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Use and design of batteries

In the following article, Riccardo Ruffo from the University of Milano Bicocca discusses the development of various classes of battery technologies.
Decorative image: Five Duracell batteries, two AA and three AAA, all lying on their side

The term battery technology refers to the research, design, manufacture, use, and end-of-life processes of closed electrochemical devices, which directly convert chemical energy into electrical energy.

When using a battery, one wants to harness its energy content (Wh) within a given time, that is, by delivering a given power (W). The energy and power of a battery depend on its size and constituent chemistries.

Battery classification

From a technological point of view, batteries can be classified as follows:

  • primary (non-rechargeable) batteries
  • secondary (rechargeable) batteries.

Primary batteries

Primary batteries are not suitable for recharging once depleted. Examples of primary batteries include alkaline batteries, Leclanchè cells, and lithium batteries, which come either in cylindrical or button shapes and are available in various sizes. Primary batteries power low-cost devices with low energy requirements. Once depleted, these batteries become waste that must be properly treated.

Secondary batteries

By contrast, secondary batteries are rechargeable; their initial chemical energy can be restored using electricity from an external source. Secondary batteries must therefore fulfil a different role from primary batteries, and, in this sense, they are also called energy storage devices. This technology must be designed and developed to ensure the highest conversion efficiencies; otherwise, parasitic chemical reactions will cause a device to die after a few charge and discharge cycles. Examples of secondary batteries include lead–acid batteries, nickel–metal hydride batteries, and lithium-ion cells.

Types of batteries

Lead-acid cell

Invented by French chemist Gaston Planté in 1866, the lead–acid cell has evolved technologically to the form we find in our automobiles. Lead–acid batteries are mainly used in SLI (starting lighting and ignition) applications in automotive and as back-up systems. Their advantages include their being inexpensive, being robust, having excellent durability, and being constructed from widely available raw materials. Currently, recycling methodologies are highly efficient, and 99% of the lead from spent accumulators is recycled.

Nickel-metal hydride batteries

Nickel-metal hydride batteries were developed in the 1980s to power cell phones, laptops, and camcorders, that is, the nascent portable electronics market. In this application, however, they have been completely supplanted by lithium-ion batteries (LIBs). In any case, nickel–metal hydride cells possess favourable characteristics, such as high discharge rate and low cost, which have enabled their widespread use in first-generation hybrid electric vehicles (HEVs) for more than 10 years.

In addition, they are widely available in the market as a rechargeable alternative to primary alkaline or Leclanchè cells given their similar operating conditions. These commercial cells, which exist in traditional cylindrical forms, suffer from severe self-discharging problems and short life-time due to memory effects, resulting in a small amount of available material at the electrodes, a problem related more to the quality of the charger than to the electrochemical technology.

Lithium-ion batteries

Lithium-ion batteries (LIBs), which are extensively covered in this course, have been commercialized since the 1990s and have found immediate commercial success in portable electronic devices, contributing exponentially to the commercialization of smartphones, digital cameras, GPS devices and laptops, among others. Endowed with vastly superior performance relative to that of the other rechargeable technologies, they have recently found application in HEVs, fully electric vehicles (EVs), and other vehicles, such as electric bikes, electric kick-scooters and electric motorcycles. They are paving the way for the current revolution in mobility under the paradigm:

‘everything that can be electrified will be electrified in the next few years.’

The following image shows three cylindrical lithium-ion cells and a 2.1 kWh battery pack used in electric scooters. On the left, there are three 18650 lithium-ion cylindrical cells. The diameter and height of each cylinder measure 18 and 650 mm, respectively. On the right, there is a 2.1 kWh battery pack for electric motorcycles (scooter sharing). The pack measures 250 mm × 250 mm ×150 mm and contains 200 lithium-ion cells in the 18650 format. With the front panel being open, the cells (red cylinders), which are arranged in 8 modules of 25 cells, can be seen.

Three cylindrical lithium-ion cells and a 2.1 kWh battery pack used in electric scooters.Click to expand

© Riccardo Ruffo-University of Milano Bicocca
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