Shengping Wang

Recent progress in polymer/sulphur composites as cathodes for rechargeable lithium–sulphur batteries

Currently, studies with sulphur electrode materials are focused primarily on carbon/sulphur and polymer/sulphur composites. Despite carbon/sulphur composites being a more popular research interest than polymer/sulphur composites, improving the cycle performance of sulphur by using polymers is also a major research focus. Therefore, we review the latest developments for polymer/sulphur composites in Li–S batteries. The various polymer/sulphur composites and their impacts on the electrochemical performance are discussed. Meanwhile, the synthesis approaches toward the various polymer/sulphur composites are also summarised. Finally, the future research directions involving polymer/sulphur composites are addressed.

In situ incorporation of a S, N doped carbon/sulfur composite for lithium sulfur batteries

A novel sulfur–nitrogen co-doped carbon material (SNC), which is obtained by taking polyaniline as the nitrogen-containing carbon precursor and then incorporating sulfur atoms in situ as the matrix material for lithium sulfur batteries, is investigated. XPS reveals the formation of strong chemical bonding (–C–S–C– and C–SOx–C (x = 2–4)) in the structure of SNC materials. Moreover, the results demonstrate that SNC–S composites showed higher specific capacity and better cycle performance than the pristine nitrogen co-doped carbon material (NC)/sulfur (NC–S) composites. Except for providing more lithium storage sites due to faradaic reactions, the incorporation of sulfur not only immobilizes the sulfur and polysulfide species, thus improving the interfacial characterization between the electrode and the electrolyte, but also influences the reversible dissolving balance of long-chain polysulfides and suppresses the “shuttle effect”, resulting in better electrochemical behavior. This facile approach of the SNC matrix could provide a practical research direction for lithium sulfur batteries.

Sulfur/Co3O4 nanotube composite with high performances as cathode materials for lithium sulfur batteries

To improve the overall electrochemical performance of the sulfur cathode in Li/S batteries, a hollow Co3O4 nanotube with a channel measuring approximately 12.5 nm in diameter is synthesized and then impregnated with sulfur via a melt-diffusion strategy. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis and thermogravimetric analysis indicate that sulfur impregnated the channels of the hollow Co3O4 nanotube. Because the sulfur is mostly restricted to the Co3O4 nanotubes, a sulfur/Co3O4 cathode with 10 wt.% sulfur loading delivers an initial discharge capacity of 963.4 mAh g-1, with much of the capacity contributed by Co3O4, and exhibits excellent reversibility with a capacity reservation of 80.8% after 100 cycles.

A lithium/polysulfide semi-solid rechargeable flow battery with high output performance

The feasibility of a semi-solid flow battery with polysulfide as catholyte is demonstrated, which gives a power density of 1.823 mW cm−2 at 4 mA cm−2. Compared to Li–S batteries with sulfur as cathode, the feasibility and flexibility using polysulfide as catholyte in flow-through mode create new potential for the practical application of conventional Li–S batteries.

How to make lithium iron phosphate better: a review exploring classical modification approaches in-depth and proposing future optimization methods

LiFePO4 is still a promising cathode, which is inexpensive, nontoxic, environmentally benign, and most importantly safe. However, LiFePO4 suffers from low conductivity and sluggish diffusion of lithium ions. Surface decoration, nanocrystallization and lattice substitution (doping) are modification approaches widely employed to promote the conductivity of electrons and the diffusion of lithium ions in the crystal lattices of LiFePO4. This review focuses on discussing the functional mechanisms of these optimization methods from the extent of electron and lithium ion migration and the features of LiFePO4, namely, its structure and phase transformation reactions. At the interface of LiFePO4 and the electrolyte, decoration layers not only ensure the stability of LiFePO4 by excluding HF corrosion and surface degradation, but also reduce charge transfer resistances for the surface reactions with fast lithium ions and electrons. When it comes to the lattices of LiFePO4, nanocrystallization unblocks the diffusion path, as well as shortens the diffusion length of lithium ions. Decoration layers in the inner surface avoid slowing down the diffusion of lithium ions in the lattices throughout the reactions and maximize the utilization of LiFePO4. Lattice substitutions, which increase the electronic conductivity by decreasing the band gap, interrupt the major advantage of LiFePO4, the structural stability, which guarantees the safety as well as the cycling and rate performances. To make the electrochemical performance of LiFePO4 better and overcome the contradiction about the miscibility gaps, [010]-oriented LiFePO4 nanoflakes/nanomeshes/nanoplates, [100]-oriented or [001]-oriented nanorod/nanowire structures and nanowires/nanorods/nanotubes with a carbon/LiFePO4/carbon coaxial structure (graphically shown in the text) can be developed in the future.

Lithium vanadium phosphate as cathode material for lithium ion batteries

Lithium vanadium phosphate (Li3V2(PO4)3) has been extensively studied because of its application as a cathode material in rechargeable lithium ion batteries due to its attractive electrochemical properties, including high specific energy, high working voltage, good cycle stability, and low price. In this review, the preparation of technology, structure, Li+ insertion/extraction mechanism, and electrochemical properties of Li3V2(PO4)3 are introduced, and with particular focus on the relationship of these topics each other. The synthetic techniques of Li3V2(PO4)3, such as high-temperature solid-state method, sol–gel method, hydrothermal method, etc. And progress of techniques in modification, such as coating and elemental doping, is reviewed. Finally, the directions for further development and prospective applications for the material are proposed.

Electrochemical characterization of nano V, Ti doped MnO2 in primary lithium manganese dioxide batteries with high rate

The nano-sized γ-MnO2 precursor is synthesized using a room temperature, liquid-phase reaction route with the assistance of ultrasonic waves. The MnO2 precursor as an electrode material in lithium manganese dioxide primary batteries displays a low capacity of 140mAhg−1 (45.5% for the theoretical capacity of MnO2) at 20mAg−1. Therefore, the doped MnO2 with cationic V or/and Ti are prepared at high temperature. After the heat treatment, the γ phase precursor powder gradually converts into the β-MnO2 and exhibits a higher specific surface area with a larger pore volume and pore size, providing significantly more electrochemically active sites for the redox reaction. The doped MnO2 matrix has advantage of the ideal lattice parameters and the higher conductivity, resulting in an enhancement of the Li+ diffusion kinetics in the tunnel structure. Especially for co-doped MnO2 with V and Ti, the modified material shows an outstanding electrochemical capacity of 190mAhg−1 (61.7% for the theoretical capacity) at 20m...

Pseudocapacitive behavior of the Fe2O3 anode and its contribution to high reversible capacity in lithium ion batteries

Pseudocapacitance, which is the storage of charge based on continuous and fast reversible redox reactions at the surface of electrode materials, is commonly observed for electrodes in lithium ion batteries, especially for transition metal oxide anodes. In this report, bare Fe2O3 of granular morphology (∼30 nm in diameter) with high purity and decent crystallinity as well as recommendable electrochemical performances is fabricated hydrothermally and employed as the subject to clarify pseudocapacitive behavior in transition metal oxide anodes. Electrochemical technologies such as galvanostatic charging/discharging, differential capacity analysis (dQ/dV) and the power law relationship (i = aνb), which can distinguish pseudocapacitive behaviors of an electrode reaction were employed to analyze the electrodes. Reversible capacities of ∼120 mA h g-1 (0.117 F cm-2) for Fe2O3 were found within particular electrochemical windows (2.3-3.0 V, 0.3-0.8 V for discharging and 2.2-3.0 V, 0.3-1.3 V for charging). A new direction of optimizing the capacities, rate and cycling performances for lithium ion batteries is pointed out with connections between the pseudocapacitive behavior and morphologies of surfaces as well as structures of the electrodes.