Insights into layered-tunnel dynamic structural evolution based on local coordination chemistry regulation for high-energy-density and long-cycle-life sodium-ion oxide cathodes

The pursuit of high energy density while achieving long cycle life remains a challenge in developing transition metal(TM)oxide cathode materials for sodium-ion batteries(SIBs).Here,we present a concept of precisely manipulating structural evolution via local coordination chemistry regulation to design high-performance composite cathode materials.The controllable structural evolution process is realized by tuning magnesium content in Na0.6Mn1-xMgxO2,which is elucidated by a combination of experimental analysis and theoretical calculations.The substitution of Mg into Mn sites not only induces a unique structural evolu-tion from layered–tunnel structure to layered structure but also mitigates the Jahn–Teller distortion of Mn3+.Meanwhile,benefiting from the strong ionic inter-action between Mg2+and O2-,local environments around O2-coordinated with electrochemically inactive Mg2+are anchored in the TM layer,providing a pinning effect to stabilize crystal structure and smooth electrochemical profile.The layered–tunnel Na0.6Mn0.95Mg0.05O2 cathode material delivers 188.9 mAh g-1 of specific capacity,equivalent to 508.0 Wh kg-1 of energy density at 0.5C,and exhibits 71.3%of capacity retention after 1000 cycles at 5C as well as excellent compatibility with hard carbon anode.This work may provide new insights of manipulating structural evolution in composite cathode materials via local coordi-nation chemistry regulation and inspire more novel design of high-performance SIB cathode materials.

Comparison of Few-layer Graphene Prepared from Natural Graphite through Fast Synthesis Approach

我们从斯里兰卡用高纯净天赋石墨在大规模上报导高质量的很少层 graphene 的合成。一个新奇热方法被改编从中间的石墨氧化物准备 graphene，它被在低温度加热中介获得(在 150 °C 上面) 在为 5 min 并且为 15 min 的在氩的在 500 °C 的随后的加热的空中。样品被 X 光检查衍射描绘， Fourier 变换红外线的光谱学，扫描电子显微镜学，拉曼光谱学等等。性质和 graphene 的表演被观察依靠石墨消息提供者。从 Kahatagaha 石墨来源的减少的石墨氧化物展出更高的 Brunauer-Emmett-Teller 特定的表面区域 ~ 500 m 2 g−1 和是的稳定的特定的能力在 Li 离子电池的阳极而 Bogala 石墨作为阳极显示出更高起始的不能反逆的性能和更高的能力，超过石墨的理论特定的能力。两 graphenes 显示出高电的电导率。graphene，在仅仅一些层的栈存在，想了是 2-6 层，将为应用程序的一个广阔变化有希望。