高安全锂离子电池复合集流体的界面强化

Interface Strengthening of Composite Current Collectors for High-Safety Lithium-Ion Batteries

面向高能量密度电池的高比容量三元正极材料的应用,使锂离子电池更容易发生热失控,这不仅降低了其安全性,也限制了锂离子电池的进一步发展。如何在提高能量密度的同时保证电池的安全性是亟待解决的问题。以绝缘高分子薄膜为支撑基材,两侧沉积金属层得到了具有夹芯结构的铝复合集流体能有效保证电池在针刺条件下的安全性,且更轻的复合集流体的使用能进一步提高电池能量密度。但高分子基材与铝金属层之间界面结合力较差,这会导致复合集流体在高温电解液浸泡中发生脱层现象,从而影响其在电池中的使用。本研究采用聚对苯二甲酸乙二醇酯(PET)作为支撑基材,通过在铝金属镀层与高分子基材之间引入氧化物中间层,有效地增强了金属与高分子基材之间的界面结合力,提升复合集流体的电解液兼容性。此外,复合集流体良好的机械性能使其能很好地兼容现有的电池制备技术,利用其制备的软包电池表现出与使用传统铝箔为集流体的电池相当的电化学性能。进一步的针刺测试表明,复合集流体能有效阻止锂电池在针刺过程中的热失控,显著改善了电池的安全性能。

The use of high-capacity ternary cathode materials for high-energy batteries can cause thermal runaway of lithium-ion batteries(LIBs),hindering their safe use and further development.Therefore,improving the energy density of LIBs while maintaining their safety is essential.Current collectors(CCs),which serve as the electron carrier during the electrochemical process,do not contribute to capacity and are regarded as“dead weight”to the cells.The use of composite CCs,which have a sandwich structure where a thin metal(e.g.,Al and Cu)layer is deposited on both sides of polymer films,can reduce the weight of CCs owing to the use of the low-density insulating substrate and improve the safety of LIBs(evaluated by the nail penetration test).However,due to the weak interfacial adhesion between the substrate and metal coating layer,the composite CCs may easily delaminate in electrolytes during high-temperature immersion,which could not meet the requirement for the long-term stability.Herein,we introduced an oxide strengthening layer between the substrate(polyethylene terephthalate,PET)and Al layer.The objective of strengthening layer is to increase the interface binding force between the metal and polymer substrate by enhancing the mechanical interlocking effect between the layers and forming a stable chemical bond at the interface.This increased interface binding force effectively improved the electrolyte compatibility of composite CCs even at a high temperature of 85℃.Based on the results of atomic force microscopy and X-ray photoelectron spectroscopy,we proposed a mechanism for the enhancement of both mechanical interlocking and chemical bonding.Additionally,the composite CCs possessed good mechanical properties that ensure their compatibility with conventional battery fabrication technologies.LIBs using composite CCs exhibited a comparable electrochemical performance to that of aluminum-CC-based(Al CCs)cells,but better performance in nail penetration test.After 280 cycles at 0.2 C,the cell showed high-capacity retention.Al-CC-based cells and PET-AlOx-Al-CC based cells remain 80.55%and 80.9%capacity retention respectively,which indicates the comparable performance.This shows that the composite CCs technology is fully adapted to the existing battery manufacturing technology,and has little influence on the electrochemical performance of LIBs.Specifically,cells with PETAlOx-Al CCs easily passed the nail penetration test under 100%state of charge without an obvious temperature rise.Furthermore,the voltage of the punctured batteries remained at~4 V and could still be charged and discharged.The composite CCs successfully prevented the internal short circuit and markedly improved the safety of LIBs during the nail penetration test.Our findings provide theoretical guidance and solutions for the industrialization of composite CCs.