What Is a Coin Cell Battery? Types, Assembly & Lab Setup Guide

If you've ever replaced the battery in a wristwatch, a car key fob, or a hearing aid, you've already held a coin cell battery in your hand — you probably just didn't think much about it. These tiny, disc-shaped power sources are everywhere, and for good reason. They're compact, reliable, and deliver a surprisingly steady voltage over long periods. But there's a lot more going on inside that little silver disc than most people realize, especially if you're approaching coin cells from a research or engineering angle.

Let's break it all down — what a coin cell actually is, the different types you'll encounter, how they're assembled, and how to set up a proper lab environment for working with them.

What Exactly Is a Coin Cell Battery?

A coin cell battery (also called a button cell) is a small, flat, cylindrical electrochemical cell. The name comes from its shape — it looks like a coin, typically ranging from about 5 mm to 25 mm in diameter and 1 mm to 6 mm in thickness. Despite their small size, they operate on the same fundamental electrochemical principles as any other battery: an anode (negative electrode), a cathode (positive electrode), an electrolyte, and a separator between the two electrodes.

What makes coin cells special in a lab setting is their versatility. Researchers use them extensively to test new electrode materials and electrolyte formulations at a small scale before scaling up. Assembling a coin cell takes only a fraction of the active material needed for a pouch or cylindrical cell, which makes them extremely cost-effective for early-stage material evaluation.

In everyday consumer applications, coin cells power devices where space is premium and energy requirements are modest — think calculators, medical implants, small IoT sensors, and computer BIOS chips.

The Naming System: How to Read a Coin Cell Code

Coin cells follow a standardized naming convention that tells you a lot about the cell before you even open the package.

For most lithium coin cells (IEC standard), the format is CR diameter height. For example:

• CR2032 — 20 mm diameter, 3.2 mm thick
• CR2025 — 20 mm diameter, 2.5 mm thick
• CR1632 — 16 mm diameter, 3.2 mm thick
• CR2016 — 20 mm diameter, 1.6 mm thick

The "CR" prefix indicates a lithium manganese dioxide chemistry. Other prefix codes indicate different chemistries — "LR" for alkaline, "SR" for silver oxide, and "BR" for lithium carbon monofluoride.

For research-grade coin cells (often referred to as half-cells or full cells in the lab), common hardware formats include the CR2016, CR2025, and CR2032, with the 2032 being the most popular due to its balance of internal volume and widespread commercial availability of hardware components.

Types of Coin Cell Batteries

Not all coin cells are the same. The chemistry inside varies significantly depending on the application, and understanding these differences is critical for anyone working in battery research.

Lithium Manganese Dioxide (Li/MnO₂) - CR Series These are the most common consumer coin cells. They offer a nominal voltage of 3 V, excellent shelf life (up to 10 years), a wide operating temperature range, and stable discharge. They're not rechargeable.

Silver Oxide (Ag₂O) - SR Series Common in watches and hearing aids. Silver oxide cells deliver 1.55 V with a very flat discharge curve, meaning the voltage stays consistent right up until the cell is exhausted. More expensive than alkaline but superior in performance for precision devices.

Alkaline (LR Series) Cheaper and widely available, but with a sloping discharge profile and lower energy density than lithium or silver oxide options. Typically rated at 1.5 V. Used in low-drain applications.

Lithium Carbon Monofluoride (Li/CFx) - BR Series These cells offer extremely high energy density and operate across an impressive temperature range (-40°C to 85°C). Used in industrial and military applications.

Research-Grade (Custom Chemistry) In a laboratory setting, the coin cell hardware (the stainless steel casing, spacers, springs, and caps) is used as a vessel to test custom electrode materials. Researchers might assemble cells with lithium metal anodes against a new cathode material, or test sodium-ion, potassium-ion, or even zinc-ion chemistries using the same coin cell format.

How Coin Cells Are Assembled

Understanding coin cell assembly is non-negotiable if you're doing battery research. The process sounds simple, but getting it right requires attention to detail and, in most cases, a controlled atmosphere.

The Components

A standard CR2032-format research coin cell consists of:

• Positive cap (cathode cup) — The bottom shell, where the cathode sits
• Cathode — The positive electrode, usually prepared as a coated film on aluminum foil
• Separator — A thin, porous membrane (commonly Celgard polypropylene or glass fiber) that prevents the electrodes from touching while allowing ion transport
• Electrolyte — The ionic liquid or salt solution that enables ion movement between electrodes
• Anode — For lithium half-cells, this is typically a lithium metal disc; for full cells, it's a separate electrode film
• Spacer(s) — Stainless steel discs used to fill space and apply pressure
• Spring-Ensures consistent contact pressure inside the cell
• Negative cap (anode cup) — The top shell that completes the enclosure

Step-by-Step Assembly

Step 1: Electrode Preparation Electrodes are prepared by mixing the active material with a conductive additive (like carbon black) and a binder (like PVDF) in a solvent (usually NMP for PVDF-based systems). The resulting slurry is coated onto a current collector foil, dried in a vacuum oven, and calendared (pressed) to the appropriate density. Discs are then punched out using a precision punch tool.

Step 2: Drying Electrodes and separators should be dried under vacuum at elevated temperatures (typically 80–120°C for at least 12 hours) to remove residual moisture. Water contamination is one of the leading causes of poor cell performance.

Step 3: Transfer to Glove Box This is where most beginners make mistakes. Lithium metal and many electrolytes are extremely sensitive to moisture and oxygen. Assembly should take place in an argon-filled glove box with water and oxygen levels below 1 ppm. Even brief exposure to ambient air can degrade lithium metal and contaminate the electrolyte.

Step 4: Assembly Sequence (inside glove box) Place the positive cap flat-side down. Add the cathode disc (coated side up). Place the separator on top. Add a few drops of electrolyte (typically 50–80 µL for a CR2032). Carefully place the anode (lithium disc or anode film). Add spacers and the spring on top. Press the negative cap over the assembly. Crimp the cell shut using a coin cell crimper.

Step 5: Crimping A coin cell crimper applies uniform pressure to seal the two caps together. Consistent crimping force is critical — too little and the cell leaks; too much and the electrodes can be damaged or short-circuited.

Step 6: Resting and Testing Let newly assembled cells rest for a few hours (or overnight) before testing to allow the electrolyte to fully wet the electrodes. Then connect to a battery cycler for electrochemical characterization.

Lab Setup Guide for Coin Cell Research

Setting up a coin cell assembly lab requires some investment, but you don't need to break the bank to get started.

Essential Equipment:

• Glove box (argon atmosphere) — The cornerstone of any lithium battery lab. Brands like MBraun, Vigor, and Inert are commonly used.
• Vacuum oven — For drying electrodes and components.
• Coin cell crimper — Manual or pneumatic. Pneumatic crimpers provide more consistent pressure.
• Electrode punch set — For cutting circular electrode discs (commonly 12 mm, 14 mm, or 16 mm for coin cell formats).
• Analytical balance — For precise electrode mass measurement (needed for calculating capacity per gram).
• Battery cycler — Systems from Neware, Arbin, BioLogic, or Gamry allow you to run charge-discharge cycles, EIS, and CV.
• Micrometer — For measuring electrode thickness.
• Micropipette — For dispensing electrolyte precisely.

Safety Considerations: Lithium metal is reactive with water and can ignite. Electrolyte solvents like EC and DMC are flammable. Always have proper fire suppression equipment nearby, wear appropriate PPE (nitrile gloves, safety glasses, lab coat), and work in a well-ventilated space outside the glove box when handling solvents.

Tips for Beginners: Start with known, well-characterized materials (like commercial LFP or NMC cathodes with standard LP30 electrolyte) before moving to novel materials. This gives you a baseline to calibrate your assembly technique before variables multiply.

Final Thoughts

Coin cells might seem like a small, niche topic — but they're the workhorse of battery research worldwide. From fundamental material studies to prototype validation, the coin cell format offers an accessible, low-cost entry point into electrochemical testing. Master the assembly process, keep your glove box clean and dry, and treat your electrode preparation with care. The data quality you get from a well-assembled coin cell can genuinely move science forward.