Low ion and electron conductivities of the cathode and poor cathode interface performance severely limit the application of garnet solid-state batteries. While various approaches have been developed to improve the cathode interface contact or enhance ion and electron transport, none of these methods can simultaneously achieve high interfacial electrochemical activity and chemical stability. In this work, we propose to develop a single-phase garnet-type mixed ionic and electronic conductor (MIEC) as the cathode framework, which is expected to achieve the unification of high activity and high stability at the cathode interface. Combining first-principles calculations and ultrafast sintering techniques, we have synthesized and screened a series of garnet-type MIECs by introducing transition metals into garnet SSEs. Among the garnet-type MIECs, Li₄₃Fe₃La₂₄Zr₁₂Ta₄O₉₆ (3Fe) not only exhibits an excellent electronic conductivity of up to 2.87 × 10⁻⁴ S cm⁻¹ but also maintains an ionic conductivity of 4.57 × 10⁻⁵ S cm⁻¹. The high electronic conductivity is believed to originate from the high-temperature reduction phase formed during the rapid sintering process under inert conditions. A small polaron hopping mechanism is proposed to explain the electronic conductivity based on electronic structure calculations and activation energy analysis. Since garnet-type MIECs have the same crystal structure as garnet solid-state electrolytes (SSEs) and transition metal elements similar to those of oxide cathode materials, they potentially have good cosintering stability with both electrolytes and cathodes. This work provides a new strategy to solve the cathode interface problem in garnet solid-state batteries.

正极低的离子和电子电导率以及较差的正极界面性能严重限制了石榴石固态电池的应用。虽然已经开发了各种方法来改善阴极界面接触或增强离子和电子传输，这些方法都不能同时实现高界面电化学活性和化学稳定性。在这项工作中，我们建议开发一种单相石榴石型混合离子和电子导体（MIEC）作为正极框架，有望在正极界面实现高活性和高稳定性的统一。结合第一性原理计算和超快烧结技术，我们通过将过渡金属引入石榴石SSEs，合成并筛选出一系列石榴石型MIECs。在石榴石型 MIECs 中，Li ₄₃ Fe ₃ La ₂₄ Zr ₁₂ Ta ₄ O ₉₆(3Fe) 不仅表现出高达 2.87 × 10 ^-4 S cm ^{-1的优异电子电导率，而且还保持 4.57 × 10 -5} S cm ^-1的离子电导率。高电子电导率被认为源于在惰性条件下快速烧结过程中形成的高温还原相。基于电子结构计算和活化能分析，提出了一种小的极化子跳跃机制来解释电子电导率。由于石榴石型 MIECs 具有与石榴石固态电解质 (SSEs) 相同的晶体结构和类似于氧化物阴极材料，它们可能与电解质和阴极具有良好的共烧结稳定性。这项工作为解决石榴石固态电池中的正极界面问题提供了一种新策略。