The all-solid-state batteries were made by stacking thin films of gold (Au; current collector), lithium cobalt oxide (LiCoO2; cathode), lithium phosphate (Li3PO4; solid electrolyte) and lithium (Li; anode) on an aluminium oxide (Al2O3) substrate. (a) Schematic cross-sectional view and (b) microscope image of the fabricated thin-film battery. Image: ACS Applied Materials & Interfaces.Scientists at Tokyo Institute of Technology in Japan have examined the mechanisms behind resistance at the electrode-electrolyte interface in all-solid-state batteries. Their findings, which are reported in a paper in ACS Applied Materials & Interfaces, will aid in the development of much better lithium-ion (Li-ion) batteries with very fast charge/discharge rates.
Li-ion batteries are already ubiquitous in the modern world, but developing improved versions, including solid-state batteries with a solid electrolyte, is crucial for extending the limits of modern electronic devices and electric vehicles. Scientists at Tokyo Institute of Technology, led by Taro Hitosugi, had previously reported a new type of all-solid-state battery, also based on lithium ions, that could overcome one of the major problems with these batteries. This is high resistance at the interface between the electrodes and the solid electrolyte, which limits fast charging/discharging.
Although the devices they produced were very promising and were much better than conventional Li-ion batteries in some regards, the mechanism responsible for the reduced interface resistance was unclear. This was due to the difficulty of analyzing the buried interfaces in the all-solid-state batteries without damaging their layers.
Not to be dissuaded, Hitosugi and his team of researchers again tried investigating the all-solid-state batteries to shed light on this topic. They suspected that crystallinity – which indicates how well-ordered and periodic a solid is – at the electrode-electrolyte interface played a key role in defining its interface resistance.
To prove this, they used a using a pulsed laser deposition technique to fabricate two different all-solid-state batteries composed of electrode and electrolyte layers. One of these batteries had high crystallinity at the electrode-electrolyte interface, whereas the other did not, which they confirmed using a novel technique called X-ray crystal truncation-rod scattering analysis.
"X-rays can reach the buried interfaces without destroying the structures," explains Hitosugi.
Based on their results, the team concluded that a highly crystalline electrode-electrolyte interface did indeed result in low interface resistance, yielding a high-performance battery. By analyzing the microscopic structure of the interfaces of their batteries, they also proposed a plausible explanation for the increased resistance of batteries with less crystalline interfaces. They suggest that lithium ions become stuck at these less crystalline interfaces, hindering ion conductivity.
"Controlled fabrication of the electrolyte/electrode interface is crucial to obtain low interface resistance," explains Hitosugi. The development of theories and simulations to further understand the migration of Li ions will be crucial for finally achieving useful and improved batteries for all kinds of electrical devices.
This story is adapted from material from Tokyo Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.