WO2023245880A1

WO2023245880A1 - T2-type lithium cobalt oxide positive electrode material with space group of cmca and preparation method therefor

Info

Publication number: WO2023245880A1
Application number: PCT/CN2022/118030
Authority: WO
Inventors: 左宇轩; 夏定国
Original assignee: 北京大学
Priority date: 2022-06-20
Filing date: 2022-09-09
Publication date: 2023-12-28
Also published as: CN114784269A; CN114784269B

Abstract

A T2-type lithium cobalt oxide positive electrode material with a space group of Cmca and a preparation method therefor. The material has a chemical formula of LixNayCoO2, where 0.6 ≤ x ≤ 1, and 0 ≤ y ≤ 0.1. Lithium ions and adjacent oxygen ions form tetrahedral coordination; and in an X-ray diffraction spectrum thereof, a main peak occurs between 17.9º and 18.1º, and a strong 131 crystal plane diffraction peak occurs within 67.0º-67.5º, which is a characteristic peak of the space group Cmca. The preparation method comprises: first synthesizing a precursor, i.e., P2-phase layered sodium cobalt oxide, by means of a solid-phase ball milling method or a coprecipitation method, and then subjecting same to ion exchange to obtain a T2-type lithium cobalt oxide layered positive electrode material.

Description

A T2 type lithium cobalt oxide cathode material with a space group of Cmca and its preparation method

Technical field

The invention belongs to the field of lithium-ion battery materials and electrochemistry, and specifically relates to a T2-type lithium cobalt oxide layered cathode material with a space group of Cmca prepared by an ion exchange method.

Background technique

Lithium-ion battery is a secondary battery with repeatable charge and discharge characteristics. It has been developed for many years. Its applications involve many fields such as transportation, entertainment, military, medical and communications. Lithium-ion batteries have been developed in recent years. Electric vehicles have high application prospects due to their environmental friendliness. However, the limitation of battery specific energy density makes electric vehicles unable to meet the needs of most users, so they have not been widely used. At present, the main factor limiting the specific energy density of batteries is the cathode material. Several mainstream materials on the market, O3-LiCoO ₂ (140mAh/g), LiFePO ₄ (160mAh/g), and LiMn ₂ O ₄ (150mAh/g), all have low specific capacities. Above 200mAh/g, the voltage decay problem of the lithium-rich manganese-based cathode xLi ₂ MnO ₃ ·(1-x)LiMO ₂ (250mAh/g) that can meet the high capacity requirements has not been solved well, so we are looking for a Creating a lithium battery cathode material with high energy density and stable structure is a major task in the current field of lithium battery research.

T2-Li _x MO ₂ (M=Co, Ni, Mn, Fe) was reported as early as 1999 (Journal of The Electrochemical Society, 146(10)3560-3565(1999)). However, this phase will only appear in Formed during electrochemical cycling. The T2 type layered lithium cobalt oxide lithium ion battery cathode material has a structural feature in which the oxygen atomic layer is periodically arranged with the distance between two transition metal layers as a period, in which lithium is located at the tetrahedral site, which is similar to the traditional commercial O3 type cobalt acid. There is a big difference in lithium at the octahedral sites.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a type of layered lithium-ion battery cathode material with ultra-high stability and rate performance and a preparation method thereof.

In order to achieve the above purpose, the present invention adopts the following technical solution: a lithium-ion battery cathode material, which is a T2-type lithium cobalt oxide layered cathode material synthesized by an ion exchange method. The component is detected by an inductively coupled plasma spectrometer as Li _x Na _y CoO ₂ , where 0.6≤x≤1, 0≤y≤0.1 (preferably, 0.6≤x≤0.8, 0≤y≤0.05), the reason why there are some residual sodium ions is because this material is made of ion exchange Prepared by the method, sodium ions are difficult to be completely exchanged by lithium ions, so there will be a small and trace amount of sodium ions in the material. The X-ray diffraction pattern of this material (copper target, wavelength 1.54 Angstroms) is characterized by the main peak 002 between 17.9 and 18.1 degrees, and a strong 131 diffraction peak at 67.0-67.5 degrees. The space group is Cmca and is cubic. Crystal system, the three turning angles of the unit cell α = β = γ = 90°, and the traditional O3 type lithium cobalt oxide belongs to the hexagonal crystal system. Since neutron diffraction is more sensitive to the occupancy of light elements, the present invention further refines the occupancy distribution of each atom in the unit cell through neutron diffraction, and finds that lithium ions occupy the 8e position, cobalt ions occupy the 4a position, and oxygen ions occupy the 8f position. , the space group belonging is also Cmca. The neutron diffraction results are consistent with the X-ray diffraction results in determining the space group, and the results show that the lithium ions in the material form a tetrahedron with the surrounding adjacent oxygen, which means that the lithium ions occupy a tetrahedral position, which is different from traditional cobalt acid. There is a big difference between the octahedral position of lithium and lithium ions.

The preparation methods of the layered Cmca phase lithium ion battery cathode material of the present invention specifically include the following two methods:

(1) Co-precipitation method + ion exchange method

1a. According to the stoichiometric ratio of cobalt and carbonate, dissolve the cobalt salt in deionized water to prepare a salt solution with a concentration of 0.5~2mol/L, and dissolve Na ₂ CO ₃ and ammonia in deionized water to prepare a pH Alkaline solution of 7 to 9;

1b. Add the above alkali solution and salt solution simultaneously and uniformly into a container containing deionized water. The pH value during the entire process is controlled between 7 and 9, and the temperature is between 50 and 80°C;

1c. After the dropwise addition is completed, let it stand for 8 to 16 hours at 50 to 80°C, then filter, wash, and dry the precipitate to obtain the precursor cobalt carbonate;

1d. Grind the precursor cobalt carbonate and sodium compounds together evenly according to the stoichiometric ratio _of cobalt and sodium shown in the chemical formula _Na , and then calcined at 600~1000℃ for 8~16h to obtain the intermediate product - P2 type precursor Na _x CoO ₂ (0.6≤x≤1);

1e. The mixture of the intermediate product obtained in step 1d and 2.5 to 10 times the molar amount of lithium salt is subjected to ion exchange reaction at 80 to 300°C for 2 to 8 hours. The obtained product is filtered, washed and dried to obtain the final product - T2 type. Lithium cobalt oxide layered cathode material.

In step 1a, the cobalt salt is preferably one or more selected from cobalt sulfate, cobalt nitrate, and cobalt chloride.

In step 1a, the amount of Na ₂ CO ₃ in the alkaline solution is twice the amount of cobalt salt, which is used as a precipitant; ammonia is used as a buffer to control the pH of the solution between 7 and 9.

In step 1b, use a peristaltic pump to add the above-mentioned alkali solution and salt solution simultaneously and uniformly into the container containing deionized water, and control the dropping speed at 0.8 to 1.8 mL/min.

In step 1d, the sodium compound is selected from one or more of sodium hydroxide, sodium carbonate, sodium acetate, and sodium nitrate, and its dosage is 0.6 to 1 times the molar amount of the precursor cobalt carbonate.

In step 1e, the lithium salt is preferably lithium nitrate.

(2) Ball milling method + ion exchange method

2a. According to the stoichiometric ratio of cobalt and sodium shown in _the chemical formula _Na After that, it is first calcined at 400-500℃ for 3-6h, and then at 600-900℃ for 8-16h, to obtain the P2 type precursor Na _x CoO ₂ ;

2b. Perform an ion exchange reaction between _the P2 type precursor _Na The T2 type lithium cobalt oxide layered cathode material.

In step 2a, the cobalt salt is selected from one or more of cobalt oxide, cobalt trioxide, cobalt tetroxide, and cobalt hydroxide.

In step 2a, the ball milling speed is preferably 100 to 500 rpm, and the ball milling time is 1 to 8 hours.

In step 2b, the lithium salt is preferably lithium nitrate.

Compared with the existing technology, the beneficial effects of the present invention are:

In the present invention _, the precursor P2 phase layered sodium cobaltate is first synthesized through a solid-phase ball milling method or a co-precipitation method, and then the _P2 type precursor Na New T2-type lithium cobalt oxide layered cathode material was obtained through low-temperature ion exchange. This material has three structural characteristics: (1) Lithium ions form tetrahedral coordination with adjacent oxygen ions; (2) The main peak 002 of the X-ray diffraction pattern of this material is between 17.9 and 18.1 degrees; (3) The The X-ray diffraction pattern of the material has a strong 131 crystal plane diffraction peak within 67.0-67.5 degrees, which is a characteristic peak of the Cmca space group. The T2 type layered lithium cobalt oxide cathode material synthesized by the present invention has a Coulombic efficiency of 125% for the first time; the cycle performance and rate performance are very excellent, and the reversible capacity is as high as 230mAh/g at a rate of 135mA/g in the 3-4.55V range; the specific capacity is compared with It is a huge improvement over the mainstream commercial cathode material O3-LiCoO ₂ (190mAh/g) in the existing market. The method for synthesizing the T2-type lithium-ion battery cathode material of the present invention is simple and easy to implement, which is convenient for industrial large-scale production, and the synthesized product has uniform particles and high crystallinity.

Description of the drawings

Figure 1. Scanning electron microscope image of the lithium cobalt oxide cathode material precursor P2-Na _0.72 CoO ₂ prepared in Example 2 of the present invention.

Figure 2. Scanning electron microscope image of the lithium cobalt oxide cathode material Li _0.7 Na _0.02 CoO ₂ for the T2-type lithium ion battery prepared in Example 2 of the present invention.

Figure 3. X-ray diffraction pattern of the lithium cobalt oxide cathode material Li _0.7 Na _0.02 CoO ₂ for the T2-type lithium ion battery prepared in Example 2 of the present invention.

Figure 4. Neutron diffraction refined image of Li _0.7 Na _0.02 CoO _2, a T2-type lithium ion battery lithium cobalt oxide cathode material prepared in Example 2 of the present invention (the numbers on the peaks represent the corresponding crystal plane index).

Figure 5. Theoretical structural model diagram of the lithium cobalt oxide cathode material Li _0.7 Na _0.02 CoO ₂ for the T2-type lithium ion battery prepared in Example 2 of the present invention.

Figure 6. Charging and discharging curves of Li _0.7 Na _0.02 CoO _2, a T2-type lithium-ion battery lithium cobalt oxide cathode material prepared in Example 2 of the present invention, at a rate of 135 mA/g.

Figure 7. Cycle performance diagram of the T2-type lithium ion battery lithium cobalt oxide cathode material Li _0.7 Na _0.02 CoO ₂ prepared in Example 2 of the present invention at a rate of 135 mA/g.

Detailed ways

Example 1 Synthesis of T2 configuration binary lithium-rich material Li _0.7 Na _0.02 CoO ₂ by ball milling method + ion exchange method

Take 1.8732g of cobalt oxide and 0.954g of sodium carbonate, add 5mL of ethanol, mix by ball milling at 300rpm for 4h, and then dry. Take out the dried mixed precursor, grind it evenly and place it in a tube furnace for pre-calcination at 450°C for 4 hours, then calcining at 800°C for 8 hours to obtain the sodium-containing precursor product - Na _0.72 CoO ₂ .

The sodium-containing precursor was ion-exchanged with 5 times the molar amount of lithium salt LiNO ₃ at 280°C for 0.5h. The obtained sample was washed twice with deionized water and dried in a blast oven at 100°C to obtain the final sample T2- Li _0.7 Na _0.02 CoO ₂ .

Mix the T2-Li _0.7 Na _0.02 CoO ₂ prepared by the above method with carbon black and PVDF (polyvinylidene fluoride) at a mass ratio of 8:1:1, grind it evenly with N-methylpyrrolidone as the solvent, and then apply it on on aluminum foil and placed in a forced air drying oven at 100°C for 24 hours. After taking it out, roll it on a rolling machine several times and then cut it into electrode discs. Use this as the positive electrode sheet, use the lithium sheet as the negative electrode sheet, the glass microfiber filter paper GF/D produced by Whatman Company as the battery separator, and the electrolyte is the lithium-ion battery high-voltage electrolyte produced by the Beijing Institute of Chemical Reagents, which is installed in the glove box. The button battery was tested on the Xinwei battery testing system at room temperature of 25°C.

Under this condition, when the voltage range of the positive electrode material is between 3.0-4.55V and the current density is 135mA/g, the first discharge capacity is 230mAh/g.

Example 2 T2 configuration binary lithium-rich material Li _0.7 Na _0.02 CoO ₂ synthesized by co-precipitation method + ion exchange method

Dissolve 0.12 mol CoSO ₄ ·6H ₂ O in 60 mL of deionized water and stir evenly to form a salt solution. Then mix 0.12 mol of Na ₂ CO ₃ and 2 mL of ammonia solution with a concentration of 18.4 mol/L and add water to make 60 mL of alkali. solution. Use a peristaltic pump to simultaneously drop the prepared alkali solution and salt solution into the deionized water, keep the pH between 7.5-8.5, and heat in a water bath at a temperature of 60°C while stirring continuously at a stirring speed of 500 rpm.

After the dropwise addition is completed, the obtained suspension is allowed to stand for more than 12 hours, then filtered with a Buchner funnel, and washed with deionized water more than three times. The precipitated material obtained by filtration is dried in a vacuum oven at 80°C for more than 8 hours, and then ground to obtain the precursor carbonate CoCO ₃ .

Mix and grind 1.15g of the precursor carbonate and 0.371g of Na ₂ CO ₃ evenly, place it in a tube furnace and pre-sinter at 500°C for 4 hours, and then calcine at 800°C for 8 hours. After taking it out, the powder sample obtained by grinding is: The scanning electron microscope picture of the sodium-containing precursor Na _0.72 CoO ₂ product, Na _0.72 CoO ₂ , is shown in Figure 1.

The sodium-containing precursor was ion-exchanged with 5 times the molar amount of lithium salt LiNO ₃ at 280°C for 0.5h. The obtained sample was washed twice with deionized water and dried in a blast oven at 100°C to obtain the final sample Li _0.7 Na _0.02 CoO ₂ .

The scanning electron microscope image of the product Li _0.7 Na _0.02 CoO ₂ is shown in Figure 2. It can be seen from the figure that the particle size is about 5 μm. The XRD pattern is shown in Figure 3. It is characterized by the main peak 002 between 17.9 and 18.1 degrees, and a strong 131 diffraction peak at 67.5 degrees. The space group belongs to Cmca, which belongs to the cubic crystal system and the three corners of the unit cell. α=β=γ=90°.

Since neutron diffraction is more sensitive to the occupancy of light elements, we further refined the occupancy distribution of each atom in the unit cell through neutron diffraction, as shown in Figure 4. Table 1 lists the atomic positions and proportions of Li _0.7 Na _0.02 CoO _2. It can be found that lithium ions occupy the 8e position, cobalt ions occupy the 4a position, and oxygen ions occupy the 8f position. The space group assignment is also Cmca, which is consistent with the XRD results. , and lithium forms a tetrahedron with the surrounding oxygen, which means that the lithium ions occupy the tetrahedral position, which is very different from the octahedral position of the traditional lithium cobalt oxide lithium ions. From this, the theoretical structure model diagram of the T2-type material Li _0.7 Na _0.02 CoO ₂ is obtained, as shown in Figure 5.

Table 1

Mix the product Li _0.7 Na _0.02 CoO ₂ with carbon black and PVDF at a mass ratio of 8:1:1, grind it evenly with N-methylpyrrolidone as the solvent, then apply it on aluminum foil and place it in a blast drying box for 100 Bake at ℃ for 1 hour, take it out, roll it several times on a rolling machine and cut it into electrode discs. The electrode disc is used as the positive electrode sheet, the lithium sheet is used as the negative electrode sheet, the glass microfiber filter paper GF/D produced by Whatman Company is used as the battery separator, and the lithium ion battery high-voltage electrolyte produced by the Beijing Institute of Chemical Reagents is used as the battery electrolyte. Install the button battery in the glove box and test it on the Xinwei battery testing system at room temperature of 25°C.

The cathode material synthesized under this condition has a first discharge capacity of 220mAh/g when the voltage range is between 3.0-4.55V (Figure 6) and the current density is 135mA/g (Figure 7).

Claims

A lithium-ion battery cathode material, characterized in that the material is a T2-type lithium cobalt oxide layered cathode material synthesized by an ion exchange method, and the composition is Li x Na y CoO 2 , where 0.6≤x≤1, 0≤ y≤0.1, the space group belongs to Cmca, and it belongs to the cubic crystal system; this material has three structural characteristics: 1) Lithium ions form a tetrahedron with adjacent oxygen; 2) The main peak of the X-ray diffraction pattern of this material is between 17.9 and 17.9 18.1 degrees; 3) The X-ray diffraction pattern of this material has a strong 131 crystal plane diffraction peak within 67.0-67.5 degrees, which is a characteristic peak of the Cmca space group.
The lithium ion battery cathode material according to claim 1, characterized in that, 0.6≤x≤0.8, 0≤y≤0.05.
The lithium ion battery cathode material according to claim 1, characterized in that the lithium ion battery cathode material is synthesized by an ion exchange method by combining the P2 type precursor Na x CoO 2 and 2.5 to 10 times the molar amount of lithium nitrate. T2 type lithium cobalt oxide layered cathode material.
A method for preparing the lithium-ion battery cathode material according to any one of claims 1 to 3, characterized in that it includes the following steps:

1a) According to the stoichiometric ratio of cobalt and carbonate, dissolve the cobalt salt in deionized water to prepare a salt solution with a concentration of 0.5~2mol/L; dissolve Na 2 CO 3 and ammonia in deionized water to prepare Alkaline solution with pH 7-9;

1b) Add the alkali solution and salt solution prepared in step 1a) dropwise into the container containing deionized water at a uniform speed at the same time. The pH value during the entire process is controlled between 7 and 9, and the temperature is between 50 and 80°C. ;

1c) After the dropwise addition, let it stand for 8 to 16 hours at 50 to 80°C, then filter, wash, and dry the precipitate to obtain the precursor cobalt carbonate;

1d) Grind the precursor cobalt carbonate and sodium compounds together evenly according to the stoichiometric ratio of cobalt and sodium shown in the chemical formula Na 8~16h, P2 type precursor Na x CoO 2 is obtained, where 0.6≤x≤1;

1e) Ion exchange reaction between the P2 type precursor Na shaped cathode material.
The method of claim 3, wherein in step 1a), the cobalt salt is selected from one or more of cobalt sulfate, cobalt nitrate, and cobalt chloride.
The method of claim 3, characterized in that in step 1b), the alkali solution and the salt solution are added simultaneously and uniformly into a container containing deionized water using a peristaltic pump, and the dripping speed is controlled at 0.8 to 1.8 mL/min.
The method of claim 3, wherein in step 1d), the sodium compound is selected from one or more of sodium hydroxide, sodium carbonate, sodium acetate, and sodium nitrate.
A method for preparing the lithium-ion battery cathode material according to any one of claims 1 to 3, characterized in that it includes the following steps:

2a) Mix cobalt salt and sodium carbonate according to the stoichiometric ratio of cobalt and sodium shown in the chemical formula Na , and then calcined at 600 to 900°C for 8 to 16 hours to obtain the P2 type precursor Na x CoO 2 , where 0.6≤x≤1;

2b) Perform an ion exchange reaction between the P2 type precursor Na Layered cathode materials.
The method of claim 8, wherein in step 2a), the cobalt salt is selected from one or more of cobalt oxide, cobalt trioxide, cobalt tetraoxide, and cobalt hydroxide; the ball milling speed is 100～500rpm, ball milling time is 1～8h.