Fibonacci Stoichiometry and Superb Performance of Nb₁₆W₅O₅₅ and Related Super-Battery Materials

作     者：Hans Hermann Otto Hans Hermann Otto

作者机构：Materialwissenschaftliche Kristallographie Clausthal University of Technology Clausthal-Zellerfeld Lower Saxony Germany 

出 版 物：《Journal of Applied Mathematics and Physics》 (应用数学与应用物理（英文）)

年 卷 期：2022年第10卷第6期

页      面：1936-1950页

学科分类：08[工学] 080502[工学-材料学] 0805[工学-材料科学与工程（可授工学、理学学位）] 

主　　题：Super Battery Niobium Tungsten Oxide Crystallographic Shear Chemical Twinning Fibonacci Stoichiometry Ti Substitution 

摘      要：In this contribution, two important crystallographic concepts for the formation of a series of block structures associated with channeling have been compared: chemical twinning and crystallographic shear. Twin planes respectively shear planes besides formed channels serve as a sink for charge carriers or, when the oxidation state of metal ions can be reduced, as a reservoir for intercalated lithium. In this way, Wadsley-Roth shear phases such as niobium tungsten oxide exhibit channels for ultra-fast lithium-ion diffusion. They are in focus as anode material for super-batteries, superb in terms of energy respectively power density, charging time, cycle life and safety. It should be noted that the transition metal to oxygen ratio TM/O = 21/55 of the title compound is a Fibonacci number quotient. Also, the crystal lattice can be traced back to Fibonacci geometry. When replacing only 0.0213 tungsten atoms in the formula with less expensive titanium, a TM/O ratio of 0.381966 =ϕ2 can be adapted besides an average valence electron concentration of 2⋅ϕ-2, where represents the most irrational number of the golden mean. The additional disorder caused by even such small titanium replacement and accompanied oxygen vacancies could fasten up the already high lithium diffusion further. Ultrasonic treatment may be applied besides thermal cycling to prepare phase-pure of the highest electrochemical performance. A replacement of oxygen by some fluorine atoms is an obvious synthesis possibility, but the higher binding energy expected between lithium and fluorine in contrast to oxygen may rather hinder than promote lithium diffusion.