Solid‐State Electrochemical Thermal Switches with Large Thermal Conductivity Switching Widths

Abstract Thermal switches that switch the thermal conductivity (κ) of the active layers are attracting increasing attention as thermal management devices. For electrochemical thermal switches, several transition metal oxides (TMOs) are proposed as active layers. After electrochemical redox treatment, the crystal structure of the TMO is modulated, which results in the κ switching. However, the κ switching width is still small (<4 W m⁻¹ K⁻¹). In this study, it demonstrates that LaNiO_x‐based solid‐state electrochemical thermal switches have a κ switching width of 4.3 W m⁻¹ K⁻¹. Fully oxidized LaNiO₃ (on state) has a κ of 6.0 W m⁻¹ K⁻¹ due to the large contribution of electron thermal conductivity (κ_ele, 3.1 W m⁻¹ K⁻¹). In contrast, reduced LaNiO_2.72 (off state) has a κ of 1.7 W m⁻¹ K⁻¹ because the phonons are scattered by the oxygen vacancies. The LaNiO_x‐based electrochemical thermal switch is cyclable of κ and the crystalline lattice of LaNiO_x. This electrochemical thermal switch may be a promising platform for next‐generation devices such as thermal displays.