Synthesis, Structure, and Electrochemical Properties of Na3MB5O10 (M = Fe, Co) Containing M2+ in Tetrahedral Coordination

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• 作者：Florian Strauss ; Gwenaëlle Rousse ; Moulay Tahar Sougrati ; Daniel Alves Dalla Corte ; Matthieu Courty ; Robert Dominko ; Jean-Marie Tarascon
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：December 19, 2016
• 年：2016
• 卷：55
• 期：24
• 页码：12775-12782
• 全文大小：484K
• ISSN：1520-510X

文摘

In the search for new cathode materials for sodium ion batteries, the exploration of polyanionic compounds has led to attractive candidates in terms of high redox potential and cycling stability. Herein we report the synthesis of the two new sodium transition-metal pentaborates Na₃MB₅O₁₀ (M = Fe, Co), where Na₃FeB₅O₁₀ represents the first sodium iron borate reported at present. By means of synchrotron X-ray diffraction, we reveal a layered structure consisting of pentaborate B₅O₁₀ groups connected through M²⁺ in tetrahedral coordination, providing possible three-dimensional Na-ion migration pathways. Inspired by these structural features, we examined the electrochemical performances versus sodium and showed that Na₃FeB₅O₁₀ is active at an average potential of 2.5 V vs Na⁺/Na⁰, correlated to the Fe³⁺/Fe²⁺ redox couple as deduced from ex situ Mössbauer measurements. This contrasts with the case for Na₃CoB₅O₁₀, which is electrochemically inactive. Moreover, we show that their electrochemical performances are kinetically limited, as deduced by complementary ac/dc conductivity measurements, hence confirming once again the complexity in designing high-performance borate-based electrodes.