The present disclosure relates to over-lithiated positive electroactive materials for use within an electrochemical cell. For example, the electrochemical cell includes a positive electrode that includes an over-lithiated positive electroactive material that includes one of LixMn2O4 (where 1.05≤x≤1.30) and LiMn(2−x)NixO4 (where 0≤x≤0.5). The electrochemical cell can include a negative electrode that includes a silicon-containing negative electroactive material having a Columbic Efficiency greater than or equal to about 80% and less than or equal to about 90%.