Unravelling gas evolution mechanisms in battery electrode materials

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium iron manganese phosphate (LiFe_xMn_1-xPO₄) offers improved battery safety, power density, and cost.
• Gas evolution in these batteries hinders cyclability and poses safety risks.
• Understanding gas evolution mechanisms is crucial for material enhancement.

Purpose of the Study:

• To investigate the mechanisms of gas evolution in LiFe_xMn_1-xPO₄-graphite full cells.
• To quantify gas production from both positive and negative electrodes.
• To develop strategies for mitigating gas evolution and improving battery performance.

Main Methods:

• Simultaneous quantification and probing of gas evolution from positive and negative electrodes in a LiFe_xMn_1-xPO₄-graphite full cell.
• Analysis of gas composition, identifying CO₂ and H₂ as primary components.
• Development and testing of LiFe_xMn_1-xPO₄ with a dense carbon layer coating.

Main Results:

• Over 90% of evolved gas was CO₂ and H₂.
• CO₂ originated from LiFe_xMn_1-xPO₄ via electrochemical and chemical side reactions.
• H₂ stemmed from graphite's solid-electrolyte interface reactions, linked to Mn/Fe ion dissolution.
• Carbon-coated LiFe_xMn_1-xPO₄ reduced metal ion dissolution by tenfold and minimized side reactions.
• A 4.1-Ah pouch cell achieved over 540 cycles with >90% capacity retention.

Conclusions:

• Identified key gas evolution pathways (CO₂ from LiFe_xMn_1-xPO₄, H₂ from graphite) and their origins.
• Demonstrated that a dense carbon coating effectively suppresses metal ion dissolution and side reactions.
• Achieved significantly enhanced cycling stability and performance in a practical battery cell format.