Your Ultimate Guide to Explore the 21700 Battery

By Gerald, Updated on August 8, 2024

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In this article, we’ll take a deep dive into the features, specifications, and typical applications of 21700 batteries. Whether you are a consumer, a manufacturer, or just someone interested in energy storage solutions, this guide will provide you with all the information you need.

Part 1. What is a 21700 Battery?

A 21700 battery is a type of lithium-ion rechargeable cell. The name “21700” refers to its physical dimensions: it has a 21mm diameter and 70mm length. This makes it larger than the popular 18650 battery, which measures 18mm x 65mm. While the 21700 may seem just slightly bigger, its larger size provides substantial benefits in terms of energy storage, power output, and overall performance.

The increased size of the 21700 battery means that it can hold significantly more energy compared to its smaller cousins. This results in a longer battery life per charge and improved efficiency in many high-demand devices.

One of the standout features of the 21700 is its higher capacity and energy density compared to smaller batteries. This allows it to power larger devices, such as electric vehicles and solar energy storage systems, with more reliable performance and fewer recharges.

Part 2. 21700 battery size

As mentioned earlier, the 21700 battery is 21mm in diameter and 70mm in length. This cylindrical shape is the same as other lithium-ion cells, but the extra length and diameter allow for greater energy storage. To put it into perspective, a typical 21700 battery can store 5,000mAh of charge, whereas the more common 18650 battery typically holds between 2,500mAh to 3,500mAh.

This size increase directly correlates with performance improvements. Larger batteries can deliver higher discharge rates, which means that devices using 21700 batteries can consume energy at a faster rate without significantly reducing the battery’s lifespan.

It’s also worth noting that the 21700 battery is widely used in applications that require both high energy density and compact size. Its ability to deliver more power with less weight makes it perfect for energy-demanding applications like electric vehicles and power tools.

Part 3. Chemistry and structure

The chemistry and internal structure of a 21700 battery can vary depending on the manufacturer and its intended application. However, most 21700 cells are based on lithium-ion (Li-ion) technology, which is widely used across many types of rechargeable batteries due to its excellent energy density and long lifespan.

There are several types of lithium-ion chemistries that could be used within the 21700 format:

Lithium Cobalt Oxide (LCO): High energy density but lower safety and lifespan.
Lithium Iron Phosphate (LiFePO4): Safer with longer cycles but lower energy density.
Nickel Manganese Cobalt (NCM): Provides a balance of energy density, cost, and safety.

The internal structure of the 21700 battery consists of several key components:

Anode: Usually made from graphite, this component stores the lithium ions during the discharge process.
Cathode: Often made from lithium cobalt oxide or similar materials, it releases lithium ions during discharge.
Electrolyte: A liquid or gel-like substance that allows the flow of lithium ions between the anode and cathode.
Separator: A non-conductive layer that prevents the anode and cathode from coming into direct contact, thus avoiding short circuits.

While 21700 batteries come in different chemistries, they all share a similar basic structure that allows them to provide excellent performance in a wide range of applications.

Part 4. Voltage

The voltage of a 21700 battery typically varies between 3.6V to 3.7V when it’s in use. However, the voltage will fluctuate depending on its state of charge:

Full Charge: The voltage will be around 4.2V.
Nominal Voltage: The 3.7V is the average voltage at which most of the battery’s charge is used.
Discharge Cutoff: Below 3.0V, the battery will lose its charge completely and may suffer permanent damage if discharged beyond this point.

The nominal voltage of 21700 batteries makes them compatible with most devices that use lithium-ion cells, including electric vehicles, flashlights, and drones. It’s important to understand these voltage ranges when selecting chargers and other accessories.

Part 5. Weight

The weight of a 21700 battery typically ranges from 50 to 70 grams, depending on the exact chemistry and the manufacturer. While this weight is heavier than that of smaller 18650 batteries, the trade-off is the higher capacity and energy density of the 21700.

For example, an 18650 battery might weigh only about 40-50 grams, but because the 21700 holds more power, it’s heavier. This makes the 21700 battery ideal for use in larger devices that need extended run times, like electric vehicles or power tools, where every extra gram is justified by the performance improvements.

Part 6. Energy Density

One of the key advantages of 21700 batteries is their energy density. Typically, 21700 batteries have an energy density ranging from 250 Wh/kg to 300 Wh/kg, depending on the chemistry used. This is a notable improvement compared to 18650 batteries, which usually offer around 180 Wh/kg to 250 Wh/kg.

The higher energy density of the 21700 battery allows for longer use times between charges. It also makes these batteries ideal for devices that require both power and portability. For instance, electric vehicles can use 21700 cells to store more energy in less space, resulting in longer driving ranges without increasing the size of the battery pack.

Part 7. 21700 cell and 21700 pack(battery)

A 21700 cell refers to an individual battery unit, while a 21700 pack is a configuration of multiple cells connected in series or parallel. The 21700 pack is typically what you find in larger, power-hungry devices like electric vehicles or solar energy storage systems.

Series Connection: This method connects cells end to end to increase the total voltage. For instance, a 3.7V 21700 cell connected in series with another would provide a 7.4V pack.
Parallel Connection: Cells are connected side by side to increase the overall capacity (mAh). This increases the total energy storage without affecting the voltage.
Series-Parallel Combination: This is the most common method, where cells are arranged in both series and parallel to achieve the desired voltage and capacity.

To safely operate a 21700 pack, it’s crucial to use a Battery Management System (BMS). The BMS monitors the voltage, temperature, and charge cycles of each individual cell within the pack to ensure safe operation.

Part 8. Typical applications

The 21700 battery is used in a variety of high-demand applications, including:

Electric Vehicles (EVs): Due to their high energy density and longevity, 21700 batteries are being adopted by companies like Tesla for use in their vehicles. These batteries help provide longer driving ranges between charges.
Power Tools: Companies like DeWalt and Makita use 21700 cells in their cordless power tools for improved runtime and power output.
Flashlights: High-performance flashlights use 21700 cells for extended run times, allowing users to operate lights for hours on a single charge.
E-cigarettes (Vaping): The 21700 battery is favored in high-wattage e-cigarettes due to its ability to deliver high current.
Drones: Drones that require extended flight times and higher power output rely on 21700 batteries for their long-lasting power.

Part 9. 21700 battery vs 18650

The most significant difference between the 21700 and 18650 batteries is their size and capacity. The 21700 is larger (21mm x 70mm) compared to the 18650 (18mm x 65mm), and this size difference allows the 21700 to store more energy.

Capacity: The 21700 typically holds 5000mAh or more, while the 18650 generally maxes out around 3500mAh.
Energy Density: 21700 batteries have a higher energy density, meaning they can deliver more power for a longer period of time, making them a better choice for high-demand applications.

You can click to view more details:

21700 vs 18650 Battery: What Difference is between them?

Part 10. How long does a 21700 battery last?

The lifespan of a 21700 battery is generally measured in charge cycles, which refers to the number of times the battery can be charged and discharged before it starts to lose capacity. On average, a 21700 battery can last between 500 to 1000 charge cycles, depending on its chemistry, usage, and maintenance.

To maximize the lifespan of your 21700 battery, avoid deep discharges (below 20% charge) and overcharging (above 100%). Proper storage at moderate temperatures also helps ensure a long lifespan.

Part 11. Charger, charging and maintenance

When charging your 21700 battery, make sure to use a compatible charger designed for lithium-ion batteries. A Battery Management System (BMS) is often required for safe charging, especially in battery packs.

Charging Tips:

Never leave your battery charging unattended.
Use a charger with overcharge protection to prevent battery damage.
Store your 21700 battery in a cool, dry place to avoid overheating.

Maintenance Tips:

Check for signs of wear, such as swelling or leakage.
Regularly clean the battery terminals to ensure proper connections.
If the battery is not used for an extended period, store it at 40-60% charge.

Part 12. Ufine 21700 battery

Ufine, a leading Chinese manufacturer of lithium batteries. They’re known for customizing battery shapes, sizes, capacities, and voltages. Whether you need lithium polymer, cylindrical, or LiFePO4 batteries, Ufine has you covered.

Their 21700 batteries are reliable and high-quality, catering to various power needs. If you’re looking for a battery that fits your specific requirements, Ufine is a great option to consider. They combine innovation with practicality, ensuring you get the best power solution for your devices.

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