Surface Stabilization with Fluorine of Layered Ultrahigh-Nickel Oxide Cathodes for Lithium-Ion Batteries

Abstract

High-nickel layered oxide cathodes are key to meet the demands of the electric vehicle industry because of their high specific capacity. However, commercialization of these materials is hindered by critical challenges, such as phase transitions, particle cracking, aggressive surface reactivity, and thermal instability. Cation doping along with surface coating has proven to be an effective way to circumvent some of these issues to a large extent. Herein, fluorine coating is employed on a high-nickel Li[Ni 0.95 Mn 0.015 Co 0.02 Al 0.01 Mg 0.005 ]O 2 (NMCAM) cathode via a solution route. Detailed structural and electrochemical analyses indicate fluorine largely decorates the surface at low enough calcination temperatures. The cathode with 1 mol % fluorine coating exhibits a capacity retention of 71% after 500 cycles as compared to 59% for the control sample when cycled to a high cutoff voltage of 4.3 V in a full cell configuration with graphite anode. Post-mortem analysis of cycled electrodes reveals that surface reactivity is a major contributor to capacity fade as compared to particle cracking. Fluorine coating reduces surface reactivity and the depth to which rock-salt phase is formed on the surface during cycling. The thermal stability is also enhanced after fluorine coating as the material shows less heat release at high states of charge. This work demonstrates an effective, economical, and scalable way to stabilize the surface with fluorine and enhance the electrochemical performance of high-nickel cathodes.

Laser-Assisted Surface Lithium Fluoride Decoration of a Cobalt-Free High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode for Long-Life Lithium-Ion Batteries

“…Elements, such as Al, Fe, Cr, Mg, etc., have been proved to improve the stability of the LNMO cathode and examined extensively to uncover the underlying composition–structure–interphase–performance relationships. − However, most elemental doping in LNMO cathodes shares the common drawbacks, including lowered capacity, possible inhomogeneous dopant distribution, and insufficient surface passivation. In comparison, surface engineering is proposed to be more beneficial due to its ability to reduce cathode–electrolyte reactivity and transition-metal dissolution and crossover. − For instance, surface Al 2 O 3 coating on the LNMO cathode through atomic layer deposition can extend the cycle life of high-mass-loading (over 3 mA h cm –2 ) Gr||LNMO full cells to almost 300 cycles . The cost, scalability, and uniformity of surface coating, however, need to be considered.…”

Regulating Single-Crystal LiNiO2 Size and Surface Coating toward a High-Capacity Cathode for Lithium-Ion Batteries

“…LNO620 shows the highest capacity which declines with the increasing LiF content. It is likely attributed to the presence of the insulating fluorine layer at the surface, 36 as the cycling performances presented in Figure 5b; after 200 cycles at 2 C, the capacity retention of fluorine-coated LNO-F1, LNO-F2, and LNO-F3 was 62.7, 65.1, and 64.4%, respectively, which is a much improved cycling stability compared to that of the uncoated LNO620 (41.6%). Although the coated cathodes show similar retention tendency, LNO-F2 shows the highest capacity retention and capacity.…”

“…This indicates that the LiF coating can mitigate capacity fading effectively. 33,36 Due to the insulating nature of the LiF coating, unwanted reactions such as electrolyte decomposition or Ni reduction can be alleviated. To further clarify the electrochemical performance improvement in LNO-F2, the cycling stability was compared with that of the large single-crystal sample, LNO700 (the higheststability sample), as shown in Figure 5e.…”

New perspectives on the multianion approach to adapt electrode materials for lithium and post-lithium batteries

“…36 The fluorination of layered Li[Ni 0.95 Mn 0.015 Co 0.02 Al 0.01 -Mg 0.005 ]O 2 was performed by adding it to a solution of NH 4 F and heated at 400 1C to form a coating, LiF is detected, and fluorine does not enter significantly in the particle bulk. 37 However, F-doping into the crystal structure by substituting oxygen could occur at higher temperatures.…”