Layered transition metal oxides are the most important cathode materials for Li/Na/K ion batteries. Suppressing undesirable phase transformations during charge-discharge processes is a critical and fundamental challenge towards the rational design of high-performance layered oxide cathodes. Here we report a shale-like NaxMnO2 (S-NMO) electrode that is derived from a simple but effective water-mediated strategy. This strategy expands the Na+ layer spacings of P2-type Na0.67MnO2 and transforms the particles into accordion-like morphology. Therefore, the S-NMO electrode exhibits improved Na+ mobility and near-zero-strain property during charge-discharge processes, which leads to outstanding rate capability (100 mAh g−1 at the operation time of 6 min) and cycling stability (>3000 cycles). In addition, the water-mediated strategy is feasible to other layered sodium oxides and the obtained S-NMO electrode has an excellent tolerance to humidity. This work demonstrates that engineering the spacings of alkali-metal layer is an effective strategy to stabilize the structure of layered transition metal oxides.

The highest pressure form of the major Earth-forming mantle silicate is MgSiO 3 post-perovskite (PPv). Understanding the fate of PPv at TPa pressures is the first step for understanding the mineralogy of super-Earths-type exoplanets, arguably the most interesting for their similarities with Earth. Modeling their internal structure requires knowledge of stable mineral phases, their properties under compression, and major element abundances. Several studies of PPv under extreme pressures support the notion that a sequence of pressure induced dissociation transitions produce the elementary oxides SiO 2 and MgO as the ultimate aggregation form at ∼3 TPa. However, none of these studies have addressed the problem of mantle composition, particularly major element abundances usually expressed in terms of three main variables, the Mg/Si and Fe/Si ratios and the Mg#, as in the Earth. Here we show that the critical compositional parameter, the Mg/Si ratio, whose * Corresponding author value in the Earth's mantle is still debated, is a vital ingredient for modeling phase transitions and internal structure of super-Earth mantles. Specifically, we have identified new sequences of phase transformations, including new recombination reactions that depend decisively on this ratio. This is a new level of complexity that has not been previously addressed, but proves essential for modeling the nature and number of internal layers in these rocky mantles.

As a parent compound of Li-rich electrodes, Li 2 MnO 3 exhibits high capacity during the initial charge, however, suffers notoriously low Coulombic efficiency due to irreversible oxygen oxidation and its associated surface activitiesreactions. Here, we successfully optimize tune the oxygen activitiesoxidation process towards reversible oxygen redox reactions by intentionally introducing protons into lithium octahedral vacancies in Li 2 MnO 3 system with its original structural integrity maintained. Combining structural probes, theoretical calculations and resonant inelastic X-ray scattering results, a moderate coupling between the introduced protons and lattice oxygen at the oxidized state is revealed, which stabilizes the oxygen activities in initialduring chargecharging. Such a coupling leads to an unprecedented initial Coulombic efficiency (99.2%) with a further greatly improved discharge capacity of 302 mAh g-1 in the protonated Li 2 MnO 3 electrodes. These findings directly demonstrate an effective concept for controlling oxygen activities in Li-rich cathodessystems, which is critical for developing high-capacity energy cathodes in batteries. TOC GRAPHICS