Study On Electrochemical Performance Of Ni-Mn Based Electrode Materials For Aqueous Supercapacitor

As electrode materials of supercapacitors,binary metal oxides have higher electrochemical performance than single metal oxides.Nickel manganese based composite nanomaterials have attracted more and more attention due to their low price and high theoretical capacity.However,the low conductivity of oxides limits their electrochemical performance,and the problems such as low actual capacitance,poor rate performance and narrow potential window also limit their development as supercapacitors.In this paper,in order to improve the conductivity,specific capacitance,working potential window and energy density of supercapacitors,carbon cloth composite self-supported Ni-Mn based electrodes are prepared by hydrothermal and annealing methods.The main conclusions are as follows:（1）Firstly,nickel manganese oxide precursors（NMO@ACC）are grown in situ on activated carbon cloth by solvothermal method and annealing treatment.And then through a method of low-temperature lithium,directly converting the NMO@ACC into LiNi_0.5Mn_1.5O₄（LNMO@ACC）at 200℃.The electrochemical test results show that the areal capacitance after lithium is 1.8 times of that before lithium,reaching 1468 m F cm^-2at 1 m A cm^-2,which shows excellent performance compared with the similar materials.Furthermore,the capacitance of LNMO@ACC is still maintained 82.5%after 4000cycles.Then we find that the charge storage mechanism of LNMO@ACC is mainly dominated by capacitive process after studying the relationship between peak current and scanning speed.In addition,density functional theory（DFT）calculations show that Li⁺has smaller adsorption energy and lower diffusion barrier on the（111）surface than on the（400）surface of LiNi_0.5Mn_1.5O₄.Finally,the LNMO//Fe₂O₃ aqueous asymmetric supercapacitor is successfully assembled,and a wide potential window of 1.8V is achieved with a volume energy density of 5.87 m Wh cm^-3,which provides a reference for the selection of positive and negative electrode materials for ASC.（2）By optimizing the composition,we find that Ni₆Mn O₈-Mn CO₃ mixed electrode with Ni/Mn molar ratio of 1（NMO-2@ACC）has the best electrochemical performance.At a current density of 2 m A cm^-2,the specific capacitance of NMO-2@ACC is 1450 m F cm^-2 and remains 80.7%after 5000 cycles.Through electrochemical test,we find that NMO-2@ACC electrode also has excellent electrochemical performance under the negative potential window of-0.8-0 V.When the aqueous symmetrical supercapacitor is assembled,two series devices can continue to light up 72 LED lights for more than 2minutes,which indicates that the materials as an energy storage device has a very good application prospect.