Encapsulating and Operating a Stable Li₃ErBr₆‐Based Solid Li–SeS₂ Battery at Room Temperature

Abstract Rare earth‐based halide solid electrolytes (RE‐HSEs) are noted due to their comprehensive properties of good ionic conductivity, electrochemical window, and deformability. However, the types and applications of RE‐HSEs need to be further expanded. Here, a highly purified RE‐HSE Li₃ErBr₆ (LErB) is synthesized successfully by a vacuum evaporation method. The prepared LErB possesses a high ionic conductivity of 1.0 mS cm⁻¹ with an electrochemical window of 1.5–3.4 V. The LErB is applied in a solid Li–SeS₂ battery, which can realize stable cycling performance for 300 cycles and good rate performance at room temperature. Moreover, to evaluate the practicability of the LErB‐based Li–SeS₂ battery, a pouch‐type cell is assembled, which can light a diode array even after bending and cutting. These results demonstrate that LErB‐based solid Li–SeS₂ cells possess advantages in battery packaging and operation, which can improve the practicability of all‐solid‐state lithium batteries.