Battery Power - Summer 2015 - (Page 6)

Feature Wearable Medical Devices Embrace Lithium Polymer Cells Jeffrey VanZwol, VP, Business Development Chris Turner, VP, Technology ICCNexergy, Inc. During the past few years, there has been an increase in demand for wearable devices from an audience both young and old. Some medical devices provide preventative functions, such as monitoring disorders, enabling early intervention and avoidance of complications. Other devices are reactive and can detect if an elderly patient has fallen, needs emergency assistance, has wandered outside a specific perimeter, or needs a reminder to take prescribed medications at the appropriate time of the day. Still other wearables allow consumers of all ages to monitor their own health and fitness, whether to help them lose weight, reach exercise/fitness goals or sleep better. There are many examples of wearable devices that feature sensors. Some use "skin-friendly" adhesive while other examples are wrist bands and shoe insoles that can measure the progress of patients and athletes. Examples of the functions include blood glucose meters, blood pressure meters, cardiac monitors and ECGs. What was once viewed as a "nice to have" device has now turned into a "must have" device to track, monitor and protect us in our everyday life. Communication with the wearable medical device is typically a wireless telemetry function, which utilizes either Bluetooth, Wi-Fi or cellular data capabilities to sync data back to a centralized monitoring program. From a power consumption standpoint, the wearable device needs appropriate and adequate power to collect, process, and sync the functional data, as well as power a wireless transceiver. There are several different means in which a wearable medical device can be affixed to a patient. Some are placed on the skin using adhesives or affixed to clothing with sensors attached to the body. Others are worn on the wrist (or chest) like a watch. The common theme with a wearable device and its rechargeable power source, is it must be small and thin. For the rechargeable power source, the additional requirements usually include an irregular (and custom) shape, only a few millimeters in thickness, and potentially mounted on a curved surface. Given these constraints, the wearable device will typically be powered by a single cell, much like a cell phone. Most wearable devices utilize Lithium Polymer batteries, given their unique characteristics that will be outlined in this article. from about 4 mm to about 12 mm. Some of the most common footprints for prismatic cells are 34 by 50 mm, 60 by 80 mm, 38 by 64 mm with thickness ranging from 4 mm to 10 mm. Lithium polymer cells, sometimes called laminate or pouch cells, are available in custom footprint sizes, which makes them appealing to wearable device manufacturers. They can be very thin or quite large depending on their intended use. The primary advantage of Lithium polymer batteries is the variety of form factors available. Polymer cells differ from prismatic cells in two key respects, one being the cell construction and the second being the electrolyte used. A polymer cell enclosure is an Aluminum foil in between two layers of polypropylene that is typically vacuumed sealed with the edges heat sealed. Additionally, the positive and negative terminals are tabs that protrude through the cell. The electrolyte is either a gel or polymer as opposed to the liquid electrolyte used in a prismatic or cylindrical cell. Cell capacities can range anywhere from 50 mAh for a small cell such as for a Bluetooth headset, up to 20 Ah or more for an electric vehicle battery. In recent years, Lithium polymer cells have been embraced by the consumer equipment manufacturers. Mobile phones, tablets and notebooks utilize polymer cells. Although still more expensive than cylindrical cells, this consumer demand for Lithium polymer cells has substantially reduced the cost per Watt-hour for Lithium polymer cells. Figure 1 indicates the leading suppliers of polymer batteries (Source: Avicenne Energy, March 2015). Advantages of Lithium Polymer Batteries The lack of a metal can allow more flexibility to manufacture custom sizes based on the constraints of the wearable device. While internally the cells are very similar to prismatic cells (i.e. the electrodes could be made from the same manufacturing lines), the enclosure provides flexibility to more easily create new sizes. The laminate material can easily be slit to different lengths and widths as opposed to having a cylindrical or prismatic can that requires new tooling to manufacture a new can size. Also, the heat sealing process is easily modified compared to crimping for cylindrical cells. This flexibility in the size options makes Lithium polymers a great choice for wearable devices. Introduction to Lithium Polymer Li-ion cells come in three basic form factors: cylindrical, prismatic and polymer cells. Cylindrical 18650 (18 mm dia. 65 mm length) cells are used not only in notebooks but also power tools, e-bikes, EVs and other industrial applications. Prismatic or rectangular shaped cells are made with Aluminum cans and are available in a myriad of sizes and are generally used in the same applications as polymer cells. Prismatic cells come in a variety of x,y footprints and with thickness typically ranging 6 Battery Power * Summer 2015 Figure 1. Market Share for Leading Lithium Polymer Manufacturers www.BatteryPowerOnline.com http://www.BatteryPowerOnline.com

Table of Contents for the Digital Edition of Battery Power - Summer 2015

Battery Power - Summer 2015
Table of Contents
Wearable Medical Devices Embrace Lithium Polymer Cells
Five Building Blocks of Self-Powered Wireless Sensor Nodes
Conference Preview: Battery Power 2015
Protecting Batteries that Protect Your Power System
Batteries
ICs & Semiconductors
Components
Chargers
Industry News
Conference Review: Battery Japan 2015
Calendar of Events
Marketplace

Battery Power - Summer 2015