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Hybrid Electric Vehicle Batteries: Charging and Discharging Research Paper

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Updated: Mar 21st, 2022

When man discovered how to use fossil fuel as a major energy source, the world was never the same again. It was a time when fossil fuels such as oil and coal were considered a cheap and abundant alternative to firewood, animal fats, etc. However, this is no longer true today. In the oil crisis of the 1970s Americans reeled from the impact of fuel shortages.

In the 21st century, many began to realize that expensive petroleum products cannot be sustained in the long run and therefore the need to find another alternative energy source especially when it comes to fuel-guzzling cars that Americans had grown to love. One temporary solution is the hybrid car – a combination of a conventional internal combustion engine and an electric motor. The only challenge is the design of the car battery for it needs to be charged and discharged. It was discovered that a solid-state lithium-ion battery is the most suited for hybrid cars.

The Battery

The inventor of the battery realized that there are only three major ingredients needed to produce a direct current: two different metals and an electrolyte (Gilles, p.404). This can even be demonstrated using a potato, an orange, or a soft drink as the electrolyte (Gilles, p.404). When two types of metals are poked into say an orange a direct current is produced and a voltmeter can then be used to measure the voltage between the two dissimilar metals (Gilles, p.404).

In the case of a battery cell, the design is more sophisticated but uses the same principle. Instead of orange and soft drinks, there is a negative and positive plate immersed in an electrolyte solution. A typical battery is composed of a positive plate made up of lead dioxide, a negative plate made up of sponge lead and an electrolyte which is made up of sulfuric acid and water (Gilles, p.407).

When a battery is charged, current flows into I,t, and the unit stores this energy until it is needed (Gilles, p.406). Charging a battery is achieved when an energy source “puts electrons on the negative plate” and as a result, the positive and negative plates will have a difference in voltage or potential (Gilles, p.406). What occurs is a voltage imbalance between the negative and positive plates and this requires equalization by creating a current path where energy can flow out of the system (Gilles, p.406).

When the voltage imbalance is equalized the battery is discharged and current flows out of it. This is made possible by what is known as the “electron current flow” – electrons passing through the electrolytes as it travels from the negative plates to the positive plates (Gilles, p.406). A chemical reaction occurs and as a result, materials are being used up in the process. The continuous charging and discharging of the battery will wear out the active material in the cell plates (Gilles, p.408). This is a problem for battery-operated devices and most especially for Hybrid-elective vehicles.


Hybrid-elective vehicles also known as HEVs are considered to be a short-term alternative to fossil fuel (Dennis & Urry, p.71). It is a temporary solution because the system does not totally eliminate the use of fossil fuels. However, it allows the car to maximize its fuel consumption; instead of solely relying on the internal combustion engine it works in tandem with an electric motor that is powered by a battery.

Therefore, HEVs engines combine “regular petrol-combustion driven mechanical drives with battery-driven long-range driving, switching to battery-electrical power assistance for initial acceleration and low-speed driving conditions” (Dennis & Urry, p.71). This is the normal configuration but this is not the only design available for HEVs. In the second generation HEVs the battery is the major power source, and as a result, the amount of battery power that can be found aboard this type of hybrid vehicle “may vary between a single battery to a pack of many batteries connected together” (ThermoAnalytics, p.1).

Based on the basic description of what goes on inside a battery there are two implications when it comes to the two types of HEVs. The first one is related to the assertion made that: “HEV batteries do not require constant recharging as in electric vehicles since they rely on a long-life battery cell and recharging via the vehicle’s kinetic motion and braking” (Dennis & Urry, p.71).

The Battery in an HEV

There are three things that must be considered in the design and manufacture of a new generation of batteries that can best serve HEVs. These are the following things to consider: a) long battery life; b) battery capacity; and c) efficient charging and discharging of the battery. There are two ways to deal with these concerns. First, engineers must continue to look for better components and better designs. Second, consumers must know how to properly take care of their batteries.

When it comes to proper handling of the batteries it must be pointed out that a battery’s life is significantly shortened by improper charging system amperage or voltage (Gilles, p.411). Too high or too low amperage is the greatest cause of shortened battery life (Gills, p.411). Extreme temperatures can harm batteries as well. Cold weather can easily reduce the cranking power of batteries by more than half (Gilles, p.411). Excess heat as a result of overcharging can cause buckled and warped plates as well as the shedding of materials from the plates (Gilles, p.412).

It is therefore important to choose the correct type of battery to be used for HEVs, one that has a long life cycle, high gravimetric and volumetric energy densities, ambient temperature operation, and good pulse power density (Dhameja, p.21). There are at least four major types of batteries used in current HEVs and these are: a) Lead acid; b) Nickel-Cadmium; c) Nickel-Metal Hydride; and d) Lithium-Ion. According to researchers lithium-ion batteries seems to be the most ideal because it is the lightweight and high electric potential of all metals (ThermoAnalytics, p.1). However, lithium is known to be an unstable metal and can ignite if it comes in contact with water, and because of that lithium batteries are limited to portable devices (ThermonAnalytics, p.1).

The most common battery type in use in many HEVs islead-acid acid type because it is easy and cheap to produce. In fact, the Toyota Prius uses a lead-acid type for their accessory battery, and for the new models they use a nickel-metal-hydride battery type (Voelcker, p.1). The only problem with the lead-acid battery is its low energy density and less impressive life cycle. The nickel-metal-hydride type of batter on the other hand is expensive to manufacture (Voelcker, p.1). There is therefore the need to revisit the lithium-ion configuration.

Scientists assert that lithium-ion is indeed much better than the other types the only thing that needs to be done is to modify it into a solid-state lithium-ion battery instead of the traditional liquid-state Li-ion battery (Dhameja, p.19). One of the benefits of the new design is the capability to store “up to three times more energy per unit weight and volume than the conventional Pb-acid and NiMH batteries” (Dhameja, p.19). This means that it is a space saver favorable for car designers. They do not have to worry about incorporating a number of battery cells within the hood of the cars.

In addition the solid-state lithium-ion battery has a low self-discharge rate as well as superior life cycle as compared to the other battery types (Dhameja, p.19). Studies reveal that a typical lead-acid battery drops to “80% of the rated capacity after 500 cycles at the C-rate” (Dhameja, p.19). A solid state lithium-ion battery, on the other hand, drops down to 80% of its rated capacity after more than 1,200 cycles (Dhameja, p.19). When engineers are able to improve the performance and safety aspect of the solid-state lithium ion battery then it would become the most popular type used in HEVs.


The need for an alternative fuel to combat the rising price of crude oil has prompted scientists to develop new technologies in order to satisfy the global energy demand. Solar energy and wind power may be feasible solutions but cannot be considered a permanent answer to acute energy needs. The most promising short-term solution in the case of the automotive industry lies in HEVs. The most critical component is the battery. The goal of researchers is to develop a vastly improved battery type that has a higher capacity while at the same time long battery life. It also helps if consumers are well aware on how to properly charge and discharge their batteries. It will increase the efficiency of their units as well as increase the life span of their batteries.


Dhameja, Sandeep. Electric Vehicle Battery Systems. MA: Butterworth-Heinemann, 2002.

Dennis, Kingsley & John Urry. After the Car. MA: Polity Press, 2009.

Gilles, Tim. Automotive Service: Inspection, Maintenance and Repair. New York: Delmar Learning.

ThermoAnalytics. “HEV Battery Types.” Web.

Voelcker, John. “Why the 2010 Toyota Prius Doesn’t Have a Lithium-Ion Battery.” Web.

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