基于木质素的锂硫电池水系粘结剂的研究

NOVEL LIGNIN BASED AQUEOUS BINDER FOR LITHIUM-SULFUR BATTERIES

吴秀芬

11749226

硕士

材料学

邓永红

2019-06-01

2019-07-13

哈尔滨工业大学

深圳

锂硫电池具有高能量密度（2600 Wh kg-1）、价格低廉、低毒环保等优势，是极具发展前景的下一代可充电电池体系。但是，由于硫绝缘特性带来的电子导电率低、充放电过程中体积膨胀大和多硫化锂存在穿梭效应等特点导致电池性能变差，阻碍了它的商业化发展。性能优良的粘结剂不仅可以支撑电极结构，而且可以从多方面改善硫电极存在问题，提高电池性能。本文首次将造纸废料中木质素磺酸盐作为锂硫电池粘结剂，验证了木质素磺酸盐直接作为环保、高性能锂硫电池粘结剂的可行性。并在其基础上进行改性，制备了聚（3,4-乙撑二氧噻吩）/木质素磺酸（PEDOT/LSA）导电粘结剂，进一步提高锂硫电池的倍率性能和循环稳定性。具体研究内容和结论如下：本文首先以木质素磺酸钠（LSNa）与木质素磺酸钙（LSCa）作为锂硫电池水系粘结剂，并探究了它们对电极性能的影响。以LSCa为粘结剂的硫基正极在1C（1C=1675 mA g-1）下循环500圈，电极放电比容量仍可达453 mAh g-1，容量保持率为50.84%，优于采用传统的PVDF作为粘结剂的硫基正极。在高硫负载（7.64 mg cm-2）和0.05C电流密度下循环100圈后，LSCa硫基正极单位面容量仍可达4.16 mAh cm-2。研究分析表明，相对PVDF粘结剂，LSCa粘结剂具有更强的吸附多硫化物能力、更快的锂离子传输能力和更强的粘结力，这些特征使采用LSCa作为粘结剂的锂硫电池展示出更优异的电化学性能。在此基础上，以木质素磺酸做分散剂和掺杂剂，通过化学氧化聚合，制备不同比例的PEDOT/LSA导电复合粘结剂。研究发现，当PEDOT:LSA=1:4时，硫基正极表现出最佳的电化学性能。PEDOT/LSA硫基正极平均剥离强度为1.8 N，大于LSCa硫基正极和传统的PVDF硫基正极。PEDOT/LSA硫基正极在1C下循环400圈后，放电比容量还有540 mAh g-1，容量保持率为72.97%。即使在5C大电流密度下，放电比容量仍有601 mAh g-1。当硫载量高达10.51 mg cm-2时，PEDOT/LSA硫基正极在0.05C下循环80圈后，单位面容量依然可以达到6.01 mAh cm-2。这些结果表明，PEDOT/LSA硫基正极的循环稳定性和倍率性能得到进一步优化。这是因为PEDOT/LSA具有更强的粘结强度和PEDOT提高了电极的导电性，改善了电池电化学性能。在本研究中，木质素（磺酸盐）被首次作为锂硫电池正极粘结剂，并制备了PEDOT/LSA复合物用作导电粘结剂，锂硫电池的性能得到改善。证实了木质素作为环保、低廉、高效的水系粘结剂在锂硫电池应用的可行性。同时，提供了一种木质素高值化利用的途径。

Lithium sulfur (Li-S) batteries are regarded as the potential candidates for the next generation secondary batteries owing to their high gravimetric energy density (2600 Wh kg-1), inexpensiveness, and eco-friendliness. However, there are still several barriers in Li-S batteries, such as the insulativity of sulfur, the large volume expansion and the nonnegligible shuttle effect from soluble polysulfides, which impede their commercial application. Functional binders can not only assist the electrode forming and structure preserving but also benefit high electrochemical performance. In this study, we explored the feasibility for directly introducing the pulping waste as ecofriendly and effective binder for Li-S batteries, and also synthesized poly(3,4-ethylenedioxythiophene)/lignosulfonic acid (PEDOT/LSA) conductive binder to further improve the cycle stability and rate performance. Specific contents are listed as follows：We first used the lignosulfonate as aqueous binder for Li-S batteries, and investigated the performance difference between sodium lignosulfonate (LSNa) and calcium lignosulfonate (LSCa). The LSCa-based electrode retains a capacity of 453 mAh g-1 after 500 cycles at 1C (1C=1675 mA g-1) with a capacity retention of 50.84%, which are much better than those of PVDF-based electrode. Furthermore, a preferable areal capacity of 4.16 mAh cm-2 is obtained after 100 cycles at 0.05C with a high sulfur loading of 7.64 mg cm-2. These achievements are ascribed to the better absorption ability to polysulfides, more favorable Li+ transportation and superior adhesion property.Based on the above experiments, we further synthesized a series of PEDOT/LSA complexes, in which LSA worked as dispersant and dopant. The complexes were applied as conductive binder for Li-S batteries. The corresponding PEDOT/LSA complex benefit the batteries best, when the ratio of PEDOT and LSA is fixed at 1:4. Peeling tests show that the average force of PEDOT/LSA-based electrode is 1.8 N, which is much higher than those of LSCa-based and PVDF-based electrodes. The PEDOT/LSA-based electrode retains a capacity of 540 mAh g-1 after 400 cycles at 1C with a capacity retention of 72.97%. It also delivers an excellent capacity of 601 mAh g-1 even at the high current density of 5C. Moreover, a preferable areal capacity of 6.01 mAh cm-2 is obtained after 80 cycles at 0.05C with a high sulfur loading of 10.51 mg cm-2. These results indicate that PEDOT/LSA binder enhances the cycle stability and rate performance of Li-S batteries. Compared to the PVDF and LSCa, this conductive binder has a better adhesion. Besides, the PEDOT improves the conductivity of electrode.In this study, lignosulfonate was used as cathode binder for Li-S batteries for the first time and derived for PEDOT/LSA conductive binder to further improve electrochemical performance. Our work not only shows the feasibility for introducing the pulping waste as ecofriendly and effective binder for Li-S batteries, but also suggests a facile and sustainable way for the high-value utilization of waste lignin.

锂硫电池 水系粘结剂 木质素 聚（3,4-乙撑二氧噻吩）

Li-S batteries aqueous binder lignin poly(3,4-ethylenedioxythiophene)

中文

联合培养

南方科技大学

吴秀芬. 基于木质素的锂硫电池水系粘结剂的研究[D]. 深圳. 哈尔滨工业大学,2019.