“Bubble-in-bowl” structured metal phosphide@N, P codoped carbon via bio-assisted combustion synthesis for high-performance potassium-ion hybrid capacitors in a wide temperature range

The kinetic imbalance between the battery-type anode and the capacitor-type cathode is a crucial issue for potassium-ion hybrid capacitors (PIHCs). Herein, novel “bubble-in-bowl” (BIB) structured transition metal phosphide (TMP)@N, P codoped carbon (NPC) is introduced as a fast and durable anode for PIHCs. The hollow nanobubbles are uniformly distributed in the bowl-like NPC framework to form the BIB structure. Each nanobubble is composed of a large amount of ultrafine TMP crystals wrapped in the NPC matrix. The dual carbon networks of the BIB structure are not only favourable for fast electron/ion transport, but also tolerant to volume expansion/contraction. Additionally, the strong interfacial interaction between TMP and NPC as well as the heteroatom codoping nature of the NPC matrix further promotes the kinetics and stability. For the first time, the CoP@NPC BIB composite is constructed via a facile and green strategy, where bio-combustion and bio-phosphoration synchronize. Moreover, the general application of this strategy in tailoring other kinds of TMPs, such as Ni2P and Fe2P, into the BIB structure is also demonstrated. Experiments and theoretical calculations collectively reveal the fast kinetics and high stability of CoP@NPC BIB for potassium-ion storage. Moreover, the PIHC full cell with the CoP@NPC BIB anode, bio-derived bowl-like carbon (MBC) cathode and polymer electrolyte achieves high energy/power density, long-life capability and high reliability in a wide temperature range. Therefore, this work not only provides a facile strategy to build efficient structures for ultrafast and durable anodes in PIHCs, but also gives a new clue to propel the development of advanced energy storage devices under extended working conditions.