Slide 1: Introduction.

            This chapter develops the fundamentals of electric vehicle batteries, because it is the most important and valuable component of the electric vehicle.

Slide 2: The battery: the most important component of the electric vehicle.

            The battery is the most important component of the electric vehicle for the following reasons:

         Energy storage.

            The battery converts the stored chemical energy into electrical current that is used to power the vehicle's electric motor, which drives the wheels.

         Autonomy.

            The range of the vehicle depends on the storage capacity of the battery, the more battery capacity the more range.

            Before purchasing an electric vehicle, you must check that the battery has the required range to provide the service.

            It must be taken into account that the real range of the electric vehicle is less than the official range of the WLTP cycle.

            The following estimates can be made for the range of the electric vehicle.

            The estimated kilometers based on our experience with similar vehicles are subtracted from the official WLTP cycle figure.

            There are companies that are dedicated to measuring the ranges and real consumption of electric vehicles such as Emissions Analytics and Green-NCAP.

            Take as a reference the KWh/Km consumption data from the tests carried out in specialized engine magazines, and divide the battery capacity by this consumption to know the autonomy.

         Recharge time.

            The battery is discharged during operation, and must be recharged. During the charging time we cannot use the vehicle if it is recharged at a fixed charging point, and it is a time in which we cannot use the vehicle to provide the service.

            Normally, in vehicle fleets, recharging is carried out at night, when the service is not provided, but in other vehicle fleets it is necessary that this recharging time be as minimal as possible, to continue providing the service.

            Depending on the type of battery, the recharge time may be longer or shorter.

            For example, the most used batteries operate at 400V, but there are 800V batteries, which take less time to recharge for the same intensity, because the recharge power is greater.

         Price.

            The price of the battery is between 1/3 and 1/2 of the value of the vehicle, making it the most expensive component.

            The battery loses storage capacity with charge/discharge cycles, it can break down, suffer a blow, catch fire, etc. so it must be changed or repaired.         

            There are vehicle manufacturers that allow damaged battery modules to be replaced, but there are other manufacturers that require replacing the entire battery; in both cases, repairing or replacing the battery is very expensive.

            It may happen that repairing or replacing the battery is more expensive than the value of the vehicle at that time and may not be cost-effective to do. 

         Battery degradation.

            The battery loses storage capacity with its use, resulting in the vehicle not having the necessary autonomy to provide the service, and therefore either the battery is changed or a new vehicle is purchased.

         Risk of fire.

            The most important risk in an electric vehicle is that a cell catches fire and causes the entire battery and the vehicle to catch fire.

            A battery fire can occur due to overheating, impact, corrosion, etc.

         Residual value of the vehicle.

            The more degraded and less autonomy the battery has, the lower the residual value of the vehicle, because the battery will probably have to be changed.

            Battery and electric vehicle technology evolves rapidly, and the energy density of batteries KWh/Kg increases over time, so our vehicle technology may become obsolete compared to new electric vehicles, reducing its value residual.

         Insurance.

            Currently, insurance companies are writing off the vehicle as an accident due to battery failure or because it has been hit, which represents a considerable loss in the value of the vehicle.

         Energy consumption in manufacturing and recycling.

            Batteries in their manufacturing and subsequent recycling consume a lot of energy, which if generated by fossil fuels emits CO2, so the net emissions cycle of the electric vehicle is not zero, if the manufacturing of the battery and the vehicle is included.

            Some manufacturers are beginning to use renewable energy in the manufacturing and recycling of the battery and the vehicle, so that the cycle of net emissions is zero. 

            Before purchasing an electric vehicle, you should know if the vehicle and the batteries have been manufactured with renewable energy.

         Later uses.

            If we change the vehicle battery, we can use it as a stationary battery in our facilities to store energy generated from renewable energy, which we will use to recharge our electric vehicles.

Slide 3: Battery components.

         A battery is a device that stores electrical energy in chemical form and releases it in direct current.

            All types of batteries contain a positive and a negative electrode immersed in an electrolyte, and the entire assembly is encapsulated.

            The components of a battery are the following:

         Anode or negative electrode: The substance that makes up the anode releases electrons.

            These electron loss reactions are called oxidation reactions.

         Cathode or positive electrode: the substance that makes up the cathode accepts electrons. These electron capture reactions are called reduction reactions. It is the inverse reaction to oxidation.  

            The poles reach their limit when the cathode becomes charged with electrons and the anode loses them and is completely oxidized.

         Electrolyte: The anode and cathode are linked in the battery through the electrolyte. They are also joined on the outside by means of an external conductor through which only electrons circulate that provide electricity for the external electrical device.

            The electrolyte allows the flow of ions but not electrons that rebalance the charge between both sides.

            In rechargeable batteries, the oxidation reactions, giving up electrons and reduction, taking electrons, are reversible, they can flow in both directions.

         Separator: it is an insulator that is placed between the positive and negative plates to prevent short circuits.

            The voltage of batteries is measured in volts, while the amount of electricity they can store, and subsequently deliver while discharging, is measured in amperes per hour.

            The voltage offered by the battery depends on the potential difference between the cathode and the anode. The greater this difference, the greater the voltage we will obtain.

Slide 4: Lithium I.

         Properties.

            Lithium is a chemical element with symbol Li, atomic number 3, univalent - a single positive charge on its ions, and an alkaline element, it also has a high specific heat and electrochemical potential.

            In its pure form, it is a soft, silver-white metal that oxidizes quickly in air or water. Its density is half that of water, being the lightest, softest and whitest metal and solid element.

            Being an alkali metal, it is univalent and very reactive, so it is not found free in nature, and it is highly flammable and slightly explosive when exposed to air and especially water.

            In nature it is found as a mixture of the isotopes Li6 and Li7.

         Risks.

            Pure lithium is highly flammable and slightly explosive when exposed to air, and especially water. It is also corrosive and slightly toxic, so it is important to handle it properly to avoid contact with skin.

         Availability in nature.

            Lithium is moderately abundant in the Earth's crust, with a concentration of 65 parts per million (ppm).

            Lithium is dispersed in certain rocks, but is never free due to its great reactivity. It is found in small quantities in volcanic rocks and natural salts, such as the Salar de Atacama in Chile, which contains the largest lithium deposit in the world, followed by the Salar de Uyuni in Bolivia.

         Uses.

            Lithium is used in the manufacture of batteries, cell phones, driers, alloys, ceramics, glass, lubricants and medicines.

         Electric vehicle batteries.

            In today's batteries, lithium is found in small amounts in the anodes and cathodes of the cells. An electric car battery usually has, on average, about 160 grams of lithium metal per kilowatt-hour (kWh). Therefore, a 66 kWh battery has around 10 kilograms of lithium.

Slide 5: Lithium II.

         Electricity.

            Electricity is the transit of electrons, so to produce electricity you need substances that tend to release them.

         Reduction potential.

            The standard reduction potential is used to determine the electrochemical potential or the potential of an electrode of an electrochemical cell or a galvanic cell.

         Lithium is the metal with the lowest reduction potential (-3.05V).

         This means that it is the chemical element that has the greatest tendency to give off electrons.

Slide 6: Lithium III.

         Atomic number 3.

            Lithium has an atomic number 3.

            It has 3 electrons, two in the first shell, and a valence electron, which is the one that tends to break away, remaining positively charged.

            It is represented as Li+ and is called lithium ion. Hence lithium batteries are also called lithium-ion batteries.

         Advantages and disadvantages of giving up electrons.

            It gives up electrons to anyone, being a very unstable metal, which oxidizes quickly in contact with air, and reacts violently in contact with water.

Slide 7: Lithium-Ion battery operation.

         Composition.

            Lithium ion batteries have a cobalt oxide cathode, and an anode made of a graphite-like material called coke.

            Both the cathode and the anode have a laminar arrangement in which they can house the lithium.

            Pure lithium is a very reactive material, but when it is part of a metal oxide it is quite stable.

            Cobalt oxide is coated on aluminum sheets and graphite on copper sheets acting as current collectors in which the positive and negative tabs are installed. 

            The anode containing the graphite has a layered structure, where lithium ions are stored.

            The electrolyte between the graphite and the metal oxide, cobalt oxide acts as a protector that only allows lithium ions to pass through.

            Safety, durability, and performance problems at critical temperatures are due to the liquid electrolyte.

            At high temperatures, it is responsible for propagating thermal runaway that can end up catching fire in a battery. At low temperatures, this liquid begins to freeze, losing all the ability to generate electricity. In many cases, this condition severely limits the effectiveness of the charging process of electric vehicles, which is a big problem in colder regions.

            In today's lithium-ion batteries, the electrolyte is a mixture of a widely available salt, lithium hexafluorophosphate, and solvents such as ethylene carbonate, responsible for dissolving the salt to form a liquid.

            The electrolyte, separator and tabs are wound around a central steel core making the cell more compact.

            A cell used in today's vehicles is between 3-4.2 volts.

            Lithium travels from cathode to anode or from anode to cathode through the electrolyte depending on the charge or discharge cycle.

            The electrons, on the other hand, circulate through an external circuit, supplying electricity to the vehicle's electric motor.

Slide 8: Lithium-Ion battery operation.

         Recharge.

            When the battery is connected for recharging like the electrical network, at the cathode the electrons are released from the lithium atoms of the metal oxide, flowing through the external circuit towards the anode, because they cannot flow through the electrolyte , reaching the graphite layer where they are stored. Positively charged lithium ions flow from the cathode to the anode through the electrolyte and are deposited on the graphite

         When all the lithium atoms reach the graphite, the cell is fully charged.

         The battery stores energy in this process because the electrochemical potential of graphite is higher than that of lithium cobalt oxide.

            This means that the lithium ions have had to rise from the cathode potential to the anode potential.

Slide 9: Lithium-Ion battery operation.

         Discharge:

            When the vehicle engine demands electricity from the battery, as the lithium ions in graphite are at a higher electrochemical potential than in lithium cobalt oxide, they fall from the anode potential to the cathode potential.

         The lithium ions want to return to their stable state as part of the metal oxide of the cathode, so the lithium ions move from the anode to the cathode, passing through the electrolyte, and the electrons through the external circuit obtaining an electric current that powers of electricity the vehicle engine.

         When all the lithium ions reach the cathode, the battery is completely discharged.

Slide 10: Lithium-Ion battery operation.

         Graphite is not involved in the chemical reaction, it is only a medium for storing lithium ions.

         If the internal temperature increases due to any abnormal condition such as high power recharging.

            The liquid electrolyte will dry out and there will be a short circuit between the anode and cathode, causing a fire or explosion. 

         The number of charge and discharge cycles of a lithium-ion battery is about 3,000.

         The electrolyte degrades if the electrons deposited in the graphite come into contact, but this never occurs through the solid electrolyte interface.

            When the battery is charged for the first time, the lithium ions move through the electrolyte, the solvent molecules in the electrolyte cover the lithium ions, when they reach the graphite the lithium ions along with the solvent molecules react with the graphite forming a layer called solid electrolyte interface, preventing any contact between electrons and the electrolyte, preventing its degradation.

            In the process of forming the solid electrolyte interface layer, 5% of the lithium is consumed. The thickness of the solid electrolyte interface layer is optimized for maximum cell performance.

Slide 11: Thank for you time.

            In this chapter, the fundamentals of electric vehicle batteries have been developed, because it is the most important and valuable component of the electric vehicle, see you soon.