(Keynote) Developing High Voltage Li-Ion Batteries Based on Lithium Cobalt Phosphate (LCP)

Abstract

Olivine structured lithium cobalt phosphate, LiCoPO4 (LCP), is an attractive cathode material that has a theoretical energy density of 802 Wh/kg based on LCP’s 4.8 V redox potential and 167 mAh/g theoretical capacity. The investigation of this material was first reported in 2000 by Amine et al. [1] realizing a capacity of only 70 mAh/g. The low capacity was attributed to both the poor electronic conductivity of LCP and the initiation of the electrolyte salt decomposition [1]. Considerable efforts worldwide since then made on improving the utilization of LCP through the reduction of particle size, carbon blending, carbon coating and morphology improvement have led to an increase of capacity utilization to 140 mAh/g [2]. Efforts have also been made in developing compatible high voltage electrolytes [3]. However, these efforts had not resulted in a rechargeable LCP without substantial loss of capacity in limited cycles. A breakthrough in improving the cycle life of LCP against Li up to 500 times with 80% capacity retention was made by substituting part of Co by Fe, which was first reported by Allen et al. in 2011 [4]. Further substitutions by Cr and Si in Fe substituted LCP (s-LCP) with improved electrolyte improve the discharge capacity to 140 mAh, coulombic efficiency to 99.7% and cycle up to 250 times with almost no capacity fade [5]. The success in realizing the potential of this material is attributed to the success in modifying the electronic structure and stabilizing the electrochemical stability of LCP through atomic level substitutions. Good cycle life has also been demonstrated in full cells made of graphite anode and s-LCP cathode in coin cells and 1.2 Ah pouch cells [6]. This talk will present a progression of the s-LCP based Li-ion cells development and the importance of the atomic level engineering in improving the performance of the high voltage cathodes. References K. Amine, H. Yasuda, M. Yamachi, Olivine LiCoPO4 as 4.8 V Electrode Material for Lithium Batteries, Electrochem. Solid-State Lett. 2000, 3(4) 178-179.S.-M. Oh, S.-T. Myung, Y.-K. Sun, Olivine LiCoPO4–carbon composite showing high rechargeable capacity, J. Mater. Chem., 2012, 22, 14932.R. Sharabi, E. Markevich, K. Fridman, G. Gershinsky, G. Salitra, D. Aurbach, G. Semrau, M. A. Schmidt, N. Schall, C. Bruenig, Electrolyte solution for the improved cycling performance of LiCoPO4/C composite cathodes. Electrochem. Commun. 2013, 28, 20-23.J. L. Allen, T. R. Jow, J. Wolfenstine, Improved cycle life of Fe-substituted LiCoPO4, J. Power Sources, 2011, 196(20), 8656-8661.J. L. Allen, J. L. Allen, T. Thompson, S. A. Delp, J. Wolfenstine, T. R. Jow, Cr and Si Substituted-LiCo0.9Fe0.1PO4: Structure, Full and Half Li-ion Cell Performance, J. Power Sources, 2016, 327, 229-234.D. Liu, W. Zhu, C. Kim, M. Cho, A. Guerfi, S. A. Delp, J. L. Allen, T. R. Jow and K. Zaghib, High-Energy Lithium-Ion Battery Using Substituted LiCoPO4: From Coin Type to 1Ah Cell, J. Power Sources, 2018, 388, 52-56.