A precursor and a method of making the same

Abstract

This application relates to the field of precursor technology, and particularly to a precursor, its preparation method, and a cathode material. The molecular formula of the precursor is Ni. a Co b (OH)₂, wherein 0.50≤a<1.0, 0<b≤0.50, and a+b=1; the precursor comprises a core and an outer shell layer bonded sequentially from the inside out, the ratio of the radius of the core to the radius of the precursor is 0.5-0.75, the core accounts for 15%-30% of the volume of the precursor, and the porosity of the core is 1%-4%, the outer shell layer accounts for 70%-85% of the volume of the precursor, and the porosity of the outer shell layer is 3%-15%; the average particle size D50 of the precursor is 3.3-3.7μm, and the specific surface area is 12-16m². 2 / g, with a whisker thickness of 60-80μm. The increased specific surface area of ​​this precursor effectively increases the number of active sites in the cathode material, thereby improving the battery's capacity and cycle performance.

Description

Technical Field

[0001] This application relates to the field of precursor technology, and in particular to a precursor and its preparation method. Background Technology

[0002] Currently, small-particle-size (particle size ≤ 4 μm) nickel-cobalt binary precursors have low specific surface area (BET) (typically ≤ 12 m²). 2 Currently, small-particle-size precursors with large specific surface areas are mainly prepared through oxidation processes. However, oxidation processes require strict control of oxygen levels, which can easily lead to over-oxidation or under-oxidation. Furthermore, the oxidation process is cumbersome and may introduce impurities that affect the performance of the cathode material. Nickel-cobalt binary precursors lack manganese, preventing the formation of fine whiskers during oxidation and resulting in only short, coarse whiskers, further reducing the specific surface area of ​​the precursor. In addition, the stability and sphericity of the precursor's internal structure also affect the cycle stability and capacity of the cathode material and the battery. Therefore, developing cathode materials with high specific surface area, high capacity, and stable cycle performance is currently a hot research topic and a significant challenge. Summary of the Invention

[0003] This application discloses a precursor, its preparation method, and a cathode material to address the problems of low specific surface area and the need to improve capacity and cycle performance of existing small-particle-size nickel-cobalt binary precursors.

[0004] To achieve the above objectives, this application provides the following technical solution:

[0005] Firstly, this application provides a precursor, the molecular formula of which is: Ni a Co b (OH)₂, wherein 0.50≤a<1.0, 0<b≤0.50, and a+b=1; the precursor comprises a core and an outer shell layer bonded sequentially from the inside out, the ratio of the radius of the core to the radius of the precursor is 0.5-0.75, the core accounts for 15%-30% of the volume of the precursor, and the porosity of the core is 1%-4%, the outer shell layer accounts for 70%-85% of the volume of the precursor, and the porosity of the outer shell layer is 5%-10%; the average particle size D50 of the precursor is 3.3-3.7μm, and the specific surface area is 12-16m². 2 / g, whisker thickness is 60-80μm.

[0006] Furthermore, the outer shell layer comprises a first surface layer and a second surface layer bonded sequentially from the inside out. The ratio of the average thickness of the first surface layer to the average thickness of the second surface layer is 0.75-1.35. The volume ratio of the first surface layer to the precursor is 25%-50%, and the porosity of the first surface layer is 3%-8%. The volume ratio of the second surface layer to the precursor is 20%-60%, and the porosity of the second surface layer is 5%-15%.

[0007] Furthermore, the precursor is a secondary particle, and the primary particle of the secondary particle is spindle-shaped, with a length of 100-500 nm, a thickness of 40-120 nm, and an aspect ratio of 2-10.

[0008] Furthermore, the tap density of the precursor is 1.40-1.90 g / cm³. 3 .

[0009] Secondly, this application provides a method for preparing a precursor of the first aspect, the method comprising the following steps:

[0010] S1. A first slurry is obtained by reacting a soluble nickel salt, a soluble cobalt salt, a first complexing agent, and a first precipitant in a solvent to undergo a first coprecipitation reaction. The pH value of the first coprecipitation reaction is 11.60-12.50, and the D50 of the precipitate in the first slurry is 2.0-2.4 μm.

[0011] S2, soluble nickel salt, soluble cobalt salt, first complexing agent, second complexing agent and first precipitant undergo a second coprecipitation reaction in the first slurry to obtain a precursor slurry. The pH value of the second coprecipitation reaction is 10.80-12.20, and the D50 of the precipitate in the precursor slurry is 3.3-3.7 μm.

[0012] The difference between the dissociation constant of the second complexing agent for nickel ions and the dissociation constant of the second complexing agent for cobalt ions is within 0.2 orders of magnitude, and the dissociation constant of the first complexing agent for nickel ions is 2.5-3.5 orders of magnitude lower than that of the second complexing agent for nickel ions.

[0013] Furthermore, the second coprecipitation reaction includes the following steps:

[0014] S2.1, soluble nickel salt, soluble cobalt salt, first complexing agent, second complexing agent and first precipitant undergo a first-stage reaction in the second slurry to obtain the second slurry, wherein the sum of the flow rates of the first complexing agent and the second complexing agent is 35-45 L / h, the flow rate ratio b1 of the first complexing agent and the second complexing agent is 1≤b1≤5, and the D50 of the precipitate in the second slurry is 2.8-3.0 μm;

[0015] S2.2 Soluble nickel salt, soluble cobalt salt, first complexing agent, second complexing agent and first precipitant undergo a second-stage reaction in the second slurry to obtain a precursor slurry, wherein the sum of the flow rates of the first complexing agent and the second complexing agent is 35-45 L / h, and the flow rate ratio b2 of the first complexing agent and the second complexing agent is 0 < b2 ≤ 0.2.

[0016] Furthermore, the first complexing agent includes at least one of ammonia, ammonium bisulfate, or ammonium sulfate, and the second complexing agent includes at least one of lactic acid, succinic acid, or sodium lactate.

[0017] Furthermore, the reaction temperatures for both the first and second coprecipitation reactions are 50-65℃.

[0018] Furthermore, the concentration of the first complexing agent is 6.0-10.0 mol / L, the concentration of the second complexing agent is 6.0-10.0 mol / L, and the concentration of the first precipitant is 10.0-15.0 mol / L.

[0019] Thirdly, this application provides a cathode material obtained by sintering a mixture of a lithium source and a precursor prepared by the first aspect, or a mixture of a lithium source and a precursor prepared by the second aspect.

[0020] The beneficial effects of adopting the technical solution of this application are as follows:

[0021] The nickel-cobalt binary precursor provided in this application comprises a core and a shell layer sequentially bonded from the inside out. The core accounts for 15%-30% of the volume percentage of the precursor and has a porosity of 1%-4%. The shell layer accounts for 70%-85% of the volume percentage of the precursor and has a porosity of 5%-10%. Therefore, this precursor has a dense core and a relatively loose shell layer, which ensures the stability of the cathode material prepared using this precursor. At the same time, the loose shell layer is conducive to lithium-ion insertion / extraction, thereby improving the battery capacity and cycle performance. In addition, the average whisker thickness of this precursor is 60-80 μm, and the specific surface area is 12-16 m². 2 / g can effectively increase the number of active sites in the cathode material, thereby improving the battery capacity and cycle performance. Attached Figure Description

[0022] Figure 1 This is a SEM image of a precursor at a magnification in Embodiment 1 of this application;

[0023] Figure 2 This is a SEM image of the precursor at another magnification in Embodiment 1 of this application;

[0024] Figure 3 This is a cross-sectional view of the precursor in Embodiment 1 of this application;

[0025] Figure 4 This is a SEM image of a precursor at a magnification in Embodiment 2 of this application;

[0026] Figure 5 This is a SEM image of the precursor at another magnification in Embodiment 2 of this application;

[0027] Figure 6 This is a SEM image of a precursor at a magnification in Embodiment 3 of this application;

[0028] Figure 7 This is a SEM image of the precursor at another magnification in Embodiment 3 of this application;

[0029] Figure 8 This is a SEM image of the precursor at one magnification in Comparative Example 1 of this application;

[0030] Figure 9 This is a SEM image of the precursor at another magnification in Comparative Example 1 of this application;

[0031] Figure 10 This is a cross-sectional view of the precursor in Comparative Example 1 of this application;

[0032] Figure 11 This is a SEM image of the precursor at one magnification in Comparative Example 2 of this application;

[0033] Figure 12 This is a SEM image of the precursor at another magnification in Comparative Example 2 of this application;

[0034] Figure 13 This is a cross-sectional view of the precursor in Comparative Example 2 of this application;

[0035] Figure 14 This is a SEM image of the precursor at one magnification in Comparative Example 3 of this application;

[0036] Figure 15 This is a SEM image of the precursor at another magnification in Comparative Example 3 of this application. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] The application scenarios described in this application are for the purpose of more clearly illustrating the technical solutions of this application, and do not constitute a limitation on the technical solutions provided in this application. Those skilled in the art will understand that with the emergence of new application scenarios, the technical solutions provided in this application are also applicable to similar technical problems. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0039] The specific surface area of ​​existing small-particle-size nickel-cobalt binary precursors is typically less than or equal to 12 m². 2 / g, and the stability and cycle performance of the precursor's internal structure need to be improved.

[0040] In view of this, embodiments of this application provide a precursor, the molecular formula of which is: Ni a Co b (OH)₂, wherein 0.50≤a<1.0, 0<b≤0.50, and a+b=1; the precursor comprises a core and an outer shell layer bonded sequentially from the inside out, the ratio of the radius of the core to the radius of the precursor is 0.5-0.75, the core accounts for 15%-30% of the volume of the precursor, and the porosity of the core is 1%-4%, the outer shell layer accounts for 70%-85% of the volume of the precursor, and the porosity of the outer shell layer is 3%-15%; the average particle size D50 of the precursor is 3.3-3.7μm, and the specific surface area is 12-16m². 2 / g, whisker thickness is 60-80μm.

[0041] In this process, the prepared precursor sample was photographed with SEM to obtain a cross-sectional image. The Metis software was used to process the image to obtain the sum of the pore areas of all pores on the cross-section and the cross-sectional area of ​​the cross-section. The porosity was then calculated according to the formula: porosity = sum of the pore areas of all pores / cross-sectional area × 100%.

[0042] Whisker thickness refers to the average width of the primary particles that constitute the precursor.

[0043] Optionally, the porosity of the core is, for example, any value between 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or 1%-4%. Optionally, the porosity of the outer shell layer is, for example, any value between 5%, 5.5%, 6%, 6.5%, 7%, 8%, 9%, 10%, or 5%-10%. Optionally, the whisker thickness is, for example, any value between 60μm, 63μm, 65μm, 70μm, 73μm, 75μm, 80μm, or 60-80μm.

[0044] In one embodiment of this application, the outer shell layer includes a first surface layer and a second surface layer bonded sequentially from the inside out. The ratio of the average thickness of the first surface layer to the average thickness of the second surface layer is 0.75-1.35, the volume ratio of the first surface layer to the precursor is 25%-50%, the porosity of the first surface layer is 3%-8%, the volume ratio of the second surface layer to the precursor is 20%-60%, and the porosity of the second surface layer is 5%-15%.

[0045] It is understandable that the precursor has a dense core with low porosity, while the porosity of the first and second surface layers increases sequentially. This improves the cycle performance and capacity of the cathode material prepared using the precursor while ensuring structural stability.

[0046] In one embodiment of this application, the precursor is a secondary particle, and the primary particle of the secondary particle is spindle-shaped, with a length of 100-500 nm, a thickness of 40-120 nm, and an aspect ratio of 2-10.

[0047] Optionally, the length of the primary particle can be any value between 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, or 100-500nm; the thickness of the primary particle can be any value between 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, or 40-120nm; and the aspect ratio of the primary particle can be any value between 2, 3, 4, 5, 6, 7, 8, 9, 10, or 2-10.

[0048] In one embodiment of this application, the tap density of the precursor is 1.40-1.90 g / cm³. 3 Optionally, the tap density of the precursor is, for example, 1.40 g / cm³. 3 1.50g / cm 3 1.60g / cm 3 1.70g / cm 3 1.80g / cm 3 1.90g / cm 3 Or 1.40-1.90 g / cm³ 3 Any value between.

[0049] The general formula, morphological characteristics, and composition of the precursors in the embodiments of this application have been described above. The preparation method of the above-mentioned precursors will be described in detail below, which includes the following steps:

[0050] S1. A first slurry is obtained by reacting a soluble nickel salt, a soluble cobalt salt, a first complexing agent, and a first precipitant in a solvent to undergo a first coprecipitation reaction. The pH value of the first coprecipitation reaction is 11.60-12.50 to generate a certain number of seed crystals, avoid agglomeration growth at small particle size, and shape good sphericity. The D50 of the precipitate in the first slurry is 2.0-2.4 μm.

[0051] S2, soluble nickel salt, soluble cobalt salt, first complexing agent, second complexing agent and first precipitant undergo a second coprecipitation reaction in the first slurry to obtain a precursor slurry. The pH value of the second coprecipitation reaction is 10.80-12.20, and the D50 of the precipitate in the precursor slurry is 3.3-3.7μm.

[0052] The dissociation constant of the second complexing agent for nickel ions is within 0.2 orders of magnitude different from that for cobalt ions, so as to achieve co-precipitation of nickel and cobalt ions. The dissociation constant of the first complexing agent for nickel ions is 2.5-3.5 orders of magnitude lower than that of the second complexing agent for nickel ions. The complexing effect of the first complexing agent on nickel ions is greater than that of the second complexing agent. Adding the second complexing agent on the basis of the first complexing agent is conducive to the formation of whiskers, weakens the promoting effect on whisker growth, thereby refining the whiskers and limiting the whiskers from being too loose to affect the stability of the structure.

[0053] In one embodiment of this application, the first complexing agent includes at least one of ammonia, ammonium bisulfate, or ammonium sulfate, and the second complexing agent includes at least one of lactic acid, succinic acid, or sodium lactate.

[0054] Referring to Table 1 below, the dissociation constants of ammonia for nickel and cobalt ions are 10. -5.59 10 -5.46 The dissociation constants of lactate with respect to nickel and cobalt ions are 10, respectively. -2.53 10 -2.44 The dissociation constant of ammonia is smaller than that of lactic acid, and the complexing ability of ammonia is stronger than that of lactic acid. Furthermore, after adding ammonia, the precipitation equilibrium constants of nickel and cobalt ions are 10... 9.11 10 9.34 The precipitation equilibrium constants of nickel and cobalt ions after the addition of lactic acid are smaller than those after the addition of ammonia. Therefore, the ability of ammonia to form nickel-cobalt hydroxide precipitates after the addition of ammonia is less than that after the addition of lactic acid. This means that ammonia is more conducive to whisker growth than whisker formation compared to lactic acid. Thus, using lactic acid to replace a portion of the ammonia as a complexing agent can further improve the whisker refining effect. Furthermore, the complexation dissociation constants of lactate for nickel and cobalt ions are similar, so it will not affect the co-precipitation of nickel and cobalt, thereby enabling the preparation of nickel-cobalt binary precursors with a larger specific surface area in the outer shell.

[0055] Table 1

[0056] Ion name <![CDATA[Ni 2+ ]]> <![CDATA[Co 2+ ]]> Precipitation equilibrium constant <![CDATA[10 14.7 ]]> <![CDATA[10 14.8 ]]> dissociation constant of ammonia <![CDATA[10 -5.59 ]]> <![CDATA[10 -5.46 ]]> dissociation constant of lactic acid <![CDATA[10 -2.53 ]]> <![CDATA[10 -2.44 ]]> dissociation constant of succinic acid <![CDATA[10 -2.40 ]]> <![CDATA[10 -2.32 ]]> Precipitation equilibrium constant (with ammonia added) <![CDATA[10 9.11 ]]> <![CDATA[10 9.34 <!-- 4 -->]]> Precipitation equilibrium constant (with lactic acid added) <![CDATA[10 12.17 ]]> <![CDATA[10 12.36 ]]> Precipitation equilibrium constant (with succinic acid added) <![CDATA[10 12.30 ]]> <![CDATA[10 12.66 ]]>

[0057] Referring to Table 1, the dissociation constants of succinic acid for nickel and cobalt ions are 10. -2.40 10 -2.32Adding succinic acid to the solution can also improve the whisker refining effect. Moreover, the succinate anion has similar complexation dissociation constants for nickel and cobalt ions, so it will not affect the co-precipitation of nickel and cobalt.

[0058] Optionally, the soluble nickel salt includes at least one of nickel sulfate, nickel nitrate, nickel chloride, or nickel acetate. The soluble cobalt salt includes at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, or nickel acetate.

[0059] The time for the first coprecipitation reaction is 8-12 hours, and examples of the time for the first coprecipitation reaction are 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or any value between 8 and 12 hours.

[0060] It is understandable that in the second coprecipitation reaction, the thickness of the whiskers is controlled by controlling the sum of the flow rates of the first and second complexing agents and their flow rate ratio, thereby regulating the specific surface area of ​​the outer shell layer.

[0061] The second coprecipitation reaction can be a continuous reaction stage with unchanged reaction conditions, or it can be divided into two or more reaction stages. The following explanation uses a second coprecipitation reaction divided into two reaction stages as an example. The second coprecipitation reaction includes the following steps:

[0062] S2.1, soluble nickel salt, soluble cobalt salt, first complexing agent, second complexing agent and first precipitant undergo a first-stage reaction in the second slurry to obtain the second slurry, wherein the sum of the flow rates of the first complexing agent and the second complexing agent is 35-45 L / h, the flow rate ratio b1 of the first complexing agent and the second complexing agent is 1≤b1≤5, and the D50 of the precipitate in the second slurry is 2.8-3.0 μm;

[0063] S2.2 Soluble nickel salt, soluble cobalt salt, first complexing agent, second complexing agent and first precipitant undergo a second-stage reaction in the second slurry to obtain a precursor slurry, wherein the sum of the flow rates of the first complexing agent and the second complexing agent is 35-45 L / h, and the flow rate ratio b2 of the first complexing agent and the second complexing agent is 0 < b2 ≤ 0.2.

[0064] In the second stage reaction, compared with the first stage reaction, the second complexing agent is used as the main complexing agent and the first complexing agent is used as an auxiliary agent to further refine the whiskers, thereby increasing the specific surface area of ​​the second surface layer, which is beneficial to the deintercalation and intercalation of lithium ions and improves the capacity of the cathode material.

[0065] In one embodiment of this application, the reaction temperature for both the first and second coprecipitation reactions is 50-65°C. Optionally, both the first and second coprecipitation reactions are carried out under stirring at a speed of 320-360 rpm.

[0066] In one embodiment of this application, the concentration of the first complexing agent is 6.0-10.0 mol / L, and the concentration of the second complexing agent is 6.0-10.0 mol / L.

[0067] Optionally, the first precipitant may include a sodium hydroxide solution or a potassium hydroxide solution. The concentration of the first precipitant is 10.0-15.0 mol / L.

[0068] In one embodiment of this application, the preparation method further includes the following steps:

[0069] 1) The precursor slurry with preset D50 obtained from the second coprecipitation reaction is injected into the aging kettle, and then introduced into a centrifuge. It is centrifuged and washed for 30-40 min with 1-3 mol / L alkaline solution as washing liquid, and then centrifuged and washed with water at 50-65℃ for 50-60 min to obtain the material to be dried.

[0070] 2) Place the material to be dried in a forced-air drying oven, dry at 120-150℃ for 20-30 hours, and sieve the dried material through a 300-360 mesh screen to remove iron and obtain the precursor.

[0071] Based on the same inventive concept, embodiments of this application provide a cathode material, which is obtained by sintering a mixture of a lithium source and a precursor prepared by various possible embodiments of this application, or a lithium source and a precursor prepared by various possible embodiments of this application.

[0072] Optionally, the molar ratio of the precursor to the lithium source is 1:1.01 to 1:1.11.

[0073] Optionally, the sintering of the lithium source and precursor includes primary sintering and secondary sintering, wherein the temperature of primary sintering is 700-900℃ and the temperature of secondary sintering is 200-500℃.

[0074] Because the cathode material is prepared using the precursor in this application, it also has a dense core and a loose outer shell, exhibiting high structural stability, high cycle performance and discharge capacity, as well as good sphericity.

[0075] The precursor, its preparation method, and the cathode material of this application will be further described in detail below with reference to specific embodiments and comparative examples.

[0076] Example 1

[0077] This embodiment describes a precursor and its preparation method, which includes the following steps:

[0078] Step 1) Prepare a mixed salt solution with a total ion concentration of 1.5 mol / L by mixing nickel sulfate and cobalt sulfate in a molar ratio of 98:2; prepare a first complexing agent solution with ammonia and deionized water at a concentration of 7.5 mol / L; prepare a second complexing agent solution with lactic acid and deionized water at a concentration of 7.5 mol / L; and prepare a first precipitant solution with a concentration of 11 mol / L by mixing sodium hydroxide.

[0079] Step 2) 2m 3 The clean reactor was filled with deionized water, the water temperature inside the reactor was maintained at 55℃, and the stirring was turned on at a speed of 320 rpm. The first complexing agent solution was introduced into the reactor, and the ammonia value inside the reactor was measured to be 2.0-2.5 g / L. The mixed salt solution, the first complexing agent solution and the first precipitant solution prepared in step 1) were introduced into the reactor in parallel to carry out the first co-precipitation reaction to obtain the first slurry. The pH was controlled at 11.9-12.20 and the ammonia value was maintained at 2.0-2.5 g / L throughout the process until the D50 of the precipitate in the first slurry reached 2.19 μm.

[0080] Step 3) The mixed salt solution, the first complexing agent solution (ammonia solution), the second complexing agent solution (lactic acid solution), and the first precipitant solution are fed into the reactor in parallel to carry out the first stage reaction to obtain the second slurry. During the entire process, the pH is controlled at 11.40-11.90, the flow rate of the ammonia solution is controlled at 30 L / h, the flow rate of the lactic acid solution is controlled at 10 L / h, and the D50 of the precipitate in the second slurry reaches 2.85 μm.

[0081] Step 4) Adjust the flow rates of ammonia and lactic acid solutions and proceed to the second stage of reaction to obtain the precursor slurry. The flow rate of ammonia solution is controlled at 8 L / h, the flow rate of lactic acid solution is controlled at 32 L / h, and the reaction is stopped when D50 reaches 3.62 μm.

[0082] Step 5) The precursor slurry is fed into an aging kettle, then into a centrifuge. It is washed with 2 mol / L hot alkali for 30 min and then washed with hot water for 60 min to obtain the material to be dried.

[0083] Step 6) Place the material to be dried in a forced-air drying oven, dry at 130°C for 30 hours, and sieve the dried material through a 325-mesh screen to remove iron, and obtain the precursor of Example 1.

[0084] Figure 1 This is a SEM image of a precursor at a magnification in Embodiment 1 of this application. Figure 2 Here is a SEM image of the precursor at another magnification in Embodiment 1 of this application, referring to... Figure 1 and Figure 2 The precursor in Example 1 has good sphericity, and the average thickness of the outer whiskers is 60 nm. Figure 3 This is a cross-sectional view of the precursor in Embodiment 1 of this application, with reference to... Figure 3 The precursor in Example 1 includes a core, a first surface layer, and a second surface layer from the inside out. The core is compact and without hollow areas, accounting for 22% of the volume of the precursor, and has a porosity of 1.2%. The first surface layer accounts for 29% of the volume of the precursor and is relatively porous, with a porosity of 6.9%. The second surface layer is even more porous, with a porosity of 10.9%, and accounts for 49% of the volume of the precursor.

[0085] Examples 2-8 and Comparative Examples 1-3

[0086] Examples 2-8 and Comparative Examples 1-3 are precursors and their preparation methods, respectively. The specific steps can be referred to in Example 1. The difference lies in the reaction reagents and reaction conditions. The specific composition is listed in Table 2.

[0087] Table 2

[0088]

[0089] Continued from Table 2

[0090]

[0091]

[0092] Examples 9-11

[0093] Examples 9-11 represent a precursor and its preparation method, respectively. The specific steps are the same as in Example 1, except that the molar ratio of nickel sulfate and cobalt sulfate is different. The precursor in Example 1 is expressed as Ni... 0.98 Co 0.02 (OH)2, the precursor in Example 9 is expressed as Ni 0.8 Co 0.2 (OH)2, the precursor in Example 10 is expressed as Ni 0.6 Co 0.4 (OH)2, the precursor in Example 11 is expressed as Ni 0.5 Co 0.5 (OH)2.

[0094] The specific surface area, tap density, and whisker thickness of the precursors in the above embodiments and comparative examples were measured. Then, the precursors in the above embodiments and comparative examples were mixed with lithium source at a molar ratio of 1:1.01 and sintered to obtain cathode material. The cathode material was used to prepare a secondary battery, and the charge-discharge capacity, first efficiency, and capacity retention rate after 300 cycles of the secondary battery were tested. The specific results are shown in Table 3 below.

[0095] Table 3

[0096]

[0097] Figure 4 This is a SEM image of a precursor at a magnification in Embodiment 2 of this application. Figure 5 Here is a SEM image of the precursor at another magnification in Embodiment 2 of this application, referring to... Figure 4 and Figure 5 Based on the data in Tables 2 and 3, it can be seen that the precursor in Example 2 has good sphericity, a whisker thickness of 70 nm, and a specific surface area of ​​15.37 m². 2 / g, secondary batteries using cathode materials prepared with this precursor have higher charge-discharge capacity and higher cycle stability.

[0098] Figure 6 This is a SEM image of a precursor at a magnification in Embodiment 3 of this application. Figure 7 Here is a SEM image of the precursor at another magnification in Embodiment 3 of this application, referring to... Figure 6 and Figure 7 Based on the data in Tables 2 and 3, it can be seen that the precursor in Example 3 has good sphericity, a whisker thickness of 75 nm, and a specific surface area of ​​14.25 m². 2 / g, secondary batteries using cathode materials prepared with this precursor have higher charge-discharge capacity and higher cycle stability.

[0099] Based on the data from Examples 1-4, it can be seen that the reaction temperature affects the whisker thickness, thereby affecting the specific surface area of ​​the precursor.

[0100] Based on the data from Examples 1 and 5, it can be seen that in the second coprecipitation reaction, when the flow rate of the second complexing agent decreases and the flow rate ratio of the first complexing agent and the second complexing agent increases, it helps the growth of the precursor, increases the thickness of the whiskers, and increases the porosity of the precursor.

[0101] Figure 8 This is a SEM image of the precursor at one magnification in Comparative Example 1 of this application. Figure 9 Here is a SEM image of the precursor at another magnification in Comparative Example 1 of this application, with reference to... Figure 8 and Figure 9 The precursor in Comparative Example 1 has good sphericity and a whisker thickness of 120 nm. Figure 10 This is a cross-sectional view of the precursor in Comparative Example 1 of this application, with reference to... Figure 10The precursor in Comparative Example 1 does not have a three-layer structure similar to the precursor in Example 1. The precursor in Comparative Example 1 is hollow inside and has a compact outer layer. According to the data in Tables 2 and 3, Comparative Example 1 only used ammonia solution as a complexing agent for the co-precipitation reaction, resulting in longer whisker thickness, lower specific surface area, and significantly lower charge / discharge capacity and cycle stability of the secondary battery compared to Example 1.

[0102] Figure 11 This is a SEM image of the precursor at one magnification in Comparative Example 2 of this application. Figure 12 Here is a SEM image of the precursor at another magnification in Comparative Example 2 of this application, with reference to... Figure 11 and Figure 12 In Comparative Example 2, no first coprecipitation reaction occurred, resulting in a precursor with poor sphericity and a whisker thickness of 150 nm. Figure 13 This is a cross-sectional view of the precursor in Comparative Example 2 of this application, with reference to... Figure 13 The precursor in Comparative Example 2 does not have a three-layer structure similar to the precursor in Example 1. The precursor in Comparative Example 2 only uses ammonia solution as a complexing agent for co-precipitation reaction, resulting in a longer whisker thickness and a lower specific surface area. The charge-discharge capacity and cycle stability of the secondary battery are significantly lower than those in Example 1.

[0103] Figure 14 This is a SEM image of the precursor at one magnification in Comparative Example 3 of this application. Figure 15 Here is a SEM image of the precursor at another magnification in Comparative Example 3 of this application, with reference to... Figure 14 and Figure 15 In Comparative Example 3, the first coprecipitation reaction was not performed, resulting in a precursor with poor sphericity. Combining the data from Tables 2 and 3, it can be seen that the precursor in Comparative Example 3 was prepared using a coprecipitation reaction with two complexing agents, and its whisker thickness was 65 nm, with a specific surface area of ​​14.34 m². 2 / g, the charge / discharge capacity and cycle stability of the secondary battery are slightly lower than those of Example 1.

[0104] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A precursor, characterized in that, The molecular formula of the precursor is: Ni a Co b (OH)2, where 0.50≤a<1.0, 0<b≤0.50, and a+b=1; The precursor comprises a core and an outer shell layer joined sequentially from the inside out. The ratio of the radius of the core to the radius of the precursor is 0.5-0.

75. The core accounts for 15%-30% of the volume of the precursor and has a porosity of 1%-4%. The outer shell layer accounts for 70%-85% of the volume of the precursor and has a porosity of 3%-15%. The porosity of the core is less than that of the outer shell layer. The outer shell layer includes a first surface layer and a second surface layer bonded together from the inside out, wherein the porosity of the first surface layer is less than that of the second surface layer; The precursor has an average particle size D50 of 3.3-3.7 μm and a specific surface area of ​​12-16 m². 2 / g, whisker thickness is 60-80nm; the whisker thickness refers to the average width of the primary particles constituting the precursor.

2. The precursor as described in claim 1, characterized in that, The ratio of the average thickness of the first surface layer to the average thickness of the second surface layer is 0.75-1.35, the volume ratio of the first surface layer to the precursor is 25%-50%, the porosity of the first surface layer is 3%-8%, the volume ratio of the second surface layer to the precursor is 20%-60%, and the porosity of the second surface layer is 5%-15%.

3. The precursor as described in claim 1 or 2, characterized in that, The tap density of the precursor is 1.40-1.90 g / cm³. 3 .

4. A method for preparing a precursor as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. A first slurry is obtained by reacting a soluble nickel salt, a soluble cobalt salt, a first complexing agent, and a first precipitant in a solvent to undergo a first coprecipitation reaction. The pH value of the first coprecipitation reaction is 11.60-12.50, and the D50 of the precipitate in the first slurry is 2.0-2.4 μm. S2, a soluble nickel salt, a soluble cobalt salt, the first complexing agent, the second complexing agent, and the first precipitant undergo a second coprecipitation reaction in a first slurry to obtain a precursor slurry. The pH value of the second coprecipitation reaction is 10.80-12.20, and the D50 of the precipitate in the precursor slurry is 3.3-3.7 μm. The difference between the dissociation constant of the second complexing agent for nickel ions and the dissociation constant of the second complexing agent for cobalt ions is within 0.2 orders of magnitude, and the dissociation constant of the first complexing agent for nickel ions is 2.5-3.5 orders of magnitude lower than the dissociation constant of the second complexing agent for nickel ions. The second coprecipitation reaction includes the following steps: S2.1 A first-stage reaction is carried out in a first slurry involving a soluble nickel salt, a soluble cobalt salt, the first complexing agent, the second complexing agent, and the first precipitant to obtain a second slurry. The sum of the flow rates of the first complexing agent and the second complexing agent is 35-45 L / h, the flow rate ratio b1 of the first complexing agent and the second complexing agent is 1≤b1≤5, and the D50 of the precipitate in the second slurry is 2.8-3.0 μm. S2.2, soluble nickel salt, soluble cobalt salt, the first complexing agent, the second complexing agent, and the first precipitant undergo a second-stage reaction in the second slurry to obtain the precursor slurry, wherein the sum of the flow rates of the first complexing agent and the second complexing agent is 35-45 L / h, and the flow rate ratio b2 of the first complexing agent and the second complexing agent is 0 < b2 ≤ 0.

2.

5. The preparation method according to claim 4, characterized in that, The first complexing agent includes at least one of ammonia, ammonium bisulfate, or ammonium sulfate, and the second complexing agent includes at least one of lactic acid, succinic acid, or sodium lactate.

6. The preparation method according to claim 4 or 5, characterized in that, The reaction temperatures for both the first and second coprecipitation reactions are 50-65℃.

7. The preparation method according to claim 4 or 5, characterized in that, The concentration of the first complexing agent is 6.0-10.0 mol / L, the concentration of the second complexing agent is 6.0-10.0 mol / L, and the concentration of the first precipitant is 10.0-15.0 mol / L.

8. A positive electrode material, characterized in that, The lithium source and the precursor as described in any one of claims 1-3, or the lithium source and the precursor prepared by the preparation method as described in any one of claims 4-7, are mixed and then sintered.

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