Nickel-rich layered oxides are promising positive electrode materials for lithium-ion batteries due to their high capacity and decreased cobalt content. The application of surface coatings is a common approach to slowing or potentially stopping deleterious reactions at the electrode−electrolyte interface of lower-Ni content layered oxides. However, their efficacy on Ni-rich LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) is less certain, and knowledge on how to design effective coatings with favorable properties is sparse. In this work, we develop a convenient solution-based deposition method for the synthesis of aluminum oxide coated NMC811 secondary particles and we study the effects of annealing temperature on their structure and electrochemical lifetime in lithium-ion batteries. Using energy-dispersive X-ray spectroscopy and X-ray fluorescence spectroscopy, we quantify the amount and distribution of aluminum oxide on the cathode particles. Changes in the coating phase and composition as a function of annealing temperature are tracked with solid-state nuclear magnetic resonance and X-ray photoelectron spectroscopy. 27 Al NMR spectroscopy at very high fields (23.5 T) provides direct evidence that after annealing up to 400 °C, 4-, 5-, and 6-coordinate aluminum is present, here assigned to an amorphous alumina coating, but after annealing to 600 °C, a γ-LiAlO 2 -like coating is observed. We further differentiate between Al in the bulk and surface phase and identify, for the first time, the critical temperature at which doping occurs in NMC811. Surface/bulk doping starts to occur in the range of 500−600 °C, with considerable bulk doping being found at 800 °C. The onset of Al diffusion coincides with the decrease in capacity retention, contradicting previous studies and giving new insight into the relationship between lifetime and lithium-ion conductivity.
In investigating and seekingt om imic the reactivity of trimethylaluminium (TMA) with synthetic, ester-based lubricating oils, the reaction of methylp ropionate 1 wase xplored with 1, 2a nd 3equivalents of the organoaluminium reagent. Spectroscopica nalysis pointst ot he formation of the adduct 1(TMA) accompanied only by the low level 1:1 production of Me 2 AlOCEtMe 2 2 and Me 2 AlOMe 3 when an equimolar amount of TMA is applied. The deploymento f excess TMA favoursr eactiont og ive 2 and 3 over 1(TMA) adductf ormation and spectroscopy reveals that in hydrocarbon solution substitution product 2 traps unreacted TMA to yield 2(TMA).
The simple inorganic cyclodiphosph(iii)azane chiral derivatisation agent ClP(μ-tBuN)2POBorn (Born = endo-(1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be effective in the measurement of ee’s of chiral amines using 31P NMR spectroscopy.
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