Redox-active Co(II) and Zn(II) Pincer Complexes as High-Capacity Anode Materials for Lithium-Ion Batteries

To address the ongoing demand for high-performance energy storage devices, it is crucial to identify new electrode materials. Lithium-ion batteries (LIBs) store energy via the electrochemical redox process, so their electrode materials should have reversible redox properties for rechargeability. On that note, redox-active metal complexes are explored as innovative electrode materials for LIBs. Redox-active metal(II) chloride complexes (MCC) demonstrate promising potential as anode materials, exhibiting high capacity and excellent rate capability. In particular, zinc(II) chloride complexes, referred to as ZCC, achieve a capacity of 1720 mAh g^-1 at 2.0 A g^-1 over 200 cycles. Additionally, the lithium-ion storage mechanism of MCC is elucidated using ex situ analyses of MCC anode's surface in its fully discharged state. The high capacity of the MCC anode is attributed to conversion reaction with Li⁺ ions forming LiCl and electrodeposition of metallic lithium from the over-lithiated Li⁺ ions. These findings support the potential use of redox-active metal complexes as novel anode materials for LIBs.