Nano-(Cd1/3Co1/3Zn1/3)CO3: a new and high capacity anode material for Li-ion batteries

Abstract

The Li-storage and cycling behavior of the mixed-metal carbonate, nano-(Cd_1/3Co_1/3Zn_1/3)CO₃ (CCZC) prepared under ambient conditions by the precipitation method are reported. A reversible capacity of 680 (±10) mAhg⁻¹, corresponding to 3.5 moles of cyclable Li per mole of the CCZC (theor., 3.33 moles of Li) stable in the range 8–60 cycles is observed when cycled at 0.09 C in the range, 0.005–3.0 V vs.Li. The nano-CCZC also shows stable and reversible capacities at various C- rates up to 170 cycles. At 0.6 C, the observed capacity of 360 (±10) mAhg⁻¹ is comparable to the theoretical capacity (372 mAhg⁻¹) of the graphite used in the present-day Li- ion batteries. On the basis of galvanostatic cycling, cyclic voltammetry, ex situ-XRD, -TEM and -SAED studies, a reaction mechanism is proposed in which the CCZC is first reduced by Li to nano-metal (M = Cd, Co and Zn) particles embedded in amorphous Li₂CO₃ and this is followed by the formation of alloys (Li–Zn and Li–Cd). Upon charging the electrode, the de-alloying reaction and metal carbonate (MCO₃) formation occurs, thereby contributing to the reversible capacity. We have shown for the first time that the carbonate ion (CO₃²⁻) is as good as the oxide, fluoride or oxy-fluoride ion in enabling the reversible ‘conversion’ and alloying–de-alloying reactions involving both transition and non-transition metal ions.