Wang Dong,Li Zhenwei,Zhang Qian,Liu Jie,Yang Yu,Han Jishu,Wang Lei
Silicon(Si) with high theoretical capacity has attracted tremendous attention as the next-generation anode material for Li-ion batteries, but the huge expansion during cycling restricts its practical application. Designing a low-cost, accessible robust network binder is a facile and effective approach to suppress the volume change effect and achieve the commercial application of Si anodes. Different previous studies focused on the network binder macromolecule main chain, this manuscript pays attention to the study of small-molecule cross-linker. Herein, cross-linked network binders using alginate acid and two kinds of cross-linkers, i.e., D -sorbitol and isosorbide(Alg-DS and Alg-IS binders) are synthesized. It was found that not only the chemical structure of the cross-linker but also the physicochemical property, such as melting point affect greatly the mechanical properties of the network binder. As a result, the Si anode with an Alg-DS binder dried below the melting point of DS shows the best cycling stability with a high capacity of 2249.8 mA·h/g and a retention rate as high as 95.9% after 100 cycles. This study gives a new view to design robust network binders for stable Si anodes.
Catalytic activities of metal laurates with different coordination capabilities and sodium salts with different ligand alkalinities toward the transesterification between isosorbide (ISB)-based polycarbonate (I c C-PC) and bisphenol-A polycarbonate (BPA-PC) are investigated to accelerate asymmetric chain exchange without aggravating chain degradation. Only catalysts capable of direct reaction with PC chains to form metal alkoxide containing active species (PC–O-M) can initiate and thus accelerate chain transesterification . Sodium salts exhibit the highest catalytic activity and can be further improved by complex formation of 15-crown-5, demonstrating the key role played by alkalinity of reactive ligands. Different from weak catalytic selectivity and serious chain scissions by tin-based catalysts, it is found that, for sodium-catalyzed systems, BPA-PC chains prefer to bond to ISB segments in endo position and the high reactivity of sodium-based catalysts not only significantly reduces essential loading but also suppresses chain degradation. We confirm that these differences must arise from whether active PC-O-M acts as a direct nucleophilic attacker or works with coordination process.
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