Designing The Next Generation Silicon/Graphite Anodes for Lithium-Ion Batteries: From The Nanoscale to The Macroscale

Reaching net-zero emissions and transitioning to widespread electrification of vehicles have emerged as key challenges for ensuring a sustainable future. Central to these goals is the critical role played by energy storage systems, which are pivotal in enabling the efficient utilisation and distribution of renewable energy. The advancement of energy storage technologies, particularly in the realm of lithium-ion batteries, holds the key to mitigating the challenges posed by intermittent renewable energy sources. Moreover, electrification of the transportation sector, primarily through electric vehicles, is fundamental to reducing greenhouse gas emissions.<br/>The operating range for electric vehicles is determined by the energy density of the battery, which in the case of anode materials is directly correlated to their lithium storage capacity. While traditional graphite anodes have a theoretical capacity of 360 mAh/g, silicon has a much larger theoretical capacity (3600 mAh/g) and silicon-based lithium-ion batteries have therefore emerged as a promising technology.<br/>However, silicon anodes suffer from large volume expansion (up to 300 %) during cycling, which cause a drop in capacity. Recent industrial advances allowed to engineer silicon/graphite composite materials with limited volume expansion and increased capacity. However, while these materials showed improved electrochemical performance, little is understood on the physicochemical mechanisms underpinning these improvements. The successful advancement of this technology necessitates a thorough understanding of intricate phenomena such as particle cracking, volume changes on various length scales (from pouch cell level down to individual particles), and the formation of solid electrolyte interphase (SEI) layers.<br/>Herein, we employed a suite of complementary physical and chemical characterisation techniques using both post-mortem and operando methods, across a range of length scales, from pouch cells down to individual particles observed at the nanoscale. Collaboration with an industrial supplier of these anodes and cells allowed the elucidation of the material degradation phenomena and the correlation to their electrochemical cycling performance.<br/>This work highlights the significance of integrating multiple characterisation methods to unravel the underlying degradation mechanisms in silicon-based anodes, paving the way for the design and engineering of efficient silicon and graphite anodes, thus propelling the evolution of lithium-ion battery technology.