Synthesis process and modification technology of lithium cobalt oxide

1. Synthesis process

There are many synthesis methods of LiCoPO4, mainly including solid state reaction, sol gel method, hydrothermal/solvothermal method, microwave method, spray thermal decomposition method, etc.

① Solid-phase reaction method

The solid-phase method has a simple process and is often used to prepare positive electrode materials,

 but the processing temperature is high, the time is long, the energy consumption is high, 

and the particle size distribution of the synthesized material is uneven, resulting in poor batch stability.

② Sol gel method

Generally speaking, the sol gel synthesis method has the advantages of accurate stoichiometry, 

uniform distribution of raw materials, relatively short processing time and low calcination temperature,  

but its disadvantages are large drying shrinkage, long synthesis cycle and high cost, so it is not suitable for industrial production.

③Hydrothermal/solvothermal method

The hydrothermal/solvothermal method has the advantages of relatively low reaction temperature,

 low energy consumption, simple equipment, high purity of the obtained material, small particles, and uniform dispersion.

 However, it requires high production equipment, and some solvents may have reducibility to the product, which limits its industrial application.

④Microwave method

Microwave method is a fast heating synthesis method with advantages such as short reaction time and energy saving.

 However, the reaction is difficult to control, side reactions occur, and the research on reaction mechanism is not deep enough. Currently, it is limited to small-scale applications in the laboratory.

⑤ Spray pyrolysis

The spray pyrolysis method requires simple equipment, which can be produced continuously, with low production cost and pollution-free reaction; 

However, due to the generally low crystallinity of the material, optimization needs to be combined with heat treatment. 

At the same time, there is insufficient research on the micro process mechanism, which mainly focuses on the laboratory research stage. 

Spray pyrolysis still needs further research in equipment development and scale production.

⑥ Other synthesis methods

The synthesis methods of LiCoPO4 positive electrode materials include rheological phase reaction method, 

co precipitation method, supercritical technology, and low-temperature solid-phase method.

2、Modification technology

The reversibility of phase transition under high voltage is the key to determining the application of lithium cobalt oxide, 

and it is unrealistic to expect a single method to solve the problem of high-voltage lithium cobalt oxide. 

Combining effective doping, co coating, high-voltage electrolyte, and new functional separators to alleviate internal failure of lithium cobalt oxide batteries and improve high-voltage lithium cobalt oxide.

1） Doping modification

Bulk doping can stabilize material structure, suppress irreversible phase transition, and improve material cycling performance. Body phase doping includes:

① Low valence cation doping: Low valence cations usually refer to ions with a valence state not higher than trivalent, mainly including lithium vacancies,

 lithium ions, magnesium ions, aluminum ions, zirconium ions, etc.

② High valence cation doping:

 High valence cation doping usually refers to ions with a valence state higher than trivalent, mainly including titanium, manganese, zirconium, molybdenum, and tungsten ions.

③ Co doping: Trace elements of titanium, magnesium, and aluminum are co doped, 

and synchrotron X-ray 3D imaging technology is used to reveal that magnesium and aluminum elements are more easily doped into the material crystal structure to suppress phase transitions at around 4.5V.

2） Coating modification

Surface coating can suppress the dissolution of surface elements, stabilize the surface structure, and enhance electrochemical performance. Surface coating includes:

① Electronic conductor coating: Carbon element is an electronic conductor material. J. Kim et al. coated carbon element on the surface of lithium cobalt oxide by low-temperature liquid-phase method. 

They found that carbon can improve cycling performance, rate performance, and high-temperature storage performance;

② Ionic conductor coating: LATP is a good ionic conductor material. 

Morimoto et al. applied mechanical methods to coat the electrolyte LATP on the surface of lithium cobalt oxide, improving its cycling and rate performance at 4.5V;

③ Electron ion dual conductor coating: The electrode is an excellent electron ion conductor.

 JoongSun Park et al. found that AlWxFy is a good electron ion conductor, and lithium cobalt oxide coating has excellent electrochemical performance at 4.5V;

④ Electronic ion double insulation coating: commonly used oxides include magnesium, aluminum, titanium, zirconium, etc.

 In 2016, XieMing et al. found that samples coated with aluminum oxide exhibited superior electrical performance at 4.7V. A. 

Yano et al. found that under high voltage cycling, 

lithium cobalt oxide coated with aluminum oxide can suppress surface material cracking and improve electrical performance. 

S. S. Jayarsee et al. found that titanium dioxide coated samples can improve stability and rate performance under high voltage.

 Multi element co coating has also become a development trend for high-pressure lithium cobalt oxide coating modification.

3、 Particle size optimization and morphology control

When LiCoO2 is used as a positive electrode material, its particle size and morphology will affect the overall electrochemical performance.

 If the particle size is too large, it will not only reduce the total contact area with the electrolyte, but also lengthen the migration path of Li+and reduce the discharge rate of the battery. 

So reducing the particle size of LiCoO2 is an effective means to improve cycling stability. 

The purpose is to increase the diffusion coefficient of ions in the electrolyte by reducing the particle size,

 and to prevent the hysteresis migration of Li+during charge and discharge from causing a decrease in capacity. 

And smaller particles experience less pressure during the charging and discharging process, which can improve the durability of the material.

4、 Other

In addition to the above technologies, 

the combination of high-pressure electrolyte and functional diaphragm is also an effective means to improve the cycling stability of materials.