Commercial Separator Research Articles

Two-dimensional nanofluidic suppressing anion mobility toward dendrite-free lithium metal anode

Modification of separator with lithium-ion redistributor has been considered to be an effective strategy to evade lithium dendrite by evening lithium-ion concentration on electrode surface. According to the Sand equation, the mobility of anion is also critical to realizing smooth lithium deposition. Herein, a fast cation conductor layer was constructed by assembling exfoliated vermiculite sheets on commercial separator to form vermiculite composite separator (VCS). The negative surface charged 2D nanofluidic channels in VCS repel anions, blocking the shuttle of anions between electrodes. Nevertheless, lithium ions are attracted, and mobility is dramatically enhanced, which increases the lithium-ion transference numbers (tLi+) and intrinsically improves the electrochemical performance. Resultantly, the Coulombic efficiency of Cu//Li battery with VCS is more than 96%, and the voltage polarization of symmetric battery is only a quarter of the commercial separator even at a high current density of 5 mA/cm2. Furthermore, the inorganic nature of the vermiculite sheet endows the VCS with excellent thermal stability. The superior electrochemical performance of VCS highlights the importance of constructing 2D nanofluidic channels and provides new avenues for the development of high-performance and long-lifespan lithium metal batteries.

Layer-by-Layer Assembly of CeO2-x@C-rGO Nanocomposites and CNTs as a Multifunctional Separator Coating for Highly Stable Lithium-Sulfur Batteries.

Commercialization of high-energy Li-S batteries is greatly restricted by their unsatisfactory cycle retention and poor cycling life originated from the notorious "shuttling effect" of lithium polysulfides. Modification of a commercial separator with a functional coating layer is a facile and efficient strategy beyond nanostructured composite cathodes for suppressing polysulfide shuttling. Herein, a multilayered functional CeO2-x@C-rGO/CNT separator was successfully achieved by alternately depositing conductive carbon nanotubes (CNTs) and synthetic CeO2-x@C-rGO onto the surface of the commercial separator. The cooperation of multiple components including Ce-MOF-derived CeO2-x@C, rGO, and CNTs enables the as-built CeO2-x@C-rGO/CNT separator to perform multifunctions from the separator surface: (i) to hinder the diffusion of polysulfide species through physical blocking or chemical adsorption, (ii) to accelerate the sluggish redox reactions of sulfur species, and (iii) to enhance the conductivity for sulfur re-activation and efficient utilization. Serving as a multilayer and powerful barrier, the CeO2-x@C-rGO/CNT separator greatly constrains and reutilizes the polysulfide species. Thus, the Li-S battery assembled with the CeO2-x@C-rGO/CNT separator demonstrates an excellent combination of capacity, rate capability, and cycling performances (an initial capacity of 1107 mA h g-1 with a low decay rate of 0.060% per cycle over 500 cycles at 1 C, 651 mA h g-1 at 5 C) together with remarkably mitigated self-discharge and anode corrosion. This work provides guidelines for functional separator design as well as rare-earth material applications for Li-S batteries and other energy storage systems.

A newly-developed heat-resistance polyimide microsphere coating to enhance the thermal stability of commercial polyolefin separators for advanced lithium-ion battery

Polymer separators with high-temp dimensional stability is strongly demanded for high-safety lithium-ion batteries (LIBs). In this study, a novel polyimide (PI) microsphere coating slurry was prepared and then plated on Celgard polypropylene (PP) separator, producing PP@PI microsphere composite separator with excellent thermal stability, flame retardancy, high liquid retention capacity and high ionic conductivity by a simple blade-coating process. The results show that the thermal stability and liquid retention capacity of the PP@PI microsphere composite separator are significantly improved. Compared with the pure commercial PP separator which sharply shrank at 150 °C, the PI microsphere composite separator shows negligible shrinkage over 150 °C. The obtained PP@PI microsphere composite separators exhibited excellent thermal stability and fire-resistance properties. At the same time, the peel strength of composite separator reached 138.6 N·m−1, with excellent adhesion. The surface density of PP@PI microsphere composite separator is 16.62 g·m−2, which is lower than 30.22 g·m−2 of ceramic coated composite separator. Electrochemical characterizations indicate that the discharge capacity and capacity retention rate of the battery assembled with PP@PI microsphere composite separator are significantly higher than those assembled with the pure PP separator. The half-cell assembled with this composite separator shows a high capacity of 144.3 mAh·g−1 at 5C, which is much higher than the 117.8 mAh·g−1 of the commercial PP separator equipped battery. Moreover, the lithium-ion batteries assembled with the PP@PI microsphere composite separator show excellent cycle stability after 200 cycles at 1C. More importantly, the lithium-ion battery assembled with PP@PI microsphere composite separator has excellent safety at high temperature. These features demonstrate the potential of PP@PI microspheres composite membrane as high-security separator for LIBs.

LiF-rich and self-repairing interface induced by MgF2 engineered separator enables dendrite-free lithium metal batteries

Lithium metal batteries (LMBs) are promising for high-energy density rechargeable batteries while suffer from uncontrolled dendrites growth and unstable solid electrolyte interface (SEI) layer on the surface of lithium (Li) metal anodes. In this study, a facile and low-cost strategy is proposed to enable dendrite-free and long-life LMBs by coating MgF2 onto commercial polyethylene separator. The composite separator possesses excellent wettability and high thermal stability. When the MgF2 coating contacts Li metal anode directly, an artificial SEI layer is in-situ formed due to the spontaneously reaction of MgF2 and Li metal, which is composed of LiF and lithiophilic Mg. More importantly, a small amount of dissolved MgF2 can fill the micro-gaps between un-contact MgF2 coating and Li anode and repair the tiny cracks in the SEI generated during repeated charge–discharge process. Hence, a continuous SEI layer is formed throughout the entire surface of Li metal anode with lithiophilic, LiF-rich and self-repairing capabilities, protecting Li metal anode, reducing the nucleation overpotential, promoting smooth Li plating and inhibiting Li dendrites growth. The Li||Li symmetric cells, Cu||Li asymmetric cells and full cells with the MgF2 coated separators delivers significantly enhanced coulombic efficiency and cycle life in both ether-based and carbonate-based electrolyte. This design of artificial LiF-rich SEI with self-repairing capability by separator engineering paves a new insight for the application of alkali metal batteries.

Mechanically robust, nonflammable and surface cross-linking composite membranes with high wettability for dendrite-proof and high-safety lithium-ion batteries

The separator plays a pivotal role to guarantee the safety and improve the electrochemical properties of lithium batteries. However, poor thermal stability and nonpolar surface of commercial polyolefin separator seriously restricted the development of the high-performance lithium battery. A "hydrophilic and cross-linking" strategy is proposed here to modify and enhance porous flame retardant poly(arylene ether nitrile) (PEN) polymer membrane to obtain high safety and heat resistant lithium batteries. The resultant PEN@PDA-PEI composite separator exhibits three-dimensional porous structure, superior thermal stability (no shrinkage up to 200 °C). Furthermore, the abundant polar groups (cyano group, amino group, hydroxyl group, etc.) from the composite membrane endow it with super electrolyte affinity (the contact angle is 0°) and the highly enhanced electrolyte uptake (from 400% to 618%). It is worth noting that the introduction of the PDA-PEI cross-linked structure on the surface of PEN membranes significantly improves the mechanical properties of PEN porous membrane. The composite membrane presents good lithium metal interface compatibility and high ionic conductivity (1.5 mS cm −1 ). As expected, the LiFePO 4 /Li battery based on PEN@PDA-PEI separator displays better rate and cycle performance than that of commercial polyolefin separator at elevated temperature. Significantly, the surface high-polarity and uniform pore structure of composite separators prevent the growth of lithium dendrite in cycle term, resulting an interesting 3D spherical morphology on Li metal anode. This work provides a new strategy for the preparation of high-performance and high-safety lithium-ion battery separator, it also paves a facile surface crosslinking strategy reinforce the mechanical strength of various porous membranes. • PDA-PEI crosslinking structure is used to modify the flame retardant PEN membrane for Li metal batteries. • Crosslinking structure with abundant polar groups improves the electrolyte affinity and mechanical strength of PEN separator. • The PEN@PDA-PEI separator shows good thermal and shrinkage stability at 200 °C. • Li ion distribution can be well regulated due to the uniform pore structures and the polar groups on PEN@PDA-PEI. • Batteries with PEN@PDA-PEI separator maintains stable cycling performance at high temperature.

Statistical investigation of pivotal physical and chemical factors on the performance of ceramic-based microbial fuel cells

Abstract The performance of four different commercial ceramic separators is inspected using response surface methodology (RSM). The thickness (A), porosity (B), SiO2 (C), and Al2O3 (D) contents of ceramics are statistically significant (P-value<0.05) for both responses of the maximum power density (MPD) and the coulombic efficiency (CE). The interactions of AB and AC have significant influences on the MPD. For highly porous ceramics, including the unglazed wall ceramic (MFC-UGWC, 30.45% porosity) and Yellow ceramic (MFC-Y, 28.9% porosity), the MPD and CE are boosted by raising the thickness of membranes. The MPD and CE values have been enhanced from 225.07 to 321.11 mW/m2 and from 51 to 68%, respectively, by thickening the UGWC from 3 to 9 mm. Similarly, the power performance and CE of the MFC-Y have been grown by 32% and 148.6%, respectively. However, both the MPD and CE responses have been reduced from 106.89 to 57.65 mW/m2 and from 29 to 18.3% for the denser unglazed floor ceramic (UGFC, 11% porosity) as a consequence of thickness increment from 3 to 6 mm. Furthermore, the chemical composition of ceramics has a crucial impact on the overall performance. Richer ceramics in SiO2 are utilized, the higher performance is achieved.

Advanced separators for lithium-ion batteries

The separator technology is a major area of interest in lithium-ion batteries (LIBs) for high-energy and high-power applications such as portable electronics, electric vehicles and energy storage for power grids. Separators play an essential part that physically prevents direct contact between positive and negative electrodes while acting as an electrolyte reservoir to transport lithium ions. The characteristics of different separators would directly affect the performance under cell abuse; hence separators are crucial for battery safety. This paper introduces the characteristics of separators, means to improve traditional commercial polymeric separators and novel materials for separators. Other novel high-performance separators are also briefly discussed in this paper. Insights from this paper illustrate that various strategies could enhance the performance of separators, and better performance and safety can be achieved in separators in high-energy lithium-ion batteries.

An ion sieving conjugated microporous thermoset ultrathin membrane for high-performance Li-S battery

Lithium-sulfur (Li-S) battery is an attractive candidate for next-generation energy storage devices due to its high theoretical energy density, but its practical applications are hindered by polysulfides shuttling and lithium dendrite growth. In this study, a solution-processable conjugated microporous thermoset (CMT) was used as an ultrathin ion sieving layer on a commercial PP separator. The CMT layer is as thin as ∼200 nm and possesses continuous sub-nanochannels. Molecular dynamic simulations show that the nanoporous polymeric network allows Li-ion passage while blocking polysulfides shuttling between the electrodes based on size-exclusive effects. In addition, the CMT layer acts as a buffer zone for the uniform distribution of Li ions on the surface of the Li anode to suppress the growth of lithium dendrites. As a result, Li-S battery employing the CMT-modified polypropylene separator achieves a high initial capacity of 849.6 mAh g−1 with an ultralow attenuation rate of 0.037% per cycle over 1000 cycles at 1 C, as well as a capacity of 619.0 mAh g−1 at an ultrahigh current density of 10 C. Remarkably, it exhibits a capacity of 727.8 mAh g−1 with ∼ 77% capacity retention over 500 cycles lifespan at a high current density of 5C, showing great potential for practical high-performance Li-S batteries.

Bi-functional Janus all-nanomat separators for acid scavenging and manganese ions trapping in LiMn2O4 lithium-ion batteries

LiMn2O4-based lithium-ion batteries (LIBs) have attracted considerable attention due to their cost advantage, but industrial use has been hindered by severe capacity deterioration during cycling with LiPF6-based carbonate electrolytes, especially under high-temperature (55 °C) cycling conditions. Herein, a bifunctional, Janus-faced, inorganic-organic hybrid separator is demonstrated to ensure long-term cycling reversibility of LiMn2O4||graphite LIBs. The monolithic all-nanomat separator is constructed by a bottom layer of poly (m-phenylene isophthalamide) nanofibers by electrospinning and a top layer of interpenetrating hydroxyapatite/bacterial cellulose fibers. Benefiting from such a unique Janus configuration, the as-formed separator exhibits synergistic coupling in functions, simultaneously scavenging trace acid and mitigating the dissolution/deposition of Mn2+ ions in batteries. Consequently, the cells with the Janus separator achieve enhanced capacity retention compared with traditional cells with the commercial polyolefin separator over 100 cycles at 55 °C. Furthermore, bulk structure and surface chemistry characterizations confirm that irreversible structural change in the LiMn2O4 cathode could be avoided, and the amount of manganese on the graphite anode from the cycled cells with the Janus separator is suppressed. This work demonstrates that a composite Janus all-nanomat separator offers an unexpected route towards highly durable LiMn2O4-based LIBs.

Regulating Li-ion flux distribution via holey graphene oxide functionalized separator for dendrite-inhibited lithium metal battery

The lithium dendrites growth limits the large-scale application of lithium metal batteries (LMBs). Regulating Li+ flux distribution is an effective method to restrain the Li dendrite growth. In this paper, a functional porous composite separator is prepared by simply vacuum filtrating holey graphene oxide onto electrospun polyacrylonitrile (HGO-PAN) fiber membranes. The pores in the basal plane of HGO and nanofluidic channels stacked by the ultra-thin HGO can create more paths for the electrolyte to penetrate, thus improving the ionic conductivity and regulating the uniform Li+ flux distribution during charge and discharge. These advantages enable HGO-PAN separator based Li/LiFePO4 cell to maintain a discharge capacity of 135.7 mAh g−1 at 2 C after 900 cycles, which is 22.3% higher than that of commercial separator based cell. Meanwhile, the long-term reversible lithium plating/stripping performance (over 800 h) under current density of 1 mA cm−2 also shows that the lithium dendrites growth is effectively inhibited. We believe that this study offers a promising strategy to inhibit the lithium dendrite growth by separator modification, developing stable, safe and sustainable LMBs.

A porous, mechanically strong and thermally stable zeolitic imidazolate framework-8@bacterial cellulose/aramid nanofibers composite separator for advanced lithium-ion batteries

Currently, the commercial polyolefin-based separators suffer from inferior electrolyte wettability and poor thermal resistance, leading to unsatisfied electrochemical performance and severe safety hazards for lithium-ion batteries (LIBs). Herein, a high-performance composite membrane composed of zeolitic imidazolate framework-8@bacterial cellulose (ZIF-8@BC) matrix and aramid nanofibers (ANFs) filler was developed as the LIB separator via the facile in-situ synthesis and subsequent filtration process. The as-prepared ZIF-8@BC/30%ANFs composite separator (with 30 wt% of ANFs) showed high tensile strength (70.7 MPa), outstanding thermal resistance and flame retardancy, which significantly enhanced the safety of LIBs during operation. Moreover, due to the well-developed porous structure and exceptional electrolyte affinity, the ZIF-8@BC/30%ANFs composite separator exhibited good electrolyte wettability and high electrolyte uptake (267.8%), which brought about superior ionic conductivity (1.60 mS cm−1) compared to commercial polypropylene separator. These synergistic advantages eventually endowed the battery with excellent rate capability and cycling performance. Accordingly, the ZIF-8@BC/30%ANFs composite separator is a promising candidate for next-generation LIBs with both high safety and enhanced performance.

Multimodal Capturing of Polysulfides by Phosphorus-Doped Carbon Composites for Flexible High-Energy-Density Lithium-Sulfur Batteries.

The widespread adoption of Li-ion batteries is currently limited by their unstable electrochemical performance and high flammability under mechanical deformation conditions and a relatively low energy density. Herein, high-energy-density lithium-sulfur (Li-S) batteries are developed for applications in next-generation flexible electronics and electric vehicles with long cruising distances. Freestanding high-S-loading carbon nanotubes cathodes are assembled with a phosphorus (P)-doped carbon interlayer coated on commercial separators. Strategies for the active materials and structural design of both the electrodes and separators are highly efficient for immobilizing the lithium polysulfides via multimodal capturing effects; they significantly improve the electrochemical performance in terms of the redox kinetics and cycling stability. The foldable Li-S cells show stable specific capacities of 850 mAh g-1 over 100 cycles, achieving high gravimetric and volumetric energy densities of 387Wh kgcell -1 and 395Wh Lcell -1 , respectively. The Li-S cells show highly durable mechanical flexibilities under severe deformation conditions without short circuit or failure. Finally, the Li-S battery is explored as a light-weight and flexible energy storage device aboard airplane drones to ensure at least fivefold longer flight times than traditional Li-ion batteries. Nanocarbon-based S cathodes and P-doped carbon interlayers offer a promising solution for commercializing rechargeable Li-S batteries.

A flame-retardant, high ionic-conductivity and eco-friendly separator prepared by papermaking method for high-performance and superior safety lithium-ion batteries

The separator plays a significant role in influencing electrochemical performances and monitoring battery safety in lithium-ion batteries. Nevertheless, suffered by commercial polyolefin separator intrinsic drawbacks of intolerable electrolyte affinity, low ionic conductivity, poor thermal stability and terrible flammability with large thermal contribution, to develop an advanced separator that meet the above requirements is imminent. In this work, an environmentally friendly bacterial cellulose and attapulgite composite separator (BA@ATP) with low cost, high ionic conductivity and excellent flame retardant performance is designed by papermaking method. With strong adsorption energy with electrolyte, the BA@ATP separator exhibits extremely high electrolyte uptake and ionic conductivity, giving rise to an enhanced specific discharge capacity with higher capacity retention and an excellent rate capability with low voltage polarization at high current density. In addition, the advanced separator displays self-extinguishing characteristic after ignition, and extremely low heat and flue gas contribution can be obtained in the combustion state, indicating promoted battery safety. After being assembled into the pouch cell, the cell with BA@ATP separator exhibits a higher self-heating temperature and lower heat release rate (HRR) and total heat release (THR) values when burning. Overall, the advanced separator has great potential to replace the polyolefin separator for attaining high performance safety batteries.

Ultra-robust polyimide nanofiber separators with shutdown function for advanced lithium-ion batteries

Safety issues have significantly impeded the development of modern lithium-ion batteries (LIBs), and fabricating advanced separators has been considered as a feasible solution to improve the security of LIBs. Here, we present an advanced polyimide (PI) nanofiber membrane (referred to as PIE) with ultrahigh strength and the shutdown function by optimizing precursor viscosity and nanofibers microstructure. Increasing chain length of the PI backbone and in -situ bonding technique can markedly promote mechanical properties of PI nanofiber separator (strength of pristine PI nonwoven >60 MPa, strength of modified PI nonwoven >90 MPa), which is a new record so far among current PI nanofiber membranes. The present PIE separator displayed superior wettability, heat-resistant, and ion conductivity compared to the commercial Celgard separator. Importantly, the excellent flame resistance and high-temperature shutdown function of PIE separators ensure the security of LIBs. Based on our rational separator design, the PIE separators possessed higher LIB capability (111.3 mAh g −1 at 10 C) than the Celgard separator (90.8 mAh g −1 at 10 C). Moreover, the PIE separator-based LIBs can run stably at 1 C and 5 C for 100 cycles. The present work demonstrated the likelihood of replacing the commercial polyolefin separator with the advanced PI nanofiber membranes. • Advanced PIE separators are prepared by increasing chain length of PI backbone and using in -situ bonding technique. • The strength of as-fabricated PI separators present a highest record so far (pristine PI nonwoven >60 MPa, modified PI nonwoven >90 MPa). • The excellent thermostability, flame resistance, and shutdown function can ensure the safety of LIBs. • PIE separators exhibit superior LIB capability and cycling stability.

Synergistic Adsorption-Electrocatalysis of 2D/2D heterostructure toward high performance Li-S batteries

The shuttle effect of polysulfides and sluggish reaction kinetics have become current major obstacles for the development of lithium-sulfur (Li-S) batteries. Herein, a novel 2D/2D heterostructure, consisting of ultrathin Ni-Co MOFs with rich unsaturated metal sites and conductive Ti3C2Tx nanosheets (Ti3C2Tx/Ni-Co MOF), is developed as a multifunctional barrier coated on commercial separators for Li-S batteries. Based on the synergistic adsorption-electrocatalysis, the modified separators not only suppress the dissolution of polysulfides and promote their conversion effectively, but also accelerate the electron/ion transfer. Moreover, density functional theory results further confirm that the heterostructure has strong adsorption energy for polysulfides and low energy barriers for their conversion. Li-S batteries with the Ti3C2Tx/Ni-Co MOF heterostructure modified separators exhibit an excellent reversible capacity of 1260 mAh g−1 at 0.2C and a remarkable cycling stability with capacity retention of 91.1 % at 0.5C after 350 cycles. When equipped with high sulfur loading of 5.8 mg cm−2 and low electrolyte/sulfur ratio of 4 uL mg−1, the cell maintains a superior capacity. This work provides a new route to the design of modified separators for high performance Li-S batteries with especially remarkable cycling stability.

Zn2+–Modulated bimetallic carbides synergized with macro-mesoporous N-rich carbon enabling accelerated polysulfides conversion for high-performance Li-S batteries

• Zn 2+ modulated Co 3 ZnC-based catalysts are constructed via a one-pot approach. • Zn 2+ could regulate the valence states of the cobalt active sites. • Co 3 ZnC@NC interlayer can promote the adsorption and redox kinetic of polysulfides. • Co 3 ZnC@NC contributes to superb cycling capacities and high-rate performance. Metal cations could serve as the active sites to adsorb lithium polysulfides (LiPSs) and catalyze the associated multi-electrons redox reactions. Valence modulating/engineering of the metal active centers is an underlying tactic to expedite the sluggish kinetics of LiPSs for high performance lithium-sulfur (Li-S) batteries. Herein, we craft Zn 2+ -modulated bimetallic carbides electrocatalyst of Co 3 ZnC-embedded carbon submicrospheres anchoring on 3D macro-mesoporous N-doped carbon (denoted as Co 3 ZnC@NC) via a facile one-pot synthesis that employs dicyandiamide as the carbon/nitrogen precursor. Results demonstrate that the balance of the predominantly active Co 2+ /Co 0 pair can be effectively modulated by the incorporated zinc cations, which leads to inhibited shuttle effect and accelerates the catalytic conversion kinetics of LiPS intermediates. When acted as the interlayer to modify commercial separator, Co 3 ZnC@NC confers the superb cycling stability on corresponding Li-S batteries with high discharge capacities and exceptionally high-rate performance, owing to the well-defined surface structure and the increased Co 2+ active sites of Co 3 ZnC@NC. Even the sulfur loading is kept at 4 mg cm −2 , the battery achieves an areal capacity of 3.22 mAh cm −2 after 50 cycles. This work unveils the potential of cation modulated bimetal-based electrocatalysts and also inspires an alternative avenue to exploit surface-mediated redox electrocatalysts for high-performance Li-S batteries.

Robust Room‐Temperature Sodium‐Sulfur Batteries Enabled by a Sandwich‐Structured MXene@C/Polyolefin/MXene@C Dual‐functional Separator

Room-temperature sodium-sulfur (RT-Na-S) batteries are attracting increased attention due to their high theoretical energy density and low-cost. However, the traditional RT-Na-S batteries assembled with glass fiber (GF) separators are still hindered by the polysulfide shuttle effect and sodium dendrite growth, limiting the battery's capacity and cycling stability. Here, a facile and effective method toward commercial polyolefin separators for constructing stable RT-Na-S batteries is presented. By coating commercial polypropylene membrane with core-shell structured MXene@C nanosheets, a powerful dual-functional separator with improved electrolyte wettability that can inhibit polysulfide migration and induce uniform sodium disposition is developed. More importantly, the modified separator can also accelerate the conversion kinetics of sodium polysulfides. Benefiting from these characteristics, the as-prepared RT-Na-S battery exhibits a remarkably enhanced capacity (1159 mAh g-1 at 0.2 C) and excellent cycling performance (95.8% of capacity retention after 650 cycles at 0.5 C). This study opens a promising avenue for the development of high-performance Na-S batteries.

Nitrogen doped hollow carbon nanospheres as efficient polysulfide restricted layer on commercial separators for high-performance lithium-sulfur batteries

The polysulfide shuttle limits the development of lithium-sulfur (Li-S) batteries with high energy density and long lifespan. Herein, nitrogen doped hollow carbon nanospheres (NHCS) derived from polymerization of dopamine on SiO2 nanospheres are employed to modify the commercial polypropylene/polyethylene/polypropylene tri-layer separators (PP/PE/PP@NHCS). The abundant nitrogen heteroatoms in NHCS exhibit strong chemical adsorption toward polysulfides, which can effectively suppress the lithium polysulfides shuttle and further enhance the utilization of active sulfur. Lithium-sulfur batteries employing the PP/PE/PP@NHCS deliver an initial discharge capacity of 1355 mAh/g and retain high capacity of 921 mAh/g after 100 cycles at 0.2 C. At a high rate of 2 C, the lithium-sulfur batteries exhibit capacity of 461 mAh/g after 1000 cycles with a capacity fading rate of 0.049% per cycle. This work demonstrates that the NHCS coated PP/PE/PP separator is promising for future commercial applications of lithium-sulfur batteries with improved electrochemical performances.

Thermal-triggered fire-extinguishing separators by phase change materials for high-safety lithium-ion batteries

High-energy lithium-ion batteries face significant challenges at abuse conditions, where thermal runaway is easily triggered and always accompanied with fire and explosion. Here we report a novel separator design that simultaneously absorbs thermal energy within the cell and improves fire safety. A thermo-responsive composite separator is fabricated by coating the commercial polyolefin separator with ceramic silica microcapsules that are internally encapsulated with both a phase-change material (PCM) and a flame retardant. As a “smart gatekeeper”, the PCM can not only store heat within the cell to minimize the temperature rise, but control the thermal-stimuli release of the flame retardant. In particular, the electrochemical performance of batteries is not sacrificed, taking advantages of the elaborate encapsulation of flame retardant and PCM inside a protective silica microcapsule and avoiding the direct dissolution of them into the electrolyte. Upon thermal stimuli, the solid-liquid transition of PCM occurs to increase molecular mobility and release the flame retardant. The low melting point of PCM could facilitate the prompt release of flame retardant at the early stage of thermal runaway, avoiding short circuit caused by thermal inertia. The PCM-based heat-regulated release system for flame retardant effectively reduces the safety risks caused by thermal runaway, which holds great promise as multifunctional separators for high-safety lithium-ion batteries.

Energy-Saving Synthesis of Functional CoS2/rGO Interlayer With Enhanced Conversion Kinetics for High-Performance Lithium-Sulfur Batteries.

Lithium sulfur (Li-S) battery has exhibited great application potential in next-generation high-density secondary battery systems due to their excellent energy density and high specific capacity. However, the practical industrialization of Li-S battery is still affected by the low conductivity of sulfur and its discharge product (Li2S2/Li2S), the shuttle effect of lithium polysulfide (Li2Sn, 4 ≤ n ≤ 8) during charging/discharging process and so on. Here, cobalt disulfide/reduced graphene oxide (CoS2/rGO) composites were easily and efficiently prepared through an energy-saving microwave-assisted hydrothermal method and employed as functional interlayer on commercial polypropylene separator to enhance the electrochemical performance of Li-S battery. As a physical barrier and second current collector, the porous conductive rGO can relieve the shuttle effect of polysulfides and ensure fast electron/ion transfer. Polar CoS2 nanoparticles uniformly distributed on rGO provide strong chemical adsorption to capture polysulfides. Benefitting from the synergy of physical and chemical constraints on polysulfides, the Li-S battery with CoS2/rGO functional separator exhibits enhanced conversion kinetics and excellent electrochemical performance with a high cycling initial capacity of 1,122.3 mAh g−1 at 0.2 C, good rate capabilities with 583.9 mAh g−1 at 2 C, and long-term cycle stability (decay rate of 0.08% per cycle at 0.5 C). This work provides an efficient and energy/time-saving microwave hydrothermal method for the synthesis of functional materials in stable Li-S battery.