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Battery powering the EVs

Energy storage system, usually battery, is a primary part of any electric vehicle be it plug-in hybrid electric vehicles (PHEVs), and hybrid electric vehicles (HEVs). Rechargeable battery acts as the power source for propulsion of the vehicle. Ideally, electric vehicle batteries should have minimum mass, i.e. high specific energy, and minimum volume, i.e. have high energy density, low cost, long life and high safety. In practice there are mainly six rechargeable types readily available, namely Lead Acid (PbA), Nickel Metal Hydride (NiMH), Nickel Cadmium (NiCad), Lithium-ion or Lithium Polymer, Lithium Manganese and Lithium Iron Phosphate batteries.

1) Lead-Acid Batteries: Lead-acid batteries are inexpensive, safe, and reliable. They have the ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. However, they have a short cycle life if used regularly in deep discharge application. They have impede their use because of their low specific energy, poor cold-temperature performance, and short lifecycle and calendar.

2) Nickel-Metal Hydride Batteries: Nickel-metal hydride batteries, usually find their application in computer and medical equipment as they offer reasonable specific energy and specific power capabilities. These batteries have higher energy density and longer life cycle as compared to lead-acid batteries and are safe and abuse tolerant. These have been widely used in HEVs. NiMH is safe for disposal in the landfill and there have replaced Nickel Cadmium (which is not safe to dispose) batteries in most consumer batteries. The high cost, high self-discharge and heat generation at high temperatures, and the need to control hydrogen loss are the main challenges faced with these batteries.

3) Nickel Cadmium batteries: Nickel Cadmium batteries have significant storage density and a lifespan of around of 500 to 1,000 charging cycles. The major disadvantage is that the battery’s performance decline if it is subject to partial “charge-drain” cycles ( this phenomenon is know as memory effect). Ni-Cd batteries are now prohibited due to the toxicity of cadmium.

4) Lithium Polymer batteries: Lithium Polymer batteries are referred as lithium-ion battery that uses a gelled (Silicon-Graphene) polymer as an electrolyte. These batteries have soft shells which makes them lighter and more flexible than other kinds of lithium-ion batteries. LiPoly cells that can handle very high discharge currents and therefore find application in the R/C crowd for electric airplanes and helicopters. These batteries are free from memory effect and therefore can be charged even after partial discharge. It's biggest disadvantage is its aging effect, i.e. the ions present in batteries lose their ability to produce maximum energy after a certain period of time.

5) Lithium Manganese batteries: Lithium manganese batteries are Li-ion cells with lithium manganese oxide as cathode material. These are heavier than lithium polymer and the lithium-cobalt packs that are usually used in laptops and consumer electronics, but are also safer. They have good discharge capabilities, for example, in an 18650 package, Li-manganese can be discharged at currents of 20–30A with moderate heat buildup. This chemistry holds its voltage better over the course of the battery discharge than Lithium Polymer batteries .Li-manganese is used for power tools, medical instruments, as well as hybrid and electric vehicles.

6) Lithium Iron Phosphate batteries: LFP batteries are less energy dense than other lithium-ion chemistries such as Nickel-Cobalt-Manganese (NCM) and Nickel-Cobalt-Aluminum (NCA).They have a much longer cycle life; typically, 1500 to 2000 cycles. They are much more thermally stable i.e. no battery fires. These batteries are only slightly lighter than NiMH and a fair bit more expensive. At the present time, the most popular EV in China – the Wuling Hongguang Mini – is using LFP and retails for US$5,000.

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