Batteries & Fuel Cells
The evolution of battery technology
As a result of the increasing demand for improved capacity and smaller/lighter packages, batteries are undergoing a radical development. However, when charging or discharging an electro-chemical reaction occurs. As the size and weight of batteries decrease production tolerances and control become even more critical. Richard Poate, senior compliance manager at TÜV SÜD Product Service, a global product testing and certification organisation talks about the different chemical forms used in some of these batteries and what are their advantages and disadvantages?
handling and transporting the batteries. Due to the current demand for higher energy capacities and a more user and environmentally friendly package, the lead acid battery has undergone some significant changes. New variants of this traditional design include the Valve Regulated Lead Acid Battery (VRLA), which offer significant advantages over older technologies. The two types of VRLA batteries are AGM and Gelled Electrolyte:
Richard Poate L Traditional wet lead acid batteries
ead acid batteries have been in use for over 100 years and are an established battery technology for emergency supplies such as Uninterruptible Power Supplies (UPS). However, they can have their drawbacks in that they have limited energy density (typically 300Wh/kg) and they can also be bulky and heavy. In addition, they can be considered environmentally unfriendly if improperly disposed of at the end of their life, and they also have a relatively short cycle life (typically 250-300 cycles). Traditional lead acid batteries are a ‘wet’ design and as such, they are prone to gassing (the release of bubbles of hydrogen and oxygen from the electrolyte during excessive charging). This limits their usefulness as they can only be used vertically, and ventilation has to be provided and precautions taken when
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1. Absorbed Glass Mat (AGM) The electrolyte (acid) is absorbed into the glass mat; this means a reduced risk of spillage, making shipping and transport easier and safer. These batteries are also recombinant - the oxygen and hydrogen recombine inside the battery, and this recombining is typically over 99 per cent efficient, so almost no water is lost through electrolysis.
AGM batteries also have a very low self- discharge rate, making them ideal for more long-term usage where reliability after long periods of dormancy is needed, such as for use with UPS.
2. Gelled Electrolyte The electrolyte is a form of gel (silica additive); so there is no risk of spillage. They are also often used in UPS applications due to their slower charge rate compared to other lead acid batteries, which is necessary to prevent excess gas.
Lithium-ion In the 1970s, non-rechargeable lithium-ion batteries first became commercially available, followed 20 years later by re- chargeable batteries. The development of Li-ion technology has played a significant role in the pace of technology evolution
and today’s user demands that mobile devices and other technologies give them increased functionality with portability. Nowadays, lithium-ion batteries do not actually contain lithium metal due to its inherent instability that can lead to a rapid increase in temperature and violent venting and flaming. The electrodes are made instead from alternative materials such as lithium cobaltate (for the cathode) and graphite (for the anode).
Lithium-ion batteries have a higher energy density than other battery technologies such as nickel-cadmium (Ni- Cd) and have a small package size and weight. Unlike Ni-Cd, lithium-ion batteries do not suffer from ‘memory effect’ and they also have a low self-discharge rate which means they can be left unused for longer.
• Life cycle testing - verifies how long a battery lasts and demonstrates the quality of the battery. These tests include cycle life testing, environmental cycle testing and calendar life testing.
• Abuse testing - simulates extreme environmental conditions and scenarios to test batteries beyond limits.
• Performance testing - demonstrates the efficiency of batteries, such as performance testing under various climatic conditions.
• Environmental and durability testing - demonstrates the quality and reliability of a battery through tests including vibration, shock, EMC, thermal cycling, corrosion, dust, salt and humidity.
Where is the future? Sodium-ion batteries are under development as an alternative to lithium- ion batteries. These offer a potential advantage as sodium salts are more widely available than lithium salts, which reduce production costs.
While Li-ion batteries still have some disadvantages, these are far outweighed by the advantages. An improvement of manufacturing processes through the introduction of more robust standards, as well as increasing consumer understanding of how to respect these batteries, means that the safety of Li-ion has dramatically improved. However, while the overall failure rate of lithium batteries in use is low, safety concerns still exist, particularly in connection with their transport in aircraft. UN/DOT 38.3 details testing requirements that are now applicable to all lithium cells and batteries, and manufacturers of lithium batteries and products using lithium batteries must account for these testing requirements in the design, manufacture and distribution of their products.
Testing
Batteries must be tested at all levels, with tests that cover investigations such as electrical, chemical, corrosive, mechanical, and abuse. These include:
This chemistry also has better performance during deep discharge. Lithium-ion batteries have cathode electrodes made of copper, which under deep discharge conditions react, causing the copper electrodes to dissolve. However, with sodium-ion batteries both the anode and the cathode are made of aluminium, so this condition does not occur. Lithium-ion batteries are also more sensitive to heat, whereas sodium-ion batteries are more robust. Higher recommended charging ambient temperatures are also possible with new chemistry, and it is predicted to have potential for static urban energy storage. For example, it has already been used in e- bikes to demonstrate its potential. Other exciting developments being made in power technology are in fuel cells, which we anticipate will revolutionise power sources for both static and portable power applications. These are highly efficient, have modular construction and produce low emissions. The main difference with a conventional battery is that methane-based gas is passed through the cell. As heat and electricity are produced they are ideal for applications such as home heating and power, as well as industrial sites. Some manufacturers are even producing fuel cells small enough to be used in hand-held devices.
www.tuv-sud.co.uk Components in Electronics April 2017 15
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