@article{6524, author = {Michael C Tucker and Lenz Kroeck and Jeffrey A Reimer and Elton J Cairns}, title = {The Influence of Covalence on Capacity Retention in Metal-Substituted Spinels ⁷Li NMR, SQUID, and Electrochemical Studies}, abstract = {

Variable-temperature\ $\ \ \ \ 7\ \ \ \ Li\\$ \ nuclear magnetic resonance and superconducting quantum interference device (NMR and SQUID) magnetometry have been used to determine the supertransferred hyperfine coupling constant, an indicator of Li-O-Mn bond covalence, for metal-substituted spinels,\ $\ \ LiM\\\ x\ \\ \ \ Mn\\\ 2\ \ \&$\#$x2212;\ \ x\ \\ \ \ O\ \ \ 4\ \ \ \$ \ $\ (\\M\\=\\Li\\,\\$ \ Zn, Al, Cr). The Curie and Weiss constants are reported for all compositions studied. The covalence of the Li-O-Mn bond is observed to increase upon substitution for all substituting metals studied. The greatest enhancement in covalence was achieved by substitution of ions that are similar in size to the\ $\ \ Mn\\\ 3.5\ \ +\ \\ \$ \ ion. The covalence values are compared to electrochemical capacity retention of the same compositions when cycled on the 4 V plateau. A positive correlation between the effectiveness of a particular substituent at improving capacity retention and the effectiveness of that substituent at enhancing covalency is observed. The bond covalence for\ $\ \ LiCr\\\ 0.175\ \\ \ \ Mn\\\ 1.825\ \\ \ \ O\ \ \ 4\ \ \ \$ \ remains unchanged upon electrochemical cycling, whereas that of\ $\ \ LiMn\\\ 2\ \\ \ \ O\ \ \ 4\ \ \ \$ increases with cycling.

}, year = {2002}, booktitle = {Journal of The Electrochemical Society}, journal = {Journal of The Electrochemical Society}, series = {Journal of The Electrochemical Society}, volume = {149}, number = {11}, pages = {A1409-A1413}, month = {09/2002}, doi = {10.1149/1.1510766}, language = {eng}, }