All-solid-state lithium batteries have been recently identified as potential candidates for energy storage devices with high reliability, energy density, and safety. Over the past few years, solid electrolytes have undergone various stages of development. However, several challenges such as chemical reaction with active materials and hydrogen sulfide generation have been encountered during the development process thus negatively impacting on the performance of the all-solid-state lithium batteries. To date, efforts have been devoted to providing solutions for overcoming the above challenges.
Among the available electrode materials, amorphous materials have particularly exhibited higher conductivities as compared to corresponding crystals. Owing to their advantages, amorphous LiCoO2-based electrode active materials have been developed for all-solid-state batteries to enhance the charge-discharge performance. However, large scale production and commercialization require the addition of lower cobalt content. Additionally, there is a need to increase the capacity of the layered Li (Ni1-x-yMnxCoy)O2 (NMC).
In this paper, researchers at Osaka Prefecture University: Dr. Kenji Nagao, Dr. Atsushi Sakuda, Professor Akitoshi Hayashi, Dr. Hirofumi Tsukasaki, Professor Shigeo Mori and Professor Masahiro Tatsumisago synthesized amorphous positive electrode materials of the NMC-Li2SO4 system based on the mechanochemical synthesis method. Various materials: NMC333, NMC532, NMC811, and LiNiO2 were used as starting materials. Based on these amorphous active materials, the corresponding all-oxide solid-state cells were fabricated and their electrical performance analyzed. Furthermore, the influence of Ni content in NMC on the charge-discharge performance of the all-solid-state cells was investigated. The main objective was to investigate the feasibility of the system for use in all-solid-state batteries. The work is published in the journal, Advanced Materials Interfaces.
Mechanochemical treatment with Li2SO4 resulted in electrode materials with excellent formability property as those of ductile solid electrolyte. Thus, the active material was pressed at room temperature to obtain a good electrode/electrolyte interface attributed to the improvement in the material’s ductility and electric conductivities. For the all-oxide solid-state cells based on 80NMCs.20Li2SO4 positive electrode material, an increase in the cell capacity with an increase in the Ni content in the NMC was observed. On the other hand, the cell-based on 80NMC811.20Li2SO4 active electrode materials exhibited a high capacity larger than 250 mAh g-1 in a voltage range of 1.6-4.8V.
It was worth noting that the bulk-type all-oxide solid-state batteries functioned as secondary batteries with excellent cycle performances. The operation of the all-solid-state batteries and ionic conductivities in the electrode layer depended on the interfacial construction. As such, the authors concluded that the development of oxide solid electrolytes with high ionic conductivities like those for sulfide solid electrolytes will enhance their operation at room temperature.
In summary, the Osaka Prefecture University scientists successfully synthesized novel amorphous positive electrode material based on the Ni-rich NMC-Li2SO4 system suitable for all-solid-state battery applications. Based on the findings, Dr. Atsushi Sakuda -the corresponding author assured Advances in Engineering that electrode material with high ductility, electronic and ionic conductivities using amorphous matrix is a promising approach for enhancing the performance of all-solid-state batteries.
Nagao, K., Sakuda, A., Hayashi, A., Tsukasaki, H., Mori, S., & Tatsumisago, M. (2019). Amorphous Ni-Rich Li (Ni1-x-yMnxCoy)O2-Li2SO4 Positive Electrode Materials for Bulk-Type All-Oxide Solid-State Batteries. Advanced Materials Interfaces, 6(8), 1802016.