Li + ion conductor based on NaBr doped with LiBH 4
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Li+ ion conductor based on NaBr doped with LiBH4 Reona Miyazaki, Masatoshi Shomura, Reina Miyagawa, and Takehiko Hihara, Department of Physical Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan Address all correspondence to Reona Miyazaki at [email protected] (Received 29 September 2018; accepted 15 November 2018)
Abstract In this work, the guest Li+ conduction properties in NaBr–LiBH4 system were investigated. It was suggested that the guest Li+ ions occupy the − + Na+ sites and BH− 4 ions substitute the Br ions in NaBr. The dominant Li conduction in NaBr–LiBH4 system was demonstrated by the combination of electrochemical measurements and time-of-flight secondary ion mass spectrometry. The guest Li+ ion conductivity of 15NaBr·LiBH4 was measured to be 1 × 10−7 S/cm at 313 K. The present results indicate that the guest Li+ conductors are not restricted to the previous reported iodides (NaI, KI), but other Li-free compounds have the possibility to become the candidates for the guest Li+ ion conductors.
Introduction Lithium ion batteries (LIBs) are widely used for the power supply of the various portable devices because of their high-energy density. Because their anode potential is below the reduction voltage of aqueous solutions, organic solvents are used as the electrolyte. One origin of the ignition of current LIBs is the flammable nature of the organic liquid electrolytes. Nonflammable solid electrolytes are the key materials for the allsolid-state batteries compatible with the safety and high-energy density of LIBs. For example, high-capacity cathodes such as sulfur can be used in all-solid-state cells without dissolution of the discharge products (lithium poly-sulfides).[1] For the high-power density of all-solid-state LIBs, high Li+ conductive solid electrolytes with low grain boundary resistances are highly required. The types of ionic conduction in the solid electrolytes are divided into two cases. One is the conduction of the host ions in a given material. Based on the host ion conduction, Li compounds are the material candidates for the fabrication of Li+ ion conductors. The sulfides are the most promising materials for the practical application because of their exceptionally high Li+ ion conductivity. The Li+ ion conductivity of 10−2 S/cm at room temperature was firstly reported for Li10GeP2S12 (LGPS) in 2010.[2] The conductivity was further enhanced by the replacement of Ge4+ with Si4+ and partial substitution of S2− with Cl−.[3] In general, the interface between the electrode active materials and the solid electrolytes must contact intimately for the facile charge transfer reaction. Regardless of the high Li+ ion conductivity in a bulk region, oxide materials are not always suitable for all-solid-state batteries due to the high grain boundary resistance.[4,5] The poor contact with the
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active materials is the bottleneck for the construction of electrochemically favorable interface.[6] In general, the conventional hig
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