Thermal degradation behavior and probable mechanism of aromatic poly(1,3,4-oxadiazole)s fibers

N-Type Polyoxadiazole Conductive Polymer Binders Derived High-Performance Silicon Anodes Enabled by Crosslinking Metal Cations

The dilemma of employing high-capacity battery materials and maintaining the electrodes' electrical and mechanical integrity requires a unique binder system design. Polyoxadiazole (POD) is an n-type conductive polymer with excellent electronic and ionic conductive properties, which has acted as a silicon binder to achieve high specific capacity and rate performance. However, due to its linear structure, it cannot effectively alleviate the enormous volume change of silicon during the process of lithiation/delithiation, resulting in poor cycle stability. This paper systematically studied metal ion (i.e., Li⁺, Na⁺, Mg²⁺, Ca²⁺, and Sr²⁺)-crosslinked PODs as silicon anode binders. The results show that the ionic radius and valence state remarkably influence the polymer's mechanical properties and the electrolyte's infiltration. Electrochemical methods have thoroughly explored the effects of different ion crosslinks on the ionic and electronic conductivity of POD in the intrinsic and n-doped states. Attributed to the excellent mechanical strength and good elasticity, Ca-POD can better maintain the overall integrity of the electrode structure and conductive network, significantly improving the cycling stability of the silicon anode. The cell with such binders still retains a capacity of 1770.1 mA h g^-1 after 100 cycles at 0.2 C, which is ∼285% that of the cell with the PAALi binder (620.6 mA h g^-1). This novel strategy using metal-ion crosslinking polymer binders and the unique experimental design provides a new pathway of high-performance binders for next-generation rechargeable batteries.

Synthesis and characterization of polyhydrazides and poly(1,3,4-oxadiazole)s containing multiple arylene ether linkages and pendent pentadecyl chains

A new diacylhydrazide monomer, namely, 4-(4-(4-(4-(hydrazinocarbonyl)phenoxy)-2-pentadecylphenoxy)phenoxy) benzohydrazide (HPPDPB), was synthesized starting from 4-(4-hydroxyphenoxy)-3-pentadecylphenol. HPPDPB was polycondensed with terephthalic acid chloride (TPC), isophthalic acid chloride (IPC) and a mixture of TPC and IPC (50:50 mol%) to obtain polyhydrazides containing multiple arylene ether linkages in the backbone and pendent pentadecyl chains. Polyhydrazides were subsequently cyclized in the presence of phosphorus oxychloride to obtain the corresponding poly(1,3,4-oxadiazole)s. Polyhydrazides and poly(1,3,4-oxadiazole)s exhibited inherent viscosities in the range 0.65–0.72 dL g−1 and 0.54–0.62 dL g−1, respectively, which indicated the formation of reasonably high-molecular weight polymers. Polyhydrazides were soluble in polar aprotic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide (DMAc), 1-methyl-2-pyrrolidinone and pyridine whereas poly(1,3,4-oxadiazole)s exhibited excellent solubility even in common organic solvents such as chloroform, dichloromethane and tetrahydrofuran. Tough, transparent and flexible films of polyhydrazides and poly(1,3,4-oxadiazole)s could be cast from DMAc and chloroform solutions, respectively. X-Ray diffraction studies revealed amorphous nature of polyhydrazides and poly(1,3,4-oxadiazole)s and the formation of layered structure was observed due to ordered packing of pentadecyl chains. The 10% decomposition temperature ( T10) values for poly(1,3,4-oxadiazole)s were in the range 425–440°C indicating their good thermal stability. Glass transition temperature ( Tg) values of polyhydrazides and poly(1,3,4-oxadiazole)s were in the range 175–192°C and 92–103°C, respectively. The excellent solubility characteristics and the large gap between Tg (92–103°C) and T10 (425–440°C) values give poly(1,3,4-oxadiazole)-containing pendent pentadecyl chains better opportunities for processability.