Electrode materials for lithium-ion batteries based on metal-organic polymers

Project Number: 16-13-00038

Project Annotation

The project is focused on creating new cathode materials for lithium-ion batteries based on polymeric complexes of transition metals with Schiff bases, modified with energy-dense nitroxyl radical redox groups (TEMPO).
The main goal is to increase the conductivity of organic battery cathode materials while maintaining sufficient specific capacity, achieved by employing highly capacitive conductive backbone materials.

Relevance and scientific novelty:

• Polymeric complexes of transition metals (e.g., nickel, copper, cobalt) with salen-type Schiff bases are a well-known class of metal-organic conductive polymers, notable for high electronic and ionic conductivity , large inherent redox capacity , and stability during cyclic redox in organic electrolytes .
• These complexes are widely used as modifiers for double-layer supercapacitor electrodes [19–23], yet little is known of their application in lithium-ion batteries.
• Conductive polymers have been widely used to improve conductivity of cathode materials based on both inorganic compounds (LiCoO₂ , LiFePO₄ ) and innovative organic redox systems .
  In comparison to studied polymers (polypyrrole, poly-3,4-ethylenedioxythiophene, etc.), salen-type metal polymer complexes provide higher conductivity and redox capacity .
• The ability to introduce various substituents without loss of electrochemical properties [18, 20, 30–37] makes these complexes handy for synthesizing new polymers containing one or more redox-active TEMPO-type groups.

TEMPO-based groups, as free molecules or in aliphatic polymer matrices, show excellent redox capacity for lithium-organic battery cathodes but suffer from low conductivity. This shortcoming can be addressed by combining TEMPO groups with highly conductive polymer complexes.

Project Approach

• Synthesize new cathode materials based on nickel and copper polymer complexes.
  • Both new compounds (with chemically linked TEMPO-group redox sites) and mechanical mixtures of known complexes with redox-active materials will be used.
• Characterize the resulting materials using various electrochemical and physical methods (cyclic voltammetry, impedance spectroscopy, electrochemical quartz microgravimetry, etc.).
• Test materials in model lithium-ion batteries to identify optimal compositions for high-power lithium-organic cathodes.
• Probe the mechanisms by which organic substituents affect the electronic structure of these materials via quantum chemical calculations.