|E-bike powered by Faradion prototype Na-ion battery pack. For the proof-of-concept, the cells were manufactured to be larger than necessary to avoid unnecessary costs and lengthy manufacturing processes at this early stage. Click to enlarge.
British battery R&D company Faradion has demonstrated a proof-of-concept electric bike powered by sodium-ion batteries at the headquarters of Williams Advanced Engineering, which collaborated in the development of the bike. Oxford University was also a partner. Although lithium-ion batteries are currently the predominant battery technology in electric and hybrid vehicles, as well as other energy storage applications, sodium-ion could offer significant cost, safety and sustainability benefits.
Sodium-ion intercalation batteries—i.e., batteries using the same process of ion insertion and removal as in Li-ion batteries—have been discussed in the literature for some time. (e.g., Earlier post.) Using sodium instead of lithium in a battery is attractive because it could potentially be much less expensive (~30% less) and safer, and it would be more environmentally benign. However, developing efficient Na+ intercalation compounds is a challenge because sodium ions are much larger than lithium ions—about 70% larger in radius. Thus, insertion/deinsertion of sodium ions in a host material is much more difficult than that of lithium ions.
Large structural change occur during Na+ insertion and de-insertion, leading to low capacity and poor cycling stability. For cathode materials, the reversible, stable capacity of bulk Na+ intercalation is usually limited to levels far below what can be obtained in Li-ion electrode materials. (Earlier post.)
The battery for the e-bike has a design energy of 418 Wh, 250 Wh of which has been used in the e-bike proof-of-concept. Faradion’s sodium-ion cells deliver a specific energy of more than 140 Wh/kg.
|A 48 cell battery pack design by Williams Advanced Engineering, incorporating Faradion’s 3 Ah Na-ion cells. Click to enlarge.
The e-bike battery pack is made up of four modules, designed and manufactured by Williams Advanced Engineering, and controlled by a Williams-designed battery management system. Each module contains 12 Faradion cells. Williams is a proven leader in the design and manufacture of battery energy storage technology, having developed batteries for the Formula E electric racing series, Jaguar C-X75 hybrid supercar, and the Kinetic Energy Recovery Systems (KERS) that helped power the company’s Formula One racing cars from 2011-2013.
Oxford University’s expertise has been used to maximize battery life and it is expected that as well as comparable performance, sodium-ion cells can offer a comparable lifetime to lithium-ion products.
As a proof-of-concept, the cells for the e-bike have been manufactured to be larger than necessary, which helps to avoid unnecessary costs and lengthy manufacturing processes at this early stage. When optimized, the cells will be comparable in size to lithium-ion battery packs already on the market. As such, there is potential to exploit the technology for use in a wide range of electric and hybrid vehicles, as well as energy storage applications.
|Faradion CEO Lawrence Bern with the e-bike battery. Click to enlarge.
The project to demonstrate Faradion’s sodium-ion battery technology has been part-funded by Innovate UK, the UK’s innovation agency in its latest competition for ‘disruptive technologies in low carbon vehicles’.
Faradion Na-ion technology. Faradion Limited was established in 2011 to develop low-cost, non-aqueous sodium-ion (Na-ion) rechargeable batteries. A typical Faradion Na-ion pouch cell would combine a hard carbon anodes, an electrolyte (typically NaClO4-PC or NaPF6 EC/DXC/PC), and a cathode material.
Faradion has screened more than 90 classes of novel active cathode materials so far, including:
Phosphates: Na7M4(P2O7)4PO4, M = V, Fe, Cr, Al etc. Na4M3(PO4)2P2O7, M = Fe, Co, Ni, Mn etc.;
Na3M12-xM2xXO6 and Na2M12-xM2xX’O6
Layered oxides, e.g. NaNi1-x-y-zM1xM2yM3zO2
Faradion’s Na-ion technology has already shown specific energy densities in full cells exceeding those of other known sodium-ion materials. The Faradion team have also already developed materials with energy densities exceeding that of lithium iron phosphate.
|Comparison of the cathode specific energy densities of some sodium ion cathode materials achieved in full cells, with LiFePO4 included as a well-known comparison. Click to enlarge.
Sung You Hong, Youngjin Kim, Yuwon Park, Aram Choi, Nam-Soon Choic and Kyu Tae Lee (2013) “Charge carriers in rechargeable batteries: Na ions vs. Li ions” Energy Environ. Sci., 6, 2067-2081 doi: 10.1039/C3EE40811F