Lee Yongju, Shin Jaewook, Kang Hyeonmuk, Lee Daehee, Kim Tae-Hee, Kwon Young-Kyun, Cho EunAe
Department of Materials Science and Engineering Korea Advanced Institute of Science & Technology Daejeon 34141 Korea.
Advanced Battery Center KAIST Institute for NanoCentury Korea Advanced Institute of Science and Technology 291 Daehak-ro, Yuseong-gu Daejeon 34141 Korea.
Adv Sci (Weinh). 2021 Jan 29;8(6):2003013. doi: 10.1002/advs.202003013. eCollection 2021 Mar.
Li-excess layered cathode (LLC) materials have a high theoretical specific capacity of 250 mAh g induced by transition metal (cationic) and oxygen (anionic) redox activity. Especially, the oxygen redox reaction related to the activation of the LiMnO domain plays the crucial role of providing a high specific capacity. However, it also induces an irreversible oxygen release and accelerates the layered-to-spinel phase transformation and capacity fading. Here, it is shown that surface doping of vanadium (V) cations into LLC material suppresses both the irreversible oxygen release and undesirable phase transformation, resulting in the improvement of capacity retention. The V-doped LLC shows a high discharge capacity of 244.3 ± 0.8 mAh g with 92% retention after 100 cycles, whereas LLC delivers 233.6 ± 1.1 mAh g with 74% retention. Furthermore, the average discharge voltage of V-doped LLC drops by only 0.33 V after 100 cycles, while LLC exhibits 0.43 V of average discharge voltage drop. Experimental and theoretical investigations indicate that doped V-doping increase the transition metal-oxygen (TM-O) covalency and affect the oxidation state of peroxo-like (O) species during the delithiation process. The role of V-doping to make the oxygen redox reversible in LLC materials for high-energy density Li-ion batteries is illustrated here.
富锂层状正极（LLC）材料因过渡金属（阳离子）和氧（阴离子）的氧化还原活性而具有250 mAh g的高理论比容量。特别是，与LiMnO域活化相关的氧氧化还原反应在提供高比容量方面起着关键作用。然而，它也会导致不可逆的氧释放，并加速层状向尖晶石的相变以及容量衰减。在此，研究表明将钒（V）阳离子表面掺杂到LLC材料中可抑制不可逆的氧释放和不良相变，从而提高容量保持率。V掺杂的LLC在100次循环后显示出244.3±0.8 mAh g的高放电容量，容量保持率为92%，而LLC的放电容量为233.6±1.1 mAh g，容量保持率为74%。此外，V掺杂的LLC在100次循环后的平均放电电压仅下降0.33 V，而LLC的平均放电电压下降0.43 V。实验和理论研究表明，掺杂的V增加了过渡金属-氧（TM-O）的共价性，并在脱锂过程中影响过氧类（O）物种的氧化态。本文阐述了V掺杂在高能量密度锂离子电池的LLC材料中使氧氧化还原可逆的作用。
