smartcard manufacturerR&D division

Delivering Better Security for Cryptocurrency CardsBattery issues were hampering the development of a state-of-the-art cryptocurrency wallet


The number of people who own cryptocurrency is increasing, thanks to the global rise of Bitcoin, followed by a range of other currencies, and an increase in the number of exchange services available. At the same time, these currencies, being essentially just encrypted data, are more susceptible to hacking and fraud. There is therefore a need to develop more advanced security measures and tools for cryptocurrency applications. The client decided to start the development of a cryptocurrency card as a “cold wallet”* for holding cryptocurrency, equipped with advanced security functions.

*A tool or device for storing cryptocurrency with disconnected from the internet.


Difficult to Find a Battery With Requested Capacity While Thin Enough for Card Use

The client was already developing a smart card with a fingerprint sensor, but felt the cryptocurrency wallet should have additional functions, such as an integrated display, and authentication via BLE communication with smart phones. However, their calculation result clearly indicated that general primary batteries did not have enough capacity to support all those functions in their card design. While the client considered replacing the fingerprint sensor or BLE module with one with lower power consumption, they began exploring the idea of using a rechargeable battery for a practical card to last at least five years. Thickness was now an issue: while to be embedded in a standard card, a rechargeable battery must be no thicker than 0.5 mm, a battery that thin would not have enough capacity to support the multiple functions the client wanted to include. The client was stuck, unable to find a battery that satisfied its capacity and thickness requirements.

Battery Swelling Was Also a Problem

With the battery selection process beset by an unexpected setback, the client concentrated on selecting the other components that would be integrated into the card. However, it realized that after the additional components of a fingerprint sensor, BLE module, and display, there would be less space than originally anticipated for the rechargeable battery. A high-capacity, small footprint battery appeared to be one solution, provided it was charged more frequently, but the client decided that the requirement for frequent recharging would make such a solution unviable. To check the possibility that the client had overlooked a potential battery option, it set about ordering various thin rechargeable batteries from around the world to use in prototypes. However, all the batteries tested had cycle lives far shorter than the card’s five-year target life. What’s more, all of the tested batteries swelled with age, causing the card itself to bulge.

Main Issues

  • In order to be more secure, the card required functions of a fingerprint authentication, BLE communication, and a visual display. Primary batteries lacked the capacity to support those functions.

  • The client considered using a rechargeable battery, but nothing available offered sufficient capacity in a package thin enough to be embedded in a card. This capacity shortfall could not be compensated for.

  • Because multiple components would be embedded in the card, little space remained for the rechargeable battery, so it was difficult to ensure enough capacity. While more frequent recharging was one solution, such a requirement would not be user friendly and unacceptable for consumers.

  • While the client built prototypes using other rechargeable batteries, all faced not only short cycle lives but also swellings which would be a critical problem in product appearance.