Extraction of lithium from spinel phases of the system Li1+xMn2-xO4-δ

The process of chemical lithium extraction from the spinel phase Li1+xMn2-xO4-delta was studied for 0 less than or equal to x less than or equal to 0.33 in acidic medium (H2SO4/H2O) and Br-2/CH3CN as proton-free extraction liquid. From a comparison of the quantitative results of chemical delithiation with the electrochemical performance there follows a subdivision into three regions. In region I (0 less than or equal to x less than or equal to 0.05) the extraction products are multiphase due to a pronounced lattice instability. The electrochemical performance is unsatisfying. The best materials for cathodes in rechargeable Li-ion batteries are situated in region II (0.05 less than or equal to x less than or equal to 0.2). All extraction products are single phase due to an improved lattice stability. In region III (0.2 less than or equal to x less than or equal to 0.33) the capacity is too low for practical applications. All materials are oxygen deficient and show a strong tendency for an ion exchange Li+ <-> H+ in protonic solvents. In acidic media, the Hunter mechanism is obeyed for x = 0. With increasing x this model is suppressed in favour of a Li+ <-> H+ exchange. (C) 1997 Elsevier Science S.A.