Towards Sustainable Lithium-Ion Batteries: A State-of-the-Art Review on Silicon Anodes, Economics, and Recycling

Abstract In recent years, natural graphite, widely used as anode material for commercial lithium-ion batteries (LIBs), has been classified by EU as a Strategic Raw Material (SRM) and its partial or total replacement with non-critical or end-of-life (EoL) material is recommended. Silicon is one of the most promising materials to replace natural graphite. In fact, it is known that silicon can form alloys with lithium, with a theoretical energy storage capacity at room temperature of 3579 mA h g −1 (when lithiated to Li 15 Si 4 ), i.e., significantly higher than that of graphite (372 mA h g −1 ) and comparable with metallic lithium (3860 mA h g −1 ). The limiting factor of silicon as anodic material for lithium-ion battery systems is represented by its volumetric expansion, which can reach values more than 300% during battery charge–discharge cycles, involving progressive fragmentation and loss of active material and resulting in rapid decrease of the accumulated capacity. Moreover, the recent inclusion of silicon into the EU list of strategic raw materials and the high environmental impact of silicon production from SiO 2 , make the recovery and recycling of this material thoroughly recommended, especially from EoL products like photovoltaic (PV) panels. The paper offers a state-of-the-art on challenges and solutions related to the use of silicon as anodic material in LIBs, besides a survey on the Technology Readiness Level (TRL) and the market penetration of silicon anode battery technology.