Wei Kong Pang

Enhanced sodium-ion battery performance by structural phase transition from two-dimensional hexagonal-SnS2 to orthorhombic-SnS

Structural phase transitions can be used to alter the properties of a material without adding any additional elements and are therefore of significant technological value. It was found that the hexagonal-SnS2 phase can be transformed into the orthorhombic-SnS phase after an annealing step in an argon atmosphere, and the thus transformed SnS shows enhanced sodium-ion storage performance over that of the SnS2, which is attributed to its structural advantages. Here, we provide the first report on a SnS@graphene architecture for application as a sodium-ion battery anode, which is built from two-dimensional SnS and graphene nanosheets as complementary building blocks. The as-prepared SnS@graphene hybrid nanostructured composite delivers an excellent specific capacity of 940 mAh g(-1)and impressive rate capability of 492 and 308 mAh g(-1) after 250 cycles at the current densities of 810 and 7290 mA g(-1), respectively. The performance was found to be much better than those of most reported anode materials for Na-ion batteries. On the basis of combined ex situ Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and ex situ X-ray diffraction, the formation mechanism of SnS@graphene and the synergistic Na-storage reactions of SnS in the anode are discussed in detail. The SnS experienced a two-structural-phase transformation mechanism (orthorhombic-SnS to cubic-Sn to orthorhombic-Na3.75Sn), while the SnS2 experienced a three-structural-phase transformation mechanism (hexagonal-SnS2 to tetragonal-Sn to orthorhombic-Na3.75Sn) during the sodiation process. The lesser structural changes of SnS during the conversion are expected to lead to good structural stability and excellent cycling stability in its sodium-ion battery performance. These results demonstrate that the SnS@graphene architecture offers unique characteristics suitable for high-performance energy storage application.

Atomic Interface Engineering and Electric-Field Effect in Ultrathin Bi2MoO6 Nanosheets for Superior Lithium Ion Storage

Ultrathin 2D materials can offer promising opportunities for exploring advanced energy storage systems, with satisfactory electrochemical performance. Engineering atomic interfaces by stacking 2D crystals holds huge potential for tuning material properties at the atomic level, owing to the strong layer-layer interactions, enabling unprecedented physical properties. In this work, atomically thin Bi2 MoO6 sheets are acquired that exhibit remarkable high-rate cycling performance in Li-ion batteries, which can be ascribed to the interlayer coupling effect, as well as the 2D configuration and intrinsic structural stability. The unbalanced charge distribution occurs within the crystal and induces built-in electric fields, significantly boosting lithium ion transfer dynamics, while the extra charge transport channels generated on the open surfaces further promote charge transport. The in situ synchrotron X-ray powder diffraction results confirm the materials excellent structural stability. This work provides some insights for designing high-performance electrode materials for energy storage by manipulating the interface interaction and electronic structure.

Enhanced Structural Stability of Nickel–Cobalt Hydroxide via Intrinsic Pillar Effect of Metaborate for High-Power and Long-Life Supercapacitor Electrodes

Layered α-Ni(OH)2 and its derivative bimetallic hydroxides (e.g., α-(Ni/Co)(OH)2) have attracted much attention due to their high specific capacitance, although their insufficient cycling stability has blocked their wide application in various technologies. In this work, we demonstrate that the cycling performance of α-(Ni/Co)(OH)2 can be obviously enhanced via the intrinsic pillar effect of metaborate. Combining the high porosity feature of the metaborate stabilized α-(Ni/Co)(OH)2 and the improved electronic conductivity offered by graphene substrate, the average capacitance fading rate of the metaborate stabilized α-(Ni/Co)(OH)2 is only ∼0.0017% per cycle within 10 000 cycles at the current density of 5 A g-1. The rate performance is excellent over a wide temperature range from -20 to 40 °C. We believe that the enhancements should mainly be ascribed to the excellent structural stability offered by the metaborate pillars, and the detailed mechanism is discussed.

Electrospun P2-type Na2/3(Fe1/2Mn1/2)O2 Hierarchical Nanofibers as Cathode Material for Sodium-Ion Batteries

Sodium-ion batteries can be the best alternative to lithium-ion batteries, because of their similar electrochemistry, nontoxicity, and elemental abundance and the low cost of sodium. They still stand in need of better cathodes in terms of their structural and electrochemical aspects. Accordingly, the present study reports the first example of the preparation of Na2/3(Fe1/2Mn1/2)O2 hierarchical nanofibers by electrospinning. The nanofibers with aggregated nanocrystallites along the fiber direction have been characterized structurally and electrochemically, resulting in enhanced cyclability when compared to nanoparticles, with initial discharge capacity of ∼195 mAh g(-1). This is attributed to the good interconnection among the fibers, with well-guided charge transfers and better electrolyte contacts.

Electrospun P2-type Na 2/3 (Fe 1/2 Mn 1/2 )O 2 hierarchical nano fibers as cathode material for sodium-ion batteries

Sodium-ion batteries can be the best alternative to lithium-ion batteries, because of their similar electrochemistry, nontoxicity, and elemental abundance and the low cost of sodium. They still stand in need of better cathodes in terms of their structural and electrochemical aspects. Accordingly, the present study reports the first example of the preparation of Na2/3(Fe1/2Mn1/2)O2 hierarchical nanofibers by electrospinning. The nanofibers with aggregated nanocrystallites along the fiber direction have been characterized structurally and electrochemically, resulting in enhanced cyclability when compared to nanoparticles, with initial discharge capacity of ∼195 mAh g(-1). This is attributed to the good interconnection among the fibers, with well-guided charge transfers and better electrolyte contacts.

Super high-rate, long cycle life of europium-modified, carbon-coated, hierarchical mesoporous lithium-titanate anode materials for lithium ion batteries

Europium-modified, carbon-coated, hierarchical mesoporous Li4Ti5O12 microspheres were prepared via the co-precipitation method. X-ray diffraction (XRD) and Raman analyses revealed that europium ions were doped into 16d Li+/Ti4+ sites of Li4Ti5O12. Microscopic observations reveal that primary nanoparticles of Li4−x/2Ti5−x/2EuxO12@C (x = 0.004) are assembled into hierarchical mesoporous microspheres, with an average particle size of about 473.4 nm and a uniform particle size distribution. X-ray photoelectron spectroscopy demonstrated that partial Ti4+ is reduced to Ti3+ induced by carbon coating and double-valence state of europium (Eu2+/Eu3+) doping into the Li4Ti5O12. The samples exhibit excellent electrochemical properties including fast lithium storage performance, outstanding cycle stability and high rate capability. The highest initial discharge capacity of Li4−x/2Ti5−x/2EuxO12@C (x = 0.004) reached 198.7 mA h g−1 and the discharge capacity still maintained 173.4 mA h g−1 at 5C after 1000 cycles. Even cycled at 100C, the discharge capacity of Li4−x/2Ti5−x/2EuxO12@C (x = 0.004) maintained 92.1 mA h g−1. The excellent electrochemical performance can be attributed to the hierarchical mesoporous structure combined with modified strategies including europium doping and carbon coating, which not only improved the lithium-ion diffusion coefficient, but also increased the electronic conductivity. Moreover, the electrical conductivity between the Li4Ti5O12 particles was enhanced by carbon coating and the bulk electronic conductivity of Li4Ti5O12 was also improved by the presence of Ti3+.

In Situ Powder Diffraction Studies of Electrode Materials in Rechargeable Batteries

The ability to directly track the charge carrier in a battery as it inserts/extracts from an electrode during charge/discharge provides unparalleled insight for researchers into the working mechanism of the device. This crystallographic-electrochemical information can be used to design new materials or modify electrochemical conditions to improve battery performance characteristics, such as lifetime. Critical to collecting operando data used to obtain such information in situ while a battery functions are X-ray and neutron diffractometers with sufficient spatial and temporal resolution to capture complex and subtle structural changes. The number of operando battery experiments has dramatically increased in recent years, particularly those involving neutron powder diffraction. Herein, the importance of structure-property relationships to understanding battery function, why in situ experimentation is critical to this, and the types of experiments and electrochemical cells required to obtain such information are described. For each battery type, selected research that showcases the power of in situ and operando diffraction experiments to understand battery function is highlighted and future opportunities for such experiments are discussed. The intention is to encourage researchers to use in situ and operando techniques and to provide a concise overview of this area of research.

One-dimensional nanostructured design of Li1+x(Mn1/3Ni1/3Fe1/3)O2 as a dual cathode for lithium-ion and sodium-ion batteries

Potency of the cathode material is an important feature for upgrading lithium-ion/sodium-ion battery technology for next-generation applications such as in electrical grids and advanced electric vehicles. Various limitations related to electrochemical and socio-economic issues of these batteries are current research challenges. Amongst the various possible solutions to address such issues, developing nanostructured cathode materials, such as one-dimensional nanostructures, by versatile and easily scaled-up processes could be one of the options. Consequently, in the present study, Li1+x(Mn1/3Ni1/3Fe1/3)O2 one-dimensional nanofibers have been fabricated via a simple and low-cost electrospinning technique and used as a cathode material in lithium-ion batteries, which showed an improved initial reversible capacity (∼109 mA h g−1) and cyclic stability at the 0.1 C rate when compared to the performance of Li1+x(Mn1/3Ni1/3Fe1/3)O2 nanoparticles. On the other hand, the feasibility of this low-cost and eco-friendly material was also tested in sodium-ion batteries, and the same trend is observed. The enhanced electrochemical and structural features in both systems could be ascribed to the exceptional features of one-dimensional nanofibers such as efficient electron transport, facile strain relaxation, and short Li+/Na+ diffusion pathways.

Na2Ti6O13 Nanorods with Dominant Large Interlayer Spacing Exposed Facet for High-Performance Na-Ion Batteries

As the delegate of tunnel structure sodium titanates, Na2 Ti6 O13 nanorods with dominant large interlayer spacing exposed facet are prepared. The exposed large interlayers provide facile channels for Na(+) insertion and extraction when this material is used as anode for Na-ion batteries (NIBs). After an activation process, this NIB anode achieves a high specific capacity (a capacity of 172 mAh g(-1) at 0.1 A g(-1) ) and outstanding cycling stability (a capacity of 109 mAh g(-1) after 2800 cycles at 1 A g(-1) ), showing its promising application on large-scale energy storage systems. Furthermore, the electrochemical and structural characterization reveals that the expanded interlayer spacings should be in charge of the activation process, including the enhanced kinetics, the lowered apparent activation energy, and the increased capacity.

The origin of capacity fade in the Li2MnO3·LiMO2 (M = Li, Ni, Co, Mn) microsphere positive electrode: an operando neutron diffraction and transmission X-ray microscopy study

The mechanism of capacity fade of the Li2MnO3·LiMO2 (M = Li, Ni, Co, Mn) composite positive electrode within a full cell was investigated using a combination of operando neutron powder diffraction and transmission X-ray microscopy methods, enabling the phase, crystallographic, and morphological evolution of the material during electrochemical cycling to be understood. The electrode was shown to initially consist of 73(1) wt % R3̅m LiMO2 with the remaining 27(1) wt % C2/m Li2MnO3 likely existing as an intergrowth. Cracking in the Li2MnO3·LiMO2 electrode particle under operando microscopy observation was revealed to be initiated by the solid-solution reaction of the LiMO2 phase on charge to 4.55 V vs Li(+)/Li and intensified during further charge to 4.7 V vs Li(+)/Li during the concurrent two-phase reaction of the LiMO2 phase, involving the largest lattice change of any phase, and oxygen evolution from the Li2MnO3 phase. Notably, significant healing of the generated cracks in the Li2MnO3·LiMO2 electrode particle occurred during subsequent lithiation on discharge, with this rehealing being principally associated with the solid-solution reaction of the LiMO2 phase. This work reveals that while it is the reduction of lattice size of electrode phases during charge that results in cracking of the Li2MnO3·LiMO2 electrode particle, with the extent of cracking correlated to the magnitude of the size change, crack healing is possible in the reverse solid-solution reaction occurring during discharge. Importantly, it is the phase separation during the two-phase reaction of the LiMO2 phase that prevents the complete healing of the electrode particle, leading to pulverization over extended cycling. This work points to the minimization of behavior leading to phase separation, such as two-phase and oxygen evolution, as a key strategy in preventing capacity fade of the electrode.