Why does researchers use lithium metal as the “cathode” when studying anode materials in batteries?
In the field of lithium battery research, many beginners often get confused about the naming of “anode” and “cathode”:
- Why, when studying anode materials, is lithium metal used as the cathode in experiments?
- Since the tested anode material gains electrons during testing, why is it still called the “anode”?
- What is the difference between researching anode materials and cathode materials?
The core of these questions actually involves the discharge principle of batteries and the commonly used half-cell testing method in the laboratory. This article will answer them step by step from the perspectives of principle, naming rules, and research focus.
1. Why is lithium metal used as the “cathode” in research?
In the lab, when studying a new anode material, the common approach is to assemble a half-cell:
Structure:
Tested anode material || Electrolyte & separator || Lithium metal
Schematic Diagram of Half-cell Structure
Here, lithium metal is used as the “cathode.” The reason is:
During discharge, the tested anode material releases lithium ions and electrons, thus acting as the anode.
Lithium metal, on the other hand, serves as a standard counter electrode. It can easily accept lithium ions and electrons (Li⁺ + e⁻ → Li), acting as the cathode in this system.
Therefore, the role of lithium foil is simply to provide a reference and lithium source, and does not mean it is the cathode in practical applications. This setup is similar to testing a new engine (the anode material) by mounting it on a standard test frame (the lithium counter electrode), instead of building a brand-new car. The test frame is universal and well-characterized, which allows accurate evaluation of the new engine’s performance.
2. Why is it still called “anode material”?
Many people are confused: during half-cell charging, the tested material gains electrons and behaves like a cathode, so why is it still called an anode material?
The key is that electrode naming is determined by their behavior during discharge.
In a full cell discharge process:
The anode undergoes oxidation (loses electrons, releases lithium ions).
The cathode undergoes reduction (gains electrons, receives lithium ions).
Schematic Diagram of Half-cell “Charging” Process
Thus, although in some moments during half-cell testing the tested material may seem to act like a cathode, its actual role in a working battery is the deciding factor.
Therefore, the researched material is ultimately the electrode that loses electrons during discharge, so it is classified as an anode material.
3. Researching anode materials vs. cathode materials
Graphite anodes are already close to their theoretical capacity limit, but applications such as electric vehicles require ever-higher energy density. This makes the development of next-generation high-capacity anodes (such as silicon and lithium metal) extremely urgent. However, these materials bring significant technical challenges, which has driven massive research efforts.
At the same time, cathode materials are equally important, often accounting for more than 40% of the total battery cost. Cathode research is also highly active, with multiple technology routes (LFP, NMC, LMO, etc.). To some extent, improvements in energy density rely more on cathodes, since cathode capacities are generally lower than anodes.
The reason we often hear more about “anode material research” is that the anode field currently has greater technical challenges and more room for improvement. The focus of research is therefore quite different between the two, as shown below:
| Characteristics | Anode Materials | Cathode Materials |
|---|---|---|
|
Current Mainstream Materials |
Graphite |
Lithium Cobalt Oxide (LCO), Lithium Iron Phosphate (LFP), Ternary Materials (NMC/NCA) |
|
Core Research Goals |
Increase capacity, improve safety, enhance rate performance |
Increase capacity/voltage, improve stability/cycle life, reduce cost |
|
Major Challenges |
|
|
|
Popular Research Directions |
|
|
4. Conclusion
Using lithium foil as the “cathode” in experiments is simply because it provides a stable counter electrode and lithium source to help evaluate the performance of new anode materials.
Electrode naming follows the discharge behavior: the studied material is called an anode material because it loses electrons during discharge, not based on its temporary role in a test.
Both anode and cathode research are crucial, but due to the huge potential for breakthroughs in energy density and safety on the anode side, anode materials have become a hot research topic in recent years.
Understanding these concepts helps clarify the logic behind lithium battery R&D and avoids the common confusion regarding electrode naming.
