Shuaifeng Lou

Facile synthesis of nanostructured TiNb2O7 anode materials with superior performance for high-rate lithium ion batteries

One-dimensional nanostructured TiNb2O7 was prepared by a simple solution-based process and subsequent thermal annealing. The obtained anode materials exhibited excellent electrochemical performance with superior reversible capacity, rate capability and cyclic stability.

Electrochemical performance degeneration mechanism of LiCoO2 with high state of charge during long-term charge/discharge cycling

Electrochemical performance degeneration of LiCoO2 electrodes under high state of charge (SOC) during long-term cycling was studied using LiCoO2/MCMB batteries. The batteries were charged/discharged at 0.6C with 30% depth of discharge (DOD) for 100, 400, 800, 1600, 2000 and 2400 cycles, respectively, and then disassembled to analyze the evolution of morphology, element content, microstructure and electrochemical performance. Through energy dispersive spectrometer (EDS), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) characterization, it was confirmed that the formation of discontinuous solid electrolyte interface (SEI) layer consisting of Li2CO3, RCOOLi and LiF led to the increase of electrochemical charge transfer resistance (Rct). Although the X-ray diffraction (XRD) refined results showed that there was no new phases were formed during the long-term cycling, the actually increased Li/Co exchange ratio of LiCoO2 from 1.6% at 800th to 2.1% at 2400th resulted in the decrease of lithium ion diffusion coefficient and deterioration of the rate performance.

Lithium deposition on graphite anode during long-term cycles and the effect on capacity loss

Lithium deposition on the surface of a graphite anode during long-term cycles was evaluated using a LiCoO2/graphite battery. The batteries were charged/discharged at 1 C and 25 °C within the voltage range of 2.75–4.2 V for 600, 700, 800, 900 and 1000 cycles. Scanning electron microscopy (SEM) results indicated that both solid electrolyte interphase (SEI) film and lithium deposition appeared on the surface of the cycled graphite anode. Dendritic and granular lithium deposits grew on the anode non-uniformly. Metallic lithium existed in the deposition according to differential scanning calorimetry (DSC) results. Capacity declined distinctly from the 800th cycle, corresponding with the growth of lithium deposits. An SEI film was formed on the surface of the lithium deposits. Results of X-ray photoelectron spectroscopy (XPS) test indicated that the composition of SEI film on the surface of the lithium deposits was the same as that of the SEI film on the surface of cycled graphite. Capacity loss from the electrolyte consumed by the formation of the SEI film was 23.61%, while the loss from other battery components was 76.39%. Formation of lithium deposits consumed active lithium in the battery and led to capacity loss. According to test results of the three-electrode cell, the average anode potential at the end of constant-current charging for full battery became more negative with the cycling, and this phenomenon was related to the generation of lithium deposits.

Two isomorphous coordination polymer-derived metal oxides as high-performance anodes for lithium-ion batteries

Two isomorphous 2D coordination polymers (CPs), [Co(L)2]n(1) and [Ni(L)2]n(2) (HL = 4-benzimidazole-1-yl-benzoic acid), have been synthesized under solvothermal conditions as precursors for metal oxides and characterized by single-crystal X-ray diffraction, revealing that both compounds 1 and 2 present porous 44 topology. The CP-derived metal oxides Co3O4 and NiO were prepared and examined as anodes for lithium-ion batteries in the potential range of 0.01–3.0 V. Both exhibit excellent cycle stability and high Coulombic efficiency at high current density, and the Co3O4 electrode presents superior electrochemical performance. Co3O4 can achieve a specific capacity of 569.8 mA h g−1 with 98% Coulombic efficiency after 50 cycles at a high current density of 2000 mA g−1.

Unravelling the interface layer formation and gas evolution/suppression on TiNb2O7 anode for lithium ion batteries

TiNb2O7 (TNO) has been regarded as a promising anode material for high-power lithium-ion batteries because of the high theoretical capacity and rate performance within the operation voltage range of 1.0-3.0 V. Herein, the electrochemical performance and interface evolution of TNO are comprehensively investigated by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The prepared TNO shows a high initial reversible capacity of 256 mA h g-1 and a satisfactory capacity retention of 68.4% after 200 cycles at 0.1 C. It is generally believed that the formation of solid electrolyte interface (SEI) film could be avoided at the high operating voltage beyond 1.0 V. However, we find that the thin SEI layer is formed during the lithium insertion process and partially dissolved during the following lithium extraction process, and subsequently the SEI layer increases gradually during long-term cycles. Most importantly, we find obvious gassing behavior in the TNO/LiFePO4 pouch cell for the first time and demonstrate effective suppression effects of VC additive on the swelling phenomenon of full batteries.