| The rapid development of lithium ion battery asks for more clearly understanding about positive electrode materials and improving urgently their electrochemical performance. This dissertation tries to meet partly this goal. The dissertation is involved in the three issues: the synthesis and electrochemical properties of nano- and sub-micrometer LiMii2O4 and its Mn-substituted compounds by a soft chemical method; the improved rate performance in multi-phase LiCoCVbased composite due to Pt additive; LiMii2O4 thin film by a sol-gel technique and its electrochemical properties.A modified citrate route with combustion for LiMii2O4 has been developed, which is simpler, time-saving and cost-cheaper. The effects of glycol addition, pH value of solution on the precursor and calcining temperature on the phase structure and charge-discharge performance have been investigated. It was optimized that the process with suitable amount of glycol, pH value of near 7 and the calcination at 800 for 24h could prepare a single phase LiMn2O4 with the spinel structure. TEM observation showed that the powder size of the typical synthesized product was 10-100nm, but they usually aggregated as granules with the size of about 6 ?m, much less than the commercial LiMnO2 The LiMn2O4 synthesized by such a processing also showed a better electrochemical performance, compared with commercial one, for the electrode application. The initial specific capacity was about 130mAh/g, but its cycleability was worse. Its electrochemical characteristics were investigated by CV and EIS techniques.Constant potential step experiment showed that the Li ion transport behavior was closely connected with the initial potential and potential step. There were three types of current relaxation curve: monotonously, with a maximum-minimum inflection andwith two maximum-minimum inflections. It is preliminarily suggested that the complicated behavior is not only connected with the diffusion in a phase, but also the evolution of phase component and movement of phase boundary during current relaxation process. Under this frame, the understanding of the inflection is given.LiMxMn2.xO4 was also synthesized by the modified citrate route to examine the elemental substitution effect on the electrochemical properties, where M is Ek AK Q\ Fe. Co. NK Ga. Except B, all substituted LiMxMn2-xO4 showed an improved cycling characteristics with a reduced slightly initial reversible capacity, Among them, Cr was the most effective, for example, the loss of discharge specific capacity in first 100 cycles for LiCr0.2Mni g at 0.5C was lower than 0.1% per cycle, however it was 0.23% per cycle for LiMn2O4. It is because of radius of Cr3+ a little less than that of Mn3+, more stable electronic configuration and stronger bond energy with O atom. With Cr substitution, the step for up-plateau around 4.1V and down-plateau around 4.0V was gradually smeared out. The experiment also demonstrated that the lost capacity of LiMCU almost occurred above 4V It may be caused by the Mn dissolving in electrolyte at high potential and the shrinking and/or destroying of spinel lattice at Li-deficient state, which limits the de-intercalating of lithium ion. The substitution of Cr for Mn can weaken those effects to stabilize the Li-deficient structure. The synthesized LiMn2O4 showed similar electrical conductivity behaviors as the one by solid-state reaction process.The influence of the initial addition of Pt (Li:Co:Pt=l:l-x:x) on the microstructure and electrochemical properties of LiCo02-based material was first investigated. A small amount of Pt additive induced Li2PtO3 and Pt in matrix LiCoO2 to form a multi-phase composite. This multi-phase composite showed the improved rate performance and cycleability at high rate in comparison with the single-phase of LiCoO2, for example, at discharge of IOC, the discharge specific capacity for LiCoO2-base sample with x= 5% kept above 87mAh/g after 50 cycle, however, it was lower than 30 mAh/g for a single phase of LiCoO2. The improved rate performance is attributed...
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