【作者】 龙江；

【导师】 张校刚；

【作者基本信息】 南京航空航天大学 ， 化学， 2023， 硕士

【摘要】 聚合物粘结剂作为电极材料的重要组成部分,虽然其质量占比较少,但其对限制硅基负极材料的体积膨胀、提升锂离子电池的电化学性能具有十分重要的影响。常用的一维(1D)线性聚合物粘结剂由于结合位点少、移动性强等缺点不足以解决硅基负极颗粒的体积膨胀问题,因此有必要通过对1D线性聚合物结构设计与改性,制备具有网络结构的粘结剂,增加与硅负极颗粒的结合位点,消散连续充放电过程中的机械应力,从而抑制硅负极颗粒的体积膨胀,提升电池的电化学性能。(1)通过对一维聚合物粘结剂聚乙烯醇(PVA)的结构改性,与甜菜碱(Bet)简单热交联,将两性离子甜菜碱引入到氢键聚乙烯醇网络中,制备了一种基于两性离子络合的新型网状粘结剂PVA-Bet。该水系粘结剂有更多的接触位点以及更多极性基团(-OH、-COO-、-N+-(CH3)4)与硅颗粒表面的Si-OH形成氢键,具有更加出色的粘附性能,从而保持电极的完整性提升电池的电化学性能。在0.2 A g-1电流密度下循环100圈后仍保持有1114 mAh g-1的容量,当电流密度增加到1 A g-1循环200圈后仍保持有648 mAh g-1的可逆比容量。对其进行原位电化学纳米膨胀(ECD)测试,PVA-Bet对于活性材料SiO/C材料的体积膨胀具有很好的抑制作用。(2)通过对一维线性聚合物聚丙烯酸(PAA)的结构改性,与糊精(Dex)原位热交联,制备了一种基于共价键与氢键协同作用的三维网状绿色粘结剂PAA-Dex9。PAA-Dex9形成的三维网络借助共价键和氢键的协同作用减少了常用一维粘结剂移动性强的缺点,从而可以缓解循环过程中SiOx负极材料的膨胀。同时,PAA-Dex9引入了更多的极性官能团(-COOH、-OH),实现一维线性粘结剂与SiOx负极材料“点线结合”向“点面结合”的转变,从而保持电极的完整性。优化后的PAA-Dex9粘结剂具有最高的剥离强度及粘结强度,提高了SiOx电极的机械强度。在0.2 A g-1时,SiOx@PAA-Dex9电极的初始库仑效率为82.4%。100次循环后,SiOx@PAA-Dex9表现出1200 mAh g-1的容量。在1 A g-1的高电流密度下,SiOx@PAA-Dex9在300次循环后仍保持607 mAh g-1的可逆比容量。SEM和原位电化学膨胀测试表明,PAA-Dex9粘结剂可以有效缓解SiOx电极的体积变化。(3)通过对一维线性聚合物聚乙烯亚胺(PEI)的结构改性,与单宁酸(TA)简单热交联制备了一种基于氢键交联的网状粘结剂PEI-TA。其具有更多的活性基团(-NH2、-NH-、-OH),增加了与SiO/C负极的接触位点,形成的基于氢键交联的网络结构,可以很好弥散SiO/C颗粒充放电过程中体积膨胀的应力,保持电极结构的稳定性,提升其电化学性能。力学性能测试表明,制备的PEI-TA粘结剂具有最高的剥离强度及粘结强度,表现出优异的拉伸性能,提高了电极的机械强度。在0.1 A g-1时,SiO/C@PEI-TA电极的初始放电容量为691 mAh g-1,库仑效率为66.8%。100次循环后,SiO/C@PEI-TA表现出346 mAhg-1的容量。在1Ag-1的高电流密度下,SiO/C@PEI-TA在500次循环后仍保持319 mAh g-1的可逆比容量。此外,SiO/C@PEI-TA具有优异的倍率性能。更多还原

【Abstract】 Polymer binder,as a critical constituent of electrode,although its mass account is relatively small,plays an important role in limiting the volume expansion of silicon-based anode materials to improve the electrochemical performance of lithium-ion batteries.The commonly used one-dimensional(1D)linear polymer is difficult to limit the volume expansion of silicon-based anode particles due to its shortcomings such as few binding sites and strong mobility.Therefore,it is necessary to design and modify the structure of 1D linear polymer to prepare binders with network structure to increase the binding sites with silicon-based anode particles and dissipate mechanical stress in the process of continuous charging and discharging,so that the binders can limit the volume expansion of siliconbased anode particles and improve the electrochemical performance of the batteries.(1)A new zwitterion-based binder PVA-BET was developed by modifying PVA through a simple thermal crosslinking method by using 1D polymer binder polyvinyl alcohol(PVA)and betaine(Bet),in which Bet is introduced into Hydrogen bond based polyvinyl alcohol network.The aqueous binder has more binding sites and more polar groups(-OH,-COO-,-N+-(CH3)4)to form hydrogen bonds with Si-OH on the surface of silicon particles,which has better adhesion performance to maintain electrode integrity and improve the electrochemical performance of the battery.The capacity of 1114 mAh g-1 is still maintained after 100 cycles at 0.2 A g-1,and when the current density increases to 1 A g-1 cycle,it still has a capacity of 648 mAh g-1 after 200 cycles.In situ electrochemical dilatometry(ECD)tests show that PVA-Bet has a good inhibition on the volume expansion of SiO/C materials.(2)A three-dimensional covalent and hydrogen bond synergistic binder PAA-Dex9 was prepared by modifying the structure of 1D linear polymer binder polyacrylic acid(PAA)with a in situ thermal crosslinking method with dextrin(Dex)The 3D network formed by PAA-Dex9 reduces the weakness of strong mobility of common 1D binders by the synergistic effect of covalent bonds and hydrogen bonds,thus alleviating the volume expansion of SiOx material during the cycling process.Meanwhile,PAA-Dex9 introduces more polar functional groups(-COOH,-OH)to realize the transformation from"Point-Line combination" to "Point-Flat combination" of one-dimensional linear binder and SiOx electrode material,which can be achieved to maintain the integrity of the electrode.The optimized PAA-Dex9 binder has the highest peeling strength and adhesion strength,and can tightly adhere to the active materials,conductive additives with the current collector,improving the mechanical strength of SiOx electrode.At 0.2 A g-1,the initial coulomb efficiency(ICE)of SiOx@PAA-Dex9 electrode is 82.4%.After 100 cycles,it exhibited the capacity of 1200 mAh g-1.At a higher current density of 1 A g-1,SiOx@PAA-Dex9 retains a reversible specific capacity of 607 mAh g-1 after 300 cycles.The results of SEM and in situ electrochemical dilatation tests show that the PAA-Dex9 binder could effectively alleviate the volume change of SiOx electrode.(3)A network binder PEI-TA based on hydrogen bond crosslinking is developed by modifying the structure of one-dimensional linear polymer PEI with a simple thermal crosslinking method with tannic acid(TA).The PEI-TA binder has more active groups(-NH2,-NH-,-OH),adding the contact sites with the SiO/C.The network structure can well disperse the stress of volume expansion during the charging and discharging of SiO/C particles,maintain the stability of the electrode structure,and improve electrochemical performance.Tests on its mechanical properties show that the prepared PEITA binder has the highest peeling strength,adhesion strength,and the prepared gel shows excellent tensile properties,which improves the mechanical strength of SiO/C electrode.At 0.1 A g-1,the initial discharge capacity of SiO/C@PEI-TA electrode is 691 mAh g-1 an ICE of 66.8%.After 100 cycles,SiO/C@PEI-TA exhibited a 346 mAh g-1 capacity.SiO/C@PEI-TA maintains a reversible specific capacity of 319 mAh g-1 after 500 cycles at a high current density of 1 A g-1.In addition,SiO/C@PEITA has excellent rate performance.更多还原