Heterostructure Interface Construction of Cobalt/Nickle Diselenides Hybridized with sp²–sp³ Bonded Carbon to Boost Internal/External Sodium and Potassium Storage Dynamics

Metal selenides exhibit great potential in energy storage systems owing to their diversified species, large interlayer spaces, and high theoretical specific capacity according to multiple ion-storage behaviors. In this work, heterostructured CoSe2/NiSe2 coupled with sp3 bonded N-doped carbon coating layers and interconnected with sp2 bonded carbon nanotubes is synthesized through a room-temperature wet-chemistry approach and a selenization route with Co–Ni Prussian blue analogues as the precursor. The hybrid exhibits enhanced energy storage properties when utilized as an anode material for sodium- and potassium-ion batteries. The excellent performance of the hybrid can be indexed to the delicately design of the CoSe2/NiSe2 heterostructure and the hybridization of it with sp2 and sp3 bonded carbonaceous materials synchronously. Experimental and theoretical calculation results demonstrate the heterostructure is constructed to acquire charge transfer driving forces to boost internal reaction dynamics. And there is a combination of the dual advantages of sp3 and sp2 bonded carbon, possessing not only the exceptional mechanics buffer capability of N-doped carbon coating layers but also the excellent electrical characteristics of carbon nanotubes to promote external reaction dynamics. In addition, to elucidate the differential sodium/potassium storage capability of the hybrid, theoretical calculations are further performed to indagate the adsorption energy of sodium and potassium on the CoSe2/NiSe2 heterointerface by establishing five Na/K adsorption sites. The research provides an effective strategy for the melioration of internal/external reaction dynamics to deliver ions durably and efficiently in energy storage regions

Reversible Li⁺ Storage in a LiMnTiO₄ Spinel and Its Structural Transition Mechanisms

In this work, LiMnTiO₄ (a structural analogue of classic spinel LiMn₂O₄) with a disordered cubic spinel structure (<i>Fd</i>3̅<i>m</i>) has been synthesized by a low-temperature sol–gel route. The as-obtained LiMnTiO₄ exhibits excellent cycling stability in a wide voltage range from 1.5 to 4.8 V with high discharge capacities of 290, 250, and 140 mA h g^–1 at a C/40, C/19, and 1C rate, respectively. Combined long- and short-range structural characterization techniques are used to reveal the correlation between structure and electrochemical behavior. During cycling, the charge/discharge profiles of LiMnTiO₄ evolve from initially two well-separated plateaus into sloping regimes. In the early stage of discharge, LiMnTiO₄ undergoes phase transitions from an initial spinel phase to mixtures of predominant rock-salt (<i>Fm</i>3̅<i>m</i>) and tetragonal (<i>I</i>4₁/<i>amd</i>) structures along with a decrease in crystallite size from 12 nm to 3 to 4 nm. During further cycling, the spinel/rock-salt phase transition was found to be reversible with the cubic framework remaining intact. The presence of the tetragonal phase after the first discharge suggests that the Mn³⁺ Jahn–Teller distortion is partially involved during lithiation from Li_1–<i>y</i>Mn^3+<i>y</i>TiO₄ to Li_1+<i>x</i>Mn^3–<i>x</i>TiO₄ and the fraction of such a tetragonal phase remains at about 30–40% during subsequent cycling

Control of Ionic Conductivity by Lithium Distribution in Cubic Oxide Argyrodites Li_6+<i>x</i>P_1–<i>x</i>Si_<i>x</i>O₅Cl

Argyrodite is a key structure type for ion-transporting materials. Oxide argyrodites are largely unexplored despite sulfide argyrodites being a leading family of solid-state lithium-ion conductors, in which the control of lithium distribution over a wide range of available sites strongly influences the conductivity. We present a new cubic Li-rich (>6 Li+ per formula unit) oxide argyrodite Li7SiO5Cl that crystallizes with an ordered cubic (P213) structure at room temperature, undergoing a transition at 473 K to a Li+ site disordered F4̅3m structure, consistent with the symmetry adopted by superionic sulfide argyrodites. Four different Li+ sites are occupied in Li7SiO5Cl (T5, T5a, T3, and T4), the combination of which is previously unreported for Li-containing argyrodites. The disordered F4̅3m structure is stabilized to room temperature via substitution of Si4+ with P5+ in Li6+xP1–xSixO5Cl (0.3 x < 0.85) solid solution. The resulting delocalization of Li+ sites leads to a maximum ionic conductivity of 1.82(1) × 10–6 S cm–1 at x = 0.75, which is 3 orders of magnitude higher than the conductivities reported previously for oxide argyrodites. The variation of ionic conductivity with composition in Li6+xP1–xSixO5Cl is directly connected to structural changes occurring within the Li+ sublattice. These materials present superior atmospheric stability over analogous sulfide argyrodites and are stable against Li metal. The ability to control the ionic conductivity through structure and composition emphasizes the advances that can be made with further research in the open field of oxide argyrodites