Study on the Insertion/desertion electrochemical behaviors of Lithium manganese oxide (LiMn_2O_4) in several neutral electrolytes

摘要

Lithium manganese oxide (LiMn_2O_4) has received huge research interests due to its highly reversible lithium insertion/desertion capacity, environmental friendly, low cost and rich in natural resources. This paper use commercial LiMn_2O_4as the active electrode material to study its different insertion/desertion electrochemical behavior in several neutral electrolytes like Li_2SO_4, Na_2SO_4,K_2SO_4, (NH_4)_2SO_4 and Mg(NO_3)_2 through Cyclic voltammetry (CV) and galvanostatic charge/discharge(CD). CV tests show that cations like Li~+, NH_4~+, Na~+, K~+, Mg~(2+)can insert/desert into the spinel structure of LiMn_2O_4 and there is a knee scan rate about 20 mV/s. below the knee scan rate, Li_2SO_4 presents the highest specific capacitance; up the knee scan rate, (NH_4)_2SO_4 presents the highest specific capacitance and the lowest capacitance fading properties. Besides, more space vacancies are waiting for the insertion of cations after charging to the set voltage and some holding time and "refresh" the capacitor using a totally new negative electrode and electrolyte, however, the specific capacitance is lower than the untreated specimen, this anomalous phenomenon is attributed to the competition of cations. Charge/discharge tests also confirm the advantages of (NH_4)_2SO_4-lower inner resistance, more linearly, and power properties responses, which all indicate the preference of using (NH_4)_2SO_4 as the electrolyte suit to the LiMn_2O_4-based supercapacitor.