How it works: delving into the anatomy of a battery
When it comes to readily available, affordable energy storage, the logical choice is lithium-ion batteries. The price of lithium-ion battery cells has declined by 97% in the last three decades, and the technology’s high energy density makes it a very attractive option, as does its scalability.
But what are the ingredients in this winning recipe? Lithium-ion cells consist of four basic components:
- The cathode, or negative electrode, which is the source of the lithium ions. The type of cathode you have determines the voltage and capacity of the battery.
- The anode, or positive electrode, which stores and releases lithium ions generated by the cathode. This allows the passage of current through the external circuit.
- The separator, which prevents contact between the cathode and the anode.
- The electrolyte, the medium through which the lithium ions move.
Lithium ions move from the cathode through an electrolyte to the anode during discharge, and back when charging. Such lithium-ion cells have a wide range of applications, and are probably most familiar to us as the devices that keep our phones and laptops running.
But when connected together in modules, they can pack a much bigger punch, suitable for utility-scale energy storage that can keep factories, commercial building and even whole communities powered up. Not all lithium-ion batteries are created equal, however.
That’s why you need to consider a range of technology attributes when assessing which is the best kind of large-scale battery for your project. As a bare minimum, you should look at the:
- Cell chemistry.
- Power electronics.
- Management software.
- Battery enclosures.
Let’s take a safari around the battery, and delve into these four essential elements, one by one.
Lithium-ion cells come in a variety of flavors, each with their own performance characteristics. The most common cell chemistries are lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese cobalt oxide and lithium iron phosphate or LFP.
As you can see, all but one of these rely on cobalt, and two on nickel. Both these elements are expensive and not always easy to source. In addition, the mining of cobalt has negative human rights and environmental implications.
LFP batteries are the exception, and in addition to having a high energy density have a long working life. Whilst other chemistries lend themselves to lighter batteries, the LFP battery is arguably one of the safest both chemically and thermically.
Unlike some other chemistries, it does not exhibit thermal runaway and is safe when fully charged, even in fairly abusive situations. LFP batteries are also safer to dispose of than lithium-ion batteries containing lithium cobalt dioxide.
LFP chemistry also offers good electrochemical performance with low impedance, thanks to the phosphate material used for the cathode.
Lithium cobalt dioxide is considered a hazardous material, as it can cause allergic reactions when exposed to the eyes and skin. It can also cause severe medical issues when swallowed. In contrast, LFP is nontoxic and thus can be disposed of more easily.
Finally, LFP chemistry also offers good electrochemical performance with low impedance, thanks to the phosphate material used for the cathode.
Not surprisingly, at Pacific Green Energy Storage Technologies we have chosen to specialize in LFP-based batteries, given their overall advantages when compared with other lithium-ion chemistries.
Power electronics are the systems designed to control and manage the flow of energy throughout an electrical system. In the case of large arrays of batteries, it is the system which controls the charging and discharging of cells.
And when those cells are stacked together in containers to provide large-scale energy storage, that power electronics system is essential to prevent overcharging and thus maintain both efficiency and safety. In addition, the power electronics system should do the following:
- Provide an appropriate regulated output voltage over a specified input voltage range and load current.
- Minimize battery size and weight, plus the overall space and mass for associated components.
- Reduce heat dissipation to eliminate the need for thermal management systems.
- Maximize available run time.
Pacific Green’s power electronics use world-class components to fulfill all these criteria, and can be optimized for different applications and configurations.
If power electronics are the nervous system of your battery array, the battery management software (BMS) is the brain, and an essential element in the overall battery management system. Management software is essential for monitoring the battery’s state, calculating and reporting secondary data.
The software plays a key role in protecting the battery and controlling its environment. Factors management software will take into account should include the following:
- The state of charge or depth of discharge, which indicates the charge level of the battery.
- The state of health and overall condition of the battery.
- The average temperature and that of individual cells.
- The total voltage, plus voltages of individual cells.
- The current going into and out of the battery.
Pacific Green’s BMS covers all these factors and more, and are optimized to offer robust reliability in both global and local applications.
Large-scale battery arrays are housed in shipping containers as standard, starting from kW/kWh systems housed in a single container up to the MW/MWh range, which combines multiple containers.
The containerized energy storage system allows fast installation, safe operation and controlled environmental conditions.
Any containerized solutions should be designed to meet the most demanding specifications and be able to cope with a wide array of adverse conditions, including high and low ambient temperature, rainfall and other precipitation and extremes of atmospheric moisture.
The container should also be mechanically adapted to integrate the air conditioning equipment necessary to maintain optimal conditions for a particular project. These solutions provide greater flexibility and robustness to renewable power production systems.
Pacific Green’s ruggedized enclosure is optimized for easy ‘drop in, switch on’ installation and operation in diverse environments. As with cell chemistry, power electronics and battery management software, the enclosure can be adapted and optimized for your project’s specific needs.