Modified anodes boost cell cycling
Researchers in South Korea have developed a new method of modifying conventional anodes to improve the cycling performance of a battery cell (writes Nick Flaherty).
The team, at the Gwangju Institute of Science and Technology, used a layer of graphene oxide – a single atomic layer of carbon – on a silicon anode to prevent irreversible volume change in the anode during the charge-discharge cycle.
During charging, lithium ions move from the cathode and combine with the nanoparticles in the anode. During discharging, the ions move back to the cathode. Over time, the nanoparticles in the anode crack and cluster together at the electrode-electrolyte interface. That causes an electrical disconnection, reducing the amount of charge the anode can store or transport.
The method developed by the researchers strengthens the anode by encapsulating the nanoparticles in an elastic web-like structure.
While the researchers used a silicon anode, the method is applicable to other anode materials, such as tin, antimony, aluminium and magnesium. The anodes can also be modified regardless of how they were manufactured, making it a universally applicable method for improving battery life.
The researchers used an anode containing silicon nanoparticles held together by a polyvinylidene fluoride polymer binder. They removed the binder by heating the anode using an annealing process and replaced it with a reduced graphene oxide (rGO) solution, which dried to form a web that held the silicon nanoparticles together and prevented them from cracking. This web also provides a conductive pathway for the electrons, allowing the nanoparticles to bind with lithium.
The rGO coating served as a seed layer for the deposition of a protective layer consisting of zinc oxide with magnesium and gallium metal oxides (MGZO) added to it. The MGZO layer provided structural stability to the anode.
Upon testing, the modified anode could retain most of its charge, even after several charge-discharge cycles. The structure retained a high storage capacity of 1566 mAh/g after 500 cycles and showed a 91% coulombic efficiency, which relates to the battery life.