Li4B10H10B12H12 as solid electrolyte for solid-state lithium batteries

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2023-09, Vol.11 (35), p.18996-19003
• Main Authors: Garcia, Andrea, Müller, Gian, Černý, Radovan, Rentsch, Daniel, Asakura, Ryo, Battaglia, Corsin, Arndt Remhof
• Format: Article
• Language: English
• Subjects: Anions; Ball milling; Cation exchange; Cation exchanging; Conductivity; Electrochemistry; Electrolytes; Feasibility studies; Ion currents; Ions; Iron phosphates; Lithium; Lithium batteries; Low temperature; Mixtures; Molten salt electrolytes; Room temperature; Solid electrolytes; Solid state; Stability analysis; Thermal stability; Titanium; Toxicity
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d3ta03914e

Hydridoborates are a promising class of solid electrolytes for solid-state batteries, combining liquid-like room temperature ionic conductivity, high (electro-)chemical stability, low gravimetric density, easy processability, and low toxicity. We show that cation exchange is a feasible method to prepare Li2B10H10 and Li2B12H12 from Na2B10H10 and Na2B12H12, respectively, with high yields. Ball milling of an equimolar mixture of Li2B10H10 and Li2B12H12 yields a single phase, isomorphic to the low temperature Li2B12H12 phase (space group Pa3) with ordered [B12H12]2− and disordered [B10H10]2− anions sharing the same position in the structure. The ionic conductivity of the equimolar mixture Li4B10H10B12H12 exhibits 4 × 10−4 S cm−1 at 25 °C and 4 × 10−3 S cm−1 at 60 °C, respectively, exceeding those of the unmixed phases by several orders of magnitude. The electrolyte possesses an oxidative stability >3 V vs. Li+/Li and thermal stability beyond 300 °C, and is evaluated in proof-of-concept solid-state batteries with a lithium metal anode and with titanium disulfide (TiS2) or lithium iron phosphate (LiFePO4) as a cathode active material. Discharge capacities of 83% and 73% of the theoretical capacity were achieved for TiS2 and LiFePO4, respectively, at the end of the first dis-/charge cycle. For LiFePO4, the de-/lithiation potential lies outside the electrochemical stability window of the electrolyte, requiring additional measures to protect the electrolyte from decomposition. Our study demonstrates the feasibility of using closo-hydridoborates as ionic conductors in solid-state lithium batteries.