Battery technology has improved a lot these days. But if there is one thing people will never be able to get enough of it is the promise of prolonged battery life. Wouldn’t it be great if our laptops and smartphones lasted a whole week of intensive use with just a single charge? Or what if electric cars could be fully charged in minutes?
With graphene batteries, it is all possible.
Graphene is currently the most researched material for charge storage. Results from various laboratories around the world confirm its potential to revolutionize the energy storage industry.
Discovered in 2004, graphene could present many new features for energy-storage devices in the next decade, such as completely rollable batteries, smaller capacitors, high-capacity and fast-charging devices, and transparent batteries.
Let’s dig deeper and learn more about this game-changing technology: how is it different from existing lithium-ion batteries, what are its applications, and why it is such a big deal.
What Exactly Is A Graphene Battery?
Graphene, a sheet of carbon atoms arranged in a two-dimensional honeycomb lattice, is recognized as a ‘wonder material’ due to its unique properties. It is an excellent conductor of heat and electricity, impressively flexible, nearly transparent, 100 times stronger than steel of the same thickness, and extremely lightweight.
Atoms in graphene arranged in a two-dimensional honeycomb lattice
And since the material is also eco-friendly and sustainable, it has unlimited possibilities in a wide range of applications. One of those promising applications is the next-generation battery.
Graphene can be integrated into different kinds of batteries: metal-air, redox flow, lithium-metal, lithium-sulfur, and more importantly, lithium-ion batteries. It can be chemically processed into different versions suitable for both the negative and positive electrodes.
Batteries made with graphene can power everything from handheld devices and electric vehicles. They hold more power and have longer life cycles than existing commercial (lithium-ion) batteries.
Graphene as a battery can also be used as a supercapacitor, which can charge and discharge incredibly quickly. In fact, they could help civilization finally move away from harmful fossil fuels.
How are they different from traditional batteries?
Graphene battery technology is similar to lithium-ion batteries: it has two solid electrodes and an electrolyte solution to enable the flow of ions. However, some graphene batteries feature solid electrolyte.
The main difference lies in the constituents of one or both electrodes. In a conventional battery, the cathode (positive electrode) is entirely made of solid-state materials. However, in a graphene battery, the cathode is made of a hybrid component that contains graphene and a solid-state metallic material.
The amount of graphene used in the electrode varies, depending on the solid-state material’s efficiency and performance requirements. Furthermore, graphene, as an anode, provides a high capacity and superior rate capability.
In recent years, researchers have demonstrated various graphene-based batteries that outperform the commercially available ones. However, the technology hasn’t entered the market yet. Two major hurdles still need to be overcome:
- The lack of efficient processes for producing high-quality graphene in large amounts
- Production costs are prohibitively high at the moment.
Producing one kilogram of graphene costs tens of thousands of dollars: the amount varies according to the requirement of materials quality. Since activated carbon currently used in supercapacitors is available at low costs ($15 per kg), it is very difficult for other materials to enter the commercial market.
12 New Features Of Graphene Batteries
Soon, graphene could establish new generation energy-storage devices with extraordinary features that are not possible with current technology.
1. Supercapacitors with AC line filtering
An electrical double-layer capacitor based on vertically oriented graphene sheets could be charged/discharged very quickly (in less than a millisecond). Dozens of materials have been tested for AC line filtering, including graphene oxide, graphene-CNT (Carbon NanoTube) carpet, and graphene quantum dots.
Such ultrafast supercapacitors could replace the large electrolytic capacitors currently used in electronics, making electronic devices lighter and smaller.
2. Flexible energy-storage devices
Existing batteries and supercapacitors are rigid: Thus, bending them may result in electrolyte leakage and cell damage. However, graphene, with its two-dimensional one-atom-thick structure, can be deformed in the direction normal to its surface without causing any damage.
In addition to this inherent mechanical flexibility, phenomenal electrical characteristics and large surface area make graphene a promising material for flexible batteries.
3. Stretchable batteries and supercapacitors
Stretchable energy-storage devices can be built by leveraging the structural stretchability of micro-honeycomb graphene-CNT/active material composite electrodes and a physically cross-linked gel electrolyte.
Graphene-CNT/active material film on the stretchable substrate | Credit: ACS Nano
Active materials interconnected via the entangled carbon nanotubes and graphene sheets provide a mechanically stable porous network framework, while the inwardly protruding framework in the honeycomb structure allows for structural stretching during deformation.
4. Fast-charging lithium-ion batteries
Since graphene enables faster ion and electron transfer in the electrodes, lithium-ion batteries equipped with graphene can be charged and discharged in much less time.
For example, a lithium-ion battery loaded with nanoscale LiFePO4 cathode and Li4Ti5O12 anode materials on flexible graphene foam can be fully charged in only 18 seconds. Pure graphene can also be used at the anode to enhance capacity and ultrafast charge/discharge rate.
5. Batteries for wearable devices
Recent advances in the coaxial and core-sheath electrodes have made it feasible to combine electrode material and current collector in a single yarn, which can be woven or knitted directly into textiles.
Graphene can be effectively assembled into multifunctional microfibers and woven into fabrics. Graphene core-sheath microfibers have already been used to demonstrate flexible and stretchable supercapacitors (with high areal capacitance) that can be incorporated into textiles using traditional weaving methods.
6. Ultrathin current collectors for lightweight devices
Existing batteries use metal foil current collectors (such as copper, aluminum, or nickel) with thickness 20-80 micrometers to facilitate electron flow between electrodes and external circuits. Since these metals do not store charge, they reduce the battery’s overall energy density. Furthermore, they suffer from corrosion, negatively impacting the cell’s internal resistance and battery lifetime.
Graphene, on the other hand, is a better alternative current collector. It has high electrical conductivity, low density, and can stably perform under extreme operating conditions. Graphene can be easily transformed into films with ripples and wrinkles on its surface, which results in better electrical contact with active materials (this further reduces the cell resistance).
7. Transparent batteries and supercapacitors
Due to its high conductivity and decent transparency (up to 97.7% transmittance), graphene can play a significant role in making transparent batteries more efficient. It can be used as an electrode material not only for developing transparent energy-storage devices but also for smart windows, solar cells, and various optoelectronic equipment.
8. Longer-lasting batteries
Today’s lithium-ion batteries use graphite anodes. Its energy density can be increased by replacing graphite with graphene.
Graphene electrodes in the form of folded graphene paper, porous graphene films, and solvated graphene frameworks offer three times more capacity than traditional graphite electrodes, promising a longer range for electric vehicles and longer run times for handheld devices.
The capacity and power density can be further improved by doping graphene anodes with nitrogen and boron.
9. Graphene oxide as solid electrolyte and separator
Graphene oxide is a good electronic insulator. It can be used as both a viable solid electrolyte and electrode separator at the same time. Some studies show that a graphene oxide film, acting as a solid electrolyte, exhibits high capacitance but with undetectable ionic diffusion similar to dielectric capacitors.
These observations may help researchers developed ultrafast, lightweight, energy-dense capacitors that do not suffer from ion diffusion, which is often responsible for electrolyte leakage hazards.
10. Supercapacitors with the energy density of batteries
Supercapacitors made with [porous and dense] graphene foams tend to have ultrahigh-energy densities comparable to lead-acid batteries. These graphene foams are made by digging tiny holes in the graphene’s basal planes and then compressing them with advanced hydraulic equipment.
The major benefit of graphene supercapacitors over traditional ones is that they operate with aqueous electrolytes and can be manufactured without any sophisticated ‘dry room’ assembly.
11. Semipermeable graphene oxide membranes
Graphene oxide membranes show various unique barrier characteristics. In the dry state, these membranes are impermeable to everything, excluding water vapor. In water, they behave as molecular sieves, blocking large ions while facilitating the transport of smaller ones.
These features may lead to the development of new-generation ion-selective membranes for supercapacitors, batteries, and fuel cells.
12. Binder and additive-free electrodes
Binder and additives together make up to 40% of the electrode’s mass. It is known as ‘dead mass’ because it doesn’t store any charge and thus decreases the overall energy density.
But since graphene can be assembled into self-standing 2D and 3D structures with high electricity conducting, it is possible to incorporate graphene into electrodes directly, without adding any binders and conductive agents.
In the recent decade, scientists have focused on improving the comprehensive electrochemical performance and reliability of existing batteries. They have developed and tested many different version batteries equipped with graphene composites.
Lithium-ion battery based on optimized graphene/silicon nanocomposites
Researchers have fabricated an optimized reduced graphene oxide/silicon composite using a facile templated self-assembly method. Graphene uniformly supports silicon nanoparticles, forming a three-dimensional network (due to the enhanced intermolecular interaction and increased specific surface area).
The synthetic strategy of the optimized RGO/Si composite | Credit: ACS Publications
It can be used as a stable solid-electrolyte interphase sheet, which increases both electrical conductivity and structural stability.
Graphene-based pouch cells
A graphene-based quasi-solid-state lithium-oxygen battery delivers gravimetric and volumetric energy densities higher than existing lithium-ion polymer batteries. It consists of a 3D porous graphene cathode, porous graphene/Li anode, and redox mediator-modified gel polymer electrolyte.
Schematic illustration graphene-based Li-O2 battery | Credit: Nature
This study opens a new avenue for developing safe and stable lithium-oxygen batteries with stable cycling at a large capacity and low charge overpotential.
Graphene laminate films for capacitive energy storage
In 2020, a team of researchers designed a freestanding graphene laminate film electrode with highly efficient pore utilization. It is easy to configure porosity by adjusting the interlayer spacing of the film. Since pores are utilized optimally, the volumetric capacitance is maximized.
Flexible graphene supercapacitor can store 10x more energy than conventional ones | Credit: University College London
This type of supercapacitors can retain 97.8% of their energy capacity after 5,000 cycles. They are also very flexible: they perform almost the same when bent 180 degrees as when they were lying flat.
Laser-induced graphene-based electrode
Scientists have fabricated a flexible micro-supercapacitor through a single pulse laser photonic reduction stamping. Using this method, 1,000 spatially shaped laser can be produced per second, and over 30,000 micro-supercapacitors can be produced within 10 minutes.
More than 30,000 MSCs are fabricated in a one-centimeter square area | Credit: Beijing Institute of Technology
This laser-induced graphene-based electrode exhibits an outstanding specific capacitance, an ultra-short time constant, an ultra-high energy density, and a long-term cyclability.
Graphene research will continue to expand during the next decade with the promise of making human lives better. In 2019, the global graphene battery market was valued at $49 million, and it is projected to reach approximately $399 million by 2027, registering a CAGR (compound annual growth rate) over 31% during the forecast period.
The market growth is driven by the use of graphene batteries in electric vehicles, portable electronic devices, and the surge in adoption of non-conventional energy resources. The automotive segment is expected to have the highest growth rate owing to the increasing demand for electric cars due to environmental concerns.
Based on the region, the Asia Pacific region is projected to account for the largest share of the graphene battery industry. The key countries contributing to the increased demand are China, Japan, and South Korea. Europe will likely have the 2nd-largest share of the global graphene battery market.