Synthesis and superior lithium storage performances of hybrid hollow urchin-like silicate constructed by nanotubes wrapped in reduced graphene oxides

Enabling high electrochemical activity of a hollow SiO2 anode by decorating it with ultrafine cobalt nanoparticles and a carbon matrix for long-lifespan lithium ion batteries

Silica is a very promising anode material for lithium-ion batteries, due to its advantages of being resource-rich and having high theoretical specific capacity. However, poor electrochemical activity severely limits its practical application. To solve this issue, a nanosheet-assembled silica hierarchical hollow sphere decorated with ultrafine cobalt nanoparticles and carbon (SiO2/Co/C) is successfully synthesized. The hollow structure can effectively alleviate the volume expansion, shorten the migration distance of lithium ions, and increase the binding site. Furthermore, the carbon matrix and highly active ultrafine cobalt nanoparticles enhance not only the electronic conductivity but also the electrochemical activity (catalyzing the breaking of Si-O and Li-O bonds) of SiO2. The resulting SiO2/Co/C composite has a high reversible capacity of 1160 mA h g-1 at 0.2 A g-1 and still has a specific capacity of 548 mA h g-1 after 1000 cycles at a high current density of 1.0 A g-1. Moreover, the SiO2/Co/C composite also exhibits good electrochemical performance in a full cell.

Facile Electrochemical Activity of Monoclinic Li2MnSiO4 as Potential Cathode for Li-Ion Batteries

Synthesis of pure single-phase Li₂MnSiO₄ is challenging because of its rich polymorphism. Here, we demonstrate our success in preparing crystalline pure, battery-grade monoclinic phase Li₂MnSiO₄ (LMS) employing the temperature-programmed reaction technique. Systematic analysis of the electrochemical behavior of Li₂MnSiO₄ reveals its excellent battery activity in the monoclinic phase, with an initial discharge capacity of ∼250 mAh g^-1 associated with the reversible intercalation of more than one Li⁺. The extraction of Li⁺ ions from Li₂MnSiO₄ corresponding to the oxidation of Mn²⁺ to Mn³⁺ then to Mn⁴⁺ appears as single oxidation/reduction peaks at 4.3/3.9 V in the first charge/discharge sweep of cyclic voltammogram within the potential window of 3.0-4.4 V. However, an extension of cathodic sweep to 2.5 V results in the appearance of an additional redox peak at 2.7/3.1 V vs Li⁺/Li^o due to the reversible phase transition of monoclinic phase into battery-active orthorhombic phase induced by Jahn-Teller-active Mn³⁺ as evident from ex situ X-ray diffractograms. Indeed, the reversible intercalation of Li⁺ into the newly formed phase accounts for the high specific capacity of LMS within the potential window of 2.5-4.4 V. The capacity loss in the repeated cycles of monoclinic Li₂MnSiO₄ is explained by the formation of Mn₂O₃ owing to the dissolution of Mn³⁺.