Rechargeable Microbatteries Research Articles

Unveiling the recent advances in micro-electrode materials and configurations for sodium-ion micro-batteries

The recent advances in portable and smart devices require modern microelectronics to be miniaturized, leading to the need for small, lightweight, reliable, and on-chip integrated energy storage systems like rechargeable micro-batteries (μBs).

Self-Assembled Epitaxial Cathode-Electrolyte Nanocomposites for 3D Microbatteries.

The downscaling of electronic devices requires rechargeable microbatteries with enhanced energy and power densities. Here, we evaluate self-assembled vertically aligned nanocomposite (VAN) thin films as a platform to create high-performance three-dimensional (3D) microelectrodes. This study focuses on controlling the VAN formation to enable interface engineering between the LiMn2O4 cathode and the (Li,La)TiO3 solid electrolyte. Electrochemical analysis in a half cell against lithium metal showed the absence of sharp redox peaks due to the confinement in the electrode pillars at the nanoscale. The (100)-oriented VAN thin films showed better rate capability and stability during extensive cycling due to the better alignment to the Li-diffusion channels. However, an enhanced pseudocapacitive contribution was observed for the increased total surface area within the (110)-oriented VAN thin films. These results demonstrate for the first time the electrochemical behavior of cathode–electrolyte VANs for lithium-ion 3D microbatteries while pointing out the importance of control over the vertical interfaces.

Rechargeable Micro‐Batteries for Wearable and Implantable Applications

The rise of wearable and implantable microelectronics calls for the corresponding high‐performance micropower sources. Rechargeable micro‐batteries (MBs) are considered the most promising candidate due to their high energy density and stable voltage output. To date, various MBs with different configurations have been designed to meet the ever‐growing high energy consumption requirements of microelectronic devices. Therefore, it is very urgent to summarize the current challenges of MBs and discuss solutions for future research. In this perspective, a comprehensive overview and insights on rechargeable MBs are carefully presented with an emphasis on the design of various configurations. The representative preparation methods and application scenarios of various MBs have been summarized. The challenges and future perspectives are also discussed to provide insights into the forward‐looking research and potential directions of this promising field.

A flexible, heat-resistant and self-healable “rocking-chair” zinc ion microbattery based on MXene-TiS2 (de)intercalation anode

The requirement for rechargeable microbatteries (MBs) continues to increase due to the rapidly development of wearable and integrated electronics. However, the ever-reported mainstream MBs, such as lithium ion MBs, have intrinsic drawbacks of security threats and environmental hazards, and are not suitable as an energy supply component for wearable electronics. Here, a safe and environmentally friendly zinc ion microbattery (ZIMB) based on MXene-TiS2 (de)intercalation anode, multi-walled carbon nanotubes-vanadium dioxide (B) (MWCNTs-VO2 (B)) cathode, zinc sulfate-polyacrylamide (ZnSO4-PAM) hydrogel electrolyte and self-healable polyurethane (PU) protective shell is exploited. The ZIMB exhibit satisfactory electrochemical performance with a capacity of 40.8 μAh cm-2, maximum power density of 32.5 μWh cm-2 and maximum energy density of 1.2 mW cm-2. In addition, the ZIMB also exhibits the excellent flexibility, thermostability and self-healability, i.e., no significant attenuation in capacity can be observed when the ZIMB is placed on the specific conditions, such as the high bending angle of 150°, high temperature of 100 °C, and multiple damage and repair cycles. This study provides a feasible strategy to develop advanced high reliable and stable micro energy storage devices for wearable and integrated electronics.

High-Performance Packaged 3D Lithium-Ion Microbatteries Fabricated Using Imprint Lithography.

Fabrication of high-energy-density and high-power-density packaged long-cycle-life rechargeable microbatteries remains a considerable challenge. Here, high-performance microbatteries with high active volume fraction, thick, 3D-structured electrodes (V2 O5 cathode and Li metal anode) are realized through a combination of imprint lithography, self-assembly, and electrodeposition. To assist the critical challenge of hermetic packaging, the microbattery is infilled with a gel electrolyte. The packaged cell exhibits high areal energy and power densities of 1.24 J cm-2 and 75.5mW cm-2 , respectively, and can be cycled 550 times in argon or 200 times in air with 75% capacity retention of the initial discharge capacity. An unpackaged cell, using a liquid electrolyte, provides a power density of 218mW cm-2 . As far as it is known, the microbatteries have the highest peak power density among all reported microbatteries.

Advanced architecture designs towards high-performance 3D microbatteries

Rechargeable microbatteries are important power supplies for microelectronic devices. Two essential targets for rechargeable microbatteries are high output energy and minimal footprint areas. In addition to the development of new high-performance electrode materials, the device configurations of microbatteries also play an important role in enhancing the output energy and miniaturizing the footprint area. To make a clear vision on the design principle of rechargeable microbatteries, we firstly summarize the typical configurations of microbatteries. The advantages of different configurations are thoroughly discussed from the aspects of fabrication technologies and material engineering. Towards the high energy output at a minimal footprint area, a revolutionary design for microbatteries is of great importance. In this perspective, we review the progress of fabricating microbatteries based on the rolled-up nanotechnology, a derivative origami technology. Finally, we discussed the challenges and perspectives in the device design and materials optimization.

Sulfide synergistic electrochemical activity for high-performance alkaline rechargeable microbatteries

Alkaline rechargeable microbatteries have attracted considerable and sustained attention in recent years. However, the complicated fabrication process and the limited specific capacitance of electrodes are still key problems for the development of microbatteries. Herein, we develop a simple approach to enhance electrochemical activity of electrodes via rational design of material components. A sulfide synergistic bimetallic electrode composed of Ni-Co layered double hydroxides (NiCo-LDHs) and Co4S3 composites (NiCo-LDHs-S) is prepared by one-step electrodeposition. Thanks to the richer redox couples in NiCo-LDHs-S and high conductivity of Co4S3, the areal capacitance of NiCo-LDHs-S cathode is ~ 5.8 times, ~ 19.7 times and 1.5 times as high as that of electrodes based on cobalt sulfur composites (Co-O-S), nickel sulfur composites (Ni-O-S) and NiCo-LDHs, respectively. A carbon-modified Fe3O4 (Fe3O4@C) anode is prepared to promote electron transfer, leading to an areal capacitance of 207.2 mC cm−2 at a current density of 2 mA cm−2. An efficient alkaline rechargeable microbattery using NiCo-LDHs-S as a cathode and Fe3O4@C as an anode is obtained and shows an areal capacitance of 61.7 mC cm−2 and an energy density of 16.4 μWh cm−2 (1.0 mW cm−2).

Dual-phase nanostructuring of layered metal oxides for high-performance aqueous rechargeable potassium ion microbatteries

Aqueous rechargeable microbatteries are promising on-chip micropower sources for a wide variety of miniaturized electronics. However, their development is plagued by state-of-the-art electrode materials due to low capacity and poor rate capability. Here we show that layered potassium vanadium oxides, KxV2O5·nH2O, have an amorphous/crystalline dual-phase nanostructure to show genuine potential as high-performance anode materials of aqueous rechargeable potassium-ion microbatteries. The dual-phase nanostructured KxV2O5·nH2O keeps large interlayer spacing while removing secondary-bound interlayer water to create sufficient channels and accommodation sites for hydrated potassium cations. This unique nanostructure facilitates accessibility/transport of guest hydrated potassium cations to significantly improve practical capacity and rate performance of the constituent KxV2O5·nH2O. The potassium-ion microbatteries with KxV2O5·nH2O anode and KxMnO2·nH2O cathode constructed on interdigital-patterned nanoporous metal current microcollectors exhibit ultrahigh energy density of 103 mWh cm−3 at electrical power comparable to carbon-based microsupercapacitors.

Electrochemical investigation and modelling of LaNi4.77Al0.23 thin-films sputtered on glass wafers

In the present work, we report on the microfabrication of metal hydride thin-film electrodes which can be utilized for rechargeable microbatteries or sensor applications. A multi-layer deposition technique is developed based on physical vapor deposition to fabricate the thin-film electrodes on a glass substrate. The morphology and the structure of the thin-film electrodes are studied by using Field Emission Scanning Electron Microscopy coupled with an Energy Dispersive Spectroscopy module. The surface composition of the thin-film electrodes are determined using X-ray Photoelectron Spectroscopy. Cyclic Voltammetry and galvanostatic charge-discharge measurements are performed to obtain insights into the electrochemical performance of the electrodes. Finally, a semi-empirical model is derived which allows for the determination of the equilibrium potential of the electrode as a function of its hydrogen content.

Characteristics of Li-ion micro batteries fully batch fabricated by micro-fluidic MEMS packaging

A cost-effective and reliable technology allowing extreme miniaturization of batteries into glass chips and electronic packages has been developed, employing a dispense-print process for battery electrodes and liquid electrolyte. Lithium-ion micro-batteries (active area 6 × 8 mm2, 0.15–0.3 mAh) with interdigitated electrodes were fabricated, tested and finally compared with the traditional battery architecture of stacked electrodes. Commercial graphite and lithium titanate anode as well as layered nickel cathode materials were used. All the processes for the micro-battery fabrication were established during this work; in particular the micro fluidic electrolyte filling process that allows simultaneous electrolyte supply to all cells on a planar substrate. Electrode mass reproducibility was sufficient for adequate electrode balancing. Current capability similar to the conventional face-to-face electrode configuration was achieved with interdigital electrodes that can be fabricated much easily on a substrate level. The cells were successfully cycled; several 100 cycles can be achieved. Additional results of life-time characteristics and electrochemical impedance spectroscopy are presented as well. These rechargeable micro-batteries can be used for future extremely miniaturized electronic products.

Dual-Graphene Rechargeable Sodium Battery.

Sodium (Na) ion batteries are attracting increasing attention for use in various electrical applications. However, the electrochemical behaviors, particularly the working voltages, of Na ion batteries are substantially lower than those of lithium (Li) ion batteries. Worse, the state-of-the-art Na ion battery cannot meet the demand of miniaturized in modern electronics. Here, we demonstrate that electrochemically exfoliated graphene (EG) nanosheets can reversibly store (PF6- ) anions, yielding high charging and discharging voltages of 4.7 and 4.3 V vs. Na+ /Na, respectively. The dual-graphene rechargeable Na battery fabricated using EG as both the positive and negative electrodes provided the highest operating voltage among all Na ion full cells reported to date, together with a maximum energy density of 250 Wh kg-1 . Notably, the dual-graphene rechargeable Na microbattery exhibited an areal capacity of 35 μAh cm-2 with stable cycling behavior. This study offers an efficient option for the development of novel rechargeable microbatteries with ultra-high operating voltage and high energy density.

The transparent all-solid-state rechargeable micro-battery manufacturing by RF magnetron sputtering

In this paper, a transparent all-solid-state battery was manufactured by RF magnetron sputter, for the first time. LiFePO4 and Li4Ti5O12 are popular cathode and anode materials, respectively. For the solid-state electrolyte coating, the Li3PO4 material is also promising solid electrolyte materials due to the high ionic conductivity. The stack structure of the battery was silver paste/anode (Li4Ti5O12)/electrolyte (Li3PO4)/cathode (LiFePO4)/ITO/glass. An indium tin oxide (ITO) coated glass substrate was used as a transparent and conductive material. The resistance of the coated ITO layer is 40 Ω. RF power for the LiFePO4,Li3PO4, and Li4Ti5O12 layers deposition process was adjusted to 100 Watt at argon atmosphere. This stack structure didn't contain any liquid or gel electrolyte layer. The fully solid electrolyte was deposited by the RF magnetron sputter. The mean crystallite sizes of the deposited layers approximately 30 nm, 21 nm and 30 nm for LiFePO4, Li3PO4 and Li4Ti5O12 layer, respectively. The transparency of the manufactured battery is approximately 80%. Electrochemical impedance analyses and cyclic voltammetry measurements were done. The Nyquist diagram and equivalent circuit model were determined. Warburg constant and Li-ion diffusion coefficient were calculated approximately 38 Ω/s−1/2 and 4.2 × 10−10 cm2/s, respectively. The capacity of the transparent all-solid-state battery was measured as to be 600 μAh/g. The value of the According to obtained results, deposited battery is a quasi-reversible system because of the differences between cathodic and anodic peak potential is calculated about 52 mV. Warburg, Li-ion diffusion coefficient and capacity of the deposited battery show very good adherence with literature.

3D Structuring of Thin Film Solid State Li-Ion Cells for Fast Charging Micro-Batteries

High energy and power density are the main requirements of today’s high demanding applications in consumer electronics. Lithium ion batteries (LIB) have the highest energy density of all known systems and are thus the best choice for rechargeable micro-batteries. Liquid electrolyte LIBs present limitations in safety, size and design, where all-solid state thin film batteries are considered to overcome these restrictions for small devices. Although planar all-solid state thin film LIBs are at present commercially available, they provide low capacity (<1mAh/cm2) which limits their application scenario. By using micro-structured surfaces (i.e. 3D batteries) and appropriate conformal coating technologies (i.e. electrochemical deposition, ALD), the capacity can be increased while still keeping a high rate performance. The main challenges in the introduction of solid-state LIBs are low ionic conductance and limited cycle life time due to mechanical stress and shearing interfaces. Novel materials and innovative nanostructures have to be explored in order to overcome these limitations. Thin film 3D compatible materials need to provide with the necessary requirements for functional and viable thin-film stacks. Thin film electrodes offer shorter Li-diffusion paths which allow them to be used at ultra-fast charging rates while keeping their maximum capacities. Thin film electrolytes with intrinsically high ion conductivity (~10-3 S/cm) do exist, but are not electrochemically stable. On the other hand, electronically insulating electrolytes with a large electrochemical window and good chemical stability are known, but typically have intrinsically low ionic conductivities (<10-6S/cm). In addition, there is the need for conformal deposition techniques which can offer pinhole-free coverage over large surface areas with large aspect ratio features for electrode, electrolyte and buffer layers. In this paper, we present the fabrication of 3D thin-film batteries using high aspect ratio silicon pillar arrays providing area enhancement of over 25x. The pillars are conformally coated with LiMn2O4 (LMO) and LixTiO2 as positive and negative electrodes, respectively. For the electrolyte, thin-film composite electrolyte films are being developed. Where we currently focus on 60 μm high pillars with a 2 μm diameter and pitch, the energy and power output per unit area of the battery can be increased by scaling towards higher aspect ratio pillars. Indeed, by increasing the height of the pillars, more active material per unit area can be deposited, resulting in a higher capacity. Simultaneously, the power output of the battery improves due to the increased internal surface of the 3D battery. Notice that a similar approach is not possible with conventional thin-film batteries. Increasing the active film thickness in these batteries results in more capacity, but this goes at the cost of power output due to the increased resistance of the thicker active layers. In addition, by decreasing the pitch between the pillars, the film thickness can be scaled down. We show that the available capacity of both the manganate and titania based films can be increased by scaling down the film thickness below 100 nm without affecting cycle life time. The thinnest films show the highest volumetric capacity and the best cycling stability. The increased stability of the LMO films below 50 nm allows cycling in both the 4 and 3V potential region, resulting in a high volumetric capacity of 1.2Ah/cm3. The potential of 3D thin-film batteries with respect to attainable energy density and C-rate performance will be discussed. Figure 1

Improved cyclic stability by octahedral Co3+ substitution in spinel lithium manganese oxide thin-film cathode for rechargeable microbattery

Co-doped lithium manganese oxide (LiCoxMn2-xO4) cathodes were prepared as thin films via a sol-gel process to investigate the effects of the octahedral Co substitution on electrochemical properties. X-ray diffraction and scanning electron microscopy results showed that the polycrystalline films (x≤0.3) were composed of phase-pure grains with the sizes distributed mainly in 100–200nm range. The cubic lattice parameters of the spinel LiCoxMn2-xO4 samples decreased gradually with increasing Co composition. X-ray photoelectron spectroscopy data indicated that cobalt ions in LiCoxMn2-xO4 exist as Co3+ mostly. The electrochemical investigations of LiCoxMn2-xO4 cathodes include cyclic voltammetry, cycling performance, charge-discharge profile, and rate capability in the 3.5–4.3V potential range. The x=0.05 cathode exhibited initial discharge capacity close to that of LiMn2O4 cathode and less capacity fading than LiMn2O4 after extended charge-discharge cycles (>200). The x=0.1 cathode exhibited a reduction in initial discharge capacity by ∼10% but the capacity was retained up to ∼300 cycles. The improved capacity retention of LiCoxMn2-xO4 cathodes is attributable to the improved structural stability by octahedral Co3+ substitution for suppressing Mn3+-related Jahn-Teller distortion and cathode dissolution into electrolyte.

Fabrication and Characterization of Thin Film Nickel Hydroxide Electrodes for Micropower Applications.

The utilization of micropower sources is attractive in portable microfluidic devices where only low-power densities and energy contents are required. In this work, we report on the microfabrication of patterned α-Ni(OH)2 films on glass substrates which can be used for rechargeable microbatteries as well as for microcapacitors. A multilayer deposition technique is developed based on e-beam evaporation, ultraviolet lithography, and electroplating/electrodeposition which creates thin-film electrodes that are patterned with arrays of micropillars. The morphology and the structure of the patterned electrode films are characterized by employing field emission scanning electron microscopy. The chemical (elemental) composition is investigated by using X-ray diffraction and X-ray photoelectron spectroscopy. Finally, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge measurements are used to evaluate the electrochemical performance of the patterned thin film electrodes compared to patternless electrodes. We observe that patterning of the electrodes results in significantly improved stability and, thus, longer endurance while good electrochemical performance is maintained.

High-performance flexible lead-free nanocomposite piezoelectric nanogenerator for biomechanical energy harvesting and storage

Environmentally friendly and flexible piezoelectric nanogenerators (PENGs) have attracted considerable interest for use in autonomous micro-/nano-systems, wearable electronics, and implantable biomedical devices. Herein, a flexible, lead-free, solution-processable and efficient PENG is demonstrated, based on a highly piezoelectric nanocomposite thin film of barium titanate nanoparticles (BT NPs) embedded into a highly crystalline polyvinylidene fluoride–trifluoroethylene (P(VDF–TrFE)) polymer for charge storage. The nanocomposite PENG (nc-PENG) with high loading of BT NPs up to 40wt% in the nanocomposite can produce output voltage as high as 9.8V and output power density of 13.5µW/cm2 under cyclic bending, comparable to the output of conventional inorganic polycrystalline lead zirconate titanate PENGs. The high performance of these nc-PENGs is primarily attributed to the very high effective piezoelectricity of the highly crystalline P(VDF-TrFE), strengthened by the BT NPs. The nc-PENG was also demonstrated to harvest biomechanical energy from simple body movements and store the generated electricity during mechanical and biomechanical motions in a rechargeable microbattery.

Conformal Electrodeposition for All-Solid-State 3D Thin-Film Batteries

For the application of durable micro-storage for autonomous systems and implants, 3D thin-film batteries are leading candidates. Lithium ion batteries have the highest energy density of all known systems and are thus the best choice for these rechargeable micro-batteries. Since liquid electrolyte based batteries present safety issues and limitations in size and design, pure solid state devices are considered particularly for miniaturization. Planar thin-film lithium and lithium ion batteries are at present commercially available but have limited capacity (<1mAh/cm2). The capacity can be increased by coating the thin-film stacks on micro-or nanostructured surfaces (3D thin-film batteries, see Figure below). The increase in surface area through 3D structuring also increases the maximum current and thus the battery power. The main challenges in the introduction of solid-state Li-ion batteries are low ionic conductance and limited cycle life time due to mechanical stress and shearing interfaces. Solid materials with intrinsically high ion conductivity (~10-3 S.cm) do exist, but are not electrochemically stable. Vice versa, electronically insulating electrolytes with a large electrochemical window and good chemical stability to metallic Li are known, but typically have intrinsically low ionic conductivities (<10-6 S cm). By scaling down the electrolyte thickness, an overall acceptable ionic conductivity can be obtained even for material with poor ionic conductivity. The latter assumes conformal and pinhole-free coverage over large effective surface areas with large aspect ratio features. ALD is a surface sensitive technique that can provide superior conformal coatings of high-aspect ratio features, crevices and corners and is suitable for (but not limited to) ultra-thin films. In this paper, the requirements for functional and viable thin-film stacks will be discussed. The need for conformal deposition techniques such as ECD, ALD and MLD for electrode, electrolyte and buffer layers will be addressed. The mechanical integrity of the all-solid state stack in corners and confined spaces is a tangible issue. Considerable mechanical stress may build up during charge and discharge due to the rigid nature of the inorganic crystals and glasses that make up the battery stack. Furthermore, in-diffusion of at interfaces may consume part of the electrode which next to capacity and power loss can affect device reliability. In this paper, the importance of thin buffer layers will be discoursed. Part of the current collector/anode/electrolyte/cathode/current collector can be made by electrochemical deposition. Electronically resistive materials such as oxides and dielectric polymers can be electrodeposited with extreme conformality as a result of the self-limiting kinetics. In this paper we will show the electrodeposition of MnO2 as potential positive Li-ion electrode and the electro-polymerization of poly phenylene oxide (PPO) as two examples were ECD can built part the battery stack on micro-structured surfaces with great potential for cost-effective up scaling to large area foil-based processing.

High power primary lithium ion microbatteries

Microbatteries are a critical component for powering autonomous and remote microdevices, but current microbatteries lack the power density and capacity required for high performance use. This paper reports primary microbatteries with high power density and capacity. The microbatteries are based on interdigitated three-dimensional nanoporous bicontinuous electrodes, which enable short ion diffusion lengths and high discharge power. The microbatteries utilize a high capacity manganese oxide cathode and lithium anode to achieve a capacity of up to 29.5 μAh/cm2μm, which is 10X the average capacity of the highest capacity rechargeable microbatteries reported.

(Invited) Conformal Deposition for 3D Thin-Film Batteries

For the application of durable micro-storage for autonomous systems and implants, 3D thin-film batteries are leading candidates. Lithium ion batteries have the highest energy density of all known systems and are thus the best choice also for these rechargeable micro-batteries. Since liquid electrolyte based batteries present safety issues and limitations in size and design, pure solid state devices are considered particularly for miniaturization. Planar thinfilm lithium and lithium ion batteries are at present commercially available but have limited capacity (<1mAh/cm2). The capacity can be increased by coating the thin-film stacks on micro-or nanostructured surfaces (3D thin-film batteries). The main advantage of thin-film (TF) batteries is that its power can be increased by scaling down the film thickness. The main technological challenges in the introduction 3D TF batteries are pinhole-free and chemically uniform conformal coating of the cathode, electrolyte and anode thin-film stack.

Fully Integrated Solar Energy Harvester and Sensor Interface Circuits for Energy-Efficient Wireless Sensing Applications

This paper presents an energy-efficient solar energy harvesting and sensing microsystem that harvests solar energy from a micro-power photovoltaic module for autonomous operation of a gas sensor. A fully integrated solar energy harvester stores the harvested energy in a rechargeable NiMH microbattery. Hydrogen concentration and temperature are measured and converted to a digital value with 12-bit resolution using a fully integrated sensor interface circuit, and a wireless transceiver is used to transmit the measurement results to a base station. As the harvested solar energy varies considerably in different lighting conditions, in order to guarantee autonomous operation of the sensor, the proposed area- and energy-efficient circuit scales the power consumption and performance of the sensor. The power management circuit dynamically decreases the operating frequency of digital circuits and bias currents of analog circuits in the sensor interface circuit and increases the idle time of the transceiver under reduced light intensity. The proposed microsystem has been implemented in a 0.18 µm complementary metal-oxide-semiconductor (CMOS) process and occupies a core area of only 0.25 mm2. This circuit features a low power consumption of 2.1 µW when operating at its highest performance. It operates with low power supply voltage in the 0.8V to 1.6 V range.