The design of new binder systems is an effective way to improve electrochemical performances of electrodes. In this work, a novel ionic copolymer, poly(acrylic acid/2-hydroxyethyl acrylate/1-vinyl-3-ethylimidazolium hexafluorophosphate) (AA-HA-VEH), was synthesized by photopolymerization for use as a cross-linked and conductive binder of LiFePO₄ cathodes. The chemical structure of the as-obtained copolymer was verified by FT-IR, ¹H NMR, and XPS. The results from peeling and morphological analysis indicated that AA-HA-VEH binder could offer strong adhesion/cohesion to maintain an integrated LiFePO₄ cathode structure during hundreds of cycles without cracks and delamination. Compared to PVDF-cathodes with a specific capacity of 17.51 mAh g^–1, the bonded LiFePO₄ cathodes presented an excellent rate performance with a high specific capacity of 98.35 mAh g^–1 at 5C rate. Moreover, the AA-HA-VEH cathodes maintained remarkable cycle stability with retention of 97.01% at 0.5C after 400 cycles. The introduction of the ionic structure of the AA-HA-VEH decreased the impedance and increased the ionic conductivity by nearly 2- to 4-fold. Therefore, the ionic units effectively contributed to the transport of Li⁺ ions between the cathode interfaces with low polarization. In summary, these findings provided novel insights into the rational design of binders that might be useful for the practical long-term cycling of Lithium-ion batteries.

中文翻译：

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具有长循环寿命的 LiFePO4 阴极导电粘合剂的设计

新型粘合剂体系的设计是提高电极电化学性能的有效途径。在这项工作中，通过光聚合合成了一种新型离子共聚物聚（丙烯酸/丙烯酸 2-羟乙酯/1-乙烯基-3-乙基咪唑鎓六氟磷酸盐）（AA-HA-VEH），用作交联和导电粘合剂LiFePO ₄阴极。所得共聚物的化学结构通过 FT-IR、¹ H NMR 和 XPS 进行了验证。剥离和形态分析的结果表明，AA-HA-VEH 粘合剂可以提供强大的粘附力/内聚力，以在数百次循环中保持完整的 LiFePO ₄正极结构而不会出现裂纹和分层。与比容量为 17.51 mAh g ^{–1 的}PVDF 阴极相比，结合的LiFePO ₄正极表现出优异的倍率性能，在5C倍率下具有98.35 mAh g ^–1的高比容量。此外，AA-HA-VEH 正极保持了显着的循环稳定性，400 次循环后在 0.5C 下的保持率为 97.01%。AA-HA-VEH 离子结构的引入降低了阻抗并将离子电导率增加了近 2 到 4 倍。因此，离子单元有效地促进了低极化阴极界面之间的Li ⁺离子传输。总之，这些发现为粘合剂的合理设计提供了新的见解，可能对锂离子电池的实际长期循环有用。