Universal one-step graphitization of silicon-enriched biomass-derived carbon in molten salts for lithium-ion battery anodes

Abstract

With the increasing demand for global carbon reduction strategies, there is growing attention on the development of renewable energy sources and the sustainable utilization of resources. Given the complex production process and high energy consumption associated with graphite as the anode material in commercial lithium-ion batteries, this paper presents a low-cost, short-process, and sustainable alternative. The study aims to valorize agricultural waste, utilizing the commonly available and abundant wheat straw, rice straw, and corn stalks as raw materials. Within a K₂CO₃–Na₂CO₃ molten salt system, by regulating the voltage and electrolysis time, amorphous carbon materials are directly converted into layered graphite in a single step. Notably, graphitization is achieved under the electrolysis conditions of K₂CO₃–Na₂CO₃, simultaneously removing silicon dioxide impurities (T = 850 °C; SiO₂ + Na₂CO₃ = Na₂SiO₃ + CO₂; ΔG = −66.57 kJ). Moreover, the porous structure formed by the removal of silicon dioxide facilitates the migration of O²⁻ ions, thereby accelerating the graphitization process. In lithium-ion battery tests, both the graphite anode and the silicon–carbon anode exhibit superior specific capacities to their commercial counterparts (graphite anode: 293 mA h g⁻¹ at 0.1 A g⁻¹ vs. commercial graphite: 287.8 mA h g⁻¹ at 0.1 A g⁻¹; silicon–carbon anode: 1954 mA h g⁻¹ at 0.1 A g⁻¹ vs. commercial silicon: 1500 mA h g⁻¹ at 0.1 A g⁻¹), and the silicon–carbon anode also demonstrates a significantly higher capacity retention rate than commercial silicon anodes. In summary, this work offers a high-value utilization pathway for silicon-containing agricultural waste and provides a low-cost, short-process, and sustainable strategy for the preparation of graphite anodes for lithium-ion batteries.