Title of Paper:Ammonia, a Switch for Controlling High Ionic Conductivity in Lithium Borohydride Ammoniates

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Affiliation of Author(s):材料科学与技术学院

Journal:Joule

Abstract:Lithium borohydride ammoniates can be readily generated by LiBH4 absorbing ammonia at room temperature. Li(NH3)nBH4 (0 < n &le; 2) performed high ionic conductivity near room temperature, e.g., 2.21 &times; 10&minus;3 S cm&minus;1 for mono-ammoniate at 40&deg;C. A drastic increase in ionic conductivity occurs around 38&deg;C due to the structural change resulting from ammonia desorption. Moreover, the jump of the ionic conductivity is reversible because ammonia absorption/desorption acts as a switch for the structural change. The experimental results show that the stable electrochemical window for the sample is &sim;4 V. The crystal structure of Li(NH3)nBH4 (0 < n &le; 1) can be easily changed while the equilibrium dynamically changes with temperature. First-principles calculation results also indicate that Li(NH3)BH4 exerts an expected compatibility in contact with lithium iron phosphate cathode material. Finally, by introducing a gas instead of substituting an element, a dynamic change of crystal structure is achieved, accompanied with the improvement of lithium ionic conductivity. The progress of lithium-ion battery technology has been inseparable from the innovation of electrolyte materials. Compared with the traditional organic liquid electrolytes, stable solid-state electrolytes are safe, easy to assemble, and inexpensive. However, the large-scale application of solid-state electrolytes is currently limited owing to its low ionic conductivity at room temperature. Generally, lithium ionic conductivity of a solid electrolyte is easily influenced by its crystal structure and defect density, rather than others, and the gas absorption/desorption reaction is an easy way to induce the structural change in solids. Here, we first propose a new concept of utilizing the gas absorption/desorption reaction to improve the ionic conductivity of solids, and demonstrate the ionic conductivity jump of lithium borohydride ammoniates switched by ammonia desorption and absorption at around room temperature. Lithium ionic conductivity up to 10&minus;3 S cm&minus;1 can be achieved from solid-state lithium borohydride ammoniates near room temperature. The gradual change of crystal structure from Li(NH3)BH4 to Li(NH3)xBH4 (0 < x < 1) with the increase of temperature indicates a dynamic equilibrium formed in a closed system. The electrochemical properties of lithium borohydride ammoniates have been investigated. The amount of ammonia as a switch is a key factor controlling the lithium ionic conductivity. &copy; 2018 Elsevier Inc.

Translation or Not:no

Date of Publication:2018-01-01

Co-author:Zhang Xiaogang

Correspondence Author:Tengfei Zhang