| LiMO2(M=Co Ni) is an ideal cathode material for lithium secondary batteries due to its good electric characteristics. Conventionally, the LiMO2 cathode materials are prepared via a solid state sintering, which is with high fabrication cost and bring about inevitable environmental pollution. Soft solution processing (SSP), which needs simple equipment and progresses at low synthesis temperatures, seems to be an environmentally friendly, economical route. In this work, thin films of LiMO2 have been prepared on the Co or Ni electrode through the hydrothermal-electrochemical method, one kind of the SSP.The reaction course for the formation of LiMO2 in a hydrothermal-electrochemical route was calculated using the thermodynamic method. The formation mechanisms of LiMO2 were discussed. The reactions involved were as follows:Co(OH)2 (sol) →HCoO2-→Co(OH)2(film)→CoOOH→LiCoO2 Ni→Ni(OH)2 (NiO, HNiO2-) →NiOOH H2O→NiOOH→LiNiO2 The reaction course was simulated by cyclic voltammetry. The scope of reaction parameters was attained through cyclic voltammetry. The scope of parameters coincided with the result of thermodynamic calculation. The reaction mechanisms were proofed by the potentiostatic method and X-ray diffraction method. The parameters of pOH and temperature exerted influences on the composition and structure of the LiMO2 thin film.LiMO2 thin films with R 3 m structure were prepared by the hydrothermal-electrochemical method. When M gradually shifts to Ni from Co, the binding energies of Lils and Co2p decreased and the binding energy of Ni2p increased. The values of lattice parameters a and c increase but the c/a value decreases. The LiNiO2 film consists of netted crystal, the others consist of even spherical crystalline grain. LiMO2 thin-film electrodes had the similar characteristics of the porous electrode, which endows them good cycling and operating life.Effects of the process parameters on the thickness, grain size and inner stress of the LiMO2 films were investigated. The thickness of the films increases with the pOH value of the solution and reaction time, but decreases with increasing of the density of the electric current. When temperature is elevated, the film thickens firstly, then keeps its thickness invariable when increasing to a certain value. The grain size of the film increases with increasing of reaction temperature, time and the film thickness, while reduces with increasing of density of the electric current and pOH value of the solution. Thermal compress stress exists between LiMO2 films and Co or Ni substrates. The stress increases with the increasing of the temperature and density of electric current. The smaller the grain size is, the greater the stress of the film. The film electrode with bigger grain size or larger thickness had lower capacity.The preferred orientation of LiMO2 film was further investigated systematically. With the increasing of reaction temperature, the current density and pOH value of the solution, the percentage of grains with their (101) or (104) planes parallel to the substrate increases. If enhancement of the ambient pressure in the reactor, whereas the (003) plane oriented films become dominant. The films with thickness less than 1 u m are mainly (101) or (104) plane oriented, while the films are mainly (003) plane oriented when the thickness of the film is smaller than 1 u m. Under the same conditions, films that are (003) plane oriented tend to form on cobalt substrate and films that are (101) or (104) plane oriented tend to form on nickel substrate. The smaller the electrode spacing, the more favorable the (101) plane preferred orientation. The (101) plane orientation is favorable for Li+ diffusion through the cathode, and therefore the (101) plane orientated film contributes to the enhanced electrochemical performance.The crystallization process was also studied on the basis of the growth unit model of anionic coordination polyhedron. It was found that the CoOOH crystals were preferentially generated on a -cobalt substrate, the growth unit was comp...
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