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. The first aspect of the application provides a positive electrode active material precursor, which has a chemical composition of Ni x Mn y (OH)2, 0.2<=x<=0.3, 0.7<=y<=0.8; the positive electrode active material precursor comprises secondary particles formed by stacking primary particles, wherein the aspect ratio of the primary particles is 5-8, and the whisker thickness is 200-400 nm; the secondary particles have a pore distribution of loose inside and compact outside. The precursor provided by the application has high tap density and specific surface area, which is beneficial to improving the capacity and rate performance of the battery; meanwhile, the secondary particles of the precursor provided by the application have good regularity and dispersity and high whisker thickness, which is beneficial to improving the stability of the positive electrode active material in the cycle process, and further improving the cycle capacity retention rate of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to a positive electrode active material precursor and a preparation method and application thereof, and relates to the technical field of secondary batteries. BACKGROUND

[0002] A secondary battery refers to a battery that can continue to be used by activating active materials through charging after the battery is discharged, mainly including positive electrode active materials and negative electrode active materials for electrochemical reactions, and the performance of the positive electrode active material determines the performance of the secondary battery. In order to reduce the cost of energy storage batteries for the middle and low-end market, manganese-rich cobalt-free positive electrode active materials without cobalt elements and high manganese elements are highly concerned.

[0003] At present, secondary batteries including manganese-rich cobalt-free positive electrode active materials are limited by their endurance and discharge rate, and the physical and chemical data of the positive electrode active material are inherited from the precursor. Therefore, how to provide a manganese-rich cobalt-free positive electrode active material precursor to improve the endurance and discharge rate of the secondary battery has attracted attention from those skilled in the art. SUMMARY

[0004] The present application provides a positive electrode active material precursor and a preparation method thereof for improving the endurance and discharge rate of a secondary battery.

[0005] The present application also provides a positive electrode active material prepared from the above-mentioned precursor and a secondary battery comprising the positive electrode active material.

[0006] The present application provides, in a first aspect, a positive electrode active material precursor, which has a chemical composition of Ni x Mn y (OH)2, 0.2≤x≤0.3, 0.7≤y≤0.8;

[0007] The positive electrode active material precursor comprises secondary particles formed by stacking primary particles, and the primary particles have an aspect ratio of 5-8 and a whisker thickness of 200-400 nm.

[0008] The D50 of the secondary particles is R1, and the secondary particles with a selected particle size of R2 are selected as test particles, 40%*R1≤R2≤60%*R1; the test particles include a first region, the distance between any position of the first region and the center of the particle is r1, 0≤r1≤30%*R2, and the porosity of the first region is not less than 50% of the porosity of the test particles.

[0009] In a specific embodiment, the porosity of the test particles is 15-25%.

[0010] In a specific embodiment, the tap density of the positive electrode active material precursor is not less than 1.2 g / cm 3Specific surface area is not less than 20 m 2 / g.

[0011] In one specific embodiment, the D50 of the positive electrode active material precursor is 4-5 μm, and (D90-D10) / D50≤0.9.

[0012] In one specific embodiment, the positive electrode active material precursor has 001 and 110 crystal planes, and the ratio D001 / D110 of the interplanar spacing of the 001 crystal plane to the interplanar spacing of the 110 crystal plane is 20-30.

[0013] The second aspect of the present application provides a preparation method of the positive electrode active material precursor described above, comprising the following steps:

[0014] Step 1, configuring a mixed salt solution, a precipitant and a complexing agent solution, wherein the mixed salt solution comprises a nickel salt, a manganese salt and a reducing agent;

[0015] Step 2, configuring a reaction bottom liquid at the bottom of a reaction kettle, and controlling the pH of the reaction bottom liquid to be 10.5-11.0 and the ammonia value to be 0.1-5 g / L;

[0016] Under a protective gas atmosphere, the mixed salt solution, the precipitant solution and the complexing agent solution are added to the reaction kettle to perform a nucleation reaction; when the D50 of the solid particles in the reaction kettle reaches D0, the addition of the complexing agent is stopped, and the solid content in the reaction kettle is controlled to be 200-300 g / L; wherein D0≤65%*D1.

[0017] Step 3, continuously feeding the mixed salt solution and the precipitant solution into the reaction kettle to perform a crystal growth process; when the D50 of the solid particles reaches a target particle size D1, the feeding is stopped and the solid product is collected, and the solid content in the reaction kettle is controlled to be 300-500 g / L;

[0018] Step 4, sequentially performing aging, water washing, centrifugation and drying on the solid product to obtain the positive electrode active material precursor.

[0019] In one specific embodiment, in Step 2, the flow rate of the mixed salt solution is controlled to be 3≤a1<5 L / h; the flow rate of the precipitant solution is controlled to be 0.8-1.8 L / h, so that the pH of the reaction system is the same as that of the reaction bottom liquid; and the flow rate of the complexing agent solution is controlled, so that the ammonia value of the reaction system is 0.1-5 g / L.

[0020] In one specific embodiment, the flow rate of the mixed salt solution is controlled to be 5≤a2≤7 L / h, and the flow rate of the precipitant solution is controlled to be 1.5-3.0 L / h, so that the pH of the reaction system is higher than that in the nucleation reaction stage, and is maintained for 2-4 hours, and then the pH of the reaction system is lowered to perform the crystal growth process.

[0021] The third aspect of the present application provides a positive electrode active material, which is prepared from the positive electrode active material precursor according to any one of the above-mentioned positive electrode active material precursors or the positive electrode active material prepared according to any one of the above-mentioned preparation methods.

[0022] The fourth aspect of the present application provides a battery comprising the positive electrode active material according to any one of the above-mentioned positive electrode active materials.

[0023] The positive electrode active material precursor provided by the present application has a pore distribution of loose inside and tight outside, which helps to improve the tap density and specific surface area of the precursor, thereby improving the capacity and rate performance of the battery; at the same time, the secondary particles of the precursor provided by the present application have good regularity and dispersity and high whisker thickness, which is conducive to improving the stability of the positive electrode active material in the cycle process, thereby improving the cycle capacity retention rate of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0025] Figure 1 The cross-sectional structure schematic diagram of the positive electrode active material precursor provided by the present application;

[0026] Figure 2 The scanning electron microscope observation diagram obtained by observing the precursor provided by the present application in Example 1 at 30K magnification;

[0027] Figure 3 The scanning electron microscope observation diagram obtained by observing the cross section of the precursor provided by the present application in Example 1 at 20K magnification;

[0028] Figure 4 The scanning electron microscope observation diagram obtained by observing the precursor provided by the present application in Comparative Example 1 at 30K magnification;

[0029] Figure 5 The scanning electron microscope observation diagram obtained by observing the cross section of the precursor provided by the present application in Comparative Example 1 at 20K magnification;

[0030] Figure 6 The scanning electron microscope observation diagram obtained by observing the precursor provided by the present application in Comparative Example 2 at 30K magnification;

[0031] Figure 7The scanning electron microscope observation figure is obtained by observing the precursor provided for the present application comparative example 3 at 30K magnification.

[0032] Figure 8 The XRD test result figure of the precursor provided for the present application example 1.

[0033] Label explanation:

[0034] 100-cross section of the test particle;

[0035] 101-first region. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the present application examples will be described clearly and completely below in combination with the present application examples. Obviously, the described examples are part of the examples of the present application, rather than all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0037] The present application provides a positive electrode active material precursor in a first aspect, which has a chemical composition of Ni x Mn y (OH)2, 0.2≤x≤0.3, 0.7≤y≤0.8.

[0038] The positive electrode active material precursor comprises secondary particles formed by stacking primary particles, the aspect ratio of the primary particles is 5-8, and the whisker thickness is 200-400 nm.

[0039] The D50 of the secondary particles is R1, the secondary particles with a particle size of R2 are selected as test particles, 40%*R1≤R2≤60%*R1, the test particles comprise a first region, the distance between any position of the first region and the particle center is r1, 0≤r1≤30%*R2, and the porosity of the first region is not less than 50% of the porosity of the test particles.

[0040] The positive electrode active material precursor provided by the present application only comprises two kinds of transition metals of nickel and manganese, does not comprise cobalt element, the nickel and manganese elements are in the form of hydroxide, and the molar amount of the manganese element is more than 70% of the total molar amount of the transition metals, which is a manganese-rich cobalt-free precursor.

[0041] Those skilled in the art will understand that precursor particles comprise a plurality of secondary particles, which are spherical or near-spherical particles formed by stacking primary particles. In the precursor provided by this invention, the aspect ratio of the primary particles is 5–8, i.e., the whisker length / whisker thickness is 5–8. Specifically, it can be 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8, or any combination thereof. The whisker thickness is within the range of 200–400 nm, specifically within the range of 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, 310 nm, 320 nm, 330 nm, 340 nm, 350 nm, 360 nm, 370 nm, 380 nm, 390 nm, 400 nm, or any combination thereof. The whisker length and thickness of the primary particles can be observed and measured using a scanning electron microscope.

[0042] In addition to meeting the aforementioned aspect ratio and whisker thickness, the primary particles also exhibit a loose internal stacking and a dense external stacking, resulting in higher porosity inside the secondary particles and lower porosity on the outside. Specifically, as... Figure 1 As shown, firstly, the D50 of the precursor is tested and denoted as R1. Particles with a diameter of 40%*R1 to 60%*R1 are selected as test particles within the field of view, and the overall porosity of the test particles is obtained using conventional techniques in the field, denoted as P1. The test particles are then cut along their diameter to obtain a cross-section 100. The area with a distance r1 from the center of the cross-section is designated as the first region 101. The porosity of the first region 101 is tested using the same testing method as for the overall porosity of the test particles, denoted as P2. P2 / P1*100% ≥ 50%. By controlling the difference in the density of the primary particle stacking, it is beneficial to improve the tap density and specific surface area of ​​the precursor, thereby improving the battery's capacity and rate performance.

[0043] In one specific embodiment, the porosity P1 of the test particles is 15% to 25%, specifically a range of 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any combination thereof; by controlling the overall porosity of the particles, structural stability, lithium insertion / extraction capacity, and lithium insertion / extraction can be effectively balanced, thereby improving the rate performance and cycle life of the battery.

[0044] In one specific embodiment, the tap density of the positive electrode active material precursor is not less than 1.2 g / cm 3 , and the specific surface area is not less than 20 m 2 / g. The tap density refers to the mass per unit volume of the precursor powder placed in a container after being vibrated under specified conditions, and the specific surface area refers to the total area possessed by the unit mass of the precursor material. Increasing the tap density of the precursor helps to increase the energy density of the battery and improve the endurance, and the internal loose and external compact precursor provided by the present application helps to further increase the specific surface area of the precursor on the basis of increasing the tap density, thereby increasing the lithium extraction speed of the positive electrode active material and improving the rate performance of the battery.

[0045] In one specific embodiment, the D50 of the positive electrode active material precursor is 4-5 μm, and the D50 refers to the particle size corresponding to the volume distribution percentage of 50% of the secondary particles in the positive electrode active material precursor. For example, it can be selected from the range consisting of 4 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.0 μm, or any two thereof; the (D90-D10) / D50 of the positive electrode active material precursor is ≤0.9, the D10 refers to the particle size corresponding to the volume distribution percentage of 10% of the secondary particles, and the D90 refers to the particle size corresponding to the volume distribution percentage of 90% of the secondary particles. When (D90-D10) / D50≤0.9, it indicates that the secondary particle size consistency of the precursor is relatively high, and the span is low, which can avoid the over-burning phenomenon caused by the presence of small particles during the sintering process of the positive electrode active material, improve the stability of the positive electrode active material during the battery cycle process, and improve the cycle capacity retention rate of the battery.

[0046] In one specific embodiment, the positive electrode active material precursor has 001 and 110 crystal planes, and the ratio D001 / D110 of the interplanar spacing of the 001 crystal plane to the interplanar spacing of the 110 crystal plane is 20-30, for example, it can be selected from the range consisting of 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, or any two thereof. When the D001 / D110 of the positive electrode active material precursor satisfies the range, it helps to improve the performance of the battery.

[0047] The second aspect of the present application provides a preparation method of the positive electrode active material precursor described above, comprising the following steps:

[0048] Step 1, configuring a mixed salt solution, a precipitant, and a complexing agent solution, wherein the mixed salt solution comprises a nickel salt, a manganese salt, and a reducing agent;

[0049] Step 2, configure a reaction bottom liquid at the bottom of a reaction kettle, and control the pH of the reaction bottom liquid to be 10.5-11.0 and the ammonia value to be 0.1-5 g / L;

[0050] Under a protective gas atmosphere, a mixed salt solution, a precipitant solution and a complexing agent solution are added to the reaction kettle to perform a nucleation reaction; when the D50 of the solid particles in the reaction kettle reaches D0, the addition of the complexing agent is stopped, and the solid content in the reaction kettle is controlled to be 200-300 g / L; wherein D0≤65%*D1;

[0051] Step 3, the mixed salt solution and the precipitant solution are continuously fed into the reaction kettle to perform a crystal growth process; when the D50 of the solid particles reaches D1, the feeding is stopped and the solid product is collected, and the solid content in the reaction kettle is controlled to be 300-500 g / L;

[0052] Step 4, the solid product is sequentially aged, washed with water, centrifuged and dried to obtain the positive electrode active material precursor.

[0053] The preparation method provided by the application adds a complexing agent in the nucleation stage, which helps to slow down the growth rate of primary particles, reduces the phenomenon of uneven deposition of metal ions, makes the crystal grow along the directional crystal face direction, obtains a crystal nucleus with regular morphology, and improves the regularity of secondary particles; no complexing agent solution is added in the growth stage, which helps to avoid the stacking of primary particles being too dense due to too high concentration of the complexing agent solution, affects the specific surface area of the particles, and also reduces the consumption of the complexing agent solution, reduces the burden of subsequent complexing agent recovery and processing, saves costs and is environmentally friendly. In addition, the preparation method provided by the application also adjusts the solid content of the reaction system in the nucleation stage and the growth stage, maintains a lower solid content in the nucleation stage, which is beneficial to improving the porosity of the particles, improving the specific surface area, and also beneficial to improving the dispersibility of the secondary particles to improve the sphericity of the precursor; and a higher solid content is maintained in the growth stage, which is beneficial to prolonging the growth time of the primary particles, making the stacking of the primary particles more regular and compact, and improving the tap density.

[0054] In a specific embodiment, the preparation method provided by the application specifically includes the following steps:

[0055] Step 1, configure a mixed salt solution, a precipitant solution and a complexing agent solution, wherein the mixed salt solution includes a nickel salt, a manganese salt and a reducing agent;

[0056] The nickel salt and the manganese salt used in the application can be conventional soluble metal salts in the art, for example, the nickel salt can be one or more of NiSO4, Ni(NO3)2, and NiCl2, and the manganese salt can be one or more of MnSO4, Mn(NO3)2, and MnCl2. The nickel salt and the manganese salt are mixed in a certain molar ratio and dissolved in the solvent deionized water to obtain a mixed salt solution. Further, the total molar concentration of metal ions in the mixed salt solution is 1.5-2 mol / L.

[0057] In addition, in order to alleviate the problem of easy oxidation of the precursor caused by the increase of the content of manganese element, the mixed salt solution provided by the application further comprises a reducing agent selected from one or both of hydrazine hydrate and ascorbic acid.

[0058] Further, the reducing agent is ascorbic acid, which as an acidic reducing agent also helps to increase the porosity of the particles and improve the specific surface area of the precursor.

[0059] Further, the amount of the reducing agent can be determined according to actual needs; for example, the mass of the reducing agent is one ten-thousandth of the mass of the manganese element.

[0060] The precipitant solution can be an alkaline solution with pH≥7, specifically an aqueous solution of one or more of sodium hydroxide, sodium bicarbonate, and potassium hydroxide; further, the concentration of the precipitant solution is 10-12 mol / L.

[0061] The complexing agent includes one or more of sodium citrate, oxalic acid, and ammonia water; the complexing agent is dissolved in deionized water to obtain a complexing agent solution. Further, the concentration of the complexing agent solution is 0.5-10 mol / L.

[0062] Step 2, configure a reaction bottom liquid at the bottom of the reaction kettle, and control the pH of the reaction bottom liquid to be 10.5-11.0 and the ammonia value to be 0.1-5 g / L;

[0063] Under the atmosphere of the protective gas, the mixed salt solution, the precipitant solution, and the complexing agent solution are added to the reaction kettle to perform a nucleation reaction; when the D50 of the solid particles in the reaction kettle reaches D0, the addition of the complexing agent is stopped, and the solid content in the reaction kettle is controlled to be 300-500 g / L.

[0064] First, the precipitant solution and the complexing agent solution are added to the reaction kettle as a reaction bottom liquid, and the pH of the reaction bottom liquid is controlled to be 10.5-11.0 and the ammonia value is controlled to be 0.1-5 g / L.

[0065] Second, the temperature of the reaction kettle is controlled to be 40-70°C, the stirrer is turned on and the rotation speed is controlled to be 300-700 rpm, and the protective gas is continuously introduced into the reaction kettle, so that the subsequent reaction is performed under the atmosphere of the protective gas, and the flow rate of the protective gas is controlled to be 0.2-0.6 m3 The protective gas can be nitrogen.

[0066] Then, the mixed salt solution, the precipitant solution and the complexing agent solution prepared in step 1 are added into the reactor to perform nucleation reaction.

[0067] During the reaction, the flow rate of the mixed salt solution is controlled to be 3≤a1<5 L / h, the flow rate of the precipitant solution is controlled to be 0.8-1.8 L / h, the pH of the reaction system is the same as the pH of the reaction bottom liquid, and the flow rate of the complexing agent solution is controlled to make the ammonia value of the reaction system be 0.1-5 g / L.

[0068] Finally, when the D50 of the solid particles in the reaction system grows to D0, the nucleation stage is ended, at this time, the addition of the complexing agent solution is stopped. D0 is not higher than 65% of the target particle size D1 of the precursor.

[0069] Step 3, the mixed salt solution and the precipitant solution are continuously fed into the reactor to perform crystal growth process, and after the D50 of the solid particles reaches D1, the feeding is stopped and the solid product is collected, and the solid content in the reactor is controlled to be 300-500 g / L.

[0070] Subsequently, the crystal growth stage is performed under the condition of no complexing agent solution, and the solid content in the reactor is increased, which is beneficial to prolong the growth time of the primary particles and make the stacking of the primary particles more regular and compact.

[0071] Further, during the crystal growth stage, the flow rate of the mixed salt solution is increased to promote the growth of the particles, specifically, the flow rate of the mixed salt solution is controlled to be 5≤a2<7 L / h, and the flow rate of the precipitant solution is controlled to be 1.5-3.0 L / h, so that the pH of the reaction system is higher than that in the nucleation reaction stage.

[0072] The preparation of the precursor is performed by the batch method, that is, the reaction system is continuously concentrated by the concentration machine during the reaction, but it is necessary to ensure that the solid content in the reaction system is 200-300 g / L after the nucleation stage is ended and the solid content in the reaction system is 300-500 g / L after the growth stage is ended.

[0073] Step 4, sequentially aging, water washing, centrifuging and drying the solid product to obtain the positive electrode active material precursor.

[0074] When the D50 of the solid particles in the reactor grows to the target particle size, the solid particles are collected, and sequentially aging, water washing, centrifuging and drying are performed on the solid particles according to the conventional technical means in the art to obtain the positive electrode active material precursor.

[0075] The third aspect of the present application provides a positive electrode active material, which is prepared from any of the positive electrode active material precursors described above or the positive electrode active material precursor prepared according to any of the preparation methods described above.

[0076] The positive electrode active material provided by the present application is obtained by mixing the positive electrode active material precursor provided by the first aspect described above and a lithium source and performing calcination treatment.

[0077] 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.

[0078] In the preparation of the positive electrode active material, the molar ratio of the positive electrode precursor to the lithium source and the calcination temperature can be selected as the conventional parameters in the art, and the present application does not make special limitations.

[0079] The fourth aspect of the present application provides a battery comprising any of the positive electrode active materials described above.

[0080] Based on the characteristics of the positive electrode active material provided by the third aspect, the lithium ion battery comprising the positive electrode active material has good rate performance, energy density and cycle performance.

[0081] In a specific embodiment, the lithium ion battery provided by the present application comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer arranged on the surface of the positive electrode current collector, and the positive electrode active layer comprises the positive electrode active material described above.

[0082] In addition to the positive electrode active material, the positive electrode active layer further comprises a conductive agent and a binder. The selection of the conductive agent and the binder is not particularly required and can be selected conventionally in the art. 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 nanotube, single-walled carbon nanotube, multi-armed carbon nanotube and carbon fiber, and the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and polyacrylic acid lithium (PAALi).

[0083] In the preparation process, first, the positive active material, the conductive agent and the binder are mixed in a certain proportion and dispersed in a solvent, generally NMP, to obtain a positive active material layer slurry after uniform stirring; second, the positive active material layer slurry is uniformly coated on the positive current collector, generally an aluminum foil, to form a positive active material layer after drying; and finally, the positive electrode sheet is obtained through sheet pressing and cutting.

[0084] The negative electrode sheet, the separator and the electrolyte are not particularly required and are commonly selected in the art.

[0085] The precursor provided by the application is described in detail below in combination with specific examples.

[0086] Example 1

[0087] The preparation method provided in this example includes the following steps:

[0088] Step 1: a mixed salt solution with a total metal molar concentration of 1.8 mol / L is configured, including a nickel salt, a manganese salt and a reducing agent ascorbic acid, wherein the molar ratio of nickel to manganese is 25:75, and the mass of the reducing agent ascorbic acid is one ten-thousandth of the mass of manganese;

[0089] An 11.0 mol / L sodium hydroxide solution is configured as a precipitating agent, and ammonia water with a certain concentration is configured as a complexing agent.

[0090] Step 2: the temperature of the reaction kettle is adjusted to 55°C, and the stirring speed is 600 rpm; the sodium hydroxide solution and the ammonia water are added to the reaction kettle as the reaction bottom liquid, the pH of the reaction bottom liquid is controlled to be 10.5, and the ammonia value is controlled to be 3 g / L; nitrogen gas is continuously introduced into the bottom of the reaction kettle, and the nitrogen gas opening degree in the nucleation stage is set to 0.6 m 3 / h;

[0091] The mixed salt solution is flowed into the reaction kettle at a flow rate of 4 L / h, the sodium hydroxide solution is flowed in at a certain flow rate to keep the pH in the range of 10.5-10.6, and the flow rate of the ammonia water is controlled to keep the ammonia value at 3 g / L; when the D50 of the solid particles in the reaction kettle grows to 3 μm, the ammonia water is turned off, and the solid content in the reaction kettle is controlled to be 200 g / L;

[0092] Step 3: the temperature of the reaction kettle is kept at 55°C, the stirring speed is kept at 600 rpm, the nitrogen gas opening degree in the growth stage is set to 0.3 m 3 / h; the flow rate of the metal salt solution is adjusted to 6 L / h, the sodium hydroxide solution is flowed in at a certain flow rate to keep the pH in the range of 10.7-10.8, and after 2 hours, the flow rate of the sodium hydroxide solution is reduced to keep the pH at 10.2 during the particle size growth; when the D50 of the solid particles in the reaction kettle reaches the qualified particle size of 4.5 μm, the feeding is stopped, and the solid content in the reaction kettle is controlled to be 420 g / L;

[0093] Step 4, aftertreatment such as aging, water washing, centrifugation, drying, etc. of the slurry to obtain the intermittent ammonia-feeding manganese-rich binary precursor Ni 0.25 Mn 0.75 (OH)2.

[0094] Example 2

[0095] The preparation method provided in this example includes the following steps:

[0096] Step 1, a mixed salt solution with a total metal molar concentration of 1.8 mol / L is configured, including nickel salt, manganese salt and reducing agent ascorbic acid, wherein the molar ratio of nickel to manganese is 25:75, and the mass of the reducing agent ascorbic acid is one ten-thousandth of the mass of manganese element;

[0097] An 11.0 mol / L sodium hydroxide solution is configured as a precipitant, and ammonia water of a certain concentration is configured as a complexing agent.

[0098] Step 2, the temperature of the reaction kettle is adjusted to 55°C, and the stirring speed is 600 rpm; the sodium hydroxide solution and ammonia water are added into the reaction kettle as the reaction bottom liquid, and the pH of the reaction bottom liquid is controlled to be 10.5 and the ammonia value is controlled to be 5 g / L; nitrogen gas is continuously introduced into the bottom of the reaction kettle, and the nitrogen gas opening degree in the nucleation stage is set to 0.6 m 3 / h;

[0099] The mixed salt solution is flowed into the reaction kettle at a flow rate of 3 L / h, the sodium hydroxide solution is flowed in at a certain flow rate to keep the pH in the range of 10.5-10.6, and the flow rate of the ammonia water is controlled to keep the ammonia value at 5 g / L; when the D50 of the solid particles in the reaction kettle grows to 2.5 μm, the ammonia water is turned off, and the solid content in the reaction kettle is controlled to be 300 g / L;

[0100] Step 3, the temperature of the reaction kettle is kept at 55°C, the stirring speed is 550 rpm, the nitrogen gas opening degree in the growth stage is set to 0.3 m 3 / h; the flow rate of the metal salt solution is adjusted to 6 L / h, the sodium hydroxide solution is flowed in at a certain flow rate to keep the pH in the range of 10.7-10.8, and after 2 hours, the flow rate of the sodium hydroxide solution is reduced to keep the pH at 10.2 during particle size growth; when the D50 of the solid particles in the reaction kettle reaches the qualified particle size of 4.5 μm, the feeding is stopped, and the solid content in the reaction kettle is controlled to be 450 g / L;

[0101] Step 4, aftertreatment such as aging, water washing, centrifugation, drying, etc. of the slurry to obtain the intermittent ammonia-feeding manganese-rich binary precursor Ni 0.25 Mn 0.75 (OH)2.

[0102] Example 3

[0103] The preparation method provided in the embodiment comprises the following steps:

[0104] Step 1, a mixed salt solution with a total metal molar concentration of 1.5 mol / L is configured, including nickel salt, manganese salt and reducing agent ascorbic acid, wherein the molar ratio of nickel to manganese is 25:75, and the mass of the reducing agent ascorbic acid is one ten-thousandth of the mass of manganese element;

[0105] An 11.0 mol / L sodium hydroxide solution is configured as a precipitant, and ammonia water with a certain concentration is configured as a complexing agent.

[0106] Step 2, the temperature of the reaction kettle is adjusted to 50℃, and the stirring speed is 600 rpm; the sodium hydroxide solution and ammonia water are added into the reaction kettle as the reaction bottom liquid, the pH of the reaction bottom liquid is controlled to be 10.6, and the ammonia value is controlled to be 1 g / L; nitrogen gas is continuously introduced into the bottom of the reaction kettle, and the opening degree of the nitrogen gas in the nucleation stage is set to be 0.6 m 3 / h;

[0107] The mixed salt solution is flowed into the reaction kettle at a flow rate of 4 L / h, the sodium hydroxide solution is flowed into the reaction kettle at a certain flow rate to keep the pH in the range of 10.6-10.7, and the flow rate of the ammonia water is controlled to keep the ammonia value at 1 g / L; when the D50 of the solid particles in the reaction kettle grows to 2.5 μm, the ammonia water is stopped, and the solid content in the reaction kettle is controlled to be 300 g / L;

[0108] Step 3, the temperature of the reaction kettle is kept at 50℃, the stirring speed is kept at 550 rpm, the opening degree of the nitrogen gas in the growth stage is set to be 0.3 m 3 / h; the flow rate of the metal salt solution is adjusted to be 6 L / h, the sodium hydroxide solution is flowed into the reaction kettle at a certain flow rate to keep the pH in the range of 10.7-10.8, and after 4 hours, the flow rate of the sodium hydroxide solution is reduced to keep the pH at 10.3 during the particle size growth; when the D50 of the solid particles in the reaction kettle reaches the qualified particle size of 4.5 μm, the feeding is stopped, and the solid content in the reaction kettle is controlled to be 430 g / L;

[0109] Step 4, after the slurry is subjected to aging, water washing, centrifugation, drying and other post-processing, the intermittent ammonia-rich manganese binary precursor Ni 0.25 Mn 0.75 (OH)2 is obtained.

[0110] Comparative Example 1

[0111] The preparation method provided in the comparative example comprises the following steps:

[0112] Step 1, a mixed salt solution with a total metal molar concentration of 1.8 mol / L is configured, including nickel salt, manganese salt and reducing agent ascorbic acid, wherein the molar ratio of nickel to manganese is 25:75, and the mass of the reducing agent ascorbic acid is one ten-thousandth of the mass of manganese element;

[0113] 11.0 mol / L of sodium hydroxide solution was configured as a precipitant solution.

[0114] Step 2, adjust the temperature of the reaction kettle to 55°C, and the stirring speed to 600 rpm; add sodium hydroxide solution into the reaction kettle as the reaction bottom solution, and control the pH of the reaction bottom solution to be 10.5; continuously introduce nitrogen into the bottom of the reaction kettle, and set the opening degree of nitrogen during the nucleation stage to be 0.6 m 3 / h;

[0115] Flow the mixed salt solution into the reaction kettle at a flow rate of 4 L / h, and flow the sodium hydroxide solution at a certain flow rate to keep the pH in the range of 10.5-10.6; when the D50 of the solid particles in the reaction kettle grows to 2.5 μm, control the solid content in the reaction kettle to be 300 g / L;

[0116] Step 3, keep the temperature of the reaction kettle at 55°C, and the stirring speed at 600 rpm, and set the opening degree of nitrogen during the growth stage to be 0.3 m 3 / h; adjust the flow rate of the metal salt solution to be 6 L / h, and flow the sodium hydroxide solution at a certain flow rate to keep the pH in the range of 10.7-10.8, and after keeping for 4 hours, reduce the flow rate of the sodium hydroxide solution to ensure that the pH during the particle size growth is 10.2; after the D50 of the solid particles in the reaction kettle reaches the qualified particle size of 4.5 μm, stop feeding;

[0117] Step 4, after the slurry is treated by aging, water washing, centrifugation, drying and other post-processing, the intermittent ammonia feeding rich-manganese binary precursor Ni 0.25 Mn 0.75 (OH)2 is obtained.

[0118] Comparative Example 2

[0119] The preparation method provided by the present comparative example comprises the following steps:

[0120] Step 1, configure a mixed salt solution with a total metal molar concentration of 1.8 mol / L, including nickel salt, manganese salt and reducing agent ascorbic acid, wherein the molar ratio of nickel to manganese is 25:75, and the mass of the reducing agent ascorbic acid is one ten-thousandth of the mass of manganese element;

[0121] 11.0 mol / L of sodium hydroxide solution was configured as a precipitant, and ammonia water with a certain concentration was configured as a complexing agent.

[0122] Step 2, adjust the temperature of the reaction kettle to 55°C, and the stirring speed to 600 rpm; add sodium hydroxide solution and ammonia water into the reaction kettle as the reaction bottom solution, and control the pH of the reaction bottom solution to be 10.5, and the ammonia value to be 3 g / L; continuously introduce nitrogen into the bottom of the reaction kettle, and set the opening degree of nitrogen during the nucleation stage to be 0.6 m 3 / h;

[0123] The mixed salt solution was flowed into the reactor at a flow rate of 4 L / h, the sodium hydroxide solution was flowed in at a flow rate to keep the pH in the range of 10.5-10.6, and the ammonia water flow was controlled to keep the ammonia value at 3 g / L; when the D50 of the solid particles in the reactor grew to 2.5 μm, the solid content in the reactor was controlled to be 300 g / L;

[0124] Step 3, the temperature of the reactor was kept at 55°C, the stirring speed was 600 rpm, the nitrogen opening degree of the growth stage was set to 0.3 m 3 / h; the flow rate of the metal salt solution was adjusted to 6 L / h, the sodium hydroxide solution was flowed in at a flow rate to keep the pH in the range of 10.7-10.8, and after 4 hours, the flow rate of the sodium hydroxide solution was reduced to keep the pH at 10.2 during particle size growth; the ammonia water was continuously flowed in and the ammonia value was kept at 3 g / L; after the D50 of the solid particles in the reactor reached the qualified particle size of 4.5 μm, the feeding was stopped;

[0125] Step 4, after the slurry was aged, washed, centrifuged, and dried, the intermittent ammonia feeding rich manganese binary precursor Ni 0.25 Mn 0.75 (OH)2 was obtained.

[0126] Comparative Example 3

[0127] The preparation method provided in the present comparative example comprises the following steps:

[0128] Step 1, a mixed salt solution with a total metal molar concentration of 1.8 mol / L was prepared, including nickel salt, manganese salt and reducing agent ascorbic acid, wherein the molar ratio of nickel to manganese was 25:75, and the mass of the reducing agent ascorbic acid was one ten-thousandth of the mass of manganese;

[0129] An 11.0 mol / L sodium hydroxide solution was prepared as a precipitant, and ammonia water with a certain concentration was prepared as a complexing agent.

[0130] Step 2, the temperature of the reactor was adjusted to 55°C, and the stirring speed was 600 rpm; the sodium hydroxide solution and ammonia water were added to the reactor as the reaction bottom liquid, the pH of the reaction bottom liquid was controlled to be 10.5, and the ammonia value was 3 g / L; nitrogen was continuously flowed into the bottom of the reactor, and the nitrogen opening degree of the nucleation stage was set to 0.6 m 3 / h;

[0131] The mixed salt solution was flowed into the reactor at a flow rate of 4 L / h, the sodium hydroxide solution was flowed in at a flow rate to keep the pH in the range of 10.5-10.6, and the ammonia water flow was controlled to keep the ammonia value at 3 g / L; when the D50 of the solid particles in the reactor grew to 2.5 μm, the solid content in the reactor was controlled to be 300 g / L;

[0132] Step 3, keep the temperature of the reactor at 55℃, the stirring speed at 600rpm, and set the nitrogen opening degree of the growth stage at 0.3m 3 / h; adjust the flow rate of the metal salt solution to 6L / h, and flow the sodium hydroxide solution at a certain flow rate to keep the pH in the range of 10.7-10.8, and after keeping for 4 hours, reduce the flow rate of the sodium hydroxide solution to ensure that the pH during the particle size growth is 10.2; after the D50 of the solid particles in the reactor reaches the qualified particle size of 4.5μm, stop feeding;

[0133] In steps 2-3, the solid content is not changed, and the solid content in the reactor is controlled to remain at 150g / L;

[0134] Step 4, after aging, washing, centrifugation, drying and other post-processing of the slurry, the precursor Ni 0.25 Mn 0.75 (OH)2is obtained.

[0135] The precursors provided in Examples 1-3 and Comparative Examples 1-3 and the cross sections are observed by scanning electron microscopy, and the porosity, tap density, specific surface area and particle size distribution of the precursors are tested by conventional technical means in the art, the electron microscopy observation results are shown in Figures 2-7 , and the test data are shown in Table 1:

[0136] Table 1

[0137]

[0138] The precursors provided in Examples 1-3 and Comparative Examples 1-3 are tested by XRD, and the interplanar spacing is calculated according to the XRD test results, the XRD test results of the positive electrode active material prepared in Example 1 are shown in Figure 8 , and the interplanar spacing and the calculation results of Examples 2-3 and Comparative Examples 1-3 are shown in Table 2.

[0139] Table 2

[0140]

[0141]

[0142] According to the data provided in Figures 2-7 and Tables 1-2, compared with the ammonia-free process provided in Comparative Example 1, the precursors prepared by the intermittent ammonia addition process used in Examples 1-3 have higher regularity and dispersity of the secondary particles, and the primary particles have higher whisker thickness, which is beneficial to improve the stability of the positive electrode active material during the cycle process, and thus improve the cycle capacity retention rate of the battery.

[0143] Compared with the continuous ammonia adding process provided by Comparative Example 2, the primary particle stack is denser, which is not conducive to the increase of the specific surface area of the precursor, while the intermittent ammonia adding process provided by Examples 1-3 can help to increase the tap density and the specific surface area of the precursor.

[0144] Compared with Comparative Example 3, the intermittent ammonia adding process provided by Examples 1-3 can help to increase the tap density and the specific surface area of the precursor.

[0145] The positive electrode active materials were prepared by mixing and calcining the precursors provided by Examples 1-3 and Comparative Examples 1-3 with a lithium source, and the batteries were prepared using the positive electrode active materials, and the capacity, the first discharge efficiency and the cycle capacity retention rate of the batteries were tested, and the test results are shown in Table 3.

[0146] Table 3

[0147] 0.33C capacity (mAh / g) 0.1C first discharge efficiency (%) Capacity retention after 100 cycles (%) Example 1 135.48 92.12 94.25 Example 2 134.82 92.09 94.07 Example 3 135.26 91.97 93.88 Comparative Example 1 133.07 90.72 90.31 Comparative Example 2 132.63 89.62 89.31 Comparative Example 3 133.52 90.45 91.51

[0148] According to Table 3, compared with Comparative Examples 1-3, the batteries prepared using the precursors provided by Examples 1-3 have higher capacity, first discharge efficiency and cycle capacity retention rate.

[0149] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode active material precursor, characterized in that, Its chemical composition is Ni x Mn y (OH)2, 0.2≤x<0.3, 0.7≤y≤0.8; The positive electrode active material precursor includes secondary particles formed by stacking primary particles, wherein the aspect ratio of the primary particles is 5 to 8 and the whisker thickness is 200 to 400 nm. The secondary particles have a D50 of R1, and secondary particles with a particle size of R2 are selected as test particles, 40%. R1≤R2≤60% R1; The test particle includes a first region, where the distance from any position in the first region to the center of the particle is r1, where 0 ≤ r1 ≤ 30%. R2, the porosity of the first region is not less than 50% of the porosity of the test particles, and the porosity of the test particles is 15~25%.

2. The positive electrode active material precursor according to claim 1, characterized in that, The tap density of the positive electrode active material precursor is not less than 1.2 g / cm³. 3 Specific surface area not less than 20 μm 2 / g.

3. The positive electrode active material precursor according to claim 1, characterized in that, The D50 of the positive electrode active material precursor is 4~5μm, and (D90-D10) / D50≤0.

9.

4. The positive electrode active material precursor according to claim 1, characterized in that, The positive electrode active material precursor has a 001 crystal plane and a 110 crystal plane, and the ratio of the interplanar spacing of the 001 crystal plane to the interplanar spacing of the 110 crystal plane, D001 / D110, is 20~30.

5. The method for preparing the 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 precipitant solution, and a complexing agent solution, wherein the mixed salt solution includes nickel salt, manganese salt, and a reducing agent; Step 2: Prepare a reaction base solution at the bottom of the reactor, and control the pH of the reaction base solution to meet the requirements of 10.5≤pH<11.0 and the ammonia value to be 0.1~5g / L; Under a protective gas atmosphere, a mixed salt solution, a precipitant solution, and a complexing agent solution are added to the reactor to initiate a nucleation reaction. When the D50 of the solid particles in the reactor reaches D0, the addition of the complexing agent is stopped, and the solid content in the reactor is controlled at 200-300 g / L; wherein D0 ≤ 65%. D1; Step 3: Continue to pass the mixed salt solution and precipitant solution into the reactor to carry out the crystal growth process. After the D50 of the solid particles reaches the target particle size D1, stop feeding and collect the solid product, and control the solid content in the reactor to be 300~500g / L. Step 4: The solid product is subjected to aging, washing, centrifugation and drying in sequence to obtain the positive electrode active material precursor.

6. The preparation method according to claim 5, characterized in that, In step 2, the flow rate of the mixed salt solution is controlled to be 3 ≤ a1 < 5 L / h; the flow rate of the precipitant solution is controlled to be 0.8~1.8 L / h, so that the pH of the reaction system is the same as the pH of the reaction substrate; the flow rate of the complexing agent solution is controlled, so that the ammonia value of the reaction system is 0.1~5 g / L.

7. The preparation method according to claim 5, characterized in that, The flow rate of the mixed salt solution is controlled at 5 ≤ a2 ≤ 7 L / h, and the flow rate of the precipitant solution is controlled at 1.5~3.0 L / h, so that the pH of the reaction system is higher than the pH of the nucleation reaction stage. After maintaining this for 2~4 hours, the pH of the reaction system is lowered to carry out the crystal growth process.

8. A positive electrode active material, characterized in that, The positive electrode active material 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 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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