Enabling Multielectron Reaction of Polyanionic Cathodes Toward High-Energy Calcium Rechargeable Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Polyanionic cathode materials are crucial for calcium-ion batteries (CIBs) due to their structural stability and ion diffusion.
• Existing polyanionic cathodes often have limited capacity stemming from single-electron transfer.

Purpose of the Study:

• To develop a novel polyanionic cathode material for high-capacity and stable CIBs.
• To investigate multielectron transfer mechanisms in polyanionic compounds for enhanced energy storage.

Main Methods:

• Synthesis and characterization of Ca$_{x}$NaV$_{1.5}$Cr$_{0.5}$(PO$_{4}$)$_{3}$ cathode material.
• Electrochemical testing including cycling performance, rate capability, and energy density measurements in CIBs and full cells.
• Analysis of structural stability and ion diffusion kinetics.

Main Results:

• The Ca$_{x}$NaV$_{1.5}$Cr$_{0.5}$(PO$_{4}$)$_{3}$ cathode demonstrated a reversible capacity of 162 mAh g$^{-1}$ at 2.5 V with an energy density of ~400 Wh kg$^{-1}$.
• Achieved excellent cycling stability with 98.2% capacity retention over 600 cycles and 80.8% over 5000 cycles, attributed to low volume changes (1.8%).
• Demonstrated a high energy density of 318 Wh kg$^{-1}$ in Ca metal full cells, rivaling state-of-the-art CIBs.

Conclusions:

• The developed Ca$_{x}$NaV$_{1.5}$Cr$_{0.5}$(PO$_{4}$)$_{3}$ material enables high-capacity and ultra-stable CIBs through multielectron redox reactions.
• This work highlights the potential of activating multielectron transfer in polyanionic cathodes for sustainable energy storage solutions.
• The findings pave the way for next-generation high-performance calcium-ion batteries.