Accurate Control of Initial Coulombic Efficiency for Lithium‐rich Manganese‐based Layered Oxides by Surface Multicomponent Integration

Abstract

Low initial Coulombic efficiency (ICE) is an obstacle for practical application of Li-rich Mn-based layered oxides (LLOs), which is closely related with the irreversible oxygen evolution owing to the overoxidized reaction of surface labile oxygen. Here we report a NH 4 F-assisted surface multicomponent integration technology to accurately control the ICE, by which oxygen vacancies, spinel-layered coherent structure, and F-doping are skillfully integrated on the surface of treated LLOs microspheres. Though the regulation on the removed amount of labile oxygen by surface integrated structure, the ICE of LLOs cathodes can adjust from starting value to 100 %. X-ray absorption spectroscopy, refined X-ray diffraction, and scanning transmission electron microscopy show that the removed labile oxygen mainly comes from Li 2 MnO 3-like structure. Even operating at a high cutoff voltage of 5 V, the capacity retention of integrated sample at 200 mA g À1 is still larger than 98 % after 100 cycles.

Effects of Various Elements Doping on LiNi0.6Co0.2Mn0.2O2 Layered Materials for Lithium‐Ion Batteries

“…[14] Other studies showed that Ti-doped Li(Ni x Mn x Co 1-2x-y Ti y )O 2 not only increased the energy density but also enhanced the structural stability upon cycling because of the elevated Ti-O bond energy. [15] Chen et al reported that when F À occupied the O sites in Li-rich layered oxides, cycling stability was enhanced by 94.8% in 50 cycles between 2.0 and 4.8 V. [16] Small amounts of Fe-doped LiNi 1/3 Co 1/3 Mn 1/3 O 2 prepared by simple sol-gel method also displayed slight volume change in the material during Li þ diffusion, resulting in excellent structural stability. [17] In addition, other elements such as Al, [18,19] Cr, [20] Zr, [21,22] and Zn [23,24] have been also explored.…”

Facile Molten Vanadate-Assisted Surface Treatment Strategy for Li2MnO3 Activation of Li-Rich Cathode Materials

“…For example, Zhang et al 9 the electrochemical process, thus promoting ICE. Luo 10 and coworkers reduced the content of unstable oxygen on the surface using F − for surface modification and greatly improved the ICE. Likewise, a lot of reagents were selected to realize pre-activation, such as Na 2 S 2 O 8 , (NH 4 ) 2 SO 4 , and NH 4 H 2 PO 4 .…”

“…Although these preactivation methods can effectively improve the performance, they also induced the deterioration of cycle stability and the voltage drop during the discharge process and thus reduced the energy density for the LRMO material. 10,16 Specially, Zhu et al 17 reported a molten-assisted way to create LRMO particles with a Li-poor surface and Li-rich core. The continuous Ligradient kept the overall structure stable and greatly improved the electrochemical performance.…”

“…For example, Zhang et al demonstrated that the oxygen vacancies on the surface formed by gas–solid interface reaction can hinder the generation of unstable O-redox during the electrochemical process, thus promoting ICE. Luo and co-workers reduced the content of unstable oxygen on the surface using F – for surface modification and greatly improved the ICE. Likewise, a lot of reagents were selected to realize pre-activation, such as Na 2 S 2 O 8 , (NH 4 ) 2 SO 4 , and NH 4 H 2 PO 4 . − The mechanism of these chemical activation is through Li + /H + exchange. , Furthermore, after calcination, a spinel layer was constructed on the surface of the material, and the specific capacity and ICE also were improved.…”

“…Likewise, a lot of reagents were selected to realize pre-activation, such as Na 2 S 2 O 8 , (NH 4 ) 2 SO 4 , and NH 4 H 2 PO 4 . − The mechanism of these chemical activation is through Li + /H + exchange. , Furthermore, after calcination, a spinel layer was constructed on the surface of the material, and the specific capacity and ICE also were improved. Although these pre-activation methods can effectively improve the performance, they also induced the deterioration of cycle stability and the voltage drop during the discharge process and thus reduced the energy density for the LRMO material. , Specially, Zhu et al reported a molten-assisted way to create LRMO particles with a Li-poor surface and Li-rich core. The continuous Li-gradient kept the overall structure stable and greatly improved the electrochemical performance.…”