Xusong Qin

Recent advances in Mn-based oxides as anode materials for lithium ion batteries

The development of new electrode materials for lithium-ion batteries (LIBs) is of great interest because available electrode materials may not meet the high-energy demands for electronic devices, especially the demands for good cyclic and rate performance. Mn-based oxides have received substantial attention as promising anode materials for LIBs due to their high theoretical specific capacities, low charge potential vs. Li/Li+, environmental benignity and natural abundance. Herein, the preparation of Mn-based oxide nanomaterials with various nanostructures and chemical compositions along with their applications as negative electrodes for LIBs are reviewed. The review covers MnO, Mn3O4, Mn2O3, MnO2, CoMn2O4, ZnMn2O4 and their carbonaceous composite/oxide supports with different morphologies and compositions. The aim of this review is to provide an in-depth and rational understanding of the relationships among the chemical compositions, morphologies and electrochemical properties of Mn-based anode materials and, to understand how electrochemical performance can be improved using materials engineering strategies. Special attention has been paid to the discussion of challenges in the practical applications of Mn-based oxides in LIB full cells.

The enhanced rate performance of LiFe0.5Mn0.5PO4/C cathode material via synergistic strategies of surfactant-assisted solid state method and carbon coating

The rate performance of LiMnPO4-based materials is further improved via synergistic strategies including a surfactant-assisted solid state method, Fe-substitution and carbon-coating. The surfactant-assisted solid state strategy effectively decreases the primary particle size of the cathode material, which can greatly shorten the diffusion distance of lithium ions. The Fe-substitution improves the effectiveness of Li+ insertion/extraction reactions in the solid phase. The uniform carbon coating layer and the conductive networks provided by the carbon between the nanoparticles ensure the continuous conductivity by the nanoparticles. As a consequence of the synergistic effects, the as prepared LiFe0.5Mn0.5PO4 sample with 6.10 wt% carbon exhibits high specific capacities and superior rate performance with discharge capacities of 155.0, 140.9 and 121 mA h g−1 at 0.1, 1 and 5 C (1 C = 170 mA g−1), respectively. Meanwhile, it shows stable cycling stability at both room temperature (25 °C, 94.8% and 90.8% capacity retention after 500 cycles at 1 and 5 C rates, respectively) and elevated temperature (55 °C, 89.2% capacity retention after 300 cycles at 5 C rate). This material may have great potential application in advanced Li-ion batteries.

Wastewater Quality Monitoring System Using Sensor Fusion and Machine Learning Techniques

A multi-sensor water quality monitoring system incorporating an UV/Vis spectrometer and a turbidimeter was used to monitor the Chemical Oxygen Demand (COD), Total Suspended Solids (TSS) and Oil & Grease (O&G) concentrations of the effluents from the Chinese restaurant on campus and an electrocoagulation-electroflotation (EC-EF) pilot plant. In order to handle the noise and information unbalance in the fused UV/Vis spectra and turbidity measurements during the calibration model building, an improved boosting method, Boosting-Iterative Predictor Weighting-Partial Least Squares (Boosting-IPW-PLS), was developed in the present study. The Boosting-IPW-PLS method incorporates IPW into boosting scheme to suppress the quality-irrelevant variables by assigning small weights, and builds up the models for the wastewater quality predictions based on the weighted variables. The monitoring system was tested in the field with satisfactory results, underlying the potential of this technique for the online monitoring of water quality.

Graphene Oxide-Immobilized NH2-Terminated Silicon Nanoparticles by Cross-Linked Interactions for Highly Stable Silicon Negative Electrodes

There is a great interest in the utilization of silicon-based anodes for lithium-ion batteries. However, its poor cycling stability, which is caused by a dramatic volume change during lithium-ion intercalation, and intrinsic low electric conductivity hamper its industrial applications. A facile strategy is reported here to fabricate graphene oxide-immobilized NH2-terminated silicon nanoparticles (NPs) negative electrode (Si@NH2/GO) directed by hydrogen bonding and cross-linked interactions to enhance the capacity retention of the anode. The NH2-modified Si NPs first form strong hydrogen bonds and covalent bonds with GO. The Si@NH2/GO composite further forms hydrogen bonds and covalent bonds with sodium alginate, which acts as a binder, to yield a stable composite negative electrode. These two chemical cross-linked/hydrogen bonding interactions-one between NH2-modified Si NPs and GO, and another between the GO and sodium alginate-along with highly mechanically flexible graphene oxide, produced a robust network in the negative electrode system to stabilize the electrode during discharge and charge cycles. The as-prepared Si@NH2/GO electrode exhibits an outstanding capacity retention capability and good rate performance, delivering a reversible capacity of 1000 mAh g(-1) after 400 cycles at a current of 420 mA g(-1) with almost 100% capacity retention. The results indicated the importance of system-level strategy for fabricating stable electrodes with improved electrochemical performance.

Ni/Mn Ratio and Morphology-Dependent Crystallographic Facet Structure and Electrochemical Properties of the High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Material

The LiNi0.5Mn1.5O4 (LNMO) spinel is an attractive cathode material for next generation lithium-ion batteries as it offers a high power capability with a discharge voltage of 4.7 V and a theoretical capacity of 147 mA h g−1. In this paper, porous LNMO microspheres/cubes, which are constructed with nanometer-sized primary particles with different Ni/Mn ratios, have been synthesized by a facile method that involves the use of MnCO3 microspheres/cubes as the self-supporting template. The effects of the morphology of the MnCO3 and the Ni/Mn ratio on the physicochemical and electrochemical properties of the as-synthesized LNMO materials were investigated in detail. Scanning electron microscopy (SEM) observation shows that the morphology of the porous MnCO3 has an important effect on the morphology and degree of dispersion of the obtained LNMO spinels, so as to the electrochemical performance. XPS and XRD results show that the Ni/Mn ratio has a significant impact on the Mn3+ content, phase purity (rock-salt phase) and crystallographic facet orientations of the LNMO-based cathode materials. In particular, the Mn3+ content, rock-salt phase and high-active (111) facet in the LNMO spinels were found to be adjusted by the Ni/Mn ratio. With the presence of a reasonable Mn3+ content, high-active facet, the absence of the impurity phase (rock-salt phase) as well as the large cationic disorder in the Cr-doping LNMO spinels, the rate performance and capacity retention of the product could be significantly improved. All these findings show the important roles of the synergic effects of the morphology and the composition on the improvement of the electrochemical performance of LNMO-based cathode materials.

Treatment of Restaurant Wastewater by Pilot-Scale Electrocoagulation-Electroflotation: Optimization of Operating Conditions

AbstractIn the present study, restaurant wastewater containing high concentrations of chemical oxygen demand (COD), total suspended solids (TSS), and oil and grease (OG) was treated by the combined electrocoagulation-electroflotation (EC-EF) process on a pilot scale. A central composite design was applied to the experiment design and the response surface methodology was adopted to build the response surface models of effluent COD, TSS, and OG. The sequential quadratic programming method was utilized to optimize the operating conditions of the treatment process. The analysis of variance of the experimental data shows that the coefficients of determination of the response surface models of effluent COD, TSS, and OG were 0.98, 0.982, and 0.989, respectively. The validity of these models was tested by confirmation experiments with satisfactory results. Zero trade effluent surcharges were achieved under optimized operating conditions. In spite of the operating cost calculated with respects to energy, electrode...

Supercritical-hydrothermal accelerated solid state reaction route for synthesis of LiMn2O4 cathode material for high-power Li-ion batteries

Abstract Synthesis of the spinel structure lithium manganese oxide (LiMn2O4) by supercritical hydrothermal (SH) accelerated solid state reaction (SSR) route was studied. The impacts of the reaction pressure, reaction temperature and reaction time of SH route, and the calcination temperature of SSR route on the purity, particle morphology and electrochemical properties of the prepared LiMn2O4 materials were studied. The experimental results show that after 15 min reaction in SH route at 400 °C and 30 MPa, the reaction time of SSR could be significantly decreased, e.g. down to 3 h with the formation temperature of 800 °C, compared with the conventional solid state reaction method. The prepared LiMn2O4 material exhibits good crystallinity, uniform size distribution and good electrochemical performance, and has an initial specific capacity of 120 mA·h/g at a rate of 0.1C (1C=148 mA/g) and a good rate capability at high rates, even up to 50C.