Electrochemical proton insertion in manganese spinel oxides from aqueous borate solution

We report the proton insertion in LiMn2O4 and Li0.32Mn2O4 compounds with the spinel structure in borate buffer at pH 9.5. LiMn2O4 exhibits a quasi-voltage plateau near -0.2 V and a second one around -0.35 V/Hg/HgO. The charge process results in a single step in the voltage range 0.1/0.8, V. This first cycle leads to new electrochemical features for the subsequent cycles with a reversible behavior and S shaped discharge-charge curves (mean discharge potential = +0.1 V) in the voltage window 0.75/-0.5 V. The proton uptake involved during insertion corresponds to a faradaic yield of 0.45 F/Mn. This new system can be observed from the first cycle when H+ insertion directly proceeds in the chemically delithiated oxide Li0.32Mn2O4. In both cases, galvanostatic cycling experiments (C/25 rate) show a stable specific capacity of 100-110 Ah kg(-1) is available near 0.1 V over 20 cycles. (C) 1999 Elsevier Science Ltd, All rights reserved.