In order to optimize the electrode system of lithium-ion batteries for problems such as lithium ion diffusion, electron transportation, and large volume changes during cycling processes, a novel anode material composed of ultrafine Sn nanoparticles (∼5 nm) anchored inside a well-connected three-dimensional (3D) polypyrrole (PPy) nanosheet network has been designed and synthesized through a simple microemulsion-based preparation of tin nanoparticles with organic crystal surface-induced PPy polymerization. In this electrode material, the ultrathin PPy coating (∼3–4 nm) plays a “flexible confinement” function to preserve the structural and interfacial stabilization of inner Sn nanoparticles as well as a “binder” function to suppress the detachment of Sn from the collector. Meanwhile, the continuous conductive PPy nanosheet network with open structures and large contact surface for Sn nanoparticle dispersion can provide easy access for Li⁺ intercalation. As a result, the integration of a 3D conductive network and ultrafine Sn nanoparticles with an ultrathin in situ PPy coating induces improved structural integrity and accessible capacity for Sn nanoparticle electrodes. It delivered a high capacity retention of 766 mA h g⁻¹ after 200 cycles at the current density of 0.2 A g⁻¹ and a reversible capacity of 583 mA h g⁻¹ when kept at a much higher current density of 2 A g⁻¹.