Gao Kevin W, Loo Whitney S, Snyder Rachel L, Abel Brooks A, Choo Youngwoo, Lee Andrew, Teixeira Susana C M, Garetz Bruce A, Coates Geoffrey W, Balsara Nitash P
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, California 94720, United States; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States; Joint Center for Energy Storage Research (JCESR), Argonne National Laboratory, Lemont, Illinois 60439, United States.
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, California 94720, United States.
Macromolecules. 2020;53(14). doi: https://doi.org/10.1021/acs.macromol.0c00747.
This study shows that it is possible to obtain homogeneous mixtures of two chemically distinct polymers with a lithium salt for electrolytic applications. This approach is motivated by the success of using mixtures of organic solvents in modern lithium-ion batteries. The properties of mixtures of a polyether, poly(ethylene oxide) (PEO), a poly(ether-acetal), poly(1,3,6-trioxocane) (P(2EO-MO)), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt were studied by small-angle neutron scattering (SANS) and electrochemical characterization in symmetric cells. The SANS data are used to determine the miscibility window and quantify the effect of added salt on the thermodynamic interactions between the polymers. In the absence of salt, PEO/P(2EO-MO) blends are homogeneous and characterized by attractive interactions, i.e., a negative Flory-Huggins interaction parameter, . The addition of small amounts of salt results in a positive effective Flory-Huggins interaction parameter, , and macrophase separation. Surprisingly, miscible blends and negative parameters are obtained when the salt concentration is increased beyond a critical value. The electrochemical properties of PEO/P(2EO-MO)/LiTFSI blends at a given salt concentration were close to those obtained in PEO/LiTFSI electrolytes at the same salt concentration. This suggests that in the presence of PEO the electrochemical properties exhibited by P(2EO-MO) chains are similar to those of PEO chains. This work opens the door to a new direction for creating new and improved polymer electrolytes either by combining existing polymers and salt or by synthesizing new polymers with the specific aim of including them in miscible polymer blend electrolytes.
本研究表明，对于电解应用而言，将两种化学性质不同的聚合物与锂盐混合以获得均匀混合物是可行的。这种方法的灵感来源于现代锂离子电池中使用有机溶剂混合物所取得的成功。通过小角中子散射（SANS）以及对称电池中的电化学表征，研究了聚醚聚环氧乙烷（PEO）、聚醚缩醛聚（1,3,6 - 三氧杂环己烷）（P(2EO - MO)）与双（三氟甲磺酰）亚胺锂（LiTFSI）盐的混合物的性质。SANS数据用于确定互溶窗口，并量化添加盐对聚合物之间热力学相互作用的影响。在无盐情况下，PEO/P(2EO - MO)共混物是均匀的，其特征在于具有吸引相互作用，即负的弗洛里 - 哈金斯相互作用参数χ。添加少量盐会导致正的有效弗洛里 - 哈金斯相互作用参数χeff以及宏观相分离。令人惊讶的是，当盐浓度增加超过临界值时，可获得互溶共混物和负χeff参数。在给定盐浓度下，PEO/P(2EO - MO)/LiTFSI共混物的电化学性质与相同盐浓度下PEO/LiTFSI电解质所获得的性质相近。这表明在PEO存在的情况下，P(2EO - MO)链所表现出的电化学性质与PEO链相似。这项工作为通过组合现有聚合物和盐或者通过合成具有特定目标（即将它们包含在互溶聚合物共混电解质中）的新聚合物来制备新型且性能更优的聚合物电解质开辟了新方向。
