Site‐Selective In Situ Electrochemical Doping for Mn‐Rich Layered Oxide Cathode Materials in Lithium‐Ion Batteries

Abstract

Various doped materials have been investigated to improve the structural stability of layered transition metal oxides for lithium‐ion batteries. Most doped materials are obtained through solid state methods, in which the doping of cations is not strictly site selective. This paper demonstrates, for the first time, an in situ electrochemical site‐selective doping process that selectively substitutes Li+ at Li sites in Mn‐rich layered oxides with Mg2+. Mg2+ cations are electrochemically intercalated into Li sites in delithiated Mn‐rich layered oxides, resulting in the formation of [Li1−xMgy][Mn1−zMz]O2 (M = Co and Ni). This Mg2+ intercalation is irreversible, leading to the favorable doping of Mg2+ at the Li sites. More interestingly, the amount of intercalated Mg2+ dopants increases with the increasing amount of Mn in Li1−x[Mn1−zMz]O2, which is attributed to the fact that the Mn‐to‐O electron transfer enhances the attractive interaction between Mg2+ dopants and electronegative Oδ− atoms. Moreover, Mg2+ at the Li sites in layered oxides suppresses cation mixing during cycling, resulting in markedly improved capacity retention over 200 cycles. The first‐principle calculations further clarify the role of Mg2+ in reduced cation mixing during cycling. The new concept of in situ electrochemical doping provides a new avenue for the development of various selectively doped materials.

Stabilizing nickel-rich layered oxide cathodes by magnesium doping for rechargeable lithium-ion batteries

“…Additionally, the cations residing in interlayers could increase the energy of TM ion migration to Li slabs and effectively restrain such migration on cycling due to electrostatic repulsion 13a,23. A recent first-principles calculation has also shown a larger Li/Ni exchange energy after Mg doping 24…”

Vanadium disulfide flakes with nanolayered titanium disulfide coating as cathode materials in lithium-ion batteries

“…d Capacity retention of VS 2 electrode and VS 2 -TiS 2 electrode at 1000 mA g −1 . e Comparison of the VS 2 -TiS 2 electrode (starred) with other commonly used cathodes [7, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49] in Li-ion batteries. The y -axis on the plot gives the specific capacity achieved by the cathode material at the completion of a specified number of charge−discharge cycles given on the x -axis of the plot.…”

Metal-to-metal charge transfer driven by electropositive species for stable anionic redox

“…10). Notably, Ni is oxidized up to approximately 3+ during charging as the redox potential of Ni increases with decreasing charge density [32][33][34] , in contrast to the perception that Ni can be oxidized to 4+ on typical NCM cathode materials 6,30 . The same is identi ed through rst-principles calculations in Supplementary Table 2, indicating that full oxidation (Ni 2+/4+ ) of partial Ni is thermodynamically hindered depending on the TM sites.…”