The new ternary alkali metal copper chalcogenide KCu4Se8 nanowires with average length of 30 mu m are synthesized using a modified composite-hydroxide mediated (M-CHM) approach. The prepared KCu4Se8 is characterized by XRD, EDS, FESEM and TEM analysis. The structure is determined by the newly developed Rotation Electron Diffraction technique. It is identified to be a body center tetragonal phase. The prepared KCu4Se8 is used to fabricate solid-state supercapacitors in which the thin film of the electrodes are made with pressure of 0 MPa, 5 MPa and 10 MPa, and their electrochemical properties are tested. It is found that 0 MPa supercapacitor displays best electrochemical performance and the specific capacitance of 25.3 F g(-1) is obtained at the scan rate of 5 mV s(-1). It also shows good long-term cycle property by recording 5000 cycles of galvanostatic charge/discharge operation. The specific capacitance can be enhanced to 93.7 F g(-1) at the scan rate of 5 mV s(-1) by coating 0.1 mg V2O5 nanowire on 0 MPa KCu4Se8 electrode. (C) 2014 Elsevier B.V. All rights reserved.