How do rechargeable batteries recharge?

[Gautama2]

Topic.

 

[futuristicmonkey]

Apply a voltage that is a little higher than the voltage of the chemical cell* inside the battery. By forcing the electrons in reverse you make the cell operate in reverse, storing the energy you force into it.

*If you're into chem, google search 'standard reduction table'.

 

[CycloWizard]

Batteries work by storing electrical potential energy in the form of ionic solutions (essentially, separating charges). There are two different cells in the battery that are separated when the thing the battery is powering is turned off. When it's turned on, the circuit is closed and current flows from the cell with higher potential to the cell with lower potential. The current is generated by ions reacting with the electrode metal. Thus, to reverse this and recharge the battery, one need only apply a current to the system to drive it in reverse and separate the charges again.

 

[Special K]

Originally posted by: CycloWizard
Batteries work by storing electrical potential energy in the form of ionic solutions (essentially, separating charges). There are two different cells in the battery that are separated when the thing the battery is powering is turned off. When it's turned on, the circuit is closed and current flows from the cell with higher potential to the cell with lower potential. The current is generated by ions reacting with the electrode metal. Thus, to reverse this and recharge the battery, one need only apply a current to the system to drive it in reverse and separate the charges again.

Then why isn't it possible to recharge all batteries, instead of just the ones that are designated as rechargeable?

 

[CycloWizard]

Originally posted by: Special K
Then why isn't it possible to recharge all batteries, instead of just the ones that are designated as rechargeable?

Because not all of the reactions that can be used to generate current are reversible.

 

[Cogman]

Originally posted by: Special K
Then why isn't it possible to recharge all batteries, instead of just the ones that are designated as rechargeable?

Interestingly enough, there was actually a product that would recharge alkaline batteries (I remember reading this on Wikipedia, should still be there). As I recall the main problem with it is that It requires exact voltages and amps. If that is incorrectly applied then your battery will blow up. This is kind of one of the major reasons that product is not on the market any more.

 

[StopSign]

There are rechargeable alkaline batteries out there. I think they used proprietary chargers.

 

[Jeff7]

Originally posted by: CycloWizard

Originally posted by: Special K
Then why isn't it possible to recharge all batteries, instead of just the ones that are designated as rechargeable?

Because not all of the reactions that can be used to generate current are reversible.

Exactly. You can't burn a stick, and then just cool down the ash to change it back.

 

[Casawi]

Chem people just all over this one, I guess not much else for a EE to say here. BTW not all batteries don't recharge because you didn't buy the ones that recharge.

 

[cougar1]

Originally posted by: CycloWizard

Originally posted by: Special K
Then why isn't it possible to recharge all batteries, instead of just the ones that are designated as rechargeable?

Because not all of the reactions that can be used to generate current are reversible.

Most of the electrochemical reactions used in batteries are reversible. However, some require very precise charging conditions (voltage and current regulation) to avoid excessive formation of heat and hydrogen gas, a potentially explosive combination.

Battery design (size, layout, chemistry, etc...) can also be an issue. When a battery charges you are essentially electroplating the cathode with a reactive metal. A rechargeable battery must be designed such that this electroplating occurs in a uniform manner, such that the reactive surface area remains fairly constant. If this is not the case, the battery's ability to generate electrical current will vary with time, leading to poor performance. Also, if the metal doesn't deposit uniformly there is the possibility the material could deposit in a filament that shorts between the electrode and the cathode, destroying the battery. Optimal battery design results in trade-offs between may factors including size, cost, battery life (both of a single charge and total life), voltage, discharge characteristics, and so on. For some applications it makes more sense, usually for reasons of cost and size, to design a battery that will not be rechargeable even though the chemistry is reversible.

 

[PCTC2]

Batteries recharge by the reversal of a controlled redox (oxidation-reduction) reaction. Electrons are stripped from one metal and transferred to another and create ions in the process. Recharging the batteries simply adds an EMF that causes the metal that gained electrons to lose them and the other to regain the lost electrons. Some batteries cannot be recharged because the metal does not reattach itself to the Cathode/Anode properly so it doesn't complete a circuit properly to be recharged. The metals do not need to be highly reactive (Lead and Copper can be used) but the combination of ions/metals and designs causes the lack of ability to be charged. A lot of batteries use Mn(OH)2 as a electrolyte bridge to connect the circuit between the electrodes. As Cougar1 stated, excess current and heat can cause it to break down into MnO and H2. H2+Heat+Pressure=Bad for really anything except an internal combustion engine. THat's why a lead-acid battery in the car can lose it's ability to recharge over time. 1) The electrode's metals/ionic compounds get knocked off and settle to the bottom and can cause a short-circuit of the batter and 2) the sulfuric acid in the battery can decompose into H2 and another sulfite/sulfate. And to CycloWizard, all reactions are reversible at some voltage, just, as Cougar1 said, designs do not allow it to happen properly.

 

[imported_Equinox]

Great responses. This thread FTW

 

[CycloWizard]

Originally posted by: cougar1
Most of the electrochemical reactions used in batteries are reversible. However, some require very precise charging conditions (voltage and current regulation) to avoid excessive formation of heat and hydrogen gas, a potentially explosive combination.

Battery design (size, layout, chemistry, etc...) can also be an issue. When a battery charges you are essentially electroplating the cathode with a reactive metal. A rechargeable battery must be designed such that this electroplating occurs in a uniform manner, such that the reactive surface area remains fairly constant. If this is not the case, the battery's ability to generate electrical current will vary with time, leading to poor performance. Also, if the metal doesn't deposit uniformly there is the possibility the material could deposit in a filament that shorts between the electrode and the cathode, destroying the battery. Optimal battery design results in trade-offs between may factors including size, cost, battery life (both of a single charge and total life), voltage, discharge characteristics, and so on. For some applications it makes more sense, usually for reasons of cost and size, to design a battery that will not be rechargeable even though the chemistry is reversible.

I can reverse any chemical reaction given enough time, energy, and equipment. Unfortunately, a typical battery doesn't offer me these things. This is why electrolysis-based fuel cells are an appealing alternative to traditional batteries, but they have their own drawbacks (mostly being expensive due to precious metal catalysts).

 

[SuperFungus]

I have a related question. Could you recharge a battery through a process like heating it up or pumping chemicals around in the battery or something to get the charges re-separated faster than simply running current through the battery? I'm thinking of electric cars here where recharging the battery is a hassle because it takes so long. It would be cool if you could build a re-charge station that used a pump or heater or something that was run off the power grid to charge the battery really fast, which it seems electric current is unable to do. Anyways just a thought.

 

[bobsmith1492]

Originally posted by: SuperFungus
I have a related question. Could you recharge a battery through a process like heating it up or pumping chemicals around in the battery or something to get the charges re-separated faster than simply running current through the battery? I'm thinking of electric cars here where recharging the battery is a hassle because it takes so long. It would be cool if you could build a re-charge station that used a pump or heater or something that was run off the power grid to charge the battery really fast, which it seems electric current is unable to do. Anyways just a thought.

Fuel cells?

 

[SuperFungus]

Nah, i'm talking about using the same chemicals. I'm thinking that you don't exhaust any of the by products (like fuel cells do with water) or introduce any new chemicals to the battery (like hydrogen). I'm asking if maybe you could use heat, or movement or something besides current to get the battery back to a chemically charged state faster than using current. Kind of like those reuseable heating pads, the kind where you can put them in boiling water for awhile and the chemicals inside return to their original state and can be used to emit heat again, but with batteries so you use the heat/whatever to bring the chemical composition of the battery back to an electrically charged state.