# Battery - theoretical specific energy

• Solitron
In summary, the conversation discusses the calculation of maximum theoretical specific energy for different battery combinations, such as Sodium-Sulfur, Potassium-Sulfur, and Rubidium-Iodine. The conversation also mentions the use of molar enthalpy of formation to calculate theoretical specific energy, with an example calculation for Lithium-Fluorine. It is suggested to use Gibbs energy instead of enthalpy for more accurate results.
Solitron
TL;DR Summary
How to calculate theoretical specific energy
I want to learn how to calculate maximum theoretical specific energy of various battery combinations consisting of a single metal and single oxidant, like for example Sodium - Sulfur, Potassium - Sulfur or even crazy stuff like Rubiddium - Iodine.

I asked this question on stackexchange but I had bad luck as the people there didnt understand what theoretical specific energy is. Its impossible to obtain in real world value based solely on the chemical potential energy between two pure elements, it ignores weight of everything else like electrolyte, separator, electrodes or copper or the metal oxide/carbon where the ions are absorbed inside in real world batteries.

The theoretical specific energy uses watt hour - kilogram units. If you never seen this I highly suggest looking at "metal air battery" Wiki page, there you can see the values for various metal - air ( oxygen ) combinations.

So far I tried calculating it by using molar entalphy of formation energy but I don't know how to do it exactly, especially for combinations that don't have 1 to 1 molar ratio, like for example lithium oxygen where you need twice as many moles of lithium as oxygen.

Here is how I tried doing Lithium - Fluorine, do you see any error?
Lithium molar mass = 6.941g
Fluorine molar mass = 18.99g
Lithium Fluoride molar mass = 25.939g
Lithium Fluoride entalphy of formation = -598.65KJ per mol

1000g : 25.939g = 38.55 LiF moles in 1kg
38.55mol × 598.65KJ/mol = 23077KJ/kg = 6410 Watt hour/kg

Last edited:
256bits
Strictly, you should use Gibbs energy rather than enthalpy.

256bits

## 1. What is theoretical specific energy?

Theoretical specific energy refers to the maximum amount of energy that a battery can store per unit mass or volume, assuming perfect efficiency and ideal conditions.

## 2. How is theoretical specific energy calculated?

Theoretical specific energy is calculated by multiplying the battery's voltage by its capacity and dividing by its weight or volume. This calculation assumes ideal conditions and does not take into account factors such as temperature, discharge rate, and internal resistance.

## 3. Why is theoretical specific energy important?

Theoretical specific energy is important because it provides a benchmark for comparing the energy storage capabilities of different battery chemistries. It also helps in the development of new and more efficient battery technologies.

## 4. What are the limitations of theoretical specific energy?

Theoretical specific energy does not take into account real-world factors such as temperature, discharge rate, and internal resistance, which can significantly affect a battery's actual energy storage capabilities. It also assumes perfect efficiency, which is not achievable in practical applications.

## 5. How does theoretical specific energy relate to practical battery performance?

Theoretical specific energy provides an upper limit for a battery's energy storage capabilities. In real-world applications, a battery's actual specific energy will be lower due to various factors such as internal resistance, self-discharge, and temperature. However, it is still a useful metric for comparing different battery chemistries and predicting their potential performance.

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