Lithium exchange across a lithium-less coating for high energy cathodes

Advances in modification methods and the future prospects of high-voltage spinel LiNi0.5Mn1.5O4— a review

“…Their explanation is that lithium is initially embedded in the coating layer and then diffuses into the cathode material, resulting in an efficient transport path for Li + across the electrode–electrolyte interface. 98 C. Yu et al chose to use structurally stable YF 3 as the coating layer of LNMO. The study found that the YF 3 coating on the surface can effectively inhibit the harmful side reactions between the electrode surface and the electrolyte, block the corrosion of HF, and thus improve the rate capacity.…”

Identification of the dual roles of Al2O3 coatings on NMC811-cathodes via theory and experiment

“…112 Haber and co-workers also used ssNMR to investigate their Al-F based coating on LiNi0.5Mn1.5O4. 42 They similarly performed Li intercalation into the coating/the formation of Li-Al-Ox phases to explain their experimental observations. We note that their coatings are more highly fluorinated and there will be a stronger driving force for the more acidic protons in the Al(OH)Fx groups to ion-exchange with Li (potentially also re-leaving protons), potentially explaining the differences between the two NMR studies. )…”

“…One hypothesis is the lithiation of alumina to form a new phase during electrochemical cycling. 19,42,105,106 Since this cannot be a redox process it would have to involve Li + -H + exchange and possibly structural rearrangements. In this study, reference 𝛾-LiAlO2 (82 ppm) 107 was compared to a cycled ALD NMC811 (charged to 4.4 VLi on cycle 2) to test for lithiation; 𝛾-LiAlO2 is appropriate as it crystallises first from an amorphous state of precursor materials.…”

“…27 Al), allowing structural characterisation of the different Al coordination environments found in Al2O3 coatings 38 to be linked to the electrochemical performance of the coated Ni-rich layered oxide. [39][40][41][42] Post-mortem analysis of Al2O3 coated NMC after electrochemical cycling with ssNMR to determine the role of the coating has been more scarce in the literature. The 27 Al spectra in past studies 40,43 suggest that little structural and chemical evolution of the Al2O3 coating have occurred, in contrast to reported HF scavenging reactions that might be expected to occur given the degradation mechanisms proposed in the literature.…”

“…For example, the proximity of 7 Li to 27 Al spins in Al-F based coatings deposited by ALD, as found in 27 Al{ 7 Li} and 7 Li{ 19 F} rotational echo double resonance (REDOR) NMR experiments, suggest the formation of a lithiated coating. 42 In this study we characterise the ALD Al 2 O 3 coatings formed on polycrystalline NMC811 and how the coatings evolve with cycling. This is achieved by using a combination of single and double-resonance ssNMR experiments that monitor the local coordination environment of Al, measuring gaseous and solution electrolyte degradation species arising from NMC811electrolyte interactions at high potentials, and density functional theory using a Hubbard correction (DFT+U) to examine the surface Ni/O electronic states to explore improved capacity retention and surface stability.…”