For many years, nickel-cadmium had been the only suitable battery for portable equipment from wireless communications to mobile computing. Nickel-metal-hydride and lithium-ion emerged In the early s, fighting nose-to-nose to gain customer's acceptance. Today, lithium-ion is the fastest growing and most promising battery chemistry.
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Pioneer work with the lithium battery began in under G.N. Lewis but it was not until the early s when the first non-rechargeable lithium batteries became commercially available. lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest energy density for weight.
Attempts to develop rechargeable lithium batteries failed due to safety problems. Because of the inherent instability of lithium metal, especially during charging, research shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy density than lithium metal, lithium-ion is safe, provided certain precautions are met when charging and discharging. In , the Sony Corporation commercialized the first lithium-ion battery. Other manufacturers followed suit.
The energy density of lithium-ion is typically twice that of the standard nickel-cadmium. There is potential for higher energy densities. The load characteristics are reasonably good and behave similarly to nickel-cadmium in terms of discharge. The high cell voltage of 3.6 volts allows battery pack designs with only one cell. Most of today's mobile phones run on a single cell. A nickel-based pack would require three 1.2-volt cells connected in series.
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 are 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 and many manufacturers remain silent about this issue. 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 (size is 18mm x 65.2mm). 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.
The lithium-polymer differentiates itself from conventional battery systems in the type of electrolyte used. The original design, dating back to the s, uses a dry solid polymer electrolyte. This electrolyte resembles a plastic-like film that does not conduct electricity but allows ions exchange (electrically charged atoms or groups of atoms). The polymer electrolyte replaces the traditional porous separator, which is soaked with electrolyte.
The dry polymer design offers simplifications with respect to fabrication, ruggedness, safety and thin-profile geometry. With a cell thickness measuring as little as one millimeter (0.039 inches), equipment designers are left to their own imagination in terms of form, shape and size.
Unfortunately, the dry lithium-polymer suffers from poor conductivity. The internal resistance is too high and cannot deliver the current bursts needed to power modern communication devices and spin up the hard drives of mobile computing equipment. Heating the cell to 60°C (140°F) and higher increases the conductivity, a requirement that is unsuitable for portable applications.
To compromise, some gelled electrolyte has been added. The commercial cells use a separator/ electrolyte membrane prepared from the same traditional porous polyethylene or polypropylene separator filled with a polymer, which gels upon filling with the liquid electrolyte. Thus the commercial lithium-ion polymer cells are very similar in chemistry and materials to their liquid electrolyte counter parts.
Lithium-ion-polymer has not caught on as quickly as some analysts had expected. Its superiority to other systems and low manufacturing costs has not been realized. No improvements in capacity gains are achieved - in fact, the capacity is slightly less than that of the standard lithium-ion battery. Lithium-ion-polymer finds its market niche in wafer-thin geometries, such as batteries for credit cards and other such applications.
Air travelers ask the question, "How much lithium in a battery am I allowed to bring on board?" We differentiate between two battery types: Lithium metal and lithium-ion.
Most lithium metal batteries are non-rechargeable and are used in film cameras. Lithium-ion packs are rechargeable and power laptops, cellular phones and camcorders. Both battery types, including spare packs, are allowed as carry-on but cannot exceed the following lithium content:
Lithium-ion batteries exceeding 8 grams but no more than 25 grams may be carried in carry-on baggage if individually protected to prevent short circuits and are limited to two spare batteries per person.
How do I know the lithium content of a lithium-ion battery? From a theoretical perspective, there is no metallic lithium in a typical lithium-ion battery. There is, however, equivalent lithium content that must be considered. For a lithium-ion cell, this is calculated at 0.3 times the rated capacity (in ampere-hours).
Example: A 2Ah Li-ion cell has 0.6 grams of lithium content. On a typical 60 Wh laptop battery with 8 cells (4 in series and 2 in parallel), this adds up to 4.8g. To stay under the 8-gram UN limit, the largest battery you can bring is 96 Wh. This pack could include 2.2Ah cells in a 12 cells arrangement (4s3p). If the 2.4Ah cell were used instead, the pack would need to be limited to 9 cells (3s3p).
When it comes to choosing the right battery for your application, you likely have a list of conditions you need to fulfill. How much voltage is needed, what is the capacity requirement, cyclic or standby, etc.
Once you have the specifics narrowed down you may be wondering, &#;do I need a lithium battery or a traditional sealed lead acid battery?&#; Or, more importantly, &#;what is the difference between lithium and sealed lead acid?&#; There are several factors to consider before choosing a battery chemistry, as both have strengths and weaknesses.
For the purpose of this blog, lithium refers to Lithium Iron Phosphate (LiFePO4) batteries only, and SLA refers to lead acid/sealed lead acid batteries.
Here we look at the performance differences between lithium and lead acid batteriesFor more Lithium Batteryinformation, please contact us. We will provide professional answers.
The most notable difference between lithium iron phosphate and lead acid is the fact that the lithium battery capacity is independent of the discharge rate. The figure below compares the actual capacity as a percentage of the rated capacity of the battery versus the discharge rate as expressed by C (C equals the discharge current divided by the capacity rating). With very high discharge rates, for instance .8C, the capacity of the lead acid battery is only 60% of the rated capacity. Find out more about C rates of batteries.
Capacity of lithium battery vs different types of lead acid batteries at various discharge currentsTherefore, in cyclic applications where the discharge rate is often greater than 0.1C, a lower rated lithium battery will often have a higher actual capacity than the comparable lead acid battery. This means that at the same capacity rating, the lithium will cost more, but you can use a lower capacity lithium for the same application at a lower price. The cost of ownership when you consider the cycle, further increases the value of the lithium battery when compared to a lead acid battery.
The second most notable difference between SLA and Lithium is the cyclic performance of lithium. Lithium has ten times the cycle life of SLA under most conditions. This brings the cost per cycle of lithium lower than SLA, meaning you will have to replace a lithium battery less often than SLA in a cyclic application.
Comparing LiFePO4 vs SLA battery cycle lifeLithium delivers the same amount of power throughout the entire discharge cycle, whereas an SLA&#;s power delivery starts out strong, but dissipates. The constant power advantage of lithium is shown in the graph below which shows voltage versus the state of charge.
Here we see the constant power advantage of lithium against lead acidA lithium battery as shown in the orange has a constant voltage as it discharges throughout the entire discharge. Power is a function of voltage times current. The current demand will be constant and thus the power delivered, power times current, will be constant. So, let&#;s put this in a real-life example.
Have you ever turned on a flashlight and noticed it&#;s dimmer than the last time you turned it on? This is because the battery inside the flashlight is dying, but not yet completely dead. It is giving off a little power, but not enough to fully illuminate the bulb.
If this were a lithium battery, the bulb would be just as bright from the beginning of its life to the end. Instead of waning, the bulb would just not turn on at all if the battery were dead.
Charging SLA batteries is notoriously slow. In most cyclic applications, you need to have extra SLA batteries available so you can still use your application while the other battery is charging. In standby applications, an SLA battery must be kept on a float charge.
With lithium batteries, charging is four times faster than SLA. The faster charging means there is more time the battery is in use, and therefore requires less batteries. They also recover quickly after an event (like in a backup or standby application). As a bonus, there is no need to keep lithium on a float charge for storage. For more information on how to charge a lithium battery, please view our Lithium Charging Guide.
Lithium&#;s performance is far superior than SLA in high temperature applications. In fact, lithium at 55°C still has twice the cycle life as SLA does at room temperature. Lithium will outperform lead under most conditions but is especially strong at elevated temperatures.
Cycle life vs various temperatures for LiFePO4 batteriesCold temperatures can cause significant capacity reduction for all battery chemistries. Knowing this, there are two things to consider when evaluating a battery for cold temperature use: charging and discharging. A lithium battery will not accept a charge at a low temperature (below 32° F). However, an SLA can accept low current charges at a low temperature.
Conversely, a lithium battery has a higher discharge capacity at cold temperatures than SLA. This means that lithium batteries do not have to be over designed for cold temperatures, but charging could be a limiting factor. At 0°F, lithium is discharged at 70% of its rated capacity, but SLA is at 45%.
One thing to consider in cold temperature is the state of the lithium battery when you want to charge it. If the battery has just finished discharging, the battery will have generated enough heat to accept a charge. If the battery has had a chance to cool down, it may not accept a charge if the temperature is below 32°F.
If you have ever tried to install a lead acid battery, you know how important it is to not install it in an invert position to prevent any potential issues with venting. While an SLA is designed to not leak, the vents allow for some residual release of the gasses.
In a lithium battery design, the cells are all individually sealed and cannot leak. This means there is no restriction in the installation orientation of a lithium battery. It can be installed on its side, upside down, or standing up with no issues.
Lithium, on average, is 55% lighter than SLA. In cycling applications, this is especially important when the battery is being installed in a mobile application (batteries for motorcycles, scooters or electric vehicles), or where weight may impact the performance (like in robotics). For standby use, weight is an important consideration in remote applications (solar fields) and where installation is difficult (up high in emergency lighting systems, for example).
A comparision of lithium and lead acid battery weightsLithium should not be stored at 100% State of Charge (SOC), whereas SLA needs to be stored at 100%. This is because the self-discharge rate of an SLA battery is 5 times or greater than that of a lithium battery. In fact, many customers will maintain a lead acid battery in storage with a trickle charger to continuously keep the battery at 100% so that the battery life does not decrease due to storage.
A quick and important note: When installing batteries in series and parallel, it is important that they are matched across all factors including capacity, voltage, resistance, state of charge, and chemistry. SLA and lithium batteries cannot be used together in the same string.
Since an SLA battery is considered a &#;dumb&#; battery in comparison to lithium (which has a circuit board that monitors and protects the battery), it can handle many more batteries in a string than lithium.
The string length of lithium is limited by the components on the circuit board. Circuit board components can have current and voltage limitations that long series strings will exceed. For example, a series string of four lithium batteries will have a max voltage of 51.2 volts. A second factor is the protection of the batteries. One battery that exceeds the protection limits can disrupt the charging and discharging of the entire string of batteries. Most lithium strings are limited to 6 or less (model dependent), but higher string lengths can be reached with additional engineering.
There are many differences between SLA and lithium battery performance. In most instances, lithium is the stronger battery. However, SLA should not be discounted as it still has an edge over lithium in some applications, like long strings, extremely high rate of discharge, and cold temperature charging. If there is an application not covered above, or if you have additional questions, please feel free to contact us.
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