The future of drones and high-performance batteries

Where the word ‘drone’ comes from

When you hear the word “drone”, you probably think of a remote controlled aircraft with propellers (rotor blades). However, all aircrafts regardless of size that fly without a pilot and can be operated remotely are referred to as an unmanned aerial vehicle (UAV), commonly known as a drone.

Although the world’s first modern UAV was a small aircraft, the current mainstream versions are rotary-wing aircrafts. An aircraft equipped with three or more rotors are collectively called multicopter, but with four, five and six rotors are respectively called quadcopter, hexacopter, and octocopters. Currently, multicopter drones are the most common type of drone.

The growth of drones

Universities and other research institutions began developing electric quadcopters in the 1980s. However, batteries at the time had low capacity and it was difficult to obtain small, high-power motors, so a wired power supply system was used. By 1987, a Japanese company began selling the world’s first unmanned industrial radio-controlled helicopter, which was classified as a drone.

After 1989, multicopters equipped with gyroscopes were introduced to the market for industrial applications. Gyroscope is a device that can detect changes in the orientation and angular velocity of an object, which greatly enhances the level of control over a drone’s positioning and motion.

In the late 2000s, electronic components necessary for today’s drones, such as gyroscopes, accelerometers, and lithium-ion batteries, began to be used in smartphones. Mass production made it possible to procure these components at a relatively low cost, which led to the development and widespread use of drones. Gyroscopes are also used for image stabilization in smartphones and digital cameras. Accelerometers are sensors that measure the position of drones and are also used in car navigation systems to detect the distance traveled by a car.

The popularity of consumer drones was spurred on by the huge success of quadcopters released in 2010. Quadcopters have fewer motors than other types of multicopters, making them lighter, less expensive, and with long range due to its small batteries.

At the same time, drones with gimbal cameras (stabilizers) began to become widely used for aerial photography/videography. The use of drones for aerial photography and high-altitude filming has eliminated the need to use heavy equipment such as cranes, thereby reducing aerial photography costs in media and video production. Aerial drone videography has allowed live sports such as the Olympics, to be captured in a way previously unimaginable.

The widespread use of camera-equipped drones has also made it possible to remotely check places that are not easily accessible, including but not limited to dams, mountains, bridges, chimneys, construction sites, and building roofs. Such industrial drones greatly improve operational efficiency. Other uses for drones include remote inspections, surveillance, surveys, and commemorative photography such as weddings.

The use of drones is expanding in the agriculture field as well. It is now possible to use drones to spray pesticides, measure ground surface temperature, determine crop growth, check for pests, and predict crop yields by attaching thermal cameras, sensors, and special cameras to drones linked with AI. The use of drones is more time efficient, increases the effectiveness of pest control and improves crop quality.

Many of the industrial and agricultural drones are multicopters with six or eight rotors. A quadcopter (4 rotors) can crash if just one of their motors encounters a problem, making them less reliable for industrial and agricultural use.

Furthermore, drone races exist to see who can operate their drone through a predetermined course as quickly as possible. Competitors wear a head-mounted display to operate the drone and show live camera feed at speeds over 100 km per hour.

Last-mile delivery drones

Drone deliveries are expected to increase in the coming years as major e-commerce companies have recently started to consider and test the concept of last-mile drone delivery services. The last mile in the e-commerce and logistics industries refers to the service of transporting goods from the final logistics hub to the end user (it does not mean “the last mile” in terms of distance, but rather the last section of logistics that delivers goods to the customer).

Since the world’s largest e-commerce site announced its intention to use drones for last-mile deliveries in 2013, experiments have been conducted mainly in the United States. However, the use of drones for commercial purposes has been delayed because it requires special permission from the Federal Aviation Administration (FAA).

As of 2022, there have been reports (e.g. Amazon Prime Air case study) with significant progress to make this a reality. In the US with its large land mass, many people live in areas where it could take more than an hour to drive to the nearest supermarket. The drone delivery service will greatly benefit both the delivery service company as well as the consumer. In addition, issues in the US such as shortage of drivers and traffic congestion in urban areas could be alleviated with drone deliveries. In recent years, drones have been used for pizza deliveries on a trial basis in New Zealand as well as in the US, and could be more widely utilized in the near future.

In Japan, it is certain that the declining and aging population, shortage of drivers, and aging infrastructure and services will progress further. Therefore, it is expected that drones will likely be used to transport medical supplies and daily necessities to local governments, mountainous areas, and remote islands. Although test flights have already begun in some areas, due to the Civil Aeronautics Act in Japan, drone flights in densely populated areas (mainly urban areas) and certain airspaces are restricted. In December 2022, the amended Civil Aeronautics Law came into effect , allowing experiments to begin in the spring of 2023 or later.

Due to the growth of drone application, it is expected that discussions on legal regulations will progress further with improved safety features of commercial drones. In addition to the Civil Aeronautics Act, there are other laws regulating drones. There are laws prohibiting flying drones around national facilities, regulating radio equipment used by drones, and local government ordinances prohibiting flights in specified areas and airspaces, as well as over private residences, apartment buildings, and certain other buildings.

While drones have various advantages, they can crash or be used to invade people’s privacy. In order to promote the safe and fair use of drones, it is necessary to address such issues. Some ways to do this include developing a system to manage drone operations, conducting training and safety education for drone pilots, implementing radio wave maintenance, and securing flight routes.

Drone batteries and their challenges

Small consumer drones generally use rechargeable lithium-ion or lithium polymer batteries. A Lithium polymer battery is a lithium-ion battery with a polymer electrolyte. Because of their light weight, lithium polymer batteries were originally widely used in radio-controlled airplanes.

Even when operating within the normal temperature range, lithium-ion batteries could undergo an exothermic reaction, resulting in a rapid temperature increase, which may lead to start smoking or catch on fire. If dropped or subjected to shock, the cell may be deformed and trigger an internal short circuit, which can lead to combustion. In the case of a multi-battery charger (one that allows the user to change the settings), it should be noted that a misbalance of cells or an incorrect charge-setting voltage can trigger an overcharge. For this reason, commercially available lithium-ion batteries must be designed with protective circuits and other safety features.

Higher battery voltage for longer flight times

The short flight time of 10 – 30 minutes presents a major challenge for the widespread use of drones for applications other than aerial photography. This is largely due to limited battery capacity. However, simply increasing battery capacity will not increase flight time beyond a certain point because the weight of the battery itself will also increase. Therefore, to further extend flight time, it is necessary to reduce the weight of the airframe and improve the performance of the battery.

Many manufacturers are working to increase the charging voltage of lithium-ion batteries and to reduce their internal resistance. Since the increase in energy per battery weight is directly related to the increase in drone flight time, there is a need for higher cell capacity, lower mass, higher density, and higher maximum power density. Extending battery life and being able to safely use batteries in a wide range of conditions are also important.

Next-generation batteries to be released in the late 2020s to 2030s aim to reach a charge/discharge cycle of 1,000 times or more and an energy density level of 400 Wh/kg. Improved battery performance will greatly increase the flight time of drones. Lithium-ion batteries that achieve high voltages of several tens of volts by connecting more than 10 cells in a single battery pack have recently been developed. When using such high-power batteries in drones, it is important to implement safety measures to prevent accidents.

High-voltage compatible secondary protection fuses for next-generation drones

Dexerials’ Self Control Protector (SCP) is secondary protection fuse that safely shuts off the circuit in the event of an overcharge/overcurrent in a lithium-ion battery (refer to this article for more information about SCPs). SCP ensures safety by cutting off the circuit when the battery is unstable and when the primary protection is not functioning properly. The role of the SCP is to immediately stop the operation of an unstable battery and safely disconnect it from the circuit.

A fuse is a protective component widely used in electrical devices. It cuts off a circuit by melting the fuse element with Joule heat in an overcurrent. However, in the case of Li-ion batteries, it is necessary to account for not only overcurrent, but overcharge. Since its launch in 1994, Dexerials’ SCP has been recognized as a standard component of secondary protection fuses for Li-ion batteries, with over 2.5 billion pieces shipped as of March 2022.

Since the electrolytes in Li-ion batteries consist of flammable organic solvent, it can lead to fire and/or explosion hazards if overcharged. Therefore, secondary protection is built into lithium-ion batteries to ensure such accidents do no occur.

When dealing with drones, shutting off the power supply to prevent over-discharge during flight could cause them to crash. Therefore, a highly robust lithium-ion battery is more suitable for drones although they are more susceptible of short-circuiting due to external shocks. To obtain the necessary performance, the cells must be connected to each other to a certain extent while preventing short circuits and to avoid accidents due to overcharging. As described in this article, safety measures can be taken by separating the charging circuit from the discharging circuit and installing a fuse only in the charging circuit. Hence, there is no need to worry about the drone crashing when the power supply stops.

As drones become more sophisticated it is certain that their battery voltages will increase. This article explains how to build a protection circuit using SCPs in high-voltage equipment. Dexerials can assist in ensuring the safety of lithium-ion batteries with its expertise as high-current and high-voltage lithium-ion batteries are increasingly being used in drones.