lecture 6 Flashcards

1
Q

battery elements // constituents

A

cathode (reduction occurs)

anode (oxidation occurs)

electroyte ( electron transport)

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2
Q

what does the electrolyte do

A

it transports electrons

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3
Q

what must a system allow the flow of

A

it must allow the flow of ions and electrons

it must be an ionic and electronic conductor

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4
Q

source of ions is the

A

anode

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5
Q

ion sink is the

A

cathode

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6
Q

what is the anode usually made up of

A

graphite carbon

or silicon (recently)

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7
Q

what does the electrolyte contain

A

lithium salt dissolved in a mixture of ionic solvents

LiPF6

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8
Q

what must be maximised to improve voltage and capacity

A

the cathode!!!

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9
Q

why is the cathode responsible for voltage and capacity

A

bc the anode can have low voltage
the capacity is taken up by the material itself ( C or Si)

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10
Q

what is the battery made up of

A

an element that can be oxidised and reduced readily

a transition metal

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11
Q

is the lithium reaction reversible

A

yes

an intercalation reaction

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12
Q

what is an intercalation reaction and where does it occur

A

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

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13
Q

high free energy // high gibbs

A

high capacity (number of lithiums per transition metal must be high)

high intercalation voltage

high energy storage ( V x Cap)

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14
Q

high energy storage equation

A

voltage x capacity

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15
Q

is the battery reaction rapid

A

yes

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16
Q

is a good electronic conductor needed

A

yes!! good ionic conductor aswell

17
Q

stability of a battery

A

no degradation (no over discharge // over charge)

can afford many charge and discharge types

18
Q

ptimisation of battery,, what to use

A
  • use transition metals (redox occurs readily)
  • use layered or channel compounds to intercalate Li ions (oxides, silicates)
  • certai nstructural features improve Li mobility
19
Q

examples and explanations of layered structures

A

LiCoO2 - lithium cobalt oxide

O2 and Li with Co inbetween

layers of Co, octahedrally coordinated

Li is intercalated

20
Q

layered vanadates are formed due to

A

increasing Li conc leading to the formation of different structures

21
Q

what else can be used

A

spinels LiMn2O4

22
Q

what affects the ranger over which a battery can operate

A

Li content + its structure impact

oxidation number of the active centre + its capacity loss

23
Q

what can we use the Ea,, activation energy to do

A

tells us the activation energy needed to remove an e- from the structure

24
Q

low Ea and pulling out an e-

A

a low activation energy is needed !! allows us to remove electrons from a structure more easily

25
what is Ea for electron removal measured in
in MeV
26
olivine material formula
LiFePO4 natural mineral natural minerals make the best batteries
27
calculating the theoretical capacity
number of moles of ion x electron charge FARADAY CONSTANT // molar mass (mr)
28
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
29
3.6C charge = what mAh/g
3.6C = 1 mAh
30
energy =
voltage x TSC
31
how to increase energy
increase number of ions to increase capacity
32
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.
33
how do we change voltage
removing and adding electrons
34
does an ideal battery material exist
nope!! but natural minerals are kinda good!