Electrochemical properties of low temperature (LT) crystallized LiCoO, are investigated. LT LiCoO, was obtained by a precipitation process in aqueous solution and a final heat-treatment at 400°C in air. Potentiometric, voltammetric, and ac impedance experiments are performed as well as x-ray diffraction measurements on electrochemically delithiated compounds. LT LiCoO2 shows electrochemical and structural properties quite different from that exhibited by the high temperature (lIT) LiCoO,. The main differences appear in terms of practical voltage, reversibility, Li transport in oxide, and structural changes as Li is deintercalated. This work clearly proves the 3D character of LT LiCoO2 (spinel-like structure). In spite of a lower working potential and a satisfactory capacity (zx = 0.5), the LT LiCoO, is highly reactive toward the electrolyte and is characterized by a slower Li transport than in layered HT LiCoO,.
The kinetics of the lithium electroinsertion in vanadium pentoxide was studied vs. Li=V=O5 composition bronzes formed during the two first processes (0 < x < 1), by means of complex impedance spectroscopy between 104 and 10 -3 Hz at 20 ~ and 50~ in 1M LiC104/propylene carbonate solutions. The interfacial charge transfer process is found to be independent ofx. At 20~ the exchange current density is equal to 1.3 _+ 0.5 10 -4 A/cm 2 and the chemical coefficient diffusion, DLi , varies between 10 -9 and 10 -11 cm 2 s -1, with a minimum value for x ~ 0.25. The partial conductivity CrLi of lithium in V205 is found to vary betwee_n 10 -6 and 10 -7 ~-1 cm-~. The E)5i and r values at 50~ are five to six times greater than those at 20~ The dependence of D~ on the composition of the Li=V205 bronzes composition was correlated with structural and thermodynamic data already reported in the literature.
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