Three-dimensional network of nitrogen-doped carbon matrix-encapsulated Si nanoparticles/carbon nanofibers hybrids for lithium-ion battery anodes with excellent capability.

Three-dimensionally structured silicon (Si)-carbon (C) nanocomposites have great potential as anodes in lithium-ion batteries (LIBs). Here, we report a Nitrogen-doped graphene/carbon-encapsulated Si nanoparticle/carbon nanofiber composite (NG/C@Si/CNF) prepared by methods of surface modification, electrostatic self-assembly, cross-linking with heat treatment, and further carbonization as a potential high-performance anode for LIBs. The N-doped C matrix wrapped around Si nanoparticles improved the electrical conductivity of the composites and buffered the volume change of Si nanoparticles during lithiation/delithiation. Uniformly dispersed CNF in composites acted as conductive networks for the fast transport of ions and electrons. The entire tightly connected organic material of NG/C@Si and CNF prevented the crushing and shedding of particles and maintained the integrity of the electrode structure. The NG/C@Si/CNF composite exhibited better rate capability and cycling performance compared with the other electrode materials. After 100 cycles, the electrode maintained a high reversible specific capacity of 1371.4 mAh/g.

Effects of a Sodium Phosphate Electrolyte Additive on Elevated Temperature Performance of Spinel Lithium Manganese Oxide Cathodes.

LiMn2O4 (LMO) spinel cathode materials suffer from severe degradation at elevated temperatures because of Mn dissolution. In this research, monobasic sodium phosphate (NaH2PO4, P2) is examined as an electrolyte additive to mitigate Mn dissolution; thus, the thermal stability of the LMO cathode material is improved. The P2 additive considerably improves the cyclability and storage performances of LMO/graphite and LMO/LMO symmetric cells at 60 °C. We explain that P2 suppresses the hydrofluoric acid content in the electrolyte and forms a protective cathode electrolyte interphase layer, which mitigates the Mn dissolution behavior of the LMO cathode material. Considering its beneficial role, the P2 additive is a useful additive for spinel LMO cathodes that suffer from severe Mn dissolution.

Synthesis and Electrochemical Performance of Electrostatic Self-Assembled Nano-Silicon@N-Doped Reduced Graphene Oxide/Carbon Nanofibers Composite as Anode Material for Lithium-Ion Batteries.

Silicon-carbon nanocomposite materials are widely adopted in the anode of lithium-ion batteries (LIB). However, the lithium ion (Li+) transportation is hampered due to the significant accumulation of silicon nanoparticles (Si) and the change in their volume, which leads to decreased battery performance. In an attempt to optimize the electrode structure, we report on a self-assembly synthesis of silicon nanoparticles@nitrogen-doped reduced graphene oxide/carbon nanofiber (Si@N-doped rGO/CNF) composites as potential high-performance anodes for LIB through electrostatic attraction. A large number of vacancies or defects on the graphite plane are generated by N atoms, thus providing transmission channels for Li+ and improving the conductivity of the electrode. CNF can maintain the stability of the electrode structure and prevent Si from falling off the electrode. The three-dimensional composite structure of Si, N-doped rGO, and CNF can effectively buffer the volume changes of Si, form a stable solid electrolyte interface (SEI), and shorten the transmission distance of Li+ and the electrons, while also providing high conductivity and mechanical stability to the electrode. The Si@N-doped rGO/CNF electrode outperforms the Si@N-doped rGO and Si/rGO/CNF electrodes in cycle performance and rate capability, with a reversible specific capacity reaching 1276.8 mAh/g after 100 cycles and a Coulomb efficiency of 99%.

Characteristics and electrochemical performances of silicon/carbon nanofiber/graphene composite films as anode materials for binder-free lithium-ion batteries.

We report the interfacial study of a silicon/carbon nanofiber/graphene composite as a potentially high-performance anode for rechargeable lithium-ion batteries (LIBs). Silicon nanoparticle (Si)/carbon nanofiber (CNF)/reduced graphene oxide (rGO) composite films were prepared by simple physical filtration and an environmentally-friendly thermal reduction treatment. The films were used as high-performance anode materials for self-supporting, binder-free LIBs. Reducing graphene oxide improves the electron conductivity and adjusts to the volume change during repeated charge/discharge processes. CNFs can help maintain the structural stability and prevent the peeling off of silicon nanoparticles from the electrodes. When the fabricated Si/CNF/rGO composites were used as anodes of LIBs, the initial specific capacity was measured to be 1894.54 mAh/g at a current density of 0.1 A/g. After 100 cycles, the reversible specific capacity was maintained at 964.68 mAh/g, and the coulombic efficiency could reach 93.8% at the same current density. The Si/CNF/rGO composite electrode exhibited a higher specific capacity and cycle stability than an Si/rGO composite electrode. The Si/CNF/rGO composite films can effectively accommodate and buffer changes in the volume of silicon nanoparticles, form a stable solid-electrolyte interface, improve the conductivity of the electrode, and provide a fast and efficient channel for electron and ion transport.

Electrolyte Additive Enabling Conditioning-Free Electrolytes for Magnesium Batteries.

Most electrolytes for rechargeable Mg batteries require time-consuming conditioning or precycling process to achieve a fully reversible Mg deposition/dissolution, which hinders the normal operation of Mg batteries. This study details a simple and effective method for eliminating this conditioning behavior using heptamethyldisilazane (HpMS) as an electrolyte additive. It was found that the HpMS additive greatly increases the current density and Coulombic efficiency of Mg deposition/dissolution from the initial cycles in various sulfone and glyme solutions containing MgCl2 or Mg(TFSI)2. The beneficial effect of HpMS was ascribed to its ability to scavenge trace water in the electrolytes and remove Mg(OH)2 and Mg(TFSI)2-decomposition products from the Mg surface. Considering its applicability for a wide range of Mg electrolytes, the use of HpMS is expected to accelerate the development of practical Mg batteries.

Recycling of spent lithium-ion battery cathode materials by ammoniacal leaching.

As the production and consumption of lithium ion batteries (LIBs) increase, the recycling of spent LIBs appears inevitable from an environmental, economic and health viewpoint. The leaching behavior of Ni, Mn, Co, Al and Cu from treated cathode active materials, which are separated from a commercial LIB pack in hybrid electric vehicles, is investigated with ammoniacal leaching agents based on ammonia, ammonium carbonate and ammonium sulfite. Ammonium sulfite as a reductant is necessary to enhance leaching kinetics particularly in the ammoniacal leaching of Ni and Co. Ammonium carbonate can act as a pH buffer so that the pH of leaching solution changes little during leaching. Co and Cu can be fully leached out whereas Mn and Al are hardly leached and Ni shows a moderate leaching efficiency. It is confirmed that the cathode active materials are a composite of LiMn2O4, LiCoxMnyNizO2, Al2O3 and C while the leach residue is composed of LiNixMnyCozO2, LiMn2O4, Al2O3, MnCO3 and Mn oxides. Co recovery via the ammoniacal leaching is believed to gain a competitive edge on convenitonal acid leaching both by reducing the sodium hydroxide expense for increasing the pH of leaching solution and by removing the separation steps of Mn and Al.