The differences between 21700 and 18650 lithium battery.

18650 batteries originally referred to nickel-hydrogen batteries and lithium-ion batteries. Since nickel-hydrogen batteries are rarely used now, they now refer to lithium-ion batteries. 21700 batteries are the model of the cylindrical battery with the name driving from the battery’s specific measurements: 18mmx65mm. The most intuitive difference between 21700 and 18650 lithium batteries is that the size has become larger.

Due to the limitation of the performance of battery materials, increasing the energy density by increasing the volume has become a key commercial consideration. It has been proposed that the energy density of the power battery cell should exceed 300Wh/kg in 2020, and the energy density of the power battery system should reach 260Wh/kg; in 2025, the energy density of the power battery system should reach 350Wh/kg. The elevated energy density requirement for power lithium batteries promotes the transformation of lithium battery models.

The energy density of the 21700 battery system is about 300Wh/kg, which is about 20% higher than the 250Wh/kg of the original 18650 battery system. The increase in battery capacity means that the number of cells required for the same energy is reduced by about 1/3, which reduces the difficulty of battery management and simplifies the number of accessories such as metal hardware. The weight and cost of the battery system PACK has been reduced at the cost of increased weight and cost of a single cell.

21700 and 18650 lithium-ion batteries share the same voltage, with the former being larger than the latter both in size and capacity.