Nickel hydroxide (Ni(OH)(2)) has been regarded as a potential candidate for battery-type supercapacitor (BTSC) electrodes, but there is still a challenging task to improve its poor cycling life and low conductivity. In this work, a BTSC positive electrode material of Ni(OH)(2)/carbon nanosheets (CNS) was prepared during carbonization of the mixture of hydrothermal peach gum and magnesium acetate, followed by the ion-exchange between Ni2+ and Mg2+ in the resultant. The ion-exchange method avoids the high-temperature treatment, and the obtained Ni(OH)(2) on CNS has nanosheet-like morphology that possesses abundant active surface, facilitating rapid electrochemical charge/discharge process. More importantly, the coupling of CNS material can improve the electric conductivity and provide developed porosities for electrolyte diffusion. A BTSC device was fabricated using the optimized Ni(OH)(2)/CNS-4 composite as the positive electrode and the SNACNS reported in our previous work as the negative electrode, which shows satisfactory capacitive behavior (166 C g(-1)) and capacitance retention of 83.9% over continuous 5000 cycles. In addition, high energy density of 36.9 Wh kg(-1) and power density of 400 W kg(-1) have been implemented, which is superior to some BTSCs reported previously. Such an attractive performance indicates that Ni(OH)(2)/CNS-4 composite can be a potential candidate for electrochemical BTSCs. (C) 2019 Elsevier Inc. All rights reserved.