Zhennan Huang

Lithium metal protected by atomic layer deposition metal oxide for high performance anodes

Lithium metal is a highly desirable anode material for lithium batteries due to its extremely high theoretical capacity (3860 mA h g−1), low potential (−3.04 V versus standard hydrogen electrode), and low density (0.534 g cm−3). However, dendrite growth during cycling and low coulombic efficiency, resulting in safety hazards and fast battery fading, are huge barriers to commercialization. Herein, we used atomic layer deposition (ALD) to prepare conformal, ultrathin aluminum oxide coatings on lithium. We investigated the growth mechanism during Al2O3 ALD on lithium by in situ quartz crystal microbalance and found larger growth than expected during the initial cycles. We also discovered that the ALD Al2O3 enhances the wettability of the Li surface towards both carbonate and ether electrolytes, leading to uniform and dense SEI formation and reduced electrolyte consumption during battery operation. Scanning electron microscopy verified that the bare Li surfaces become rough and dendritic after electrochemical cycling, whereas the ALD Al2O3 coated Li surfaces remain smooth and uniform. Analysis of the Li surfaces after cycling using X-ray photoelectron spectroscopy and in situ transmission electron microscopy revealed that the ALD Al2O3 coating remains intact during electrochemical cycling, and that Li ions diffuse through the coating and deposit on the underlying Li. Coin cell testing demonstrated more than two times longer cycling life for the ALD Al2O3 protected Li, and a coulombic efficiency as high as ∼98% at a practical current rate of 1 mA cm−2. More significantly, when the electrolyte volume was reduced from 20 to 5 μL, the stabilizing effect of the ALD coating became even more pronounced and the cycling life was around four times longer. These results indicate that ALD Al2O3 coatings are a promising strategy to stabilize Li anodes for high performance energy storage devices such as Li–S batteries.

Local Lattice Distortion Activate Metastable Metal Sulfide as Catalyst with Stable Full Discharge–Charge Capability for Li–O2 Batteries

The direct lattice strain, either distortion, compressive, or tensile, can efficiently alter the intrinsic electrocatalytic property of the catalysts. In this work, we report a novel and effective strategy to distort the lattice structure by constructing a metastable MoSSe solid solution and thus, tune its catalytic activity for the Li-O2 batteries. The lattice distortion structure with inequivalent interplanar spacing between the same crystals plane were directly observed in individual MoSSe nanosheets with transmission electron microscopy and aberration-corrected transmission electron microscopy. In addition, in situ transmission electron microscopy analysis revealed the fast Li+ diffusion across the whole metastable structure. As expected, when evaluated as oxygen electrode for deep-cycle Li-O2 batteries, the metastable MoSSe solid solution deliver a high specific capacity of ∼730 mA h g-1 with stable discharge-charge overpotentials (0.17/0.49 V) over 30 cycles.

Carbothermal shock synthesis of high-entropy-alloy nanoparticles

Nanoparticle synthesis gets a shock Nanoparticles are useful in a wide range of applications such as catalysis, imaging, and energy storage. Yao et al. developed a method for making nanoparticles with up to eight different elements (see the Perspective by Skrabalak). The method relies on shocking metal salt-covered carbon nanofibers, followed by rapid quenching. The “carbothermal shock synthesis” can be tuned to select for nanoparticle size as well. The authors successfully created PtPdRhRuCe nanoparticles to catalyze ammonia oxidation. Science, this issue p. 1489; see also p. 1467 Shocking metal salts dispersed on carbon nanofibers produces nanoparticles composed of up to eight metals. The controllable incorporation of multiple immiscible elements into a single nanoparticle merits untold scientific and technological potential, yet remains a challenge using conventional synthetic techniques. We present a general route for alloying up to eight dissimilar elements into single-phase solid-solution nanoparticles, referred to as high-entropy-alloy nanoparticles (HEA-NPs), by thermally shocking precursor metal salt mixtures loaded onto carbon supports [temperature ~2000 kelvin (K), 55-millisecond duration, rate of ~105 K per second]. We synthesized a wide range of multicomponent nanoparticles with a desired chemistry (composition), size, and phase (solid solution, phase-separated) by controlling the carbothermal shock (CTS) parameters (substrate, temperature, shock duration, and heating/cooling rate). To prove utility, we synthesized quinary HEA-NPs as ammonia oxidation catalysts with ~100% conversion and >99% nitrogen oxide selectivity over prolonged operations.

In Situ High Temperature Synthesis of Single-Component Metallic Nanoparticles

Nanoparticles (NPs) dispersed within a conductive host are essential for a range of applications including electrochemical energy storage, catalysis, and energetic devices. However, manufacturing high quality NPs in an efficient manner remains a challenge, especially due to agglomeration during assembly processes. Here we report a rapid thermal shock method to in situ synthesize well-dispersed NPs on a conductive fiber matrix using metal precursor salts. The temperature of the carbon nanofibers (CNFs) coated with metal salts was ramped from room temperature to ∼2000 K in 5 ms, which corresponds to a rate of 400,000 K/s. Metal salts decompose rapidly at such high temperatures and nucleate into metallic nanoparticles during the rapid cooling step (cooling rate of ∼100,000 K/s). The high temperature duration plays a critical role in the size and distribution of the nanoparticles: the faster the process is, the smaller the nanoparticles are, and the narrower the size distribution is. We also demonstrated that the peak temperature of thermal shock can reach ∼3000 K, much higher than the decomposition temperature of many salts, which ensures the possibility of synthesizing various types of nanoparticles. This universal, in situ, high temperature thermal shock method offers considerable potential for the bulk synthesis of unagglomerated nanoparticles stabilized within a matrix.

Energy-driven surface evolution in beta-MnO2 structures

Exposed crystal facets directly affect the electrochemical/catalytic performance of MnO2 materials during their applications in supercapacitors, rechargeable batteries, and fuel cells. Currently, the facet-controlled synthesis of MnO2 is facing serious challenges due to the lack of an in-depth understanding of their surface evolution mechanisms. Here, combining aberration-corrected scanning transmission electron microscopy (STEM) and high-resolution TEM, we revealed a mutual energy-driven mechanism between beta-MnO2 nanowires and microstructures that dominated the evolution of the lateral facets in both structures. The evolution of the lateral surfaces followed the elimination of the {100} facets and increased the occupancy of {110} facets with the increase in hydrothermal retention time. Both self-growth and oriented attachment along their {100} facets were observed as two different ways to reduce the surface energies of the beta-MnO2 structures. High-density screw dislocations with the 1/2<100> Burgers vector were generated consequently. The observed surface evolution phenomenon offers guidance for the facet-controlled growth of beta-MnO2 materials with high performances for its application in metal-air batteries, fuel cells, supercapacitors, etc.

Elevated‐Temperature 3D Printing of Hybrid Solid‐State Electrolyte for Li‐Ion Batteries

While 3D printing of rechargeable batteries has received immense interest in advancing the next generation of 3D energy storage devices, challenges with the 3D printing of electrolytes still remain. Additional processing steps such as solvent evaporation were required for earlier studies of electrolyte fabrication, which hindered the simultaneous production of electrode and electrolyte in an all-3D-printed battery. Here, a novel method is demonstrated to fabricate hybrid solid-state electrolytes using an elevated-temperature direct ink writing technique without any additional processing steps. The hybrid solid-state electrolyte consists of solid poly(vinylidene fluoride-hexafluoropropylene) matrices and a Li+ -conducting ionic-liquid electrolyte. The ink is modified by adding nanosized ceramic fillers to achieve the desired rheological properties. The ionic conductivity of the inks is 0.78  × 10 -3 S cm-1 . Interestingly, a continuous, thin, and dense layer is discovered to form between the porous electrolyte layer and the electrode, which effectively reduces the interfacial resistance of the solid-state battery. Compared to the traditional methods of solid-state battery assembly, the directly printed electrolyte helps to achieve higher capacities and a better rate performance. The direct fabrication of electrolyte from printable inks at an elevated temperature will shed new light on the design of all-3D-printed batteries for next-generation electronic devices.

Novel ALD Chemistry Enabled Low-Temperature Synthesis of Lithium Fluoride Coatings for Durable Lithium Anodes

Lithium metal anodes can largely enhance the energy density of rechargeable batteries because of the high theoretical capacity and the high negative potential. However, the problem of lithium dendrite formation and low Coulombic efficiency (CE) during electrochemical cycling must be solved before lithium anodes can be widely deployed. Herein, a new atomic layer deposition (ALD) chemistry to realize the low-temperature synthesis of homogeneous and stoichiometric lithium fluoride (LiF) is reported, which then for the first time, as far as we know, is deposited directly onto lithium metal. The LiF preparation is performed at 150 °C yielding 0.8 Å/cycle. The LiF films are found to be crystalline, highly conformal, and stoichiometric with purity levels >99%. Nanoindentation measurements demonstrate the LiF achieving a shear modulus of 58 GPa, 7 times higher than the sufficient value to resist lithium dendrites. When used as the protective coating on lithium, it enables a stable Coulombic efficiency as high as 99.5% for over 170 cycles, about 4 times longer than that of bare lithium anodes. The remarkable battery performance is attributed to the nanosized LiF that serves two critical functions simultaneously: (1) the high dielectric value creates a uniform current distribution for excellent lithium stripping/plating and ultrahigh mechanical strength to suppress lithium dendrites; (2) the great stability and electrolyte isolation by the pure LiF on lithium prevents parasitic reactions for a much improved CE. This new ALD chemistry for conformal LiF not only offers a promising avenue to implement lithium metal anodes for high-capacity batteries but also paves the way for future studies to investigate failure and evolution mechanisms of solid electrolyte interphase (SEI) using our LiF on anodes such as graphite, silicon, and lithium.