Technology has required the need for energy storage devices to become lightweight and small to accommodate a range of devices. These devices need storage devices that can store high amounts of energy that can provide for long periods of time.
High-density energy storage has become the frontier of custom battery design with manufacturers creating batteries that provide high energy density without increasing size and weight.
What is Energy Density in Batteries?
Energy density is the electrical characteristic of a battery. It evaluates the materials, chemistry, and other features to determine the energy it can provide to a device based on its volume. It is the amount of energy that can be stored, discharged, and charged for a certain amount of time.
High-density energy battery pack-ups for use when loss of power.
For batteries, energy density is measured by watt-hours per kilogram, or kilo-watt-hours. It should not be confused with power density. A battery's power density is a measurement of how much output power it can provide. Power density is measured as watt output per kilogram or kilo-watt.
Difference Between Standard Density and High-Density Battery
Standard-density batteries are cells that are standard in materials and chemistry throughout the industry. There are no changes made to increase either its size, weight, or chemistry. The specific energy density can vary based on the chemistry type.
- Lead acid: 30-50 Wh/kg
- NiCd: 45-80 Wh/kg
- NiMH: 60-120 Wh/kg
- Lithium-ion: 90-195 Wh/kg (depending on materials such as cobalt, phosphate, or manganese)
In decades past, boosting the energy density offered to a device would mean adding additional cells or increasing the weight of the battery. This aspect makes sense for energy storage since the larger the storage device becomes, the more energy it can hold as it could provide this energy for an increased amount of time. Unfortunately, this increase in size and weight would cause serious operational problems with devices that have limited amounts of available space. Also, the extra weight could make the device inoperable under certain conditions.
Custom battery pack design has made huge advancements when it comes to offering high-density energy storage without increasing the size. This feature allows for devices to operate for longer periods of time due to the large amount of stored energy in batteries. Now, battery manufacturers are shrinking the size of the batteries, such as lithium-ion, without changing the high energy density of the cells. These energy storage options provide customers with the opportunity to create smaller and more lightweight devices for portability. High density lithium-ion batteries may reach measurements of 150-220 Wh/kg.
What Determines High Energy in a Battery?
Lithium-ion batteries are considered high-energy density cells. There are several different types although all of them contain varying amounts of lithium as a characteristic. In general, most types of lithium-ion batteries have an anode of graphite or carbon with an aluminum-backed cathode and an electrolyte solution of lithium salts. Varying the types of materials for the cathodes and anodes, as well as changing the electrolyte composition, controls the amount of energy density of the cells.
Lithium titanate (LTO) batteries have the lowest energy density of 50-80 Wh/kg but have the most stable chemistry. They are expensive to make and are usually reserved for commercial applications.
Lithium cobalt oxide (LCO) has a very high energy density of 150-190 Wh/kg. The cathode has cobalt oxide. They are used for applications such as smartphones, laptops, and electric vehicles. The scarcity of cobalt for manufacturing as well as the instability of the material requires careful consideration for the battery pack and enclosure design.
To deal with the instability, manganese and nickel are added to create lithium nickel manganese cobalt oxide (NMC) batteries. These additions help with the stability of the batteries while still offering a high energy density ranging from 150-220 Wh/kg.
Safety Features for High-Density Batteries
Lithium-ion battery characteristics are considered volatile and unstable. Some issues include high temperatures and thermal runaway, which could lead to fire and explosions. When designing lithium-ion batteries to be high-density energy storage, this feature increases the amount of power that is stored, which can lead to an increase in danger during charging and discharging.
Manufacturers place several layers of protection in high-density batteries. They first limit the amount of active, unstable materials. They also place electronic protection circuits (PTC) and other safety mechanisms into the battery packs. These circuits monitor the charging and discharging states of the battery.
If there is the potential for high temperatures and pressure due to high charge cycles, a circuit interrupt device opens the circuit path. To prevent over-discharging, a control circuit cuts off the path of the current. The battery enclosure is also designed with cooling venting capabilities to control temperatures and allow for the release of gas buildup from the cell's pressure.
For shipping, all lithium batteries are categorized as hazardous materials. They must be shipped according to the hazardous goods codes of the U.S. Department of Transportation (DOT), International Maritime Organization (IMO), and the International Civil Aviation Organization (ICAO) shipping restrictions.
Future of High-Density Batteries
Currently, lithium-ion cells are at the pinnacle of high-density energy storage applications. To advance forward, manufacturers are looking to change the types of materials used to create the cells.
One option is to change the electrolyte from a liquid state to a solid state, called solid-state batteries. Solid-state batteries could offer higher densities of 2.5 times greater than lithium-ion batteries.
Another option is to switch to lithium-sulfur cells. Lithium-sulfur offers a higher energy density potential that is 4 times greater than lithium-ion while being more readily available versus cells that contain cobalt.
Summary
The frontier of high-density energy storage is continually advancing, driven by the ever-increasing demands of modern technology. Custom battery design, particularly in lithium-ion cells, has achieved remarkable feats in providing high energy density without the trade-offs of increased size and weight.
As we look to the future, innovations such as solid-state batteries and lithium-sulfur cells promise even greater energy storage capabilities, potentially revolutionizing the landscape of portable power. These advancements not only enhance the performance and longevity of devices but also open new possibilities for innovation across various industries, ensuring that our technological progress remains both robust and sustainable.
