3D aligned-carbon-nanotubes@Li2FeSiO4 arrays as high rate capability cathodes for Li-ion batteries

Abstract

3D aligned-carbon-nanotubes (ACNTs)@Li2FeSiO4 nanocomposite arrays on Al foil were developed as cathode materials for Li-ion batteries. The ACNTs were grown directly on an Al foil by a chemical vapor deposition method to achieve a 3D current collector structure for direct charge transport. Li2FeSiO4 nanoparticles were deposited on the surface of the ACNTs by a polyvinylalcohol (PVA)-assisted sol–gel method. The 3D samples showed a high degree of alignment of nanotubes with a favorable pore morphology before and after cycling. According to electrochemical measurements, the 3D sample with optimized mass ratio of ACNTs and Li2FeSiO4 (2:1) showed excellent rate capability and capacity retention, delivering a discharge specific capacity of 142 mAh g−1 at a rate of 0.5 C (C = 160 mAg−1) and maintaining 99% of the initial discharge capacity after 50 cycles at 24 ° C. Up to 20 C, the delivered charge/discharge capacity was 94 mAh g−1 after 172 cycles, which is 54% of the value obtained at C/20 (175 mAh g−1). In comparison, carbon coated nanoporous Li2FeSiO4 obtained under analogous conditions by a PVA-assisted sol–gel method can only deliver a capacity of 80 mAh g−1 and showed poor rate capability. In addition, despite amorphization, dissolution and chemical composition changes occurring in the 3D samples upon extended cycling, the 3D samples showed good long-term cycling stability at a high current density (5 C), maintaining ~80% of the initial discharge capacity after 1000 cycles and ~70% after 2000 cycles.