Sallaz et al. Hybrid all-solid-state thin film MSC based on quasi amorphous ALD TiO$_2$ electrode

• Published in: ACS applied energy materials Vol. 6; no. 1; pp. 201 - 210
• Main Authors: Sallaz, Valentin, Poulet, Sylvain, Boissel, Jean-Marc, Rouchou, Jouhaiz, Lamy, Yann, Voiron, Frederic, Oukassi, Sami
• Format: Journal Article
• Language: English
• Published: ACS 2022
• Subjects: Engineering Sciences; Other
• ISSN: 2574-0962; 2574-0962
• DOI: 10.1021/acsaem.2c02742

In this work, nanometric (6–21 nm thick) amorphous TiO$_2$ films have been elaborated and characterized in liquid- and solid-state electrolyte (LiPON) half-cell architectures. For all considered configurations, the volumetric capacity extracted from cyclic voltammetry and galvanostatic cycling within the 0.5–3 V potential range almost corresponds to the theoretical value expected for the Li$_x$TiO$_2$ (x ∼ 1) phase at low current density. Interestingly, TiO$_2$ films after LiPON deposition exhibited a thickness-independent constant initial amount of intercalated lithium ions and did not require a first activation process, in comparison to the liquid electrolyte configuration. Furthermore, the cooperative effects of high Li$^+$ intercalation kinetics and low interfacial charge transfer resistance for a 6 nm TiO$_2$ electrode led to an outstanding surface capacity of 0.7 μAh cm$^{–2}$ at 1 μA cm$^{–2}$ and high rate performance with 60% capacity holding ratio at 1 mA cm$^{–2}$, thus highlighting the extrinsic pseudocapacitive behavior of our sub-10 nm TiO$_2$ electrodes. A Li$_x$TiO$_2$ 6 nm/LiPON 100 nm/Pt hybrid micro-supercapacitor has been successfully fabricated, achieving an operating voltage window of 3 V and a surface capacitance of 94 μF cm$^{–2}$ at 50 mV s$^{–1}$. In addition, the device also exhibited 97% coulombic efficiency upon cycling for 10,000 continuous charge–discharge cycles. This work proposes an approach that allows us to adjust the Li-ion storage properties of TiO$_2$ by nanoengineering and gives insights into the electrochemical performance enhancement by taking advantage of the pseudocapacitance-assisted lithium storage mechanism.