Synthesis and electrochemical properties of calcium cobaltate as novel anode material

Abstract

The calcium cobaltate (Ca3Co4O9) is synthesized through rheological phase reaction method using calcium gluconate (Ca(C6H12O6)2), citric acid (C6H8O7) and cobalt acetate tetrahydrate (CoAc2·4H2O) as raw materials. The germanium dioxide (GeO2) and bismuth nitrate pentahydrate (Bi (NO3)3·5 H2O) or both of them are used as precursors to synthesize Ge and Bi cation-doped calcium cobaltate (Ca3Co4O9) to improve its electrochemical properties. At first, the precursors were formed at 120 °C for 12 h using rheological phase mixtures of designed raw materials. Then, precursors were heated at different temperatures to obtain calcium cobaltate (Ca3Co4O9) samples. Because of doping of Ge4+ or Bi3+ or both of them, the conductivity and electrochemical performances for Ca3Co4O9 could be improved to a certain degree. The electrochemical tests showed that its electrochemical performances are depended on its calcination temperature and different kinds of doping. When calcined temperature was set at 750 °C, sample doped by both Ge4+ and Bi3+ (such as designed expected compound Ca2.85Bi0.15Co3.85Ge0.15O9) exhibited high reversible capacity at current density of 100 mAg−1 in voltage range of 0.01–3.0 V, and its reversible capacity could maintain at 550 mAhg−1 after 50 cycles. The reasons for Ca2.85Ge0.15Co3.85Bi0.15O9 to exhibit outstanding electrochemical properties were discussed also. The calcium cobaltate (Ca3Co4O9) doped by both Ge4+ and Bi3+ is a promising anode material for lithium ion battery application.