(Invited) Innovative Olivine Cathodes for High-Voltage and High-Rate Lithium Batteries

Lithium batteries (LiBs) are among the most promising systems that could address today’s strongly increasing needs for an efficient, compact and reversible electrochemical storage of energy [1]. Indeed, LiBs are characterized by a high specific capacity, a high efficiency, and a long lifespan [2]. Unfortunately, improvements in the working potential, in the specific energy, and in the rate capability properties of the cathodes are still needed to comply with the specifications required by practical applications. This work describes the synthesis and the characterization of a new family of high-voltage and high-rate cathodes for LiBs. A high-performing olivine material of the type LiMPO4 (M = Fe, Ni, and Co) [3] has been modified by inserting into the structure high-valence transition metal ions (e.g., V(V), Nb(IV), and Ta(IV)) [4]. The effects of the insertion of the different ions on the structural, morphological, electrical and electrochemical properties of the materials have been thoroughly studied. The stoichiometry is evaluated by means of Inductively-Coupled Plasma Atomic Emission Spectroscopy (ICP-AES); the morphology and size distribution of the grains are characterized by Scanning Electron Microscopy (SEM) and High-Resolution Transmission Electron Microscopy (HR-TEM); the structure is examined by powder X-Ray Diffraction (XRD) as well as a variety of IR spectroscopy techniques. The electrochemical characterization is carried out by Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and charge/discharge tests at different current rates. Finally, the conductivity mechanism is studied by Broadband Electrical Spectroscopy (BES). The cathode materials described in this report exhibit a high performance in terms of working potential (4.0 ÷ 5.0 V vs. Li/Li+), specific capacity (149 mAh∙g-1), and specific energy (656 mWh∙g-1). Moreover, the insertion of high-valence transition metals results in an improvement of the rate capability of the cathodes, allowing for fast charge and discharge processes. References [1] V. Di Noto, T. A. Zawodzinski, A. M. Herring, G. A. Giffin, E. Negro, S. Lavina, Int. J. Hydrogen Energy 37 (2012) 6120-6131. [2] B. Scrosati, J. Garche, J. Power Sources 195 (2010) 2419-2430. [3] G. Pagot, F. Bertasi, G. Nawn, E. Negro, G. Carraro, D. Barreca, C. Maccato, S. Polizzi, V. Di Noto, Adv. Funct. Mater. 25 (2015) 4032-4037. [4] G. Pagot, M. Bandiera, K. Vezzù, A. Migliori, R. Bertoncello, E. Negro, V. Morandi, V. Di Noto, Journal of Materials Chemistry A, doi: 10.1039/D0TA06865A