A Four-Electron-Transfer Robust Small-Molecule Organic Anode for Low-Strain Potassium Storage

Potassium-ion batteries (PIBs) are promising for large-scale energy storage owing to abundant potassium resources. However, their development is constrained by the lack of high-capacity and durable anodes capable of accommodating the large-radius K⁺. Herein, a small-molecule organic compound, 2,2'-bipyridine-4,4'-dicarboxylic acid (BDA), is presented as a promising anode for PIBs. The cooperative multielectron redox activity of the carbonyl and imine moieties affords a high reversible capacity, while the conjugated framework and dense molecular packing strengthen the structural stability. Consequently, BDA delivers a specific capacity of 398 mAh g^-1 at 100 mA g^-1 and retains 186 mAh g^-1 after 1000 cycles at 1000 mA g^-1. Combined in situ/ex situ characterizations and theoretical calculations reveal that pristine BDA undergoes an irreversible deprotonation/potassiation during the initial discharge, generating an activated K₂BDA phase. The subsequent reversible K-storage is dominated by the carbonyl and imine sites, and involves only minor lattice variation, which accounts for the low volume fluctuation and outstanding cycling stability. In addition, an all-organic PIB assembled with a pre-potassiated BDA anode and a PTCDA cathode delivers a high energy density of 174 Wh kg^-1 (based on the mass of both electrodes). This study establishes a viable small-molecule organic anode for high-performance PIBs.