WO2020215601A1

WO2020215601A1 - Metal-organic framework material-coated ternary positive electrode material and preparation method therefor

Info

Publication number: WO2020215601A1
Application number: PCT/CN2019/106539
Authority: WO
Inventors: 吴浩斌; 赵博; 刘倩倩; 许亦非
Original assignee: 浙江大学
Priority date: 2019-04-26
Filing date: 2019-09-18
Publication date: 2020-10-29
Also published as: CN110165204A; CN110165204B

Abstract

A metal-organic framework material-coated ternary positive electrode material and preparation method therefor. The preparation method comprises the following steps: (1) uniformly dispersing a ternary positive electrode material in a mixed solution of absolute ethanol and N,N-dimethyl sulfoxide; (2) sequentially adding, with stirring, zirconium salt and an organic ligand to the dispersion, and fully stirring the dispersion; (3) transferring the uniform dispersion obtained in (2) to a reaction kettle for a solvothermal reaction; (4) taking out the reaction kettle, collecting the product at the bottom, centrifugally washing the product, and drying the centrifugated product to obtain a metal-organic framework material-coated ternary positive electrode material. The method can uniformly coat a layer of metal-organic framework material on the surface of the ternary positive electrode material, and the coating thickness is controllable. The ternary positive electrode material surface-modified by the metal-organic framework material can effectively reduce corrosion decomposition of the ternary positive electrode material in an electrolyte, thereby improving battery cycling stability.

Description

Metal-organic frame material coated ternary cathode material and preparation method thereof

Technical field

The invention belongs to the technical field of new energy materials, and specifically relates to a metal-organic frame material coated ternary cathode material and a preparation method thereof

Background technique

Lithium-ion batteries have a series of excellent properties such as high working voltage, large specific energy, long cycle life, green pollution-free and no memory effect, which also makes lithium-ion batteries widely used as power sources for various electronic products. As one of the core components of the battery, the electrode material has a significant impact on the overall performance of the battery. At this stage, the positive electrode material series that show great advantages are nickel-cobalt-manganese ternary positive electrode materials, which have great advantages in terms of high energy, long cycle life and high safety. However, like most battery cathode materials, during battery cycling, irreversible side reactions occur at the interface between the electrode material and the electrolyte, leading to corrosion of the electrode material, reducing battery charge and discharge efficiency, and affecting battery capacity and cycle life.

At present, in response to the above problems, researchers have proposed improved methods for surface modification of cathode materials to reduce side reactions at the interface between electrode materials and electrolyte. Surface modification includes surface doping modification and coating modification. Studies have shown that the effect of surface doping is limited due to technical limitations. As a more commonly used surface modification method, coating is technically mature, and it is also the most commonly used surface modification method in industrialization. The coating materials of ternary cathode materials for lithium-ion batteries include B ₂ O ₃ , Al ₂ O ₃ , AlPO ₄ , LiAlO ₂ , AlF ₃ , TiO ₂ , V ₂ O ₅ , and carbon. There are pros and cons. The coating methods used include precipitation, ball milling, and vapor deposition. The ball milling method is more widely used due to its low technical requirements, but the coating layer thickness distribution after this method is not uniform, which affects the performance of the electrode material; the meteorological deposition method is usually used for the coating of carbon materials, and for metal salts or metals Oxides are used less frequently.

Summary of the invention

The purpose of the present invention is to solve the problem that the surface of the battery cathode material in the prior art is prone to irreversible side reactions with the electrolyte, thereby causing corrosion, and to provide a novel metal-organic framework material-coated ternary cathode material preparation method, The material adopts the solvent thermal precipitation method, the thickness of the coating layer is uniform, the process is simple, the cost is low, and it is convenient for industrial production. The most important thing is that the cycle stability of the battery is excellent after coating modification.

To achieve the above-mentioned purpose of the invention, the present invention specifically adopts the following technical solutions:

A method for preparing a metal-organic frame material coated ternary cathode material includes the following steps:

(1) Disperse the ternary positive electrode material into a mixed solution of absolute ethanol and N,N-dimethylformamide, and obtain the first dispersion after uniform dispersion;

(2) Under stirring conditions, add the zirconium salt and organic ligands to the first dispersion liquid, and obtain the second dispersion liquid after uniform dispersion; the organic ligands are benzoic acid and terephthalic acid;

(3) Transfer the second dispersion liquid in (2) to the reaction kettle, perform a solvothermal reaction, and form an organic frame coating layer of metal zirconium on the surface of the ternary cathode material;

(4) Collect the bottom product of the reaction kettle, centrifuge and wash it in anhydrous ethanol solution to obtain the centrifuged product, and dry it to obtain the ternary positive electrode material coated with the metal-organic frame material.

In the above scheme, the specific parameters of each step are preferably as follows:

Preferably, in the mixed solution described in step (1), the volume ratio of absolute ethanol and N,N-dimethylformamide is 1:10-1:100.

Preferably, the chemical formula of the ternary cathode material described in step (1) is LiNi _x Co _y Mn _1-xy O, wherein 1>x>0, 1>y>0, and 1>x+y.

Further, the ternary cathode material includes LiNi _0.8 Co _0.1 Mn _0.1 O, LiNi _0.6 Co _0.2 Mn _0.2 O, LiNi _0.5 Co _0.2 Mn _0.3 O, LiNi _1/3 Co _1/3 Mn _1/3 O.

Preferably, in steps (1) and (2), the uniform dispersion mode is stirring for 1-5 h.

Preferably, the zirconium salt is one or more of zirconium acetate, hydrochloride, and organic salt.

Preferably, in step (2), the feeding amount of the zirconium salt and the organic ligand satisfies: the molar ratio of zirconium atom, benzoic acid, and terephthalic acid is 1:5:1-1:15:5. .

Preferably, the reaction kettle is preferably a reaction kettle with a polytetrafluoroethylene liner.

Preferably, in step (3), the solvothermal co-precipitation method is used for coating, and the reaction conditions are 80-180°C for 4-24 hours. After completion, the reaction kettle is placed in an oven to naturally cool down to 40°C.

Preferably, the drying method described in step (4) is: placing the product after centrifugation in a vacuum drying oven, and vacuum drying at 50-90° C. for 6-12 hours.

Another object of the present invention is to provide a metal-organic framework material coated ternary cathode material prepared by the method described in any of the above solutions.

The beneficial effects of the present invention include:

1. In the present invention, the ternary cathode material is dispersed in a mixed solution of absolute ethanol and N,N-dimethylformamide, and zirconium salt is added and stirred uniformly, so that zirconium ions can be adsorbed on the surface of the ternary cathode material particles. Furthermore, during the solvothermal reaction with the organic ligands, it grows epitaxially along the surface of the ternary cathode material to form an organic frame coating layer of metal zirconium. The zirconium atom is the center of the site, and the organic ligands are connected to each other and uniformly coated The surface of the ternary cathode material, and the coating thickness is controllable, effectively preventing the non-aqueous liquid organic electrolyte from contacting the cathode material, reducing the irreversible side reaction between the electrolyte and the electrode material, increasing the electrode material capacity, and showing excellent performance的cyclic stability.

2. In this metal-organic framework structure, the site center of metal zirconium can adsorb the anion of the lithium salt in the electrolyte, promote the dissociation of lithium ions and anions in the lithium salt, and produce more lithium ions, while the organic Many micropores are distributed inside the frame structure, which can conduct lithium ions quickly and conveniently, which is beneficial to improve the mobility of lithium ions, thereby improving the electrochemical performance of the ternary cathode material.

Description of the drawings

The present invention will be further described below in conjunction with the drawings and Embodiment 1.

FIG. 1 is an SEM picture of the ternary cathode material LiNi _0.6 Co _0.2 Mn _0.2 O material of Example 1.

2 is a SEM image of a ternary cathode material LiNi _0.6 Co _0.2 Mn _0.2 O coated with an organic frame material of metal zirconium in Example 1.

FIG. 3 is an SEM picture of the reaction of zirconium n-butoxide and benzoic acid as a precursor to coat the ternary cathode material LiNi _0.6 Co _0.2 Mn _0.2 O in Example 1.

Fig. 4 is an SEM picture of the reaction of zirconium n-butoxide and terephthalic acid as a precursor to coat the ternary cathode material LiNi _0.6 Co _0.2 Mn _0.2 O in Example 1.

5 is an XRD data diagram of the organic frame material of metal zirconium coated with a ternary cathode material LiNi _0.6 Co _0.2 Mn _0.2 O in Example 1.

6 is a comparison diagram of the cycle performance data of a lithium-ion button half-cell using a metal zirconium organic frame material coated ternary positive electrode material and original LiNi _0.6 Co _0.2 Mn _0.2 O as the positive electrode material in Example 1.

Detailed ways

The present invention will be further elaborated and illustrated below in conjunction with the drawings and specific embodiments.

Example 1

In this embodiment, the method for preparing the metal-organic frame material coated ternary cathode material includes the following steps:

(1) Put 500mg of ternary cathode material LiNi _0.6 Co _0.2 Mn _0.2 O into 50ml of absolute ethanol and N,N-dimethylformamide mixed solution, the volume of absolute ethanol and N,N-dimethylformamide The ratio is 1:49, stirring for 1 hour to obtain the first dispersion;

(2) Under stirring conditions, add 35μl of zirconium n-propoxide (70wt.% n-propanol solution), 42mg of benzoic acid, and 12mg of terephthalic acid to the first dispersion, and stir for 2h to obtain a uniformly stirred second dispersion liquid. The molar ratio of zirconium atom, benzoic acid and terephthalic acid is 1:12:2.5;

(3) Transfer the uniform dispersion in (2) to a reaction kettle with a polytetrafluoroethylene liner for solvothermal reaction. The reaction conditions are kept at 120°C for 8 hours, and after completion, the temperature is naturally cooled to 40°C in an oven;

(4) Take out the reaction kettle, pour off the supernatant, collect the bottom product, centrifuge and wash in anhydrous ethanol solution, the centrifuge speed is 2000r/min, the time is 5min, and the product after centrifugation is obtained;

(5) Dry the product after centrifugation in a vacuum drying oven at 70° C. for 6 hours to obtain a ternary cathode material coated with a metal-organic frame material.

At the same time, this embodiment sets two sets of controls (Figure 3, Figure 4), the difference is that the organic ligand only adds benzoic acid and only terephthalic acid, and the rest are the same as the embodiment.

In this embodiment, the scanning electron microscope picture of the original ternary cathode material LiNi _0.6 Co _0.2 Mn _0.2 O is shown in FIG. 1. The SEM picture of the surface wrapped with zirconium metal-organic frame material is shown in Figure 2. It can be seen from the scanning electron microscope picture in Figure 2 that the surface of LiNi _0.6 Co _0.2 Mn _0.2 O is evenly coated with a layer of zirconium metal-organic frame material. Due to the small thickness of the surface coating layer and low crystallinity, the XRD data ( Figure 5) only shows obvious peaks of LiNi _0.6 Co _0.2 Mn _0.2 O, and no diffraction peaks of surface zirconium metal-organic framework materials are observed. On the surface of the ternary positive electrode material of the two control groups, there was no corresponding metal zirconium organic framework material, indicating that the benzoic acid and terephthalic acid in the organic ligands must be added at the same time.

The ternary positive electrode material coated with the metal-organic frame material obtained in this embodiment was subjected to the cycle performance test of the button half-cell. The result (Figure 6) shows that the LiNi _0.6 Co _0.2 Mn _0.2 O cathode material coated with metal zirconium-organic framework material (UIO-66) has a specific discharge capacity of 160mAh g ^-1 at a current density of 100mA g ^-1 . The charge-discharge efficiency of the coil is 83%, and the capacity retention rate after 100 cycles is 72%; the original LiNi _0.6 Co _0.2 Mn _0.2 O cathode material has a discharge point specific capacity of 157 mA g ^-1 when the current density is 100 mA g ^-1 . The loop charge and discharge efficiency was 79%, and the capacity retention rate was 54% after 100 cycles. .

Example 2

(1) Disperse 500 mg of ternary cathode material LiNi _0.6 Co _0.2 Mn _0.2 O into 50 ml of a mixed solution of absolute ethanol and N,N-dimethylformamide. The volume ratio is 1:49, stirring for 1 hour to obtain a uniform dispersion;

(2) Under stirring conditions, 35 μl of zirconium n-propoxide (70 wt.% n-propanol solution), 17.5 mg of benzoic acid, and 4.8 mg of terephthalic acid were added to the dispersion, and stirred for 2 hours to obtain a uniform dispersion. The molar ratio of zirconium atom, benzoic acid, and terephthalic acid is 1:5:1.

Similar to Example 1, the surface of the ternary cathode material of this example is also evenly coated with a layer of zirconium metal-organic frame material, which can reduce the irreversible side reaction between the electrolyte and the electrode material, increase the electrode material capacity, and make it Has better cycle stability.

Example 3

(2) Under stirring conditions, 35 µl of zirconium n-propoxide (70 wt.% n-propanol solution), 52.5 mg of benzoic acid, and 24 mg of terephthalic acid were added to the dispersion, and stirred for 2 hours to obtain a uniform dispersion. The molar ratio of zirconium atom, benzoic acid, and terephthalic acid is 1:15:5.

Example 3

(1) Disperse 500 mg of ternary cathode material LiNi _0.8 Co _0.1 Mn _0.1 O into 50 ml of a mixed solution of absolute ethanol and N,N-dimethylformamide. The volume ratio is 1:49, stirring for 1 hour to obtain a uniform dispersion;

(2) Under stirring conditions, 35 μl of zirconium n-propoxide (70 wt.% n-propanol solution), 42 mg of benzoic acid, and 12 mg of terephthalic acid were added to the dispersion, and stirred for 2 hours to obtain a uniform dispersion. The molar ratio of zirconium atom, benzoic acid, and terephthalic acid is 1:12:2.5.

Example 4

(1) Disperse 500 mg of ternary cathode material LiNi _0.5 Co _0.2 Mn _0.3 O into 50 ml of a mixed solution of absolute ethanol and N,N-dimethylformamide. The volume ratio is 1:49, stirring for 1 hour to obtain a uniform dispersion;

Example 5

(1) Disperse 500 mg of ternary cathode material LiNi _1/3 Co _1/3 Mn _1/3 O into 50 ml of anhydrous ethanol and N,N-dimethylformamide mixed solution, anhydrous ethanol and N,N- The volume ratio of dimethylformamide is 1:49, stir for 1 hour to obtain a uniform dispersion;

(4) Take out the reaction kettle, pour out the supernatant, collect the bottom product, centrifuge and wash it in absolute ethanol solution, the centrifuge speed is 2000r/min, the time is 5min, and the product after centrifugation is obtained;

The above-mentioned embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. Those of ordinary skill in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. For example, in addition to zirconium n-propoxide, zirconium salts can also be zirconium acetates, hydrochlorides, organic salts, and the like. The specific methods of dispersion, drying, centrifugation, etc. in the preparation process can also be adjusted as needed, and are not limited. Therefore, all technical solutions obtained by equivalent substitutions or equivalent transformations fall within the protection scope of the present invention.

Claims

A method for preparing a metal-organic frame material coated ternary cathode material, which is characterized in that it comprises the following steps:

(1) Disperse the ternary positive electrode material into a mixed solution of absolute ethanol and N,N-dimethylformamide, and obtain the first dispersion after uniform dispersion;

(2) Under stirring conditions, add the zirconium salt and organic ligands to the first dispersion liquid, and obtain the second dispersion liquid after uniform dispersion; the organic ligands are benzoic acid and terephthalic acid;

(3) Transfer the second dispersion liquid in (2) to the reaction kettle, perform a solvothermal reaction, and form an organic frame coating layer of metal zirconium on the surface of the ternary cathode material;

(4) Collect the bottom product of the reaction kettle, centrifuge and wash it in anhydrous ethanol solution to obtain the centrifuged product, and dry it to obtain the ternary positive electrode material coated with the metal-organic frame material.
The method for preparing a metal-organic frame material coated ternary positive electrode material according to claim 1, characterized in that: in the mixed solution described in step (1), anhydrous ethanol and N,N-dimethyl The volume ratio of base formamide is 1:10-1:100.
A method for preparing a metal-organic frame material coated ternary cathode material according to claim 1, wherein the chemical formula of the ternary cathode material in step (1) is LiNi x Co y Mn 1- xy O, where 1>x>0, 1>y>0, and 1>x+y.
A method for preparing a metal-organic frame material coated ternary cathode material according to claim 3, wherein the ternary cathode material comprises LiNi 0.8 Co 0.1 Mn 0.1 O, LiNi 0.6 Co 0.2 Mn 0.2 O, LiNi 0.5 Co 0.2 Mn 0.3 O, LiNi 1/3 Co 1/3 Mn 1/3 O.
The method for preparing a metal-organic frame material-coated ternary positive electrode material according to claim 1, characterized in that: in steps (1) and (2), the uniform dispersion method is stirring for 1-5 hours.
The method for preparing a metal-organic frame material coated ternary positive electrode material according to claim 1, wherein the zirconium salt is one of zirconium acetate, hydrochloride, and organic salt. Many kinds.
The method for preparing a metal-organic framework material-coated ternary positive electrode material according to claim 1, characterized in that the amount of zirconium salt and organic ligand in step (2) meets: zirconium atom, benzoic acid, The molar ratio of terephthalic acid is 1:5:1-1:15:5.
The method for preparing a metal-organic frame material coated ternary positive electrode material according to claim 1, wherein in step (3), a solvothermal co-precipitation method is used for coating, and the reaction conditions are 80-180 Keep the temperature at ℃ for 4-24h. After the end, put the reactor in an oven and naturally cool down to 40℃.
The method for preparing a metal-organic frame material coated ternary cathode material according to claim 1, wherein the drying method in step (4) is: placing the product after centrifugation in a vacuum drying oven , Vacuum drying at 50-90℃ for 6-12h.
A metal-organic frame material coated with a ternary cathode material prepared by the method of any one of claims 1-9.