Instantaneous Activation of NiCl2 Cathode towards Thermal Battery by Constructing NiCl2–NiO Heterojunction

The application of nickel chloride (NiCl2) in thermal battery has been restrained for its poor electronical conductivity, which causes the voltage delay at the initial discharging process. In this research, a convenient oxygen etching method is put forward to construct a NiCl2–NiO heterojunction interface and improve its intrinsic conductivity. As the cathode for thermal battery, the activation time of pristine NiCl2 nanosheets (NNs) is up to 7.8 s, whereas NiCl2 nanosheets etched by oxygen for 5 min (OENNs-5) exhibit the performance of instantaneous activation and rapid response. Additionally, the remission of ohmic polarization caused by conductivity optimization generates the reduction of the initial total polarization (0.09 Ω) to 36% of that of pristine nanosheets. Density functional theory (DFT) calculations demonstrate continuous electron occupation at the Fermi-level in oxygen etching NiCl2 nanosheets (OENNs). Electrons are concentrated around the NiCl2 layer and are depleted from the NiO layer in the NiCl2–NiO heterojunction, resulting in the formation of a p-type doped NiCl2. The shortened band gap is a result of the bent band in the heterojunction, lowering the barrier for electronic transition. This research provides a simply equipped strategy for enhancing semiconductor material conductivity.