Editors' Choice—Coating-Dependent Electrode-Electrolyte Interface for Ni-Rich Positive Electrodes in Li-Ion Batteries

Abstract

Surface chemistry modification of positive electrodes has been used widely to decrease capacity loss during Li-ion battery cycling. Recent work shows that coupled LiPF 6 decomposition and carbonate dehydrogenation is enhanced by increased metal-oxygen covalency associated with increasing Ni and/or lithium de-intercalation in metal oxide electrode, which can be responsible for capacity fading of Ni-rich oxide electrodes. Here we examined the reactivity of lithium nickel, manganese, cobalt oxide (LiNi 0.6 Mn 0.2 Co 0.2 O 2 , NMC622) modified by coating of Al 2 O 3 , Nb 2 O 5 and TiO 2 with a 1 M LiPF 6 carbonate-based electrolyte. Cycling measurements revealed that Al 2 O 3 -coated NMC622 showed the least capacity loss during cycling to 4.6 V Li compared to Nb 2 O 5 -, TiO 2 -coated and uncoated NMC622, which was in agreement with smallest electrode impedance growth during cycling from electrochemical impedance spectroscopy (EIS). Ex-situ infrared spectroscopy of charged Nb 2 O 5 -and TiO 2 -coated NMC622 pellets (without carbon nor binder) revealed blue peak shifts of 10 cm −1 , indicative of dehydrogenation of ethylene carbonate (EC), but not for Al 2 O 3 -coated NMC622. X-ray Photoelectron Spectroscopy (XPS) of charged TiO 2 -coated NMC622 electrodes (carbon-free and binder-free) showed greater salt decomposition with the formation of lithium-nickel-titanium oxyfluoride species, which was in agreement with ex-situ infrared spectroscopy showing greater blue shifts of P-F peaks with increased charged voltages, indicative of species with less F-coordination than salt PF 6 − anion on the electrode surface. Greater salt decomposition was coupled with the increasing dehydrogenation of EC with higher coating content on the surface. This work shows that Al 2 O 3 coating on NMC622 is the most effective in reducing carbonate dehydrogenation and accompanied salt decomposition and rendering minimum capacity loss relative to TiO 2 and Nb 2 O 5 coating.

A Sieve‐Functional and Uniform‐Porous Kaolin Layer toward Stable Zinc Metal Anode

“…The first one with a resistance of 243.9 Ω is associated with ion adsorption and desorption for the coating interface at the high‐frequency region. Another circle of 70.35 Ω is due to the charge transfer resistance at the medium‐frequency region, [ 22 ] which is almost ten times lower than that of bare Zn. Hence, the ion transport capability along with suitable active sites for kaolin coating could effectively shorten the migration path of zinc ions besides the function of artificial SEI layer.…”

Revealing electrolyte oxidation via carbonate dehydrogenation on Ni-based oxides in Li-ion batteries by in situ Fourier transform infrared spectroscopy

“…Energy & Environmental Science Paper coating did not cause visible solvent decomposition, which implies a more stable interface. This explains the mechanism for surface coatings such as Al 2 O 3 , 78,79,83 HfO 2 81 or ZrO 2 80 to increase cycling stability and capacity retention. Another strategy to design a stable interface is to tune the solvent activity, e.g.…”

Surface/Interface Structure Degradation of Ni‐Rich Layered Oxide Cathodes toward Lithium‐Ion Batteries: Fundamental Mechanisms and Remedying Strategies

“…Now that the parasitic side reactions start from the interfaces between the solid cathodes and liquid electrolytes, the most effective method is to avoid their direct contact by introducing passive physical protection layer on the cathode surface . In general, the employed coating species can be categorized into i) the chemically and electrochemically inactive coatings, including metal oxides (Al 2 O 3 , TiO 2 , MgO, SiO 2 , ZrO 2 , V 2 O 5 , Nb 2 O 5 , ZnO, MoO 3 , and Y 2 O 3 ,) and phosphates (AlPO 4 , MnPO 4 , Mn 3 (PO 4 ) 2 , La(PO 4 ) 3 , Ni 3 (PO 4 ) 2 , Co 3 (PO 4 ) 2 , ZrP 2 O 7 , and FePO 4 ) as well as some fluorides (AlF 3 and LiF); ii) the Li + conductive coatings, mainly refer to the Li‐containing compounds such as LiAlO 2 , Li 2 ZrO 3 , Li 3 VO 4 , Li 2 MnO 3 , LiMn 2 O 4 , Li 3 PO 4 (LPO), LiFePO 4 (LFP), LiMnPO 4 , Li 2 TiO 3 , LiTiO 2 , Li 2 O‐2B 2 O 3 , LiTi 2 (PO 4 ) 3 , LiZr 2 (PO 4 ) 3 , Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 , Li 0.5 La 0.5 TiO 3 , LiTaO 3 , Li 4 SiO 4 , and LiAlF 4 as well as some heterostructured electrochemical active cathodes (Li 1.2 Ni 0.2 Mn 0.6 O 2 , Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 and NCM333); and iii) the electron conducting coating, representatively, reduced graphene oxide (rGO), permeable poly (3,4‐ethylenedioxythiophene) (PEDOT),…”

“…As widely known, among the metal oxides, the Al 2 O 3 coating has been proven to be one of the most effective approach to protect the electrode surface from the corrosive HF . In common, the Al 2 O 3 coating layer is considered to be chemically and electrochemically inactive, which can partially slow down the Li + migration across the interface .…”