Preparation of Thermally Imidized Polyimide Nanofiltration Membranes with Macrovoid-Free Structures

Having Your Cake and Eating It Too: Electrode Processing Approach Improves Safety and Electrochemical Performance of Lithium-Ion Batteries

A layered Li[Ni_xCo_yMn_1-x-y]O₂ (NCM)-based cathode is preferred for its high theoretical specific capacity. However, the two main issues that limit its practical application are severe safety issues and excessive capacity decay. A new electrode processing approach is proposed to synergistically enhance the electrochemical and safety performance. The polyimide's (PI) precursor is spin-coated on the LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) electrode sheet, and the homogeneous sulfonated PI layer is in situ produced by thermal imidization reaction. The PI-spin coated (PSC) layer provides improvements in capacity retention (86.47% vs 53.77% after 150 cycles at 1 C) and rate performance (99.21% enhancement at 5 C) as demonstrated by the NCM523-PSC||Li half-cell. The NCM523-PSC||graphite pouch full cell proves enhanced capacity retention (76.62% vs 58.58% after 500 cycles at 0.5 C) as well. The thermal safety of the NCM523-PSC cathode-based pouch cell is also significantly improved, with the critical temperature of thermal safety T₁ (the beginning temperature of obvious self-heating temperature) and thermal runaway temperature T₂ increased by 60.18 and 44.59 °C, respectively. Mechanistic studies show that the PSC layer has multiple effects as a passivation layer such as isolation of electrode-electrolyte contact, oxygen release suppression, solvation structure tuning, and the decomposition of carbonate solvents as well as LiPF₆ inhibition. This work provides a new path for a cost-effective and scalable design of electrode decoration with synergistic safety-electrochemical kinetics enhancement.

Pervaporation as a Successful Tool in the Treatment of Industrial Liquid Mixtures

Pervaporation is one of the most active topics in membrane research, and it has time and again proven to be an essential component for chemical separation. It has been employed in the removal of impurities from raw materials, separation of products and by-products after reaction, and separation of pollutants from water. Given the global problem of water pollution, this approach is efficient in removing hazardous substances from water bodies. Conventional processes are based on thermodynamic equilibria involving a phase transition such as distillation and liquid-liquid extraction. These techniques have a relatively low efficacy and nowadays they are not recommended because it is not sustainable in terms of energy consumption and/or waste generation. Pervaporation emerged in the 1980s and is now becoming a popular membrane separation technology because of its intrinsic features such as low energy requirements, cheap separation costs, and good quality product output. The focus of this review is on current developments in pervaporation, mass transport in membranes, material selection, fabrication and characterization techniques, and applications of various membranes in the separation of chemicals from water.

Carbon molecular sieve hollow fiber composite membrane derived from PMDA-ODA polyimide for gas separation

Carbon molecular sieve (CMS) membranes have excellent gas separation property over conventional polymeric membranes and superior anti-swelling property. PMDA-ODA polyimide has high thermal stability and good mechanical property. It has been extensively adopted as the precursor of CMS membrane. However, due to the insoluble nature, PMDA-ODA CMS membranes are limited to configurations like dense symmetric films or composite membranes using porous inorganic or metal substrates. In this work, CMS hollow fiber composite membranes based on an asymmetric PMDA-ODA hollow fiber were successfully prepared for the first time. The neat PMDA-ODA hollow fiber membrane was crosslinked by polyethyleneimine to alleviate pore collapsing during carbonization and then dip-coated by a PMDA-ODA PAA solution to seal the surface defects. The PDMA-ODA CMS composite hollow fiber membranes showed gas permeances of 93.4 GPU, 19.6 GPU, 6.5 GPU, and 4.7 GPU for CO2, O2, N2, and CH4, respectively, with an ideal selectivity of 14.4, 3.0, and 19.8 for CO2/N2, O2/N2, and CO2/CH4 gas pairs, respectively. The attractive gas separation property shows a great potential for industrial application.

Scalable Polyimide-Poly(Amic Acid) Copolymer Based Nanocomposites for High-Temperature Capacitive Energy Storage

The developments of next-generation electric power systems and electronics demand for high temperature (≈150 °C), high energy density, high efficiency, scalable, and low-cost polymer-based dielectric capacitors are still scarce. Here, the nanocomposites based on polyimide-poly(amic acid) copolymers with a very low amount of boron nitride nanosheets are designed and synthesized. Under the actual working condition in hybrid electric vehicles of 200 MV m^-1 and 150 °C, a high energy density of 1.38 J cm^-3 with an efficiency higher than 96% is achieved. This is about 2.5 times higher than the room temperature energy density (≈0.39 J cm^-3 under 200 MV m^-1 ) of the commercially used biaxially oriented polypropylene, the benchmark of dielectric polymer. Especially, the energy density and efficiency at 150 °C show no sign of degradation after 20 000 cycles of charge-discharge test and 35 days' high-temperature endurance test. This research provides an effective and low-cost strategy to develop high-temperature polymer-based capacitors.

Enhancement in Flux and Antifouling Properties of Polyvinylidene Fluoride/Polycarbonate Blend Membranes for Water Environmental Improvement

In this work, to overcome the fouling phenomenon of hydrophobic polymer membranes, polyvinylidene fluoride (PVDF) was blended with hydrophilic polycarbonate (PC) to prepare ultrafiltration membranes via the nonsolvent-induced phase separation method. The effects of PC content on membrane morphology, pore size distribution, and surface porosity were characterized and investigated by FE-SEM and image analyzer software. Solubility parameters calculated by molecular dynamics (MD) simulation showed that PVDF and PC are compatible and the results were confirmed by differential scanning calorimetry and wide angle X-ray diffractometry. The long-term chemical stability against NaOH and mechanical property before and after the abrasion test of the prepared membranes were also characterized by dynamic thermomechanical analysis. It was found that the hydrophilicity, water flux, abrasion resistance, and antifouling properties as the performance criteria of polymeric membranes were improved because of the presence of PC, and the separation efficiency of PVDF/PC membranes is much higher than that of the pristine PVDF membrane. The exemplary water filtration performances of these polymer membranes are harnessed here in this work to purify raw water polluted by natural organic matters, addressing the key environmental issue of water contamination.