This article deals mostly with disposable lithium metal batteries – see What are Lithium-Ion batteries for more information on rechargeable lithium batteries and a full breakdown on their manufacturing process.
Basic Structure of a Lithium Cell Battery
A lithium battery is made up of an Anode (Negative) and a Cathode (Positive) immersed in electrolyte. When connected to an outside device, chemical reactions take place between the plates. These plates cannot touch or they would immediately short out the battery, so a porous separator is placed between them allowing the electrolyte to move, while keeping the plates separate.
The electrolyte can take many forms. For example in some battery designs the separator is first soaked in electrolyte before being wound into a spiral with the Anode and Cathode. In other cases a gel like electrolyte is injected after the wound plates are placed in a case.
Terminal plates are placed at the top and bottom of the battery with terminal leads acting as connectors to the Cathode (Positive Terminal) and Anode (Negative Terminal)
The line of connections can also be thought of this way:
- Cathode (Positive Electrode) connects to Positive Terminal Lead connects to Positive Terminal.
- Anode (Negative Electrode) connects to Negative Terminal Lead connects to Negative Terminal.
Shapes and sizes
One of the assets which sets lithium batteries apart, is the incredibly thin width of the plates and separator – sometimes less than half that of a human hair. This means they can be wound into a large number of shapes that are small enough to fit in a credit card or brick sized to power larger appliances.
This micro technology also makes it possible to create batteries which can quite literally bend and flex, although costs mean much of this is reserved for rechargeable lithium-ion batteries (see What are lithium-ion batteries).
Safety devices built into lithium batteries
The image above (Basic structure of a lithium cell battery) shows the essential elements needed for a lithium battery to operate. However manufacturing defects, abuse or incorrect charging can cause lithium batteries to overheat to such an extent that they can catch fire or explode.
Reputable manufacturers have recognized the need to add elements within the battery which can reduce these hazards. The image below shows some of the most common additions.
- Gasket Seal – the negative terminal is often connected directly to the battery case in effect making the entire battery case the negative terminal. The gasket seal separates the case from the positive terminal
- Positive Terminal Vents – these are simply holes in the positive terminal to let out any gases that are realeased by the pressure vent in the CID (see below)
- PTC (Positive Temperature Coefficient also sometimes referred to as the “Pressure, Temperature, Current Switch“) – if the battery becomes excessively hot this material increases in resistance effectively cutting the positive terminal off from the battery.
- CID ( Circuit Interrupt Device ) – a metal alloy element that changes shape when the temperature rises above a certain point and by doing so cuts the positive terminal off from the battery.
- Pressure Vent – malfunctioning batteries can generate large volumes of hot gases which, if not released, can cause fire or an explosion.
- CID Insulator – makes sure the tag mounting disk does not touch the Circuit Interrupt Device anywhere except at the point designed to change shape at high temperatures.
- Tag mounting disk – ensures a strong connection with the positive tab.
Pros and Cons of a Lithium Battery
- Can deliver high energy fast to devices such as cameras.
- Can operate at extreme temperatures from -40°F (-40°C) to 140°F (60°C) .
- Very long shelf life when not in use – up to twenty years on some household applications such as smoke alarms.
- Long lasting in slow drain applications – up to fifteen years for specialized medical uses such as pacemakers.
- Lighter than other batteries with comparable power.
- Consistent power (see below).
- Expensive to produce.
- Travel and shipping restrictions by air.
- Difficult to recycle.
- Low on demand power (e.g. recharging a camera flash fast)
It should be noted that although lithium batteries can be more expensive per unit than their counterparts they do last longer. This PC Mag article compared the lives of several different battery types in a digital camera with the following results:
|Duracell Ultra||Alkaline||522 shots||$0.50 per shot||1.5 volt discharge|
|Panasonic Oxyride||Nickel/Alkaline||989 shots||$0.25 per shot||1.7 volt discharge|
|Energizer e2||Lithium||2,676 shots||$0.20 per shot||1.3 volt discharge|
That doesn’t mean that the lithium battery wins hands down. The last column shows how much power the different batteries could deliver. In this situation, if you were taking rapid shots with a flash, the Panasonic Oxyride is a much better choice. The Panasonic Oxyride can deliver more to recharge the flash faster, even if it doesn’t last as long.
However, lithium batteries provide more consistent constant power than their Alkaline counterparts. Energizer compared their L91 1.5 volt 2.5 Amp battery with a similar Alkaline model and demonstrated that the capacity of alkaline batteries drops off quickly compared to their lithium model (see chart right).
In other words, if constant power is more important than high power for short periods, lithium batteries are a better choice.