多功能复合型粘结剂的结构和组成设计及其在高负载锂硫电池中的作用机制研究

Lithium-sulfur batteries have been deemed as one of the most promising high-energy-density secondary battery systems. However, the intrinsic insulating nature of sulfur, as well as the special "solid-liquid-solid" phase transitions of sulfur cathode during cycling, would give rise to the dissolution and shuttle of the high-order lithium polysulfides (Li2Sn, 4 ≤ n ≤ 8) and marked volume change (~79.2%). This might in turn result in the severe loss of active materials, limited Coulombic efficiency and heavy polarization, rendering the high-loading sulfur cathode to suffer from low capacity and poor cyclability. In recent years, growing research efforts have manifested that a great deal of key battery characteristics, encompassing reversible capacity, rate capability, and stability, are critically dependent upon the electrically inactive components, such as functional binders. These binders can either provide polar functional groups to capture soluble lithium polysulfides and suppress the shuttle effect, or aid to construct three-dimensional high-strength and high-conductivity skeleton to maintain the structural/electrical integrity of the electrode during long-term cycling. Nevertheless, daunting challenges still remain when being used in high-loading sulfur cathodes, including the functional limitation of the single-component binders, weak interaction between the polymeric binder and sulfur material, low reversibility of the binder-captured Li2Sn and intrinsic insulating nature of polymeric binders. In this project, we propose a novel strategy to develop multifunctional composite binders to surmount the above-mentioned obstacles by synthesizing high-strength + functional, high-strength + high-adhesion + functional, high-strength + high-conductivity + functional binders. By employing these multifunctional composite binders, we aim to construct a three-dimensional high-strength network that enables the effective integration of the active materials, conductive agents and current collector, reduce the polarization and accordingly, fabricate high-loading sulfur cathodes that can work at high-current densities with stable cycling performance. Meanwhile, the underlying working mechanism of such multifunctional composite binders in high-loading sulfur electrodes will be systematically investigated with the aid of in-situ characterization techniques such as in operando Raman and in operando UV-Vis spectroscopy.

锂硫电池是高能量密度二次电池的重要体系，但硫材料固有的绝缘属性以及硫正极在电化学循环中特殊的“固-液-固”反应历程，易导致“穿梭”效应、剧烈体积变化等负面影响，造成高负载硫正极性能发挥和稳定循环的极大困难。近年来，作为非活性组分的粘结剂在锂硫电池中被赋予了丰富的功能，如有效捕捉溶解性多硫化锂以及维持电极/导电结构长期循环稳定性等。但高负载硫正极用粘结剂仍存在：单组份粘结剂功能限制、硫材料与粘结剂弱相互作用、粘结剂“捕获”多硫化锂的反应可逆性以及自身电子绝缘性等关键问题。本项目提出发展多功能复合型粘结剂的研究思路，拟通过研制强度型+功能型、高强度+高粘附性功能型、高强度+高电子电导功能型三类复合粘结剂，克服上述瓶颈问题，将硫材料、粘结剂和导电剂构建为高强度一体化结构，降低极化，制备出可在大倍率下稳定循环的高负载硫正极；同时结合电化学原位谱学表征，阐明上述粘结剂在高负载硫正极中的有效工作机制。

锂硫电池是高能量密度二次电池的重要体系，但硫材料固有的绝缘属性以及硫正极在电化学循环中特殊的“固-液-固”反应历程，易导致“穿梭”效应、剧烈体积变化等负面影响，造成高负载和低电解液/硫比等极端条件下硫正极性能发挥和稳定循环的极大困难。项目针对上述基础科学问题，从硫电极中的非活性组分粘结剂入手，创新性地提出多种兼具高粘附力、高机械强度、强极性的复合功能型粘结剂，将硫材料、粘结剂和导电剂构筑为高强度一体化结构；同时借助粘结剂中的极性官能团或引入高性能宿主和隔膜夹层材料等，对溶解性多硫化锂中间产物进行高效锚定和限域，显著降低穿梭效应，制备出可在大倍率下稳定循环的高负载硫正极。我们也借助多种原位谱学表征手段，阐明了上述粘结剂体系对高负载锂硫电池性能提升的工作机制。.项目取得了三方面重要研究成果：1）提出基于聚多巴胺+交联聚丙烯酰胺（PDA/c-PAM）的高粘附性+高强度功能型、基于光固化交联乙氧基化三羟甲基丙烷三丙酸酯+聚偏氟乙烯（c-ETPTA/PVDF）的强度型+功能型以及具有优良机械柔韧性的聚（乙烯-alt-马来酸酐）（P（E-alt-MA））这三类新型粘结剂，成功应用于高硫负载、长寿命锂硫电池的制备；2）开发出导电NiCo2S4纳米管、MnS-MoS2 p-n异质结和非对称电子结构的N2-Fe-B2单原子催化剂等先进宿主材料，以及基于缺陷工程构筑的D-UiO-66-NH2-4/G膜电极，大幅提升硫的氧化还原反应动力学，制备得到硫负载最高为14.7 mg cm-2的稳定硫正极；3）发展了水解聚马来酸酐/聚氧化乙烯（PEO-HPMA-TEGDME）和金属有机框架三维共价交联（PTMG-PUHI）这两类准固体电解质，尝试从根本上抑制甚至消除硫氧化还原过程中的液相步骤及其相应的穿梭，为高负载准/全固态锂硫电池的研制打下了基础。.项目已在Chem. Soc. Rev., Adv. Mater., Coord. Chem. Rev., Adv. Energy Mater., ACS Nano, Adv. Funct. Mater., Energy Storage Mater., J. Energy Chem.,《科学通报》、《高等学校化学学报》、《物理化学学报》等杂志以通讯作者发表论文24篇，IF>10论文15篇；申请专利7项，授权2项；获得“万人计划”青年拔尖人才的立项支持。