Secondary cells Flashcards
what are secondary cells
cells that are rechargable, act as galvanic cells during discharge and electrolytic cells during recharge
what happens during discharge
the spontaneous redox reactions occur, the products remain in contact with the electrodes at which they are produced
what is the process of recharge
the positive terminal of the charger is connected to the positive terminal of the betttery or cells, and negative to negative. this forces the electrons to travel in the reverse direction and as the products are in contact with the electrodes, the original reactions are reversed
what are the two types of secondary cells
lithium ion batteries and lead acid batteries
what are lithium ion batteries used in
laptops and other larger modern devices
what are lead acid batteries used in
cars and other motor vehicles
what voltage must be applied to recharge a cell
a voltage slightly higher than the potential difference of the cell during discharge
requirements for recharge
a device must be used to force the electrons to flow in the opposite direction to discharge, the dewvice must operate as a slightly higher voltage than the normal operating voltage of the cell, products of discharge must be able to be reversed and not lost through side reactions or solid coating physically falling off electrode surfaces
lead acid battery
consists of lead oxide, lead plates and sulfuric acid, consists of six cells, each with a potential difference of just over 2V
positive and negative electrode and electrolyte is amde up of what in a lead acid battery
positive: lead plates packed with lead oxide negative: lead plates packed with powdered lead electrolyte: solution of sulfuric acid (4M)
lead oxide formula
PbO2
disadvantages of lead acid batteries
very heavy, contain toxic materials, sulfuric acid is corrosive (presents difficulty of disposal)
lithium ion batteries
contain graphite, lithium, colbalt oxide
positive and negative electrodes and electrolyte in lithium ion batteries
positive: colbalt oxide that has been covered with lithium ions negative: graphite soaked with lithium electrolyte: various non aqueous electrolytes are used, along with a solid seperator
why is colbalt/other transition metal oxides used in lihtium ion batteries
due to their multiple possible oxidation states
why is a solid seperator between electrodes used in lithium ion batteries
is used that is permeable to lithium ions but prevents the electrodes from coming into contact with one another
disadvantages of lithium ion batterie
global shortage of lithium (unsustainable), if cells arent recycled, lithium becomes lost to future generations, lithium is highly reactive (lithium-ion cell fires)
