Chemistry – Lithium Ion

A lithium-ion battery

Although Lead-Acid batteries are cheap and are usable in a EV (Electric Vehicle) conversion, their energy to weight density do not make them to best option for an Electric Vehicle. However they are cheap and easy to obtain.

Lithium-Ion is at present to best viable option in terms of energy density, longevity and weight. However they are not cheap and do require a substantial amount of personal investment in the technology. Lithium-Ion battery packs do require monitoring in regards to Heat and Cold they operate best at specific temperatures.

Lithium-Ion also require a BMS (Battery Management System) in order to maintain an appropriate charge/discharge state.

Lithium-ion battery – Wikipedia, the free encyclopedia

A lithium-ion battery (sometimes Li-ion battery or LIB) is a member of a family of rechargeable battery types in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. Li-ion batteries use an intercalated lithium compound as one electrode material, compared to the metallic lithium used in a non-rechargeable lithium battery. The electrolyte, which allows for ionic movement, and the two electrodes are the consistent components of a lithium-ion cell.

Lithium-ion batteries are common in consumer electronics. They are one of the most popular types of rechargeable batteries for portable electronics, with a high energy density, no memory effect, and only a slow loss of charge when not in use. Beyond consumer electronics, LIBs are also growing in popularity for military, electric vehicle and aerospace applications.[6] For example, lithium-ion batteries are becoming a common replacement for the lead acid batteries that have been used historically for golf carts and utility vehicles. Instead of heavy lead plates and acid electrolyte, the trend is to use lightweight lithium-ion battery packs that can provide the same voltage as lead-acid batteries, so no modification to the vehicle’s drive system is required.

Chemistry, performance, cost and safety characteristics vary across LIB types. Handheld electronics mostly use LIBs based on lithium cobalt oxide (LiCoO
2
), which offers high energy density, but presents safety risks, especially when damaged. Lithium iron phosphate (LFP), lithium manganese oxide (LMO) and lithium nickel manganese cobalt oxide (NMC) offer lower energy density, but longer lives and inherent safety. Such batteries are widely used for electric tools, medical equipment and other roles. NMC in particular is a leading contender for automotive applications. Lithium nickel cobalt aluminum oxide (NCA) and lithium titanate (LTO) are specialty designs aimed at particular niche roles.

Lithium-ion batteries can be dangerous under some conditions and can pose a safety hazard since they contain, unlike other rechargeable batteries, a flammable electrolyte and are also kept pressurized. Because of this the testing standards for these batteries are more stringent than those for acid-electrolyte batteries, requiring both a broader range of test conditions and additional battery-specific tests

Other LFPs (lithium iron phosphate) vs. FLA (Flooded Lead Acid) Advantages

Lighter weight. For about the same usable energy capacity, LFPs are about one-third the weight. The reduction of weight contributed significantly to my vehicle’s increased acceleration and range, and decreased the amount of energy used per mile.

Less space. LFPs are about half of the volume of FLAs—I was able to consolidate all of my batteries in the bed of the pickup (instead of putting some under the hood), while retaining the pre-upgrade cargo space. This left more room under the hood for future enhancements, such as regenerative braking.

Improved capacity at low-temperatures. In cold (say, -4°F), the capacity of FLAs drops to about 50%. LFP capacity only drops by about 8% at that temperature. Although winters where I live aren’t that cold, I still had to reduce my winter driving range expectations by about 25% with FLAs—with LFPs my range reduction is less than 10%.

Steady discharge voltage & low impedance. An FLA’s discharge voltage tapers significantly as its state-of-charge decreases, whereas an LFP’s remains fairly constant until the battery is close to empty. Also, with one-quarter of the internal resistance (impedance) of FLAs, LFPs supply more power to the motor and lose less to heat. The steady discharge voltage and the lower impedance, along with the weight reduction, also improved the vehicle’s acceleration and range.

Higher charge & discharge current. LFPs can be safely charged and discharged at a much higher current than FLAs. A suitably large charger is capable of charging a nearly empty pack within about one-third of an hour (based on a 3C charge rate). To keep costs down, I kept my 30 A Manzanita Micro PFC-30 charger. The higher discharge capability allowed me to increase the battery amp setting on my Zilla controller, adding a few more horsepower to improve acceleration.

Less self-discharge. When not being charged, FLAs can lose 4% to 15% of their energy per month (depending on temperature), compared to 1% to 3% for LFPs. I can now let my EV sit for long periods without having to worry about recharging the batteries.

In addition to these measurable ones, there are some less tangible advantages that also make a big difference:

No idle memory. Although a phenomenon that is not well-documented, experienced EVers know that FLAs temporarily lose capacity when left idle. Prior to the battery upgrade, if the EV was idle for several days, the apparent capacity on the first drive/charge cycle was reduced by up to 25%. LFPs don’t experience this.

No maintenance. LFP batteries need no regular maintenance, eliminating the risk of damage that can result to FLAs if they are not watered—the reason that I got only 60% of the useful life out of my original batteries. There are “zero-maintenance” sealed lead-acid batteries, but these have a lower cycle life and a higher cost than vented FLAs, and they can still lose capacity if left in even a partially discharged state.

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