Complex Hydrides for Electrochemical Energy Storage

Abstract

Complex hydrides have energy storage-related functions such as i) solid-state hydrogen storage, ii) electrochemical Li storage, and iii) fast Li-and Naionic conductions. Here, recent progress on the development of fast Li-ionic conductors based on the complex hydrides is reported. The validity of using them as electrolytes in all-solid-state lithium rechargeable batteries is also examined. Not only coated oxides but also bare sulfi des are found to be applicable as positive electrode active materials. Results related to fast Na-ionic conductivity in the complex hydrides are presented. In the last section, the future prospects for battery assemblies with high-energy densities, and Mg ion batteries with the liquid and the solid-state electrolytes are discussed. Figure 1. Crystal structures of a) LT phase and b) HT phase of LiBH 4 . [ 16 ]Adv. FEATURE ARTICLEto fast Li-ionic conduction, the advantages of the use of complex hydrides as rechargeable battery electrolytes are as follows, iii) Fast Li-and Na-ionic conductions: One of the important challenges in the fi eld of battery research is the development of fast ionic conductors because this class of materials enables the assembly from micro- [ 24 ] to bulk-type [25][26][27] all-solid-state rechargeable cells, which allows the broader applications. With this background, various solid-state electrolytes have been developed so far, however, the materials showing suffi cient ionic conductivity as well as good stability in the voltage ranges for battery operation are limited to a few cases. [ 28 ] Therefore, novel solid-state electrolytes are urgently required for the development of future generation batteries. Since the discovery of fast Li-ionic conduction in the HT phase of LiBH 4 , [ 29 ] we have developed numerous solid-state electrolytes based on the complex hydrides that exhibit fast Li-and Na-ionic conductions. [ 30 ] Herein, we briefl y report recent progress in the development of the complex hydrides that exhibit fast Li-ionic conduction. All-solid-state Li rechargeable batteries were subsequently assembled using coated-LiCoO 2 and TiS 2 positive electrodes, and LiBH 4 -based electrolytes. The validity of the use of the complex hydrides as electrolytes in a rechargeable battery was examined on the basis of charge-discharge measurements. In the following section, our recent development of fast Na-ionic conductors based on the complex hydrides is summarized. We discuss the future prospects for the development of high energy density rechargeable batteries, and Mg-ion batteries that use nonaqueous and solid-state electrolytes based on the complex hydrides. FEATURE ARTICLEhexagonal phase of LiBH 4 (fast Li-ion conduction phase) even at room temperature when x exceeds 0.25. And then, the solid-solution, Li 4 (BH 4 ) 3 I, exhibits fast Li-ionic conductivity of 2 × 10 −5 S cm −1 at 300 K. [ 34,[51][52][53] This phenomenon might be due to increased neighboring distance of [BH 4 ] − [ 54 ] and induced lattice anharmonicity by the partial substitution of I − instead of ...

Rotational disorder in lithium borohydride

“…− anion in the terahertz regime as well as by translational mobility of the [Li] + cation, leading to high ionic conductivity (σ ∼ 10 −3 S/cm) [7,8]. Disorder can be imposed below the phase transition temperature by ion substitution or by nano-confinement.…”

“…Apart from its classical application as a reducing agent or as a starting compound for the synthesis of organometallic derivatives, the light-weight LiBH 4 , together with its chemical relatives such as NaBH 4 have recently been discussed as synthetic fuels either in the direct borohydride fuel cell [4] or as hydrogen storage materials for mobile applications [5,6]. In addition, owing to its high lithium ion conductivity, LiBH 4 and related compounds are considered as potential solid-state electrolytes for lithium-ion batteries [7,8].…”

Complex hydrides as room-temperature solid electrolytes for rechargeable batteries

“…Also TiS 2 was tested as a positive electrode [53], and the solid electrolyte was even combined with a metal hydride negative electrode [54]. More details on complex metal hydrides for bulk-type all-solid-batteries can be found in [28].…”

“…Subsequently, we will also discuss alternative complex metal hydrides with high ionic mobilities, and we will end with a brief conclusion and outlook. More details on complex metal hydrides as solid-state electrolytes can also be found in [28].…”

In-situ powder neutron diffraction study on the formation process of LaMg 2 NiH 7

“…The complex hydrides are attractive due to a wide variety of functionalities, such as hydrogen storage, superconductivity, fast ionic conductivity, magnetism, and metal-insulator transition [1][2][3][4][5][6].…”