Mesfin Kebede

Microwave-assisted optimization of the manganese redox states for enhanced capacity and capacity retention of LiAlxMn2−xO4 (x = 0 and 0.3) spinel materials

Microwave irradiation at the pre- and post-annealing steps of the synthesis of LiAlxMn2−xO4 (x = 0 and 0.3) spinel cathode materials for rechargeable lithium ion batteries is a useful strategy to optimize the average manganese valence number (nMn) for enhanced capacity and capacity retention. The strategy impacts on the lattice parameter, average manganese valence, particle size and morphology, reversibility of the de-intercalation/intercalation processes, and capacity retention upon continuous cycling. Microwave irradiation is able to shrink the particles for improved crystallinity. The XPS data clearly suggest that microwave irradiation can be used to tune the manganese valence (nMn), and that the LiAlxMn2−xO4 with nMn ≈ 3.5+ gives the best electrochemical performance. These new findings promise to revolutionize how we use microwave irradiation in the preparation of energy materials and various other materials for energy storage and conversion materials for enhanced performance.

Rapid and large-scale synthesis of Co3O4 octahedron particles with very high catalytic activity, good supercapacitance and unique magnetic properties

The scarcity of rapid and large scale synthesis of functional materials hinders the progress from the laboratory scale to commercial applications. In this study, we report a rapid and large scale synthesis of micron size (1.3 μm) Co3O4 octahedron particles enclosed by (111) facets. The octahedron particles were composed of ±25 nm rectangular/cube shaped particles as seen from the TEM images. We have characterized and evaluated the catalytic, supercapacitance and magnetic properties of the as prepared material. The Co3O4 octahedron particles were highly active in heterogeneous PMS activation reaction. Formation of Co–OH bonding due to water molecule dissociation on the (111) surface of the particles was evident from the ELNEFS analysis. The as prepared octahedron materials showed >4 times higher pseudocapacitance properties (182 F g−1) with good capacity retention ability (up to the 1000 cycles studied) compared to commercial microcrystalline Co3O4 powder (43 F g−1). The material showed interesting magnetic properties at low temperature. The coexistence of superparamagnetic single domain and linear/quadratic behaviours was observed at low temperature for the as prepared Co3O4 octahedron particles.

Stable nickel-substituted spinel cathode material (LiMn1.9Ni0.1O4) for lithium-ion batteries obtained by using a low temperature aqueous reduction technique

A nickel substituted spinel cathode material (LiMn1.9Ni0.1O4) with enhanced electrochemical performance was successfully synthesized by using a locally-sourced, low-cost manganese precursor, electrolytic manganese dioxide (EMD), and NiSO4·6H2O as a nickel source by means of a low temperature aqueous reduction synthesis technique. This synthesis protocol is convenient to scale up the production of the spinel cathode material, with minimal nickel content (Ni = 0.1) in the structure, for lithium-ion battery applications. Ni-ions substituting Mn-ions was confirmed using XRD, EDS, XPS and electrochemical performance studies. LiMn1.9Ni0.1O4 materials showed an octahedral shape with clearly exposed (111) facets that enhanced the Li-ion kinetics and improved the cycling performance compared to the pristine spinel sample (LiMn2O4). The LiMn1.9Ni0.1O4 sample exhibited superior capacity retention by retaining 84% of its initial capacity (128 mA h g−1) whereas pristine LiMn2O4 retained only 52% of its initial capacity (137 mA h g−1). XPS confirmed that the Mn3+/Mn4+ ratio changed with nickel substitution and favored the suppression of capacity fading. The study clearly suggests that the integration of small amounts of Ni into the spinel structure is able to eliminate the disadvantageous Jahn–Teller effects in the LiMn2O4.

Molten salt-directed synthesis method for LiMn2O4 nanorods as a cathode material for a lithium-ion battery with superior cyclability

A molten salt synthesis technique has been used to prepare nanorods of Mn2O3 and single-crystal LiMn2O4 nanorods cathode material with superior capacity retention. The molten salt-directed synthesis involved the use of NaCl as the eutectic melt. The as-synthesized LiMn2O4 nanorods cathode material showed superior electrochemical performance compared to the LiMn2O4 sample obtained via the solid state method. The as-synthesized LiMn2O4 nanorods maintained more than 95% of the initial discharge capacity of 107 mA h g−1 over 100 cycles at a rate of 0.1 C, whereas the LiMn2O4 sample synthesized using the solid state reaction method maintained 88% of the initial discharge capacity of 98 mA h g−1 over 100 cycles at a rate of 0.1 C. Compared to the literature, the molten salt-directed method for the preparation of high-performance LiMn2O4 is simpler and less expensive, with greater potential for industrial scale-up.

Metal Oxides and Lithium Alloys as Anode Materials for Lithium-Ion Batteries

Metal oxides such as TiO2, Li4Ti5O12, SnO2, SnO, M2SnO4 (\( \mathrm{M} = \mathrm{Z}\mathrm{n} \), Co, Mn, Mg), TMO (\( \mathrm{T}\mathrm{M} = \mathrm{M}\mathrm{n} \), Fe, Co, Ni, or Cu), TM3O4 (\( \mathrm{T}\mathrm{M} = \mathrm{C}\mathrm{o} \), Fe, or Mn), and lithium alloys Li–Sn, Li–Si are among the next-generation anode materials for lithium–ion batteries with high prospect of replacing graphite. Most of these anode materials have higher specific capacities between the range of \( 600 - 1000\ \mathrm{m}\mathrm{A}\ \mathrm{h}\ {\mathrm{g}}^{-1} \) compared with \( 340\ \mathrm{m}\mathrm{A}\ \mathrm{h}\ {\mathrm{g}}^{-1} \) of graphite. These high-capacity anode materials normally face poor cycle performance due to severe volume change during the discharge/charge reactions which leads to crack and pulverization. To overcome these limitations, two commonly adopted strategies are nano-engineering and coating with carbon. In this chapter, we have discussed the metal oxides and lithium alloy anodes in three sections, with emphasis on their electrochemical reaction mechanisms with lithium. We have also presented a brief historical review based on the development of the metal oxides and lithium alloys as anode materials for lithium–ion battery, highlighted ongoing research strategies, and discussed the challenges that remain regarding the synthesis, characterization, and electrochemical performance of the materials.

Next-Generation Nanostructured Lithium-Ion Cathode Materials: Critical Challenges for New Directions in R&D

Every market analysis predicts that lithium-ion batteries (LIBs) will dominate energy storage technologies for now and the foreseeable future. LIBs will drive many applications ranging from portable electronics to electric vehicles and smart grids, while also permitting a greener and more sustainable global environment. The few successful cathode materials today are those of the layered, spinel and olivine structures. Despite their success, they still fall short of some requirements (such as high energy, high-rate performance, low cost, cycle life and safety) of modern portable electronics, electric vehicles, grid applications and home storage. For example, it has been well established that the realisation of electric vehicles is highly dependent on LIBs with high energy and power density, durability, safety and reduced cost. In addition, the design, development and innovation of high-performing portable electronics are limited by the size, power and cycle life of the batteries that drive them. Nano-sizing of electrode materials has emerged as one of the most promising strategies to dramatically improve the performance of LIBs, including capacity, rate capability, cycle life, cost reduction and safety. This review chapter provides the readership an understanding of the critical scientific challenges faced by the existing cathode materials used in LIBs and the critical roles engineered nanostructures can play in the realisation of next-generation LIBs for the ever-emerging technologies.