粘结剂对形貌各异的石墨负极电化学性能的影响（英文）

Effect of Binder Conformity on the Electrochemical Behavior of Graphite Anodes with Different Particle Shapes

本文通过不同形貌的石墨材料,研究了聚丙烯腈-丁二烯(NBR)作为锂离子电池粘结剂的电化学性能,并与商业化粘结剂聚偏氟乙烯(PVDF)进行了对比。由于NBR无定形的晶体结构和连续性的特点,使其能够更好的粘结在活性材料表面,在球型和片状石墨表面都能形成均一的具有抑制副反应和提高锂离子传输能力的保护层。实验证明,片层状石墨在以PVDF作粘结剂时,电化学性能较差。然而,以NBR作为粘结剂时,球型和片状的石墨材料在库伦效率、循环稳定性和传输动力学上都有明显的提升。此项研究证实了粘结剂和活性材料的一致性对于提高锂离子电池电化学性能的重要性。

As an important component in electrodes,the choice of an appropriate binder is significant when fabricating lithium-ion batteries(LIBs)with good cycle stability and rate capability,which are used in numerous applications,especially portable electronics and eco-friendly electric vehicles(EVs).Semi-crystalline poly(vinylidene fluoride)(PVDF),which is a traditional and widely used binder,cannot efficiently accommodate the volume changes observed in the anode during the charge-discharge process while binding all the components in the electrode together,which results in increased internal cell resistance,detachment of the electrode components,and capacity fading.Herein,we have investigated a highly polar and elastomeric polyacrylonitrile-butadiene(NBR)rubber for use as a binder in LIBs,which can accommodate graphite particles of different shapes compared to semi-crystalline PVDF.Prior to our electrochemical tests,NBR was analyzed using thermogravimetric analysis(TGA)and X-ray diffraction(XRD),showing good thermal stability and an amorphous morphology.NBR is more conformable to irregular surfaces,which results in the formation of a homogeneous passivation layer on both spherical and flaky graphite particles to effectively suppress any electrolyte side reactions,further allowing more uniform and fast Li ion diffusion at the electrolyte/electrolyte interface.As a result,the electrochemical performance of both spherical and flaky shape graphite electrodes was significantly improved in terms of their first cycle Coulombic efficiency(CE)and cycle stability.With comparative specific capacity,the first cycle CE of the NBR-based spherical and flaky graphite electrodes were 87.0%and 85.5%,compared to 85.3%and 82.6%observed for their corresponding PVDF-based electrodes,respectively.After 1000 discharge-charge cycles at 1C,the capacity retention of the NBR-based graphite electrodes was significantly higher than that of PVDF-based electrodes.This was attributed to the good stability of the solid electrolyte interphase(SEI)formed on the graphite electrodes and the high stretching ability of the elastomeric NBR binder,which help to accommodate the repeated volume fluctuation of graphite observed during long-term charge-discharge cycling.Electrochemical impedance spectroscopy(EIS)and microscopic analysis(SEM and TEM)were carried out to investigate the formation and evolution of the SEI layers formed on the spherical and flaky graphite electrodes.The results show that thin,homogeneous,and stable SEI layers are formed on the surface of both spherical and flaky graphite electrodes prepared using the NBR binder.When compared to the PVDFbased graphite electrodes,the graphite electrodes constructed using NBR showed decreased resistance in the SEI layer and faster charge transfer,thus enhancing the electrode kinetics for Li ion intercalation/deintercalation.Our study shows that the electrochemical performance of spherical and flaky graphite electrodes prepared using the NBR binder is significantly improved,demonstrating that NBR is a promising binder for these electrodes in LIBs.