Lithiation-induced controllable vacancy engineering for developing highly active Ni3Se2 as a high-rate and large-capacity battery-type cathode in hybrid supercapacitors

The poor rate capability and low capacity are huge barriers to realize the commercial applications of battery-type transition metal compounds (TMCs) cathode. Herein, numerous Se vacancy defects are introduced into the Ni3Se2 lamellas by pre-lithiation technique, which can be acted as a novel class of battery-type cathode for hybrid supercapacitors. Appropriately modulating the contents of the pre-embedded lithium (Li) ions can induce a controllable vacancy content in the series of as-prepared products, effectively endowing a fast reaction kinetic and high activity for the cathode. Benefiting from the distinct design, the optimized cathode (Li2-Ni3Se2) presents a high specific capacity of 236 mA h g−1 at 1 A g−1, importantly, it can still possess 117 mA h g−1 when the current density is increased up to 100 A g−1, exhibiting relatively high rate capability. It is much superior to other battery-type TMC cathodes reported in previous studies. Moreover, the cathode also shows the excellent cycling stability with 92% capacity retention after 3,000 cycles. In addition, a hybrid supercapacitor (HSC) is assembled with the obtained Li2-Ni3Se2 as the cathode and active carbon (AC) as the anode, which delivers a high energy density of 77 W h kg−1 at 4 kW kg−1 and long-term durability (90% capacitance retention after 10,000 cycles). Therefore, the strategy not only provides an effective way to realize the controllable vacancy content in TMCs for achieving high-performance cathodes for HSC, but also further promotes their large-scale applications in the energy storage fields.