Compensating K Ions through an Organic Salt in Electrolytes for Practical K-Ion Batteries.

K-ion batteries face significant challenges due to a severe shortage of active K ions, with cathode materials typically containing less than 70% K ions and first-cycle irreversible reactions consuming up to 20% more. Conventional K-ion compensation methods fail to supply sufficient K ions without compromising cell integrity. To address this, we introduce potassium sulfocyanate (KSCN) as an electrolyte additive capable of delivering up to 100% active K ions. During initial charging, KSCN undergoes oxidative decomposition at 3.6 V, releasing active K ions and forming the cosolvent thiocyanogen ((SCN)2). This molecule, meeting diverse electrochemical properties, was identified using unsupervised machine learning and cheminformatics. The approach demonstrated full KSCN conversion and excellent compatibility with all cell components. The presence of (SCN)2 cosolvent enhanced the rate capability of anodes by promoting K-ion desolvation. In a hard carbon|K0.5Mg0.15[Mn0.8Mg0.05]O2 pouch cell, this approach tripled the capacity through supplying 58% active K ions, showcasing a practical solution for active K-ion compensation in K-ion batteries.