Solid state lithium ion batteries based on a novel hybrid solid state electrolyte

Abstract

Solid state electrolytes; e.g. LISICON, garnets, perovskites, etc.; potentially enhance the safety of lithium-ion batteries, but typically suffer from low ionic conductivities (<10-4 S/cm). [1] Also the interfacial resistance between the electrode and these typical solid electrolytes is high and needs to be reduced. Hybrid solid state electrolytes can overcome aforementioned issues and as such enable implementation of solid state batteries. Hybrid solid state electrolytes combine the desirable properties of both liquid and solid electrolytes by confining liquid electrolytes within a (meso-)porous solid framework. [2,3] The confined liquid typically consists of a Li-salt (e.g. LiPF6, LiFSI, LiTFSI,…) dissolved in an ionic liquid, which acts as a solvent, similar to carbonates in conventional liquid electrolytes. The resulting “ionogel” electrolyte, i.e. the confined ionic liquid electrolyte (ILE), allows a high ionic conductivity (>10-3 S/cm) and an intimate electrode/electrolyte interface. However, ionic liquids are very costly, which hinders their practical use. In this work, the ionic liquid is replaced by an inexpensive complexing agent to lower the cost of this hybrid electrolyte. Moreover, the hybrid electrolyte is synthesized in a facile one-pot synthesis at room temperature. A high ionic conductivity of up to 1.15 mS/cm is found via electrochemical impedance spectroscopy (EIS). Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) reveal a beneficial anodic stability limit of 4.8 V vs. Li+/Li. LiFePO4 (LFP) half-cells were assembled with these hybrid solid state electrolyte membranes. These cells display highly reversible capacities of about 110 mAh/g for over 100 cycles (at 0.1C, 16 °C), which are comparable to LFP half-cells assembled with a conventional liquid electrolyte (1M LiPF6, 50/50 vol% EC/DEC, 115 mAh/g at 0.1C). The rate capability still has room for improvement. Hence the hybrid solid electrolyte at hand is promising for implementation in Li-ion battery technology. Acknowledgements B. Joos is a PhD fellow of the Research Foundation – Flanders (FWO Vlaanderen). This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg (project number EFRO936). The authors would like to thank other group members for their assistance. References [1] C. Cao, Z. Li, X. Wang, X Zhao, W. Han, Frontiers in Energy Research, 2 (2014), 1-10. [2] G. Tan, F. Wu, C. Zhan, J. Wang, D. Mu, J. Lu, K. Amide, Nano Lett., 16 (2016), 1960-1968. [3] X. Li, S. Li, Z. Zhang, J. Huang, L. Yang, S. Hiranob, J. Mater. Chem. A., 4 (2016), 13822-13829.