DEVELOPMENT OF IRON BASED OXIDES AS PROSPECTIVE ANODES FOR NEXT-GENERATION LI-ION BATTERIES

Abstract

Development of high-performance next-generation rechargeable lithium-ion batteries (LIBs) have been a keen interest to achieve the demands of present-day portable electronics, electrified vehicles, and smart grid. Hence, research and development of these LIBs is dominated by application specific targets, which predominantly focus on cost and performance targets, including high gravimetric energy, volumetric energy, and related power densities, while ensuring a high safety and long life time. The energy/power density, cycle-life, and cost of LIBs significantly depend on the choice of the electrode materials. Moreover, these materials must be commercially viable, cost-effective and should be environment friendly. Furthermore, to achieve high energy/ power densities in LIBs, either develop high voltage cathode and/ or highcapacity anode materials. However, developing cathode materials which exhibits high working voltage of ∼5 V are extremely challenging. This is due to the conventional organic solvent-used in electrolytes are not stable at > 4.5 V. Hence, more attention has been given to developing anode materials with high and stable capacity. Commercial LIBs anode (graphite) exhibits poor experimental capacity (~330 mAh g-1) and low insertion voltage. These are the limiting factors to get them used for the high-end application. Specifically, the working potential of graphite is too close (̴ 0.2 vs Li/Li+) to the formation potential of Li dendrite during cycling, which may cause the internal short circuit, electrolyte inflammable, and even explosion in LIBs. Further, the formation of Li dendrite increases as the charging rate of LIBs increases. Hence, in order to meet the increasing demand of high energy/power density, rate capacity and safety for high-end applications, extensive efforts are being put forward to develop the alternative anode materials for next-generation LIBs. In the development of anode materials, Iron based oxides are recognized as prospective anode materials because of their higher experimental capacity (almost three times to commercial graphite), lower cost, rich resources, and environmental benignity. However, this class of materials suffers from low electronic/ionic conductivity, easily aggregation, a rapid capacity fading due to electrode pulverization caused by the large volume variation during charge/discharge process, large irreversible capacity loss (ICL), potential hysteresis and the higher working potential (̴ 2 V vs. Li/Li+) which further hinder their commercialization. To overcome these drawbacks and improve the Li-storage performance, both structural stability as well as enhancing the electronic/ionic conductivity should be taken into consideration. In this regard, various strategies are being employed. A general strategy to alleviate these problems is to prepare iron-based oxides containing a homogeneous electrochemically inactive component (matrix) such as metal oxides: MO (M= Zn, Ca, Sn, Mg, etc.). These matrices are proposed to buffer the unit cell volume variation during cycling and provide better stability in capacity values over prolonged cycles. Owing to this, inactive component of CaO could be the appropriate choice because of its excellent high ductility as well as high strength for iron oxides. Another effective strategy is nanostructuring of electrode materials which shown a constructive impact on the Li-storage properties owing to the alternation of ion/electron transport. Recently, introduction of oxygen defects in the electrode materials is being adopted which is believed to enhance the ionic/electronic conductivity and therefore improved Li-storage performance is being realized.