The liquid-like feature of thermoelectric superionic conductors is a double-edged sword: the long-range migration of ions hinders the phonon transport, but their directional segregation greatly impairs the service stability. We report the synergetic enhancement in figure of merit (ZT) and stability in Cu_1.99Se-based superionic conductors enabled by ion confinement effects. Guided by density functional theory and nudged elastic band simulations, we elevated the activation energy to restrict ion migrations through a cation–anion co-doping strategy. We reduced the carrier concentration without sacrificing the low thermal conductivity, obtaining a ZT of ∼3.0 at 1,050 K. Notably, the fabricated device module maintained a high conversion efficiency of up to ∼13.4% for a temperature difference of 518 K without obvious degradation after 120 cycles. Our work could be generalized to develop electrically and thermally robust functional materials with ionic migration characteristics.

热电超离子导体的类液体特性是一把双刃剑：离子的长距离迁移阻碍了声子输运，但它们的定向偏析极大地损害了使用稳定性。_{我们报告了通过离子限制效应实现的 Cu 1.99} Se 基超离子导体的品质因数 (ZT) 和稳定性的协同增强。在密度泛函理论和微动弹性带模拟的指导下，我们通过阳离子-阴离子共掺杂策略提高活化能来限制离子迁移。我们在不牺牲低热导率的情况下降低了载流子浓度，在 1,050 K 下获得了∼ 3.0 的 ZT。值得注意的是，所制造的器件模块在 518 K 的温差下保持了高达 ∼ 13.4 % 的高转换效率，并且在120 个周期。我们的工作可以推广到开发具有离子迁移特性的电学和热学稳健的功能材料。