Boosted sodium ion storage performance in MnO_(2):Understanding the bond angle-mediated orbital overlap in MnO_(6)units for fast charge transfer

Symmetric six oxygen-coordinated Mn structural units(MnO6)in MnO2 with small Mn–O orbital overlap hamper electron transfer rates during energy storage.Herein,we report a novel bond angle modulation strategy to manipulate Mn–O orbital overlap in MnO2 through the construction of Mn vacancies(MnO2-VMn),aiming at expediting electron transfer,and thus enhancing energy storage performance.Both experimental and theoretical results disclose that the amplification of Mn–O–Mn bond angles exclusively augments the Mn(dx2-y2)-O(py)orbital overlap and triggers the electron redistribution in MnO2-VMn,inducing an augmented Mn dx2-y2 electron occupation.This heightened presence of active electrons in the Mn dx2-y2 orbital paves the way for accelerating electron transfer and ion transfer in MnO2-VMn.Notably,MnO2-VMn delivers an improved specific capacitance of 425 F g−1 at 1 A g−1 and a superior rate capacity of 265 F g−1 at 20 A g−1.Furthermore,an asymmetric supercapacitor(MnO2-VMn//AC ASC)was fabricated,exhibiting a high energy density of 64.3 Wh kg−1 at a power density of 1000 W kg−1.Furthermore,theoretical insights uncover the profound implications of metal–oxygen–metal bond angle regulation on interatomic orbital overlap modulation.These revelations illuminate pathways for the design of advanced energy storage materials.

Maximizing ionic transport of Li1+xAlxTi2-xP3O12 electrolytes for all-solid-state lithium-ion storage:A theoretical study

The concept of all-solid-state batteries provides an efficient solution towards highly safe and long-life energy storage,while the electrolyte-related challenges impede their practical application.Li1+xAlxTi2-xP3O12(0≤x≤1)with superior Li ionic conductivity holds the promise as an ideal solidstate electrolyte.The intrinsic mechanism to reach the most optimum ionic conductivity in Al-doped Li1+xAlxTi2-xP3O12,however,is unclear to date.Herein,this work intends to provide an atomic scale study on the Li-ion transport in Li1+xAlxTi2-xP3O12electrolyte to rationalize how Al-dopant initiates interstitial Li activity and facilitate their easy mobility combining Density Functional Theory(DFT)and ab initio Molecular dynamics(AIMD)simulations.It is discovered that the interstitial Li ions introduced by Al dopants can effectively activate the neighboring occupied intrinsic Li-ions to induce a long-range mobility in the lattice and the maximum Li ionic conductivity is achieved at 0.50 Al doping concentration.The Li-ion migration paths in Li1+xAlxTi2-xP3O12have investigated as the degree of distortion of[PO4]tetrahedra and[TiO6]octahedra resulted by different Al doping concentrations.The asymmetry of the surrounding distorted[PO4]and[TiO6]polyhedrons play a critical role in reducing the migration barrier of Li ions in Li1+xAlxTi2-xP3O12.The flexible[Ti O6]polyhedrons with a capacity to accommodate the structural distortion govern the Li ionic conductivity in Li1+xAlxTi2-xP3O12.This work rationalizes the mechanism for the most optimum Li ionic conductivity in Al-doped Li Ti2P3O12electrolyte and,more importantly,paves a road for exploring novel all-solid-state lithium battery electrolytes.