Electric bicycles, or e-bikes, operate on a combination of electrical and manual power. Similar to a traditional bicycle, e-bikes can be powered solely through pedaling. Through pedaling and the motion of the bike, e-bikes convert manual power to electricity, which is then stored in the bicycle's battery. This electricity can then be used to power the bike's motor, either assisting your pedaling or replacing manual power entirely.
Types of Batteries
There are four main types of batteries used in e-bikes: sealed lead acid, or SLA; nickel-metal-hydride, or NiMH; lithium-ion, or Li-ion; and lithium-polymer, or Li-Po. The inexpensive SLA batteries are the most common and have a long history of use in e-bikes. However, these batteries are heavy, take a long time to charge and eventually decline in performance and stop working. Lighter weight NiMH batteries are quicker to charge, but suffer from poor performance in cold weather. In comparison, Li-ion and Li-Po batteries are lightweight, require no maintenance, charge quickly and hold more energy, but come with a higher price tag than the other battery types.
Lithium-Ion Batteries
First experimented with in 1912 by G.H. Lewis, the non-rechargeable lithium battery managed to attain popularity in the 1970s due to its low weight and high energy density. Experiments with rechargeable batteries led to the creation of the Li-ion battery, slightly lower in energy density but more stable than lithium batteries. The first commercially-produced Li-ion battery, created by Sony, appeared in 1991. The Li-ion battery became increasingly popular through the 1990s and 2000s due to the rise of portable technologies. Able to hold and disperse a charge equivalent to that of three traditional nickel-cadmium cells, a single Li-ion cell could be used to reduce the weight of portable devices considerably.
Lithium-Ion and Electric Bikes
Li-ion batteries are well-suited to e-bikes. Replacing your heavy SLA battery with a lightweight Li-ion battery can greatly reduce the weight of your bike, as lithium is a lightweight metal and fewer cells are required to provide and maintain an adequate charge. Li-ion batteries charge quickly, allowing you to use and replenish your battery's power supply numerous times over the course of your ride.
Like most other types, Li-ion batteries have a limited lifespan. While the amount of time for which they can hold a charge gradually diminishes, the power output remains steady over the course of the battery's lifespan. The higher production costs of Li-ion batteries result in higher prices than with SLA or NiMH batteries, which can greatly add to the cost of your e-bike. Due to the instability of lithium, Li-ion batteries require a protection circuit to ensure that their voltage and current do not exceed a safe level. If this protection circuit fails, the battery will eventually become overheated and, if this continues for an extended period of time, your Li-ion battery will either stop working or explode.
Lithium-Polymer and Lithium Iron Phosphate
More flexible and lighter than Li-ion, Li-Po batteries are equally suite to e-bikes, have similar benefits as Li-ion and are more stable under a variety of conditions. Due to these added benefits over those of Li-ion, Li-Po batteries are the most expensive of the four primary e-bike battery types.
Lithium iron phosphate, or LFP, batteries were first created in 1996 by Dr. John Goodenough and colleagues at the University of Texas. Safer than Li-ion and Li-Po, the added phosphate group removes much of the oxidation that leads to the instability of other lithium-based batteries. While heavier and more expensive than Li-ion and Li-Po, LFP batteries are flexible, durable, environmentally-friendly and perform well at a range of temperatures. Despite their recent invention and introduction to the market, LFP batteries are now available on a range of e-bikes.
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