Mitigating voltage decay in high-capacity Li_1.2Ni_0.2Mn_0.6O₂ cathode material by surface K⁺ doping

The lithium-rich layered materials have received much attention as high-energy-density cathodes to cater for future lithium-ion batteries. However, the growth of detrimental spinel configuration upon cycling can destroy the stability of structures and become the significant challenge for their commercialization. In view of previous research of alkali metal doping, we have successfully prepared the surface K⁺ doped Li_1.2Ni_0.2Mn_0.6O₂, which delivers an outstanding cycling durability with 99.96% of fully activated capacity (260 mAh g⁻¹) even after 100 cycles. Moreover, the K⁺ doped material displays less voltage fading, demonstrating the alleviation of structure transformation from layered toward spinel phase. The effects of K⁺ doping were further investigated by the soft X-ray absorption spectroscopy. The Mn L-edges and the O K-edge prove that the doped K⁺ may play an indispensable role in stabilizing the surface O₂ ²⁻ and facilitating the reduction of Mn³⁺ ion with undesirable Jahn-Teller effect towards lower valence Mn²⁺.