Bio-Derived Surface Layer Suitable for Long Term Cycling Ni-Rich Cathode for Lithium-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Surface Chemistry

Background:

• Nickel-rich cathode materials are prone to degradation from moisture and residual lithium compounds, impacting battery performance.
• Surface modification is crucial for enhancing the stability and lifespan of these advanced cathode materials.
• Hydroxyapatite, a tooth-derived material, offers excellent mechanical and thermodynamic stability for potential surface protection applications.

Purpose of the Study:

• To investigate the efficacy of hydroxyapatite as a surface protective layer for nickel-rich Li[Ni0.8Co0.15Al0.05]O2 cathode materials.
• To evaluate the impact of hydroxyapatite modification on reducing surface lithium residues and improving electrochemical performance.
• To understand the degradation mechanisms and the role of the modified surface layer in enhancing cycling stability.

Main Methods:

• Synthesis of lithium-doped hydroxyapatite (Ca4.67Li0.33(PO4)3(OH)) layer on Li[Ni0.8Co0.15Al0.05]O2.
• Characterization of surface lithium content reduction.
• Long-term galvanostatic cycling tests to assess electrochemical stability.
• Morphological analysis to observe surface changes during cycling.
• Density Functional Theory (DFT) calculations to elucidate degradation mechanisms.

Main Results:

• A ≈10-nm layer of Ca4.67Li0.33(PO4)3(OH) significantly reduced surface lithium residues from 22364 ppm to 2879 ppm.
• The modified electrode exhibited ultra-long cycling stability, retaining 66.3% of its initial capacity after 1000 cycles.
• Morphological degradation, including micro-cracking and amorphization, was significantly suppressed.
• In-situ transformation of the hydroxyapatite layer to stable Ca4.67Li0.33(PO4)3F and CaF2 layers was observed during cycling.

Conclusions:

• Hydroxyapatite is a highly effective surface modifying agent for nickel-rich cathode materials, mitigating performance degradation.
• The formation of stable CaF2-based layers derived from hydroxyapatite plays a critical role in protecting the cathode during electrochemical cycling.
• The study demonstrates a promising strategy for developing highly stable and durable nickel-rich cathode materials for advanced energy storage applications.