Lina Cong

Self-organization towards complex multi-fold meso-helices in the structures of Wells–Dawson polyoxometalate-based hybrid materials for lithium-ion batteries

We utilised the rich coordination character of Wells–Dawson polyoxometalates (POMs) to explore the higher-level helical conformation of hybrids. Herein, two compounds, [Ag26(Trz)16(OH)4][P2W18O62] (1) and Na[Ag16(Trz)9(H2O)4][P2W18O62]·H2O (2) (Trz = 1,2,3 triazole), with multi-fold meso-helices were successfully isolated. Both 1 and 2 displayed two different types of four-fold meso-helices, which are composed of POMs and organic–metal subunits. The interesting thing is that the four-fold helixes of 2 sequentially evolve into the most complex eight-fold meso-helices by sharing the building blocks. In addition, the multi-chelate patterns of Wells–Dawson POMs in 2 represent the highest coordination numbers to date, which dominates the evolution from four-fold to eight-fold meso-helices. For the first time, the Wells–Dawson POMs-based hybrids 1 and 2 have been used as anode materials in lithium-ion batteries (LIBs). The initial specific capacities of 1077 mA h g−1 for 1 and 1094 mA h g−1 for 2 were much higher than those of (NBu4)6[P2W18O62] and commercial graphite as reference anodes at a current density of 100 mA cm−2. Also, both of them showed stable performance after 100 cycles.

LiV3O8 nanorods as cathode materials for high-power and long-life rechargeable lithium-ion batteries

Nowadays one of the principal challenges for the development of lithium-ion batteries (LIBs) is fulfilling the burgeoning demands for high energy and power density with long cycle life. Herein, we demonstrate a two-step route for synthesizing LiV3O8 nanorods with a confined preferential orientation by using VO2(B) nanosheets made in the laboratory as the precursor. The special structures of nanorods endow the LiV3O8 materials with markedly enhanced reversible capacities, high-rate capability and long-term cycling stability as cathodes for lithium storage. The results show that very desirable initial capacities of 161 and 158 mA h g−1 can be achieved for the LiV3O8 nanorods at extremely high rates of 2000 and 3000 mA g−1, with minimal capacity loss of 0.037% and 0.031% per cycle throughout 300 and 500 cycles, respectively. The energetically optimized electron conduction and lithium diffusion kinetics in the electrode process may shed light on the superior electrochemical properties of the LiV3O8 nanorods, primarily benefitting from the small particle size, large surface area and restricted preferential ordering along the (100) plane.

Yolk–shell Co2CrO4 nanospheres as highly active catalysts for Li–O2 batteries: understanding the electrocatalytic mechanism

Controlling the geometric morphology and distributive location of discharge products play an important role in the reversibility and efficiency of Li–O2 batteries. This work presents novel Co2CrO4 nanospheres (CCO) prepared via a facile method, which are applied as the electrocatalysts for Li–O2 batteries. The as-prepared CCO was characterized by XRD, XPS, SEM, TEM, BET, and TG measurements. The CCO exhibited a yolk–shell microstructure, which could facilitate fast Li+ and O2 diffusion as well as possessing enough space for the discharge product deposition. In comparison to the performance of the cell without catalyst, the overpotential of the cell with CCO was apparently reduced and the cyclability significantly enhanced. Based on the experimental results and DFT calculations, direct evidence of the CCO employment being linked to the Li2O2 morphology was provided. In addition, a catalytic mechanism was proposed. Furthermore, fundamental information about the key factors and steps involved in the Li2O2 formation and decomposition was revealed. We expect that this study gives insight into the development of electrocatalysts, the selection of O2 electrode materials, and the design of O2 electrodes for Li–O2 batteries, as well as advancing our understanding of the catalytic mechanism.

A study of the electrochemical behavior at low temperature of the Li3V2(PO4)3 cathode material for Li-ion batteries

In this paper, glucose and carbon nanotube (CNT) modified Li3V2(PO4)3 have been synthesised via a carbon thermal reduction method. The structure of Li3V2(PO4)3 has been confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning and transmission electron microscopy. The CNT modified Li3V2(PO4)3 materials, combined with the synthesized electrolyte, overcome the limitations of the low temperature performance of Li-ion batteries. The synthesized electrolyte is made up of 1.2 M LiPF6 dissolved in EC : DMC : EMC (1 : 1 : 1 in volume) with vinylene carbonate (VC) and propylene sulfite (PS) as the additive agents. The electrochemical behaviors of the cells have been evaluated by electrochemical tests over the temperature range from 25 to −20 °C. The specific capacities are 116.2, 108.2, 103.7, 96.3, and 86.1 mA h g−1 at 0.5C, 1C, 2C, 5C, and 10C, respectively, between 3.0 and 4.3 V at −20 °C. After 300 cycles, the capacity retention still reached 97% even at −20 °C. The excellent rate capability and low temperature performance are attributed to the synergistic effect between the CNTs and the synthesized low temperature electrolyte.

Fabrication of CNTs/MnO2 composite as a wrapping layer for surface modification of Cr-doped LiNi0.5Mn1.5O4 for lithium ion batteries

Needle-like MnO2 is deposited on the surface of CNTs using a simple redox reaction and simultaneously forms a special wrapping layer on the surface and among the particles of Cr-doped LiNi0.5Mn1.5O4 through an auto-grow process. The CNTs act as a conductive network of electrons and the needle-like MnO2 increases the contact points among the particles and furthermore provides additional Li+ diffusion paths. The CNTs/MnO2 composite is also a protective layer to suppress the side reaction between the electrode and the electrolyte. The CNTs/MnO2-coated, Cr-doped LiNi0.5Mn1.5O4 (CNTs/MnO2–Cr-LNMO) shows superior electrochemical properties, with a high specific capacity and excellent cycling stability at high voltage and high rate.

Self-assembled layer-by-layer partially reduced graphene oxide–sulfur composites as lithium–sulfur battery cathodes

Constructing a reliable conductive carbon matrix is essential for the sulfur-containing cathode materials of lithium–sulfur batteries. A ready-made conductive matrix infiltrated with sulfur as the cathode is the usual solution. Here, a partially reduced graphene oxide–sulfur composite (prGO/S) with an ordered self-assembled layer-by-layer structure is introduced as a Li–S battery cathode. The prGO/S composites are synthesized through a facile one-step self-assembly liquid route. An appropriate amount of sulfur is in situ deposited on the surface of the prGO nanosheets by adjusting the reduction degree of the GO nanosheets. The combined effect of the electrostatic repulsions and surface energy makes the sulfur wrapped prGO nanosheets self-assemble to form an ordered layer-by-layer structure, which not only ensures the uniform distribution of sulfur but also accommodates the volume change of the sulfur species during cycling. Moreover, the conductivity of the prGO/S composites improves when the reduction time increases. XPS spectra confirm that sulfur is still chemically bonded to the prGO. After applying the prGO coating of the prGO/S composite particle and as an interlayer in a lithium–sulfur battery configuration, a high initial discharge capacity of 1275.8 mA h g−1 is achieved and the discharge capacity of the 100th cycle is 1013.8 mA h g−1 at 0.1C rate.

Binary Mixtures of Highly Concentrated Tetraglyme and Hydrofluoroether as a Stable and Nonflammable Electrolyte for Li–O2 Batteries

Developing a long-term stable electrolyte is one of the most enormous challenges for Li-O2 batteries. Equally, the high flammability of frequently used solvents seriously weakens the electrolyte safety in Li-O2 batteries, which inevitably restricts their commercial applications. Here, a binary mixture of highly concentrated tetraglyme electrolyte (HCG4) and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) was used for a novel electrolyte (HCG4/TTE) in Li-O2 batteries, which exhibit good wettability, enhanced ionic conductivity, considerable nonflammability, and high electrochemical stability. Being a co-solvent, TTE can contribute to increasing ionic conductivity and to improving flame retardance of the as-prepared electrolyte. The cell with this novel electrolyte displays an enhanced cycling stability, resulting from the high electrochemical stability during cycling and the formation of electrochemically stable interfaces prevents parasitic reactions occurring on the Li anode. These results presented here demonstrate a novel electrolyte with a high electrochemical stability and considerable safety for Li-O2 batteries.