High Power and High Capacity 3D-Structured TiO2 Electrodes forLithium-Ion Microbatteries

An on-chip compatible method to fabricate high energy density TiO2 thin film electrodes on 3D-structured silicon substrates was demonstrated. 3D-structured electrodes are fabricated by combining reactive ion etching (RIE) with low pressure chemical vapor deposition (LPCVD), enabling accurate control of the aspect ratio of substrates and the subsequent deposition of TiO2 thin film electrodes onto these structured substrates. The prepared 3D-TiO2 electrodes exhibit a current-dependent increase in storage capacity of a factor up to 16 as compared to conventional planar electrodes. In addition, these 3D electrodes also reveal excellent power and cycling performance. This work demonstrates that LPCVD is capable of depositing homogeneous film electrodes on highly structured substrates and the prepared 3D-electrodes also shows significant improve in storage capacity and power density

Feasibility and Limitations of High-Voltage Lithium-Iron-Manganese Spinels

Positive electrodes with high energy densities for Lithium-ion batteries (LIB) almost exclusively rely on toxic and costly transition metals. Iron based high voltage spinels can be feasible alternatives, but the phase stabilities and optimal chemistries for LIB applications are not fully understood yet. In this study, LiFe$_{x}$Mn$_{2-x}$O$_{4}$ spinels with x = 0.2 to 0.9 were synthesized by solid-state reaction at 800 °C. High-resolution diffraction methods reveal gradual increasing partial spinel inversion as a function of x and early secondary phase formation. Mössbauer spectroscopy was used to identify the Fe valences, spin states and coordination. The unexpected increasing lattice parameters with Fe substitution for Mn was explained considering the anion-cation average bond lengths determined by Rietveld analysis and Mn$^{3+}$ overstoichiometries revealed by cyclic voltammetry. Finally, galvanostatic cycling of Li-Fe-Mn-spinels shows that the capacity fading is correlated to increased cell polarization for higher upper charging cut-off voltage, Fe-content and C-rate. The electrolyte may also contribute significantly to the cycling limitations

Strategies towards enabling lithium metal in batteries: interphases and electrodes

Despite the continuous increase in capacity, lithium-ion intercalation batteries are approaching their performance limits. As a result, research is intensifying on next-generation battery technologies. The use of a lithium metal anode promises the highest theoretical energy density and enables use of lithium-free or novel high-energy cathodes. However, the lithium metal anode suffers from poor morphological stability and Coulombic efficiency during cycling, especially in liquid electrolytes. In contrast to solid electrolytes, liquid electrolytes have the advantage of high ionic conductivity and good wetting of the anode, despite the lithium metal volume change during cycling. Rapid capacity fade due to inhomogeneous deposition and dissolution of lithium is the main hindrance to the successful utilization of the lithium metal anode in combination with liquid electrolytes. In this perspective, we discuss how experimental and theoretical insights can provide possible pathways for reversible cycling of twodimensional lithium metal. Therefore, we discuss improvements in the understanding of lithium metal nucleation, deposition, and stripping on the nanoscale. As the solid–electrolyte interphase (SEI) plays a key role in the lithium morphology, we discuss how the proper SEI design might allow stable cycling. We highlight recent advances in conventional and (localized) highly concentrated electrolytes in view of their respective SEIs. We also discuss artificial interphases and three-dimensional host frameworks, which show prospects of mitigating morphological instabilities and suppressing large shape change on the electrode level

Aspects and prospects of 'in-operando' magnetic-resonance investigations to study lithium-ion and metal-oxygen batteries.

To develop energy storage devices with enhanced capacity, specific energy or improved cycle life, insights in the fundamental transport and transformation processes on an atomic scale are mandatory. For that purpose, nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy provide sensitive methods to study Li-diffusion, characterize the impact of aliovalent doping on the defect chemistry in Li-ion batteries and contribute to the understanding of working mechanism of the oxygen-reduction electrocatalyst in metal-air batteries. However, owing the reactive environment in a battery, the standard techniques of magnetic resonance need to be modified towards ‘in-situ’ and ‘in-operando’ setups. It will be discussed how advanced magnetic resonance experiments can aid in gathering insights into fundamental reaction mechanisms during battery operation and battery degradation