Nickel Oxalate Dihydrate Nanorods Attached to Reduced Graphene Oxide Sheets As a High Capacity Anode for Rechargeable Lithium Batteries

Abstract

In the search for high capacity anode materials, a facile hydrothermal route has been developed to synthesize phase-pure NiC 2 O 4 ·2H 2 O nanorods, which were crystallized to orthorhombic structure without using templates. To ensure the electric conductivity of the nanorods, the produced NiC 2 O 4 ·2H 2 O nanorods were attached to reduced graphene oxide sheets via self-assembly layer-by-layer processes utilizing the electrostatic adsorption that occurs in a poly(diallyldimethylammonium chloride) solution. High electric conductivity aided by the presence of reduced graphene oxide (rGO) significantly improved the electrochemical properties: 933 mAh g -1 for the charge capacity (oxidation), which showed 87.5% efficiency at the first cycle with its retention approximately 85% for 100 cycles, and 586 mAh g -1 at 10 C-rates (10 A g -1 ) for the NiC 2 O 4 ·2H 2 O/rGO electrode were measured. We determined the details of the lithium storage processes involved with the conversion reaction, which were fairly reversible via a transformation to Ni metal accompanied by the formation of a lithium oxalate compound on discharge (reduction) and restoration to the original NiC 2 O 4 ·2H 2 O on charge (oxidation); this was confirmed via X-ray diffraction, transmission electron microscopy, X-ray photoelectron microscopy, and time-of-flight secondary ion mass spectroscopy. We believe that the high rate capacity and rechargeability upon cycling are a result of the unique features of the highly crystalline NiC 2 O 4 ·2H 2 O nanorods assisted by conducting rGOs.