Rodney M. LaFollette

Microscopic Nickel-Zinc Batteries for Use in Autonomous Microsystems

Microscopic nickel-zinc batteries have been built using microfabrication procedures similar to those used in the microelectronics industry. These batteries were designed for use with autonomous microsystems and are of particular interest for applications that involve remote sensing. It is envisioned that the batteries would he part of a hybrid micropower system that would also include a device for scavenging energy from the environment in order to recharge the batteries and provide for a long operational lifetime. The nickel-zinc batteries that have been developed have a typical footprint of 0.02 cm 2 and a capacity of approximately 0.555 mWh/cm 2 . Over 1000 batteries have been fabricated on a single 4 in, wafer, One of the most important characteristics of these batteries is their ability to discharge at high rates (≥100 mA/cm 2 ), making it possible to extract more than I mW (per cell) from these very small cells Also, initial results show that more than 2000 cycles of a microelectromechanical systems (MEMS) type duty cycle are possible. The high rate performance, small size and long cycle life of these batteries make them suitable for microsystem applications. In addition, the microfabrication procedure that has been developed should enable the fabrication of these batteries on the same substrate used for other system components

Design Fundamentals of High Power Density, Pulsed Discharge, Lead Acid Batteries I . Experimental

In this paper the design of a battery with maximum specific power to be discharged for 0.01 s or less is explored. Key elements of the design are bipolar construction, using thin components with high electronic conductivity in the bipolar separator and high ionic conductivity in the electrolyte, and the use of an electrochemical couple with high open-circuit potential and fast electrode kinetics. Bipolar lead-acid stacks were assembled which showed specific powers of 100--800 kW/kg with current densities of up to 10--40 A/cm{sup 2} for up to 100 {mu}s. Single lead-acid cell tests showed that acid concentration, separator thickness and conductivity, discharge potential, and PbO{sub 2} formation time all had a major impact on the cell power output. Tests showed that these cells are capable of well over a million shallow discharge/charge cycles. Evidence indicates that PbSO{sub 4} formation severely reduces cell current densities after 200--400 {mu}s of discharge. In the first 200 {mu}s, H{sub 2}SO{sub 4} concentration depletion at the reaction interface appears to be a factor in current decline.

Design fundamentals of high power density, pulsed discharge, lead-acid batteries. II, Modeling

Two time-dependent, one dimensional mathematical models of lead-acid cells have been solved to help understand the pulsed discharge behavior (0.002 second discharge) of thin cells. One model considered only the outer (cross-sectional) surface area of the electrodes; the other assumed that only the surface area internal to the porous electrodes contributed significantly. The porous electrode model was a macroscopic model which ignored the concentration gradients within the microscopic electrode pores. it was found that the model which considered the outer surface area more accurately predicted experimentally observed behavior during the initial 0.0001 s of discharge. When the porous electrode model was altered to include acid concentration variations within the electrode pores, it also predicted the behavior of experimental cells during this initial 0.001 s of discharge. The effects of delayed PbSO{sub 4} precipitation were also included in the porous electrode model. When this was done, the model successfully predicted the shape of discharge curves from experimental cells for longer time periods.

Properties of electrochemically generated poly(p-phenylene)

Abstract Poly( p -phenylene) (PPP) electrodes formed by anodic oxidation of biphenyl in acetonitrile solutions were examined. As a cell, we observe generally high discharge current densities and rapid discharge rates. PPP electrochemistry and cell performance were found to depend significantly on the nature of the supporting electrolyte present during electrosynthesis and doping. These electrodes were also found to catalyse O 2 reduction. Raman and scanning electron microscopic results are also presented.

Mathematical Model of the Discharge Behavior of a Spirally Wound Lead‐Acid Cell

A mathematical model has been developed in order to simulate the three-dimensional, transient behavior during discharge of a spirally wound lead-acid battery cell designed for use in hybrid-electric vehicles. Several aspects of battery behavior are predicted, including potential and current distributions, heat generation rates, concentration changes, and temperature. The influence of the lead grids which support both electrodes has been described and found to have a significant impact on both the power available from the cell and heat generation rates in the cell. The model predictions compared well with available experimental data (current-voltage-time). Models such as the one presented in this paper represent a valuable tool for understanding battery behavior, solving problems with existing battery designs, and generating and optimizing new designs.

An Analysis of Coal Particle Temperature Measurements with Two-color Optical Pyrometers

Abstract Two-color optical pyrometers have been used to measure the temperature of reacting pulverized coal particles. An analysis of such measurements was performed to determine the effect of several possible conditions on the measured temperature. The conditions investigated were the use of a single photomultiplier to alternately measure the radiant emission at the two selected wavelengths, the presence of soot, light extinction, the choice of wavelengths used to compute the two-color temperature, and non-uniform particle clouds. A computer model of a one-dimensional coal particle cloud was written for this analysis. Results of calculations showed that artificially high temperatures can result if a pyrometer with a single photodetector is used to measure temperatures in a rapidly fluctuating flame. Emission by soot in the coal particle cloud caused unrealistically high temperature measurements. Light absorption by soot lowered the two-color temperature, but not enough to compensate for the rise in obser...

Microscopic batteries for micro electromechanical systems (MEMS)

Over the last decade, the same micromachining manufacturing methods that have made microelectronic circuitry and microcomputer technology possible have also made microelectromechanical systems (MEMS) a reality. Most machines require power and autonomous power is usually most desirable. Because its possible to manufacture machines small enough to fit on a microchip, there is a need for microscopic batteries, which can also reside on the chip, to power them. The ability to store energy in miniature, rechargeable devices, which are integrated into a MEMS circuit, would enhance MEMS technology in several ways. Bipolar Technologies of Prove, Utah, USA, has completed a Phase I, SBIR project which was divided into three specific tasks: (1) preliminary design; (2) development of fabrication processes; and (3) evaluation of test cells. The purpose of the first task was to describe an energy storage approach, suitable for in MEMS, involving microscopic batteries. During the design task numerous electrochemical couples were screened by testing small, flat cells. Developing fabrication processes was an important Phase I objective. It had to be demonstrated that traditional micromachining processes could be devised to manufacture microbattery components. The resultant design activities were followed by the performance of proof-of-concept experiments to demonstrate the feasibility of microscopic batteries for MEMS.

Prototype silicon micropower supply for sensors

Miniature, remote, autonomous sensors generally have a relatively large power supply compared to the size of the sensor and sensor conditioning electronic circuitry. An integrated micropower supply made in a silicon wafer offers the prospect of shrinking the power supply size down to the size of the sensor and conditioning circuitry. In this paper, we describe a prototype silicon micropower supply comprising a nickel-zinc microbattery integrated in a silicon wafer interfaced to a miniature silicon solar array via an adaptable charge controller that can optimally supply charging current from the miniature solar array to the microbattery. Details of each of the subsystems are described together with test results on a multichip, hybrid implementation of an all-silicon, miniature power supply.

Thin Film Copper Vanadium Oxide Electrodes for Thermal Batteries

In this work, thin film copper vanadium oxide electrodes including Cu3V2O8 and Cu5V2O10 were prepared by an aqueous process for thermal batteries. The electrochemical performances of thin film electrodes were tested and evaluated in thermal cells. Comparing with pressed pellet electrodes, the thin film electrodes were able to deliver higher specific capacities. Without any organic solvent and binder, the process for making the film electrodes is low cost and environmental benign.

RF-recharged microbattery for powering miniature sensors

A novel power source for miniature sensors, comprising an RF-recharged microbattery is presented. The microbattery comprises a silicon wafer-fabricated aqueous Ni-Zn microbattery that is capable of delivering /spl sim/10 mA for a few seconds. In this paper, we present charge/discharge test results on the microbattery itself and details of the RF charger circuit design and experimental test results on fabricated RF charger boards. Finally, we present test results on a sensor platform comprising an Analog Devices MEMS accelerometer, a microchip microcontroller, and an RF transmitter, all powered by the RF recharged microbattery.