Improvement of the Cathode Electrolyte Interphase on P2-Na_2/3Ni_1/3Mn_2/3O₂ by Atomic Layer Deposition

Abstract

Atomic layer deposition (ALD) is a commonly used coating technique for lithium ion battery electrodes. Recently, it has been applied to sodium ion battery anode materials. ALD is known to improve the cycling performance, Coulombic efficiency of batteries, and maintain electrode integrity. Here, the electrochemical performance of uncoated P2-NaNiMnO electrodes is compared to that of ALD-coated AlO P2-NaNiMnO electrodes. Given that ALD coatings are in the early stage of development for NIB cathode materials, little is known about how ALD coatings, in particular aluminum oxide (AlO), affect the electrode-electrolyte interface. Therefore, full characterizations of its effects are presented in this work. For the first time, X-ray photoelectron spectroscopy (XPS) is used to elucidate the cathode electrolyte interphase (CEI) on ALD-coated electrodes. It contains less carbonate species and more inorganic species, which allows for fast Na kinetics, resulting in significant increase in Coulombic efficiency and decrease in cathode impedance. The effectiveness of AlO ALD coating is also surprisingly reflected in the enhanced mechanical stability of the particle which prevents particle exfoliation.

Hierarchical Engineering of Porous P2‐Na2/3Ni1/3Mn2/3O2 Nanofibers Assembled by Nanoparticles Enables Superior Sodium‐Ion Storage Cathodes

“…The electrochemical impedance spectra (EIS) of the above three samples are compared in Figure S9 (Supporting Information). The CV curves and charge/discharge profiles featuring smoother peaks or plateaus than those of the bulk materials, [28,36,41,43,44,46] along with the well-maintained voltage plateau at ≈4.2 V during cycling, suggest that the hierarchical nanofibers could effectively alleviate the Na + /vacancy ordering and P2-O2 phase transition occurring for the pristine materials. In addition, the electrochemical performance of the P3-type Na 2/3 Ni 1/3 Mn 2/3 O 2 (annealed at 700 °C for 6 h) has also been evaluated ( Figure S10 in the Supporting Information), which shows a much lower specific capacity with inferior cycling stability relative to the P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 nanofibers.…”

“…This is because the P2 phase material possesses facile Na-ion diffusion in the presence of multi-Na vacancies compared with the P3 phase. [28,35,36,38,39,41,42,[44][45][46]48,51,53] This originates from the delicately tailored fibrous nanostructure composed of nanograins with high reactivity and high porosity that would accelerate the electronic/ionic transportation. The CV curves and charge/discharge profiles featuring smoother peaks or plateaus than those of the bulk materials, [28,36,41,43,44,46] along with the well-maintained voltage plateau at ≈4.2 V during cycling, suggest that the hierarchical nanofibers could effectively alleviate the Na + /vacancy ordering and P2-O2 phase transition occurring for the pristine materials.…”

“…[36,37] Dahn's group first investigated the Na-intercalation/deintercalation of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 , [38] revealing that the rapid capacity decay caused by the undesirable P2-O2 phase transition (with a large volume change of ≈23%) when charged to above 4.2 V was the main challenge hindering the wide application of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 . doping to stabilize the crystal structure, [28,[41][42][43] surface coating to suppress the unfavorable side reactions, [44][45][46] and lowering the charge cut-off voltage to eliminate the phase transformation, [36,47,48] have been adopted for modifying P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 . doping to stabilize the crystal structure, [28,[41][42][43] surface coating to suppress the unfavorable side reactions, [44][45][46] and lowering the charge cut-off voltage to eliminate the phase transformation, [36,47,48] have been adopted for modifying P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 .…”

“…doping to stabilize the crystal structure, [28,[41][42][43] surface coating to suppress the unfavorable side reactions, [44][45][46] and lowering the charge cut-off voltage to eliminate the phase transformation, [36,47,48] have been adopted for modifying P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 . [44] Recently, Chou's team tested the cycling performance of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 in the voltage range of 2.0-4.0 V; the electrode maintained 89 mA h g −1 at 0.1 C and exhibited a significantly enhanced capacity retention of 71.2% even after 1200 cycles at 10 C. [36] Though these are very encouraging results, it should be noted that metal doping and surface modification cannot preclude the phase transition intrinsically, and the cyclic stability is still limited; additionally, narrowing the electrochemical window would sacrifice a large amount of capacity. [44] Recently, Chou's team tested the cycling performance of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 in the voltage range of 2.0-4.0 V; the electrode maintained 89 mA h g −1 at 0.1 C and exhibited a significantly enhanced capacity retention of 71.2% even after 1200 cycles at 10 C. [36] Though these are very encouraging results, it should be noted that metal doping and surface modification cannot preclude the phase transition intrinsically, and the cyclic stability is still limited; additionally, narrowing the electrochemical window would sacrifice a large amount of capacity.…”

Electrode Engineering by Atomic Layer Deposition for Sodium‐Ion Batteries: From Traditional to Advanced Batteries

“…e) Nyquist plots of uncoated P2‐NaNiMnO cycled electrodes (red) and Al 2 O 3 ‐coated cycled electrodes (blue) and uncoated (blue), cycle 100. f) Elemental atomic percentage of the uncoated and ALD‐coated cycled electrodes at first charge 4.1, 4.5 V, 5 cycles, and 100 cycles. Reproduced with permission . Copyright 2017, American Chemical Society.…”