In this current series on lithium cell manufacturing we are going to be looking at the processes that are used to construct a lithium battery cell. These processes are highly technical and require complete precision in order to make an individual battery cell function according to the specific power demands of the device that the cell will ultimately be used within.
On a macro level when we look at a battery we see completed unit (which we call a battery) however the battery is actually an assembled collection of material and hardware. The outside plastic cover is called the casing. The casing encloses and hermetically seals the battery cell and specialized hardware. Battery casing is manufactured in layers. The casing layers are developed from various raw materials and can include one or two, for example, of polyethylene terephthalate layers, a polymer layer, and a polypropylene layer. Another example may be a casing with layers of carbonized plastic.
Within the casing is the hardware and the battery cell. When we look inside a lithium based battery cell, for example, there are four main components and they include:
- The lithium (which acts as an anode)
- The metallic oxide cathode
- The electrolyte
- The metallic current collector
As noted above lithium within the battery cell is used as the battery’s anode. The anode is the part of the cell that acts an electrical conductor (electrode) through which electrical current flows into a polarized device. As current flows into the lithium, a chemical process called intercalation occurs. Intercalation is the joining of a molecule (or molecule group) between two other molecules (or groups). When it comes to charging your battery you are in effect pushing ions in and out of solid lithium compounds. These compounds have minuscule spaces between the crystallized planes for small ions, such as lithium, to insert themselves from a force of current. In effect ionizing the lithium loads the crystal planes to the point where they are forced into a current flow. The current flow is then channeled back and forth from anode to cathode and thereby creating an electrical flow to power on your device.
To create an electrical flow from lithium you have to move the lithium. To move the lithium chemistry (lithium-ion, lithium polymer, lithium iron phosphate, etc) you have to have a minimum voltage applied to the lithium. Most battery cells are charged up to 4.2 volts with relative safe workings at about 3.8 volts. Anything less than 3.3 volts will not be enough to charge or move the chemistry. One thing to note here is that volts are an algorithmic measurement of current. So in a sense to create current through your battery you have to introduce current into your battery’s lithium.
The Metallic Oxide Cathode
The cathode is an electrode (electrical conductor) by which electrical current flows out of a polarized electrical device. The metallic oxide component of the cathode is the composition of the cathode. Metal oxides are crystalline solids that contain a metal cation (an ion with more protons than electrons)and an oxide anion (an ion with more electrons than protons).
In the battery cell the electrolyte solution is the conducting medium in which the flow of electric current passes through between the electrodes. Electrolytes can be wet, solid, gel, or dry. Dry polymer design offers simplifications with respect to fabrication, ruggedness, safety and thin-profile geometry. Dry polymers do not conduct electricity but allows for ion exchange. The real benefit is the fact that the dry polymer design is only one millimeter (0.039 inches) thick. The drawback is that the dry polymer design suffers from poor conductivity. Today lithium hexafluorophosphate and tetrafluoroborate are the preferred electrolyte salts for lithium batteries.
The Metallic Current Collector
A current collector is an inert structure of high electrical conductivity used to conduct/transmit current from or to an electrode during discharge or charge. There a variety of metal based current collector from zinc to liquid metal that can provide a good conductive path between the electrodes.
From the above we can see that a battery cell, being just one component of a battery is a highly complex system. As we move into the next portion of the series we will break down each of these 4 key components of a battery cell and see how they are actually made.
Until next time, Dan Hagopian – www.batteryship.com
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