A positive electrode active material precursor, a preparation method therefor, and use thereof

Abstract

The application provides a positive electrode active material precursor and a preparation method and application thereof. x Co y M 1‑x‑y (OH)2, 0.8<=x<1.0, 0<y<0.2, and M is one of Mn and Al. The secondary particles of the positive electrode active material precursor have two different porosities, the relatively dense structure in the inside helps to improve the structural stability of the positive electrode active material, avoids cracks and pulverization in the inside of the particles caused by the process of deintercalation of lithium, avoids the side reaction caused by the electrolyte entering the inside of the particles, improves the cycle performance and service life of the battery, and the relatively loose structure in the outside is beneficial to improving the intercalation amount of lithium of the positive electrode active material and the process of deintercalation of lithium, and improves the electrochemical performance of the battery.

Description

Technical Field

[0001] This invention relates to a positive electrode active material precursor, its preparation method, and its application, and relates to the field of battery technology. Background Technology

[0002] Lithium-ion batteries are widely used in the new energy industry due to their high discharge specific capacity, long cycle life, low self-discharge rate, and environmental friendliness. With the rapid development of the new energy industry, higher requirements are being placed on the energy density, safety, cycle life, and manufacturing cost of lithium-ion batteries.

[0003] High-nickel ternary cathode active materials (such as ternary nickel-cobalt-manganese and ternary nickel-cobalt-aluminum) help improve the energy density of lithium-ion batteries. However, as the nickel content increases, the structural stability of the cathode active material deteriorates, and the surface is prone to phase transition, gradually transforming from a layered structure to a spinel structure and a rock salt structure. Moreover, the transformation process is irreversible. During charging and discharging, the phase transition on the particle surface will gradually extend inward, causing cracks in the particles and resulting in the lithium deintercalation and insertion failure of the cathode active material.

[0004] Precursors for positive electrode active materials are the main raw materials for preparing positive electrode active materials. Positive electrode active materials can well inherit the internal structural characteristics of the precursors; therefore, the quality of the precursors directly determines the quality of the positive electrode active materials. How to provide a positive electrode active material precursor with good structural stability has attracted the attention of those skilled in the art. Summary of the Invention

[0005] This invention provides a positive electrode active material precursor, in which the secondary particles have two different porosities. The dense internal structure helps to improve the structural stability of the positive electrode active material, avoids cracks and pulverization inside the particles caused by the lithium insertion / extraction process, avoids side reactions caused by electrolyte entering the particles, and improves the cycle performance and service life of the battery. The loose external structure is conducive to increasing the lithium insertion amount of the positive electrode active material and facilitates the lithium insertion / extraction process, thereby improving the electrochemical performance of the battery.

[0006] The present invention also provides a method for preparing the above-mentioned positive electrode active material precursor and its application.

[0007] The first aspect of this invention provides a positive electrode active material precursor, wherein the chemical composition of the positive electrode active material precursor is Ni. x Co y M 1-x-y (OH)2, 0.8≤x<1.0, 0<y<0.2, M is one of Mn and Al;

[0008] The positive electrode active material precursor includes secondary particles, which are divided into a first region and a second region. The first region is located inside the secondary particles, and the second region is located outside the first region away from the center of the particles. The average porosity of the first region is 3% to 8%, and the average porosity of the second region is 8% to 14%. The average porosity of the first region is less than that of the second region.

[0009] The radius of the secondary particle is D, and the radius r1 of the first region is 0.5*D.

[0010] In one specific embodiment, the average porosity of the secondary particles is 6% to 12%.

[0011] In one specific embodiment, the secondary particles have a D50 of 5 to 16 μm and a (D90-D10) / D50 of 0.6 to 0.8.

[0012] In one specific embodiment, in the X-ray diffraction pattern, the positive electrode active material precursor has a 001 peak with a 2θ of 18° to 20° and a 101 peak with a 2θ of 38° to 40°, and the peak intensity ratio I

[001] / I

[101] of the 001 peak and the 101 peak is 0.8 to 1.2.

[0013] In one specific embodiment, the secondary particles are formed by stacking primary particles, wherein the length of the primary particles is 200-600 nm and the width is no more than 100 nm.

[0014] A second aspect of the present invention provides a method for preparing the precursor of any of the above-described positive electrode active materials, comprising the following steps:

[0015] Step 1: Prepare a mixed salt solution, a hydroxide solution and a complexing agent solution, wherein the mixed salt solution includes nickel salt, cobalt salt and a soluble salt containing element M;

[0016] Step 2: Add the hydroxide solution and complexing agent solution to the reaction vessel to obtain the first reaction base liquid, wherein the N value of the first reaction base liquid is 0.8-8 g / L and the pH is 11.0-13.0;

[0017] Under a protective gas atmosphere, the mixed salt solution, hydroxide solution and complexing agent solution are introduced into the reactor to carry out the first crystallization reaction. When the D50' of the solid particles in the reactor grows to 40% to 60% of the target D50 and the solid content of the first reaction slurry in the reactor is 350 to 450 g / L, the first reaction slurry is collected and centrifuged to obtain the first particles.

[0018] Step 3: Add the hydroxide solution and complexing agent solution to the reaction vessel to obtain the second reaction base liquid. The N value of the second reaction base liquid is 0.8-8 g / L and the pH is 9.0-12.0.

[0019] Under a protective gas atmosphere, the first particles, mixed salt solution, hydroxide solution and complexing agent solution are fed into the reactor. The initial solid content in the reactor is controlled to be 25-225 g / L. The second crystallization reaction is carried out. When the D50 of the solid particles in the reactor grows to the target D50, the feeding is stopped to obtain the second reaction slurry.

[0020] Step 4: After aging, washing, centrifuging, drying and sieving the second reaction slurry, the positive electrode active material precursor is obtained.

[0021] In one specific embodiment, the temperature of the first crystallization reaction is 40–70°C, the N value of the reaction system is maintained at 0.8–8 g / L, the pH is maintained at 10.0–12.0, and the reaction time is 60–80 h.

[0022] In one specific embodiment, the temperature of the second crystallization reaction is 40–70°C, the N value of the reaction system is maintained at 0.8–8 g / L, the pH is maintained at 9.0–11.0, and the reaction time is 30–60 h.

[0023] A third aspect of the present invention provides a positive electrode active material, which is prepared from any of the positive electrode active material precursors described above, or from a positive electrode active material precursor prepared according to any of the preparation methods described above.

[0024] A fourth aspect of the present invention provides a battery comprising the above-described positive electrode active material.

[0025] This invention provides a high-nickel ternary cathode active material precursor with a gradient distribution of internal pores. The precursor has low internal porosity and a relatively dense structure, while the external porosity is high and the structure is relatively loose. When this precursor is used as a cathode active material in a battery, during charge-discharge cycles, the relatively dense internal structure helps prevent internal cracking and pulverization of particles during lithium ion insertion / extraction, and avoids electrolyte ingress into the particle interface causing side reactions that could affect battery performance. The relatively loose external structure helps increase the amount of lithium ion inserted and facilitates the lithium insertion / extraction process, thereby improving the battery's electrochemical performance.

[0026] This invention uses a segmented crystallization reaction process to prepare the above-mentioned precursor, and controls the porosity and pore gradient distribution inside the precursor by controlling the solid content, reaction conditions and time of the reaction system. It has the advantages of simple operation and stable product performance. Attached Figure Description

[0027] Figure 1 This is a cross-sectional schematic diagram of a positive electrode active material precursor provided in an embodiment of the present invention;

[0028] Figure 2 The image is an observation obtained by observing the surface of the positive electrode active material precursor provided in Example 1 under a scanning electron microscope at a magnification of 10K.

[0029] Figure 3 This is an observation image obtained by observing the cross-section of the positive electrode active material precursor provided in Example 1 under a scanning electron microscope at a magnification of 10K.

[0030] Figure 4 The XRD pattern of the positive electrode active material precursor provided in Embodiment 1 of the present invention;

[0031] Figure 5 This is an observation image obtained by observing the cross-section of the positive electrode active material precursor provided in Comparative Example 1 under a scanning electron microscope at a magnification of 10K.

[0032] Figure 6 This is an observation image obtained by observing the cross-section of the positive electrode active material precursor provided in Comparative Example 2 under a scanning electron microscope at a magnification of 10K.

[0033] Figure 7 This is an observation image obtained by observing the cross-section of the positive electrode active material precursor provided in Comparative Example 3 under a scanning electron microscope at a magnification of 10K.

[0034] Explanation of reference numerals in the attached figures:

[0035] 100 - Cross-section of the positive electrode active material precursor;

[0036] 101 - First Area;

[0037] 102 - Second Region. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0039] The performance of the cathode active material precursor determines the performance of the cathode active material. The cathode active material precursor is a secondary particle formed by the stacking of primary particles. The internal porosity of the particles determines the overall structure of the cathode active material particles. Although a loose structure is beneficial to increasing the lithium insertion and extraction of the cathode active material particles and is conducive to the lithium insertion and extraction process, an overly loose structure can lead to the generation of cracks in the cathode active material particles, allowing electrolyte to seep into the particles and causing interfacial side reactions, which affects the performance of the battery. On the other hand, a dense structure helps to improve the structural stability of the cathode active material, but it is not conducive to increasing the lithium insertion and extraction.

[0040] Therefore, the first aspect of the present invention provides a positive electrode active material precursor, the chemical composition of which is Ni. x Co y M 1-x-y (OH)2, 0.8≤x<1.0, 0<y<0.2, M is one of Mn and Al.

[0041] The positive electrode active material precursor provided by this invention consists of several secondary particles. These secondary particles have a spherical or near-spherical shape. Taking a sphere as an example, based on the distance between any position within the secondary particle and the particle's center, the secondary particle is divided into a first region and a second region. The first region is located inside the secondary particle, and the second region is located outside the first region, away from the particle's center. Figure 1 Taking the secondary particle cross-section shown as an example, the secondary particle is cut along its diameter, and the cross-section is as follows: Figure 1 The circle shown is divided into a first region 101 and a second region 102 within the circular region, depending on the distance between any position of the cross-section and the center of the circle. The first region 101 is located inside the circular region, and the second region 102 is located outside the circular region. Specifically, the radius of the cross-section 100 of the positive electrode active material precursor is D. The center of the first region 101 overlaps with the center of the cross-section, and the radius of the first region 101 is 50% of the radius D of the cross-section. The second region 102 is an annular region, which is the region in the cross-section other than the first region 101.

[0042] Compared to the first region 101, the second region 102 has a more porous structure. Specifically, the average porosity of the first region 101 is 3%–8%, and the average porosity of the second region 102 is 8%–14%, with the average porosity of the first region 101 being less than that of the second region 102. For example, the average porosity of the first region 101 can be 3%, 4%, 5%, 6%, 7%, 8%, or any combination thereof, and the average porosity of the second region 102 can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, or any combination thereof. Average porosity refers to the average percentage of the area of ​​pores relative to the area of ​​the corresponding region in several secondary particles. In the actual measurement process, the positive electrode active material precursor can be placed under a scanning electron microscope, cut along the diameter of the secondary particles at a certain magnification, and the resulting cross-section can be observed. According to the distance from the center, the cross-section is divided into a first region 101 and a second region 102. The percentage of the area of ​​the pores located in the first region 101 / second region 102 to the total area of ​​the first region 101 / second region 102 is calculated. The porosity of 20 secondary particles is tested using the same method, and the average porosity of the 20 secondary particles is taken to obtain the average porosity.

[0043] Meanwhile, the secondary particles of the precursor provided by this invention have a radial internal structure, which helps to provide channels for lithium insertion / extraction for the positive electrode active material, thereby improving the battery's capacity and cycle performance.

[0044] This invention provides a high-nickel ternary cathode active material precursor with a gradient distribution of internal pores. The precursor has low internal porosity and a relatively dense structure, while the external porosity is high and the structure is relatively loose. When this precursor is used as a cathode active material in a battery, during charge-discharge cycles, the relatively dense internal structure helps prevent internal cracking and pulverization of particles during lithium ion insertion / extraction, and avoids electrolyte ingress into the particle interface causing side reactions that could affect battery performance. The relatively loose external structure helps increase the amount of lithium ion inserted and facilitates the lithium insertion / extraction process, thereby improving the battery's electrochemical performance.

[0045] In one specific embodiment, the average porosity of the positive electrode active material precursor is 6% to 12%, specifically referring to the percentage of pore area to the total cross-sectional area in the secondary particles, for example selected from a range of 6%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, or any combination thereof. By controlling the overall average porosity of the secondary particles, structural stability, lithium insertion / extraction, and lithium deintercalation can be effectively balanced, thereby improving the electrochemical performance and cycle life of the battery.

[0046] In one specific embodiment, the D50 of the positive electrode active material precursor is 5 to 16 μm, for example selected from the range of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm or any two of these; and the (D90-D10) / D50 is 0.6 to 0.8, for example selected from the range of 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.8 or any two of these. D50 refers to the particle size corresponding to a cumulative particle size distribution percentage of 50% for secondary particles in the cathode active material precursor; D10 refers to the particle size corresponding to a cumulative particle size distribution percentage of 10% for secondary particles; and D90 refers to the particle size corresponding to a cumulative particle size distribution percentage of 90% for secondary particles. Based on the D50 of the cathode active material precursor, it can be seen that the precursor has a polycrystalline structure, which helps to improve the energy density and cycle performance of the battery. A ratio of (D90-D10) / D50 within the range of 0.6 to 0.8 indicates that the precursor has a suitable particle size distribution, avoiding the generation of fine powder during the preparation of the cathode active material and preventing the fine powder from affecting the battery's internal resistance.

[0047] In one specific embodiment, in the X-ray diffraction pattern, the positive electrode active material precursor has a 001 peak with a 2θ of 18°–20° and a 101 peak with a 2θ of 38°–40°. The peak intensity ratio I

[001] / I

[101] of the 001 peak and the 101 peak is 0.8–1.2, specifically 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, or any combination thereof. When the ratio of I

[001] / I

[101] is between 0.8 and 1.2, the precursor has an XRD diffraction peak intensity ratio close to that of pure-phase nickel hydroxide, cobalt hydroxide, and manganese hydroxide, which helps to improve the crystallinity of the precursor.

[0048] In one specific embodiment, the secondary particles are formed by stacking primary particles. The primary particles have good morphological consistency, and the secondary particles have good overall crystallinity and sphericity. The primary particles are needle-shaped, with a length of 200-600 nm and a width of no more than 100 nm, which is beneficial for lithium ion intercalation.

[0049] A second aspect of the present invention provides a method for preparing a precursor of any of the above-described positive electrode active materials, comprising the following steps:

[0050] Step 1: Prepare a mixed salt solution, a hydroxide solution and a complexing agent solution, wherein the mixed salt solution includes nickel salt, cobalt salt and a soluble salt containing element M;

[0051] Step 2: Add the hydroxide solution and complexing agent solution to the reaction vessel to obtain the first reaction base liquid, wherein the N value of the first reaction base liquid is 0.8-8 g / L and the pH is 11.0-13.0;

[0052] Under a protective gas atmosphere, the mixed salt solution, hydroxide solution and complexing agent solution are introduced into the reactor to carry out the first crystallization reaction. When the D50' of the solid particles in the reactor grows to 40% to 60% of the target D50 and the solid content of the first reaction slurry in the reactor is 350 to 450 g / L, the first reaction slurry is collected and centrifuged to obtain the first particles.

[0053] Step 3: Add the hydroxide solution and complexing agent solution to the reaction vessel to obtain the second reaction base liquid. The N value of the second reaction base liquid is 0.8-8 g / L and the pH is 9.0-12.0.

[0054] Under a protective gas atmosphere, the first particles, mixed salt solution, hydroxide solution and complexing agent solution are fed into the reactor. The initial solid content in the reactor is controlled to be 25-225 g / L. The second crystallization reaction is carried out. When the D50 of the solid particles in the reactor grows to the target D50, the feeding is stopped to obtain the second reaction slurry.

[0055] Step 4: After aging, washing, centrifuging, drying and sieving the second reaction slurry, the positive electrode active material precursor is obtained.

[0056] In one specific embodiment, the preparation method includes the following steps:

[0057] Step 1: Prepare a mixed salt solution, a hydroxide solution and a complexing agent solution, wherein the mixed salt solution includes nickel salt, cobalt salt and a soluble salt containing element M.

[0058] Nickel salts, cobalt salts, and soluble salts containing element M are all conventional materials in this field. Specifically, nickel salts include one or more of nickel sulfate, nickel chloride, and nickel nitrate; cobalt salts include one or more of cobalt sulfate, cobalt chloride, and cobalt nitrate; and soluble salts containing element M include one or more of sulfates, chlorides, and nitrates containing element M, such as conventional materials like manganese sulfate, aluminum sulfate, manganese chloride, aluminum chloride, manganese nitrate, and aluminum nitrate.

[0059] The above three materials are mixed and dissolved in deionized water to prepare a mixed salt solution, wherein the total concentration of metal ions in the mixed salt solution is 0.5 to 2.5 mol / L; the molar ratio of nickel salt, cobalt salt, and soluble salt containing element M can be determined according to the molar ratio of the three elements in the positive electrode active material precursor.

[0060] The hydroxide solution is one or both of sodium hydroxide solution and potassium hydroxide solution, and the complexing agent is selected from one or more of ammonia water, ammonium sulfate, ammonium chloride, ammonium nitrate, sodium ethylenediaminetetraacetate, and sodium cyclohexanediaminetetraacetate.

[0061] Furthermore, the concentration of the hydroxide solution is 5–15 mol / L, and the concentration of the complexing agent solution is 6–12 mol / L.

[0062] Step 2: Mix the mixed salt solution, hydroxide solution and complexing agent solution and carry out the first crystallization reaction to obtain the first particles.

[0063] The precursor provided by this invention is prepared by an intermittent method. In the preparation process, a hydroxide solution and a complexing agent solution are first introduced into a reaction vessel as a reaction base liquid. The N value and pH of the reaction base liquid are kept slightly higher than the subsequent crystallization reaction conditions. Specifically, the pH of the reaction base liquid is controlled to be 11.0 to 13.0 and the N value is 0.8 to 8 g / L.

[0064] Subsequently, the temperature inside the reactor is controlled at 40–70°C, the stirrer is turned on, and a protective gas is introduced into the reactor. Under an inert gas atmosphere, the mixed salt solution, hydroxide solution, and complexing agent solution are introduced into the reactor to carry out a co-precipitation reaction. During the reaction, the material circulation system and filtration and sludge removal function of the reactor and the filter concentrator are turned on to keep the liquid level in the reactor and the filter concentrator stable.

[0065] During the reaction, the N value of the reaction system is maintained at 0.8-8 g / L and the pH at 10.0-12.0. The reaction is continued for 60-80 h. When the D50' of the solid particles in the reactor grows to 40%-60% of the target D50 and the solid content of the first reaction slurry in the reactor is 350-450 g / L, the feeding is stopped and the first reaction slurry is obtained.

[0066] The first reaction slurry is centrifuged, and the solid particles are collected to obtain the first particles, with the water content of the first particles being <10%.

[0067] Solid content refers to the mass of solid particles contained in each liter of liquid in the reactor.

[0068] Step 3: The first particle, mixed salt solution, hydroxide solution and complexing agent solution are subjected to a second crystallization reaction. After the reaction is completed, the precursor of the positive electrode active material is obtained.

[0069] Similar to step 2, the reaction vessel is cleaned, and the hydroxide solution and complexing agent solution are introduced into the reaction vessel to obtain a second reaction base liquid with a pH of 9.0 to 12.0 and an N value of 0.8 to 8 g / L.

[0070] Subsequently, under a protective gas atmosphere, the first particles, mixed salt solution, hydroxide solution, and complexing agent solution are fed into the reactor to reduce the initial solid content in the reactor to 25-225 g / L for the second crystallization reaction. When the D50 of the solid particles in the reactor grows to the target D50, the feeding is stopped, and the second reaction slurry is obtained.

[0071] The temperature during the second crystallization reaction is 40–70℃, the N value is 0.8–8 g / L, the pH is 9.0–11.0, and the reaction lasts for 30–60 hours.

[0072] Compared to step 2, step 3 has a lower solid content, a lower reaction pH, and a shorter reaction time, which helps to generate needle-shaped primary particles. As the needle-shaped primary particles gradually aggregate on the surface of the first particle, a second region with a loose and porous structure is obtained.

[0073] Step 4: After aging, washing, centrifuging, drying and sieving the second reaction slurry, the positive electrode active material precursor is obtained.

[0074] Finally, the second reaction slurry was aged, washed, centrifuged, dried, and sieved in accordance with conventional techniques in the field to obtain the positive electrode active material precursor.

[0075] Specifically, aging can be carried out in an aging kettle for 30 to 120 minutes.

[0076] The washing process employs a two-step method: first, an alkaline wash, followed by a water wash. The alkaline wash uses at least one strong alkaline solution, either NaOH or KOH, with a concentration of 3–10 mol / L and a washing time of 30–60 min. The water wash uses deionized water, with the washing temperature controlled at 40–80℃ and a washing time of 10–60 min.

[0077] Centrifugation can be performed inside a centrifuge to remove moisture.

[0078] The centrifuged solid particles are placed in a forced-air drying oven and dried at 100-120℃ for 10-20 hours. The dried material is then sieved through a 300-400 mesh screen.

[0079] A third aspect of the present invention provides a positive electrode active material, which is prepared from any of the positive electrode active material precursors described above.

[0080] The cathode active material precursor of the present invention has two regions with different porosities. The cathode active material prepared from the cathode active material precursor has high structural stability and lithium insertion capacity, and facilitates lithium insertion / extraction, thereby improving the electrochemical performance and cycle performance of lithium-ion batteries.

[0081] The positive electrode active material provided by the present invention is obtained by mixing the positive electrode active material precursor provided in the first aspect above with a lithium source and then subjecting it to calcination.

[0082] The lithium source is selected from one or more of lithium hydroxide, lithium sulfate, lithium nitrate, lithium chloride, lithium hypochlorite, lithium perchlorate, lithium carbonate, and lithium acetate.

[0083] In the process of preparing positive electrode active materials, parameters such as the molar ratio of the positive electrode precursor and the lithium source, and the calcination temperature can be selected from conventional parameters in the field, and this invention does not impose any particular limitations.

[0084] In one specific embodiment, the molar ratio of the positive electrode precursor to the active metal source is 1:(1.05 to 1.3).

[0085] In one specific embodiment, the calcination is a single-stage calcination or a two-stage calcination. In the single-stage calcination, the calcination temperature is 600–800°C and the holding time is 8–20 h. In the two-stage calcination, the calcination temperature of the first stage is 700–900°C and the holding time is 8–20 h, and the calcination temperature of the second stage is 600–750°C and the holding time is 8–20 h.

[0086] A fourth aspect of the present invention provides a battery comprising the above-described positive electrode active material.

[0087] Based on the characteristics of the positive electrode active material provided in the third aspect, lithium-ion batteries containing this positive electrode active material exhibit good electrochemical performance and cycle performance.

[0088] In one specific embodiment, the lithium-ion battery provided by the present invention includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the positive electrode sheet includes a positive current collector and a positive active layer disposed on the surface of the positive current collector, and the positive active layer includes the aforementioned positive active material.

[0089] In addition to the positive electrode active material, the positive electrode active layer also includes a conductive agent and a binder. There are no special requirements for the selection of the conductive agent and binder; they can be conventional choices in the field. For example, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, single-walled carbon nanotubes, multi-arm carbon nanotubes, and carbon fibers; the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and lithium polyacrylate (PAALi).

[0090] In the preparation process, the positive electrode active material, conductive agent and binder are first mixed in a certain proportion and dispersed in a solvent, usually NMP, and stirred evenly to obtain a positive electrode active material layer slurry; secondly, the positive electrode active material layer slurry is evenly coated on the positive electrode current collector, usually the surface of aluminum foil, and dried to form a positive electrode active material layer; finally, the positive electrode sheet is obtained by pressing and cutting.

[0091] There are no special requirements for the selection of the negative electrode, separator, and electrolyte; all are conventional choices in this field.

[0092] The positive electrode active material precursor of the present invention will be described in detail below through specific embodiments.

[0093] Example 1

[0094] The method for preparing the positive electrode active material precursor provided in this embodiment includes the following steps:

[0095] Step 1: Prepare a mixed salt solution with a total ion concentration of 1.5 mol / L by mixing nickel sulfate, cobalt sulfate, manganese sulfate and deionized water, wherein the molar ratio of Ni, Co and Mn is 83:6:11;

[0096] Step 2: Prepare a 10 mol / L sodium hydroxide solution by mixing sodium hydroxide and deionized water; prepare a 0.5 mol / L complexing agent solution by mixing ammonia and deionized water.

[0097] Step 3: Fill a 100L clean reactor with deionized water, maintain the liquid temperature in the reactor at 55℃ using a water bath, and start stirring at 650rpm; introduce the complexing agent solution into the reactor, and after measuring the N value in the reactor to be 2.0~3.0g / L, introduce the hydroxide solution into the reactor and adjust the pH in the reactor to 11.40~11.60; introduce nitrogen gas at a flow rate of 0.3L / h;

[0098] Step 4: The mixed salt solution, hydroxide solution, and complexing agent solution are introduced into the reactor using a precision constant flow pump. The flow rate of the mixed salt solution is 6 L / h, the flow rate of the hydroxide solution is 1.3–1.5 L / h, and the flow rate of the complexing agent solution is adjusted to stabilize the N value at 2.0–3.0 g / L. The material circulation and purging functions of the filter thickener are activated to maintain stable liquid levels in the reactor and the filter thickener. The reaction time is controlled at 70 h to allow the average particle size D50' to steadily grow to 4–6 μm, and the solid content in the reaction slurry in the reactor is 400 g / L, thus obtaining the first reaction slurry.

[0099] Step 5: Input the first reaction slurry into a centrifuge and centrifuge for 30 minutes to control the moisture content of the first particles to <10%;

[0100] Step 6: Wash the reaction vessel and the filter concentrator with deionized water, add deionized water to the reaction vessel and the filter concentrator, turn on the stirrer, maintain the reaction temperature at 55°C, add hydroxide solution and complexing agent solution to obtain the second reaction base liquid with pH of 10.00~10.20 and N value of 2.0~3.0g / L;

[0101] Step 7: Place a portion of the first particles into the reactor, controlling the initial solid content in the reactor to be 150 g / L; maintain the liquid temperature in the reactor at 55°C using a water bath and start stirring at 550 rpm; activate the material circulation system between the reactor and the filtration and concentrator, and the filtration and clearing function of the filtration and concentrator to maintain stable liquid levels in both reactors and filtration and concentrators; introduce nitrogen gas at a flow rate of 0.3 L / h; introduce the mixed salt solution, hydroxide solution, and complexing agent solution into the reactor using a precision constant flow pump, with the mixed salt solution flow rate at 6 L / h; the hydroxide solution flow rate at 1.3–1.5 L / h, and the pH at 10.00–10.20; and the complexing agent solution flow rate to stabilize the N value at 2.0–3.0 g / L; control the reaction time at 50 h to allow the average particle size D50 to steadily grow to 9.5–11.5 μm, obtaining the second reaction slurry;

[0102] Step 8: Pour the second reaction slurry into the aging kettle for aging, and the aging time is 60 minutes;

[0103] Step 9: Pour the aged slurry into a centrifuge, wash it with a sodium hydroxide solution with a concentration of 5 mol / L and a temperature of 50℃ for 30 minutes, then rinse it with deionized water at a temperature of 50℃ for 30 minutes, and centrifuge to dry the material to be dried.

[0104] Step 10: Place the material to be dried in a forced-air drying oven, dry at 110℃ for 15 hours, and sieve the dried material through a 325-mesh sieve to obtain the precursor.

[0105] Example 2

[0106] The preparation method of the positive electrode active material precursor provided in this embodiment can refer to Embodiment 1. The difference is that in step 1, nickel sulfate, cobalt sulfate, aluminum sulfate and deionized water are prepared into a mixed salt solution with a total ion concentration of 1.5 mol / L, wherein the molar ratio of Ni, Co and Al is 83:6:11.

[0107] Example 3

[0108] The method for preparing the positive electrode active material precursor provided in this embodiment includes the following steps:

[0109] Step 1: Prepare a mixed salt solution with a total ion concentration of 1.5 mol / L by mixing nickel sulfate, cobalt sulfate, manganese sulfate and deionized water, wherein the molar ratio of Ni, Co and Mn is 83:12:5;

[0110] Step 2: Prepare a 10 mol / L sodium hydroxide solution by mixing sodium hydroxide and deionized water; prepare a 0.5 mol / L complexing agent solution by mixing ammonia and deionized water.

[0111] Step 3: Fill a 100L clean reactor with deionized water, maintain the liquid temperature in the reactor at 65℃ using a water bath, and start stirring at 600rpm; introduce the complexing agent solution into the reactor, and after measuring the N value in the reactor to be 2.0~3.0g / L, introduce sodium hydroxide solution into the reactor and adjust the pH in the reactor to 11.20~11.40; introduce nitrogen gas at a flow rate of 0.3L / h;

[0112] Step 4: The mixed salt solution, hydroxide solution, and complexing agent solution are introduced into the reactor using a precision constant flow pump. The flow rate of the mixed salt solution is 6 L / h, and the flow rate of the hydroxide solution is 1.3–1.5 L / h. The flow rate of the complexing agent solution is adjusted to stabilize the nitrogen value at 2.0–3.0 g / L. The material circulation and scavenging functions of the filter thickener are activated to maintain stable liquid levels in the reactor and the filter thickener. By adjusting the pH, the reaction time is controlled at 80 h, allowing the average particle size D50' to steadily grow to 7–8 μm. The solid content in the reaction slurry in the reactor is 450 g / L, yielding the first reaction slurry.

[0113] Step 5: Transfer the first reaction slurry into a centrifuge and centrifuge for 30 minutes to control the moisture content to <10%.

[0114] Step 6: Wash the reaction vessel and filter concentrator with deionized water, add deionized water to the reaction vessel and filter concentrator, turn on the stirrer, maintain the reaction temperature at 65℃, add hydroxide solution and complexing agent solution to obtain an initial mixture with pH of 9.80~10.00 and N value of 2.0~3.0g / L;

[0115] Step 7: Place a portion of the first particles into the reactor, controlling the initial solid content in the reactor to be 150 g / L; maintain the liquid temperature in the reactor at 65°C using a water bath and start stirring at 500 rpm; activate the material circulation system between the reactor and the filtration and concentrator, and the filtration and clearing function of the filtration and concentrator to maintain stable liquid levels in both reactors and filtration and concentrators; introduce nitrogen gas at a flow rate of 0.3 L / h; introduce the mixed salt solution, hydroxide solution, and complexing agent solution into the reactor using a precision constant flow pump, with the mixed salt solution flow rate at 6 L / h; the hydroxide solution flow rate at 1.3–1.5 L / h; and the complexing agent solution flow rate to stabilize the N value at 2.0–3.0 g / L; control the reaction time at 60 h to allow the average particle size D50 to steadily grow to 14.0–16.0 μm, obtaining the second reaction slurry;

[0116] Step 8: Pour the second reaction slurry into the aging kettle for aging, and the aging time is 60 minutes;

[0117] Step 9: Pour the aged slurry into a centrifuge, wash it with a sodium hydroxide solution with a concentration of 5 mol / L and a temperature of 50℃ for 30 minutes, then rinse it with deionized water at a temperature of 50℃ for 30 minutes, and centrifuge to dry the material to be dried.

[0118] Step 10: Place the material to be dried in a forced-air drying oven, dry at 110℃ for 15 hours, and sieve the dried material through a 325-mesh sieve to obtain the precursor.

[0119] Example 4

[0120] The preparation method of the positive electrode active material precursor provided in this embodiment can be referred to in Embodiment 3, with the difference being:

[0121] Step 3: Fill a 100L clean reactor with deionized water, maintain the liquid temperature in the reactor at 65℃ using a water bath, and start stirring at 700rpm; introduce the complexing agent solution into the reactor, and after measuring the N value in the reactor to be 2.0~3.0g / L, introduce the hydroxide solution into the reactor and adjust the pH in the reactor to 11.40~11.60; introduce nitrogen gas at a flow rate of 0.3L / h;

[0122] Step 4: The mixed salt solution, hydroxide solution, and complexing agent solution are introduced into the reactor using a precision constant flow pump. The flow rate of the mixed salt solution is 6 L / h, and the flow rate of the sodium hydroxide solution is 1.5–1.7 L / h. The flow rate of the complexing agent solution is adjusted to stabilize the nitrogen value at 2.0–3.0 g / L. The material circulation and scavenging functions of the filter thickener are activated to maintain stable liquid levels in the reactor and the filter thickener. By adjusting the pH, the reaction time is controlled at 60 h, allowing the average particle size D50' to steadily grow to 2–4 μm. The solid content in the reaction slurry in the reactor is 350 g / L, yielding the first reaction slurry.

[0123] Step 6: Wash the reaction vessel and filter concentrator with deionized water, add deionized water to the reaction vessel and filter concentrator, turn on the stirrer, maintain the reaction temperature at 65℃, add hydroxide solution and complexing agent solution to obtain an initial mixture with pH of 10.00~10.20 and N value of 2.0~3.0g / L;

[0124] Step 7: Place a portion of the first particles into the reactor, controlling the initial solid content in the reactor to be 150 g / L; maintain the liquid temperature in the reactor at 65°C using a water bath and start stirring at 600 rpm; activate the material circulation system between the reactor and the filtration and concentrator, and the filtration and clearing function of the filtration and concentrator to maintain stable liquid levels in the reactor and filtration and concentrator; introduce nitrogen gas at a flow rate of 0.3 L / h; introduce the mixed salt solution, hydroxide solution, and complexing agent solution into the reactor using a precision constant flow pump, with the flow rate of the mixed salt solution being 6 L / h; the flow rate of the hydroxide solution being 1.5–1.7 L / h; and the flow rate of the complexing agent solution being adjusted to stabilize the N value at 2.0–3.0 g / L; control the reaction time at 40 h to allow the average particle size D50 to steadily grow to 5.0–7.0 μm, obtaining the second reaction slurry.

[0125] Example 5

[0126] The preparation method of the positive electrode active material precursor provided in this embodiment can refer to Embodiment 1. The difference is that in step 7, a portion of the first particles are placed into the reaction vessel, the initial solid content in the reaction vessel is controlled to be 100 g / L, and the reaction time is controlled to be 40 h.

[0127] Example 6

[0128] The preparation method of the positive electrode active material precursor provided in this embodiment can refer to Embodiment 1. The difference is that in step 7, a portion of the first particles are placed into the reaction vessel, the initial solid content in the reaction vessel is controlled to be 50 g / L, and the reaction time is controlled to be 30 h.

[0129] Example 7

[0130] The preparation method of the positive electrode active material precursor provided in this embodiment can refer to Embodiment 1. The difference is that in step 7, a portion of the first particles are placed into the reaction vessel, the initial solid content in the reaction vessel is controlled to be 200 g / L, and the reaction time is controlled to be 60 h.

[0131] Comparative Example 1

[0132] The preparation method of the positive electrode active material precursor provided in this comparative example includes the following steps:

[0133] Step 1: Prepare a mixed salt solution with a total ion concentration of 1.5 mol / L by mixing nickel sulfate, cobalt sulfate, manganese sulfate and deionized water, wherein the molar ratio of Ni, Co and Mn is 83:6:11;

[0134] Step 2: Prepare a 10 mol / L hydroxide solution by mixing sodium hydroxide and deionized water; prepare a 0.5 mol / L complexing agent solution by mixing ammonia and deionized water.

[0135] Step 3: Fill a 100L clean reactor with deionized water, maintain the liquid temperature in the reactor at 55℃ using a water bath, and start stirring at 650rpm; introduce the complexing agent solution into the reactor, and after measuring the N value in the reactor to be 2.0~3.0g / L, introduce the hydroxide solution into the reactor and adjust the pH in the reactor to 11.40~11.60; introduce nitrogen gas at a flow rate of 0.3L / h;

[0136] Step 4: The mixed salt solution, hydroxide solution, and complexing agent solution are introduced into the reactor using a precision constant flow pump. The flow rate of the mixed salt solution is 6 L / h, and the flow rate of the hydroxide solution is 1.3–1.5 L / h. The flow rate of the complexing agent solution is adjusted to stabilize the nitrogen value at 2.0–3.0 g / L. The material circulation and scavenging functions of the filter thickener are activated to maintain stable liquid levels in the reactor and filter thickener. By adjusting the pH to 11.00–11.40, the average particle size D50' steadily grows to 9.5–11.5 μm, yielding a qualified reaction slurry.

[0137] Step 8: Pour the qualified reaction slurry into the aging kettle for aging, and the aging time is 60 minutes;

[0138] Step 9: Pour the aged slurry into a centrifuge, wash it with a sodium hydroxide solution with a concentration of 5 mol / L and a temperature of 50℃ for 30 minutes, then rinse it with deionized water at a temperature of 50℃ for 30 minutes, and centrifuge to dry the material to be dried.

[0139] Step 10: Place the material to be dried in a forced-air drying oven, dry at 110℃ for 15 hours, and sieve the dried material through a 325-mesh sieve to obtain the precursor.

[0140] Comparative Example 2

[0141] The preparation method of the positive electrode active material precursor provided in this comparative example includes the following steps:

[0142] Step 1: Prepare a mixed salt solution with a total ion concentration of 1.5 mol / L by mixing nickel sulfate, cobalt sulfate, manganese sulfate and deionized water, wherein the molar ratio of Ni, Co and Mn is 83:6:11;

[0143] Step 2: Prepare a 10 mol / L hydroxide solution by mixing sodium hydroxide and deionized water; prepare a 0.5 mol / L complexing agent solution by mixing ammonia and deionized water.

[0144] Step 3: Fill a 100L clean reactor with deionized water, maintain the liquid temperature in the reactor at 55℃ using a water bath, and start stirring at 650rpm; introduce the complexing agent solution into the reactor, and after measuring the N value in the reactor to be 2.0~3.0g / L, introduce the hydroxide solution into the reactor and adjust the pH in the reactor to 11.40~11.60; introduce nitrogen gas at a flow rate of 0.3L / h;

[0145] Step 4: The mixed salt solution, hydroxide solution, and complexing agent solution are introduced into the reactor using a precision constant flow pump. The flow rate of the mixed salt solution is 6 L / h; the flow rate of the hydroxide solution is 1.3–1.5 L / h; and the flow rate of the complexing agent solution is adjusted to stabilize the nitrogen value at 2.0–3.0 g / L. A continuous process is used without a filter thickener. The pH is controlled at 11.40–11.60 to allow the average particle size D50 to steadily grow and stabilize at 9.5–11.5 μm, resulting in a qualified reaction slurry.

[0146] Step 5: Pour the qualified reaction slurry into the aging kettle for aging, and the aging time is 60 minutes;

[0147] Step 6: Pour the aged slurry into a centrifuge, wash it with a sodium hydroxide solution with a concentration of 5 mol / L and a temperature of 50℃ for 30 minutes, then rinse it with deionized water at a temperature of 50℃ for 30 minutes, and centrifuge to dry the material to be dried.

[0148] Step 7: Place the material to be dried in a forced-air drying oven, dry at 110℃ for 15 hours, and sieve the dried material through a 325-mesh sieve to obtain the precursor.

[0149] Comparative Example 3

[0150] The preparation method of the positive electrode active material precursor provided in this comparative example can refer to Example 1. The difference is that in step 4, the first crystallization reaction time is controlled at 90h, and the solid content of the reaction slurry at the end of the reaction is 600g / L; in step 7, the initial solid content in the reactor is controlled at 200g / L, and the reaction time is 60h.

[0151] The positive electrode active material precursor provided in Example 1 was observed by scanning electron microscopy, and the observation results are as follows: Figure 2 As shown, the cross-sections of the positive electrode active material precursors provided in Example 1 and Comparative Examples 1-3 were observed, and the observation results are as follows. Figure 3 , 5 As shown in Figures 7-7, it can be seen that the inner layer of the secondary particle profile in Example 1 has a lower porosity and a relatively dense structure, while the outer layer has a higher porosity and a relatively loose structure. The secondary particle profile in Comparative Example 1 has a uniformly distributed pore size, a higher porosity, and a relatively loose structure. The secondary particle profile in Comparative Example 2 has a lower overall porosity and a relatively dense structure. The secondary particle profile in Comparative Example 3 has a dense structure in the middle and a loose structure on the outside.

[0152] The precursor secondary particles were cut along the diameter, and the area within 50% of the cross-sectional radius was designated as the first region, while the annular area outside the first region was designated as the second region. Based on the cross-sectional electron microscopy observation results, the average porosity of the corresponding regions of the positive electrode active material precursors provided in Examples 1-7 and Comparative Examples 1-3 was statistically analyzed. The average porosity of 20 secondary particles was taken as the average porosity, and the statistical results are shown in Table 1.

[0153] Figure 4 The XRD pattern of the positive electrode active material precursor provided in Embodiment 1 of the present invention is shown below. Figure 4 As shown, in the X-ray diffraction pattern, there are peaks 001 and 101, and the peak intensity ratio I

[001] / I

[101] of peak 001 and peak 101 is 0.99.

[0154] The particle size of the positive electrode active material precursors provided in Examples 1-7 and Comparative Examples 1-3 was statistically calculated using a particle size analyzer, and the results are shown in Table 1.

[0155] Table 1. Performance test results of the positive electrode active material precursors provided in Examples 1-7 and Comparative Examples 1-3.

[0156]

[0157]

[0158] The positive electrode active material precursors provided in Examples 1-7 and Comparative Examples 1-3 were mixed with battery-grade lithium hydroxide at a ratio of Li:(Ni+Co+Mn)=1.05 and subjected to a second calcination treatment under an oxygen atmosphere. The first calcination was carried out at 750°C for 20 hours, and the second calcination was carried out at 650°C for 15 hours to obtain the positive electrode active material.

[0159] The prepared positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 94:3:3 to obtain a positive electrode active material slurry, which was then uniformly coated on the surface of the positive electrode current collector to obtain a positive electrode sheet. A Celgard polypropylene separator and a lithium metal sheet were used as negative electrode sheets, and a 1 mol / L LiPF6 + DEC / EC (volume ratio 1:1) mixed solution was used as the electrolyte to obtain a coin cell. The coin cell was tested for charge-discharge specific capacity and capacity retention rate at 25℃, 2.5–4.3V, and 0.2C. The test results are shown in Table 2.

[0160] Table 2 shows the performance test data of the coin cells provided in Examples 1-7 and Comparative Examples 1-3.

[0161]

[0162] According to the data provided in Table 2, the secondary particles of the precursors provided in Comparative Examples 1 and 2 do not have a pore gradient distribution, resulting in low initial charge-discharge specific capacity and cycle capacity retention of the lithium-ion batteries prepared from them. In contrast, the secondary particles of the precursors provided in Comparative Example 3 are relatively dense with low porosity, which can easily affect the lithium-ion insertion channels of the positive electrode active material, resulting in low discharge specific capacity. In contrast, the secondary particles of the precursors provided in Examples 1 to 7 of this invention have a suitable pore distribution, which helps to improve the electrochemical performance and cycle performance of the batteries.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode active material precursor, characterized in that, The chemical composition of the positive electrode active material precursor is Ni. x Co y M 1-x-y (OH)2, 0.8≤x<1.0, 0<y<0.2, M is one of Mn and Al; The positive electrode active material precursor includes secondary particles, which are divided into a first region and a second region. The first region is located inside the secondary particles, and the second region is located outside the first region away from the center of the particles. The average porosity of the first region is 3% to 8%, and the average porosity of the second region is 8% to 14%. The average porosity of the first region is less than that of the second region. The radius of the secondary particle is D, and the radius r1 of the first region is 0.

5. D; The secondary particles have a D50 of 5~16 μm and a (D90-D10) / D50 of 0.6~0.

8.

2. The positive electrode active material precursor according to claim 1, characterized in that, The average porosity of the secondary particles is 6% to 12%.

3. The positive electrode active material precursor according to claim 1, characterized in that, In the X-ray diffraction pattern, the positive electrode active material precursor has a 001 peak with a 2θ of 18°~20° and a 101 peak with a 2θ of 38°~40°, and the peak intensity ratio I[001] / I[101] of the 001 peak and the 101 peak is 0.8~1.

2.

4. The positive electrode active material precursor according to claim 1, characterized in that, The secondary particles are formed by stacking primary particles, and the length of the primary particles is 200~600 nm and the width is no more than 100 nm.

5. A method for preparing a positive electrode active material precursor according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Prepare a mixed salt solution, a hydroxide solution and a complexing agent solution, wherein the mixed salt solution includes nickel salt, cobalt salt and a soluble salt containing element M; Step 2: Add the hydroxide solution and complexing agent solution to the reaction vessel to obtain the first reaction base liquid, wherein the N value of the first reaction base liquid is 0.8~8 g / L and the pH is 11.0~13.0; Under a protective gas atmosphere, the mixed salt solution, hydroxide solution and complexing agent solution are introduced into the reactor to carry out the first crystallization reaction. When the D50' of the solid particles in the reactor grows to 40%~60% of the target D50 and the solid content of the first reaction slurry in the reactor is 350~450g / L, the first reaction slurry is collected and centrifuged to obtain the first particles. Step 3: Add the hydroxide solution and complexing agent solution to the reaction vessel to obtain the second reaction base liquid, wherein the N value of the second reaction base liquid is 0.8~8 g / L and the pH is 9.0~12.0; Under a protective gas atmosphere, the first particles, mixed salt solution, hydroxide solution and complexing agent solution are fed into the reactor. The initial solid content in the reactor is controlled to be 25~225 g / L. The second crystallization reaction is carried out. When the D50 of the solid particles in the reactor grows to the target D50, the feeding is stopped to obtain the second reaction slurry. Step 4: After aging, washing, centrifuging, drying and sieving the second reaction slurry, the positive electrode active material precursor is obtained.

6. The preparation method according to claim 5, characterized in that, The temperature of the first crystallization reaction is 40~70℃, the N value of the reaction system is maintained at 0.8~8 g / L, the pH is 10.0~12.0, and the reaction time is 60~80h.

7. The preparation method according to claim 5, characterized in that, The temperature of the second crystallization reaction is 40~70℃, the N value of the reaction system is maintained at 0.8~8 g / L, the pH is 9.0~11.0, and the reaction time is 30~60h.

8. A positive electrode active material, characterized in that, It is prepared from the positive electrode active material precursor according to any one of claims 1 to 4, or from the positive electrode active material precursor prepared by the preparation method according to any one of claims 5 to 7.

9. A battery, characterized in that, Includes the positive electrode active material as described in claim 8.

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