Tissue-derived carbon microbelt paper: a high-initial-coulombic-efficiency and low-discharge-platform K+-storage anode for 4.5 V hybrid capacitors

Hard carbon (HC) is a promising anode material for K+-storage due to its randomly oriented turbostratic structure. However, most reported HC anodes exhibit low initial coulombic efficiency (ICE) and no obvious discharge platform during K+-intercalation/deintercalation, thus restricting their practical application. Herein, cheap and renewable sanitary tissue is utilized as the precursor to construct a flexible self-supporting hard carbon microbelt paper (HCMB). As a binder-free anode, the HCMB can achieve a high ICE value of 88% with a high charge capacity below 1 V (204 mA h g(-1) at 100 mA g(-1)), excellent rate capability (151 mA h g(-1) at 1000 mA g(-1)) and superior cycling stability in a conventional KPF6-based electrolyte. More importantly, the HCMB-based anodes exhibit a rather low discharge platform, which is close to a graphite anode (0.25 V vs. K/K+). To demonstrate its practical use, a novel 4.5 V potassium ion capacitor (PIC) device is successfully constructed based on the HCMB anode and an activated carbon cathode together with a gel polymer electrolyte. The energy density of this hybrid system is up to 152 W h kg(-1), and is still maintained as high as 112 W h kg(-1) at a high power density of 17 500 W kg(-1). In addition, the effect of the carbonization temperature on the K+-storage behavior of HCMB and its comparison with carbon counterparts (graphite and soft carbon) are systematically investigated.

Automated summary

Hard carbon microbelt paper (HCMB) prepared from cheap and renewable sanitary tissue as a binder-free anode exhibits high initial coulombic efficiency, excellent rate capability, and superior cycling stability. HCMB-based anodes demonstrate low discharge platform similar to graphite, suitable for potassium ion capacitors. Additionally, the effect of carbonization temperature on the K+-storage behavior of HCMB is systematically investigated and compared with graphite and soft carbon counterparts.