Synthesis of Nanocrystalline Electrode Materials by Hydrothermal Reaction

3 Synthesis of Nanocrystalline Electrode Materials by Hydrothermal Reaction 

Hydrothermal s3mthesis has been applied successfully to various nanociystalline electrode materials such as LiCo02, LiNi02, UMn204, and LiFeP04, Table 7.1 summarizes selected previous reports on the hydrothermal s mthesis of nanocrystalline cathode materials. 

For fabrication of nanocrystalline cathode materials with a short Li-ion diffusion length, reaction temperature and reaction time are apparently the most important parameters. As shown in Table 7.1, regardless of the target material, lower reaction temperature and 

Regarding LiCo02, the most commonly used cathode material in the commercial Li-ion batteries, many groups have reported synthesis of nanocrystalline LiCo02 by a post-templating method, a sol-gel method, a spray-drying method, and a coprecipitation method. As shown in Table 7.1, the hydrothermal method has also been applied successfully by some groups. However, accurate control of crystallite size has not been achieved, and thus it has been difficult to discuss systematically the nanosize effect on structural, physical, and electrochemical properties. 

As discussed above, to synthesize a nanocyrstal by the hydrothermal method, the precursor needs to be as small as possible. Therefore, nanocrystalline CoOOH was selected as a precursor for the synthesis of nanocrystalline LiCo02. The crystallite size of CoOOH can be easily controlled by s mthetic conditions during the oxidation reaction of Co(OH)2. In fact, by controlling oxidation conditions (low temperature and high pH), we obtained nanoplate CoOOH with a thickness of 8 nm (Fig. 7.3). This extremely nanosized precursor enabled quick fabrication of the extremely nanosized LiCo02 with control of the crystallite size by varying the reaction temperature, concentration of LiOH aqueous solution, and reaction time. 

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