Indispensable to next-generation devices Ultra-thin battery that brings a new lifestyle The 0.45-mm-thick ceramic rechargeable battery “EnerCera® Pouch”, enabling electronic functions to be incorporated into countless devices

©Nikkei BP "Nikkei xTECH Special" First published: September 7 to October 4, 2020

To realize a productive life or find solutions to problems, effective use of the large amounts of data that are continuously generated in abundance daily through various social activities becomes vital.

As a result, wearable devices that help with our daily activities and IoT devices that carefully keep an eye on the flow of tangible items or social movement are in use in numerous places. However, “there is a problem that, with the current types of wearables or IoT devices, it is not always possible to freely add the necessary electronic functions to everything everywhere required to collect data for its effective use,” says Iwao Ohwada, Vice President of NGK Insulators.

There are many advanced electronic functions that wearables or IoT devices preferably possess, such as sensing, wireless communication systems, information processing and displaying. However, operating these functions requires batteries with reasonably high levels of power and capacity. The conventional Li-ion rechargeable batteries, widely used for portable devices, have difficulty in meeting these requirements. Batteries with high power and high-capacity are bulky, heavy and rigid. As exemplified by the fact that a battery takes up most of the body of a smartphone, high-spec batteries are one of the biggest challenges for device downsizing. To ensure safety, it is necessary for batteries to be packaged in a hard case, which further adds restrictions to the shape and design freedom of the applied devices.

Great potential hidden behind modest self-presentation

The ultra-thin ceramic rechargeable battery “EnerCera Pouch”, from NGK Insulators, may solve this battery problem through a new approach (Figure 1). With the use of the company’s original crystal-oriented ceramic plate as the positive electrode, despite being just 0.45mm thick, the EnerCera Pouch battery exhibits an energy density, charge-discharge characteristics and a long service life comparable to or exceeding those of the existing Li-ion rechargeable batteries.

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Figure 1: Li-ion rechargeable batteries generally use a powder-coated electrode for the positive electrode. During production, an active positive electrode material powder such as lithium cobalt oxide is bound by an organic binder and a conductive auxiliary agent is added for conductivity. In this method, it is difficult for lithium ions to pass through positive electrodes and deterioration may occur due to high temperature. However, with the crystal-oriented ceramic positive electrode, the crystal orientation of lithium cobalt oxide is aligned in such a way as to make lithium ions easy to pass with low resistance. Furthermore, with no organic binders or conductive auxiliary agents contained, the energy density gets high and high-temperature mounting becomes possible.

The EnerCera Pouch battery is durable against bending until the radius of curvature reaches 40 mm, which meets the international standard for contactless IC cards (ISO14443-1). While the requirement of the standard is to withstand the bending test 1,000 times, it has been demonstrated that the appearance and performance of EnerCera Pouch battery remain unchanged even being bent 6,000 times. With the highly reliable sealing design and assembly in a strictly controlled dry environment, no battery swelling due to gas generation occurs if it is kept within the range of recommended environmental conditions for use. Moreover, while compliance with the “IEC62133” safety test standard is par for the course, it has also been verified that any types of load exceeding the levels specified by the standards such as overcharging, nail penetration, cutting and high-temperature heating do not cause the battery to rupture or ignite, or electrolyte to disperse (Figure 2).

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Figure 2: Applied of all types of load to verify the safety and reliability

The EnerCera Pouch battery, which boasts the safety and reliability crucial to wearables or IoT devices, are now being adopted as an effective power source for smart cards by multiple manufacturers. New smart cards with built-in electronic functions such as a display, fingerprint authentication sensor, and wireless communication system can be realized by incorporating the EnerCera Pouch battery. These new smart cards are going to prevail in the market.

The EnerCera Pouch battery is characterized by an unparalleled advantage: the capability to be incorporated into places where it was impossible with conventional rechargeable batteries. This is the very origin of innovation for battery systems, and some projects are already under way. By making use of the characteristically advantageous properties of the EnerCera Pouch battery (that is, ultra-thin and bendable), Prof. Tokito of Yamagata University has developed a thin logistic IC tag with a thermal sensor that can adhere to a curved surface. For example, if this logistic IC tag is attached to a wine bottle, it can provide evidence that the bottle was transported at an appropriate temperature. This may create new values for retailers and consumers.

Another recent notable technological advancement is energy harvesting wherein energy sources in the environment surrounding a device in operation such as light, temperature differences and vibrations are converted into usable electricity. In Japan, the Ministry of Internal Affairs and Communications is taking the lead to develop practical applications for wireless power transfer technology which can transmit electricity similar to sending data through Wi-Fi routers for the first time in the world. However, in this method, as the power receiver can obtain only very small levels of power in the order of μW, direct application is not good enough to operate advanced electronic functions. How would the situation change if the EnerCera Pouch battery is used? With the EnerCera Pouch battery in use, such micro power can be constantly received/stored in a cumulative manner and can be used in one go when it is required. While this way of using electricity may be possible with the use of other types of rechargeable batteries, it is only possible if their sizes can increase. The EnerCera Pouch battery stands out in this regard, that is, being thin and therefore applicable anywhere, it can expand the field of energy harvesting applications.

Let’s think about an example of using an electronic shelf label (ESL) system to display product prices in a supermarket. If a wireless communication system is used in an electronic shelf label system, advanced marketing methods such as omni-channel pricing strategy and dynamic pricing become applicable. For example, prices for the merchandise in a shop can be changed immediately during a limited-time offer. If, at that time, power can be supplied through wireless power transfer technology, manual battery replacement or battery recharging becomes unnecessary. Meanwhile, the wireless power transfer technology, for which practical application is expected to start in 2021, has an upper transmission output limit of 1 W (920 MHz range). In this case, the power which the receiver can obtain will be at the level of several μW and will not be able to directly operate the electronic shelf label system. However, “if the EnerCera Pouch battery is adopted here, it would store all the power that is constantly obtainable in the several μW range and could produce a pulse output of several hundred mW, which is required to change a screen display and operate a wireless data communication system. Therefore, even if there is an upper limit to transmission output, the electronic shelf label system is still operable.” says Ohwada (Figure 3). With primary batteries currently in use, the battery life restriction reduces price changes to a maximum of twice a day. The EnerCera Pouch battery, however, allows prices to be changed frequently.

Furthermore, the EnerCera Pouch battery, being 0.45 mm thick, outclasses the standard coin cell batteries of 5 mm thickness. In the case of introducing a conventional electronic shelf label system powered by standard coin cell batteries, special holders are required. However, the electronic shelf label system with EnerCera Pouch batteries can replace the paper price tags without the need for such holders, since batteries can be made into the smart card type. Such high compatibility with the current environment for use is one of the advantages that the EnerCera Pouch battery can boast as the slimmest of the slim.

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Figure 3: An example of “EnerCera Pouch” battery applications

Maintenance-free electronic price tag with the use of wireless power transmission

When it comes to wearable devices, possible applications include making the insoles of running shoes smart (Figure 4). By incorporating pressure sensors, a wireless communication system and EnerCera Pouch batteries in the insoles, data are collected while running and are analyzed to visualize the patterns in running on a PC or smartphone. By setting up a wireless charger in the shoe rack, charging could be done without much trouble.

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Figure 4: Smart insoles that make use of high safety and reliability

Innovation in your hand

Four types of EnerCera Pouch batteries are available: “high power,” “high capacity,” “high heat resistance” and “fast charging” (Figure 5). The high power and high capacity types have already been mass-produced at NGK’s factory in Tsuru City, Japan. The production of the remaining other two types will start in October 2020.

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Figure 5: Product lineup of the “EnerCera Pouch”

The high-power type has achieved a peak discharge current of 500 mA. It is therefore possible to add a large-output wireless communication function such as cellular LPWA to card-type devices. It is also possible to operate a small display and show information. The high capacity type exhibits a high energy density of 200 mWh/cc. “As a property of rechargeable batteries, the length of battery runtime has often been the center of interest. However, operating advanced functions requires a large current. Device developers are getting interested in high output. Also, because of the increased energy density combined with the small size and light weight of the EnerCera pouch batteries, there is an increasing number of companies benefitting by diversifying the methods for embedding the batteries into various devices (Ohwada).

The high heat resistance type has attained an in-process upper temperature limit of 135°C, which can withstand the hot lamination process (thermocompression bonding) of IC card production. Since other rechargeable batteries used for IC card application only have low heat resistance characteristics, there is no choice but to employ a room temperature process using an adhesive. This lowers the production throughput to nearly 1/10. Also, the adhesive area may get detached, which compromises the reliability. The fast charging type, in which ceramics are used for the negative electrode as well, enables high-voltage application from the beginning of charging, and the charge percentage can increase from a state of charge of 0% to 80% in about 10 minutes. The charge-discharge cycle life is long. After repeating 1,500 cycles between 0% and 100% state of charge, the battery still retains more than 95% of the capacity (Figure 6).

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Figure 6: Charge-discharge cycle properties

The application of the EnerCera Pouch battery is limitlessly expandable with imagination. Some companies have already taken up the challenge to create a new battery system by combining the EnerCera pouch battery with new technologies such as energy harvesting and wireless power supply. NGK Insulators’ joint development projects with other companies are under way, including power IC modules with companies such as Torex Semiconductor, which has rich expertise in power semiconductors, environmental sensing devices for smart agricultural applications, with companies such as Renesas Electronics, and power supply systems using energy harvesting with companies such as Ricoh. The achievements will be presented on the NGK Insulator’s website as well as at exhibitions such as CEATEC to be held this fall.

Starting this fall, the EnerCera battery series have become available for online purchase. Easy access to the EnerCera battery series brings more opportunities to test new application ideas. Creation of innovation will be further accelerated. Keep an eye on the new battery trends that will lead us to the future.


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