An Air-Operated, High-Performance Fe-Ion Secondary Battery Using Acidic Electrolyte

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Aqueous batteries are promising for low-cost, safe energy storage.
• Iron(II) (Fe²⁺) is an ideal charge carrier but prone to oxidation.
• Assembling iron-ion batteries typically requires oxygen-free gloveboxes due to Fe²⁺ instability.

Purpose of the Study:

• To overcome the challenge of direct air assembly for aqueous iron-ion batteries.
• To investigate the inhibition of Fe²⁺ oxidation in ambient conditions.
• To develop a stable and high-performance aqueous iron-ion battery operable with air assembly.

Main Methods:

• Utilized an acidic electrolyte to inhibit Fe²⁺ oxidation.
• Investigated the proton/O₂ competitive mechanism in the Fe²⁺ solvated shell.
• Examined the in situ formation of active cathode materials in acidic conditions.
• Performed electrochemical testing to evaluate battery performance.

Main Results:

• Fe²⁺ oxidation was completely inhibited in an acidic electrolyte.
• A proton/O₂ competitive mechanism was identified, reducing O₂ coordination.
• Air-operated assembly of aqueous iron-ion batteries was achieved for the first time.
• In situ growth of α-FeOOH derivative on VOPO₄·2H₂O cathode was observed.
• The battery demonstrated a high specific capacity (192 mAh g^-1) and stable cycling (>1300 cycles).

Conclusions:

• Acidic electrolytes are effective in preventing Fe²⁺ oxidation, enabling air assembly of aqueous iron-ion batteries.
• The study reveals novel insights into the proton/O₂ competitive mechanism and cathode surface chemistry.
• This breakthrough facilitates the development of practical, low-cost, and safe aqueous iron-ion energy storage systems.