Application of Battery Types in Hybrid Vehicles (Hybrid Cars, Electric Cars)

[latexpage]

Teknikimobil.com – After discussing various types of batteries, for example lead-acid , this time we will discuss the application of battery types in hybrid vehicles. It is known that over the last decade, battery technology has improved drastically and many high-performance batteries have been developed. As a result, various batteries can be used to apply to hybrid vehicles. Therefore, an explanation of the typical batteries used in hybrid electric vehicles including HEV, plug-in HEV, and BEV is important to know.

Benoit cars

Lead-Acid Batteries

This type of battery is one of the oldest rechargeable batteries. Two types of lead-acid batteries, starting and deep cycle, are used for vehicle applications. Early type lead-acid batteries consist of many thin plates to achieve maximum surface area for maximum current output, whereas heavy cycle lead-acid batteries have thicker plates to achieve longer service life. Early lead-type batteries began to be used to start engines and were then kept in a current state of charge. If this type of battery is repeatedly charged/discharged, such as the battery in a hybrid vehicle, it will eventually cause damage. For hybrid vehicle applications, specially designed deep cycle lead-cell cells are required to withstand frequent charging/discharging; Basic technical requirements for this type of battery are listed in the following table.

Basic Technical Requirements for Lead-Acid Cells in HEV/EV Applications

Also read: How to replace the front brake pads on a Honda CR-V

Meanwhile, the main advantages of lead-acid batteries include:

· Low cost compared to other batteries

· The cell open circuit voltage is high

· Easily recycle cell components

· Accurate indication of SOC as the electrolyte taking part in the reaction resulting in that SOC can be determined by measuring the specific gravity of the electrolyte.

And the main weaknesses include several things, namely:

· Relatively low cycle life, typically 500-800 full cycles

· Low energy density, typically 30-40 Wh/kg

· High self-discharge rate

· Low cost/discharge efficiency

Nickel-Cadmium Battery (NiCd)

Nickel-cadmium (NiCd) batteries have extraordinary high charge/discharge capabilities and have been widely used in applications requiring high power charge/discharge services. For hybrid vehicle applications, the basic technical requirements for NiCd cells are listed in the following.

Basic Technical Requirements for NiCd Cells in HEV / EV Applications

Compared with other batteries, NiCd batteries have the following advantages for hybrid vehicle applications:

· High Charge/Discharge Rate NiCd cells are capable of recharging at a high rate within one hour under controlled conditions.

· High Discharge Rate Due to its low internal resistance and flexibility, NiCd batteries are well suited for applications with high discharge or current such as hybrid vehicles.

· Wide Temperature Range NiCd cells can operate from -40 to 50◦C.

· Long Cycle Life NiCd batteries can usually last more than 1000 full charge/discharge cycles.

· Long Shelf Life in SOC NiCd batteries can be stored at SOC level even when fully discharged without damaging their life.

Meanwhile, the main weaknesses of NiCd batteries are as follows:

· Low capacity compared to other competitive batteries

· Memory effect: sometimes called fade or voltage depression, can cause power and capacity degradation with cycling

· Environmental concerns with cadmium use

Nickel–Metal Hydride (NiMH) Battery

Nickel-metal hydride (NiMH) batteries use hydrogen absorbed in a metal alloy for the active negative material. Because metal hydride electrodes have a higher energy density than cadmium electrodes, NiMH batteries have higher capacity and longer lifespan than NiCd batteries. Additionally, NiMH batteries are free from cadmium and are thus considered environmentally friendly batteries. The higher specific energy and cycle life make NiMH batteries especially suitable for HEV/EV applications. Basic technical requirements for NiMH cells are listed in the following table.

Basic Technical Requirements for NiMH Cells in HEV / EV Applications

Lithium-Ion (Li-ion) Battery

Due to the outstanding features of lithium metal, Li-ion batteries have recently quickly penetrated into hybrid vehicle propulsion systems. Lithium ion batteries have high efficiency, special power and energy density, low self-discharge rate and long service life. They are environmentally friendly because their components can be recycled. For HEV/EV applications, the basic technical requirements of Li-ion cells are listed in the following table.

Basic Technical Requirements for Li-Ion Cells in HEV / EV Applications

The following advantages make Li-ion batteries much more suitable for HEV/EV applications:

· High Open-Circuit Voltage Lithium ion can have an open-circuit voltage higher than 4 V, which can significantly reduce the number of cells in a battery pack.

· High-Energy Density Lithium ion batteries generally have an energy of more than 200 Wh/L, which makes them very compact.

· High Specific Energy Lithium ion batteries can have an energy density of more than 250 Wh/kg, which lightens the overall weight of the vehicle.

· Wide Operating Temperature Range Many Lithium ion batteries can be operated at temperatures between -30 and 50°C without reducing battery life.

· High-Power Capability Lithium ion batteries can be discharged and charged at higher C rates under normal operating conditions, so small batteries can meet peak power requirements and absorb most of the regenerative energy.

· Flat Open-Circuit Voltage and Internal Resistance Characteristics Lithium ion batteries typically have flat open-circuit voltage versus SOC characteristics as well as flat open-circuit voltage versus SOC characteristics, which makes it easier to control HEV/EV power flow.

Currently, the main disadvantage of Li-ion batteries for HEV/EV applications is safety concerns when the battery is overcharged or overheated. By the nature of Li-ion batteries, if the cell is overcharged, its positive active material can be released to the point of instability, causing thermal decomposition and possible fire; Overheating or overheating Li-ion cells can also produce exothermic reactions between lithium ions and electrolyte. To avoid overcharged and overheated, the following two steps must be carried out in the Li-ion battery system:

· Special electrical circuits are required within the battery pack to provide protection from overdischarging and overcharging, and cell balancing circuits are also usually required.

· It is also necessary to have over-temperature and over-pressure protection devices in the Li-ion battery system.

Lithium–Iron–Phosphate Batteries

With the advancement of hybrid electric vehicle technology, requirements for battery performance, durability and cost are becoming increasingly stringent. Lithium–iron–phosphate (LiFePO4) batteries are a type of Li-ion battery that has been newly developed to meet these increasing requirements. Compared with conventional Li-ion batteries, lithium–iron–phosphate batteries have the following general advantages:

· More environmentally friendly due to recycling of iron and phosphate

· Safety characteristics are better because the cathode material used has excellent thermal stability characteristics

· Lower costs due to abundance and low prices of iron and phosphate

· Longer life cycle and durability due to the use of phosphate materials

Basic Technical Requirements for LiFePO4 Cells in HEV / EV Applications

The main disadvantage of LiFePO4 batteries is the superﬂat slope of Voc versus SOC, which makes it very challenging to estimate SOC and balance cells between battery systems. For HEV/EV applications, the basic technical requirements for this cell type are listed in the above.

Ultracapacitors

Ultracapacitors, which are also called supercapacitors, are electrochemical double-layer capacitors. Unlike batteries, ultracapacitors directly store electrical energy by physically storing separate positive and negative charges. For conventional capacitors, electrical energy is stored through a number of charges on two metal plates that have a certain potential. To increase the capacitance, various materials, called dielectrics, are generally inserted between the plates so that a higher voltage can be stored. In contrast to conventional capacitors, ultracapacitors structurally use an electrical double layer to form a very large surface area allowing large amounts of charge to be stored. For HEV applications, ultracapacitors have the following advantages:

· Significantly Higher Power Density Unlike batteries, ultracapacitors can be charged or discharged at very high C-rates, and the temperature of the electrodes heated by the current is the only limiting factor. It is not difficult for an ultracapacitor to have a power density of 2500 W/kg.

· Excellent Cycle Life Compared to batteries, ultracapacitors can withstand millions of charge/discharge cycles, which makes it possible to capture all the regenerative energy present in a HEV.

· Environmentally Friendly Due to the lack of non-recyclable parts during the entire working life

· Higher Efﬁciency Ultracapacitors have very low internal resistance so they produce little heat during operation. The efficiency of ultracapacitors can be more than 97%, which is higher than that of batteries.

There are two main disadvantages of ultracapacitors for HEV applications:

· The energy density is much lower than that of batteries, generally only 1/10 of the same size battery.

· There is a large leakage resistance resulting in a higher self-discharge rate.

Also read: Tesla Model How and Like What?

References: 1) Linden, D., and Reddy, TB Handbook of Batteries, 3rd ed. McGraw Hill, New York,

2) http://www.nrel.gov 3) http://www.sae.org.[]