Ultrahigh “relative energy density” and mass loading of carbon cloth anodes for K-ion batteries

Mass loading and potential plateau are the two most important issues of potassium (K)-ion batteries (KIBs), but they have long been ignored in previous studies. Herein, we report a simple and scalable method to fabricate acidized carbon clothes (A-CC) as high mass loading (13.1 mg cm⁻²) anode for KIBs, which achieved a reversible areal-specific capacity of 1.81 mAh cm⁻² at 0.2 mA cm⁻². Besides, we have proposed the concept of “relative energy density” to reasonably evaluate the electrochemical performance of the anode. According to our calculation method, the A-CC electrode exhibited an ultrahigh relative energy density of 46 Wh m⁻² in the initial charge process and remained at 40 Wh m⁻² after 50 cycles. Furthermore, we performed the operando Raman spectroscopy (ORS) to investigate the K-ion storage mechanism. We believe that our work might provide a new guideline for the evaluation of anode performance, thereby, opening an avenue for the development of commercial anode.