All-solid-state Li–Se battery shows great potential as a candidate for next-generation energy storage devices due to its high energy density and safety. However, the low ionic conductivity of the solid electrolytes and large volume changes of Se active materials are two of the major issues that limit its applications. Herein, a simple solid-state reaction method is applied to synthesize chlorine-rich argyrodite Li_5.5PS_4.5Cl_1.5 electrolyte with high conductivity of 6.25 mS·cm⁻¹ at room temperature. Carbon nanotube (CNT) is introduced as the host for Se to obtain Se/CNT composite with both enhanced electronic conductivity and lower volume expansion during the electrochemical reaction process. All-solid-state Li–Se battery using Li_5.5PS_4.5Cl_1.5 as solid electrolyte combined with Se/CNT cathode and Li-In anode shows a discharge capacity of 866 mAh·g⁻¹ for the 2nd cycle under 0.433 mA·cm⁻² at room temperature. Moreover, the assembled battery delivers a high discharge capacity of 1026 mAh·g⁻¹ for the 2nd cycle when cycled at the same current density at 60 °C and maintains a discharge capacity of 380 mAh·g⁻¹ after 150 cycles. Owing to the high Li-ion conductivity of Li_5.5PS_4.5Cl_1.5 electrolyte, the assembled battery displays a high discharge capacity of 344 mAh·g⁻¹ under 0.113 mA·cm⁻² at − 20 °C and remains 66.1% after 200 cycles. In addition, this all-solid-state Li–Se battery shows ultralong cycling performances up to 1000 cycles under 0.433 mA·cm⁻² at − 20 °C. This work offers the design clue to fabricate the all-solid-state Li–Se battery workable at different operating temperatures with an ultralong cycling life. Graphical abstract 摘要 全固态锂-硒电池具有能量密度高, 安全性好等优点, 在新一代储能设备中具有广泛的应用前景 然而, 固体电解质的离子电导率低和硒活性材料的体积变化大是限制其实用化的两个主要问题. 本文采用简单的固相反应法合成了室温下电导率为 6.25 mS•cm-1 的富氯硫银锗矿 Li_5.5PS_4.5C_l1.5 电解质. 引入碳纳米管 (Carbon nanotube, CNT) 作为Se的载体, 在电化学反应过程中获得了电子导电性增强和体积膨胀降低的 Se/CNT 复合材料. 以Li5.5PS4.5Cl1.5 为固体电解质, 结合 Se/CNT 阴极和 Li-In 阳极的全固态 Li-Se 电池, 室温下电流密度为 0.433 mA•cm-2 循环时第二次放电容量为 866 mAh•g-1. 在60 °C条件, 在相同电流密度下, 组装后的电池第二次循环放电容量为 1026 mAh•g-1, 循环150次后放电容量保持在380 mAh•g-1. 由于 Li_5.5PS_4.5C_l1.5 电解液具有较高的锂离子电导率, 在−20 °C 下放电容量为 0.113 mA•g-2, 放电容量为 344 mAh•g-1, 循环200次后放电容量仍为 66.1%. 此外, 该全固态 Li-Se 电池在−20°C下, 在 0.433 mA•cm-2 的温度下显示了 1000次超长循环性能. 这一工作为制备在不同工作温度下具有超长循环寿命的全固态锂硒电池提供了思路.