High-loading Lithium-sulfur Batteries Research Articles

Vanadium Monoxide-Based Free-Standing Nanofiber Hosts for High-Loading Lithium-Sulfur Batteries

We report the fabrication of free-standing vanadium monoxide-based carbon nanofiber/sulfur (VO-CNFs/S) cathodes via electrospinning and in situ carbothermal reduction reaction followed by sulfur impregnation using an ultrarapid (<90 s) hybrid solution/melt deposition technique. The assembled Li-S batteries using VO-CNFs/S cathodes delivered a stable capacity of 950 mAh·g–1 with 97% retention after 200 cycles at a 0.5 C rate with a moderate electrolyte/sulfur ratio of 20 mL·g–1 of sulfur. Additionally, we develop cathodes with a high sulfur loading of 8.32 mg·cm–2 that exhibits a stable capacity of 900 mAh·g–1 after a few cycles with near 100% retention over 100 cycles. These cells correspond to a stable aerial capacity of 7.5 mAh·cm–2. We integrate our fabrication and electrochemical performance study with fundamental investigations of Li+ diffusion kinetics, in situ visual monitoring of polysulfides, and ex situ post-mortem X-ray photoelectron spectroscopy study to elucidate polysulfide shuttling and polysulfide–host interactions. The unique integration of oxide and nitride groups in this work results in a synergistic effect of strong Lewis acid–base interactions originating from the vacant d-orbitals of the vanadium monoxide phase and improved conductivity originating from the nitrogen doping in CNFs from a polymeric precursor, thus offering active sites for strong polysulfide binding as well as faster reaction kinetics.

P-doped NiSe2 nanorods grown on activated carbon cloths for high-loading lithium-sulfur batteries

Although lithium-sulfur batteries have drawn widespread attentions due to their high energy densities at low costs, the scale-up applications are still hindered by issues such as dissolution of lithium polysulfides (LiPSs) and slow oxidation/reduction kinetics. Herein, we report a novel cathode composite composed of “moss-like” P-doped NiSe2 arrays grown on activated carbon cloth substrates (P-NiSe2/ACC). Experiments and DFT calculations together suggest that P-doping enhances the electron transfers between P-NiSe2 and LiPSs, leading to improved chemical adsorptions and catalytic effects towards the redox conversions of the active sulfur species. This effectively inhibits the shuttling of LiPSs and maximizes the utilization of sulfur towards high specific capacities and stable long-term cycling at high sulfur loadings. The strong interactions and effective catalysis of P-NiSe2 on LiPSs also enables three-dimensional growth of Li2S2/Li2S on the P-NiSe2/ACC cathode, realizing effective accommodation of volume expansions and significant alleviation of cathode passivation. As a result, the P-NiSe2/ACC cathode provides a high specific capacity of 1211 mAh g−1 at 0.2 C and an outstanding high-rate performance of 679 mAh g−1 at 3 C. At the high sulfur loading of 9.9 mg cm−2, an area capacity of 8.42 mAh cm−2 is achieved with stable cycling for 100 charge/discharge cycles.

Mediator–Assisted Catalysis of Polysulfide Conversion for High–Loading Lithium–Sulfur Batteries Operating Under the Lean Electrolyte Condition

The kinetics of S ↔ Li2S conversion in lithium–sulfur (Li–S) batteries can be improved with electrocatalysts to increase the application performance. The effectiveness of electrocatalysis reduces under the lean electrolyte condition due to the preponderance of solid reaction products (sulfur and Li2S) in a small amount of electrolyte; and the difficulty of catalyzing solid sulfur and Li2S. In this report, we describe the development of a mediated catalytic pathway in which a solid cathode catalyst is used alongside a soluble mediator to enable a cooperative catalysis that increases the sulfur utilization from 44% to 61% for high–loading (5.6 mg cm–2) lean–electrolyte (5.0 µL mg–1) Li–S batteries. The improved sulfur utilization is due primarily to the mediator working as a scavenger to capture and reutilize the otherwise “inactive” sulfur species (S/Li2S) in the cathode. Mediated catalysis is therefore a new strategy to noticeably improve polysulfide catalysis and sulfur utilization beyond what is possible with conventional use of catalysts.

Cobalt-embedded hierarchically-porous hollow carbon microspheres as multifunctional confined reactors for high-loading Li-S batteries

Abstract The shuttle effect of dissolved polysulfides migrating to and depositing on anodes often leads to low round-trip efficiency and short cycle life for lithium-sulfur (Li-S) batteries. Herein, we report the rational design of cobalt-embedded nitrogen-doped hollow carbon microspheres (Co@N-HCMSs) as a multifunctional sulfur host for Li-S batteries. The hollow carbon microspheres exhibit large central cavities wrapped by a hierarchically porous shell, showing a large surface area of 1954 m2 g−1. Furthermore, the carbon shells display a unique porous architecture, in which small pores are scattered on the outside and large pores are inside, thereby functioning as a selection barrier to confine polysulfides and diffuse Li+ simultaneously. Moreover, the highly dispersed cobalt nanoparticles in the porous shell activate the surrounding N-doped carbon layer, which not only promote chemical adsorption of polysulfides but also catalyze polysulfide conversion. This facilitation effect has been confirmed by Bader charge and density function theory (DFT) calculations. When applied in Li-S batteries, the sulfur-impregnated Co@N-HCMSs cathode material exhibits excellent electrochemical performances, especially with a high sulfur content of 90.5 wt% and a high areal sulfur loading of 5.1 mg cm−2.

Fast polysulfide catalytic conversion and self-repairing ability for high loading lithium-sulfur batteries using a permselective coating layer modified separator.

Li-S batteries are considered as one of the most promising battery systems because of their large theoretical capacity and high energy density. However, the "shuttle effect" of soluble polysulfides and sluggish electrochemical redox kinetics of Li-S batteries could cause a broken electrode structure and poor electrochemical performance. Herein, a high-performance and stable Li-S battery has been demonstrated by employing organo-polysulfide chain modified acetylene black (ABPS) as the coating layer on the separator. In addition to the traditional advantages of fast electron transport and polysulfide-interception ability of the carbon coating layer, the grafted organo-polysulfide chain endows the ABPS coating layer with permselectivity for lithium ion against polysulfides, electrocatalytic ability for the sluggish redox kinetics and self-repairing ability for the broken electrode. Hence, the battery prepared using an ABPS-coated separator delivers the best cycling performance (970 mA h g-1 at 0.2 C after 100 cycles) and rate performance (805 mA h g-1 at 2 C) as compared to the cells using acetylene black (AB)-coated or Celgard separators. Moreover, the Li-S battery prepared using an ABPS-coated separator exhibits a stable cycling performance at 1 C over 500 cycles with a low degradation of 0.04% per cycle, and a high coulombic efficiency (near 100%). Furthermore, as the sulfur loading was increased to 6.8 mg cm-2, the Li-S battery using the ABPS-coated separator still could deliver a high areal capacity of 6.03 mA h cm-2 with a low electrolyte/sulfur ratio (E/S = 4, μLelectrolyte mgS-1) after 170 cycles. Significantly, ABPS is an effective coating layer material for improving and stabilizing Li-S batteries.

Low tortuosity thick cathode design in high loading lithium sulfur batteries enabled by magnetic hollow carbon fibers

The sluggish kinetic is the key factor to restrain electrochemical performance of high sulfur loading thick electrode. With thickness increase, the high tortuosity and long ion-path way lead to the sluggish kinetic in the electrode. Low tortuosity structure design can facilitate lithium ion (Li+) diffusion and electrolyte percolation into the electrode, which is an appropriate method to improve electrochemical performance. This paper focuses on the construction of low tortuosity electrode design. The hollow carbon micro-fibers of carbonized kapok fibers (CKFs) are decorated by superparamagnetic Co3O4 derived from ZIF-67, which are utilized to provide the vertical channel in the thick electrode. The orientation of CKFs@Co3O4 in the magnetic field provides the directional pathway to improve the kinetics of mass transport in the thick electrode. Compared with the conventional electrode, the low tortuosity electrode shows better electrochemical performance. With sulfur loading of 6 mg cm−2 and around 300 μm thickness, it exhibits the excellent reversible capacity of 866.2 mAh g-1at 0.2C after 100 cycles and delivers a high initial capacity of 479.1 mAh g−1 at 2C. The low tortuosity structure design reported from this paper is effective to relieve the sluggish kinetic of the thick electrode and is potential for practical application.

Renewable Polysulfide Regulation by Versatile Films toward High-Loading Lithium–Sulfur Batteries

The development of a high specific energy lithium-sulfur battery is heavily hindered by the so-called "shuttle effect". Nevertheless, as an effective strategy, most modified separators cannot block and reuse polysulfides simultaneously. Here, a unique and versatile film fabricated by nitrogen and phosphorus co-doped carbon nanofibers uniformly anchored with TiC nanoparticles is incorporated between the separator and cathode of the lithium-sulfur battery. The battery armed with this functional film exhibits a high capacity of 737.1 mA h g-1 at 5 C with a slow capacity-fading rate of 0.06%/cycle over 500 cycles. Even when augmenting the sulfur loading to 17.1 mg cm-2, it can achieve a capacity of 837.3 mA h g-1 with a retention of ∼80% after 50 cycles. The TiC nanoparticles as well as heteroatom doping in the porous carbon nanofiber exhibit strong physiochemical adsorption and catalytic effect, which is proven by experiments and theoretical calculations. Thus, the diffusion of polysulfides can be effectively inhibited. Meanwhile, heteroatom doping can further enhance the conductivity and reaction activity of this film. Hence, the adsorbed polysulfides could be revived and renewed during the subsequent cycling process, which is accurately observed and confirmed by experiments for the first time.

Achieving multiplexed functionality in a hierarchical MXene-based sulfur host for high-rate, high-loading lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries hold their promise in high energy-density, low-cost energy storage. However, the areal sulfur loading and rate performance in most Li-S batteries do not suffice practical applications due to severe polysulfides shuttling and sluggish reaction kinetics. Here, we report a novel sulfur host comprising planted carbon nanotubes with embedded cobalt on a nitrogen doped hollow MXene scaffold. In this hierarchical structure, the macropores in the hollow scaffold facilitate mass transports and accommodate volumetric changes upon electrochemical lithiation/delithiation, while the cobalt, supported by the conductive carbon nanotube, accelerates polysulfides and Li2S conversion kinetics. At last, the nitrogen dopants enhance the chemisorption of sulfur species on MXene. The above multiplexed functionality enables 840 stable cycles with high capacity 900 mAh g−1 at 2.5 mg cm−2 S-loading and 1C. Even at a sulfur loading of 6 mg cm−2, we can still achieve 170 cycles with a capacity retention 85.8%.

Promoted Deposition of Three-Dimensional Li2S on Catalytic Co Phthalocyanine Nanorods for Stable High-Loading Lithium-Sulfur Batteries.

The sulfur redox in Li-S batteries involves a complex sequence of solid-liquid-solid conversions, and reaction catalysis has recently become a focused area for further advancement. The deposition of solid Li2S from liquid Li2S4 contributes to three-quarters of the total theoretical capacity and is therefore of great significance over the entire cathode reaction. This study demonstrates a cathode material composed of carbon nanofibers decorated with catalytic Co phthalocyanine nanorods (CoPc@CNF), which are highly effective in promoting the deposition of Li2S in three-dimensional (3D) fine particles rather than 2D thin films. This significantly alleviates cathode passivation during cell charge and discharge, leading to obviously improved sulfur utilization and cycling stability for high loading cathodes. DFT calculations indicate that the promoted 3D deposition of Li2S is related to the facilitated migration of deposition precursors (Li2S4 and Li-ions) to migrate on the CoPc nanorods. Lithium-sulfur (Li-S) pouch cells were prepared with high specific (954 mAh g-1), areal (4.8 mAh cm-2), and total (235 mAh) capacities achieved at 0.5 C under high sulfur content. As metal phthalocyanines possess a high structural variability, this study provides opportunities to the design of a new class of Li-S cathode materials.

Integrated 3D electrodes based on metal-nitrogen-doped graphitic ordered mesoporous carbon and carbon paper for high-loading lithium-sulfur batteries

Abstract The overall performances of (Li–S) lithium-sulfur batteries are highly dependent on the structure and surface feature of carbon scaffolds as well as the architecture of sulfur cathodes. Herein, a series of semi-graphitic ordered mesoporous carbons with metal/nitrogen doping (Me–N-GOMCs; Me = Fe, Co, Ni, and Cu) are designed as sulfur hosts with abundant porosity and high electrical conductivity. It is revealed that the carbon capability of anchoring polysulfides can be remarkably enhanced through the synergistic effect of Fe and N doping. Moreover, by implanting the Fe–N-GOMC/S composite within the void space of carbon papers (CPs), free-standing integrated sulfur cathodes with the architecture of a continuous conductive 3D network are constructed. The robust ion/electron transport and redox kinetics enable Li–S batteries with excellent sulfur utilization at high loading. The as-acquired CP/Fe–N-GOMC/S electrode with a sulfur loading of ~3 mg cm−2 exhibits a high initial capacity of 1473 mA h g−1 and superior cycle stability with a capacity fading as low as 0.075% per cycle over 500 cycles at 0.5C. Even at a sulfur loading up to ~6 mg cm−2, the electrode still achieves a steady areal capacity (~5 mA h cm−2) for over 120 cycles at 1C.

Built-In Catalysis in Confined Nanoreactors for High-Loading Li-S Batteries.

A cathode host with strong sulfur/polysulfide confinement and fast redox kinetics is a challenging demand for high-loading lithium-sulfur batteries. Recently, porous carbon hosts derived from metal-organic frameworks (MOFs) have attracted wide attention due to their unique spatial structure and customizable reaction sites. However, the loading and rate performance of Li-S cells are still restricted by the disordered pore distribution and surface catalysis in these hosts. Here, we propose a concept of built-in catalysis to accelerate lithium polysulfide (LiPSs) conversion in confined nanoreactors, i.e., laterally stacked ordered crevice pores encompassed by MoS2-decorated carbon thin layers. The functions of S-fixability and LiPS catalysis in these mesoporous cavity reactors benefit from the 2D interface contact between ultrathin catalytic MoS2 and conductive C pyrolyzed from Al-MOF. The integrated function of adsorption-catalysis-conversion endows the sulfur-infused C@MoS2 electrode with a high initial capacity of 1240 mAh g-1 at 0.2 C, long life cycle stability of at least 1000 cycles at 2 C, and high rate endurance up to 20 C. This electrode also exhibits commercial potential in view of considerable capacity release and reversibility under high sulfur loading (6 mg cm-2 and ∼80 wt %) and lean electrolyte (E/S ratio of 5 μL mg-1). This study provides a promising design solution of a catalysis-conduction 2D interface in a 3D skeleton for high-loading Li-S batteries.

Highly integrated sulfur cathodes with strong sulfur/high-strength binder interactions enabling durable high-loading lithium–sulfur batteries

Abstract The development of high-sulfur-loading Li–S batteries is a key prerequisite for their commercial applications. This requires to surmount the huge polarization, severe polysulfide shuttling and drastic volume change caused by electrode thickening. High-strength polar binders are ideal for constructing robust and long-life high-loading sulfur cathodes but show very weak interfacial interaction with non-polar sulfur materials. To address this issue, this work devises a highly integrated sulfur@polydopamine/high-strength binder composite cathodes, targeting long-lasting and high-sulfur-loading Li–S batteries. The super-adhesion polydopamine (PD) can form a uniform nano-coating over the graphene/sulfur (G–S) surface and provide strong affinity to the cross-linked polyacrylamide (c-PAM) binder, thus tightly integrating sulfur with the binder network and greatly boosting the overall mechanical strength/conductivity of the electrode. Moreover, the PD coating and c-PAM binder rich in polar groups can form two effective blockades against the effusion of soluble polysulfides. As such, the 4.5 mg cm−2 sulfur-loaded G–S@PD-c-PAM cathode achieves a capacity of 480 mAh g−1 after 300 cycles at 1 C, while maintaining a capacity of 396 mAh g−1 after 50 cycles at 0.2 C when the sulfur loading rises to 9.1 mg cm−2. This work provides a system-wide concept for constructing high-loading sulfur cathodes through integrated structural design.

Propelling polysulfide conversion for high-loading lithium–sulfur batteries through highly sulfiphilic NiCo2S4 nanotubes

Li–S batteries have received unprecedented attention owing to their exceptionally high energy density and low cost. Nevertheless, the daunting challenges of insulating properties, soluble polysulfide shuttling, drastic volume change and sluggish polysulfide conversion kinetics, still hinder their application towards commercialization. Very recently, exciting progresses have been made on inorganic/organic polar hosts as either polysulfide immobilizers or polysulfide redox accelerators, targeting durable Li–S batteries. Herein, self-assembled NiCo2S4 granules comprising secondary open-hole tubular structures are first devised as highly-efficient host materials for high-sulfur-loading and durable Li–S batteries. NiCo2S4 hosts are featured with their large porosity, high electronic conductivity, rapid ion conduction, strong polysulfide immobilization capability and catalytic effect on polysulfide redox, thus greatly ameliorating the polysulfide-shuttle issue and accelerating the polysulfide conversion kinetics. Therefore, the NiCo2S4/S cathode shows a reversible capacity of 1387 ​mAh g−1 at 0.2C and retains a value of 543 ​mAh g−1 after 500 cycles at 2 ​C. Impressively, the NiCo2S4/S cathode with a sulfur loading of 8.9 ​mg ​cm−2 exhibits high areal capacity of 8.3 ​mAh cm−2, low polarization and high cycling stability. Moreover, the as-derived soft-package battery with a 4.5 ​mg ​cm−2 sulfur loading can power 169 light-emitting diodes, verifying its great potential for practical application.

A reinforced-concrete-like ultrathick cathode supported by carbonization kapok fibers for high loading lithium sulfur batteries

It’s a focus on high sulfur loading electrode for lithium sulfur batteries (LSBs) to improve the practical energy density. Blade casting method is an ideal method due to its efficiency and convenience that means thick electrode was utilized to increase sulfur loading. However, the weak strength and sluggish kinetics hinder to improve the practical energy density. To overcome issues, carbonization kapok fibers (CKFs) were overlapped to form the percolation network like rebar in the reinforced concrete. The cathode (sulfur loading: 8.22 mg cm−2) exhibits the superior initial capacity (1090mAhg−1 at 0.1C) and cycling performance (728mAhg−1 after 80 cycles).

Free-standing ZIF-8 derived nitrogen and sulfur co-doped porous carbon nanofibers host for high mass loading lithium-sulfur battery

Lithium–sulfur batteries are promising next-generation energy storage device, but polysulfide shuttling which results in the capacity decay, still remains a great challenge. In this work, we proposed a sulfur and nitrogen co-doped strategy to increase interaction between the lithium sulfides and host. Herein, free-standing S and N dually doped porous carbon nanofibers (donated as SN-PCNF) are prepared and serve as efficient sulfur host materials. Benefitting from the S and N co-doped strategy, the chemical adsorption of lithium polysulfides increases, thus the free-standing SN-PCNF@S cathode delivers an initial discharge capacity of 1133 mA h·g−1 with 80% sulfur loading. Furthermore, the DFT calculations reveals the stronger polysulfide binding with nitrogen and sulfur co-doped carbons than that with nodoped or nitrogen single-doped carbons.

A “boxes in fibers” strategy to construct a necklace-like conductive network for high-rate and high-loading lithium–sulfur batteries

Following a “boxes in fibers” strategy, a 3D conductive network is constructed by necklace-like N-doped carbon nanofibers with carbon nanoboxes and TiC as an efficient sulfur host, showing excellent performance even under high-rate and high-loading.

Boosting the anchoring and catalytic capability of MoS2 for high-loading lithium sulfur batteries

The limit of polysulfides anchoring and the catalytic capability of MoS2 is approached by the design of 1T MoS2 nanodots.

Graphene quantum dots as the nucleation sites and interfacial regulator to suppress lithium dendrites for high-loading lithium-sulfur battery

Lithium–sulfur battery is one of the most promising candidates to take over from the conventional lithium-ion batteries for the next-generation high energy storage devices. Although plausible advances have been made on the performances of the composite cathode with high sulfur loading, the development of compatible protection strategies for lithium anode is seriously lagging behind. Here we report a new strategy to suppress the dendrite growth in lithium-sulfur batteries with high sulfur loading by introducing graphene quantum dots into the electrolyte. The graphene quantum dots serve as the heterogeneous sites for uniform nucleation and provide continual regulation for the dendrite-free lithium deposition. The in-situ Raman spectroscopy reveals the enrichment of the GQDs at the electrode-electrolyte interface for the regulated electric field and ion flux, resulting in the dendrite-free Li deposition. As a result, the critical current of short circuit induced by lithium dendrite increases up to 7.44 mA cm−2, and the soft-short risk is excluded when cycling at the current density of 3 mA cm−2 with areal capacity of 3 mAh cm−2 for more than 500 h, demonstrating the excellent dendrite suppressing action of the GQDs. As a proof of concept, high-loading lithium-sulfur batteries using the GQDs-modified anolyte are fabricated with stable Coulombic efficiency of 99% at the current density of 3 mA cm−2 with sulfur loading of 4 mg cm−2 over 200 cycles. Our results provide a novel and facile approach to tackle the intrinsic problem on the lithium anode for high-loading lithium-sulfur batteries.

Chemical-dealloying to fabricate nonconductive interlayers for high-loading lithium sulfur batteries

Lithium sulfur batteries have been recognized as a promising on-board energy-storage technology. One of the challenges in this system is the efficient inhibition of polysulfides shuttle with the low-cost sulfur hosts. In this work, we report the fabrication of nanoporous CeO2 and TiO2 by a novel chemical dealloying approach as a thin nonconductive interlayer to confine polysulfides in the cathodes. The abundant pores provide channels for the transportation of electrolyte, whereas the dissolved polysulfide species are chemically interacted with the metal oxides. Between the two interlayers, CeO2 demonstrates superior performance over TiO2, which is attributed to the appropriate redox window of the Ce3+/Ce4+ couple to in-situ catalyse the polysulfides. The cells with such a configuration exhibit significantly enhanced capacities and long-term stability. Even at a high sulfur loading of 6 mg cm−2, it is demonstrated stable capacities of ∼600 mAh g−1 over 120 cycles. These results suggest chemical dealloying is an efficient approach to prepare desired nanoporous interlayers to achieve practical cycling performance with a commercial sulfur host.

N/O dual-doped hollow carbon microspheres constructed by holey nanosheet shells as large-grain cathode host for high loading Li-S batteries

Lithium-sulfur (Li-S) battery is one of the most prospective energy storage systems beyond lithium ion battery technologies owing to its super-high theoretical energy density and low cost. However, the dissolution of polysulfide intermediates and low level of sulfur loading still retard the practical application of Li-S batteries. Here, a self-sacrifice templating strategy is reported to synthesize N/O dual-doped hollow carbon microspheres (HCMs) by carbonization of polydopamine coating carbon nitride hollow spheres. The HCM host is constructed by holey nanosheets in shell with a large surface area (873 m2/g) and pore volume (4.84 cm3/g), high N/O doping contents (5.36 and 6.99 atom%). Benefiting from the confinement effect, wetting capability, lithiophilic adsorption and catalytic conversion, HCMs-S cathode enables a reversible capacity around 900 mAh/g at 1–2 C and a retention capacity of 530 mAh/g after 900 cycles. HCMs-S also enables an endurance of high mass and areal S loadings (90% and 4.84 mg/cm2) with a reversible capacity around 700 mAh/g. Long-term and high-rate cycling does not degrade the homogeneous deposition of nanostructured Li2S at cathode side and dendrite-free Li plating at anode side. This work demonstrates a facile approach to micro-sized C-S grains with desirable three-dimensional architecture composed of two-dimensional building blocks and interconnected mass/charge transport channels for high loading Li-S batteries.