Stabilizing the Interphase in Cobalt‐Free, Ultrahigh‐Nickel Cathodes for Lithium‐Ion Batteries

Abstract

High-nickel layered oxide cathodes, such as LiNi 1-x-y Mn x Co y O 2 (NMC) and LiNi 1-x-y Co x Al y O 2 (NCA), are at the forefront for implementation in highenergy-density lithium-ion batteries. The presence of cobalt in both cathode chemistries, however, largely deters their application due to fiscal and humanitarian issues affiliated with cobalt sourcing. Increasing the Ni content drives down the Co content, but introduces additional structural and electrochemical problems attributed to high-Ni cathodes. Herein a dually modified cobalt-free ultrahigh-nickel cathode 0.02B-LiNi 0.99 Mg 0.01 O 2 (NBM) is presented with 1 mol% Mg and 2 mol% B that exhibits a high initial 1C discharge capacity of 210 mA h g -1 with a 20% capacity retention improvement over 500 cycles when benchmarked against LiNiO 2 (LNO) in pouch full cell configurations with graphite anode. Postmortem analyses reveal the enhanced performance stems from reduced active lithium inventory loss and localized surface reactivity in the NBM cathode. The stabilized cathode-electrolyte interphase subsequently reduces transition-metal dissolution and ensuing chemical crossover to the graphite anode, which prevents further catalyzed parasitic reactions that harmfully passivate the anode surface. Altogether, this study aims to highlight the importance of electrode characterization and analysis from an interphasial viewpoint and to push the ongoing research to stabilize cobalt-free ultrahigh-Ni cathodes for industrial feasibility.

Roles of Mn and Co in the Air Synthesizability of Layered Oxide Cathodes for Lithium-Based Batteries

“…The proliferation of lithium-ion batteries (LIBs) for portable electronics, electric vehicles (EVs), and grid energy storage has led to a mass production of layered LiNi 1– x – y Mn x Co y O 2 (NMC) cathodes with wide compositional variations that can be tailored toward different applications. − The appetite for a longer driving range in EVs is pushing an increase in the Ni content in NMC. − However, the increase in the Ni content to >70 mol % exacerbates progressively the chemical and structural degradations . As such, NMC cathodes with moderately high Ni contents of 70–80 mol % are typically utilized in present-day commercial cells.…”

“…The challenge to keep Ni as Ni 3+ during calcination and the air instability of high-Ni cathodes lead to increased Li + /Ni 2+ mixing in the layers, surface lattice reconstruction, and residual lithium formation, which collectively impair the rate capability and cyclability. − Consequently, high-Ni cathodes are calcined under flowing oxygen atmospheres to stabilize Ni 3+ , thereby minimizing adverse problems. Additional modifications to effectively reduce the air instabilities of high-Ni cathodes have also been widely explored, which include washing, doping, and dry coating. ,− However, the cost of securing pure O 2 gas compared to ambient air coupled with the additional steps and costs associated with implementing these modifications will deter cathode production scalability …”

Tuning and understanding the solvent ratios of localized saturated electrolytes for lithium-metal batteries

“…The Ni(OH) 2 precursor was synthesized in-house by transitionmetal hydroxide coprecipitation, which is further detailed in our previous studies. 22,23 The synthesized hydroxide precursor was mixed with LiOH$H 2 O at a molar ratio of 1 : 1.03 and calcined at 655 °C for 12 h under owing oxygen to yield LiNiO 2 (LNO). Cathode slurries were then made by mixing the calcined LiNiO 2 with poly(vinylidene uoride) (PVDF) binder and conductive carbon (Super P) in a 90 : 5 : 5 weight ratio in Nmethyl-2-pyrrolidone (NMP) solvent.…”

Synergy of Epitaxial Layer and Bulk Doping Enables Structural Rigidity of Cobalt‐Free Ultrahigh‐Nickel Oxide Cathode for Lithium‐Ion Batteries

“…Recently, Co‐free ultrahigh‐Ni oxide cathodes with different compositional regulations have been developed for overcoming price fluctuation and prolonging cycle stability. The substitution of Co with cost‐efficient elements is a prevalent approach, such as Mg, Al, Mn, and Ti as in LiNi 0.99 Mg 0.01 O 2 , [ 19 ] LiNi 0.94 Al 0.06 O 2 , [ 20 ] LiNi 0.9 Mn 0.1 O 2 , [ 21 ] and LiNi 0.96 Mg 0.02 Ti 0.02 O 2 , [ 22 ] respectively. In particular, the addition of Al into the layered oxide can perturb the long‐range metal–metal interaction and reduce the long‐range metal–oxygen covalence, making the lattice robust and thereby inhibiting metal ion dissolution and improving cycling stability.…”