A Silicon Hollow Graphene Nanoshell Li-Ion Anode Composite Material

The Li-ion battery provides the majority of powertrain energy for today’s electric vehicles (EVs). The usable range of EVs is largely limited by the Li-ion storage capacity in a Li-ion cell. In addition to low range, most EVs require 4 - 12 hours of charge time. Silicon, a Li-alloy alternative anode, has much greater gravimetric and volumetric capacities compared to graphite (3579 mAh/g vs. 372 mAh/g and 8335 mAh/cm3 vs. 818 mAh/cm3 for Li15Si4 vs. LiC6). In addition to the increase in capacity, Si is nontoxic, highly abundant, and inexpensive. Despite these advantages, the volumetric expansion of LixSi and poor electrical conductivity of Si makes developing a pure silicon anode with reasonable cycle life a seemingly insurmountable challenge. Composite electrodes of Si and C could represent the next-generation of Li-ion anodes for EVs. Hollow graphene nanoshells (HGNS) are a conductive graphitic carbon ~50 nm in diameter that can charge in minutes and have cycle lives of over 1000 cycles with minimal fade making them a promising support material for silicon nanostructures of higher capacity. Utilizing a facile low-temperature solution synthesis method, silicon was synthesized onto the HGNS to produce Si/HGNS composites in high yield and purity. The electrochemical performance of the composite material had a reversible capacity of ~3500 mAh/g Si (1400 mAh/g composite) after a C/20 formation cycle with 80% first cycle Coulombic efficiency. At an increased rate of C/2, a reversible capacity of ~2800 mAh/g Si (1100 mAh/g composite) is achieved with stable cycling performance. Utilizing this solution synthesis method, efficient mixing of Si with HGNS can produce Li-ion anode composites greater than 3 times the capacity of graphite with stable performance at charging rates required for upcoming EV powertrains.