EXTRACTION OF LITHIUM FROM SPINEL PHASES OF THE SYSTEM LI1-XO4-DELTA(XMN2)

The process of chemical lithium extraction from the spinel phase Li1+x Mn2-xO4-delta was studied for 0 less than or equal to x less than or e qual to 0.33 in acidic medium (H2SO4/H2O) and Br-2/CH3CN as proton-fre e extraction liquid. From a comparison of the quantitative results of chemical delithiation with the electrochemical performance there follo ws 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 multipha se due to a pronounced lattice instability. The electrochemical perfor mance is unsatisfying. The best materials for cathodes in rechargeable Li-ion batteries are situated in region II (0.05 less than or equal t o x less than or equal to 0.2). All extraction products are single pha se 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. I n acidic media, the Hunter mechanism is obeyed for x = 0. With increas ing x this model is suppressed in favour of a Li+ <-> H+ exchange. (C) 1997 Elsevier Science S.A.