Reversible Li⁺ Storage in CF-Based Cathodes through Transition Metal Decomposition.

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Graphite fluorides (CF) are used in primary lithium batteries due to high capacity and low self-discharge.
• The primary discharge of CF with Li+ is largely irreversible, limiting its use in rechargeable batteries.

Purpose of the Study:

• To develop rechargeable CF-based cathodes by incorporating transition metals.
• To improve the reversibility of the electrode reaction for enhanced lithium-ion storage.

Main Methods:

• Fabrication of CF-based cathodes with transition metals (e.g., copper).
• Electrochemical testing to evaluate primary and reversible capacities.
• Ex situ X-ray diffraction to confirm the formation of metal fluorides (MF).

Main Results:

• CF-Cu electrodes demonstrated a high primary capacity (898 mAh g-1) and a reversible capacity (383 mAh g-1 in the second cycle).
• Transition metals facilitate the re-conversion of LiF into MF during the charge process, enabling subsequent Li+ storage.
• Excessive transition metal decomposition negatively impacts electrode stability.

Conclusions:

• Introducing transition metals into CF cathodes enables rechargeable lithium-ion storage.
• Controlling transition metal oxidation through methods like building a compact counter electrolyte interface (CEI) is crucial for cathode reversibility and structural stability.