A battery converts energy stored in the chemical bonds of a material into electrical energy via a set of oxidation/reduction (commonly abbreviated to redox) reactions [1]. There are two types of batteries based on their ability to convert chemical energy to electrical energy; Primary batteries can perform this process in only one way hence they are not rechargeable. Common alkaline batteries sold for small devices like an alarm clock are examples of primary batteries. Secondary batteries can do this conversion in reverse order and are rechargeable, examples include batteries used in electronics like mobile phones, laptops and so on.
Basics
The process of converting chemical energy to electrical energy done by batteries is as a result of the Redox (Oxidation and Reduction) reactions. An oxidation reaction involves the giving off or donation of electrons while a reduction reaction involves the acceptance of electrons. The components of a battery that makes this reaction possible includes a container/casing, cathode (positive electrode), anode (negative electrode), electrolyte (KOH, LiPF6, ZnCl2 etc.), semipermeable barrier/separator and load. The chemical reaction involves the flow of electrons from an electrode to another through the external circuit. The voltage difference between an oxidation and reduction reaction arises from the different electrochemical potentials [2] which also determines the cell's voltage.
LITHIUM ION BATTERY
Lithium-ion batteries generate electricity through chemical reactions of lithium. Like the battery cells described previously, lithium ion batteries have the same basic components.
Cathode: Determines the capacity and voltage of a lithium ion battery. Lithium oxide (Li2O) is the material used since lithium is unstable on its own.
Anode: Sends electrons through the wire and is coated with active materials. When the battery is being charged, lithium ions are stored in the anode. Graphite is used as a stable structure for the anode.
Electrolyte: It allows the movement of ions, the lithium ions move via the electrolyte between the cathode and anode. Lithium salt (LiPF6) is a common electrolyte used in lithium batteries alongside some solvents and additives.
Separator: It is used as a barrier between the cathode and anode to prevent direct flow of lithium ions between them.
There are several types of lithium batteries based on the type of electrolyte used in its cells like lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium iron phosphate (LFP) and so on. The different types all have the same voltage ratings with the only deferring qualities being the energy produced (Wh/kg), capacity (mAh/g) and cycle life.
Advantages
More Energy: Energy density (Wh/kg) is used to measure the amount of energy that a battery possesses. Lithium ion batteries have a high energy density of about 100 - 265 Wh/kg because of lithium's small size (atomic number is 3) and weight as an element. The lithium ions are small enough to move through the separator at a much faster rate.
No Memory Effect: Memory effect occurs when batteries are recharged repeatedly after being only partially discharged, they gradually loose usable capacity due to a reduced working voltage [5]. Lithium batteries have been shown to have no memory effect unlike many other commonly used batteries like nickel-cadmium or nickel-metal-hydride. In other batteries the memory effect causes a reduced working voltage.
Discharging: Self-discharge refers to self-running electrochemical processes which cause batteries (accumulators) to discharge more or less quickly, even if no electrical consumers are connected. The rate at which a battery self discharges determines the fraction of the stored charge that can be used after storage. Lithium ion cells have a lower self discharge rate than other rechargeable cells. This discharge rate is higher while the battery is still fully charged.
Light Weight: With the sophistication in electronics designed recently, the need for a light weight and generally portable battery is glaring. Lithium ion batteries are typically 50% the mass of lead acid batteries while providing more energy.
Quick and Efficient: Lithium batteries charge and discharge at a fast rate thereby reducing downtime accompanied with its high discharge rate. Lithium batteries are used under high stress situations or situations that require quick charge or discharge without much lag time.
Disadvantages
Toxicity: Some possible lithium ion battery materials are toxic, carcinogenic, or could undergo chemical reactions that produce hazardous heat or gasses [6]. Exposure to lithium can potentially cause loss of appetite, nausea, diarrhea, abdominal pain and vomiting. Even though lithium ion batteries are safer than lead acid batteries, they are not very safe especially when in contact with human beings.
Overheating: When overheating occurs, the performance, reliability, durability, and safety of Li-ion batteries can be seriously deteriorated [7]. All batteries and mechanical devices have a tendency to overheat for various reasons, Lithium ion batteries specifically overheat as a result of high discharge rate and abnormal discharges as a result of short circuits. The irony presented here shows that one of the various reasons (high discharge rate) why Lithium ion batteries are preferred over other types of batteries results in a potentially hazardous situation - Overheating.
Health and Safety Hazard: This is specifically encountered when lithium ion batteries are improperly disposed of. Fires are unintentionally started in landfills or battery recycling facilities. Lithium ion batteries contain cobalt, nickel, manganese and so on that can contaminate water supplies and ecosystems.
Cost: This is a factor that affects the decision when using them for mass production of consumer items. Lithium-ion batteries are about 40% more costly than nickel-containing cells in the market. Importation costs and limitations due to shipping restrictions also influence the cost of these batteries. Another reason why Lithium batteries are more expensive is because they utilize metals that have limited availability on planet earth.
Uses
Electronics like phones, laptops, cameras etc.
Appliances.
Uninterrupted power supply like solar inverters.
Electric vehicles.
Renewable power storage.
HYDROGEN FUEL CELLS
Fuel cells are not batteries, they perform a similar function to batteries by taking chemical energy and transforming it to electricity and other byproducts. The chemical energy transformed here is gotten from a fuel in this case we are looking at hydrogen fuels. Fuel cells work as batteries or storage devices as energy can be input to create hydrogen and oxygen which remains in the cell till it is used.
Why Hydrogen?
Hydrogen as a fuel is a relatively recent concept with research actively ongoing. Hydrogen is used only because of its high energy density i.e. 121Mj/kg and because the only byproduct generated alongside electricity is water. The hydrogen fuel used is gotten from other extensive processes like electrolysis where water or hydrocarbons produce relatively pure hydrogen. Hydrogen production is typically characterized into three:
Green Hydrogen: Hydrogen is produced from water that goes through the extensive electrolysis process. No carbon footprint is associated with its production.
Blue Hydrogen: Similar to green hydrogen generation process but not all the CO2 is captured.
Pink Hydrogen: Hydrogen is produced from nuclear energy. A more controversial and evolving technology but has less carbon footprint.
Advantages
Renewable: Hydrogen is the most abundant element in the universe and despite the challenges associated with its extraction from water, is a uniquely abundant and renewable source of energy, perfect for our future zero-carbon needs for combined heat and power supplies [10]. Two out of the hydrogen fuel generation methods have little to no carbon emissions with green hydrogen being the most common.
Energy Efficiency: Hydrogen has the highest energy content of any common fuel weight and compared to the energy storage density of other batteries. This gives them an advantage when used in electric vehicles where hydrogen fuel cells have an energy density of 35,000 W/kg.
Weight: Hydrogen fuel cells have an energy weight ratio that is 10:1 i.e hydrogen fuel weighs less while having a larger energy density. The weight disparity between hydrogen fuel cells and lithium ion cells are as a result of their overall weight with hydrogen (atomic number 1) weighing drastically less than lithium (atomic number 3).
Charging Speed: Hydrogen fuel cells take very little time to charge, similar to internal combustion engines. Hydrogen fuels take about 1/6th the time required by normal fuel cells to charge. This charging speed also translates to long usage times of the cells and is as a result of its greater efficiency.
Disadvantages
Quantity: Even Though hydrogen fuel cells have a high energy density compared to smaller batteries, when they are used in large applications (like in public transportation) the 35,000W/kg falls short. To combat this demand very large quantities of hydrogen stored as compressed gas needs to be stored properly to be readily available.
Production: The process of extracting/producing hydrogen fuel in its purest form whether green, blue or pink is quite complex and requires a lot. For instance, green hydrogen requires a lot of water which goes through electrolysis then is split and hydrogen is a byproduct alongside oxygen.
Cost: The cost of using hydrogen fuel cells is a lot higher than other typical battery cells. This cost is high because of the constituting material involved in its production and the lack of knowledge associated with the new technology. For this reason, hydrogen fuel cells are more widely used in industrial settings.
Hazards: Hydrogen gas is a very flammable fluid and because hydrogen fuel is stored in a compressed gas state the risk becomes higher. Hydrogen gas burns in air at concentrations ranging from 4 to 75% [11]. Apart from possible fire/explosion hazards, hydrogen gas build up in the air can displace the oxygen in the air thereby causing asphyxiation.
Uses
Electric vehicles (EVs).
Buses, trains, ferries and planes.
Power generation.
Cell phones.
Laptops.
CONCLUSION
Lithium ion batteries and hydrogen fuel cells are used for the same purposes with common overlap being in electric vehicles, alternative power supply and electronics. The main point of comparisons are the energy density which translates to efficiency and cost. Using those two points, hydrogen fuel cells are more efficient but cost more while lithium ion batteries are less efficient but cost less. Considering that with the awareness and the effort put into research of hydrogen fuels we can predict a 50 - 60% decrease in its cost, hydrogen fuel cells are recommended.
REFERENCES
[1] https://www.pveducation.org/pvcdrom/batteries/battery-basics
[2] https://www.pveducation.org/pvcdrom/battery-basics/electrochemical-potential
[3] https://www.nature.com/articles/s41928-018-0048-6
[4] https://batteryguy.com/kb/knowledge-base/what-are-lithium-ion-batteries/
[5] https://www.tytlabs.co.jp/en/review/issue/files/453_057sasaki.pdf
[6] https://afdc.energy.gov/files/pdfs/2953.pdf
[9] https://energyeducation.ca/encyclopedia/Fuel_cell