Enhanced electrochemical performance of Li-rich cathode Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ by surface modification with lithium ion conductor Li₃PO₄

Highlights: • Li-rich cathode Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ coated with lithium ion conductor Li₃PO₄ was synthesized. • Electrochemical performance was significantly improved by Li₃PO₄ coating. • Li₃PO₄ coating layer facilitates the Li⁺ diffusion and suppresses the side reaction. - Abstract: Li-rich layered cathode Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ is prepared via a co-precipitation followed with high-temperature calcination, and then successfully modified with nano-Li₃PO₄ by ball milling and annealing. The TEM and EDS reveal that Li₃PO₄ is homogeneously coated on the particle surface of Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂. And the electrochemical performance of Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ is significantly improved by coating with lithium ion conductor Li₃PO₄. The Li₃PO₄-coated sample delivers a high initial discharge capacity of 284.7 mAhg⁻¹ at 0.05 C, and retains 192.6 mAhg⁻¹ after 100 cycles at 0.5 C, which is higher than that of the pristine sample (244 mAhg⁻¹ at 0.05 C and 168.2 mAhg⁻¹ after 100 cycles at 0.5 C). The electrochemical impedance spectroscopy (EIS) demonstrates that the resistance for Li/Li₃PO₄-coated Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ cell was reduced compared to Li/Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂, which indicates the Li₃PO₄ coating layer with high ionic conductivity (6.6 × 10⁻⁸ S cm⁻¹) facilitates the diffusion of lithium ions through the interface between electrode and electrolyte and accelerates the charge transfer process. What is more, the Li₃PO₄ coating layer can also act as a protection layer to protect the cathode material from encroachment of electrolyte. The two aspects account for the enhanced electrochemical performance of Li₃PO₄-coated Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂.