Seite - 111 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 1314 3.BatteryDiscussion Batterieshavebecomean indispensableproduct insociety; theyarebeingused inavarietyof products rangingfromcellphonesuptoelectricvehicles. Themostpopularbattery technologiesare the lithium-ionbatteriesdue to theirhighenergy-andpower-densityaswell as theirhigh lifetime comparedtoother types [29]. Theelectrochemical storageofenergy ina lithium-ionbattery isachievedthroughintercalation in thepositiveandnegativeelectrode, shownbyEquation(1) [30]. Li++e−+θ←→Li−θ (1) With: θ The insertionmaterial θ−Li Lithiuminserted inmaterialθ e− Anelectron Li+ Alithium-ion Figure3.Schematic illustrationof thecharge/dischargeprocess ina lithium-ionbattery, reproduced from[31]. The functioning of a lithium-ion battery is summarized below; however, a more extended explanation can be found in literature, for example [32,33]. The intercalation of lithium-ions in the electrodes is themain reason for its long lifetime of this type of batteries. However, lithium undergoesnumerousside-reactions, reducingtheconcentrationof lithiumavailable for intercalation, causing thebattery todecrease in capacityover lifetime. Aschematic illustrationof a lithium-ion battery’s functioning is showninFigure3. Abatteryconsistsof fourmaincomponents: anegative electrodeoroftencalledananode,apositiveelectrodeoroftencalledacathode,anelectrolyteand aseparator. Thevarietyandpropertiesofseveralanodesandcathodeswillbediscussedinthenext sectionsexcept theseparatorandelectrolytesince inmostcasecommerciallyavailableonesareused. Themainpropertyof theelectrolyte is to transport ions fromtheanodeto thecathodeorvice-versa, whileensuringas littleaspossiblesidereactionswiththeLi-ions.Mostly itconsistsofwaterwithsome dissolvedsalts, lithiumhexafluorophosphatemostused, toensuregoodionconductivity. Thepurpose of theseparator is tostopthe transportofelectronswhile intervening in therestof theprocessesas littleaspossible. 111