Enhanced Electrochemical Performance of Thin-Film Li-Ion Batteries By Electrodeposition of Polymer Electrolyte into Microporous Electrodes
Authors: Djenizian Thierry 
Published: February 2020

Shrinking Lithium ion batteries (LIBs) is continuously investigated to satisfy the market requirements of autonomous microelectronic devices such as wearable, Internet of Things… The challenge relies on decreasing the size of the batteries while ensuring good energy and power densities. Thus, several sort of Li-ion microbatteries have been proposed and developed [1]. Particularly, it has been reported that nanomaterials used as electrodes such as self-supported arrays of titania nanotubes (TiO2nts) can be utilized to improve the electrochemical performance of Li-ion microbatteries [2-5]. The enhanced electrochemical properties of thin-film batteries using TiO2nts have been mainly attributed to the large area of the microporous material promoting the storage of charges at the surface according to a pseudo-capacitive mechanism [6]. Our group has reported in 2014 the fabrication of the first Li-ion microbattery using TiO2nts as anode, LiNi0.5Mn1.5O4 (LNMO) as cathode, and a drop-casted layer of polymethyl methacrylate-polyethylene glycol (PMMA-PEG) acting as electrolyte and separator [7]. In order to fully exploit the large surface offered by the nanotubes, the conformal electrodeposition of PMMA-PEG into TiO2nts has been also proposed to establish a better electrode/electrolyte interface [8-10]. But electrochemical tests were only done for the anode (TiO2nts) in the Swagelok test cells.

In this work, we report the fabrication of a high performance thin-film microbattery composed of TiO2nts as anode, a polymer thin layer as electrolyte, and porous LiNi0.5Mn1.5O4 as cathode. The effect of electrolyte electrodeposition into both the anode and cathode prior assembling shows a significant increase of the discharge capacity values due to the improvement of the electrode-electrolyte interface. The full microbattery reveals an operating voltage of 2.1 V with high electrochemical performance at C/10 with a discharge capacity of 169 mAh g−
1 (82 μAh cm−
2 μm−
1) at the first cycle and 150 mA h g−
1 (70 μAh cm−
2 μm−
1) at the 10th cycle. Comparison of the capacities at C/10 and C/2 with the microbattery composed of raw electrodes revealed an increment of around 100% even for 100 cycles.

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