New Insights\ninto Phytolith Characteristics in Wild\nGrass as the Source of Sustainable Silicon Oxide Anodes

Silicon oxide (SiO<sub><i>x</i></sub>) is a\npromising\nSi-based anode due to its abundant natural resources and high theoretical\ncapacity. Beyond the Earth’s crust, extracting SiO<sub><i>x</i></sub> from phytolith-rich plants offers a sustainable\nalternative, where the organic carbon can naturally occlude within\nthe phytolith structure. This work examines the phytolith characteristics\nand the anode performance of the resultant SiO<sub><i>x</i></sub>/carbon composite (SiO<sub><i>x</i></sub>/C) derived\nfrom wild grass phytolith-rich plants (i.e., Goosegrass and Ghaeri’s\nRush). While Ghaeri’s Rush phytoliths exhibit cavate morphology\nwith occluded carbon located within thin silica walls and cavities,\nGoosegrass solid phytoliths feature a dense solid silica matrix with\noccluded carbon tightly isolated throughout the solid silica matrix.\nThis characteristic leads to superior characteristics for SiO<sub><i>x</i></sub>/C anodes derived from Goosegrass, which\nexhibit a larger amount of active SiO<sub><i>x</i></sub>, wider surface area (1408 m<sup>2</sup> g<sup>–1</sup>),\nand a higher amount of defective carbon, compared to those derived\nfrom Ghaeri’s Rush. In addition, X-ray photoelectron spectroscopy\nshows that the Si content in SiO<sub><i>x</i></sub>/C derived\nfrom Goosegrass mostly consists of active SiO<sub><i>x</i></sub> with a low organosilicon content (12.96%). These characteristics\nof Goosegrass improve the SiO<sub><i>x</i></sub>/C anode’s\ngravimetric capacity, cycling durability, and capability of the charge–discharge\nrate, delivering 704 mAh g<sup>–1</sup> after 500 charge–discharge\ncycles at 200 mA g<sup>–1</sup> without any capacity degradation.\nIt also achieves a capacity as high as 330 mAh g<sup>–1</sup> during a rate capability test at 1000 mA g<sup>–1</sup>.\nThis study highlights the potential of phytolith-rich wild grasses\nfor sustainable and stable Li-ion battery technology by emphasizing\nthe influence of phytolith characteristics on the SiO<sub><i>x</i></sub>/C anode properties.