Toward 3D Thin-Film Batteries: Optimal Current-Collector Design and Scalable Fabrication of TiO₂ Thin-Film Electrodes

Abstract

Three-dimensional (3D) thin-film solid-state batteries are an interesting concept for microstorage, promising high footprint capacity, fast charging, safety and long lifetime. However, to realize their commercialization, several challenges still need to be overcome. In this work, we focus on two issues: the conformal coating and the high throughput deposition of thin-film layers. First, to facilitate conformal deposition, a design based on 3D micropillars is chosen. Although such a design has been suggested in the past, we calculate for the first time what (footprint) capacities can be expected when using fully optimized pillar geometries, while taking practical manufacturability into consideration. Next, spatial atomic layer deposition (S-ALD) is investigated as a scalable and conformal deposition technique. As proofof-concept, 100 nm Cl-doped am-TiO2 thin-film electrodes are deposited by S-ALD on TiNcoated silicon micropillars. The influence of deposition parameters (i.e. exposure time and temperature) on the conformality and uniformity across the micropillar substrate is investigated. The results are discussed in terms of precursor diffusion and depletion, which is supported by an analytical model developed for our micropillar array. Furthermore, the Li-ion insertion properties of 3D electrodes fabricated by S-ALD and conventional ALD are compared. This research highlights the challenges and promises of 3D microbatteries and guides future S-ALD development to enable conformal and high-throughput thin-film deposition.

Organic electrode materials with solid-state battery technology

“…135,[144][145][146][147][148] Thin lms of the organic electrode and inorganic solid-electrolyte materials deposited from gaseous precursors on top of each other is in principle the simplest form of a microbattery, 109,149 andpotentiallyby moving from planar to three-dimensional substrates high footprint capacity can be achieved. 150 In addition, since the ALD/MLD fabricated thin-lm microbattery can be made without any additives it forms the simplest system where the interactions of the layers could in principle be studied in an electrochemical half-cell. This unique possibility has not yet truly challenged, though, leaving exciting possibilities to foreseen future.…”

Advances in 3D Thin‐Film Li‐Ion Batteries

“…The results of these optimization studies were recently published and are shown in Figure 6. [34] Here, the capacity is plotted as a function of h and l1, with Cv = Cv,2 = 1000 mAh cm −3 , lsse = 100 nm and G = 1. Figure 6 reveals that a high capacity can achieved in two different ways: increasing the aspect ratio (and the pillar density) or increasing the film thickness.…”

“…Analogous to the historical development of transistors (see Moore's law), the roadmap for such 3D thin-film batteries will be the continuous increase in pillar density to enhance the (charging) speed. Adapted with permission from [34] . Copyright 2019 American Chemical Society.…”

3D LiMn2O4 thin-film electrodes for high rate all solid-state lithium and Li-ion microbatteries

“…As a solution for the low capacity of planar thin-film batteries, the concept of 3D thin-film Liion batteries has been introduced. [14][15][16][17] Here, the complete cathode/electrolyte/anode thin-film stack is coated over 3D microstructured current collector substrates. The increased effective surface area increases the actual amount of active material per footprint area.…”

“…More details on the progress toward the 3D all solid-state thin-film Lithium and Li-ion batteries and the prognosis in capacity of such microbatteries can be found in recent publications of our group. [16][17] Conformal deposition of thin-film electrode materials over microstructured substrates has been shown for e.g. MnO2 and CuSb by electrochemical deposition (ECD) [18][19] and TiO2 by chemical solution deposition (CSD) where conformal coating was demonstrated by spray coating and atomic layer deposition.…”