Boosting capacitive storage of cathode for lithium-ion capacitors: Combining pore structure with P-doping

Abstract

The capacity mismatch resulted from the low capacity of capacitor-type cathode restricts the energy-power characteristics of lithium-ion capacitors (LICs). Optimizing the pore structure and heteroatom doping are effective methods to boost the capacitive storage of carbon cathode. Herein, the P-doped activated carbon (PAC-6) is synthesized by carbonizing cross-linked precursor acquired from starch and phytic acid (PA), in which PA plays a bifunctional role: activation reagent and P dopant. As-prepared PAC-6 shows a large specific surface area (1488 m2g−1) with appropriate pore structure and high P content (3.57 at%). Significantly, the large pore volume in 1.25–3 nm endows the balance of capacity and rate capability, which not only provides plentiful sites for ions adsorption/desorption, but also facilitates rapid transport of ions. Moreover, the pseudocapacitance could be enhanced by P-doped. As a result, PAC-6 exhibits a high specific capacitance of 147.1 F g−1 at 0.05 A g−1 with superior rate capability (76 F g−1 at 6.4 A g−1) and 90% capacity retention after 5000 cycles at 1.6 A g−1. Furthermore, PHC-4//PAC-6 LIC fabricated with pre-lithiated P-doped hard carbon (PHC-4) anode and PAC-6 cathode delivers outstanding energy-power characteristics (maximum 122 Wh kg−1, 9775 W kg−1).