The introduction of lithium-ion cells was driven by the need for a lightweight rechargeable cell to power the rapidly growing market for portable electronic equipment in the 1990’s. Starting with cameras and mobile phones, the technology has become the power source of choice for everything from cordless power tools to large scale energy storage and automotive applications.
Why Choose Lithium-ion?
The high-energy density and large number of discharge cycles provided by lithium-ion cells are the most important factors, which make them indispensable in mobile phones and electric vehicles alike. However, there are many other ways in which they are superior to traditional battery chemistries. As well as the high-energy density of the cells, they are able to discharge at a higher power and can then be re-charged much more quickly. In applications where charging power or time may be limited, such as solar PV systems or stop-start cars, it is not harmful to operate lithium-ion cells continuously at partial state of charge. This gives them greater operating flexibility than lead acid cells.
The interaction between lithium-ion cells and the environment is very mild. There are no gas emissions from charging cells and heat loss, due to charging inefficiency, is very low. This means that it is possible to use lithium-ion cells in closed cabinets, completely isolated from their surroundings. At end of life the cells should be recycled but they contain no controlled toxic materials such as cadmium, mercury and lead.
Lithium-ion operation employs the same principles as any other rechargeable battery. During discharge, electrical charge moves through an external wire circuit between the electrodes of the battery. To balance the charge transfer within the cell, positively charged lithium-ions move through an internal electrolyte circuit between the positive and negative electrodes. During re-charge the process goes into reverse and lithium-ions move back through the electrolyte.
Many different types of chemical can be used to make the electrode materials which carry the lithium-ions. This is a very active area of research and development, which is promoting the use of lithium-ion batteries in an increasing number of applications. Some examples of the chemicals that can be paired together to make cells are shown below:
As each pair of materials will make a cell with different electrical properties, it is important to select the right cell for a particular application and not to mix or replace cells with different chemistries. For example, Lithium Iron Phosphate (LFP) cells combine a carbon negative electrode with an iron phosphate positive electrode to make a cell with an operating voltage of 3.2V. Four of these cells can be connected in series to make a 12Volt automotive battery, which is directly compatible with most vehicle electrical systems. This would not be possible with a Lithium Cobalt Oxide (LCO) cell, as it has an operating voltage of 3.7V.
Cell structure – The cell structure for larger capacity cells uses a prismatic design with robust metal walls. This provides the optimum combination of packing density, thermal management and protection required for industrial and automotive applications.
Battery Management Systems – Battery Management Systems (BMS) are an essential component for the safe operation of multi-cell lithium-ion batteries. The primary function of the BMS is to bring all the cells in a battery to the same state of charge and to maintain them in that condition throughout the life of the battery. The BMS achieves this by monitoring the voltages of all individual cells within a battery. Cells with higher voltages are discharged to bring them in line with the rest of the pack.
The large quantity of information collected by the BMS allows the battery condition to be monitored precisely and gives enhanced security compared with traditional battery technology. This increased intelligence also reduces the costs for maintenance and extends the operating life of battery systems.
Transportation – The transportation of lithium-ion batteries is regulated because their high energy content must be controlled with standard packing procedures. Lithium-ion batteries are Class 9 Hazardous Materials and all packaging must be labelled accordingly with the UN3480 identification number. Commercial cells must have passed the series of safety tests defined in UN Manual of Tests and Criteria Part III subsection 38.3. Certification and packaging advice can be provided by GS Yuasa Technical Services for transportation related issues.
Standardisation – Standardisation of lithium-ion batteries has evolved rapidly to reflect the growing range of application areas for this technology. For industrial uses, the main body of internationally recognised standards is provided by the International Electro-Technical Commission (IEC). Cell and battery performance standard requirements are contained in IEC62620 (2014). Safety standard requirements are contained in IEC62133-2 (2017) for portable appliance applications and IEC62619 (2017) for industrial systems.
Benefits of Lithium-ion Batteries
1. High-rate discharge with consistent capacity
2. Fast Charging
- Lithium-ion Battery – Re-charge within 1 hour
- Lead Acid Battery – More than 9 hours
3. Small footprint and floor loading
4. Long cycle life and energy throughput
- Lithium-ion Battery – 50Ah capacity, 25000Ah throughput
- Lead Acid Battery – 100Ah capacity, 5000Ah throughput
5. High energy efficiency
- Lithium-ion Battery – 4% heat loss with 96% output
- Lead Acid Battery – 15% heat loss with 85% output
6. Partial State of Charge excellence
7. Power Security
- Lithium-ion Battery – Battery Management Systems detect failures and communicate information
- Lead Acid Battery – No information
8. Wide charging temperature range – without voltage compensation
9. Lower cost thermal management
- Lithium-ion Battery – Air circulation acceptable
- Lead Acid Battery – Air conditioning required
10. No gas emission
- Lithium-ion Battery – Operates in sealed container
- Lead Acid Battery – Hydrogen ventilation required
11. Non-toxic with no recycling restrictions