Browsing by Author "Thurgate, S"

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    Olivine-type cathode for rechargeable batteries: role of chelating agents
    (Elsevier, 2012-11-01) Kandhasamy, S; Singh, P; Thurgate, S; Ionescu, M; Appadoo, D; Minakshi, M
    Olivine (LiCo 1/3Mn 1/3Ni 1/3PO 4) powders were synthesized at 550-600°C for 6 h in air by a sol-gel method using multiple chelating agents and used as a cathode material for rechargeable batteries. Range of chelating agents like a weak organic acid (citric acid - CA), emulsifier (triethanolamine - TEA) and non-ionic surfactant (polyvinylpyrrolidone - PVP) in sol-gel wet chemical synthesis were used. The dependence of the physicochemical properties of the olivine powders such as particle size, morphology, structural bonding and crystallinity on the chelating agent was extensively investigated. Among the chelating agents used, unique cycling behavior (75 mAh/g after 25 cycles) is observed for the PVP assisted olivine. This is due to volumetric change in trapped organic layer for first few cycles. The trapped organic species in the electrode-electrolyte interface enhances the rate of lithium ion diffusion with better capacity retention. In contrast, CA and TEA showed a gradual capacity fade of 30 and 38 mAh/g respectively after multiple cycles. The combination of all the three mixed chelating agents showed an excellent electrochemical behavior of 100 mAh/g after multiple cycles and the synergistic effect of these agents are discussed. © 2012 Elsevier Ltd.
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    TEM characterization of MnO2 cathode in an aqueous lithium secondary battery
    (Australian Institute of Physics, 2006-12-05) Minakshi, M; Mitchell, DRG; Singh, P; Thurgate, S
    The discharge characteristics of manganese dioxide cathode in the presence of small amounts (1, 3 and 5 wt. %) of TiS2 additive has been investigated in an alkaline cell using aqueous lithium hydroxide as the electrolyte [1]. The incorporation of small amounts of TiS2 additives into MnO2 was found to improve the battery discharge capacity from 150 to 270 mAh/g. However, increasing the additive from 3 to 5 wt. % causes a decrease in the discharge capacity. Hence, the objective is to gain insight into the role of TiS2 in MnO2 and its lithiation mechanism. For this purpose, we have used transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The valence state determination of the discharged MnO2 was performed using EELS. The Mn L2,3 edge contains two white lines (strong peaks) at about 640 eV (L3) and 650 eV (L2). The relative intensities of these Mn L2,3 peaks varies as a function of valence state in the Mn oxides i.e. MnO, Mn2O3 and MnO2 [2]. As-received MnO2 has a valence state of 4, as expected. However, Li intercalated materials showed evidence for reduction, the extent of which depended on the amount of TiS2 additive. The valance state of Li intercalated MnO2 with 3 wt. % TiS2 additive was 3.1 while that for the equivalent material with 5wt. % TiS2 additive was 3.5. Reduction of Mn occurs as a result of Li intercalation, the extent being more marked for the 3 wt. % TiS2 loading. This result is in accordance with the discharge behavior, since the capacity of the 3 wt. % material (270 mAh/g) was significantly larger than that for the equivalent 5 wt. % material (75 mAh/g)). TEM imaging showed a presence of nano particulate Mn oxides, of about 50 nm diameter, in the 5 wt. % TiS2 material. This could inhibit the lithium intercalation resulting in a valence state of 3.5 and thereby low discharge capacity whereas this nano particulate material is not present in 1 and 5 wt. % TiS2 loaded material.