Separators For Lithium-ion Batteries Research Articles

Surfactant-Enabled BM particle-embedded coaxial PVDF/PEI electrospun membranes enhancing Lithium-Ion battery safety

In response to the issue of thermal runaway in lithium-ion batteries, a new battery separator with high safety was developed in this study. By incorporating trace amounts of the surfactant sodium dodecyl sulfate (SDS) into the boehmite (BM) slurry, uniform infiltration of the polyvinylidene fluoride/polyetherimide (PVDF/PEI) coaxial electrospun fiber membrane was successfully achieved, thereby significantly enhancing the membrane’s flame retardancy and thermal stability at high temperatures. This method is straightforward and versatile, facilitating a tight integration of BM with individual fibers. Owing to the synergistic effects of the fiber structure, polymer matrix, BM, and binder, the separator also exhibits excellent electrolyte wettability, thermal conductivity, and toughness. Batteries assembled with this membrane demonstrated an initial discharge capacity of 142.1 mAh/g at a 0.5C charge–discharge rate, with a capacity retention of 97.4 % after 120 cycles. This research provides an innovative solution for the fabrication of high-safety lithium-ion battery separators, holding profound scientific significance and promising application prospects.

The Mechanism of Inhomogeneous Mass Transfer Process of Separators in Lithium-Ion Batteries.

The liquid-phase mass transport is the key factor affecting battery stability. The influencing mechanism of liquid-phase mass transport in the separators is still not clear, the internal environment being a complex multi-field during the service life of lithium-ion batteries. The liquid-phase mass transport in the separators is related to the microstructure of the separator and the physicochemical properties of electrolytes. Here, in-situ local electrochemical impedance spectra were developed to investigate local inhomogeneities in the mass transfer process of lithium-ion batteries. The geometric microstructure of the separator significantly impacts the mass transfer process, with a reduction in porosity leading to increased overpotentials. A competitive relationship among porosity, tortuosity, and membrane thickness in the geometric parameters of the separator were established, resulting in a peak of polarization. The resistance of the liquid-phase mass transfer process is positively correlated with the viscosity of the electrolyte, hindering ion migration due to high viscosity. Polarization is closely related to the electrochemical performance, so a phase diagram of battery performance and inhomogeneous mass transfer was developed to guide the design of the battery. This study provides a foundation for the development of high stability lithium-ion batteries.

Electrospun Poly(vinyl Alcohol)/Chitin Nanofiber Membrane as a Sustainable Lithium-Ion Battery Separator.

Commercial battery separators are made of polyolefin polymers due to their desired mechanical strength and chemical stability. However, these materials are not biodegradable and are challenging to recycle. Considering the environmental issues from polyolefins, biodegradable polymers can be developed as separators to reduce the potential waste from polyolefin separators. In this work, we investigated the potential of poly(vinyl alcohol)/chitin nanofiber (PVA/CHNF) nanofiber as a sustainable lithium-ion battery separator, which was successfully fabricated via the electrospinning and cross-linking method. The PVA/CHNF separator is biodegradable and has an ionic conductivity (1.41 mS cm-1), desirable porosity (86%), good thermal stability (1.4% shrinkage upon heating at 90 °C for 1 h), as well as high electrolyte uptake (388%). The PVA/CHNF separator is also evaluated in the assembled Li//LiFePO4 cells, showing an improved performance compared to the cell with the commercial separator. It shows a discharge capacity of 142 mAh g-1, which is stable throughout 120 charge-discharge cycles. Hence, according to these resulting properties, the PVA/CHNF separator shows promise as a sustainable and environmentally friendly lithium-ion battery separator, offering a high-value use of waste chitin materials.

Lithium-Ion Battery Separator with Dual Safety of Regulated Lithium Dendrite Growth and Thermal Closure by Assisted Assembly Technology

Lithium-Ion Battery Separator with Dual Safety of Regulated Lithium Dendrite Growth and Thermal Closure by Assisted Assembly Technology

Regulating chiral nematic liquid crystal of hydroxypropyl methylcellulose coating on separator for High-Safety Lithium-Ion batteries

The conventional commercial polypropylene separator (PP) struggles to inhibit the thermal runaway triggered by dendrite short circuits, and its safety cannot meet the needs of the development of high-energy–density batteries. Herein, an easily commercializable design strategy was employed to induce the aqueous solution of natural polymer hydroxypropylmethylcellulose (HPMC) to self-assemble on the surface of the PP separator by Na2SO4, MnSO4, and Al2(SO4)3 to form the chiral nematic liquid crystal (CLC) with excellent performance, and finally the thermally stable separators (H-Na@PP, H-Mn@PP, and H-Al@PP) were obtained. Theoretical calculations and experiments demonstrate that the CLC induced by Na+, Mn2+, and Al3+ can interact with the electrolyte solvent to form a desolvation structure of Li+, which reduces the migration barrier of Li+ through the separator and accelerate the Li+ transport. Furthermore, the ordered CLC structure can ensure uniform electric field and Li+ flux. Hence, Li//LFP, Li (50 μm)//LFP, and Li//NCM811cells are assembled using these modified separators, featuring remarkable cycling stability and high Coulombic efficiency. As the result, H-Na@PP, H-Mn@PP, and H-Al@PP separators in Li//LFP cell display a high initial capacity of 141.2 mAh/g, 146.7 mAh/g and 130.7 mAh/g at 1C, respectively and stable cycling performance over 1000 cycles. Notably, the capacity retention rate remains high at 87 %, 69 %, and 59 % even after 700 cycles, respectively, which are higher than the 21 % capacity retention rate of PP separator. Meanwhile, the pouch cells equipped with these separators deliver exceptional electrochemical performance and show a lower temperature distribution without thermal runaway behavior under the Φ3 mm nail penetration test, indicating its feasibility for high-safety energy storage systems.

A cellulose-based lithium-ion battery separator with regulated ionic transport and high thermal stability for extreme environments

A cellulose-based lithium-ion battery separator with regulated ionic transport and high thermal stability for extreme environments

Polypyrrole as the MOFs/polymer interfacial binder applied in mixed matrix porous separator for high temperature safe lithium-ion batteries

Uniform distribution of two-dimensional (2D) metal organic frameworks (MOFs) in polymer composites is crucial for fabricating mixed matrix porous separators (MMPS) for metal-ion (M+) batteries (MIBs). However, effectively incorporating 2D MOFs into mechanically robust and highly transportive MMPS, without agglomeration and leaching, has been challenging. Herein, we report the post-polymerization of polypyrrole (PPy) on 2D Cu-MOFs nanosheets, and their uniform distribution in the poly-(arylene ether benzimidazole) (OPBI) to prepare highly porous and mass transportive MMPS using non-solvent induced phase separation (NIPS) method for lithium ion (Li+) batteries (LIBs) applications. The polymerization of PPy not only improved the dispersibility of the Cu-MOFs nanosheets, but also acted as an interfacial binder, ensuring compatibility between the MOFs and OPBI chains. The PPy@Cu-MOFs nanosheets increased the pore size and porosity of the OPBI-based MMPS, creating wider and more uniform cross-sectional channels, thereby enhancing Li+ flux between the anode and cathode during battery charge/discharge cycles. The thermally stable, electrolyte-affinitive, and lithophilic PPy@Cu-MOFs/OPBI MMPS, when assembled in LIBs, achieved a discharge capacity of 150.2 mAh· g−1 with sustained performance over 200 cycles, showing no capacity fading even at elevated temperature. This work provides new insights into polymerizing conjugated polymer on 2D-MOFs nanosheets for improved dispersibility and uniform distribution, enabling the design of high-performance, mass transportive MMPS for safe LIBs application to meet current green energy demands.

Mechanical Characterization and Modeling of Large-Format Lithium-Ion Battery Cell Electrodes and Separators for Real Operating Scenarios

This study presents a novel application-oriented approach to the mechanical characterization and subsequent modeling of porous electrodes and separators in lithium-ion cells to gain a better understanding of their real mechanical operating behavior. An experimental study was conducted on the non-linear stiffness of LiNi0.8Co0.15Al0.05O2 and graphite electrodes as well as PE separators, harvested from large-format lithium-ion cells, using compression tests. The mechanical response of the components was determined for different operating conditions, including nominal stress levels, mechanical loading rates, and mechanical cycles. The presented work describes the test procedure, the experimental setup, and an objective evaluation method, allowing for a detailed summary of the observed mechanical behavior. A distinct nominal stress level and mechanical cycle dependency of the non-linear stiffnesses of the porous materials were found. However, no clear dependency on compression rate was observed. Based on the experimental data, a poroelastic mechanical model was utilized to predict the non-linear behavior of these porous materials under real mechanical operating scenarios with a normalized root-mean-squared error less than 5.5%. The results provide essential new insights into the mechanical behavior of porous electrodes and separators in lithium-ion cells under real operating conditions, enabling the accelerated development of high-performing and safe batteries for various applications.

Enhancing Stability of Glass Fiber Separators in Lithium-Ion Batteries through Sol-Gel Hybrid Coatings

Lithium ion batteries are largely divided into an anode, a cathode, and a separator impregnated with an electrolyte. It is well known that the battery separator is an important element in all batteries, as it physically separates the anode and cathode to prevent the direct flow of electrons, and allows the flow of charge through the movement of ions. Polyolefin-based separators, which are widely used in existing batteries, are vulnerable to rapid environmental changes, drastically reducing battery performance. Additionally, the thermal contraction and expansion that leads to a short circuit significantly reduces the stability of the battery. To overcome stability in such extreme environments, glass fiber separators are emerging as an alternative. To overcome stability in such extreme environments, glass fiber separators are emerging as an alternative. Glass fiber has excellent mechanical properties, electrical insulation, heat resistance, and chemical resistance, so it can drastically improve the stability of the battery. It can also improve electrolyte impregnation by controlling porosity to improve battery performance.In this study, a sol-gel hybrid coating solution was synthesized and coated on a glass fiber separator to enhance the ionic conductivity and stability. The coating on glass fiber was performed using a dip coating method. The optimization of the hybrid solution and coating conditions led to a reduction in the porosity and enhancement of the flexibility of the glass fiber separators. The adhesion of the coating was evaluated by measuring the hardness of the coating using pencil hardness, and the results showed that the tensile strength of the coated glass fiber separator was improved by about two times compared to before coating. Finally, as a result of evaluating the electrical performance according to the coating, the battery performance was similar at room temperature. On the other hand, it was confirmed that the operating voltage and discharge time at low temperatures were increased by the sol-gel hybrid coating. These results suggest that the coated glass fiber separators are promising candidates for overcoming the stability of battery operation in extreme environments.

Advancements in Thin Solid-State Electrolytes for High-Energy Lithium Metal Batteries

ABSTRACT In the next generation of lithium-ion batteries (LIBs) utilizing lithium metal as the anode material, a theoretical capacity of 3860 mAh·g-1 can be expected [1]. However, several challenges such as safety issues due to lithium dendrite diffusion during charge-discharge cycling still remain unresolved [2]. The penetration of lithium dendrites remains a concern in traditional solution-based LIBs [3]. As an alternative approach to address the challenges of LIBs, solid-state electrolytes (SSEs) with high ionic conductivity and lithium metal stability have garnered attention [4]. The SSE category includes polymer electrolytes, inorganic sulfide electrolytes, and inorganic oxide electrolytes [5]. Among SSEs, garnet-type Li7La3Zr2O7 (LLZO), is a promising candidate due to its high ionic conductivity within the range of 10- 4 to 10- 3 S∙cm- 1 as well as its thermodynamics reduction stability against Li metal [6, 7].The introduction of SSB oxide electrolytes would improve packing density and could potentially lead to batteries with negligible self-discharge and longer lifespan of over 104 cycles [8]. During cell operation, solid electrolytes should be mechanically robust and as thin as possible to maximize the valuable volume remaining for the electrodes in SSB cell designs [9]. To compete with the approximately 20μm-thick polymer separators in traditional LIBs, ceramic manufacturing strategies for SSB electrolytes are necessary [10]. Recent estimations suggest that assuming a 25μm-thick solid electrolyte, a lithium metal SSB pouch cell could offer an energy density of 350Wh/kg [11]. In our study, we achieved ultra-thin electrolytes via tape-casting technique into Li-metal battery system. Li symmetric cells based on the ultra-thin electrolyte show exceptional low bulk resistance, attributed to extremely thin electrolyte. Moreover, symmetrical Li cell maintains steady Li plating/stripping cycles for long duration. Keywords: Lithium-ion batteries, LLZTO, thick solid electrolyte References [1] J. M. Tarascon, M. Armand, Nat., 414, (2001) 359-367.[2] J. Qian, W. A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin, J. G. Zhang, Nat Commun., 6, (2015) 6362.[3] Y. Guo, H. Li, T. Zhai, Adv. Mater., 29, (2017) 29.[4] J. Janek, W. G. Zeier, Nat. Energy., 1, (2016) 16141.[5] L. J. Miara, S. P. Ong, Y. Mo, W. D. Richards, Y. Park, J. M. Lee, H. S. Lee, G. Ceder, Chem. Mater., 25, (2013) 3048-3055.[6] L. J. Miara, S. P. Ong, Y. Mo, W. D. Richards, Y. Park, J. M. Lee, H. S. Lee, G. Ceder, Chem. Mater., 25, (2013) 3048-3055.[7] Y. Zhu, X. He, Y. Mo, ACS Appl. Mater. Interfaces, 7, (2015) 23685-23693.[8] T. Mageto, S. D. Bhoyate, F. M. de Souza, K. Mensah-Darkwa, A. Kumar, R. K. Gupta, J. Energy Storage, 55, (2022) 105688.[9] M. Balaish, J. C. Gonzalez-Rosillo, K. J. Kim, Y. Zhu, Z. D. Hood, J. L. M. Rupp, Nat. Energy, 6, (2021), 227–239.[10] L. Li, Y. Dian, Polymers, 15, (2023) 3690.[11] X. Wu, K. Pan, M. Jia, Y. Ren, H. He, L. Zhang, S. J. Zhang, GEE, 4, (2019) 360-374.

Anti-swelling gel polymer electrolyte membrane for high-performance lithium-ion battery

Gel polymer electrolyte (GPE) represents an effective and advanced substitution of polyolefin separator in high-rate lithium-ion rechargeable batteries. We here develop a novel pyridine ionic liquid (IL)-based GPE membrane for that purpose via a one-step reactive vapor-induced phase separation (RVIPS) method. Casting mixture solution of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) and 1-butylpyridinium hexafluorophosphate ([C4Py]PF6) to evaporate solvent in ammonia water vapor, the IL-based membrane was successfully prepared in one step. The effects of the IL content on the membrane microstructure were investigated in detail. Our results demonstrate that the pyridine IL plays a role as plasticizer to suppress crystallization of the polymer, while the RVIPS process can induce dehydrofluorination-crosslinking of PVDF-HFP to greatly reduce swelling of the membrane in liquid electrolyte. Based on those, the GPE from the membrane containing 10 % [C4Py]PF6 exhibits the best electrochemical properties (ionic conductivity of 1.48 mS cm−1, Li+ transference number of 0.66, and electrochemical stable window of 5.2V), though it uptakes a moderate amount of liquid electrolyte. Moreover, the long-term interfacial stability of the GPE with the metal anodes was checked to indicate its suitability as excellent GPE. According to the battery tests, the GPE exhibits superior discharge capacities at high C-rates, achieving 129.7 mAh g−1 at 3C and 115.5 mAh g−1 at 5C, while remains a low capacity decay of 0.014 % per cycle over 300 cycles at 3C. Therefore, our work provides a facile strategy of one-step RVIPS to prepare pyridine ionic liquid-based GPE, which demonstrates promising potential for high-performance rechargeable lithium-ion battery.

A sustainable green strategy: Flame-retardant cellulose-based separators for enhancing the safety and cycle stability of lithium-ion batteries

Lithium-ion battery (LIB) separators act an essential role on maintaining electrochemical properties and safety, while polyolefin-based separators exhibit poor thermal stability, resulting in potential safety concerns. In this work, based on 4-aminopyridine (4-AP) and hexachlorocyclotriphosphazene (HCCP), cellulose-based separator modified by HCCP cross-linked 4-AP, named CBS@H-AP, is fabricated to improve the safety and electrochemical stability of LIB. CBS@H-AP is synthesized through the crosslinking reaction of H-AP on the cellulose surface. CBS@H-AP demonstrates low flammability (self-extinguishing) and high thermal-dimensional stability (no apparent heat shrinkage at 240 °C for 5 min). Furthermore, CBS@H-AP discloses high porosity (68.4 %) and wettability (a contact angle of electrolyte of 15.1°). LIB utilizing CBS@H-AP separator unfolds excellent cycle stability, maintaining a capacity retention of 97.2 % and an average coulombic efficiency of 99.2 % at 0.5C over 100 cycles. This work opens up new possibilities for the application of cellulose-based separators in enhancing the safety and cycle stability of LIBs.

Controlled phase separation of regenerated cellulose with super-engineering thermoplastics into porous membranes with hierarchical morphology as high-performance separators for lithium-ion batteries

In this work, a highly porous cellulose/polyarylene ether nitrile (CE/PEN) membrane, bearing hierarchical beads-on-string structures, has been fabricated using regenerated cellulose derived from low-cost waste cigarette butts and PEN via the classical phase conversion method. More specifically, the sequential nucleation of CE and PEN macromolecules from dope solution results in adjustable surface segregation behavior during non-solvent induced phase separation (NIPs), leading to the formation of in-situ assembled rough beads-on-string on the external surfaces and inner pore walls of the membranes. The formation mechanism of a porous membrane with selective component distribution is investigated through thermodynamic and molecular dynamics simulations of phase separation. The resulting composite separator not only exhibits optimal physical properties, including improved mechanical strength, prominent liquid electrolyte wettability (electrolyte contact angle of 0°) and high-thermal resistance, but also demonstrates high ionic conductivity and lower interface resistance. Consequently, the CE/PEN separator enables stable lithium metal anode interface and effectively suppresses the growth of lithium dendrites. More significantly, the resulted lithium metal battery displays remarkable enhancement in capacity, cycling stability (98.6 % for 200 cycles), and rate property (101mAh/g at 10C rate).

Constructing polyolefin-based lithium-ion battery separators membrane for energy storage and conversion

Owing to the escalating demand for environmentally friendly commodities, lithium-ion batteries (LIBs) are gaining extensive recognition as a viable means of energy storage and conversion. LIBs comprise cathode and anode electrodes, electrolytes, and separators. Notably, the separator, a crucial and indispensable element in LIBs that mainly comprises a porous membrane material, necessitates substantial research focus. Scholars have consequently strived to devise novel systems that augment separator efficiency, bolster safety measures, and surmount existing constraints. This review endeavors to equip researchers with comprehensive information on polyolefin-based separator membranes, encompassing performance prerequisites, functional attributes, scientific advancements, and so on. Specifically, it scrutinizes the latest innovations in porous membrane configuration, fabrication, and enhancement that utilize the most prevalent polyolefin materials today. Consequently, robust and enduring membranes fabricated have demonstrated superior effectiveness across diverse applications, facilitating a circular economy that curbs waste materials, reduces operational expenses, and mitigates environmental impact.

Calcium Alginate Fibers/Boron Nitride Composite Lithium-Ion Battery Separators with Excellent Thermal Stability and Cycling Performance.

As one of the most critical components in lithium-ion batteries (LIBs), commercial polyolefin separators suffer from drawbacks such as poor thermal stability and the inability to inhibit the growth of dendrites, which seriously threaten the safety of LIBs. In this study, we prepared calcium alginate fiber/boron nitride-compliant separators (CA@BN) through paper-making technology and the surface coating method using calcium alginate fiber and boron nitride. The CA@BN had favorable electrolyte wettability, flame retardancy, and thermal dimensional stability of the biomass fiber separator. Meanwhile, the boron nitride coating provided excellent thermal conductivity and mechanical strength for the composite separator, which inhibited the growth of lithium dendrites and enabled lithium-ion symmetric batteries to achieve more than 1000 stable and long cycles at a current density of 0.5 mA cm-2. The interwoven fiber mesh formed by the boron nitride coating and the calcium alginate provided multiple pathways for ion migration, which enhanced the storage capacity of the electrolyte, improved the interfacial compatibility between the separator and the electrode, widened the window of electrochemical stability, and enhanced ionic migration. This eco-friendly bio-based separator paves a new insight for the design of heat-resistance separators as well as the safe running of LIBs.

High porosity, excellent mechanical strength, interpenetrating network-reinforced double network regenerated cellulose separators for lithium-ion battery

Cellulose material is emerging as a promising alternative to polyolefin separators in lithium-ion batteries (LIBs) due to its wide availability, electrolyte wettability and thermal stability. Based on the non-solvent induced phase separation, dissolving and regenerating the cellulose material by environmentally friendly solvents and non-solvent enables the efficient and pollution-free preparation of porous regenerated cellulose separator (RCS), greatly expanding their application potential in LIBs. However, the mechanical strength of pure RCS still hardly satisfactory, due to the weak intermolecular bonding and loose porous structure. Therefore, this study introduced an acrylic acid/acrylamide (AA/AM) polymer cross-linking system forming an interpenetrating network with the cellulose framework to produce a double network regenerated cellulose separator (DN-RCS) with high mechanical strength and high porosity. At meantime, the special functional group on AA/AM can influence the transport process of Li+ and PF6− in the electrolyte, helping to form a stable interface on the electrolyte/lithium anode surface to reduce the formation of lithium dendrites. The results showed that DN-RCS possessed excellent mechanical strength and porosity compared to RCS. The high ionic conductivity of DN-RCS (1.03 mS cm−1) enabled the assembled cell with excellent cycling stability (90.8 % at 0.5C for 100 cycles) and rate performance (65.2 % at 5C). This work provides a further feasible strategy for the preparation of a high-performance cellulose-based separator.

Tailoring poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) membrane microstructure for lithium-ion battery separator applications

Novel battery separators based on poly(vinylidene fluoride-co-trifluoroethylene-chlorofluoroethylene)– P(VDF-TrFE-CFE)- were produced by different processing techniques (non-solvent and thermally induced phase separation, salt leaching and electrospinning), in order to evaluate their effect on separator morphology, degree of porosity and pore size, electrochemical parameters and battery cycling behavior. It has been demonstrated that the different processing techniques have a significant influence on the morphology and mechanical properties of membranes. The degree of porosity varies between 23 % and 66 %, for membranes obtained by salt leaching and thermally induced phase separation, respectively.The membranes present a high ionic conductivity value ranging between 1.8 mS.cm−1 for the electrospun membrane and 0.20 mS.cm−1 for the membrane processed by thermally induced phase separator. The lithium transference number value for all membranes is above 0.20, the highest value of 0.55 being obtained for samples prepared by salt leaching and thermally induced phase separation.For all membranes, battery capacity values have been obtained at different C-rates with excellent reversibility. P(VDF-TrFE-CFE) samples present an excellent battery performance at 1C-rate after 100 cycles with 74 mAh.g−1 and excellent coulombic efficiency, for membrane processed by the salt leaching technique. This work demonstrates that P(VDF-TrFE-CFE) terpolymer can be used as a porous membrane in lithium-ion battery separator application, the membrane processing technique allowing to tailor its morphology and, consequently, battery performance.

Robust, High-Temperature-Resistant Polyimide Separators with Vertically Aligned Uniform Nanochannels for High-Performance Lithium-Ion Batteries.

Separator is an essential component of lithium-ion batteries (LIBs), playing a pivotal role in battery safety and electrochemical performance. However, conventional polyolefin separators suffer from poor thermal stability and nonuniform pore structures, hindering their effectiveness in preventing thermal shrinkage and inhibiting lithium (Li) dendrites. Herein, we present a robust, high-temperature-resistant polyimide (PI) separator with vertically aligned uniform nanochannels, fabricated via ion track-etching technology. The resultant PI track-etched membranes (PITEMs) effectively homogenize Li-ion distribution, demonstrating enhanced ionic conductivity (0.57 mS cm-1) and a high Li+ transfer number (0.61). PITEMs significantly prolong the cycle life of Li/Li cells to 1200 h at 3 mA cm-2. For Li/LiFePO4 cells, this approach enables a specific capacity of 143 mAh g-1 and retains 83.88% capacity after 300 cycles at room temperature. At 80 °C, the capacity retention remains at 85.92% after 200 cycles. Additionally, graphite/LiFePO4 pouch cells with PITEMs display enhanced cycling stability, retaining 73.25% capacity after 1000 cycles at room temperature and 78.41% after 100 cycles at 80 °C. Finally, PITEMs-based pouch cells can operate at 150 °C. This separator not only addresses the limitations of traditional separators, but also holds promise for mass production via roll-to-roll methods. We expect this work to offer insights into designing and manufacturing of functional separators for high-safety LIBs.

Reversible Li plating regulation on graphite anode through a barium sulfate nanofibers-based dielectric separator for fast charging and high-safety lithium-ion battery

Poor Li plating reversibility and high thermal runaway risks are key challenges for fast charging lithium-ion batteries with graphite anodes. Herein, a dielectric and fire-resistant separator based on hybrid nanofibers of barium sulfate (BS) and bacterial cellulose (BC) is developed to synchronously enhance the battery’s fast charging and thermal-safety performances. The regulation mechanism of the dielectric BS/BC separator in enhancing the Li+ ion transport and Li plating reversibility is revealed. (1) The Max-Wagner polarization electric field of the dielectric BS/BC separator can accelerate the desolvation of solvated Li+ ions, enhancing their transport kinetics. (2) Moreover, due to the charge balancing effect, the dielectric BS/BC separator homogenizes the electric field/Li+ ion flux at the graphite anode-separator interface, facilitating uniform Li plating and suppressing Li dendrite growth. Consequently, the fast-charge graphite anode with the BS/BC separator shows higher Coulombic efficiency (99.0% vs. 96.9%) and longer cycling lifespan (100 cycles vs. 59 cycles) than that with the polypropylene (PP) separator in the constant-lithiation cycling test at 2 mA cm−2. The high-loading LiFePO4 (15.5 mg cm−2)//graphite (7.5 mg cm−2) full cell with the BS/BC separator exhibits excellent fast charging performance, retaining 70% of its capacity after 500 cycles at a high rate of 2C, which is significantly better than that of the cell with the PP separator (retaining only 27% of its capacity after 500 cycles). More importantly, the thermally stable BS/BC separator effectively elevates the critical temperature and reduces the heat release rate during thermal runaway, thereby significantly enhancing the battery’s safety.

Uniform Poly(vinyl ethylene carbonate) based metal-organic framework separator for smooth lithium-ion electrodeposition

Nanoporous feature in Metal-Organic Frameworks (MOFs) could tune Li+-solvated species and provide high potential for stabilizing lithium metal anodes. However, the inevitable voids within MOF crystallites accommodating free liquid electrolyte, which re-solvates Li+-solvated compounds and vanishes nanopores' advantage for controlling Li+-solvates. Herein, we report an in-situ carbonate photopolymerization reaction within MOF channel that constitutes a uniform nanoporous separator (PVEC-MOF) for smoothing Li+ electrodeposition. PVEC-MOF membrane exhibits accelerating lithium-ion conduction and superior electrochemical performance according to the interconnected ionic nano-channels, whose overpotential maintains at about 0.01 V after 600 cycles in Li-symmetric cell without forming lithium dendrite. Furthermore, employing PVEC-MOF separator in high-voltage cathode material (LiNi0.6Co0.2Mn0.2O2) based Li-metal batteries could effectively enhance electrochemical property and prolong cycling lifespan. This work provides a novel strategy to convert traditional MOF family into uniform nanoporous lithium-ion battery separator, which promotes Li+ smooth electrodeposition and inhibits lithium dendrites in high-energy-density lithium-metal batteries.