|Capacity vs. cycle number. Source: Power Japan Plus. Click to enlarge.|
Start-up Power Japan Plus announced plans to commercialize a dual-carbon battery technology, which it calls the Ryden dual carbon battery. Power Japan Plus says that its battery currently offers energy density comparable to a lithium-ion battery, but with a much more rapid rate of charge and the ability for full discharge over a much longer functional lifetime with improved safety and cradle-to-cradle sustainability.
Dual-carbon (also called dual-graphite) batteries were first introduced by McCullough and his colleagues at Dow Chemical in a 1989 patent, and were subsequently studied by Carlin et al. (1994) and Seel and Dahn (2000), along with many others. The basic concept of the cell is that lithium ions from the electrolyte are inserted/deposited into/on the anode (negative electrode), while the corresponding electrolyte anions are intercalated into the cathode (positive electrode). Both electrodes are carbon (e.g., graphite). During discharge, both anions and lithium ions are released back into the electrolyte. As Rothermel et al. noted in their 2013 review of challenges and opportunities for the technology, the electrolyte in such a system thus not only acts as charge carrier, but also as the active material.
|Cartoon of charge and discharge in the dual carbon battery. Source: Power Japan Plus. Click to enlarge.|
The Power Japan Plus cell is based on the work of Professor Tatsumi Ishihara at Kyushu University in Japan; Power Japan Plus will continue developing the dual carbon battery technology in partnership with Prof. Ishihara and the university. In a 2013 patent filing on the technology, Ishihara and his colleagues explain the charge and discharge reactions thusly, using a LiPF6 salt (as did Seel and Dahn):
Positive electrode: PF6− + nC ⇄ Cn(PF6)+e−
Negative electrode: Li+ + nC+e− ⇄ LiCn
→ charging reaction; ← discharge reaction
Discharged capacity is determined by the anion storage capacity of the positive electrode; the amount of possible anion release of the positive electrode; the cation storage capacity of the negative electrode; the amount of possible cation release of the negative electrode; and the amount of anions and cations in the non-aqueous electrolyte.
To improve the discharged capacity in the dual carbon cell, it is necessary to increase not only the positive-electrode active material and the negative-electrode active material but also the amount of the non-aqueous electrolyte including a lithium salt. Because the ion concentration of the electrolyte changes during cycling, there must be enough electrolyte salt in the cell to guarantee conductivity, and there must be enough solvent to enable the salt to be disolved at any state of charge or discharge.
In their patent filing, Ishihara and colleagues note that in such a dual carbon cell, precipitation and dissolution of a lithium salt as a supporting salt may take place at any location in the cell where a non-aqueous electrolyte exists. However, precipitation of a large amount of the supporting salt on electrode surfaces causes a problem of decreased power density of the cell because the supporting salt in a solid state is an insulator.
Prof. Ishihara and his team claim, among other things, that they have devised a way to prevent the supporting salt from precipitating on an electrode surface, along with improved high discharged capacity and improved gravimetric energy density.
Power Japan Plus says that its battery charges 20 times faster than lithium ion batteries; is rated for more than 3,000 cycles; and can slot directly into existing manufacturing processes, requiring no change to existing manufacturing lines.
The ability to charge the battery so rapidly could, the company proposes, enable longer-range electric vehicles, as regenerative breaking will be more efficient. Because the dual carbon battery can be 100% discharged, it can further extend the length of each usable charge cycle, the company also suggests.
Power Japan Plus will begin benchmark production of 18650 Ryden cells later this year at the company’s production facility in Okinawa, Japan. This facility will allow the company to meet demand for specialty energy storage markets such as medical devices and satellites. For larger demand industries, such as electric vehicles, Power Japan Plus says it will operate under a licensing business model, providing technology and expertise to existing battery manufacturers to produce the Ryden battery.
Jeffrey A. Read, Arthur V. Cresce, Matthew H. Ervin and Kang Xua (2014) “Dual-graphite chemistry enabled by a high voltage electrolyte” Energy Environ. Sci. 7, 617-620 doi: 10.1039/C3EE43333A
Tatsumi Ishihara, Yuji Yokoyama, Futoshi Kozono, Hidemi Hayashi (2011) “Intercalation of PF6- anion into graphitic carbon with nano pore for dual carbon cell with high capacity,” Journal of Power Sources, Volume 196, Issue 16, Pages 6956-6959
J. A. Seel and J. R. Dahn (2000) “Electrochemical Intercalation of PF 6 into Graphite” J. Electrochem. Soc. vol. 147, issue 3, 892-898 doi: 10.1149/1.1393288
Carlin, R. T.; Delong, H. C.; Fuller, J.; Trulove, P. C. (1994), “Dual Intercalating Molten Electrolyte Batteries” Journal of the Electrochemical Society141, (7), L73-L76 doi: 10.1149/1.2055041