Thin Film Microbatteries Research Articles

Large-Scale Exploration of the LiSiPON System Using a High Throughput Experimental Method

Amorphous thin film materials in the LiPON(1) or LiSiPON(2) systems have been prepared for the first time in the early 1990s using magnetron sputtering. Since then, LiPON materials have been used as state-of-the-art solid electrolytes into all-solid-state thin film micro-batteries thanks to their outstanding properties (electrochemical stability vs Li°, wide electrochemical stability window of ~[4-0] V vs. Li+/Li0, isotropic and homogeneous medium, beneficial mechanical properties(3), very low electronic conductivity). The ionic conductivity of LiPON prepared from Li3PO4 targets remains rather moderate, reaching a maximum of 3.10-6 S.cm-1 at room temperature. However, it has recently been demonstrated that the introduction of SiO2 as a second glass former can increase this value up to 2.10-5 S.cm-1, and also that the ionic conductivity of these compounds does not increase steadily with their Li content.(4)This highlights the convoluted effects of mixed formers(5) (Si, P, B...), mixed anions(6) (O, N, S...) and Li concentration on the ionic conductivity. Nevertheless, the latter are usually observed on limited series of compositions, and barely not studied on large sets of samples, which can limit the understanding of composition-structure-conductivity relationships.In this context the aim of our work was to build a High Throughput Screening (HTS) approach to explore the LixSiyPzOuNw system as a case study (Fig.1). Indeed, HTS approaches aim to accelerate material breakthrough discovery, and to understand beyond the material mechanisms. In material science, the goal is to accelerate the discovery of new keys organic, inorganic or composite materials. It may also bring beyond ‘classical’ iterative method regarding the study of complex systems (ternary, quaternary...)(7). To do so, wide ranges of material libraries are synthesized, prior to be tested through an automated characterization workflow.Our specific approach starts with the preparation of material libraries by combinatorial synthesis using magnetron co-sputtering with tilted targets, then goes through automated and fast characterizations targeting specific properties, relevant to its application as ionic conductor.Deposition of thin films displaying composition and thickness gradients at the surface of a 4’’ silicon substrate is achieved by co-sputtering three target materials in a pure Ar or N2 atmosphere. Deposition through a shadow mask allows to discretize the continuum and to prepare a library of 76 separate LixSiyPzOuNw samples in one experiment. Then, by tuning the sputtering parameters (i.e discharge gas, gas pressure, incident power, target tilt, target-to-substrate distance,...) different compositional domains can be explored.Relevant automated characterization techniques are then applied to the material library spread on the 4’’ substrate. For the assessment of these amorphous ionic conducting films, dimensional (thickness), physical-chemical (composition & local structure) and functional properties (ionic/electronic conductivities) are studied.In this sequence, determining the composition of the thin film is a real challenge due to a number of requirements :(i) light elements analysis, especially lithium; (ii) need of localized analysis (mapping) on few mm² over large substrate (4” wafer); (iii) scarce material quantity available (~ μg) and finally (iv) fast analysis. Over lab-scale techniques available, only Laser Induced Breakdown Spectroscopy technique (LIBS) seems to fulfil all these requirements. To this purpose, LIBS is developed as a HTS mapping technique for chemical analysis. A sample calibration approach is implemented through coupling with robust chemical analysis techniques (RBS, NRA, ICP-OES, SEM-EDS).In short, this specific HTS procedure will be discussed and results about composition-structure-conductivity relationships in the LiSiPON system will be presented (Fig.2).References J. B. Bates et al., J. Power Sources. 43, 103–110 (1993).N. J. Dudney, J. B. Bates, J. D. Robertson, J. Vac. Sci. Technol. A. 11, 377–389 (1993).A. S. Westover et al., Chem. Mater. 35, 2730–2739 (2023).T. Famprikis, J. Galipaud, O. Clemens, B. Pecquenard, F. Le Cras, ACS Appl. Energy Mater. 2, 4782–4791 (2019).Y. Su et al., Phys. Status Solidi B. 254, 1600088 (2017).N. Mascaraque, J. L. G. Fierro, A. Durán, F. Muñoz, Solid State Ion. 233, 73–79 (2013).E. J. Amis, X.-D. Xiang, J.-C. Zhao, MRS Bull. 27, 295–300 (2002). Figure 1

Mechanistic insight into the impact of dry-state prelithiated SiOx thin-film anode toward extremely fast-charging and long-term stability

Silicon suboxides (SiOx) have achieved partial success in commercialization as high-capacity anode materials to replace graphite because of optimal electrochemical properties over silicon. Unfortunately, the further development has been sluggish, jeopardizing the urgent need of green energy. The daunting challenges to tackle include low initial coulombic efficiency (ICE) and low charging rate due to poor electron and ionic conductivity. In the context of thin film microbattery, we propose to precisely control the chemical states of SiOx films through varying sputtering power followed by dry-state pre-lithiation through Li-metal thermal evaporation, superior to the current pre-lithiation approaches for SiOx thin-film anodes. We addressed the leading roles of the surface chemical states of the as-deposited SiOx in the formation of the high ionic conductive Li4SiO4 phase as the pre-solid electrolyte interphase during the proposed dry-state prelithiation process. Ultimately, the prelithiated SiOx successfully mitigated the most confronted issues as low ICE and C-rate limitation, achieving an unprecedented rate performance of 72.8 % at 20 C, and ultra-long-cycle retention of 54.2 % over 5000 cycles at 10 C. These results strongly prove that appropriate pre-lithiation provides tremendous advantages to SiOx thin film anode not only in prolonging electrode stability but also promoting a significant fast-cycling.

Conformal High-Aspect-Ratio Solid Electrolyte Thin Films for Li-Ion Batteries by Atomic Layer Deposition.

Lithium phosphorus oxynitride (LiPON) is a state-of-the-art solid electrolyte material for thin-film microbatteries. These applications require conformal thin films on challenging 3D surface structures, and among the advanced thin-film deposition techniques, atomic layer deposition (ALD) is believed to stand out in terms of producing appreciably conformal thin films. Here we quantify the conformality (i.e., the evenness of deposition) of thin ALD-grown LiPON films using lateral high-aspect-ratio test structures. Two different lithium precursors, lithium tert-butoxide (LiOtBu) and lithium bis(trimethylsilyl)amide (Li-HMDS), were investigated in combination with diethyl phosphoramidate as the source of oxygen, phosphorus, and nitrogen. The results indicate that the film growth proceeded significantly deeper into the 3D cavities for the films grown from LiOtBu, while the Li-HMDS-based films grew more evenly initially, right after the cavity entrances. These observations can be explained by differences in the precursor diffusion and reactivity. The results open possibilities for the use of LiPON as a solid electrolyte in batteries with high-surface-area electrodes. This could enable faster charging and discharging as well as the use of thin-film technology in fabricating thin-film electrodes of meaningful charge capacity.

Highly Conformal Solid Electrolyte for Li-Ion Batteries By Atomic Layer Deposition

Lithium phosphorus oxynitride (LiP x O y N z , commonly known as LiPON) is a state-of-the-art solid electrolyte material with suitably low resistivity and high ionic conductivity for all-solid-state thin-film microbatteries [1,2]. Thin and pinhole-free layers of LiPON can be fabricated using atomic layer deposition (ALD) [3]. Uniquely among thin-film fabrication methods, ALD is a technique that works for coating even challenging 3D interfaces [4,5]. In this work, LiPON ALD processes were optimized for two different lithium precursors at reasonable temperatures (~300 °C) and precursor pulse/purge lengths (< 5 s), and LiPON films were deposited onto PillarHall® lateral high-aspect-ratio (LHAR) test structures to investigate the conformality of the material. Comparative testing was performed between the two lithium precursors.The results indicated that more conformal LiPON films can be deposited using the appropriate precursors – in this case, lithium tert-butoxide (LiO t Bu) yielded greater penetration depths than lithium hexamethyldisilazide (Li-HMDS). The improved conformality observed when using LiO t Bu indicates that this precursor is a better choice for LiPON coatings on high-aspect-ratio structures. The ALD technique allowed for the deposition of highly conformal LiPON films, ~50–115 µm deep into 100–500 nm gaps. This opens possibilities for the use of LiPON as a solid electrolyte in batteries with high-surface-area electrodes. High surface areas are important not only for unlocking higher power densities (faster charging and discharging) in batteries, but also for enabling the use of thin-film technology in fabricating microbatteries with meaningful energy storage capacities.

Exploring the Electrochemical Properties of Ultrathin LiMn1.5Ni0.5O4 Films at High and Low Current Rates for Lithium-Ion Micro Battery Applications

The development in the miniaturized - smart electric and electronic gadgets with the advancement in technologies has dramatically enhanced the demand for cobalt free-high energy density batteries. Among various choice of high-performance cathode materials Ni substituted LiMn2O4 spinel of composition LiMn1.5Ni0.5O4 (LMNO) has proved to be one of the solutions to yield a high-performance high-energy density battery which can operate at a higher potential window. Ultra - thin films of LMNO fabricated by Pulsed laser deposition method at 600 °C substrate temperature using 2000 pulses. LMNO films fabricated on SrTiO3 (STO) and stainless steel (SS) substrates are employed for a detailed structural and electrochemical performance analysis. Disordered phase corresponding to fd3m space group of LMNO thin film exhibits better electrochemical performance compared to the ordered phase. Phase formation of LMNO thin films are studied employing X-ray diffraction and Raman spectroscopy methods. The morphology obtained for the film of thickness 41.63 nm identified from the scanning electron microscopy (SEM) images clearly reveals the effect of growth conditions such as substrate temperature and base pressure on the growth behavior of these films. Since the electrochemical data obtained for the films are area limited, the capacity of the ultra-thin film is significantly low and can be ameliorate by controlling the area. Kinetic study of LMNO film reveals that the lithium diffusion during the charge storage mechanism resembles to a diffusion-limited process similar to a faradic process. The cycling stability and rate capability at different current densities of LMNO thin film electrodes are further investigated. Charge discharge profile for both higher (25, 50, 75, 100 and 125 mA) and lower (5, 10, 15, 20, and 25 mA) current densities are obtained and subjected for 500 cycles. The thin film electrode shows a stable profile for 500 cycles. Areal discharge capacity of 1.3 μAh/cm2 is observed at a higher current density while at lower current density an areal discharge capacity obtained is 2.13 μAh/cm2 with a coulombic efficiency of around 80% and 96% respectively. Electrochemical impedance spectroscopy studies carried out on LMNO films before and after cycle shows a strong contribution of charge-transfer resistance along with film resistance and solution resistance and the equivalent circuit model for the same is evolved. Present studies indicates that LMNO ultra-thin films can be employed as a cathode layer for fabricating the all-solid thin film micro-batteries for energy applications. Figure 1

Identification of phosphorus sites in amorphous LiPON thin film by observing internuclear proximities

Amorphous lithium phosphorus oxynitrides (LiPON), prepared by reactive magnetron sputtering, have become the electrolytes of choice for all-solid-state thin film microbatteries since its discovery in early 1990s. Nevertheless, there is still a lack of understanding of their atomic-level structure and its influence on ionic conductivity. Solid-state NMR spectroscopy represents a promising technique to determine the atomic-level structure of LiPON glasses but is challenging owing to its low sensitivity in the case of thin film materials. Recently, 31P solid-state NMR spectra of LiPON thin films were acquired under magic-angle spinning (MAS) conditions and assigned with the help of density functional theory (DFT) calculations of NMR parameters. However, the identification of the different P local environments in these materials is still a challenge owing to their amorphous structure and the lack of resolution of the 31P MAS NMR spectra. We show herein how the NMR observation of internuclear proximities helps to establish the nature of P sites in LiPON thin films. The 31P-14N proximities are probed by a transfer of population in double resonance (TRAPDOR) experiment, whereas 31P-31P proximities are observed using one-dimensional (1D) 31P double-quantum (DQ)-filtered and two-dimensional (2D) 31P homonuclear correlation spectra as well as dipolar dephasing experiments using DQ-DRENAR (DQ-based dipolar-recoupling effects nuclear alignment reduction) technique. The obtained NMR data further support the recently proposed assignment of 31P NMR signals of LiPON thin films. With the help of this assignment, the simulation of the quantitative 1D 31P NMR spectrum indicates that PO43- orthophosphate anions prevail in LiPON thin films and N atoms are mainly incorporated in [O3PNPO3]5− dimeric anions. PO3N4− isolated tetrahedra and [O3POPO3]4− anions are also present but in smaller amounts.

Stability of the Interface Between LIPON and LCO During TEM Sample Preparation by FIB.

An amorphous interphase between lithium phosphorus oxynitride (LIPON) solid electrolyte and lithium cobalt oxide (LCO) has been reported recently in several electron microscopy studies of Li ion thin-film micro-batteries (TFMB), along with its implications to battery operation. However, the origin of the observed interphase at the as-made LIPON/LCO interface remained obscure. In this work, this interface has been characterized comprehensively by scanning electron microscope (SEM) imaging at all steps of the in situ focused ion beam (FIB) lift-out procedure for transmission electron microscopy (TEM) sample preparation. It was found that the interphase is formed during TEM lamella preparation when the portion of LIPON layer contained within the lamella is physically disconnected from the rest of the LIPON layer by FIB. Therefore, it was demonstrated that a disordered interphase can form in LCO at its interface with LIPON during TEM sample preparation by the FIB lift-out procedure and that subtle nature of the interphase formation makes it likely to go unnoticed during the preparation. This interphase was not produced even after galvanostatic charging of a battery with a Li metal anode but inevitably appeared after the FIB lift-out of that sample.

Zinc film anodes for air microbatteries: fabrication, approaches, and utilization optimization

Portable and autonomous microdevices often require on-board power sources such as thin film microbatteries. Air microbatteries are an attractive power source for such devices due to their high specific energy density. One particularly appropriate air chemistry is based on Zn, due to the multiple microfabrication approaches compatible with Zn anode formation. We demonstrate fabrication approaches to realize Zn film anodes in different thickness regimes using microelectromechanical systems based fabrication techniques—evaporation, electrodeposition, and laser micromachining; and evaluate their relative performance as power sources in a primary battery configuration. These fabrication techniques enable films in thickness regimes ranging from the micron scale to hundreds of microns. The fabricated films have been characterized using scanning electron microscopy and energy dispersive x-ray spectroscopy, and were found to be dense and reasonably free from impurities. The electrochemical and discharge properties of the fabricated films were studied in an air battery configuration comprising a Zn anode-alkaline hydrogel electrolyte-metal catalyst stack, in which the anode had a surface area of 0.78 cm2. Evaporated Zn anodes (1–10 µms) yielded Zn utilizations of 96.5% and 82% at 10 and 1 mA discharge rates, respectively. The specific capacity of the evaporated Zn anodes was 791 mAh g−1 when discharged at 10 mA, close to the Zn theoretical specific capacity of 820 mAh g−1. Electrodeposited Zn anodes (10–100 µms) yielded utilizations of 90.2% and 75.6% at 10 and 1 mA discharge rates, respectively. Laser micromachined Zn anodes (250 µms) yielded Zn utilization of 90% when discharged at 10 mA. These fabrication techniques offer the potential to realize high energy density Zn anodes of different thickness ranges for thin film microbatteries, which can be tailored to microdevice-based applications of interest.

(Digital Presentation) Electrode and Electrolyte Materials for Thin Film Microbatteries

Electrode and Electrolyte Materials for Thin Film Microbatteries, Aaron O’Donoghue, Louise McGrath, Ian Povey and James Rohan In this work we assess the electrochemical performance of electrodeposited, binder-free V2O5 thin films with Li metal anodes in liquid and polymer gel electrolytes based on a pyrrolidinium based ionic liquid (C4mpyrTFSI). Coulombic efficiencies >99%, with electrode capacities >120 mAh g-1 are obtained in cyclic voltammetry analysis of crystalline V2O5 with C4mpyr-based Ionic liquid (IL) electrolytes. A polymer gel electrolyte suited to layer by layer microbattery fabrication was synthesised and tested with the crystalline V2O5 and gave large electrode capacities at a relatively high rate (110 mAh g-1 at 2 C) similar to those obtained in liquid electrolytes. Stable long-term cycling (up to 400 cycles) is obtained with Li metal anodes without capacity fade or short circuits developing in either the VC containing IL or the polymer gel analogue. In addition, no V2O5 deterioration is observed with the polymer gel electrolyte as the capacity recovered to ~125 mAh g-1 after cycling at 5 C.Furthermore, we assess surface modification of V2O5 by depositing 3nm Al2O3 via ALD which has been shown to improve the charge-discharge kinetics of oxide electrode materials. Coulombic efficiencies >99%, with peak electrode capacities >120 mAh g-1 are obtained and long-term cycling stabilities up to 625 cycles.1) L. M. McGrath and J. F. Rohan, Batteries & Supercaps, 4 (2021) 485 – 492, High rate lithium ion cycling in electrodeposited binder-free thin film vanadium oxide cathodes with lithium metal anodes in ionic liquid and polymer gel analogue electrolytes.2) L. M. McGrath and J. F. Rohan, Molecules, (2020), 25. 6002, Pyrrolidinium containing ionic liquid electrolytes for Li-based batteries.3) T. Teranishi, Y. Yoshikawa, M. Yoneda, A. Kishimoto, J. Halpin, S. O’Brien, M. Modreanu and I. M. Povey, (2018), ACS Applied Energy Materials, 1(7), pp. 3277-3282, Aluminum Interdiffusion into LiCoO2 Using Atomic Layer Deposition for High Rate Lithium Ion Batteries. Figure 1: Charge/Discharge capacity of 3nm Al2O3 coated V2O5 vs Li foil in 1M LiPF6 in EC:DEC (1:1) Figure 1

Microstructure and Electrochemical Performance of Rapidly Sintered LiCoO2 Cathodes

Lithium ion battery technology based upon liquid carbonate electrolytes and intercalation electrodes has achieved widespread commercial success. The batteries power mobile devices like cell phones, laptop computers and cordless power tools. They are used in hybrid and all electric vehicles to reduce greenhouse gas emissions and dependency on limited petrochemical resources. They have been demonstrated to stabilize electric grids at local and national levels under periods of high demand. Even with these remarkable achievements, improvements in energy density are sought in batteries for most applications. Lithium metal batteries are being pursued around the world to meet this need.Rapid, continuous, roll-to-roll sintering of alumina ceramic tapes was recently demonstrated at Corning Incorporated [1]. The process is based on the pioneering work of Ketcham et al [2]. The ceramic tape, because it is thin, is flexible and may be heated, sintered, and cooled back to room temperature in less than one hour without cracking. One application of this technology is for manufacture of thin, <30 µm, solid electrolyte separators. Another is to enable novel, cathode-supported battery architectures. To that end, rapid sintering has been extended to lithium cobaltite (LCO). Continuous sintering and winding of LCO is shown in Fig. 1. The LCO cathode because it is sintered and self-supporting may be used to reduce the proportions of inactive components to dramatically increase energy density. Both composite and dense cathodes can be envisioned.One possible way of creating a solid-state battery with LCO ribbon is to capitalize on the LiPON solid electrolyte originally developed at ORNL for thin-film micro-batteries (TFMB’s) [3, 4]. The materials in TFMB’s have proven track records and attractive performance attributes. The LiPON solid electrolyte in contact with a lithium metal anode is resistant to dendrite formation even at current densities >5 mA/cm²; a claim that cannot be made for lithium garnet and lithium phosphosulfide glass [5, 6].TFMB’s also have tremendous cycling longevity and retain more than 90% of capacity after over 104 charge-discharge cycles [7]. The challenge with the technology is the high cost associated with growth of the cathode by sputtering processes; thicknesses are limited to ~2-3 µm. As a consequence, TFMB’s are a good fit for applications where small size power sources are needed like smart cards, medical implants, RFID tags, and wireless sensing. A thicker, rapidly sintered cathode could address the cost-capacity limitation. The cathode for this architecture could be made in a dense, closed pore form or with 15-25% porosity to host and electrolyte. The later would be expected to offer greater rate performance due to shorter diffusion distances and greater surface area for charge transfer. Energy density of more than 1,500 Wh/L is theoretically achievable.The performance of cathode materials like LCO depends upon synthesis conditions, process history, design and microstructure. We explore the electrochemical attributes of free standing LCO cathodes with thickness of 15 to 80 µm and porosity ranging from closed (dense) to ~25%. Cathodes were tested in 2032 coin cells using Whatman glass fiber as the separator and 1 M LiPF6 in 1:1 EC:DMC. Capacity of the cathodes regardless of microstructure is near the theoretical value. Lithium diffusivity of dense polycrystalline cathodes was characterized by galvanostatic intermittent titration and averages 1.13×10-9 cm²/s over the potential window of 3.0 to 4.3 V. Surface XRD shows the grain texture to be nominally random. Approximately 50% capacity was available at C/2 at a 23 µm thickness. Resistance of porous cathodes decreased with perimeter-to-surface area, and effective resistances below 10 Ωcm² were observed. Cycling endurance of porous sintered cathodes with 2.4 mAh/cm² capacity was evaluated with lithium titanate working electrodes. More than 90% capacity was retained after 1000 cycles between 3.0 and 4.3 V vs Li at 3C rate.[1] C. Kim, et al, “5G mm Wave Patch Antenna on Multi-layered Alumina Ribbon Ceramic Substrates,” IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting, July 2020, pp. 65-66.[2] T.D. Ketcham, et al., US 5,089,455, Feb 18, 1992.[3] J.B. Bates, et al., Solid State Ionics, 53-56 (1992) 647-654.[4] J.B. Bates, et al., U.S. 5,561,004, Oct 10, 1996.[5] F.D. Han, et al., Nat. Energy, (2019) 1-10.[6] J.C. Li, et al., Adv. Energy. Mater., 5 (2015) 1401408.[7] J. Xie, et al., Solid State Ionics, 178 (2008) 362-370. Figure 1

High-performance Ti-doped ZnS thin film anode for lithium-ion batteries

Thin film microbattery is urgently needed to provide a long-term stable on-chip power for various kinds of microdevices or microsystems. Anode is a core component in thin film lithium ion microbattery, however, previous researches mostly focused on metal oxide or Si-based thin film anodes, and the reports of metal sulfide thin film anodes are limited. Herein, we present a new type of Ti-doped ZnS thin film fabricated by radio frequency (RF) magnetron co-sputtering. The Ti doping is designed to enhance the overall electrical conductivity of the ZnS thin film, since the insulation of ZnS is one of the major barriers to deliver its lithium storage performance. As an anode applied in lithium ion battery, the Ti-doped ZnS thin film exhibits good cycling stability up to 500 cycles at a current density of 1.0 A·g−1, and remains a higher specific capacity of 463.1 mAh·g−1 than that of the pure ZnS thin film, showing its better electrochemical reaction reversibility. The rate capability and EIS measurements manifest the more favorable electrochemical reaction kinetics of the Ti-doped ZnS thin film, moreover, the CV tests at various scan rates indicate the improved Li+ diffusion kinetics in the electrode after Ti doping.

In Situ tem Cycling of Semi-Solid State Micro-Battery in Liquid Electrolyte

All solid state Li-ion micro-battery is a promising candidate to power miniaturized sensors for Internet of things (IOT) and other electronic devices. In recent times, the spinel LiMn1.5Ni0.5O4 (LNMO) has demonstrated as a potential positive electrode material for Li-ion thin film batteries offering a theoretical capacity of 147 mAh/g (65 µAh/cm2/µm for a bulk density of 4.47 g/cm3) and operates up to now at the highest potential (around 4.7 V vs. Li+/Li) [1]. In this work, we report our first successful in situ TEM attempts to observe the morphological, structural and interfacial changes in the positive electrode layer of FIB prepared sample which undergo after cycling using liquid electrolyte. More precisely we compared the morphological and structural evolution between a pristine and cycled microbattery by 4D STEM-ASTAR technique to highlight the key information to improve the deposition conditions that will enhance the reliability and production quality of such micro power devices. The in situ cycling in liquid TEM has given this opportunity to study the battery electrode materials so as to spot the slightest modifications of the materials resulting in important advances in knowledge on electrochemical energy storage [2-3].Here, our approach is based on the cycling a FIB lamella sample inside the TEM using liquid-electrochemical TEM holder with conventional liquid electrolyte (1M LiClO4, EC: DMC 1:1). The cross-section image of as prepared FIB sample with homogeneous deposition of distinctive layers of different thickness [from bottom to top-Si (0.385mm)/ Al2O3 (100nm)/ Pt (630nm) / LNMO (400nm)] is shown in figure 1a. The Pt current collector of FIB lamella sample is connected to the Pt working electrode on the e-chips used for TEM study (figure 1b). First, using FIB preparation technique, we sliced a full 2-D “thin film micro-battery” making it as thin to observe/analyse under TEM. Then, we modified the FIB lamellar design using FIB-SEM tool to get good electrical contact and reduced polarisation. Several technological problems have to be overcome in the process. For the instance, it is mandatory to obtain a good electrical contact between the Pt working electrode of e-chip and Pt current collector of FIB lamellar, which is later achieved by depositing extra Pt between the two contacts forming a platinum bridge. A 4-Probe electrical conductivity performed locally confirms the good electrical contact between the as prepared FIB lamella sample and Pt working electrode of e-chip. The cross-section bright field TEM image of a final modified version of FIB lamella sample used in the study is shown in figure 1d.The FIB lamella sample is then later cycled inside the liquid electrochemical TEM holder (fig 1c) in potential window of 4.1 V-4.8 V vs. Li+/Li. The flow of the electrolyte (LiClO4 EC:DMC 1:1) inside the TEM holder was further controlled by microfluidic controller with the flow rate of 2 µL/min. CV was recorded at a sweep rate of 0.1mV/s and two plateaus at 4.4 V and 4.6 V was observed corresponding to Ni2+/3+ and Ni3+/4+ oxidation respectively (Fig 1f). The basic redox steps observed during the charge are same as observed in the case of cycling bulk 2D thin film in a homemade flat cell.The comparison between the cycled and pristine microbattery sliced by FIB and observed by TEM allowed us to clearly demonstrate the formation of cracks inside the LMNO layer, loss of contact between the LMNO layer and the platinum current collector, as well as the agglomeration of the organic compounds produced due to the electrolyte decomposition. Moreover, 4D STEM-ASTAR technique provided us with the crucial information regarding the grain size reduction from 20 nm in pristine to 12 nm in cycled sample, confirming the continuous electrode-electrolyte reaction happening over the cycling. Also, the decrease in crystallinity and increase in the amorphization of the LMNO grains by 38 % in the cycled sample compared to pristine as shown in figure 1e and g clearly prove the fast capacity fading phenomenon observed in bulk microbattery. Furthermore, a thickness of ~20nm along the platinum layer, a (111) preferred orientation is observed exhibiting the epitaxial effect of LMNO on platinum layer which has been further supported by the precision electron diffraction (PED) recorded on both LMNO and platinum grains.

Studies on Electrochemical Performances of CZTS Anode for Lithium-Ion Batteries at Low-Temperature

Lithium-ion batteries (LIBs) function as power sources in various environments and the effect of temperature is one of the major factors which limits the performance and proper operations in in cold climates or high altitude areas and in space applications. Hence, the poor charge/discharge rate and short lifetime of LIBs in low-temperature areas have restricted its application for electric vehicle (EV) or a hybrid EV. In this work, copper zinc tin sulfide (CZTS) thin-film anode materials with different mixtures of electrolytes has been prepared to study the electrochemical performance at low-temperature environments. The CZTS anode, prepared from EC/DEC/DMC electrolyte has demonstrated higher efficiency and reversible capacity at -10 oC as compared to the binary electrolyte obtained from EC/DEC electrolyte. The performance of the electrolyte at different temperature ranges and the corresponding electrochemical performance of CZTS electrode is systematically analyzed. The Kinetics and surface morphology of the as-prepared CZTS anode has been analyzed using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and Scanning electron microscope (SEM) respectively. As compared to the room temperature capacity, the CZTS has demonstrated outstanding capacity retention around 55.3 % at -10 oC in the ternary solvent electrolyte mixtures after 100 cycles at 500 mA/g current density. However, in the binary EC-DEC based electrode, a rapid capacity degradation with a capacity retention of only around 27.2 % of the room temperature capacity has been observed at the same experimental conditions. This method could be an alternative approach to study the effect of electrolyte and the performance of the anode materials in the design of thin-film micro-batteries for next-generation sub-zero temperature applications. The detail characterization and experimental results with the future perspective of this study will be discussed here.

Fundamentals, impedance, and performance of solid-state Li-metal microbatteries

The authors report novel results toward optimizing the electrochemical performance of high vacuum deposited lithium-based all solid-state thin film microbatteries. This study investigated hermetic encapsulation, interfacial lithium formation processes, and the role of Li-blocking and Li-nucleating layers for improved Li-metal plating on copper anodes. Photoresist was found to be an effective temporary encapsulation material, where prior to cycling, well-encapsulated Li-metal full cells yielded a total resistance reduction of nearly two orders of magnitude (282 Ω cm2) and a total capacitance increase of roughly an order of magnitude (1.35 × 10−10 F/cm2) compared with nonencapsulated Li-metal full cells. To accelerate potential failure mechanisms, high stress applied currents were used during the electrochemical formation processes. Initial cycles caused high resistance voids to form at the lithium phosphorous oxy-nitride (LiPON)/copper interface of well-encapsulated half cells. Well-encapsulated full cells, in contrast, resulted in a very low resistance composite Li-Cu anode, with a void-free LiPON interface, two orders of magnitude lower resistance (0.43 Ω cm2) and three orders of magnitude higher capacitance (6.56 × 10−8 F/cm2) compared with the half cell. Cycling performance was investigated using both Li-blocking nickel-copper and Li-nucleating gold-copper metal bilayer anodes in 100-μm diameter half cells. Nickel-copper anodes facilitated higher discharge capacity (&amp;gt;9 μAh/cm2) at high charge rates (&amp;gt;12.7 mA/cm2) due to uniform Li-metal plating on blocking electrodes. Low charge rates (&amp;lt;0.7 mA/cm2) displayed low discharge capacity and immediate corrosion of the cell. Gold-copper anodes displayed the opposite effect, showing sustainable cycling, minimal cell corrosion, and a discharge capacity of &amp;gt;6 μAh/cm2 at lower charge rates (∼0.025 mA/cm2). The work expands on fundamentals in understanding the role of the metallic anode encapsulation, interface formation, and charge storage mechanisms with respect to sustainable cell impedance for applications such as solid-state lithium metal microbatteries and microelectrochemical resistance-modulated memory devices.

A new neutron depth profiling spectrometer at the JCNS for a focused neutron beam

A new neutron depth profiling (NDP) spectrometer has been designed and built for the use at a high intensity focused cold neutron beam of the reflectometer MARIA at the Heinz Maier-Leibnitz Zentrum (MLZ, Germany). The extremely high neutron flux at the sample position of MARIA joined with the multiple charged particle detectors allows less than 10 s sampling rate and paves the way to study the kinetics of Li ions in thin-film microbatteries. The performance of the spectrometer with standard calibration samples and amorphous thin films is presented; possibilities to operando study the Li distribution inside thin-film rechargeable lithium batteries are discussed.

Layer-by-Layer Assembly of Polyaniline Nanofibers and MXene Thin-Film Electrodes for Electrochemical Energy Storage.

The growing demand for compact energy storage devices may be met through the use of thin-film microbatteries, which generally rely on charge storage in thin or conformal layers. A promising technique for creating thin-film electrodes is layer-by-layer (LbL) assembly, based on the alternating adsorption of oppositely charged species to a surface to form a nanostructured electrode. Thin-film energy storage devices must have a high energy density within a limited space, so new electrode structures, materials, and assembly methods are important. To this end, both two-dimensional MXenes and polyaniline nanofibers (PNFs) have shown promising energy storage properties. Here, we report on the LbL assembly of positively charged PNFs and negatively charged Ti3C2Tx MXenes into hybrid electrodes for thin-film energy storage devices. The successful assembly is demonstrated in which MXenes and PNFs are deposited in films of 49 nm/layer pair thickness. The resulting composition was 77 wt % PNFs and 23 wt % MXenes. The charge storage process was deconvoluted into faradaic/non-faradaic contributions and separated into contributions from PNFs and MXenes. A sandwich cell showed a maximum areal capacity, energy, and power of 17.6 μA h cm-2, 22.1 μW h cm-2, and 1.5 mW cm-2, respectively, for PNF/MXene multilayers of about 2 μm thickness. This work suggests the possibility of using LbL PNF/MXene thin films as electrode materials for thin-film energy storage devices used in next-generation small electronics.

Electrode, Electrolyte and Architecture Assessment for High Power Thin Film Microbatteries

Silicon integrated on-chip energy storage is an attractive goal for hybrid power sources coupled with energy harvesting for ‘Internet of Things’ devices and applications. Typical thin film microbatteries are limited to low power and energy outputs in the 2D planar formats. One of the issues with solid-state thin film microbatteries is the high resistance of the electrolyte which can lead to significant potential drop when powering devices during sensor operation and communication. The ability to provide high currents in a small form factor is a critical need for the development of realistic long life devices. In this work we will describe the use of Comsol finite element simulations to assess electrode materials, appropriate electrolytes and optimised architectures for improved microbattery power outputs. The simulations were of a microbattery stack where non-porous additive-free LiCoO2 is the cathode, lithium metal is the anode and solid-state, polymer, polymer-gel and liquid electrolytes were investigated. The simulations show the material utilisation and overall electrochemical cell behaviour of Li-ion electrode materials at typical and high power rates. Core-shell structures based on nanoarchitectures for electronic contact and active electrode materials have been investigated to improve power delivery for nanoscale active materials and for low conductivity oxide cathodes. The simulations indicate that the implementation of nanoarchitectures such as 3D and 3D core-shell nanoarchitectures when coupled with the appropriate electrolytes and interfacial reactions can have a significant advantage in terms of areal energy and power capabilities compared to a thin-film geometry for a microbattery cell. The deployment of these architectures for microbatteries where area is at a premium and high power capabilities are desirable should result in better performing hybrid energy and less complex power management systems. Acknowledgments The authors would like to acknowledge the financial support from Science Foundation Ireland (SFI) Grant number: 12/IP/1722, Nanomaterials design and fabrication for energy storage. This work is supported in part by a research grant from SFI co-funded by the European Regional Development Fund under Grant Number 13/RC/2077. This work is also supported in part by a research grant from the EU Horizon 2020 work programme – Enables, European Infrastructure Powering the Internet of Things, project number 730957.

Silicon Encapsulated All Solid-State Li-ion Microbatteries

The demand for safe, all solid-state energy storage for microelectronic devices is sharply increasing with the evolution of micro-electronics, namely Internet of Things (IoT). Microelectronics applications in IoT and health care industries progressively demand higher all-solid state volumetric, gravimetric and areal capacity packed in smaller volumes and areas – driving competitive exploration of next generation materials and designs especially via the solid state microbattery model. Conventional all-solid-state Li-ion batteries maintain control of performance via standard thin film encapsulation and packaging techniques (2.5D packaging), where theoretically high capacity 3D thin film microbatteries continue to fail the commercial sector due to leakage, dielectric breakdown, 3D fabrication, and parasitic cell degradation. 3D microbattery milestone failures, combined with cost, time of assembly and large active/packaging areas (>1mm2) of 2.5D form factors, limit the commercial practicality of current microbattery demand in an ever-shrinking foot print market. The work presented herein is a novel approach in addressing the above issues through silicon-based encapsulation and packaging in conjunction with composite silicon-based electrode material. Methods were developed to fabricate conformally deposited all-solid-state Li-ion materials into 3D trench patterned silicon substrates using advanced solid polymer electrolyte (SPE), interfacial additives (e.g. LiTFSI containing Polyaniline (PANI)) and commercial electrode materials (e.g., graphite & LFP). 3D features (≤1mm2) in crystalline silicon substrates were created via standard microfabrication methods (e.g. through silicon via (TSV) reactive ion etching (RIE))— where 16 trenches (1mm2 area, 350mm depth, 2mm pitch) enabled 35mm x 35mm chiplets on a 200mm silicon wafer (Figure 1a). The field, sidewalls and base of the 3D trenches were conformally patterned with electron/ion insulating materials (e.g., SiO2 &/or Si3N4) (Figure 1b). Insulation was partially etched away at trench bases to create an electrical connection between the active battery material and silicon substrate. Active battery material slurries (graphite, solid polymer electrolyte (SPE), interfacial additives) filled the insulated trenches, were pressed, heated, and dried—yielding low impedance functioning composite cells (Figure 1c). The top of the trench was subsequently planarized with a metal contact laminated cathode material (LFP) via conductive epoxy. Finished In-silicon microbattery cell(s) were encapsulated with coin cells as a second-generation (Gen 2) test model. By adjusting the formulation of an interfacial additive, a thinner interphase was achieved with superior interlayer adhesion of an electrochemically tailored (in-situ formed) silicon/additive/anode composite. Composite cells with Li-containing PANI compared with non-Li-containing PANI interfacial additive resulted in a charge transfer resistance 5 orders of magnitude lower and 2.8x greater areal discharge capacity (1.74uAh/mm2), lasting 60 rechargeable cycles with an average working voltage range of 2.5V to 1.0V (Figure 1d). Gen 2+ test modules consisted of single, stand-alone, ~2.6mm2 packaging area In-silicon microbatteries with full cell charge transfer interfacial impedance less than 120W at the pre-cycle stage with the lowest interfacial impedance observed after more than 80 cycles (<50W). EIS measurements illustrated reduction in cell impedance due to in-situ formation of a composite anode containing crystalline silicon, a silicon/lithium bilayer, interfacial additive and graphite (Figure 1e). The Gen 2+ stand-alone module yielded top areal capacity greater than 1.50uAh/mm2, with more than 100 rechargeable cycles obtained over an average voltage range of 3.5V to 1.0V. Minimum rechargeable capacities of Gen 2+ test modules (1mB) were double that of Gen 2 (4mB-parallel), as enabled via an 18x reduction in packaging area, resulting in nearly 3x reduction in composite cell impedance and consequently, a 1.2 volt increase of onset discharge voltage (Figure 1f). Active Battery to Packaging Area Ratios for the Gen 2+ In-silicon microbattery module (0.51) have already begun to rival industry standard ratios (e.g., 0.59 with ~25mm x 25mm thin film microbattery footprint). The next generation design for In-silicon microbatteries is predicted to advance active/packaging ratios higher than the thin film standard @ a ratio of 0.64 as the optimization of silicon encapsulation thickness to active battery area is realized. It is projected that with the In-silicon microbattery technology presented, combined with current state of the art solid-state materials, In-silicon microbatteries can exceed performance of commercially available microbattery products (e.g., >2.5uAh/mm2, >200mAh/g). The In-silicon microbattery design provides superior ease of integration with any Si or non-Si based integrated circuit (IC) technology obtained via common microfabrication infrastructure, at low tool cost & production steps. Future efforts will demonstrate that In-silicon microbattery technology is scalable not only to (IoT) applications, yet with Gen 3 form factors and composite cells, such all-solid-state Lithium based capability is scalable to established mobile applications (smart phones) and extremely high energy applications including renewables, grid storage and electric vehicles (EV). Figure 1

Fabrication and Characterization of Porous Thin Film Cathodes Prepared By RF Sputtering for Li-Ion Microbatteries

Li-ion batteries play an important role in powering the electronic devices and in storing energy due to its high energy and power density, which are expected to be a solution for the future energy storage requirements. Due to the lack of suitable on-board power sources, the advances in the miniaturization of microelectronics is growing which then open up the opportunities to explore the both cathode and anode materials [1]. Olivine-type LiFePO4 becomes a popular cathode owing to its thermally stable, low cost, more abundant, and less toxic [2]. The strong Fe-O covalent bonds in LiFePO4 cathodes has such a special characteristic compared to layered LiCoO2-type materials. This covalent bond greatly improve the stability of O in the lattice, thus increasing the safety of the materials [2]. In the field of thin-film microbatteries, a study of the thin film cathodes is essential for the fundamental research and application since neither binder nor conductive carbon additive are utilized. It means a good contact between the active material and the current collector could be greatly established [3]. By using the thin film cathodes, the intrinsic drawbacks such as a low electronic conductivity and low Li+ diffusion mobility can also be suppressed because the thickness of the cathode material has been reduced. It would also help facilitating the transport and diffusion of electrons and ions through the thin electrodes compared to their bulk counterparts [4]. Similar to olivine-type LiFePO4, NASICON type-Li3Fe2(PO4)3 showed their own advantages such as low toxicity, low cost, a good ionic conductor and naturally abundant [5]. In addition, the synthesis of Li3Fe2(PO4)3 is easier because the Li3Fe2(PO4)3 cathode can be prepared directly in air without avoiding the oxidation of Fe2+. In the present work, radio frequency (RF) sputtering is utilized to fabricate the thin film cathodes. The results show that the annealing temperatures at 500 °C after deposition is found to be an optimal condition to obtain a porous olivine type-LiFePO4 film (Figure 1a). By further increasing the annealing temperature up to 700 °C , a complete transformation from porous olivine type-LiFePO4 to porous NASICON-type Li3Fe2(PO4)3 can be observed (Figure 1b); this film provides better cycling stability. Porous NASICON-type Li3Fe2(PO4)3 film attains a good capacity of ~103 mAh g-1 (~32 µAh cm-2 µm-1) at C/10 rate with an excellent cycling performance over 110 cycles. In this work, the effect of various annealing temperatures on morphology and electrochemical performances of the thin film cathodes will be discussed.

Cycle life and statistical predictive reliability model for all-solid-state thin film microbatteries

This paper focuses on the development of a predictive cycle life model of all-solid-state thin film Cu/Li/LiPON/LiCoO2 microbatteries based on experimental accelerated aging tests. More than 120 samples were tested in 8 different conditions including several electrochemical cycling modes and different temperature levels. Hence, an original reliability model, based on an exponential function especially designed to describe the degradation mechanism occurring at the positive electrode, is proposed to describe the observed capacity loss evolution of microbatteries. An extended mathematical model, which includes a large set of accelerated factors, physicochemical considerations and statistical parameters is then built around such an exponential function. This model thus enables to simulate a wide variety of battery aging profiles from input parameters such as temperature, depth of charge (DoC), discharge rate, failure rate and capacity fade. We believe that the development of such a reliability model is of most importance not only from an industrial point of view, since it enables to determine precisely the expected behavior of microbatteries in various mission profile conditions, but it represents also a key tool that enables to further understand the observed degradation mechanisms, and to identify any technological optimization opportunities.