In this paper, the capacity titration technique （CT technique） was developed on basis of the RPG （ratio of potentio-charge capacity to galvano-charge capacity） method to continuously determine the solid diffusion coefficient D of the intercalary species within insertion-host materials with a small voltage region. The linear equations of D vs. q （value of ratio of the potentio-charge capacity to the galvano-charge capacity） were given in different range of q. By the CT technique,the Li^＋ solid diffusion coefficients D within LiMn2O4 at different voltages were determined. The results showed that the values of D varied from 3.447×10^-9 cm^2/s to 7.60×10^-11 cm^2/s in the voltage range of charge from 3.3V to 4.3V as a function of voltage with “W” shape.
In this paper,the method of UV-visible reflection spectrum（UV method） was theoretically and experimentally proposed to investigate the initial kinetic characters of the solid-solid reaction with the mixture of dimethylglyoxime and Ni（Ac）2·4H2O,and the mixture of dimethylglyoxime and anhydrous Ni（Ac）2 as the modeling reaction examples.The results indicated that the UV method was very sensitive in the initial period of solid-solid reaction.The reactive rates for above two reaction systems were varied non-linearly with the change of reaction time.The fastest reaction rates can be reasonably explained by the formation of the cold-melting layer or cold-dissolvingmelting layer.
The phase transition of Li2Mn2O4 spinel at high temperature was investigated by XRD, TG/DTA, average oxidation state of Mn and cyclic voltammeric techniques. The results reveal that the Li2Mn2O4 spinel is unstable. At high temperature, it is easy to transform into [Li2-2x]tet[Mn2-xLix]octO4, which accompanies the formation of Li2MnO3 impurities. The phase transition is associated with the transfer of Li+ from tetrahedral 8a sites to octahedral 16d sites. With the increasing sintering temperature from 450 ℃ to 850 ℃, the phase structure varies from lithiated-spinel Li2Mn2O4 to Li4Mn5O12-like to LiMn2O4-like and finally to rock-salt LiMnO2-like. In addition, a way of determining x with average oxidation state of Mn and the content of Li2MnO3 was also demonstrated.
The cold-melting mechanism and the cold-dissolving-melting mechanism w ere further studied by TG/DTA and in situ micro-photographs techniques with the mixture of dimethylglyoxime and Ni(Ac)2·4H2O, and the mixture of dimethylglyoxi me and anhydrous Ni(Ac)2 as the modeled reactive examples. The endothermic peaks on the DTA curves at about 38 ℃ revealed the formation process of the cold-mel ting layer and cold-dissolving-melting layer on the surface of reactant particle s. Further, the cold-melting state and the cold-dissolving-melting state were ob served by the micrographs. These results provided the direct evidences for the t heories of cold-melting mechanism and the cold-dissolving-melting mechanism.
The capacity intermittent titration technique (CITT) was developed based on the ratio of potentio-charge capacity to galvano-charge capacity (RPG) method, to continuously determine the solid diffusion coefficient (D) of the intercalary species within insertion-host materials with a small voltage region. The linear equations of D vs the value of ratio of the potentio-charge capacity to the galvano-charge capacity (q) were given. By the CITT technique,the Li+ solid diffusion coefficients within LiMn2 O4 at different voltages were determined. The results show that the values of D varied from 3. 447× 10-9 to 7.60× 10-11 cm2/s in the voltage range of charge from 3.3 to 4.3 V as a function of voltage with "W" shape.
