Commercial Separator Research Articles

Lithiated-Polyamic Acid-Coated Glass Fiber As a Functional Separator for High-Performance Li-S Batteries

Lithium sulfur batteries (LSB) can offer great opportunities for the next-generation energy storage systems required for electrical vehicles and grid energy storage applications due to its very high theoretical specific energy (2500 Wh kg−1). For the practical applications, the sulfur loading in the cathode should not be lower than 70wt% in order to achieve a high energy density. However, the electrical and/or ionic conductivity of the cathode can be reduced with a high S loading, respectively, leading to reduced sulfur utilization and slurry reaction kinetic. In order to overcome this issue, sulfur active species were first dissolved together with Li2S in the electrolyte to form lithium polysulfide (LiPolS) (e.g., Li2S8 and Li2S6) solution or catholyte. During cycling, the active sulfur (Li2S8) is deposited from the electrolyte into the S-free cathode conductive matrix, which could be made from carbon nanotube and carbon nanofiber. It has been demonstrated that the specific/areal capacity of Li – lithium polysulfide (Li-LiPS) cells show high specific capacity, indicating high S utilization as well as high reaction kinetic. However, the problem is the penetration of dissolved LiPSs through the separator to react with the Li metal anode and reduce to form short-chain LiPSs, resulting to the passivation of the anode with irreversible deposits on its surface. In order to mitigate this problem, a lithiated-polyamic acid functionalized glass microfibers (GF@PALi) was utilized as a functional separator to selectively transfer Li+ ions. The GF@PALi was prepared by simply dipping of commercial GF into aqueous solution of 5 wt% lithiated-polyamic acid and dried overnight at 60 oC in vacuum oven. Combined with CNTs on Ni foam electrode, catholyte of 0.4 M LiTFSI + 2.0 M Li2S8 + 1.0 M LiNO3 in DME/DOL and lithium anode, the fabricated LSB cell exhibits a high specific and areal capacities of 803 mAh g-1 and 2.43 mAh cm-2 at C/2 rate, respectively. In addition, the LSB cell with the GF@PALi separator presents a remarkable cycling durability until 200 cycles with 76% capacity retention, which is much more stable than the LSB cell with commercial Celgard PP separator working until 86 cycles. Such high durability could be attributed to the retarding polysulfide migration of the as-prepared GF@PALi separator. Figure 1

Design Considerations for Practical Li-S Battery Components for Electric Aviation

The development of high-energy, high-safety, and high-power batteries beyond electric automobile requirements is vital for future electric aviation applications. The transition to non-volatile solid-state electrolytes (SSE) promises many advantages over traditional flammable liquid electrolytes and may also be an enabling technology for next generation chemistries. However, significant manufacturing challenges must be overcome before the adoption of such technology. This study focuses on advancement of previous electrolyte development to produce sulfide-polymer composites with densified thicknesses between 20-30 microns using a tape-casting technique with an elastomer binder [1]. Parameters such as binder type, binder loading, and filler loading are modified to determine their impact on electrochemical performance and mechanical stability. The composites were determined to retain reasonable ionic conductivity with improved flexibility and scalability critical for practical manufacturing of such cells. Films were produced 10-15 times thinner than comparable bulk powder electrolytes and within the range of commercial polyolefin separators (25 micron) used in commercial liquid containing lithium-ion cells. Composite conductivities were maintained above 0.2mS/cm, which holds promise for future electric aviation applications. Processing techniques are investigated to further improve electrochemical performance.[1] Donald A. Dornbusch, Rocco P. Viggiano, John W. Connell, Yi Lin, Vadim F. Lvovich. Practical considerations in designing solid state Li-S cells for electric aviation, Electrochimica Acta, 2021, 139406, ISSN 0013-4686, https://doi.org/10.1016/j.electacta.2021.139406.

Separator Dependency on Cycling Stability of Lithium Metal Batteries Under Practical Conditions

Development of practical lithium (Li) metal batteries (LMBs) remains challenging despite promises of Li metal anodes (LMAs), owing to Li dendrite formation and highly reactive surface nature. Polyolefin separators used in LMBs may undergo severe mechanical and chemical deterioration when contacting with LMAs. To identify the best polyolefin separator for LMBs, this study investigated the separator‐deterministic cycling stability of LMBs under practical conditions, and redefined the key influencing factors, including pore structure, mechanical stability, and chemical affinity, using 12 different commercial separators, including polyethylene (PE), polypropylene (PP), and coated separators. At extreme compression triggered by LMA swelling, isotropic stress release by balancing the machine direction and transverse direction tensile strengths was found to be crucial for mitigating cell short‐circuiting. Instead of PP separators, a PE separator that possesses a high elastic modulus and a highly connected pore structure can uniformly regulate LMA swelling. The ceramic coating reinforced short‐circuiting resistance, while the cycling efficiency degraded rapidly owing to the detrimental interactions between ceramics and LMAs. This study identified the design principle of separators for practical LMBs with respect to mechanical stability and chemical affinity toward LMAs by elucidating the impacts of separator modification on the cycling performance.

Superdry poly(vinylidene fluoride-co-hexafluoropropylene) coating on a lithium anode as a protective layer and separator for a high-performance lithium-oxygen battery

In this study, a dense polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) coating is fabricated on a lithium (Li) anode sheet, which acts as a synergistic protective layer and electrolyte separator for Li-oxygen (Li-O2) batteries. This thin coating is dried through slow solvent evaporation and vacuum drying methods. The solvent-free, dense PVDF-HFP coating has a thickness of 45 µm and can absorb 62% of electrolyte. The battery containing the PVDF-HFP coating demonstrates a maximum peak power density of 3 mW cm−2, significantly higher than that of the battery with the PVDF coating (0.8 mW cm−2) but lower than that without coating (equipped with a commercial glass fiber separator, 7.3 mW cm−2). However, the PVDF-HFP coating enables the Li-O2 battery to reach a capacity of 4400 mA h g−1, much higher than that without the coating (glass fiber separator, 850 mA h g−1). The symmetric Li-Li cells further confirm steady and low overpotentials using the anode coating at a high current density of 1.0 mA cm−2, indicating stable Li plating/stripping process. The PVDF-HFP-coated battery has a longer cycling lifetime (1700 h) than those with the PVDF coating (120 h) and a glass fiber separator (670 h). The Raman spectra show that there are lithium compounds (mainly lithium hydroxide) and residual PVDF-HFP on the aged anode surface. The dense PVDF-HFP coating on the Li anode plays dual roles: it creates a strong protective layer for stabilizing the solid-electrolyte interface (in the solid phase), and acts as a separator for modulating the Li metal deposition and stripping behaviors in liquid electrolyte.

Natural Halloysite Nanotubes Coated Commercial Paper or Waste Newspaper as Highly‐Thermal‐Stable Separator for Lithium‐Ion Batteries

AbstractCommercial polypropylene (PP) and polyethylene (PE) films are widely used as separators for lithium‐ion batteries (LIBs). However, owing to the poor thermal stability of PP and PE films, current LIBs suffer from serious safety risks in their practical applications. As an effective path, the design of novel high‐safety composite separators can significantly overcome the safety issues of LIBs. Herein, a universal and cost‐effective strategy is developed to fabricate highly‐thermal‐stable separators via coating natural halloysite nanotubes (HNTs) on both sides of commercial papers or waste newspaper. The resulted separators show superior properties, including thermal stability, heat conduction, wettability, and electrolyte uptake. Compared with commercial PP separators, both HNTs coated A4 paper and waste newspaper composite separators enable better cycling and rate performance for Li/LiFePO4 cells. Even after burning in fire or treating under 180 °C, the composite separators still present a normal structure, and the assembled cell can perform as regular. Furthermore, the nail penetration test of pouch cells illustrates that such separator significantly prevents thermal runaway of LIBs. The inexpensive and environmentally friendly materials with a facile coating process provide a highly‐thermal‐stable separator for commercial LIBs.

Thermostable and nonflammable polyimide/zirconia compound separator for lithium-ion batteries with superior electrochemical and safe properties

Separators are applied to segregate cathode and anode, and provide ion transport channels in lithium-ion batteries (LIBs). Nevertheless, present commercial polyolefin separators represent high thermal shrinkage and inferior electrolyte wettability, seriously limiting wider development of LIBs. In this work, we prepared zirconia (ZrO2) nanolayer encapsulated polyimide (PI) nanofiber compound separator through in-situ polar adsorption and hydrolysis strategy. The obtained PI/ZrO2 compound separator has superior thermal stability, electrolyte wettability and flame retardance in comparison with polypropylene (PP) separator. The shrinkage ratio of prepared PI/ZrO2 compound separator is 0 even at 300 °C, while the PP separator significantly shrank at 160 °C. Furthermore, the ionic conductivity of PI/ZrO2 separator reaches up to 1.32 mS cm−1, far higher than 0.34 mS cm−1 of PP separator. Besides, the coin batteries of LiNi0.8Co0.1Mn0.1O2 (NCM811)/electrolyte-separator/lithium (Li) assembled with PI/ZrO2 compound separator exhibit enhanced rate performance, high discharge capacity retention rate of 88.3% after 100 cycles at 1C and excellent battery safety performance even at 140 °C. Thus, combined with its advantages, such as preparation, thermostability, electrolyte wettability, electrochemical property and safety, the PI/ZrO2 compound separator exhibits promising prospect in the application of commercial LIBs.

A thermal resistant and flame retardant separator reinforced by attapulgite for lithium-ion batteries via multilayer coextrusion

Multilayer separators are widely used due to their wide shutdown window by combining lower melting temperature and higher melting temperature of different layers. With the development of high power lithium-ion batteries, multilayer separators equipped with effective thermal stability and flame retardancy are highly required. Herein, the poly(methyl methacrylate) modified attapulgite (ATPM) is selected as the heat resistant reinforcing component and blended with polypropylene (PP)/polyethylene (PE) respectively. Then we prepare PP(ATPM)/PE(ATPM) separators via multilayer coextrusion efficiently without multiple stretching processes, which can avoid serious separator shrinkage at elevated temperature. The intertwined ATPM could not only enhance the separator integrity, but also produce water vapor and oxide anti-flaming isolation layers at high temperatures. The as-prepared separators, referred to as MC-TIPS PP/PE/ATPM, exhibit higher thermal stability (with negligible dimensional shrinkage up to 180 °C), better flame retardancy and wider shutdown temperature window (124–183 °C) than the commercial multilayer separators. Moreover, the introduction of ester and hydroxyl groups could improve the wettability and electrolyte uptake of the separators. These properties, as well as the potential for large-scale production of multilayer coextrusion, make MC-TIPS PP/PE/ATPM an ideal choice for high-power battery separators. • A robust multilayer separator of polypropylene and polyethylene reinforced by poly(methyl methacrylate) modified attapulgite (ATPM) is prepared via multilayer coextrusion without multiple stretching processes, then can avoid serious separator shrinkage at elevated temperature. • The addition of hydrous and heat-resistant ATPM can not only enhance thermal integrity of separator, but also produce water vapor/oxide anti-flaming isolation layers at high temperature, thus improve the flame retardancy of separator. • This preparation method can be extended to fabricate other multilayer separators by choosing other suitable polymeric matrix and reinforce filler (inorganic nanowire/fibre, flame retardant powder, etc).

Cobalt/three-dimensional carbon/reduced graphene oxide modified PP separator for Li-S batteries

In this work, a composite of cobalt metal nanoparticles/three-dimensional carbon/reduced graphene oxide (Co-3DC-rGO) was synthesized using corn husk, ZIF-67, and graphene oxide as precursors. The Co-3DC-rGO was used to modify commercial PP to prepare the Co-3DC-rGO/PP separator. The performance of Co-3DC-rGO/PP separator was evaluated in lithium-sulfur batteries (LSBs). SEM images exhibited that a three-dimensional carbon (3DC) skeleton was obtained by corn husk transformation, and the ZIF-67-derived cobalt-decorated carbon dodecahedrons were homogeneously filled into the hierarchical pores of the 3DC structure. TEM images displayed that Co metal nanoparticles can escape from ZIF-67 and scatter on the rGO nano-sheets and 3DC skeleton. Benefitting from the synergy effects of the 3D carbon skeleton, rGO, and Co metal nanoparticles, the electrochemical performance of LSBs with Co-3DC-rGO/PP separator is better than LSBs with commercial PP separator. When tested at 1C, the LSB with Co-3DC-rGO/PP separator presents a high stable reversible capacity of 516.3 mA h g −1 after 500 cycles. This research provides new ideas for the preparation of LSBs separator. • Co/3D carbon/rGO decorated PP separator was prepared and used in Li-S batteries. • Co/3D carbon/rGO can inhibit the shuttle of lithium polysulfides to the Li anode. • Co/3D carbon/rGO accelerate the conversion of lithium polysulfides to Li2S. • The Li-S battery with Co/3DC/rGO/PP separator delivers excellent electrochemical performance.

Composite cathodes and modified separators based on corn-silk-based porous carbon for high performance lithium–sulfur batteries

Corn by-products have been widely studied as a precursor of biomass carbon in energy storage systems. Without further doping or coating processes corn silk can achieve a high electrochemical performance when used as an anode of sodium and potassium ion batteries. Nonetheless, there is no report about corn silk used as a cathode for lithium-sulfur batteries. In this work, corn silk was made into porous carbon and used as sulfur scaffolds and modified materials for commercial separator in lithium-sulfur batteries. Corn silk possesses a natural pipe shape which grants the porous carbon a high specific surface area. With a simple dissolution crystallization method approximately 80% of the sulfur could be easily accommodated onto the porous carbon. The hierarchic pores not only limited the particle size of the sulfur to nanometers, but also buffered the volume expansion of sulfur and absorbed it tightly. Furthermore, with an ultralight porous carbon modified separator, significant improvement was achieved in the utilization of sulfur, cycling stability and alleviation of the polysulfide shuttling efficiently. The batteries delivered a specific capacity of 1290 mAh g-1 in the first discharge and 746 mAh g-1 after 100 cycles. The good electrochemical performance can be ascribed to the rational design of battery configuration.

Cellulose-reinforced poly(cyclocarbonate-ether)-based composite polymer electrolyte and facile gel interfacial modification for solid-state lithium-ion batteries

Synthesizing high-performance solid electrolytes with simple methods and common materials has long been a desire for lithium-ion batteries. Here, easy-available composite polymer electrolytes (CPEs) were prepared via UV curing of novel P(VEC-co-EGDMA) matrix and ionic liquid (IL) with commercial cellulose separator (CL). Loose complexation environment enabled cyclic carbonate of vinyl ethylene carbonate (VEC) to have higher Li+ migration capacity than EO, and poly (ethylene glycol) dimethacrylate (PEGDMA) was introduced as a flexible crosslinker to avoid excessively rigid structure. Furthermore, the IL with high voltage stability and CL with polar groups on the surface achieved liquid plasticization and mechanical reinforcement of P(VEC-co-EGDMA) matrix, synergistically improving the electrochemical performance and safety of CPEs. The ionic conductivity, electrochemical stability window and tensile strength of the optimal sample (PI64/CL) even reached 3.60 × 10−4 S cm−1 (25 °C), 5.6 V and 4.50 MPa, respectively. Finally, a 5 μm-thick PEO-LLZTO-IL gel transition layer was added at the electrolyte/cathode interface by a facile casting-curing method to optimize their interfacial contact, enabling the assembled solid-state battery to exhibit impressive rate and cycle performance, its specific capacity reached 151.6 mAh g−1 (1C) at 40 °C with the 89.1% capacity retention rate after 280 cycles, corresponding to 148.6 mAh g−1 (0.5C), 98.7%, 120 cycles at room temperature.

Bifunctional separator with high thermal stability and lithium dendrite inhibition toward high safety lithium-ion batteries

Coating inorganic ceramic particles on commercial polyolefin separators has been considered as an effective strategy to improve thermostability of separator. However, the introduction of the coating layer could induce pore blockage on the surface of the polyolefin separator. Herein, a ceramic composite layer that consists of alumina nanoparticles (n-Al2O3) and halloysite nanotubes (HNTs) is designed to modify the polyethylene (PE) separator (the modified separator is denoted as AH-PE). The HNTs with hollow nanotubular structure construct a light skeleton and provide fast ion transport channels while Al2O3 particles function as heat-resistant fillers to inhibit the shrinkage of the separator at elevated temperatures. The total thickness of AH-PE separator is only 14 µm. Consequently, the mass increment of AH-PE separator decreases from 5 g/m2 to 3.5 g/m2, and the Gurley value reduces by 23%, compared with Al2O3 coated PE separator (A-PE). Due to the synergistic effects of Al2O3 and HNTs, AH-PE separator exhibits highly improved thermal stability (almost no shrinkage at 170 °C for 30 min), high Li+ transference number (up to 0.47), and long cycle life of 450 h for Li|Li cells. Moreover, the LiFePO4/Li cells assembled with AH-PE separators demonstrate improved rate capability and safety performance.

Multifunctional robust aerogel separator towards high-temperature, large-rate, long-cycle lithium-ion batteries

Separators is indispensable for the normal operation of lithium-ion batteries (LIBs). However, the widely used commercial polyolefin separators have some inherent deficiencies such as poor thermotolerance, high inflammability and inferior electrolyte wettability, which restrict their further applications of the advanced and safe batteries. Herein, we design a novel thermotolerant (a shrinkage percentage of 0% at 300°C) and flame retarded aerogel separator consisting of aramid nanofibers (ANFs). Because of its high porosity (86.5%±6.1%) and excellent electrolyte uptake (695%), the ANFs aerogel separator has an ionic conductivity of 1.04 mS/cm and a high lithium-ion transference number (0.67), which can endow LIBs with outstanding rate performance and superior cycling performance. Specifically, the ANFs aerogel separator-based batteries possess a discharge specific capacity of 102 mAh/g with a capacity retention of 90.7% and a Coulombic efficiency of 99.3% after 600 cycles at 5 C. In addition, under an operated temperature of 90 ℃, the battery with ANFs aerogel separator can still conduct the very steady charge-discharge, presenting a capacity retention of 90.1% and a Coulombic efficiency of 99.6% after 200 cycles at 3 C. Accordingly, the separator can probably serve as a potential candidate for application to advanced and safe LIBs.

Highly porous and thermally stable zeolitic imidazolate framework-8/aramid nanofibers composite separator for lithium-ion batteries

Currently, the inferior electrolyte wettability and poor thermal stability of conventional polyolefin separators have impeded the development of high-performance lithium-ion batteries (LIBs). Herein, a novel zeolitic imidazolate framework-8 (ZIF-8)/aramid nanofibers (ANFs) composite separator was fabricated via in-situ assembling ZIF-8 on ANFs followed by filtration process. The ZIF-8 particles prevented the dense packing of ANFs and significantly improved the porosity from 23.8% (in pure ANFs separator) to 61.6% (in composite separator). Combining the well-developed porous structure and exceptional electrolyte affinity, the as-prepared 30%ZIF-8/ANFs composite separator (with 30 wt% of ZIF-8) exhibited high electrolyte uptake (224.0%) and good electrolyte wettability, which brought about superior ionic conductivity (1.37 mS cm−1), excellent rate performance and cycling stability. Furthermore, compared to commercial polypropylene separator, the 30%ZIF-8/ANFs separator showed suitable mechanical strength, outstanding thermal resistance and flame retardancy, which ensured higher safety during battery operation. Accordingly, the 30%ZIF-8/ANFs composite separator with both enhanced performance and high safety is a promising candidate for next-generation LIBs.

Electrospun poly(ionic liquid) nanofiber separators with high lithium-ion transference number for safe ionic-liquid-based lithium batteries in wide temperature range

Ionic-liquid electrolytes (ILEs) promise high-safety lithium-metal batteries (LMBs) because of their wide electrochemical stability window and nonflammability. However, existing commercial polyolefin separators for LMBs are incompatible with ILEs owing to poor wettability and thermal stability. Also, conventional ILE/separator systems suffer from the inherent sluggish Li+ transport kinetics. Here we report on a novel highly Li+-conductive poly(ionic liquid) nanofiber membrane (PILNM) separator. It exhibits nonflammability, excellent thermal stability, and remarkable wettability with ILEs, achieving high ionic conductivity (3.81 mS cm−1) and significantly improved Li+ transference number (0.47). Benefiting from desirable interactions between the charged PILNM and ions of the ILE, the first solvation shell of [lithium-bis(trifluoromethane)sulfonimidex]1−x ([Li-TFSIx]1−x) complex is regulated. Fast Li+ transport and dendrite-free lithium metal anode are achieved. The PILNM combined with the ILE enables Li||LiFePO4 cells with enhanced capacities and rate capability in a wide temperature range from 25 °C to 120 °C. Notably, the thermal safety of Li|PILNM/ILE|LiFePO4 pouch cells at elevated temperatures has been further verified by adiabatic accelerating rate calorimetry. This work provides a new strategy to design and fabricate functionalized, thermally durable separators towards high-safety ILE-based LMBs.

A Single-Layer Composite Separator with 3D-Reinforced Microstructure for Practical High-Temperature Lithium Ion Batteries.

Incorporation of ceramic materials into separators has been frequently applied in both research and industry to improve the overall high-temperature performances of lithium ion batteries. However, inorganic ceramic particles tend to form aggregation in separators and even fall off in the separator matrix due to the inferior combination between ceramic particles and polymer matrix, giving rise to a decrease in separator porosity and thus the degradation of battery performances. Herein, a single-layer core-shell architecture is designed to reinforce the polymer matrix through encircling Al2 O3 particles by poly(vinylidene fluoride) with strong inter-molecular interaction. The 3D-reinforced microstructure effectively improves pore distribution and thermal stability to resist the dimensional deformation at high temperatures, thus giving rise to a high Coulombic efficiency of 99.16% and 87.5% capacity retention after 500 cycles at 80°C for LiFePO4 /Li batteries. In particular, the excellent performances of the proposed separator microstructure are confirmed with a thickness value of commercial separators. This work provides a promising strategy to fabricate a core-shell structural composite separator for stable lithium ion batteries at high temperatures.

Suppression of Self‐Discharge in Aqueous Supercapacitor Devices Incorporating Highly Polar Nanofiber Separators

One of the major problems limiting the applications of electric double‐layer (EDLC) supercapacitor devices is their inability to maintain their cell voltage over a significant period. Self‐discharge is a spontaneous decay in charged energy, often resulting in fully depleted devices in a matter of hours. Here, a new method for suppressing this self‐discharge phenomenon is proposed by using directionally polarized piezoelectric electrospun nanofiber films as separator materials. Tailored engineering of polyvinylidene fluoride (PVDF) nanofiber films containing a small concentration of sodium dodecyl sulfate (SDS) results in a high proportion of polar β phases, reaching 38 ± 0.5% of the total material. Inducing polarity into the separator material provides a reverse‐diode mechanism in the device, such that it drops from an initial voltage of 1.6 down to 1 V after 10 h, as opposed to 0.3 V with a nonpolarized, commercial separator material. Thus, the energy retained for the polarized separator is 37% and 4% for the nonpolarized separator, making supercapacitors a more attractive solution for long‐term energy storage.

ZIF-8/Ketjen Black derived ZnO/N/KB composite for separator modification of lithium sulfur batteries

Lithium-sulfur batteries have the advantages of high specific capacity, high energy density, environmental friendliness, and low price, and have become one of the most promising new electrochemical technologies. However, during the charge-discharge reaction, the shuttle effect of the reaction intermediate polysulfides leads to a decrease in battery activity, which limits its development and commercialization. In this paper, we prepared a novel ZnO/N/Ketjen Black (KB) composite to act as a separator barrier to reduce the influence of polysulfides shuttle effects. A simple aqueous solution reaction was used to mix Zn(NO3)2∙6H2O with KB and ZIF-8/KB was obtained by adding dimethylimidazole, and then ZIF-8/KB precursor was carbonized at high temperature in inert gas atmosphere to obtain ZnO/N/KB composite. Finally, the prepared ZnO/N/KB composite was coated on commercial PE separator. Through the dual effects of adsorption and catalysis, the shuttle effect of polysulfides is sufficiently inhibited by the ZnO/N/KB layer, therefore the electrochemical performances of lithium-sulfur batteries are largely improved. The results show that when the sulfur cathode of Li-S battery contains 3 mg cm−2 active material, the specific discharge capacity can be as high as 1284.5 mAh g−1 at 0.05 C. Furthermore, at a higher rate of 0.5 C, the initial discharge specific capacity also reaches 868.3 mAh g−1. After 400 cycles of the charge/discharge process, it still remains 495.9 mAh g−1, which means a capacity retention rate of 57.1%.

Safety and cycling stability enhancement of cellulose paper-based lithium-ion battery separator by aramid nanofibers

Commercial polyolefin separators suffer from poor electrolyte wettability and low thermal stability, which give rise to unsatisfied electrochemical performance and severe safety hazards for lithium-ion batteries (LIBs). Herein, a novel paper-based composite separator composed of electrolyte-affinitive cellulose fibers (CFs) and thermally stable aramid nanofibers (ANFs) was successfully fabricated through the traditional papermaking method. The ANFs as a functional nanofiller played crucial roles in improving the defects of pure CF separator including large-sized pores, low mechanical strength and high flammability. Specifically, the CF/ANF composite separator with 20 wt% ANFs (CF/ANF-20) possessed narrow micropores, satisfied tensile strength (33 MPa), excellent thermal resistance (without dimensional shrinkage up to 200 °C) and flame retardancy, which greatly enhanced the safe operation of battery. Moreover, inheriting from the highly porous structure and exceptional electrolyte affinity of CF separator, the CF/ANF-20 composite separator exhibited appropriate porosity and superior electrolyte wettability, which brought about a high electrolyte uptake (157%), thus endowing it with better ionic conductivity (0.75 mS cm−1) and lower interfacial resistance compared to commercial polypropylene separator. Accordingly, the LiFePO4/Li half cells using CF/ANF-20 separator delivered outstanding rate capability and stable cycling performance. All results indicate that the CF/ANF-20 separator shown great balance between the electrochemical performance and safety is an intriguing candidate for advanced LIBs.

Thermally Conductive AlN-Network Shield for Separators to Achieve Dendrite-Free Plating and Fast Li-Ion Transport toward Durable and High-Rate Lithium-Metal Anodes.

Lithium‐metal anodes suffer from inadequate rate and cycling performances for practical application mainly due to the harmful dendrite growth, especially at high currents. Herein a facile construction of the porous and robust network with thermally conductive AlN nanowires onto the commercial polypropylene separator by convenient vacuum filtration is reported. The so‐constructed AlN‐network shield provides a uniform thermal distribution to realize homogeneous Li deposition, super electrolyte‐philic channels to enhance Li‐ion transport, and also a physical barrier to resist dendrite piercing as the last fence. Consequently, the symmetric Li|Li cell presents an ultralong lifetime over 8000 h (20 mA cm−2, 3 mAh cm−2) and over 1000 h even at an unprecedented high rate (80 mA cm−2, 80 mAh cm−2), which is far surpassing the corresponding performances reported to date. The corresponding Li|LiFePO4 cell delivers a high specific capacity of 84.3 mAh g−1 at 10 C. This study demonstrates an efficient approach with great application potential toward durable and high‐power Li–metal batteries and even beyond.

Constructing Atomic Fe and N Co-doped Hollow Carbon Nanospheres with a Polymer Encapsulation Strategy for High-Performance Lithium-Sulfur Batteries with Accelerated Polysulfide Conversion.

As competitive next-generation rechargeable batteries, lithium-sulfur batteries (LSBs) suffer from the shuttle effect and the sluggish kinetics of intermediate polysulfides during charge and discharge processes, adversely affecting their electrochemical performances and actual applications. Herein, we demonstrate a polymer encapsulation strategy to synthesize atomic Fe and N co-doped hollow carbon nanospheres (Fe-NHC) with Fe-Nx sites for modifying commercial PP separator of LSBs to suppress the shuttle effect and promote the kinetics of intermediate polysulfides. Benefiting from the excellent structural design, the doped-N with positive charges could effectively adsorb negatively charged soluble polysulfides, help attract the soluble polysulfides to the Fe atoms and boost the catalytic transformation of the soluble polysulfides. Additionally, such a thin carbon shell could provide a short mass diffusion pathway and hence promote the adsorption and the catalytic conversion. Therefore, the battery with the Fe-NHC/PP separator delivers outstanding cycling and rate performances. At the large current density of 1 C, the specific capacity is 1079 mA h g-1 and maintains a low loss of 0.076 % per cycle within 500 cycles. Even at a harsh current density of 4 C, a high capacity of 824 mA h g-1 is still achieved, indicating the advantage of the Fe-NHC/PP separator in LSBs.