Electrochemical lithium extraction and insertion in has been investigated by high throughput cyclic voltammetry on an array of samples with different degrees of carbon coating to assist electron transfer. A linear decrease in the capacity was observed with an increase in the value of and was explained by a gradual loss of electronic conductivity due to the manganese substituent. Slow scan voltammograms show differences in peak shapes corresponding to a heterogeneous (two-phase) reaction in and a homogeneous (one-phase) reaction of iron in , illustrating a general interpretation of voltammograms to differentiate these mechanisms.