19 January 2018
While lithium metal-based batteries are attractive in theory, practical applications have run into problems ranging from rapid degradation to catastrophic failure. Researchers have tried to overcome these problems by creating a ‘scaffold’ on which lithium ions can be deposited. However, as the volume of lithium ions changes during the charging cycle, expansion can destroy the scaffold.
Looking to solve this problem, Professor Jiaxing Huang and collaborators from Northwestern University have taken an approach which is said to make batteries lighter and able to hold more lithium. Their solution is based on a scaffold made from crumpled graphene balls. These can stack with ease to form a porous scaffold, not only preventing dendrite growth, but also coping with the stress generated by the fluctuating volume of lithium.
“One general philosophy for making something that can maintain high stress is to make it so strong that it’s unbreakable,” said Prof Huang. “Our strategy is based on an opposite idea. Instead of trying to make it unbreakable, our scaffold is made of loosely stacked particles that can readily restack.”
The balls are conductive, which allows lithium ions to flow rapidly along their surface, creating a continuously conductive network for lithium.
Compared to batteries that use graphite as the host material in the anode, Prof Huang’s solution is said to be lighter and to stabilise a higher load of lithium during cycling. Whereas typical batteries encapsulate lithium that is just tens of microns thick, Prof Huang’s battery is said to hold a 150µm high stack of lithium.