Like any other battery, a rechargeable lithium-ion battery is made of one or more power-generating compartments called cells. Each cell has essentially three components: a positive electrode (connected to the battery's positive or + terminal), a negative electrode (connected to the negative or − terminal), and a chemical called an electrolyte in between them. The positive electrode is typically made from a chemical compound called lithium-cobalt oxide (LiCoO2) or, in newer batteries, from lithium iron phosphate (LiFePO4). The negative electrode is generally made from carbon (graphite) and the electrolyte varies from one type of battery to another.
All lithium-ion batteries work in broadly the same way. When the battery is charging up, the lithium-cobalt oxide, positive electrode gives up some of its lithium ions, which move through the electrolyte to the negative, graphite electrode and remain there. The battery takes in and stores energy during this process. When the battery is discharging, the lithium ions move back across the electrolyte to the positive electrode, producing the energy that powers the battery. In both cases, electrons flow in the opposite direction to the ions around the outer circuit.
There are many different types of Li-ion batteries as determine by the different chemical composition. Changing the chemicals produces different properties. A lithium iron phosphate cell (LFP or LIFePO4) produces an electrochemical potential of 3.3V and an energy density of 120Wh/Kg Lithium cobalt oxide cell (LCO or LiCoO2) produces 3.7V electrochemical potential and 200Wh/Kg. However a LFP is very stable and extremely safe with very high rechargeable cycles of 2000+. The LCO has low thermal stability and lower life span of less than 1000 recharges. Below are some of the most common battery chemistries available. Note the lower end of the chart is the older technologies of lead acid, NiCad and NiMH. These all have much lower electrochemical potentials with 2V and 1.2V compared to Li-ion with 3.7V (LFP 3.3V).
In order to improve the efficiency and decrease the charge time of lithium-ion batteries, many companies and researchers are using nanotechnology to make better battery materials.
A lot of research is focused on using nanotechnology to make better electrodes. Using nanomaterials in the electrodes increases their surface area, which provides more places for the lithium ions to make contact. This makes the battery more efficient and also makes it recharge faster. These changes should make electronic devices that use lithium-ion batteries (e.g. laptops) lighter, and also allow them to go a longer time before recharging.
This technology, originally developed by Professor Yet-Ming Chiang and coworkers at MIT, also takes advantage of the increased surface area provided by nanomaterials. This allows the battery to go through thousands of charges, an estimated two to three times more than other lithium ion batteries, without changes in performance. In addition to the longer life, the nanophosphate batteries are much lighter than other lithium-ion batteries and charged within 15 minutes. Professor Yet-Ming Chiang was a co-founder of A123 systems which use nanotechnology in all their cells.