Due to an ultrahigh theoretical specific capacity of 3860 mAh g−1, lithium (Li) is regarded as the ultimate anode for high‐energy‐density batteries. However, the practical application of Li metal anode is hindered by safety concerns and low Coulombic efficiency both of which are resulted fromunavoidable dendrite growth during electrodeposition. This study focuses on a critical parameter for electrodeposition, the exchange current density, which has attracted only little attention in research on Li metal batteries. A phase‐field model is presented to show the effect of exchange current density on electrodeposition behavior of Li. The results show that a uniform distribution of cathodic current density, hence uniform electrodeposition, on electrode is obtained with lower exchange current density. Furthermore, it is demonstrated that lower exchange current density contributes to form a larger critical radius of nucleation in the initial electrocrystallization that results in a dense deposition of Li, which is a foundation for improved Coulombic efficiency and dendrite‐free morphology. The findings not only pave the way to practical rechargeable Li metal batteries but can also be translated to the design of stable metal anodes, e.g., for sodium (Na), magnesium (Mg), and zinc (Zn) batteries.

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Sodium, in contrast to other metals, cannot intercalate in graphite, hindering the use of this cheap, abundant element in rechargeable batteries. Here, we report a nanometric graphite-like anode for Na+ storage, formed by stacked graphene sheets functionalized only on one side, termed Janus graphene. The asymmetric functionalization allows reversible intercalation of Na+, as monitored by operando Raman spectroelectrochemistry and visualized by imaging ellipsometry. Our Janus graphene has uniform pore size, controllable functionalization density, and few edges; it can store Na+ differently from graphite and stacked graphene. Density functional theory calculations demonstrate that Na+ preferably rests close to -NH2 group forming synergic ionic bonds to graphene, making the interaction process energetically favorable. The estimated sodium storage up to C6.9Na is comparable to graphite for standard lithium ion batteries. Given such encouraging Na+ reversible intercalation behavior, our approach provides a way to design carbon-based materials for sodium ion batteries.

This review provides an accessible analysis of the processes on reference electrodes and their applications in Li-ion and next generation batteries research. It covers fundamentals and definitions as well as specific practical applications and is intended to be comprehensible for researchers in the battery field with diverse backgrounds. It covers fundamental concepts, such as two- and three-electrodes configurations, as well as more complex quasi- or pseudo- reference electrodes. The electrode potential and its dependance on the concentration of species and nature of solvents are explained in detail and supported by relevant examples. The solvent, in particular the cation solvation energy, contribution to the electrode potential is important and a largely unknown issue in most the battery research. This effect can be as high as half a volt for the Li/Li+ couple and we provide concrete examples of the battery systems where this effect must be taken into account. With this review, we aim to provide guidelines for the use and assessment of reference electrodes in the Li-ion and next generation batteries research that are comprehensive and accessible to an audience with a diverse scientific background.

of state-of-the-art cathodic materials in Li-ion cells. Furthermore, in contrast to materials in standard intercalation-based electrodes, [2] sulfur is highly abundant, [3] has a low cost, and is non-toxic. [3,4] Considering also that a typical sulfur composite cathode contains only sulfur, carbon, and binder, these metrics bear the promise of a sustainable, cost-effective, and high energy density next-generation energy storage technology.The high specific capacity stems from the conversion reaction where elemental sulfur (S 8 ) is converted to lithium sulfide (Li 2 S) during discharge. The conversion mechanism is complex and multiple reaction pathways have been proposed. [5,6] Common to the different pathways is that it takes place through a series of soluble intermediate polysulfide species (Li 2 S n ), where the specific speciation can vary with, for example, electrolyte composition and amount, or operating conditions. Irrespective of pathway, the conversion process leads to several challenges in the realization of practical high energy density LiS cells. [4,[6][7][8] Polysulfides created during the electrochemical conversion are highly soluble in common liquid electrolytes and their presence in the liquid phase leads to their In this work, light is shed on the dissolution and precipitation processes S8 and Li 2 S, and their role in the utilization of active material in LiS batteries. Combining operando X-ray Tomographic Microscopy and optical image analysis, in real-time; sulfur conversion/dissolution in the cathode, the diffusion of polysulfides in the bulk electrolyte, and the redeposition of the product of the electrochemical reaction, Li 2 S, on the cathode are followed. Using a customdesigned capillary cell, positioning the entire cathode volume within the field of view, the conversion of elemental sulfur to soluble polysulfides during discharge is quantitatively followed. The results show the full utilization of elemental sulfur in the cathode in the initial stage of discharge, with all solid sulfur converted to soluble polysulfide species. Optical image analysis shows a rapid diffusion of polysulfides as they migrate from the cathode to the bulk electrolyte at the start of discharge and back to the cathode in the later stages of discharge, with the formation and precipitation of Li 2 S. The results point to the redeposition of Li 2 S on all available surfaces in the cathode forming a continuous insulating layer, leaving polysulfide species remaining in the electrolyte, and this is the process limiting the cell's specific capacity.