Nickel–Salen-Type Polymer as Conducting Agent and Binder for Carbon-Free Cathodes in Lithium-Ion Batteries

Abstract

Systematic physical and electrochemical characterizations revealed unique positive multifunction of a polymeric salen-type nickel(II) complex, poly[Ni(CH 3salen)], as an additive for conventional cathodes in lithiumion batteries. Due to its promising electrochemical and mechanical properties, combined with its unique threedimensional weblike electron-network structure, the redoxactive-organometallic polymer can eliminate conductive carbon and replace a significant portion of the poly(vinylidene fluoride) (PVdF) binder that has been used in conventional LiFePO 4 cathodes. By replacing such electrochemically inactive components (i.e., carbon and PVdF), LiFePO 4 cathodes with poly[Ni(CH 3 -salen)] deliver improved energy density compared with the conventional LiFePO 4 cathode. Facile electron transfer via large-area contact at polymer/LiFePO 4 interfaces significantly accelerates charge-transfer reactions and consequently improves the rate capability of the cathodes. In addition, unlike PVdF, poly[Ni(CH 3 -salen)] retains steady Young's modulus values after immersing in an electrolyte solvent, which enhances the mechanical integrity of the cathodes during the cycling of battery cells and thereby improves their cycle life. The unique multifunction of the poly[Ni(CH 3 -salen)] will be of broad interest for its application in next-generation energy-storage devices.

Reversible Redox Processes in Polymer of Unmetalated Salen-Type Ligand: Combined Electrochemical in Situ Studies and Direct Comparison with Corresponding Nickel Metallopolymer

“…The introduction of transition metal centers into the conjugated backbone could significantly expand the applications and functionality of such materials. Metal-containing polymers based on transition metal complexes with Salen-type Schiff base ligands are widely studied as promising materials for many different applications [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. The properties of these materials largely depend on substituents in the ligand environment and the metal center, special attention has been given to polymeric nickel(II) complexes with Salen-type ligands.…”

6,6′-{[Ethane-1,2-diylbis(azaneylylidene)]bis(methaneylylidene)}bis[2-(hexyloxy)phenolato] Nickel(II)

“…These polymeric complexes are known for unique properties, such as reversible electrochemical oxidation in a wide range of potentials, thermal stability, high redox and electronic conductivity, and high specific capacities [10,14,15]. Polymeric NiSalens met their application in Li-ion batteries as cathode active materials [16] and binders [17].…”

Organic Semiconductor Cocrystal for Highly Conductive Lithium Host Electrode

“…However, nonconductive nature of active materials limits battery performance because the cell can operate only with the conducting agent to transport electrons during discharging and charging processes that ultimately reduce the energy density of batteries due to the increasing the dead weight of electrodes . To increase conductivity and lithium ion (Li + ) transport, numerous approaches that can readily combine with LIBs system, such as artificial solid‐electrolyte‐interface (SEI) coating, metallic Li 7 Ti 5 O 12 , conducting binder, and buffering matrix, have been applied. However, the main active materials, which are prepared with the proposed materials, are still nonconductive.…”