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# Batteries: thermo-electro-chemical modeling

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(electro-chemical:batteries:intro)=
## Introduction and working principles
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A battery is an electrochemical system that converts chemical energy directly into electrical energy via spontaneous reduction-oxidation (redox) reactions. It acts as an electrochemical reactor where the spatial separation of the oxidation and reduction steps forces electrons to flow through an external load to perform work.

**Core components.**

* Anode (negative electrode): the electrode where oxidation (loss of electrons) occurs during discharge.
* Cathode (positive electrode): the electrode where reduction (gain of electrons) occurs during discharge.
* Electrolyte: a medium containing mobile ions that carries ionic current inside the cell while remaining electronically insulating.
* Separator: a permeable membrane that prevents physical contact between the anode and cathode to avoid internal short circuits.

**Classification.**

* Primary (non-rechargeable): the underlying chemical reactions are thermodynamically irreversible or physically difficult to reverse. Once the reactants are depleted, the battery cannot be recharged (e.g., Alkaline, Zinc-carbon).
* Secondary (rechargeable): the redox reactions are highly reversible. Applying an external electrical potential drives the current in reverse, regenerating the initial chemical reactants (e.g., Lithium-ion, Lead-acid, NiMH).

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(electro-chemical:batteries:examples)=
## Examples
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**Examples.**
* [Daniell cell](electro-chemical:batteries:daniell)
* [Li-ion bettery](electro-chemical:batteries:li)


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(electro-chemical:batteries:regimes)=
## Operational Regimes

(electro-chemical:batteries:regimes:open-circuit)=
### Open-circuit equilibrium


(electro-chemical:batteries:regimes:load)=
### Operation under loads
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