W.S. Li

Triple-shelled Mn2O3 hollow nanocubes: force-induced synthesis and excellent performance as the anode in lithium-ion batteries

In this paper, we report a novel structure of Mn2O3, the triple-shelled Mn2O3 hollow nanocube, as the anode material for high-energy lithium-ion batteries, synthesized through a programmed annealing treatment with cubic MnCO3 as precursor. This hierarchical structure is developed through the interaction between the contraction force from the decomposition of MnCO3 and the adhesion force from the formation of Mn2O3. The structure has been confirmed by characterization with XRD, FESEM, TEM, and HRTEM. The charge–discharge tests demonstrate that the resulting Mn2O3 exhibits excellent cycling stability and rate capability when evaluated as an anode material for lithium-ion batteries. It delivers a reversible capacity of 606 mA h g−1 at a current rate of 500 mA g−1 with a capacity retention of 88% and a remaining capacity of 350 mA h g−1 at 2000 mA g−1.

Crystallographic facet- and size-controllable synthesis of spinel LiNi0.5Mn1.5O4 with excellent cyclic stability as cathode of high voltage lithium ion battery

We report a novel synthesis of spinel LiNi0.5Mn1.5O4, in which cubic and porous Mn2O3 nanoparticles, obtained from cubic MnCO3, are used as templates to induce the formation of crystallographic facet- and size-defined spinel. This is done to accomplish excellent cyclic stability of the spinel as a cathode of a high voltage lithium ion battery. The uniformly dispersed pores in the template, whose size can be controlled by limiting the annealing time of MnCO3, facilitate the incorporation of lithium and nickel ions and ensure the formation of spinel with a predominant (111) facet, while the spinel inherits the particle size of the template under controlled temperatures. The characterizations from SEM, TEM and XRD confirm the structure and morphology of the precursors and the resulting product. The charge–discharge test demonstrates the excellent cyclic stability of the resulting products, especially at elevated temperatures: capacity retention of 78.1% after 3000 cycles with 10 C rate at room temperature and that of 83.2% after 500 cycles with 5 C rate at 55 °C.

Porous LiMn2O4 cubes architectured with single-crystalline nanoparticles and exhibiting excellent cyclic stability and rate capability as the cathode of a lithium ion battery

Porous LiMn2O4 was fabricated with cubic MnCO3 as precursor and characterized in terms of structure and performance as the cathode of a lithium ion battery. The characterizations from SEM, TEM and XRD demonstrate that the fabricated product has a cubic morphology with an average edge of 250 nm, which it inherits from the precursor, and a porous structure architectured with single-crystalline spinel nanoparticles of 50 nm, which imitates the Mn2O3 that results from the thermal decomposition of the precursor. The charge–discharge tests show that the synthesized product exhibits excellent rate capability and cyclic stability: delivering a reversible discharge capacity of 108 mA h g−1 at a 30 C rate and yielding a capacity retention of over 81% at a rate of 10 C after 4000 cycles. The superior performance of the synthesized product is attributed to its special structure: porous secondary cube particles consisting of primary single-crystalline nanoparticles. The nanoparticle reduces the path of Li ion diffusion and increases the reaction sites for lithium insertion/extraction, the pores provide room to buffer the volume changes during charge–discharge and the single crystalline nanoparticle endows the spinel with the best stability.

Fabrication of core–shell porous nanocubic Mn2O3@TiO2 as a high-performance anode for lithium ion batteries

A novel composite, porous cubic Mn2O3@TiO2, was fabricated via a simple and cost-effective approach and characterized in terms of structure and performance as an anode for lithium ion batteries. The porous Mn2O3 cubes were developed by calcining cubic MnCO3 particles without using any template and then coated with TiO2 from heat decomposition of tetrabutyl titanate. The characterization from FESEM, TEM, HRTEM, XPS, BET, and XRD indicates that the as-fabricated Mn2O3@TiO2 takes a hierarchically porous cubic morphology with an edge of ∼340 nm and a core–shell structure with porous cubic Mn2O3 as the core, which consists of nanoparticles of ∼30 nm, and a layer of porous single-crystalline spinel TiO2 as the shell, which consists of smaller nanoparticles of ∼5 nm. The charge–discharge tests demonstrate that this unique configuration endows the as-fabricated Mn2O3@TiO2 with superior charge–discharge performance, to be specific, a rate capacity of 263 mA h g−1 at 6000 mA g−1 compared to the 9.7 mA h g−1 of Mn2O3, and a cyclic capacity of 936 mA h g−1 after 100 cycles at 200 mA g−1 compared to the 443 mA h g−1 of Mn2O3. The nanosized particles of Mn2O3 and TiO2 and the hierarchically porous structure among them provide paths for lithium-ion diffusion and sites for lithium-ion intercalation/deintercalation, while the chemically and mechanically stable TiO2 ensures the structural stability of Mn2O3 cubes, yielding excellent rate capability and cyclic stability of the as-fabricated Mn2O3@TiO2 as an anode for lithium ion batteries.

Improved power output by incorporating polyvinyl alcohol into the anode of a microbial fuel cell

In this study, polyvinyl alcohol (PVA) is proposed as a new binder to improve the power output of a microbial fuel cell. The physical and chemical properties of PVA are characterized with Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), contact angle testing, density functional theory calculations, and scanning electron microscopy (SEM). The electrochemical performance of an anode using carbon nanotubes as an electrocatalyst and PVA as a binder are evaluated in an Escherichia coli based fuel cell using chronoamperometry, electrochemical impedance spectroscopy (EIS), and polarization curve measurements, and a comparison is made with the conventional binder, polytetrafluoroethylene (PTFE). It is found that PVA is more hydrophilic and has stronger interactions with the bacterial membrane than PTFE. Accordingly, the anode with PVA as a binder facilitates the formation of biofilms and thus exhibits improved electron transfer kinetics between bacteria and the anode of the microbial fuel cell compared to the anode using PTFE. The MFC using PVA produces the largest maximum output power, 1.631 W m−2, which is 97.9% greater than the largest one produced by the MFC using PTFE (0.824 W m−2).