Manganese oxides can undergo an electrochemical activation step that leads to greater capacitances, of which the structural change and mechanism remains poorly understood. Herein we present a wideranging study on a manganese oxide synthesised by annealing manganese(II) acetate precursor to 300 C, which includes in operando monitoring of the structural evolution during the activation process via in situ Raman microscopy. Based on powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron and ex situ Raman microscopy, the as prepared manganese oxide was characterised as hausmannite-Mn 3 O 4 with a minor portion of MnO 2 . The activation process of converting as-prepared hausmannite-Mn 3 O 4 into amorphous MnO 2 (with localised birnessite structure) by electrochemical cycling in 0.5 M Na 2 SO 4 was examined. After activation, the activated MnO x exhibited capacitive performance of 174 F g À1 at a mass loading of 0.71 mg cm À2 . The charge storage mechanism is proposed as the redox reaction between Mn(III) and Mn(IV) at outer surface active sites, since the disordered birnessite-MnO 2 does not provide an ordered layer structure for cations and/or protons to intercalate. † Electronic supplementary information (ESI) available: Literature comparison, potential of quasi reference electrode measurement, Lorentz tting of ex situ Raman spectra, XPS data and PXRD pattern of MnO x aer activation. See

Multinary lithium oxides with the rock salt structure are of technological importance as cathode materials in rechargeable lithium ion batteries. Current state-of-the-art cathodes such as LiNi1/3Mn1/3Co1/3O2 rely on redox cycling of earth-abundant transition-metal cations to provide charge capacity. Recently, the possibility of using the oxide anion as a redox center in Li-rich rock salt oxides has been established as a new paradigm in the design of cathode materials with enhanced capacities (>200 mAh/g). To increase the lithium content and access electrons from oxygen-derived states, these materials typically require transition metals in high oxidation states, which can be easily achieved using d0 cations. However, Li-rich rock salt oxides with high valent d0 cations such as Nb5+ and Mo6+ show strikingly high voltage hysteresis between charge and discharge, the origin of which is uninvestigated. In this work, we study a series of Li-rich compounds, Li4+x Ni1–x WO6 (0 ≤ x ≤ 0.25) adopting two new and distinct cation-ordered variants of the rock salt structure. The Li4.15Ni0.85WO6 (x = 0.15) phase has a large reversible capacity of 200 mAh/g, without accessing the Ni3+/Ni4+ redox couple, implying that more than two-thirds of the capacity is due to anionic redox, with good cyclability. The presence of the 5d0 W6+ cation affords extensive (>2 V) voltage hysteresis associated with the anionic redox. We present experimental evidence for the formation of strongly stabilized localized O–O single bonds that explain the energy penalty required to reduce the material upon discharge. The high valent d0 cation associates localized anion–anion bonding with the anion redox capacity.

Carbon‐coated Zn0.9Fe0.1O is a promising anode material for lithium‐ion batteries with good cycling performance and a theoretical specific capacity of 966 mAh g−1, as a result of the combined conversion‐alloying reaction during lithiation. The solid electrolyte interphase (SEI) formed on this electrode was investigated by in‐situ Raman spectroscopy and in‐situ shell‐isolated nanoparticles for enhanced Raman spectroscopy (SHINERS) during the first discharge/charge cycle. The spectra collected via in‐situ Raman spectroscopy showed that the carbon coating is also (de)lithiated and it remains mechanically intact after the first complete cycle. There was no evidence of peaks related to the SEI due to the absence of surface enhancement of the Raman effect in this material, as was previously observed for carbon‐coated ZnFe2O4. However, bands assigned to polyethylene oxide species (PEO) and different lithium alkyl carbonate compounds (i. e., ROCO2Li, ROLi and RCOOLi) from the SEI were observed via SHINERS. The enhancement of the Raman effect by Au−SiO2 core‐shell nanoparticles allows the detection of surface films at potentials at which the SEI is formed and their chemical composition, which is not possible otherwise due to the intrinsically weak scattering process. Therefore, these results show that the SHINERS technique is a powerful method to investigate the structural evolution of the electrode material with potential and interfacial reactions on lithium‐ion batteries.

A critical and detailed assessment of using Shell Isolated Nanoparticles for Enhanced Raman Spectroscopy (SHINERS) on different electrode substrates was carried out, providing relative enhancement factors, as well as an evaluation of the distribution of shell-isolated nanoparticles upon the electrode surfaces. The chemical makeup of surface layers formed upon lithium metal electrodes and the mechanism of the oxygen reduction reaction on carbon substrates relevant to lithium-oxygen cells are studied with the employment of the SHINERS technique. SHINERS enhanced the Raman signal at these surfaces showing a predominant LiO based layer on lithium metal in a variety of electrolytes. The formation of LiO and LiO, as well as degradation reactions forming LiCO, upon planar carbon electrode interfaces and upon composite carbon black electrodes were followed under potential control during the reduction of oxygen in a non-aqueous electrolyte based on dimethyl sulfoxide.