Researchers at Rice University, Texas, have developed a relatively soft and flexible material that could offer a new approach to solid-state battery electrolytes by combining selective lithium-ion transport with greater mechanical adaptability.
The material, known as ZnBTCA, is a metal-organic framework (MOF) made from metal atoms connected by organic molecules. Its porous structure contains ordered channels that can be tailored to transport specific ions.
Unlike many MOFs investigated for battery electrolytes, which use rigid aromatic linkers, ZnBTCA incorporates a flexible aliphatic linker. This makes the framework softer while retaining a negatively charged structure that favours the movement of positively charged lithium ions. The material also uses relatively abundant and low-cost components, including zinc.
“MOF electrolytes are often designed primarily around how effectively they transport ions,” said first author Zina Deriche, a graduate student in chemical and biomolecular engineering at Rice. “Here, we’re showing that the mechanical properties of the framework can also be an important part of the design.”
Testing found that after sodium ions were exchanged for lithium, around 95% of the mobile charge-balancing ions were lithium, while the framework remained structurally intact. Lithium ions also carried about 79% of the ionic current through the material.
The researchers incorporated ZnBTCA into a solid electrolyte membrane positioned between two lithium-metal electrodes. The cells operated stably for nearly 300 hours as current was progressively increased, with no evidence of short-circuiting under the conditions tested.
The findings suggest mechanical flexibility could become another consideration in the design of MOF electrolytes alongside chemical composition, pore structure and charge.
“What this work shows is that we can think beyond just the chemistry and pore structure of these materials. Mechanical flexibility can also become a design tool for developing MOF electrolytes for solid-state batteries,” said Sibani Lisa Biswal, chair of chemical and biomolecular engineering at Rice.
The research was published in the journal Chemical Science.
Image: Dr Sibani Lisa Biswal. Credit: Rice.
