One-Step Synthesis of Co@C Composite as High-Performance Anode Material for Lithium-ion Batteries

A carbon-coated cobalt (Co@C) composite was synthesized by a one-step method using ionic liquid as carbon source and reducing agent. The Co@C composite exhibited a core-shell structure, in which the cobalt nanoparticles uniformly embedded in the carbon matrix. When used as the anode material for lithium ion batteries, the cobalt nanoparticles enhanced the kinetics of Li+ and electronic transport during the charge/discharge process. The Co@C composite material delivered a reversible capacity of 657.3 mAh g-1 after 60 cycles at a current density of 0.1C and exhibits improved rate performance when compared with pure carbon

On the r-free values of the polynomial x^2+y^2+z^2+k

Let k be a fixed integer. We study the asymptotic formula of R(H, r, k), which is the number of positive integer solutions x, y, z greater than or equal to 1 and less than or equal to H such that the polynomial x^2+y^2+z^2+k is r-free. We obtained the asymptotic formula of R(H, r, k) for all r greater than or equal to 2. Our result is new even in the case r = 2. We proved that R(H, 2, k) = ckH^3 + O(H^(9/4+epsilon)), where ck > 0 is a constant depending on k. This improves upon the error term O(H^(7/3+epsilon)) obtained by Zhou and Ding.Comment: 12 page

A Comparative Study on LiFePO\u3csub\u3e4\u3c/sub\u3e/C by In-Situ Coating with Different Carbon Sources for High-Performance Lithium Batteries

LiFePO4/C materials are synthesized via in-situ coating of LiFePO4 by using 1-butyl-3-methylimidazolium dicyanamide ([BMIm][N(CN)2]) and glucose as carbon sources, respectively. The structure characterization results indicate that the carbon sources have no effect on the LiFePO4 particles, but have remarkable influence on the coated carbon films. It is found that the [BMIm][N(CN)2] carbon source leads to ultrathin (1–2 nm), uniform and highly graphitized carbon films. Due to this unique structure, the electrode materials fabricated by using [BMIm][N(CN)2] exhibit a superior electrode reaction reversibility, a capacity retention of 160.6 mAhg−1 (1.47% decay rate) after 50 cycles and a specific discharge capacity of 143.6 mAhg−1 at 1C, which is much better than the performance of the electrode materials synthesized with glucose

Co3O4/Carbon Nano-Onions Composite as Supercapacitor Electrode and Its Excellent Electrochemical Performance

An ionic liquid derived Co3O4/carbon nano-onions composite has been prepared by carbothermal reduction followed by oxidation. The introduction of carbon nano-onions improves the conductivity and structural stability of Co3O4 electrode material. Electrochemical measurements indicate that the redox reversibility is significantly improved. The Co3O4/carbon nano-onions composite shows a large specific capacitance of 402.35 F g–1 at a current density of 0.5 A g–1. After 9000 cycles, the specific capacitance retention remained 76% at 1 A g–1. The as-prepared Co3O4/carbon nano-onions composite delivers superior capacitive performance with good rate capability, large specific capacitance, and excellent cyclic performance, showing great application potential for high-performance electrochemical supercapacitors. Read More: https://www.hanser-elibrary.com/doi/abs/10.3139/146.11168

In Situ Coating on LiFePO 4 with Ionic Liquid as Carbon Source for High-Performance Lithium Batteries

LiFePO4/C materials were synthesized via an in situ coating on LiFePO4 with 1-butyl-3-methylimidazolium dicyanamide [BMIm][N(CN)2] as a carbon source. The electrode materials were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results revealed that 1–2 nm carbon films were successfully coated on the LiFePO4 particles. The electrochemical properties of LiFePO4/C composite were investigated by cyclic voltammetry (CV) curves, electrochemical impedance spectra (EIS), and electrochemical analysis. The test results showed that the LiFePO4/C composite possessed outstanding reversibility, cycle performance, and rate performance. The discharge capacities of LiFePO4/C were 161.5 mAh g−1 at 0.1 C and 143.6 mAh g−1 at 1 C, respectively. The excellent electrochemical properties of the LiFePO4/C electrode were mainly due to the thin, uniform, and highly graphitized carbon films

In-Situ Reduction Derived Nitrogen Doped Carbon Anchored Cobalt Nanoparticles as Highly Capacity and Long Life Lithium Ion Battery Anodes

A novel composite with embedded cobalt nanoparticles in nitrogen doped carbon (Co@NDC) is synthesized by the in-situ reduction of Co(OH)2 using ionic liquid [HMIm]N(CN)2 as carbon precursor. Due to the special structure, this composite can form more stable solid electrolyte interface (SEI) film than cobalt nanoparticles when used as anode. The Co@NDC electrode shows a high discharge capacity of 1322 mAh g−1 after 850 cycles at 0.5 C, and an extremely long cycle life (436 mAh g−1 after 2400 cycles at 5 C). This excellent electrochemical performance can be attributed to the catalytic lithium-carbon reaction of cobalt nanoparticles, high conductivity of the carbon material, and the thin and stable SEI film

Natural Soft/Rigid Superlattices as Anodes for High-Performance Lithium-Ion Batteries

© 2020 Wiley-VCH GmbH Volume expansion and poor conductivity are two major obstacles that hinder the pursuit of the lithium-ion batteries with long cycling life and high power density. Herein, we highlight a misfit compound PbNbS3 with a soft/rigid superlattice structure, confirmed by scanning tunneling microscopy and electrochemical characterization, as a promising anode material for high performance lithium-ion batteries with optimized capacity, stability, and conductivity. The soft PbS sublayers primarily react with lithium, endowing capacity and preventing decomposition of the superlattice structure, while the rigid NbS2 sublayers support the skeleton and enhance the migration of electrons and lithium ions, as a result leading to a specific capacity of 710 mAh g−1 at 100 mA g−1, which is 1.6 times of NbS2 and 3.9 times of PbS. Our finding reveals the competitive strategy of soft/rigid structure in lithium-ion batteries and broadens the horizons of single-phase anode material design

Natural Soft/Rigid Superlattices as Anodes for High‐Performance Lithium‐Ion Batteries

© 2020 Wiley-VCH GmbH Volume expansion and poor conductivity are two major obstacles that hinder the pursuit of the lithium-ion batteries with long cycling life and high power density. Herein, we highlight a misfit compound PbNbS3 with a soft/rigid superlattice structure, confirmed by scanning tunneling microscopy and electrochemical characterization, as a promising anode material for high performance lithium-ion batteries with optimized capacity, stability, and conductivity. The soft PbS sublayers primarily react with lithium, endowing capacity and preventing decomposition of the superlattice structure, while the rigid NbS2 sublayers support the skeleton and enhance the migration of electrons and lithium ions, as a result leading to a specific capacity of 710 mAh g−1 at 100 mA g−1, which is 1.6 times of NbS2 and 3.9 times of PbS. Our finding reveals the competitive strategy of soft/rigid structure in lithium-ion batteries and broadens the horizons of single-phase anode material design