Chemistry, performance, cost and safety characteristics vary across LIB types. Handheld electronics mostly use LIBs based on lithium cobalt oxide (LiCoO 2), which offers high energy density but presents safety risks, especially when damaged. Lithium iron phosphate (LiFePO 4), lithium ion manganese oxide battery (LiMn 2O 4, Li 2MnO 3, or LMO), and lithium nickel manganese cobalt oxide (LiNiMnCoO 2 or NMC) offer lower energy density but longer lives and less likelihood of unfortunate events in real-world use (e.g., fire, explosion, etc.). Such batteries are widely used for electric tools, medical equipment, and other roles. NMC in particular is a leading contender for automotive applications. Lithium nickel cobalt aluminum oxide (LiNiCoAlO 2 or NCA) and lithium titanate (Li 4Ti 5O 12 or LTO) are specialty designs aimed at particular niche roles. The newer lithium–sulfur batteries promise the highest performance-to-weight ratio.
Lithium-ion batteries can pose unique safety hazards since they contain a flammable electrolyte and may be kept pressurized. A battery cell charged too quickly could cause a short circuit, leading to explosions and fires. Because of these risks, testing standards are more stringent than those for acid-electrolyte batteries, requiring both a broader range of test conditions and additional battery-specific tests. There have been battery-related recalls by some companies, including the 2016 SamsungGalaxy Note 7 recall for battery fires.
Research areas for lithium-ion batteries include life extension, energy density, safety, cost reduction, and charging speed, among others. Research has also been under way for aqueous lithium-ion batteries, which have demonstrated fewer potential safety hazards due to their use of liquid electrolytes.
International industry standards differentiate between a cell and a battery. A cell is a basic electrochemical unit that contains the electrodes, separator, and electrolyte. A battery or battery pack is a collection of cells or cell assemblies. These may be made ready for use by providing an appropriate housing, electrical interconnections, and possibly electronics to control and protect the cells from failure. (Failure in this case is used in the engineering sense and may include thermal runaway, fire, and explosion as well as more benign events such as loss of charge capacity.)
For example, battery electric vehicles, may have a battery system of 400 V, made of many individual cells. The term module is often used, where a battery pack is made of modules, and modules are composed of individual cells.
Anode, cathode, electrode
In electrochemistry, the anode is the electrode where oxidation is taking place in a cell, i.e. electrons get free and flow out of the cell (conventional current flowing into it). However, for rechargeable cells, the electrode where electrons flow out during discharging will become the electrode where electrons flow in during charging and vice versa, therefore the anode and the cathode will swap places when the cell switches between charging and discharging states. The less ambiguous terms are positive (cathode on discharge) and negative (anode on discharge) electrodes, which, when connected to the positive and negative terminals of a voltmeter, show a positive reading. For rechargeable cells, the term cathode designates the electrode where reduction is taking place during the discharge cycle, even though both oxidation and reduction reactions take place there, depending on whether the cell is in charging or discharging mode. For lithium-ion cells the positive electrode ("cathode") is the lithium-based one.