Multi-scale boron penetration toward stabilizing nickel-rich cathode

Abstract

Nickel-rich layered oxides LiNixCoyMn1-x-yO2 (x ≥ 0.8) have been recognized as the preferred cathode materials to develop lithium-ion batteries with high energy density (>300 Wh kg−1). However, the poor cycling stability and rate capability stemming from intergranular cracks and sluggish kinetics hinder their commercialization. To address such issues, a multi-scale boron penetration strategy is designed and applied on the polycrystalline LiNi0.83Co0.11Mn0.06O2 particles that are pre-treated with pore construction. The lithium-ion conductive lithium borate in grain gaps functions as the grain binder that can bear the strain/stress from anisotropic contraction/expansion, and provides more pathways for lithium-ion diffusion. As a result, the intergranular cracks are ameliorated and the lithium-ion diffusion kinetics is improved. Moreover, the coating layer separates the sensitive cathode surface and electrolyte, helping to suppress the parasitic reactions and related gas evolution. In addition, the enhanced structural stability is acquired by strong B-O bonds with trace boron doping. As a result, the boron-modified sample with an optimized boron content of 0.5% (B5-NCM) exhibits a higher initial discharge capacity of 205.5 mAh g−1 at 0.1C (1C = 200 mA g−1) and improved capacity retention of 81.7% after 100 cycles at 1C. Furthermore, the rate performance is distinctly enhanced by high lithium-ion conductive LBO (175.6 mAh g−1 for B5-NCM and 154.6 mAh g−1 for B0-NCM at 5C).

Keywords

• Nickel-rich layered oxides
• Lithium borates
• Intergranular cracks
• Lithium-ion diffusion kinetics
• Trace boron doping
• Gas evolution