Preparation method of nickel-rich hydroxide precursor material and preparation method of nickel-rich oxide positive electrode material

Abstract

The invention provides a preparation method of a nickel-rich hydroxide precursor material and a nickel-rich oxide positive electrode material, and the preparation method comprises the following steps: (1) preparing an aqueous solution A in which a metal ion raw material is dissolved, an aqueous solution B with a manganese source, an aqueous solution C in which a precipitator is dissolved, and an aqueous solution D in which a chelating agent is dissolved, pouring the aqueous solution A, the aqueous solution C and the aqueous solution D into a continuous Taylor flow reactor, and carrying out a first coprecipitation reaction; (2) pouring the aqueous solution B into a continuous Taylor flow reactor for secondary coprecipitation reaction; and (3) washing the precipitate after the secondary coprecipitation reaction, and drying the precipitate in a drying oven to obtain the nickel-rich hydroxide precursor material. The nickel-rich hydroxide precursor prepared by the method can reduce the impedance of lithium ions during transmission and increase the migration path of the lithium ions, and the nickel-rich oxide positive electrode material prepared from the nickel-rich hydroxide precursor can improve the electrochemical performance and mechanical stability of the lithium ion battery, such as charge-discharge rate, long-term cycle life and the like.

Description

Technical Field

[0001] The present invention provides a method for preparing a nickel-rich hydroxide precursor material and a nickel-rich oxide cathode material, particularly regarding a method for preparing a nickel-rich hydroxide precursor material and a nickel-rich oxide cathode material with an elemental concentration gradient distribution by means of a continuous Taylor flow reactor through coprecipitation reaction and ball milling mixing. Background Art

[0002] With the rapid increase in consumers' energy demand, such as in hybrid electric vehicles, smart grids, and power stations, lithium-ion batteries (LIBs) are being widely studied as a promising energy storage technology and seem to be one of the best energy storage solutions to address energy problems. Although lithium-ion batteries are the preferred battery type for most consumer electronic devices, their available oxide cathodes may have problems such as poor mechanical properties of the materials, the need to have a high specific capacity, and a long cycle life. Therefore, the research on next-generation oxide cathode materials is still ongoing, mainly focusing on improving the mechanical strength of the materials, the cycle life of the battery, the specific capacity, and the safety during the charge and discharge process of lithium-ion batteries.

[0003] To meet the requirements of technological development, nickel-rich layered oxide cathodes are promising cathode materials with a theoretical specific capacity of up to about 275 mAh / g and a high working voltage of 2.8 to 4.3 V. Compared with the currently widely used lithium cobalt oxide cathode material (LiCoO2), these nickel-rich oxide cathodes are attractive due to their lower toxicity and lower cost. However, when the nickel concentration is too high, it may accelerate the capacity decay of the battery, especially at high temperatures and high working voltages, causing structural and chemical instabilities and posing serious safety risks. When the nickel-rich oxide cathode is charged to a high voltage, unstable Ni 4+ ions are generated on the surface, which may then lead to the formation of NiO-type impurity phases and the release of oxygen-containing substances. These highly active Ni 4+ ions may also accelerate the decomposition of the electrolyte, resulting in the depletion of the electrolyte and the loss of the battery's cycle performance. In addition, electrochemically inert NiO-type impurity phases will increase the impedance of lithium-ion diffusion and reduce the rate capability of charge and discharge. At the same time, the O2 released by the oxide will react with the organic electrolyte, leading to the problem of battery thermal runaway.

[0004] Cation mixing, that is, Li + ions (ionic radius about ) and Ni 2+ ions (ionic radius about )The process of exchanging positions in their respective layers is the main cause of the capacitance decay and structural phase transformation of the nickel-rich oxide cathode. This kind of ion exchange is achieved through similar ionic radii. In addition, excessive side reactions between the nickel-rich oxide and air or moisture may produce unnecessary surface residues (such as LiOH and Li2CO3), and these residues will interact with the electrolyte to generate an insulating surface layer, resulting in overvoltage during the charging of lithium-ion batteries. For the reasons mentioned above, traditional nickel-rich oxides are still challenging in commercial battery applications such as electric vehicles and smart grids

[0005] To improve the structural stability of the nickel-rich oxide cathode and the long-term cycle life of the battery, the strategies include: changing the composition, adjusting the preparation conditions and surface modification, etc. Especially the concentration gradient structure, also known as the core / shell structure, in which the electrochemically active transition metal (TM) is mainly restricted to the core part of the active material particles, and the inactive transition metal serves as the shell, thereby enhancing the structural stability of the nickel-rich oxide cathode and the cycle performance of the lithium-ion battery. In the prior art, Li[Ni 0.8 Co 0.2 x [Ni 0.2 Mn 0.8 1-x (1>x>0.5) oxides are used as the outer layer to prove that the side reactions on the surface can be minimized. Since the manganese element in these materials generally has a tetravalent oxidation state on average, it has excellent structural stability and maintains its hexagonal shape during cycling, even at higher voltages Prior art documents Non-patent literature

[0006] [Non-patent literature 1] J.Y. Liao, A. Manthiram, Surface-modified concentration-gradient Ni-rich layered oxide cathodes for high-energy lithium-ion batteries, Journal of Power Sources 282 (2015) 429–436 Summary of the invention [Technical problems to be solved by the invention]

[0007] However, there are still no related inventions for nickel-rich oxide cathode materials with long-term cycle stability and capable of effectively suppressing the generation of side reactions [Technical means]

[0008] ​​Accordingly, the present invention provides a method for preparing a nickel-rich hydroxide precursor material, and further provides a method for synthesizing a quaternary oxide cathode material with an element concentration gradient distribution through the nickel-rich hydroxide precursor material; in the present invention, the definition of nickel-rich is that the molar ratio of nickel content exceeds 50% of the overall compound. The nickel-rich hydroxide precursor material of the present invention is nickel cobalt manganese hydroxide and has a homogeneous structure; that is, different from the prior art which synthesizes a core-shell structure with different compositions for the core and the shell, such as a binary material for the core and a ternary material for the shell, etc., the element compositions of the inner layer and the outer layer of the nickel-rich hydroxide precursor material of the present invention are the same, and each layer has nickel, cobalt, and manganese, only the concentration ratios of each layer are different.

[0009] The nickel-rich hydroxide precursor prepared by the preparation method of the present invention has a homogeneous element distribution structure with a nickel-rich inner layer and a manganese-rich outer layer, which can reduce the interfacial impedance during lithium ion transmission and increase its lithium ion migration path, thereby improving the electrochemical performance and cycle stability of the prepared electrode; the nickel-rich oxide cathode material prepared by the preparation method of the present invention also has a homogeneous structure with an element concentration gradient distribution and has aluminum element as a structure stabilizing element, which can improve electrochemical performances such as the charge and discharge rate of the lithium ion battery and the mechanical strength of the electrode material.

[0010] The method for preparing the nickel-rich hydroxide precursor material of the present invention includes pouring an aqueous solution A containing nickel ions and cobalt ions, a precipitant (aqueous solution C), and a chelating agent (aqueous solution D) into a continuous Taylor flow reactor (TFR) for the first coprecipitation reaction, and then adding an aqueous solution B containing manganese ions for the second coprecipitation reaction. After washing and drying the precipitate, a nickel cobalt manganese hydroxide precursor is obtained.

[0011] The method for preparing the nickel-rich oxide cathode material of the present invention includes mixing an ethanol solution containing aluminum ions with the aforementioned nickel cobalt manganese hydroxide precursor and drying, grinding and mixing the dried mixture with a lithium source in a ball mill, and then performing a three-stage calcination heat treatment to obtain a lithium nickel cobalt manganese aluminum oxide cathode material.

[0012] Specifically, the present invention provides a method for preparing a nickel-rich hydroxide precursor material, the nickel-rich hydroxide precursor material is nickel cobalt manganese hydroxide with a homogeneous structure having an element concentration gradient distribution, and the preparation method includes: (1) Preparing an aqueous solution A in which metal ion raw materials are dissolved; Preparing an aqueous solution B in which a manganese source is dissolved; Preparing an aqueous solution C in which a precipitant is dissolved; Preparing an aqueous solution D in which a chelating agent is dissolved; Pour the aqueous solution A, the aqueous solution C, and the aqueous solution D into a continuous Taylor flow reactor, and carry out the first co-precipitation reaction for 2 to 7 hours; Among them, the metal ion raw material is a nickel source and a cobalt source; Among them, the nickel source is at least one selected from the group consisting of nickel sulfate, nickel oxalate, nickel acetate, nickel nitrate, nickel chloride, and nickel hydroxide; The cobalt source is at least one selected from the group consisting of cobalt sulfate, cobalt oxalate, cobalt carbonate, cobalt acetate, cobalt nitrate, cobalt chloride, and cobalt hydroxide; The manganese source is at least one selected from the group consisting of manganese sulfate, manganese oxalate, manganese carbonate, manganese citrate, manganese acetate, manganese nitrate, manganese phosphate, electrolytic manganese dioxide, and manganese oxide; (2) Pour the aqueous solution B into the continuous Taylor flow reactor to carry out the second co-precipitation reaction for 5 to 70 hours; among them, The reaction temperature of the second co-precipitation reaction is 30°C to 80°C, the pH value of the reaction environment is 9.5 To 12.5, the rotation speed of the inner cylinder of the continuous Taylor flow reactor is 200 rpm to 1500 rpm; (3) Wash the precipitate after the second co-precipitation reaction and then place it in an oven for drying to obtain the Nickel-rich hydroxide precursor material.

[0013] Furthermore, the concentration of the aqueous solution A is 1.6 M to 1.92 M.

[0014] Furthermore, the concentration of the aqueous solution B is 0.08 M to 0.4 M.

[0015] Furthermore, the concentration of the aqueous solution C is 2.0 M to 6.0 M, and the weight molar concentration ratio of the aqueous solution A to the aqueous solution C is 1:1 to 1:5.

[0016] Furthermore, the concentration of the aqueous solution D is 2.5 M to 9.0 M, and the weight molar concentration ratio of the aqueous solution A to the aqueous solution D is 1:1 to 1:5.

[0017] Furthermore, the drying temperature of the oven is 60°C to 120°C, and the drying time is 6 to 24 hours.

[0018] Furthermore, the feeding rate of the aqueous solution A and the aqueous solution B is 1.0 to 3.0 ml / min.

[0019] The present invention also provides a preparation method of a nickel-rich oxide cathode material, which uses the preparation method of the aforementioned nickel-rich hydroxide precursor material, and the nickel-rich oxide cathode material has a homogeneous structure with an element concentration gradient distribution. The preparation method includes: (a) Disperse the aluminum source in ethanol, then add the nickel-rich hydroxide precursor material and mix them. Obtain a mixture, and heat the mixture at 80 °C until completely dry to obtain mixture a. Among them, the aluminum source is at least one selected from the group consisting of aluminum hydroxide, aluminum oxalate, aluminum carbonate, aluminum sulfate, aluminum acetate, aluminum nitrate, and aluminum phosphate. (b) Grind and mix the mixture a in step (a) with the lithium source at a molar ratio of 1:1.01 to 1:1.25. After that, obtain mixture b. The lithium source is at least one selected from the group consisting of lithium hydroxide, lithium nitrate, lithium acetate, lithium chloride, lithium hydrogen phosphate, lithium phosphate, and lithium carbonate. (c) Perform three-stage calcination heat treatment on the mixture b in step (b) to obtain the nickel-rich oxide cathode material.

[0020] Furthermore, the conditions for the grinding are set such that the rotation speed of the ball mill is 50 to 200 rpm and the grinding time is 2 to 10 hours.

[0021] Furthermore, the temperature and time of the three-stage calcination heat treatment are respectively: the temperature of the first stage is 100 °C to 200 °C and the time is 1 to 3 hours, the temperature of the second stage is 500 °C to 600 °C and the time is 4 to 8 hours, the temperature of the third stage is 700 °C to 800 °C and the time is 10 to 40 hours, and the heating rate of the three-stage calcination heat treatment is 0.1 to 20 °C / min. [Inventive Effect]

[0022] The nickel-rich oxide cathode material with a homogeneous structure having an element concentration gradient distribution prepared by the method of the present invention has an element concentration gradient distribution with a nickel-rich inner layer and a manganese-rich outer layer, as well as a surface layer containing aluminum. This particle structure helps the cathode material to maintain its mechanical stability as an electrode material at high charge and discharge rates, and can also effectively inhibit the side reactions between the cathode material and the electrolyte.

[0023] Accordingly, compared with the oxide cathode material with a general uniform concentration, the lithium-ion battery composed of the nickel-rich oxide cathode material prepared by using a continuous Taylor flow reactor has more excellent electrochemical performance, such as high charge and discharge rates, and can still maintain a high specific capacity retention rate under long-term charge and discharge cycles.

[0024] Moreover, in the method of the present invention, the nickel-rich hydroxide precursor prepared by co-precipitation reaction using a continuous Taylor flow reactor has uniform, concentrated particles with a relatively large particle size, and has a needle-like primary particle morphology, so that the secondary particles formed by their orderly arrangement have a structure that can resist the tensile / compressive stress generated during long-term charge and discharge, prevent the problem of micro-crack generation, and can improve the preparation efficiency in large-scale production.

[0025] In summary, the present invention provides a method for preparing a nickel-rich hydroxide precursor and a nickel-rich oxide cathode material with a homogeneous structure having an elemental concentration gradient distribution, which is suitable for large-scale production. The nickel-rich hydroxide precursor has a uniform and stress-resistant structure, and the nickel-rich oxide cathode material has good charge and discharge efficiency and long-term cycle stability, which can greatly improve the electrochemical performance of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of synthesizing a nickel-rich hydroxide precursor with a concentration gradient using a continuous Taylor flow reactor. Figure 2 Flow chart of (a) the preparation method of the nickel-rich hydroxide precursor and (b) the preparation method of the nickel-rich oxide according to an embodiment of the present invention. Figure 3 Comparison of XRD patterns of the element concentration gradient CG-NCM precursor and the uniform concentration UC-NCMA precursor synthesized using TFR. Figure 4 Comparison of particle size distributions of the element concentration gradient CG-NCM precursor and the uniform concentration UC-NCMA precursor prepared using TFR. Figure 5 (a1)-(a4) SEM images of the morphology of the uniform concentration UC-NCMA precursor prepared using TFR at different magnifications; (b1)-(b4) are SEM images of the morphology of the element concentration gradient CG-NCM precursor prepared using TFR at different magnifications. Figure 6 (a) High-magnification SEM image of the CG-NCM precursor, (b) low-magnification SEM image of the CG-NCM precursor, (c) cross-sectional view and EDS line scan spectrum of the CG-NCM precursor cut by FIB, (d) XRD pattern of the sample of the synthesized nickel-rich hydroxide precursor with a concentration gradient CG-NCM. Figure 7 ​​​​​​​High-magnification SEM images of (a) uniformly concentrated UC-NCMA particle samples, (b) concentration gradient CG-NCMA particle samples, (c) low-magnification SEM images of uniformly concentrated UC-NCMA particle samples, (d) low-magnification SEM images of concentration gradient CG-NCMA particle samples, (e) EDS Mapping elemental distribution maps of UC-NCMA oxides, and (f) EDS Mapping elemental distribution maps of CG-NCMA oxides. Figure 8 (a) Comparison of XRD patterns of UC-NCMA and CG-NCMA oxide powder samples, (b) XRD pattern of the UC-NCMA oxide powder sample refined by the Rietveld method, and (c) XRD pattern of the CG-NCMA oxide powder sample refined by the Rietveld method. Figure 9 (a) TEM micrographs, selected area electron diffraction (SAED) patterns, and EDS Mapping elemental distribution maps of UC-NCMA and (b) CG-NCMA particle samples. Figure 10 XPS spectra of the elemental compositions of UC-NCMA powder samples and CG-NCMA powder samples: (a) Ni 2p, (b) O 1s, (c) Co 2p, (d) Mn 2p, (e) Li 1s, and (f) C 1s. Figure 11 Comparison of the electrochemical performance of two lithium-ion batteries, UC-NCMA / / Li and CG-NCMA / / Li: (a) First charge / discharge curves at a rate of 0.1C and a temperature of 25°C, (b) Comparison of the electrical performance of the batteries at low / high rates from a rate of 0.2C to 10C, (c) Comparison of the electrical performance of the batteries after 100 cycles at a rate of 1C and a temperature of 25°C, (d) Histogram of the capacitance retention rate of the batteries at different rates (0.2C to 10C), and (e) Comparison of the electrical performance of the batteries after 200 cycles at a rate of 1C and a temperature of 25°C. Figure 12 (a) Comparison of the discharge curves of the UC-NCMA / / Li battery's rate capabilities (0.2C to 10C) and (b) comparison of the discharge curves of the CG-NCMA / / Li battery's rate capabilities (0.2C to 10C). Figure 13 ​​​​​​Comparison of the electrochemical properties of NCMA / / Li batteries: (a) UC-NCMA oxide cathode and (b) CG-NCMA oxide cathode, differential capacitance and voltage curves of the lithium-ion batteries composed thereof at a rate of 0.1C for 3 cycles (voltage range: 2.8 to 4.3V), (c) UC-NCMA oxide cathode and (d) CG-NCMA oxide cathode, discharge curves of the lithium-ion batteries composed thereof at a rate of 1C / 1C for 100 cycles. Figure 14 (a) Cyclic voltammograms of UC-NCMA / / Li battery and (b) CG-NCMA / / Li battery (at a rate of 0.1C / 0.1C, 3 cycles and voltage range of 2.8 to 4.3V); Electrochemical impedance change diagrams of UC-NCMA / / Li battery and CG-NCMA / / Li battery at a charge / discharge rate of 1C / 1C, (c) before cycling and (d) after 100 cycles. Figure 15 (a) In-situ XRD patterns of the charge / discharge cycles of UC-NCMA cathode material, (b) In-situ XRD patterns of the charge / discharge cycles of CG-NCMA cathode material. Figure 16 During a single charge / discharge cycle, contour maps of the main characteristic peaks in the in-situ XRD patterns of (a) UC-NCMA cathode material and (b) CG-NCMA cathode material in the range of 10 - 80° correspond to voltage vs. time plots of the charge / discharge process, and changes in lattice parameters calculated from the in-situ XRD patterns during the charge / discharge cycle, where (c) lattice parameter a-axis of the (101) crystal plane, (d) lattice parameter c-axis of the (003) crystal plane, and (e) volume change of the lattice. Figure 17 (a) Comparison of XRD patterns of the batteries composed of UC-NCMA cathode material and CG-NCMA cathode material after 100 cycles at a charge / discharge rate of 1C / 1C, (b) Comparison of the displacement of the (003) characteristic peak of the electrodes of the batteries composed of UC-NCMA cathode material and CG-NCMA cathode material after cycling, (c) SEM micrographs comparison of the electrodes of UC-NCMA cathode material and (d) CG-NCMA cathode material after 100 cycles at a charge / discharge rate of 1C / 1C. Figure 18 ​​​​​Comparison of cross-sectional SEM images of active material particles of the electrode after 100 cycles under the charge-discharge rate of 1C / 1C: (a), (b) active material particles of the UC-NCMA oxide cathode, and (c), (d) active material particles of the CG-NCMA oxide cathode. SEM microscopic images of the cathode after 100 cycles under the charge-discharge rate of 1C / 1C, and (e) TEM microscopic images of the active material particles of the UC-NCMA cathode and (f) active material particles of the CG-NCMA cathode, and selected area electron diffraction patterns corresponding to the marked regions I and II. Detailed implementation mode

[0027] The preparation methods of the nickel-rich hydroxide precursor material and the nickel-rich oxide cathode material of the present invention are described below by way of exemplary embodiments. It should be noted that the following exemplary embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. [Preparation method of nickel-rich hydroxide precursor material]

[0028] First, a nickel-rich hydroxide precursor with an element concentration gradient is synthesized by a co-precipitation reaction using a continuous Taylor flow reactor (TFR, 1L, Laminar Co., Korea), and the schematic diagram is as Figure 1 shown.

[0029] As Figure 2 (a) shows, the preparation method steps of the nickel-rich hydroxide precursor of the present invention are as follows: S11: Uniformly mix metal ion raw materials in deionized water to form a metal ion mixed solution (aqueous solution A); S12: Dissolve the manganese source in deionized water to form an aqueous solution B; S13: Pour aqueous solution A, a precipitant aqueous solution (aqueous solution C), and a chelating agent aqueous solution (aqueous solution D) into a continuous Taylor flow reactor filled with deionized water for the first co-precipitation reaction; S14: Pour aqueous solution B into the continuous Taylor flow reactor for the second co-precipitation reaction; S15: Collect the precipitate of the second co-precipitation reaction, wash it with ethanol and deionized water to remove residual ions, and then place it in an oven for drying to obtain a nickel-rich hydroxide precursor.

[0030] Specifically, the preparation methods of each solution are as follows.

[0031] Preparation of the mixed metal ion solution (aqueous solution A): Dissolve and uniformly mix the metal ion raw materials in deionized water to prepare aqueous solution A of the mixed metal ion solution. In one embodiment, the metal ion raw materials are a nickel source and a cobalt source. In one embodiment, the nickel source as the metal ion raw material is at least one selected from the group consisting of nickel sulfate, nickel oxalate, nickel acetate, nickel nitrate, nickel chloride, and nickel hydroxide, and the cobalt source as the metal ion raw material is at least one selected from the group consisting of cobalt sulfate, cobalt oxalate, cobalt carbonate, cobalt acetate, cobalt nitrate, cobalt chloride, and cobalt hydroxide. In one embodiment, the concentration of aqueous solution A is 1.6 M to 1.92 M, preferably 1.7 M to 1.92 M, more preferably 1.8 M to 1.92 M, and even more preferably 1.92 M.

[0032] Preparation of aqueous solution B: Dissolve the manganese source in deionized water to prepare aqueous solution B. In one embodiment, the manganese source is at least one selected from the group consisting of manganese sulfate, manganese oxalate, manganese carbonate, manganese citrate, manganese acetate, manganese nitrate, manganese phosphate, electrolytic manganese dioxide, and manganese oxides (such as α-MnO2, β-MnO2, γ-MnO 2、 Mn2O3, Mn3O4). In one embodiment, the concentration of aqueous solution B is 0.08 M to 0.4 M, preferably 0.08 M to 0.2 M, more preferably 0.08 M to 0.1 M, and even more preferably 0.08 M.

[0033] Preparation of the precipitant aqueous solution (aqueous solution C): Dissolve and uniformly mix the precipitant in deionized water to prepare the precipitant aqueous solution for the subsequent coprecipitation reaction. In one embodiment, the precipitant is sodium hydroxide. In one embodiment, the concentration of aqueous solution C is 2.0 M to 6.0 M, preferably 2.5 M to 5.0 M, more preferably 3.0 M to 4.5 M, and even more preferably 4 M. In one embodiment, the weight molar concentration ratio of aqueous solution A to aqueous solution C is 1:1 to 1:5, preferably 1:1 to 1:4, more preferably 1:1 to 1:3, and even more preferably 1:2.

[0034] Preparation of the chelating agent aqueous solution (aqueous solution D): Dissolve and uniformly mix the chelating agent in deionized water to prepare the chelating agent aqueous solution for the subsequent coprecipitation reaction. In one embodiment, the chelating agent is ammonia water. In one embodiment, the concentration of aqueous solution D is 2.5 M to 9.0 M, preferably 4.0 M to 9.0 M, more preferably 6.0 M to 8.0 M, and even more preferably 7.2 M. In one embodiment, the weight molar concentration ratio of aqueous solution A to aqueous solution D is 1:1 to 1:5, preferably 1:1 to 1:4, more preferably 1:1 to 1:3, and even more preferably 1:3.

[0035] In one embodiment, before carrying out the coprecipitation reaction, all the aforementioned aqueous solutions are first filtered to remove unnecessary impurities.

[0036] The schematic diagram of preparing nickel-rich hydroxide precursor using TFR is as follows Figure 1 As shown, when the inner cylinder of TFR rotates, aqueous solutions A, C, and D are fed into the front inlet end of the cylindrical chamber of TFR filled with deionized water. After the first co-precipitation reaction, aqueous solution B is then introduced from the inlet end on the upper side of TFR, and the second co-precipitation reaction is carried out through the mixing solution of aqueous solutions A, C, and D in the cylindrical chamber of TFR. In one embodiment, the time of the first co-precipitation reaction is 2 to 7 hours, preferably 3 to 6 hours, more preferably 5 hours. In one embodiment, the time of the second co-precipitation reaction is 5 to 70 hours, preferably 15 to 55 hours, more preferably 20 to 30 hours. In one embodiment, the temperature of the second co-precipitation reaction can be 30°C to 80°C, preferably 45°C to 70°C, more preferably 60°C, where 60°C can make the co-precipitation reaction most complete and produce a spherical secondary particle structure composed of needle-like primary particles to achieve an ideal orderly arrangement and compactness; the environmental pH value can be 9.5 to 12.5, preferably 10.0 to 12.0, more preferably 11.2, and the flow rate of aqueous solution C is controlled to maintain the reaction constant, where the pH value of 11.2 can make the co-precipitation reaction in a steady state and thus achieve the best particle size distribution. In one embodiment, the rotational speed of the inner cylinder of TFR can be 200 rpm to 1500 rpm, preferably 400 rpm to 1000 rpm, more preferably 500 rpm to 800 rpm, and even more preferably 600 rpm, where 600 rpm is most helpful for generating secondary particles with a particle size of about 8 - 12 μm, which is most ideal for the polycrystalline cathode material; the feeding rate is 1.0 ml / min to 3.0 ml / min, preferably 1.5 ml / min to 2.0 ml / min, more preferably 1.703 ml / min, for continuous production.

[0037] It should be further noted here that the present invention uses TFR to prepare the hydroxide precursor. Compared with the reaction kettle (batch reactor) used in the traditional continuous stirred tank reactor (CSTR), preparing with TFR has advantages in the following characteristics:

[0038] Controllability and uniformity: The TFR can achieve various fluid flow patterns by controlling the rotation speed of the inner cylinder of the reactor. In this embodiment, it is the fluid mixing pattern of Taylor flow, which belongs to a micro-scale mixing and can make the co-precipitation reaction environment more conducive to preparing a more uniform nickel-rich hydroxide precursor. In contrast, traditional reactors use the flow pattern of turbulent flow for mixing, which belongs to macro mixing. Therefore, differences and variations in particle size and material composition may occur, especially affecting material uniformity and preparation efficiency in large-scale production applications.

[0039] Scalability: Generally, the preparation of nickel-rich hydroxide precursors can be scaled up from laboratory scale to industrial production scale, that is, the required capacity of the reactor is from 1L to 1000L. Accordingly, due to the continuous operation and scalability characteristics of the TFR, the quality consistency of mass production can be ensured. Traditional reactors are more suitable for small-scale research and development applications and it is difficult to maintain the same reaction conditions and product quality consistency in mass production.

[0040] Reaction time and preparation efficiency: During the preparation of nickel-rich hydroxide precursors, the continuous production and micro-mixing characteristics of the TFR can effectively shorten the material preparation time, thereby improving production efficiency. Traditional reactors, due to their macro-mixing mechanism, require a longer reaction time and thus have lower efficiency in continuous and large-scale production processes.

[0041] It should also be further noted that the reaction parameters such as the environmental reaction temperature, pH value, inner cylinder rotation speed, and feed rate in the TFR have a great impact on the characteristics of the prepared nickel-rich hydroxide precursor. Therefore, the setting and control of the above conditions are very important. (1) Reaction temperature: The temperature in the reaction environment has a significant impact on the shape of nickel-rich hydroxide precursor particles. If the temperature is too low, particle formation will be incomplete. If the temperature is too high, the formed primary particles may be different from the expected shape. (2) Inner cylinder rotation speed: The inner cylinder rotation speed of the TFR can directly affect the particle size of the precursor. Increasing the rotation speed will generate smaller eddies, thereby generating smaller particle nuclei and thus producing a large number of small-sized particles. If the particle size is too small, it is likely to have a negative impact on its electrochemical performance during the subsequent preparation of the cathode material, because too small particle size (particle diameter about <1 - 3 μm) will produce a larger surface area and a higher solid electrolyte interface (SEI) resistance. Conversely, too large particle size (particle diameter about >20 - 30 μm) will cause the lithium ion diffusion rate to slow down due to its longer lithium ion transport path, and the overall electrochemical performance of the cathode material will also decrease accordingly. To make the cathode material have the best electrochemical performance, the ideal particle size of the material prepared by the method of the present invention is 8 - 12 μm. (3) Feed rate and pH value: When the feed rate is too fast or the pH value is too high, a large number of hydroxide particle nuclei will be generated, resulting in incomplete particle formation or loose structure. Such particles are likely to disintegrate and powder during subsequent process treatment. When prepared at too low a feed rate, the residence time of the particles in the reaction chamber is prolonged, reducing the preparation efficiency, and too low a pH value will also directly affect the shape of the particles.

[0042] Accordingly, control the reaction of the mixed solution in the cylindrical chamber of the TFR under the above conditions. Then, the precipitate of the coprecipitation reaction can be collected at the outlet end of the cylinder, and then washed with ethanol and deionized water to remove the residual Na + , SO4 2- and other ions, and placed in an oven for drying. In one embodiment, the oven temperature can be 60 °C to 120 °C, preferably 60 °C to 100 °C, more preferably 60 °C to 80 °C, and even more preferably 60 °C; the drying time can be 6 to 24 hours, preferably 8 to 20 hours, more preferably 10 to 15 hours, and even more preferably 12 hours. After the drying treatment, a nickel-rich hydroxide precursor Ni x Co y Mn 1-x-y (OH)2 with a concentration gradient is obtained. [Preparation method of nickel-rich oxide cathode material]

[0043] As Figure 2 (b) shown, the preparation method steps of the nickel-rich oxide of the present invention are as follows: S21: Disperse the aluminum source in ethanol, then add the nickel-rich hydroxide precursor for mixing to obtain a mixture, and heat the mixture to complete drying to obtain mixture a; S22: Grind and mix the mixture a of the lithium source and S21 using grinding balls by a ball mill to obtain mixture b; S23: Conduct three-stage calcination heat treatment on the mixture b of S22 in a high-temperature furnace.

[0044] Disperse the aluminum source in an appropriate amount of ethanol, add the previously prepared nickel-rich hydroxide precursor powder and mix well, and heat to complete dryness at a certain temperature to obtain mixture a. In one embodiment, the aluminum source is Al(OH)3. In one embodiment, the certain temperature is 70°C to 90°C, preferably 80°C.

[0045] Next, add the lithium source to the aforementioned mixture a. In one embodiment, the lithium source is the lithium salt LiOH·H2O. In one embodiment, the molar ratio of the mixture a to the lithium source is 1:1.01 to 1:1.25, preferably 1:1.01 to 1:1.20, more preferably 1:1.01 to 1:1.10, and even more preferably 1:1.05.

[0046] Next, use a ball mill and grind and mix using PU balls or agate balls to obtain mixture b. The rotation speed of the ball mill is 50 rpm to 200 rpm, preferably 70 rpm to 150 rpm, more preferably 80 rpm to 125 rpm, and even more preferably 100 rpm; the grinding time is 2 to 10 hours, preferably 3 to 8 hours, more preferably 4 to 6 hours, and even more preferably 5 hours; the sample ratio of the PU balls or agate balls to the aforementioned mixture and the lithium source is 1:1 to 1:20, preferably 1:1 to 1:10, more preferably 1:1 to 1:5, and even more preferably 1:1.

[0047] Next, conduct three-stage calcination heat treatment on mixture b in a high-temperature furnace in an air or pure oxygen environment, with the pure oxygen environment being ideal. The temperature of the first stage of the aforementioned three-stage calcination heat treatment is 100°C to 200°C, preferably 120°C to 180°C, more preferably 140°C to 160°C, and even more preferably 150°C, and the time is 1 to 3 hours, preferably 1.5 to 2.5 hours, more preferably 2 hours; the temperature of the second stage is 500°C to 600°C, preferably 520°C to 580°C, more preferably 540°C to 560°C, and even more preferably 550°C, and the time is 4 to 8 hours, preferably 5 to 7 hours, more preferably 6 hours; the temperature of the third stage is 700°C to 800°C, preferably 710°C to 775°C, more preferably 720°C to 750°C, and even more preferably 730°C, and the time is 10 to 40 hours, preferably 15 to 30 hours, more preferably 20 hours. The heating rate of this three-stage calcination heat treatment is 0.1 to 20°C / min, preferably 0.5 to 10°C / min, more preferably 1 to 5°C / min, and even more preferably 2°C / min.

[0048] Accordingly, a nickel-rich oxide cathode material with a homogeneous structure having an elemental concentration gradient distribution is obtained.

[0049] For the nickel-rich oxide cathode material prepared in this embodiment, according to the change in the metal ion ratios of nickel, cobalt, manganese, and aluminum, its electrochemical performance also has obvious differences. Among them, when the nickel content is higher, the specific capacity of the oxide cathode material is higher. If it has a higher content of aluminum or manganese, it can provide better material structure stability.

[0050] The following examples respectively synthesize a nickel-rich hydroxide precursor material and a nickel-rich oxide cathode material through the preparation methods of the nickel-rich hydroxide precursor material and the nickel-rich oxide cathode material described above, and measure the relevant material characteristics and evaluate the battery electrical properties. [Example 1] Nickel-rich hydroxide precursor material [Ni 0.91 Co 0.05 Mn 0.04 (OH)2

[0051] Dissolve NiSO4·6H2O with a molar concentration of 1.82M and CoSO4·7H2O with a molar concentration of 0.1M as metal ion raw materials in deionized water to form aqueous solution A; then dissolve MnSO4·H2O with a molar concentration of 0.08M in deionized water to form aqueous solution B. In addition, dissolve sodium hydroxide as a precipitant in deionized water to prepare an aqueous solution C with a molar concentration of 4M, and dissolve ammonia water as a chelating agent in deionized water to prepare an aqueous solution D with a molar concentration of 7.2M. Before the coprecipitation reaction, filter all the aforementioned aqueous solutions to remove any unwanted impurities. Among them, the weight molar concentration ratio of aqueous solution A to aqueous solution C is 1:2, and the weight molar concentration ratio of aqueous solution A to aqueous solution D is 1:3.

[0052] Pour aqueous solutions A, C, and D into a continuous Taylor flow reactor for the first coprecipitation reaction for 5 hours, and then pour aqueous solution B into the continuous Taylor flow reactor to carry out the second coprecipitation reaction between aqueous solution B and aqueous solution A for 25 hours. Moreover, the reaction temperature of the second coprecipitation reaction is 60°C, the pH value of the reaction environment is 11.2, and the flow rate of NaOH is kept constant. The inner cylinder rotation speed of the continuous Taylor flow reactor is 600 rpm, and continuous production is carried out at a feeding rate of 1.703 ml / min. Collect the precipitate after the second coprecipitation reaction at the outlet end of the cylinder, wash it several times with ethanol and deionized water to remove excess residual ions, and place it in an oven for drying at 60°C for 12 hours to obtain [Ni 0.91 Co 0.05 Mn 0.04(OH)2 hydroxide precursor, represented by CG-NCM precursor in this embodiment. [Example 2] Nickel-rich oxide cathode material Li[Ni 0.90 Co 0.04 Mn 0.03 Al 0.03 O2

[0053] Disperse 0.15 g of Al(OH)3 in 20 ml of ethanol, then add 5 g of the powder of CG-NCM precursor and mix well. After completion, heat it to 80 °C until the mixture is completely dry to obtain mixture a. Then, mix LiOH·H2O and mixture a in a molar ratio of 1:1.05 and grind and mix them for 5 hours at a rotation speed of 100 rpm using a ball mill. In this embodiment, PU or agate balls are used for grinding and mixing (the ratio of the sample to the balls is 1:1) to obtain mixture b. Finally, perform three-stage calcination heat treatment on mixture b in a pure oxygen environment. The temperature of the first stage is 150 °C and the time is 2 hours, the temperature of the second stage is 550 °C and the time is 6 hours, and the temperature of the third stage is 730 °C and the time is 20 hours. The heating rate of the three stages is set to 2 °C / min, and Li[Ni 0.90 Co 0.04 Mn 0.03 Al 0.03 O2 with a homogeneous structure having an elemental concentration gradient distribution is obtained, represented by CG-NCMA oxide in this embodiment.

[0054] Compare the performance of oxide cathode materials with two different types of concentration distributions. [Comparative Example 1] Use TFR to prepare a batch of hydroxide precursors with a uniform concentration distribution in the same method as in Example 1, and all the nickel, cobalt, manganese, and aluminum metal ion raw materials are dissolved in a single solution and directly fed into TFR for coprecipitation reaction to obtain a [Ni 0.90 Co 0.04 Mn 0.03 Al 0.03 (OH)2 hydroxide precursor, represented as UC-NCMA precursor. [Comparative Example 2] Calcinate and heat-treat the dried powder of UC-NCMA precursor under the same conditions as in Example 2 to obtain a Li[Ni 0.90 Co 0.04 Mn 0.03 Al 0.03 O2 oxide sample, represented as UC-NCMA oxide.

[0055] The following analyzes and identifies each material to compare the examples and comparative examples of the present invention. [Analysis of crystal plane strength ratio]

[0056] The X-ray diffractometer (XRD) was used to analyze the crystal plane strength ratio of two different hydroxide precursors, CG-NCM and UC-NCMA. As Figure 3 shown, the preferred crystal orientation of the UC-NCMA precursor prepared using TFR is the (001) crystal plane (2θ = 19.2°); while the preferred crystal orientation of the CG-NCM precursor prepared using TFR in the method of the present invention is the (101) crystal plane (2θ = 38.6°). It can be seen that the intensity ratio (Intensity ratio, I (101) / I (001) ) of the (101) and (001) crystal planes of the CG-NCM precursor prepared by TFR is 1.45, far exceeding the I (101) / I (001) = 0.82 of the UC-NCMA precursor prepared by TFR. [Particle size analysis]

[0057] Dynamic Light Scattering (DLS) was used to analyze the particle size of two different hydroxide precursors, CG-NCM and UC-NCMA, prepared by TFR. As Figure 4 shown, the two peaks of the particle size distribution of the UC-NCMA precursor are located at 0.24 μm and 6.76 μm respectively, while the two peaks of the particle size distribution of the CG-NCM precursor are located at 0.26 μm and 8.15 μm respectively. It can be seen that the particle size of the CG-NCM precursor is relatively large and more uniformly concentrated. [Surface morphology analysis]

[0058] The surface morphologies of two different hydroxide precursors, CG-NCM and UC-NCMA, prepared by TFR were observed by a Scanning electron microscope (SEM). Figure 5 (a1) to Figure 5 (a4) are SEM photos of the UC-NCMA precursor at different magnifications; Figure 5 (b1) to Figure 5 (b4) are SEM photos of the CG-NCM precursor at different magnifications. As Figure 5 (a3) and Figure 5(As shown in (a4), the morphology of the primary particles of the uniformly concentrated UC-NCMA precursor is granularly distributed and forms its secondary particles, such as Figure 5 (a1) and Figure 5 (a2); in addition, as shown in Figure 5 (b3) and Figure 5 (b4), the morphology of the primary particles of the CG-NCM precursor is needle-like and forms its secondary particles, such as Figure 5 (b1) and Figure 5 (b2). The one-dimensional structure of the needle-like primary particles of the CG-NCM precursor can resist the micro-cracks caused by the tensile stress and compressive stress of the expansion and contraction generated during the long-term charge and discharge process.

[0059] In summary, in the method of the present invention, TFR is used to prepare the CG-NCM hydroxide precursor. In addition to improving the preparation efficiency of continuous and large-scale production, the particles of the prepared nickel-rich hydroxide precursor are uniform and the particle size is concentrated, and it has a special needle-like primary particle morphology in the one-dimensional direction. [Observation of the distribution of metal element components in nickel-rich oxides] [Analytical instruments and methods]

[0060] Powder diffraction patterns of the CG-NCM precursor and the CG-NCMA oxide were obtained using a Bruker D2 PHASER (Cu Kα5, λ = 0.1534753 nm, 30 kV; Germany), and quantitative evaluation was performed using the Rietveld refinement method with TOPAS software (v. 4.0). The microstructure, surface morphology, and cross-sectional profile of the prepared powder samples were observed using a scanning electron microscope (SEM, JOEL, JSM-IT200 InTouch Scope TM, 15 kV; Japan), and energy-dispersive X-ray spectroscopy (EDS) was carried out. To understand the elemental distribution in the particle internal structure of the CG-NCM precursor and CG-NCMA oxide powders, cross-section analysis of the particle samples was performed using a focused ion beam (FIB; FEI Helios G4 UX). A high-resolution transmission electron microscope (HR-TEM; JEOL JEM-2100F; Japan) was used to study the characteristics of the microcrystalline structure. X-ray photoelectron spectroscopy (XPS; PHI 5600, PerkinElmer; USA) was used to study the oxidation states of transition metal elements, C, and O atoms, and data fitting and analysis were performed using an Al Kα (1486.6 eV) excitation source and XPSPEAK 4.1. [FIB / SEM EDS Scanning Analysis]

[0061] The CG-NCM precursor of Example 1 of the present invention was prepared in a TFR at an ideal rotation speed (600 rpm) and pH value (11.2), so the obtained microsphere particle structure has a concentrated particle size distribution and good sphericity. And the obtained CG-NCM precursor with a manganese concentration gradient was fully mixed with an aluminum source, and under ideal calcination heat treatment conditions, a CG-NCMA oxide cathode material rich in manganese elements in the outer layer and containing aluminum elements on the surface layer was obtained. Figure 6 (a) and Figure 6 (b) are respectively high- and low-magnification SEM images of the CG-NCM precursor prepared by the method of the present invention. The high-magnification SEM image shows the nano-scale needle-like morphology of its primary particles, and the low-magnification SEM image shows its spherical secondary particles (particle size about 8 - 12 μm). And by cross-sectioning the particles of the CG-NCM precursor with FIB, the metal element composition distribution in its cross-section was determined by linear scanning. Figure 6(c) shows the elemental composition distribution of the CG-NCM precursor along the cross-section (arrow marked). It can be seen that the nickel concentration in the inner layer is higher than that in the outer layers near the left and right ends, while the manganese concentration shows a concentration gradient distribution gradually increasing from the inner layer to the outer layer. Through Figure 6 (d), it can also be known that the XRD pattern of the CG-NCM precursor has quite distinct characteristic peaks and no extra impurity phases, indicating that although the outer layer of the particles is rich in manganese elements, the manganese cations have been incorporated into the structure of the CG-NCM precursor, representing that the CG-NCM precursor is a homogeneous structure with an elemental concentration gradient distribution from the inner layer to the outer layer, rather than a separately formed manganese hydroxide crystal phase.

[0062] As Figure 7 (a) to Figure 7 (d) respectively show that in addition to the spherical morphology of the secondary particles of the UC-NCMA oxide and CG-NCMA oxide after calcination heat treatment being retained, the nanoscale needle-like primary particles of the CG-NCMA oxide form a well-crystallized strip-like particle distribution. And from Figure 7 (e) and Figure 7 (f) of the EDS Mapping spectra, it can be known that the surface of a single spherical secondary particle is composed of four elements: nickel, cobalt, manganese, and aluminum, and all the metal element components are evenly distributed. [Rietveld Refinement Analysis of XRD Patterns]

[0063] Figure 8 (a) is a comparison of the XRD patterns of the powder samples of the UC-NCMA oxide and CG-NCMA oxide prepared by the method of the present invention. And it can be seen from the figure that all diffraction peaks can be correctly corresponded to the hexagonal α-NaFeO2 structure with a high crystallinity of the R-3m space group. Among them, it is also found that the (006) / (012) and (018) / (110) characteristic peaks have clear bifurcation results, indicating that the analyzed material is an ordered crystal structure. In addition, the ratio R of the (003) / (104) peak of the UC-NCMA oxide prepared by the method of the present invention is 1.68, while the ratio R of the (003) / (104) peak of the CG-NCMA oxide is 1.55, both far exceeding 1.2, indicating that the powder samples of the UC-NCMA oxide and CG-NCMA oxide are prepared under the condition of low cation mixing. Therefore, this kind of NCMA-based cathode material has a good crystal structure. Then, the Rietveld refinement method is used to fit the XRD pattern, and the lattice parameters and analysis results of the two powder samples are compared, as shown in Figure 8 (b) and Figure 8 (c), and the relevant data are listed in Table 1.

[0064] Table 1 [TEM Microscopic Image Analysis]

[0065] As Figure 9 (a) and Figure 9 (b) show, the TEM images were used to observe the microstructures of the UC-NCMA oxide and CG-NCMA oxide samples respectively. The samples of the primary particles of the UC-NCMA oxide and CG-NCMA oxide prepared by the method of the present invention have a clear layered crystal structure. By using digital microscopic image software to match the lattice fringes in the two samples of the primary particles with the crystal plane of the hexagonal phase (003), it is found that their interplanar spacings are all about 0.47 nm. In addition, the selected area electron diffraction (SAED) patterns show that these samples of the primary particles have good crystallinity and perfect stacking structure. Figure 9 (b) The TEM-EDS measurement and analysis also show the concentration gradient distribution of the samples of the primary particles of the CG-NCMA oxide. The results show that all metal elements are uniformly distributed in the whole primary particle, and the concentrations of manganese and aluminum elements on the surface of the particle are much higher than that of the nickel element, which is consistent with the results of the aforementioned FIB / SEM EDS line scan. When the particle surface at the grain boundary has a higher concentration of manganese and aluminum elements, it can reduce the side reaction between the cathode material and the surrounding electrolyte, and at the same time enhance the structural stability of the cathode material, thereby improving the charge and discharge cycle performance of the lithium-ion battery. [XPS Energy Spectrum Measurement and Analysis]

[0066] The samples of the CG-NCMA oxide and UC-NCMA oxide were measured by an XPS spectrometer to study the elemental composition and valence states of the transition metals. As Figure 10 (a) shows, the Ni 2p energy spectrum has two different peaks at about 855 eV (Ni 2p3 / 2) and 872 eV (Ni 2p1 / 2), and is accompanied by two satellite peaks. The peak located at 855 eV is the Ni 3+ and Ni 2+ obtained by superimposing and fitting the two peaks. If the Ni 2+ ions easily migrate from the TM layer to the lithium layer and occupy the sites of the Li + ions, it may cause permanent dislocation and result in the loss of the battery's capacitance.

[0067] The semi-quantitative analysis shows that, as can be seen from Figure 10 (a), the proportion of Ni 2+ ions in the CG-NCMA oxide is much lower than that in the UC-NCMA oxide (CG-NCMA: 6%, UC-NCMA: 46%). In addition, Mn 4+The concentration gradient distribution of ions can promote the change of Ni in the surface region of the cathode material 3+ to Ni 2+ , reducing the number of Ni ions in the surface region and thus changing the valence state of Ni ions in the surface region. Moreover, the CG-NCMA oxide has a relatively high proportion of Ni 3+ ions, indicating that this material has a high oxidation state after high-temperature calcination, which can effectively reduce cation mixing.

[0068] Figure 10 (b) shows the fitting of the characteristic peaks of O1s spectra corresponding to O elements in the lattice and surface, and the characteristic peaks are located at about 529 eV and 532 eV respectively. The intensity of the C=O oxygen signal of the CG-NCMA oxide is low, indicating that the amount of Li2CO3 residue on the surface is small. Figure 10 (c) and Figure 10 (d) are the fitted XPS spectra of Co 2p and Mn 2p respectively. The valence of cobalt is +3 (Co 3+ ), and the valence of manganese is +4 (Mn 4+ ). From Figure 10 (c) and Figure 10 (d), it can be seen that compared with the UC-NCMA oxide, the CG-NCMA oxide has a lower signal intensity of Co 2p and a higher signal intensity of Mn 2p, indicating that the CG-NCMA oxide has a higher concentration of manganese elements in the surface region.

[0069] From Figure 10 (e) of Li 1s and Figure 10 (f) of C1s XPS spectra, it can also be known that the signal intensities of surface Li and C=O carbon atoms of the CG-NCMA oxide are weaker than those of the UC-NCMA oxide, indicating that the formation of lithium-containing impurities (such as Li2CO3 and LiOH) on the surface of the CG-NCMA oxide is less. [Electrochemical Measurements]

[0070] The NCMA-based (including UC-NCMA oxide and CG-NCMA oxide cathode) positive electrode is formed by coating the electrode slurry on an aluminum foil. The formulation of the electrode slurry contains 80% of the NCMA-based positive electrode active material (Active material), 10% of conductive carbon black (Super ) and 10% of polyvinylidene fluoride (PVDF) binder, as well as N-methylpyrrolidone (NMP) as a solvent. The positive electrode is placed in a vacuum oven at 120 °C and dried for 12 hours. A disk-shaped electrode with a diameter of 13 mm is punched out on the electrode (mass loading: 2.5 mg / cm 2) and using a lithium metal foil as the negative electrode, and then assembling a CR-2032 button-type battery with an electrolyte of 1 M LiPF6 plus ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume percentage of 1:1.

[0071] All electrochemical measurements in the present invention were performed using a BCS-805 workstation (BioLogic, France) for charge-discharge tests. The lithium-ion battery fabricated by the aforementioned method was subjected to constant current charge-discharge tests within a voltage range of 2.8 to 4.3 V (versus Li / Li + ). The cycle life test was carried out at a charge-discharge rate of 1C / 1C (1C = 200 mA / g) for 100 and 200 charge-discharge cycles. The rate capability test was performed at low / high current rates from 0.2C to 10C. The cyclic voltammetry experiment was controlled within a voltage range of 2.5 to 4.3 V and measured at a scan rate of 0.01 mV / s. Using a MetrOhm system for electrochemical impedance spectroscopy (EIS) analysis, with a frequency range from 100 kHz to 0.01 Hz and an AC amplitude of 5 mV.

[0072] As Figure 11 (a) shows the initial charge-discharge curves of the UC-NCMA and CG-NCMA positive electrodes after testing in a half-cell of NCMA / / Li within a voltage range of 2.8 to 4.3 V at a charge-discharge rate of 0.1C. Among them, the initial discharge specific capacity of the UC-NCMA oxide positive electrode is approximately 213 mAh / g, while that of the CG-NCMA oxide positive electrode is approximately 209 mAh / g, which is slightly lower than that of the UC-NCMA oxide positive electrode. The reason is that the content of nickel element with a concentration gradient distribution in the outer layer of the CG-NCMA oxide is relatively low, and the presence of aluminum element in its surface layer also contributes to this result.

[0073] As Figure 11 (b) and Figure 11 (d) show that under the condition of an upper limit voltage of 4.3 V, the rate performance tests of the two positive electrodes were carried out at low / high discharge rates of 0.2, 0.5, 1, 3, 5, and 10C. The results show that the discharge specific capacity of the CG-NCMA oxide positive electrode is higher than that of the UC-NCMA oxide positive electrode. Especially at high discharge rates of 5C and 10C, the discharge specific capacities of the CG-NCMA oxide positive electrode are 168.7 and 159.5 mAh / g respectively, while those of the UC-NCMA oxide positive electrode are only 146.8 and 127.7 mAh / g respectively. The low / high discharge curves of the two positive electrodes are as shown in Figure 12 . In addition, Figure 11(d) shows that at a high discharge rate of 10 °C, the CG-NCMA oxide cathode can maintain a capacitance retention rate of approximately 83% of the 0.2C discharge specific capacity (100%), while the UC-NCMA oxide cathode only has approximately 67%.

[0074] In summary, the use of the CG-NCMA oxide cathode can improve the electrochemical performance of lithium-ion batteries, which can be attributed to the complete and stable crystal structure and the tolerance of the structure to material strain during charge and discharge. In contrast, the UC-NCMA oxide cathode is prone to discharge specific capacity loss at higher discharge rates, which may be caused by microcracks in the cathode material and phase transformation of the oxide structure.

[0075] Figure 11 (c) is a comparison of the electrochemical performance of the UC-NCMA oxide cathode and the CG-NCMA oxide cathode under the conditions of a charge-discharge rate of 1C / 1C, a cut-off voltage of 2.8 to 4.3V, and an ambient temperature of 25 °C after 100 charge-discharge cycles. The results show that the retention rate of the initial specific capacity of the CG-NCMA oxide cathode reaches 91.5%, showing excellent cycle stability, while the UC-NCMA oxide cathode only has a retention rate of 83.4% of the initial specific capacity. In addition, under the same conditions, a 200 charge-discharge cycle test was carried out. As Figure 11 (e) shows, the retention rate of the initial specific capacity of the CG-NCMA oxide cathode can still be maintained at 80.2%, while the UC-NCMA oxide cathode only remains 64.1%.

[0076] Table 2 shows a comparison of the electrochemical performance of the NCMA / / Li battery composed of the cathode material with an element concentration gradient prepared by the method of the present invention and several prior art lithium-ion batteries. It can be seen from Table 2 that the CG-NCMA oxide cathode of the present invention has a considerable advantage in cycle stability because the concentrations of manganese and aluminum elements in the outer layer of the CG-NCMA oxide are relatively high, having better stability of the material structure, and this distribution with an element concentration gradient can also effectively inhibit the side reactions formed by the contact of the cathode with the electrolyte during long-term cycling.

[0077] Table 2 Prior art source: 1.Y.Zhang,H.Li,J.Liu,J.Zhang,F.Cheng,J.Chen,LiNi 0.90 Co 0.07 Mg 0.03O2cathode materials with Mg-concentration gradientfor rechargeable lithium-ionbatteries,Journal of Materials Chemistry A7(36)(2019)20958–20964。 2.C.-L.Xu,W.Xiang,Z.-G.Wu,Y.-D.Xu,Y.-C.Li,M.-Z.Chen,G.XiaoDong,G.-P.Lv,J.Zhang,B.-H.Zhong,Constructing a ProtectivePillaring Layer byIncorporating Gradient Mn 4+ to Stabilize theSurface / Interfacial Structure ofLiNi 0.815 Co 0.15 Al 0.035 O2 Cathode,ACSApplied Materials&Interfaces 10(33)(2018)27821–27830。 3.U.-H.Kim,S.-T.Myung,C.S.Yoon,Y.-K.Sun,Extending the BatteryLifeUsing an Al-Doped Li[Ni 0.76 Co 0.09 Mn 0.15 ]O2 Cathode withConcentration Gradientsfor Lithium Ion Batteries,ACS Energy Letters 2(8)(2017)1848–1854。 4.P.Hou,F.Li,Y.Sun,H.Li,X.Xu,T.Zhai,Multishell PrecursorsFacilitatedSynthesis of Concentration-Gradient Nickel-Rich Cathodes forLong-Life andHigh-Rate Lithium-Ion Batteries,ACS Applied Materialsand Interfaces 10(29)(2018)24508–24515。 5.K.Du,C.Hua,C.Tan,Z.Peng,Y.Cao,G.Hu,A high-powered concentration-gradient Li(Ni 0.85 Co 0.12 Mn 0.03 )O2 cathode material for lithium ion batteries,Journal of Power Sources 263(2014)203–208。

[0078] Figure 13 (a) and Figure 13 (b) are the curves of differential capacity analysis (Differential capacity analysis, DCA; dQ / dV vs. V) after 3 cycles at a charge-discharge rate of 0.1C. Three typical phase transitions between the hexagonal phase and the monoclinic phase can be observed. Due to the polarization phenomenon in subsequent cycles, the negative and positive peaks shift positively and negatively respectively. Figure 13 (a) and Figure 13 (b) mostly overlap well in 3 cycles, indicating that both the UC-NCMA oxide cathode and the CG-NCMA oxide cathode have high stability and electrochemical reversibility at low charge-discharge rates.

[0079] However, as can be seen from Figure 13 (c), when the UC-NCMA oxide cathode undergoes 100 charge-discharge cycles at a charge-discharge rate of 1C, an obvious and serious polarization phenomenon occurs. The positive peak at 4.2V is a measure of the phase transition reversibility. In contrast, during 100 charge-discharge cycles of the CG-NCMA oxide cathode at a charge-discharge rate of 1C, the curves of dQ / dV vs. V almost remain overlapping, as shown in Figure 13 (d). Accordingly, the CG-NCMA oxide cathode prepared by the method of the present invention has good internal structural stability and can effectively improve the electrochemical performance of lithium ion batteries.

[0080] By analyzing the reversibility of the positive electrode electrochemical reaction of a lithium ion battery through cyclic voltammetry (CV), the results of the first 3 cycles of the UC-NCMA oxide cathode and the CG-NCMA oxide cathode are shown in Figure 14 (a) and Figure 14 (b) respectively, for qualitative analysis of the voltage of the electrochemical reaction and electron transfer in the electrode. A typical CV curve has three pairs of oxidation / reduction peaks, representing caused by the intercalation / extraction of Li + ions Phase transition. The delayed dynamic response of the phase transition from H1 to M during the initial delithiation process leads to a slightly higher oxidation potential. In addition, after the first cycle activation, the symmetrical redox peaks of the second and third cycles almost completely overlap, indicating that the cathode material has excellent electrochemical reversibility.

[0081] The polarization voltage is defined as the difference between the first negative and positive peaks around 3.7-4.0 V in the first activation cycle (ΔV), which is a measure of the reversibility of the positive electrode material. The first negative peak and positive peak of the CG-NCMA oxide positive electrode and the UC-NCMA oxide positive electrode are The ΔV values between them are 192.7 mV and 211.6 mV, respectively. The CG-NCMA oxide positive electrode has a lower polarization voltage difference, indicating that it has a higher structural stability and therefore has a good reversible kinetic reaction.

[0082] Figure 14 (c) and Figure 14 (d) The electrochemical impedance spectra of the UC-NCMA oxide positive electrode and the CG-NCMA oxide positive electrode at the initial and 100 cycles at a charge and discharge rate of 1C, respectively, where each curve has an arc area at high frequency (and medium and high frequency) and a straight line area at low frequency. The proposed equivalent circuit model is used to fit the EIS curve, where R b is the body resistance, R sei is the solid electrolyte interphase (SEI) resistance, R ct is the charge transfer resistor, CPE (Constant phase element) is the constant phase angle component, Z W is the Warburg impedance value, representing Li + Diffusion impedance of ions in a solid electrode.

[0083] After fitting the electrochemical impedance spectra of the UC-NCMA oxide positive electrode and the CG-NCMA oxide positive electrode to their respective equivalent circuit models using ZView software, the obtained values are listed in Table 3. The results in this table show that the initial R ct =263.1Ω, much lower than the initial R of the UC-NCMA oxide positive electrode ct =355.6Ω, indicating that when the nickel-rich UC-NCMA-based cathode is exposed to the electrolyte, it is easier to form an inactive area similar to NiO on its surface, thereby increasing the charge transfer resistance. Figure 14As shown in (d), after 100 cycles at a charge-discharge rate of 1C / 1C, the two EIS curves of the UC-NCMA oxide cathode and the CG-NCMA oxide cathode both present as arcs, and then they are fitted into an equivalent circuit model ( Figure 14 (inset of (d)), in addition to having a lower R after cycling for the CG-NCMA oxide cathode ct value, it can also be observed that the R of the CG-NCMA oxide cathode sei = 66.7 Ω is also lower than the trend of R of the UC-NCMA oxide cathode sei = 95.4 Ω, which is consistent with the previous experimental results.

[0084] Table 3

[0085] During the long-term cycling process, the active secondary particles are easily affected by hydrofluoric acid (HF) that may be generated in the electrolyte or the inevitable impurity residues produced by side reactions. Therefore, for the CG-NCMA oxide cathode with an elemental concentration gradient prepared by the method of the present invention, its outer layer and surface layer respectively have rich manganese and aluminum element components, which can effectively inhibit the occurrence of side reactions at the interface between the cathode material and the electrolyte, prevent the damage of the electrode structure, and thereby improve the overall electrochemical performance and cycling stability of the lithium-ion battery. [In-situ X-ray diffraction analysis]

[0086] One of the most important functions of the concentration gradient is to enclose the nickel-rich phase in the inner layer of the active material particles to maximize the discharge specific capacity. However, the improvement of the cycling and electrode structure stability of this battery is not only attributed to the concentration gradient. The reason is that the CG-NCMA oxide still contains a large amount of nickel component (Ni content 90%), and the volume change of the battery during the charge-discharge cycle will generate a huge pressure on the cathode structure. In addition, this strain is anisotropic because most of the expansion and contraction occur in the c-axis direction. Generally, during the process of Li + ion extraction (i.e., charging) and subsequent insertion (i.e., discharging) into the cathode, the anisotropic strain is adjusted through the relevant directions of the plane formed by the a-axis and the b-axis.

[0087] Use the in-situ XRD method to detect the change of the lattice parameter during the second charge-discharge cycle to understand the mechanism and reason for the capacity decay of this battery. Figure 15 (a) and Figure 15 (b) respectively show the XRD patterns of the UC-NCMA oxide cathode and the CG-NCMA oxide cathode during the charge-discharge process. From Figure 15 (a) and Figure 15(b) Extract the contour lines and compare them for different characteristic peaks, such as Figure 16 (a) and Figure 16 (b) shown. During the charging process, due to the electrostatic repulsion between adjacent O layers, when Li + ions are extracted from the positive electrode, the (003) characteristic peak will continuously shift to the left (i.e., the lattice expands in the c-axis direction), and due to the transition from the H2 phase to the H3 phase, it rapidly drops to a higher angular displacement at 4.1 V, which is the lattice contraction behavior, as described in the previous Figure 13 (a)–(d) and Figure 14 (a), (b) shown.

[0088] In addition, during the charging process, the (101) characteristic peak also shifts to the right, indicating a-axis contraction, which is caused by the reduction of the ionic radius in the TM layer; during the discharging process, the same process repeats in the opposite direction, and all the peaks finally shift back to the original Bragg positions at the end of the discharging process, proving the structural reversibility of the NCMA-based positive electrode. Other peaks also follow the same shifting process, which are the lattice expansion or contraction processes respectively. Although both positive electrodes experience the same charge-discharge process and the same level of strain, Figure 16 (b) shows that the CG-NCMA oxide positive electrode has a lower degree of expansion and contraction during cycling, which is beneficial to extending the cycle life of the lithium-ion battery.

[0089] Table 4 and Figure 16 (c) to Figure 16 (e) are the results of the changes in lattice parameters during the Li + ion extraction / insertion process. It can be found that the phase change is the most severe, that is, the lattice change Δc of the (003) crystal plane of the CG-NCMA oxide positive electrode is 1.92%, much smaller than Δc = 3.38% of the UC-NCMA oxide positive electrode, and the lattice change Δa = 1.64% and the lattice volume change Δvol = 3.78% of the (101) crystal plane of the CG-NCMA oxide positive electrode are much lower than Δa = 2.36% and Δvol = 7.80% of the UC-NCMA oxide positive electrode. The changes in the three lattice parameters (i.e., Δa, Δc, and Δvol) show the same trend.

[0090] Table 4

[0091] Through the aforementioned in-situ X-ray diffraction analysis, it can be found that the primary particles of the CG-NCMA oxide cathode have a unique one-dimensional needle-like spatial structure distribution. Coupled with a strong outward extension ability, it can effectively reduce the volume change of the CG-NCMA oxide cathode during deep charging and improve its cycle stability. In addition, the anisotropic shrinkage / expansion of randomly arranged primary particles will cause local tensile / compressive stress concentration, which will further generate microcracks and cause structural collapse. In the case of using the CG-NCMA oxide cathode, the outer layer and the manganese-rich and locally aluminum-rich regions of the surface layer of the active material particles can inhibit the high volume change rate that may occur during the charge and discharge process of this structure, thereby significantly and effectively improving the electrochemical performance and stability of the CG-NCMA cathode material. [Failure analysis]

[0092] To deeply understand the concentration gradient on the structure and mechanical strength of the NCMA-based cathode, the NCMA-based / / Li half-cell after charge and discharge cycling was disassembled, and the NCMA-based electrode after cycling was observed through XRD and SEM.

[0093] Figure 17 (a) In the XRD pattern, there are no obvious differences in the positions, shapes, and relative intensities of the characteristic peaks of the UC-NCMA oxide cathode and the CG-NCMA oxide cathode, indicating that the capacitance decay of the lithium-ion battery is not entirely caused by the collapse of the electrode structure or irreversible phase displacement. However, Figure 17 As shown in the partially enlarged XRD pattern of (b), compared with the CG-NCMA oxide cathode, the (003) characteristic peak of the UC-NCMA oxide cathode has a more significant shift towards a lower angle, with a shift difference of Δ2θ = 0.54° from the (003) characteristic peak of the CG-NCMA oxide cathode, indicating that long-term cycling will cause irreversible damage to the structure of the active material particles of the UC-NCMA oxide, while the CG-NCMA oxide cathode has a better tolerance to mechanical stress during long-term cycling.

[0094] Figure 17 (c) and Figure 17 (d) are SEM images of the UC-NCMA oxide cathode and the CG-NCMA oxide cathode cycled 100 times at a high charge and discharge rate of 1C / 1C, respectively. During the charge and discharge process, Li + ions will repeatedly intercalate / deintercalate from the lattice and generate certain mechanical stress, thereby generating cracks along the grain boundaries of the primary particles and further causing disintegration; Figure 17(c) shows that the secondary particles of the UC-NCMA oxide cathode have been crushed into many primary particles after long-term cycling, indicating that its particle structure itself is not strong enough to withstand long-term charge-discharge cycling tests; in contrast, Figure 17 (d) shows that even after 100 cycles at a high charge-discharge rate, the secondary particles of the CG-NCMA oxide cathode remain intact, with only a few cracks, indicating that the CG-NCMA oxide cathode material is structurally strengthened enough to withstand the mechanical stress generated during long-term cycling at a high charge-discharge rate. In addition, the distribution of manganese-rich and aluminum-containing elements on the outer and surface layers of the CG-NCMA oxide cathode also helps the CG-NCMA cathode play a role in stabilizing the structure at high voltages (≧4.3V) and high charge-discharge rates (≧1C).

[0095] Next, the secondary particles of the NCMA-based electrode after charge-discharge cycling were sectioned using the focused ion beam (FIB) technique, and the internal structure of the cross-section of the sectioned particles was observed using SEM to further understand the degree of microcracks in the internal structure of the secondary particles formed after long-term charge-discharge cycling of the lithium-ion battery. As Figure 18 (a) and Figure 18 (b) show, the primary particles inside the secondary particles of the UC-NCMA oxide cathode have obvious microcracks along the grain boundaries of the particles. After repeated charge-discharge cycling, the primary particles will begin to separate from each other, resulting in structural damage; in contrast, as Figure 18 (c) and Figure 18 (d) show, the CG-NCMA oxide cathode still shows a complete arrangement of primary particles after repeated charge-discharge cycling, and almost no cracks are generated at the grain boundaries of the primary particles.

[0096] The experimental results after FIB cross-sectioning confirm that due to the long-term charge-discharge cycling of the UC-NCMA oxide cathode, microcracks are easily formed at the grain boundaries of the primary particles in the secondary particles of the cathode and the crack range is extended. Coupled with the subsequent penetration and reaction of the electrolyte, the mechanical integrity of the structure is accelerated to be lost. Moreover, as the surface area of the particles exposed to the electrolyte increases with the long-term cycling of the battery, the microscopic structural damage on the particle surface also gradually becomes serious, resulting in the fragmentation of the particles of the UC-NCMA oxide cathode; in contrast, the stable structure of the manganese-rich outer layer and aluminum-containing surface layer of the CG-NCMA oxide cathode can effectively inhibit the generation and expansion of microcracks and prevent its secondary particles from forming microcracks and disintegrating into powder during long-term cycling.

[0097] At a high charge-discharge rate of 1C / 1C, after 100 charge-discharge cycles, TEM was used to observe that the surface structures of the active material particles of the UC-NCMA oxide cathode and the CG-NCMA oxide cathode continuously caused different degrees of phase change during the charge-discharge cycle. As Figure 18 (e) shows, the primary particles of the UC-NCMA oxide cathode after long-term charge-discharge cycles underwent obvious phase transitions due to frequent Li + insertion / extraction. The selected area electron diffraction (SAED) pattern of region I showed a perfect R-3m layered structure with alternating TM layers and Li ion layers. Moreover, due to the presence of active Ni 4+ substances at the particle edges (a common phenomenon in nickel-rich oxide cathodes during charge-discharge cycles), a NiO-like Fm-3m surface layer could be detected in region II. On the other hand, as Figure 18 (f) shows, since the NiO-like damage layer found in the CG-NCMA oxide cathode was limited to approximately 1 nm at the particle edges, it was impossible to distinguish using electron diffraction in selected regions I and II.

[0098] In summary, the objective of the present invention is to provide a preparation method for a nickel-rich cathode material applied to lithium-ion batteries. Through this method, the electrochemical performance of lithium-ion batteries and the mechanical stability of the cathode material can be improved. The method is to use a continuous Taylor flow reactor under ideal conditions such as ambient temperature, pH value, heating time, and feed rate. After preparing a CG-NCM precursor with an elemental concentration gradient using the coprecipitation method, CG-NCMA oxide is further prepared, which has a high concentration of manganese and aluminum element distributions on its surface. EDS line scanning confirmed that the CG-NCMA oxide cathode material has a homogeneous structure with an elemental concentration gradient distribution, that is, its nickel element concentration decreases layer by layer from the inner layer to the outer layer, while the manganese element concentration increases layer by layer from the inner layer to the outer layer, and its surface layer also has a homogeneous distribution of aluminum elements in the NCMA quaternary element structure.

[0099] The CG-NCMA oxide cathode prepared by the method of the present invention has excellent electrochemical performance. At a charge-discharge rate of 20 mA / g, its initial discharge specific capacity Q sp,dchg,ini ≈209 mAh / g, and its initial Coulombic efficiency (ICE) is 89.4%, which is higher than the CE = 82.9% of the UC-NCMA oxide cathode. When the CG-NCMA oxide cathode undergoes 100 charge-discharge cycles at a charge-discharge rate of 1C / 1C, its capacitance retention rate is CR 1-100= 91.5%, after 200 charge-discharge cycles, its capacitance retention rate still remains at CR 1-200 = 80.2%, both are much higher than those of the UC-NCMA oxide cathode (CR 1-100 = 83.4% and CR 1-200 = 64.1%).

[0100] In addition, from the analysis results of cyclic voltammetry and differential capacitance vs. voltage, it can be seen that the voltage polarization degree of the CG-NCMA oxide cathode is significantly reduced. The in-situ X-ray diffraction analysis results can illustrate the mechanical stress borne on the electrode during the charge-discharge process and its impact on battery performance. Among them, the stress change on the CG-NCMA oxide cathode is relatively low, making the possibility of the structure collapsing smaller. After long-term charge-discharge cycles, XRD and SEM failure analyses of the electrode can also confirm the above experimental results. Among them, the secondary particles of the UC-NCMA oxide cathode material have disintegrated into many primary particles, while the secondary particles of the CG-NCMA oxide cathode material can still maintain a relatively complete structure.

[0101] In summary, through the use of a continuous Taylor flow reactor in combination with the co-precipitation method to obtain a nickel-rich hydroxide precursor, the homogeneous structure with an element concentration gradient distribution in its nickel-rich inner layer and manganese-rich outer layer can reduce the interfacial impedance during lithium-ion transport and increase its lithium-ion migration path; moreover, preparing a nickel-rich oxide cathode material with an element concentration gradient distribution from this nickel-rich hydroxide precursor can improve the charge-discharge rate, long-term cycle stability and other electrochemical properties of the lithium-ion battery, as well as the structural stability of this nickel-rich cathode material.

[0102] The above embodiments should be understood as illustrative examples of the present invention, presented for the purpose of presenting the features of the present invention, but not intended to be exhaustive or limited to the form of the disclosed technical concepts. Without departing from the scope and spirit of the present invention, many modifications and variations are obvious to those of ordinary skill in the art of the present invention. The selection and description of the embodiments are for the purpose of best explaining the principles and practical applications of the present invention, and enabling those of ordinary skill in the art of the present invention to understand the present invention with various modifications suitable for the specific uses considered.

Description of the Reference Numerals

[0103] S11: Uniformly mix the metal ion raw materials in deionized water to form a metal ion mixed solution (aqueous solution A) S12: Dissolve the manganese source in deionized water to form an aqueous solution B S13: Pour the aqueous solution A, the precipitant aqueous solution (aqueous solution C) and the chelating agent aqueous solution (aqueous solution D) into a continuous Taylor flow reactor filled with deionized water for the first co-precipitation reaction S14: Pour aqueous solution B into a continuous Taylor flow reactor for the second co-precipitation reaction. S15: Collect the precipitate from the second co-precipitation reaction, wash it with ethanol and deionized water to remove residual ions, and then place it in an oven for drying to obtain a nickel-rich hydroxide precursor. S21: Disperse the aluminum source in ethanol, then add the nickel-rich hydroxide precursor and mix to obtain a mixture, and heat the mixture to complete dryness to obtain mixture a. S22: Grind and mix the lithium source and mixture a from S21 using grinding balls in a ball mill to obtain mixture b. S23: Conduct a three-stage calcination heat treatment on mixture b from S22 in a high-temperature furnace.

Claims

1. A preparation method of a nickel-rich hydroxide precursor material, wherein the nickel-rich hydroxide precursor material is nickel cobalt manganese hydroxide with a homogeneous structure having an elemental concentration gradient distribution, and the preparation method comprises: (1) Prepare an aqueous solution A dissolved with metal ion raw materials; Prepare an aqueous solution B dissolved with a manganese source; Prepare an aqueous solution C dissolved with a precipitant; Prepare an aqueous solution D dissolved with a chelating agent; Pour the aqueous solution A, the aqueous solution C and the aqueous solution D into a continuous Taylor flow reactor, and carry out the first co-precipitation reaction for 2 to 7 hours; Among them, The metal ion raw materials are a nickel source and a cobalt source; Wherein, the nickel source is at least one selected from the group consisting of nickel sulfate, nickel oxalate, nickel acetate, nickel nitrate, nickel chloride, nickel hydroxide; The cobalt source is at least one selected from the group consisting of cobalt sulfate, cobalt oxalate, cobalt carbonate, cobalt acetate, cobalt nitrate, cobalt chloride, cobalt hydroxide; The manganese source is at least one selected from the group consisting of manganese sulfate, manganese oxalate, manganese carbonate, manganese citrate, manganese acetate, manganese nitrate, manganese phosphate, electrolytic manganese dioxide, manganese oxide; (2) Pour the aqueous solution B into the continuous Taylor flow reactor for the second co-precipitation reaction for 5 to 70 hours; wherein, The reaction temperature of the second co-precipitation reaction is 30°C to 80°C, the pH value of the reaction environment is 9.5 to 12.5, and the rotation speed of the inner cylinder of the continuous Taylor flow reactor is 200 rpm to 1500 rpm; (3) Wash the precipitate after the second co-precipitation reaction and then place it in an oven for drying to obtain the nickel-rich hydroxide precursor material.

2. The preparation method of the nickel-rich hydroxide precursor material according to claim 1, wherein, The concentration of the aqueous solution A is 1.6M to 1.92M.

3. The preparation method of the nickel-rich hydroxide precursor material according to claim 1, wherein, The concentration of the aqueous solution B is 0.08M to 0.4M.

4. The preparation method of the nickel-rich hydroxide precursor material according to claim 1, wherein, The concentration of the aqueous solution C is 2.0M to 6.0M, and the weight molar concentration ratio of the aqueous solution A to the aqueous solution C is 1:1 to 1:

5.

5. The preparation method of the nickel-rich hydroxide precursor material according to claim 1, wherein, The concentration of the aqueous solution D is 2.5M to 9.0M, and the weight molar concentration ratio of the aqueous solution A to the aqueous solution D is 1:1 to 1:

5.

6. The preparation method of the nickel-rich hydroxide precursor material according to claim 1, wherein, The drying temperature of the oven is 60°C to 120°C, and the drying time is 6 to 24 hours.

7. The preparation method of the nickel-rich hydroxide precursor material according to claim 1, wherein, The feeding rate of the aqueous solution A and the aqueous solution B is 1.0 to 3.0 ml / min.

8. A preparation method of a nickel-rich oxide cathode material, which uses the preparation method of the nickel-rich hydroxide precursor material as described in claim 1, and the preparation method comprises: (a) Disperse an aluminum source in ethanol, then add the nickel-rich hydroxide precursor material for mixing to obtain a mixture, and heat the mixture to complete drying at a temperature of 80°C to obtain a mixture a; Among them, The aluminum source is at least one selected from the group consisting of aluminum hydroxide, aluminum oxalate, aluminum carbonate, aluminum sulfate, aluminum acetate, aluminum nitrate, aluminum phosphate; (b) Grind and mix the mixture a in step (a) with a lithium source at a molar ratio of 1:1.01 to 1:1.25 to obtain a mixture b; The lithium source is at least one selected from the group consisting of lithium hydroxide, lithium nitrate, lithium acetate, lithium chloride, lithium hydrogen phosphate, lithium phosphate, lithium carbonate; (c) The mixture b in step (b) is subjected to a three-stage calcination heat treatment to obtain the nickel-rich oxide cathode material.

9. The preparation method of the nickel-rich oxide cathode material according to claim 8, wherein, The conditions for the grinding are that the rotation speed of the ball mill is set at 50 to 200 rpm, and the grinding time is 2 to 10 hours.

10. The preparation method of the nickel-rich oxide cathode material according to claim 8, wherein, The temperatures and times of the three-stage calcination heat treatment are as follows: the temperature in the first stage is 100°C to 200°C, and the time is 1 to 3 hours; the temperature in the second stage is 500°C to 600°C, and the time is 4 to 8 hours; the temperature in the third stage is 700°C to 800°C, and the time is 10 to 40 hours. The heating rate of the three-stage calcination heat treatment is 0.1 to 20°C / min.

Images