Hybrid All-Solid-State Thin-Film Micro-supercapacitor Based on a Pseudocapacitive Amorphous TiO₂ Electrode

Abstract

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.

Sustainable Approach for the Development of TiO2-Based 3D Electrodes for Microsupercapacitors

“…Therefore, 120 nm is the optimal film thickness that realizes a suitable compromise that leads to good capacitance while imposing limited constraints on the electric/ionic conductivity. The capacitance values of ~8.1 mF cm −2 at 0.01 mA cm −2 (corresponding to ~4.5 µAh cm −2 ) for the 120 nm-thick film are similar to the values reported in the literature for 2D electrodes operating in organic electrolytes with TiO2 films prepared using ALD, making a substantial contribution to the development of capacitive processes to be used in supercapacitors [50].…”

“…This pseudocapacitive character affords fast charge-discharge kinetics, which is compatible with the power demand of a supercapacitor. To obtain a major contribution of capacitive processes and to keep a high rate capability, Sallaz et al [50] reported that the thickness of a TiO 2 film deposited on 2D Pt via ALD should not be more than 6-11 nm to find a balance between capacitance and rate capability. However, the effect of further structuration of TiO 2 thin films on 3D substrates in the organic electrolyte-based microsupercapacitors has not been reported in the literature.…”

Advances on Microsupercapacitors: Real Fast Miniaturized Devices toward Technological Dreams for Powering Embedded Electronics?

“…Coulombic efficiency, which is the ratio of discharge to charge capacity, can give an idea about the cycle life and rate capabilities of MSCs . Depending on electrode material, Coulombic efficiency can vary from 97% for the amorphous TiO 2 Electrode to 100% (Fe,Mn) 3 O 4 for spinel oxide …”

Wafer-Scale Performance Mapping of Magnetron-Sputtered Ternary Vanadium Tungsten Nitride for Microsupercapacitors

“…Despite their high power densities, high rate capabilities, and long-life cycling, MSCs still suffer from low energy density compared to MB . To improve the energy density, increasing the working cell voltage, by either an asymmetric configuration or a hybrid MSC, is an interesting and promising solution. − In addition, enhancing the capacitance of electrode materials through research on capacitive materials (such as active carbon), pseudocapacitive materials (conductive polymer, transition metal oxide or nitride), − or a new class of materials such as MXene series, multicationic, or multianionic materials is also a very fascinating approach.…”