Lithium-ion – A lithium atom that has an electron removed, leaving the atom in an electrically positive charged state. The size of the lithium ion allows it to readily migrate though the cell’s electrolyte and between electrodes – its travel direction based whether it is being charged or discharged. Lithium-ion (Li-ion) cell – any storage system that depends on this lithium ion storage and transport principal which supports repeated energy charge, store, discharge and recharge. Li-ion cells: Chemistry – there are many (patented) chemistries and nanostructures, broadly identified by nomenclature describing the cathode electrode’s dominant active component - where the Anode is typically graphite (carbon) based. The exception is the LTO (below) where the name defines the anode, the cathode usually being one of the other materials described.
● ● Lithium nickel cobalt aluminium oxide (NCA) ● ● Lithium nickel-manganese-cobalt oxide (NMC) ● ● Lithium cobalt oxide (LCO) ● ● Lithium manganese oxide (LMO) ● ● Lithium iron phosphate (LFP) ● ● Lithium titanate (LTO)
These chemistries offer different price-performance options (including temperature sensitivity, internal resistance, storage density, charge/discharge rates, longevity, stability…). This makes generalisations about their use problematic, especially as various users of these batteries (Tesla, Toyota, etc). However, some examples are: ● ● Tesla use NMC and NCA (EVs and storage) cylindrical.
● ● BYD (EVs and buses) use LFP cylindrical. ● ● Chevrolet EVs use NMC/LMO hybrid pouch.
Li-ion battery Cells: Structure – two separated electrodes (cathode and anode) are embedded in an electrolyte. These electrodes act to transport the electrical current into and through the electrolyte to provide storage and discharge. Lithium is in the electrolyte as a lithium salt. There are many cell architectures that are designed to meet specific functional requirements. These include: ● ● Cylinder – similar to traditional “disposable” batteries, these combine structural integrity and energy storage in one device by (effectively) rolling ribbons of cathode, separator, electrolyte and anode into a “swiss roll” and sealing it in a container (Panasonic); ● ● Prismatic – Instead of rolling the ribbons of cathode, separator, electrolyte and anode into a cylindrical shape, they are structured into a “flat pack” allowing them to be designed to fit particular installations. This flat design may be achieved by folding continuous electrodes (i.e. Samsung) or multiple layering of electrodes (LG Chem). ● ● Button – a sandwich of electrodes, separator and electrolyte into a standard shape device suitable for watches, remotes, etc. ● ● Pouch cell (often called lithium polymer) – the evolution of a layered design into a lightweight package enabled by improvements in production technology.
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