Biomass Waste Walnut Shells Derived Silicon‐Doped Carbon Rich in C─O─Si Bonds for Energy Storage Devices: Lithium‐Ion Batteries and Supercapacitors

Biomass waste conversion to energy storage devices has gained significant attention. Here, we report a silicon‐doped carbon material (Si─WH─Carbon) rich in C─O─Si bonds, synthesized from walnut shells (WH) and SiCl 4 via an in situ doping strategy. This sustainable approach yields a dual‐functional material. As a lithium‐ion battery anode, Si─WH─Carbon delivers a high discharge capacity of 604.8 mAh·g −1 at 0.05 A·g −1 over 100 cycles, which is higher than 460.3 mAh·g −1 for the undoped carbon, owing to C─O─Si bonds that buffer silicon's volume expansion. Additionally, in supercapacitor applications, the material achieves a specific capacitance of 322.9 F·g −1 at 0.5 A·g −1 . Silicon doping introduces polar Si─O─C groups that enhance wettability and promote efficient electrolyte–electrode contact, thereby improving charge transfer efficiency. This work offers a novel, cost‐effective strategy for developing biomass‐derived carbon materials with superior dual energy storage capabilities.