Lithium metal anodes are potentially key for next-generation energy-dense batteries because of the extremely high capacity and the ultralow redox potential. However, notorious safety concerns of Li metal in liquid electrolytes have significantly retarded its commercialization: on one hand, lithium metal morphological instabilities (LMI) can cause cell shorting and even explosion; on the other hand, breaking of the grown Li arms induces the so-called "dead Li"; furthermore, the continuous consumption of the liquid electrolyte and cycleable lithium also shortens cell life. The research community has been seeking new strategies to protect Li metal anodes and significant progress has been made in the last decade. Here, an overview of the fundamental understandings of solid electrolyte interphase (SEI) formation, conceptual models, and advanced real-time characterizations of LMI are presented. Instructed by the conceptual models, strategies including increasing the donatable fluorine concentration (DFC) in liquid to enrich LiF component in SEI, increasing salt concentration (ionic strength) and sacrificial electrolyte additives, building artificial SEI to boost self-healing of natural SEI, and 3D electrode frameworks to reduce current density and delay Sand's extinction are summarized. Practical challenges in competing with graphite and silicon anodes are outlined.

Perovskites (ABX3) are promising oxygen evolution reaction (OER) catalysts for their highly intrinsic activity. The in‐depth understanding and the adjustment of dynamic reconstruction of active phases for perovskites in OER are still a daunting challenge. Here, a refined A‐site management strategy is proposed for perovskite oxides, which facilitates the surface reconstruction of the B‐site element based active phase to enhance the OER performance. Electrocatalyst LaNiO3 displays a dynamic reconstruction feature during OER with the growth of a self‐assembled NiOOH active layer, based on the in situ electrochemical Raman technology. Precise A‐site Ce doping lowers the reconstruction potential for the active phase and the dynamic structure–activity correlation is well established. Theoretical calculations demonstrate that A‐site Ce substitution upshifts the O 2p level for greater structural flexibility with optimized oxygen vacancy content, thereby activating the B‐site atom and promoting the active phase reconstruction. These results suggest that A‐site management prompts the B‐site element based active phase dynamic reconstruction via engineered X‐site content as a bridge. Therefore, indicating the strong correlation of each‐site component in perovskite oxides during OER and deepening the understanding of the fundamental processes of the structural transformation and further benefiting the accurate design of high‐efficiency perovskite OER electrocatalysts.

Tin foil should have outstanding volumetric capacity as a Li-ion battery anode; however, it suffers from an unacceptable initial coulombic efficiency (ICE) of 10-20%, which is much poorer than that of Si or SnO 2 nanoparticles. Herein, we demonstrate that bare Sn catalyzes liquid electrolyte decomposition at intermediate voltages to generate gas bubbles and Leidenfrost gas films, which hinder lithium-ion transport and erode the solid-electrolyte interphase (SEI) layer. By metallurgically pre-alloying Li to make Li x Sn foil, the lower initial anode potential simultaneously suppresses gassing and promotes the formation of an adherent passivating SEI. We developed a universally applicable roll-to-roll mechanical prelithiation method and successfully prelithiated Sn foil, Al foil and Si/C anodes. The as-prepared Li x Sn foil exhibited an increased ICE from 20% to 94% and achieved 200 stable cycles in LiFePO 4 //Li x Sn full cells at B2.65 mA h cm À2 . Surprisingly, the Li x Sn foil also exhibited excellent air-stability, and its cycling performance sustained slight loss after 12 h exposure to moist air. In addition to LiFePO 4 , the Li x Sn foil cycled well against a lithium nickel cobalt manganese oxide (NMC) cathode (4.3 V and B4-5 mA h cm À2 ). The volumetric capacity of the Li x Sn alloy in the LFP//Li x Sn pouch cell was up to B650 mA h cm À3 , which is significantly better than that of the graphite anode on a copper collector, with a rate capability as high as 3C. Broader contextSelf-supporting tin foil is a high-volumetric-capacity alternative to the graphite LIB anode; however, it shows an exceptionally low initial coulombic efficiency (10-20%), even lower than that of Si and SnO 2 nanoparticles with 410 3 Â contact area with the electrolyte, which is quite strange. Inspired by previous reports that tin catalyzes the decomposition of organic solvents, herein, we proved that bare Sn indeed catalyzes electrolyte decomposition at an intermediate voltage to generate gas bubbles and Leidenfrost films, which cut off the transport of lithium ions and prevent the formation of an adherent SEI. However, when the absolute potential is below 1 V (vs. Li/Li + ), it simultaneously promotes the formation of a solid SEI and mechanical adherence, which can in turn suppress future gassing. Therefore, we developed a roll-to-roll mechanical prelithiation process for tin foil, which lowers its absolute potential before contacting the electrolyte, promotes adherent passivation film formation, and greatly improves its coulombic efficiency and capacity retention so that it can perform well in full cells. Also, the striking air stability of the Li x Sn foil makes it much easier to handle than the bare Li metal anode. Our study provides vital new insights into why self-supporting metallic anodes do not appear to work in LIBs and develops an effective mitigation strategy by cheap and scalable metallurgical prelithiation, which is also applicable to other metallic alloy anode materials.

No abstract

The thickness-dependent electronic states and physical properties of two-dimensional materials suggest great potential applications in electronic and optoelectronic devices. However, the enhanced surface effect in ultra-thin materials might significantly influence the structural stability, as well as the device reliability. Here, we report a spontaneous phase transformation of gallium telluride (GaTe) that occurred when the bulk was exfoliated to a few layers. Transmission electron microscopy (TEM) results indicate a structural variation from a monoclinic to a hexagonal structure. Raman spectra suggest a critical thickness for the structural transformation. First-principle calculations and thermodynamic analysis show that the surface energy and the interlayer interaction compete to dominate structural stability in the thinning process. A two-stage transformation process from monoclinic (m) to tetragonal (T) and then from tetragonal to hexagonal (h) is proposed to understand the phase transformation. The results demonstrate the crucial role of interlayer interactions in the structural stability, which provides a phase engineering strategy for device applications.

Graphite and lithium metal are two classic anode materials and their composite has shown promising performance for rechargeable batteries. However, it is generally accepted that Li metal wets graphite poorly, causing its spreading and infiltration difficult. Here we show that graphite can either appear superlithiophilic or lithiophobic, depending on the local redox potential. By comparing the wetting performance of highly ordered pyrolytic graphite, porous carbon paper (PCP), lithiated PCP and graphite powder, we demonstrate that the surface contaminants that pin the contact-line motion and cause contact-angle hysteresis have their own electrochemical-stability windows. The surface contaminants can be either removed or reinforced in a time-dependent manner, depending on whether the reducing agents (C6→LiC6) or the oxidizing agents (air, moisture) dominate in the ambient environment, leading to bifurcating dynamics of either superfast or superslow wetting. Our findings enable new fabrication technology for Li–graphite composite with a controllable Li-metal/graphite ratio and present great promise for the mass production of Li-based anodes for use in high-energy-density batteries.

Transition metal dichalcogenides (TMDs) have attracted considerable interest for exploration of next-generation electronics and optoelectronics in recent years. Fabrication of in-plane lateral heterostructures between TMDs has opened up excellent opportunities for engineering two-dimensional materials. The creation of high quality heterostructures with a facile method is highly desirable but it still remains challenging. In this work, we demonstrate a one-step growth method for the construction of high-quality MoS2–WS2 in-plane heterostructures. The synthesis was carried out using ambient pressure chemical vapor deposition (APCVD) with the assistance of sodium chloride (NaCl). It was found that the addition of NaCl played a key role in lowering the growth temperatures, in which the Na-containing precursors could be formed and condensed on the substrates to reduce the energy of the reaction. As a result, the growth regimes of MoS2 and WS2 are better matched, leading to the formation of in-plane heterostructures in a single step. The heterostructures were proved to be of high quality with a sharp and clear interface. This newly developed strategy with the assistance of NaCl is promising for synthesizing other TMDs and their heterostructures.

No abstract