Sputtered Porous Li-Fe-P-O Film Cathodes Prepared by Radio Frequency Sputtering for Li-ion Microbatteries

Abstract

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.

Direct Pre-lithiation of Electropolymerized Carbon Nanotubes for Enhanced Cycling Performance of Flexible Li-Ion Micro-Batteries

“…Li-ion batteries (LIBs) have been successfully employed in a wide range of applications, such as electric vehicles, microelectronic devices, etc., due to their remarkable properties such as high energy density, lack of memory effect, long cycle life, low self-discharge and high thermal resistance [1][2][3]. A large variety of carbon-based materials for LIBs have been widely investigated, such as graphene, fullerene and carbon nanotubes (CNT) [4][5][6][7][8][9][10].…”

Low Temperature Deposition of Highly Cyclable Porous Prussian Blue Cathode for Lithium‐Ion Microbattery

“…The electrode (PBA-5) exhibited reversible gravimetric capacity of ≈110 mAh g −1 (at 0.1 mA cm −2 ), consistent with previous reports with the iron hexacyanoferrate based materials [31,33,34] and a huge areal capacity of ≈650 µAh cm −2 (≈5.41 µAh cm −2 µm −1 ) as compared to other cathodic materials for microbattery applications. [17,[35][36][37][38][39][40][41][42] Indeed, the size and the compactness being the primary selection criteria, it is imperative to consider all reported properties normalized to the footprint area on the chip. The different porous Li-Fe-PBA electrodes show good rate stability with excellent capacity retention upon reverting to slower rates (Figure S4, Supporting Information).…”

“…Moreover, the low temperature deposition techniques developed here are fully compatible with the existing microfabrication facilities of the microelectronic industry and will help to accelerate the development on-chip energy storage systems for the IoT. [17,[35][36][37][38][39][40][41][42] In green: low temperature synthesis compatible with microfabrication process.…”

Physical Vapor Deposition of Cathode Materials for All Solid-State Li Ion Batteries: A Review

“…Many research groups have used PVD to make sulfide/phosphate (including LiFePO 4 )/tungstate electrodes for all solid-state thinfilm batteries (Yufit et al, 2003;Mazor et al, 2009;Sugiawati et al, 2019;Ioanniti et al, 2020). Not many have actually demonstrated such ASTBs.…”