Evolution of Micro Batteries, the Energy Source for Wearable Devices

Seiko Instruments Inc.

Wearable electronic devices are evolving towards miniaturization, high performance, high density and high functionality. There is no doubt that all the technologies that go into wearable devices are leading-edge. However, without an energy source, these devices would be nothing more than boxes. What is this energy source? Naturally, it is a "micro battery." Along with--or even leading--the evolution of various electronic devices, the micro battery has kept evolving through the endless pursuit of ever-higher levels of performance, density and functionality. Seiko Instruments Inc. (SII) established its own development and manufacturing systems for electronic components in time for the development of the quartz watch. Since then, the company has especially accumulated its own technologies in the field of micro batteries, a basic component of the quartz watch. SII has provided various products to high-technology industries to keep pace with the diversification of and advances in electronic devices. This article reports on various micro batteries SII is proud to have developed, including silver oxide batteries, lithium ion secondary rechargeable batteries, and reflowable capacitors. We hope that readers will recognize the importance of micro batteries as an energy source for wearable devices such as cellular phones, laptop computers and digital cameras.

Kinds and Categories of Batteries

We hope that the readers will allow us to show a complicated chart here. There are various kinds of batteries, depending on purpose, performance and shape. As we go upstream, we find that there are two main streams. One is chemical batteries and the other is physical batteries. Chemical batteries store chemical energy, which changes substances by chemical reactions such as oxidation and reduction. (Normally, the word "battery" refers to a chemical battery.) A physical battery, on the other hand, converts solar energy and thermal energy to electrical energy directly, without changing any substance. The thermoelectric device depicted in the previous issue of Nature Interface is a physical battery. Biological batteries make up another battery category, but we would like to elaborate here on chemical batteries, since they are the most commonly and closely used in our daily life.

There are roughly two kinds of chemical batteries, primary batteries (such as manganese dry batteries and silver oxide batteries) and secondary batteries. A primary battery is one that must be replaced with a new one when the energy is discharged. On the other hand, a secondary battery can be repeatedly charged and discharged. They are the rechargeable batteries (storage batteries) that can recover by charging with DC current from an outside source.

By effectively using these batteries in very precise ways depending on the type of device, wearable technologies became more usable, and therefore closer, to human beings.

Although we are not completely confident that this is the best example, the batteries for miniature racing cars, which require high power output in brief spurts, is one example of our point. Other examples are batteries that provide electricity precisely over long periods; these are found in watches, computer memory devices and heart pacemakers, for example. A wide range of batteries have been developed to meet a wide range of requirements. The development of such a range is surely part of battery evolution.

History of SII's Battery Development

As described in the first part of this article, SII's history of battery development is deeply related to the quartz watch, which debuted in 1969. The start of this history was obviously the commercialization (mass-production) of a reliable silver oxide battery for use as the energy source of the quartz watch. In a sense, the battery has been destined to be the energy source for wearable devices since its birth.

Since that beginning, as the quartz watch became more common as a product, SII developed such technologies as leak protection, the lithium primary battery, the lithium primary paper battery (which corresponds to the increase in density of LSIs), the lithium ion rechargeable battery and the development of products for the reflow process. In this way, the company kept developing and commercializing products powered by micro batteries, which are the essential energy sources for the wearable high-technology devices that are now emerging. The company has established its position as a global manufacturer.

The features of SII's micro batteries are as follows.

Superior leak protection

In watches, measurement equipment and precision equipment, even a small leak of liquid from a battery causes bad electrical contact. This makes the operation of the equipment unstable. SII's micro batteries use special sealing material and process technologies. They have achieved a highly durable structure that prevents leaks in any environment.

High battery capacity

To achieve a longer operation time in a limited space, higher electrical capacity per unit volume is required. SII's micro batteries have achieved high electrical capacity by using high-purity materials and a unique design emphasizing careful balance among materials. Among the materials, the silicon oxide used in the anode of a rechargeable battery has the highest electrical capacity among the commercialized lithium ion rechargeable batteries.

Stable operating voltage

Battery voltage varies depending on temperature and depth of discharge. Constant voltage is demanded because fluctuations affect various characteristics of the equipment. SII's micro batteries provide stable operating voltage in a wide range of temperatures and discharge states, because the materials and their portions are carefully chosen.

High reliability

Batteries are required to operate at constant characteristics in any situation. SII's micro batteries are manufactured in a continuous way under very tight quality control, beginning in the parts producing stage. Only quality-guaranteed batteries are released to the market.

SII Micro Parts Ltd.

A basic overview of SII's micro batteries has been given so far. Continuous production, from development and design to manufacturing, is conducted by SII Micro Parts Ltd., which has its headquarters and manufacturing base in Sendai city, Miyagi prefecture, Japan.

The company was founded as the Sendai Precision Materials Laboratory in 1953, a center for research and development of metal materials and for industry-academia collaboration with Tohoku University. It became a corporation in 1957. This company had an excellent reputation as a group of engineers with high levels of expertise in energy sources for mechanical watches.

It is said that SII Micro Parts began developing and mass-producing the button battery (silver oxide battery) as the energy source of the quartz watch because this company had dealt with both watch and energy sources technologies. Later, the company became the leader in the field by steadily accumulating technologies and know-how. The company now enjoys a position as an established, global manufacturer of micro batteries, as mentioned previously.

In the plant in the Ayashi area, Aoba Ward, Sendai City, there are production facilities equipped with high-purity and an ultra-low-humidity (<1%) room having ISO-14001 certification.

The Sendai complex also includes R&D facilities that introduce many kinds of batteries, one by one, such as capacitors for reflow process, which were mass-produced at Sendai for the first time in the world, MS (manganese silicon) lithium ion rechargeable batteries and TS (titanium silicon) lithium ion rechargeable batteries.

Mr. Takiguchi, President of SII Micro Parts, speaks passionately: "In our company, we always have programs to deploy production and R&D forces in ways that anticipate the high-technology market 24 months in advance. I don't deny that manufacturers are obliged to follow market demands, but at the same time we are keen to create new demands. Therefore, we mean two things when we say that we anticipate the market by 24 months. One is to react to situations, and the other is to create them-that is, to create breakthroughs."

Recycling for Environmental Protection and Coexistence

As stated at the beginning, there are many kinds of batteries, depending on purpose, performance and shape. We must think carefully about the environment when we produce batteries, as well as when we eventually dispose of them. It is obvious that manufacturers must choose environmentally friendly materials and must not create any pollution in production processes. At the same time, users must be careful when disposing of batteries.

Batteries generally contain materials that are precious resource-wise, and some batteries contain hazardous materials. It is desirable to collect batteries for recycling, but some are simply disposed of.

The Battery Association of Japan (http://www.baj.or.jp/e/index.html), whose members are battery manufacturers, has been spreading knowledge about the proper ways to recycle or dispose of batteries. The association asks consumers to observe these rules when they have batteries to get rid of.

Used button batteries and small secondary cells must be brought to waste boxes found at stores that sell or service watches, appliances or cameras.