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[en] Highlights: • Mn silicate hollow spheres are enclosed in reduced graphene oxide (rGO). • Manganese silicates provide advantageous de-/lithiation potentials with regard to energy density. • Mn silicate hollow spheres remain unaltered even after 350 full dis-/charge cycles. • The incorporation of rGO enhances the achievable capacity and rate capability. - Abstract: Herein is presented a new composite material consisting of nanostructured Mn silicate hollow spheres enclosed in a matrix of reduced graphene oxide (rGO), synthesized via a facile and low-cost hydrothermal method. The hollow structure provides free space to accommodate the volume expansion occurring upon lithiation, while the rGO facilitates the electron transport, thus enhancing the lithiation kinetics. Remarkably, the composite provides a continuously increasing reversible capacity up to ca. 1300 mAh g−1 after 350 cycles. This increase in capacity is ascribed in part to the steadily rising fraction of Mn2+/Mn3+ being oxidized to Mn4+ as well as the reversible formation of the solid electrolyte interphase. The particle morphology, in fact, remains unaltered, as evidenced by ex situ scanning electron microscopy – even after 350 cycles. Additionally, the implementation of manganese as transition metal for the reversible conversion reaction appears advantageous with regard to the overall electrochemical performance and the relatively lower lithiation potential.
[en] Highlights: • Carbon coated, mixed phase TiO_2 anode has been prepared from commercial P90 TiO_2. • Electrochemical lithiation-delithiation mechanisms investigated. • Improved stability of carbon coated mixed phase TiO_2 demonstrated. • Anode in high performance Li-ion battery configuration coupled with LiNi_0_._5Mn_1_._5O_4 - Abstract: In this paper we propose a carbon-coated, nano-sized TiO_2 anode for application in lithium-ion batteries. The lithiation-delithiation process characteristic of this mixed anatase/rutile material has been investigated in detail, in order to define the optimal operating voltage range and to further enhance the electrode cycle life. Ex-situ x-ray diffraction measurements demonstrate that the rutile phase becomes electrochemically inactive toward lithium intercalation after the first cycle and remains inactive by cycles. The TiO_2 electrochemical behavior is studied by means of various techniques, including galvanostatic cycling and potentiodynamic cycling with galvanostatic acceleration. We show that the combination of the TiO_2 anode with a high-voltage, LiNi_0_._5Mn_1_._5O_4 spinel cathode results in an advanced li-ion battery able to exchange reversibly a capacity higher than 100 mAh/g for over 70 cycles at the high rate of 1C. Considering an average working voltage of about 2.9 V, the theoretical energy content of the cell here disclosed is about 300 Wh kg"−"1. Taking into account the energy content and high safety level of the full cell, due to the use of a TiO_2-based electrode, by operating at a voltage value well far from the one associated to the common electrolyte decomposition, i.e. about 1.7 V, we may propose the anode here studied as suitable material for advanced energy storage systems.