Basic Knowledge of Battery -Types and Characteristics-

Battery Types and Problems

There are various types of electrical appliances around us. Except for large-sized electric appliances such as TVs and refrigerators that take power from outlets, they operate with batteries.
For example, they are smartphones, tablets and handheld music player. For large ones, such as electric cars. Many batteries are used for remote controllers for TV, air conditioners and so on. Recently, a large storage battery for home use has been developed and sold to store electrical power generated by solar panels and to be usable at night. There are also ideas to use electric vehicles as storage batteries.

Various types of batteries and rechargeable batteries are built-in these products and used properly according to the application. You can learn the types of batteries and the problems in this page.

First, we introduce the type of battery. It can be divided into primary cells such as dry-cell batteries, secondary cells (rechargeable batteries) that can be recharged and used repeatedly, and fuel cells that continuously generate electrical power by chemical reactions. The primary cell is disposable, and it generates electrical power by chemical reaction, and it cannot be used any more if there is no substance that initiate the chemical reaction.

On the other hand, rechargeable batteries can be repeatedly charged and discharged. It also generates electrical power by chemical reactions, but it is different from primary cells in the reversibility of chemical reaction. After discharging, there is no substance that undergoes a chemical reaction, "charging" can be done to return from the state after reaction to the state before reaction.

(a) This is Transfer of Electron In case of charge (b) This is Transfer of Electron In case of discharge

However, charge-discharge cycles have an upper limit, and may cause a temporary voltage drop due to memory effects.
Fuel cells generate electrical power by reacting hydrogen and oxygen. In this case, hydrogen is extracted from a hydrogen storage alloy, or liberates hydrogen contained in hydrocarbons such as methane, ethane, propane and butane in city gas, and reacts with oxygen in air. Therefore, if we can continue to provide hydrogen source materials, we can continue extracting electrical power.

Features of Each Battery

Let's introduce the features of each battery.

NiCd (Nickel-cadmium Battery), NiMH (Nickel-metal-hydride Battery)

Both NiCd and NiMH use nickel hydroxide for the positive electrode. NiCd uses cadmium for the negative electrode, NiMH uses a hydrogen storage alloy, and the electrolyte is an aqueous solution mainly composed of KOH (potassium hydroxide).
Although both NiCd and NiMH can be used for high-power applications such as motors, NiCd is being replaced with the safer NiMH because NiCd contains cadmium that caused pollution-related disease. Now, most of the rechargeable batteries are NiMH. Batteries like dry-cell, for example eneloop and evolta, are also NiMH.
As a feature of NiMH, it is resistant to repeated charging and discharging, and has high safety. On the other hand, NiMH has strong memory effect, and there is a problem that the amount of electrical power that can be generated decreases as the battery charge is continued. To reset this memory effect, it must be fully discharged and then recharged.

LiB (Lithium Ion Storage Battery)

Lithium ion storage battery is used in various products such as personal computers, smartphones and tablets. You may think that almost all LiB is used in batteries that exist around you. It is also widely expected as a battery for electric vehicles.
Since LiB has a very high energy density, about 2.5 times that of NiMH, it is an essential storage battery for reducing the weight of mobile devices such as mobile phones. In addition, since there is no memory effect, it is also an advantage that it is possible to add charge, and it does not self-discharge very much even if it is left for a long time.

Table. Self-discharge Rate of Each Battery
battery type self-discharge rate [%/month]
lead storage battery 3 to 20 %
nickel-cadmium battery 20 to 45 %
nickel-metal-hydride battery 15 to 40 %
lithium-ion battery 1 to 5 %

However, because the energy density is high, even a slight voltage fluctuation results in overcharging, which leads to extremely shortening the battery life. In addition, if overcharging or overdischarging is repeated, the internal pressure of the battery will rise, causing a burst or fire accident. You may have seen the news that smartphone has exploded and caused a major burn, or that the aircraft has exploded a battery.

Solid-state Battery

One of the problems with the above batteries is "leakage". If it is left for a long time, the electrolyte contained in battery may leak out. Leakage can cause a short circuit, and in some cases, can damage the internal circuitry.
Leakage occurs because an aqueous solution is used for the electrolyte, and to avoid this, a solid-state battery with a solid electrolyte has been developed. The advantage is that it is easy to handle, and it is less likely to cause an accident.
On the other hand, there is also a drawback. The solid-state battery developed by Toyota for electric vehicles is a lithium ion storage battery that uses a sulfide-based solid electrolyte and a layered oxide positive electrode, and currently has a volumetric energy density of only about 200 Wh/L. This is less than half. In order to extend the cruising distance, it is necessary to raise the volumetric energy density to 400 to 600 Wh/L, and its development is currently in progress.

Metal-air Battery

A metal-air battery uses oxygen in air for the positive electrode and metal for the negative electrode. It is used for small and light electric appliances such as hearing aids and kitchen timers.
Alkali metals such as Li, Na and Ca and alkaline earth metals are chemically reacted with oxygen in the air to extract electricity. Therefore, when not in use, keep it shielded to block oxygen and peel off the shield when it is used. Battery performance varies depending on the metal (element) used, and the merit is that it can be downsized because it does not require an electrolyte. On the other hand, it is difficult to develop as a rechargeable battery, because metal causes dendrite growth at the time of charging, and an infrastructure for recycling is necessary.

Fuel Battery

Fuel batteries are fundamentally different from the rechargeable batteries introduced so far. Basically, you can think of it as the same as a generator. In other words, by continuing to provide some kind of fuel, the generator is continued generating electrical power.

Though there is an impression that is not likely to be around ours, Panasonic's "ENE-FARM" is a typical example of a household fuel battery. The hydrogen that is provided as fuel and the oxygen in the air react with each other to produce water and generate electrical power. Electrical power is generated by the reverse reaction of the water electrolysis experiment conducted in science experiments.
However, since hydrogen has a high reaction rate and needs attention in handling, for example, for a fuel battery considered for mounting on an electric vehicle, it should not be accumulated even if hydrogen leaks or hydrogen does not leak to the surroundings.

Double-layer Capacitor

It is a kind of capacitor that become the focus of attention in recent years. Like a battery, it is composed of an electrode and an electrolyte, but when a voltage is applied between the electrodes (to the extent that the electrolyte does not decompose), there is a region where the charge of the electrode and the opposite sign increases around the electrode. Then, it can store potential like a capacitor, and this is called an electric double-layer capacitor.

(a) Structure of Electric typical capacitor (b) Structure of Electric double-layer capacitor

Similar to rechargeable batteries, it can be repeatedly charged and discharged, but it is characterized by its high charge and discharge speed because it only forms the electric double-layer. However, the energy density is smaller compared to rechargeable batteries.
On the other hand, the energy density is higher than ceramic capacitors, but the rated voltage is lower.

Relevant technical knowledge

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