lecture 6 Flashcards
battery elements // constituents
cathode (reduction occurs)
anode (oxidation occurs)
electroyte ( electron transport)
what does the electrolyte do
it transports electrons
what must a system allow the flow of
it must allow the flow of ions and electrons
it must be an ionic and electronic conductor
source of ions is the
anode
ion sink is the
cathode
what is the anode usually made up of
graphite carbon
or silicon (recently)
what does the electrolyte contain
lithium salt dissolved in a mixture of ionic solvents
LiPF6
what must be maximised to improve voltage and capacity
the cathode!!!
why is the cathode responsible for voltage and capacity
bc the anode can have low voltage
the capacity is taken up by the material itself ( C or Si)
what is the battery made up of
an element that can be oxidised and reduced readily
a transition metal
is the lithium reaction reversible
yes
an intercalation reaction
what is an intercalation reaction and where does it occur
it occurs in a battery
its the reversible inclusion or insertion of a molecule (or ion) into layered materials with layered structures.
reversible process or removing or moving an ion in or out a layered structure
high free energy // high gibbs
high capacity (number of lithiums per transition metal must be high)
high intercalation voltage
high energy storage ( V x Cap)
high energy storage equation
voltage x capacity
is the battery reaction rapid
yes
is a good electronic conductor needed
yes!! good ionic conductor aswell
stability of a battery
no degradation (no over discharge // over charge)
can afford many charge and discharge types
ptimisation of battery,, what to use
- use transition metals (redox occurs readily)
- use layered or channel compounds to intercalate Li ions (oxides, silicates)
- certai nstructural features improve Li mobility
examples and explanations of layered structures
LiCoO2 - lithium cobalt oxide
O2 and Li with Co inbetween
layers of Co, octahedrally coordinated
Li is intercalated
layered vanadates are formed due to
increasing Li conc leading to the formation of different structures
what else can be used
spinels LiMn2O4
what affects the ranger over which a battery can operate
Li content + its structure impact
oxidation number of the active centre + its capacity loss
what can we use the Ea,, activation energy to do
tells us the activation energy needed to remove an e- from the structure
low Ea and pulling out an e-
a low activation energy is needed !! allows us to remove electrons from a structure more easily
what is Ea for electron removal measured in
in MeV
olivine material formula
LiFePO4
natural mineral
natural minerals make the best batteries
calculating the theoretical capacity
number of moles of ion x electron charge FARADAY CONSTANT // molar mass (mr)
calculating theoretical capacity eg: calculate it for LiFePO4 if the molecular weight is 158g/mol
LiFePO4 -> 1Li
(1Li x 96487) / 158
then divide by 3.6
= 170 mAh/g
3.6C charge = what mAh/g
3.6C = 1 mAh
energy =
voltage x TSC
how to increase energy
increase number of ions to increase capacity
what is a negative about increasing energy
to increase energy u must increase the number of ions which increases the weight of the battery which then limits its use.
how do we change voltage
removing and adding electrons
does an ideal battery material exist
nope!!
but natural minerals are kinda good!
