Life-cycle evolution and failure mechanisms of metal-contaminant defects in lithium-ion batteries

Cathodic metal-contaminant defects are frequently introduced into lithium-ion batteries (LIBs) during production. The life-cycle evolution and influence mechanisms of cathodic metal contaminants in LIBs are the key for revealing their influence on the safety and durability of LIBs after long-term cycling, but few relevant research has been conducted. Here copper (Cu) particles are chosen and placed on the cathode of LIBs. The variation characteristics in the electrical properties of defective batteries, the evolution process of metal particles and the influence mechanisms of the metal contaminants on LIBs throughout their entire life cycle are studied. Interestingly, the short-circuit points caused by the metal contaminants continuously dissolve under cathode potential, which makes the ISC phenomenon gradually vanished with time. The metal is finally dispersed in a large area, which creates a barrier but is insufficient to cause lithium plating. In addition, the cycle performance of the defective batteries is better because a small amount of Cu ions that enter the cathode lattice retard the Li/Ni ion mixing and consequently slow down the loss of cathode. However, the excessive incorporation of Cu increases the dissolution of transition-metal ions, which accelerates the degradation of the defective batteries after cycling for a long time.