Synthesis and Electrochemical Reaction of Tin Oxalate-Reduced Graphene Oxide Composite Anode for Rechargeable Lithium Batteries

Unlike for SnO₂, few studies have reported on the use of SnC₂O₄ as an anode material for rechargeable lithium batteries. Here, we first introduce a SnC₂O₄-reduced graphene oxide composite produced via hydrothermal reactions followed by a layer-by-layer self-assembly process. The addition of rGO increased the electric conductivity up to ∼10^–3 S cm^–1. As a result, the SnC₂O₄-reduced graphene oxide electrode exhibited a high charge (oxidation) capacity of ∼1166 mAh g^–1 at a current of 100 mA g^–1 (0.1 C-rate) with a good retention delivering approximately 620 mAh g^–1 at the 200th cycle. Even at a rate of 10 C (10 A g^–1), the composite electrode was able to obtain a charge capacity of 467 mAh g^–1. In contrast, the bare SnC₂O₄ had inferior electrochemical properties relative to those of the SnC₂O₄-reduced graphene oxide composite: ∼643 mAh g^–1 at the first charge, retaining 192 mAh g^–1 at the 200th cycle and 289 mAh g^–1 at 10 C. This improvement in electrochemical properties is most likely due to the improvement in electric conductivity, which enables facile electron transfer via simultaneous conversion above 0.75 V and de/alloy reactions below 0.75 V: SnC₂O₄ + 2Li⁺ + 2e^– → Sn + Li₂C₂O₄ + <i>x</i>Li⁺ + <i>x</i>e^– → Li_<i>x</i>Sn on discharge (reduction) and vice versa on charge. This was confirmed by systematic studies of ex situ X-ray diffraction, transmission electron microscopy, and time-of-flight secondary-ion mass spectroscopy

Fabrication of a Nondegradable Si@SiO_<i>x</i>/n-Carbon Crystallite Composite Anode for Lithium-Ion Batteries

A Si-based anode maintaining its high electrochemical performance with cycles was prepared for the nondegradable lithium-ion battery. Nanoscaled Si particles were mechanochemically coupled with approximately 3 nm thick oxide layer and n-carbon (nanoscaled carbon) crystallites to overcome silicon’s inherent problems of poor electronic conductivity and severe volume change during lithiation and delithiation cycling. The oxide layer of SiO_<i>x</i> was chemically formed via a controlled oxygen environment during the process; meanwhile, the n-carbon crystallites were obtained by mechanical fragmentation from ∼70 μm sized multilayered graphene powders with a low degree of agglomeration. The Si-based composite anode, processed by the above-mentioned mechanochemical coupling, maintained a superior discharge capacity of 1767 mA h/g through 100 cycles with a Coulombic efficiency exceeding 98% at a current density of 100 mA/g. According to our current study, the coupling of the Si particles with oxide layer and n-carbon crystallites was found to be a significantly efficient way to prevent the performance degradation of the Si-based anode

Simulation Protocol for Prediction of a Solid-Electrolyte Interphase on the Silicon-based Anodes of a Lithium-Ion Battery: ReaxFF Reactive Force Field

We propose the ReaxFF reactive force field as a simulation protocol for predicting the evolution of solid-electrolyte interphase (SEI) components such as gases (C₂H₄, CO, CO₂, CH₄, and C₂H₆), and inorganic (Li₂CO₃, Li₂O, and LiF) and organic (ROLi and ROCO₂Li: R = −CH₃ or −C₂H₅) products that are generated by the chemical reactions between the anodes and liquid electrolytes. ReaxFF was developed from ab initio results, and a molecular dynamics simulation with ReaxFF realized the prediction of SEI formation under real experimental conditions and with a reasonable computational cost. We report the effects on SEI formation of different kinds of Si anodes (pristine Si and SiO_<i>x</i>), of the different types and compositions of various carbonate electrolytes, and of the additives. From the results, we expect that ReaxFF will be very useful for the development of novel electrolytes or additives and for further advances in Li-ion battery technology

Characterization of Hydrothermally Prepared Titanate Nanotube Powders by Ambient and In Situ Raman Spectroscopy

This letter reports on the successful synthesis of hydrogen titanate nanotubes (H−Ti-NT) and TiO₂ (anatase) nanotubes and their thermal solid-state transformational chemistry and clarifies some of the confusion surrounding their literature Raman vibrational assignments. Hydrothermally prepared titanate nanotube powders with negligible (<0.1 wt % Na, H−Ti-NT) and high (∼7.0 wt % Na, Na/H−Ti-NT) Na content, that underwent freeze-drying and thermal treatments, were prepared and characterized with ambient and in situ Raman spectroscopy. The H−Ti-NT phase gives rise to Raman bands at ∼195, 285, 458, ∼700, 830, and 926 cm⁻¹. The Raman bands above 650 cm⁻¹ were found to be sensitive to the presence of moisture, which indicates that they are related to surface vibrational modes. The titanate nanotube Raman band at ∼926 cm⁻¹ was shown not be related to a Na−O−Ti vibration, which was previously assigned in the literature, since its intensity does not vary with Na content, which varied by a factor of >70. The nanotubular H−Ti-NT phase was found to be thermally stabilized, <700 °C, by Na that had been entrapped during synthesis. The Na-free H−Ti-NT phase, however, transformed to TiO₂ (anatase) nanotubes upon heating above 200 °C and was stable up to 700 °C