Lithium-Ion and Other Cell Chemistries 81 5.0 4.0 Voltage (Li+/Li) 3.0 2.0 1.0 0.0 0 500 1000 1500 Capacity (mAh/cc) 2000 2500 3000 Commercialized Pre-commercialization Stage Research Stage Figure 6 Anode material performance comparison. major hurdles that need to be addressed before they can be commercialized. For instance, both tin and silicon cause a volumetric growth of between 250 and 300% during cycling which causes reduced cycle life. Today, these are all still in the early development stages but there is good hope that in the not-too-distant future we will be able to overcome some of the obstacles to make these anode chemistries realities.
Separators The next component within the lithium-ion cell for us to consider is the separator. A separator is a thin piece of material, often a plastic or ceramic, which separates the anode from the cathode. In use, the separator material must be able to withstand the often corrosive hydrocar- bon (HC)-based electrolytes that are used in lithium-ion cells while still maintaining the isolation of the two electrodes within the cell. The main purpose of the separator is to do just that, to separate the anode from the cathode. If the two halves of the electrode come into contact, an internal short circuit will occur, causing a cell failure.
Therefore, the separator is of key importance in any lithium-ion cell design. Some cells use a multilayer PP or PE plastic to separate the anodes and cathode. This material allows the lithium-ions to pass from anode to cathode while still protecting the cell from short circuiting. Some cell manufacturers use a trilayer PP/PE/PP in order to allow the middle layer to melt at higher temperatures ( 135 °C) while still ensuring the separation of anode and cathode by ensuring that the outside PP layers do not melt until they reach a higher tempera- ture ( 155 °C).
At high temperatures, the pores in the PP begin to melt which prohibits the Anode m Anode m aterial Li 4Ti 5O 12 Sn-Me Li 2.6Co 0.4N Si-Me La Co Sn 3 2 7 HC SiO Li C Si