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.

Tris(2,2,2-trifluoroethyl) phosphite (TTFEP) is investigated as an electrolyte additive to improve the electrochemical performance of LiNi1/3Co1/3Mn1/3O2 cathode at high operating voltage (4.6 V). Charge/discharge measurements demonstrate that TTFEP is effective to improve the cycling stability and rate capability of LiNi1/3Co1/3Mn1/3O2 cathode. The capacity retention of LiNi1/3Co1/3Mn1/3O2/Li cell with 1% TTFEP-containing electrolyte reaches up to 85.4% after 100 cycles at 0.5C (1C = 160 mA g−1), while that of the cell with the baseline electrolyte (1 M LiPF6 in EC/DMC electrolyte) only remains 74.2%. Moreover, the discharge capacity of the cathode with 1% TTFEP-containing electrolyte could maintain around 112.0 mAh g−1 at 4C. Based on the characterization of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), a protective interphase film formed on the cathode surface can be found due to the preferential oxidation of TTFEP, which inhibits the electrolyte decomposition and mitigates the cathode structural destruction, leading to the improved electrochemical performance of LiNi1/3Co1/3Mn1/3O2 cathode at high voltage.

Metallic oxide ZnO is considered to be a promising alternative anode material for lithium ion battery because of its high theoretical capacities (978 mA h g−1). However, its inherent low electronic conductivity and undesirable large volume change result in inferior electrochemical performances and hinder its practical application. Herein, ZnO/ZnO@C composites are prepared by a simple carbonization process of ZnO/ZnO@ZIFs-8, which are constructed by using ZnO particles as both template and zinc sources for zeolitic imidazolate frameworks-8 (ZIF-8) preparation via a facile solution reaction. When evaluated as anode for lithium ion batteries, the as-prepared composites show an initial capacity of 878 mA h g−1 at current density of 0.1 A g−1 with high capacity retention of 95.6% after 50 cycles, and an initial capacity of 359 mA h g−1 tested at 5.0 A g−1 with a capacity retention of 85.3% after 500 cycles, exhibiting outstanding cycling stability and excellent rate capability. The ameliorated electrochemical performances are mainly attributed to the elevated conductivity and cushioning effects provided by carbon framework derived from ZIF-8, and the enhanced pseudocapacitance behavior originated from the decreased size of ZnO particles and high surface area of ZIFs-derived carbon.

•HTN improve the electrochemical performances of Li1.2Ni0.13Co0.13Mn0.54O2 cathode.•The effects of HTN on cathode surface properties were investigated at high voltage.•A stable film formed on cathode surface with interaction between C≡N and metal ion.1,3,6-Hexanetricarbonitrile (HTN) has been investigated as an electrolyte additive to improve the electrochemical performance of the Li1.2Ni0.13Co0.13Mn0.54O2 cathode at high operating voltage (4.8 V). Linear sweep voltammetry (LSV) results indicate that HTN can improve the oxidation potential of the electrolyte. The influences of HTN on the electrochemical behaviors and surface properties of the cathode at high voltage have been investigated by galvanostatic charge/discharge test, electrochemical impedance spectroscopy (EIS), and ex-situ physical characterizations. Charge-discharge results demonstrate that the capacity retention of the Li1.2Ni0.13Co0.13Mn0.54O2 cathode in 1% HTN-containing electrolyte after 150 cycles at 0.5 C is improved to 92.3%, which is much higher than that in the standard electrolyte (ED). Combined with the theoretical calculation, ICP tests, XRD and XPS analysis, more stable and homogeneous interface film is confirmed to form on the cathode surface with incorporation of HTN, meanwhile, the electrolyte decomposition and the cathode structural destruction are restrained effectively upon cycling at high voltage, leading to improved electrochemical performance of Li1.2Ni0.13Co0.13Mn0.54O2 cathode.Download high-res image (244KB)Download full-size image

In this work, the electrochemical performance of LiNi1/3Co1/3Mn1/3O2 cathode is investigated under high voltage with fluoroethylene carbonate (FEC) as co-solvent for lithium ion battery. Charge/discharge tests show that the cycling and rate performances of LiNi1/3Co1/3Mn1/3O2 are dramatically improved at high voltage operation when ethylene carbonate (EC) is replaced by FEC in electrolyte solution. After 100 cycles between 3.0 and 4.6 V (vs. Li/Li+) at 0.2C rate, the capacity retention of LiNi1/3Co1/3Mn1/3O2 with FEC/dimethyl carbonate (DMC) (1/4, vol.%) solution is 82.7%, while the EC-containing electrolyte is only 41.3%. The effects of FEC on the high-voltage performance and the surface properties of the LiNi1/3Co1/3Mn1/3O2 cathode are characterized by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It is found that FEC as co-solvent participates in the formation of protective surface films on the LiNi1/3Co1/3Mn1/3O2 cathode, which efficiently suppresses the decomposition of the electrolyte, prevents the severe structure destruction and improves the cycling stability and rate capability of LiNi1/3Co1/3Mn1/3O2 electrode under high voltage.

•Layer-by-layer SnO2 nanosheet/Pt/graphene was prepared by multi-stepped polyol process.•The layer-by-layer structure was confirmed upon physical characterization.•The ethanol electro-oxidation performance and mechanism were studied in detail.•SnO2/Pt/graphene shows superior ethanol oxidation activity and durability.•SnO2/Pt/graphene possesses better selectivity from ethanol to CO2 and CH3COOH.We designed and synthesized a layer-by-layer SnO2/Pt/graphene electro-catalyst through multi-microwave method. The experimental results show that the activity for the ethanol oxidation strongly depends on the content of graphene and the highest catalytic activity occurs at ∼30 wt%, followed by ∼40 wt%, and ∼20 wt%. Without any other metal component, the ultrathin SnO2/Pt/graphene exhibits enhanced not only EOR activity but also durability compared with Pt/graphene. More importantly, the differential electrochemical mass spectrometry (DEMS) study reveals that the layer-by-layer ultrathin SnO2/Pt/graphene composites induces improved selectivity to acetic acid (CH3COOH) and carbon dioxide (CO2) compared to Pt/graphene. The present work sheds light on ways to optimize electro-catalysts for EOR by smartly tailoring the nanostructure of composition of materials based on platinum, metal oxide and carbon.Layer-by-layer structured SnO2/Pt/G hybrids promote the ethanol oxidation selectivity towards CO2 and CH3COOH formation.

•Accelerated cycling tests in a long-term shallow charge and discharge process.•The degradation mechanism of the LiCoO2/MCMB full cell is proposed.•The percentage of each aging factor is calculated.•The accelerated rate range ensuring no changes in aging mechanism is found out.A series of LiCoO2/mesocarbon microbeads (MCMB) commercial cells cycled at different rates (0.6C, 1.2C, 1.5C, 1.8C, 2.4C and 3.0C) are disassembled and the capacity fade mechanism is proposed by analyzing the structure, morphology and electrochemical performance evolution at the capacity retention of 95%, 90%, 85%, 80%. The capacity deterioration of the commercial cell is mainly caused by the decay of the reversible capacity of LiCoO2 cathode, the irreversible loss of active lithium and the lithium remaining in anode. The proportions of effects by the above three factors are calculated accurately. The consumption of the active lithium leads to a cell imbalance between the anode and the cathode. The electrochemical test results indicate that the capacity fade of the active materials at the low rate is more obvious than that at the high rate. The influence of the active lithium is gradually increscent with the increasing rate. The rate of 1.5C is the optimal value to accelerate the aging of the full cell by comparing the testing results at different capacity retentions in the specific condition of low charge/discharge rate and shallow depth of discharge.

•P-Pt/rGO@TiO2 composite has been prepared by photoreduction method.•Pt nanoparticles (ca. 2.2 nm) are deposited in the interface between TiO2 and rGO.•P-Pt/rGO@TiO2 exhibits higher methanol electro-oxidation activity compared with m-Pt/rGO@TiO2.•The electrochemical durability of p-Pt/rGO@TiO2 is improved by a factor of 2 more as compared with m-Pt/rGO@TiO2.Pt/TiO2-decorated reduced graphene oxide composite as catalyst for methanol electro-oxidation with three phase junction structure has been synthesized by UV-photoreduction (denoted as p-Pt/rGO@TiO2). The obtained p-Pt/rGO@TiO2 has been detailedly characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and chronoamperometry (CA). XRD and TEM characterizations indicate that photoreduction is favorable to anchoring Pt nanoparticles (NPs) (ca. 2.2 nm) at the interface between TiO2 and reduced graphene oxide (rGO), and forming the Pt, TiO2 and rGO three phase junction structure. P-Pt/rGO@TiO2 exhibits a higher activity for methanol electro-oxidation than m-Pt/rGO and m-Pt/rGO@TiO2 (prepared by microwave-assisted polyol process). Lifetime tests demonstrate that the electrochemical durability of p-Pt/rGO@TiO2 is improved by a factor of 2 or more as compared with m-Pt/rGO and m-Pt/rGO@TiO2. XPS characterizations of p-Pt/rGO@TiO2 reveal stronger interaction between Pt and support hybrid compared with m-Pt/rGO@TiO2, which facilitates poisoning species removal and prevents Pt nanoparticles from migrating/agglomerating on or detaching from carbon support. This provides a facile and promising strategy to improve both the activity and durability of electrocatalysts for DMFCs.