Rhus typhina wood-based biochar electrodes for high effective potassium storage capacity

With the growing demand for secondary energy storage, potassium-ion batteries have garnered significant attention. However, the radius of potassium ions is too large, and the intercalation and detachment during charging and discharging will cause damage to the material structure. Therefore, the design and preparation of anode materials with high capacity and stability is the key to the development of potassium-ion batteries. Biomaterial has a significant place in energy storage for its utilization of renewable and cost-effective advantages. In this work, biomass branches are applied to serve as an inexpensive carbon precursor to fabricate porous carbon microstructure via hydrothermal treatment and a two-step activation method. The pore structure characteristics of the carbon were tuned by adjusting the activator ratio. This results in a porous structure with high conductivity, which is suitable for the rapid diffusion of potassium ions. The activated CK-1:4 successfully constructed a large number of mesoporous and microporous structures on the surface of the biochar by SEM and TEM tests, providing more active sites for the storage of potassium ions. When used as a PIB anode, CK-1:4 has a high reversible capacity of 108.4 mAh g⁻¹ at 0.2 C and stable cycling performance (at a high current density of 0.2 C, it still exhibits an ultra-long cycling stability with a discharge capacity of 62.4 mAh g⁻¹ after 1000 cycles). The in-depth electrochemical potassium storage mechanism is elaborated, which mainly relies on the capacitance-controlled contribution, further revealing the rapid reaction kinetics. In summary, the application of activated porous biochar materials to potassium-ion batteries can significantly improve the cycling performance of potassium-ion batteries. The results provide a new efficient and low-cost route for the development of anode materials for potassium-ion batteries.