The challenging problems of SnO2 anode material for lithium ion batteries are the poor electronic conductivity and the low oxygen reutilization due to the irreversibility of Li2O generated in the initial discharge leading to a theoretical initial Coulombic efficiency (ICE) of only 52.4%. Different from these strategies, this work proposes a novel strategy to level up the oxygen reutilization in SnO2 by introducing Co3Sn2 nanoalloys which can release Co atoms to reversibly react with Li2O instead. According to this protocol, multi-yolk–shell SnO2/Co3Sn2@C nanocubes are designed and successfully prepared using hollow CoSn(OH)6 nanocubes as precursors followed a hydrothermal carbon coating and calcination treatment. The unique multi-yolk–shell nanostructure offers adequate breathing space for the volumetric deformation during long-term cycling. Moreover, the removal of Li2O allows a high electronic conductivity and resultant rate performance. As a result, the efficient reutilization of oxygen enables a high ICE of 71.7% and a reversible capacity of 1003 mA h g–1 after 200 cycles at 100 mA g–1. Cyclic voltammetry, cycling performance at different voltage windows, and X-ray photoelectron spectroscopy confirm the proposed mechanism. This strategy employing oxygen-poor metals or alloys provides a novel approach to enhance the oxygen reutilization in SnO2 for higher reversibility.Keywords: Coulombic efficiency; lithium ion batteries; multi-yolk−shell structures; oxygen reutilization; reversible conversion;

The extremely large volume variation and poor electronic conductivity of Si anode materials for lithium ion batteries have seriously hampered their performances and practical applications. SiOx materials are regarded as ideal alternatives to high-capacity Si anode materials for Li-ion batteries, since the generated Li2O matrix from Li–SiOx reactions can effectively accommodate the large volume swing of Si. Furthermore, micron-sized particles with much smaller surface area always present higher initial coulombic efficiency and tap density than nanomaterials. Based on the above considerations, SiOx microparticles with homogeneously-embedded Si nanocrystals and nanopores were fabricated by magnesiothermic reduction in this work and were further modified by high-electronic-conductivity and flexible polyaniline (PANI)–Ag shell. Profiting from these favorable features, the obtained SiOx–PANI–Ag micron-composites exhibited better cycling performances (with a reversible capacity of 1149 mA h g−1 after 100 cycles), good initial coulombic efficiency and tap density in comparison with SiOx-based materials in other works. This study promotes us to exploit advanced Si- or Sn-based materials for Li ion batteries and preparing micro/nano complex structures for promising applications.

As substitutions for transition metal oxides (MOs), transition metal carbonates (MCO3) have been attracting more and more attention because of their lithium storage ability in recent years. Is MCO3 better than MOs for lithium storage? To answer this question, monodisperse CoCO3 and CoO microspindles with comparable structures were synthesized and investigated as a case study. Excluding its structural effect, we found CoCO3 still exhibited reversible capacities and rate capabilities much higher than those of CoO. The reversible capacity of CoCO3 after 10 cycles was 1065 mAh g–1, 48.2% higher than that (∼720 mAh g–1) of CoO. Furthermore, the greatly different electrochemical behaviors were investigated by analyzing the discharge–charge profiles, cyclic voltammetry curves, and Nyquist plots in depth. This work can improve our understanding of the lithium storage advantages of MCO3 against MOs and enlighten us in terms of developing high-performance MCO3 with favorable structures.Keywords: anodes; batteries; lithium storage; transition metal carbonates; transition metal oxides

•A core-shell yolk-shell Si@C@void@C nanohybrid is proposed for the first time.•The Si@C@void@C provides better conductivity and corrosion resistance.•The Si@C@void@C exhibits high reversible capacity and good rate capability.Yolk-shell Si@void@C nanostructure has greatly improved the low Li+/electron conductivity and buffered the huge volume variation of Si, whereas the surface corrosion and passivation of the Si yolks in electrolytes still limit the lithium storage capability. Herein, core-shell yolk-shell Si@C@void@C nanohybrids were proposed and successfully prepared for the first time. Compared with Si@void@C, the newly-proposed structure introduced core-shell Si@C nanoparticles as the yolks instead. Such extra carbon shell can not only decrease the electrical resistance between Si yolks and hollow carbon shells but also effectively protect Si yolks from electrolyte corrosion, i.e., the formation of Li2SiF6 layers on Si surface confirmed by X-ray diffraction and transmission electron microscopy. As a result, the Si@C@void@C electrodes exhibited remarkably enhanced reversible capacity, cycling stability (∼1366 mA h g−1 after 50 cycles at 500 mA g−1, with a capacity retention of ∼71% with respect to the initial reversible capacity of 1910 mAh g−1 at 100 mA g−1), and rate performance (with a capacity retention of ∼60% at 4000 mA g−1). This work shows the paramount role of the inner carbon shell of Si@C@void@C in limiting the electrolyte corrosion and probably improving the electronic conductivity.

The extremely large volume variation and poor electronic conductivity of Si anode materials for lithium ion batteries have seriously hampered their performances and practical applications. SiOx materials are regarded as ideal alternatives to high-capacity Si anode materials for Li-ion batteries, since the generated Li2O matrix from Li–SiOx reactions can effectively accommodate the large volume swing of Si. Furthermore, micron-sized particles with much smaller surface area always present higher initial coulombic efficiency and tap density than nanomaterials. Based on the above considerations, SiOx microparticles with homogeneously-embedded Si nanocrystals and nanopores were fabricated by magnesiothermic reduction in this work and were further modified by high-electronic-conductivity and flexible polyaniline (PANI)–Ag shell. Profiting from these favorable features, the obtained SiOx–PANI–Ag micron-composites exhibited better cycling performances (with a reversible capacity of 1149 mA h g−1 after 100 cycles), good initial coulombic efficiency and tap density in comparison with SiOx-based materials in other works. This study promotes us to exploit advanced Si- or Sn-based materials for Li ion batteries and preparing micro/nano complex structures for promising applications.