Silicon carbide-free graphene growth on silicon for lithium-ion battery with high volumetric energy density

Silicon is receiving discernable attention as an active material for next generation lithium-ion battery anodes because of its unparalleled gravimetric capacity. However, the large volume change of silicon over charge-discharge cycles weakens its competitiveness in the volumetric energy density and cycle life. Here we report direct graphene growth over silicon nanoparticles without silicon carbide formation. The graphene layers anchored onto the silicon surface accommodate the volume expansion of silicon via a sliding process between adjacent graphene layers. When paired with a commercial lithium cobalt oxide cathode, the silicon carbide-free graphene coating allows the full cell to reach volumetric energy densities of 972 and 700 Whl(-1) at first and 200th cycle, respectively, 1.8 and 1.5 times higher than those of current commercial lithium-ion batteries. This observation suggests that two-dimensional layered structure of graphene and its silicon carbide-free integration with silicon can serve as a prototype in advancing silicon anodes to commercially viable technology.

Sn0.9Si0.1/carbon core-shell nanoparticles for high-density lithium storage materials

Sn0.9Si0.1 core/carbon shell nanoparticles, with the sizes of 16 and 10 nm, were prepared by annealing as-prepared butyl-capped Sn0.9Si0.1 particles with an average particle size of 1 ??m. Even though as-prepared samples were severely encapsulated by butyl terminators, annealing led to pulverization of the bulky particles into core - shell nanoparticles with a shell thickness dependent on the annealing temperature. The core Sn0.9Si0.1 size was estimated to be constant at 6 nm, and the carbon shell thickness decreased from 10 to 4 nm with increasing annealing temperature from 600 to 700??C, respectively. In addition, the carbon shell was found to be more ordered at 700??C than at 600??C. Sn0.9Si0.1 core/carbon shell nanoparticles exhibited excellent lithium storage ability at a high current rate, resulting in a value of 964 mA??h/g at a rate of 0.3 C (1 C = 1200 mA/g), and demonstrated good capacity retention after 50 cycles.close363

Synthesis and optimization of nanoparticle Ge confined in a carbon matrix for lithium battery anode material

Ge nanoparticles with different particle sizes confined in a carbon matrix were prepared by annealing Ge nanoparticles terminated with butyl groups at 400, 600, and 800°C. X-ray diffraction and transmission electron microscopy results showed that the Ge nanoparticles' size increased from 8 to 100 nm as the annealing temperature of the as-prepared samples increased from 400 to 800°C. Raman spectra confirmed that the parts of the Ge nanoparticles were not covered by the carbon starting at 600°C after annealing for 9 h. Moreover, the graphitization degree of the carbon increases with increasing temperature, and the sample, annealed at 800°C for 3 h, showed the graphitization degree. Electrochemical cycling results revealed that the 10 nm Ge nanoparticles, confined in a carbon matrix obtained after annealing the as-prepared sample at 600°C for 3 h, showed the best charge capacity of 1067 mAhg with 12% capacity loss after 30 cycles. On the other hand, Ge nanoparticles that had not been covered with the carbon matrix showed a rapid capacity decrease, along with pulverization of Ge nanoparticles to a size of about 5-10 nm after cycling.close515

Observation of reversible pore change in mesoporous tin phosphate anode material during Li alloying/dealloying

We observed the pore expansion and contraction of mesoporous tin phosphate during Li alloying/dealloying using small-angle X-ray scattering and transmission electron microscopy. As-prepared mesoporous tin phosphate showed pore and porewall sizes of 3 and 2 nm, respectively. During lithium alloying (discharging), pore size was slightly contracted, but porewall size was slightly expanded within the range of 1 nm. However, during lithium dealloying (charging), pore and porewall sizes recovered to their original sizes before cycling. The charged sample had a nanoscale pore (∼3 nm) array with a more or less uniformly sized open-porewall structure of amorphous lithium phosphates with metallic α-Sn face-centered-cubic nanocrystals ∼2 nm in diameter.close101

Ni-stabilizing additives for completion of Ni-rich layered cathode systems in lithium-ion batteries: An Ab initio study

We propose the development of Ni-stabilizing electrolyte additives to fundamentally prevent the degradation of Ni-rich layered cathode systems in lithium-ion batteries because unstable surface Ni and the dissolved Ni2+ are the major problems of those systems. The Ni2+-affinity is investigated as a key factor of the Ni-stabilizing additives. However, when providing a noble function to the electrolyte additive, the redox stability of the additives should be also understood. Thus, in addition to the intrinsic oxidation energy, the protonation and dehydrogenation energies of the additive molecules are calculated to determine the H-transfer-driven electrolyte oxidation. The Li+-complexation is considered to model the electrolyte reduction. We investigate the molecular-leveled computed factors of electrolyte materials using fully automated high-throughput ab initio calculations. Those computed factors for representative molecules based on CO3, SO4, SO3, SO2, PC3, PO3, and OPO3, which are of great interest as major parts of electrolyte materials, are discussed to guide the additive development. In particular, SO2 and OPO3 molecules, which can strongly stabilize Ni2+ in a structurally stable form, have great advantages as Ni-stabilizing electrolyte additives for completion of Ni-rich layered cathode systems

Cycling Stability of a VO_<i>x</i> Nanotube Cathode in Mixture of Ethyl Acetate and Tetramethylsilane-Based Electrolytes for Rechargeable Mg-Ion Batteries

The electrochemical cycling performance of vanadium oxide nanotubes (VO_<i>x</i>-NTs) for Mg-ion insertion/extraction was investigated in acetonitrile (AN) and tetramethylsilane (TMS)-ethyl acetate (EA) electrolytes with Mg­(ClO₄)₂ salt. When cycled in TMS-EA solution, the VO_<i>x</i>-NT exhibited a higher capacity retention than when cycled in AN solution. The significant degradation of capacity in AN solution resulted from increased charge-transfer resistance caused by the reaction products of the electrolyte during cycling. Mixed TMS-EA solvent systems can increase the cell performance and stability of Mg-electrolytes owing to the higher stability of TMS toward oxidation and the strong Mg-coordination ability of EA. These results indicate that the interfacial stability of the electrolyte during the charging process plays a crucial role in determining the capacity retention of VO_<i>x</i>-NT for Mg insertion/extraction