Electrochemical proton insertion in manganese spinel oxides from aqueous borate solution

We report the proton insertion in LiMn2O4 and Li0.32Mn2O4 compounds with th e spinel structure in berate buffer at pH 9.5. LiMn2O4 exhibits a quasi-vol tage 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 fir st cycle leads to new electrochemical features for the subsequent cycles wi th a reversible behavior and S shaped discharge-charge curves (mean dischar ge 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. Th is new system can be observed from the first cycle when H+ insertion direct ly proceeds in the chemically delithiated oxide Li0.32Mn2O4. In both cases, galvanostatic cycling experiments (C/25 rate) show a stable specific capac ity of 100-110 Ah kg(-1) is available near 0.1 V over 20 cycles. (C) 1999 E lsevier Science Ltd, All rights reserved.