Silicon-loaded Lithium-Carbon Composite Microspheres as Lithium Secondary Battery Anodes

Lithium metal is the most promising anode material for Li (ion) batteries from the viewpoint of energy density because of its high theoretical specific capacity (3860 mAh.g(-1), 2061 mAh.cm(-3)) and low reduction potential (-3.04 V vs standard hydrogen electrode (SHE)). Lithium has been used as an anode material for lithium metal batteries since the 1970s. However because of the serious reaction between Li and non-aqueous electrolytes, the large volume expansion during Li plating, and the formation of Li dendrites during cycling, Li batteries with Li metal anodes show very low Coulombic efficiency (CE) and are easily short-circuited. This limits the widespread commercialization of Li metal anodes for Li batteries. Motivated by our previous study on the development of a Li carbon nanotube (Li-CNT) composite anode material, in this study, we prepared a Si-loaded Li carbon nanotube composite (Li-CNT-Si) via a facile molten impregnation method. The introduction of Si nanoparticles increased the Li content of the composite, thus increasing its specific capacity (the specific capacity of the Li-CNT composite increased from 2000 mAh.g(-1) to 2600 mAh.g(-1) with the addition of 10% Si (mass fraction)). Moreover, Si nanoparticles decreased the polarization for Li plating/stripping, resulting in an improved electrochemical performance. The Li-CNT-Si composite showed the merits of the Li-CNT composite with the advantages of limited electrode volume expansion and negligible Li dendrite formation during cycling. Furthermore, the Si nanoparticles filled the pores inside the Li-CNT microspheres, thus preventing the electrolyte from flowing into the microspheres to corrode the Li metal present inside them. Hence, the incorporation of Si nanoparticles improved the CE of the composite anode. When the 10% Si-loaded Li-CNT-Si composite was used as an anode and coupled with a commercial LiFePO4 cathode, the resulting battery showed more than 900 stable cycles in an ether-based electrolyte at a charge/discharge rate of 1C (0.7 mA.cm(-2)) corresponding to a CE of 96.7%, which is considerably higher than those of the Li-CNT (90.1%) and Li metal foil (79.3%) anodes obtained under the same conditions. We believe that the Li-CNT-Si composite prepared in this study is a promising anode material for Li secondary batteries having high energy density, particularly for those employing Li-free cathodes, e.g., Li-sulfur and Li-oxygen batteries.