Uncovering the Root Cause of Low Energy Efficiency in Lithium-Rich Cathode Materials

Asymmetric pathways in crystal structure change at the moment of charge/discharge reaction.

A research team from Japan has presented a surprising revelation about the voltage hysteresis in Li2RuO3, a high-energy-density rechargeable battery cathode material.

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It is   a collaboration between the National Institute for Materials Science (NIMS) and Softbank Corp. Contrary to conventional theory, the team discovered that voltage hysteresis results from differences in the intermediate crystalline phases formed during charge and discharge processes.

Li-rich electrode materials, that are known for their potential to store larger amounts of Li ions and having an energy capacity twice that of conventional cathode materials, have long been considered for the next-generation, high-energy-density Li-ion battery cathodes. However, their disavantage of charge/discharge energy efficiency due to significant voltage hysteresis has impeded their application. The research focused on Li2RuO3 as a model Li-rich electrode material, observing changes in its crystalline structure during charge and discharge. Surprisingly, the crystalline structure changed reversibly, recovering its initial pre-charge state by the end of discharge. Despite this, voltage hysteresis was evident in Li2RuO3, challenging the established understanding that irreparable crystalline structure changes cause this phenomenon.

 The reseachers identified a divergence in the intermediate crystal phase formed during charge and discharge processes as the cause of voltage hysteresis, suggesting different reaction pathways rather than irreversible structural changes. The research team plans to evaluate Li-rich electrode materials by focusing on chemical reaction pathways during charge and discharge cycles, alongside measuring voltage hysteresis.

The study, led by Marcela Calpa, Kei Kubota, Shoichi Matsuda, and Kazunori Takada at the NIMS-SoftBank Advanced Technologies Development Center, was published in Energy Storage Materials on November 6, 2023, Japan Time.

 This research symbolises a significant step towards the development and understanding of high-perfomance Li-ion battery cathodes for future energy storage solutions.

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