Lithium-Ion Information Guide

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Technology Profile

Battery packs built to customer specifications using Lithium-Ion and Lithium-Polymer cells have been Designed and Developed at SWE for over 20 years. SWE has invested extensively in acquiring technology and creating intellectual property associated with development of battery packs and battery systems that utilize Lithium-Ion and Lithium-Polymer chemistry. SWE participates with the intellectual community in sharing technical advances via international battery technology conferences and technical journals. SWE has produced a number of patents directly related to the control of Lithium-Ion batteries and has various related trade secrets – some of which are being considered for future patent applications.  SWE has reduced to practice all of this intellectual property in delivered products used in above-ground, down hole and subsea applications.

Introduction To Lithium-Ion

Lithium-ion batteries have advanced to the level where there are very few applications that cannot take advantage of the excellent cycle life, power & energy density and wide operating temperature range inherent in Lithium-ion technology. Lithium-ion batteries are also Environmentally Friendly.

Lithium-ion batteries are common in consumer electronics. They are one of the most popular types of battery for portable electronics, with one of the best energy-to-weight ratios, no memory effect, and a very slow loss of charge when not in use. In addition to consumer electronics, smaller versions of lithium-ion batteries can be found in specialty applications ranging from human implantable cells to various satellites, to hybrid vehicles and military craft.  Lithium-ion batteries are growing in popularity for defense, automotive, and aerospace applications due to their high energy density.

Recent advances in Battery Management System (BMS) electronic technology for the Lithium-Ion battery and new modular design concepts for construction of complex battery systems have resulted in battery systems which are safer, more robust, more flexible, longer life, and easier to charge and maintain. Pack protection circuits (PTCs), shutdown separators, etc. (developed for mass consumer use) provide several layers of safety not available in other chemistries.

All cells sold by SWE are qualified by the manufacturer to UL 1642 requirements.

Lithium-Ion Battery Transportation Safety

Until 2003, there were no DOT restrictions on transportation of Li-Ion cells or batteries. However, beginning in 2003/2004, the DOT required battery packs to pass new DOT tests. This requirement is exempted for prototype battery packs.

Lithium-Ion Battery Features

Lithium-Ion batteries can be customized to customer needs for size, fit, and performance. Lithium-Ion batteries have a high ENERGY DENSITY (weight to size ratio).

VOLTAGE PER CELL: Lithium-Ion batteries have a nominal voltage of 3.7 volts per cell. By using the cells in series, a battery pack can have any voltage possible in 3.7 volt steps. Ex. Lithium-Ion batteries use 3 cells to provide an 11.1 volt battery, 4 cells to provide a 14.8 volts battery or 10 cells to provide 37 volts battery.

CAPACITY: Lithium-Ion cells are place in parallel to provide the amount of amp-hours (Ah) required. The Ahs can range from a few amps to hundred of amps, depending on the application requirement. Ex. Lithium-Ion batteries use three 2.6Ah cells in parallel will produce 7.8 Ah or use ten 2.6Ah cells in parallel to produce 26 Ah. There a number of cells with high Ah rating that can be used to provide you with the CAPACITY that is required for your application.

MAX CHARGE RATE: Lithium-Ion has a nominal Maximum Charge rate of 1C and Lithium-Polymer of 2C. There are cells that have charge rates up to 10C. By selecting the correct cell you can have a Lithium-Ion battery pack that will meet your requirements.

CHARGE TECHNOLOGY: Lithium-Ion batteries using a typical Pack Protect circuit have a complex charging profile and only a charger that was design for that battery should be used. But if you use the SWE BMS (Battery Management System) with the Pulse Charging on board you will need only a simple DC power supply with constant power to charge the battery pack, or connect it directly to a Solar panel with only an isolation Diode. In other words, no special Li-Ion charger is necessary, thereby reducing the cost of the system.

MAX DISCHARGE RATE: Lithium-Ion has a Maximum Discharge rate of 2C and Lithium-Polymer at 3C (Note: there are selections of Lithium-Polymer cells that have discharge rates greater than a 30C rate).

DISCHARGE TEMPERATURE RANGE: Lithium-Ion and Lithium-Polymer have a limit of discharging from -20C to 60C. SWE has selected Chemistry and empirical data with an increased limit on discharging down to -50°C.

STORAGE: Recommended temperature range for storage: -20°C to 60°C (storage at temperatures below 20°C reduces permanent capacity loss).Recommended voltage range for short term storage is 3.0 to 4.2 V per cell in series.Prolonged storage periods: Store Li-Ion batteries at about 75% capacity (3.85 V to 4.0 V) and at low temperature to reduce permanent capacity loss over long storage periods.

PRECAUTIONARY NOTES: Lithium-Ion cells have very high power and energy density. Exercise common sense precautions when handling or testing. DO NOT replace individual cells or modules, or combine this battery in series or parallel with other batteries as this may present a risk of fire or explosion.

CAUTION: Lithium-Ion batteries may present a risk of fire or chemical burn if mistreated. DO NOT short circuit, overcharge, crush, mutilate, nail penetrate, reverse polarity, disassemble, expose to temperatures above 100°C (212°F), or incinerate.

DISPOSAL: Lithium-Ion batteries do not contain materials that harm the environment; therefore, there are no disposal rules or restrictions. Lithium-Ion batteries can be recycled to recover the relatively expensive cobalt contained in the Cathode. At end of life, dispose of the used battery safely. Keep away from children.  Do not disassemble and do not dispose of in fire.

SWE Li-Ion Battery Management System (BMS)

SWE has a variety of BMS’s to meet customer needs, from a 1 series pack to 10 series pack. The BMS’s can be stacked in Series to meet requirements for voltage and placed in parallel to provide the current requirements.

Battery Pack Protection: The BMS provides the following: Battery Overcharge Protection (Most critical), - Battery Over-discharge Protection, - Discharge Over-current Protection, - Charge Over-current Protection, - Load short-circuit Protection, and Inhibit 0V charging condition.

Charge Management: Charge Temperature Monitoring: - Pulse charging on board and Charge control can be set to a percent of capacity per customer requirement.

Fuel Gauge: Accurate Battery Fuel Gauging, - Cell Temperature monitoring, and Industry standard serial bus Protocols. SMBus, I2C, RS485, and others.

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Recommended Max Currents:  8 Amps continuous, up to 20 Amp pulse for 30ms. (Note: 5 series to 10 series BMS an addition 4 current booster PCAs of 16 Amps per can be added allowing a total of 72 Amps per BMS.)

Cell Balancing: Each module contains cell balancing circuits to balance the series connected sections during charge or continuous balancing.

SUMMARY DESCRIPTION: The BMS provides necessary protection against Overcharge, Over-discharge, and abnormal charge, discharge current and short-circuit load.

The integrated Pulse Charge Management enables end-user to utilize a simple DC power supply with constant power to charge the battery pack or connect direct to a Solar panel with only an isolation Diode. In other words, no special Lithium-Ion charger is necessary there-by reducing the cost of the system. Charging is also inhibited outside a pre-set temperature window, typical, 0°C to 45°C charging.

Lithium-Ion batteries do not have to be frequently fully discharged and recharged ("deep-cycled"), but this may be necessary after about every 30th recharge to recalibrate any electronic "fuel gauge" if used. This prevents the fuel gauge from showing an incorrect battery charge.

Lithium-Ion Battery Storage

The speed at which a Lithium-Ion battery ages is governed by temperature and the state-of-charge. Lithium-Ion batteries should be kept cool. Ideally, they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. 

The recommended Battery systems storage temperature is room temperature or colder. The batteries should be monitored and recharged as required. Typically, the battery should be checked every 90 days to determine whether the pack should be recharge or not.

Lithium-Ion batteries should never be depleted to below their minimum voltage, 2.4 V to 3.0 V per cell.

Like all rechargeable batteries, Lithium-Ion batteries should be charged early and often.  However, if they are not used for a long time, they should be brought to a charge level of around 80% or less depending on the energy of the pack and the length of storage time.

A Lithium-Ion battery will lose storage capacity if it is kept at 100% state of charge during storage.

Depending on the design and chemistry of your lithium cell, you may see them sold under different nominal "voltages". For example, almost all lithium polymer batteries are 

 or 

batteries. What this means is that the 

 voltage of the cell is 

 and that the "nominal" (average) voltage is 

. As the battery is used, the voltage will drop lower and lower until the minimum which is around 3.0V. You should see the number 

 written on the battery itself somewhere.

For example, here is a profile of the voltage for a 'classic' 

 battery. The voltage starts at 4.2 maximum and quickly drops down to about 3.7V for the majority of the battery life. Once you hit 3.4V the battery is dead and at 3.0V the cutoff circuitry disconnects the battery (more on that later.

You may also run across 

 batteries. These are older than 4.2V/3.7V - they use a slightly different chemistry and you'll see the 3.6V marking on the cell.

Nowadays you may also be able to purchase 4.35V cells! These are the latest chemistry, they have a little more power as indicated by the voltage being higher than 4.2V. They tend to be cylinder lithium ion's used for laptop batteries, and lights so its not terribly likely you'll just run into one unless you're looking for it.

Make sure when you're buying batteries and chargers to match them up! Overcharging a 3.6V battery by attaching it to a 4.2V battery charger can at the very least permanently damage your battery and at worst cause a fire!

Important Note! When charging batteries you must make sure that the charger voltage is less than or equal to the battery voltage. For the best battery performance/life you should have them matched. For example: 3.7/4.2V battery and 3.7/4.2V charger: OK - 3.7/4.2V battery and 3.6/4.1V charger: OK (but not ideal) - 3.6/4.1V battery and 3.6/4.1V charger: OK - 3.6/4.1V battery and 3.7/4.2V charger NOT OK!

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