and a flow rate of 25 mL / min were continuously fed into the reactor. The pH of the reaction system was controlled at 11.8, and the complexing agent concentration was 4.5 g / L. When the particle size D150 grew to 3.5 μm, an aluminum alkali solution with a concentration of 2.0 mol / L was started to be fed into the reactor at a flow rate of 25 mL / min. At the same time, the flow rate of the sodium hydroxide solution was reduced to 45 mL / min, and the flow rate of the ammonia water was increased to 55 mL / min. Other conditions remained unchanged, and the pH of the reaction system was controlled at 11.2, and the complexing agent concentration was 7.6 g / L. Feeding into the reactor was stopped when the particle size D250 reached 3.9 μm, yielding a hydroxide precursor slurry. The obtained slurry was subjected to solid-liquid separation, washing, drying, and sieving processes to obtain a core-shell structured composite hydroxide precursor. The obtained composite hydroxide precursor was subjected to a first pre-sintering process in an atmosphere furnace under a nitrogen protective atmosphere with an initial oxygen content of 20 ppm. The temperature was increased to 380℃ at a heating rate of 5℃ / min and held for 10 hours. After cooling, an oxide precursor was obtained.

[0038] The obtained oxide precursor was mixed with Li₂O and LiOH at a Li:Ni molar ratio of 2.1:1, with a Li:Ni mass ratio of 9.2:1. After uniform mixing, a second sintering was performed in a nitrogen-protected furnace with an initial oxygen content of 20 ppm. The temperature was increased to 720℃ at a rate of 2℃ / min, held for 10 hours, and then allowed to cool naturally to room temperature. After crushing, pulverizing, and sieving, a composite lithium supplement material, Li₂Ni, with internal Al doping and a surface coating of Li-Al-O compounds, was obtained. 0.998 Al 0.002 O2.

[0039] Comparative Example 4

[0040] Nickel sulfate was prepared into a nickel salt solution with a metal ion concentration of 2.0 mol / L using pure water. Pure water, ammonia, and sodium hydroxide solution were added to a reactor to obtain a mixture used as the bottom solution. The pH of this bottom solution was 11.8, and the ammonia concentration was 4.5 g / L. The stirring speed of the reactor was set to 400 rpm, and the temperature inside the reactor was controlled at 50℃. Simultaneously, a nickel salt solution at a flow rate of 95 mL / min, a sodium hydroxide solution at a flow rate of 80 mL / min (4.0 mol / L), and ammonia at a flow rate of 25 mL / min (3.5 mol / L) were continuously fed into the reactor. The pH of the reaction system was controlled at 11.8, and the complexing agent concentration was 4.5 g / L, until the particle size D50 grew to 3.9 μm. Feeding into the reactor was then stopped, yielding a hydroxide precursor slurry. The obtained slurry underwent solid-liquid separation, washing, drying, and sieving processes to obtain the hydroxide precursor. The obtained hydroxide precursor was pre-sintered in an atmosphere furnace under a nitrogen protective atmosphere with an initial oxygen content of 20 ppm. The temperature was increased to 380℃ at a heating rate of 5℃ / min and held for 10 hours. After cooling, the oxide precursor was obtained.

[0041] The obtained oxide precursor was mixed with Li₂O, LiOH, and Al₂O₃ at a Li:Ni molar ratio of 2.1:1 and a Ni:Al molar ratio of 99.5:0.5, with a Li₂O:LiOH mass ratio of 9.2:1. After uniform mixing, a second sintering was performed in a nitrogen-protected furnace with an initial oxygen content of 20 ppm. The temperature was increased to 720℃ at a rate of 2℃ / min, held for 10 hours, and then allowed to cool naturally to room temperature. The resulting material, Li₂Ni, was then crushed, pulverized, and sieved to obtain the lithium supplement material. 0.995 Al 0.005 O2.

[0042] Comparative Example 5

[0043] Nickel sulfate was prepared into a nickel salt solution with a metal ion concentration of 2.0 mol / L using pure water. Pure water, ammonia, and sodium hydroxide solution were added to a reactor to obtain a mixture used as the bottom solution. The pH of this bottom solution was 11.8, and the ammonia concentration was 4.5 g / L. The stirring speed of the reactor was set to 400 rpm, and the temperature inside the reactor was controlled at 50℃. Simultaneously, a nickel salt solution at a flow rate of 95 mL / min, a sodium hydroxide solution at a flow rate of 80 mL / min (4.0 mol / L), and ammonia at a flow rate of 25 mL / min (3.5 mol / L) were continuously fed into the reactor. The pH of the reaction system was controlled at 11.8, and the complexing agent concentration was 4.5 g / L, until the particle size D50 grew to 3.9 μm. Feeding into the reactor was then stopped, yielding a hydroxide precursor slurry. The obtained slurry underwent solid-liquid separation, washing, drying, and sieving processes to obtain the hydroxide precursor. The obtained hydroxide precursor was pre-sintered in an atmosphere furnace under a nitrogen protective atmosphere with an initial oxygen content of 20 ppm. The temperature was increased to 380℃ at a heating rate of 5℃ / min and held for 10h. After cooling, the oxide precursor was obtained.

[0044] The obtained oxide precursor was mixed with Li2O and LiOH at a Li to Ni molar ratio of 2.1:1, with a Li2O to LiOH mass ratio of 9.2:1. After uniform mixing, a second sintering was performed in an atmosphere furnace under a nitrogen protective atmosphere with an initial oxygen content of 20 ppm. The temperature was increased to 720℃ at a heating rate of 2℃ / min, held for 10 hours, and then allowed to cool naturally to room temperature. After crushing, pulverizing, and sieving, undoped and uncoated lithium supplement material Li2NiO2 was obtained.

[0045] Experimental Example 1

[0046] The composite lithium supplement material Li₂Ni, internally doped with Al and coated with Li-Al-O compound as described in Example 1, was selected. 0.996 Al 0.004 O2 was used as a lithium supplement agent. Polycrystalline NCM831205 was selected as the positive electrode active material, and the lithium supplement agent was added at 3 wt% of the positive electrode active material. The positive electrode active material and the lithium supplement agent were combined to form a composite positive electrode active material. A solution with a solid content of 70% was prepared according to the mass ratio of composite active positive electrode material: conductive agent SP: binder PVDF = 9.2:0.5:0.3. The solution was stirred evenly to obtain a positive electrode slurry, which was then coated on aluminum foil and assembled into a 2016 type coin cell. After the coin cell was prepared, conventional formation was performed with a formation voltage of 3.0-4.3V and a charge / discharge rate of 0.1C.

[0047] Experimental Example 2

[0048] The composite lithium supplement material Li₂Ni, internally doped with Al and surface coated with Li-Al-O compound, was selected from Example 2. 0.992 Al 0.008 O2 was used as a lithium supplement agent. Polycrystalline NCM831205 was selected as the positive electrode active material, and the lithium supplement agent was added at 3 wt% of the positive electrode active material. The positive electrode active material and the lithium supplement agent were combined to form a composite positive electrode active material. A solution with a solid content of 70% was prepared according to the mass ratio of composite active positive electrode material: conductive agent SP: binder PVDF = 9.2:0.5:0.3. The solution was stirred evenly to obtain a positive electrode slurry, which was then coated on aluminum foil and assembled into a 2016 type coin cell. After the coin cell was prepared, conventional formation was performed with a formation voltage of 3.0-4.3V and a charge / discharge rate of 0.1C.

[0049] Experimental Example 3

[0050] Comparative Example 1 used Li₂Ni, a composite lithium supplement material internally doped with Al and coated with Li-Al-O compounds. 0.9993 Al 0.0007 O2 was used as a lithium supplement agent. Polycrystalline NCM831205 was selected as the positive electrode active material, and the lithium supplement agent was added at 3 wt% of the positive electrode active material. The positive electrode active material and the lithium supplement agent were combined to form a composite positive electrode active material. A solution with a solid content of 70% was prepared according to the mass ratio of composite active positive electrode material: conductive agent SP: binder PVDF = 9.2:0.5:0.3. The solution was stirred evenly to obtain a positive electrode slurry, which was then coated on aluminum foil and assembled into a 2016 type coin cell. After the coin cell was prepared, conventional formation was performed with a formation voltage of 3.0-4.3V and a charge / discharge rate of 0.1C.

[0051] Test Example 4

[0052] Comparative Example 2 used Li₂Ni, a composite lithium supplement material internally doped with Al and coated with Li-Al-O compounds. 0.985 Al 0.015 O2 was used as a lithium supplement agent. Polycrystalline NCM831205 was selected as the positive electrode active material, and the lithium supplement agent was added at 3 wt% of the positive electrode active material. The positive electrode active material and the lithium supplement agent were combined to form a composite positive electrode active material. A solution with a solid content of 70% was prepared according to the mass ratio of composite active positive electrode material: conductive agent SP: binder PVDF = 9.2:0.5:0.3. The solution was stirred evenly to obtain a positive electrode slurry, which was then coated on aluminum foil and assembled into a 2016 type coin cell. After the coin cell was prepared, conventional formation was performed with a formation voltage of 3.0-4.3V and a charge / discharge rate of 0.1C.

[0053] Experimental Example 5

[0054] Comparative Example 3 used Li₂Ni, a composite lithium supplement material internally doped with Al and coated with Li-Al-O compounds. 0.998 Al 0.002 O2 was used as a lithium supplement agent. Polycrystalline NCM831205 was selected as the positive electrode active material, and the lithium supplement agent was added at 3 wt% of the positive electrode active material. The positive electrode active material and the lithium supplement agent were combined to form a composite positive electrode active material. A solution with a solid content of 70% was prepared according to the mass ratio of composite active positive electrode material: conductive agent SP: binder PVDF = 9.2:0.5:0.3. The solution was stirred evenly to obtain a positive electrode slurry, which was then coated on aluminum foil and assembled into a 2016 type coin cell. After the coin cell was prepared, conventional formation was performed with a formation voltage of 3.0-4.3V and a charge / discharge rate of 0.1C.

[0055] Experimental Example 6

[0056] Lithium supplement material Li2Ni was selected as the material used in Comparative Example 4. 0.995 Al 0.005 O2 was used as a lithium supplement agent. Polycrystalline NCM831205 was selected as the positive electrode active material, and the lithium supplement agent was added at 3 wt% of the positive electrode active material. The positive electrode active material and the lithium supplement agent were combined to form a composite positive electrode active material. A solution with a solid content of 70% was prepared according to the mass ratio of composite active positive electrode material: conductive agent SP: binder PVDF = 9.2:0.5:0.3. The solution was stirred evenly to obtain a positive electrode slurry, which was then coated on aluminum foil and assembled into a 2016 type coin cell. After the coin cell was prepared, conventional formation was performed with a formation voltage of 3.0-4.3V and a charge / discharge rate of 0.1C.

[0057] Experimental Example 7

[0058] Undoped and uncoated lithium replenishing agent material Li2NiO2 (Comparative Example 5) was selected as the lithium replenishing agent, and polycrystalline NCM831205 was selected as the positive electrode active material. The amount of lithium replenishing agent added was 3 wt% of the positive electrode active material. The positive electrode active material and the lithium replenishing agent were combined as a composite positive electrode active material. A solution with a solid content of 70% was prepared according to the mass ratio of composite active positive electrode material: conductive agent SP: binder PVDF = 9.2:0.5:0.3. The solution was stirred evenly to obtain a positive electrode slurry, which was then coated on aluminum foil and assembled into a 2016-type coin cell. After the coin cell was prepared, conventional formation was performed with a formation voltage of 3.0-4.3V and a charge / discharge rate of 0.1C.

[0059] The purity, residual lithium, capacity, rate capability, and cycle life of the modified cathode lithium replenishment material were evaluated using the following methods.

[0060] (1) Purity

[0061] The powder sample was placed in the sample holder and compacted, then placed on the sample holder of the XRD diffractometer, and the instrument door was closed. The scanning range was set to 15°–75°, and the scanning speed was 15° / min. The test was then started. The test results were quantitatively analyzed using XRD analysis software to calculate the relative mass fraction of the contained substances.

[0062] (2) Residual lithium

[0063] Preparation of sample solution: Place a 250mL dry beaker on an analytical balance and weigh 20g ± 0.0005g of lithium supplement material sample (recorded as m). Place a stir bar in the beaker and accurately measure 100mL of RO water at 25±2℃ using a 100mL graduated cylinder. Slowly add the water to the beaker, then seal the mouth of the beaker with plastic film and place it on a magnetic stirrer. Stir at room temperature for 20 minutes. Within 5 minutes after stirring, filter the solution into a 50mL volumetric flask. Rinse the funnel and volumetric flask 2-3 times with the filtrate and cool to room temperature. Use a clean pipette to pipette the filtrate until the concave surface of the filtrate is tangent to the graduation mark on the volumetric flask to obtain the sample solution.

[0064] Lithium residue determination: Pour 50 mL of the sample solution from the volumetric flask into a 250 mL Erlenmeyer flask. Rinse the volumetric flask three times with distilled water, transferring the rinsing solution into the Erlenmeyer flask as well. Add 1-2 drops of phenolphthalein indicator to the Erlenmeyer flask, and select an appropriate concentration of hydrochloric acid standard solution C. HCL Titrate the test solution until the red color completely disappears, reaching the endpoint of the first titration step. Record the volume of hydrochloric acid standard solution consumed, V1. Add 4-5 drops of methyl red indicator to the Erlenmeyer flask and continue titrating with hydrochloric acid standard solution until the solution changes from yellow to bright red, which is the endpoint of the second titration step. Record the volume of hydrochloric acid standard solution consumed at this point, V2.

[0065] The content of Li₂CO₃ and LiOH, expressed as a mass percentage, is calculated using the following formula:

[0066]

[0067] In the formula:

[0068] V1---The volume of hydrochloric acid standard solution consumed in the first titration step, in mL;

[0069] V2---The total volume of hydrochloric acid standard solution consumed in the two-step titration, in mL;

[0070] m --- Sample mass, in grams;

[0071] C HCL ---Molar concentration of standard hydrochloric acid solution, in mol / L.

[0072] (3) Capacity

[0073] The modified positive electrode lithium replenishing agent material was assembled into a 2016 type coin cell. The slurry formula was lithium replenishing agent: conductive agent SP: binder PVDF = 9.2:0.5:0.3. After the preparation was completed, it was formed at 23℃ with a charge-discharge ratio of 0.1C and a voltage range of 3-4.3V. The cutoff current was 0.01C.

[0074] (4) Ratio performance

[0075] The coin cells obtained from the experimental example were subjected to discharge tests at different rates at room temperature (23°C). The charging rate was uniformly set at 0.5C, and the discharge rates were 1C, 3C, and 5C. The specific capacity retention rate at different discharge rates was calculated.

[0076] (5) Cyclic performance

[0077] The formed coin cells obtained from the experimental example were subjected to cycle testing at a high temperature of 45°C with a charging rate of 0.5C and a discharging rate of 1C. The discharge specific capacity retention rate at different cycle numbers was calculated.

[0078] Table 1 Comparison data between the examples and comparative examples

[0079]

[0080] Table 2 Comparison data of experimental cases

[0081]

[0082] evaluate

[0083] From Table 1 and Figure 1 It can be seen that, compared with the modified positive electrode lithium replenishing agent material prepared in Example 1, the positive electrode lithium replenishing agent materials prepared in Comparative Examples 1 and 5 have higher residual lithium, and the cycling performance of Experiments 3 and 7 is poor. This is because the lithium replenishing agent prepared in Comparative Example 1 has less Al metal element added, and the lithium replenishing agent prepared in Comparative Example 5 has no doping or coating, so it cannot effectively react with the residual lithium remaining on the surface of the lithium replenishing agent material, and cannot play a role in stabilizing the structure of the lithium replenishing agent material. This leads to high residual lithium in the positive electrode lithium replenishing agent material and poor cycling performance when mixed with lithium battery positive electrode materials.

[0084] From Table 1, Table 2 and Figure 1It can be seen that, compared with the modified cathode lithium replenishing agent material prepared in Example 1, the cathode lithium replenishing agent material prepared in Comparative Example 2 has lower purity and lower irreversible specific capacity. The poor rate performance and cycle performance of Example 4 are due to the excessive addition of Al metal element in the lithium replenishing agent prepared in Comparative Example 2, which reduces the lithium replenishing agent material content, leading to lower purity and lower irreversible specific capacity. This results in poor rate performance and cycle performance when mixed with lithium battery cathode materials. Therefore, the shell thickness of the composite hydroxide precursor should be controlled within a certain range of 0.15-0.50 μm, and the particle size D250-D150 should be controlled within 0.3-1.0 μm.

[0085] from Figure 1 It can be seen that compared with the modified cathode lithium replenishment material prepared in Example 1, the cathode lithium replenishment materials prepared in Examples 5 and 6 have poorer cycling performance. This is because the Al metal element added to the lithium replenishment material prepared in Comparative Example 3 is only on the surface of the hydroxide precursor. Subsequent sintering cannot allow Al to be well distributed within the lithium replenishment material structure. When mixed with the lithium battery cathode material, it cannot effectively mitigate the damage to the structure caused by repeated volumetric strain during cycling, resulting in poor local stress, structural collapse, and poor cycling performance. In Comparative Example 4, the Al metal element added to the lithium replenishment material is added during the mixing process before sintering. Particle size differences and interface differences lead to uneven mixing, resulting in uneven doping and surface coating. When mixed with the lithium battery cathode material, it cannot effectively mitigate the damage to the structure caused by repeated volumetric strain during cycling, resulting in poor local stress, structural collapse, and poor cycling performance. In the lithium replenishing agent material prepared in Example 1, the metal element Al was added in two steps. Through the subsequent sintering process, the metal element Al can be doped into the lithium replenishing agent material and form a coating layer on the surface. This can not only stabilize the internal structure well, but also reduce the side reactions with the electrolyte. When used in combination with lithium battery cathode materials, the cycle performance is significantly better.

[0086] It should be noted that the descriptions of these embodiments are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described above can be combined with each other as long as they do not conflict with each other. The above are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a modified positive electrode lithium replenishing agent material, wherein the general chemical formula of the lithium replenishing agent material is Li₂Ni. a Al b O2, wherein 0.990 < a < 0.999, 0.001 < b < 0.010, is characterized in that, The preparation method includes the following steps: (1) Preparation of composite hydroxide precursor: Nickel salt solution, two different concentrations of aluminum alkali solution, precipitant and complexing agent were prepared and co-precipitated. Pure water, precipitant and complexing agent were added to the reactor to prepare a mixed solution as the bottom liquid. Then, nickel salt solution, low concentration aluminum alkali solution, precipitant and complexing agent were pumped into the reactor at the same time. The flow rate of precipitant and complexing agent was adjusted, pH was controlled at 11.0-12.5, and complexing agent content was 3-8 g / L. When the particle size D150 grew to 3.0-4.0 μm, the low concentration aluminum alkali solution was replaced with a high concentration aluminum alkali solution. At the same time, the flow rate of precipitant was reduced and the flow rate of complexing agent was increased. The pH was controlled at 10.5-12.0 and complexing agent content was 5-10 g / L. When the particle size D250 grew to the target value, the reaction was stopped. After the reaction, the material obtained from the reaction was subjected to solid-liquid separation, washing, drying and sieving to obtain core-shell structured composite hydroxide precursor. (2) Preparation of oxide precursor: The above-obtained composite hydroxide precursor is pre-sintered once, held at 300-560℃ for 2-8h, with a heating rate of 1-5℃ / min, and the sintering atmosphere is nitrogen or argon. After cooling, aluminum-doped oxide precursor is obtained. (3) Mixed sintering: The aluminum-doped oxide precursor obtained above is uniformly mixed with lithium salt and then sintered at high temperature. The temperature is maintained at 650-820℃ for 6-20h, the heating rate is 1-3℃ / min, and the sintering atmosphere is nitrogen or argon. After cooling, it is crushed, pulverized and sieved to obtain a modified positive electrode lithium replenishing agent material with aluminum doping inside and aluminum coating on the surface.

2. The preparation method of the modified positive electrode lithium replenishing agent material as described in claim 1, characterized in that, In step (1), the nickel salt is any one or more of nickel sulfate, nickel chloride, or nickel nitrate; the aluminum salt is any one or more of aluminum sulfate, aluminum chloride, aluminum nitrate, or sodium aluminate; the precipitant is any one or two of sodium hydroxide or potassium hydroxide; and the complexing agent is any one or more of ammonia, sodium citrate, ammonium sulfate, or EDTA. The aluminum alkali solution is prepared by dissolving the aluminum salt in sodium hydroxide solution or potassium hydroxide solution.

3. The preparation method of the modified positive electrode lithium replenishing agent material as described in claim 1, characterized in that, In step (1), the pH of the bottom solution is controlled at 11.0-12.5, the metal ion concentration of the nickel salt solution is 1.0-2.5 mol / L, and the flow rate is 50-150 mL / min; the metal ion concentration of the low-concentration aluminum alkali solution is 0.05-2.00 mol / L, the metal ion concentration of the high-concentration aluminum alkali solution is 2.00-4.5 mol / L, and the flow rate is 10-120 mL / min; the concentration of the precipitant is 1-8 mol / L, and the flow rate is 20-150 mL / min; the concentration of the complexing agent is 2-10 mol / L, and the flow rate is 0.5-100 mL / min; the reaction temperature is controlled at 40-80℃, and the rotation speed is controlled at 300-850 rpm.

4. The preparation method of the modified positive electrode lithium replenishing agent material as described in claim 1, characterized in that, In step (1), the shell thickness of the composite hydroxide precursor is controlled within a certain range of 0.15-0.50 μm, and the particle size D250-D150 is controlled within 0.3-1.0 μm.

5. The preparation method of the modified positive electrode lithium replenishing agent material as described in claim 1, characterized in that, The oxygen content of the sintering atmosphere in steps (2) and (3) is <100ppm.

6. The preparation method of the modified positive electrode lithium replenishing agent material as described in claim 1, characterized in that, The lithium salt in step (3) is a mixture of two lithium salts, including Li2O and LiOH, wherein the mass ratio of Li2O to LiOH is (8.0-9.5):1, and the molar ratio of the total Li in the two lithium salts to the Ni in the aluminum oxide precursor is (2.00-2.25):

1.

7. The method for preparing a modified positive electrode lithium replenishing agent material as described in claim 1, characterized in that, The prepared lithium replenishing agent material has a purity >96.0%, a total residual lithium <2.9%, an initial charge specific capacity >425mAh / g, and an irreversible specific capacity of 285-318mAh / g.

8. A modified positive electrode lithium replenishing agent material, characterized in that, It is prepared by any one of the methods described in claims 1-7.

9. A lithium-ion battery, characterized in that, The modified positive electrode lithium replenishing agent material described in claim 1 is used.

10. The application of the modified positive electrode lithium replenishing agent material as described in claim 8.

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