Graphene, a sheet of carbon atoms connected in a honeycomb pattern, is recognized as a "wonder material" due to its numerous amazing properties. It is a powerful conductor of electrical and thermal energy, extremely lightweight, chemically inert, and flexible with a large surface area. Additionally, it is considered environmentally friendly and sustainable, with limitless possibilities for numerous applications.
Benefits of Graphene Batteries
In the field of batteries, conventional battery electrode materials (and potential materials) are significantly enhanced when reinforced with graphene. A graphene battery can be lightweight, durable, and suitable for high-capacity energy storage, while also reducing charging times. It will extend the battery's lifespan, which is negatively correlated with the amount of carbon coated on the material or added to electrodes to achieve conductivity, and graphene adds conductivity without the amounts of carbon used in conventional batteries.
Graphene and Battery Characteristics
Graphene can improve battery characteristics such as energy density and shape in various ways. Li-ion batteries (and other types of rechargeable batteries) can be enhanced by introducing graphene into the anode of the battery and taking advantage of the conductivity and large surface area properties of the material to achieve morphological optimization and performance.
It has also been discovered that creating hybrid materials can also be useful in achieving battery improvement. For example, a hybrid of Vanadium Oxide (VO2) and graphene can be used on Li-ion cathodes and provide rapid charging and discharging, as well as large charge cycle durability. In this case, VO2 offers high energy capacity but poor electrical conductivity, which can be resolved by using graphene as a kind of structural "backbone" to which VO2 is attached—creating a hybrid material that has both increased capacity and excellent conductivity.
Another example is LFP (Lithium Iron Phosphate) batteries, which are a type of rechargeable Li-ion battery. They have a lower energy density than other Li-ion batteries but a higher power density (an indicator of the rate at which energy can be delivered by the battery). Enhancing LFP cathodes with graphene made the batteries lightweight, charge much faster than Li-ion batteries, and have a higher capacity than conventional LFP batteries.
In addition to revolutionizing the battery market, the combined use of graphene batteries and graphene supercapacitors could yield amazing results, such as the noted concept of improving the range and efficiency of electric cars. Although graphene batteries are not yet widely commercialized, battery breakthroughs are being reported worldwide.
Battery Basics
Batteries serve as a portable power source, allowing electrical devices to operate without being directly connected to a power outlet. While there are many types of batteries, the basic concept by which they function remains similar: one or more electrochemical cells convert stored chemical energy into electrical energy. A battery typically consists of a metal or plastic casing, with a positive terminal (an anode), a negative terminal (a cathode), and electrolytes that allow ions to move between them. A separator (a permeable polymer membrane) creates a barrier between the anode and cathode to prevent electrical short circuits while allowing the transport of ionic charge carriers necessary to close the circuit during the flow of current. Finally, a collector is used to conduct the charge outside the battery, through the connected device.
When the circuit between the two terminals is completed, the battery produces electricity through a series of reactions. The anode undergoes an oxidation reaction where two or more ions from the electrolyte combine with the anode to produce a compound, releasing electrons. Simultaneously, the cathode undergoes a reduction reaction where the cathode substance, ions, and free electrons combine to form compounds. Simply put, the anode reaction produces electrons while the reaction in the cathode absorbs them, and from that process, electricity is produced. The battery will continue to produce electricity until the electrodes no longer have the necessary substance for the creation of reactions.
Battery Types and Characteristics
Batteries are divided into two main types: primary and secondary. Primary batteries (disposable) are used once and rendered useless because the electrode materials in them irreversibly change during charging. Common examples are the zinc-carbon battery and the alkaline battery used in toys, flashlights, and a multitude of portable devices. Secondary batteries (rechargeable) can be discharged and recharged multiple times because the original composition of the electrodes is able to regain functionality. Examples are lead-acid batteries used in vehicles and lithium-ion batteries used for portable electronics.
Batteries come in different shapes and sizes for countless different purposes. Different types of batteries exhibit various advantages and disadvantages. Nickel-cadmium (NiCd) batteries have a relatively low energy density and are used where long life, high discharge rate, and economic price are critical. They can be found in video cameras and power tools, among other applications. NiCd batteries contain toxic metals and are environmentally unfriendly. Nickel-metal hydride batteries have a higher energy density than NiCd batteries but also a shorter lifecycle. Applications include mobile phones and laptops. Lead-acid batteries are heavy and play an important role in large power applications, where weight is not crucial but economic price is. They are common in applications such as hospital equipment and emergency lighting.
Lithium-ion (Li-ion) batteries are used where high energy and minimal weight are important, but the technology is fragile and a protection circuit is needed to ensure safety. Applications include mobile phones and various types of computers. Lithium-ion polymer (Li-ion polymer) batteries are mostly found in mobile phones. They are lightweight and have a slimmer form than Li-ion batteries. They are also generally safer and last longer. However, they seem to be less common because Li-ion batteries are cheaper to produce and have a higher energy density.
Batteries and Supercapacitors
While there are certain types of batteries that can store a large amount of energy, they are very large, heavy, and release energy slowly. Capacitors, on the other hand, can charge and discharge quickly but contain much less energy than a battery. However, the use of graphene in this area offers exciting new possibilities for energy storage, with high charge and discharge rates and even economic affordability. Graphene-enhanced performance thereby erases the conventional line of distinction between supercapacitors and batteries.
Almost Here: Graphene-Enhanced Batteries
Graphene-based batteries have exciting potential, and while they are not yet fully commercially available, R&D is intensive and hopefully will yield results in the future. Companies around the world (including Samsung, Huawei, and others) are developing various types of graphene-enhanced batteries, some of which are now entering the market. The main applications are in electric vehicles and mobile devices.
Some batteries use graphene in peripheral ways—not in the battery chemistry. For example, in 2016, Huawei unveiled a new graphene-enhanced Li-Ion battery that uses graphene to remain functional at higher temperatures (60 degrees instead of the existing 50-degree limit) and provide double the operational time. Graphite is used in this battery for better heat dissipation—it lowers the operating temperature of the battery by 5 degrees.
