Unravelling gas evolution mechanisms in battery electrode materials

LiFe_xMn_1-xPO₄ 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_xMn_1-xPO₄ batteries are poorly understood, impeding the material improvement efforts. Here we examine a LiFe_xMn_1-xPO₄-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 CO₂ and H₂. CO₂ originated from side reactions at LiFe_xMn_1-xPO₄, with almost equal contributions from electrochemical and chemical pathways. H₂ 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_xMn_1-xPO₄. We developed a LiFe_xMn_1-xPO₄ 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.