Electrochemical sensors, which I have been researching since my student days, are a specific molecule detection system in which the chemical change that accompanies the molecular recognition of a chemical substance is converted into an easily processed electrical signal. It is similar to battery mechanisms in which electricity is generated by converting the energy change from a chemical reaction into electrical energy, or stored by the opposite reaction.
Most sensors deal with a chemical reaction that has a minute energy change, so long as the signal converted to electrical energy is big enough to enable signal processing or detection. Batteries, however, need to produce a lot of electrical energy and so take a different approach, selecting and utilizing a chemical reaction with a greater energy change and converting all that energy efficiently into electrical energy.
Since the 2011 Great East Japan Earthquake, hopes for the introduction of new energy technologies have grown. Batteries are one area of focus, but how much can we really expect of them? I would like to consider the actual situation and challenges involved.
Use of environmentally friendly energy
In the rolling blackouts caused by the shutdown of nuclear power plants in the aftermath of the 2011 Great East Japan Earthquake, many people were temporarily forced to live without electricity, having to use candles to light their homes, cook on gas stoves, and so on. The experience made people aware of our dependence on electricity and raised feelings of insecurity about interruptions to the electricity supply. Meanwhile, witnessing the damage done in Fukushima by the nuclear accident has made us look once again at the possibility of other forms of power generation. Thermal power generation, which is heavily used at present, relies on the import of most of our energy resources and, being the primary cause of carbon dioxide emissions, goes against worldwide decarbonizing efforts aimed at reducing the burden on the global environment.
The above has led to expectations for the use of renewable energies in the form of new energy technologies that cut carbon dioxide emissions. However, when we think about the use of renewable energies such as wind energy and solar power, there is still the question of balancing. Balancing, or equalizing the electrical supply and electrical demand, is necessary for stabilizing the electrical frequency provided by electrical energy. One reason for this is that energy cannot be stored for a long time in the form of electricity.
When using renewable energies, which are dependent on the weather, supply and demand amounts need to be regulated using other new energy technologies. Considering technologies with high conversion efficiency that enable storage of energy exceeded by instantaneous increase in energy supply, a leading candidate is the storage of energy as chemical energy using batteries.
Problems with using batteries
There are two main uses of batteries in new energy technologies, use as stationary batteries and use as distributed energy on board vehicles. In both cases, for an increased use of batteries there is the challenge of lowering resource limitations and costs while sustaining high-energy density, but I’d like to put those to one side for now and talk instead about the big problem of improving safety.
Are batteries one hundred percent safe?
Readers will probably remember the incidents onboard Boeing 787 aircraft in January 2013 when lithium ion batteries used to start the auxiliary power unit and as an emergency backup caught fire.
Lithium ion batteries are commonly used as secondary batteries for mobile devices because of their high energy density, the amount of energy stored per unit volume or unit weight, but they are expected to play active parts in automobiles, aircraft and stationary energy storage facilities.
There have also been reports of lithium ion batteries in mobile phones and other mobile devices catching fire (causing burn injuries etc.), but the total quantity of stored energy is greater in batteries used for automobiles, aircraft and stationary energy storage facilities.
Energy is the capacity of an object to do work. Of course there is a greater danger from operational mistakes when a large amount of energy is stored. We know that lithium ion batteries can undergo an exothermic reaction due to overvoltage, overcurrent, short circuit between electrodes, and so on, and when the temperature of a battery exceeds a certain point it triggers a chain reaction that causes the battery temperature to rise even higher, a state known as thermal runaway. Thermal runaway can also lead to fire because the organic solvents practically used as electrolytes in consideration of ion-conduction, are ignitable.
According to a report issued in February 2013 by the US National Transportation Safety Board, there is a strong possibility that these accidents occurred because of a short circuit among the lithium ion battery cells leading to thermal runaway, which then spread to other cells and caused a fire.
The batteries were required to be installed in such a way that thermal runaway could not spread between cells. However, the batteries are connected to an electrical system that is not all manufactured by one company, and so as of May 2013 it was still difficult to clarify the cause of the fires. Nevertheless, the incidents have taught us the following things.
Because of the remote possibility of the unexpected happening, systems must be built which decrease the probability of accidents endangering human life. Recent material research has been done into electrolytes that have less ignitability or liquidity, electrode materials and separators that do not easily cause short circuits, and so on. Added to this, demand is increasing for research and development of systems for predicting and avoiding triggers for incidents such as cell short circuits. I think it is also important to understand the effects of the operating environment and take measures accordingly. For example, aircraft and automobiles obviously have different environments. Their external air pressure and its variations are distinctive, and their vibration levels are different too. To widen the assumption, basic research into the influence of environment of batteries on their is needed to prevent the repetition of mistakes. But that is not enough. Measures taken after any unexpected event must be prepared. Recently, there has been research into mechanisms of absorbing excess energy with another organic compound reaction (using redox shuttle material, etc.) just in case the circuit design for preventing overcharge fails to work. It would be a smart move to take measures not only on the outside of the electric cell but on the inside too. All of the above shows that it is pertinent to have multi-layered insurance for batteries and their peripheral devices in consideration of the operating environment. Such thorough preparatory measures have long been one of our country’s strengths, and I wish Japan could demonstrate leadership in this area.
My aim is to improve the performance of electrochemical systems such as batteries through material research using electrochemical analysis and nanotechnology, and to contribute to the establishment of application technologies (such as battery safety diagnostics) based on the analytical data. In the electrical related departments of Japanese universities nowadays, there are hardly any researchers who specialize in the electrochemical field, and who understand the chemistry and cover from material fabrication to analysis.
I intend to take full advantage of the environment in Chuo University’s Department of Electrical, Electronic, and Communication Engineering with its wide range of experts, as its name suggests, and to conduct research and development that also considers the peripheral technologies.