| Abstract | Carbon graphite is commonly used as an anode material in lithium-ion batteries because of its long cycle life and moderate cost. However, it has a theoretical capacity that is limited to 372 mAh g-1. In 2000, transition-metal oxides were proposed as alternative anode materials for lithiumion batteries. Poizot et al. have shown that these oxides react with lithium via a reversible conversion reaction where the metal oxide is reduced into metal nanoparticles (1-2 nm) embedded into a matrix of lithium oxide upon discharge (1). The best materials were found to be CoO and Co3O4 with reversible capacities of 700 mAh g-1 and 900 mAh g-1, respectively (1). The same reaction occurs with other transition-metal oxides (Cr, Mn, Fe, etc…). Recently, we reported on the synthesis and the electrochemical characterization of ZnMn2O4 (2), a high capacity anode material for lithium-ion batteries (784 mAh g-1). ZnMn2O4 was synthesized through a simple coprecipitation route using oxalic acid. The precipitate was filtered, dried and calcined at temperatures ranging from 400 °C to 1000 °C. A capacity of 690 mAh g-1 was obtained at C/10, along with good rate capability and excellent capacity retention (88%) with ZnMn2O4 calcined at 800 °C, and using lithium carboxymethlycellulose (LiCMC) as a binder (hereafter referred to as ‘optimized ZnMn2O4’). In this paper, we present a study of the effect of the electrolyte and the cycling temperature on the performance of ZnMn2O4. In addition, a study of the composition of the solid electrolyte interphase (SEI) of ZnMn2O4 electrodes by XPS will be presented. As illustrated in Figure 1, ZnMn2O4 adopts the I41/amd tetragonal structure for all calcination temperatures with crystallite sizes ranging from 11.4(2) nm at 400 °C to 324(14) nm at 1000 °C. The effect of the electrolyte on the performance of optimized ZnMn2O4 is shown in Figure 2. Three different electrolytes were tested using 1M LiPF6 as salt: EC:DMC (1:1), EC:DEC (3:7) and PC. A discharge capacity of 800 mAh g-1 after 100 cycles was obtained for ZnMn2O4 in EC:DEC electrolyte while the use of PC provided a capacity of 600 mAh g-1 after 100 cycles. A good rate capability and capacity retention were obtained for all electrolytes. The influence of the cycling time, the cycling temperature and the electrolyte on the composition of the SEI, studied by XPS, will be discussed. Figure 3 shows the C 1s, O 1s, and Li 1s spectra of a ZnMn2O4 pristine cast, and the ZnMn2O4 electrodes from batteries opened after being cycled 100 times in EC:DMC and EC:DEC. Different species such as LiF, polyethers and carbonates were identified as components of the SEI. |
|---|
