CN108281604B - A method for solvothermal synthesis of positive electrode materials for lithium ion batteries - Google Patents

Abstract

The invention discloses a method for solvothermal synthesis of positive electrode materials of lithium ion batteries, which belongs to the technical field of positive electrode materials of new energy lithium batteries. The method of the invention is as follows: dissolving acetate and urea in an organic solvent, then transferring the above uniformly mixed solution to an autoclave, under high temperature and high pressure, the urea decomposes _CO bubbles and reacts with metal ions Crystals are formed, and precipitation occurs along with the growth of the crystals; the obtained product is then filtered, dried, ground with lithium doped, and then calcined to obtain the final positive electrode material of the lithium ion battery. The positive electrode material of the lithium ion battery prepared by the method of the invention can improve the charge-discharge capacity and cycle stability of the battery.

Description

A method for solvothermal synthesis of positive electrode materials for lithium ion batteries

technical field

The invention relates to a method for preparing a positive electrode material of a lithium ion battery by a solution heat method, and belongs to the technical field of positive electrode materials of a new energy lithium battery.

Background technique

Lithium transition metal oxides (LiMO ₂ , M = Mn, Co, Ni, etc.) are considered to have great potential as high energy and Cathode materials for high-capacity batteries, but poor rate performance and cycle stability limit their large-scale production and application.

Existing methods for preparing cathode materials for lithium-ion batteries mainly include high-temperature solid-phase synthesis method, sol-gel method, co-precipitation method, solvent (hydro) thermal method and molten salt method. Among them, the high-temperature solid-phase synthesis method has a simple operation process, but the product has a limited degree of uniform mixing and requires long-term high-temperature treatment. In order to complete the reaction, the material must be processed, the reaction energy consumption is large, the lithium loss is serious, and it is easy to form a heterophase; sol; - The gel method can achieve molecular-level mixing, and the required calcination temperature is low, but a variety of agents need to be added in the reaction process, and the process is more complicated; the co-precipitation method is easy to control the distribution of cations to synthesize uniform and stable products, and the operation process is more complicated , is a commonly used synthesis method at present; the solvent (hydro) thermal method has a simple operation process, is not easy to introduce impurities, and can achieve molecular-level mixing; the molten salt method uses less chemicals and avoids the energy-consuming ball milling process, but requires The operation is kept at high temperature for a long time, and the amount of molten salt cannot be accurately controlled, resulting in tedious steps such as separation of the generated product and molten salt.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for solvothermal synthesis of positive electrode materials for lithium ion batteries, through solvothermal method, urea is decomposed to generate tiny CO ₂ bubbles, and after acetate is adsorbed on the surface, it reacts with metal cations and starts to crystallize, accompanied by crystal growth. The large start of assembly to form microspheres includes the following steps:

( ₁ ) Add CH3COOLi _· 2H2O, Ni(CH3COO) _{2 ·} 4H2O, Co(CH3COO) _{2 ·} 4H2O, Mn _{( CH3COO )2 · 4H2O} and urea into diethylene glycol, stir and mix well to obtain a mixed solution, in which the concentration of CH ₃ COOLi·2H ₂ O is 1.0~1.1 mol/L, and the concentration of Ni(CH ₃ COO) ₂ ·4H ₂ O is 0.5~ 0.8mol/L, the concentration of Co(CH ₃ COO) ₂ ·4H ₂ O is 0.1~0.2mol/L, the concentration of Mn(CH ₃ COO) ₂ ·4H ₂ O is 0.1~0.3mol/L, the concentration of urea is 2~5mol/L;

(2) Transfer the mixed solution prepared in step (1) into a magnetic stirring autoclave, and react at a temperature of 160-200° C. for 8-12 hours.

(3) The turbid liquid after the completion of the reaction in step (2) is subjected to suction filtration, the filter cake is vacuum-dried, ground and passed through a 300-mesh sieve, calcined and naturally cooled to obtain a positive electrode material for lithium ion batteries, namely LiNi _x Co _y Mn _z O ₂ , where 0 ≤ x ≤ 1, 0 ≤ y≤ 1, 0 ≤ z ≤ 1, and x + y + z = 1.

The conditions for calcination in step (3) of the present invention are that the temperature is kept at 500-600° C. for 5-8 hours, and then the temperature is raised to 800-850° C. for 10-12 hours.

Beneficial effects of the present invention:

(1) The method of the present invention has a simple operation process, and various parameters are easy to control.

(2) The method of the present invention does not require an additional lithium doping process in the process of synthesizing the positive electrode material, thereby avoiding the introduction of impurity atoms.

(3) The positive electrode material prepared by the method of the present invention has a microsphere morphology composed of layered microstructures, and the size is highly uniform. Due to the use of diethylene glycol as a solvent, the lithium ion and transition The simultaneous precipitation of metal cation elements ensures that all cations are uniformly mixed at the molecular level, which is beneficial to the diffusion and propagation of lithium ions and electrons and improves the rate performance.

(4) The positive electrode material prepared by the method of the present invention has a microsphere morphology composed of layered microstructures, which significantly shortens the propagation distance of lithium ions and electrons and improves the rate performance; it is beneficial to reduce lithium ions and electrons. The structural changes caused by ion intercalation and deintercalation ensure the structural stability; the contact area between the electrode and the electrolyte is reduced, and the cycle stability is improved; the spherical morphology can improve the tap density and volumetric energy density of the cathode material.

Description of drawings

Fig. 1 is the SEM image of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ synthesized in Example 1 of the present invention;

Fig. 2 is the XRD pattern of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ synthesized in Example 1 of the present invention;

FIG. 3 is a first discharge specific capacity diagram of Examples 1 to 5 of the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific examples. It should be noted that the following examples are only used to illustrate the specific implementation method of the present invention, and cannot limit the protection scope of the present invention.

Example 1

(1) Configuration of the solvothermal reaction solution: at room temperature, CH ₃ COOLi·2H ₂ O, Ni(CH ₃ COO) ₂ ·4H ₂ O, Co(CH ₃ COO) ₂ ·4H ₂ O, Mn(CH 3 COO) 2 . ₃ COO) ₂ ·4H ₂ O and urea were put into 65ml of diethylene glycol, stirred for 1h to form a mixed solution; the concentration of CH ₃ COOLi·2H ₂ O in the mixed solution was 1.05mol/L, Ni(CH ₃ COO ) The concentration of ₂ ·4H ₂ O is 0.5mol/L, the concentration of Co(CH ₃ COO) ₂ ·4H ₂ O is 0.2mol/L, and the concentration of Mn(CH ₃ COO) ₂ ·4H ₂ O is 0.3mol/L L, the concentration of urea is 3.0mol/L.

(2) Transfer the mixed solution obtained in step (1) into a 100ml magnetic stirring autoclave, and react at a temperature of 160°C for 10h.

(3) The turbid liquid after the completion of the reaction in step (2) is subjected to suction filtration, and the filter cake is vacuum-dried, ground and passed through a 300-mesh sieve. The ground powder is kept at 550 ° C for 6 hours, and then heated to 850 ° C for calcination for 12 hours. , the final lithium-ion battery positive electrode material is obtained after natural cooling.

The XRD image of the positive electrode material obtained in this example is shown in Figure 1. It can be seen from the figure that the obtained positive electrode material is indeed a LiNi _0.5 Co _0.2 Mn _0.3 O ₂ positive electrode material, with no impurity phase and high phase purity; the SEM image of the obtained positive electrode material As shown in Figure 2, it can be seen that the particles are composed of many tiny layered structures, and the particle size distribution is uniform. The first discharge specific capacity of the positive electrode material obtained in this example is 172.98 mAhg ^-1 .

Example 2

(1) Configuration of the solvothermal reaction solution: at room temperature, CH ₃ COOLi·2H ₂ O, Ni(CH ₃ COO) ₂ ·4H ₂ O, Co(CH ₃ COO) ₂ ·4H ₂ O, Mn (CH 3 COO) 2 . ₃ COO) ₂ ·4H ₂ O and urea were put into 65ml of diethylene glycol, stirred for 1h, and made into a mixed solution; in the mixed solution, the concentration of CH ₃ COOLi·2H ₂ O was 1.05mol/L, Ni (CH ₃ COO ) The concentration of ₂ ·4H ₂ O is 0.5mol/L, the concentration of Co(CH ₃ COO) ₂ ·4H ₂ O is 0.2mol/L, and the concentration of Mn(CH ₃ COO) ₂ ·4H ₂ O is 0.3mol/L L, the concentration of urea is 3.0mol/L.

(2) Transfer the mixed solution obtained in step (1) into a 100ml magnetic stirring autoclave, and react at a temperature of 180°C for 10h.

(3) The turbid liquid after the completion of the reaction in step (2) is subjected to suction filtration, and the filter cake is vacuum-dried, ground and passed through a 300-mesh sieve. The ground powder is kept at 550 ° C for 6 hours, and then heated to 850 ° C for calcination for 12 hours. , the final lithium-ion battery positive electrode material is obtained after natural cooling.

The positive electrode material obtained in this example is indeed a LiNi _0.5 Co _0.2 Mn _0.3 O ₂ positive electrode material, with high phase purity, relatively uniform particle size distribution, and little agglomeration. It can be seen from Figure 3 that the first discharge specific capacity of the positive electrode material is 170.09mAhg ^-1 .

Example 3

(1) Configuration of solvothermal reaction solution: at room temperature, CH ₃ COOLi·2H ₂ O, Ni(CH ₃ COO) ₂ ·4H ₂ O, Co(CH ₃ COO) ₂ ·4H ₂ O, Ni(CH ₃ COO) ₂ · 4H ₂ O and urea were put into 65ml of diethylene glycol, stirred for 1h to form a mixed solution. In the mixed solution, the concentration of CH ₃ COOLi·2H ₂ O was 1.0 mol/L, the concentration of Ni(CH ₃ COO) ₂ ·4H ₂ O was 0.8 mol/L, and the concentration of Co(CH ₃ COO) ₂ ·4H ₂ O was The concentration is 0.1 mol/L, the concentration of Mn(CH ₃ COO) ₂ ·4H ₂ O is 0.1 mol/L, and the concentration of urea is 5 mol/L.

(2) Transfer the mixed solution obtained in step (1) into a 100 ml magnetic stirring autoclave, and react at a temperature of 160° C. for 8 hours.

(3) The turbid liquid after the completion of the reaction in step (2) is subjected to suction filtration, and the filter cake is vacuum-dried, ground and passed through a 300-mesh sieve. The ground powder is kept at 550 ° C for 6 hours, and then heated to 850 ° C for calcination for 12 hours. , the final lithium-ion battery positive electrode material is obtained after natural cooling.

The positive electrode material obtained in this example has high phase purity and little impurity phase content. The material is composed of many tiny layered structures, with consistent particle size and uniform size distribution. It can be seen from Figure 3 that the first discharge specific capacity of the positive electrode material is 164.16mAhg ^-1 .

Example 4

(1) Configuration of solvothermal reaction solution: at room temperature, CH ₃ COOLi·2H ₂ O, Ni(CH ₃ COO) ₂ ·4H ₂ O, Co(CH ₃ COO) ₂ ·4H ₂ O, Ni(CH ₃ COO) ₂ · 4H ₂ O and urea were put into 65ml of diethylene glycol, stirred for 1h to form a mixed solution. In the mixed solution, the concentration of CH ₃ COOLi·2H ₂ O was 1.1 mol/L, the concentration of Ni(CH ₃ COO) ₂ ·4H ₂ O was 0.6 mol/L, and the concentration of Co(CH ₃ COO) ₂ ·4H ₂ O was The concentration is 0.2 mol/L, the concentration of Mn(CH ₃ COO) ₂ ·4H ₂ O is 0.2 mol/L, and the concentration of urea is 3 mol/L.

(2) Transfer the mixed solution obtained in step (1) into a 100ml magnetic stirring autoclave, and react at a temperature of 200°C for 10h.

(3) Perform suction filtration on the turbid liquid after the reaction in step (2), the filter cake is vacuum-dried, ground and passed through a 300-mesh sieve, and the ground powder is kept at 500 °C for 8 hours and then heated to 800 °C and calcined for 10 hours , the final lithium-ion battery positive electrode material is obtained after natural cooling.

The positive electrode material obtained in this example has relatively high phase purity, the material particles rarely agglomerate, the particle size difference is small, and the particle size distribution is relatively uniform ^{. 1} .

Example 5

(1) Configuration of solvothermal reaction solution: at room temperature, CH ₃ COOLi·2H ₂ O, Ni(CH ₃ COO) ₂ ·4H ₂ O, Co(CH ₃ COO) ₂ ·4H ₂ O, Ni(CH ₃ COO) ₂ · 4H ₂ O and urea were put into 65ml of diethylene glycol, stirred for 1 h, to form a mixed solution; the concentration of CH ₃ COOLi·2H ₂ O in the mixed solution was 1.1mol/L, Ni (CH ₃ COO ) The concentration of ₂ ·4H ₂ O is 0.8mol/L, the concentration of Co(CH ₃ COO) ₂ ·4H ₂ O is 0.1mol/L, and the concentration of Ni(CH ₃ COO) ₂ ·4H ₂ O is 0.1mol/L L, the concentration of urea is 4mol/L.

(2) Transfer the mixed solution obtained in step (1) into a 100 ml magnetic stirring autoclave, and react at a temperature of 180° C. for 12 hours.

(3) The turbid liquid after the completion of the reaction in step (2) is subjected to suction filtration, and the filter cake is vacuum-dried, ground, and passed through a 300-mesh sieve. The ground powder is kept at 600 °C for 6 hours, and then heated to 850 °C for calcination for 10 hours. , the final lithium-ion battery positive electrode material is obtained after natural cooling.

The positive electrode material obtained in this example has high phase purity, no obvious agglomeration of material particles, relatively consistent particle size, and uniform particle size distribution. It can be seen from Figure 3 that the first discharge specific capacity of the positive electrode material is 168.37mAhg ^-1 .

Claims (2)

1. a lithium ion battery positive electrode material solvothermal synthesis method, is characterized in that, specifically comprises the following steps: ( ₁ ) Add CH3COOLi _· 2H2O, Ni(CH3COO) _{2 ·} 4H2O, Co(CH3COO) _{2 ·} 4H2O, Mn _{( CH3COO )2 · 4H2O} and urea into diethylene glycol, stir and mix well to obtain a mixed solution, in which the concentration of CH ₃ COOLi·2H ₂ O is 1.0~1.1 mol/L, and the concentration of Ni(CH ₃ COO) ₂ ·4H ₂ O is 0.5~ 0.8mol/L, the concentration of Co(CH ₃ COO) ₂ ·4H ₂ O is 0.1~0.2mol/L, the concentration of Mn(CH ₃ COO) ₂ ·4H ₂ O is 0.1~0.3mol/L, the concentration of urea is 2~5mol/L; (2) Transfer the mixed solution prepared in step (1) into a magnetic stirring autoclave, and react at a temperature of 160-200° C. for 8-12 hours; (3) The turbid liquid after the completion of the reaction in step (2) is subjected to suction filtration, the filter cake is vacuum-dried, ground and passed through a 300-mesh sieve, calcined and naturally cooled to obtain a positive electrode material for lithium ion batteries, namely LiNi _x Co _y Mn _z O ₂ , where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z = 1. 2 . The method for solvothermal synthesis of positive electrode materials for lithium ion batteries according to claim 1 , wherein the calcination condition is to keep the temperature at 500° C. to 600° C. for 5 to 8 hours, and then to heat up to 800 to 850° C. for 10 to 12 hours of calcination. 3 .

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