Comparative calculation on Li~+ solvation in common organic electrolyte solvents for lithium ion batteries

It is important for the electrolytes to maintain and enhance the lithium ion battery electrochemical performance,and solvation of Li^+is a key parameter for the property of the electrolytes.The comparative study on Li^+ solvation structures,energy,enthalpy,Gibbs free energy,infrared and Raman spectra in common organic electrolyte solvents is completed by density functional theory(DFT)method.The solvation reaction energy results suggest that the Li^+solvation priority order is propylene carbonate(PC)>ethylene carbonate(EC)>ethyl methyl carbonate(EMC)>diethyl carbonate(DEC)>tetrahydrofuran(THF)>dimethyl carbonate(DMC)>1,3-dioxolane(DOL)>dimethoxyethane(DME)to form 5sol Li^+.It is also indicated that the most innermost solvation shell compounds formations by stepwise spontaneous solvation reaction are four cyclic solvent molecules and three linear solvent molecules combining one Li^+ forming 4sol-Li^+ and 3sol-Li^+,respectively,at room temperature.Besides,the vibration peaks for C=O and C-O bonds in carbonate ester solvents-Li^+ compounds shift to lower frequency and higher frequency,respectively,when the Li^+ concentration increases in the solvation compounds.All Li-O stretching vibration peaks shift to higher frequency until forming 2solvent-Li^+ complexes,and C-H stretching also shifts to higher frequency except for nDME-Li^+ solvation compounds.The Raman spectrum is more agile to characterize C-H vibrations and IR is agile to C=O,C-O,and Li-O vibrations for Li^+solvation compounds.     

First-principles study of interphase Ni3Sn in Sn--Ni alloy for anode of lithium ion battery

This paper investigates the mechanism of Li insertion into interphase Ni3Sn in Ni-Sn alloy for the anode of lithium ion battery by means of the first-principles plane-wave pseudopotential. Compared with other phases, it is found that the Ni3Sn has larger relative expansion ratio and lower electrochemical potential, with its specific plateaus voltage around 0.3 eV when lithium atoms are filled in all octahedral interstitial sites, and the relative expansion ratio increasing dramatically when the lithiated phase transits from octahedral interstitial sites to tetrahedral interstitial sites. So this phase is a devastating phase for whole alloy electrode materials.     

First-principle study on phase Al0.8Ni3Sn0.2 in Sn-Ni-Al alloy as anode for lithium ion battery

The mechanism of lithium intercalation/deintercalation for phase Al 0.8 Ni 3 Sn 0.2 as anode material used in lithium ion battery was studied carefully based on the first-principle plane wave pseudo-potential method.The calculated results indicated that Sn-Ni-Al alloy had high theoretical capacity when used as anode material,however,there was high initial irreversible capacity loss because of the large volume expansion.Therefore the technological parameters during preparing the Sn-Ni-Al anode should be controlled strictly to make the content of Al 0.8 Ni 3 Sn 0.2 phase as low as possible and to make the anode consist of promising Sn-Ni and Al-Ni phases.For comparison,an experiment based on magnetron sputtering was done.The result showed that the calculation is in good agreement with the experiment.We found that the first-principle investigation method is of far-reaching significance in synthesising new commercial anode materials with high capacity and good cycle performance.     

Study of the electrochemical performance of VO2+/VO2 + redox couple in sulfamic acid for vanadium redox flow battery

The present work was performed in order to evaluate sulfamic acid as the supporting electrolyte for VO²⁺/VO₂ ⁺ redox couple in vanadium redox flow battery. The oxidation process of VO²⁺ has similar electrochemical kinetics compared with the reduction process of VO₂ ⁺. The exchange current density and standard rate constant of VO²⁺/VO₂ ⁺ redox reaction on a graphite electrode in sulfamic acid are determined as 7.6?×?10^?4 A cm^?2 and 7.9?×?10^?5 cm s^?1, respectively. The energy efficiency of the cell employing sulfamic acid as supporting electrolyte in the positive side can reach 75.87 %, which is adequate for redox flow battery applied in energy storage. The addition of NH₄ ⁺ to the positive electrolyte can enhance the electrochemical performance of the cell, with larger discharge capacity and energy efficiency. The preliminary exploration shows that the vanadium sulfamate electrolyte is promising for vanadium redox flow battery and is worthy of further study.     

Electron paramagnetic resonance study of Mn2+ in ferroelectric lithium ammonium tartarate monohydrate

EPR studies of Mn²⁺ in ferroelectric lithium ammonium tartarate monohydrate (LAT) show that there are four Mn²⁺ complexes, which group themselves into two chemically different sets each containing two physically related sites at room temperature. It is inferred that Mn²⁺ enters into NH₄⁺ site. The hyperfine separation of the central group ($\text{1}\text{2}$ → ? $\text{1}\text{2}$) is found to be constant, which is not observed usually. It is suggested that the space group of LAT below T_c is P2₁.     

锂离子电池SnSb/C复合负极材料的热碳还原法制备及电化学性能研究

采用高温还原技术,以SnO2,SbO3为原料,分别以葡萄糖、中间相碳微球(MCMB)作为还原剂,制备了两种结构的SnSb/C复合材料,并对比了它们的形貌和电化学性能.采用X射线衍射技术、拉曼技术、扫描电子显微镜技术对材料的结构和形貌进行了表征,并且通过测试恒电流充放电曲线、循环伏安曲线和交流阻抗谱分析了材料的电化学性能.实验结果表明:葡萄糖作为还原剂时,形成以合金颗粒为内核,絮状碳壳均匀包裹的微米球状结构,首次放电比容量为793.379 mA·h·g-1,循环50周后仍维持在449.987 mA·h·g-1;而以MCMB作为还原剂时,形成合金颗粒与MCMB混合共存并部分包覆的结构,首次放电比容量为1164.938 mA·h·g-1,50周后的比容量仅有290.807 mA·h·g-1.     

Superiority of DFT+U with non-linear core correction for open-shell binary rare-earth metal oxides: a case study of native point defects in cerium oxides

We successfully proposed a newly corrected density functional theory plus Hubbard U parameter (DFT + U) based on partial core correction on the orbitals within norm-conserving lanthanide atomic pseudopotentials. A related and comprehensive investigation of native point defects in cerium oxides has also been performed as an examine by practice.     

Theoretical study on behaviors of 1s22s-1s2np transition for Co24+ ion in the whole energy region

Non-relativistic energies of 1s²2s and 1s² np (n⩽9) states for Co²⁴⁺ ion are calculated by using the full-core plus correlation method. Our results of 1s²2s and 1s²2p states agree well with the high-precision results of Yan et al. Based on calculating the first-order corrections to the energy from relativistic and mass-polarization effects, we estimate the higher-order relativistic contribution and QED correction to the energy under a hydrogenic approximation. The transition energies, wavelengths and oscillator strengths for the 1s²2s−1s² np (n⩽9) transitions of this ion are calculated. The results agree with the experimental data available in literature satisfactorily. By combining with quantum defect theory, our theoretical predictions on the energy and oscillator strength of this ion are extrapolated to the whole energy region including continuous states.     

Effect of local structure on electron paramagnetic resonance spectra for trigonal [Cr(H2O)6]3+coordination complex in the sulfate alums series: a ligand field theory study

A simple theoretical method is introduced for studying the interrelation between electronic and molecular structures.By diagonalizing the 120 × 120 complete energy matrices,the relationships between zero-field splitting(ZFS) parameter D and local distortion parameter △θ for Cr 3+ ions doped,separately,in α-and β-alums are investigated.Our results indicate that there exists an approximately linear relationship between D and △θ in a temperature range 4.2-297 K and the signs of D and △θ are opposite to each other.Moreover,in order to understand the contribution of spin-orbit coupling coefficient ζ to ZFS parameter D,the relation between D and ζ is also discussed.