High performance separator coated with amino-functionalized SiO2 particles for safety enhanced lithium-ion batteries

Functionalized Separators Boosting Electrochemical Performances for Lithium Batteries

The growing demands for energy storage systems, electric vehicles, and portable electronics have significantly pushed forward the need for safe and reliable lithium batteries. It is essential to design functional separators with improved mechanical and electrochemical characteristics. This review covers the improved mechanical and electrochemical performances as well as the advancements made in the design of separators utilizing a variety of techniques. In terms of electrolyte wettability and adhesion of the coating materials, we provide an overview of the current status of research on coated separators, in situ modified separators, and grafting modified separators, and elaborate additional performance parameters of interest. The characteristics of inorganics coated separators, organic framework coated separators and inorganic-organic coated separators from different fabrication methods are compared. Future directions regarding new modified materials, manufacturing process, quantitative analysis of adhesion and so on are proposed toward next-generation advanced lithium batteries.

Fabrication of Network Spherical α-Al2O3 and Its Application on the Separator of Lithium-Ion Batteries

Ceramic-coated polyolefin separator technology is considered a simple and effective method for the improvement of lithium-ion battery (LIB) safety. However, the characteristics of ceramic powder can adversely affect the surface structure and ion conductivity of the separators. Therefore, it is crucial to develop a ceramic powder that not only improves the thermal stability of the separators but also enhances ion conductivity. Herein, network spherical α-Al2O3 (N-Al2O3) with a multi-dimensional network pore structure was constructed. Furthermore, N-Al2O3 was applied as a coating to one side of polyethylene (PE) separators, resulting in N-Al2O3-PE separators that exhibit superior thermal stability and enhanced wettability with liquid electrolytes. Notably, the N-Al2O3-PE separators demonstrated exceptional ionic conductivity (0.632 mS cm-1), attributed to the internal multi-dimensional network pore structures of N-Al2O3, which facilitated an interconnected and efficient "highway" for the transport of Li+ ions. As a consequence, LiCoO2/Li half batteries equipped with these N-Al2O3-PE separators showcased remarkable rate and cycling performance. Particularly at high current densities, their discharge capacity and capacity retention rate significantly outperformed those of conventional PE separators.

Review of Progress in the Application of Polytetrafluoroethylene-Based Battery Separators

Batteries have broad application prospects in the aerospace, military, automotive, and medical fields. The performance of the battery separator, a key component of rechargeable batteries, is inextricably linked to the quality of the batteries. The polytetrafluoroethylene (PTFE)-based membrane, in addition to PTFE's intrinsic properties of corrosion resistance and high temperature resistance, also possesses characteristics such as high porosity and high strength, making it an ideal substrate for the separator in current high-performance batteries, such as fuel cells (FC), all-vanadium redox liquid current batteries (VRBs), solid-state batteries (SSBs), and lithium-ion batteries (LIBs). This paper introduces the PTFE membrane's main preparation methods and application fields and outlines its advantages as a battery separator. It then comprehensively describes the status of PTFE-based battery separator applications, sums up the advantages and development prospects of PTFE-based battery separators, and looks forward to the important role and challenges PTFE-based battery separators will play in the future of rechargeable batteries and even in new energy equipment with even more harsh and complex electrolytes. In the future, PTFE-based battery separators will be used in rechargeable batteries and even in new energy devices with more severe and complex electrolytes, which will play an important role and challenge in providing a reference for the research on PTFE-based battery separators.

Pilot Scale Hybrid Organic/Inorganic Coatings on a Polyolefin Separator to Enhance Dimensional Stability for Thermally Stable Long-Life Rechargeable Batteries

The electric vehicle and energy storage markets have grown rapidly in recent years. Thermal runaway caused by malfunctioning Li-ion batteries is an urgent issue with many causes (e.g., mechanical, electrical, and thermal abuse). The most common cause of thermal runaway is the formation of an internal short circuit because of damage to the separator. There has been significant effort to improve the design of separators, but to our knowledge, only inorganic nanoparticle coatings are used in commercial Li-ion batteries. Here, hybrid organic/inorganic coating layers are synthesized in a pilot-scale process that was developed from a crosslinkable polyamide-imide synthesis technique. The fabrication process is optimized to achieve reproducible hybrid organic/inorganic coating layers that are thin (≤4 μm), permeable (≤250 s/100 cc), and thermally stable beyond 150 °C. The hybrid coating layer is applied to mini-18650 Li-ion cells to show that the discharge capacity did not change at low discharge rates, and the retention capacity after 500 cycles was better than that of the reference cells used for comparison. This work demonstrates that a novel hybrid coating layer has the potential to improve the stability of commercial Li-ion batteries.

Fabrication and Investigation of PE-SiO2@PZS Composite Separator for Lithium-Ion Batteries

Commercial polyolefin separators exhibit problems including shrinkage under high temperatures and poor electrolyte wettability and uptake, resulting in low ionic conductivity and safety problems. In this work, core–shell silica-polyphosphazene nanoparticles (SiO₂@PZS) with different PZS layer thicknesses were synthesized and coated onto both sides of polyethylene (PE) microporous membranes to prepare composite membranes. Compared to pure silica-coated membranes and PE membranes, the PE-SiO₂@PZS composite membrane had higher ionic conductivity. With the increase in the SiO₂@PZS shell thickness, the electrolyte uptake, ionic conductivity and discharge capacity gradually increased. The discharge capacity of the PE-SiO₂@PZS composite membrane at 8 C rate was 129 mAh/g, which was higher than the values of 107 mAh/g for the PE-SiO₂ composite membrane and 104 mAh/g for the PE membrane.

High-performance composite separators based on the synergy of vermiculite and laponite for lithium-ion batteries

The electrochemical performance and safe operation of the separator plays an important role in lithium-ion batteries. The introduction of inorganic nanoparticles into the separators with organic matter as the matrix effectively improves the thermal stability and wettability of the composite separators, but it also blocks some pores and adversely affects the electrochemical performance. Herein, vermiculite and laponite nanoparticles are introduced into a poly(vinylidene fluoride) matrix to prepare organic-inorganic composite separators for lithium-ion batteries and the synergistic effect of the two inorganic nanofillers is explored. By adding the same amount of the two nanoparticles into the polymer matrix, the prepared separator has the highest ionic conductivity (0.72 mS cm^-1) at room temperature and the lowest interfacial impedance (283 Ω). It has an initial discharge capacity of 161.2 mA h g^-1 at a rate of 0.5C, a coulombic efficiency of 99.5% after 100 cycles, and a high capacity retention rate of 98.4%, which shows excellent rate performance. The results show that the two clay nanoparticles exert their respective advantages and exhibit a synergistic enhancement effect on the battery performance, which inspires new ideas for the preparation of new organic-inorganic composite separators.

A Review on Lithium-Ion Battery Separators towards Enhanced Safety Performances and Modelling Approaches

In recent years, the applications of lithium-ion batteries have emerged promptly owing to its widespread use in portable electronics and electric vehicles. Nevertheless, the safety of the battery systems has always been a global concern for the end-users. The separator is an indispensable part of lithium-ion batteries since it functions as a physical barrier for the electrode as well as an electrolyte reservoir for ionic transport. The properties of separators have direct influences on the performance of lithium-ion batteries, therefore the separators play an important role in the battery safety issue. With the rapid developments of applied materials, there have been extensive efforts to utilize these new materials as battery separators with enhanced electrical, fire, and explosion prevention performances. In this review, we aim to deliver an overview of recent advancements in numerical models on battery separators. Moreover, we summarize the physical properties of separators and benchmark selective key performance indicators. A broad picture of recent simulation studies on separators is given and a brief outlook for the future directions is also proposed.

Assembly of MXene/PP Separator and Its Enhancement for Ni-Rich LiNi0.8Co0.1Mn0.1O2 Electrochemical Performance

In this work, a few-layer MXene is prepared and sprinkled on a commercial polypropylene (PP) separator by a facile spraying method to enhance the electrochemistry of the Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode. Scanning electron microscope (SEM) and X-ray diffraction (XRD) are used to characterize the morphology and structure of MXene. Fourier transform infrared spectroscopy (FT-IR) and a contact angle tester are used to measure the bond structure and surface wettability PP and MXene/PP separator. The effect of the MXene/PP separator on the electrochemical performance of ternary NCM811 material is tested by an electrochemical workstation. The results show that the two-dimensional MXene material could improve the wettability of the separator to the electrolyte and greatly enhance the electrochemical properties of the NCM811 cathode. During 0.5 C current density cycling, the Li/NCM811 cell with MXene/PP separator remains at 166.2 mAh/g after the 100 cycles with ~90.7% retention. The R_ct of MXene/PP cell is measured to be ~28.0 Ω. Combining all analyses results related to MXene/PP separator, the strategy by spraying the MXene on commercial PP is considered as a simple, convenient, and effective way to improve the electrochemical performance of the Ni-rich NCM811 cathode and it is expected to achieve large-scale in high-performance lithium-ion batteries in the near future.

High performance of boehmite/polyacrylonitrile composite nanofiber membrane for polymer lithium-ion battery

In this study, a novel boehmite/polyacrylonitrile (BM/PAN) composite nanofiber membrane was prepared using the electrospinning technique. The physical and electrochemical properties of different contents of BM/PAN composite nanofiber membranes were investigated as separators for lithium ion batteries (LIBs). Compared to the commercial polypropylene (PP) separator, the experimental results show that the BM/PAN composite nanofiber separator possesses a unique three-dimensional (3D) interconnected structure and exhibits higher porosity, greater electrolyte up-take, higher thermal stability and better electrochemical performance in a LiCoO₂/Li cell. Besides, batteries containing 30 wt% BM/PAN membranes display the highest ionic conductivity (2.85 mS cm⁻¹), widest electrochemical stability window (5.5 V vs. Li⁺/Li), leading to the highest initial discharge capacity (162 mA h g⁻¹) and the largest capacity retention ratio (90.7%) at 0.5C after 100 cycles. These findings reveal that the BM/PAN composite nanofiber membranes are promising candidates as commercial separators for high performance LIBs.

In this study, a novel boehmite/polyacrylonitrile (BM/PAN) composite nanofiber membrane was prepared using the electrospinning technique.

High Temperature Resistant Separator of PVDF-HFP/DBP/C-TiO2 for Lithium-Ion Batteries

To improve the thermal shrinkage and ionic conductivity of the separator for lithium-ion batteries, adding carboxylic titanium dioxide nanofiber materials into the matrix is proposed as an effective strategy. In this regard, a poly(vinylidene fluoride-hexafluoro propylene)/dibutyl phthalate/carboxylic titanium dioxide (PVDF-HFP/DBP/C-TiO₂) composite separator is prepared with the phase inversion method. When the content of TiO₂ nanofibers reaches 5%, the electrochemical performance of the battery and ion conductivity of the separator are optimal. The PVDF-HFP/DBP/C-TiO₂ (5%) composite separator shows about 55.5% of porosity and 277.9% of electrolyte uptake. The PVDF-HFP/DBP/C-TiO₂ (5%) composite separator has a superior ionic conductivity of 1.26 × 10 ⁻³ S cm⁻¹ and lower interface impedance at room temperature, which brings about better cycle and rate performance. In addition, the cell assembled with a PVDF-HFP/DBP/C-TiO₂ separator can be charged or discharged normally and has an outstanding discharge capacity of about 150 mAh g⁻¹ at 110 °C. The battery assembled with the PVDF-HFP/DBP/C-TiO₂ composite separator exhibits excellent electrochemical performance under high and room temperature environments.

A Review on Inorganic Nanoparticles Modified Composite Membranes for Lithium-Ion Batteries: Recent Progress and Prospects

Separators with high porosity, mechanical robustness, high ion conductivity, thin structure, excellent thermal stability, high electrolyte uptake and high retention capacity is today's burning research topic. These characteristics are not easily achieved by using single polymer separators. Inorganic nanoparticle use is one of the efforts to achieve these attributes and it has taken its place in recent research. The inorganic nanoparticles not only improve the physical characteristics of the separator but also keep it from dendrite problems, which enhance its shelf life. In this article, use of inorganic particles for lithium-ion battery membrane modification is discussed in detail and composite membranes with three main types including inorganic particle-coated composite membranes, inorganic particle-filled composite membranes and inorganic particle-filled non-woven mates are described. The possible advantages of inorganic particles application on membrane morphology, different techniques and modification methods for improving particle performance in the composite membrane, future prospects and better applications of ceramic nanoparticles and improvements in these composite membranes are also highlighted. In short, the contents of this review provide a fruitful source for further study and the development of new lithium-ion battery membranes with improved mechanical stability, chemical inertness and better electrochemical properties.

A SuperLEphilic/Superhydrophobic and Thermostable Separator Based on Silicone Nanofilaments for Li Metal Batteries

Conventional polyolefin separators suffer from poor wettability to liquid electrolytes (LEs). Although some modified separators exhibit improved wettability, they are hydrophilic, causing inevitable moisture uptake. Trace water could result in poor performance and safety hazard of Li metal batteries. Here, we report a design idea of superLEphilic/superhydrophobic and thermostable separators by modifying the Celgard separator using silicone nanofilaments. The separator features low moisture uptake (∼0%), fast LE diffusion (454 ms), and high LE uptake (287.8%), LE retention rate, and Li⁺ conductivity. Consequently, the Li/LiFePO₄ cells show high cycling stability (96.05% after 350 cycles), good rate performance (125 mA h g⁻¹ at 5.0 C), low resistance, and stable open circuit voltage at 160°C. Moreover, the separator could improve performance of the other Li metal batteries with high-voltage cathodes and the LiFePO₄/graphite pouch cells. This work provides an avenue for designing advanced separators by using bioinspired superwetting surfaces.

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A superLEphilic/superhydrophobic separator is first reported for Li metal batteries

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The separator has low moisture uptake and could improve performance of Li/Li cells

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The separator features fast LE diffusion, high LE uptake, and Li⁺ conductivity

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The separator could enhance performance of high-voltage Li metal batteries

Polymer Template Synthesis of Soft, Light, and Robust Oxide Ceramic Films

Oxide ceramic materials underpin a wide variety of technologies. However, the inherent fragility of these materials limits their use in emerging fields like wearable electronics and soft energy storage devices. Here, we develop a sol-gel electrospinning technique followed by calcination to create a range of oxide ceramic nanofiber films that exhibit significant softness without fragility after various deformations. This approach causes the ceramic crystals to fuse together at a low temperature during their growth within the polymer nanofiber templates. All the synthesized ceramic films, from SiO₂ to BaTiO₃, Li_0.33La_0.56TiO₃, and Li₇La₃Zr₂O₁₂, have silk-like softness of <31 mN, low density of <0.36 g/cm³ and robust fire resistance to 1,000°C. Fabricated separators based on these films display large electrolyte uptakes of >900% and high thermal insulation performance, enhancing the rate capability and safety of lithium batteries. The reported method allows scalable synthesis of soft oxide ceramic films with properties appealing for applications.

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A scalable method is developed for the fabrication of soft oxide ceramic films

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A wide variety of soft, light, and robust oxide ceramic films are fabricated

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A detailed soft deformation mechanism of the ceramic films is illustrated

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The soft ceramic films exhibit appealing properties for applications

A Novel Self-Binding Composite Separator Based on Poly(tetrafluoroethylene) Coating for Li-Ion Batteries

In this study, a novel composite separator based on polytetrafluoroethylene (PTFE) coating layers and a commercial polyethylene (PE) separator is developed for high performance Li-ion batteries. This composite separator is prepared by immersing a PE separator directly into a commercial PTFE suspension to obtain a self-binding PTFE/PE/PTFE tri-layered structure. Then, the as-prepared composite separator is further treated with a H₂O₂/H₂SO₄ solution to enhance its electrolyte affinity. The results show that the coating layer, consisting of close-packed PTFE particles, possesses a highly ordered nano-porous structure and an excellent electrolyte wettability property, which significantly enhance the ionic conductivity of the composite separator. Due to the presence of the PTFE-based coating layer, the composite separator exhibits better thermal stability compared with the PE separator, reaching the thermal-resistant grade of commercial ceramic-coated separators. By using different separators, CR2032-type unit half-cells composed of a Li anode and a LiFePO₄ cathode were assembled, and their C-rate and cycling performances were evaluated. The cell assembled with the composite separator was proven to have better C-rate capability and cycling capacity retention than the cell with the polyethylene separator. It is expected that the composite separator can be a potential candidate as a coating-type separator for high-performance rechargeable Li-ion batteries.

Design Principles of Functional Polymer Separators for High-Energy, Metal-Based Batteries

Next-generation rechargeable batteries that offer high energy density, efficiency, and reversibility rely on cell configurations that enable synergistic operations of individual components. They must also address multiple emerging challenges,which include electrochemical stability, transport efficiency, safety, and active material loss. The perspective of this Review is that rational design of the polymeric separator, which is used widely in rechargeable batteries, provides a rich set of opportunities for new innovations that should enable batteries to meet many of these needs. This perspective is different from the conventional view of the polymer separator as an inert/passive unit in a battery, which has the sole function to prevent direct contact between electrically conductivecomponents that form the battery anode and cathode. Polymer separators, which serve as the core component in a battery, bridge the electrodes and the electrolyte with a large surface contact that can be utilized to apply desirable functions. This Review focuses specifically on recent advances in polymer separator systems, with a detailed analysis of several embedded functional agents that are incorporated to improve mechanical robustness, regulate ion and mass transport, and retard flammability. The discussion is also extended to new composite separator concepts that are designated traditionally as polymer/gel electrolytes.

Highly Conductive Solid-State Hybrid Electrolytes Operating at Subzero Temperatures

We report a unique, highly conductive, dendrite-inhibited, solid-state polymer electrolyte platform that demonstrates excellent battery performance at subzero temperatures. A design based on functionalized inorganic nanoparticles with interconnected mesopores that contain surface nitrile groups is the key to this development. Solid-state hybrid polymer electrolytes based on succinonitrile (SN) electrolytes and porous nanoparticles were fabricated via a simple UV-curing process. SN electrolytes were effectively confined within the mesopores. This stimulated favorable interactions with lithium ions, reduced leakage of SN electrolytes over time, and improved mechanical strength of membranes. Inhibition of lithium dendrite growth and improved electrochemical stability up to 5.2 V were also demonstrated. The hybrid electrolytes exhibited high ionic conductivities of 2 × 10^-3 S cm^-1 at room temperature and >10^-4 S cm^-1 at subzero temperatures, leading to stable and improved battery performance at subzero temperatures. Li cells made with lithium titanate anodes exhibited stable discharge capacities of 151 mAh g^-1 at temperatures below -10 °C. This corresponds to 92% of the capacity achieved at room temperature (164 mAh g^-1). Our work represents a significant advance in solid-state polymer electrolyte technology and far exceeds the performance available with conventional polymeric battery separators.