Sieving carbons: Ideal anodes for high-energy sodium-ion batteries

The exponentially increasing implementation of renewable energy systems, such as wind and solar energy, are urgently demanding the development of large-scale energy storage devices with flexibility, high energy conversion efficiency, and simple maintenance. Among diverse candidates, due to the natural abundance and low cost of sodium reserves, sodium-ion batteries (SIBs) have recently captured widespread attention from both the academia and industry as a sustainable supplement to lithium-ion batteries (LIBs).

Non-graphitic carbons are the most promising anode candidates for SIBs. However, challenged by their variable and complicated microstructures, what is the ideal carbon anode for SIBs that can play a similar role to what graphite does in lithium-ion batteries and how to rationally design the ideal carbon anodes are fundamental but remains poorly understood. This inevitably impedes the commercialization of SIBs.

Led by Prof. Quan-Hong Yang, Dr. Jun Zhang (Tianjin University) and Prof. Yong Yang (Xiamen University), a recent study proposed sieving carbons (SCs), featuring highly tunable nanopores with the tightened pore entrance, as the practical anodes for high-energy SIBs with the extensible and reversible low-potential charge/discharge plateaus (LPPs, <0.1 V vs. Na+/Na).

This study showed that the small pore entrance diameter (<0.4 nm) helped screen out the solvated sodium ions and induce the formation of solid electrolyte interphase (SEI) mainly outside the nanopores. By using SCs as the ideal carbon models for investigating the mechanism related to the LPPs, it was shown that bare sodium ions firstly adsorbed on the defective pore surface, and aggregated to finally form the quasi-metallic sodium clusters inside nanopores.

With spectroscopic and theoretical studies, an approximately linear correlation between the specific surface area in SCs and the plateau capacity was revealed, leading to a record-high plateau capacity of 400 mAh g-1.

A pore body diameter with an upper limit (~2.0 nm) was further proved to guarantee the reversibility of the LPPs, critical for enhancing the cycling stability of SC anodes. More promisingly, the reported way of preparing SCs was potential to be scalable for modifying commercial porous carbons to be practical anode materials, paving the way for the rapid commercialization of SIBs.

"The proposed sieving carbons is a conceptual advance for the carbon anode design for high-energy SIBs, and potential to play a similar role to what graphite does in lithium-ion batteries." Prof. Quan-Hong Yang said, "The structural tunability makes sieving carbons also promising for practical use in high-energy or high-power lithium-ion batteries, potassium-ion batteries and so on."

Research Report:Sieving carbons promise practical anodes with extensible low-potential plateaus for sodium batteries