Effect of Liquid Phase Sintering of Composite Electrode Containing 0.44LiBO2·0.56LiF Solid Electrolyte for All-Solid-State Batteries

All-solid-state batteries have received significant attention around the world because of high safety, reliability and energy density [1]. Over the past 20 years, all-solid-state batteries fabricated by using thin film techniques have been thoroughly investigated [2, 3]. These batteries are developed as micro-batteries because typically their total thickness is approximately 15 μm, including the protective packaging. Their specific capacities are only between 5 and 100 μAh cm^-2, depending on the thickness of electrodes [4]. The main challenge facing all-solid-state batteries is to enhance the surface capacity influenced by the thickness of cathode electrode. However, many attempts to increase the electrode thickness have not been successful because micro-cracks between the components are formed due to the stress generated at the solid electrode-electrolyte interface. Strong kinetic limitations due to the low mobility of the ions and electrons in the increased electrode is also another problem. To overcome these problems, a composite electrode made of multifunctional materials can be used as cathode electrode. The composite electrode should contain the electrochemically active material and should be able to transport electrons and ions in the electrode. In this study, a 0.44LiBO₂∙0.56LiF solid electrolyte was used for Li⁺ conduction pathway in the composite electrode because it has a low melting point (> 700 °C) [5] and is expected to act as a bonding material at the interface resulted from liquid phase sintering. The composite electrode with a strong mechanically framework was fabricated by a simple one-step spark plasma sintering (SPS) technique. The composite formulation as well as sintering parameters were determined by the electrical properties and sintering behaviors of electrode materials. The composite electrode was very dense with very few voids visible in the TEM images (Fig. 1.). The 0.44LiBO₂∙0.56LiF solid electrolyte was in close contact with the active materials due to liquid phase sintering. A Li-ion conduction path was formed along the electrode particles. In order to analyze the effects of liquid phase sintering systematically, the electrochemical performance of composite electrode is discussed in detail.

References

[1] C.W. Ahn, J.J. Choi, J.H. Ryu, B.D. Hahn, J.W. Kim, W.H. Yoon, J.H. Choi, J.S. Lee, D.S. Park, J. Power Sources 272 (2014) 554-558.

[2] N.J. Dudney, Y. I. Jang, J. Power Sources, 119-121 (2003) 300-304.

[3] Y.N. Zhou, M.Z. Xue, Z.W. Fu, J. Power Sources 234 (2013) 310-332.

[4] A. Patil, V. Patil, D. W. Shin, J. W. Choi, D. S. Paik, S. J. Yoon, Mater. Res. Bull., 43 (2008) 1913-1916.

[5] K. Chen, Y. Shen, Y. Zhang, Y. Lin, C. Nan, J. Power Sources 249 (2014) 306-310.