CN111816866B

CN111816866B - Method for preparing lithium-rich manganese-based positive electrode material by co-precipitation-hydrothermal combination

Info

Publication number: CN111816866B
Application number: CN202010692502.0A
Authority: CN
Inventors: 卑凤利; 温乐; 赵淑宁; 刘晋利
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2020-07-17
Filing date: 2020-07-17
Publication date: 2022-05-27
Anticipated expiration: 2040-07-17
Also published as: CN111816866A

Abstract

The invention discloses a method for preparing a lithium-rich manganese-based positive electrode material by co-precipitation-hydrothermal combination. Firstly, nickel sulfate, cobalt sulfate and manganese sulfate are used as a nickel source, a cobalt source and a manganese source, dissolved in deionized water to form a uniform light orange transparent solution, then a certain amount of complexing agent ammonia water and a precipitator sodium hydroxide are respectively added into the solution, and a preparation method combining coprecipitation and hydrothermal reaction is adopted to obtain Mn_0.54Co_0.13Ni_0.13(OH)₂And (3) precursor. And sintering by using lithium carbonate as a lithium source, and naturally cooling to obtain the cathode material. The method has the advantages of simple process, wide raw material source and contribution to large-scale industrial production, and the coprecipitation method is combined with the hydrothermal method to obtain the lithium-rich manganese-based cathode material, the electrochemical performance of the material is obviously improved compared with that of the material prepared by the traditional coprecipitation method, and the capacity is still maintained at 201.2 mAh.g after the material is circulated for 50 circles at the multiplying power of 0.2C^‑1。

Description

Method for preparing lithium-rich manganese-based positive electrode material by co-precipitation-hydrothermal combination

Technical Field

The invention relates to the technical field of lithium ion battery anode materials, in particular to a lithium-rich manganese-based anode material Li_1.2Mn_0.54Co_0.13Ni_0.13O₂The preparation method of (1).

Background

The electric automobile is a novel strategic product for solving the problems of energy and environment, but the current electric automobile still faces the problems of short driving mileage, high cost, poor safety and the like, and the large-scale popularization and application of the electric automobile are seriously restricted. Therefore, research and development of a new generation of 300-400 Wh/kg power lithium battery is a necessary trend for future lithium battery materials and technical development. From the current technology, the energy density of the battery is improved by reducing the mass ratio of the inactive substances in the battery core, the technical limit is almost reached, and the adoption of the cathode material with higher energy density is a more effective technical approach for improving the energy density of the battery.

Among the known anode materials, the lithium-rich manganese-based anode material has the specific discharge capacity of 250mAh g^-1Above, almost twice the actual capacity of the currently commercialized positive electrode materials; meanwhile, the material is mainly made of cheaper manganese element, has low content of precious metal, and has low cost and good safety compared with the common lithium cobaltate and nickel cobalt manganese ternary system anode material. Therefore, the lithium-rich manganese-based positive electrode material is considered as an ideal choice for the next generation of lithium power batteries, and although the lithium-rich manganese-based positive electrode material has the absolute advantage of specific discharge capacity, the following key technical problems must be solved to actually apply the lithium-rich manganese-based positive electrode material to the lithium power batteries: firstly, the first irreversible capacity loss is reduced; second, improve the multiplying power performance and cycle life; and thirdly, inhibiting voltage attenuation in the cyclic process.

At present, the main methods for synthesizing lithium ion ternary cathode materials include a coprecipitation method, a hydrothermal method, a sol-gel method, a high-temperature solid phase method and the like, wherein the chemical process of the sol-gel method comprises the steps of firstly dispersing raw materials in a solvent, then generating an active monomer through a hydrolysis reaction, polymerizing the active monomer to form sol, further generating gel with a certain space structure, and preparing nanoparticles and required materials through drying and heat treatment, but the electrochemical performance of the ternary cathode materials prepared by the method is unsatisfactory. The coprecipitation method can accurately control the content of each component, so that the different elements can be uniformly mixed at the molecular atomic level, and the material with the same proportion as the initial designed elements can be easily prepared. Compared with other methods, the material prepared by the coprecipitation method has the characteristics of high tap density, good fluidity, stable electrochemical performance and good reproducibility, but the particles prepared by the coprecipitation method are large and uneven in particle size, the hydrothermal method is a powder preparation method for generating a target compound by reacting a raw material compound with water at a certain temperature and under a certain pressure, and the hydrothermal method has the advantages of uniform phase, small particle size of a product, controllable shape and the like, so that the hydrothermal method and the coprecipitation method are combined, and experiments prove that the electrochemical performance of the material can be improved.

Disclosure of Invention

The invention provides a preparation method of a lithium-rich manganese-based positive electrode material, which is used for preparing Li with small particle size and uniform dispersion_1.2Mn_0.54Co_0.13Ni_0.13O₂The lithium ion battery anode material improves the electrochemical performance of the material and improves the rate capability and the cycle performance of the material.

The technical solution for realizing the purpose of the invention is as follows: preparation of Li by combination of hydrothermal method and coprecipitation method_1.2Mn_0.54Co_0.13Ni_0.13O₂The method for preparing the lithium-rich manganese-based cathode material comprises the following steps of:

(1) with NiSO₄·6H₂O、CoSO₄·7H₂O、MnSO₄·H₂O is taken as a raw material, added into deionized water respectively to form a uniform and transparent mixed solution, and NH is respectively dripped at the speed of 2 s/drop at the temperature of 60 ℃ under the condition of continuous stirring and nitrogen atmosphere₃·H₂O and NaOH to precipitate metal ions and control the pH value of the reaction system to be 12;

(2) stirring the solution for 8h, aging for 12h, directly placing the mother liquor and the precipitate into a reaction kettle after aging, and carrying out hydrothermal reaction under certain conditions to obtain Mn_0.54Co_0.13Ni_0.13(OH)₂A precursor;

(3) mixing the obtained precursor with Li₂CO₃Mixing and grinding the materials according to a certain proportion, and sintering the materials in a tube furnace to obtain Li_1.2Mn_0.54Co_0.13Ni_0.13O₂The lithium ion battery is a lithium-rich manganese-based positive electrode material.

In the step (1), NiSO₄·6H₂O、CoSO₄·7H₂O、MnSO₄·H₂The mass ratio of O is 1:1: 4.

In the step (1), the molar concentration of the total metal ions in the uniform and transparent mixed solution is 2 mol. L^-1。

In the step (1), the molar concentration of 2 mol. L is used^-1The pH value of the reaction system is controlled to be 12 by using the dilute hydrochloric acid.

In the step (2), the hydrothermal reaction temperature is 200 ℃, and the hydrothermal reaction time is 12 h.

In the above step (2), Li₂CO₃With Mn_0.54Co_0.13Ni_0.13(OH)₂The mass ratio of the precursor is as follows: 1.26:1.

In the step (3), the sintering is carried out in a tube furnace in a sectional way, and the calcining temperature and the calcining time are respectively as follows: 450 ℃ for 5 h; 850 ℃ and 15 h.

Compared with the prior art, the invention has the following positive effects:

(1) the lithium-rich manganese-based material has the problems of complex crystal structure, poor rate capability and poor cycle performance, and in order to achieve uniform coprecipitation as much as possible to form a regular precursor, the invention designs a preparation method combining coprecipitation and a hydrothermal method, the uniform precipitation is generated in the solution as much as possible by controlling the conditions of pH value, water bath temperature and the like of the coprecipitation, then the solution is aged, the crystal structure can be improved by aging, impurity ions wrapped in the crystal are dissociated, small particles can be dissolved on large particles to be recrystallized and grown, incomplete crystal particles can be recrystallized and grown by contacting with mother liquor, so that the crystal structure tends to be regular, but a small amount of particles are agglomerated, and the uniformity and the dispersibility of the particles are poor. Therefore, a high-temperature and high-pressure environment is generated under hydrothermal conditions, so that particles are crushed to be fine, the grains are further developed completely, the growth of the grains is promoted, the particles with better dispersity and uniform size are favorably formed, the temperature and time required by subsequent high-temperature calcination can be reduced, and the lithium-rich manganese-based anode material with a more regular and complete crystal structure is prepared, so that the rate capability and the cycle performance are improved; (2) the whole process of forming the precipitate in the aqueous solution is completed in the nitrogen atmosphere, so that the Mn can be effectively solved²⁺Easy oxidation under alkaline condition, and uniform Mn_0.54Co_0.13Ni_0.13(OH)₂The formation of a precipitate; (3) mn in oxygen atmosphere_0.54Co_0.13Ni_0.13(OH)₂The precursor is mixed with lithium salt and then sintered at high temperature, so that the crystallinity of the material is improved, and the synthesized material has uniform sizeLi rich in Li and Mn_1.2Mn_0.54Co_0.13Ni_0.13O₂A positive electrode material; the raw materials used in the invention have wide sources, low price, simple process, ideal electrochemical performance of the material, and large-scale production, and have great economic benefit.

Drawings

FIG. 1 shows preparation of Li by coprecipitation_1.2Mn_0.54Co_0.13Ni_0.13O₂TEM images of and Li preparation using hydrothermal and co-precipitation coupled methods_1.2Mn_0.54Co_0.13Ni_0.13O₂The TEM images of (a) - (b) are TEM images of comparative examples at different magnifications, and (d) - (f) are TEM images of examples at different magnifications.

FIG. 2 shows preparation of Li by coprecipitation_1.2Mn_0.54Co_0.13Ni_0.13O₂XRD patterns of and Li preparation using hydrothermal and co-precipitation coupled processes_1.2Mn_0.54Co_0.13Ni_0.13O₂XRD pattern of (a).

FIG. 3 shows Li prepared by coprecipitation_1.2Mn_0.54Co_0.13Ni_0.13O₂And Li prepared using a combination of hydrothermal and co-precipitation_1.2Mn_0.54Co_0.13Ni_0.13O₂First discharge specific capacity plot at 0.1C.

FIG. 4 is Li prepared using co-precipitation_1.2Mn_0.54Co_0.13Ni_0.13O₂And Li prepared by hydrothermal and coprecipitation method_1.2Mn_0.54Co_0.13Ni_0.13O₂Discharge specific capacity graph under different multiplying factor condition.

FIG. 5 shows Li prepared by coprecipitation method_1.2Mn_0.54Co_0.13Ni_0.13O₂And Li prepared using a combination of hydrothermal and co-precipitation_1.2Mn_0.54Co_0.13Ni_0.13O₂Discharge specific capacity cycling plot of 50 cycles at 0.2C rate.

Detailed Description

The embodiments of the present invention will be described in detail with reference to the accompanying drawings so that the advantages and features of the invention can be more easily understood by those skilled in the art, and the scope of the invention will be clearly and clearly defined.

The invention relates to a lithium-rich manganese-based cathode material Li of a lithium ion battery as a target product_1.2Mn_0.54Co_0.13Ni_0.13O₂The preparation method comprises the following steps:

comparative example

The target product of the invention is Li-rich manganese-based anode material_1.2Mn_0.54Co_0.13Ni_0.13O₂Prepared by a coprecipitation method:

(1) firstly, 6.42g of MnSO is weighed₄·H₂O、2.4g NiSO₄·6H₂O、2.56g CoSO₄·7H₂Placing the O powder in a 50ml beaker, pouring 36ml of deionized water into the beaker, and continuously stirring by using a glass rod to completely dissolve the powder to form a light orange transparent solution which is marked as solution 1; 30ml of the solution is prepared, and the concentration is 3 mol.L^-1NH of (2)₃·H₂Placing the O solution in a small beaker for later use; 8.4g NaOH was weighed out and dissolved completely in 54ml deionized water and placed in a beaker for use.

(2) Placing the solution 1 in nitrogen atmosphere, and placing the prepared NH under the condition that the water bath temperature is 60 DEG C₃·H₂Respectively dripping O solution and NaOH solution into the light orange transparent solution under the condition of continuously stirring, dripping dilute hydrochloric acid after the dripping is finished to maintain the pH value of the solution at 12, continuing stirring for 24 hours under the condition after the pH value is stable, cooling the solution to room temperature after the stirring is finished, and aging the solution for 24 hours to obtain pink precipitate Mn_0.54Co_0.13Ni_0.13(OH)₂。

(3) The obtained precursor Mn_0.54Co_0.13Ni_0.13(OH)₂Washed three times with deionized water and ethanol, respectively, and then dried overnight in a drying oven at 90 ℃. After drying, it is reacted with Li₂CO₃Fully mixing and grinding the powder, wherein the precursor is mixed with the lithium carbonate powderThe ratio of the amount of the powder material was 1:1.26, the fully ground powder was placed in a crucible, placed in a tube furnace, and heated to O₂Presintering for 5h at 450 ℃ and sintering for 15h at 850 ℃ in the atmosphere to obtain the Li rich in lithium manganese_1.2Mn_0.54Co_0.13Ni_0.13O₂And (3) a positive electrode material.

Examples

Target product Li of the invention_1.2Mn_0.54Co_0.13Ni_0.13O₂The preparation method is characterized by combining a hydrothermal method and a coprecipitation method:

(2) Placing the solution 1 in nitrogen atmosphere, and placing the prepared NH under the condition that the water bath temperature is 60 DEG C₃·H₂Respectively dripping the O solution and the NaOH solution into the light orange transparent solution under the condition of continuously stirring, dripping dilute hydrochloric acid after the dripping is finished to maintain the pH value of the solution at 12, continuing stirring for 8 hours after the pH value is stable, aging the solution for 12 hours after the stirring is finished, transferring the solution into a hydrothermal kettle, carrying out hydrothermal reaction in a muffle furnace, setting the temperature of the hydrothermal reaction at 200 ℃, and setting the time of the hydrothermal reaction for 12 hours.

(3) After the hydrothermal reaction is finished, cooling the reaction product to room temperature, and then obtaining a precursor Mn_0.54Co_0.13Ni_0.13(OH)₂Washed three times with deionized water and ethanol, respectively, and then dried overnight in a drying oven at 100 ℃. After drying, it is reacted with Li₂CO₃Fully mixing and grinding the powder, wherein the mass ratio of the precursor to the lithium carbonate powder is 1:1.26, and fully grindingThe powder of (2) is placed in a crucible, placed in a tube furnace, in O₂Presintering for 5h at 450 ℃ in the atmosphere, and sintering for 15h at 850 ℃ to obtain the lithium-rich manganese-based positive electrode material.

(5) Observing and analyzing the morphology of the product by adopting a Transmission Electron Microscope (TEM), wherein (a), (b) and (c) in the attached drawing 1 are materials prepared by combining a hydrothermal method and a coprecipitation method, and (d), (e) and (f) in the attached drawing 1 are Li prepared by a coprecipitation method₁.₂Mn_0.54Co_0.13Ni_0.13O₂And (3) a positive electrode material. As can be seen from (d) and (e) in the attached drawing 1, most of the particles prepared by the coprecipitation method are spherical, the particle size is large and is about 200-300 nm, the thickness is thick, and the dispersity is poor, and as can be clearly seen from (f) in the attached drawing 1, a plurality of spherical particles are aggregated together, the aggregation phenomenon is serious, the lithium ion transmission is not facilitated, and the electrochemical performance of the material is poor. As can be seen from the attached drawing 1 (a), the material prepared by combining the hydrothermal method and the co-precipitation method is of a diamond sheet structure, the particle size is smaller and is about 100-200 nm, the particles can be clearly seen from the attached drawing 1 (b) and (c), the particles are uniformly dispersed, the agglomeration problem of the particles is effectively improved, the thickness of the material is thinner than that of the material prepared by the co-precipitation method, the specific surface area of the material is larger, the effective contact area with an electrolyte is larger, the lithium ion transmission path can be shortened, the lithium ion transmission dynamic performance can be improved, and the material has important significance for effectively improving the rate capability and the cycle performance of the lithium-rich manganese-based anode material. FIG. 2 shows the respective preparation of Li using two preparation methods_1.2Mn_0.54Co_0.13Ni_0.13O₂The XRD pattern of the cathode material can be seen from the X-ray diffraction pattern, and the diffraction peaks of the materials prepared by the two methods correspond to the layered alpha-NaFeO₂The structure belongs to a hexagonal system, and R3m space group. Wherein, a superlattice diffraction peak exists between 20 DEG and 25 DEG, which shows that Li₂MnO₃The existence of ordered structure micro-regions, the phase is also a layered structure and belongs to a C/2m space group; the ratio of (003) to (104) intensities of the crystal planes can reflect the degree of disorder of the layered material, when I₍₀₀₃₎/I₍₀₀₄₎＞1.2When the materials are described as having a good layered structure, it can be seen from FIG. 2 that I of two materials₍₀₀₃₎/I₍₀₀₄₎All are more than 1.2, which shows that the prepared materials all have good laminated structures; the peaks of diffraction peaks (018) and (110) around 65 ° split clearly, indicating that the layered structure has higher crystallinity; it can be clearly seen from the figure that the peak strength of the material prepared by combining the hydrothermal method and the co-precipitation method is higher than that of the material prepared by the co-precipitation method, which indicates that the crystallinity of the material prepared by combining the hydrothermal method and the co-precipitation method is better. FIG. 3 is a graph of the first charge-discharge specific capacity of two materials under the conditions of a voltage range of 2.0-4.8V and 0.1C, and it can be seen from the graph that the two materials are both typical curves of the first charge of lithium-rich layered oxide, and have two obvious charge platforms, the first charge platform is about 4.0V and corresponds to Li⁺De-intercalation from the structure of space group R3m accompanied by Ni²⁺/Ni⁴⁺Oxidation of (2); the second plateau is above 4.5V, and when the voltage is higher than 4.5V, Li is activated₂MnO₃Phase, this process is irreversible and therefore only appears in the first charge curve. As can be seen from the figure, the first charge capacities of the materials prepared by the two methods are not much different, and are 290 mAh g^-1However, the material prepared by combining the hydrothermal method and the coprecipitation method has the discharge specific capacity as high as 250 mAh.g^-1Is obviously superior to the material prepared by a coprecipitation method, and the specific discharge capacity of the material is only 200 mAh.g^-1. FIG. 4 shows the specific discharge capacities of the two materials under different multiplying powers of 0.1C, 0.2C, 0.5C, 1C, 2C, 5C and 0.1C, respectively, and it can be seen from the figure that the specific discharge capacities of the materials prepared by the hydrothermal method and the coprecipitation method are higher than those of the materials prepared by the coprecipitation method, and the specific discharge capacity of the materials is up to 225 mAh.g at 0.1C^-1The discharge capacity of the material reaches 79 mAh g under the high multiplying power of 5C^-1Much higher than the material prepared by coprecipitation method (the discharge capacity is only 60mAh g)^-1). FIG. 5 is a discharge specific capacity cycle chart of two materials circulating 50 times at 0.2C rate, and it can be seen from the chart that under the condition of 0.1C rate, after 50 cycles of charge and discharge, the specific capacity of the material prepared by using a coprecipitation method is only 170 mAhg^-1The specific capacity of the material prepared by the hydrothermal method and the coprecipitation method is still kept at 200 mAh.g^-1Obviously superior to the former, and fully illustrates the superiority of the method.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A method for preparing a lithium-rich manganese-based positive electrode material by co-precipitation-hydrothermal combination is characterized in that the positive electrode material is of a rhombic sheet structure, has a small particle size of 100-200 nm, and comprises the following steps:

(1) with NiSO₄·6H₂O、CoSO₄·7H₂O、MnSO₄·H₂Adding O as raw material into water respectively to obtain uniform and transparent mixed solution, and dripping NH at a speed of 2 s/drop at 60 deg.C under stirring and nitrogen atmosphere₃·H₂O and NaOH to precipitate metal ions and control the pH value of the reaction system to be 12;

2. The method of claim 1, wherein in step (1), NiSO is₄·6H₂O、CoSO₄·7H₂O、MnSO₄·H₂The mass ratio of O is 1:1: 4.

3. The method according to claim 1, wherein in the step (1), the molar concentration of the total metal ions in the uniformly transparent mixed solution is 2 mol-L^-1。

4. The method of claim 1, wherein in step (1), a molarity of 2 mol-L is used^-1The pH value of the reaction system is controlled to be 12 by using the dilute hydrochloric acid.

5. The method according to claim 1, wherein in the step (2), the hydrothermal reaction temperature is 200 ℃ and the hydrothermal reaction time is 12 h.

6. The method of claim 1, wherein in step (2), Li₂CO₃With Mn_0.54Co_0.13Ni_0.13(OH)₂The mass ratio of the precursor was 1.26: 1.

7. The method according to claim 1, wherein in the step (3), the sintering is carried out in a tube furnace in a segmented mode, and the calcining temperature and the calcining time are respectively as follows: 450 ℃ for 5 h; 850 ℃ and 15 h.