The increasing demands from micro-power applications call for the development of the electrode materials for Li-ion microbatteries using thin-film technology. Porous Olivine-type LiFePO
4
(LFP) and NASICON-type Li
3
Fe
2
(PO
4
)
3
have been successfully fabricated by radio frequency (RF) sputtering and post-annealing treatments of LFP thin films. The microstructures of the LFP films were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the LFP films were evaluated by cyclic voltammetry and galvanostatic charge-discharge measurements. The deposited and annealed thin film electrodes were tested as cathodes for Li-ion microbatteries. It was found that the electrochemical performance of the deposited films depends strongly on the annealing temperature. The films annealed at 500 °C showed an operating voltage of the porous LFP film about 3.45 V vs. Li/Li
+
with an areal capacity of 17.9 µAh cm
−2
µm
−1
at C/5 rate after 100 cycles. Porous NASICON-type Li
3
Fe
2
(PO
4
)
3
obtained after annealing at 700 °C delivers the most stable capacity of 22.1 µAh cm
−2
µm
−1
over 100 cycles at C/5 rate, with an operating voltage of 2.8 V vs. Li/Li
+
. The post-annealing treatment of sputtered LFP at 700 °C showed a drastic increase in the electrochemical reactivity of the thin film cathodes vs. Li
+
, leading to areal capacity ~9 times higher than as-deposited film (~27 vs. ~3 µAh cm
−2
µm
−1
) at C/10 rate.
Self-organized Titanium dioxide (TiO 2) nanotubes grown on Ti grid acting as anode for Li-ion microbatteries were prepared via an electrochemical anodization. By tuning the anodization time, the morphology and length of the nanotubes were investigated by scanning electron microscope. When the anodization time reached 1.5 h, the TiO 2 nts/Ti grid anode showed a well-defined nanotubes, which are stable, well-adherent ∼90 nm with a length of 1.9 ± 0.1 µm. Due to their high surface utilization, surface area, and material loading per unit area, TiO 2 nts/Ti grid anode using polymer electrolyte exhibited a high areal capacity of 376 µAh cm −2 at C/10 rate and a stable discharge plateau at 1.8 V without using a polymer binder and conductive additive. The storage capacity of the TiO 2 nts/Ti grid after 10 cycles is 15 times higher compared to previous reports using planar Ti foils.
We report the electrodeposition of polymer electrolyte (PMMA-PEG) in porous lithium nickel manganese oxide (LiNi0.5Mn1.5O4) cathode layer by cyclic voltammetry. The cathode-electrolyte interface of the polymer-coated LNMO electrode has been characterized by scanning electron microscopy and electrochemical techniques. Electrochemical measurements consisting of galvanostatic cycling tests and electrochemical impedance spectroscopy revealed a significant improvement of the capacity values and the increase of the operating voltage. These effects are attributed to the total filling of pores by the electrodeposited polymer that contributes to improve the reversible insertion of Li+. A complete all-solid-state microbattery consisting of electropolymerized LNMO as the cathode, a thin polymer layer as the electrolyte, and TiO2 nanotubes as the anode has been successfully fabricated and tested.
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