Lithium–oxygen batteries have an ultrahigh theoretical energy density, almost ten times higher than lithium‐ion batteries. The poor conductivity of the discharge product Li2O2, however, severely raises the charge overpotential and pulls down the cyclability. Here, a simple and effective strategy is presented for regular formation of lithium vacancies in the discharge product via tuning charge/discharge mode, and their effects on the charge transfer behavior. The effects of the discharge current density on the lithium vacancies, ionic conductivity, and electronic conductivity of the discharge product Li2O2 are systematically investigated via electron spin resonance, spin‐alignment echo nuclear magnetic resonance, and tungsten nanomanipulators, respectively. The study by density functional theory indicates that the lithium vacancies in Li2O2 generated during the discharge process are highly dependent on the current density. High current can induce a high vacancy density, which enhances the electronic conductivity and reduces the overpotential. Meanwhile, with increasing discharge current, the morphology of the Li2O2 changes from microtoroids to thin nanoplatelets, effectively shortening the charge transfer distance and improving the cycling performance. The Li2O2 grown in fast discharge mode is more easily decomposed in the following charging process. The lithium–oxygen battery cycling in fast‐discharge/slow‐charge mode exhibits low overpotential and long cycle life. 相似文献
Measurements are presented for the nucleate pool boiling of LiBrH2O solutions at concentrations typically used in LiBrH2O air conditioning systems. A commercial grade copper tube was used for all tests as being typical of the testing surface likely to be used in a commercial plant.The object of this work was to correlate nucleate boiling heat transfer for pure water and aqueous solutions using Re, Pr number expressions and thermophysical properties of the boiling liquid and vapour at a clean surface. Such an equation is proposed and tested. 相似文献
Lithium/sulfur (Li/S) cells have great potential to become mainstream secondary batteries due to their ultra-high theoretical specific energy. The major challenge for Li/S cells is the unstable cycling performance caused by the sulfur’s insulating nature and the high-solubility of the intermediate polysulfide products. Several years of efforts to develop various fancy carbon nanostructures, trying to physically encapsulate the polysulfides, did not yet push the cell’s cycle life long enough to compete with current Li ion cells. The focus of this review is on the recent progress in chemical bonding strategy for trapping polysulfides through employing functional groups and additives in carbon matrix. Research results on understanding the working mechanism of chemical interaction between polysulfides and functional groups (e.g. O–, B–, N–and S–) in carbon matrix, metal-based additives, or polymer additives during charge/discharge are discussed.
Lithium (sodium)‐metal batteries are the most promising batteries for next‐generation electrical energy storage due to their high volumetric energy density and gravimetric energy density. However, their applications have been prevented by uncontrollable dendrite growth and large volume expansion during the stripping/plating process. To address this issue, the key strategy is to realize uniform lithium (sodium) deposition during the stripping/plating process. Herein, a thin lithiophilic layer consisting of RuO2 particles anchored on brush‐like 3D carbon cloth (RuO2@CC) is prepared by a simple solution‐based method. After infusion of Li, the RuO2@CC transfers to Li‐Ru@CC. Ru nanoparticles not only play a role in leading Li+ (Na+) to plate on the 3D carbon framework, but also lower local current density because of the good electrical conductivity. Furthermore, density functional theory calculations demonstrate that Ru metal, the reaction product of alkali metal and Ru, can lead Li+ to plate evenly around carbon fiber owing to the strong binding energy with Li+. The Li‐Ru@CC anode shows ultralong cycle life (1500 h at 5 mA cm?2). The full cell of Li‐Ru@CC|LiFePO4 exhibits lower polarization (90% capacity retention after 650 cycles). In addition, sodium metal batteries based on Na‐Ru@CC anodes can achieve similar improvement. 相似文献
