Free-standing Interlayer Research Articles

A Freestanding Multifunctional Interlayer Based on Fe/Zn Single Atoms Implanted on a Carbon Nanofiber Membrane for High-Performance Li-S Batteries

By virtue of the high theoretical energy density and low cost, Lithium–sulfur (Li-S) batteries have drawn widespread attention. However, their electrochemical performances are seriously plagued by the shuttling of intermediate polysulfides and the slow reaction kinetics during practical implementation. Herein, we designed a freestanding flexible membrane composed of nitrogen-doped porous carbon nanofibers anchoring iron and zinc single atoms (FeZn-PCNF), to serve as the polysulfide barrier and the reaction promotor. The flexible porous networks formed by the interwoven carbon nanofibers not only offer fast channels for the transport of electrons/ions, but also guarantee the structural stability of the all-in-one multifunctional interlayer during cycling. Highly dispersed Fe and Zn atoms in the carbon scaffold synergistically immobilize sulfur species and expedite their reversible conversion. Therefore, employing FeZn-PCNF as the freestanding interlayer between the cathode and separator, the Li-S battery delivers a superior initial reversible discharge capacity of 1140 mA h g−1 at a current density of 0.5 C and retains a high capacity of 618 mA h g−1 after 600 cycles at a high current density of 1 C.

Controlled Construction of Cobalt-Doped Carbon Nanofiber–Carbon Nanotubes as a Freestanding Interlayer for Advanced Lithium–Sulfur Batteries

Controlled Construction of Cobalt-Doped Carbon Nanofiber–Carbon Nanotubes as a Freestanding Interlayer for Advanced Lithium–Sulfur Batteries

Magneli Ti4O7 nanotube arrays as a free-standing efficient interlayer for fast-delivery and high-energy density lithium-sulfur batteries

Improving lithium sulfur (Li-S) batteries performance has been a challenge due to sulfur drawbacks. Here, it addresses the use of Magneli Ti4O7 nano-tube arrays (MTNTAs) as free-standing interlayer in conjunction with carbon-coated separator (CCS) to improve the performance of lithium-sulfur batteries. The electrochemical catalytic activity of MTNTAs showed stable cycling and outstanding rate performance. The battery equipped with MTNTAs, and CCS delivered 723 mAh.g−1 with a low capacity-fading rate of 0.07% per cycle at 0.5 C after 500 cycles. The remarkably fast Li ion diffusion and low internal resistance of MTNTAs provided a discharge capacity of 407 mAh.g−1 after 500 cycles at 10 C. The high-sulfur loaded cathode (6.7 mg S. cm−2) can offer a discharge capacity of 719 mAh.g−1 at 0.1 C corresponding to areal capacity of 4.8 mAh.cm−2. The outperformance of the cell became drastically attractive when the cathode was fabricated with the simple blade-casting method using pure sulfur. The sulfur cathode delivered a superior discharge capacity of 471 mAh.g−1 after 250 cycles with coulombic efficiency> 95% at 0.2 C. The result of this study demonstrates that the coexistence of MTNTAs and CCS in the battery can offer a long-life cycle with outstanding properties such as fast charging and discharging, and high-energy density which is highly desirable for transportation sectors.

CO2-derived free-standing carbon interlayer embedded with molecular catalysts for improving redox performance in Li-S batteries

The use of a free-standing carbon interlayer is a promising approach for the development of lithium-sulfur (Li-S) batteries because it suppresses the shuttle phenomenon and provides outstanding flexible characteristics. However, the thickness required to maintain the unique properties of the free-standing interlayer inevitably inhibits the transport of Li ions, causing sluggish redox kinetics. This work tackles the critical problem of the interlayer by synthesizing a composite in which Fe-based molecular catalysts are atomically incorporated into carbon nanofibers with superior pore characteristics realized by CO2 treatment. The templates self-generated during CO2 annealing provide high porosity and surface area, leading to effective Li-ion diffusion, and homogeneous distribution of the catalytic sites in the form of Fe-N2 to the free-standing paper. The Fe-N2 configuration thermodynamically aids in overcoming the energy barrier of the rate-limiting step of Li2S4 to Li2S conversion while minimizing the shuttle phenomenon. Based on the effective Li-ion transport by improved pore properties, and the superior redox reaction ability of Fe-N2, the assembled cell maintains a coulombic efficiency of 95% up to 1600 cycles at 3.0 C. In addition, a maximum areal capacity of 2.9 mAh cm−2 is delivered for a high loading electrode with 4.2 mg cm−2 at 45 °C.

Bioderived carbon fiber conductive networks with inlaid electrocatalysts as an ultralight freestanding interlayer for working Li–SeS2 pouch cells

Introducing a freestanding functional interlayer has been a conventional tactic to immobilize the soluble polysulfide intermediate in Li–S batteries. However, most of the designed interlayers possess extra heavy weight, casting additional technical challenges toward practical high-specific-energy batteries. Herein, an ultralight self-standing interlayer with an extremely low mass loading (∼0.14 mg cm−2), composed of porous curly carbon fibers derived from natural biomass with inlaid cobalt electrocatalysts (CF–Co), was engineered via a convenient way. After replacing the poor conductivity sulfur (∼10−28 S m−1) by higher conductivity selenium disulfide (SeS2, ∼10−6 S m−1) as active cathode materials, the hierarchically porous-structured, conductive CF-Co interlayer with outstanding adsorptive and electrocatalytic effects is introduced into the resulted Li–SeS2 batteries to capture dual-intermediate polysulfides/polyselenides, boost their conversion kinetics, and ensure favorable running of Li–SeS2 cells with high SeS2 loading and lean electrolyte. Consequently, the coin cells deliver outstanding high-rate capability (404 mAh g−1 at 8 A g−1) and superior cycling stability (∼81.5% areal capacity retention in 125 cycles) under high SeS2 loading (5.0 mg cm−2). Significantly, practical high-areal-capacity (>5.5 mAh cm−2) Li–SeS2 pouch cells can be realized by assembling this interlayer with double-side SeS2-loading cathodes (132 mg), working stably at relatively lower electrolyte condition (6.0 μL mg−1).

High-performance lithium-sulfur battery enabled by jointing cobalt decorated interlayer and polyethyleneimine functionalized separator

Lithium-sulfur (Li-S) battery is considered as one of the most promising alternatives for next-generation electrochemical energy storage systems due to its high energy density and low cost. Unfortunately, several issues of Li-S battery, such as sluggish reaction kinetics, severe polysulfides shuttle effect and volume expansion, still hinder the commercialization of Li-S battery. Herein, a synergistic strategy is proposed, which comprises polyethyleneimine (PEI)-multi-walled carbon nanotube-Super P (PMS) coating modified on PP separator and uniformly distributed cobalt nanocrystals in N-doped porous carbon nanofiber (Co/PCNF) as a freestanding interlayer in the cathodic side of Li-S battery. Benefiting from abundant amino/imine groups of protonated PEI and catalytic Co active sites in conductive porous carbon skeleton, the Co/PCNF-PMS bilayer architecture can not only intensely anchor the negatively charged polysulfides via electrostatic interaction but also fast electrocatalyze the sulfur redox reaction. The synergistic effect of the Co/PCNF-PMS bilayer enable the Li-S battery with a high initial capacity of 1537 mAh g−1 at 200 mA g−1, extended cycling stability of only 0.06% per cycle capacity fade over 300 cycles at 2000 mA g−1 and outstanding performance under high raised sulfur loading up to 6 mg cm−2.

Flexible ordered MnS@CNC/carbon nanofibers membrane based on microfluidic spinning technique as interlayer for stable lithium-metal battery

In this work, the novel flexible ordered carbon nanofibers membrane including cellulose nanocrystal (CNC) and MnS nanoparticles (MnS@CNC/CNFs) were prepared through the microfluidic spinning technology (MST) and carbonization process. Then the application of the prepared MnS@CNC/CNFs as the interlayer between the separator and lithium (Li) anode for lithium-metal battery (LMBs) was systematically investigated. The ordered carbon nanofibers framework with a regular arrangement structure could induce more uniform deposition of Li ions. Moreover, the MnS@CNC/CNFs interlayer possessed remarkable electrical conductivity and large specific surface area, which not only provided a high transmission channel for ions and electrons but also enhanced the interfacial compatibility between the Li anode or separator and interlayer. The doped MnS in the interconnected CNFs skeleton could provide more active sites to trigger the analogous alloying reaction with Li, and the polar hydroxyl groups (-OH) in the CNC could also induce strong chemical interactions toward Li ions. These comprehensive effects brought out the more homogeneous distribution of Li ions flux and the dendrite-free electrode. The assembled Li|LiFePO4 (LFP) batteries with the freestanding interlayer achieved an initial discharge capacity of 148.2 mAh g−1 and retention rate of 83.1% after 600 cycles at 1 C. The Li/Li symmetric batteries further indicated that the flexible ordered MnS@CNC/CNFs membrane could effectively inhibit the Li dendrite growth and enhance the cycling stability. The design of the MnS@CNC/CNFs based on MST offered a facile method for preparing CNFs and a potential solution for highly safe LMBs.

Freestanding interlayers for Li–S batteries: design and synthesis of hierarchically porous N-doped C nanofibers comprising vanadium nitride quantum dots and MOF-derived hollow N-doped C nanocages

Herein, a hierarchically developed multifunctional, porous, and freestanding interlayer is utilized for efficient polysulfide absorption and superior electrochemical performance in lithium–sulfur cells with sulfur cathode and low electrolyte volume.

Synergistic confining polysulfides by rational design a N/P co-doped carbon as sulfur host and functional interlayer for high-performance lithium–sulfur batteries

Despite promising characteristics of high energy density and low material cost, lithium-sulfur (LiS) batteries show practical limitations in poor cycling life and low Coulombic efficiency due to the fatal “shuttle effect” of soluble polysulfides. Here, a dual polysulfide confinement strategy is designed by fabricating an in-situ N/P co-doped carbon, which is originating from versatile silk cocoons through a combined technology of phosphoric acid activation and carbonization and acts as both sulfur host and self-standing interlayer in LiS batteries. The N/P co-doped porous carbon host (NPPC) provides both the physical restriction and chemical adsorption of polysulfides, while the polar interlayer is used as not only an efficient barrier for blocking polysulfides but also a second current collector, which can reuse the sulfur species, enhance the cycling stability and rate capacity. With this rational design, the NPPC/S cathode with the free-standing interlayer exhibits an initial specific capacity of 1412.6 mAh g−1 at 0.1 C, outstanding cycling stability with the ultra-low capacity decay of 0.032% per cycle over 500 cycles at 1.0 C and splendid rate performance with 758.1 mAh g−1 at 2.0 C. Our work provides an eco-friendly and dual employed strategy for boosting the commercialization of LiS batteries.

Electrospun Ti4O7/C conductive nanofibers as interlayer for lithium-sulfur batteries with ultra long cycle life and high-rate capability

In this work, a free-standing and flexible Ti4O7/C nanofibers (TCNFs) interlayer is prepared via one-step electrospinning. The TCNFs interlayer acts as both physical barrier and chemical adsorption agent for lithium polysulfides (LiPSs), in which the 3D CNFs network with large volume and high conductivity contributes to LiPSs conversion and electron transfer, while the ‘sulphiphilic’ Ti4O7 with strong chemical bonding to the soluble long-chain LiPSs contributes to less LiPSs dissolution and higher coulombic efficiency. In a lithium-sulfur (Li-S) cell, CMK3/S cathode with TCNFs interlayer exhibits greatly enhanced electrochemical capability than CMK3/S with CNFs interlayer and without interlayer, and a capacity of 560 mAh g−1 after 1000 cycles is obtained under a high current density of 1 C. Even at 3 C, the capacity decay is merely 0.030% per cycle over 2500 cycles. Notably, the simple, affordable and scalable fabrication method to form a controllable free-standing interlayer that brings a novel horizon on material structure design and performance improvement in practical application of Li-S batteries.

In-situ wrapping of tin oxide nanoparticles by bacterial cellulose derived carbon nanofibers and its application as freestanding interlayer in lithium sulfide based lithium-sulfur batteries

Lithium-Sulfur (Li-S) batteries are mostly known for their high energy density and cost-effectiveness. However, their intrinsic problems hinder their implementation into the marketplace. The most pronounced problems are the parasitic reactions which occur between lithium polysulfides species and lithium metal anode, the volume expansion of sulfur (80%) at the end of discharge and the safety issues which are linked with the use of lithium metal. Herein this work, two approaches are applied to prevent these effects; one approach is the use of Li2S as cathode material, instead of starting from sulfur powder, both to circumvent the volume expansion of sulfur taking place during discharge and to enable lithium-free anodes cell assembling (i.e. Si-Li2S or Sn-Li2S cell configurations). Second approach deals with the lithium anode protection by SnO2 containing freestanding pyrolyzed bacterial cellulose interlayers located between anode and cathode electrodes. Since bacterial celluloses are formed in the presence of SnO2 nanoparticles, the resulting structure enables intimate contact between carbon and SnO2 nanoparticles. By employing Li2S cathode and freestanding interlayer concurrently, 468 mAh g−1 discharge capacity is obtained at C/10 current density over 100 cycles.

High Rate Li-S Batteries: Hollow TiO2 Webbed Carbon Nanotubes with Dual Functional Porous Carbon-Paper

The Li–S batteries are becoming attractive due to the abundance of elemental sulfur and its environmental compatibility. In addition, sulfur undergoes a two-electron redox reaction with lithium and offers an extremely high theoretical specific capacity of 1675 mAh g−1 and a high energy density of 2600 Wh kg−1.1 Despite these advantages, several issues have hampered the practical use of Li–S batteries. For example, the insulating character of sulfur and lithium sulfide impede the full electrochemical utilization of sulfur. Moreover, the dissolution of lithium polysulfide inter-mediates in the electrolyte triggers undesirable shuttle reactions. Other issues such as low Coulombic efficiency, high self-discharge, and huge volume change remain unsolved. To overcome these drawbacks, several mitigation strategies have been explored by various research groups. One of the most followed routes deals with the mixing/impregnation/confinement of sulfur within highly conducting carbons. carbon nanotube-based composites have been used for high sulfur loading amount. Another approach is the use of metal oxides. In particular, TiO2 is a promising host for sulfur containment owing to its high absorption ability2. Further enhancement in the capacity and cycle life of Li–S batteries has been realized by Manthiram’s group by employing a free-standing interlayer (between the sulfur cathode and the separator) that plays the bifunctional role as a trap for mobile polysulfides and as an upper current collector for fast electron transport3.Herein, we synthesized and characterized (i) a S-HMT@CNT sulfur cathode comprised of hollow, spherical, nanostructured TiO2 and carbon nanotubes and (ii) DF-PCW interlayer comprised of highly porous carbon spheres and carbon nanotubes. The pores of TiO2 allowed for high sulfur loadings and accommodation of the volume expansion at the electrode level. The CNT component provided an overlap-ping network that improved both the electronic conductivity and mechanical strength of the S-HMT@CNT and DF-PCW. The pores in the carbon interlayer played the role of a medium that scavenged the dissolved lithium polysulfides, while improving Li-ion and electron transports. Owing to our cathode characteristics and cell design, the lithium–sulfur cell fabricated demonstrated good cycle life, high efficiency, and high rate capability. Of significance, the excellent cycling realized at the 2C and 5C rates is appealing for utilizing the lithium–sulfur batteries in high power applications