Comparative Electrochemical Study of Metal Oxalate As Anode for Lithium Batteries

Rechargeable lithium ion batteries (LIB) are the most advanced power sources for portable electronic devices, hybrid electric vehicles, transportation sectors and military applications. Metal oxalate is technologically important and functional material, because of its applications for use in energy storage such for Li ion batteries. Thus, these materials have been investigated as alternative negative materials for LIB owing to high capacity (700 ~ 1,000 mAhg^-1) based on a conversion mechanism.

Several metals based oxalates with different aspect ratios have been synthesized by hydrothermal reaction of metals (= Ni, Co, Mn) with Na₂C₂O₄ and H₂O in the presence of ethylene glycol (EG). Control over the aspect ratios of oxalates were achieved by adjusting the hydrothermal reaction temperature and time.

The electrode was fabricated by mixing 70 wt% active material, 10 wt% carbon black (electronic conductive additive) and polyacrylic acid (PAA, binder) in N-methylpyrrolidinone (20 wt%). A solution of 1 M LiPF₆ dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (3 : 7 weight ratio) was used as the electrolyte in the cell. Electrochemical test was carried out in coin type cell. Galvanostatic electrochemical charge and discharge test were made between 0V and 3.0V at 100 mAg^-1 current at room temperature.

The hydrothermal method is useful to synthesize metal oxalate with particles and crystallization. Nickel and manganese oxalate crystallize in the monoclinic phase, while the cobalt compound adopts the orthorhombic phase.  

The as-prepared metal oxalates demonstrate a high performance as anode material for LIB. Among them, nickel oxalate showed a high initial discharge capacity of 1321 mAhg^-1. The first charge capacity of the as-prepared electrode at a current density of 100 mAg^-1 reach 786 mAhg^-1 with good capacity retention.