Effects of Ni/Co Doping on the Properties of LiFeαNiβCoγPO4 Cathodes for Lithium Batteries

Introduction Nowadays, rapid development in portable electronics, load leveling/peak shaving for the power grid and electric automotive, requires significant progress in high voltage and high capacity storage systems [1]. Lithium batteries are, to date, the most promising systems that can sustain this demand [2]; they have high specific energy, high efficiency and a long lifespan [3]. Lithium cobalt oxide (LiCoO2) based cathode materials currently dominate the market [4], however, due to a low working potential (3.0 – 4.0 V vs. Li) and a high cost and toxicity, there is broad scope for the development of new cathodic materials [5]. Lithium-transition metal-phosphates (LiMPO4, M=Co, Fe, Mn or Ni) show very good performance: their olivine structure, consisting of a 2D framework of crossed tunnels, allows the insertion and de-insertion of lithium ions during the discharge/charge of the battery [6, 7]. Materials and methods LFNCPx Li2CO3 (1.00 g, BDH), (NH4)2HPO4 (3.57 g, Riedel-de Haën), Fe2O3 (0.72 g, Baker), NiO (1.21-1.01-0.68-0.34-0.14 g, Carlo Erba) and 2CoCO3∙2Co(OH)2∙nH2O (0.22-0.54-1.05-1.58-1.90 g, 50% Co2+ assay, Carlo Erba) are mixed in a planetary ball miller (2 h, 500 rpm). After the machination process, pellets of each sample are obtained by sintering the powders under a pressure of 4 tons. Each pellet is then put into a furnace at 700 °C in air for 24 h before being allowed to cool slowly. Finally, at the end of the pyrolysis, materials are ground again via planetary ball milling (2 h, 500 rpm). Stoichiometry is evaluated using an Inductively Coupled Plasma Atomic Emission. High Resolution – Thermo Gravimetric Analyses (HR-TGA) are carried out in order to study the thermal stability of the materials. Morphology and size distributions are observed by Scanning Electron Microscope. Microstructure is also characterized with High Resolution Transmission Electron Microscope. Powder X-Ray Diffraction analyzes and vibrational (FT-MIR and FT-FIR) measurements are carried out in order to study the structure of LFNCPx materials. Electrochemical characteristics are evaluated with CV and EIS measurements. Battery prototype (CR2032) testing is conducted using an amperostatic procedure. Results and discussion Five different lithium based cathode materials consisting of various nickel and cobalt contents are synthesized and extensively characterized [8]. It is observed that differing relative ratios of cobalt and nickel does not affect the morphology of the compounds, but does play a crucial role in modulating the resulting electrochemical properties of the materials. Indeed, it is found that the material composition affects: a) the structure elasticity of olivines and b) the electronic density of states of insertion/de-insertion Li+ ion channels. As a whole, this study shows that transition metal doped LiMPO4 results in high performance materials for lithium secondary batteries. This new family of compounds could address the current demands for improved energy storage and conversion technologies. Bibliography [1] M. Armand, J.M. Tarascon, Nature, 451 (2008) 652-657. [2] V. Di Noto, T.A. Zawodzinski, A.M. Herring, G.A. Giffin, E. Negro, S. Lavina, Int. J. Hydrogen Energy, 37 (2012) 6120-6131. [3] B. Scrosati, J. Garche, J. Power Sources, 195 (2010) 2419-2430. [4] K. Zaghib, A. Mauger, H. Groult, J.B. Goodenough, C.M. Julien, Mater., 6 (2013) 1028-1049. [5] K. Zaghib, J. Dubé, A. Dallaire, K. Galoustov, A. Guerfi, M. Ramanathan, A. Benmayza, J. Prakash, A. Mauger, C.M. Julien, J. Power Sources, 219 (2012) 36-44. [6] N.N. Bramnik, K.G. Bramnik, T. Buhrmester, C. Baehtz, H. Ehrenberg, H. Fuess, J. Solid State Electrochem., 8 (2004) 558-564. [7] A.K. Padhi, K.S. Nanjundaswamy, J.B. Goodenough, J. Electrochem. Soc., 144 (1997) 1188-1194. [8] 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.