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Small All Solid-State SMD Batteries Fill Gap of Conventional Batteries
B

y laminating thin battery-constituting materials, FDK Corporation has developed batteries that have characteristics significantly different from conventional rechargeable batteries (Table, Fig. 1).

These are small all solid-state surface mount devices (SMD) batteries that do not include electrolytic solution, have high resistance to high temperatures, and can be resin molded. With these three characteristics, these batteries are expected to be used in applications that do not employ conventional batteries.

Table: Specifications of a small all solid-state SMD battery
Table of Specifications of a small all solidstate SMD battery
* equivalent to electrostatic energy of 1.4F capacitor with transition 3V->2V
Cut model of a small all solid-state SMD battery
Fig. 1: Cut model of a small all solid-state SMD battery
High Safety
First, they do not include electrolytic solution.

Normally, a battery consists of positive electrode (cathode), negative electrode (anode), and electrolyte (Fig. 2). Cathode and anode are materials that generate electric energy, and ions flow between cathode and anode instead of electrons. The foundation for the flow of ions is electrolyte. Conventionally, electrolyte as liquid is the norm. However, solid electrolytes that can let lithium ions flow have been discovered, and the development of batteries using solid electrolyte has begun.

The absence of electrolytic solution has eliminated liquid leakage, thereby minimizing the possibilities of gas generation and ignition stemming from flammable electrolytic solution.

Use under Harsh Environments
Second, they are resistant to high temperatures.

FDK’s small all solid-state SMD batteries are produced using a process called sintering, which has not been used for conventional batteries. In the sintering process, batteries are exposed to high temperatures of several hundred degrees in the atmosphere to promote the welding of particles and to be formed as batteries. Hence, unlike batteries, in which electrolytic solution is used, all solid-state batteries do not deteriorate significantly even when they are used under an environment around 100°C. In addition, they are resistant to the reflow process in which temperature rises up to 260°C, and therefore, small all solid-state SMD batteries can be mounted on printed circuit boards (PCBs) using a chip mounter and the reflow process like other electronic components. Thus, they can be joined with PCBs at lower costs than conventional rechargeable batteries. In addition, they can also be installed near heat sources, such as central processing units (CPUs), memories, and automotive engines, which tend to become hot. This has not been possible with conventional rechargeable batteries.

Schematic diagram for batteries
Fig. 2: Schematic diagram
System in Package
Third, they can be covered by resin.

As described above, small all solid-state SMD batteries do not have electrolytic solution and are free from liquid leakage. With this characteristic, they can be molded with resin like System in Packages (SiP).

Here are some application examples. Conventionally, when a real time clock (RTC) module is provided with a power compensation function, it has been necessary to arrange passive components and a battery holder in the periphery, requiring space and labor to install them. However, if a small all solid-state SMD battery is molded together with an RTC microcontroller, crystal oscillator, and power supply IC, an RTC chip with a power compensation function is completed (Fig. 3). The RTC chip eliminates the labor for arranging and managing components, allowing mounting with ease. If a small all solid-state SMD battery is molded together with a memory chip instead of an RTC microcontroller, it will create a memory chip with power compensation function. If it is molded with resin together with a communication module and a microcontroller, a security chip that emits emergency communication at the time of power shutdown, can be implemented. Depending on designs, various chips can be implemented.

RTC chip with power compensation function
Fig. 3: RTC chip with power compensation function
FDK’s small all solid-state SMD batteries are capable of pulse output of several tens of milliwatt, which is necessary for Bluetooth Low Energy (BLE) communications. Therefore, their use in internet of things (IoT) devices (sensor beacons) in factories, and buildings, as well as in the agriculture, automotive, medical and healthcare markets can be expected.

Paves Way for New Applications
As described above, FDK’s small all solid-state SMD batteries have three characteristics that are not seen in conventional rechargeable batteries. With these characteristics, they will give birth to applications, such as smaller IoT devices, power supplies in harsh high temperature environments, and distributed power supplies on PCBs, and their markets.

At present, FDK is developing small all solid-state SMD batteries targeting mass production in 2021 at the earliest. The company will improve performance and quality of the batteries so that they can transform devices made by manufacturers to devices more required by the society than they are today.

About This Article:
The author, Ichiro Torii, is from the All Solid-State Battery Business Promotion Office, FDK Corporation.