Overcoming copper-induced conversion reactions in nickel disulphide anodes for sodium-ion batteries.

Employing copper (Cu) as an anode current collector for metal sulphides is perceived as a general strategy to achieve stable cycle performance in sodium-ion batteries, despite the compatibility of the aluminium current collector with sodium at low voltages. The capacity retention is attributed to the formation of copper sulphide with the slow corrosion of the current collector during cycling which is not ideal. Conventional reports on metal sulphides demonstrate excellent electrochemical performances using excessive carbon coatings/additives, reducing the overall energy density of the cells and making it difficult to understand the underlying side reaction with Cu. In this report, the negative influence of the Cu current collector is demonstrated with in-house synthesised, scalable NiS2 nanoparticles without any carbon coating as opposed to previous works on NiS2 anodes. Ex situ TEM and XPS experiments revealed the formation of Cu2S, further to which various current collectors were employed for NiS2 anode to rule out the parasitic reaction and to understand the true performance of the material. Overall, this study proposes the utilisation of carbon-coated aluminium foil (C/Al) as a suitable current collector for high active material content NiS2 anodes and metal sulphides in general with minimal carbon contents as it remains completely inert during the cycling process. Using a C/Al current collector, the NiS2 anode exhibits stable cycling performance for 5000 cycles at 50 A g-1, maintaining a capacity of 238 mA h g-1 with a capacity decay rate of 8.47 × 10-3% per cycle.

Effect of Cross-Linking and Surface Treatment on the Functional Properties of Electrospun Polybenzimidazole Separators for Lithium Metal Batteries.

In this work, electrospun PBI separators with a highly porous structure and nanofiber diameter of about 90-150 nm are prepared using a multi-nozzle under controlled conditions for lithium metal batteries. Cross-linking with α, α-dibromo-p-xylene and surface treatment using 4-(chloromethyl) benzoic acid successfully improve the electrochemical as well as mechanical properties of the separators. The resulting separator is endowed with high thermal stability and excellent wettability (1080 to 1150%) with commercial liquid electrolyte than PE and PP (Celgard 2400) separators. Besides, attractive cycling stability and rate capability in LiFePO4/Li cells are attained with the modified separators. Prominently, CROSSLINK PBI exhibits a stable Coulombic efficiency of more than 99% over 100 charge-discharge cycles at 0.5 C, which is superior to the value of cells using commercial PE and PP (Celgard 2400) separators. The half cells assembled using the CROSSLINK PBI separator can deliver a discharge capacity of 150.3 mAh g-1 at 0.2 C after 50 cycles corresponding to 88.4% of the theoretical value of LiFePO4 (170 mAh g-1). This work offers a worthwhile method to produce thermally stable separators with noteworthy electrochemical performances which opens new possibilities to improve the safe operation of batteries.

A Hierarchically Ordered Mesoporous-Carbon-Supported Iron Sulfide Anode for High-Rate Na-Ion Storage.

Sodium-ion batteries (SIBs) are promising alternatives to lithium-based energy storage devices for large-scale applications, but conventional lithium-ion battery anode materials do not provide adequate reversible Na-ion storage. In contrast, conversion-based transition metal sulfides have high theoretical capacities and are suitable anode materials for SIBs. Iron sulfide (FeS) is environmentally benign and inexpensive but suffers from low conductivity and sluggish Na-ion diffusion kinetics. In addition, significant volume changes during the sodiation of FeS destroy the electrode structure and shorten the cycle life. Herein, we report the rational design of the FeS/carbon composite, specifically FeS encapsulated within a hierarchically ordered mesoporous carbon prepared via nanocasting using a SBA-15 template with stable cycle life. We evaluated the Na-ion storage properties and found that the parallel 2D mesoporous channels in the resultant FeS/carbon composite enhanced the conductivity, buffered the volume changes, and prevented unwanted side reactions. Further, high-rate Na-ion storage (363.4 mAh g-1 after 500 cycles at 2 A g-1, 132.5 mAh g-1 at 20 A g-1) was achieved, better than that of the bare FeS electrode, indicating the benefit of structural confinement for rapid ion transfer, and demonstrating the excellent electrochemical performance of this anode material at high rates.

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.

High power Na3V2(PO4)3 symmetric full cell for sodium-ion batteries.

Sodium-ion batteries (SIBs) are a viable substitute for lithium-ion batteries due to the low cost and wide availability of sodium. However, practical applications require the development of fast charging sodium-ion-based full-cells with high power densities. Na3V2(PO4)3 (NVP) is a bipolar material with excellent characteristics as both a cathode and an anode material in SIBs. Designing symmetric cells with NVP results in a single voltage plateau with significant specific capacity which is ideal for a full cell. Here we demonstrate for the first time a tremendous improvement in the performance of NVP symmetric full cells by introducing an ether-based electrolyte which favors fast reaction kinetics. In a symmetric full cell configuration, 75.5% of the initial capacity was retained even after 4000 cycles at 2 A g-1, revealing ultra-long cyclability. Excellent rate performances were obtained at current densities as high as 1000C, based on the cathode mass, revealing ultrafast Na+ transfer. The power density obtained for this NVP symmetric cell (48 250 W kg-1) is the best among those of all the sodium-ion-based full cells reported to date.

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.

An Electrospun Core-Shell Nanofiber Web as a High-Performance Cathode for Iron Disulfide-Based Rechargeable Lithium Batteries.

FeS2 /C core-shell nanofiber webs were synthesized for the first time by a unique synthesis strategy that couples electrospinning and carbon coating of the nanofibers with sucrose. The design of the one-dimensional core-shell morphology was found to be greatly beneficial for accommodating the volume changes encountered during cycling, to induce shorter lithium ion diffusion pathways in the electrode, and to prevent sulfur dissolution during cycling. A high discharge capacity of 545 mAh g-1 was retained after 500 cycles at 1 C, exhibiting excellent stable cycling performance with 98.8 % capacity retention at the last cycle. High specific capacities of 854 mAh g-1 , 518 mAh g-1 , and 208 mAh g-1 were obtained at 0.1 C, 1 C, and 10 C rates, respectively, demonstrating the exceptional rate capability of this nanofiber web cathode.

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.

Tailor-Made Electrospun Multilayer Composite Polymer Electrolytes for High-Performance Lithium Polymer Batteries.

A novel tailor-made multilayer composite polymer electrolyte, consisting of two outer layers of electrospun polyacrylonitrile (PAN) and one inner layer of poly(vinyl acetate) (PVAc)/poly(methyl methacrylate) (PMMA)/poly(ethylene oxide) (PEO) fibrous membrane, was prepared using continuous electrospinning. These membranes, which are made up of fibers with diameters in the nanometer range, were stacked in layers to produce interconnected pores that result in a high porosity. Gel polymer electrolytes (GPEs) were prepared by entrapping a liquid electrolyte (1 M LiPF6 in ethylene carbonate/dimethyl carbonate) in the membranes. The composite membranes exhibited a high electrolyte uptake of 450-510%, coupled with an improved room temperature ionic conductivity of up to 4.72 mS cm-1 and a high electrochemical stability of 4.6 V versus Li/Li+. Electrochemical investigations of a composite membrane of PAN-PVAc-PAN, with a LiFePO4 cathode synthesized in-house, showed a high initial discharge capacity of 145 mAh g-1, which corresponds to 85% utilization of the active material, and displayed stable cycle performance.