Chiu Li-Ling, Chung Sheng-Heng
Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan.
Hierarchical Green-Energy Materials Research Center, National Cheng Kung University, Tainan 701, Taiwan.
Polymers (Basel). 2021 Feb 11;13(4):535. doi: 10.3390/polym13040535.
In lithium-sulfur cells, the dissolution and relocation of the liquid-state active material (polysulfides) lead to fast capacity fading and low Coulombic efficiency, resulting in poor long-term electrochemical stability. To solve this problem, we synthesize a composite using a gel polymer electrolyte and a separator as a functional membrane, coated with a layer of poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The PEO/LiTFSI-coated polypropylene membrane slows the diffusion of polysulfides and stabilizes the liquid-state active material within the cathode region of the cell, while allowing smooth lithium-ion transfer. The lithium-sulfur cells with the developed membrane demonstrate a high charge-storage capacity of 1212 mA∙h g, 981 mA∙h g, and 637 mA∙h g at high sulfur loadings of 2 mg cm, 4 mg cm, and 6 mg cm, respectively, and maintains a high reversible capacity of 534 mA∙h g after 200 cycles, proving its ability to block the irreversible diffusion of polysulfides and to maintain the stabilized polysulfides as the catholyte for improved electrochemical utilization and stability. As a comparison, reference and control cells fabricated using a PEO-coated polypropylene membrane and a regular separator, respectively, show a poor capacity of 662 mA∙h g and a short cycle life of 50 cycles.
在锂硫电池中，液态活性材料（多硫化物）的溶解和迁移会导致快速的容量衰减和低库仑效率，从而导致较差的长期电化学稳定性。为了解决这个问题，我们合成了一种复合材料，它使用凝胶聚合物电解质和作为功能膜的隔膜，并涂覆有一层聚环氧乙烷（PEO）和双（三氟甲磺酰）亚胺锂（LiTFSI）。涂覆有PEO/LiTFSI的聚丙烯膜减缓了多硫化物的扩散，并使液态活性材料在电池的阴极区域内保持稳定，同时允许锂离子顺利转移。具有这种开发的隔膜的锂硫电池在硫负载量分别为2 mg/cm²、4 mg/cm²和6 mg/cm²时，表现出高电荷存储容量，分别为1212 mA∙h/g、981 mA∙h/g和637 mA∙h/g，并且在200次循环后保持534 mA∙h/g的高可逆容量，证明了其能够阻止多硫化物的不可逆扩散，并将稳定的多硫化物作为阴极电解液以提高电化学利用率和稳定性。作为比较，分别使用涂覆有PEO的聚丙烯膜和常规隔膜制造的参比电池和对照电池，表现出较差的容量，为662 mA∙h/g，以及较短的循环寿命，为50次循环。
