Freestanding Flexible Li₂S Paper Electrode with High Mass and Capacity Loading for High‐Energy Li–S Batteries

Abstract

rate of active mass and high electrode polarization; ii) the dissolution of sulfur to soluble polysulfides in an organic electrolyte induces severe loss of active mass and notorious shuttle effect; iii) the huge volume change of sulfur (about 80%) upon lithiation/deli thiation results in fast pulverization and failure of the cathode; iv) highly reactive metallic-Li anode pairs with a flammable organic electrolyte to trigger serious safety hazards. The formation of dendrites on metallic-Li anodes during cycling may penetrate the separator and cause short-circuiting within the cell. Even though great efforts have been devoted to solving this problem, [7][8][9][10][11] the commercialization of metallic-Li anodes has not yet been achieved in rechargeable batteries with a liquid electrolyte.Replacing the sulfur with its fully lithiated phase, lithium sulfide (Li 2 S), paves an attractive way to partially address the above issues because of its high capacity of 1166 mA h g −1 and superior structural stability to sulfur for Li uptake. [12][13][14][15] With as high as 66.67 at% of Li in the structure, the Li 2 S phase already occupies the maximum volume to avoid volume expansion during lithiation/delithiation. [16,17] This remarkable feature makes it particularly suitable for manufacturing the electrode with high mass and energy loading, in which the negative effect of volume variation could not accumulate with thicker electrodes. The Li 2 S could also be the promising substitute of metallic Li to pair with Li-free high-capacity anode materials, such as Si-based materials, giving rise to the cell with attractive energy density and high safety. [13] Similar to sulfur, however, the Li 2 S cathode also suffers from low electronic conductivity (10 −13 S cm −1 ) and polysulfide shuttle problem. Confining micro/nanosized Li 2 S within conductive carbonaceous matrix, such as carbon nanotubes, graphene, and porous carbon, could significantly enhance the reaction kinetics and structural stability of Li 2 S cathodes for electrochemical cycling. [17][18][19][20][21][22][23][24][25][26] But the high melting point (1372 °C) of Li 2 S [27] makes it difficult to be conformably sealed into the carbon hosts by popular meltinginfiltration approach for making sulfur/carbon composites. Various alternative methods, such as ball-milling, solution impregnation, or precipitation from organic lithium compounds, have been developed to yield nanostructured Li 2 S/C composites with impressive performance. [16,[24][25][26][28][29][30][31][32] Nevertheless, there are still some obstacles for the implementation of Li 2 S cathodes in Li-S cells. For example, the high capacity Lithium-sulfur (Li-S) batteries are a very appealing power source with extremely high energy density. But the use of a metallic-Li anode causes serious safety hazards, such as short-circuiting and explosion of the cells. Replacing a sulfur cathode with a fully-lithiated lithium sulfide (Li 2 S) to pair with metallic-Li-free high-capacity anodes paves a feasible way to address this...

Lithium Sulfide as Cathode Materials for Lithium-Ion Batteries: Advances and Challenges

“…Such a facile, cost-effective method has attracted the attention of many researchers [42][43][44][45][46][47][48][62][63][64]. rough the above method, Li 2 S can be combined with carbon in various structures by dispersing Li 2 SO 4 in different carbon matrixes.…”

“…e glucose and Li 2 SO 4 mixture was first heated to 600°C for the carbonization, and the Li 2 SO 4 particles were homogeneously distributed in the carbon matrix without turning into Li 2 S. en, the temperature went up to 800°C, and Li 2 SO 4 totally converted into Li 2 S. It is believed that the glucose carbonization can effectively inhibit the growth or aggregation of nano-Li 2 SO 4 , which is the key to form homogeneously distributed Li 2 S-porous carbon composites [43]. More novel structures, such as one-dimensional fibers, two-dimensional sandwich plates, and three-dimensional networks, were also synthesized through the similar method [42,46,47]. e Li 2 S-carbon composites exhibit a broad application prospect in lithium ions batteries because more and more advanced preparation technologies will be developed.…”

In Situ Electrochemically Derived Amorphous‐Li2S for High Performance Li2S/Graphite Full Cell

“…On the sulfur cathode side, around 80% volume expansion upon discharging also brings a challenge for achieving high cycle stability. In contrast, Li 2 S, a fully lithiated cathode with a high theoretical capacity of 1166 mAh g −1 , can not only be coupled with a lithium‐free anode of graphite, tin, silicon, and metal oxides but also circumvent the volume expansion issue. Therefore, Li 2 S cathode is regarded as a promising candidate for new‐generation energy‐dense lithium ion batteries.…”

“…So far, the most challenging problem for these Li 2 S‐based batteries is its high activation potential barrier, which generally leads to a low initial utilization of Li 2 S active materials. Although many efforts have been made to design conductive coating layers or improving the contact between Li 2 S and electrical conductors, it is still hard to completely extract lithium from Li 2 S due to its insulating nature.…”

“…Nevertheless, detrimental effect may occur at such a high cutoff voltage, such as electrolyte decomposition and Al foil corrosion in LiTFSI‐salt‐based electrolyte, which could make the cell failure after a short cycling. On the other hand, nanosizing of particles is considered to be another way to reduce the potential barrier . For example, the activation voltage for Li 2 S particles with tens of nanometer can be reduced to 3.2 V .…”