In Situ Electrochemical Zn²⁺-Doping for Mn-Rich Layered Oxides in Li-Ion Batteries

Abstract

Mn-rich layered oxide materials have been considered as promising cathode materials for large scale Li-ion batteries because Mn is more inexpensive than Co and Ni. In this connection, a variety of dopedmaterials have been examined to improve the electrochemical performance of Mn-rich cathode materials. Doped-materials are conventionally synthesized using solid state synthesis at high temperatures, where most dopants are located at transition metal sites. The amount of redox-active transition metals decreases with increasing the amount of dopants in transition metals sites, resulting in the reduced reversible capacity of doped-materials. This paper demonstrates an in situ electrochemical doping of Zn 2+ that is site-selective. Li + at Li sites in Mn-rich layered oxides is selectively replaced by Zn 2+ during cycling. Zn 2+ ions in electrolytes are irreversibly inserted to Li sites in delithiated Mn-rich cathode materials during discharge, leading to the formation of Zn 2+ -doped Mn-rich layered oxides, [Li 1−x Zn y ][Mn 1−z M z ]O 2 (M = Ni and Co). In contrast to conventional doped-materials, Zn 2+ dopants at Li sites do not reduce the reversible capacity of Mn-rich oxide materials. Zn 2+ at the Li sites diminishes both cation disorder and electrolyte decomposition during cycling, leading to the improved capacity retention over 100 cycles. In addition, the Zn 2+ intercalation is dependent on the amount of Mn in layered oxides and, thereby, only available for Mn-rich cathode materials. Moreover, the in situ electrochemical Zn 2+ -doping is facile and practical in the aspect of processability, because this only requires an electrolyte additive, such as Zn(TFSI) 2 .

Towards commercialization of fluorinated cation-disordered rock-salt Li-ion cathodes

“…Current commercial cathodes have introduced an interphase, which can prevent the material surface from direct contact with the electrolytes, to overcome the issues from unstable surfaces, and this has been shown to be a successful strategy. There are many ways to form the interphases, including ex-situ coating, in-situ interphase formation using electrolyte additives, surface doping, and chemical treatment as illustrated in Figure 2A (Choi et al, 2019;Huang et al, 2019;Lim et al, 2019;Naylor et al, 2020;Kim et al, 2021). The methods are not limited by their scalability and have an advantage from the perspective of commercialization.…”

Demystifying the Lattice Oxygen Redox in Layered Oxide Cathode Materials of Lithium-Ion Batteries

“…Different doping methods can boost the electrochemical property of LRM oxide electrode materials to a certain degree. Alkali metal elements, such as K, Na, alk-earth metal elements Mg and TMs including Fe, Cr, Ti, Ce, Zr and La, have been applied to improve the ionic dispersion rate and strengthen the crystal structure stabilization. − In all, the underlying effects of the doping can be reviewed as follows: (1) inhibiting the crystal structure transformation to lower the formation of the distortion and stress; (2) maintaining the LOR reactions to keep the crystal structure stability of the LRM oxide cathode materials; (3) magnifing the interlayer spacing to mitigat the TM migration and promote the Li + irradiation; (4) adjusting the electron structure to improve the electronic conductivity. According to previous report, most of the normal doping methods will provoke the production of a slender layer on the outside of the electrode materials because of the difference ionic radii between the Li + and the dopan .…”

Understanding the Effects of Tetrahedral Site Occupancy by the Zn Dopant in Li-NMCs toward High-Voltage Compositional–Structural–Mechanical Stability via Operando and 3D Atom Probe Tomography Studies

“…or incorporation of “inactive” dopants (say, Mg 2+ , Al 3+ , Zn 2+ , Na + , etc.) in the T M /Li-layer, or both. − …”