Electrochemical studies of LiMnPO4 as aqueous rechargeable lithium–ion battery electrode

Abstract

A study of the electrochemical behavior of LiMnPO4 prepared by RAPET method in different aqueous electrolytes using cyclic voltammetry (CV), galvanostatic charge–discharge experiments, and electrochemical impedance spectroscopy is reported. CV peak current is proportional to the square root of scan rate under 0.2 mV s−1. The system satisfied the required conditions for a reversible system with a resistive behavior. LiMnPO4 was found to undergo proton insertion at lower concentrations of electrolyte. At higher concentrations or saturated solutions of electrolytes, lithium insertion/de-insertion becomes the main reaction though the effect of proton insertion/de-insertion reaction cannot be ignored. Electrochemical insertion/de-insertion of lithium in LiMnPO4 was studied using EIS technique. The kinetic parameter, charge transfer resistance (R ct), obtained by simulating the experimental impedance data with an equivalent circuit showed a minimum at the potential close to the CV peak potential. The cell LiTi2(PO4)3/5 M LiNO3/LiMnPO4 delivers a discharge capacity of 84 mAh g−1 in the first cycle at an applied current of 0.2 mA cm−2 and it retains its initial capacity over 50 cycles with good rate capability.