Constructing an electrode integrating ultralow SnO₂ size, stable carbon barriers and well-developed pore structure are effective to address the issues of crack and pulverization for SnO₂-based electrode during lithiation/delithiation process. But until now, it is still a challenge to exploit simple and robust method to fabricate ultrasmall SnO₂ particles embedded in a carbon matrix. Herein, we develop a rapid strategy to prepare SnO₂/C nanospheres using a simple Friedel–Crafts crosslinking of triphenyltin chloride for only 15 min and subsequent carbonization. The SnO₂/C nanospheres (∼500 nm) have ultrasmall SnO₂ particles of 4 nm, which were dispersed in carbon continuous phase. Moreover, the pyrolysis of the polymer during carbonization creates considerable micropores inside the carbon phase and leads to a surface area of 463.3 m² g⁻¹. When used as electrode materials in a lithium-ion battery, the ultrasmall SnO₂ particles can prevent the cracking of the electrode, the carbon continuous phase can act as a buffer to protect SnO₂ particles from aggregation, and micropores will supply expansive space for volume change. Thus, the SnO₂/C nanosphere exhibits superior electrochemical performance, e.g., the first discharge and charge capacities can reach 1453 and 719 mA h g⁻¹ respectively, and 120 cycles later, its capacity remains 629 mA h g⁻¹, indicating a capacity retention of 87.4% (C^120th/C^2nd).