Batteries. History, technology, reality.

#Battery

Batteries. History, technology, reality.

Vasiliev Vladimir Yuryevich
Petrov Nikolay Nikolaevich,
Candidate of Technical Sciences

The article attempts to present information about batteries currently used in radio engineering equipment in a concise form.

The article is of a review nature and is intended for readers of our magazine working with batteries.

All materials used are provided with permission from Mr. Isidor Buchmann, founder and head of the Canadian company Cadex Electronics Inc., in Burnaby (Vancouver) British Columbia, Canada.

More detailed information in Russian about batteries for mobile communication equipment, computers and other portable devices, tips on operation and maintenance can be found on the page:    Batteries for mobile devices and portable devices. Condition assessment.

Sealed lead-acid batteries.

In the international interpretation, the designation is SEALED LEAD ACID BATTERY or SLA for short.

The lead-acid battery, invented in 1859, was the first rechargeable battery designed for commercial use.

Today, flooded lead-acid batteries are used in cars and equipment that require high power output.

Portable devices use sealed batteries or batteries with a regulating valve that opens when the pressure inside the case increases above a specified threshold value.

There are several technologies for manufacturing SLA batteries: Gelled Electrolite (GEL), Absorptive Glass Mat (AGM), as well as various hybrid technologies that use one or more methods to improve battery parameters.

When manufactured using GEL technology, by adding special substances to the electrolyte, it is ensured that it turns into a gelatinous state a few hours after filling the battery.

In the thickness of the gelatinous electrolyte, pores and cavities are formed, which have a significant volume and surface area, where oxygen and hydrogen molecules meet and recombine to form water.

As a result, the amount of electrolyte remains unchanged and no water top-up is required throughout the entire service life.

AGM technology uses a porous filler made of glass fiber impregnated with liquid electrolyte. The micropores of this material are not completely filled with electrolyte.

The free volume is used for gas recombination.

SLA batteries are usually used in cases where high power output is required, weight is not critical, and the cost should be minimal. The range of capacity values ​​for portable devices is from 1 to 30 A*hour.

Large SLA batteries for stationary applications have a capacity of 50 to 200 A*h.

SLA batteries are not subject to the memory effect”.

It is permissible to leave the battery in the charger on a float charge for a long time without any harm.

Charge retention is the best among rechargeable batteries.

Whereas NiCd batteries self-discharge 40% of their stored energy in three months, SLA batteries self-discharge the same amount in one year.

These batteries are inexpensive, but their operating costs may be higher than NiCd batteries if they require a large number of charge/discharge cycles during their service life.

SLA batteries are not suitable for fast charging. Typical charging times are 8 to 16 hours.

Unlike NiCd batteries, SLA batteries do not like deep discharge cycles and storage in a discharged state.

This causes sulfation of the battery plates, making them difficult, if not impossible, to charge.

Effectively, each charge/discharge cycle takes a small amount of capacity away from the battery. This loss is very small if the battery is in good condition, but becomes more noticeable as soon as the capacity drops below 80% of the nominal capacity.

This is also true to varying degrees for batteries of other electrochemical systems. To reduce the effects of deep discharge, a slightly larger SLA battery can be used.

Depending on the depth of discharge and operating temperature, an SLA battery provides between 200 and 500 charge/discharge cycles. The main reason for the relatively small number of cycles is the expansion of the positive plates as a result of internal chemical reactions.

This phenomenon is most pronounced at higher temperatures.

SLA batteries have a relatively low energy density compared to other batteries and, as a result, are not suitable for compact devices.

This becomes especially critical at low temperatures, since the ability to deliver current to the load at low temperatures is significantly reduced.

Paradoxically, the SLA battery charges very well with alternating discharge pulses.

During these pulses, the discharge current can reach a value of more than 1C (nominal capacity).

Due to the high lead content, SLA batteries are environmentally harmful if disposed of incorrectly.

Nickel-cadmium batteries.

In the international interpretation, the designation is NICKEL-CADMIUM BATTERY or NiCd for short.

The technology for producing alkaline nickel batteries was first proposed in 1899.

The materials used in them were expensive at the time and the batteries were used only in the manufacture of special equipment.

In 1932, active substances were added to the porous nickel plate electrode, and in 1947, research began on sealed NiCd batteries, in which the internal gases released during charging were recombined inside, rather than released outside as in previous versions.

These improvements led to the modern sealed NiCd battery that is used today.

The NiCd battery is a veteran in the mobile and portable devices market.

The well-established technology and reliable operation have ensured its widespread use for powering portable radios, medical equipment, professional video cameras, recording devices, powerful hand tools and other portable equipment and machinery.

The emergence of batteries of newer electrochemical systems, although it led to a decrease in the use of NiCd batteries, however, the identification of the shortcomings of new types of batteries led to a renewed interest in NiCd batteries.

Their main advantages:

• fast and simple charging method;
• long service life — over a thousand charge/discharge cycles subject to the rules of operation and maintenance;
• Excellent load capacity, even at low temperatures. NiCd battery can be recharged at low temperatures;
• Easy storage and transportation. NiCd batteries are accepted by most air cargo companies;
• Easy recovery after capacity reduction and long-term storage;
• Low sensitivity to incorrect actions of the consumer;
• Affordable price;
• A wide range of standard sizes.

The NiCd battery is like a strong and silent worker who works hard and does not cause much trouble.

It prefers fast charging over slow charging and pulse charging over constant current charging.

Improved efficiency is achieved by distributing discharge pulses between charge pulses.

This charging method, commonly referred to as reversible charging, restores the structure of the cadmium anodes, thereby eliminating the «memory effect» and increasing the efficiency and service life of the battery.

In addition, reversible charging allows for higher current charging in less time, as it helps recombine the gases released during charging.

As a result, the battery heats up less and charges more efficiently compared to the standard constant current charging method.

Research conducted in Germany has shown that reversible charging adds about 15% to the service life of a NiCd battery.

NiCd batteries are not good for being left in a charger for several days.

In fact, NiCd batteries are the only type of battery that performs best when they are periodically fully discharged, and if they are not, they gradually lose efficiency due to the formation of large crystals on the cell plates, a phenomenon called the “memory effect.”

For all other types of batteries, a shallow discharge is preferable according to the electrochemical system.

Among the disadvantages of the NiCd battery, it should be noted:

• the presence of a “memory effect” and, as a result, the need for full periodic discharge to maintain operational properties;
• high self-discharge (up to 10% during the first 24 hours), so batteries must be stored in a discharged state;
• the battery contains cadmium and requires special disposal. In a number of countries, for this reason, it is currently banned from use.

Nickel-metal hydride batteries.

In the international interpretation, the designation is NICKEL METAL-HYDRIDE BATTERY or NiMH for short.

Research in the field of NiMH battery manufacturing technology began in the seventies with the aim of overcoming the shortcomings of nickel-cadmium batteries.

However, the metal hydride compounds used at that time were unstable and the required characteristics were not achieved.

As a result, developments in the field of NiMH batteries slowed down.

New metal hydride compounds stable enough for use in batteries were developed in the 1980s.

Since the late 1980s, NiMH battery technology has been constantly improving, and the energy density of the batteries has increased.

Some of the distinctive advantages of today's NiMH batteries:

• approximately 40 — 50% higher specific capacity compared to standard NiCd batteries;
• less prone to the «memory effect» than NiCd. Periodic recovery cycles must be performed less frequently;
• less toxic. NiMH technology is considered environmentally friendly.

Unfortunately, NiMH batteries have disadvantages and are inferior to NiCd in some parameters:

• the number of charge/discharge cycles for NiMH batteries is approximately 500. A shallow rather than a deep discharge is preferable. The durability of batteries is directly related to the depth of discharge;
• NiMH battery generates significantly more heat during charging than NiCd and requires a more complex algorithm to detect when the battery is fully charged unless temperature control is used. Most NiMH batteries are equipped with an internal temperature sensor to provide an additional criterion for detecting when the battery is fully charged. NiMH battery cannot be charged as quickly as NiCd; charging time is usually twice as long as NiCd. Float charge must be more controlled than for NiCd batteries;
• The recommended discharge current for NiMH batteries is from 0.2C to 0.5C, which is significantly less than for NiCd. This disadvantage is not critical if the required load current is low. For applications that require a high load current or have a pulsed load, such as portable radios and powerful hand tools, NiCd batteries are recommended;
• NiMH batteries self-discharge is 1.5-2 times higher than NiCd;
• NiMH batteries are approximately 30% more expensive than NiCd. However, this is not the main problem if the user requires high capacity and small dimensions.

The technology for manufacturing nickel-metal hydride batteries is constantly being improved.

For example, GP Batteries International Limited manufactures NiMH batteries for Motorola cell phones with the following characteristics: number of charge/discharge cycles – 1000, no “memory effect” and no need to discharge the battery before charging.

Lithium-ion batteries.

In the international interpretation, the designation is LITHIUM ION BATTERY or Li-ion for short.

Lithium is the lightest metal and has a strongly negative electrochemical potential.

This is why lithium has the highest theoretical specific electrical energy.

The first work on lithium batteries dates back to 1912. However, it was not until 1970 that commercial examples of lithium power sources were first manufactured.

Attempts to develop rechargeable lithium power sources were made in the 80s, but were unsuccessful due to the impossibility of ensuring an acceptable level of safety during their operation.

As a result of research conducted in the 80s, it was established that during the cycling of a power source with a metallic lithium electrode, a short circuit may occur inside the lithium power source.

In this case, the temperature inside the battery can reach the melting point of lithium. As a result of the violent chemical interaction of lithium with the electrolyte, an explosion occurs.

Therefore, for example, a large number of lithium batteries supplied to Japan in 1991 were returned to the manufacturers after several people suffered burns as a result of explosions of cell phone batteries.

In the process of creating a safe lithium-based power source, research has led to the replacement of metallic lithium, which is unstable during cycling, with its compounds with other substances.

These electrode materials have several times less specific electrical energy than lithium, however, batteries based on them are quite safe, provided that certain precautions are taken during charging/discharging.

In 1991, Sony began commercial production of lithium-ion batteries and is currently one of the largest suppliers.

To ensure safety and durability, each battery must be equipped with an electrical control circuit to limit the peak voltage of each cell during charging and to prevent the cell voltage from falling below an acceptable level during discharge.

In addition, the maximum charge and discharge current must be limited and the cell temperature must be monitored.

If these precautions are observed, the possibility of metallic lithium forming on the surface of the electrodes during operation (which most often leads to undesirable consequences) is practically eliminated.

Based on the material of the negative electrode, lithium-ion batteries can be divided into two main types: with a negative electrode based on coke (Sony) and based on graphite (most other manufacturers).

Current sources with a negative electrode based on graphite have a smoother discharge curve with a sharp drop in voltage at the end of the discharge, compared to the flatter discharge curve of a battery with a coke electrode.

Therefore, in order to obtain the maximum possible capacity, the final discharge voltage of batteries with a negative coke electrode is usually set lower (up to 2.5 V), compared to batteries with a graphite electrode (up to 3.0 V).

In addition, batteries with a negative graphite electrode are capable of providing a higher load current and less heating during charging and discharging than batteries with a negative coke electrode.

The end-of-discharge voltage of 3.0 V for batteries with a negative graphite electrode is its main advantage, since the useful energy in this case is concentrated within a tight upper voltage range, thereby simplifying the design of portable devices.

Manufacturers are constantly improving Li-ion battery technology.

There is a constant search and improvement of electrode materials and electrolyte composition.

In parallel, measures are being taken to improve the safety of Li-ion batteries, both at the level of individual current sources and at the level of control electrical circuits.

Since these batteries have a very high specific energy, care must be taken when handling and testing them: do not short-circuit the battery, overcharge, destroy, disassemble, connect in reverse polarity, do not expose them to high temperatures.

Violation of these rules may lead to physical and material damage.

Lithium-ion batteries are the most promising batteries at present and are beginning to be widely used in portable computers and mobile communication devices.

This is due to:

• high electrical energy density, at least twice as high as that of NiCd of the same size, and therefore twice as small in size with the same capacity;
• a large number of charge/discharge cycles (from 500 to 1000);
• good performance at high load currents, which is necessary, for example, when using these batteries in cell phones and laptops;
• fairly low self-discharge (2-5% per month plus approximately 3% for powering the built-in electronic protection circuit);
• absence of any maintenance requirements, except for the need for preliminary charging before long-term storage;
• allow charging at any degree of battery discharge.

But there is a fly in the ointment here too: some manufacturers guarantee operation only at positive temperatures, have a high price (approximately twice the price of NiCd batteries) and are susceptible to the aging process, even if the battery is not used. Deterioration of parameters is observed after about one year from the date of manufacture.

After two years of service, the battery often becomes faulty.

Therefore, it is not recommended to store Li-ion batteries for a long time. Use them as much as possible while they are new.

In addition, Li-ion batteries must be stored charged. If stored for a long time in a deeply discharged state, they fail.

Li-ion batteries are the most expensive today.

Improving their production technology and replacing cobalt oxide with a less expensive material can reduce their cost by up to 50% over the next few years.

Lithium polymer batteries.

In the international interpretation, the designation is LITHIUM POLIMER BATTERY or Li-Pol for short.

Lithium-polymer batteries are the latest innovation in lithium technology.

Having approximately the same energy density as Li-ion batteries, lithium-polymer batteries can be manufactured in various plastic geometric shapes that are unconventional for conventional batteries, including those that are quite thin in thickness and can fill any free space in the equipment being developed.

This battery, also called «plastic», is structurally similar to Li-ion, but has a gel electrolyte.

As a result, it becomes possible to simplify the design of the element, since any leakage of electrolyte is impossible.

Li-pol batteries are beginning to be used in portable computers and cell phones.

For example, Panasonic GD90 and Ericsson T28s (GSM 900/1800 standard) are equipped with lithium-polymer batteries that are only 3 mm thick and have a capacity sufficient for 3 hours of talk time and up to 90 hours of standby time.

Fuel cells.

Motorola is currently developing a miniature fuel cell that can be used as a power battery for small computers, cell phones, and other electronic devices.

According to the company, this technology will increase the service life of batteries by 10 times.

Motorola is working on this project together with specialists from the Los Alamos National Laboratory. According to the developers, such fuel cells will go on sale in 3 years.

So far, only a prototype fuel cell has been developed.

Its area is 6.45 square cm, and its thickness is about 2.5 mm.

It uses liquid methyl alcohol, which produces an electric current when it reacts chemically with oxygen.

According to the developers, fuel cells will be able to power cell phones for more than a month, and they will weigh much less than conventional batteries.

Not all battery manufacturers provide consumers with the necessary information about the characteristics of their products.

A pleasant exception in this regard is Panasonic.

Its website provides detailed information about the NiCd, NiMH and Li-ion batteries it produces: appearance; internal structure; electrochemical reactions occurring inside the battery; features; main characteristics: charging, discharging, number of charge/discharge cycles, storage (self-discharge), safety, as well as various recommendations.

Below, with permission from LANDATA, is a table of comparative characteristics of the most common types of batteries.

Notes:

1. With proper and regular maintenance, the number of working charge cycles/can reach 4000 versus 1500 cycles guaranteed by the manufacturer. Without training cycles, the number of working cycles can decrease three times.
2. The number of working cycles depends on the depth of discharge. A small depth of discharge will provide more cycles.
3. Self-discharge practically stops after the first 24 hours after a full charge of the battery. Self-discharge of NiCd batteries is 10% during the first 24 hours, then decreases to 10% per month. Self-discharge increases with increasing temperature.
4. The built-in protection circuit consumes about 3% per month.
5. 1.25 is the voltage value of one element, 1.2 is often found in literature and descriptions. Both values ​​refer to the same element type.
6. 2.5-3.0 depending on the positive electrode material.
7. A short-term load current of up to 1C is allowed.
8. Applies only to discharge; the charging temperature range is more limited.
9. The cost value is given at the time the table was created.