Li 2 S encapsulated by nitrogen-doped carbon for lithium sulfur batteries

Xia

et al. 2017

Chemistry A European J

Construction of a novel matrix with both high conductivity and an excellent confinement effect for polysulfides is of great importance for developing high-performance lithium-sulfur (Li-S) batteries. In this work, we have developed a double-modification strategy to integrate lithium sulfide (Li S) into a conductive composite network consisting of vertical graphene (VG) arrays and an amorphous carbon shell, forming an integrated cathode (VG/Li S-C). Facile liquid-solution/evaporation methods in combination with chemical vapor deposition were successfully adopted for preparation of the above cathode. Due to the enhanced electrical conductivity and noticeable blocking effect for the shuttle of polysulfides, the binder-free flexible VG/Li S-C cathode exhibits high rate performance and reinforced cycles (656.2 mAh g after 100 cycles). The pronounced electrochemical performance is ascribed to the unique architecture with a coherent conductive network of VG and the carbon shell, which not only provides a conductive network for fast reaction kinetics, but also forms a durable protective shield to suppress the shuttle of polysulfides. Our research further demonstrates the synergistic effectiveness by means of inner and outer carbon matrixes for electrochemical enhancement of Li-S batteries.

Section: Introductionmentioning

confidence: 99%

Vertical‐Aligned Li₂S–Graphene Encapsulated within a Carbon Shell as a Free‐Standing Cathode for Lithium–Sulfur Batteries

Xia

et al. 2017

Chemistry A European J

Advanced Energy Materials

“…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.…”

mentioning

confidence: 99%

Highly Nitridated Graphene–Li₂S Cathodes with Stable Modulated Cycles

Qiu

Rong

Yang

et al. 2015

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 ...

“…The particle size of ball-milled Li 2 S is about 400 nm, while nanoLi 2 S@C has a particle size of ~100 nm, as described previously. 30,31,32 The detailed preparation procedures can be found in the (ESI).…”

Section: Effects Of the Volume Expansion And Shrinkage Of LI 2 S Cathmentioning

confidence: 99%

New insights into the electrode mechanism of lithium sulfur batteries via air-free post-test analysis

et al. 2016

Self Cite

Effects of the volume expansion and shrinkage of Li2S cathodes on electrochemical cycle life are investigated via post-test analysis without exposure to air. The engineered electrodes that confine volume changes within micro-reactors have significantly longer life than the electrodes without the micro-reactor structure, providing the first unambiguous evidence of the importance of confining volume changes for improved battery performance.