Lithium ions are the workhorse in many common battery applications, including electric vehicles. During operation, these ions move back and forth between the anode and cathode through an electrolyte as part of the battery’s charge-discharge cycle. A battery’s performance thus depends largely on the materials used in the electrodes and electrolyte, which need to be able to store and transfer many lithium ions in a short period – all while remaining electrochemically stable – so they can be recharged hundreds of times. Maximizing the performance of all these materials at the same time is a longstanding goal of battery research, yet in practice, improvements in one usually comes at the expense of the others.
“A typical trade-off lies in the storage capacity and rate capability of the electrode material,” co-team leader Hengxing Ji tells Physics World. “For example, anode materials with high lithium storage capacity, such as silicon, are usually reported as having low lithium-ion conductivity, which hinders fast battery [charging]. As a result, the increase in battery capacity usually leads to a long charging time, which represents a critical roadblock for more widespread adoption of EVs.”
New black phosphorus anode material
The anode in most lithium-ion batteries is made of graphite. Researchers led by Ji at USTC and Xiangfeng Duan at the University of California, Los Angeles, made their new anode material by combining graphite with black phosphorus. This 2D layered material had been considered before as a candidate for anodes, but tests showed that its electrochemical performance was far below its theoretical potential.
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