Elucidation\non Abnormal Capacity Increase in SiO<sub>2</sub>@C Core–Shell\nNanospheres Anode for Lithium-Ion Battery

An abnormal capacity increase stage has been observed\nin nanostructured\nSiO<sub>2</sub> after the initial capacity drop stage. To investigate\nthe Li<sup>+</sup> storage kinetic mechanism for each stage, SiO<sub>2</sub>@C core–shell nanospheres with a total diameter of\n∼108 to 170 nm but an adjustable C shell thickness of ∼4\nto 31 nm have been fabricated. First, the existence form and specific\ncontent of SiO<sub>2</sub> nanoparticles with a size of ∼6–10\nnm, which are embedded in the outer C shell of SiO<sub>2</sub>@C core–shell\nnanospheres, were confirmed by SEM, TEM, BET, and TGA, respectively.\nIt was found that the initial stage for capacity drop happens at 15–43\ncycles and is followed by an enhancement stage, which presents an\nincrease of ∼120 to 180% in capacity relative to the lowest\ncapacity value during cycling. Among them, the sample of P-1 with\na diameter of 109 nm for the SiO<sub>2</sub> core and thickness of\n31 nm for the C shell delivers the highest specific capacity of 1060\nmAh/g at 100 mA/g and a capacity increase rate of ∼180% through\n300 cycles. XPS analysis for the delithiation process indicates that\nthe capacity drop and increase stage involves the partial oxidation\nof Li silicate, which is correlated to the formation of Li<sub>2</sub>Si<sub>2</sub>O<sub>5</sub>. Our study can be used to explain the\nmechanism of the abnormal capacity increase phenomenon for the SiO<sub>2</sub> anode and provide a high-capacity anode material for LIB\napplication.