Cathode materials for batteries
Researchers using the HP-CAT 16-ID-B beamline at the APS are exploring potential cathode materials for rechargeable lithium batteries.
Pressure-induced polymerization of triple bonds would produce conductive conjugated double bonds. To find a metal cyanide with a low polymerization pressure, anhydrous Li3Fe(CN)6 is synthesized and its crystal structure is determined. The irreversible bonding between the CN− can be realized by use of the industrial apparatus. The conductivity is enhanced by more than 3 orders of magnitude, which makes the polymerized Li3Fe(CN)6 a potential cathode material for rechargeable lithium batteries.
Pressure-induced polymerization of charged triple-bond monomers like acetylide and cyanide could lead to formation of a conductive metal–carbon network composite, thus providing a new route to synthesize inorganic/organic conductors with tunable composition and properties. The industry application of this promising synthetic method is mainly limited by the reaction pressure needed, which is often too high to be reached for gram amounts of sample. Here we successfully synthesized highly conductive Li3Fe(CN)6 at maximum pressure around 5 GPa and used in situ diagnostic tools to follow the structural and functional transformations of the sample, including in situ X-ray and neutron diffraction and Raman and impedance spectroscopy, along with the neutron pair distribution function measurement on the recovered sample.
The cyanide anions start to react around 1 GPa and bond to each other irreversibly at around 5 GPa, which are the lowest reaction pressures in all known metal cyanides and within the technologically achievable pressure range for industrial production. The conductivity of the polymer is above 10–3 S·cm–1, which reaches the range of conductive polymers. This investigation suggests that the pressure-induced polymerization route is practicable for synthesizing some types of functional conductive materials for industrial use, and further research like doping and heating can hence be motivated to synthesize novel materials under lower pressure and with better performances.
Kuo Li, Haiyan Zheng, Takanori Hattori, Asami Sano-Furukawa, Christopher A. Tulk, Jamie Molaison, Mikhail Feygenson, Ilia N. Ivanov, Wenge Yang and Ho-kwang Mao, “Synthesis, Structure, and Pressure-Induced Polymerization of Li3Fe(CN)6 Accompanied with Enhanced Conductivity,” Inorganic Chemistry, Article ASAP, DOI: 10.1021/acs.inorgchem.5b01851, Published Online November 17, 2015.