The wide application of lithium-ion batteries as power sources in electronic devices is attributed to their excellent cycle performance and high energy density. Lately, they have been increasingly used in large energy batteries and electric vehicles, a move that has been limited by longer charging times, low battery capacity and other related risks like electrolyte leakage. To overcome these limitations, all-solid-state lithium-ion battery (ASS-LIB) was developed. Instead of liquid electrolyte, ASS-LIB uses solid electrolyte, which not only reduces the risk of electrolyte leakage but also endows the battery with improved energy density, durability and safety.
ASS-LIBs have drawn attention as next-generation secondary batteries. Nevertheless, their development faces two key challenges associated with constructing solid-solid interfaces between the solid electrolyte (SE) and the active material (AM) and developing inorganic solid electrolytes with high ionic conductivity. Most importantly, the electrode structure and the contact interface between the SE and AM are important factors determining the overall battery performance.
Several strategies have been employed to develop inorganic solid electrolytes and form interfacial contacts between the SE and AM. Among them is producing core-shell particles via high-temperature pulsed laser deposition and high temperature pressing to produce dense AM-SE interfaces. Despite the remarkable progress, other problems like high costs, AM related damages and difficulties scaling up are still being encountered. While most of these problems have been addressed by dry coating process utilized in recent studies to form the interfacial contacts between SE and AM, the influence of surface morphologies of the composite particles on the ASS-LIB performance is still poorly understood.
On this account, Dr. Eiji Hayakawa, Professor Hideya Nakamura, Professor Shuji Ohsaki and Professor Satoru Watano from Osaka Metropolitan University (formerly known as Osaka Prefecture University) investigated the effects of surface morphologies of SE/AM composite particles on cathode layer structure and performance of all-solid-state batteries. In their approach, the dry coating time was adjusted to prepare composite particles with continuous- or discrete-coating of the SE layers, while die compression was used to prepare all-solid-state half-cells. Charge/discharge tests and electrochemical impedance spectroscopy were used to investigate the battery performance. Their work is currently published in the journal, Advanced Powder Technology.
The researchers showed that the surface morphologies changed from discrete to continuous as the dry coating process progressed. Compared with the cathode prepared using simple mixture, the cathode prepared with composite particle exhibited higher ionic conductivity attributed to the well-percolated ionic conductivity path. Composite particles with different surface morphologies were compared and evaluated. The discrete-coating particles-based cell exhibited excellent electrical and ionic conductivity paths resulting in lower internal resistance. To this end, discrete-coated particles were considered ideal candidates for forming higher electrical/ionic conductivity composite cathodes than continuous-coating particles.
The surface morphology-induced differences in the electrode structure significantly affected the charge/discharge rate capabilities of the resulting cells. The ASS half-cell fabricated with continuous-coating particles reported a low battery capacity at 0.1C. It, however, exhibited higher capacity retention and discharge capacity at a higher charge rate compared with that prepared by discrete-coating particles. In contrast, among all the studied samples, the ASS half-cells fabricated with discrete-coating particles reported the highest charge rate capability.
In summary, the authors characterized the SE/AM composite particles with different surface morphologies. The charge/discharge rate-limiting factors were considered different in this study owing to the high dependence of the electrical conductivity and the state of charge. As such, the charge and discharge rate performance were mainly affected by the contact area between the AM-AM and AM-SE, respectively. In a joint statement to Advances in Engineering, the authors explained their study findings will advance and improve the performance of all-solid-state batteries and expand their application scope.
Hayakawa, E., Nakamura, H., Ohsaki, S., & Watano, S. (2022). Characterization of solid-electrolyte/active-material composite particles with different surface morphologies for all-solid-state batteries. Advanced Powder Technology, 33(3), 103470.