The global need for high-energy-density batteries has pushed for the development of high-performance battery materials such as cathodes and anodes to meet the huge energy demands in our modern society. Graphite (Gr) is the dominant anode material for lithium-ion batteries but possesses a lower theoretical capacity of 372 mAh g⁻¹, which hinders the fabrication of more powerful batteries. On the other hand, silicon (Si) possesses an extremely higher theoretical capacity than graphite (4200 mAh g⁻¹ in a composite of Li_4.4Si vs graphite: 372 mAh g⁻¹). Unfortunately, Si anode has issues with high volume changes (up to 400%) during cycling. Mixing/compositing silicon with carbon (Si/C) is set to be a realistic strategy to overcome issues related to the volume changes of Si and the low capacity of graphite. Instead, coupling both elements enables the combination of the two main materials’ properties, such as the high lithiation performance of Si and outstanding mechanical stability and conductivity of the carbon, which allows the battery to reach high storage capacity under elevated stability over longer cycles. In this review, Si/C materials anode materials synthesis methods, structural and morphological characteristics, and electrochemical performances are discussed as well as major challenge to overcome pulverization of Si during the charge/discharge process, and potential challenges of designing Si/C.

Natural graphite is currently considered as a critical raw material in EU. The demand for graphite is still increasing as it is commonly used in the anodes of the Li-ion batteries (LIBs). The total graphite content for energy storage applications such as LIBs should be more than 99.95%. Several purification processes for natural graphite exist but the requirement of high purity is challenging. Here we present the high temperature thermal treatment for natural graphite ores. Thermal treatment at 2400 °C for 15 min can produce battery-grade graphite with high purity and crystallinity needed for the optimum performance of the battery cells. In addition, the crystallinity and crystalline structure of graphite was improved during the treatment. The electrochemical studies of thermally treated graphite powders showed increased electrochemical performance compared to the untreated graphite samples. The improved performance was attributed to the increased purity and crystallinity of the thermally treated powders. Graphical Abstract

Silicon, a material with high theoretical energy density, holds great promise as a candidate material for anodes in lithium-ion batteries. However, due to an alloying mechanism the material undergoes volume expansion of up to 300%, which results in rapid capacity fading. The coating of silicon with carbon is done by using a biomass-based carbon precursor. The effects of annealing temperature on the morphology of the silicon-carbon structures is presented herein. The mechanically and chemically treated barley straw is mixed with silicon particles and induction annealed in argon atmosphere under different temperatures. The material transformation from carbon-coated silicon (Si@C) to graphite-coated silicon carbide (SiC@graphite) is studied. The Si@C displayed initial specific capacity of 1200 mAh g ⁻¹ at 0.1 A g ⁻¹ , while the capacity retention analysis of Si@C revealed improved cycling stability compared to bare silicon.