A cathode for high-rate performance lithium-ion batteries (LIBs) has been developed from a crystal habit-tuned nanoplate Li(Li(0.17)Ni(0.25)Mn(0.58))O₂ material, in which the proportion of (010) nanoplates (see figure) has been significantly increased. The results demonstrate that the fraction of the surface that is electrochemically active for Li(+) transportation is a key criterion for evaluating the different nanostructures of potential LIB materials.
We report a new method to promote the conductivities of metal-organic frameworks (MOFs) by 5 to 7 magnitudes, thus their potential in electrochemical applications can be fully revealed. This method combines the polarity and porosity advantages of MOFs with the conductive feature of conductive polymers, in this case, polypyrrole (ppy), to construct ppy-MOF compartments for the confinement of sulfur in Li-S batteries. The performances of these ppy-S-in-MOF electrodes exceed those of their MOF and ppy counterparts, especially at high charge-discharge rates. For the first time, the critical role of ion diffusion to the high rate performance was elucidated by comparing ppy-MOF compartments with different pore geometries. The ppy-S-in-PCN-224 electrode with cross-linked pores and tunnels stood out, with a high capacity of 670 and 440 mAh g at 10.0 C after 200 and 1000 cycles, respectively, representing a new benchmark for long-cycle performance at high rate in Li-S batteries.
The effects of electrolyte on selectivity and activity were investigated in the electrochemical reduction of CO 2 on the Sn electrode. The production of formate, the primary product in our three-electrode cell was quantitatively characterized by solution phase 1 H NMR spectroscopy. Both SO 4 2− and Na + favor higher faradaic and energy efficiencies, while HCO 3 − and K + enable a higher rate of formate production. The faradaic efficiency was as high as ∼95% for 0.1 M Na 2 SO 4 at a potential of −1.7 V vs. a Saturated Calomel Electrode (SCE). 0.5 M KHCO 3 was an optimal electrolyte for obtaining a high production rate of formate which can reach over 3.8 μmol min −1 cm −2 at a potential of −2.0 V vs. SCE while maintaining a faradaic efficiency of ∼63%. A trend we observed was that the faradaic efficiency increases as the concentration of electrolyte is diluted. Our studies also show the degradation of electrocatalytic activity of the Sn electrode in this three-electrode cell can be attributed to the electrodeposition of trace amounts of Zn onto the surface of the Sn electrode, which reduces the active surface area.
Owing to high specific capacity of ∼250 mA h g, lithium-rich layered oxide cathode materials (LiNi CoMnO) have been considered as one of the most promising candidates for the next-generation cathode materials of lithium ion batteries. However, the commercialization of this kind of cathode materials seriously restricted by voltage decay upon cycling though Li-rich materials with high cobalt content have been widely studied and show good capacity. This research successfully suppresses voltage decay upon cycling while maintaining high specific capacity with low Co/Ni ratio in Li-rich cathode materials. Online continuous flow differential electrochemical mass spectrometry (OEMS) and in situ X-ray diffraction (XRD) techniques have been applied to investigate the structure transformation of Li-rich layered oxide materials during charge-discharge process. The results of OEMS revealed that low Co/Ni ratio lithium-rich layered oxide cathode materials released no lattice oxygen at the first charge process, which will lead to the suppression of the voltage decay upon cycling. The in situ XRD results displayed the structure transition of lithium-rich layered oxide cathode materials during the charge-discharge process. The LiNiMnO cathode material exhibited a high initial medium discharge voltage of 3.710 and a 3.586 V medium discharge voltage with the lower voltage decay of 0.124 V after 100 cycles.
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