WO2020029028A1

WO2020029028A1 - Method for preparing positive electrode material, positive electrode material, and lithium ion battery

Info

Publication number: WO2020029028A1
Application number: PCT/CN2018/099018
Authority: WO
Inventors: 战鹏; 刘亮; 黄勇; 黄双
Original assignee: 中天新兴材料有限公司
Priority date: 2018-08-06
Filing date: 2018-08-06
Publication date: 2020-02-13
Also published as: CN111095619A; CN111095619B

Abstract

Provided is a method for preparing a positive electrode material, the method comprising the steps of: dissolving a positive electrode material precursor in a solvent to obtain a mixed solution; dropwise adding an alkaline solution to the mixed solution to obtain an alkaline pretreatment solution; simultaneously dropwise adding a zirconium source acidic titration solution and an aluminum source alkaline titration solution to the pretreatment solution for co-precipitation to obtain a coated positive electrode material precursor; and mixing a lithium source with the coated positive electrode material precursor at a preset ratio, and sintering same to prepare a composite oxide-coated positive electrode material.

Description

Method for preparing positive electrode material, positive electrode material and lithium ion battery

Technical field

The present invention relates to the technical field of lithium ion batteries, and in particular, to a method for preparing a positive electrode material, a positive electrode material, and a lithium ion battery.

Background technique

This section is intended to provide a background or context to the embodiments of the invention that are set forth in the claims. The description herein is not admitted to be prior art by inclusion in this section.

Positive grade materials are the key components of electrode materials. During the charge and discharge of lithium batteries, they are in direct contact with the electrolyte, and the transition metal oxide-type positive electrode materials are easily dissolved and attacked, in other words, it is easy to cause the transition metal ions to dissolve; The free radicals generated by the oxidative decomposition of the electrolyte may also cause the electrode materials to dissolve, and the side reactions that occur may also produce harmful substances. In order to solve the above problems, a common solution is to coat the surface of the positive electrode material, and use a coating layer to isolate the active material (transition metal ions) in the battery from the electrolyte, which can effectively reduce the occurrence of side reactions and suppress the transition metal. Ions dissolve and reduce the decomposition of the electrolyte, improving the cycling performance of lithium batteries. Not only that, some cladding layers have better conductivity, can improve the conductivity of the electrode, and are beneficial to the rate performance of lithium batteries. In the existing coating technology, a plurality of raw materials of a precursor and a coating material are directly mechanically mixed, and then heat treated to obtain an oxide-coated positive electrode material. However, this coating method cannot obtain a uniform, complete and efficient coating layer. At the same time, the use of multiple raw materials has a high production cost, and the obtained single-oxide-coated positive electrode material has limited improvement in the electrochemical performance of the battery.

Summary of the invention

In view of the above, it is necessary to provide an improved method for preparing a positive electrode material. By simultaneously titrating the coating precursor solution and coprecipitating the coating layer in situ, the coating layer of the obtained positive electrode material can be tightly attached to the positive electrode material The surface of the substrate has good uniformity and strong binding force, which can effectively protect the positive electrode material, avoid contact with the electrolyte and cause side reactions, and the prepared lithium battery has good electrochemical performance.

The technical solution provided by the present invention is: a method for preparing a positive electrode material, including the following steps:

Dissolving the positive electrode material precursor in a solvent to obtain a mixed solution;

Adding an alkaline solution dropwise to the mixed solution to obtain an alkaline pretreatment solution;

Adding a zirconium source acidic titration solution and an aluminum source alkaline titration solution to the pretreatment solution simultaneously and co-precipitating to obtain a coated cathode material precursor;

The lithium source and the coated positive electrode material precursor are mixed according to a preset lithium-to-metal ratio, and a composite oxide coated positive electrode material is obtained by sintering.

Further, the positive electrode material precursor has the following chemical formula to indicate its composition: Ni _x Co _y Mn _z (OH) ₂ (x + y + z = 1, 0≤x≤1, 0≤y≤1, 0≤z ≤1).

Further, the solvent is one of an aqueous solution or an ethanol solution, and during the dissolution process, the temperature of the aqueous solution or the ethanol solution is controlled to 25 ° C-80 ° C.

Further, stirring is performed simultaneously during the dissolution process, and the stirring speed is 200 rpm-450 rpm.

Further, the aluminum source includes one of sodium metaaluminate and potassium metaaluminate; the zirconium source includes one of zirconium oxychloride, zirconium sulfate, and zirconium nitrate.

Further, the alkaline solution is one or a combination of a sodium hydroxide solution, a sodium metaaluminate solution, or an aqueous ammonia solution.

Further, the pH value of the pretreatment solution is 8-11, and the pH value is stabilized to a preset value during the co-precipitation process.

Further, a preset lithium-to-metal ratio of the lithium source to the coated cathode material precursor is 1.00 to 1.20, a heat treatment temperature during the sintering process is 300 ° C. to 1000 ° C., and a heat treatment time is 3 h to 24 h.

The invention also provides a positive electrode material, which is prepared by the following method steps:

The present invention further provides a lithium-ion battery, which includes a positive electrode sheet formed by pressing the positive electrode material.

Compared with the prior art, the method for preparing a positive electrode material provided by the present invention includes the following steps: dissolving a positive electrode material precursor in a solvent to obtain a mixed solution; and adding an alkaline solution dropwise to the mixed solution to obtain an alkaline pretreatment. Treatment solution; simultaneous addition of a zirconium source acidic titration solution and an aluminum source alkaline titration solution to the pretreatment solution for co-precipitation to obtain a coated positive electrode material precursor; press the lithium source and the coated positive electrode material precursor according to The lithium is mixed with a predetermined metal ratio and sintered to obtain a composite oxide-coated positive electrode material. The invention adopts simultaneous titration to form a coprecipitation for coating, and then sintering to finally obtain a composite oxide-coated positive electrode material. The coating layer has the characteristics of good uniformity and strong binding force. In the fabricated lithium ion battery, the positive electrode material coating layer is in direct contact with the electrolyte, which effectively inhibits the dissolution of the active material of the positive electrode material, and reduces the decomposition of the electrolyte, thereby improving the cycle performance of the lithium ion battery. Moreover, the method has simple steps, easy control, short preparation time, energy saving and low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a preparation flow chart of the cathode material of the present invention.

FIG. 2 is an XRD pattern of the uncoated positive electrode material obtained in the first and second embodiments of the present invention.

FIG. 3A is a SEM image of the positive electrode material obtained in the first and second embodiments in FIG. 2.

FIG. 3B is an energy spectrum of the positive electrode material obtained in the first and second embodiments in FIG. 2.

FIG. 4 is a first-time charge and discharge curve diagram of the cathode material shown in FIG. 2.

FIG. 5 is a cycle characteristic curve diagram of a lithium ion battery using the cathode material shown in FIG. 2.

Reference sign description:

no.

The following specific implementations will further explain the embodiments of the present invention with reference to the foregoing drawings.

detailed description

In order to more clearly understand the foregoing objectives, features, and advantages of the embodiments of the present invention, the following describes the present invention in detail with reference to the accompanying drawings and specific implementations. It should be noted that, in the case of no conflict, the features in the embodiments of the present application may be combined with each other.

In the following description, many specific details are set forth in order to fully understand the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other implementations obtained by a person of ordinary skill in the art without making creative efforts fall within the protection scope of the embodiments of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art belonging to the embodiments of the present invention. The terms used herein in the description of the present invention are only for the purpose of describing specific implementations, and are not intended to limit the embodiments of the present invention.

Lithium-ion batteries have the advantages of high specific capacity, good cycling performance, good thermal stability, and environmental friendliness. They have been widely used in the field of mobile electronic equipment, energy storage equipment, electric vehicles, and hybrid electric vehicles. Ternary materials have become a hot topic in battery cathode materials because they have the advantages of high specific capacity, good safety performance, and lower cost than ordinary lithium batteries. However, the existing cathode materials are susceptible to corrosion due to side reactions with the electrolyte during the charge and discharge process. , Which causes its metal ions to dissolve and produce harmful substances, which seriously affects the performance of lithium-ion batteries and limits its applications.

The method for preparing a cathode material provided by the present invention is described in detail below with reference to FIG. 1.

The method of the present invention includes the following steps:

101: Dissolve a positive electrode material precursor in a solvent to obtain a mixed solution;

among them,

The positive electrode material precursor has the following chemical formula to indicate its composition: Ni _x Co _y Mn _z (OH) ₂ (x + y + z = 1, 0≤x≤1, 0≤y≤1, 0≤z≤1) .

The solvent is one of an aqueous solution or an ethanol solution.

During the dissolution process, the temperature of the aqueous solution or the ethanol solution is controlled to 25 ° C to 80 ° C. In actual operation, a fixed value within the temperature range is adopted and stabilized at this value ("stable" includes floating within an acceptable range, such as within ± 1 ° C of the set value).

During the dissolution process, stirring is performed at the same time, and the stirring speed is 200 rpm-450 rpm. The allowable error is also kept in practice.

102: Add an alkaline solution dropwise to the mixed solution to obtain an alkaline pretreatment solution;

among them,

The alkaline solution is one or a combination of a sodium hydroxide solution, a sodium metaaluminate solution, or an ammonia solution.

The pH value of the pretreatment solution is 8-11, and the pH value is stable to a preset value during the co-precipitation process. The preset value is a fixed value within a preset range, such as PH = 8, 9, 10, 11 and so on.

103: Simultaneously adding a zirconium source acidic titration solution and an aluminum source alkaline titration solution to the pretreatment solution for co-precipitation to obtain a coated cathode material precursor;

among them,

The aluminum source includes one of sodium metaaluminate and potassium metaaluminate; the zirconium source includes one of zirconium oxychloride, zirconium sulfate, and zirconium nitrate.

104: Mix the lithium source and the coated positive electrode material precursor at a preset lithium-to-metal ratio, and sinter to obtain a composite oxide-coated positive electrode material. The "lithium" in the preset lithium-to-metal ratio corresponds to the lithium element in the lithium source; the "metal" corresponds to the metal element in the precursor covering the positive electrode material; the ratio refers to the mass ratio.

among them,

The preset lithium ratio of the lithium source to the coated cathode material precursor is 1.00-1.20, the temperature of the heat treatment during the sintering process is 300 ° C-1000 ° C, and the time of the heat treatment is 3h-24h.

The following method is used as an example to prepare the positive electrode material and the lithium battery, and characterize the performance of the product obtained in the specific embodiment.

First, prepare a 0.05 mol / L Zr source acidic titration solution, that is, a Zr source acid coating precursor solution (referred to as a Zr solution) for later use; prepare a 0.05 mol / L Al source alkaline titration solution, that is, an Al source alkaline The coating precursor solution (Al solution for short) is reserved.

Example 1

Weigh the positive electrode material precursor (Ni ₅ Co ₂ Mn ₃ (OH) ₂ ), place it in a 50 ° C constant temperature aqueous solution, and stir at 300 rpm to obtain a mixed solution;

Dropwise adding a 32% sodium hydroxide solution to obtain a pretreatment solution with a pH value close to 9;

The Zr solution is added dropwise to the pretreatment solution, wherein the amount of Zr element is calculated as 0.05% of the mass of the cathode material precursor, and the dropping speed is 8.5ml / min; meanwhile, the Al solution is added dropwise to the pretreatment The solution stabilizes its pH value close to 9, and the dropping rate is 10 ml / min. After the Zr solution and the Al solution are added dropwise, a co-precipitation reaction occurs. Zr ions and Al ions settle together to form nano-sized uniform zirconium hydroxide particles and hydroxide. Aluminum particles, two kinds of particles are evenly adsorbed on the surface layer of the positive electrode material precursor particles. After the chemical reaction is completed, an equal amount of constant temperature water at 50 ° C is added, stirred for half an hour, and centrifuged to obtain a composite hydroxide-coated positive electrode material precursor;

The lithium carbonate and the coated positive electrode material precursor are mixed according to a lithium-to-metal ratio of 1: 1.05, heated to 700 ° C at 3 ° C / min, and held for 3h, and then heated to 940 ° C at 3 ° C / min, and held for 12h. To obtain a composite oxide-coated positive electrode material, that is, a finished ternary material.

Example 2

Dropwise adding a 32% sodium hydroxide solution to obtain a pretreatment solution with a pH value close to 10;

The lithium carbonate and the metal element in the coated positive electrode material precursor were mixed according to a lithium-to-metal ratio of 1: 1.05, heated to 700 ° C at 3 ° C / min, held for 3 hours, and then heated to 940 ° C at 2 ° C / min. After 12 hours of heat preservation, a composite oxide-coated positive electrode material was obtained, that is, a finished ternary material.

Example 3

Weigh the positive electrode material precursor Ni ₅ Co ₂ Mn ₃ (OH) ₂ , place it in a 50 ° C constant temperature aqueous solution, and stir at 400 rpm to obtain a mixed solution;

Example 4

Weigh the positive electrode material precursor Ni ₅ Co ₂ Mn ₃ (OH) ₂ , place it in a 60 ° C constant temperature aqueous solution, and stir at 300 rpm to obtain a mixed solution;

The Zr solution is added dropwise to the pretreatment solution, wherein the amount of Zr element is calculated as 0.05% of the mass of the cathode material precursor, and the dropping speed is 8.5ml / min; meanwhile, the Al solution is added dropwise to the pretreatment The solution stabilizes its pH value close to 9, and the dropping rate is 10 ml / min. After the Zr solution and the Al solution are added dropwise, a co-precipitation reaction occurs. Zr ions and Al ions settle together to form nano-sized uniform zirconium hydroxide particles and hydroxide. Aluminum particles, two kinds of particles are evenly adsorbed on the surface layer of the positive electrode material precursor particles. After the chemical reaction is completed, an equal amount of constant temperature water at 60 ° C. is added, stirred for half an hour, and centrifuged to obtain a composite hydroxide-coated positive electrode material precursor;

Example 5

Weigh the positive electrode material precursor Ni ₅ Co ₂ Mn ₃ (OH) ₂ , place it in a 50 ° C constant temperature aqueous solution, and stir at 300 rpm to obtain a mixed solution;

The lithium carbonate and the coated positive electrode material precursor were mixed according to a lithium-to-metal ratio of 1: 1.06, heated to 700 ° C at 3 ° C / min, and maintained for 3 hours, and then heated to 940 ° C at 3 ° C / min, and maintained for 12 hours. To obtain a composite oxide-coated positive electrode material, that is, a finished ternary material.

Example 6

The lithium carbonate and the coated positive electrode material precursor were mixed according to a lithium-to-metal ratio of 1: 1.05, heated to 680 ° C at 3 ° C / min, and maintained for 3 hours, and then heated to 960 ° C at 3 ° C / min, and maintained for 15 hours. To obtain a composite oxide-coated positive electrode material, that is, a finished ternary material.

The performance tests of the positive electrode materials obtained in the above Examples 1 and 2 are performed below, including tests of the phase composition, micro-morphology, first charge-discharge performance, and cycle performance. First, FIG. 2 shows XRD spectra of the coated positive electrode materials obtained in Example 1 and Example 2. The uncoated positive electrode material precursor has a typical β-M (OH) ₂ (M is Ni, Co , Mn) layered structure, the strongest diffraction peak appears around 20 ° corresponding to the (001) crystal plane, in addition to (101), (100), (102), (110), (111) and other crystal planes also occur Diffraction peaks; the positions and relative intensities of the diffraction peaks in the XRD pattern of the positive electrode material obtained after coating in FIG. 2 are basically the same, indicating that the coating material does not damage the layered structure of the precursor. Combined with the scanning photo of the positive electrode material shown in FIG. 3A, it can be seen that the coated particles have the same size and are gathered on the surface of the matrix particles (large particles) of the layered structure; as shown in FIG. 3B, aluminum is viewed from the energy spectrum. The distribution of the elements and zirconium elements coincide, and it can be seen that the composite oxide layer is uniformly and densely coated on the surface layer of the matrix particles. In order to characterize the electrical properties of the above-mentioned cathode materials, the first charge-discharge curve (as shown in FIG. 4) and the cycle performance curve (as shown in FIG. 5) were further tested. FIG. 5 shows the first charge and discharge curves of the positive electrode materials in Examples 1 and 2 at the same current density (1C) in the range of 2.8V-4.4V. The materials all show a relatively obvious charge and discharge platform. The charging platform is Around 3.78V, the discharge platform is about 3.68V, and the first discharge capacity of the two is about 165mAh / g. FIG. 6 compares the cycle performance of the lithium battery made of the positive electrode material in Example 1 and Example 2. It can be seen that the cycle characteristic curves of Example 1 and Example 2 have basically the same trend. The battery cycle in Example 1 After charging and discharging 100 times, the specific capacity is about 136.5mAh / g, which is equivalent to 90.7% of the initial specific capacity of 150.5mAh / g. In Example 2, the specific capacity of the battery after charging and discharging 100 times is about 137.0mAh / g, which is equivalent to the initial The specific capacity is 91.3% of 150.0mAh / g, in short, the cycle performance of the battery is better. The structure and performance of the ternary materials obtained in Examples 3 to 6 were further verified and tested. The results are basically similar to those in Examples 1 and 2. Therefore, the method of the present invention can obtain a lithium battery anode material with better cycle performance. . In other embodiments, the cathode material precursor is not limited to Ni ₅ Co ₂ Mn ₃ (OH) ₂ , the solvent is not limited to water, and may be ethanol; and the stability of the aqueous solution is not limited to 50 ° C., 60 ° ℃, can be any value between 25 ℃ -80 ℃, including this number; the stirring speed is not limited to this embodiment, and can be any value between 200rpm-450rpm; the Zr source can also be zirconia Or zirconium nitrate; the aluminum source may also be potassium metaaluminate. In other embodiments, the lithium-to-metal ratio, heat treatment temperature, heat treatment time, and solution pH value, the lithium source is not limited to this embodiment.

In summary, the present invention forms two-component coated positive electrode materials of composite zirconia and alumina by co-precipitation of two coating precursors at the same time, and co-precipitation, drying, and sintering. The dissolution of metal ions and the reduction of the electrolytic solution make the cycle performance of the fabricated lithium battery significantly improved.

The above implementations are only used to describe the technical solutions of the embodiments of the present invention and are not restrictive. Although the embodiments of the present invention have been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that the techniques of the embodiments of the present invention can be Modifications or equivalent replacements of the solutions should not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

A method for preparing a positive electrode material is characterized in that it includes the following steps:

Dissolving the positive electrode material precursor in a solvent to obtain a mixed solution;

Adding an alkaline solution dropwise to the mixed solution to obtain an alkaline pretreatment solution;

At the same time, a zirconium source acidic titration solution and an aluminum source alkaline titration solution were added dropwise to the pretreatment solution to co-precipitate to obtain a coated cathode material precursor;

A lithium source and the coated positive electrode material precursor are mixed at a lithium-to-metal ratio and sintered to obtain a composite oxide-coated positive electrode material.
The method for preparing a positive electrode material according to claim 1, wherein the precursor of the positive electrode material has the following chemical formula to indicate its composition: Ni x Co y Mn z (OH) 2 (x + y + z = 1, 0 ≤x≤1, 0≤y≤1, 0≤z≤1).
The method for preparing a positive electrode material according to claim 1, wherein the solvent is one of an aqueous solution or an ethanol solution, and the temperature of the aqueous solution or the ethanol solution is controlled to 25 ° C during the dissolution process. -80 ° C.
The method for preparing a positive electrode material according to claim 3, characterized in that: stirring is performed simultaneously during the dissolution process, and the stirring speed is 200 rpm-450 rpm.
The method of claim 1, wherein the aluminum source includes one of sodium metaaluminate and potassium metaaluminate; the zirconium source includes one of zirconium oxychloride, zirconium sulfate, and zirconium nitrate. .
The method of claim 1, wherein the alkaline solution is one or a combination of a sodium hydroxide solution, a sodium metaaluminate solution, or an ammonia solution.
The method of claim 1, wherein the pH value of the pretreatment solution is 8-11, and the pH value is stabilized to a preset value during the co-precipitation process.
The method for preparing a positive electrode material according to claim 1, wherein a lithium-to-metal ratio of the lithium source to the coated positive electrode material precursor is 1.00 to 1.20, and a heat treatment temperature during sintering is 300 ° C -1000 ℃, heat treatment time is 3h-24h.
A positive electrode material, which is obtained by the method according to any one of claims 1 to 8.
A lithium-ion battery, comprising a positive electrode sheet pressed and formed from the material according to claim 9.