Lithium Ion (Li-Ion) Battery Packs
Lithium ion (Li-ion) battery packs are the preferred power source for handheld devices due to their small size and light weight. Li-ion battery packs have no “memory effect” (also known as voltage depression) , common in older cell chemistries. With a higher energy density than Nickel-based battery packs and a low self discharge rate, Li-ion battery packs have revolutionized the design of portable devices that were previously restricted by power source size, weight, and run-time limitations.
Due to the more volatile nature of Lithium versus Nickel battery packs and high energy density every Lithium battery pack is designed with special attention to safety considerations, from the design phase to volume manufacturing.
Lithium-ion is a low maintenance battery, an advantage that most other chemistries cannot claim. There is no memory and no scheduled cycling is required to prolong the battery's life. In addition, the self-discharge is less than half compared to nickel-cadmium, making lithium-ion well suited for modern fuel gauge applications. Lithium-ion cells cause little harm when disposed.
Despite its overall advantages, lithium-ion has its drawbacks. It is fragile and requires a protection circuit to maintain safe operation. Built into each pack, the protection circuit limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current on most packs is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.
Aging is a concern with most lithium-ion batteries. Some capacity deterioration is noticeable after one year, whether the battery is in use or not. The battery frequently fails after two or three years. It should be noted that other chemistries also have age-related degenerative effects. This is especially true for nickel-metal-hydride if exposed to high ambient temperatures. At the same time, lithium-ion packs are known to have served for five years in some applications.
Manufacturers are constantly improving lithium-ion. New and enhanced chemical combinations are introduced every six months or so. With such rapid progress, it is difficult to assess how well the revised battery will age.
Storage in a cool place slows the aging process of lithium-ion (and other chemistries). Manufacturers recommend storage temperatures of 15°C (59°F). In addition, the battery should be partially charged during storage. The manufacturer recommends a 40% charge.
The most economical lithium-ion battery in terms of cost-to-energy ratio is the cylindrical 18650 (18 is the diameter and 650 the length in mm). This cell is used for mobile computing and other applications that do not demand ultra-thin geometry. If a slim pack is required, the prismatic lithium-ion cell is the best choice. These cells come at a higher cost in terms of stored energy.
Lithium Ion Battery Advantages
- High energy density - potential for yet higher capacities.
- Does not need prolonged priming when new. One regular charge is all that's needed.
- Relatively low self-discharge - self-discharge is less than half that of nickel-based batteries.
- Low Maintenance - no periodic discharge is needed; there is no memory.
- Specialty cells can provide very high current to applications such as power tools.
Limitations of Li-Ion Batteries
- Requires protection circuit to maintain voltage and current within safe limits.
- Subject to aging, even if not in use - storage in a cool place at 40% charge reduces the aging effect.
- Transportation restrictions - shipment of larger quantities may be subject to regulatory control. This restriction does not apply to personal carry-on batteries. (See last section)
- Expensive to manufacture
- Not fully mature - metals and chemicals are changing on a continual basis.
Restrictions on Shipment of Lithium-ion BatteriesAnyone shipping lithium-ion batteries in bulk is responsible to meet transportation regulations. This applies to domestic and international shipments by land, sea and air. Lithium-ion cells whose equivalent lithium content exceeds 1.5 grams or 8 grams per battery pack must be shipped as "Class 9 miscellaneous hazardous material." Cell capacity and the number of cells in a pack determine the lithium content. Exception is given to packs that contain less than 8 grams of lithium content. If, however, a shipment contains more than 24 lithium cells or 12 lithium-ion battery packs, special markings and shipping documents will be required. Each package must be marked that it contains lithium batteries. All lithium-ion batteries must be tested in accordance with specifications detailed in UN 3090 regardless of lithium content (UN manual of Tests and Criteria, Part III, subsection 38.3). This precaution safeguards against the shipment of flawed batteries. Cells & batteries must be separated to prevent short-circuiting and must be packaged in strong boxes
Applications of Lithium-Ion Battery Packs
Portable Medical Equipment
- Infusion pumps
- Portable X-ray systems
- Surgical tools
- Patient monitoring devices
- Motorized beds and carts
- Muscle stimulators
- Handheld printers
- Measurement devices
- Data collection devices
- Gas detection systems
- Image capture devices
Safety and Security
- Night vision cameras
- Surveillance equipment
- Thermal imaging devices
- Wearable gas detection systems
- Personal alarms
- Ruggedized Portable communications equipment
- Ruggedized Computing devices
- Power Tools and Appliances
- Measuring equipment and Lasers
- Construction/Assembly equipment
- Mobile Phones
- Mobile Electronic Devices
- Mobile industrial Computers