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This work reports the growth of graphene nanobuds (GNB) on Cu foil by chemical vapor deposition and its direct application as an electrode in lithium-ion batteries. The obtained novel GNB anode exhibited a superhigh specific capacity of 2813 mAh g−1 at a current rate of 4 A g−1 with a reversible coulombic efficiency of 78% in the first cycle. The most important advantage of using GNB as an anode was its outstanding cycled performance, maintaining a stable capacity of 1600 mAh g−1 at 8 A g−1 for at least 330 charge/discharge cycles with a coulombic efficiency of 99%. More significantly, the cell still maintained a retention capacity of 870 mAh g−1 when cycled at the very high current rate of 40 A g−1. The exceptional electrochemical performance in storage capacity and rate capability of GNB can be mainly attributed to the nanobuds having more loose space in their adjacent walls and hollow spaces; and to the intrinsic nano-oriented structure of few-layered graphene. This unique structure enables better Li-ion diffusion and higher Li-ion storage capacity. The outstanding electrochemical performance of the GNB as an anode places it as one of the most promising advanced carbon materials for next-generation lithium-ion batteries. [Display omitted] • A new material assembly approach on graphene nanobuds for advanced Li-ion batteries. • Graphene nanobuds with exceptional energy storage using a novel anode design paradigm. • Graphene nanobuds exhibited a relatively high efficiency and good reversibility. • The semifullerenes-graphene network enhances the diffusion and storage of Li-ion. • Direct deposit of GNB on the electrodes improves the electrical conductivity. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Novel Li 2 FeSiO 4 mesocrystals exhibit improved Li-ion storage properties. • EDTA-regulated formation of impurity-free and defect-free hollow Pmn2 1 crystals. • Li 2 FeSiO 4 mesocrystals form via a 4-step hydrothermal crystallization mechanism. Abstract Lithium transition metal orthosilicates such as Li 2 FeSiO 4 (LFS) have been recognized as promising cathode materials for application in Li-ion batteries because of their high theoretical energy density, safety, and benign/abundant element composition. Their development, however, has been hampered by the challenge of obtaining phase-pure and defect-free Li 2 FeSiO 4 nanoparticles as non-optimized crystal properties have an adverse effect on structural stability and electrochemical performance. Considering the sustainable potential of hydrothermal synthesis in producing electrode materials, here we employ this process to systematically study critical synthesis parameters for optimal control of particle size, morphology, phase purity, and defects of Li 2 FeSiO 4 crystallized in the orthorhombic crystal system with space group Pmn 2 1. It is shown that via a combination of elevated FeSO 4 concentration regime and use of EDTA as a complexing agent, phase-pure Pmn 2 1 particle formation can be controlled. Synchrotron-based XRD Rietveld refinement and 57Fe Mössbauer spectroscopy reveal a significant reduction in Li-Fe antisite defects and presence of Fe3+. Additionally, the use of EDTA promotes the formation of unique peanut-shell looking hollow mesocrystals that are advantageous in maximizing electrode/electrolyte contact resulting in higher Li-ion storage capacity than dense LFS particles. On the basis of detailed XRD, SEM, and TEM characterizations, a four-step crystallization mechanism is proposed to explain the formation of the hollow mesocrystals. These findings bring new insight into our pursuit of optimization of Li 2 FeSiO 4 as a cathode material for Li-ion batteries. [ABSTRACT FROM AUTHOR]

Zero-strain and long-term stability of nanoscale lithium titanate (LTO) anode materials make possible the fabrication of exceptionally stable lithium ion batteries. But one issue must be considered that of nanostructure-induced relaxation in 2D LTO nanosheets which profoundly modifies their Li storage properties and structural stability. Excessively intercalated Li ions at both 8 a and 16 c sites trigger nucleation of the relaxed LTO structure in the near-surface region, which impedes Li-ion diffusion and causes the increasing polarization of LTO nanosheet electrodes. Nuclei of relaxed LTO then undergo isotropic growth along the 3D Li-ion pathways in LTO to completely convert near-surface regions into relaxed LTO. With increasing population of trapped Li ions, the enhanced conductivity due to Ti4+/Ti3+ reduction gradually eliminates the raised polarization. In the meantime, spontaneous electrolyte/LTO reduction to form the solid electrolyte interphase starts playing a major role in capacity loss once the transformation of near-surface region into relaxed LTO becomes saturated. Elucidation of these fundamental intercalation-induced surface structure transformations contribute greatly into the design of highly performing 2D nanoscaled LTO and other electrode materials. [ABSTRACT FROM AUTHOR]

Li 2 FeSiO 4 (LFS) has drawn much attention as cathode for high capacity Li-ion batteries. Even though significant volume of study has been devoted to its crystal chemistry and electrochemistry, many questions relating to its Li-ion storage dynamics remain yet to be fully elucidated. In this context, synchrotron-based X-ray diffraction and absorption spectroscopies are employed to characterize the phase stability and charge compensation mechanism in a metastable Li 2 FeSiO 4 nanostructured cathode as a function of state-of-charge (Li 2− x FeSiO 4 , x = 0, 0.25, 0.50, 0.75, 1.0) and cycling at very low current. The results demonstrate (i) no detectable phase transition from monoclinic to orthorhombic phase during the first charge-discharge cycle but rather formation of antisite defects that progressively induce phase transformation after several electrochemical cycles; (ii) characteristics of solid solution Li-ion storage (Li 2− x FeSiO 4 , x = 0–1); and (iii) the charge compensation for the first Li extraction does not come solely from the ferrous to ferric conversion, but interestingly from prominent participation of lattice oxygen as well that appears to destabilize the cycled LFS structure with significant performance implications. [ABSTRACT FROM AUTHOR]