Citrate‐Assisted Solvothermal Synthesis of SnO₂ Porous Microflowers as Efficient Cathode for Advanced Hybrid Supercapacitor

Herein, mesoporous tin dioxide materials with distinct structures (SnO 2 microflowers and SnO 2 microsheets) were, respectively, prepared via a citrate‐mediated solvothermal route along with a post‐annealing treatment in air. Electrochemical tests revealed a typical battery‐type charge storage behavior of SnO 2 materials. Attributing to the 3D hierarchical flower‐like structure and its good conductivity, the SnO 2 microflowers possessed a specific capacity of 177.2 C g −1 , slightly greater than 159.0 C g −1 achieved by SnO 2 microsheets under 1 A g −1 . When assembled into hybrid supercapacitors (HSCs) utilizing activated carbon (AC) as an anode, the SnO 2 microflowers//AC HSC device delivered a high energy density (ED) of 29.5 W h kg −1 at 883.9 W kg −1 , surpassing SnO 2 microsheets//AC HSC (26.9 W h kg −1 at 881.7 W kg −1 ). Furthermore, both SnO 2 //AC HSCs exhibited long‐term stability, showing 113.2% (SnO 2 microflowers//AC) and 106.4% (SnO 2 microsheets//AC) capacity retention over 5000 cycles. Notably, this synthesis strategy achieves facile morphological control and improved electrochemical properties of SnO 2 materials by adjusting the sodium citrate amount. These results indicate that SnO 2 microflowers and SnO 2 microsheets are attractive candidates for high‐performance HSC assembly. Furthermore, this cost‐effective approach can provide a reference for synthesizing other advanced metal oxide‐based electrode materials.