Lotus Leaf-Derived Hierarchically Porous Hard Carbon Nanosheets as Anode for Highly Robust Potassium-Ion Batteries

Owing to abundant resources, low redox potential, and low expense, potassium-ion batteries (PIBs) have received continuous attention as a rookie of renewable electricity storage equipment. To obtain high-performance PIBs based energy storage, the energy storage anode must provide a stable and suitable structure for large-sized active potassium ions. To this end, a lotus leaf-derived, hierarchically porous activated carbon (LHPAC) was mainly obtained by a bionic strategy. The prepared LHPAC with a hierarchically porous structure not only affords fast transportation for both electrons and potassium ions but also supplies the necessary void space to avoid structural instability incurred by volume dilatation in the process of electrode operation. Therefore, the LHPAC exhibited exceptional reversible capacity (170 mA · h · g–1 at 50 mA · g–1) and superb cycle solidity (0.016% tiny capacity attenuation per cycle at 200 mA · g–1, capacity retention rate of 86.3% after 870 cycles), as well as inimitable rate performance. This work demonstrates the great application prospects of biomass-derived carbon materials as anode for sturdy PIBs.

Pure shear deformation and its induced mechanical responses in metallic glasses

Shear is a basic deformation mode governing yielding, plasticity and fracture in metallic solids. For amorphous metals, due to various constraints, little work is available in addressing directly shear deformation and shear-induced mechanical property changes which are vital to the mechanistic understanding of this new class of disordered materials. Here, by using a finite deformation theory, we examine the pure shear deformation in a bulk metallic glass in a large range of shear strains. With the continuum approach, we show systematically for the first time the detailed shear deformation behaviours, shear-induced normal stress and strain relations, softening in the elastic constants, volume dilatation and free energy change induced by the shear deformation. These results point to two major consequences from the shear deformation, one is the mechanical degradations and the other material degradation which is responsible for the changes in the mechanical properties of the disordered materials.

Thermal expansion of alunite up to dehydroxylation and collapse of the crystal structure

The high-temperature (HT) behaviour of a sample of natural alunite was investigated by means of in situ HT single-crystal X-ray diffraction from room temperature up to the dehydroxylation temperature and consequent collapse of the crystal structure. In the temperature range 25–500°C, alunite expands anisotropically, with most of the contribution to volume dilatation being produced by expansion in the c direction. The thermal expansion coefficients determined over the temperature range investigated are: αa = 0.61(2) × 10–5 K–1 (R2 = 0.988), αc = 4.20(7) × 10–5 K–1 (R2 = 0.996), αc/αa = 6.89, αV = 5.45(7) × 10–5 K–1 (R2 = 0.998). At ∼275–300°C, a minor discontinuity in the variation of unit-cell parameters with temperature is observed and interpreted on the basis of loss of H3O+ that partially substitutes for K+ at the monovalent A site in the alunite structure. Increasing temperature causes the Al(O,OH)6 sheets, which remain almost unaltered along the basal plane, to move further apart, and this results in an expansion of the coordination polyhedron around the intercalated potassium cation. Sulfate tetrahedra act as nearly rigid units, they contract a little in the lower temperature range to accommodate the elongation of the Al octahedra.

A NUMERICAL STUDY OF FLUID INJECTION AND MIXING UNDER NEAR-CRITICAL CONDITIONS

Nitrogen injection under conditions in close vicinity of liquid-gas critical point is studied through numerical simulation. The thermodynamic and transport properties of fluid exhibit anomalies in the near-critical fluid regime. These anomalies can cause distinctive effects on heat transfer and hydrodynamics. To focus on the influence of the highly variable properties and avoid the difficulties encountered in modeling high Reynolds number flows, a relatively low injection Reynolds number is adopted. A reference case with the same configuration and Reynolds number is also simulated in the ideal gas regime. Full conservation laws, real-fluid thermodynamic and transport phenomena are accommodated in the model. The obtained results reveal that the flow features of the near-critical fluid jet are significantly different from the ideal gas case. The near-critical fluid jet spreads faster and mixes better with the ambient fluid compared to the ideal gas jet. It is also identified that vortex pairing process develops faster in the near-critical case than in the ideal gas case. Detailed analysis of data at different streamwise positions including both flat shear layer region and fully developed vortex region reveals the effect of volume dilatation and baroclinic torque plays an important role in the near-critical fluid case. The volume dilatation effect disturbs the shear layer and makes it more unstable. The volume dilatation and baroclinic effects strengthen the vorticity and stimulate the vortex rolling up and pairing process.