Energy storage is the incarceration of energy at one time for use at a later time to reduce imbalances between energy demand and energy production. Accumulators or batteries are devices that store energy. From the more economical Nissan Leaf to the high-end Tesla Model S, there are many different models of commercially successful BEVs on the road. Furthermore, as there have been great investments in support of infrastructure, battery electric vehicles have become a greatly viable and feasible option in the automotive market for consumers.
While most BEV production models utilize one type of battery, there are several different types of batteries that are available in battery electric vehicles.
Lead Acid Battery
The lead-acid battery is a type of rechargeable battery first invented in 1859 by French physicist Gaston Planté. It is the first type of rechargeable battery. In contrast to later types of rechargeable batteries, Lead-Acid batteries have the lowest energy density. A lead-acid battery consists of a negative electrode made of spongy or porous lead. The lead is porous to facilitate the formation and dissolution of lead. The positive electrode consists of lead oxide. Both electrodes are immersed in an electrolytic solution of sulfuric acid and water. These batteries found in commercially available electric-drive vehicles for ancillary loads are quite heavy.
- No danger of under or over-charging and a high level of operating safety (due to tray insulation)
- Poor specific energy (34 Wh/kg)
- Short Cycle life (700 cycles)
- Poor cold-temperature performance
- Heavy (material – lead)
Nickel-Metal Hydride Batteries (NiMH)
These came into commercial use a little earlier in the late 1980s. These are used routinely in computer & medical equipment and some Hybrid Electric Vehicles as they offer reasonable specific energy and specific power capabilities.
The negative active material, in the charged state, is hydrogen in the form of a metal hydride. As the battery is charged and discharged, a reversible hydrogen absorption–desorption reaction occurs. The electrolyte is aqueous potassium hydroxide, with lithium hydroxide additive to improve the charging efficiency of the positive electrode, by reducing oxygen evolution. Almost all Ni–MH batteries are of the sealed type. They exhibit high power capability, tolerance to overcharge/discharge, and environmental compatibility and safety, which make them appropriate for portable power tools and HEVs, although their energy density is relatively low compared to Li-ion batteries.
- Specific energy (68 Wh/kg), which is double in contrast to lead-acid batteries.
- Much longer life cycle(5-7 years) than lead-acid batteries though lesser than Lithium-ion batteries
- Low charging efficiency
- High Self-discharging rate up to 12.5% per day at room temperature which increases at higher temperatures
- Generation of heat during fast charging & discharging.
In the early 1990s Lithium batteries came into the commercial, holding an elevated energy density. Unlike most batteries, these are unlikely to lose their charge when not being used. Lithium-ion (Li-ion) batteries are the standard for modern battery electric vehicles. There are many types of Li-ion batteries that each have different characteristics, but vehicle manufactures are focused on variants that have excellent longevity. This is a feature called self-discharge.
In the batteries, lithium ions move from the negative electrode through an electrolyte to the positive electrode during discharge, and back when charging. Li-ion batteries use an intercalated lithium compound as the material at the positive electrode and typically graphite at the negative electrode.
- Firstly excellent specific energy (140 Wh/kg) and secondly energy density
- Low self-discharge rate (5% per day) which is much lower than Nickel Metal Hydride & Lead Acid batteries
- Good high-temperature performance
- Lighter and smaller in size in comparison to others for the same battery size
- Very high cycle life (6000 cycles)
- Almost negligible maintenance cost and easily recyclable, hence more reliable
- More expensive
- Major safety concerns regarding the overcharging & overheating as it can experience a thermal runaway, which can trigger vehicle fires or explosions, if not taken care of.
Types of Lithium-ion batteries
1. LCO (Lithium Cobalt Oxide)
Its high specific energy makes Li-cobalt the popular choice for mobile phones, laptops, and digital cameras. The battery consists of a cobalt oxide cathode and a graphite carbon anode. The drawback of Li-cobalt is its relatively short life span, low thermal stability, and limited load capabilities.
2. LMO (Lithium Manganese Oxide)
Li-ion with manganese spinel was first published in the Materials Research Bulletin in 1983. Firstly, the architecture forms a three-dimensional spinel structure that improves ion flow on the electrode, which results in lower internal resistance and improved current handling. A further advantage of spinel is high thermal stability and safety. However, the cycle and calendar life limits itself. Moreover, in power tools, medical instruments, as well as hybrid and electric vehicles LMO, can be found.
3. NMC (Lithium Nickel Manganese Cobalt Oxide)
One of the most successful Li-ion systems is a cathode combination of nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems are tailors to serve as Energy Cells or Power Cells.
The secret of NMC lies in combining nickel and manganese. Nickel has high specific energy but poor stability; manganese has the benefit of forming a spinel structure to achieve low internal resistance but offers low specific energy. NMC is the battery of choice for power tools, e-bikes, and other electric powertrains.
4. LFP (Lithium Iron Phosphate)
Li-phosphate offers good electrochemical performance with low resistance. Moreover, nano-scale phosphate cathode material turned this into reality. The key benefits are high current rating and long cycle life, besides good thermal stability, enhanced safety, and tolerance if abused.
Li-phosphate often replaces the lead-acid starter battery. Moreover, Li-phosphate is more tolerant to full charge conditions and is less stressed than other lithium-ion systems if kept at high voltage for a prolonged time. Further, it maintains the full charge level and prevents sulfation on lead-acid batteries.
5. NCA (Lithium Nickel Cobalt Aluminum Oxide)
Lithium nickel cobalt aluminum oxide battery, or NCA, has been around since 1999 for special applications. It shares similarities with NMC by offering high specific energy, reasonably good specific power, and a long life span. Moreover, less flattering are safety and cost. It is applied on medical devices, industrial & electric powertrains.
6. LTO (Lithium Titanite)
Li-titanate replaces the graphite in the anode of a typical lithium-ion battery and the material forms into a spinel structure. The cathode can be lithium manganese oxide or NMC. LTO (commonly Li4Ti5O12) has advantages over the conventional cobalt-blended Li-ion with graphite anode by attaining zero-strain property, no SEI film formation, and no lithium plating when fast charging and charging at low temperature. Thermal stability under high temperatures is also better than other Li-ion systems; however, the battery is expensive. It is used in UPS, electric powered train & solar-powered street lighting.
Having excellent specific energy and low self-discharge rate, variants of Li-ion batteries are now the dominant type of battery. Moreover, lead-acid and NiMH batteries no longer appear to be appropriate for use.
To sum up, with the evolving technology, the need for batteries is also growing at an astronomical pace.
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