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What is a graphene battery?

Li-Ion batteries have good capacity compared to their volume and weight. There is a drawback, however: they take a long time to charge. Another drawback is their maximum power output. Li-Ion batteries may have a large capacity but their maximum power output is limited because the risk of overheating.

Graphene batteries are made by enhancing existing Li-Ion batteries. This is achieved by enriching the electrodes with graphene which changes their chemical and physical properties. The results are improved charge/discharge rate characteristics as well as improved capacity. Improved discharge rate means that graphene batteries have a higher maximum power output.

Graphene batteries are new technology and as of 2013, they are just entering mass production. This means that they are still under research. Optimal manufacturing processes are yet to be discovered. There is a lack of knowledge in this area, and peer-reviewed scientific materials are still scarce. We will try to explain the working principle using one example that can be found in scientific literature. If you are interested in investing in graphene, take a look at Investing in Graphene

How are graphene batteries made?

Vanadium-oxide graphene battery

Researchers at Rice University have discovered a new material, which is a hybrid of vanadium oxide (VO2) and graphene. This hybrid can be used in Li-Ion batteries cathodes.

Measurements show that these hybrid cathodes can fully charge and discharge within 20 seconds and withstand more than 1000 charge cycles. After 1000 cycles, the capacity was still better than 90% of nominal.

Vanadium oxides offer high energy capacity when used in Li-Ion batteries. This is because they collect lithium ions like a sponge. The drawback of using vanadium oxide (VO2) or vanadium pentoxide (VO5) is that oxides in general are bad electrical conductors. The low conductivity results in a slower charge/discharge rate.

Scientists found a way to use graphene, which is an excellent conductor, as a structural backbone to which vanadium oxide is attached. This hybrid inherits good capacity properties from vanadium oxide and good conductivity from graphene which allows for a fast recharge.

The process consists of mixing graphite oxide nanosheets with powdered VO5. The mixture is suspended in water and heated to a high temperature. At these temperatures, vanadium pentoxide reduces to VO2, while graphite oxide reduces to graphene. As VO2 crystalizes, it forms nano-ribbons about 10 nm thick and 600 nm wide, with a single-atom thick coating of graphene. These ribbons are tens of micrometers long, and they have a very large specific surface area which allows for very fast diffusion of electrons and Li-Ions due to VO2’s ion-soaking properties and graphene’s high conductivity. These two properties combined allow for quick charge and discharge rates, as well as high maximum power outputs for these batteries.

The real technical difficulty in making graphene batteries is the actual manufacturing of the VO2-graphene hybrid material. In order to produce the hybrid, the process conditions such as temperature, pressure and mixture concentrations must be controlled very precisely. The process parameters are now relatively well-known and can be easily controlled, allowing large-scale manufacture.

LiFePo4 graphene battery

LiFePo4 batteries, also called LFP (Lithium Iron Phosphate) rechargeable batteries use LiFePo4 as the cathode. The LFP battery is a type of rechargeable lithium-ion batteries. Even though they have a lower energy density than some other consumer-grade lithium-ion batteries, they have a higher power density. Power density is an indicator of the rate at which energy can be supplied by the battery. Due to their higher power density, they are especially interesting for use in electric vehicles. LiFePo4 batteries are also much safer than other lithium-ion technologies due to their better thermal and chemical stability. They are very hard to ignite during the charging process, and LFP batteries can handle much more abuse than other Li-Ion batteries before failing.

In September 2010, a group of scientists has, for the first time, published a paper on enhancing a LiFePo4 battery cathode using graphene. The results of their research were astonishing. Not only did their graphene batteries charge many times faster than Li-Ion, they also had a greater capacity, which was larger than the theoretical maximum for classic LFP batteries.

How did they manage to make this graphene-enhanced battery? Basically, they created a new, composite material consisting of LiFePo4 and graphene. To do this, they mixed LiFePo4 nanoparticles with graphene oxide nanosheets and used processes such as spray-drying and annealing. The result was a material consisted of LiFePo4 primary nanoparticles embedded in secondary spherical microparticles, which were wrapped together loosely using a 3D network of graphene sheets.

Electron mobility and migration was greatly improved with the use of graphene, which is an extremely good electrical conductor. Nano-sized holes in graphene sheets allow for increased Li+ mobility throughout the 3D graphene matrix. What they created was basically an Ion sponge which could soak up Li+ ions while at the same time allowing for electrons to move freely within the matrix.

When applied to graphene batteries, this new LiFePo4-graphene composite material yields great results and allows the battery to have some great properties. To begin with, the specific capacity is 70 mAh per gram. This means that your cell phone battery could weigh under 20 grams. The reduction in weight is a warmly welcomed improvement to electric cars, which could use hundreds of kilograms of batteries to run. The charge and discharge rates were also improved. These improved LFP graphene batteries could charge at 10C and discharge at 20C for 1000 cycles with only under 15% capacity decay rate. To better understand this, if a battery is rated at 1200 mAh, this means that it can, in theory, provide 1200 mA of current for one hour. In this context, 1C represents the rated current, which is 1200 mA in our example. Ordinary Li-Ion batteries charge at 0.5 - 0.8C and discharge at up to 1C. On the other hand, these improved graphene batteries were capable of reliably charging and discharging at rates 20 times higher than classic Li-Ion batteries. Peak discharge rates were safely ramped up to 70C, which is a 70-fold improvement in battery power density.

Graphene battery applications

Quickly charging graphene batteries could be the next step in electric car energy storage cells. Conventional electric car batteries take a long time to fully charge - up to 5 hours in some cases. Even at full charge, they offer a range of only about 50 miles in some cars. Graphene batteries could offer the same range, but the charge time could be reduced to under half an hour.

IEEE spectrum -


This page was last modified: April 26th, 2013.