Silicon oxide (SiO_x, 0 < x ≤ 2) has been recognized as a prominent anode material in lithium-ion batteries and sodium-ion batteries due to its high theoretical capacity, suitable electrochemical potential, and earth abundance. However, it is intrinsically poor electronic conductivity and excessive volume expansion during potassiation/depotassiation process hinder its application in potassium-ion batteries. Herein, we reported a hierarchical porous C/SiO_x potassium-ion batteries anode using lignite as raw material via a one-step carbonization and activation method. The amorphous C skeleton around SiO_x particles can effectively buffer the volume expansion, and improve the ionic/electronic conductivity and structural integrity, achieving outstanding rate capability and cyclability. As expected, the obtained C/SiO_x composite delivers a superb specific capacity of 370 mAh g⁻¹ at 0.1 A g⁻¹ after 100 cycles as well as a highly reversible capacity of 208 mAh g⁻¹ after 1200 cycles at 1.0 A g⁻¹. Moreover, the potassium ion storage mechanism of C/SiO_x electrodes was investigated by ex-situ X-ray diffraction and transmission electron microscopy, revealing the formation of reversible products of K_6.8Si_45.3 and K₄SiO₄, accompanied by generation of irreversible K₂O after the first cycle. This work sheds light on designing low-cost Si-based anode materials for high-performance potassium-ion batteries and beyond.

Organic redox compounds are attractive cathode materials in aqueous zinc-ion batteries owing to their low cost, environmental friendliness, multiple-electron-transfer reactions, and resource sustainability. However, the realized energy density is constrained by the limited capacity and low voltage. Herein, copper-tetracyanoquinodimethane (CuTCNQ), an organic charge–transfer complex is evaluated as a zinc-ion battery cathode owing to the good electron acceptation ability in the cyano groups that improves the voltage output. Through electrochemical activation, electrolyte optimization, and adoption of graphene-based separator, CuTCNQ-based aqueous zinc-ion batteries deliver much improved rate performance and cycling stability with anti-self-discharge properties. The structural evolution of CuTCNQ during discharge/charge are investigated by ex situ Fourier transform infra-red (FT-IR) spectra, ex situ X-ray photoelectron spectroscopy (XPS), and in situ ultraviolet visible spectroscopy (UV–vis), revealing reversible redox reactions in both cuprous cations (Cu⁺) and organic anions (TCNQ^x-1), thus delivering a high voltage output of 1.0 V and excellent discharge capacity of 158 mAh g⁻¹. The remarkable electrochemical performance in Zn//CuTCNQ is ascribed to the strong inductive effect of cyano groups in CuTCNQ that elevated the voltage output and the graphene-modified separator that inhibited CuTCNQ dissolution and shuttle effect in aqueous electrolytes.