From 18650 to 21700: The Evolution of Cylindrical Batteries

In the development history of lithium-ion batteries, the 18650 and 21700 models are milestone. Their evolution is not just a change in 

numbers, but represents a leapfrog breakthrough in new energy technologies.

18650: The Classic That Launched the Lithium Battery Era

The 18650 battery was mass-produced by Sony in 1991, defining the standard for cylindrical lithium batteries. Its design with a diameter 

of 18mm and length of 65mm achieved a balance between volume and energy density in small electronic products. In 2008, Tesla 

Roadster first connected thousands of 18650 batteries in series, pioneering the era of electric vehicles. However, this battery, designed 

for consumer electronics, has inherent limitations: the single-cell capacity is only 1.8-3.5Ah. After grouping, complex thermal management 

and structural protection are required, leading to increased weight and rising costs. Take the Model S as an example, its 85kWh battery 

pack consists of about 7,000 18650 cells, with a system energy density of only 250Wh/kg, making it difficult for range and cost to meet 

the needs of large-scale popularization.

21700: The Innovator Reconstructing Battery Performance

The 21700 battery (21mm in diameter, 70mm in length) mass-produced in 2016 completely changed this situation. By increasing the cell 

volume, its single-cell capacity has been increased to 5Ah, which is more than 35% higher than that of 18650. More importantly, the 

adoption of a new material system of nickel-cobalt-aluminum oxide (NCA) cathode and silicon-carbon composite anode has increased 

the system energy density to 300Wh/kg, an increase of 20%. This means that under the same weight, the range of the 21700 battery 

pack can be increased by 20%, while the number of cells is reduced by 30%, significantly simplifying the battery pack structure. Taking 

the Tesla Model 3 as an example, after switching to 21700, the battery system cost has been reduced by 9%, with the cost per kWh 

dropping from 171 to 155.

The Core Code of Technological Breakthroughs

The progress of 21700 stems from multiple innovations:

1.Material Upgrade: High-nickel and low-cobalt NCA cathode and silicon-based anode improve capacity while reducing costs.

2.Structural Optimization: Larger cells reduce metal connectors and shell materials, reducing the weight of the battery pack by more 

than 10%.

3.Process Innovation: For example, the tabless design of Ruien New Energy reconstructs the electron transmission path, reducing 

internal resistance by 80% and temperature rise by 30%, supporting 80% charging in 10 minutes.

4.Thermal Management Evolution: The fourth-generation thermal management system integrates waste heat recovery technology, 

keeping the battery at the optimal operating temperature and extending its service life by 20%.

Industry Changes and Future Outlook

The mass production of 21700 batteries has triggered cross-industry chain reactions. In the energy storage field, its high energy 

density and low-cost characteristics have promoted a 40% increase in the capacity of home energy storage systems, shortening 

the investment payback period of household photovoltaic energy storage from 8 years to 6 years and accelerating the popularization 

of renewable energy. In the power tools industry, due to a 25% reduction in battery weight and a 50% extension in range, new 

equipment such as cordless industrial-grade impact wrenches have been developed, completely changing the construction scene.

In the field of portable devices, 21700 has brought a 35% increase in the range of drones, expanding their single operation area in 

agricultural plant protection from 100 mu to 135 mu; and smart home devices using 21700 batteries have a standby time exceeding 

18 months, reducing the trouble of frequent battery replacement.

The next generation of battery technologies is already in the making. The 46800 large cylindrical battery will increase charge-discharge 

efficiency by another 20% through an all-tab design, and solid-state electrolyte technology is expected to solve the safety hazards of 

liquid electrolytes. In the longer term, the development of sodium-ion batteries and lithium manganese iron phosphate batteries will 

further reduce dependence on rare metals and promote the transformation of the battery industry towards resource sustainability. 

The evolution from 18650 to 21700 has proved that every breakthrough in battery technology is reshaping the way humans use 

energy, and this innovation will continue to ferment in broader fields such as the energy internet and space exploration.