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Question 1

What is a battery?

Answer 1

a device consisting of one or more electrically connected electrochemical cells which is designed to receive, store, and deliver electric energy.

Question 2

what is an electrochemical cell

Answer 2

a self contained system consisting of an anode, cathode, and an electrolyte,

plus some connections (electrical and mechanical)
as may be needed to allow the cell to deliver or
receive electrical energy.

Question 3

what is an anode and cathode

Answer 3

Anode: Electrode whose active material is oxidised (gains e-) during discharge. Negative electrode as seen by the user (delivering electrons to the load).

Cathode: Electrode whose active material is reduced (loses e-) during discharge. Positive electrode as seen by the user (receiving electrons from the load)

Question 4

what is an electrolyte

Answer 4

Ionically conductive salt by itself or dissolved

Question 5

what does a separator do

Answer 5

prevents the electrodes from shorting

Question 6

what are the two metrics for battery life

Answer 6

Ah/ampere hour capacity, equivalent to charge (current x time)

Wh/watt-hour enegy, equivalent to voltage x charge.

Question 7

what are the two metrics for energy density

Answer 7

Gravimetric: Energy per mass unit. mWh/g = Wh/kg

Volumetric: Energy contained in a volume element. mWh/cm^3 = Wh/l

Question 8

what is the average for “low” and “medium” power requirement

Answer 8

Low power: average <1mW

Medium power: average 1-100mW

Question 9

given the complex impedance of implantable batteries, it is more complex to obtain a constant current output.

what is the maximum phase width to ensure that the battery of a cochlear implant will preceive phase durations as an average load (flat current, with some voltage ripple) i.e. the maximum phase width before pulsed load considerations are needed.

Answer 9

usually 10-50us.

Question 10

what type of solid state battery does a pacemaker have?

Answer 10

Li/I2-PVP (Lithium/Iodine-Polyvinylpyridine)

Question 11

are pacemaker batteries rechargable

Answer 11

no, must replace pacemaker at knee point

Question 12

what is the equilibrium potential difference of pacemaker batteries

Answer 12

2.8V

Question 13

what is the battery life of pacemakers

Answer 13

5-10 years depending on the number of pulses required

Question 14

what is the base and pulse load of pacemakers

Answer 14

base: load required to keep device running
pulse: load required for pacemaking function

Question 15

what are the advantages of Lithium iodine batteries

Answer 15

good conducting solid while not conducting electrons or I ions

LiI is both electrolyte and separator; self forming, self healing. allows for energy dense battery

Structure greatly modified by coating anode with PVP - helps the battery to work more effectively

the cathode is conducting

Question 16

what type of battery is used in neurostimulators

Answer 16

Li-ion

Question 17

what is the capacity, energy and energy density of neurostimulor batteries

Answer 17

capacity: 200mAh
energy: 200mAh x 3.6V = 720mWh

energy density: 720mWh / 3.3cm^3 = 220mWh/cm^3

Question 18

how do li-ion batteries typically work? (charge and discharge)

Answer 18

anode is Li-graphite, cathode is Li-oxides

Charge: powering the battery, Li+ to anode, e- to anode.

Discharge: powering the device, Li+ to cathode, e- to load (towards cathode?).

Question 19

what are some advantages of li-ion batteries

Answer 19

They are rechargable.

The cycle life / energy content / charge voltage of the battery can be modified by modifying the chemical composition ( # of Li atoms)

Question 20

when is the best time to discharge a li-ion battery

Answer 20

around knee point for best battery life per charge

Question 21

how do you design a li-ion battery to obtain zero volt discharge capacity

zero volt discharge capacity means the battery is fully charged - desired if battery is hard to charge or if it is inconvenient to charge often

Answer 21

Requires additives or certain current collector materials.

Question 22

how do you make a li-ion battery safer and more long lasting (cycle life)

Answer 22

Reduce energy density.
Increase impedance.
Reduce charge voltage,
Constructive precautions to prevent Li metal from plating across electrode ridges or glass to metal seal (feedthrough).

Question 23

what is a cycle life

Answer 23

The cycle life is the number of complete charge/discharge cycles that the battery is able to support before that its capacity falls under 80% of it’s original capacity.

Question 24

what effect does reducing the charge voltage of a battery have, and what is the rule of thumb for this effect

Answer 24

reducing charge voltage reduces the % capacity of the battery, therefore increasing the cycle life.

Rule of thumb: Vcharge -0.1V => Cycle life x2 & capacity -10%

Question 25

It is desireable for batteries to charge fast, however there are repercussions for this.

what are those repercussions?

Answer 25

the charger coil will heat

the charger link would consume more power (W) (good efficiency is 40%)

Question 26

what are some sources of variability in neurostimulator batteries

Answer 26

Irreversible capacity losses over time.

More recharge cycles for shorter recharge intervals???

Proprietary effects: actual base load, heating, buffer to allow for safe replacement.