Graphitic Grain-Network Nanoarchitecture for Ultrahigh-Rate and Exceptionally Durable Potassium Ternary Intercalation.

Potassium-ternary graphite intercalation compounds (K+-T-GICs) are promising high-power potassium-ion storage materials, but their low reversible capacity and poorly understood electrolyte-dependent behavior have limited their practical viability. Herein, this sensitivity is traced to salt-dependent electrolyte decomposition that drives resistance growth, blocks K+ diffusion, and induces graphene-layer exfoliation. Decomposition products accumulate not only at the electrode-electrolyte interface but also deep within the graphite host, where they progressively impede ion transport and trigger structural degradation. Guided by these insights, a disordered grain-network graphitic nanosheet (DGN-GNS) architecture is engineered, in which interconnected turbostratic nanograins suppress exfoliation while preserving continuous ion-transport pathways. The DGN-GNS electrode delivers a high reversible capacity of ∼165 mA h g- 1 through synergistic K+ storage that couples co-intercalation with desolvation-driven intercalation within the porous grain network. Even under ultrafast operation, it sustains ∼80 mA h g- 1 at 30 A g- 1 and retains nearly 100% of its capacity over 10 000 cycles. These metrics represent the highest reversible capacity reported for alkali-ion-based T-GICs, and the simultaneous realization of such capacity with ultrahigh-rate operation and extended cycling stability is unprecedented for K+-T-GIC anodes, establishing a new benchmark for K+-T-GIC anodes.