As global demand grows for safe, low-cost, and sustainable energy storage technologies, aqueous zinc-ion batteries (AZIBs) have gained increasing attention due to their high theoretical capacity, environmental friendliness, and intrinsic safety. However, their practical application has long been hindered by two major challenges: uncontrolled zinc dendrite growth and hydrogen evolution reactions (HER), both of which degrade battery performance and lifespan.
Now, a collaborative research team from Nanjing University, The University of Queensland, and Shanghai Jiao Tong University has developed an innovative solution using zwitterionic electrolyte additives. Their findings, published in Nano-Micro Letters, offer a promising pathway toward ultra-stable and long-life AZIBs.
Why This Matters
* Dendrite-Free Zinc Deposition: The additive promotes uniform deposition along the Zn (002) crystal plane, effectively suppressing dendrite formation.
* Hydrogen Evolution Suppression: It stabilizes the local pH environment, significantly reducing HER and associated parasitic reactions.
* Long Cycle Life: The modified electrolyte enables over 4,000 charge-discharge cycles with an ultra-low average capacity decay of just 0.014% per cycle.
Key Innovation: Molecular Design Matters
The researchers systematically compared three zwitterionic compounds -- CBMA, SBMA, and MPC -- all featuring the same quaternary ammonium cation but different anionic groups: carboxylate, sulfonate, and phosphate, respectively.
Among them, MPC (2-methacryloyloxyethyl phosphorylcholine) emerged as the most effective additive due to its unique dual functionality:
* pH Buffering: The phosphate group can buffer both H⁺ and OH⁻ ions, maintaining a stable electrolyte environment during cycling.
* Zn (002) Orientation: Promotes dense, flat zinc deposition, minimizing surface roughness and suppressing dendrite formation.
* Enhanced Desolvation: Reduces the activation energy required for Zn desolvation, mitigating water-induced side reactions and improving plating/stripping reversibility.
Performance Highlights
* Zn//Zn symmetric cell: Stable cycling for over 5,000 hours at 1 mA cm without short-circuiting.
* Zn//Cu half-cell: Achieves a high Coulombic efficiency of 99.6% over 600 cycles.
* Full cell (Zn//NaVO): Demonstrates exceptional stability over 4,000 cycles at 5 A g with only 0.014% capacity fade per cycle.
* Pouch cell prototype: Retains 86.6% of its initial capacity after 300 cycles under high current density and low N/P ratio (~3.6), showing strong practical potential.
Mechanistic Insights
Using a combination of electrochemical analysis, DFT calculations, and molecular dynamics simulations, the team revealed that:
* Zwitterions adsorb preferentially on the Zn surface, forming a protective interfacial layer.
* MPC enhances Zn flux uniformity and guides oriented deposition along the thermodynamically stable (002) plane.
* The additive reconstructs the solvation shell of Zn, reducing water activity and suppressing HER.
Future Outlook
This work highlights the critical role of anionic group selection in zwitterionic additives and demonstrates how molecular-level electrolyte engineering can solve long-standing challenges in AZIBs. The compatibility, low cost, and scalability of MPC make it a highly promising candidate for next-generation energy storage systems.
Moreover, the MPC molecule includes a polymerizable methacrylate group, opening the door for future development of functional polymer electrolytes and solid-state batteries.
Stay tuned for more exciting developments from this interdisciplinary research team as they continue to push the boundaries of safe, sustainable, and high-performance energy storage technologies!