Influence of gradient Ni incorporation on the structural, surface, and electrochemical properties of LiCoO₂ thin-film cathodes.
4 affiliations
- 1CEMMPRE, ARISE, Mechanical Engineering Department, University of Coimbra 3030-788 Coimbra Portugal [email protected].
- 2Laboratory of Multifunctional Materials and Applications (LaMMA), Faculty of Sciences of Sfax, University of Sfax BP 1171 Sfax 3000 Tunisia.
- 3Environmental Engineering Department, University of Coimbra 3030-790 Coimbra Portugal.
- 4IPN-LED & MAT-Instituto Pedro Nunes, Laboratory of Tests, Wear and Materials Rua Pedro Nunes 3030-199 Coimbra Portugal.
Abstract
Layered LiCoO₂ thin-film (LCO) cathodes are attractive for lithium-ion microbatteries, but their use is constrained by structural instability, modest rate capability, and progressive capacity loss. In this work, we show that spatially graded Ni incorporation, achieved via controlled RF/DC co-sputtering, provides a promising strategy to tune structural and electrochemical limitations in layered LiNi x Co1-x O₂ (LNCO) thin film cathodes. Three architectures were developed: LCO, uniformly Ni-incorporated LNCO-0.25A, and gradient Ni-incorporated LNCO-G, the latter obtained by progressively increasing the Ni target current from 0.20 to 0.40 A during deposition, producing a depth-dependent Ni distribution. XRD and Raman analyses show that Ni incorporation is accompanied by sharper reflections and reduced Raman peak broadening, consistent with improved local structural order. Cross-sectional HAADF-STEM and STEM-EDS mapping confirm a dense microstructure and a continuous Ni gradient increasing progressively from the substrate interface toward the coating surface. Depth-resolved XPS shows that, although all films develop surface carbonate species upon air exposure, LNCO-G exhibits a reduced hydroxyl/carbonate contribution compared with LNCO-0.25A, which is consistent with a less hydrated near-surface chemistry. Electrochemically, LNCO-G delivers higher current densities (≈3-5× increase) and more defined high-voltage redox features than the uniformly incorporated counterpart. In a preliminary 10-cycle diagnostic test under an aggressive 1.0-4.9 V window, LNCO-G achieves an initial discharge capacity of ∼100-120 mAh g⁻¹ at 0.5C and retains ∼55% of its capacity. This short, aggressive protocol was intentionally chosen as a materials-level screening test to amplify differences in polarization and early degradation among the three architectures. Post-cycling EIS shows a 59% reduction in charge-transfer resistance (67.7 Ω vs. 164.3 Ω) and a lower Warburg coefficient (21.3 vs. 44.1 Ω s-1/2) relative to LNCO-0.25A. These results demonstrate that compositional Ni grading is associated with a measurable performance advantage over the uniform incorporation strategy studied here, although the comparison is not composition-matched and therefore reflects combined effects of Ni content, distribution, and secondary-phase fraction. These findings identify spatial Ni grading as a promising route for tuning coupled structural, interfacial, and kinetic properties in sputtered LiCoO₂-based thin-film cathodes.
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BibTeX
@article{benzarti2026influence,
title = {{Influence of gradient Ni incorporation on the structural, surface, and electrochemical properties of LiCoO₂ thin-film cathodes.}},
author = {Z Benzarti and C Vicente and J D Castro and S Cruz and S Carvalho},
journal = {RSC advances},
year = {2026},
month = oct,
doi = {10.1039/d6ra06673a},
url = {https://europepmc.org/article/MED/42923757},
note = {CC BY},
}
RIS
TY - JOUR
TI - Influence of gradient Ni incorporation on the structural, surface, and electrochemical properties of LiCoO₂ thin-film cathodes.
AU - Z Benzarti
AU - C Vicente
AU - J D Castro
AU - S Cruz
AU - S Carvalho
PY - 2026
DA - 2026/10/22
JO - RSC advances
DO - 10.1039/d6ra06673a
UR - https://europepmc.org/article/MED/42923757
AB - Layered LiCoO₂ thin-film (LCO) cathodes are attractive for lithium-ion microbatteries, but their use is constrained by structural instability, modest rate capability, and progressive capacity loss. In this work, we show that spatially graded Ni incorporation, achieved via controlled RF/DC co-sputtering, provides a promising strategy to tune structural and electrochemical limitations in layered LiNi x Co1-x O₂ (LNCO) thin film cathodes. Three architectures were developed: LCO, uniformly Ni-incorporated LNCO-0.25A, and gradient Ni-incorporated LNCO-G, the latter obtained by progressively increasing the Ni target current from 0.20 to 0.40 A during deposition, producing a depth-dependent Ni distribution. XRD and Raman analyses show that Ni incorporation is accompanied by sharper reflections and reduced Raman peak broadening, consistent with improved local structural order. Cross-sectional HAADF-STEM and STEM-EDS mapping confirm a dense microstructure and a continuous Ni gradient increasing progressively from the substrate interface toward the coating surface. Depth-resolved XPS shows that, although all films develop surface carbonate species upon air exposure, LNCO-G exhibits a reduced hydroxyl/carbonate contribution compared with LNCO-0.25A, which is consistent with a less hydrated near-surface chemistry. Electrochemically, LNCO-G delivers higher current densities (≈3-5× increase) and more defined high-voltage redox features than the uniformly incorporated counterpart. In a preliminary 10-cycle diagnostic test under an aggressive 1.0-4.9 V window, LNCO-G achieves an initial discharge capacity of ∼100-120 mAh g⁻¹ at 0.5C and retains ∼55% of its capacity. This short, aggressive protocol was intentionally chosen as a materials-level screening test to amplify differences in polarization and early degradation among the three architectures. Post-cycling EIS shows a 59% reduction in charge-transfer resistance (67.7 Ω vs. 164.3 Ω) and a lower Warburg coefficient (21.3 vs. 44.1 Ω s-1/2) relative to LNCO-0.25A. These results demonstrate that compositional Ni grading is associated with a measurable performance advantage over the uniform incorporation strategy studied here, although the comparison is not composition-matched and therefore reflects combined effects of Ni content, distribution, and secondary-phase fraction. These findings identify spatial Ni grading as a promising route for tuning coupled structural, interfacial, and kinetic properties in sputtered LiCoO₂-based thin-film cathodes.
SN - 2046-2069
ER -