• Hays, Kevin Alan
• Wagner, Michael J.
• Banek, Nathan A.
• Mckenzie, Kevin

Abstract

<jats:p>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/cm<jats:sup>3</jats:sup> vs. 818 mAh/cm<jats:sup>3</jats:sup> for Li<jats:sub>15</jats:sub>Si<jats:sub>4</jats:sub> vs. LiC<jats:sub>6</jats:sub>). In addition to the increase in capacity, Si is nontoxic, highly abundant, and inexpensive. Despite these advantages, the volumetric expansion of Li<jats:sub>x</jats:sub>Si 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.</jats:p>

Topics

• impedance spectroscopy
• Carbon
• composite
• Silicon
• electrical conductivity