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
Q

what is Ea for electron removal measured in

A

in MeV

26
Q

olivine material formula

A

LiFePO4

natural mineral
natural minerals make the best batteries

27
Q

calculating the theoretical capacity

A

number of moles of ion x electron charge FARADAY CONSTANT // molar mass (mr)

28
Q

calculating theoretical capacity eg: calculate it for LiFePO4 if the molecular weight is 158g/mol

A

LiFePO4 -> 1Li

(1Li x 96487) / 158

then divide by 3.6

= 170 mAh/g

29
Q

3.6C charge = what mAh/g

A

3.6C = 1 mAh

30
Q

energy =

A

voltage x TSC

31
Q

how to increase energy

A

increase number of ions to increase capacity

32
Q

what is a negative about increasing energy

A

to increase energy u must increase the number of ions which increases the weight of the battery which then limits its use.

33
Q

how do we change voltage

A

removing and adding electrons

34
Q

does an ideal battery material exist

A

nope!!

but natural minerals are kinda good!