The development of low-cost, high-energy cathodes from nontoxic, broadly available resources is a big challenge for the next-generation rechargeable lithium or lithium-ion batteries. As a promising alternative to traditional intercalation-type chemistries, conversion-type metal fluorides offer much higher theoretical capacity and energy density than conventional cathodes. Unfortunately, these still suffer from irreversible structural degradation and rapid capacity fading upon cycling. To address these challenges, here a versatile and effective strategy is harnessed for the development of metal fluoride-carbon (C) nanocomposite nanofibers as flexible, free-standing cathodes. By taking iron trifluoride (FeF 3 ) as a successful example, assembled FeF 3 -C/Li cells with a high reversible FeF 3 capacity of 550 mAh g −1 at 100 mA g −1 (three times that of traditional cathodes, such as lithium cobalt oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese oxide) and excellent stability (400+ cycles with littleto-no degradation) are demonstrated. The promising characteristics can be attributed to the nanoconfinement of FeF 3 nanoparticles, which minimizes the segregation of Fe and LiF upon cycling, the robustness of the electrically conductive C network and the prevention of undesirable reactions between the active material and the liquid electrolyte using the composite design and electrolyte selection.

Lithium sulfide (Li2S) with a high theoretical specific capacity of 1166mAh g(-1) is a promising cathode material for next-generation Li-S batteries with high specific energy. However, low conductivity of Li2S and polysulfide dissolution during cycling are known to limit the rate performance and cycle life of these batteries. Here, we report on the successful development and application of a nanocomposite cathode comprising graphene covered by Li2S nanoparticles and protected from undesirable interactions with electrolytes. We used a modification of our previously reported low cost, scalable, and high-throughput solution-based method to deposit Li2S on graphene. A dropwise infiltration allowed us to keep the size of the heterogeneously nucleated Li2S particles smaller and more uniform than what we previously achieved. This, in turn, increased capacity utilization and contributed to improved rate performance and stability. The use of a highly conductive graphene backbone further increased cell rate performance. A synergetic combination of a protective layer vapor-deposited on the material during synthesis and in situ formed protective surface layer allowed us to retain ∼97% of the initial capacity of ∼1040 mAh gs(-1) at C/2 after over 700 cycles in the assembled cells. The achieved combination of high rate performance and ultrahigh stability is very promising.

Lithium sulfide (Li2S) cathodes have been viewed as very promising candidates for next-generation lightweight Li and Li-ion batteries.

devices, backup power supplies, and a broad range of other important applications. [2] Recent developments of smart textiles [3] and flexible electronics [4] will benefit greatly from the development of robust, safe-to-use, low-cost, and flexible energy storage that could be integrated into fabrics. [5] Commercial SCs are electrical doublelayer capacitors (EDLCs) based on activated carbons that store energy by the accumulation of electrostatic charge on their internal surface area. However, the low density of activated carbon (typically below 0.7 g cm −3 ) and limited specific capacitance of carbon electrodes (typically 70-250 F g −1 , depending on the electrolyte used) result in rather moderate volumetric energy density characteristics of EDLCs. [6] Besides, the common use of organic electrolytes in EDLCs induces additional fire hazard, [7] which is a particularly sensitive topic if those are integrated into clothing. In contrast to EDLCs, asymmetric SCs (ASCs) that use a dense pseudocapacitive (or a battery-like) electrode together with an EDLC (or a different kind of pseudocapacitive) electrode may offer higher volumetric energy storage characteristics even with nonflammable aqueous electrolytes. [8][9][10] In the latter case, such a hybrid design relies on different potential windows for positive and negative electrodes, achieving high electrode capacity, a relatively high cell voltage, and a resulting high-energy density. [9,11] Transition metal oxides (TMOs) are attracting great interest for applications in ASCs, because they can benefit from fast reversible redox reactions and offer significantly higher volumetric capacitance than porous carbon materials. [12] Among TMOs, ruthenium oxide (RuO 2 ) is considered as "gold standard" pseudocapacitive materials with high conductivity, high specific capacitance, and excellent rate performance, but its extremely high cost seriously limits its large-scale applications. [9,13] Vanadium oxides were demonstrated to exhibit very large specific capacitance, [14] but are too toxic for wearable applications. In sharp contrast, both iron and manganese oxides (Fe 2 O 3 and MnO 2 ) offer good electrochemical activity, very low cost, environmental friendliness, and great abundance in Earth's crust. [15][16][17] Besides, the large potential windows of Fe 2 O 3 (−0.8-0 V vs Ag/AgCl) and MnO 2 (0−0.8 V vs Ag/AgCl) allow ASCs based on such electrodes have a moderately high operating Aqueous asymmetric supercapacitors (ASCs) may offer comparable or higher energy density than electric double-layer capacitors (EDLCs) based on organic electrolytes. As such, ASCs may be more suitable for integration into smart textiles, where the use of flammable organic solvents is not acceptable. However, reported ASC devices typically suffer from poor rate capability and low areal loadings. This study demonstrates the development of nitrogendoped carbon (N-C) nanowire/metal oxide (Fe 2 O 3 and MnO 2 ) nanocomposite electrodes directly produced on the internal surface of a conductive fabric ...

Porous carbons suffer from low specific capacitance, while intercalation-type active materials suffer from limited rate when used in asymmetric supercapacitors. We demonstrate that nanoconfinement of intercalation-type lithium titanate (Li4Ti5O12) nanoparticles in carbon nanopores yielded nanocomposite materials that offer both high ion storage density and rapid ion transport through open and interconnected pore channels. The use of titanate increased both the gravimetric and volumetric capacity of porous carbons by more than an order of magnitude. High electrical conductivity of carbon and the small size of titanate crystals allowed the composite electrodes to achieve characteristic charge and discharge times comparable to that of the electric double-layer capacitors. The proposed composite synthesis methodology is simple, scalable, and applicable for a broad range of active intercalation materials, while the produced composite powders are compatible with commercial electrode fabrication processes.