CN113851633B - Niobium-doped high-nickel ternary cathode material coated with niobium phosphate and preparation method thereof - Google Patents

Niobium-doped high-nickel ternary cathode material coated with niobium phosphate and preparation method thereof Download PDF

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CN113851633B
CN113851633B CN202111428230.4A CN202111428230A CN113851633B CN 113851633 B CN113851633 B CN 113851633B CN 202111428230 A CN202111428230 A CN 202111428230A CN 113851633 B CN113851633 B CN 113851633B
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田庆华
姚渝
童汇
郭学益
喻万景
丁治英
毛高强
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Central South University
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Abstract

The invention discloses a niobium-doped high-nickel ternary cathode material coated with niobium phosphate, which comprises a niobium-doped high-nickel ternary cathode material and niobium phosphate coated on the surface of the niobium-doped high-nickel ternary cathode material; the niobium-doped high-nickel ternary cathode material is characterized in that a niobium element is doped in the high-nickel ternary cathode material, and the molar ratio of the doping amount of the niobium element to the total molar amount of nickel, cobalt and manganese transition metals in the high-nickel ternary cathode material is (0.005-0.1): 1, the mass ratio of the coating amount of the niobium phosphate to the niobium-doped high-nickel ternary cathode material is (0.01-0.1): 1. the invention also provides a preparation method of the niobium-doped high-nickel ternary cathode material coated with niobium phosphate. According to the invention, niobium is utilized to firstly carry out bulk phase doping on the ternary cathode material, then the surface of the cathode material is coated with niobium phosphate, and the high-nickel ternary material is subjected to double modification and synergistic modification treatment through ion doping and metal phosphate coating, so that excellent cycle stability and rate capability are obtained.

Description

Niobium-doped high-nickel ternary cathode material coated with niobium phosphate and preparation method thereof
Technical Field
The invention belongs to the field of battery materials, and particularly relates to a modified high-nickel ternary cathode material and a preparation method thereof.
Background
High nickel ternary positive electrode material Li (Ni)xCoyMn1-x-y)O2The (LNCM) has higher specific capacity and energy density, has greater advantages in the application of novel lithium ion batteries, and is considered to be one of the most promising positive electrode materials of the power lithium ion batteries. However, the high nickel cathode material has the problems of easy phase change of surface particles, poor rate and cycle performance, unstable surface layer structure, poor thermal stability and the like. The electrochemical performance of the high-nickel ternary material can be improved to a certain extent by doping elements.
The results of the prior research show that Nb5+The doped layered transition metal oxide anode material can stabilize the material structure and improve the multiplying power and the cycle performance. For example, chinese patent publication No. CN107785568A discloses a niobium-doped nickel-cobalt-manganese lithium ion battery positive electrode material, which is doped with a nanoscale niobium compound to effectively improve the conductivity and specific discharge capacity of the positive electrode material. However, ion doping does not affect the surface of the anode material, and the problems of instability, transition metal dissolution, electrolyte corrosion and the like still exist on the surface of the structure.
Disclosure of Invention
The invention aims to overcome the defects and defects in the background art and provide a niobium-doped high-nickel ternary cathode material coated with niobium phosphate and having good structural stability, good cycle performance, good rate performance and other electrochemical properties and a preparation method thereof. In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises a niobium-doped high-nickel ternary cathode material and niobium phosphate coated on the surface of the niobium-doped high-nickel ternary cathode material; the niobium-doped high-nickel ternary cathode material is characterized in that a niobium element is doped in the high-nickel ternary cathode material, and the molar ratio of the doping amount of the niobium element to the total molar amount of nickel, cobalt and manganese transition metals in the high-nickel ternary cathode material is (0.005-0.1): 1 (more preferably 0.01: 1), wherein the mass ratio of the coating amount of the niobium phosphate to the niobium-doped high-nickel ternary cathode material is (0.01-0.1): 1 (more preferably 0.01: 1).
In the niobium-doped high-nickel ternary cathode material coated with niobium phosphate, preferably, the chemical formula of the high-nickel ternary cathode material is LiNixCoyMn(1-x-y)O2Wherein x is more than 0.6 and less than 0.9, y is more than 0.05 and less than 0.2, the niobium-doped high-nickel ternary cathode material coated by the niobium phosphate is in a sphere-like shape, and the particle size is 6-12 mu m. The niobium-doped high-nickel ternary cathode material coated by the niobium phosphate is spherical-like, so that the appearance and the particle size distribution of the secondary spherical particles of the original ternary material are ensured. The original spheroidal structure of the material is not changed in the high-nickel ternary cathode material after niobium phosphate coated and doped niobium, which shows that the coating doping modification does not influence the morphology and particle size of the material.
As a general technical concept, the invention also provides a preparation method of the niobium-doped high-nickel ternary cathode material coated with niobium phosphate, which comprises the following steps:
(1) preparing a nickel-cobalt-manganese hydroxide precursor by utilizing a coprecipitation reaction; preparing niobium phosphate by utilizing a niobium source and phosphoric acid;
(2) uniformly mixing the nickel-cobalt-manganese hydroxide precursor obtained in the step (1) with a lithium source and a niobium source, sintering in an oxidizing atmosphere (air atmosphere and/or oxygen atmosphere), and cooling to room temperature to obtain a niobium-doped ternary cathode material;
(3) and (3) grinding and uniformly mixing the niobium phosphate obtained in the step (1) and the niobium-doped ternary cathode material obtained in the step (2), and sintering to obtain the niobium-doped high-nickel ternary cathode material coated by the niobium phosphate.
In the above preparation method, preferably, the preparation of the nickel-cobalt-manganese hydroxide precursor by using a coprecipitation reaction includes the following steps: pumping the nickel-cobalt-manganese solution into a continuous stirring reaction kettle filled with an ammonia solution, heating and introducing a protective atmosphere (nitrogen atmosphere and/or argon atmosphere), pumping a complexing agent and a precipitator solution simultaneously, stirring for coprecipitation reaction, and then aging, filtering, washing and drying to obtain the nickel-cobalt-manganese hydroxide precursor.
The nickel source, the manganese source and the cobalt source in the nickel-cobalt-manganese solution are respectively soluble nickel salt, soluble manganese salt and soluble cobalt salt. The soluble nickel salt is one or more of nickel sulfate, nickel nitrate, nickel acetate or nickel chloride, and hydrates thereof. The soluble cobalt salt is one or more of cobalt sulfate, cobalt nitrate, cobalt acetate or cobalt chloride, and hydrate thereof. The soluble manganese salt is one or more of manganese sulfate, manganese nitrate, manganese acetate or manganese chloride, and hydrates thereof. The total molar concentration of nickel, cobalt and manganese ions in the nickel-cobalt-manganese solution is 0.1-3.0mol/L (more preferably 1.5-2.5 mol/L), and the molar ratio of the nickel, cobalt and manganese ions is (6-9): (0.5-5.0): (0.5-5.0). If the concentration of the metal ions is too low, the subsequent precipitation process is not facilitated, and the precipitation time is longer, so that the production efficiency is not facilitated to be improved; if the concentration of the metal ions is too high, complete dissolution of the metal salt is not facilitated.
The feeding speed of the nickel-cobalt-manganese solution is 80-120mL/h (more preferably 90-110 mL/h); if the feed rate is too fast, then can lead to pH variation range great for the precipitant is difficult to carry out effectual precipitation to metal ion, is unfavorable for the formation of control reaction process crystal nucleus and growth thereof, if the feed rate is too slow, then the granule is agglomerated easily, also is unfavorable for improving production efficiency simultaneously.
The molar concentration of the ammonia water solution in the reaction kettle is 0.1-5.0 mol/L; the complexing agent is an ammonia water solution, the mass concentration of ammonia water in the ammonia water solution is 25-28%, and the ammonia water concentration of a reaction system is adjusted by using ammonia water to be kept at 0.1-5.0 mol/L; if the molar concentration of the aqueous ammonia solution is too low, it is difficult to completely complex the metal ions, and if the molar concentration of the aqueous ammonia solution is too high, it is not favorable for the metal ions to form hydroxide precipitates. The precipitant solution is one or more of sodium hydroxide, potassium hydroxide or lithium hydroxide with the molar concentration of 1.0-7.0mol/L, and the precipitant solution is used for adjusting the pH value of the reaction system to be kept at 10-12; too high or too low a molar concentration of the hydroxide precipitant solution does not allow accurate control of the reaction process. At the pH value, the growth speed of the particles is controlled not to be too fast or too slow.
Controlling the volume ratio of the ammonia water solution, the precipitator solution and the nickel-cobalt-manganese solution in the reaction kettle to be (0.1-10): (1-2): (1-2); under the feeding proportion, the crystal grain formation and the crystal growth in the crystallization process are facilitated.
Controlling the stirring speed at 800-; if the stirring speed is too slow, the primary particles are easy to agglomerate, and if the stirring speed is too fast, the grown crystals are easy to break; in the temperature range, the growth of crystals is more facilitated; the reaction time is determined by the raw material content and the feeding speed. The aging temperature is 30-60 deg.C (preferably 40-50 deg.C), and the aging time is 8-24 h; the aging process can replace sulfate radical and other anions inside the material and is favorable to the homogeneity of the particle surface. If the aging time is too short, it is difficult to ensure the ion exchange of anions, which also affects the subsequent washing process, and if the aging time is too long, it is not favorable for production application and uniformity of material surface. The aging temperature is kept consistent with the temperature of the coprecipitation reaction, which is beneficial to the uniform dispersion and non-agglomeration of the material and ensures that the primary particles grow into the secondary particles uniformly. The washing is that deionized water and ethanol are respectively used for alternately washing the filtered substances for more than or equal to 6 times; the drying temperature is 80-100 ℃, and the drying time is 12-24 h. If the drying temperature is too low or the drying time is too short, the material is difficult to dry, and if the drying temperature is too high or the drying time is too long, other side reactions can occur on the surface of the material, so that the performance of the material is influenced, and the industrial production is not facilitated due to too long period.
In the above preparation method, preferably, the preparation of niobium phosphate from niobium source and phosphoric acid comprises the following steps: dissolving a niobium source and phosphoric acid in a deionized water solution, stirring and dissolving, performing condensation reflux reaction in an oil bath kettle, filtering, washing and drying to obtain a niobium phosphate material; the stirring speed in the stirring and dissolving process is 200-500r/min, and the stirring time is 2-6 h; the reaction temperature is controlled to be 80-150 ℃ during the condensation reflux reaction, and the reaction time is 12-18 h. If the reaction temperature is too low or the reaction time is too short, the reaction cannot be completed, an ideal material cannot be obtained, and if the reaction temperature is too high or the reaction time is too long, danger is easily caused, and energy waste is caused.
In the above preparation method, preferably, the lithium source is lithium hydroxide and/or lithium carbonate, and the molar ratio of the total molar amount of nickel, cobalt, and manganese elements in the nickel-cobalt-manganese hydroxide precursor to the molar amount of lithium elements in the lithium source is 1: (1.02-1.2).
In the above preparation method, preferably, the niobium source is one or more of niobium ethoxide, niobium oxalate or niobium oxide, and the molar ratio of the total molar amount of nickel, cobalt and manganese elements in the nickel-cobalt-manganese hydroxide precursor to the molar amount of niobium element in the niobium source for doping is 1: (0.005-0.1). Too high doping element niobium can introduce too many inactive substances, resulting in reduced capacity; the dosage of the doping element niobium is too low, the doping is not uniform, the influence on the material is not obvious, and the doping effect cannot be achieved.
In the above preparation method, preferably, in the step (2), the sintering treatment is two-stage sintering, wherein the temperature is raised to 350-. In the two-section temperature-rising sintering process, the temperature of the second section of sintering is higher than that of the first section of sintering. In the first stage of sintering process, decomposition reaction of the precursor and the lithium source mainly occurs, and in the second stage of sintering process, combination reaction of the precursor and the oxide decomposed by the lithium source under the oxygen atmosphere mainly occurs. If the sintering temperature is too high or the sintering time is too long, the material is easy to agglomerate, the capacity is difficult to release in the charging and discharging process, and if the sintering temperature is too low or the sintering time is too short, the required morphology is difficult to form, and the electrochemical performance is influenced. If the temperature rise rate is too fast, it is difficult to ensure sufficient reaction of the material, especially to influence the diffusion of lithium ions into the material structure, and if the temperature rise rate is too slow, it is not favorable for industrial production.
In the above preparation method, preferably, the mass ratio of the niobium-doped ternary cathode material to niobium phosphate is controlled to be 1: (0.01-0.2). If the consumption of the niobium phosphate is too much, the coating layer on the surface of the material is too thick, and even the coating aggregates, which can affect the kinetics of the reaction process of the material, thereby affecting the performance of the material. If the amount of niobium phosphate is too small, the coating effect is difficult to achieve, and the raw material is wasted.
In the above preparation method, preferably, in the step (3), the sintering treatment is performed by heating to 450-. The sintering treatment mainly aims to make the niobium phosphate adsorbed on the surface of the ternary material and permeate into the surface of the ternary material to form a stable niobium phosphate coating layer which is uniformly coated on the surface of the ternary material. If the temperature rise rate is too fast, it is difficult to ensure sufficient reaction of the material, and if the temperature rise rate is too slow, it is not favorable for industrial production. If the sintering temperature is too low, the coating material is difficult to completely coat, and if the sintering temperature is too high, ions may enter the material bulk phase, causing a change in the material structure. If the sintering time is too short, the coating may not be uniform, and if the sintering time is too long, unnecessary side reactions may occur, and the production efficiency may be deteriorated. The invention adopts low-temperature sintering coating, which is beneficial to the uniform coating of niobium phosphate on the surface of the ternary material and the synergistic effect of niobium phosphate and doped niobium.
According to the invention, firstly, niobium is utilized to dope a ternary anode material in a bulk phase, then the surface of the anode material is coated with niobium phosphate, and the high-nickel ternary material is modified through doping of niobium element ions and coating of metal phosphate of corresponding elements, so that the cycle performance and the rate capability of the material are synergistically improved. Specifically, the method comprises the following steps: niobium ions with stronger Nb-O bond dissociation energy are doped with the high-nickel ternary material, Nb-O bonds with stronger bond energy are doped in a crystal structure, the strong Nb-O bonds enhance a TM-O layer by reducing cation mixed discharge and reserving lattice oxygen, the crystal boundary strength of the material is enhanced, the crystal structure of the material is stabilized, and phase change in a circulation process is inhibited; niobium doping can play a role in supporting ions, inhibit structural change of a transition metal layer, stabilize a layered structure of the material, inhibit structural collapse of material lattices in a lithium removal state, reduce generation of microcracks, keep the integrity of secondary particles in a circulating process, and reduce generation of irreversible capacity, so that the circulating performance of the high-nickel ternary material is improved. And Nb5+Higher valence states may improve the electronic conductivity of the material due to valence state equilibrium. The prepared niobium phosphate material with two-dimensional layer space characteristics and large specific surface area is coated on the surface of the anode material, and the surface layer of the high-nickel ternary material is modified by coating the niobium phosphate material, so that the side reaction of the material surface in the charge-discharge cycle process is prevented, and the ion exchange of the material interface is accelerated by the large specific surface area; in addition, the relatively large gaps in the metal phosphate structure can effectively improve the reaction kinetics of the nickel-rich cathode material, and the metal phosphate structure has better Li than oxide+The migration capacity and the electron transfer capacity are favorable for the rapid transmission of lithium ions, and the strong P = O bond energy exists, so that the corrosion of the electrolyte can be reduced, and the rate capability of the material can not be reduced.
In addition, the invention combines the advantages of niobium element doping and niobium phosphate surface coating, adopts niobium element for doping and coating, utilizes the same element to participate in doping and coating at the same time, is more favorable for the advantage complementation of double modification processes and the synergistic effect of the two in the doping and coating processes, ensures the stability of the structure through double modification, and finally realizes the excellent rate performance and cycle stability of the high-nickel material. The specific synergistic effect is mainly embodied in the following aspects: 1. the invention firstly adopts a solid-phase sintering doping process, diffusion occurs under the influence of dynamics, and niobium completely enters the material to realize bulk phase doping. In the subsequent sintering process of coating niobium phosphate, the metal phosphate can also diffuse into the material under the kinetic influence, and the early niobium doping can prevent the niobium in the metal phosphate from diffusing into the material, so that the uniform coating of the surface metal phosphate is favorably realized. 2. Because niobium doped in a material body with high valence state needs more electrons to maintain valence balance, on one hand, the niobium phosphate has high electron transfer capacity and is beneficial to providing more electrons, and on the other hand, the niobium phosphate has lower valence state of phosphorus, so that more electrons are beneficial to being gathered and provided for the doping element niobium, and the valence balance of the doping element is beneficial to. Moreover, the electron donor of the coated niobium phosphate and the electron needed by the doped niobium are beneficial to the mutual attraction and combination of the coated niobium phosphate and the doped niobium, namely, the existence of the doped element niobium is beneficial to the more compact coating of the specific coated niobium phosphate, so that the niobium phosphate is combined with the material body more tightly. 3. After being coated by the niobium phosphate, the niobium element is beneficial to being stabilized in the coated substrate and the function of the doping element is beneficial to being exerted. Based on the synergistic effect, the niobium doping is beneficial to the coating of the niobium phosphate, the coating of the niobium phosphate is beneficial to the stable doping of the niobium, and the synergistic effect of the niobium phosphate and the niobium phosphate is obvious. It should be emphasized that we studied various doping and coating materials, and only found that the synergistic effect of niobium doping and niobium phosphate is more significant, and the coating effect of niobium doping and other niobium compounds is inferior to that of the niobium doping and niobium phosphate coating of the present invention, which may be closely related to the above synergistic mechanism.
In the invention, because the same element is adopted for doping and coating, in order to ensure the synergistic effect of niobium element doping and niobium phosphate surface coating, the dosage of the doping element and the coating element needs to be reasonably optimized, and the molar ratio of the doping amount of the niobium element to the total molar amount of the nickel-cobalt-manganese transition metal in the high-nickel ternary cathode material is controlled to be (0.005-0.1): 1, the mass ratio of the coating amount of the niobium phosphate to the niobium-doped high-nickel ternary cathode material is (0.01-0.1): 1, the synergistic effect of the doping elements and the coating material is better exerted.
Compared with the prior art, the invention has the advantages that:
1. according to the invention, niobium is utilized to dope a ternary anode material in a bulk phase, then the surface of the anode material is coated with niobium phosphate, the high-nickel ternary material is subjected to double modification and synergistic modification treatment through ion doping and metal phosphate coating, the doping element stabilizes the crystal structure of the material, the coating layer niobium phosphate is used as a protective layer to reduce the erosion of electrolyte to the material, a good lithium ion transmission channel is provided, the electronic conductivity is enhanced, the doping of niobium ensures the structural integrity in the charging and discharging processes, the niobium phosphate coating reduces the generation of mechanical damage and microcracks, and excellent cycle stability and rate capability are obtained.
2. According to the preparation method, the niobium-doped niobium phosphate coating is carried out on the ternary cathode material by a solid phase method, the doping coating adopts the solid phase method, the process is simple, the used raw materials are easy to obtain, the modification effect is obvious, and the preparation method is suitable for industrial production.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is an XRD pattern of the niobium phosphate coated niobium doped high nickel ternary cathode material of example 1.
FIG. 2 is an XRD pattern of niobium phosphate in example 1.
Fig. 3 is an SEM image of the niobium phosphate coated niobium doped high nickel ternary cathode material of example 1.
Fig. 4 is an SEM image (left panel (a)) and an EDS image (right panel (b)) of the niobium phosphate coated niobium doped high nickel ternary cathode material of example 1.
Fig. 5 is a charge-discharge cycle curve and a charge-discharge coulomb graph of a battery assembled by the niobium-doped high-nickel ternary cathode material coated with niobium phosphate in example 1.
Fig. 6 is a discharge rate graph of a battery assembled with the niobium phosphate coated niobium doped high nickel ternary cathode material in example 1.
Detailed Description
In order to facilitate an understanding of the invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of the invention is not limited to the specific embodiments below.
Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
Example 1:
a niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises a niobium-doped high-nickel ternary cathode material and niobium phosphate coated on the surface of the niobium-doped high-nickel ternary cathode material; the niobium-doped high-nickel ternary cathode material is characterized in that a niobium element is doped in the high-nickel ternary cathode material, and the molar ratio of the doping amount of the niobium element to the total molar amount of nickel, cobalt and manganese transition metals in the high-nickel ternary cathode material is 0.01: 1, the mass ratio of the coating amount of the niobium phosphate to the niobium-doped high-nickel ternary cathode material is 0.01: 1. the high-nickel ternary positive electrode material is LiNi0.733Co0.131Mn0.136O2The particle is a sphere-like secondary particle aggregate, the average particle size is 9 mu m, the appearance is regular, and the distribution is uniform.
The preparation method of the niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises the following steps of:
(1) pumping 4L of a mixed solution of transition metal solution nickel sulfate, cobalt sulfate and manganese sulfate, wherein the total molar concentration of Ni ions, Co ions and Mn ions is 2.0mol/L, pumping the mixed solution into a reaction kettle filled with 2L ammonia water solution and 2mol/L ammonia water solution at a feeding speed of 100mL/h, adjusting the ammonia water concentration of a reaction system to be 2mol/L by using 25% by mass ammonia water, adjusting the pH value of the reaction system to be 11.4 by using 4L sodium hydroxide precipitant solution and 5mol/L sodium hydroxide precipitant solution, heating and stirring at 1000r/min and 50 ℃ under a high-purity nitrogen atmosphere, carrying out coprecipitation reaction for 40h, stirring and aging for 12h at 45 ℃, filtering, respectively and sequentially and crossly washing the filtrate for 6 times by using deionized water and ethanol, and drying for 12h at 90 ℃ to obtain a nickel-cobalt-manganese hydroxide precursor;
(2) mixing and grinding 1.0g of nickel-cobalt-manganese hydroxide precursor (Ni 7.70411mmol, Co 1.37791mmol and Mn 1.42883 mmol) obtained in the step (1) with 0.4944g (11.03639 mmol) of lithium hydroxide monohydrate and 0.013969g (0.1051085 mmol) of niobium pentoxide, heating to 450 ℃ at the speed of 5 ℃/min in the atmosphere of high-purity oxygen, sintering for 4h, heating to 750 ℃ at the speed of 5 ℃/min, sintering for 12h, performing two-stage sintering, and cooling to room temperature to obtain the niobium-doped high-nickel ternary LiNi0.733Co0.131Mn0.136O2A material;
(3) dissolving 0.5g of niobium oxalate and 35mL of industrial-grade phosphoric acid diluted by 100 times in a round-bottom flask, transferring and fixing the flask on an oil bath kettle reaction system provided with a condensation reflux device, continuously stirring the reaction solution until a transparent clear solution is formed, adjusting the reaction temperature to 120 ℃ for 15h reaction, cooling the system to room temperature after the reaction is finished, and filtering, washing and drying the obtained product to obtain a niobium phosphate material;
(4) fully grinding 0.0025g of niobium phosphate obtained in the step (2) and the step (3) and 0.25g of niobium-doped high-nickel ternary positive electrode material in a mortar, and uniformly mixing;
(5) and (4) transferring the powder obtained in the step (4) into a tubular furnace, heating to 500 ℃ at the speed of 5 ℃/min in the oxygen atmosphere, sintering for 5h, and cooling to room temperature to obtain the niobium-doped high-nickel ternary cathode material coated by niobium phosphate.
As shown in fig. 1, the niobium-doped high-nickel ternary cathode material coated with niobium phosphate and the PDF card LiNiO of the present embodiment2The characteristic peak of (PDF # 85-1966) is in accordance with (because the nickel content of the high-nickel ternary material is very high, the characteristic peak reflected by XRD is almost the same as that of pure lithium nickelate, and the structural characteristics are consistent), and no impurity phase is generated.
As shown in FIG. 2, NbOPO synthesized in this example4And PDF card NbOPO4·H2The characteristic peaks of O (PDF # 09-0063) were in total agreement.
As shown in fig. 3, the niobium doped high nickel ternary cathode material coated with niobium phosphate of the present embodiment has a good morphology, inherits the morphology of the high nickel ternary material, and the secondary particles are spheroidal and have an average particle size of 9 μm.
As shown in fig. 4, the left panel (a) is an SEM image of the ternary cathode material, and the right panel (b) is an EDS image of the ternary cathode material shown in fig. (a). EDS mapping results of the niobium-doped high-nickel ternary cathode material coated with niobium phosphate in the embodiment show that niobium is uniformly distributed on the material.
Assembling the battery: 0.08g of niobium-doped high-nickel ternary cathode material coated with niobium phosphate obtained in the embodiment is weighed, 0.01g of acetylene black serving as a conductive agent and 0.01g of PVDF polyvinylidene fluoride serving as a binder are added, and N-methylpyrrolidone is used as a solventMixing and grinding the mixture to form a positive electrode material; coating the obtained anode material on the surface of an aluminum foil to prepare a pole piece; in a sealed glove box filled with argon, the pole piece is taken as a positive electrode, a metal lithium piece is taken as a negative electrode, a microporous polypropylene film is taken as a diaphragm, and 1mol/L LiPF6EC: DMC: EMC (volume ratio 1: 1: 1) is electrolyte, and the button cell of CR2025 is assembled and is tested for charge and discharge performance.
As shown in FIG. 5, the initial discharge specific capacity of the assembled battery is 172.6mAh/g, the charge specific capacity is 196.6mAh/g, the initial charge-discharge coulombic efficiency is 88.97% under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), the discharge specific capacity can still reach 160.4mAh/g after 100 cycles, and the capacity retention rate is 92.93%. The niobium-doped high-nickel ternary cathode material coated with niobium phosphate in the embodiment is beneficial to the transmission of lithium ions in the charging and discharging processes, and has stable discharging specific capacity, charging and discharging performance, coulombic efficiency and good cycle performance.
As shown in fig. 6, the specific discharge capacity at 10C current density can reach 143.9mAh/g for the rate curve of the assembled battery, further illustrating that the lithium ion transport performance of the niobium-doped high-nickel ternary material is improved during the charge-discharge cycle process through the surface modification of niobium phosphate.
Example 2:
the niobium phosphate-coated niobium-doped high-nickel ternary cathode material of the present example is the same as that of example 1.
The preparation method of the niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises the following steps of:
(1) same as example 1, step (1);
(2) mixing and grinding 1.0g of nickel-cobalt-manganese hydroxide precursor (Ni 7.70411mmol, Co 1.37791mmol and Mn 1.42883 mmol) obtained in the step (1) with 0.4944g (11.03639 mmol) of lithium hydroxide monohydrate and 0.013969g (0.105108 mmol) of niobium pentoxide, heating to 450 ℃ at the speed of 5 ℃/min in the atmosphere of high-purity oxygen, sintering for 4h, heating to 750 ℃ at the speed of 5 ℃/min, sintering for 12h, performing two-stage sintering, and cooling to room temperature to obtain the niobium-doped high-nickel ternary LiNi0.733Co0.131Mn0.136O2A material;
(3) dissolving 1g of niobium oxalate and 70mL of industrial-grade phosphoric acid diluted by 100 times in a round-bottom flask, transferring and fixing the flask on an oil bath reaction system with a condensation reflux device, continuously stirring the reaction solution until a transparent clear solution is formed, adjusting the reaction temperature to 120 ℃ for 15h reaction, cooling the system to room temperature after the reaction is finished, filtering, washing and drying the obtained product to obtain a niobium phosphate material;
(4) fully grinding 0.003g of niobium phosphate obtained in the step (2) and the step (3) and 0.3g of niobium-doped high-nickel ternary positive electrode material in a mortar, and uniformly mixing;
(5) and (4) transferring the powder obtained in the step (4) into a tubular furnace, heating to 450 ℃ at a speed of 5 ℃/min under an oxygen atmosphere, sintering for 5h, and cooling to room temperature to obtain the niobium-doped high-nickel ternary cathode material coated with niobium phosphate.
Assembling the battery: the same as in example 1.
The first discharge specific capacity of the assembled battery is 168.6mAh/g, the charge specific capacity is 192.2mAh/g, the first charge-discharge coulombic efficiency is 87.72 percent under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), the discharge specific capacity can still reach 152.7mAh/g after 100 cycles, and the capacity retention rate is 90.57 percent. The niobium-doped high-nickel ternary cathode material coated with niobium phosphate in the embodiment is beneficial to the transmission of lithium ions in the charging and discharging processes, and has stable discharging specific capacity, charging and discharging performance, coulombic efficiency and good cycle performance.
Example 3:
the niobium phosphate-coated niobium-doped high-nickel ternary cathode material of the present example is the same as that of example 1.
The preparation method of the niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises the following steps of:
(1) same as example 1, step (1);
(2) mixing 1.0g of nickel-cobalt-manganese hydroxide precursor (Ni 7.70411mmol, Co 1.37791mmol and Mn 1.42883 mmol) obtained in the step (1) with 0.4944g (11.03639 mmol) of lithium hydroxide monohydrate and 0.013969g (0.105108 mmol) of niobium pentoxide, and grindingAfter grinding, firstly heating to 450 ℃ at the speed of 5 ℃/min under the atmosphere of high-purity oxygen, sintering for 4h, then heating to 750 ℃ at the speed of 5 ℃/min, sintering for 12h, carrying out two-stage sintering, and cooling to room temperature to obtain the niobium-doped high-nickel ternary LiNi0.733Co0.131Mn0.136O2A material;
(3) dissolving 0.5g of niobium oxalate and 35mL of industrial-grade phosphoric acid diluted by 100 times in a round-bottom flask, transferring and fixing the flask on an oil bath kettle reaction system provided with a condensation reflux device, continuously stirring the reaction solution until a transparent clear solution is formed, adjusting the reaction temperature to 120 ℃ for 15h reaction, cooling the system to room temperature after the reaction is finished, and filtering, washing and drying the obtained product to obtain a niobium phosphate material;
(4) fully grinding 0.002g of niobium phosphate obtained in the step (2) and the step (3) and 0.2g of niobium-doped high-nickel ternary positive electrode material in a mortar, and uniformly mixing;
(5) and (4) transferring the powder obtained in the step (4) into a tubular furnace, heating to 550 ℃ at a speed of 5 ℃/min under an oxygen atmosphere, sintering for 5h, and cooling to room temperature to obtain the niobium-doped high-nickel ternary cathode material coated by the niobium phosphate.
Assembling the battery: the same as in example 1.
The battery assembled in the embodiment has the first discharge specific capacity of 170.2mAh/g, the charge specific capacity of 190.5mAh/g and the first charge-discharge coulombic efficiency of 89.34% under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), and after 100 cycles, the discharge specific capacity can still reach 153.2mAh/g and the capacity retention rate is 90.01%. The niobium-doped high-nickel ternary cathode material coated with niobium phosphate in the embodiment is beneficial to the transmission of lithium ions in the charging and discharging processes, and has stable discharging specific capacity, charging and discharging performance, coulombic efficiency and good cycle performance.
Example 4:
a niobium-doped high-nickel ternary cathode material coated with niobium phosphate is characterized in that a niobium element is doped in the high-nickel ternary cathode material, the surface of the niobium-doped high-nickel ternary cathode material is coated with the niobium phosphate, and the doping amount of the niobium element and the high-nickel ternary cathode material are equalThe molar ratio of the total molar weight of the medium nickel cobalt manganese transition metal is 0.005: 1, the mass ratio of the coating amount of the niobium phosphate to the niobium-doped high-nickel ternary cathode material is 0.01: 1. the high-nickel ternary positive electrode material is LiNi0.733Co0.131Mn0.136O2The particle is a sphere-like secondary particle aggregate, the average particle size is 9 mu m, the appearance is regular, and the distribution is uniform.
The preparation method of the niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises the following steps of:
(1) same as example 1, step (1);
(2) mixing and grinding 1.0g of nickel-cobalt-manganese hydroxide precursor (Ni 7.70411mmol, Co 1.37791mmol and Mn 1.42883 mmol) obtained in the step (1) with 0.4944g (11.03639 mmol) of lithium hydroxide monohydrate and 0.00698g (0.052554 mmol) of niobium pentoxide, heating to 450 ℃ at the speed of 5 ℃/min in the atmosphere of high-purity oxygen, sintering for 4h, heating to 750 ℃ at the speed of 5 ℃/min, sintering for 12h, performing two-stage sintering, and cooling to room temperature to obtain the niobium-doped high-nickel ternary LiNi0.733Co0.131Mn0.136O2A material;
(3) dissolving 0.5g of niobium oxalate and 35mL of industrial-grade phosphoric acid diluted by 100 times in a round-bottom flask, transferring and fixing the flask on an oil bath kettle reaction system provided with a condensation reflux device, continuously stirring the reaction solution until a transparent clear solution is formed, adjusting the reaction temperature to 120 ℃ for 15h reaction, cooling the system to room temperature after the reaction is finished, and filtering, washing and drying the obtained product to obtain a niobium phosphate material;
(4) fully grinding 0.0025g of niobium phosphate obtained in the step (2) and the step (3) and 0.25g of niobium-doped high-nickel ternary positive electrode material in a mortar, and uniformly mixing;
(5) and (4) transferring the powder obtained in the step (4) into a tubular furnace, heating to 550 ℃ at a speed of 5 ℃/min under an oxygen atmosphere, sintering for 5h, and cooling to room temperature to obtain the niobium-doped high-nickel ternary cathode material coated by the niobium phosphate.
Assembling the battery: the same as in example 1.
The battery assembled in the embodiment has the first discharge specific capacity of 163.9mAh/g, the charge specific capacity of 188.9mAh/g and the first charge-discharge coulombic efficiency of 86.78% under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), and after the battery is cycled for 100 circles, the discharge specific capacity can still reach 143.4mAh/g, and the capacity retention rate is 87.49%. The niobium-doped high-nickel ternary cathode material coated with niobium phosphate in the embodiment is beneficial to the transmission of lithium ions in the charging and discharging processes, and has stable discharging specific capacity, charging and discharging performance, coulombic efficiency and good cycle performance.
Example 5:
the niobium-doped high-nickel ternary cathode material coated with niobium phosphate is characterized in that a niobium element is doped in the high-nickel ternary cathode material, the surface of the niobium-doped high-nickel ternary cathode material is coated with niobium phosphate, and the molar ratio of the doping amount of the niobium element to the total molar amount of nickel-cobalt-manganese transition metals in the high-nickel ternary cathode material is 0.02: 1, the mass ratio of the coating amount of the niobium phosphate to the niobium-doped high-nickel ternary cathode material is 0.01: 1. the high-nickel ternary positive electrode material is LiNi0.733Co0.131Mn0.136O2The particle is a sphere-like secondary particle aggregate, the average particle size is 9 mu m, the appearance is regular, and the distribution is uniform. .
The preparation method of the niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises the following steps of:
(1) same as example 1, step (1);
(2) mixing and grinding 1.0g of nickel-cobalt-manganese hydroxide precursor (Ni 7.70411mmol, Co 1.37791mmol and Mn 1.42883 mmol) obtained in the step (1) with 0.4944g (11.03639 mmol) of lithium hydroxide monohydrate and 0.02794g (0.210216 mmol) of niobium pentoxide, heating to 450 ℃ at the speed of 5 ℃/min in the atmosphere of high-purity oxygen, sintering for 4h, heating to 750 ℃ at the speed of 5 ℃/min, sintering for 12h, performing two-stage sintering, and cooling to room temperature to obtain the niobium-doped high-nickel ternary LiNi0.733Co0.131Mn0.136O2A material;
(3) dissolving 0.5g of niobium oxalate and 35mL of industrial-grade phosphoric acid diluted by 100 times in a round-bottom flask, transferring and fixing the flask on an oil bath kettle reaction system provided with a condensation reflux device, continuously stirring the reaction solution until a transparent clear solution is formed, adjusting the reaction temperature to 120 ℃ for 15h reaction, cooling the system to room temperature after the reaction is finished, and filtering, washing and drying the obtained product to obtain a niobium phosphate material;
(4) fully grinding 0.0025g of niobium phosphate obtained in the step (2) and the step (3) and 0.25g of niobium-doped high-nickel ternary positive electrode material in a mortar, and uniformly mixing;
(5) and (4) transferring the powder obtained in the step (4) into a tubular furnace, heating to 550 ℃ at a speed of 5 ℃/min under an oxygen atmosphere, sintering for 5h, and cooling to room temperature to obtain the niobium-doped high-nickel ternary cathode material coated by the niobium phosphate.
Assembling the battery: the same as in example 1.
The battery assembled in the embodiment has the first discharge specific capacity of 159.9mAh/g, the charge specific capacity of 179.0mAh/g and the first charge-discharge coulombic efficiency of 89.37% under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), and after 100 cycles, the discharge specific capacity can still reach 147.4mAh/g, and the capacity retention rate is 92.18%. The niobium-doped high-nickel ternary cathode material coated with niobium phosphate in the embodiment is beneficial to the transmission of lithium ions in the charging and discharging processes, and has stable discharging specific capacity, charging and discharging performance, coulombic efficiency and good cycle performance.
Example 6:
a niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises a niobium-doped high-nickel ternary cathode material and niobium phosphate coated on the surface of the niobium-doped high-nickel ternary cathode material; the niobium-doped high-nickel ternary cathode material is characterized in that a niobium element is doped in the high-nickel ternary cathode material, and the molar ratio of the doping amount of the niobium element to the total molar amount of nickel, cobalt and manganese transition metals in the high-nickel ternary cathode material is 0.01: 1, the mass ratio of the coating amount of the niobium phosphate to the niobium-doped high-nickel ternary cathode material is 0.005: 1. the high-nickel ternary positive electrode material is LiNi0.733Co0.131Mn0.136O2The particle is a sphere-like secondary particle aggregate, the average particle size is 9 mu m, the appearance is regular, and the distribution is uniform.
The preparation method of the niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises the following steps of:
(1) same as example 1, step (1);
(2) mixing and grinding 1.0g of nickel-cobalt-manganese hydroxide precursor (Ni 7.70411mmol, Co 1.37791mmol and Mn 1.42883 mmol) obtained in the step (1) with 0.4944g (11.03639 mmol) of lithium hydroxide monohydrate and 0.013969g (0.1051085 mmol) of niobium pentoxide, heating to 450 ℃ at the speed of 5 ℃/min in the atmosphere of high-purity oxygen, sintering for 4h, heating to 750 ℃ at the speed of 5 ℃/min, sintering for 12h, performing two-stage sintering, and cooling to room temperature to obtain the niobium-doped high-nickel ternary LiNi0.733Co0.131Mn0.136O2A material;
(3) dissolving 0.5g of niobium oxalate and 35mL of industrial-grade phosphoric acid diluted by 100 times in a round-bottom flask, transferring and fixing the flask on an oil bath kettle reaction system provided with a condensation reflux device, continuously stirring the reaction solution until a transparent clear solution is formed, adjusting the reaction temperature to 120 ℃ for 15h reaction, cooling the system to room temperature after the reaction is finished, and filtering, washing and drying the obtained product to obtain a niobium phosphate material;
(4) fully grinding 0.002g of niobium phosphate obtained in the step (2) and the step (3) and 0.4g of niobium-doped high-nickel ternary positive electrode material in a mortar, and uniformly mixing;
(5) and (4) transferring the powder obtained in the step (4) into a tubular furnace, heating to 500 ℃ at the speed of 5 ℃/min in the oxygen atmosphere, sintering for 5h, and cooling to room temperature to obtain the niobium-doped high-nickel ternary cathode material coated by niobium phosphate.
Assembling the battery: the same as in example 1.
The battery assembled in the embodiment has the first discharge specific capacity of 167.4mAh/g, the charge specific capacity of 189.8mAh/g and the first charge-discharge coulombic efficiency of 88.20% under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), and after 100 cycles, the discharge specific capacity can still reach 148.1mAh/g, and the capacity retention rate is 88.47%. The niobium-doped high-nickel ternary cathode material coated with niobium phosphate in the embodiment is beneficial to the transmission of lithium ions in the charging and discharging processes, and has stable discharging specific capacity, charging and discharging performance, coulombic efficiency and good cycle performance.
Example 7:
a niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises a niobium-doped high-nickel ternary cathode material and niobium phosphate coated on the surface of the niobium-doped high-nickel ternary cathode material; the niobium-doped high-nickel ternary cathode material is characterized in that a niobium element is doped in the high-nickel ternary cathode material, and the molar ratio of the doping amount of the niobium element to the total molar amount of nickel, cobalt and manganese transition metals in the high-nickel ternary cathode material is 0.01: 1, the mass ratio of the coating amount of the niobium phosphate to the niobium-doped high-nickel ternary cathode material is 0.02: 1. the high-nickel ternary positive electrode material is LiNi0.733Co0.131Mn0.136O2The particle is a sphere-like secondary particle aggregate, the average particle size is 9 mu m, the appearance is regular, and the distribution is uniform.
The preparation method of the niobium-doped high-nickel ternary cathode material coated with niobium phosphate comprises the following steps of:
(1) same as example 1, step (1);
(2) mixing and grinding 1.0g of nickel-cobalt-manganese hydroxide precursor (Ni 7.70411mmol, Co 1.37791mmol and Mn 1.42883 mmol) obtained in the step (1) with 0.4944g (11.03639 mmol) of lithium hydroxide monohydrate and 0.013969g (0.1051085 mmol) of niobium pentoxide, heating to 450 ℃ at the speed of 5 ℃/min in the atmosphere of high-purity oxygen, sintering for 4h, heating to 750 ℃ at the speed of 5 ℃/min, sintering for 12h, performing two-stage sintering, and cooling to room temperature to obtain the niobium-doped high-nickel ternary LiNi0.733Co0.131Mn0.136O2A material;
(3) dissolving 0.5g of niobium oxalate and 35mL of industrial-grade phosphoric acid diluted by 100 times in a round-bottom flask, transferring and fixing the flask on an oil bath kettle reaction system provided with a condensation reflux device, continuously stirring the reaction solution until a transparent clear solution is formed, adjusting the reaction temperature to 120 ℃ for 15h reaction, cooling the system to room temperature after the reaction is finished, and filtering, washing and drying the obtained product to obtain a niobium phosphate material;
(4) fully grinding 0.008g of niobium phosphate obtained in the step (2) and the step (3) and 0.4g of niobium-doped high-nickel ternary positive electrode material in a mortar, and uniformly mixing;
(5) and (4) transferring the powder obtained in the step (4) into a tubular furnace, heating to 500 ℃ at the speed of 5 ℃/min in the oxygen atmosphere, sintering for 5h, and cooling to room temperature to obtain the niobium-doped high-nickel ternary cathode material coated by niobium phosphate.
Assembling the battery: the same as in example 1.
The battery assembled in the embodiment has the first discharge specific capacity of 160.7mAh/g, the charge specific capacity of 182.1mAh/g and the first charge-discharge coulombic efficiency of 88.24% under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), and after 100 cycles, the discharge specific capacity can still reach 146.1mAh/g and the capacity retention rate is 90.91%. The niobium-doped high-nickel ternary cathode material coated with niobium phosphate in the embodiment is beneficial to the transmission of lithium ions in the charging and discharging processes, and has stable discharging specific capacity, charging and discharging performance, coulombic efficiency and good cycle performance.
Comparative example 1:
a preparation method of a high-nickel ternary cathode material comprises the following steps:
(1) same as example 1, step (1);
(2) mixing and grinding 1.0g of the nickel-cobalt-manganese hydroxide precursor (Ni 7.70411mmol, Co 1.37791mmol and Mn 1.42883 mmol) obtained in the step (1) and 0.4944g (11.03639 mmol) of lithium hydroxide monohydrate, heating to 450 ℃ at the speed of 5 ℃/min in the atmosphere of high-purity oxygen, sintering for 4h, heating to 750 ℃ at the speed of 5 ℃/min, sintering for 12h, performing two-stage sintering, and cooling to room temperature to obtain the high-nickel ternary LiNi0.733Co0.131Mn0.136O2A material;
assembling the battery: the same as in example 1.
The battery assembled in the comparative example has the first discharge specific capacity of 174.8mAh/g, the charge specific capacity of 200.3mAh/g and the first charge-discharge coulombic efficiency of 87.27% under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), and after 100 cycles, the discharge specific capacity is 143.3mAh/g and the capacity retention rate is 81.98%; the specific discharge capacity at the current density of 10C is only 124.6 mAh/g. The comparative example shows that the charge-discharge reaction reversibility and circulation stability of the unmodified material are poor.
Comparative example 2:
a preparation method of a niobium-doped high-nickel ternary cathode material comprises the following steps:
(1) same as example 1, step (1);
(2) same as example 1, step (2).
Assembling the battery: the same as in example 1.
The battery assembled in the comparative example has the first discharge specific capacity of 170.5mAh/g, the charge specific capacity of 192.2mAh/g and the first charge-discharge coulombic efficiency of 88.71% under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), and after 100 cycles of circulation, the discharge specific capacity is 154.2mAh/g and the capacity retention rate is 90.44%; the specific discharge capacity at the current density of 10C is only 131.4 mAh/g. The comparative example shows that the rate performance of the cathode material only doped with niobium is still poor.
Comparative example 3:
a preparation method of a niobium phosphate coated high-nickel ternary cathode material comprises the following steps:
(1) same as example 1, step (1);
(2) the same as the step (2) of the comparative example 1;
(3) same as example 1, step (3);
(4) 0.0025g of niobium phosphate obtained in the step (2) and the step (3) and 0.25g of high-nickel ternary LiNi0.733Co0.131Mn0.136O2Fully grinding the materials in a mortar, and uniformly mixing;
(5) and (4) transferring the powder obtained in the step (4) into a tubular furnace, heating to 500 ℃ at the speed of 5 ℃/min in the oxygen atmosphere, sintering for 5h, and cooling to room temperature to obtain the niobium phosphate coated high-nickel ternary cathode material.
Assembling the battery: the same as in example 1.
The battery assembled in the comparative example has the first discharge specific capacity of 172.3mAh/g, the charge specific capacity of 197.5mAh/g and the first charge-discharge coulombic efficiency of 87.24% under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), and after 100 cycles of circulation, the discharge specific capacity is 144.9mAh/g and the capacity retention rate is 84.09%. The results of the comparative example show that the cycle stability of the cathode material coated only with niobium phosphate is still poor.
Comparative example 4:
a preparation method of a niobium-doped high-nickel ternary cathode material coated with niobium oxide comprises the following steps:
(1) same as example 1, step (1);
(2) same as example 1, step (2);
(3) fully grinding 0.0025g of niobium pentoxide and 0.25g of the niobium-doped high-nickel ternary positive electrode material obtained in the step (2) in a mortar, and uniformly mixing;
(4) and (4) transferring the powder obtained in the step (3) into a tubular furnace, heating to 500 ℃ at the speed of 5 ℃/min in the oxygen atmosphere, sintering for 5h, and cooling to room temperature to obtain the niobium-doped high-nickel ternary cathode material coated with niobium oxide.
Assembling the battery: the same as in example 1.
The battery assembled in the comparative example has the first discharge specific capacity of 176.6mAh/g, the charge specific capacity of 199.3mAh/g and the first charge-discharge coulombic efficiency of 88.86% under the conditions that the charge-discharge voltage is 2.7-4.3V and the current density is 1C (200 mA/g), and after 100 cycles, the discharge specific capacity is 145.2mAh/g and the capacity retention rate is 83.64%; the specific discharge capacity at the current density of 10C is only 121.6 mAh/g. The comparative example results show that the niobium doped material coated with niobium pentoxide has poor charge-discharge cycle stability and low rate performance.

Claims (8)

1. A niobium-doped high-nickel ternary cathode material coated with niobium phosphate is characterized by comprising a niobium-doped high-nickel ternary cathode material and niobium phosphate coated on the surface of the niobium-doped high-nickel ternary cathode material; the niobium-doped high-nickel ternary cathode material is characterized in that a niobium element is doped in the high-nickel ternary cathode material, and the molar ratio of the doping amount of the niobium element to the total molar amount of nickel, cobalt and manganese transition metals in the high-nickel ternary cathode material is (0.005-0.1): 1, the mass ratio of the coating amount of the niobium phosphate to the niobium-doped high-nickel ternary cathode material is (0.01-0.1): 1;
the high-nickel ternary positive electrode materialThe chemical formula of the material is LiNixCoyMn(1-x-y)O2Wherein x is more than 0.6 and less than 0.9, y is more than 0.05 and less than 0.2, the niobium-doped high-nickel ternary cathode material coated by the niobium phosphate is in a sphere-like shape, and the particle size is 6-12 mu m;
when the niobium-doped high-nickel ternary cathode material coated with niobium phosphate is prepared, niobium is firstly utilized to carry out bulk phase doping on the high-nickel ternary cathode material to obtain the niobium-doped high-nickel ternary cathode material, and then the surface of the niobium-doped high-nickel ternary cathode material is coated with niobium phosphate.
2. The method for preparing the niobium phosphate coated niobium doped high nickel ternary cathode material as claimed in claim 1, characterized by comprising the following steps:
(1) preparing a nickel-cobalt-manganese hydroxide precursor by utilizing a coprecipitation reaction; preparing niobium phosphate by utilizing a niobium source and phosphoric acid;
(2) uniformly mixing the nickel-cobalt-manganese hydroxide precursor obtained in the step (1) with a lithium source and a niobium source, and then sintering in an oxidizing atmosphere to obtain a niobium-doped ternary cathode material;
(3) grinding and uniformly mixing the niobium phosphate obtained in the step (1) and the niobium-doped ternary cathode material obtained in the step (2), and sintering to obtain a niobium-doped high-nickel ternary cathode material coated by the niobium phosphate;
in the step (3), the sintering treatment is carried out by heating to 450-550 ℃ at a heating rate of 1-10 ℃/min, and sintering for 4-6 h.
3. The preparation method according to claim 2, wherein the preparation of the nickel-cobalt-manganese hydroxide precursor by using the coprecipitation reaction comprises the steps of: adding the nickel-cobalt-manganese solution into a continuous stirring reaction kettle filled with an ammonia solution, heating and introducing into a protective atmosphere, simultaneously adding a complexing agent and a precipitator solution, stirring for coprecipitation reaction, and then aging, filtering, washing and drying to obtain the nickel-cobalt-manganese hydroxide precursor.
4. The method of claim 2, wherein the step of using the niobium source and phosphoric acid to produce niobium phosphate comprises the steps of: dissolving a niobium source and phosphoric acid in a deionized water solution, stirring and dissolving, performing condensation reflux reaction in an oil bath kettle, filtering, washing and drying to obtain a niobium phosphate material; the reaction temperature is controlled to be 80-150 ℃ during the condensation reflux reaction, and the reaction time is 12-18 h.
5. The production method according to any one of claims 2 to 4, wherein the lithium source is lithium hydroxide and/or lithium carbonate, and the molar ratio of the total molar amount of nickel, cobalt, and manganese elements in the nickel-cobalt-manganese hydroxide precursor to the molar amount of lithium elements in the lithium source is 1: (1.02-1.2).
6. The method according to any one of claims 2 to 4, wherein the niobium source is one or more of niobium ethoxide, niobium oxalate or niobium oxide, and the molar ratio of the total molar amount of the nickel, cobalt and manganese elements in the nickel-cobalt-manganese hydroxide precursor to the niobium element in the niobium source for doping is 1: (0.005-0.1).
7. The method as claimed in any one of claims 2-4, wherein in the step (2), the sintering treatment is two-stage sintering, wherein the temperature is raised to 550 ℃ at a temperature raising rate of 1-10 ℃/min, and the temperature is raised to 1000 ℃ at a temperature raising rate of 1-10 ℃/min after sintering for 2-8h, and the sintering time is 8-20 h.
8. The preparation method according to any one of claims 2 to 4, wherein the mass ratio of the niobium-doped ternary cathode material to niobium phosphate is controlled to be 1: (0.01-0.2).
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