High Mass Loading of Flowerlike Ni-MoS₂ Microspheres toward Efficient Intercalation Pseudocapacitive Electrodes

Abstract

This work reports the exploration of intercalation pseudocapacitance in a thicker electrode of flowerlike Ni-doped MoS₂ microspheres that features a mass loading of ~10 mg/cm² without sacrificing the gravimetric capacitance (~425 F/g at 5 mV/s). Integration of Ni atoms into MoS₂ microspheres not only stabilized the structural integrity but also ameliorated the rapid intercalation and deintercalation of electrolyte ions even at a commercial-level mass loading. The energy instability by Ni doping significantly changed the local bonding behavior and the overall electronic structure of MoS₂, facilitating the breaking of the MoS₂ layer and generation of more active edge sites, which are responsible for faster reaction kinetics. The experiments attribute the overall capacitance enhancement in (Mo-Ni)S₂ to the increased rate of electrolyte ion insertion and extraction, which is confirmed by b-values close to 0.5, at different potentials, indicating that the current response predominantly depends on the diffusive mechanism for both MoS₂ and Ni-MoS₂ thicker electrodes. The symmetric device constructed with Ni-MoS₂ microspheres exhibited a capacitance value of 101 F/g in 1 mV/s, for which the energy density is 9 Wh/kg, as well as attained an outstanding cycling stability of 10000 cycles with 60% retention at 2 A/g. In addition to providing insights into the development of 2D TMDs, this work explores the design of robust and highly efficient intercalation electrode material for electrochemical energy storage devices.