Positive electrode material precursor and preparation method thereof, positive electrode material

Abstract

The present invention provides a positive electrode material precursor and a preparation method thereof, and a positive electrode material; the positive electrode material precursor comprises an inner layer and an outer layer from the inside to the outside, the outer layer comprises a plurality of triangular-shaped primary particles, and the triangular-shaped primary particles are closely interspersed on the outer surface of the inner layer along the radial direction of the inner layer. The outer layer of the precursor has multiple gaps, thereby improving the lithium ion conduction ability, thereby accelerating the lithium ion deintercalation process, and further improving the battery rate performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode material precursor and a preparation method thereof, and a positive electrode material. Background Art

[0002] Lithium-ion secondary batteries using ternary polymers such as lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide as positive electrode materials are referred to as ternary lithium-ion batteries (LIBs). They have high energy density, power density, good cycle stability, and low-temperature electrochemical performance, and are widely used in transportation and portable electronic devices, such as electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs) and renewable energy storage. In order to pursue higher energy density while taking into account battery longevity and safety, people urgently need to develop and research lithium-ion battery materials with better performance.

[0003] High nickel cathode materials have the advantage of high energy density, but pure lithium nickel oxide (LiNiO 2 ) has poor structural stability. Researchers have invented a multi-component solid solution nickel-cobalt-aluminum (NCA) ternary positive electrode material doped with Co and Al to improve the cycle stability, rate capability, and safety performance of lithium nickel oxide materials, while also having high energy density. Since the current NCA positive electrode materials still have problems such as large capacity attenuation, increased impedance, unsatisfactory safety performance, poor rate performance, and insufficient endurance during the charge and discharge cycle, the large-scale application of NCA positive electrode materials is limited. The positive electrode material has a great inheritance of the structure and morphology of the precursor. If the performance of the positive electrode material is to be improved, the structure and morphology of the precursor material must be regulated, and the purpose can be achieved by controlling the morphology and arrangement of the primary particles. Summary of the invention

[0004] In view of at least some of the problems of conventional positive electrode materials, such as poor rate performance and large capacity attenuation, the present invention provides a positive electrode material precursor and a preparation method thereof, and a positive electrode material.

[0005] According to one aspect of the present invention, a positive electrode material precursor is provided, the precursor comprising an inner layer and an outer layer from inside to outside, the outer layer comprising a plurality of triangular-shaped sheet-like primary particles, the triangular-shaped sheet-like primary particles being closely interspersed on the outer surface of the inner layer along the radial direction of the inner layer.

[0006] In the above technical scheme of the present invention, the outer layer primary particles of the precursor are of a triangular structure. Such triangular sheet-shaped primary particles have high strength and strong mutual bonding force, which is beneficial to improving the strength and structural stability of the precursor material; at the same time, the outer surface of the precursor particles is made concave and convex, which increases the specific surface area of ​​the precursor material, thereby increasing the contact area with the electrolyte, reducing the internal resistance, and is beneficial to improving the battery rate performance.

[0007] In a further preferred embodiment, the chemical formula of the precursor is Ni 1-x-y M x Al y (OH) 2 , where 0≤x≤0.3, 0≤y≤0.1, and M includes at least one of Co, Mg, Ti, Zr, Mo, and Cr. The precursor provided in this solution is a high-nickel product, which has the advantages of good cycle performance, high energy density, good stability and safety performance. In addition, the internal structure of the precursor can provide more lithium ion insertion and extraction channels, which can increase the lithium ion diffusion rate when used in batteries, which is conducive to improving rate performance.

[0008] In a further preferred embodiment, adjacent triangular-shaped tab-shaped primary particles are not parallel to each other, which can further improve the structural stability of the precursor and the contact area between the material and the electrolyte.

[0009] In a further preferred embodiment, a plurality of gaps exist in the cross section of the outer layer of the positive electrode material precursor; and the radial length of the gaps is 0.02-1.0 μm.

[0010] In this solution, the formed precursor particles have multiple radial gaps inside, which can provide migration channels for lithium ions, thereby improving the migration ability of lithium ions, thereby accelerating the lithium ion deintercalation process, and further improving the battery's rate performance.

[0011] In a further preferred embodiment, the average particle size D50 of the precursor is 2.0-5.0 μm, and the particle size distribution span = (D90-D10) / D50 is 0.6-1.2;

[0012] The inner layer has an average diameter of 1.0-1.2 μm.

[0013] In this scheme, by controlling the reaction conditions, the outer triangular sheet-like primary particles can be interspersed to form multiple gaps, which extend from the outer surface of the inner layer to the outer surface of the precursor particles to provide multiple lithium ion migration channels, thereby accelerating the deintercalation of lithium ions; at the same time, the structural stability of the precursor particles is guaranteed, and the product does not have the problem of particle structure collapse after normal processing. In addition, in this scheme, a precursor material with a narrow particle size distribution and good secondary particle sphericity can be obtained. The precursor particles are approximately spherical, which can increase the filling density and further increase the battery energy density.

[0014] Preferably, the average particle size D50 of the precursor is 2.2-3.8 μm, and the particle size distribution span is 0.7-0.8; at this time, the structural stability of the precursor particles and the uniformity of the particle size distribution can be further improved, while the lithium ion migration ability can be guaranteed.

[0015] Preferably, the tap density of the precursor is 1.4-1.6 g / cm 3 , with a specific surface area of ​​13-25m 2 / g. When used in batteries, it is beneficial for the full contact between the positive electrode material and the electrolyte, reducing the internal resistance and further improving the battery's conductivity.

[0016] In a further preferred embodiment, in the X-ray diffraction pattern of the precursor, the peak intensity ratio of the (101) crystal plane to the (001) crystal plane is 101 / I 001 0.7-1.0, I 101 / I 001 The peak intensity ratio is less than 1.0, and the half-peak width of the (001) plane is 0.19°-0.37°. The half-peak width is narrow, indicating that the (001) plane of the precursor is more exposed and has higher crystallinity, which is beneficial to the cyclic performance of the material. Therefore, the precursor designed in this scheme can improve the cyclic stability of the positive electrode material.

[0017] According to another aspect of the present invention, a method for preparing a positive electrode material precursor is provided, wherein a metal salt mixed solution and an alkali aluminum solution are prepared respectively;

[0018] Water, pH regulator and complexing agent are added to the reaction kettle to prepare a base liquid, and the metal salt mixed solution and the alkali aluminum solution are simultaneously pumped into the base liquid for reaction. After the reaction is completed, the average particle size of the positive electrode material precursor is 2.0-5.0 μm.

[0019] In the above technical scheme of the present invention, a mixed solution of metal salts, an alkali aluminum solution, a pH regulator and a complexing agent are added to the base liquid at the same time, and the metal ions and the pH regulator react, and coprecipitate and crystallize under the complexing action of the complexing agent, and a positive electrode material precursor is prepared by a coprecipitation method. The outer primary particles of the obtained precursor are in the shape of triangular inserts, and there are multiple gaps in the outer layer. The gaps are lithium ion channels, which can accelerate the lithium ion deintercalation process, which is beneficial to improve the rate performance and cycle performance. At the same time, the outer layer of the primary particles of the prepared precursor is tightly arranged, which is beneficial to improve the compaction density of the material, thereby improving the specific capacity.

[0020] In a further preferred embodiment, the metal salt mixed solution contains a first metal ion and a second metal ion, the total concentration of metal ions in the metal salt solution is 1.5-4.5 mol / L, and the molar ratio of the first metal ion to the second metal ion is (66.58-100):(0-33.28);

[0021] The aluminum concentration in the alkali aluminum solution is 0-1.0 mol / L, and the alkali concentration is 5.0-10.0 mol / L.

[0022] By controlling the relative amounts of the first metal, the second metal and aluminum, on the one hand, it is beneficial to form a precursor with multiple gaps in the outer cross-section, and on the other hand, it is beneficial to improve the structural stability of the high-nickel material, thereby improving the material cycle stability.

[0023] In a further preferred embodiment, the pH value of the base solution is 11.8-13.0, and the concentration of the complexing agent is 0.3-1.7 mol / L;

[0024] Preferably, before adding the metal salt mixed solution and the alkali aluminum solution, the stirring speed in the reactor is 600-800 r / min.

[0025] By controlling the reaction condition parameters, especially the pH value and the concentration of the complexing agent, it is beneficial to quickly form precursor particles with a loose inner layer, a tight outer layer, an uneven surface, and primary particles in the shape of triangular plugs, thereby providing more lithium ion channels. In addition, by controlling the stirring speed, the number of initial crystal nuclei can be increased, thereby increasing the yield and sphericity of the precursor.

[0026] In a further preferred embodiment, the reaction specifically comprises the following steps:

[0027] The metal salt mixed solution, the alkali aluminum solution, the pH adjuster and the complexing agent are added to the base liquid at the same time, the reaction temperature is adjusted to 45-80°C, the pH value is 11.0-12.0, and the concentration of the complexing agent is 0.3-1.7 mol / L for reaction. After the reaction is completed, the average particle size of the positive electrode material precursor is 2.0-5.0 μm.

[0028] Under the reaction temperature, pH value and complexing agent concentration conditions of this scheme, it is conducive to co-precipitation to obtain precursor particles with a loose inner layer, a compact outer layer and primary particles in the shape of triangular inserts. In addition, the existing nano-scale gaps and the uneven outer surface of the secondary particles are conducive to the lithium ion insertion and extraction process, thereby improving the rate performance of the material.

[0029] Preferably, the feeding flow rate of the metal salt mixed solution and the alkali-aluminum solution is 1% / h-6% / h of the total capacity of the reaction container; by adjusting the feeding flow rate of the metal salt mixed solution and the alkali-aluminum solution, the inner and outer layer structures and physical and chemical properties of the material can be controlled, and the outer layer of triangular-shaped primary particles can be formed.

[0030] Preferably, the reaction temperature is 50-70° C., the pH value is 11.0-11.7, and the concentration of the complexing agent is 0.3-1.0 mol / L; at this time, the reaction rate of forming the target precursor can be further improved.

[0031] Preferably, the pH regulator is a sodium hydroxide aqueous solution with a concentration of 5-12 mol / L, and the complexing agent is an ammonia aqueous solution with a concentration of 5-12 mol / L. The sodium hydroxide aqueous solution and the ammonia aqueous solution in the concentration range of this solution can effectively regulate the pH value and ammonia concentration of the reaction solution, and further facilitate rapid reaction to form a precursor with a loose inner layer, a compact outer layer, an uneven surface, and an outer layer primary particle in the shape of a triangular insert.

[0032] Preferably, the stirring speed during the reaction is 400-700 r / min, which is conducive to the rapid precipitation of metal ions to form precursor particles without nucleation, thereby improving the preparation efficiency.

[0033] According to another aspect of the present invention, a positive electrode material is provided, which is prepared by mixing the above-mentioned positive electrode material precursor with a lithium salt and sintering in pure oxygen. When the prepared positive electrode material is used in a battery, it can improve the compaction density, structural stability, and migration rate of lithium ions of the positive electrode material, reduce the internal resistance of the battery, and improve the specific capacity, energy density, rate capability, and cycle stability of a high-nickel ternary lithium-ion battery.

[0034] In summary, the positive electrode material precursor and preparation method thereof, and the positive electrode material provided by the present invention have at least the following beneficial effects:

[0035] 1. The outer layer of the precursor includes unique triangular-shaped primary particles. Multiple triangular-shaped primary particles are arranged radially along the inner layer, and adjacent triangular-shaped primary particles are not parallel to each other, so that the outer cross-section of the secondary particles of the precursor has obvious lithium ion channels, which can accelerate the lithium ion deintercalation process and improve the battery's rate performance.

[0036] 2. The multiple triangular-shaped sheet-like primary particles in the outer layer of the precursor are closely interlaced and the adjacent triangular-shaped sheet-like primary particles are not parallel to each other, which is beneficial to improving the compaction density of the precursor material, thereby improving the specific capacity, energy density and cycle stability of the precursor material.

[0037] 3. The outer primary particles of the precursor are triangular-shaped insert structures. Compared with primary particles of general structures, such triangular particles have high strength and strong mutual bonding force, which is beneficial to improving the strength and structural stability of the precursor material. In addition, the outer surface of the precursor particles in the present invention is concave-convex, which increases the specific surface area of ​​the precursor material, thereby increasing the contact area with the electrolyte, reducing the internal resistance, and is beneficial to improving the battery rate performance.

[0038] 4. The precursor has good crystallinity and a relatively complete crystal form. The positive electrode material prepared by the precursor has high specific capacity while taking into account good electrochemical properties such as good rate capability and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 is a SEM morphology image of the NCA precursor provided in Example 1;

[0041] Figure 2 This is the CP cross-sectional morphology of the NCA precursor provided in Example 1

[0042] Figure 3 is the XRD analysis spectrum of the NCA precursor provided in Example 1;

[0043] Figure 4 is a microscopic morphology of the NCA precursor provided in Example 2;

[0044] Figure 5 is the XRD analysis spectrum of the NCA precursor provided in Example 2;

[0045] Figure 6 This is a SEM morphology of the NCA precursor provided in Comparative Example 1;

[0046] Figure 7 is a CP cross-sectional morphology diagram of the NCA precursor provided in Comparative Example 1;

[0047] Figure 8 This is the XRD analysis spectrum of the NCA precursor provided in Comparative Example 1. DETAILED DESCRIPTION

[0048] It should be understood that the specific embodiments given herein are for the purpose of explaining to those skilled in the art and are merely illustrative rather than restrictive.

[0049] In the following description, many specific details are set forth to provide a thorough understanding of the present invention. However, it is apparent to one of ordinary skill in the art that specific details need not be adopted to practice the present invention. In other cases, well-known steps or operations are not described in detail to avoid obscuring the present invention.

[0050] The embodiment of the present invention provides a positive electrode material precursor, the surface of the precursor is uneven, the inner layer is loose, the outer layer is compact, the outer layer is formed by closely interlaced triangular-shaped primary particles, and adjacent triangular-shaped primary particles are not parallel to each other. The chemical formula of the precursor is Ni 1-x-y M x Aly (OH) 2 , wherein 0≤x≤0.3, 0≤y≤0.1, and M includes at least one of Co, Mg, Ti, Zr, Mo, and Cr. The special structure of the precursor in this embodiment can provide more lithium ion deintercalation channels, increase the lithium ion diffusion rate, and thus improve the rate performance of the positive electrode material. In addition, the densely and uniformly interspersed primary particles are conducive to improving the specific capacity, energy density, and cycle stability of the material.

[0051] In some optional embodiments, adjacent triangular-shaped tab-shaped primary particles are not parallel to each other.

[0052] In some optional embodiments, there are multiple gaps in the cross section of the outer layer of the positive electrode material precursor; the radial length of the gap is 0.02-1.0 μm. For example, the radial length of the gap can be 0.02 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1.0 μm or any value between 0.02-1.0 μm.

[0053] In some optional embodiments, the average particle size D50 of the precursor is 2.0-5.0 μm, and the average particle size D50 of the precursor is preferably 2.2-3.8 μm; for example, the average particle size of the precursor can be 2.0 μm, 2.2 μm, 2.5 μm, 3.0 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.5 μm, 5.0 μm or any value between 2.0-5.0 μm.

[0054] The particle size distribution span is 0.6-1.2, and the particle size distribution span is preferably 0.7-0.8. For example, the particle size distribution span can be 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2 or any value between 0.6-1.2.

[0055] The average diameter of the inner layer is 1.0-1.2 μm. For example, the average diameter of the inner layer can be 1.0 μm, 1.01 μm, 1.02 μm, 1.03 μm, 1.04 μm, 1.05 μm, 1.06 μm, 1.07 μm, 1.08 μm, 1.09 μm, 1.1 μm, 1.2 μm or any value between 1.0-1.2 μm.

[0056] In some optional embodiments, the tap density of the precursor is 1.4-1.6 g / cm 3 , for example, the tap density of the precursor can be 1.4 g / cm 3 , 1.41g / cm 3 , 1.42g / cm 3 , 1.43g / cm 3, 1.44g / cm 3 , 1.45g / cm 3 , 1.46g / cm 3 , 1.47g / cm 3 , 1.48g / cm 3 , 1.49g / cm 3 , 1.50g / cm 3 , 1.51g / cm 3 , 1.52g / cm 3 , 1.54g / cm 3 , 1.56g / cm 3 , 1.58g / cm 3 , 1.6g / cm 3 or 1.4-1.6g / cm 3 Any value between 13 and 25 m 2 / g, for example, the specific surface area of ​​the precursor can be 13.00m 2 / g, 13.34m 2 / g, 14.00m 2 / g, 15.00m 2 / g, 16.00m 2 / g, 17.00m 2 / g, 18.00m 2 / g, 19.00m 2 / g, 20.00m 2 / g, 20.46m 2 / g, 21.00m 2 / g, 23.00m 2 / g, 25.00m 2 / g or 13-25m 2 Any value between / g.

[0057] In some optional embodiments, in the X-ray diffraction pattern of the precursor, the peak intensity ratio of the (101) crystal plane to the (001) crystal plane is 101 / I 001 The half-peak width of the (001) crystal plane is narrow and is 0.19°-0.28°, indicating that the (001) crystal plane grows preferentially. The half-peak width of the (101) crystal plane is also narrow, indicating that the material has a high degree of crystallinity along the (001) crystal plane and the (101) crystal plane, that is, the material has good crystallinity. The positive electrode material prepared using this precursor has good cycle stability while taking into account high specific capacity.

[0058] According to another embodiment of the present invention, a method for preparing a positive electrode material precursor is provided, comprising: separately preparing a metal salt mixed solution and an alkali aluminum solution; adding water, a pH adjuster and a chelating agent into a reaction kettle to prepare a base liquid, and simultaneously adding the metal salt mixed solution and the alkali aluminum solution to the base liquid for reaction, wherein after the reaction is completed, the average particle size of the positive electrode material precursor is 2.0-5.0 μm.

[0059] In some optional embodiments, the metal salt mixed solution contains a first metal ion and a second metal ion, the total concentration of the metal ions in the metal salt mixed solution is 1.5-4.5 mol / L, and the molar ratio of the first metal ion to the second metal ion is (66.58-100):(0-33.28), wherein the content of the second metal ion is greater than 0;

[0060] The aluminum concentration in the alkali aluminum solution is 0-1.0 mol / L, and the alkali concentration is 5.0-10.0 wt.%.

[0061] In some optional embodiments, the pH value of the base solution is 11.8-13.0, and the concentration of the complexing agent is 0.3-1.7 mol / L. For example, the pH value of the base solution can be 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, 13.0 or any value between 11.8 and 13.0; the concentration of the complexing agent can be 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L or any value between 0.3 and 1.7 mol / L.

[0062] In some optional embodiments, before adding the metal salt mixed solution and the alkali aluminum solution, the stirring speed in the reactor is 600-800 r / min. For example, the stirring speed can be 600 r / min, 620 r / min, 640 r / min, 660 r / min, 680 r / min, 700 r / min, 720 r / min, 740 r / min, 760 r / min, 780 r / min, 800 r / min or any value between 600-800 r / min.

[0063] In a further preferred embodiment, the reaction specifically includes the following steps: adding a metal salt mixed solution, an alkali aluminum solution, a pH adjuster and a complexing agent to the base liquid at the same time, adjusting the reaction temperature to 45-80°C, the pH value to 11.0-12.0, and the complexing agent concentration to 0.3-1.0 mol / L for reaction, and after the reaction is completed, the average particle size of the positive electrode material precursor is 2.0-5.0 μm.

[0064] In some optional embodiments, the feeding flow rates of the metal salt mixed solution and the alkali-aluminum solution are both 1% / h-6% / h of the total capacity of the reaction container; by adjusting the feeding flow rates of the metal salt mixed solution and the alkali-aluminum solution, it is beneficial to quickly form a loose inner layer, and the outer layer is wrapped around the surface of the inner layer at a slower speed, and the triangular sheets are arranged tightly.

[0065] In some optional embodiments, the reaction temperature is 50-70°C, the pH value is 11.0-11.7, and the complexing agent concentration is 0.3-1.0 mol / L; at this time, the risk of forming new nuclei during the reaction can be reduced, the particle size distribution can be avoided from becoming wider, and the tap density of the material can be increased.

[0066] In some optional embodiments, the pH regulator is a sodium hydroxide aqueous solution with a concentration of 5-12 mol / L, and the complexing agent is an ammonia solution with a concentration of 5-12 mol / L. For example, the concentration of the sodium hydroxide aqueous solution and the concentration of the ammonia solution can be 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, 12 mol / L or any value between 5-12 mol / L. It is understood that the complexing agent can also be any one or more of citric acid, ethanolamine or acetylacetone.

[0067] Preferably, the stirring speed during the reaction is 400-700 r / min, which is beneficial to reduce the risk of forming new nuclei during the reaction and avoid the particle size distribution of the precursor particles from becoming wider while ensuring the sphericity and yield of the particles. For example, the stirring speed during the reaction can be 400 r / min, 450 r / min, 500 r / min, 550 r / min, 600 r / min, 650 r / min, 700 r / min or any value between 400-700 r / min.

[0068] In the embodiment of the present invention, a positive electrode material precursor is prepared by a coprecipitation method. Specifically, a metal salt mixed solution, an alkali aluminum solution, a sodium hydroxide solution and ammonia water are pumped into a reactor at the same time, and metal ions, aluminum ions and sodium hydroxide react, and coprecipitate crystals under the complexation of ammonia water. The whole reaction process is in a dynamic equilibrium state. Among them, the complexing agent can control the crystallization speed and morphology, and pH, ammonia concentration, and reaction temperature mainly affect the crystallization process. In combination with the synergistic effect of stirring speed, feed flow rate and other conditions, under high ammonia concentration and low pH conditions, the outer primary particles of the positive electrode material precursor obtained by coprecipitation are in the shape of triangular inserts, and there are multiple radial gaps in the outer cross section. The gap is a reserved channel for lithium ions, which can accelerate the deintercalation process of lithium ions and improve the rate performance of the positive electrode material. At the same time, the outer primary particles of the precursor are closely arranged, which is conducive to improving the compaction density of the precursor material and ensuring the high specific capacity of the precursor material. In addition, the addition of Al improves the structural stability of the high-nickel material and can improve its cycle stability.

[0069] According to another aspect of the present invention, a positive electrode material is provided, which is prepared by mixing and sintering the positive electrode material precursor and a lithium salt. Specifically, the positive electrode material precursor and lithium hydroxide (LiOH) or lithium carbonate (Li 2 CO 3 ) or lithium nitrate (LiNO 3 ) are mixed evenly in a certain proportion, transformed into oxides through high-temperature solid-phase sintering in a pure oxygen atmosphere, and then crushed and graded to form positive electrode materials. The prepared positive electrode materials have good electrochemical properties and thermal stability.

[0070] In order to make the purpose, technical solutions and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. However, the described specific embodiments are only used to explain the present invention and are not used to limit the present invention.

[0071] Example 1

[0072] Prepare a positive electrode material precursor, whose chemical formula is Ni 0.885 Co 0.09 Al 0.025 (OH) 2 .

[0073] The method for preparing the positive electrode material precursor in this embodiment comprises the following steps:

[0074] Step 1: prepare a nickel-cobalt metal salt mixed solution with a total metal ion concentration of 2.5 mol / L according to a Ni:Co molar ratio of 0.908:0.092, prepare a sodium hydroxide aqueous solution with a concentration of 12 mol / L as liquid alkali, prepare ammonia water with a concentration of 10 mol / L, add liquid alkali to the aluminum sulfate solution to prepare an alkali-aluminum solution with a concentration of 0.05 mol / L, wherein the sodium hydroxide accounts for 7 wt.%;

[0075] Step 2: Add pure water to the reactor, then add an appropriate amount of ammonia water in step 1 to make the ammonia concentration 1.2 mol / L, add an appropriate amount of liquid alkali in step 1 to make the pH = 12.6, use the above solution as the base liquid, and start the stirring speed at 462 r / min;

[0076] Step 3: Adjust the stirring speed of the reactor to 694r / min, pump 2.5mol / L of nickel-cobalt metal salt mixed solution, 0.05mol / L of alkali-aluminum solution, 12mol / L of sodium hydroxide aqueous solution and 10mol / L of ammonia water into the reactor from their respective feed pipes at the same time, control the flow rate of nickel-cobalt metal salt and alkali-aluminum solution to 2.0% / h of the total capacity of the reaction container, control the reaction temperature to 60±1°C, control the pH range to 11.0-11.7, and the ammonia concentration range to 0.3-1.0mol / L, and stop feeding when the D50 of the sampled particles reaches 3.5±0.3μm;

[0077] Step 4: The reaction slurry of step 3 is subjected to solid-liquid separation, washing, dehydration by centrifuge, drying and sieving to finally obtain a cathode material precursor.

[0078] The obtained cathode material precursor has a D50 of 3.408 μm, a span of 0.733, and a tap density of 1.52 g / cm 3 , with a specific surface area of ​​13.34m 2 / g, morphology Figure 1 and Figure 2 As shown, the average diameter of the inner layer is 1.099 μm, the primary particles in the inner layer are needle-shaped and randomly distributed, and the primary particles on the outer layer surface are triangular insert-shaped; the primary particles form secondary particles with a sphericity of 90.5% (the sphericity is calculated by αvizo software), and there are multiple gaps in the outer layer cross section, which are reserved channels for lithium ions. Figure 2 The gaps a, b, c, and d of the outer layer cross section are marked as examples. They are mainly arranged along the radial direction from the inner layer to the outer layer. The gaps are in the shape of long and thin strips with lengths of 0.37 μm, 0.75 μm, 0.85 μm, and 0.06 μm, respectively, and an average length of 0.51 μm. Figure 3This is the phase analysis of NCA. It can be seen that there is a short peak at 11° in the spectrum, which is the layered double hydroxide (LDH) peak of the NCA precursor. Its existence indicates that Al, Ni and Co form a solid solution, and the crystal form is a layered structure with a P-3m1 space lattice group, which is conducive to stabilizing the structure and improving the cycle stability of the precursor material. 101 / I 001 The peak intensity ratio is 0.869, the half-peak width of the (001) crystal plane is 0.199°, and the half-peak width of the (101) crystal plane is 0.253°, indicating that the (001) plane is more exposed, and the precursor has good crystallinity and a relatively complete crystal form. The precursor can be used to develop NCA positive electrode materials with high specific capacity and cycle stability.

[0079] Example 2

[0080] Prepare a positive electrode material precursor, whose chemical formula is Ni 0.88 Co 0.09 Al 0.03 (OH) 2 .

[0081] The method for preparing the positive electrode material precursor in this embodiment comprises the following steps:

[0082] Step 1: prepare a nickel-cobalt metal salt mixed solution with a total metal ion concentration of 2.5 mol / L according to a Ni:Co molar ratio of 0.907:0.093, prepare a sodium hydroxide aqueous solution with a concentration of 12.0 mol / L, prepare an ammonia solution with a concentration of 10.0 mol / L, add liquid caustic soda to the aluminum sulfate solution to prepare an alkali-aluminum solution with a concentration of 0.06 mol / L, wherein the sodium hydroxide accounts for 7 wt.%;

[0083] Step 2: Add pure water to the reactor, then add an appropriate amount of ammonia water in step 1 to make the ammonia concentration 1.2 mol / L, add an appropriate amount of liquid alkali in step 1 to make the pH = 12.6, use the above solution as the base liquid, and start the stirring speed at 462 r / min;

[0084] Step 3: Adjust the stirring speed of the reactor to 694r / min, pump 2.5mol / L nickel-cobalt metal salt aqueous solution, 0.06mol / L alkali-aluminum solution, 12.0mol / L sodium hydroxide aqueous solution and 10.0mol / L ammonia water into the reactor from their respective feed pipes at the same time, control the flow rate of nickel-cobalt metal salt and alkali-aluminum solution to 2.0% / h of the total capacity of the reaction container, control the reaction temperature to 60±1°C, control the pH range to 11.0-11.7, and the ammonia concentration range to 0.3-1.0mol / L, and stop feeding when the D50 of the sampled particles reaches 2.5±0.3μm;

[0085] Step 4: The reaction slurry of step 3 is transferred into a centrifuge for solid-liquid separation, washing, dehydration, drying, and screening to finally obtain a positive electrode material precursor.

[0086] The obtained cathode material precursor has a D50 of 2.586 μm, a span of 0.722, and a tap density of 1.41 g / cm 3 , the specific surface area is 20.46m 2 / g, such as Figure 4 As shown, the primary particles on the outer layer are in the shape of triangular inserts. The average diameter of the inner layer is close to 1.1μm, the primary particles are needle-shaped and randomly distributed, and there are multiple gaps in the cross section of the outer layer, which are reserved channels for lithium ions. Figure 4 Gaps A, B, C, and D of the outer layer cross section are marked as examples. They are mainly arranged along the radial direction from the inner layer to the outer layer. The gaps are in the shape of long and thin strips with lengths of 0.90 μm, 0.41 μm, 0.89 μm, and 0.12 μm, respectively, and an average length of 0.58 μm. Figure 5 There is a short peak at 11° in the XRD spectrum, which is the LDH peak. Its existence indicates that Al, Ni and Co form a layered solid solution, which can further stabilize the layered structure and improve the cycle stability of the positive electrode material. The narrow (001) plane half-peak width and large peak intensity ratio of the precursor indicate that it has good crystallinity. The precursor can still be used to develop NCA positive electrode materials with good rate performance and cycle stability. If the solid content of the reaction is further increased or the particle size of the secondary particles is increased, its specific capacity and cycle stability can be further improved.

[0087] Example 3

[0088] Prepare a positive electrode material precursor, whose chemical formula is Ni 0.75 Co 0.2 Al 0.05 (OH) 2 .

[0089] The method for preparing the positive electrode material precursor in this embodiment comprises the following steps:

[0090] Step 1: prepare a nickel-cobalt metal salt mixed solution with a total metal ion concentration of 2.5 mol / L according to a Ni:Co molar ratio of 0.789:0.211, prepare a sodium hydroxide aqueous solution with a concentration of 12 mol / L as liquid alkali, prepare ammonia water with a concentration of 10 mol / L, add liquid alkali to the aluminum sulfate solution to prepare an alkali-aluminum solution with a concentration of 0.11 mol / L, wherein the sodium hydroxide accounts for 7 wt.%;

[0091] Step 2: Add pure water to the reactor, then add an appropriate amount of ammonia water in step 1 to make the ammonia concentration 1.2 mol / L, add an appropriate amount of liquid alkali in step 1, use the above solution as the base liquid, and start stirring at a speed of 462 r / min;

[0092] Step 3: Adjust the stirring speed of the reactor to 694r / min, pump 2.5mol / L of nickel-cobalt metal salt mixed solution, 0.11mol / L of alkali-aluminum solution, 12mol / L of sodium hydroxide aqueous solution and 10mol / L of ammonia water into the reactor from their respective feed pipes at the same time, control the flow rate of nickel-cobalt metal salt and alkali-aluminum solution to 2.0% / h of the total capacity of the reaction container, control the reaction temperature to 60±1°C, control the pH range to 11.0-11.8, and the ammonia concentration range to 0.3-1.0mol / L, and stop feeding when the D50 of the sampled particles reaches 3.5±0.3μm;

[0093] Step 4: The reaction slurry of step 3 is subjected to solid-liquid separation, washing, dehydration by centrifuge, drying and sieving to finally obtain a cathode material precursor.

[0094] The obtained cathode material precursor has a D50 of 3.502 μm, a span of 0.728, and a tap density of 1.568 g / cm 3 , with a specific surface area of ​​12.54m 2 / g, the average diameter of the inner layer is 1.015μm, the primary particles in the inner layer are needle-shaped and randomly distributed, and the primary particles on the outer layer surface are triangular-shaped inserts; the primary particles form secondary particles with a sphericity of 89.8%, and there are multiple gaps in the outer layer cross section, which are reserved channels for lithium ions. The gaps are in the shape of long and thin strips with lengths of 0.26μm, 0.61μm, 0.82μm, and 0.09μm, respectively, and an average length of 0.45μm.

[0095] Comparative Example 1

[0096] Compared with Example 1, except for the different pH value of the precursor product preparation process, the other process parameters are the same. Specifically as follows:

[0097] Prepare a positive electrode material precursor, whose chemical formula is Ni 0.885 Co 0.09 Al 0.025 (OH) 2 , including the following steps:

[0098] Step 1: prepare a nickel-cobalt metal salt mixed solution with a total metal ion concentration of 2.5 mol / L according to a Ni:Co molar ratio of 0.908:0.092, prepare a sodium hydroxide aqueous solution with a concentration of 12 mol / L as liquid alkali, prepare ammonia water with a concentration of 10 mol / L, add liquid alkali to the aluminum sulfate solution to prepare an alkali-aluminum solution with a concentration of 0.05 mol / L, wherein the sodium hydroxide accounts for 7 wt.%;

[0099] Step 2: Add pure water to the reactor, then add an appropriate amount of ammonia water in step 1 to make the ammonia concentration 1.2 mol / L, add an appropriate amount of liquid alkali in step 1 to make the pH = 12.6, use the above solution as the base liquid, and start the stirring speed at 462 r / min;

[0100] Step 3: Adjust the stirring speed of the reactor to 694r / min, pump 2.5mol / L of nickel-cobalt metal salt mixed solution, 0.05mol / L of alkali-aluminum solution, 12.0mol / L of sodium hydroxide aqueous solution and 10.0mol / L of ammonia water into the reactor from their respective feed pipes at the same time, control the flow rate of the nickel-cobalt metal salt solution and the alkali-aluminum solution to 2.0% / h of the total capacity of the reaction container, control the reaction temperature to 60±1°C, control the pH range to 11.7-12.2, and the ammonia concentration range to 0.3-1.0mol / L, and stop feeding when the D50 of the sampled particles reaches 3.5±0.3μm;

[0101] Step 4: The reaction slurry in step 3 is transferred into a centrifuge for solid-liquid separation and washing, and then dehydrated by a centrifuge and dried and sieved to finally obtain a positive electrode material precursor.

[0102] The obtained cathode material precursor has a D50 of 3.631 μm, a span of 0.848, and a tap density of 1.87 g / cm 3 , the specific surface area is 10.81m 2 / g, morphology Figure 6 , Figure 7 As shown, the average diameter of the inner layer is 1.366 μm, the primary particles form secondary particles with a sphericity of 94.1%, the primary particles on the particle surface are rice-grain-shaped, and the outer primary particles are radially arranged in a columnar shape. Figure 8 The phase analysis of NCA shows that there is no obvious LDH characteristic peak in the XRD spectrum, the half-peak width of the (001) crystal plane is 0.581°, the half-peak width of the (101) crystal plane is 0.667°, the (001) plane is less exposed, and its crystallinity is worse than that of the embodiment. 101 / I 001 The peak intensity ratio is 0.925. The NCA cathode material prepared by this precursor has a higher specific capacity, but poor cycle stability.

[0103] Table 1 Physical and chemical properties of precursor materials of Examples 1-3 and Comparative Example 1:

[0104]

[0105]

[0106] Performance Testing

[0107] The high-temperature solid phase method was used to sinter the uniformly mixed NCA precursor and lithium hydroxide into a positive electrode material, and its physical and chemical properties were tested, and the electrochemical performance, including the first efficiency, charge and discharge specific capacity, rate capability and cyclability, was verified. The specific operation is as follows:

[0108] Take two equal parts of the positive electrode material precursor obtained in Example 1, mix them with lithium hydroxide in proportion, place one part in an oxygen atmosphere furnace at 830°C for 10 hours, and place the other part in an oxygen atmosphere furnace at 720°C for 12 hours. Prepare the positive electrode materials from the sintered materials, which are respectively recorded as LNCAO-1 (830°C) single crystal positive electrode material and LNCAO-2 (720°C) polycrystalline positive electrode material. The electrochemical properties are shown in the following table, where there are 4 single crystal and polycrystalline parallel samples, and the average value is taken in the table.

[0109] The cathode material precursor obtained in Example 2 was mixed evenly with lithium hydroxide in a certain proportion, sintered at 830°C for 10 h, and then crushed with a mortar to obtain LiNi 0.88 Co 0.09 Al 0.03 O 2 The positive electrode material is LNCAO-3 (830°C) single crystal positive electrode material. The electrochemical performance thereof is shown in the following table, where there are 4 parallel samples and the table shows the average value.

[0110] The cathode material precursor obtained in Example 3 was mixed evenly with lithium hydroxide in proportion, sintered at 830°C for 10 h, and then crushed with a mortar to obtain LiNi 0.75 Co 0.20 Al 0.05 O 2 The positive electrode material is LNCAO-4 (830°C) single crystal positive electrode material. The electrochemical performance thereof is shown in the following table, where there are 4 parallel samples and the table shows the average value.

[0111] Take two equal parts of the positive electrode material precursor obtained in Comparative Example 1, mix them with lithium hydroxide in proportion, place one part in an oxygen atmosphere furnace at 830°C for 10 hours, and place the other part in an oxygen atmosphere furnace at 720°C for 12 hours. Prepare the positive electrode materials from the sintered materials, which are respectively recorded as LNCAO-5 (830°C) single crystal positive electrode material and LNCAO-6 (720°C) polycrystalline positive electrode material. The physical and chemical properties and electrochemical properties are shown in the following table, where there are 4 parallel samples of single crystal and polycrystalline, and the average value is taken in the table.

[0112] Table 2 Electrochemical properties of positive electrode materials made from precursors of Examples 1-3 and Comparative Example 1.

[0113]

[0114] It can be seen from Table 1 and Table 2 that the first charge specific capacity of Examples 1-3 at room temperature 0.1C exceeds 229mA·h / g, and the first discharge specific capacity exceeds 200mA·h / g; and the rate capability of samples LNCAO-1, ​​LNCAO-2, LNCAO-3 and LNCAO-4 of Examples 1-3 is about 91%, which is better than LNCAO-5 and LNCAO-6 of the comparative examples. Regardless of single crystal and polycrystalline, the capacity retention rate of samples LNCAO-1 and LNCAO-2 of Example 1 after 50 cycles at 1C is higher than that of the comparative example, and the retention rate reaches 89.8% and 91.9%. The cycle retention rates of Examples 2 and 3 are also 88.7% and 92.2%, respectively, which are better than the comparative example. It can be proved that the triangular-like primary particles and their arrangement are beneficial to improving the cycle stability and rate capability of NCA positive electrode materials.

[0115] Conventional NCA materials generally have the problem of capacity decay during cyclic charge and discharge, which is related to the Li + / Ni 2+ The positive electrode material undergoes volume expansion or contraction and structural deformation during the cycle charge and discharge, resulting in capacity loss and cycle performance degradation during the charge and discharge process. In addition, the high oxidation state Ni of the NCA positive electrode material in the charging state 4+ Side reactions occur when in contact with the electrolyte, and the increased impedance will reduce the specific capacity and rate performance, and the heat and oxygen generated will reduce the safety of the battery. The present invention provides a positive electrode material precursor, in which the outer layer of the particles is interspersed with triangular-shaped primary particles, and the structure is stable, and it has a special lithium ion migration channel. The NCA positive electrode material prepared thereby has a uniform nano-gap inside, whether it is a single crystal or a polycrystalline, and the layered structure is relatively stable, especially the polycrystalline secondary material, which not only has a high specific capacity, but also improves the cycle stability and rate performance of the NCA positive electrode material, and has a lot of room for development for practical market applications. In addition, the NCA precursor in the embodiment is sintered with lithium hydroxide, and after dehydration, multiphase reaction, melting and recrystallization processes, the triangular-shaped primary particles do not fall off or peel, indicating that the primary particles are tightly combined, and the structural stability of the material is strong.

[0116] The various technical features described above can be combined arbitrarily. Although all possible combinations of these technical features are not described, any combination of these technical features should be considered to be covered by this specification as long as there is no contradiction in such combination.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cathode material precursor, characterized in that: The precursor comprises an inner layer and an outer layer from the inside to the outside, wherein the outer layer comprises a plurality of triangular-shaped primary particles, and the triangular-shaped primary particles are closely interspersed on the outer surface of the inner layer along the radial direction of the inner layer, wherein the chemical formula of the precursor is Ni 1-x-y M x Al y (OH)2, wherein 0≤x≤0.3, 0≤y≤0.1, and M includes at least one of Co, Mg, Ti, Zr, Mo, and Cr.

2. The cathode material precursor according to claim 1, characterized in that: Adjacent triangular-shaped sheet-like primary particles are not parallel to each other.

3. The cathode material precursor according to claim 1, characterized in that: There are a plurality of gaps in the cross section of the outer layer of the positive electrode material precursor, and the radial length of the gaps is 0.02-1.0 μm.

4. The cathode material precursor according to claim 1, characterized in that: The average particle size D50 of the precursor is 2.0-5.0 μm, and the particle size distribution span=(D90-D10) / D50 is 0.6-1.2; the average diameter of the inner layer is 1.0-1.2 μm.

5. The cathode material precursor according to claim 4, characterized in that: The average particle size D50 of the precursor is 2.2-3.8 μm, and the particle size distribution span is 0.7-0.

8.

6. The cathode material precursor according to claim 4, characterized in that: The tap density of the precursor is 1.4-1.6 g / cm 3 , with a specific surface area of ​​13-25m 2 / g.

7. The cathode material precursor according to claim 1, characterized in that: In the X-ray diffraction pattern of the precursor, the peak intensity ratio of the (101) crystal plane to the (001) crystal plane is 101 / I 001 The half-peak width of the (001) crystal plane is 0.19°-0.37°.

8. A method for preparing a positive electrode material precursor, characterized in that: The preparation method comprises the following steps: preparing a metal salt mixed solution and an alkali aluminum solution respectively; Add water, pH regulator and complexing agent to the reaction kettle to prepare a base liquid, and add the metal salt mixed solution, the alkali aluminum solution, pH regulator and complexing agent to the base liquid at the same time, adjust the reaction temperature to 45°C-80°C, and the pH value to 11.0-12.0 for reaction, and obtain a positive electrode material precursor after the reaction is completed, wherein the positive electrode material precursor includes an inner layer and an outer layer from the inside to the outside, wherein the outer layer includes a plurality of triangular-shaped primary particles, and the triangular-shaped primary particles are closely interspersed on the outer surface of the inner layer along the radial direction of the inner layer, and the chemical formula of the precursor is Ni 1-x-y M x Al y (OH)2, wherein 0≤x≤0.3, 0≤y≤0.1, and M includes at least one of Co, Mg, Ti, Zr, Mo, and Cr.

9. The method for preparing a cathode material precursor according to claim 8, characterized in that: The metal salt mixed solution contains a first metal ion and a second metal ion, the total concentration of the metal ions in the metal salt mixed solution is 1.5-4.5 mol / L, and the molar ratio of the first metal ion to the second metal ion is (66.58-100):(0-33.28); The aluminum concentration in the alkali aluminum solution is 0-1.0 mol / L, and the alkali concentration is 5.0-10.0 wt.%.

10. The method for preparing a cathode material precursor according to claim 8, characterized in that: The pH value of the base solution is 11.8-13.0, and the concentration of the complexing agent is 0.3-1.7 mol / L.

11. The method for preparing a cathode material precursor according to claim 10, characterized in that: Before adding the metal salt mixed solution and the alkali aluminum solution, the stirring speed in the reactor is 600-800 r / min.

12. The method for preparing a cathode material precursor according to claim 8, characterized in that: During the reaction, the concentration of the complexing agent is 0.3-1.7 mol / L, and the average particle size of the positive electrode material precursor is 2.0-5.0 μm.

13. The method for preparing a cathode material precursor according to claim 12, characterized in that: The feed flow rates of the metal salt mixed solution and the alkali aluminum solution are both 1% / h-6% / h of the total capacity of the reaction container.

14. The method for preparing a cathode material precursor according to claim 12, characterized in that: During the reaction, the reaction temperature is 50-70° C., the pH value is 11.0-11.7, and the concentration of the complexing agent is 0.3-1.0 mol / L.

15. The method for preparing a cathode material precursor according to claim 12, characterized in that: The pH regulator is a sodium hydroxide aqueous solution with a concentration of 5-12 mol / L, and the complexing agent is an ammonia aqueous solution with a concentration of 5-12 mol / L.

16. The method for preparing a cathode material precursor according to claim 12, characterized in that: The stirring speed during the reaction is 400-700 r / min.

17. A positive electrode material, characterized in that: The cathode material is prepared by mixing and sintering the cathode material precursor according to any one of claims 1 to 7 and a lithium salt.

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