Battery Basics III: Half vs Full Cell

This week’s newsletter is a long overdue explanation from a question on our Bluesky account.

TLDR: a half cell is testing only one commercially viable electrode, and a full cell pairs the two commercial electrodes together to test the complete battery system.

This gets confusing when switching between a Li-ion system and a lithium metal system. When we study solid electrolytes we typically use full cell to mean with the ideal Li metal anode. However in lithium ion cells, a li metal electrode is a half cell, and the li metal is in excess. 🤯🤯🤯

In battery testing, the terms half-cell and full cell refer to different configurations used to evaluate the electrochemical properties of the battery’s components or the complete system.

What is a half cell?

A half-cell consists of a single electrode (anode or cathode) paired with a stable reference electrode, such as lithium metal, and an electrolyte.

Purpose: used to test the individual performance of an anode or cathode material in isolation.

Counter Electrode: The working electrode is paired with a counter electrode that is not commercially viable due to it having excess capacity (therefore lowering energy density). In the lithium ion system, lithium metal serves as the counter/reference electrode as it provides the working ion (Li+) in excess.

Li-ion Example: Testing a graphite anode against a lithium metal counter electrode to measure its reversible capacity.

What is a full cell?

A full cell combines a specific anode and cathode material with an electrolyte to form a complete working battery.

Purpose: evaluates the overall performance of the battery, including energy density, power density, and long-term cycling stability.

Electrodes: Both the anode and cathode materials are application-specific and must balance in capacity for optimal performance.

Li-ion Example: Pairing a graphite anode with an NMC cathode to test the complete battery performance.

In summary, half-cells are ideal for research and development of electrode materials, while full cells are used to test the overall performance and compatibility of the battery system.

Read more here. 

Some Resources We Love (a repeat):

• Jill Pestana’s Battery Industry Onboarding, week 5 has free online Electrochemistry courses!

• If you are considering a PhD, this is one of my favorite articles on the topic