Structurally engineered high performance layered oxide cathodes for NA-ION batteries

Abstract

In recent years, rapid developments in Li-ion batteries (LIBs) have made these a popular choice for secondary energy storage applications. However, as the demand for energy storage systems for mobility and portable electronics applications rises, scarcity of Li deposits and the issues related to Li recycling is expected to cause the demand for Li to exceed its supply, leading to high LIBs prices. Na-ion batteries (NIBs) are widely regarded as a possible alternative to replace LIBs to meet future demands, especially in stationary storage applications such as grid storage. This is primarily because of the comparatively natural abundance of Na and the commonalities that NIBs share with LIBs in terms of components and manufacturing techniques, paving the way for their seamless integration into the current battery eco-systems. Cathode materials, being the primary source of ions, play a pivotal role in deciding the performance and properties of ion storage batteries. Layered oxides are considered the most attractive cathode materials for commercial Na-ion batteries because of their higher specific capacity, cyclability, and easier synthesis compared to their competitors. As most of the cathode materials used in commercial Li-ion batteries are based on the same structure, certain aspects of the research and development of these materials can be translated to the advancement of Na-ion batteries. This thesis reports on the structural, electrical, and electrochemical properties of P2-type Na0.70Ni0.20Cu0.15Mn0.65-xTixO2 (NNCMT-x (x = 0, 0.025, 0.05,0.075, 0.1)) ceramic fabricated via a sol-gel method. The Rietveld refinement of the room temperature XRD diffraction data confirmed the formation of a single P2-type phase with space group P63/mmc for the powder calcined at 850 ℃. Complex impedance spectroscopy was used to deconvolute the contributions of grains and grain boundaries to the overall conduction inside the parent material Na0.70Ni0.20Cu0.15Mn0.65O2 (NNCM-0). The room temperature conductivity of the grains and grain boundaries calculated for the NNCM-0 ceramic sintered at 1000 ℃ were estimated to be (5.25 ± 0.03)  10-5 Scm-1 and (4.70 ± 0.05)  10-6 Scm-1 , respectively. The respective activation energies for the grain and grain boundary conduction were 0.189 ± 0.008 eV and 0.22 ± 0.01 eV, respectively. Moreover, NNCM exhibited a sodium-ion transference number of  0.86, suggesting that the conduction in this material is dominated by the Na-ions.