Monocrystal nickel-rich positive electrode material and preparation method and application thereof

Abstract

The invention provides a single-crystal nickel-rich positive electrode material as well as a preparation method and application thereof. The single-crystal nickel-rich positive electrode material comprises a doped nickel-rich single-crystal inner core and a fast ion conductor coating layer arranged on the surface of the doped nickel-rich single-crystal inner core, wherein the surface layer of the doped nickel-rich single crystal inner core is doped with an Nb element, and the Nb element is doped in the surface layer of the doped nickel-rich single crystal inner core in a gradient increasing manner from inside to outside. The niobium is doped on the surface layer of the nickel-rich single crystal core of the positive electrode material in a gradient manner, the fast ion conductor is coated on the outer layer, and through'bulk phase-interface 'dual optimization, not only can the structural stability of the positive electrode material be improved, but also the charge transfer performance of the positive electrode material can be improved, so that the rate capability and the cycle performance of the material are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials and relates to a single crystal nickel-rich positive electrode material and a preparation method and application thereof. Background Art

[0002] With the growing global demand for clean energy, lithium-ion batteries have been widely used in electric vehicles, energy storage systems and other fields due to their advantages such as high energy density and long cycle life. x Co y Mn 1-x- y O2, x≥0.8) has become a key material for improving the energy density of lithium-ion batteries due to its high specific capacity and low cost, and is regarded as one of the positive electrode materials with the greatest development potential.

[0003] However, nickel-rich cathode materials still face many challenges in practical applications. On the one hand, the lattice structure of nickel-rich cathode materials is prone to phase changes during the charge and discharge process, resulting in unstable material structure, which in turn causes capacity decay and decreased cycle performance. On the other hand, nickel-rich cathode materials have high surface activity and serious side reactions with the electrolyte, which not only consume active lithium and reduce the battery's initial coulombic efficiency, but also form an unstable solid electrolyte interface (SEI) film on the material surface, affecting the transmission of lithium ions and further deteriorating battery performance. In addition, nickel-rich cathode materials have poor thermal stability and are prone to thermal runaway in high-temperature environments, posing a safety hazard.

[0004] CN117913270A discloses a nickel-rich ternary single crystal positive electrode material and its preparation method and use. The method comprises the following steps: pre-treating a nickel-rich precursor to obtain a first material; mixing the first material with a second portion of a lithium source and performing a first sintering to obtain a second material, and then performing a first crushing; the pre-treatment comprises mixing the first portion of the lithium source, magnesium chloride hexahydrate, aluminum chloride hexahydrate and water to obtain a mixed solution, mixing the mixed solution with the nickel-rich precursor and then drying.

[0005] CN116354416A discloses a method for preparing a nickel-rich ternary single crystal positive electrode material, which comprises: contacting a mixed solution of sodium chloride, potassium chloride and a first lithium source with a nickel-rich precursor and drying; mixing the nickel-rich precursor with a second lithium source and performing a first sintering to obtain a sintered material; washing and drying the sintered material, supplementing lithium and performing a second sintering; and after sintering, crushing and screening to obtain a nickel-rich ternary single crystal positive electrode material.

[0006] The above scheme adopts modification methods such as element doping and surface coating to change the lattice structure and electronic structure of the material by introducing aliovalent ions, thereby improving the structural stability and thermal stability of the material. However, the above scheme is difficult to achieve precise control of material properties and cannot fully exert the rate performance and cycle performance of nickel-rich positive electrode materials. Summary of the Invention

[0007] The purpose of the present invention is to provide a single-crystal nickel-rich positive electrode material, a preparation method and application thereof. The present invention gradiently dopes niobium on the surface of the nickel-rich single-crystal core of the positive electrode material and coats the outer layer with a fast ion conductor. Through the dual optimization of "bulk phase-interface", not only the structural stability of the positive electrode material can be improved, but also the charge transfer performance of the positive electrode material can be improved, thereby improving the rate performance and cycle performance of the material.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a single-crystal nickel-rich positive electrode material, comprising a doped nickel-rich single-crystal core and a fast ion conductor coating layer disposed on the surface of the doped nickel-rich single-crystal core;

[0010] The surface layer of the doped nickel-rich single crystal core is doped with Nb element, and the Nb element is doped in the surface layer of the doped nickel-rich single crystal core in a gradient increasing manner from the inside to the outside.

[0011] In the single crystal nickel-rich cathode material of the present invention, the surface layer of the core is doped with niobium (Nb) in a gradient manner from the inside to the outside to replace Ni. 2 + site, strong Nb-O bond can stabilize lattice oxygen, stabilize the crystal structure of nickel-rich cathode, inhibit cation mixing and microcracks, and improve electronic conductivity. Niobium gradient distribution avoids stress mutation between the bulk and the interface, and reduces microcracks caused by lattice distortion during cycling. Fast ion conductors have high Li + conductivity, which can significantly enhance the Li + Diffusion dynamics, reduce interface side reactions. At the same time, a small amount of Nb gradient doping near the surface improves the reversibility of the H2-H3 phase transition, reduces the surface lattice oxygen activity, and prevents the formation of a disordered rock salt phase due to strong Nb-O bonds.

[0012] The present invention improves bulk electron conduction by gradient doping Nb on the surface of the nickel-rich single crystal core, and coats the core surface with a fast ion conductor to optimize surface ion conduction, thereby jointly reducing polarization. At the same time, the charge compensation effect of Nb can alleviate the electronic insulation of the fast ion conductor coating layer, thus avoiding Li + They accumulate at the interface, and the synergistic effect of the two can optimize the charge transfer performance of the positive electrode material and improve the rate performance of the nickel-rich positive electrode material.

[0013] The fast ion conductor coating of the present invention can also block the corrosion of the nickel-rich surface by the electrolyte, inhibit the dissolution of transition metals, and reduce surface side reactions (such as Ni 3+ →Ni 2+ reduction), reducing the interface impedance growth.

[0014] The niobium doped in the core surface of the single crystal high nickel cathode material of the present invention can reduce the cracks and phase changes inside the cathode particles, and prevent the LYZP coating layer from failing due to matrix cracking. The LYZP coating layer can protect the active sites on the surface of the cathode material, prevent the direct contact between the electrolyte and the Nb doped area, and avoid the local redox reaction of Nb (such as Nb 5+ →Nb 4 + ). The synergistic effect of the two can significantly improve the stability of high nickel cathode materials.

[0015] Preferably, the fast ion conductor material in the fast ion conductor coating layer includes Li 1+m Y m Zr 2-m P3O 12 , m is 0.2 to 0.5, for example: 0.2, 0.22, 0.3, 0.4 or 0.5, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0016] Preferably, the thickness of the fast ion conductor coating layer is 10 nm to 40 nm, for example, 10 nm, 20 nm, 30 nm, 35 nm or 40 nm, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0017] Preferably, the chemical formula of the doped nickel-rich single crystal core is Li 1+a Ni x Co y Mn z Nb b O2, where 0≤a≤0.2, 0.8≤x<1, 0 <y<0.2,0<z<0.2,x+y+z+b=1,0.001≤b≤0.02。

[0018] Preferably, taking the radius of the doped nickel-rich single crystal core as 100%, the doping depth of the Nb element is 10% to 50%, for example: 10%, 20%, 30%, 45% or 50%, etc., and is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0019] The doping depth of the Nb element in the present invention is the thickness of the surface layer of the doped nickel-rich single crystal core.

[0020] In a second aspect, the present invention provides a method for preparing the single crystal nickel-rich positive electrode material as described in the first aspect, the preparation method comprising the following steps:

[0021] (1) injecting a nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a first complexing agent solution into the bottom liquid in parallel to perform a first coprecipitation reaction to generate a precursor core, maintaining the feed rate of other solutions unchanged, and simultaneously introducing a niobium source solution to perform a second coprecipitation reaction to obtain a doped precursor;

[0022] (2) mixing a lithium source, a yttrium source, a zirconium source, a phosphorus source and a solvent to obtain a mixed solution, and adding a second complexing agent and a cross-linking agent to the mixed solution to form a sol;

[0023] (3) dispersing the doped precursor in a sol, spray drying the resulting coated powder, and sintering the resulting coated powder to obtain the single crystal nickel-rich cathode material;

[0024] Wherein, the introduction rate of the niobium source solution in step (1) is gradually increased.

[0025] The present invention does not limit the order of operations of step (1) and step (2), and step (1) or step (2) can be performed first.

[0026] The present invention pre-prepares a niobium gradient-doped precursor, then coats its surface with a LYZP precursor via a sol-gel method. This is then spray-dried and sintered to produce a single-crystal nickel-rich cathode material. In this method, the LYZP precursor sol (a mixed solution of lithium, yttrium, zirconium, and phosphorus sources) undergoes a hydrolysis-polycondensation reaction to form an amorphous gel layer on the surface of the precursor particles. This layer is then converted into a dense LYZP layer after spray drying and sintering. This method achieves uniform nanoscale coating on the cathode material surface, avoiding the agglomeration problem associated with physical mixing.

[0027] Preferably, the total mass concentration of metal ions in the nickel-cobalt-manganese mixed salt solution in step (1) is 50 g to 150 g / L, for example, 50 g / L, 80 g / L, 100 g / L, 120 g / L or 150 g / L, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0028] Preferably, the precipitant solution in step (1) comprises sodium hydroxide solution.

[0029] Preferably, the mass concentration of the precipitant solution in step (1) is 20% to 50%, for example, 20%, 25%, 30%, 40% or 50%, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the first complexing agent solution in step (1) comprises aqueous ammonia.

[0031] Preferably, the mass concentration of the first complexing agent solution in step (1) is 10% to 30%, for example, 10%, 15%, 20%, 25% or 30%, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0032] Preferably, the base liquid in step (1) includes ammonia water.

[0033] Preferably, the ammonia mass concentration in the base liquid in step (1) is 1 g / L to 10 g / L, for example: 1 g / L, 2 g / L, 5 g / L, 8 g / L or 10 g / L, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0034] Preferably, the feeding rate of the nickel-cobalt-manganese mixed salt solution in step (1) is 6 L / h to 10 L / h, for example: 6 g / L, 7 g / L, 8 g / L, 9 g / L or 10 g / L, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the feed rate of the precipitant solution in step (1) is 2 L / h to 3 L / h, for example: 2 g / L, 2.2 g / L, 2.5 g / L, 2.8 g / L or 3 g / L, etc., not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] Preferably, the feeding rate of the first complexing agent solution in step (1) is 0.6 L / h to 1 L / h, for example: 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L or 1 g / L, etc., not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, the temperature of the first coprecipitation reaction in step (1) is 30°C to 80°C, for example, 30°C, 40°C, 50°C, 70°C or 80°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0038] Preferably, the pH of the first coprecipitation reaction in step (1) is 10 to 12, for example, 10, 10.5, 11, 11.5 or 12, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0039] Preferably, stirring is performed during the first coprecipitation reaction in step (1).

[0040] Preferably, the stirring speed is 100 rpm to 500 rpm, for example, 100 rpm, 200 rpm, 300 rpm, 400 rpm or 500 rpm, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0041] Preferably, the median particle size D50 of the precursor core in step (1) is 2 μm to 3 μm, for example, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm or 3 μm, etc., and is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0042] Preferably, the solute of the niobium source solution in step (1) includes niobium nitrate and / or niobium chloride.

[0043] Preferably, the mass concentration of the niobium source solution in step (1) is 1 g / L to 3 g / L, for example, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L or 3 g / L, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0044] Preferably, the introduction rate of the niobium source solution in step (1) is 0.2 L / h to 0.5 L / h, for example, 0.2 L / h, 0.25 L / h, 0.3 L / h, 0.4 L / h or 0.5 L / h, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable and the speed gradually increases.

[0045] Preferably, the pH of the second coprecipitation reaction in step (1) is 8.5 to 9.5, for example, 8.5, 8.8, 9, 9.2 or 9.5, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0046] Preferably, the median particle size D50 of the doped precursor in step (1) is 3 μm to 4 μm, for example, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm or 4 μm, etc., and is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0047] Preferably, the lithium source in step (2) includes lithium hydroxide and / or lithium nitrate.

[0048] The lithium source in step (2) is the source of all lithium in the positive electrode material, including lithium in the positive electrode material and the fast ion conductor, so it needs to be added according to the amount of the two.

[0049] Preferably, the yttrium source in step (2) comprises yttrium nitrate.

[0050] Preferably, the zirconium source in step (2) comprises zirconium nitrate.

[0051] Preferably, the phosphorus source in step (2) includes ammonium dihydrogen phosphate and / or ammonium hydrogen phosphate.

[0052] Preferably, the solvent in step (2) comprises ethanol.

[0053] Preferably, the second complexing agent in step (2) comprises citric acid.

[0054] Preferably, the molar ratio of the total molar amount of yttrium ions and zirconium ions in the sol of step (2) to the second complexing agent is 1:(1.5-3), for example: 1:1.5, 1:1.8, 1:2, 1:2.5 or 1:3, etc., is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0055] Preferably, the cross-linking agent in step (2) comprises ethylene glycol.

[0056] Preferably, the molar ratio of the second complexing agent to the crosslinking agent in the sol of step (2) is 1:(1-2), for example: 1:1, 1:1.2, 1:1.5, 1:1.8 or 1:2, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0057] Preferably, the mixture is stirred after adding the second complexing agent in step (2).

[0058] Preferably, the pH of the solvent in step (2) is 3 to 5, for example, 3, 3.5, 4, 4.5 or 5, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0059] Preferably, the dispersion method in step (3) includes ultrasound.

[0060] Preferably, the dispersion time in step (3) is 20 min to 40 min, for example, 20 min, 25 min, 30 min, 35 min or 40 min, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0061] Preferably, the dispersion temperature in step (3) is 60°C to 80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C.

[0062] Preferably, the inlet temperature of the spray drying in step (3) is 180°C to 220°C, for example, 180°C, 190°C, 200°C, 210°C or 220°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0063] Too high an inlet temperature of the spray drying process of the present invention may cause premature crystallization or cracking of the LYZP precursor.

[0064] Preferably, the outlet temperature of the spray drying in step (3) is 90°C to 120°C, for example, 90°C, 95°C, 100°C, 110°C or 120°C, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0065] If the outlet temperature of the spray drying of the present invention is too low (<90° C.), solvent residue may result; if it is too high (>120° C.), local sintering of LYZP may occur, thereby destroying the coating uniformity.

[0066] Preferably, the sintering treatment in step (3) includes pre-firing and calcining.

[0067] Preferably, the pre-firing temperature is 300°C to 500°C, for example, 300°C, 350°C, 400°C, 450°C or 500°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0068] Preferably, the pre-burning time is 2 hours to 5 hours, for example, 2 hours, 2.5 hours, 3 hours, 4 hours or 5 hours, etc., and is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0069] Preferably, the heating rate from pre-calcination to calcination is 1°C / min to 3°C / min, for example, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min or 3°C / min, etc., and is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0070] The present invention can remove residual organic matter through low-temperature pre-calcination (lower than the decomposition temperature of the ternary precursor) and promote the transformation of the LYZP amorphous phase into the ion conductive phase.

[0071] Preferably, the calcination temperature is 700°C to 850°C, for example, 700°C, 750°C, 800°C, 820°C or 850°C, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0072] In the present invention, the calcination temperature is controlled within the above range to ensure that LYZP is crystallized and that no Li3PO4 impurity phase is generated.

[0073] Preferably, the calcination time is 3 h to 8 h, for example, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, etc., and is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0074] In a third aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the single crystal nickel-rich positive electrode material as described in the first aspect.

[0075] Compared with the prior art, the present invention has the following beneficial effects:

[0076] (1) The present invention gradiently dopes niobium on the surface of the nickel-rich single crystal core of the positive electrode material and coats the outer layer with a LYZP fast ion conductor. Through the dual optimization of "bulk phase-interface", not only the structural stability of the positive electrode material can be improved, but also the charge transfer performance of the positive electrode material can be improved, thereby improving the rate performance and cycle performance of the material.

[0077] (2) The battery made of the single crystal nickel-rich positive electrode material of the present invention has an initial discharge capacity of more than 206.3 mAh / g at 0.1C, a discharge capacity of more than 194.3 mAh / g at 0.1C after 100 cycles, and a capacity retention rate of more than 93.1% after 100 cycles at 0.1C. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 This is an SEM image of the single crystal nickel-rich positive electrode material provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0079] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0080] Example 1

[0081] This embodiment provides a single-crystal nickel-rich positive electrode material, which includes a doped nickel-rich single-crystal core and a Li-ion battery disposed on the surface of the doped nickel-rich single-crystal core. 1.3 Y 0.3 Zr 1.7 P3O 12 The LYZP fast ion conductor coating layer has a thickness of 30 nm, the surface layer of the doped nickel-rich single crystal core has a thickness of 0.6 μm, the median particle size D50 of the doped nickel-rich single crystal core is 4 μm (radius is 2 μm), niobium is doped in a gradient-increasing manner from the inside to the outside in the surface layer of the doped nickel-rich single crystal core, and the chemical formula of the doped nickel-rich single crystal core is Li 1.1 Ni 0.8 Co 0.1 Mn 0.1 Nb 0.01 O2;

[0082] The single crystal nickel-rich positive electrode material is prepared by the following method:

[0083] (1) A nickel-cobalt-manganese sulfate solution with a concentration of 100 g / L, a sodium hydroxide solution with a mass concentration of 30%, and an ammonia solution with a mass concentration of 20% were added simultaneously and concurrently to a reactor containing a bottom liquid with a temperature of 60°C, an ammonia concentration of 5 g / L, and a pH of 11 at feed rates of 8 L / h, 2.5 L / h, and 0.8 L / h, respectively, and a co-precipitation reaction was carried out at a stirring rate of 300 rpm. During the reaction, the pH of the reaction system was controlled to be 11, the ammonia concentration was 5 g / L, and the temperature was 60°C. The particle size was continuously monitored. Before the particle size reached the required value, a high-efficiency concentrator was used in the reaction process to collect all the particles and return them to the reactor for continuous reaction growth. When the particle size D 50 When the particle size reaches 2.8 μm, keep the feeding speed of other materials unchanged, introduce niobium nitrate solution with a mass concentration of 2 g / L, control the pH to 8, and gradually increase the speed of 0.3 L / h until the particle size D 50 When the particle size reaches 4 μm, the reaction is stopped and the solid-liquid separation is performed to obtain the doped precursor.

[0084] (2) Lithium hydroxide, yttrium nitrate, zirconium nitrate, and ammonium dihydrogen phosphate were dissolved in ethanol, citric acid and ethylene glycol were added (citric acid: Y + Zr = 2:1, citric acid: ethylene glycol = 1:1.5), the pH was adjusted to 3.5 with nitric acid, and the mixture was stirred at 70°C for 3 h until transparent to obtain a sol;

[0085] (3) The doped precursor is dispersed into the sol, ultrasonicated at 70°C for 30 minutes, and then spray-dried. The inlet temperature of the spray drying is 200°C, and the outlet temperature is 100°C. The spray-dried material is pre-calcined at 400°C for 3 hours, and then heated to 800°C at a heating rate of 2°C / min. The calcination is continued for 5 hours to obtain the single crystal nickel-rich positive electrode material.

[0086] The SEM image of the single crystal nickel-rich positive electrode material is as follows Figure 1 shown.

[0087] Example 2

[0088] This embodiment provides a single-crystal nickel-rich positive electrode material, which includes a doped nickel-rich single-crystal core and a Li-ion battery disposed on the surface of the doped nickel-rich single-crystal core. 1.3 Y 0.3 Zr 1.7 P3O 12 The LYZP fast ion conductor coating layer has a thickness of 10 nm, the surface layer of the doped nickel-rich single crystal core has a thickness of 0.15 μm, the median particle size D50 of the doped nickel-rich single crystal core is 3 μm (radius is 1.5 μm), niobium is doped in a gradient-increasing manner from the inside to the outside in the surface layer of the doped nickel-rich single crystal core, and the chemical formula of the doped nickel-rich single crystal core is Li 1.1Ni 0.8 Co 0.1 Mn 0.1 Nb 0.001 O2;

[0089] The single crystal nickel-rich positive electrode material is prepared by the following method:

[0090] (1) A nickel-cobalt-manganese sulfate solution with a concentration of 50 g / L, a sodium hydroxide solution with a mass concentration of 20%, and an ammonia solution with a mass concentration of 10% were added simultaneously and concurrently to a reactor containing a bottom liquid with a temperature of 30°C, an ammonia concentration of 5 g / L, and a pH of 10 at feed rates of 10 L / h, 10 L / h, and 1 L / h, respectively, and a co-precipitation reaction was carried out at a stirring rate of 300 rpm. During the reaction, the pH of the reaction system was controlled to be 11, the ammonia concentration was 5 g / L, and the temperature was 60°C. The particle size was continuously monitored. Before the particle size reached the required value, a high-efficiency concentrator was used in the reaction process to collect all the particles and return them to the reactor for continuous reaction growth. When the particle size D 50 When the particle size reaches 2.7 μm, keep the feeding speed of other materials unchanged, introduce niobium nitrate solution with a mass concentration of 2 g / L, control the pH to 8.5, and gradually increase the speed of 0.5 L / h until the particle size D 50 When the particle size reaches 3 μm, the reaction is stopped and the solid-liquid separation is performed to obtain the doped precursor.

[0091] (2) Lithium hydroxide, yttrium nitrate, zirconium nitrate, and ammonium dihydrogen phosphate were dissolved in ethanol, citric acid and ethylene glycol were added (citric acid: Y + Zr = 2:1, citric acid: ethylene glycol = 1:1.5), the pH was adjusted to 3 with nitric acid, and the mixture was stirred at 70°C for 3 h until transparent to obtain a sol;

[0092] (3) The doped precursor is dispersed into the sol, ultrasonicated at 60°C for 20 minutes, and then spray-dried. The inlet temperature of the spray drying is 180°C, and the outlet temperature is 90°C. The spray-dried material is pre-calcined at 300°C for 5 hours, and then heated to 700°C at a heating rate of 1°C / min, and calcined for 8 hours to obtain the single crystal nickel-rich positive electrode material.

[0093] Example 3

[0094] This embodiment provides a single-crystal nickel-rich positive electrode material, which includes a doped nickel-rich single-crystal core and a Li-ion battery disposed on the surface of the doped nickel-rich single-crystal core. 1.3 Y 0.3 Zr 1.7 P3O 12The LYZP fast ion conductor coating layer has a thickness of 50 nm, the surface layer of the doped nickel-rich single crystal core has a thickness of 0.9 μm, the median particle size D50 of the doped nickel-rich single crystal core is 3.6 μm (radius is 1.8 μm), niobium is doped in a gradient-increasing manner from the inside to the outside in the surface layer of the doped nickel-rich single crystal core, and the chemical formula of the doped nickel-rich single crystal core is Li 1.1 Ni 0.8 Co 0.1 Mn 0.1 Nb 0.02 O2;

[0095] The single crystal nickel-rich positive electrode material is prepared by the following method:

[0096] (1) A nickel-cobalt-manganese sulfate solution with a concentration of 150 g / L, a sodium hydroxide solution with a mass concentration of 50%, and an ammonia solution with a mass concentration of 30% were simultaneously added to a reactor containing a bottom liquid with a temperature of 80°C, an ammonia concentration of 10 g / L, and a pH of 12 at a feed rate of 10 L / h, 10 L / h, and 1 L / h, and a co-precipitation reaction was carried out at a stirring rate of 500 rpm. During the reaction, the pH of the reaction system was controlled to be 12, the ammonia concentration was 10 g / L, and the temperature was 80°C. The particle size was continuously monitored. Before the particle size reached the required value, a high-efficiency concentrator was used in the reaction process to collect all the particles and return them to the reactor for continuous reaction growth. When the particle size D 50 When the particle size reaches 1.8 μm, keep the feeding speed of other materials unchanged, introduce niobium nitrate solution with a mass concentration of 3 g / L, control the pH to 9.5, and gradually increase the speed of 0.2 L / h until the particle size D 50 When the particle size reaches 3.6 μm, the reaction is stopped and the solid-liquid separation is performed to obtain the doped precursor.

[0097] (2) Lithium hydroxide, yttrium nitrate, zirconium nitrate, and ammonium dihydrogen phosphate were dissolved in ethanol, citric acid and ethylene glycol were added (citric acid: Y + Zr = 2:1, citric acid: ethylene glycol = 1:1.5), the pH was adjusted to 5 with nitric acid, and the mixture was stirred at 80°C for 3 h until transparent to obtain a sol;

[0098] (3) The doped precursor is dispersed into the sol, ultrasonicated at 80°C for 20 minutes, and then spray-dried. The inlet temperature of the spray drying is 220°C, and the outlet temperature is 120°C. The spray-dried material is pre-calcined at 500°C for 2 hours, and then heated to 850°C at a heating rate of 3°C / min, and calcined for 3 hours to obtain the single crystal nickel-rich positive electrode material.

[0099] Example 4

[0100] The only difference between this embodiment and embodiment 1 is that the LYZP fast ion conductor is replaced with LLZO (Li7La3Zr2O12 ) fast ion conductor, and other conditions and parameters are exactly the same as those in Example 1.

[0101] Example 5

[0102] The only difference between this embodiment and embodiment 1 is that the niobium doping amount in the core is controlled to be 0.05% (ie, b=0.0005). Other conditions and parameters are exactly the same as those in embodiment 1.

[0103] Example 6

[0104] The only difference between this embodiment and embodiment 1 is that the niobium doping amount in the core is controlled to be 3% (ie, b=0.003). Other conditions and parameters are exactly the same as those in embodiment 1.

[0105] Example 7

[0106] The only difference between this embodiment and embodiment 1 is that the thickness of the LYZP fast ion conductor coating layer is controlled to be 5 nm, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0107] Example 8

[0108] The only difference between this embodiment and embodiment 1 is that the thickness of the LYZP fast ion conductor coating layer is controlled to be 50 nm, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0109] Comparative Example 1

[0110] The only difference between this comparative example and Example 1 is that the niobium nitrate solution is introduced at the beginning of the coprecipitation, thereby doping niobium into the core. Other conditions and parameters are exactly the same as those in Example 1.

[0111] Comparative Example 2

[0112] The only difference between this comparative example and Example 1 is that the flow rate of the niobium nitrate solution remains unchanged, and the surface of the single crystal core is uniformly doped with niobium. Other conditions and parameters are exactly the same as those in Example 1.

[0113] Comparative Example 3

[0114] The only difference between this comparative example and Example 1 is that the LYZP fast ion conductor is not coated, and other conditions and parameters are exactly the same as those in Example 1.

[0115] Performance testing:

[0116] The single crystal nickel-rich positive electrode material, conductive agent (such as acetylene black) and binder (such as polyvinylidene fluoride, PVDF) are mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent in a certain mass ratio (usually 8:1:1 or other suitable ratios) and stirred evenly to form a slurry. The slurry is evenly coated on an aluminum foil current collector and then dried in a vacuum oven at 100 ° C. The positive electrode sheet is cut to obtain a positive electrode sheet. In an argon-filled glove box, the prepared positive electrode sheet, lithium metal sheet (as the negative electrode), separator (Celgard2400 polypropylene separator) and electrolyte (1 mol / LLiPF6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed solvent, volume ratio 1:1) are assembled into a CR2032 button cell. Its rate performance and cycle performance are tested. The test results are shown in Table 1:

[0117] Table 1

[0118]

[0119] As can be seen from Table 1, from Examples 1-8, the 0.1C initial discharge specific capacity of the battery made of the single crystal nickel-rich positive electrode material of the present invention can reach more than 206.3 mAh / g, the 0.1C 100-week discharge specific capacity can reach more than 194.3 mAh / g, and the 0.1C cycle capacity retention rate after 100 cycles can reach more than 93.1%.

[0120] By comparing Example 1 and Example 4, it can be seen that the material type of the fast ion conductor coating layer of the single crystal nickel-rich positive electrode material of the present invention affects its performance. The LLZO fast ion conductor easily reacts with H2O / CO2 to form Li2CO3, resulting in increased interfacial impedance. The present invention uses LYZP as the phosphorus (P) stabilizing framework of the fast ion conductor coating layer to neutralize HF in the electrolyte and inhibit transition metal dissolution. The LYZP stabilizing framework (PO43-) can also inhibit lattice oxygen escape, reduce gas production and phase change, and Nb doping further stabilizes the positive electrode surface and reduces side reactions between LYZP and the electrolyte. LYZP has high air stability and low interfacial impedance, which can significantly improve the material's cycle stability.

[0121] From the comparison between Example 1 and Examples 5-6, it can be seen that the niobium doping amount in the core of the single crystal nickel-rich cathode material of the present invention affects its performance. When the niobium doping amount in the core is controlled at 0.1% to 2%, the performance of the single crystal nickel-rich cathode material is better. If the niobium doping amount in the core is too high, Nb occupies the transition metal sites (Ni / Co / Mn), and excessive doping will reduce the active Ni 2 + / Ni 3+ content, resulting in a decrease in reversible capacity. Excessive Nb leads to excessively high electronic conductivity, which can trigger local charge accumulation and exacerbate interfacial side reactions. If the niobium doping level in the core is too low, the H2→H3 phase transition cannot be effectively suppressed, leading to lattice distortion and microcracks. It also increases nickel-lithium mixing, resulting in a decrease in cycling performance.

[0122] By comparing Example 1 with Examples 7-8, it can be seen that the thickness of the fast ion conductor coating layer of the single crystal nickel-rich positive electrode material of the present invention will affect its performance. When the thickness of the fast ion conductor coating layer is controlled within the range of 10nm to 40nm, the performance of the single crystal nickel-rich positive electrode material is better. If the thickness of the fast ion conductor coating layer is too large, the excessively thick LYZP layer increases the Li + The diffusion path leads to a decrease in rate performance, and the electronic insulation of LYZP hinders charge transfer, increasing the polarization voltage. If the thickness of the fast ion conductor coating is too thin, it cannot effectively block electrolyte corrosion, the amount of transition metal dissolution increases, the diffusion of oxygen vacancies on the material surface accelerates under high voltage, and thermal stability decreases.

[0123] Comparison of Example 1 and Comparative Examples 1-2 demonstrates that the present invention's gradient doping of niobium within the core and surface of a single-crystal nickel-rich cathode material inhibits surface degradation and protects the core's activity. Furthermore, the gradual change in elastic modulus from the core (low Nb) to the surface (high Nb) buffers anisotropic stresses during charge and discharge, reducing microcracks. Uniform doping, due to excessive bulk rigidity, can lead to interfacial stress concentration and surface spalling. Gradient doping of the core and surface with niobium also optimizes interfacial lithium ion transport and improves ion conduction efficiency.

[0124] From the comparison between Example 1 and Comparative Example 3, it can be seen that the fast ion conductor coating layer on the surface of the single crystal nickel-rich positive electrode material of the present invention can not only physically block the positive electrode from the electrolyte, prevent HF corrosion and transition metal dissolution, but also provide Li + It provides a low-impedance diffusion path and reduces interface polarization. It works synergistically with the niobium on the surface to achieve low impedance and high stability of the positive electrode material.

[0125] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A single crystal nickel-rich cathode material, characterized in that: The single crystal nickel-rich positive electrode material comprises a doped nickel-rich single crystal core and a fast ion conductor coating layer arranged on the surface of the doped nickel-rich single crystal core; The surface layer of the doped nickel-rich single crystal core is doped with Nb element, and the Nb element is doped in the surface layer of the doped nickel-rich single crystal core in a gradient increasing manner from the inside to the outside.

2. The single crystal nickel-rich cathode material according to claim 1, characterized in that The fast ion conductor material in the fast ion conductor coating layer includes Li 1+m Y m Zr 2-m P3O 12 , m is 0.2~0.5; Preferably, the thickness of the fast ion conductor coating layer is 10 nm to 40 nm.

3. The single crystal nickel-rich cathode material according to claim 1 or 2, characterized in that The chemical formula of the doped nickel-rich single crystal core is Li 1+a Ni x Co y Mn z Nb b O2, where 0≤a≤0.2, 0.8≤x<1, 0 <y<0.2,0<z<0.2,x+y+z+b=1,0.001≤b≤0.02; Preferably, based on the radius of the core of the doped nickel-rich single crystal being 100%, the doping depth of the Nb element is 10% to 50%.

4. A method for preparing a single crystal nickel-rich cathode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) injecting a nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a first complexing agent solution into the bottom liquid in parallel to perform a first coprecipitation reaction to generate a precursor core, maintaining the feed rate of other solutions unchanged, and simultaneously introducing a niobium source solution to perform a second coprecipitation reaction to obtain a doped precursor; (2) mixing a lithium source, a yttrium source, a zirconium source, a phosphorus source and a solvent to obtain a mixed solution, and adding a second complexing agent and a cross-linking agent to the mixed solution to form a sol; (3) dispersing the doped precursor in a sol, spray drying the resulting coated powder, and sintering the resulting coated powder to obtain the single crystal nickel-rich cathode material; Wherein, the introduction rate of the niobium source solution in step (1) is gradually increased.

5. The preparation method according to claim 4, wherein The total mass concentration of metal ions in the nickel-cobalt-manganese mixed salt solution in step (1) is 50 g to 150 g / L; Preferably, the precipitant solution in step (1) comprises a sodium hydroxide solution; Preferably, the mass concentration of the precipitant solution in step (1) is 20% to 50%; Preferably, the first complexing agent solution in step (1) comprises aqueous ammonia; Preferably, the mass concentration of the first complexing agent solution in step (1) is 10% to 30%; Preferably, the base liquid in step (1) includes ammonia water; Preferably, the ammonia mass concentration in the base liquid in step (1) is 1 g / L to 10 g / L; Preferably, the feeding rate of the nickel-cobalt-manganese mixed salt solution in step (1) is 6 L / h to 10 L / h; Preferably, the feed rate of the precipitant solution in step (1) is 2 L / h to 3 L / h; Preferably, the feeding rate of the first complexing agent solution in step (1) is 0.6 L / h to 1 L / h; Preferably, the temperature of the first coprecipitation reaction in step (1) is 30° C. to 80° C.; Preferably, the pH of the first coprecipitation reaction in step (1) is 10 to 12; Preferably, stirring is performed during the first coprecipitation reaction in step (1); Preferably, the stirring speed is 100 rpm to 500 rpm; Preferably, the median particle size D50 of the precursor core in step (1) is 2 μm to 3 μm.

6. The preparation method according to claim 4 or 5, characterized in that The solute of the niobium source solution in step (1) includes niobium nitrate and / or niobium chloride; Preferably, the mass concentration of the niobium source solution in step (1) is 1 g / L to 3 g / L; Preferably, the introduction rate of the niobium source solution in step (1) is gradually increased at a rate of 0.2 L / h to 0.5 L / h; Preferably, the pH of the second coprecipitation reaction in step (1) is 8.5 to 9.5; Preferably, the median particle size D50 of the doped precursor in step (1) is 3 μm to 4 μm.

7. The preparation method according to any one of claims 4 to 6, characterized in that The lithium source in step (2) includes lithium hydroxide and / or lithium nitrate; Preferably, the yttrium source in step (2) comprises yttrium nitrate; Preferably, the zirconium source in step (2) comprises zirconium nitrate; Preferably, the phosphorus source in step (2) comprises ammonium dihydrogen phosphate and / or ammonium hydrogen phosphate; Preferably, the solvent in step (2) comprises ethanol; Preferably, the second complexing agent in step (2) comprises citric acid; Preferably, the molar ratio of the total molar amount of yttrium ions and zirconium ions in the sol of step (2) to the second complexing agent is 1:(1.5-3); Preferably, the cross-linking agent in step (2) comprises ethylene glycol; Preferably, the molar ratio of the second complexing agent to the crosslinking agent in the sol of step (2) is 1:(1-2); Preferably, the step (2) is followed by stirring after adding the second complexing agent; Preferably, the pH of the solvent in step (2) is 3-5.

8. The preparation method according to any one of claims 4 to 7, wherein: The dispersion method in step (3) includes ultrasound; Preferably, the dispersion time in step (3) is 20 min to 40 min; Preferably, the dispersion temperature in step (3) is 60°C to 80°C; Preferably, the inlet temperature of the spray drying in step (3) is 180°C to 220°C; Preferably, the outlet temperature of the spray drying in step (3) is 90°C to 120°C.

9. The preparation method according to any one of claims 4 to 8, wherein The sintering treatment in step (3) includes pre-firing and calcining; Preferably, the pre-firing temperature is 300°C to 500°C; Preferably, the pre-burning time is 2h to 5h; Preferably, the heating rate from pre-calcination to calcination is 1°C / min to 3°C / min; Preferably, the calcination temperature is 700°C to 850°C; Preferably, the calcination time is 3 hours to 8 hours.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the single crystal nickel-rich positive electrode material according to any one of claims 1 to 3.

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