Method for improving core-shell layering of core-shell precursor

Abstract

The invention provides an improvement method for core-shell layering of a core-shell precursor, and belongs to the technical field of new energy battery materials. According to the preparation method disclosed by the invention, a precursor with a core-shell structure is gradually constructed through four stages of coprecipitation reactions. In each stage, a nickel-cobalt-manganese ternary mixed salt solution, an alkali solution and a complexing agent solution are injected into a reaction base solution in a parallel flow mode, and accurate control over precursor particles is achieved by controlling the conditions such as the concentration, the dosage and the pH value of the salt solution and the concentration of the complexing agent. The composition of a nickel-cobalt-manganese ternary mixed salt solution is designed and adjusted by adding two transition periods in a core-shell reaction stage, so that the problem that core-shell separation is generated after a positive electrode material end is sintered due to remarkable change of components and untight particle accumulation in the core-shell stage is solved, and the core-shell connection part of the prepared core-shell precursor has no layering phenomenon; the connection is tight, and the electrochemical performance is good.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy battery materials, and particularly relates to a method for improving the core-shell stratification of a core-shell precursor. Background Art

[0002] Due to its unique structural advantages, the core-shell precursor plays an increasingly important role in the preparation of high-performance cathode materials. This material not only has high capacity but also high safety, which makes it show great development potential and application prospects in the fields of energy storage and conversion, especially in lithium-ion battery technology.

[0003] The preparation process of the core-shell precursor usually involves multiple steps, including raw material preparation, precursor preparation, drying and screening, sintering, grinding and packaging. During the precursor preparation process, metal salts are dissolved to form metal ions. By regulating the pH value and temperature, the metal ions undergo a precipitation reaction to form a ternary precursor. This process is crucial for the formation of the core-shell structure.

[0004] In the shell reaction stage of the precursor prepared by the traditional process, due to the drastic change in the raw material components, the core-shell connection separates during the sintering process at the cathode material end, forming a cavity phenomenon. This structural defect will lead to insufficient cycle life and poor electrical performance of the cathode material, which is not conducive to large-scale mass production. Therefore, there is an urgent need to develop a method for improving the core-shell stratification of the core-shell precursor. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides a method for improving the core-shell stratification of a core-shell precursor, aiming to solve the technical problem that due to the drastic change in the raw material components during the core-shell formation stage, the particles are not tightly packed, resulting in core-shell detachment after sintering at the cathode material end.

[0006] In the first aspect, the present invention provides a method for improving the core-shell stratification of a core-shell precursor, including the following steps: Inject the nickel-cobalt-manganese ternary mixed salt solution A, the alkali solution, and the complexing agent solution into the reaction bottom liquid in parallel flow to carry out the first co-precipitation reaction to obtain the first slurry; Inject the nickel-cobalt-manganese ternary mixed salt solution B, the alkali solution, and the complexing agent solution into the first slurry in parallel flow to carry out the second co-precipitation reaction to obtain the second slurry; Inject the nickel-cobalt-manganese ternary mixed salt solution C, the alkali solution, and the complexing agent solution into the second slurry in parallel flow to carry out the third co-precipitation reaction to obtain the third slurry; Inject the nickel-cobalt-manganese ternary mixed salt solution D, the alkali solution, and the complexing agent solution into the third slurry in parallel flow to carry out the fourth co-precipitation reaction to obtain the fourth slurry; The fourth slurry undergoes washing, dehydration, drying, screening, and iron removal processes to obtain the core-shell precursor; Among them, the molar concentration of nickel ions in the ternary mixed salt solutions A, B, C, and D decreases in turn; The molar concentration of cobalt ions in the ternary mixed salt solutions A, B, C, and D increases in turn; The molar concentration of manganese ions in the ternary mixed salt solutions A, B, C, and D increases in turn.

[0007] Preferably, the total mass concentration of metal ions in the nickel-cobalt-manganese ternary mixed salt solution A is 30-150 g / L; the total mass concentration of metal ions in the nickel-cobalt-manganese ternary mixed salt solution B is 30-150 g / L; the total mass concentration of metal ions in the nickel-cobalt-manganese ternary mixed salt solution C is 30-150 g / L; the total mass concentration of metal ions in the nickel-cobalt-manganese ternary mixed salt solution D is 30-150 g / L; The molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary mixed salt solution A is 60-98:1-20:1-20; the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary mixed salt solution B is 30-90:5-35:5-35; the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary mixed salt solution C is 20-80:10-40:10-40; the molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary mixed salt solution D is 10-70:15-45:15-45.

[0008] Preferably, the nickel salt used in the nickel-cobalt-manganese ternary mixed salt solution includes at least one of nickel sulfate, nickel chloride, and nickel nitrate; the cobalt salt used includes at least one of cobalt sulfate, cobalt chloride, and cobalt nitrate; the manganese salt used includes at least one of manganese sulfate, manganese chloride, and manganese nitrate.

[0009] Preferably, the lye includes sodium hydroxide solution; the mass concentration of the lye is 10-30 wt%; for example, 10 wt%, 25 wt%, or 30 wt%, but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0010] Preferably, the complexing agent includes ammonia water; the mass concentration of the complexing agent is 10-30 wt%; for example, 10 wt%, 25 wt%, or 30 wt%, but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0011] Preferably, the reaction bottom liquid includes water, lye, and complexing agent.

[0012] Preferably, the pH of the reaction bottom liquid is 9.0-13.0, such as 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, or 13.0, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0013] Preferably, the concentration of the complexing agent in the reaction bottom liquid is 5 to 15 g / L, such as 5 g / L, 10 g / L, or 15 g / L, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0014] Preferably, the flow rate of the inert gas is 0.5 to 8.0 m³ / h; such as 0.5 m³ / h, 1 m³ / h, 2 m³ / h, 5 m³ / h, or 8.0 m³ / h, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0015] Preferably, the median particle size D50 of the first slurry is a, the median particle size D50 of the second slurry is b, the median particle size D50 of the third slurry is c, and the median particle size D50 of the fourth slurry is d, satisfying the following relational expressions: 6.0 μm ≤ a ≤ 15.0 μm, 0.2 μm ≤ b - a ≤ 2 μm, 0.2 μm ≤ c - b ≤ 2 μm, 0.2 μm ≤ d - c ≤ 2 μm.

[0016] Preferably, the reaction temperature of the first coprecipitation reaction is 40 to 70 °C, the reaction temperature of the second coprecipitation reaction is 40 to 70 °C, the reaction temperature of the third coprecipitation reaction is 40 to 70 °C, and the reaction temperature of the fourth coprecipitation reaction is 40 to 70 °C; such as 40 °C, 50 °C, 60 °C, or 70 °C, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0017] Preferably, the pH value of the first coprecipitation reaction is 9.0 to 13.0, the pH value of the second coprecipitation reaction is 9.0 to 13.0, the pH value of the third coprecipitation reaction is 9.0 to 13.0, and the pH value of the fourth coprecipitation reaction is 9.0 to 13.0; such as 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0018] Preferably, the concentration of the complexing agent in the first coprecipitation reaction is 5 to 15 g / L, the concentration of the complexing agent in the second coprecipitation reaction is 5 to 15 g / L, the concentration of the complexing agent in the third coprecipitation reaction is 5 to 15 g / L, and the concentration of the complexing agent in the fourth coprecipitation reaction is 5 to 15 g / L; such as 5 g / L, 10 g / L, or 15 g / L, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0019] Preferably, the drying temperature is 100 to 120 °C, such as 100 °C, 110 °C, or 120 °C, etc., but not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0020] In a second aspect, the present invention provides a core-shell precursor, which is prepared by using the method for improving the core-shell layering of the core-shell precursor described in the first aspect.

[0021] The core-shell precursor prepared by using the method for improving the core-shell layering of the core-shell precursor described in the first aspect of the present invention has no delamination phenomenon at the core-shell joint and is tightly connected.

[0022] In a third aspect, the present invention provides a cathode material, which is obtained by sintering the core-shell precursor described in the second aspect of the present invention after mixing it with a lithium salt.

[0023] In a fourth aspect, the present invention provides a lithium-ion battery, which includes the cathode material described in the third aspect of the present invention.

[0024] The core-shell precursor prepared by using the method for improving the core-shell layering of the core-shell precursor described in the first aspect of the present invention shows good electrochemical performance when applied to a lithium battery.

[0025] The preparation method of the present invention gradually constructs a precursor of a core-shell structure through a four-stage co-precipitation reaction. In each stage, a nickel-cobalt-manganese ternary mixed salt solution, an alkali solution, and a complexing agent solution are injected into the reaction bottom liquid in parallel flow. By controlling conditions such as the salt solution concentration, dosage, pH value, and complexing agent concentration, precise control of the precursor particles is achieved. The first addition of the nickel-cobalt-manganese ternary mixed salt solution A forms the inner core, the second and third additions of the nickel-cobalt-manganese ternary mixed salt solutions B and C are two additional transition segments added in the middle of the core-shell reaction, and the fourth addition of the nickel-cobalt-manganese ternary mixed salt solution D forms the outer shell. The purpose of the stage added between the core and shell reactions is to gradually adjust the compositional change between the core and shell, relieve the structural stress caused by the sudden change in composition, and maintain the integrity of the material. This gradual transition method helps to relieve the detachment problem of the core-shell structure during the sintering process.

[0026] Compared with the prior art, the present invention has the following beneficial effects: (1) The method for improving the core-shell layering of the core-shell precursor of the present invention can reduce the structural stress caused by the drastic change in the raw material components, maintain the integrity of the material, reduce the void phenomenon during the sintering process, and the SEM detection shows that the improvement effect is good by adding two transition segments between the core and shell and controlling the decreasing gradient of the nickel ion molar concentration, the increasing gradient of the cobalt ion molar concentration, and the increasing gradient of the manganese ion molar concentration in the ternary mixed salt solution in the four co-precipitation reaction stages.

[0027] (2) The core-shell precursor prepared by the method for improving the core-shell lamination of the present invention has no delamination at the core-shell joint, and the connection is tight. During the sintering process of preparing the cathode material, the core-shell does not detach. Finally, when applied to the battery, it can improve the energy density, cycle life and safety of the battery. Description of the Drawings

[0028] Figure 1 It is a schematic flow chart of the method for improving the core-shell lamination of the core-shell precursor in Example 1 of the present invention; Figure 2 is a SEM image of the core-shell precursor material prepared in Example 1 of the present invention. Among them, Figure 2(a) is a low-magnification SEM image of the core-shell precursor material prepared in Example 1, and Figure 2(b) is a high-magnification SEM image of a partial enlargement of the core-shell precursor material prepared in Example 1. Specific Embodiments

[0029] Hereinafter, embodiments of the technical solution of the present invention will be described in detail with reference to the drawings. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, so they are only examples and cannot be used to limit the protection scope of the present invention.

[0030] For those not specifying specific techniques or conditions in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For those reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0031] Example 1 Please refer to Figure 1 The schematic flow chart of the method for improving the core-shell lamination of the core-shell precursor shown. A method for improving the core-shell lamination of the core-shell precursor includes the following steps: (1) Prepare nickel-cobalt-manganese ternary sulfate solution A with a total metal ion mass concentration of 60 g / L and a nickel-cobalt-manganese molar ratio of 90:8:2; prepare nickel-cobalt-manganese ternary sulfate solution B with a total metal ion mass concentration of 60 g / L and a molar ratio of 70:15:15; prepare nickel-cobalt-manganese ternary sulfate solution C with a total metal ion mass concentration of 60 g / L and a molar ratio of 50:20:30; prepare nickel-cobalt-manganese ternary sulfate solution D with a total metal ion mass concentration of 60 g / L and a molar ratio of 38:18:44; prepare a 15% NaOH aqueous solution as the alkali solution and a 10% ammonia water solution as the complexing agent; (2) Add 0.5 m³ of deionized water to a 1 m 3 reaction kettle, add an appropriate amount of 15% NaOH aqueous solution, and 10% ammonia water solution as the reaction bottom liquid. Control the initial pH of the reaction bottom liquid to be 12, the ammonia concentration to be 10 g / L, introduce 2 m³ / h of N2 as the protective gas, heat up to 45 °C and maintain stability; (3) Set the stirring speed to 300 r / min, and inject the ternary liquid A, NaOH aqueous solution, and ammonia water prepared in the above (1) into the reaction kettle in a co-current manner to carry out the first co-precipitation reaction. Control the feed flow rate of the nickel-cobalt-manganese ternary mixed salt solution A to be 80 L / h, the reaction temperature to be 45 °C. By adjusting the dosages of NaOH and ammonia water, control the ammonia value of the supernatant to be stable at 10 g / L, the pH value to be 11.0, and react until the particle D50 reaches 11.0 μm to obtain the first slurry; (4) Inject the ternary liquid B, NaOH aqueous solution, and ammonia water prepared in the above (1) into the first slurry in a co-current manner through a metering pump to carry out the second co-precipitation reaction. Set the stirring speed to 300 r / min, the reaction temperature to be 45 °C. By adjusting the dosages of NaOH and ammonia water, control the ammonia value of the supernatant to be stable at 10 g / L, the pH value to be 11.0, and react until the particle D50 continuously grows to 11.5 μm to obtain the second slurry; (5) Inject the ternary liquid C, NaOH aqueous solution, and ammonia water prepared in the above (1) into the second slurry in a co-current manner through a metering pump to carry out the third co-precipitation reaction. Set the stirring speed to 300 r / min, the reaction temperature to be 45 °C. By adjusting the dosages of NaOH and ammonia water, control the ammonia value of the supernatant to be stable at 10 g / L, the pH value to be 11.0, and react until the particle D50 continuously grows to 12.2 μm to obtain the third slurry; (6) Inject the ternary liquid C, NaOH aqueous solution, and ammonia water prepared in the above (1) into the second slurry in a co-current manner through a metering pump to carry out the fourth co-precipitation reaction. Set the stirring speed to 300 r / min, the reaction temperature to be 45 °C. By adjusting the dosages of NaOH and ammonia water, control the ammonia value of the supernatant to be stable at 10 g / L, the pH value to be 11.0, and react until the particle D50 continuously grows to 13.5 μm to obtain the fourth slurry; (7) The fourth slurry is washed, dehydrated, dried at 110 °C, screened, de-ironed, and packaged to obtain the final product of the core-shell precursor.

[0032] Figure 2 is the SEM image of the core-shell precursor prepared in this example. Figure 2(a) is the low-magnification SEM image of the core-shell precursor material prepared in Example 1, and Figure 2(b) is the high-magnification SEM image of the partial enlargement of the core-shell precursor material prepared in Example 1. It can be seen that there is no delamination phenomenon at the core-shell joint of the core-shell precursor, and the connection is tight.

[0033] Example 2 A method for improving the core-shell delamination of a core-shell precursor, comprising the following steps: (1) Prepare nickel-cobalt-manganese ternary sulfate solution A with a total metal ion mass concentration of 100 g / L and a nickel-cobalt-manganese molar ratio of 60:20:20; prepare nickel-cobalt-manganese ternary sulfate solution B with a total metal ion mass concentration of 100 g / L and a molar ratio of 30:35:35; prepare nickel-cobalt-manganese ternary sulfate solution C with a total metal ion mass concentration of 100 g / L and a molar ratio of 20:40:40; prepare nickel-cobalt-manganese ternary sulfate solution D with a total metal ion mass concentration of 100 g / L and a molar ratio of 10:45:45; prepare a 20% by mass NaOH aqueous solution as the alkali solution and a 15% by mass ammonia water as the complexing agent. (2) Add 0.5 m³ of deionized water, an appropriate amount of 20% by mass NaOH aqueous solution, and 15% by mass ammonia water to a 1 m 3 reaction kettle as the reaction bottom liquid. Control the initial pH of the reaction bottom liquid to be 10, the ammonia concentration to be 12 g / L, introduce 2 m³ / h of N2 as the protective gas, heat up to 50 °C and maintain stability. (3) Set the stirring speed to 300 r / min, and inject the ternary solution A, NaOH aqueous solution, and ammonia water prepared in (1) above into the reaction kettle in parallel through a metering pump for the first co-precipitation reaction. Control the feeding flow rate of the nickel-cobalt-manganese ternary mixed salt solution A to be 80 L / h, the reaction temperature to be 50 °C. By adjusting the amounts of NaOH and ammonia water, control the ammonia value of the supernatant to be stable at 12 g / L and the pH value to be 10.0. React until the particle D50 reaches 8.0 μm to obtain the first slurry. (4) Inject the ternary solution B, NaOH aqueous solution, and ammonia water prepared in (1) above into the first slurry in parallel through a metering pump for the second co-precipitation reaction. Set the stirring speed to 300 r / min and the reaction temperature to be 50 °C. By adjusting the amounts of NaOH and ammonia water, control the ammonia value of the supernatant to be stable at 12 g / L and the pH value to be 10.0. React until the particle D50 continuously grows to 9.0 μm to obtain the second slurry. (5) Inject the ternary solution C, NaOH aqueous solution, and ammonia water prepared in (1) above into the second slurry in parallel through a metering pump for the third co-precipitation reaction. Set the stirring speed to 300 r / min and the reaction temperature to be 50 °C. By adjusting the amounts of NaOH and ammonia water, control the ammonia value of the supernatant to be stable at 12 g / L and the pH value to be 10.0. React until the particle D50 continuously grows to 10.2 μm to obtain the third slurry. (6) The ternary liquid C, aqueous NaOH solution, and ammonia water prepared in the above (1) are injected into the second slurry in a co-current manner by a metering pump for the fourth co-precipitation reaction. The stirring speed is set at 300 r / min, and the reaction temperature is 50 °C. By adjusting the dosages of NaOH and ammonia water, the ammonia value of the supernatant is controlled to be stable at 12 g / L, and the pH value is 10.0. The reaction continues until the particle D50 grows continuously to 11.5 μm, obtaining the fourth slurry. (7) The fourth slurry is washed, dehydrated, dried at 110 °C, sieved, de-ironed, and packaged to obtain the final product of the core-shell precursor.

[0034] Example 3 A method for improving the core-shell stratification of a core-shell precursor, comprising the following steps: (1) Prepare a nickel-cobalt-manganese ternary sulfate solution A with a total metal ion mass concentration of 50 g / L and a nickel-cobalt-manganese molar ratio of 98:1:1; prepare a nickel-cobalt-manganese ternary sulfate solution B with a total metal ion mass concentration of 50 g / L and a molar ratio of 90:5:5; prepare a nickel-cobalt-manganese ternary sulfate solution C with a total metal ion mass concentration of 50 g / L and a molar ratio of 80:10:10; prepare a nickel-cobalt-manganese ternary sulfate solution D with a total metal ion mass concentration of 50 g / L and a molar ratio of 70:15:15; prepare an aqueous NaOH solution with a mass percentage concentration of 20% as the alkali solution and ammonia water with a mass percentage concentration of 12% as the complexing agent. (2) Add 0.5 m³ of deionized water to a 3 reaction kettle, add an appropriate amount of aqueous NaOH solution with a mass concentration of 20% and ammonia water with a mass percentage concentration of 12% as the reaction bottom liquid. Control the initial pH of the reaction bottom liquid to be 12 and the ammonia concentration to be 10 g / L. Introduce N2 at a flow rate of 2 m³ / h as the protective gas, heat up to 55 °C and maintain stability. (3) Set the stirring speed at 300 r / min. The ternary liquid A, aqueous NaOH solution, and ammonia water prepared in the above (1) are injected into the reaction kettle in a co-current manner by a metering pump for the first co-precipitation reaction. Control the feeding flow rate of the nickel-cobalt-manganese ternary mixed salt solution A to be 80 L / h, and the reaction temperature to be 55 °C. By adjusting the dosages of NaOH and ammonia water, control the ammonia value of the supernatant to be stable at 10 g / L and the pH value to be 12.0. The reaction continues until the particle D50 reaches 10.0 μm, obtaining the first slurry. (4) The ternary liquid B, aqueous NaOH solution, and ammonia water prepared in the above (1) are injected into the first slurry in a co-current manner by a metering pump for the second co-precipitation reaction. Set the stirring speed at 300 r / min and the reaction temperature at 55 °C. By adjusting the dosages of NaOH and ammonia water, control the ammonia value of the supernatant to be stable at 10 g / L and the pH value to be 12.0. The reaction continues until the particle D50 grows continuously to 10.8 μm, obtaining the second slurry. (5) The ternary liquid C, aqueous NaOH solution, and ammonia water prepared in the above (1) are injected into the second slurry in a co-current manner through a metering pump for the third co-precipitation reaction. The stirring speed is set at 300 r / min, and the reaction temperature is 55 °C. By adjusting the dosages of NaOH and ammonia water, the ammonia value of the supernatant is controlled to be stable at 10 g / L, and the pH value is 12.0. The reaction continues until the particle D50 grows continuously to 11.5 μm to obtain the third slurry. (6) The ternary liquid C, aqueous NaOH solution, and ammonia water prepared in the above (1) are injected into the second slurry in a co-current manner through a metering pump for the fourth co-precipitation reaction. The stirring speed is set at 300 r / min, and the reaction temperature is 55 °C. By adjusting the dosages of NaOH and ammonia water, the ammonia value of the supernatant is controlled to be stable at 10 g / L, and the pH value is 12.0. The reaction continues until the particle D50 grows continuously to 12.5 μm to obtain the fourth slurry. (7) The fourth slurry is washed, dehydrated, dried at 110 °C, sieved, de-ironed, and packaged to obtain the final product of the core-shell precursor.

[0035] Comparative Example 1 This comparative example provides a method for improving the core-shell stratification of the core-shell precursor. Compared with Example 1, the difference is only that: a nickel-cobalt-manganese ternary mixed salt solution A is introduced for the first co-precipitation reaction, and after obtaining the first slurry, a nickel-cobalt-manganese ternary mixed salt solution D is introduced for the second co-precipitation reaction to obtain the second slurry. The second slurry is washed, dehydrated, dried, sieved, and de-ironed to obtain the core-shell precursor; the two co-precipitation reactions in the intermediate transition section are omitted.

[0036] Comparative Example 2 This comparative example provides a method for improving the core-shell stratification of the core-shell precursor. Compared with Example 1, the difference is only that: the nickel-cobalt-manganese ternary mixed salt solution B, the alkali solution, and the complexing agent solution are injected into the first slurry in a co-current manner for the second co-precipitation reaction. After obtaining the second slurry, the nickel-cobalt-manganese ternary mixed salt solution D, the alkali solution, and the complexing agent solution are injected into the second slurry in a co-current manner for the third co-precipitation reaction to obtain the third slurry. The third slurry is washed, dehydrated, dried, sieved, and de-ironed to obtain the core-shell precursor; this comparative example has only one transition stage.

[0037] Test Example 1 The core-shell precursors prepared in the above examples and comparative examples are respectively mixed uniformly with lithium carbonate at a molar ratio of 2:1.1, sintered in an air atmosphere at a temperature of 850 °C for 16 h, and the obtained cathode materials are respectively prepared into lithium-ion batteries, charged at 0.5C and discharged at 5C, and the specific capacity and cycle capacity retention rate are respectively tested. The test results are shown in Table 1.

[0038]

[0039] As can be seen from Table 1, the core-shell precursors obtained by the preparation method of the present invention are applied to lithium batteries and show good electrochemical performance. In the preparation process of the core-shell precursor used in Comparative Example 1, the two coprecipitation reactions in the intermediate transition section are omitted, and the raw material components of the core layer and the shell layer change drastically. When the positive electrode material is prepared and sintered, a void separation occurs at the core-shell connection, and the electrochemical performance is poor. Comparative Example 2 has only one transition stage, and the drastic degree of change of the raw material components of the core layer and the shell layer is slowed down, which has a certain impact on the electrochemical performance, and the improvement effect is not as good as that of Example 1.

[0040] In summary, the preparation method of the present invention synthesizes the precursor through a four-step coprecipitation method, especially intervenes in the shell reaction stage, and controls the nickel ion molar concentration gradient of the ternary mixed salt solution to decrease, the cobalt ion molar concentration gradient to increase, and the manganese ion molar concentration gradient to increase in the four coprecipitation reaction stages. This can reduce the structural stress caused by the drastic change of the raw material components, maintain the integrity of the material, and reduce the void phenomenon during the sintering process, so that the prepared lithium-rich nickel-based positive electrode material has better discharge capacity, rate performance and cycle performance.

[0041] It should be noted that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present invention are all included in the technical scope of the present invention. In addition, without departing from the scope of the main purpose of the present invention, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present invention.

Claims

1. A method for improving the core-shell layering of a core-shell precursor, characterized in that It includes the following steps: Inject the nickel-cobalt-manganese ternary mixed salt solution A, the lye, and the complexing agent solution into the reaction bottom liquid in a co-current manner to carry out the first co-precipitation reaction to obtain the first slurry; Inject the nickel-cobalt-manganese ternary mixed salt solution B, the lye, and the complexing agent solution into the first slurry in a co-current manner to carry out the second co-precipitation reaction to obtain the second slurry; Inject the nickel-cobalt-manganese ternary mixed salt solution C, the lye, and the complexing agent solution into the second slurry in a co-current manner to carry out the third co-precipitation reaction to obtain the third slurry; Inject the nickel-cobalt-manganese ternary mixed salt solution D, the lye, and the complexing agent solution into the third slurry in a co-current manner to carry out the fourth co-precipitation reaction to obtain the fourth slurry; The fourth slurry undergoes washing, dehydration, drying, screening, and iron removal processes to obtain the core-shell precursor; Among them, the molar concentration of nickel ions in the ternary mixed salt solutions A, B, C, and D decreases in sequence; The molar concentration of cobalt ions in the ternary mixed salt solutions A, B, C, and D increases in sequence; The molar concentration of manganese ions in the ternary mixed salt solutions A, B, C, and D increases in sequence.

2. The improvement method for the core-shell layering of the core-shell precursor according to claim 1, wherein, The total mass concentration of metal ions in the nickel-cobalt-manganese ternary mixed salt solution A is 30~150 g / L; The total mass concentration of metal ions in the nickel-cobalt-manganese ternary mixed salt solution B is 30~150 g / L; The total mass concentration of metal ions in the nickel-cobalt-manganese ternary mixed salt solution C is 30~150 g / L; The total mass concentration of metal ions in the nickel-cobalt-manganese ternary mixed salt solution D is 30~150 g / L; The molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary mixed salt solution A is 60~98:1~20:1~20; The molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary mixed salt solution B is 30~90:5~35:5~35; The molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary mixed salt solution C is 20~80:10~40:10~40; The molar ratio of Ni:Co:Mn in the nickel-cobalt-manganese ternary mixed salt solution D is 10~70:15~45:15~45.

3. The improvement method for core-shell layering of the core-shell precursor according to claim 1, wherein The nickel salts used in the nickel-cobalt-manganese ternary mixed salt solution include at least one of nickel sulfate, nickel chloride, and nickel nitrate, the cobalt salts used include at least one of cobalt sulfate, cobalt chloride, and cobalt nitrate, and the manganese salts used include at least one of manganese sulfate, manganese chloride, and manganese nitrate.

4. A method for improving the core-shell layering of a core-shell precursor, according to claim 1, wherein The lye includes a sodium hydroxide solution, and the mass concentration of the lye is 10~30 wt%; the complexing agent includes ammonia water, and the mass concentration of the complexing agent is 10~30 wt%.

5. The improvement method for the core-shell layering of the core-shell precursor according to claim 1, characterized in that The reaction bottom liquid includes water, lye, and complexing agent; the pH of the reaction bottom liquid is 9.0~13.0, and the complexing agent concentration of the reaction bottom liquid is 5~15 g / L.

6. The improvement method for nuclear shell layering of a core-shell precursor according to claim 1, characterized in that The median particle size D50 of the first slurry is a, the median particle size D50 of the second slurry is b, the median particle size D50 of the third slurry is c, and the median particle size D50 of the fourth slurry is d, satisfying the following relational expressions: 6.0 μm ≤ a ≤ 15.0 μm, 0.2 μm ≤ b - a ≤ 2 μm, 0.2 μm ≤ c - b ≤ 2 μm, 0.2 μm ≤ d - c ≤ 2 μm.

7. The improvement method for the core-shell layering of the core-shell precursor according to claim 1, wherein, The reaction temperature of the first coprecipitation reaction is 40 - 70 °C, the pH is 9.0 - 13.0, and the complexing agent concentration is 5 - 15 g / L; The reaction temperature of the second coprecipitation reaction is 40 - 70 °C, the pH is 9.0 - 13.0, and the complexing agent concentration is 5 - 15 g / L; The reaction temperature of the third coprecipitation reaction is 40 - 70 °C, the pH is 9.0 - 13.0, and the complexing agent concentration is 5 - 15 g / L; The reaction temperature of the fourth coprecipitation reaction is 40 - 70 °C, the pH is 9.0 - 13.0, and the complexing agent concentration is 5 - 15 g / L.

8. A core-shell precursor, characterized in that, Prepared by the method for improving the core - shell layering of the core - shell precursor according to any one of claims 1 - 7.

9. A cathode material, characterized in that, The positive electrode material is obtained by sintering after mixing the core - shell precursor according to claim 8 with a lithium salt.

10. A lithium-ion battery, characterized in that, The lithium - ion battery includes the positive electrode material according to claim 9.

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