Highly Nitridated Graphene–Li₂S Cathodes with Stable Modulated Cycles

Abstract

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 ...

A flexible S1−xSex@porous carbon nanofibers (x≤0.1) thin film with high performance for Li-S batteries and room-temperature Na-S batteries

“…28, 29 Cui's group has done many impressive works to improve the electrochemical performance of Li-S batteries. [30][31][32][33] Among them, infiltrating S into porous carbon has been demonstrated as one of the most effective approaches to improve the electrochemical performance of Li-S batteries. 6,8,16,34 As a conductive matrix, the porous carbon possess excellent conductivity, large surface area and strong physical adsorption capability, which can improve the conductivity of S and alleviate the shuttle phenomenon of polysulfides.…”

Metal Sulfide‐Decorated Carbon Sponge as a Highly Efficient Electrocatalyst and Absorbant for Polysulfide in High‐Loading Li2S Batteries

“…[15][16][17][18][19] Owing to its high theoretical specific capacity (1166 mA h g −1 ) and particularly its ability to be paired with a lithium-metal-free anode, Li 2 S has been regarded as a more attractive and safer cathode for nextgeneration advanced Li-S batteries. [25][26][27][28] To address such issues, several strategies have been pursued in the literature. [25][26][27][28] To address such issues, several strategies have been pursued in the literature.…”

A Novel Polar Copolymer Design as a Multi-Functional Binder for Strong Affinity of Polysulfides in Lithium-Sulfur Batteries

“…Polysulfides dissolve into the electrolyte and penetrate through the separator to the lithium metal anode and then they are reduced to solid precipitates (Li 2 S), leading to quick capacity decay with the loss of active materials and an additional problem of low Coulombic efficiency in a rechargeable Li-S battery [7–10]. Although various approaches have been employed to overcome this problem [11–14], such as N-doped materials [15–17], carbon-based materials [18], conductive polymers [19, 20], metal oxides [21–23], and transition metal disulfides [24]. None have proven commercially viable due to its high cost and not suitable for large scale manufacturing.…”