The concept of electrochemical batteries is not new – large numbers of batteries with different material combinations and performance characteristics are available in the market, with lithium-ion batteries leading the way.

Lithium-ion batteries are the battery of choice for many electrical energy storage systems – from mobile phones to electric vehicles – because they provide the highest energy density than any other available battery for rechargeable devices.

Patent filings in this domain suggest that cutting-edge research may be developing batteries with the same storage capacity and performance characteristics as lithium-ion batteries, but at a cost that is 80% lower than that of a high-performance lithium-ion battery.

Stanford University researchers have developed a sodium-ion battery based on a compound related to table salt in which sodium and myo-inositol maximise the battery’s electron flow and significantly boost its performance potential.

According to chemical engineer Zhenan Bao, “nothing may ever surpass lithium in performance… but lithium is so rare and costly that we need to develop high-performance but low-cost batteries based on abundant elements like sodium”.

Until now, research has focused solely on comparing cost performance between sodium-ion batteries and state-of-the-art lithium; going forward, volumetric energy density will be just as important (ie, the size requirements of a sodium-ion battery for storing the same energy as a lithium-ion battery).

The potential of sodium-ion batteries as an alternative to lithium-ion batteries must be determined on the grounds of:

  • high energy storage capacity;
  • compact size;
  • low cost; and
  • high efficiency.

The patent landscape shows a gradual increase in the number of patents filed in this domain until 2017, with an average growth rate of 20.7% per year. The majority of research has been carried out in China, the United States, Japan, South Korea and Germany, with China leading the way in sodium-ion batteries.

In 2015, Faradion, a leading player providing the next-generation low-cost materials employed in sodium-ion batteries, collaborated with Sharp Corporation, a leading global specialist in solar energy solutions, filing three patents relating to energy storage systems for small renewable energy harvesting and power generation.

In 2017, several new entrants such as Ningbo Jidianxin New Material Technology, Suzhou Sichuangyuanbo Electronic Technology, Dongguan Jiaqian New Mat Technology and China Electronic New Energy Research Institute filed patents mainly relating to electrode and electrolyte materials in sodium-ion batteries.

Patent literature in this domain reveals how research is targeting the use of carbonaceous materials such as hard carbon and graphene for making sodium-ion battery anodes. These patents also disclosed the use of other materials like transition metal oxides, transition metal sulfides, transition metal phosphides, binary-metallic compounds, organic compounds and metallic sodium.

Since 2008 a significant number of patents have been filed for improving sodiation and desodiation mechanisms as well as the electrochemical performance of such materials. While a few patents initially disclosed the use of metallic sodium as an anode material, due to several technical challenges such as dendrite formation, high reactivity and an unstable passivation layer, its use is no longer preferable.

Most patents disclosed the use of sodiated transition metal oxides for making sodium-ion battery cathodes. Among all electrolyte materials, organic electrolytes were prevalent, often using propylene carbonate and ethylene carbonate or a combination of both as organic solvent and sodium perchlorate and sodium hexafluorophosphate as salt. After 2004, solid electrolytes became the focus for sodium-ion batteries.

IP filings also determine that nothing has replaced vinylene carbonate, fluoroethylene carbonate and transdifluoroethylene carbonate as additives in electrolytes. Materials such as polyethylene, polypropylene, polyvinyl chloride, polytetrafluoroethylene and glass fibre are used as separators, with glass fibre the most popular.

The most active players in this domain include:

  • NGK insulators;
  • Hitachi;
  • Zhejiang University;
  • Shaanxi University of Science and Technology;
  • Central South University; and
  • Yuasa battery.

Patent filings in this domain suggest that the major focus of all inventions lies in:

  • improving electrode material properties;
  • improving electrolyte conductivity;
  • improving cycle performance charge and discharge;
  • improving sodium-ion battery manufacturing methods;
  • reducing dendrite formations; and
  • improving the mechanical stability of solid electrolyte interphase layers.

As lithium-ion battery systems are likely to remain expensive, perhaps low-cost sodium-based systems are the way forward. Compared with other energy storage technologies, sodium-ion battery systems are a promising method for large-scale electricity storage because of their flexibility, high energy conversion efficiency and simple maintenance. Further, the growing availability of a wide range of materials promises greater opportunities in chemicals research relating to electrodes and electrolytes for sodium-ion batteries.

Faced with this prospect, the industry would be wise to address the following questions:

  • Can sodium-ion batteries ensure a driving range of 500km to 1,000 km in electric vehicles?
  • Can mass energy storage systems (eg, battery farms) leverage the low-cost sodium batteries?
  • Can sodium-based batteries match the versatility of lithium-ion batteries?

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