How a Lithium Ion Battery Works

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Lithium ion batteries were conceptualized back in the 1970s by chemists who were hard at work to find a rechargeable chemistry that was more powerful and more environmentally friendly than the era’s nickel cadmium and lead-acid mainstays.

But unlike other outcrops from the late 1960s and 1970s, lithium ion batteries weren’t introduced until the early 1990s and weren’t popularly used until the 2000s. Nowadays, they’re found in anything from alarm clocks to smart phones and electric cars. The reason is simple, they pack the most punch. For every kilogram (or pound) of battery weight, you get a lot more energy than other batteries’ chemical compounds, as shown in the graph (below).

 

So if lithium can store so much more than its predecessor, why aren’t batteries getting a lot smaller? Well, they are shrinking, but they are fighting an uphill battle as phones require more and more power for advanced processors, features, and larger, brighter displays (see Battery Drains below).

For everyone who dozed through their high school chemistry, lithium ion batteries are first and foremost, well, batteries. Which means they share several aspects with all other batteries. The heart of the battery is the positively charged ion of lithium (the lithium ion) that moves around and creates the current. But first, lets discuss voltage and current.What is voltage and current? If you know this, skip to the next section, if not read on and you will probably know more than the “smart” guy who just skipped this section.

What is voltage and current? If you know this, skip to the next section, if not read on and you will probably know more than the “smart” guy who just skipped this section.

Voltage is the electrical driving force, or potential between two points. Voltage is simply the potential of electricity to flow, while current is the actual flow of electricity. Think of a bird standing on a 10,000 V power line. The bird  is completely fine, but only because each foot is at the same voltage (there is no pressure difference to cause current to flow). If the bird keeps one foot on the wire and steps onto a nearby tree branch at zero volts, fireworks begin as current flies through the bird. In this case, the current does the damage (or work), but the voltage difference causes the current to flow.  In a battery, the voltage is created by the atomic charge from the chemicals in the battery. Different batteries (and their respective chemical compounds) have different voltage. Li-on produces 3.7V per cell, alkaline cells composed of zinc and carbon generate 1.5V, where Ni-Cad and NiMH produce 1.2V per cell. Voltage, is measured in volts, named for the Italian Physicist Alessandro Volta who was credited with inventing the battery.

Current (or amps) describes the flow of electricity and is caused by electrons flowing from one point to another. Without a voltage difference, there will be no current flow. There also has to be a connection to carry the current.  In the bird example above, the tree and power wire are happy to coexist at different voltages when they are not connected. But when the branch touches the wire, or you turn on your phone, current will flow. Current does the work, but voltage causes current to flow. Current is measured in amps, short for ampere from André-Marie Ampère, a French physicist and mathematician.

Fortunately, volts and amps are standard nomenclature throughout the world. A volt is a volt in Germany, China, Swaziland, and Kentucky. Of course, they come in millivolts (mV) and kilovolts (kV), as do amps, but that is common too. A battery capacity is measured in milliamp hours (mAh) and is the number of milliamps that a battery can supply for one hour (at its rated voltage).[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/1″][vc_toggle title=”Did you know?” open=”true”]By convention, we define current as flowing from positive to negative (or less positive) voltage. But it is really negatively charged electrons that are moving, they flow from negative to positive (opposites attract). So why do we show current flowing toward the negative terminal? Well, it’s convenient, and we can because we are bigger than the electrons! Now, lets talk about how the battery works: The main functional parts of the Li-ion battery are shown (right).

The Anode: The positive half of the whole, the anode is any conductive material that stores the positive charge. Lithium ions are driven to the anode during charging. Currently, the anode is composed of lithium cobalt oxide (or LiCo02 to impress your friends). Why do we care? Because this material may be changing in future Li-ion batteries to improve capacity (see What is coming next).

The Cathode: The negative half, cathodes are any conductive material that collect positive ions during discharge to complete the circuit. The cathode is commonly composed of graphite (or carbon).

The Electrolyte: Not a mere marketing gimmick of Gatorade, the electrolyte is an organic solvent that submerges the anodes and cathodes, but allows the ions to move from one to the other.

The Separator: This is a porous plastic sheet that keeps the anode and cathode from touching and shorting, but allows ions to pass.

We will go into a bit of a deep dive here because charging significantly influences the capacity (run time) of the battery and the life (how many times you can charge the battery before it croaks).

Charging essentially occurs in two stages. Each stage lasts about one hour, so total charging takes about two hours. The stages are illustrated in the graph below which shows the relationship between charge current, voltage and resulting battery capacity (charge). While it is a complicated process, your phone controls the voltage and current so your battery is protected and not overcharged.

Li-ion batteries can be charged hundreds of times, but they last longest when they are not deeply discharged. Ideally, the battery should be operated between 40 and 80 percent charge. Leaving your phone plugged in overnight, while not a best practice, is better than letting the battery deeply discharge. The phone has protection circuitry to prevent the battery from discharging completely. However, if it does discharge because of a short (water intrusion, damage etc), the last ions through the separator blow up the tunnel because they don’t come back; the battery is toes up (dead) and must be replaced.

Stage 1:  The first stage is a constant current, increasing voltage process where the bulk of the charging takes place. The initial charge rate of a typical Li-ion battery is between 0.5 and 1C, where C is the battery capacity in mAh. So with a typical 1100 mAh phone battery, you are talking about up to 1.1 amps, which is more current than some chargers can produce (see section on chargers below). While most of the charging is done in the first hour (longer if your charger can’t supply the amperage), it is only about 70% of the capacity. It is interesting to note that even though you are dumping a lot of energy into the battery during charging, it remains cool (the battery guts that is). The phone may heat up because some circuitry is working during the charge cycle, but it is not coming from the battery itself. If the battery is getting hot, you have charging problems and may have a grenade.

Stage 2:  The second stage is a constant voltage decreasing current phase and takes the battery to full charge. It is interesting that you cannot fool nature here by increasing the charge current. Doing so does not hasten the full-charge state by much. Although the battery reaches the voltage peak quicker with a fast charge, the saturation charge will take longer accordingly. The amount of charge current applied simply alters the time required for each stage; Stage 1 will be shorter but the saturation Stage 2 will take longer. A high current charge will, however, quickly fill the battery to about 70 percent. It is not harmful to pull the charger before reaching full charge, in fact, it may be beneficial to the battery, though not your talk time.

There is no third stage, other than you unplugging the phone and texting your friends. Lithium ion batteries cannot be trickle charged like Ni Cad or Lead Acid batteries. If left in the charger for long periods, the charger will turn back on periodically to top off the battery.As mentioned earlier, all chargers are not created equal. While all USB chargers supply 5 volts, they differ in the amount of current, or amps they produce. Computer USB ports typically supply 0.5A (one half amp), which is sufficient to slow charge a phone, or power a tablet (but not charge it). To rapid charge a phone can require 1A and up to 2A for a tablet. If your charger cannot supply the maximum current, charging can take longer. So, if your phone is dead, and you only have a little time to charge it, find a wall charger, rather than your computer USB for the biggest bang for your charging minutes.

As mentioned earlier, all chargers are not created equal. While all USB chargers supply 5 volts, they differ in the amount of current, or amps they produce. Computer USB ports typically supply 0.5A (one half amp), which is sufficient to slow charge a phone, or power a tablet (but not charge it). To rapid charge a phone can require 1A and up to 2A for a tablet. If your charger cannot supply the maximum current, charging can take longer. So, if your phone is dead, and you only have a little time to charge it, find a wall charger, rather than your computer USB for the biggest bang for your charging minutes.

Multi-port charger are one of the greatest achievement of the 21st century to deal with the one-outlet provision of hotels designed in the 20th century. But beware, not all ports put out the same current. If it is a good charger, it will tell you the output power. For example 5V1A means that port can put out 1 amp and can rapid charge your phone. 5V2A means it could rapid charge your phone or tablets. Don’t worry, you will not overdrive your phone with a high current port, the phone regulates the current. Some multi-port chargers share the current between ports. So one device may get 2 amps, but plug in more and the current is divided… not good for rapidly charging all parties.

Li-ion batteries don’t like heat. Their self discharge rate increases with temperature as shown below.  In fact, Li-ion batteries age even when not being used.  But they age at a much faster rate when it’s hot, so avoid leaving your phone in a hot car all the time. It is also important when replacing a battery to make sure you are getting fresh cells. A new cell pack sitting in a hot warehouse for a couple of years could have lost half of its capacity.

Lithium-ion operates safely within the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a higher than specified voltage. Li-ion is especially exciting because the electrolyte is flammable (that’s why the airlines and postal service like them so much… not!). When overcharged, they can explode or burn, or both.

When trying to maximize battery life, it is important to know what feature consumes the most current. While it is not possible to avoid all these suckers (and still have a working phone), it is good to know what are the things that take the most juice from your battery.  Below is a list in approximate order of battery drainers:

  1.  Display backlight – minimize display brightness
  2.  GPS – turn off when not using
  3. Bluetooth – turn off when not using
  4. Wi-Fi – turn off when out of range, but turn on when in a hot spot (it reduces transmitter power draw)
  5. Out of cell range – consider turning off phone when you know you are out of coverage
  6. Skype
  7. Talking – give your friends a rest and send ’em a text instead
  8. Push Notifications and Data-Fetching
  9. Speaker phone
  10. Mobile data (Android)
  11. Apps (especially free, ad-powered)
  12. Music player – just hum to yourself

 

Lithium ion technology might be over its infancy, but it’s still wobbling around. Batteries with a cathode of vanadium phosphate appeared in 2013  and offer more voltage and longevity than those using cobalt oxide.

Iron phosphate has also been proven a far more stable, less dense, and more conductive cathode than lithium cobalt oxide, particularly when “doped” with impurities of elements like aluminum, niobium, and zirconium.

Said research means more power, less space, and better longevity. From the local dump to the Nigerian coast, that means less technological waste hazards. More importantly, it also means more capable phones.

Quantum processors are expected to require significant charge, as are other innovations like holograms, smart apparel, and bio-manufacturing plants.  More power means more processing, and the more condensed, the more portable.

In the meantime, a basic knowledge of lithium ion technology can help us make good choices. An old battery may be less of a steal than you think, so be smart when browsing your local parts store, flee market, or black market-esque van.

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