Christine C. Ho

Direct write dispenser printing of a zinc microbattery with an ionic liquid gel electrolyte

The need for energy dense microbatteries with miniature dimensions has prompted the development of unconventional materials, cell geometries, and processing methods. This work will highlight our materials investigations, deposition methods and the device performance of a printed zinc–manganese dioxide rechargeable microbattery utilizing an ionic liquid gel electrolyte. We have developed a direct write dispenser printing method with the ability to fabricate multilayer structures and precisely deposit and pattern these components onto any substrates. The use of a unique room-temperature ionic liquid swelled into a polymer to form a gel electrolyte with solid-like mechanical strength and liquid-like ion transport properties has enabled the simple fabrication of stacked microbattery structures with the potential to be easily integrated directly onto a microdevice substrate. Initial microbattery tests and cycle behavior are discussed, and after an initial activation of the cathode material, an experimental cell discharge capacity and energy density of 0.98 mA h cm−2 and 1.2 mW h cm−2 were measured, respectively.

A super ink jet printed zinc–silver 3D microbattery

A novel super ink jet printing (SIJP) system was used to fabricate 3D zinc–silver microbatteries directly on a substrate. The SIJP provides a simple and flexible method to deposit interesting 2D and 3D structures of varying morphologies without the waste and large energy inputs typical of standard microfabrication technologies. The system was used to print pairs of silver electrodes with arrays of pillars on glass substrates, and in the presence of an electrolyte, the battery self-assembled during the first charge. Using an aqueous electrolyte solution of KOH with dissolved ZnO, the SIJP printed structures showed similar electrochemical behavior to batteries composed of silver foil electrodes. For a sparse array of pillars (~2.5% footprint area of each electrode pad occupied by pillars), a capacity increase of 60% was achieved in comparison with a cell with planar electrodes.

Dispenser Printing of Solid Polymer-Ionic Liquid Electrolytes for Lithium Ion Cells

Microfabrication of on-chip solid state electrochemical cells has provided a robust challenge to industry for the past decade. Previous efforts include RF Sputtering, screen-printing, and laser printing. All have merit in the laboratory but have proven difficult to scale due a combination of equipment cost and proper isolation from water and oxygen. We present a promising method for printing additively all structures necessary for a working lithium polymer battery that is both small enough to fit in a compact glovebox, yet scaleable for industrial production.

Integration of a low frequency, tunable MEMS piezoelectric energy harvester and a thick film micro capacitor as a power supply system for wireless sensor nodes

This work presents an integration approach towards manufacturing a MEMS piezoelectric vibration energy harvester and an electrochemical capacitor on the same substrate. Vibration energy harvesters have been fabricated to resonate at low frequencies, matching ambient vibrations found abundantly in buildings. For cost-effective resonance tuning, a direct write dispenser printer can be used to print additional mass at the tips of the beams, and is also used to deposit a capacitor in the open space surrounding the beam. The implementation of a power supply on a single platform is of great value especially for autonomous wireless sensors with long lifetime and small device volume requirements.

Direct-write dispenser-printed energy storage devices

The simultaneous decrease in electronic device form factors yet increase in functionality has motivated a shift in energy storage design and manufacture to accommodate novel and unconventional materials, new device geometries, and nontraditional fabrication methods. We are developing a simple, low-cost, solution-based method for integrating custom energy storage components directly onto a device. A direct write dispenser printing system is used to pattern solutionsbased materials into multilayer devices. Along with this fabrication method, we discuss the materials design and device characterization of two printed energy storage devices: a carbon electrochemical microcapacitor and a zinc-metal oxide microbattery. The two components will be used as a hybrid energy storage system, capable of providing an energy dense storage buffer while also being able to address high power pulse loads, all within a limited footprint area.

Printed electrochemical capacitors for energy scavenging sensor networks

The application of energy scavenging technology significantly improves wireless sensor network nodes long-term operation and ensures minimal user attendance. For most of the scavenging technologies, ambient energy is available only under particular environmental conditions. For this reason, wireless sensor nodes have to keep the scavenged energy in storage elements. In this paper we present a kind of electrochemical capacitors manufactured using the direct write technology. This technology allows the super capacitors to be printed directly on board of the sensor nodes. The experimental results on scavenging outdoor solar radiation and indoor light, stored on the printed capacitors, demonstrate high potential in terms of supplying the sensor nodes.

Surface shape capture with boundary electrodes

A system is proposed for monitoring changes in surface shape that is portable, inexpensive, durable, and works in many places where traditional shape monitoring techniques would fail. This system is ideally suited to monitoring large-scale surface deformations on surfaces like cloth without excessive wiring or the need for special purpose equipment. It is composed of a semiconductor-insulator-semiconductor sandwich of carbon-loaded polymer and unloaded polymer with electrodes attached at the boundary. The electrical properties of the material are sampled by applying currents and measuring resulting voltages at the boundary electrodes. The piezoresistive and geometry changes of the semiconductor layers results in resistance variations across the surface according to local curvature. Through sufficient sampling, a system of equations can be solved for the interior curvature properties. The local curvature data is integrated to yield an approximation of the surface shape. Various results are given that demonstrate the feasibility of the sensor with a prototype device.