SIMES Publications

Abstract

Abstract

Inactive components and safety hazards are two critical challenges in realizing high-energy lithium-ion batteries. Metal foil current collectors with high density are typically an integrated part of lithium-ion batteries yet deliver no capacity. Meanwhile, high-energy batteries can entail increased fire safety issues. Here we report a composite current collector design that simultaneously minimizes the ‘dead weight’ within the cell and improves fire safety. An ultralight polyimide-based current collector (9 μm thick, specific mass 1.54 mg cm−2) is prepared by sandwiching a polyimide embedded with triphenyl phosphate flame retardant between two superthin Cu layers (~500 nm). Compared to lithium-ion batteries assembled with the thinnest commercial metal foil current collectors (~6 µm), batteries equipped with our composite current collectors can realize a 16–26% improvement in specific energy and rapidly self-extinguish fires under extreme conditions such as short circuits and thermal runaway.

Abstract

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.

Abstract

Lithium metal is a promising anode to provide high energy density for next-generation batteries. However, it has not been implemented due to its low cycling efficiency, which results from the formation of an unstable solid electrolyte interphase (SEI). The SEIs formed with traditional liquid electrolytes are heterogeneous and easy to crack during cycling, thus resulting in the formation of dendritic and dead Li, and further devastating the electrode performance. To solve these issues, efforts have been made to replace natural SEIs with artificial SEIs (ASEIs). Here, we discuss critical design principles of ASEIs based on the understanding of SEI failure mechanisms. Three key principles for a successful ASEI are identified: (1) mechanical stability, which can be either high strength or adaptivity, (2) spatially uniform Li⁺ transport with moderate conductivity and even single-ion conduction, and (3) chemical passivation to mitigate Li-electrolyte parasitic reactions. Selected examples of recently developed ASEIs are categorized and elaborated. Finally, future directions are given for ASEI designs.

Abstract

Li-ion battery safety issues related to fires and explosions are frequently triggered by Li dendrite growth, which is a predominant reason for separator piercing and cell shorts and is very difficult to detect in the early state. Here, we developed a sensitive detection method based on H₂ gas capture that could detect trace amounts of Li dendrite formation. H₂ gas was generated due to reaction of metallic Li with polymer binders. Even micron-scale Li dendrite (∼2.8 × 10⁻⁴ mg and 50 μm) growth can trigger H₂ capture. Overcharge experiment with a LiFePO₄-graphite battery pack (8.8 kWh) shows that H₂ was captured first among H₂, CO, CO₂, HCL, HF, and SO₂, and the capture time was 639 s earlier than smoke and 769 s earlier than fire. The Li dendrite growth can be completely prevented once H₂ is captured, with neither smoke nor fire observed, which provides an effective method for early safety warning.

Abstract

It is highly attractive to develop efficient methods to directly extract Li from seawater to secure the supply of Li. However, high concentration of Na in the seawater poses a great challenge in Li extraction. Here, we developed pulsed-rest and pulse-rest-reverse pulse-rest electrochemical intercalation methods with TiO₂-coated FePO₄ electrodes for Li extraction. The method can lower the intercalation overpotential and successfully boost the Li selectivity. Moreover, the pulse-rest-reverse pulse-rest method can also promote electrode crystal structure stability during the co-intercalation of Li and Na and prolong the lifetime of the electrode. We demonstrated 10 cycles of successful and stable Li extraction with 1:1 of Li to Na recovery from authentic seawater, which is equivalent to the selectivity of ∼1.8 × 10⁴. Also, with lake water of higher initial Li/Na ratio of 1.6 × 10⁻³, we achieved Li extraction with more than 50:1 of Li to Na recovery.

Abstract

Solid-electrolyte-based molten-metal batteries have attracted considerable attention for grid-scale energy storage. Although ZEBRA batteries are considered one of the promising candidates, they still have the potential concern of metal particle growth and ion exchange with the β”-Al₂O₃ electrolyte. Herein, a Li_6.4La₃Zr_1.4Ta_0.6O₁₂ solid-electrolyte-based molten lithium−molybdenum−iron(II) chloride battery (denoted as Li−Mo−FeCl₂) operated at temperature of 250 °C, comprising a mixture of Fe and LiCl cathode materials, a Li anode, a garnet-type Li-ion ceramic electrolyte, and Mo additive, is designed to overcome these obstacles. Different from conventional battery reaction mechanisms, this battery revolutionarily synchronizes the reversible Fe−Mo alloying−dealloying reactions with the delithiation−lithiation processes, meaning that the porous Mo framework derived from Fe−Mo alloy simultaneously suppresses the growth of pure Fe particles. By adopting a Li anode and a Li-ion ceramic electrolyte, the corrosion problem between the cathode and the solid electrolyte is overcome. With similar battery cost ($12 kWh⁻¹), the theoretical energy density of Li−Mo−FeCl₂ battery surpasses that of a Na−FeCl₂ ZEBRA battery over 25%, to 576 Wh kg⁻¹ and 2216 Wh L⁻¹, respectively. Experimental results further prove this cell has excellent cycling performance (472 mAh g_LiCl⁻¹ after 300 cycles, 50 mg active material) and strong tolerance against the overcharge− overdischarge (3−1.6 V) and freezing−thawing (25−250 °C) incidents.

Abstract

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.

Abstract

Solid-state Li−S batteries are attractive due to their high energy density and safety. However, it is unclear whether the concepts from liquid electrolytes are applicable in the solid state to improve battery performance. Here, we demonstrate that the nanoscale encapsulation concept based on Li₂S@TiS₂ core−shell particles, originally developed in liquid electrolytes, is effective in solid polymer electrolytes. Using in situ optical cell and sulfur Kedge X-ray absorption, we find that polysulfides form and are welltrapped inside individual particles by the nanoscale TiS₂ encapsulation. This TiS₂ encapsulation layer also functions to catalyze the oxidation reaction of Li₂S to sulfur, even in solid-state electrolytes, proven by both experiments and density functional theory calculations. A high cell-level specific energy of 427 W·h· kg⁻¹ is achieved by integrating the Li₂S@TiS₂ cathode with a poly(ethylene oxide)-based electrolyte and a lithium metal anode. This study points to the fruitful direction of borrowing concepts from liquid electrolytes into solid-state batteries.

Abstract

The COVID-19 pandemic is currently causing a severe disruption and shortage in the global supply chain of necessary personal protective equipment (e.g., N95 respirators). The U.S. CDC has recommended use of household cloth by the general public to make cloth face coverings as a method of source control. We evaluated the filtration properties of natural and synthetic materials using a modified procedure for N95 respirator approval. Common fabrics of cotton, polyester, nylon, and silk had filtration efficiency of 5−25%, polypropylene spunbond had filtration efficiency 6−10%, and paper-based products had filtration efficiency of 10−20%. An advantage of polypropylene spunbond is that it can be simply triboelectrically charged to enhance the filtration efficiency (from 6 to >10%) without any increase in pressure (stable overnight and in humid environments). Using the filtration quality factor, fabric microstructure, and charging ability, we are able to provide an assessment of suggested fabric materials for homemade facial coverings.