Using cryogenic transmission electron microscopy, we revealed three-dimensional (3D) structural details of the electrochemically plated lithium (Li) flakes and their solid electrolyte interphase (SEI). As the SEI skin layer is largely composed of nanocrystalline LiF and Li2O in amorphous polymeric matrix, when complete Li stripping occurs, the compromised SEI 3D framework buckles and wrinkles. The flexibility and resilience of the SEI skin layer plays a vital role in preserving an intact SEI 3D framework after Li stripping. The intact SEI network enables the nucleation and growth of newly plated Li inside the previously formed SEI network in subsequent cycles, preventing additional large amounts of SEI formation. In addition, cells cycled under the accurately controlled uniaxial pressure can further enhance the repeated utilization of the SEI and improve the Coulombic efficiency (CE) by up to 97%, demonstrating an effective strategy for reducing the formation of additional SEI and inactive “dead” Li.

Lithium (Li) metal offers the highest projected energy density as a battery anode, however its extremely high reactivity induces dendrite growth and dead Li formation during repeated charge/discharge processes, resulting in both poor reversibility and catastrophic failure. Approaches reported to date often seek to suppress dendrites formation at the expense of energy density. Here, a strategy that resolves the above conflict and achieves a dendrite-free and long-term reversible Li metal anode is reported. A self-organized core–shell composite anode, comprising an outer sheath of lithiated liquid metal (LixLMy) and an inner layer of Li metal, is developed, which posesses high electrical and ionic conductivity, and physically separates Li from the electrolyte. The introduction of LixLMy not only prevents dendrite formation, but also eliminates the use of copper as an inert substrate. Full cells made of such composite anodes and commercially available LiNi0.6Co0.2Mn0.2O2 (NCM622) cathodes deliver ultrahigh energy density of 1500 Wh L−1 and 483 Wh kg−1. The high capacity can be maintained for more than 500 cycles, with fading rate of less than 0.05% per cycle. Pairing with LiNi0.8Co0.1Mn0.1O2 (NCM811) further raises the energy density to 1732 Wh L−1 and 514 Wh kg−1.

Cryogenic transmission electron microscopy (cryo-TEM) is a valuable tool recently proposed to investigate battery electrodes. Despite being employed for Li-based battery materials, cryo-TEM measurements for Na-based electrochemical energy storage systems are not commonly reported. In particular, elucidating the chemical and morphological behavior of the Na-metal electrode in contact with a non-aqueous liquid electrolyte solution could provide useful insights that may lead to a better understanding of metal cells during operation. Here, using cryo-TEM, we investigate the effect of fluoroethylene carbonate (FEC) additive on the solid electrolyte interphase (SEI) structure of a Na-metal electrode. Without FEC, the NaPF6-containing carbonate-based electrolyte reacts with the metal electrode to produce an unstable SEI, rich in Na2CO3 and Na3PO4, which constantly consumes the sodium reservoir of the cell during cycling. When FEC is used, the Na-metal electrode forms a multilayer SEI structure comprising an outer NaF-rich amorphous phase and an inner Na3PO4 phase. This layered structure stabilizes the SEI and prevents further reactions between the electrolyte and the Na metal.

The practical application of all -solid-state lithium metal batteries (ASLMBs) has hindered by Li filament infiltration and ensuing short-circuit, which attributed to inhomogeneous interfacial ion transport and leakage current by electrons transport at grain boundaries. Herein, we verified the novel solid-state sintering strategy that to construct LiAlO2 (LAO) 3D ion transport network and suppress the electron conduction at grain boundaries (GBs) by introducing Li3AlF6 (LAF) nanoparticles can noteworthy inhibit Li infiltration. Through cryo-transmission electron microscopy, we discovered the sintering additive Li3AlF6 (LAF) decomposed into LAO, which possess higher energy bandgap (4.6 eV) than some reduced bandgap of GBs (~1-3 eV) in Li7La3Zr2O12 (LLZO) to prevent current leakage. Meanwhile, F atoms substitute O site in LLZO lattice, which improve the bandgap and phase stability of LLZO bulk. We identified the LAO can synergize ion transport in ceramic duplex structure by solid-state NMR, which result in lower surface potential difference (16.4 mV) to promote homogeneous Li plating. Integrated regulating grain boundaries contribute to the long-term Li/LLZO@LAF/Li symmetric cell stable cycling almost 1300 h at 0.2 mA cm-2 and the superior performance of ASLMBs to cycle over 1000 times.

The performance of halide perovskite solar cells is often dominated by structural defects. However, atomic scale characterization of the crystalline defects in organic–inorganic hybrid perovskites is hindered by the electron-beam sensitivity of the organic components in the structure. Here we reported the atomic scale characterization of CH3NH3PbI3 (MAPbI3) single crystal using the state-of-the-art cryo-transmission electron microscopy. We confirm that the MAPbI3 structure is intact during high resolution cryo-TEM analysis by probing the content of carbon, nitrogen from the [CH3NH3]+ component using electron energy loss spectroscopy. Atomic steps of {200}T surfaces were observed which shed light on the crystal growth details and low-energy surfaces. Surprisingly, high density of stacking faults are observed in the hybrid perovskite materials. We believe these fault structures serves the role of micro-interface between otherwise perfect lattices which facilitates charge separation and reduces the photon-generated carrier recombination within the crystal solids. First-principles calculations show that the presence of such stacking faults significantly changes the electronic structures of the materials, which may play a critical role in further optimizing the properties such as charge-carrier mobility, the carrier diffusion length and energy conversion efficiency of organic-inorganic hybrid perovskite-based energy harvesting devices.