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The solid electrolyte interphase (SEI) dictates the cycling stability of lithium‐metal batteries. Here, direct atomic imaging of the SEI's phase components and their spatial arrangement is achieved, using ultralow‐dosage cryogenic transmission electron microscopy. The results show that, surprisingly, a lot of the deposited Li metal has amorphous atomic structure, likely due to carbon and oxygen impurities, and that crystalline lithium carbonate is not stable and readily decomposes when contacting the lithium metal. Lithium carbonate distributed in the outer SEI also continuously reacts with the electrolyte to produce gas, resulting in a dynamically evolving and porous SEI. Sulfur‐containing additives cause the SEI to preferentially generate Li2SO4 and overlithiated lithium sulfate and lithium oxide, which encapsulate lithium carbonate in the middle, limiting SEI thickening and enhancing battery life by a factor of ten. The spatial mapping of the SEI gradient amorphous (polymeric → inorganic → metallic) and crystalline phase components provides guidance for designing electrolyte additives.

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Stable layered LiNi0.9Co0.07Al0.03O2 microspheres show large discharge capacity and good cycling performance as cathode for lithium ion batteries.

the ultimate choice with no competition [2] because of its ultrahigh specific capacity (3860 mAh g −1), lightweight (0.53 g cm-3) and the lowest electrochemical potential (−3.040 V versus standard hydrogen electrode). [1,3] Replacing graphite anodes in Li-ion batteries with Li metal would lead to an immediate increase of energy density by 40%. [1,2] In a broader context, Li anodes are also indispensable components for next-generation concept battery chemistries such as Li-sulfur and Li-air couples, whose energy density are expected to exceed 370 and 1700 Wh kg −1 , respectively. [4-6] The major obstacle impeding the electrochemical cycling of Li metal is its high reactivity with electrolytes, which results in uncontrolled growth of Li dendrites and incessant formation of dead lithium. These reactions not only consume lithium resource at the expense of reversibility, but also often induce safety hazards. [1,5,6,7] In the past decades, many strategies have been proposed to suppress the parasitic reactions between Li metal and electrolytes, with focus frequently directed at the dendrite growth. [8-13] These strategies include: i) designing high-concentration salt liquid electrolytes to mitigate the inhomogeneous distribution of Li ions; [14] ii) optimizing electrolyte additives to stabilize 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 dendritefree and long-term reversible Li metal anode is reported. A self-organized core-shell composite anode, comprising an outer sheath of lithiated liquid metal (Li x LM y) 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 Li x LM y 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 LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM 622) 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 LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811) further raises the energy density to 1732 Wh L −1 and 514 Wh kg −1. The rapid development of mobile electronics, internet-of-things and electrical vehicles imposes an insatiable demand for highenergy-density rechargeable batteries, which relies on the discoveries of better electrodes, electrolytes and interphases. [1] Among all possible anode material candidates, [1] Li metal is

We reported a one-step dry coating of amorphous SiO on spherical Ni-rich layered LiNiCoAlO (NCA) cathode materials. Combined characterization of XRD, EDS mapping, and TEM indicates that a SiO layer with an average thickness of ∼50 nm was uniformly coated on the surface of NCA microspheres, without inducing any change of the phase structure and morphology. Electrochemical tests show that the 0.2 wt% SiO-coated NCA material exhibits enhanced cyclability and rate properties, combining with better thermal stability compared with those of pristine NCA. For example, 0.2 wt% SiO-coated NCA delivers a high specific capacity of 181.3 mA h g with a capacity retention of 90.7% after 50 cycles at 1 C rate and 25 °C. Moreover, the capacity retention of this composite at 60 °C is 12.5% higher than that of pristine NCA at 1 C rate after 50 cycles. The effects of SiO coating on the electrochemical performance of NCA are investigated by EIS, CV, and DSC tests, the improved performance is attributed to the surface coating layer of amorphous SiO, which effectively suppresses side reactions between NCA and electrolytes, decreases the SEI layer resistance, and retards the growth of charge-transfer resistance, thus enhancing structural and cycling stability of NCA.

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