Types of rechargeable batteries: nickel-cadmium (Ni-Cd), nickel-metal hydride (Ni–MH), lithium-ion (Li-Ion), sealed lead-acid (SLA), lithium-polymer (Li-Pol)

The following types of batteries are most commonly used in mobile phones and radio communications:

nickel-cadmium (Ni-Cd)
nickel-metal hydride (Ni–MH)
lithium-ion (Li-Ion)
sealed lead-acid (SLA)
lithium-polymer (Li-polymer)

Different types of rechargeable batteries not only vary in cost but also differ in key parameters: the number of charge-discharge cycles, maximum storage life, delivered capacity, dimensions, operating temperature range, fast charging capability, maximum discharge current, etc.

Batteries may be manufactured either as a single cell or as several cells connected in series and housed in a single case – a battery pack. Some battery models incorporate electronic control elements that ensure proper charging mode and protect the battery from incorrect operation.

As a rule, each manufacturer applies proprietary production technology and therefore develops its own design solutions for specific models. Nevertheless, several general approaches to the design of different types of batteries can be distinguished.

For example, a lead-acid battery usually consists of two plates (electrodes) placed in an electrolyte (aqueous solution of sulfuric acid).

In a nickel-cadmium cell, the negative and positive plates are rolled together and placed in a metal cylinder. The positive plate consists of nickel hydroxide, while the negative plate is composed of cadmium hydroxide. The two plates are separated by a separator impregnated with electrolyte.

A nickel-metal hydride battery is structurally similar to a nickel-cadmium battery, but it has a different chemical composition of the electrolyte and electrodes. In a lithium-ion battery, the electrodes and separator are immersed in an electrolyte based on lithium salt.

Capacity, expressed in ampere-hours (A·h, mA·h) or watt-hours (W·h), is the amount of energy that the battery can deliver to a load within one hour.

In practice, battery capacity is usually measured with a battery analyzer. For example, a rechargeable battery with a nominal capacity of 1200 mA·h delivers a current of 1200 mA for one hour.

In theory, the energy expenditure over a shorter time should be the same as in the case of a slower discharge, since the same amount of energy is delivered but over a shorter period – however, in practice this is not the case, mainly due to the finite value of the battery’s internal resistance. When discharging a battery installed in an analyzer that allows adjustment of various discharge currents, a higher amount of energy will be delivered if the battery is discharged at a lower current.

Types of Rechargeable Batteries

Nickel-Cadmium (Ni-Cd) Batteries

Nickel-cadmium batteries have been manufactured in various countries around the world since approximately 1950. Today, more than 50% of all batteries for portable equipment are nickel-cadmium.

Main advantages of this type of battery:

• low cost;
• high resistance to temperature fluctuations;
• good tolerance to high charge and discharge currents, since low internal resistance allows the delivery of large currents (other battery types cannot withstand this);
• a large number of charge-discharge cycles.

Among all battery types, the nickel-cadmium battery is the only one that best delivers maximum capacity and ensures a large number of charge-discharge cycles, provided that deep discharges (down to 1 V per cell) are periodically performed.

Disadvantages of the nickel-cadmium battery:

• the presence of the so-called “memory effect”;
• this type of battery is environmentally hazardous, as cadmium is a highly toxic substance. Additional issues also arise with its recycling;
• comparatively low specific capacity, although in many cases this may not be critical.

Nickel-Metal Hydride (Ni-MH) Batteries

They have been available on the market since the late 1980s. The primary impetus for the development and production of these batteries was their higher energy density compared to Ni-Cd.

Some of the distinctive advantages of today’s Ni-MH batteries compared to Ni-Cd:

• greater specific capacity (for the same dimensions, capacity is about 30% higher), lighter weight;
• less prone to the “memory effect”;
• contains fewer toxic metals, and is currently considered environmentally safe.

Unfortunately, the Ni-MH battery also has disadvantages compared to the Ni-Cd battery, namely:

• it has far fewer charge-discharge cycles (see the chapter on cycle life);
• the price of a Ni-MH battery is higher than that of a Ni-Cd, although this may not always be a significant issue if the user prefers smaller size and lighter weight;
• its operating temperature range is narrower than that of a Ni-Cd battery;
• compared to Ni-Cd and Li-Ion batteries, Ni-MH has the lowest load capability – it cannot deliver large currents;
• this type of battery is sensitive to deep discharges, as battery life is directly linked to discharge depth;
• self-discharge is more than 1.5 times higher than that of Ni-Cd batteries, which is an important factor during storage;
• Ni-MH does not tolerate high charging currents as well as Ni-Cd, since significantly more heat is generated during charging. In addition, a more complex algorithm is required in the charger to detect full charge than in the case of a Ni-Cd battery.

A modern Ni-MH battery is equipped with an internal temperature sensor to assist in detecting full charge. Overcharging the battery in a low-cost charger (without automatic cut-off) can lead to overheating and complete destruction of the battery.

Lithium-Ion (Li-Ion) Batteries

The production of lithium-ion batteries began in the early 1990s. Today, the largest supplier of this type of battery is Sony. The main advantage of lithium-ion batteries is their high specific capacity, at least twice that of Ni-Cd batteries.

Lithium is a very light metal with the highest electrochemical potential, providing the highest energy content.

In addition, Li-Ion has a relatively low self-discharge rate and is completely free from the “memory effect,” allowing periodic recharging of a partially discharged battery. The number of charge-discharge cycles, according to most manufacturers (each has its own technology, so the numbers vary somewhat), is slightly higher than that of Ni-MH batteries.

Main disadvantages of lithium-ion (Li-Ion) batteries:

• high cost and a narrow operating temperature range, although this is not always a critical factor;
• modern lithium-ion (Li-Ion) battery designs contain so-called smart microchips. These allow the charger to be controlled in such a way that the charging process is most efficient depending on the number of completed charge-discharge cycles.

A new type of battery – Lithium-Polymer (Li-Polymer)

The initial concept of lithium-polymer batteries is based on the use of a solid polymer-based electrolyte. This idea ensures manufacturability in production and, accordingly, a low price. The energy density of this type of battery is even higher, approximately three times that of a nickel-cadmium battery, while the self-discharge rate is significantly lower.

The use of a solid electrolyte makes it possible to reduce the thickness of battery elements to 1 mm. Since this design does not contain liquid electrolyte and is realized using layers of various films, highly flexible structural shapes can be obtained. A battery of this type has a very small thickness, which allows it to be formed into the required shape (for example, to match the shape of a mobile phone).

The disadvantage of the lithium-polymer battery is that it cannot deliver large discharge currents and, like lithium-ion (Li-Ion), it does not perform well at low temperatures.

Lead-Acid (SLA) Batteries

Unlike other types of rechargeable batteries, lead-acid batteries are typically used when large capacity is required, weight requirements are not critical, and the cost of the battery must remain low.

Advantages of sealed lead-acid (SLA) batteries:

• relatively low cost;
• complete absence of the “memory effect”;
• low self-discharge;
• in modern sealed lead-acid batteries, depending on the average depth of discharge, the number of cycles can reach 800–1000!

Disadvantages of SLA batteries:

• among rechargeable batteries, SLA has the lowest specific capacity, although in many cases this may not be critical;
• unlike Ni-Cd, SLA batteries are vulnerable to deep discharge cycles, which directly leads to a reduction in the number of charge-discharge cycles.

Additional information:

Battery internal resistance, Battery capacity, WET batteries, AGM batteries, EFB batteries, GEL batteries