Carbon-reinforced Ni₃S₂/Ti₃C₂T_x MXene composite as an anode for superior-performance lithium-ion capacitors

Lithium ion capacitors (LICs) are a new generation of energy storage devices that combine the super energy storage capability of lithium ion batteries with the satisfactory power density of supercapacitors. The development of high-performance LICs still faces great challenges due to the unbalanced reaction kinetics at the anode and cathode. Therefore, it is an inevitable need to enhance the electron/ion transfer capability of the anode materials. In this paper, to obtain a superior-rate and high-capacity Ni₃S₂-based anode, highly conductive Ti₃C₂T_x MXene sheets were introduced to sever as the carrier of Ni₃S₂ nanoparticles and simultaneously an amorphous carbon layer which coats onto the surface of Ni₃S₂ nanoparticles was in-situ generated by the carbonization of dopamine reactant. The as-synthesized Ni₃S₂/Ti₃C₂T_x/C composite exhibits a high specific surface area (112.6 m²/g) because of the addition of Ti₃C₂T_x that can reduce the aggregation of Ni₃S₂ nanoparticles and the in-situ generated amorphous carbon layer that can suppress the growth of Ni₃S₂ nanoparticles. The Ni₃S₂/Ti₃C₂T_x/C anode possesses a remarkable reversible discharge specific capacity (626.0 mAh/g under 0.2 A/g current density), which increases to 1150.8 mAh/g after 400-cycle charge/discharge measurement at the same measurement condition indicating eminent cyclability, along with superior rate capability. To construct a superior-performance LIC device, a sterculiae lychnophorae derived porous carbon (SLPC) cathode with an average discharge specific capacity of 73.4 mAh/g@0.1A/g was prepared. The Ni₃S₂/Ti₃C₂T_x/C//SLPC LIC device with optimal cathode/anode mass ratio has a satisfactory energy density ranging from 32.8 to 119.1 Wh kg^-1 at the corresponding power density of 8799.4 to 157.5 W kg^-1, together with a prominent capacity retention (95.5 %@1 A/g after 10,000 cycles).