Synergistic Structural Engineering of Tunnel‐Type Polyantimonic Acid Enables Dual‐Boosted Volumetric and Areal Lithium Energy Storage

Abstract Tunnel‐structured polyantimonic acid (PAA) is an intriguing high‐capacity anode candidate for alkali‐metal‐ion storage; however, the awful electroconductivity of PAA (≈10 –10 S cm –1 ) normally requires coupling with large‐surface‐area conductive substrate (e.g., graphene), conversely leading to poor scalability, ultralow density, and execrable volumetric energy. Synergistic structural engineering of PAA via bulk‐phase ion substitution and incorporation with low‐cost flake graphite (FG) is presented here to construct composite electrodes for lithium‐storage. The full‐occupation of Mn 2+ into the tunnel‐centers of PAA synchronously improves its bulk conductivity (≈10 –5 S cm –1 ) and true density (4.58 g cm –3 ), whilst less than 20% volume expansion of PAA is consequently achieved by FG confinement with enhanced multielectron‐reaction kinetics, unveiled by ex/in situ techniques. Besides delivering considerable volumetric capacity (>1200 mAh cm –3 at 0.1 A g –1 ), thus‐fabricated high‐tap‐density composite favors the construction of conducting additive‐free, high‐loading thick electrodes (>6.0 mg cm –2 ), exhibiting dual‐boosted areal/volumetric capacities (4.2 mAh cm –2 /743 mAh cm –3 ), and fast‐charging capability (75% capacity charged within ≈13 min). Moreover, 3D‐printed composite electrodes with tunable shape and mass‐loading are also implemented to showcase impressive areal/volumetric Li + ‐storage performance. Paring with high‐loading and high‐compact‐density LiCoO 2 cathodes (e.g., 18.0 mg cm –2 /3.53 g cc –1 ), full‐cells achieve remarkable electrode‐level areal‐/volumetric‐energy‐densities beyond 7.0 mWh cm –2 /850 Wh L –1 cathode+anode .