Stable Interface Formation between TiS₂ and LiBH₄ in Bulk-Type All-Solid-State Lithium Batteries

Abstract

In this study, we assembled a bulk-type all-solid-state battery comprised of a TiS 2 positive electrode, LiBH 4 electrolyte, and Li negative electrode. Our battery retained high capacity over 300 discharge-charge cycles when operated at 393 K and 0.2 C. The 2 nd discharge capacity was as high as 205 mAh g -1 , corresponding to a TiS 2 utilization ratio of 85 %. The 300 th discharge capacity remained as high as 180 mAh g -1 with nearly 100 % coulombic efficiency from the 2 nd cycle. Negligible impact of the exposure of LiBH 4 to atmospheric-pressure oxygen on battery cycle life was also confirmed. To investigate the origin of the cycle durability for this bulk-type all-solid-state TiS 2 /Li battery, electrochemical measurements, thermogravimetry coupled with gas composition analysis, powder X-ray diffraction measurements and first-principles molecular dynamics simulations were carried out. Chemical and/or electrochemical oxidation of LiBH 4 occurred at the TiS 2 surface at the battery operating temperature of 393 K and/or during the initial charge. During this oxidation reaction of LiBH 4 with hydrogen (H 2 ) release just beneath the TiS 2 surface, a third phase, likely including Li 2 B 12 H 12 , precipitated at the interface between LiBH 4 and TiS 2 . Li 2 B 12 H 12 has a lithium ionic conductivity of log(σ / S cm -1 ) = -4.4, charge transfer reactivity with Li electrodes, and superior oxidative stability to LiBH 4 , and thereby can act as a stable interface that enables numerous discharge-charge cycles. Our results strongly suggest that the creation of such a stable interfacial layer is due to the propensity of forming highly stable, hydrogen-deficient polyhydro-closo-polyborates such as Li 2 B 12 H 12 , which are thermodynamically available in the ternary Li-B-H system.

Bulk-Type All-Solid-State Lithium Batteries Using Complex Hydrides Containing Cluster-Anions

“…The tenth discharge capacity remained as high as 193 mAh g −1 . Regardless of the battery operating temperature, our battery realized a high coulombic ef ciency, which is de ned by the ratio of the discharge capacity to the charge capacity, at the initial cycle as is expected for this electrolyte 18) and summarized in Table 1. The stability of this electrolyte will be discussed later.…”

“…These values were similar to the literature data in which a = 0.95771(2) nm. 35) Regardless of the preparation method, Li 2 B 12 H 12 allowed for the assembly of the bulk-type all-solid-state batteries merely by uniaxial pressing at room temperature, i.e., cold-pressing similar to that used for LiBH 4 , because of their high deformability, 7,[16][17][18][19][20] as a photograph shown in Fig. 2.…”

“…7) Recently, we demonstrated the repeated operation of a bulk-type all-solid-state lithium rechargeable battery that uses the LiBH 4 -based electrolytes. 7,[16][17][18][19][20] Hence, this class of the materials is considered to represent the third family of solid-state electrolyte, after sul des and oxides. The solid-state battery that uses LiBH 4 could only operate at temperatures above 393 K, at which point, the LiBH 4 electrolyte exhibited high lithium-ionic conductivity.…”

“…As a result, over 300 dischargecharge cycles were successfully demonstrated. 18) We explored a series of complex hydrides having a cluster anion as a novel electrolyte design guide, and discovered various fast lithium 26,27) and sodium ionic conductors; [26][27][28][29][30] the ionic conductivities of a selection of these compounds are shown in Fig. 1.…”

Complex hydrides as room-temperature solid electrolytes for rechargeable batteries

“…[50]. 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].…”