LAUSR

Although organic electrode materials have merits of abundant resources, diverse structures and environmental friendliness, their performance for electrochemical energy storage is far insufficient. In this work, a thiourea-based polyimide/reduced graphene oxide (PNTCSA/RGO) composite was synthesized via a condensation polymerization method. As a cathode material in lithium-ion batteries, excellent performance is demonstrated with high reversible capacity (144.2 mA h g −1 ), high discharge voltage (∼2.5 V), and long cycling life (over 2000 cycles at 500 mA g −1 ), which are comparable to those of other well documented in organic electrodes. Encouraging electrochemical performance is also demonstrated for sodium ion batteries (a cycling life of 800 cycles at 500 mA g −1 ), while poor performance is delivered in potassium ion batteries. Theoretical studies reveal that the active sites are carbonyl groups for all alkali ions but one inserted alkali metal ion is shared by two carbonyl groups from the two neighbor units. More importantly, K ions have stronger interaction with S atoms than Li/Na ions, which may lead to poor structure reversibility and account for the poor cycling performance. Our findings provide a fundamental understanding of polyimide based polymer electrodes and help to design and develop high performance organic electrode materials for alkali metal ion batteries. 尽管有机电极材料具有资源丰富、 结构多样及环境友好等 特点, 但是它们的电化学性能仍然不理想. 本文通过缩聚法合成了 一种硫脲基聚酰亚胺/还原氧化石墨烯复合物. 当其作为正极材料 应用于锂离子电池时, 展现出优异的电化学性能, 如高可逆比容量 (144.2 mA h g −1 ), 高放电电压(∼2.5 V)和长循环寿命(在500 mA g −1 电流密度下超过2000次), 可以和其他发展较好的无机正极材料相媲美. 当其作为正极材料应用于钠离子电池时, 也可获得较好的电化学性能(在500 mA g−1电流密度下循环寿命达800次), 但是作为钾离子电池正极材料时的性能较差. 理论计算表明羰基是和三种碱金属离子结合的活性位点, 且插入的金属离子被邻位的两个羰基共用. 更重要的是, 硫原子和钾之间的作用力要远远大于和锂/钠之间的作用力, 使得该聚合物在钾离子电池中表现出较差的可逆性和循环稳定性. 我们的发现不仅为聚酰亚胺基的聚合物电极的设计和开发提供了理论基础, 同时也为高性能的碱金属离子电池有机电极材料的设计和开发提供了帮助.