Do electrons flow through the battery?

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Sulvek

Joined Aug 27, 2022
20
I think electricity flows through the battery because I don't understand how a battery in series that is placed between others like the one in the picture could give or receive electrons. I recently saw in a youtube video that electricity only flows through the circuit. Similiar to a capacitor it doesn't flow through it self. I took it as truth as considered it to be one of them mind blowers but it didn't seem right and after trying to disprove it in my head I thought about batteries in series. The idea of all the electrons leaving the negative for positive as well seemed like you would just mount of electrons on the positive side and run out. I'm assuming the basics of electron flow is the same in all batteries? I understand there is differences physically and in the chemistry. Thanks yall!
 

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nsaspook

Joined Aug 27, 2009
10,409
No, individual electrons don't typically flow through the electro-chemical battery. If they do it's a leakage current that's not desirable. Batteries supply electrical energy to a circuit using chemistry to separate charges with chemical reactions that results in the energy released being stored in an electric field across the battery plates. The batteries total number of electrons doesn't changed when charged or discharged.

https://van.physics.illinois.edu/ask/listing/583
https://www.science.org.au/curious/technology-future/batteries
 

MrSalts

Joined Apr 2, 2020
2,350
No, individual electrons don't typically flow through the electro-chemical battery. If they do it's a leakage current that's not desirable. Batteries supply electrical energy to a circuit using chemistry to separate charges with chemical reactions that results in the energy released being stored in an electric field across the battery plates. The batteries total number of electrons doesn't changed when charged or discharged.

https://van.physics.illinois.edu/ask/listing/583
https://www.science.org.au/curious/technology-future/batteries
The first link is confusing because they gave an overly simplified answer to the question and tried to backpeddle and refine with each addition question from the public.
The second is just wrong. Note their image of the "battery pile" with anode as the source of electrons to drive the load (backwards). It also claims electrons "accumulate" at the anode. Confused and wrong.
 

nsaspook

Joined Aug 27, 2009
10,409
The first link is confusing because they gave an overly simplified answer to the question and tried to backpeddle and refine with each addition question from the public.
The second is just wrong. Note their image of the "battery pile" with anode as the source of electrons to drive the load (backwards). It also claims electrons "accumulate" at the anode. Confused and wrong.
Tiny quibbles of little importance as usual.
 

WBahn

Joined Mar 31, 2012
27,391
No, individual electrons don't typically flow through the electro-chemical battery. If they do it's a leakage current that's not desirable. Batteries supply electrical energy to a circuit using chemistry to separate charges with chemical reactions that results in the energy released being stored in an electric field across the battery plates. The batteries total number of electrons doesn't changed when charged or discharged.

https://van.physics.illinois.edu/ask/listing/583
https://www.science.org.au/curious/technology-future/batteries
So are you saying that if we consider a plane that cuts a battery in half that there are no "electricity", i.e., flow of charge, flowing through that plane?

If so, then electrons that leave the negative terminal of the battery would result in that half of the battery developing a net-positive charge while the positive terminal that is receiving electrons from the circuit would develop a net-positive charge. The forces that would build up between these charge separations would be enormous. So there must be (and there is) a mechanism whereby the negative charge due to electrons entering the positive terminal is conveyed, through the battery, to the negative terminal to replace the electrons that left it.
 

MrSalts

Joined Apr 2, 2020
2,350
So are you saying that if we consider a plane that cuts a battery in half that there are no "electricity", i.e., flow of charge, flowing through that plane?

If so, then electrons that leave the negative terminal of the battery would result in that half of the battery developing a net-positive charge while the positive terminal that is receiving electrons from the circuit would develop a net-positive charge. The forces that would build up between these charge separations would be enormous. So there must be (and there is) a mechanism whereby the negative charge due to electrons entering the positive terminal is conveyed, through the battery, to the negative terminal to replace the electrons that left it.
The mechanism is that electrons leave the cathode of the battery and flow to the load, at the same time, the materials used to make the cathode are oxidized ( because they lost an electron that is flowing out). Those oxidized materials in the battery tend to migrate towards the anode (or they get expelled as a gas if the cathode material was a chloride ion (Cl-) and an electron is removed, Cl2 gas can be evolved. This is just a "half reaction" inside the battery.

In all cases a second half-reaction where some anode material gets reduced (opposite of oxidation) by the incoming electron.
 

WBahn

Joined Mar 31, 2012
27,391
I think electricity flows through the battery because I don't understand how a battery in series that is placed between others like the one in the picture could give or receive electrons. I recently saw in a youtube video that electricity only flows through the circuit. Similiar to a capacitor it doesn't flow through it self. I took it as truth as considered it to be one of them mind blowers but it didn't seem right and after trying to disprove it in my head I thought about batteries in series. The idea of all the electrons leaving the negative for positive as well seemed like you would just mount of electrons on the positive side and run out. I'm assuming the basics of electron flow is the same in all batteries? I understand there is differences physically and in the chemistry. Thanks yall!
As noted in my prior post, "electricity" must flow through the battery when it is in operation to avoid an ever increasing separation of charge between the terminals.

There is a natural tendency to want to equate batteries with capacitors, but they are fundamentally different.

When you charge a capacitor, you ARE creating a net-positive charge on one plate and a net-negative charge on the other PRECISELY because no charge flows between the plates internally. But physical charge separations involve enormous forces at the distance scales we are talking about.

Let's get a feel for the numbers involved. A D-cell has an outside length of 60 mm. Let's assume that the plates are located there (to keep things simple -- the internal structure of a battery can be very complicated). That D-cell has a nominal capacity rating of 20,000 mAh (at 25 mA draw). That's 72,000 coulombs of charge. So if we were to take -72 kC worth of electrons on the top plate and park them on the negative plate, the force between them would be:

|F| = |k·q1·q2 / r²| = | (9x10^9 N·m²/C²) (+72 kC) (-72 kC) / (60mm)² | = 1.3x10^22 N

To put that in perspective, the Artemis launch vehicle produces about 39x10^6 N.

So, clearly, the notion of charging a capacitor to hold anywhere near the amount of charge that a battery can deliver is a fool's errand.

So what does happen to take those two plates and make them into a battery?

We put stuff in between the plates that causes chemical reactions to occur that move electrical charge (in the form of ions) from one plate to the other within the cell at the same rate that electrons are moving around the external circuit being powered by the battery.

So here's a pretty simplified view of what happens.

Take a piece of metal like zinc and put it in plain old water. Some of the zinc will actually diffuse (dissolve) off the metal into the water in the force of Zn ions (which happen to be deficient two electrons). Those two electrons are then left on the zinc metal, making it negatively charged. But this can't continue very long before the build up of negative charge on the zinc metal is too strong for any more zinc ions to continue diffusing off the metal and into the water. So an equilibrium is reached with the zinc after it reaches a certain level of charge (and this level of charge is pretty miniscule).

Now do the same thing with a different metal, say tin, in a different bucket of water. The same thing happens and the piece of tin becomes negatively charged up to the point that the minuscule charge separate is enough to stop further diffusion.

But there's a difference in the amount of electrons that collect on the two pieces of metal such that (assuming the two bodies of water can be kept at the same potential), one of the metals (zinc, as it turns out) is more negative than the other (the tin). That makes the tin the positive electrode and the zinc the negative electrode since the tin electrode is more positive than the zinc, regardless of whether it's net charge is positive or negative -- remember, voltage is about potential differences.

What happens if we connect the two pieces of metal with a wire? Current flows in the form of electrons flowing from the zinc to the tin. As these electrons flow off the zinc, the restoring electric field is reduced and more zinc can diffuse into the water. But at the tin electrode, the addition of electrons increases the restoring force and tin ions are essentially pulled back out of solution and deposited back onto the electrode. This quickly halts the reaction -- what is actually happening is the two bodies of water are becoming charged so as to offset the initial imbalance between the two electrodes such that there is almost instantaneously no potential difference between them (it is completely offset by the potential difference in the other direction between the two bodies of water).

What we need is a way for charge to flow between the two bodies of water without letting the zinc and tin mix. Enter the salt bridge. This is a saturates solution of something like potassium chloride that has lots of both positive potassium ions and negative chloride ions that can move pretty freely. So when an electron leaves the zinc metal into the external circuit, a chloride ion is pulled from the bridge to replace the electron (not the salt bridge is negatively charged), but at the same time the electron that flowed through the circuit onto the tin electrode, a potassium ion is pulled from the bridge to absorb that new electron (which restores the electrical neutrality of the bridge overall. Since ions can flow freely within the bridge, the shuffle around to prevent any charge separate from building up within it.

So that's a battery (though a pretty bad one just using water). For a real battery, we put stuff in the water (or replace the water altogether with something else, such as an acid) that is able to dissolve a lot more metal into the solution. We also put stuff in there to deal with any undesirable effects of these ions entering the solutions from the salt bridge. Or we devise an electrolyte chemistry that can go directly between the electrode plates. Perhaps the classic example of this is the lead-acid battery in which one electrode is made from lead (Pb) while the other is made from lead oxide (PbO2) and the electrolyte is sulfuric acid, which disperses both negative HSO4 ions and positive hydronium (H3O) ions throughout the cell. The lead electrode wants to grab a HSO4 ion to make lead sulfate (PbSO4) and one hydronium ion while releasing two electrons into the external circuit, while at the same time the lead oxide electrode wants to take the two electrons coming in from the circuit along with one of the positive ions, three of the negative ions and make lead sulfate on that electrode, too.
 

nsaspook

Joined Aug 27, 2009
10,409
So are you saying that if we consider a plane that cuts a battery in half that there are no "electricity", i.e., flow of charge, flowing through that plane?

If so, then electrons that leave the negative terminal of the battery would result in that half of the battery developing a net-positive charge while the positive terminal that is receiving electrons from the circuit would develop a net-positive charge. The forces that would build up between these charge separations would be enormous. So there must be (and there is) a mechanism whereby the negative charge due to electrons entering the positive terminal is conveyed, through the battery, to the negative terminal to replace the electrons that left it.
Note, that I said (and provided links that said) individual (as in free electrons in a copper wire) electrons don't flow through a battery just like they don't 'flow' through a capacitor.
1664557254309.png
https://forum.allaboutcircuits.com/threads/small-solar-panel-charges-big-battery.161452/post-1412556

https://www.pveducation.org/pvcdrom/battery-basics/basic-battery-operation
Electrons travel from the anode to the cathode, but do not return from the cathode to the anode. Instead, electrical neutrality is maintained by the movement of ions in the electrolyte. If each redox reaction has a different electrolyte, a salt bridge joins the two electrolyte solutions. The direction of the ion movement acts to prevent a charge build-up at either the anode or the cathode. In most practical battery systems, the same electrolyte is used for both the anode and the cathode, and ion transport can take place via the electrolyte itself, eliminating the need for a salt bridge. However, in this case a separator is also inserted between the anode and the cathode. The separator prevents the anode and cathode from physically touching each other since they are usually in very close physical proximity to one another, and if they were to touch it would short out the battery as the electrons can be transferred directly without flowing through the external circuit and load.
https://www.hollingsworth-vose.com/blog/introduction-battery-separators/
Batteries consist of the following basic components: an anode, a cathode, and an electrolyte. However, another key part that is often overlooked is the battery separator. This component is vital to the functionality and performance of batteries. Below, we outline what it is, its origins, and its applications.

A battery separator is a type of polymeric membrane that is positioned between the positively charged anode and the negatively charged cathode. This positioning helps prevent electrical short circuiting.

When the membrane becomes moistened by the electrolyte, it acts as a catalyst that increases the movement of ions from one electrode to the other. The ions move from the cathode to the anode when the battery is being charged and from the anode to the cathode when the battery is being discharged. Since the membrane controls the number of ions that move between terminals, it is also responsible for the charge and discharge of the battery under ideal conditions.

One thing to keep in mind is that separators allow ions to pass through freely, but they are not electrically conductive. Therefore, they always act as isolators.
 
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Tonyr1084

Joined Sep 24, 2015
7,088
School me if my assumptions are wrong, but in a case where there are more than one cell, multiple cells in series increases the electric pressure (voltage). Suppose you're using three cells: Are there no electrons passing through at least two cells? Like I said, school me if my assumption is in error. I'm not an expert here.

My comment is meant to evoke thinking on a scale that I suspect no one has covered or considered before. This is not a hijacking of the thread.
 

MrSalts

Joined Apr 2, 2020
2,350
School me if my assumptions are wrong, but in a case where there are more than one cell, multiple cells in series increases the electric pressure (voltage). Suppose you're using three cells: Are there no electrons passing through at least two cells? Like I said, school me if my assumption is in error. I'm not an expert here.

My comment is meant to evoke thinking on a scale that I suspect no one has covered or considered before. This is not a hijacking of the thread.
The whole of the battery is conductive electrolyte (like saltwater or a salty paste or gel. An electron can move into the cell and one correspondingly leaves the cell. The electrolyte has some micro-homes to dozens of ohms of resistance (internal resistance). The you can think about it as you want but I wouldn't think of it as flowing "through" the cell. I would think of it as loading and unloading simultaneously.
 

nsaspook

Joined Aug 27, 2009
10,409
School me if my assumptions are wrong, but in a case where there are more than one cell, multiple cells in series increases the electric pressure (voltage). Suppose you're using three cells: Are there no electrons passing through at least two cells? Like I said, school me if my assumption is in error. I'm not an expert here.

My comment is meant to evoke thinking on a scale that I suspect no one has covered or considered before. This is not a hijacking of the thread.
1664643814826.png
As I said before individual electron A doesn't pass through the battery(s). Even in a typical good conductor individual electron A moves very slowly with little KE. The electrochemical reaction ion flow (a equivalent ion current that can be singly-, doubly-, etc. charged to the external electron current) inside the battery produces by charge separation the electric field and energy that drives electrons (that don't carry the electrical energy of the circuit) in external conductors. As usual, thinking about electrons as some sort of circuit theory energy carrier is usually misleading, Think about how the battery converts chemical energy into electrical field energy and how charges (usually electrons ) in conductors guide that energy surrounding the wires from source to load.

https://www.degruyter.com/document/doi/10.1515/jnet-2020-0070/html?lang=en
 
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MrSalts

Joined Apr 2, 2020
2,350
The battery doesn't care and cannot differentiate whether it is in a stack of cells or a single cell powering the load. For each electron leaving the cathode, one enters the anode when a circuit is compete (whether charging or discharging).

Note that the terminology of anode and cathode flip when charging vs discharging. Electrons always leave the cathode. It may feel more comfortable. Calling them negative terminals and positive terminals instead of anode and cathode to prevent confusion.
 

DickCappels

Joined Aug 21, 2008
9,297
It is enough for me to just assume that current flows through the battery - there are IR drops, I^2R heating etc. associated with current that occur within a battery whether charging or discharging said battery.
 

nsaspook

Joined Aug 27, 2009
10,409
It is enough for me to just assume that current flows through the battery - there are IR drops, I^2R heating etc. associated with current that occur within a battery whether charging or discharging said battery.
That's the logical and correct way to think about it.
 

WBahn

Joined Mar 31, 2012
27,391
School me if my assumptions are wrong, but in a case where there are more than one cell, multiple cells in series increases the electric pressure (voltage). Suppose you're using three cells: Are there no electrons passing through at least two cells? Like I said, school me if my assumption is in error. I'm not an expert here.

My comment is meant to evoke thinking on a scale that I suspect no one has covered or considered before. This is not a hijacking of the thread.
If 1 A of current is flowing in the external circuit from the positive terminal to the negative terminal, then 1 A of current is flowing in the internal battery from the negative terminal to the positive terminal.

In the external circuit, the flow is due to the electric field that is established throughout and along the circuit due to the potential difference between the positive terminal of the battery and the negative terminal. The charge carriers in the external circuit at almost always electrons.

The movement of charge in the internals of the battery are NOT due to the electric fields inside the battery -- they are the wrong direction. Within the battery, charge has to flow in opposition to the electric field. This is essential because work has to be done against the field in order to create the energy potential that creates the electric field that can then do work on the charge carriers (electrons) in the external circuit.

That is where the chemistry comes in -- chemical reactions within the cell move electrically-charged particles (ions) according to the chemistry involved and those ions constitute the flow of charge within the cell. To keep the charge balance throughout the cell, the net flow must either be positive ions flowing from the negative terminal to the positive terminal or negative ions flowing from the positive terminal to the negative terminal. Most cells result in the former. In either case, the chemical movement of charged is opposed by the electric field within the cell at the same time that it is strengthening it, the end result is that, at some point, the electric field is strong enough to stop the further movement of charge via chemical means. That is the equilibrium voltage of the cell that gets printed on the side of the package at the supermarket.
 

MrSalts

Joined Apr 2, 2020
2,350
equilibrium voltage
The voltage of an electrochemical reaction is determined by the standard reduction potential of the two half-reactions (one oxidation and one reduction). The value of this voltage does change if the concentration of dissolved reactants changes but dissolved reactants in a lithium metal or lead-acid battery do not typically change too much (dissolved reactants are available in excess) and the solid components (lithium metal or lead metal) do not change the standard reduction potentials (added together to get the battery voltage). What kills battery voltage is a combination of diffusion of electrolyte (internal resistance) and accessible surface area of the solid components as the battery comes to end of life (end of charge).

https://chem.libretexts.org/Bookshe.../Redox_Chemistry/Standard_Reduction_Potential
 

WBahn

Joined Mar 31, 2012
27,391
The voltage of an electrochemical reaction is determined by the standard reduction potential of the two half-reactions (one oxidation and one reduction). The value of this voltage does change if the concentration of dissolved reactants changes but dissolved reactants in a lithium metal or lead-acid battery do not typically change too much (dissolved reactants are available in excess) and the solid components (lithium metal or lead metal) do not change the standard reduction potentials (added together to get the battery voltage). What kills battery voltage is a combination of diffusion of electrolyte (internal resistance) and accessible surface area of the solid components as the battery comes to end of life (end of charge).

https://chem.libretexts.org/Bookshe.../Redox_Chemistry/Standard_Reduction_Potential
And none of that has any bearing on the point at hand. The half-reaction potentials are the result of the chemical reactions producing a charge separation that results in an electric field that opposes the chemical reactions. The half-cell potentials are the voltage at which these are in equilibrium. The standard potentials are generally specified with a one molar concentration of the ion involved in the reaction at the electrode.
 

BobTPH

Joined Jun 5, 2013
5,748
If electrons simply flowed through the battery, there is no chemical reaction that depletes the battery. It should last forever. In reality, the electrons coming in replace an electron in the anode that neutralizes a positive ion. And the electron comes out of the cathode is replaced by an electron given up by a negative ion. To flow through the battery the electron would have to jump from the anode to the cathode, which woukd be the leakage current that has been mentioned.
 
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