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Rechargeable lithium (Li) metal batteries must have long cycle life and calendar life (retention of capacity during storage at open circuit). Particular emphasis has been placed on prolonging the cycle life of Li metal anodes, but calendar ageing is less understood. Here, we show that Li metal loses at least 2–3% of its capacity after only 24 hours of ageing, regardless of the electrolyte chemistry. These losses of capacity during calendar ageing also shorten the cycle life of Li metal batteries. Cryogenic transmission electron microscopy shows that chemical corrosion of Li and the continuous growth of the solid electrolyte interphase—a passivation film on Li—cause the loss of capacity. Electrolytes with long cycle life do not necessarily form a solid electrolyte interphase with more resistance to chemical corrosion, so functional electrolytes must simultaneously minimize the rate of solid electrolyte interphase growth and the surface area of electrodeposited Li metal. Batteries keep degrading even when they are not in operation, but their calendar life is rarely studied in advanced batteries that are still in the development stage. Here the authors quantify the calendar ageing of Li metal anodes and report its underlying mechanisms.

Advanced electrolytes were developed to improve the cyclability of lithium (Li) metal anodes, yet their working mechanisms remain unclear. Here, we study the Li cycling performance under different ...

Electrolyte engineering is critical for developing Li metal batteries. While recent works improved Li metal cyclability, a methodology for rational electrolyte design remains lacking. Herein, we propose a design strategy for electrolytes that enable anode-free Li metal batteries with single-solvent single-salt formations at standard concentrations. Rational incorporation of –CF2– units yields fluorinated 1,4-dimethoxylbutane as the electrolyte solvent. Paired with 1 M lithium bis(fluorosulfonyl)imide, this electrolyte possesses unique Li–F binding and high anion/solvent ratio in the solvation sheath, leading to excellent compatibility with both Li metal anodes (Coulombic efficiency ~ 99.52% and fast activation within five cycles) and high-voltage cathodes (~6 V stability). Fifty-μm-thick Li|NMC batteries retain 90% capacity after 420 cycles with an average Coulombic efficiency of 99.98%. Industrial anode-free pouch cells achieve ~325 Wh kg−1 single-cell energy density and 80% capacity retention after 100 cycles. Our design concept for electrolytes provides a promising path to high-energy, long-cycling Li metal batteries. The realization of the full potential of Li metal batteries requires high-performance electrolytes. Here Z. Bao and colleagues develop low-concentration electrolytes with a single-solvent and single-salt formulation, offering promise for high-energy and long-cycling batteries.

Nanoporous silicon is a promising anode material for high energy density batteries due to its high cycling stability and high tap density compared to other nanostructured anode materials. However, the high cost of synthesis and low yield of nanoporous silicon limit its practical application. Here, we develop a scalable, low-cost top-down process of controlled oxidation of Mg2Si in the air, followed by HCl removal of MgO to generate nanoporous silicon without the use of HF. By controlling the synthesis conditions, the oxygen content, grain size and yield of the porous silicon are simultaneously optimized from commercial standpoints. In situ environmental transmission electron microscopy reveals the reaction mechanism; the Mg2Si microparticle reacts with O2 to form MgO and Si, while preventing SiO2 formation. Owing to the low oxygen content and microscale secondary structure, the nanoporous silicon delivers a higher initial reversible capacity and initial Coulombic efficiency compared to commercial Si nanoparticles (3,033 mAh/g vs. 2,418 mAh/g, 84.3% vs. 73.1%). Synthesis is highly scalable, and a yield of 90.4% is achieved for the porous Si nanostructure with the capability to make an excess of 10 g per batch. Our synthetic nanoporous silicon is promising for practical applications in next generation lithium-ion batteries.

Summary Lithium (Li) metal is the ultimate anode material for Li batteries because of its highest capacity among all candidates. Recent research has focused on stable interphase and host materials to address its low stability and reversibility. Here, we discover that tortuosity is a critical parameter affecting the morphology and electrochemical performances of hosted Li anodes. In three types of hosts—vertically aligned, horizontally aligned, and random reduced graphene oxide (rGO) electrodes with tortuosities of 1.25, 4.46, and 1.76, respectively—we show that high electrode tortuosity causes locally higher current density on the top surface of electrodes, resulting in thick Li deposition on the surface and degraded cycling performance. Low electrode tortuosity in the vertically aligned rGO host enables homogeneous Li transport and uniform Li deposition across the host, realizing greatly improved cycling stability. Using this principle of low tortuosity, the designed electrode shows through-electrode uniform morphology with anodic Coulombic efficiency of ∼99.1% under high current and capacity cycling conditions.

The stability of lithium batteries is tied to the physicochemical properties of the solid-electrolyte interphase (SEI). Owing to the difficulty in characterizing this sensitive interphase, the nano...

Lithium (Li) pulverization and associated large volume expansion during cycling is one of the most critical barriers for the safe operation of Li-metal batteries. Here, we report an approach to minimize the Li pulverization using an electrolyte based on a fluorinated orthoformate solvent. The solid–electrolyte interphase (SEI) formed in this electrolyte clearly exhibits a monolithic feature, which is in sharp contrast with the widely reported mosaic- or multilayer-type SEIs that are not homogeneous and could lead to uneven Li stripping/plating and fast Li and electrolyte depletion over cycling. The highly homogeneous and amorphous SEI not only prevents dendritic Li formation, but also minimizes Li loss and volumetric expansion. Furthermore, this new electrolyte strongly suppresses the phase transformation of the LiNi0.8Co0.1Mn0.1O2 cathode (from layered structure to rock salt) and stabilizes its structure. Tests of high-voltage Li||NMC811 cells show long-term cycling stability and high rate capability, as well as reduced safety concerns. Parasitic reactions between Li metal and electrolytes need to be mitigated in Li-metal batteries. Here, the authors report the use of a fluorinated orthoformate-based electrolyte, leading to a monolithic solid–electrolyte interphase and subsequently a high-performance Li-metal battery.

Operations of lithium-ion batteries have long been limited to a narrow temperature range close to room temperature. At elevated temperatures, cycling degradation speeds up due to enhanced side reactions, especially when high-reactivity lithium metal is used as the anode. Here, we demonstrate enhanced performance in lithium metal batteries operated at elevated temperatures. In an ether-based electrolyte at 60 °C, an average Coulombic efficiency of 99.3% is obtained and more than 300 stable cycles are realized, but, at 20 °C, the Coulombic efficiency drops dramatically within 75 cycles, corresponding to an average Coulombic efficiency of 90.2%. Cryo-electron microscopy reveals a drastically different solid electrolyte interface nanostructure emerging at 60 °C, which maintains mechanical stability, inhibits continuous side reactions and guarantees good cycling stability and low electrochemical impedance. Furthermore, larger lithium particles grown at the elevated temperature reduce the electrolyte/electrode interfacial area, which decreases the per-cycle lithium loss and enables higher Coulombic efficiencies. The performance of Li-ion batteries deteriorates at elevated temperatures due to increased activity of electrode materials and parasitic reactions. Here Yi Cui and colleagues report much-improved battery cyclability at 60 °C and use cryo-electron microscopy to shed light on the origin of the phenomenon.

High-capacity silicon anodes suffer from rapid capacity decay due to large volume expansion, which causes mechanical fracture, electrical contact loss and unstable solid electrolyte interphase (SEI). Nanostructuring has proved to be effective in addressing these problems over the past decade; however, new issues such as poor initial Coulombic efficiencies due to increased surface area remain unsolved. Here we develop a surface-engineering strategy by depositing a dense silicon skin onto each mesoporous silicon microparticle and further encapsulating it with a conformal graphene cage, which improves both the initial and later-cycle Coulombic efficiencies. The silicon skin lowers the unfavorable electrolyte/electrode contact area and minimizes SEI formation, resulting in an initial Coulombic efficiency over twice as high as that without silicon skin coating. The graphene cage combined with the inner void space of mesoporous silicon allow for silicon expansion, which guarantees structural integrity and SEI stability, resulting in high later-cycle Coulombic efficiencies (99.8–100% for later cycles) and impressive cycling stability.

Cryogenic electron microscopy (cryo-EM) was the basis for the 2017 Nobel Prize in Chemistry for its profound impact on the field of structural biology by freezing and stabilizing fragile biomolecules for near atomic-resolution imaging in their native states. Beyond life science, the development of cryo-EM for the physical sciences may offer access to previously inaccessible length scales for materials characterization in systems that would otherwise be too sensitive for high-resolution electron microscopy and spectroscopy. Weakly bonded and reactive materials that typically degrade under electron irradiation and environmental exposure can potentially be stabilized by cryo-EM, opening up exciting opportunities to address many central questions in materials science. New discoveries and fundamental breakthroughs in understanding are likely to follow. In this Perspective, we identify six major areas in materials science that may benefit from the interdisciplinary application of cryo-EM: (1) batteries, (2) soft polymers, (3) metal-organic frameworks, (4) perovskite solar cells, (5) electrocatalysts, and (6) quantum materials. We highlight long-standing questions in each of these areas that cryo-EM can potentially address, which would firmly establish the powerful tool's broad scope and utility beyond biology.

Metallic lithium (Li) anodes are crucial for the development of high specific energy batteries yet are plagued by their poor cycling efficiency. Electrode architecture engineering is vital for maintaining a stable anode volume and suppressing Li corrosion during cycling. In this paper, a reduced graphene oxide "host" framework for Li metal anodes is further optimized by embedding silicon (Si) nanoparticles between the graphene layers. They serve as Li nucleation seeds to promote Li deposition within the framework even without prestored Li. Meanwhile, the Li

Summary Battery decay and failure depend strongly on the solid electrolyte interphase (SEI), a surface corrosion layer that forms on the surface of all battery electrodes. Recently, we revealed the atomic structure of these reactive and sensitive battery materials and their SEIs using cryoelectron microscopy (cryo-EM). However, the SEI nanostructure's fundamental role and effect on battery performance remain unclear. Here, we use cryo-EM to discover the function of two distinct SEI nanostructures (i.e., mosaic and multilayer) and correlate their stark effects with Li metal battery performance. We identify fluctuations in crystalline grain distribution within the SEI as the critical feature differentiating the mosaic SEI from the multilayer SEI, resulting in their distinct electrochemical stripping mechanisms. Whereas localized Li dissolution occurs quickly through regions of high crystallinity in the mosaic SEI, uniform Li stripping is observed for the more ordered multilayer SEIs, which reduces Li loss during battery cycling by a factor of three. This dramatic performance enhancement from a subtle change in SEI nanostructure highlights the importance of cryo-EM studies in revealing crucial failure modes of high-energy batteries at the nanoscale.

Dust filtration is a crucial process for industrial waste gas treatment. Great efforts have been devoted to improve the performance of dust filtration filters both in industrial and fundamental research. Conventional air-filtering materials are limited by three key issues: (1) Low filtration efficiency, especially for particulate matter (PM) below 1 μm; (2) large air pressure drops across the filter, which require a high energy input to overcome; and (3) safety hazards such as dust explosions and fires. Here, we have developed a “smart” multifunctional material which can capture PM with high efficiency and an extremely low pressure drop, while possessing a flame retardant design. This multifunctionality is achieved through a core–shell nanofiber design with the polar polymer Nylon-6 as the shell and the flame retardant triphenyl phosphate (TPP) as the core. At 80% optical transmittance, the multifunctional materials showed capture efficiency of 99.00% for PM2.5 and >99.50% for PM10–2.5, with a pressure drop of only 0.25 kPa (0.2% of atmospheric pressure) at a flow rate of 0.5 m s–1. Moreover, during direct ignition tests, the multifunctional materials showed extraordinary flame retardation; the self-extinguishing time of the filtrate-contaminated filter is nearly instantaneous (0 s/g) compared to 150 s/g for unmodified Nylon-6., A “smart” air filter which can efficiently capture tiny particulate matters while possessing a flame retardant property is developed.

The stability of modern lithium-ion batteries depends critically on an effective solid-electrolyte interphase (SEI), a passivation layer that forms on the carbonaceous negative electrode as a result of electrolyte reduction. However, a nanoscopic understanding of how the SEI evolves with battery aging remains limited due to the difficulty in characterizing the structural and chemical properties of this sensitive interphase. In this work, we image the SEI on carbon black negative electrodes using cryogenic transmission electron microscopy (cryo-TEM) and track its evolution during cycling. We find that a thin, primarily amorphous SEI nucleates on the first cycle, which further evolves into one of two distinct SEI morphologies upon further cycling: (1) a compact SEI, with a high concentration of inorganic components that effectively passivates the negative electrode; and (2) an extended SEI spanning hundreds of nanometers. This extended SEI grows on particles that lack a compact SEI and consists primarily of alkyl carbonates. The diversity in observed SEI morphologies suggests that SEI growth is a highly heterogeneous process. The simultaneous emergence of these distinct SEI morphologies highlights the necessity of effective passivation by the SEI, as large-scale extended SEI growths negatively impact lithium-ion transport, contribute to capacity loss, and may accelerate battery failure.

Battery performance is critically dependent on the nanostructure and electrochemical properties of the solid-electrolyte interphase (SEI)—a passivation film that exists on most lithium-battery anodes. However, knowledge of how the SEI nanostructure forms and its impact on ionic transport remains limited due to its sensitivity to transmission electron microscopy and difficulty in accurately probing the SEI impedance. Here, we track the voltage-dependent, stepwise evolution of the nanostructure and impedance of the SEI on CuO nanowires using cryogenic-electron microscopy (cryo-EM) and electrochemical impedance spectroscopy (EIS). In carbonate electrolyte, the SEI forms at 1.0 V vs Li/Li+ as a 3 nm thick amorphous SEI and grows to 4 nm at 0.5 V; as the potential approaches 0.0 V vs Li/Li+, the SEI on the CuO nanowires forms an 8 nm thick inverted multilayered nanostructure in ethylene carbonate/diethyl carbonate (EC/DEC) electrolyte with 10 vol % fluoroethylene carbonate (FEC) and a mosaic nanostructure in E...

Atomic layer deposition enables stable cycling of Li metal in a three-dimensional lithium host., Lithium metal has long been considered one of the most promising anode materials for advanced lithium batteries (for example, Li-S and Li-O2), which could offer significantly improved energy density compared to state-of-the-art lithium ion batteries. Despite decades of intense research efforts, its commercialization remains limited by poor cyclability and safety concerns of lithium metal anodes. One root cause is the parasitic reaction between metallic lithium and the organic liquid electrolyte, resulting in continuous formation of an unstable solid electrolyte interphase, which consumes both active lithium and electrolyte. Until now, it has been challenging to completely shut down the parasitic reaction. We find that a thin-layer coating applied through atomic layer deposition on a hollow carbon host guides lithium deposition inside the hollow carbon sphere and simultaneously prevents electrolyte infiltration by sealing pinholes on the shell of the hollow carbon sphere. By encapsulating lithium inside the stable host, parasitic reactions are prevented, resulting in impressive cycling behavior. We report more than 500 cycles at a high coulombic efficiency of 99% in an ether-based electrolyte at a cycling rate of 0.5 mA/cm2 and a cycling capacity of 1 mAh/cm2, which is among the most stable Li anodes reported so far.

With more phonons carrying the energy in the lattice, the phonon density of states in diamond extends to a much higher frequencies than that of any other material. This is related to the Debye temperature of diamond, being the highest of any bulk materials and of having the highest sound velocity of any known bulk materials. However, the thermal conductivity not only depends on the number of phonons and how fast they are, but also on how long they can travel without being disturbed or scattered. The measurement of this length of travel is the Mean Free Path of the phonons, l, which depends on the number of phonons in the lattice through the 3-phonon processes (Normal and Umpklapp), and the imperfections in the lattice (boundaries, grain boundaries, non sp3 bonds, isotopes, impurities, extended defects, dislocations, etc.). Consequently, the “real world” thermal conductivity of a given piece of diamond will depend on the “quality” of the lattice, yielding values from 1 W/m°K (ultra-nanocrystalline diamond) to more than 3400 W/m°K for isotopically pure single crystal diamond.