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The diffusion behavior of iodine in micro/nano-porous graphite under high-temperature conditions was studied using analysis methods such as Rutherford backscattering Spectrometry, scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The results indicate that iodine diffusion leads to the Lattice Contractions in Microcrystals, a decrease in interlayer spacing, and a rise of defect density. And the reversal or repair of microstructure change was observed: the microcrystal size of the graphite increases, the interlayer spacing appears to return to the initial state, and the defect density decreases, upon diffusion of iodine out of iodine-loaded graphite. The comparative study comparing the iodine diffusion performance of nanoporous graphite (G400 and G450) between microporous graphite (G500), showed that nanoporous graphite exhibits a better barrier to the iodine diffusion. The study on the diffusion behavior of iodine in micro/nano-porous graphite holds substantial academic and engineering value for the screening, design, and performance optimization of nuclear graphite. [ABSTRACT FROM AUTHOR]

The influence of partial substitution of manganese by nickel or magnesium in Na0.44MnO2on cathode performance in sodium ion batteries has been investigated. Partial substitution changes the structure of parent Na0.44MnO2 from tunnel into layered P2-type, or a mixture of P2- and P3-type materials. Substitution smoothes the charge/discharge curves and may significantly improve capacity, albeit with a lower capacity retention relative to pristine Na0.44MnO2. In particular, high discharge capacities are found in the voltage range 2.0–4.2 V at 0.1 C rate for Na0.44Mn0.89Ni0.11O2 (193 mAh g−1) and Na0.44Mn0.89Mg0.11O2 (188 mAh g−1), with a capacity retention of 74% and 81%, respectively, after 70 cycles. [ABSTRACT FROM AUTHOR]

Li metal has been considered to be the optimal anode material for the next generation high-density batteries due to its very high specific capacity and lowest electrochemical potential. However, various challenges, such as dendrite growth, volume change and low coulombic efficiency, have limited the practical applications of Li metal anodes. Herein, we report a 3D porous Cu current collector with a unique biporous and bicontinuous structure fabricated via a phase inversion tape casting method. It has two types of pores: “finger-like” pores, serving as microchannels for efficient electrolyte and Li ion diffusion, and random small pores, serving as “cages” to accommodate Li deposits. Moreover, the high areal current density can be dissipated remarkably because of the large surface area, resulting in a stable solid electrolyte interphase and dendrite-free anode. The as-prepared porous Cu current collector maintains stable performance and ultra-low voltage hysteresis for over 2000 h in symmetric cells and maintains a CE of 97.6% for 200 cycles in half cells. The porous Cu@Li//LiFePO4 full cells also present excellent cycling and rate performances. In addition, the phase inversion method is very suitable for mass production, indicating great potential for practical applications of Li metal anodes. [ABSTRACT FROM AUTHOR]

LiNi0.80Co0.15Al0.05O2 (NCA) is explored to be applied in a hybrid Li+/Na+ battery for the first time. The cell is constructed with NCA as the positive electrode, sodium metal as the negative electrode, and 1 M NaClO4 solution as the electrolyte. It is found that during electrochemical cycling both Na+ and Li+ ions are reversibly intercalated into/de-intercalated from NCA crystal lattice. The detailed electrochemical process is systematically investigated by inductively coupled plasma-optical emission spectrometry, ex situ X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The NCA cathode can deliver initially a high capacity up to 174 mAh g−1 and 95% coulombic efficiency under 0.1 C (1 C = 120 mA g−1) current rate between 1.5-4.1 V. It also shows excellent rate capability that reaches 92 mAh g−1 at 10 C. Furthermore, this hybrid battery displays superior long-term cycle life with a capacity retention of 81% after 300 cycles in the voltage range from 2.0 to 4.0 V, offering a promising application in energy storage. [ABSTRACT FROM AUTHOR]

Layer-structured O3 type cathode materials Na1−xCr1−xTixO2 (x=0, 0.03, 0.05) are fabricated by a thermo-polymerization method. The structures and morphologies are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. It has been found that the appropriate Ti doping effectively leads to the formation of uniform morphology. As a cathode, the x=0.03 sample delivers a quite high discharge capacity of 110 mAh/g at 32 C in the voltage range from 2.0 V to 3.6 V (vs. Na/Na+) and with a capacity retention of 96% after 100 cycles at 0.2 C. The Na//Na0.97Cr0.97Ti0.03O2 cell exhibits very high coulombic efficiency (above 96%). All these results suggest that Na0.97Cr0.97Ti0.03O2 is very promising for high-rate sodium ion batteries. [ABSTRACT FROM AUTHOR]

We report, for the first time, that a nanocrystalline layered TiP2O7 as a cathode material for Li-, Na- and K-alkali metal batteries is prepared by a solvothermal process followed by a heat treatment at 600 °C. For comparison, a crystalline cubic TiP2O7 is also synthesized at 800 °C. It is clarified that the layered TiP2O7 is slightly poorer for lithium storage but much better for sodium and potassium storages than the cubic phase. The detailed electrochemical processes are investigated by means of ex situ XRD analyses. Different from the two-phase co-existence mechanism for the cubic phase, a solid-solution mechanism is identified for the layered phase to follow in the Li/Na/K intercalation reactions based on electrochemical and structural studies. To overcome the poor electronic conductivity limit for high rate applications, carbon coating is employed on the TiP2O7 samples. The carbon-coated layered phase TiP2O7 (600 °C) displays fairly reversible capacity close to 100 mA h g−1 in both Li and Na rechargeable alkali metal batteries. It is a promising electrode material for large energy storage systems. [ABSTRACT FROM AUTHOR]

A solid-state reaction process with poly(vinyl alcohol) as the carbon source is developed to synthesize LiFePO4-based active powders with or without modification assistance of a small amount of Li3V2(PO4)3. The samples are analyzed by X-ray diffraction, scanning/transmission electron microscopy, and Raman spectroscopy. It is found that, in addition to the minor effect of a lattice doping in LiFePO4 by substituting a tiny fraction of Fe2+ ions with V3+ ions, the change in the form of carbon coating on the surface of LiFePO4 plays a more important role to improve the electrochemical properties. The carbon changes partially from sp3 to sp2 hybridization and thus causes the significant rise in electronic conductivity in the Li3V2(PO4)3-modified LiFePO4 samples. Compared with the carbon-coated baseline LiFePO4, the composite material 0.9LiFePO4·0.1Li3V2(PO4)3 shows totally different carbon morphology and much better electrochemical properties. It delivers specific capacities of 143.6 mAh g−1 at 10 C rate and 119.2 mAh g−1 at 20 C rate, respectively. Even at the low temperature of −20 °C, it delivers a specific capacity of 118.4 mAh g−1 at 0.2 C. [ABSTRACT FROM AUTHOR]

The surface lithium residues on Li-rich layered cathode materials xLi 2 MnO 3 ·(1-x)LiMO 2 (M = Mn, Co, Ni, etc.) are harmful to their electrochemical properties. In this work, the surface lithium residues of Li-rich Li 1.2 Ni 0.2 Mn 0.6 O 2 (LNMO) are identified as Li 2 CO 3 and LiOH by Fourier transform IR for the first time. To overcome this issue, Ni/Mn acetates are used to react with the surface lithium residues to form a LiNi 0.5 Mn 1.5 O 4 spinel coating layer on LNMO particles. Compared with the bare LNMO sample, the 1 wt% LiNi 0.5 Mn 1.5 O 4 coated LNMO shows improved long-term cycling stability and rate capability both at room temperature and 55 °C . The coated one delivers an initial discharge capacity of 236 mAh g −1 with 99.6% capacity retention after 100 cycles at 0.5 C, while it is only 230 mAh g −1 with 91% capacity retention for the bare LNMO. After the surface modification, the rate capacity increases from 155 mAh g −1 to 180 mAh g −1 at 5 C at room temperature while the energy efficiency is improved from 78% to 85%. [ABSTRACT FROM AUTHOR]

A simple two-step solid-state-reaction process is adopted to synthesize carbon-coated Mg-doped Li(Mn,Fe)PO 4 (LMMFP) nano-particles. As positive electrode materials for lithium-ion batteries, the carbon-coated LMMFP samples show excellent electrochemical properties in a temperature range from −20 to 55 °C. For example, LiMn 0.48 Fe 0.5 Mg 0.02 PO 4 can deliver a capacity of 146.2 mAh g −1 at 3C rate and retain 95.3% after 450 cycles at 25 °C. It can also deliver 160.7 mAh g −1 at 1C and retain 97.7% after 100 cycles at 55 °C. Even at −20 °C, it gives a capacity of 109.5 mAh g −1 with an average discharge voltage of 3.37 V at 0.2C. In Na/LMMFP cells, the LMMFP electrodes can be electrochemically converted into Mg-doped Na(Mn,Fe)PO 4 (NMMFP) electrodes for sodium-ion batteries (SIBs). Ex-situ XRD proves that the derived NMMFP have an olivine-type structure and can reversibly extract and insert sodium ions. For example, NaMn 0.48 Fe 0.5 Mg 0.02 PO 4 can deliver a reversible specific capacity of 126.9 mAh g −1 after 30 cycles at 0.1C with an average discharge voltage of 3.1 V. This study opens up a new direction on exploring olivine-type SIB cathodes. [ABSTRACT FROM AUTHOR]