Crosslinker free thermally induced crosslinking of hydrogenated nitrile butadiene rubber

Spiro-Twisted Benzoxazine Derivatives Bearing Nitrile Group for All-Solid-State Polymer Electrolytes in Lithium Batteries

In this study, two nitrile-functionalized spiro-twisted benzoxazine monomers, namely 2,2′-((6,6,6′,6′-tetramethyl-6,6′,7,7′-tetrahydro-2H,2′H-8,8′-spirobi[indeno[5,6-e][1,3]oxazin]-3,3′(4H,4′H)-diyl)bis(4,1-phenylene))diacetonitrile (TSBZBC) and 4,4′-(6,6,6′,6′-tetramethyl-6,6′,7,7′-tetrahydro-2H,2′H-8,8′-spirobi[indeno[5,6-e][1,3]oxazin]-3,3′(4H,4′H)-diyl)dibenzonitrile (TSBZBN) were successfully developed as cross-linkable precursors. In addition, the incorporation of the nitrile group by covalent bonding onto the crosslinked spiro-twisted molecular chains improve the miscibility of SPE membranes with lithium salts while maintaining good mechanical properties. Owing to the presence of a high fractional free volume of spiro-twisted matrix, the –CN groups would have more space for rotation and vibration to assist lithium migration, especially for the benzyl cyanide-containing SPE. When combined with poly (ethylene oxide) (PEO) electrolytes, a new type of CN-containing semi-interpenetrating polymer networks for solid polymer electrolytes (SPEs) were prepared. The PEO-TSBZBC and PEO-TSBZBN composite SPEs (with 20 wt% crosslinked structure in the polymer) are denoted as the BC20 and BN20, respectively. The BC20 sample exhibited an ionic conductivity (σ) of 3.23 × 10⁻⁴ S cm⁻¹ at 80 °C and a Li⁺ ion transference number of 0.187. The LiFePO₄ (LFP)|BC20|Li sample exhibited a satisfactory charge–discharge capacity of 163.6 mAh g⁻¹ at 0.1 C (with approximately 100% coulombic efficiency). Furthermore, the Li|BC20|Li cell was more stable during the Li plating/stripping process than the Li|BN20|Li and Li|PEO|Li samples. The Li|BC20|Li symmetric cell could be cycled continuously for more than 2700 h without short-circuiting. In addition, the specific capacity of the LFP|BC20|Li cell retained 87% of the original value after 50 cycles.

Quantification of the ion transport mechanism in protective polymer coatings on lithium metal anodes

Protective Polymer Coatings (PPCs) have been proposed to protect lithium metal anodes in rechargeable batteries to stabilize the Li/electrolyte interface and to extend the cycle life by reducing parasitic reactions and improving the lithium deposition morphology. However, the ion transport mechanism in PPCs remains unclear. Specifically, the degree of polymer swelling in the electrolyte and the influence of polymer/solvent/ion interactions are never quantified. Here we use poly(acrylonitrile-co-butadiene) (PAN-PBD) with controlled cross-link densities to quantify how the swelling ratio of the PPC affects conductivity, Li+ ion selectivity, activation energy, and rheological properties. The large difference in polarities between PAN (polar) and PBD (non-polar) segments allows the comparison of PPC properties when swollen in carbonate (high polarity) and ether (low polarity) electrolytes, which are the two most common classes of electrolytes. We find that a low swelling ratio of the PPC increases the transference number of Li+ ions while decreasing the conductivity. The activation energy only increases when the PPC is swollen in the carbonate electrolyte because of the strong ion-dipole interaction in the PAN phase, which is absent in the non-polar PBD phase. Theoretical models using Hansen solubility parameters and a percolation model have been shown to be effective in predicting the swelling behavior of PPCs in organic solvents and to estimate the conductivity. The trade-off between conductivity and the transference number is the primary challenge for PPCs. Our study provides general guidelines for PPC design, which favors the use of non-polar polymers with low polarity organic electrolytes.