Batteries are everywhere around us. They can be found both in mobile gadgets familiar to every user and in complex backup power systems. Each of the areas uses its own type of battery, in which its characteristics are “revealed” in the best way. In this article, we will talk about the types of battery cells, areas of application and basic rules of operation.
Batteries. General principles
By historical standards, the battery is a rather “young” invention, which is a little over 160 years old. The basic principle of operation of any battery cell is the occurrence of a reversible electrochemical reaction in it, that is, when a constant voltage is applied to the contacts of a cell, electrical energy accumulates on its plates (electrodes), and when a load is applied, it is consumed. Moreover, such a reaction proceeds over a large number of charge / discharge cycles. As a rule, the possible number of recharges depends on the type of battery cell, but on average, a modern battery is capable of providing 300-1000 full cycles.
A battery is considered to be efficient if its residual capacity is 70–80% of the initial one. Elements with less residual capacity are considered unsuitable for further operation, since they cannot provide the calculated autonomy.
Whatever type of battery is, the skeleton of the structure and the basic principle of operation remain unchanged. Each battery has two electrodes (positive and negative, otherwise called anode and cathode), immersed in a special medium – an electrolyte, which is an excellent “supplier” of ions due to electrolytic dissociation.
Ion is an atom or molecule that carries an electric charge. If the ion is positively charged, it is called a cation, if it is negatively charged, it is called an anion.
Depending on the used electrode material and the type of electrolyte used, there are various variations of battery cells, each of which has its own design and operational features. Below we will talk about the most common types of batteries, their areas of application and operation features.
Lead Acid Batteries
Despite the advanced age of the technology, lead-acid batteries are still successfully used in backup power systems, automobile transport, storage systems for renewable energy sources (solar and wind energy, hydropower, etc.).
As the name implies, lead is the main material from which the electrodes are made. More precisely, for the production of positive electrodes – just lead, and for the manufacture of negative electrodes – lead oxide. The electrolyte is usually a sulfuric acid solution.
There are a large number of lead-acid battery designs to improve its performance. Since lead itself is a rather soft metal with low physical strength, in its pure form it hardly resists vibration loads, therefore, for the use of batteries, for example, in transport, calcium is added to the lead alloy, which makes the metal structure more durable.
To use a lead-acid battery in uninterruptible power supplies , in order to prevent the user’s contact with acid, eliminate the need for maintenance, and also not create conditions for the explosion of hydrogen released from the battery when it is charged, lead-acid batteries of a certain type are used. Such batteries are power supplies of the AGM type (Absorbent Glass Mat), in which a special porous glass fiber mat is impregnated with absorbed electrolyte (not liquid).
Quite often, lead-acid batteries made using AGM technology are mistakenly called gel batteries. In fact, this is not the case. Gel batteries are a separate branch of the development of lead-acid power supplies.
Batteries in which a solution of sulfuric acid acts as an electrolyte in a jelly-like state are called gel batteries. They are designed for slow energy release, so their main area of application is in inert energy storage and consumption systems (solar energy, power supply for wheelchair motors, golf carts, etc.).
The indisputable advantages of lead-acid batteries include their low cost and the ability to operate in a wide range of ambient temperatures (from -40 to + 40 ° C).
One lead storage cell produces a voltage of about 2 V and is capable of delivering specific energy at the rate of 30–60 W * h per 1 kg of mass, which, in comparison with other types, is quite small. Such batteries have high self-discharge values, and their deep discharge leads to destruction and shattering of the electrode plates and irreversible damage to the battery.
Nickel cadmium batteries
The next type of battery cells that are actively used in many areas are nickel-cadmium batteries (NiCd). They can be found in toys, control panels, flashlights , handheld cordless power tools , etc.
The design of the element has not changed, only nickel and cadmium, or rather the hydrates of the oxide of these metals, are used as a material for the manufacture of electrodes. Potassium hydroxide is used as an electrolyte. One cell based on these metals can provide a voltage of 1.2-1.35 V, and the specific energy value is in the range of 40-80 W * h / kg.
Nickel-cadmium batteries are among the most frost-resistant. They operate without a significant loss of their capacity at temperatures close to -50 ° С, moreover, they are absolutely not afraid of deep discharge, and after a charging cycle they fully restore their operational characteristics.
It is recommended to store NiCd batteries completely discharged.
The negative aspects include their low specific capacity, high self-discharge, long charging time (energy needs to be replenished with small charging currents) and a pronounced “memory effect”.
In order not to damage the battery, it must be charged only after a complete discharge! Neglecting this rule will lead to a rapid loss of capacity and failure of the element.
NiCd cells are charged with low charging currents, the values of which are about 10% of the battery capacity.
Nickel metal hydride batteries
Nickel-metal hydride (NiMH) batteries became a logical continuation of nickel-cadmium batteries. They took into account and practically eliminated the disadvantages of their predecessors. Accumulators with the same weight and dimensions have 2–3 times larger capacity, have high reliability, easily tolerate deep discharge and recharge, and are less susceptible to the memory effect.
An important role in the popularization and widespread use of NiMH elements was played by the fact that they do not contain cadmium, a metal that is very harmful to the environment. Consequently, the issues of proper storage and disposal of such elements are removed from the agenda.
For the production of the anode, nickel hydride with lanthanum or lithium is used – the so-called metal hydride electrode. Nickel oxide is used as a cathode. The electrolyte is a compound of potassium hydroxide.
Nickel-metal hydride batteries are charged with large (in comparison with NiCd-cells) currents, the values of which are about 20-25% of the battery capacity, but it is very important to control the cell temperature during charging. If it exceeds 45 ° C, the charging process must be interrupted immediately, otherwise there is a risk of damage to the cell.
The NiMH charger can be paired with NiCd cells. Backward compatibility is invalid! Nickel-cadmium charging algorithms are more primitive and can harm the NiMH cell.
Nickel-metal hydride batteries are stored fully charged. Since this type of cell is characterized by a high self-discharge, in order to maintain the performance of the cell, it must be periodically subjected to a full discharge / charge cycle.
Nickel-metal hydride batteries are used in the same areas as nickel-cadmium batteries, however, due to their increased capacity, they are readily used in photographic equipment that uses AA and AAA cells for power supply .
NiMH cells are the most frost-resistant. They can easily withstand operation at extremely low temperatures, reaching -60 ° C. For this reason, they are quite successfully used in power tools used when working outdoors in the winter.
One element generates 1.2–1.25 V EMF, and its specific energy is 60–75 W * h / kg. The theoretical calculated “ceiling” of this parameter is at the level of 300 W * h / kg, but apparently the technologies for the production of NiMH cells are not yet completely perfect.
Today’s mobile devices are hard to imagine without lithium-ion batteries. It was their development that gave a powerful impetus to the development of light and miniature solutions for power supplies, and, as a result, miniaturization of the entire segment of mobile gadgets.
The strong points of Li-ion are the high density of accumulated energy, its specific value, in most cases, is a solid 280 W * h / kg, unattainable when using another type of battery. It is for this reason that Li-ion batteries are used not only to power personal gadgets, but also to propel various scooters , bicycles with an electric motor and even cars.
For the sake of fairness, it should be said that “lithium-ion battery” is a generalized name for a whole group of electrochemical elements, in which lithium ions act as a charge carrier. The difference lies in the composition of the cathode material and the type of electrolyte.
The most widespread in the household segment are lithium-polymer batteries, in which a special solid polymer is used as an electrolyte, and the cathode and anode material are deposited on thin layers of aluminum and copper foil, respectively. Such a constructive solution allows producing batteries of any shape and size, gracefully “fitting” them into the devices being developed.
A significant drawback of a solid polymer is its poor conductivity at normal ambient temperatures (+ 25 ° C). The best performance is achieved when the temperature rises to + 60 ° C, and this is already dangerous from the point of view of normal use. Therefore, manufacturers go to small tricks, adding electrolyte to the polymer in a liquid or jelly state.
A significant difference in the design of lithium-ion batteries from the traditional design is the mandatory presence of a separator that excludes the free movement of lithium ions when the battery is not in use.
Another element that must be present in the battery circuit is the BMS controller (Battery Management System), which is responsible for the correct and balanced charging of the battery cells.
Li-ion batteries have a high specific capacity and are lightweight. It doesn’t take too long to charge them. They have practically no memory effect and self-discharge. Lithium-ion batteries do not have special requirements for compliance with charge / discharge cycles. You can charge them at any convenient time, without being tied to the value of the residual charge of the cell. It is recommended to keep Li-ion batteries half charged.
The most significant drawback of a lithium-ion cell is its categorical “unwillingness” to fully operate at low temperatures. Operating a lithium cell in the cold will very quickly bring its failure closer.