Realizing High-Performance Li/Na-Ion Half/Full Batteries via the Synergistic Coupling of Nano-Iron Sulfide and S-doped Graphene.

Iron sulfide (FeS) anodes are plagued by severe irreversibility and volume changes that limit cycle performances. Here, a synergistically coupled hybrid composite, nanoengineered iron sulfide/S-doped graphene aerogel, was developed as high-capacity anode material for Li/Na-ion half/full batteries. The rational coupling of in situ generated FeS nanocrystals and the S-doped rGO aerogel matrix boosted the electronic conductivity, Li+ /Na+ diffusion kinetics, and accommodated the volume changes in FeS. This anode system exhibited excellent long-term cyclability retaining high reversible capacities of 422 (1100 cycles) and 382 mAh g-1 (1600 cycles), respectively, for Li+ and Na+ storage at 5 A g-1 . Full batteries designed with this anode system exhibited 435 (FeS/srGOA||LiCoO2 ) and 455 mAh g-1 (FeS/srGOA||Na0.64 Co0.1 Mn0.9 O2 ). The proposed low-cost anode system is competent with the current Li-ion battery technology and extends its utility for Na+ storage.

Controlling the Voltage Window for Improved Cycling Performance of SnO2 as Anode Material for Lithium-Ion Batteries.

Transition metal oxide materials with high theoretical capacities have been studied as substitutes for commercial graphite in lithiumion batteries. Among these, SnO2 is a promising alloying reaction-based anode material. However, the problem of rapid capacity fading in SnO2 due to volume variation during the alloying/dealloying processes must be solved. The lithiation of SnO2 results in the formation of a Li2O matrix. Herein, the volume variation of SnO2 was suppressed by controlling the voltage window to 1 V to prevent the delithiation reaction between Li2O and Sn. Using this strategy the unreacted Li2O matrix was enriched with metallic Sn particles, thereby providing a pathway for lithium ions. The specific capacity decay in the voltage window of 0.05-3 V was 1.8% per cycle. However, the specific capacity decay was improved to 0.04% per cycle after the voltage window was restricted (in the range of 0.05-1 V). This strategy resulted in a specific capacity of 374.7 mAh g-1 at 0.1 C after 40 cycles for the SnO2 anode.

Effect of Ordered Carbon Structures on Electrochemical Properties of Carbon/Sulfur Composites in Lithium-Sulfur Batteries.

In this paper, the relationship between the pore spatial structures, pore sizes, and pore types of highly ordered mesoporous CMK-based carbons (CMK-1, CMK-3, and CMK-5) and their electrochemical performance in Li-S batteries is investigated. CMK-1 has a complex spatial structure and small pores. The structure is good for limiting polysulfide in the pores, but not for rapid transfer of Li+ ions in the cell. CMK-3 and CMK-5 have similar spatial structures and pore sizes, but different pore types. Compared to the single pore structure of CMK-3, the bimodal pore structure of CMK-5 not only improves the electrolyte accessibility, but also increases the number of reaction sites, resulting in better electrochemical performance. Studying the correlation between the physical structure of carbon-based materials and their electrochemical performance in Li-S batteries will provide new insights for optimizing porous electrode materials.

Designing a Safe Electrolyte Enabling Long-Life Li/S Batteries.

Lithium-sulfur (Li/S) batteries suffer from "shuttle" reactions in which soluble polysulfide species continuously migrate to and from the Li metal anode. As a consequence, the loss of active material and reactions at the surface of Li limit the practical applications of Li/S batteries. LiNO3 has been proposed as an electrolyte additive to reduce the shuttle reactions by aiding the formation of a stable solid electrolyte interphase (SEI) at the Li metal, limiting polysulfide shuttling. However, LiNO3 is continuously consumed during cycling, especially at low current rates. Therefore, the Li/S battery cycle life is limited by the LiNO3 concentration in the electrolyte. In this work, an ionic liquid (IL) [N-methyl-(n-butyl)pyrrolidinium bis(trifluoromethylsulfonyl)imide] was used as an additive to enable longer cycle life of Li/S batteries. By tuning the IL concentration, an enhanced stability of the SEI and lower flammability of the solutions were demonstrated, that is, higher safety of the battery. The Li/S cell built with a high sulfur mass loading (4 mg cm-2 ) and containing the IL-based electrolyte demonstrated a stable capacity of 600 mAh g-1 for more than double the number of cycles of a cell containing LiNO3 additive.

Boosting High Energy Density Lithium-Ion Storage via the Rational Design of an FeS-Incorporated Sulfurized Polyacrylonitrile Fiber Hybrid Cathode.

In order to satisfy the escalating energy demands, it is inevitable to improve the energy density of current Li-ion batteries. As the development of high-capacity cathode materials is of paramount significance compared to anode materials, here we have designed for the first time a unique synergistic hybrid cathode material with enhanced specific capacity, incorporating cost-effective iron sulfide (FeS) nanoparticles in a sulfurized polyacrylonitrile (SPAN) nanofiber matrix through a rational in situ synthesis strategy. Previous reports on FeS cathodes are scarce and consist of an amorphous carbon matrix to accommodate the volume changes encountered during the cycling process. However, this inactive buffering matrix eventually increases the weight of the cell, reducing the overall energy density. By the rational design of this hybrid composite cathode, we ensure that the presence of covalently bonded sulfur in SPAN guarantees high sulfur utilization, while effectively buffering the volume changes in FeS. Meanwhile, FeS can compensate for the conductivity issues in the SPAN, thereby realizing a synergistically driven dual-active cathode material improving the overall energy density of the composite. Simultaneous in situ generation of FeS nanoparticles within the SPAN fiber matrix was carried out via electrospinning followed by a one-step heating procedure. The developed hybrid cathode material displays enhanced lithium-ion storage, retaining 688.6 mA h g(FeS@SPAN composite)-1 at the end of 500 cycles at 1 A g-1 even within a narrow voltage range of 1-3.0 V. A high discharge energy density > 900 W h kg(FeS@SPAN composite)-1, much higher than the theoretical energy density of the commercial LiCoO2 cathode, was also achieved, revealing the promising prospects of this hybrid cathode material for high energy density applications.

Carbon-Coated Ordered Mesoporous SnO2 Composite Based Anode Material for High Performance Lithium-Ion Batteries.

Recently, tin oxide (SnO2) has received significant attention for use as an anode material for next generation lithium-ion batteries (LIBs) owing to its high theoretical capacity (782 mAh g-1), which is more than twice of that of the commercialized graphite (372 mAh g-1). Several additional advantages, such as low cost, environmental friendliness, easy fabrication and natural abundance improve its promise. Although the theoretical capacity of SnO2 is high, volume expansion during cycling causes issue with cycling stability. In this study, an ordered mesoporous SnO2 was synthesized using a hard template (SBA-15), such that its mesoporous structure can buffer SnO2 particles from cracks caused by volume expansion. It can also allow effective electrolyte infiltration to ensure better reactivity of the active material with Li+ ions. The capacity of synthesized mesoporous SnO2 improved to 218.4 mAh g-1 compared regular SnO2 nanoparticles (69.6 mAh g-1) after 50 cycles at a rate of 0.1 C. Furthermore, carbon-coated mesoporous SnO2 enhanced capacity retention upon cycling (844.6 mAh g-1 after 50 cycles at 0.1 C) by insulating and preventing the cracking of the active material during lithiation and delithiation.