With an aim to develop a better understanding of the capacity fade mechanisms of manganese spinel oxide cathodes, the amount of metal ion dissolution from various lithium ion battery cathodes ͑layered, orthorhombic LiMnO 2 , 4 V spinel, 5 V spinel, and olivine͒ is compared. Orthorhombic LiMnO 2 , layered LiMn 0.8 Cr 0.2 O 2 , and spinel LiMn 2 O 4 containing Mn 3+ exhibit much higher amounts of manganese dissolution irrespective of the structure compared to the total transition metal ion dissolution found from cathodes containing Mn 4+ , such as layered LiNi 1/3 Mn 1/3 Co 1/3 O 2 and 5 V spinel LiMn 1.5 Ni 0.5 O 4 or from layered LiCoO 2 and olivine LiFePO 4 . However, the manganese dissolution from the Mn 3+ -containing spinel oxides could be lowered significantly to the levels found from LiCoO 2 , LiFePO 4 , and LiMn 1.5 Ni 0.5 O 4 by appropriate cationic and anionic ͑fluorine͒ substitutions, which leads to excellent capacity retention at elevated temperatures. For example, LiMn 1.85 Li 0.075 Ni 0.075 O 4 and LiMn 1.85 Li 0.075 Ni 0.075 O 3.94 F 0.06 exhibit manganese dissolutions of 1.5 and 1.1%, respectively, compared to 3.2% for LiMn 2 O 4 . Furthermore, manganese dissolution is found to bear a clear relationship to the lattice parameter difference ⌬a between the two cubic phases formed during the charge-discharge process; Mn dissolution decreases with decreasing ⌬a.Lithium ion batteries have become attractive for portable electronic devices such as cell phones and laptop computers due to their higher energy density compared to other rechargeable systems. However, the high cost, toxicity, and safety issues associated with the currently used layered LiCoO 2 cathode remain as an impediment for employing the lithium ion battery technology for electric vehicles ͑EV͒ and hybrid electric vehicles ͑HEV͒. In this regard, spinel LiMn 2 O 4 is appealing as Mn is inexpensive and environmentally benign and the Mn 3+/4+ couple is chemically more stable with good safety characteristics compared to the Co 3+/4+ couple. Also, the high rate capability of spinel oxides makes them attractive for EV and HEV applications.However, LiMn 2 O 4 is plagued by severe capacity fade at elevated temperatures. The capacity fade has been attributed to several mechanisms such as the formation of tetragonal Li 2 Mn 2 O 4 on the surface due to Jahn-Teller distortion at the end of discharge, 1-3 electrochemical reaction with the electrolyte at high voltages, 4,5 loss of crystallinity during cycling, 6,7 cation mixing between the lithium and manganese sites in the spinel lattice, 8 formation of oxygen-deficiency, 9 formation of two cubic phases with a large difference in lattice parameter during the charge-discharge process, 10-13 instability of the two-phase structure in the charged state resulting in a loss of MnO to form a more stable single-phase structure, 14-17 and manganese dissolution from the lattice into the electrolyte due to the disproportionation of Mn 3+ ͑into Mn 2+ and Mn 4+ ͒ caused by trace amounts of hydrofluoric acid ͑HF͒ pre...
