Ionically conducting Li- and Na-phosphonates as organic electrode materials for rechargeable batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Optimizing ionic transport in electrode materials is crucial for rapid charge transfer in batteries.
• Few lithium-ion (Li-ion) and sodium-ion (Na-ion) organic cathode materials exist, with even fewer possessing intrinsic solid-phase ionic conductivity.

Purpose of the Study:

• To introduce novel tetra-lithium and sodium salts, A4-Ph-CH3P and A4-Ph-PhP, as alkali-ion reservoir cathode materials.
• To investigate the ionic conductivity and electrochemical performance of these new organic compounds for battery applications.

Main Methods:

• Synthesis and characterization of tetra-lithium and sodium salts (A4-Ph-CH3P and A4-Ph-PhP).
• Measurement of Li-ion and Na-ion conductivity in the dry state.
• Theoretical calculations to understand electrochemical activity and electronic properties.
• Electrochemical testing, including charge-discharge cycling and rate performance analysis.

Main Results:

• A4-Ph-PhP salts exhibit significant Li-ion (2.6 × 10⁻⁷ S cm⁻¹) and Na-ion (1.4 × 10⁻⁷ S cm⁻¹) conductivities at 30 °C.
• These are the first reported small-molecule organic cathode materials with intrinsic Li+ and Na+ conductivity.
• Na4-Ph-PhP shows distinct charge-discharge plateaus and stable cycling over 1000 cycles at 1C rate.

Conclusions:

• The developed phosphonate-based organic salts expand the range of materials for phenolate-based organic batteries.
• These findings highlight the potential of phosphonate-based organic materials for next-generation energy storage solutions.
• The intrinsic ionic conductivity in small-molecule organic cathodes represents a significant advancement in battery material design.