How the battery works: device, principle of operation, designs

Rechargeable batteries (accumulators) are used everywhere as mobile and stationary power sources: in material handling equipment, as elements of emergency and backup power supply, are the basis for the autonomy of a huge variety of portable devices. Understanding how the battery works will help you charge your smartphone properly and extend the life of your car's battery.

Historical overview

The development of the first electrochemical cell is credited to the Italian physicist Alessandro Volta. He conducted a series of experiments with electrochemical phenomena during the 1790s and around 1800 created the first battery, which his contemporaries called the "voltaic pillar." The device consisted of alternating zinc and silver discs separated by layers of paper or cloth soaked in sodium hydroxide solution.

These experiments became the basis for the work on the quantitative laws of electrochemistry for Michael Faraday. He described the principle of operation of the battery and based on the work of the scientist, the first commercial electrical elements were created.

. Further evolution looked like this:

• In 1836, the British chemist John Daniel presented an improved cell model, consisting of copper and zinc electrodes immersed in hydrochloric acid. Daniel's cell was able to provide constant voltage incomparably more efficiently than Volta's devices.
• 1839 Further progress took place thanks to the physicist Grove with his two-liquid cell, consisting of zinc, immersed in dilute sulfuric acid, located in a porous container. The latter separated sulfuric acid from a vessel containing nitric acid with a platinum cathode placed in it. Nitric acid served as an oxidizing agent to prevent voltage loss due to hydrogen build-up at the cathode. German chemist Robert Bunsen replaced platinum with inexpensive coal in the Grove's cell and thereby promoted widespread acceptance of this type of battery.
• In 1859, Gaston Plante invented the lead-acid cell, the forerunner of the modern car battery. Plante's device was able to produce an unusually high current, but was only used for experiments in laboratories for nearly two decades.
• 1895-1905 years. Invention of alkaline elements of nickel-cadmium and nickel-iron type. This made it possible to create systems with a significant number of charge-discharge cycles.
• Since the 1930s, the development of silver-zinc and mercury-zinc alkaline batteries began, which provided a high energy density per unit of weight and volume.
• Since the mid-20th century, advances in manufacturing technology and the emergence of new materials have led to the creation of even more powerful and compact batteries. Most notable has been the emergence of nickel-metal hydride and lithium batteries on the market.

Device and principle of operation

A battery is a device that converts the energy of chemical reactions into electrical energy. Although the term "battery" denotes an assembly of two or more electrochemical cells capable of this conversion, it is broadly applied to a single cell of this type.

Each such cell has a cathode (positive electrode) and an anode (negative). These electrodes are separated by an electrolyte, which ensures the exchange of ions between them. Electrode materials and electrolyte composition are selected to provide sufficient electromotive force between the battery terminals.

Since the electrodes contain a limited potential of chemical energy, the battery will be depleted during operation. The type of voltaic cell that is adapted to be replenished after a partial or full discharge is called rechargeable batteries. An assembly from such interconnected cells - a rechargeable battery. The operation of the battery assumes a cyclical change of two states:

• Charging - the battery works as a receiver of electricity, inside the cells, electrical energy is converted into chemical changes.
• Discharge - the device functions as a source of electric current by converting the energy of chemical reactions into electrical energy.

Features of charging and discharging

The energy used to restore the capacity of the battery comes from chargers connected to the mains. To force current to flow inside the cells, the source voltage must be higher than that of the battery. A significant excess of the calculated charging voltage can lead to battery failure.

Charging algorithms directly depend on how the battery is arranged and what type it belongs to. For example, some batteries can safely be replenished from constant voltage sources. Others work only with a regulated current source, capable of changing parameters depending on the level of charge.

Improper charging can damage the battery. In extreme cases, the battery may catch fire or its contents may explode. There are smart batteries equipped with voltage monitoring devices. The main parameters to consider when using reversible galvanic batteries:

• Life expectancy. Even with proper handling, the number of charging cycles of the battery is limited. Different battery systems do not always wear out for the same reasons. But in general, the battery life is limited primarily by the number of full discharge-charge cycles, and secondly, by the design service life without reference to the intensity of use.
• Charge time. The basic design of the battery does not imply charging at an arbitrarily high speed: internal resistance a galvanic cell will convert the excess charging current into heat, which can irreversibly damage device. From a physical point of view, the charging time is limited by the maximum diffusion rate of the active material through the electrolyte. In simple terms, it can be considered that restoring full capacity in one hour is a good indicator.
• Discharge depth. It is indicated as a percentage of the rated power. It characterizes the useful capacity. The recommended operating discharge level may differ for different types of batteries. Due to changes during operation or aging, the maximum depth indicator loses its original value.

Battery types

Structurally, batteries differ depending on the purpose and on the type of electrochemical reactions occurring in them. By the way they are used, batteries can be divided into two main categories:

1. Integrated into the network. These batteries are used as a storage device that is constantly charged from the main power source and supplies electricity to the load in cases where the main source is absent or insufficient to fulfill tasks. Examples of such applications are automotive and aviation systems, uninterruptible and backup power, hybrid installations.
2. Autonomous. These batteries are designed for devices in which the battery is discharged in the same way as a conventional non-reversible battery and then recharged when it is depleted. In such cases, reversible batteries are used for convenience, cost savings (capacity replenishment is cheaper than replacement) or to power equipment beyond the capabilities of conventional galvanic cells. Batteries for most consumer electronics, vehicles, traction and cargo industrial equipment, and some stationary devices fall into this category.

In addition to the ability to recharge, rechargeable batteries, in comparison with conventional electroplating elements, characterized by high power density and good performance even at low temperatures. Depending on the electrolyte composition, electrode materials and design features, three common types of batteries can be distinguished.

Lead acid

These batteries have the longest history of popularity as stand-alone power supplies. Most of these batteries are made of lead plates or grids, where one of the grids (positive electrode) is coated with crystalline lead dioxide. The electrolyte, consisting of sulfuric acid, is involved in the reactions of lead and lead dioxide to form lead sulfate. The movement of ions of the latter forms a discharge current. Charging occurs by restoring the lead dioxide charge at the cathode by the current.

This type of battery has been in demand for over a hundred years due to the following features:

• a wide range of possibilities for both the production of high and low currents;
• reliability for hundreds of cycles in the presence of charge control;
• relatively low cost (lead is cheaper in terms of capacity than nickel, cadmium, lithium or silver);
• long shelf life for a rechargeable device;
• high voltage of a single cell;
• ease of manufacture (casting, welding, rolling).

A car battery is the most well-known lead-acid rechargeable power supply. They are widely used as traction vehicles in vans, forklifts and other vehicles. While most are portable, some can weigh several tons.

Alkaline batteries

In this type of battery, electrical energy is generated by chemical reactions in an alkaline solution using various electrode materials. The most famous of them:

• Nickel-cadmium. Capable of delivering exceptionally high currents, recharging hundreds of times, tolerant of maintenance errors. But, in comparison with lead acid, they are heavy and have a limited energy density. Their durability is directly dependent on complete discharge in each cycle. If you do not do it, the elements exhibit the so-called memory effect, which is expressed in a decrease in their capacity. They are widely used for starting aircraft engines, emergency life support systems and in combination with solar energy sources.
• Nickel-zinc. The most attractive in terms of their development. If their lifespan is significantly extended, systems of this kind could be a viable replacement for nickel-cadmium and lead-acid batteries.
• Nickel iron. Can provide thousands of cycles, but do not recharge effectively. When replenishing the tank, they noticeably generate heat and consume a lot of electricity.
• Nickel-hydrogen. They were invented primarily for the US space program. Hydrogen in such systems serves as an active anode material. Replaces nickel cadmium in many areas due to high power per volume and tolerance for quality of service. Used in electric vehicles.
• Zinc-manganese. They are used in systems that do not need a lot of electricity. The high energy density and low cost of these batteries encourages further engineering work to improve them.
• Silver zinc. Some of the most expensive. They are used where high power density, light weight and small volume are critical: in special vehicles and portable radar units.

Lithium rechargeable devices

These include batteries with a lithium anode or the use of lithium ions in an electrochemical reaction. At the time of their introduction, lithium metal batteries were promising due to their impressive potential for miniaturization, but proved to be extremely unstable due to the risk of violent chemical reactions at the anode. Therefore, the main commercial success of this type of battery took place with the use of lithium-ion technologies, the essence of which was that, together with the abandonment of the metal anode, the role of the electrolyte was assumed by complex salts lithium.

Due to its high energy density and negligible self-discharge, this type of battery is popular as a power source for consumer electronics. The main disadvantage of lithium batteries is the risk of unexpected ignition from overheating. Even the most modern of them are equipped with additional electronic control of charging and discharging processes for safety reasons. Lithium polymer batteries are more advanced in their class. Instead of a liquid electrolyte, they use a solid polymer. These batteries are lighter than conventional lithium-ion batteries., but due to the high price, they could not completely replace them.

Progress does not stand still. Now engineers and technologists are developing models of the fundamental device of the batteries of the future, which will replace the lithium-ion batteries.

The emergence of nanomaterials can give an impetus to a new round of battery evolution with such amazing modern devices with properties such as instant charging, elasticity, ultra-compactness and environmental security.