Unravelling gas evolution mechanisms in battery electrode materials

LiFe x Mn 1 − x PO 4 positive electrode materials show significant potential for enhancing battery safety, power density and cost-effectiveness. However, gas evolution shortens the cyclability and raises additional safety concerns, presenting a major challenge. The gas evolution mechanisms in LiFe x Mn 1 − x PO 4 batteries are poorly understood, impeding the material improvement efforts. Here we examine a LiFe x Mn 1 − x PO 4 -graphite full cell, simultaneously quantifying and probing gas evolution from positive and negative electrodes. We found over 90% of the evolved gas was composed of CO 2 and H 2 . CO 2 originated from side reactions at LiFe x Mn 1 − x PO 4 , with almost equal contributions from electrochemical and chemical pathways. H 2 resulted from chemical side reactions at the graphite’s solid–electrolyte interface and was closely associated with the dissolution of Mn/Fe ions from the LiFe x Mn 1 − x PO 4 . We developed a LiFe x Mn 1 − x PO 4 with a dense carbon layer coating, which inhibited metal ion dissolution by an order of magnitude and minimized side reactions at both electrodes. A 4.1-Ah pouch cell exhibited stable performance over 540 cycles with over 90% capacity retention.