An in situ electrochemical scanning electronic microscopy method is developed to systematically study the lithium plating/stripping processes in liquid electrolytes. The results demonstrate that the lithium dendrite growth speed and mechanism is greatly affected by the additives in the ether-based electrolyte.

an effective strategy for the redeposition of lithium polysulfi des due to their affi nities for these materials, which leads to significant improvement of corresponding Li/S cells.Li 2 S is a promising prelithiated cathode material with a high theoretical capacity of 1166 mA h g −1 . Unlike conventional sulfur cathode, Li 2 S cathode shrinks as it delithiates initially, producing voids for subsequent lithiation/delithiation cycling, hence protecting the electrode structure from damage. More importantly, Li 2 S can be matched with lithium metal-free anodes (such as silicon and tin), thus eliminating serious safety issues associated with the formation of "dendrites." Despite of these merits, the performance of Li 2 S-based cathode significantly lags behind its sulfur counterpart. [ 9,10,30,31 ] A key issue for the Li 2 S material seems to be in its ineffi cient activation and redeposition process. [ 32,33 ] To understand the actual electrochemical activation processes, we fi rst developed in situ scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques to study the cathode material structural changes on delithiation. The newly developed in situ SEM set-up is shown in Figure 1 a,b. A liquid cell contains one electrode with graphene and Li 2 S particles on a 50 nm thick SiN x window, and the other electrode with Li metal on Cu foil. The cell is fi lled by a liquid electrolyte (see the Experimental Section). When charged at 3.5 V, the conversion reaction from Li 2 S to polysulfi des occurs fi rst at their surfaces (Figure 1 c and Figure S1 and Movie 1, Supporting Information). We see that the Li 2 S particles on graphene become smaller and smaller upon charging due to gradual dissolution of lithium polysulfi des into the electrolyte. The phenomenon is also supported by in situ Raman spectroscopy (see Figure S2, Supporting Information). The observed phenomenon could be explained by that Li 2 S was chemically converted to soluble lithium polysulfi des upon charging. The process was further examined by in situ TEM study. A newly designed in situ TEM microchip (Figure 1 d) was fabricated and schematically shown in Figure 1 e. The main part is an Au wire, of which one end was connected to one electrode of the chip by silver paste, and the other end was glued with the graphene− Li 2 S sample. The surface of the other electrode of the chip was deposited by Li metal. The graphene−Li 2 S sample and Li metal were connected via an ionic liquid electrolyte. When charged at 3.5 V, Li 2 S particles encapsulated in the graphene gradually disappeared (Figure 1 f and Movie 2, Supporting Information). The processes could be explained by the dissolution of the generated lithium polysulfi des in the ionic liquid electrolyte. The observed The development of high-capacity cathode materials is critical for applications such as mobile devices and electric vehicles. Li/S batteries represent a promising system based on sulfurconductive additive composite as the cathode. [1][2][3][4][5] However, various factors ...

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Newly developed in‐situ electron microscopy methods were employed to understand the dissolution processes of the intermediate lithium polysulfides in liquid Li2S‐C/Li cells by Yi Cui, Yuegang Zhang and co‐workers in article number 1501369. Based on an understanding of the capacity loss mechanism, high‐rate, ultralong cycle‐life Li2S‐C/Li batteries are demonstrated by combining a highly nitridated graphene–Li2S cathode with a new charging protocol.

Using transmission electron microscopy (TEM) to directly observe a dynamic chemical reaction process in liquid-phase environment is a big challenge because it is difficult to keep liquid reactants under vacuum. In this work, we reported a liquid-based cell that enables in-situ observation of a solution reaction process under TEM. The novel liquid cell design not only realizes the self-alignment of top/bottom windows, but also achieves an adjustable liquid layer thickness down to nanometer scale. The cell consists of top and bottom frames, both of which are fabricated from silicon wafers using conventional micro-fabrication techniques. The transparent observation windows are made of silicon nitride (SiN x ) membranes. In a typical assembling process, an ethanol solution containing silver nanowires and an ethanol solution containing saturated sulfur were sequentially dropped into the liquid tank of the bottom-frame of a liquid cell by using 1 mL syringe. Then, the liquid tank was covered by the top-frame with a window direction of 90 degrees, and an epoxy was used to seal the edge between the top-frame and bottom-frame. Using this assembled liquid cell, we performed in-situ TEM observation of the chemical reaction between Ag nanowires and sulfur in ethanol solution. Additional ex-situ X-ray diffraction (XRD) and Raman spectroscopy were also performed to study the reaction intermediates and final products. Instead of a simple reaction process in which sulfur diffuses into Ag to form the final product of Ag 2 S, we found that the real reaction process involves the formation of a soluble intermediate phase (Ag 2 S 4 ), which led to a partial dissolution of Ag nanowires in ethanol solution during reaction. These results well demonstrate that the in-situ TEM technique is a powerful tool to reveal the "real" chemical reaction mechanism. The experimental technique developed here could also be used to study a broad range of dynamic phenomena in liquid environment.

An in-situ liquid-phase electrochemical scanning electronic microscopy (EC-SEM) method is developed to systematically study the lithium plating/stripping processes in liquid electrolytes, as described in article number 1606187 by Yuegang Zhang and co-workers. The results demonstrate that the lithium dendrite growth speed and mechanism are greatly affected by the additives in the ether-based electrolyte.