Schematic of flexible lithium-ion conducting ceramic fibrous textile, which retains the physical characteristics of the original fabric template. The unique structure enables long-range lithium-ion transport pathways via continuous fibers, high surface/volume ratio of solid ion conductors, and multilevel porosity.
(a) Scanning electron microscopy (SEM) image of pretreated textile template; (b) SEM image of template impregnated with precursor solution; (c) SEM image of garnet textile; (d) model of garnet textile flatness from 3D laser scanning; (e) flexibility, workability, and solvent tolerance of garnet textile.
3D garnet textile electrode architecture for lithium-sulfur batteries: (a) photo of garnet textile sintered onto dense supporting electrolyte; (b) SEM image of sulfur cathode infiltrated garnet textile electrode architecture.State-of-the-art lithium-ion batteries have revolutionized electronics and transport, providing host of devices with a mobile power source. But despite their success, lithium-ion batteries can explode or catch fire because of the flammable liquid electrolytes on which they rely. A safer alternative is solid-state batteries that employ solid electrolytes.
Now a team from the University of Maryland has designed a novel solid-state battery based on a lithium-ion conducting ceramic textile [Gong et al., Materials Today (2018), doi: 10.1016/j.mattod.2018.01.001].
“We used simple commercial fabric as a template to make lithium-ion conducting garnet fiber mat textiles and then filled the pore space between fibers with a solid polymer electrolyte,” explains Eric D. Wachsman, who led the research.
Crystalline garnet-like structures (with the chemical formula Li7La3Zr2O12) are one of the most promising solid conductors because their cubic structure rapidly conducts lithium ions and they have high chemical stability, from lithium metal to high voltage cathodes. To create a garnet ‘textile’, the researchers simply soaked cellulose-based textiles in a garnet precursor solution, following by firing (or calcination) in a furnace at various temperatures. The sintering process burns off the textile template, leaving behind the garnet, which retains the structural characteristics of the fabric including interwoven fibers separated by interconnected pores. The pores can be easily impregnated with a lithium ion/polymer mixture. The garnet textile simultaneously provides a three-dimensional conducting framework for lithium ions and a physically robust support for the polymer electrolyte.
“The structure has ability to enable fast ion conduction through the continuous ceramic fibers but at same time as providing the flexibility and ability to use roll-to-roll processing of more traditional polymer electrolytes,” points out Wachsman.
Conventional batteries use liquid electrolytes, which are prone to shorting because of the formation of lithium dendrites during operation. Polymer electrolytes help block dendrite formation because they are harder, but ceramic electrolytes are even harder and, therefore, more effective.
“The issue with polymers is their low conductivity and chemical instability in contact with lithium metal. By contrast, garnet ceramics have much higher conductivity and are stable in contact with lithium metal, but are inflexible. Our hybrid provides the best properties for all,” says Wachsman.
Prototype electrodes constructed from the garnet textile for lithium-sulfur batteries achieve very high sulfur loading of 10.8 g/cm2 and stable cycling of lithium over 500 hours, the researchers report.
Wachsman and his group are taking the technology forward and are now working on making the textile thinner to reduce resistance to ionic transport and optimizing the densification process to increase the garnet phase volume fraction.