摘要
Due to their capability of reversibly accepting multi lithium ions,polyoxometalates(POMs)have been widely regarded as promising candidates for electrochemical lithium storage.Nevertheless,the insulating nature of POMs hinders fast migration kinetics of lithium within the bulk of these materials.Herein,we propose the introduction of a local electric field surrounding the POM nanoparticles consisting of Mn and V where the concomitant Coulomb forces can accelerate the migration of lithium ions.After rationally hybridizing POMs with MXene nanosheets,the imbalanced charge distribution emerging at their interface produces the local electric field,thereby leading to a 250-fold increase of lithium diffusion coefficient.In this regard,a capacitive contribution as high as 81.7%at 1.0 mV sis observed.Moreover,the POM nanoparticles could densely assemble on the surface of MXene nanosheets,offering highly packed electrodes and thus high volumetric capacities.Due to the improved lithiumion transfer kinetics,the POMs/MXenes composites are paired with activated carbon to produce lithium-ion capacitors which could offer a high energy density of 195.5 W h kgand a large power capability of 3800 W kg.The findings in this work could build a clear relationship between materials with different conductivities for designing electrode materials.
杂多酸(POMs)具有可逆接收/脱除多个锂离子的能力,被认为是具有广泛应用前景的电化学储锂材料.然而,POMs的绝缘特性阻碍了锂离子在其中的快速迁移.鉴于此,我们提出在由Mn和V组成的POMs纳米颗粒周围引入局部电场,通过同步产生的库仑力加速锂离子的迁移.将POMs与MXenes纳米片复合后,界面处的不平衡电荷分布诱导产生了局部电场,使得锂扩散系数提高了250倍.在1.0 mV s的低扫速下,复合材料赝电容贡献高达81.7%.此外,POMs的纳米颗粒可以在MXene纳米片表面致密组装,赋予电极材料高体积容量.由于改善的锂离子传输动力学,POMs/MXenes复合材料与商业活性炭组装的锂离子电容器可输出195.5 W h kg^(-1)的能量密度和3800 W kg^(-1)的功率密度.本研究为高性能电极材料的设计提供了新思路.
基金
supported by the National Natural Science Foundation of China(21975258,22179145,and 22138013)
the Natural Science Foundation of Shandong Province(ZR2020ZD08)
the startup support grant from China University of Petroleum(East China)
Taishan Scholar Project(ts201712020)。
