Bond Softening and Elastic Confinement of Monolithic Dense Binary Alloys for High Volumetric Capacity of K-Ion Battery Anodes.

Two-dimensional (2D) Sb─Bi alloys are considered as the promising high-capacity and high-rate anodes of potassium-ion batteries, yet their practical application is limited by low density and structural degradation. Herein, we propose an intrinsic-extrinsic dual-stabilization strategy that integrates 2D binary Sb0.6Bi0.4 nanosheets into 3D elastic graphene networks, constructing a highly dense monolithic architecture (HD-Sb0.6Bi0.4@G). This design features with high density (2.6 g cm-3) and electrical conductivity (555.6 S m-1), delivering large volumetric capacity (1355.1 mAh cm-3) and high areal capacity (11.4 mAh cm-2) at an ultra-high loading of 27.6 mg cm-2, along with long-term cyclability (65.4% capacity retention after 1500 cycles) and stable full-cell performance. Experimental and theoretical analyses reveal that the Sb─Bi alloy exhibited "bond softening" with the optimized interlayer spacing and moderate bond energy, facilitating rapid K+ diffusion and buffering strain. Furthermore, the elastic graphene network provides nanoscale confinement, accommodating volume expansion and preserving structural and electrical integrity. Strong electronic coupling at the alloy-graphene interface further reduces K+ adsorption and diffusion energy barriers, enabling fast ion transport under the high-loading anodes. This intrinsic-extrinsic synergy between binary-alloy bond softening and nanoscale elastic confinement provides a universal strategy for compact, high-loading electrodes with high volumetric and areal energy storage.