The success of lithium-ion batteries is partly due to their very high energy density, the absence of the "memory effect" (where batteries become more difficult to recharge over time) that existed with previous battery technologies, and their relatively low production cost.
Lithium-ion batteries consist of two positive and negative electrodes separated by a liquid electrolyte such as ethylene carbonate or diethyl carbonate. The chemical composition of these batteries limits their shape, which is often rectangular. The capacity of lithium-ion batteries decreases with each charging cycle and can even discharge when not in use, which is undesirable. Worse still, the electrolyte can become unstable under extreme temperatures or if punctured, leading to thermal runaway and fire. However, this is very rare because electronic controllers typically regulate charging and discharging power to prevent the battery from overheating.
Lithium polymer battery technology is more advanced than lithium-ion batteries. It only emerged in the 1970s and has only recently been incorporated into smartphones. For example, Samsung only switched to lithium polymer in its Galaxy S20 series, while other manufacturers used the technology much earlier. Samsung then reverted to lithium-ion in its Galaxy Note20 series.
Lithium polymer technology also uses positive and negative electrodes, but instead of a liquid, it uses a dry, solid, porous chemical, or gel-like electrolyte. Therefore, polymer batteries can deliver a smaller form factor, more flexible and robust designs, and are less prone to thermal runaway due to electrolyte leakage. In short, they are safer.
A significant drawback of this technology is its considerably higher manufacturing cost. Lithium polymer batteries also have a shorter lifespan and store less energy than lithium-ion batteries of the same size. Furthermore, these batteries still rely on protection circuits to ensure the voltage remains within safe operating ranges.
Both types of batteries have their advantages and disadvantages. Generally speaking, lithium-ion batteries have the largest capacity and are cheaper. The disadvantage of lithium-ion batteries is that they gradually self-discharge, but this is not too important for phones that are always on, and the possibility of safety issues is small, but not zero.
In comparison, lithium polymer batteries are safer. This is especially important in today's era of rapid development in fast-charging technology. These batteries also have a very low self-discharge rate, so they don't lose much power when not in use. However, this also results in a higher price, shorter lifespan, and lower capacity density. Although the lightweight nature of lithium polymer batteries contributes to their overall better energy density.
