Correlationship between electrode mechanics and long-term cycling performance for graphite anode in lithium ion cells

In the development of lithium ion batteries for electric vehicle applications, much effort has been made in fabrication and optimization of active materials. Mechanical properties of the electrode laminate, which are also very critical determining the durability of the cell, have long been ignored. In this study, graphite laminates of the same chemical composition are prepared by using different mixing technologies. With similar breaking strength, Young’s modulus of the laminate is found to be very different according to the mixing order. Electrochemical performances of the graphite laminates are investigated against Li anode and Li[Ni1/3Co1/3Mn1/3]O2 cathode, respectively. Long-term cycling performance is closely related with the Young’s modulus of the graphite laminate. Whereas the laminates of low modulus cycles well during the investigated 600 deep charge–discharge cycles, the electrodes of high modulus fail at around 350 cycles. Electrochemical degradation mechanism for the laminate of high modulus is associated with the significant impedance rise aroused from mechanical failure. After the long-term cycling test, lots of cracks are observed on the high modulus electrode along the particle boundaries while the mechanical integrity of the low modulus laminate is well maintained.

► Cycling performance of a graphite anode is correlated with its mechanics.
► The graphite laminate of lower modulus has longer durability.
► Impedance rise is responsible for the electrochemical deterioration.
► Crack formation and propagation within the laminate causes the impedance rise.