Look Out Lithium, Here Comes Sodium

Econintersect:  Rechargeable batteries for applications ranging from cellphones to electric cars have been considered to be a domain for lithium ion systems.  The relatively high cost of the elemental raw material as naturally occurring salts has been considered one of the limitations of the technology.  Now new research indicates that sodium based battery systems may become feasible to compete with lithium.  If new research described in R&D Magazine comes to commercial fruition the resource limits currently existing for lithium could be mitigated.  Sodium is more than 1,000 times as plentiful in the earth’s crust (Wikipedia) and more than 100,000 times more plentiful in seawater (Marine Science).

Sodium (in the form of sodium chloride, common salt) is the most commonly available non-metallic mineral in the world.  Comparing the prices of ACS Reagent Grade NaCl  (99% pure) with the same grade of LiCl, it appears that pure quantities of laboratory quantities are 5-8X more costly for the Li salt.

The power of the sodium ion system is 5-10X that of the common lithium battery chemistries, which are compared to the older common battery systems in the following graph from Battery University.

A key limitation on the implementation of the highest powered lithium chemistry battery systems is overheating.  The current paper does not address what limitations thermal factors will have on the sodium ion systems.  The research paper does say that the sodium ion systems will operate “at ambient temperature” but do not specify what that encompasses and what if any cooling mechanisms would be needed to maintain “ambient.”

The paper states that the V₂O₅ was annealed in oxygen atmosphere at 500 °C so that part of the structure can be assumed stable up to that temperature.  However, the paper does not discuss the temperatures of the test systems in the extended charge/discharge cycling that was done.

The research is described in an article in ACS Nano Journal (American Chemical Society) published 12 December 2011.  The authors are all from Argonne National Laboratory (Illinois):  Sanja Tepavcevic, Hui Xiong†, Vojislav R. Stamenkovic, Xiaobing Zuo, Mahalingam Balasubramanian, Vitali B. Prakapenka, Christopher S. Johnson, and Tijana Rajh.

Here is the Conclusion of the ACS Nano article:

In this work, we show that electrochemical synthesis is a method of choice for preparation of nanoscale architectures that require electronic conductivity, and it eliminates the need for conductive carbon additives and binders typically used in electrodes that alter their long-term stability. In addition, the electronically interconnected porosity of the electrochemically prepared nanoscale organized electrodes allows excellent ion transport while the large surface area provides an electrochemically active surface that is not constrained by diffusion limitations. It is at the nanoscale that near theoretical capacity and high-power electrodes can be achieved using simple self-organization processes. We show the ability of the open frame layered structure to accommodate for a large volume of Na ions by adjusting the layer spacing upon exposure of reduced layered structure to a high concentration of Na ions. The electrostatic attraction of electrochemically altered vanadium oxide layers provides a strong driving force for the diffusion of a large concentration of transporting ions into the open layer frameworks. This consequently leads to ordering of the overall structure with appearance of both short-range order within the layers and long-range order between the layers. Upon deintercalation of sodium, the long-range order is lost while intralayer structure is still preserved. Inducing ordering of nanomaterials in operando allows realization of the highest possible electrode capacity by optimizing the balance of electrostatic forces. We developed a nanoscale ordered bilayered V₂O₅ cathode that operates at room temperature above the theoretical capacity of 250 mAh/g, with redox potentials of 3 V, giving an energy density of 760 Wh/kg. The small diffusion length and large surface area of nanostructures also enable fast charging of V₂O₅ leading to high power of 1200 W/kg at a cycling rate of C/8. We believe that the small thickness of the bilayered structure is also responsible for improved elasticity and exceptional long-term stability of this open frame structure making bilayered V₂O₅ a suitable cathode material for high-energy density rechargeable sodium batteries.

Sources and References:

• Nano-structured electrodes form basis for new sodium-ion batteries (R&D Magazine, 13 February 2012)

• Abundance of elements in Earth’s crust (Wikipedia)

• Seawater Composition (Marine Science)

• Nanostructures Bilayered Vanadium Oxide Electrodes for Rechargeable Sodium-Ion Batteries (Sanja Tepavcevic, Hui Xiong†, Vojislav R. Stamenkovic, Xiaobing Zuo, Mahalingam Balasubramanian, Vitali B. Prakapenka, Christopher S. Johnson, and Tijana Rajh, ACS Nano Journal, 12 December 2011)

• Types of Lithium-ion (Battery University)