Examining Current Advances in Battery Technologies

Lithium-ion batteries have in the past few years become the preferred choice in a broad spectrum of applications. It is easy to see why. They tick the eight key requirements of the ideal battery, namely: high specific energy, high specific power, affordability, long life, safety, wide operating range, low toxicity and the ability to be charged rapidly.

On top of that, lithium-ion batteries are highly versatile, boast high energy density and low self-discharge – below half of that of nickelbased batteries – and require little maintenance. They also fulfil the key requirement of any battery, which is the ability to provide instant start-up when needed.

But they have their limitations too: issues around transportation have become well-documented and lithium-ion batteries are also subject to aging, even when they are not in use, while a protection circuit is invariably needed to maintain voltage and current within safe limits.

 

Figure 1: The search for the ‘perfect’ battery solution continues unabated

 

Developments continue apace in lithium-ion batteries, specifically through the employment of single crystal cathode material instead of graphite. This is set to to deliver major benefits in the rapidly developing electric vehicle sector which is striving for the twin aims of ever greater battery capacities as well as longer service life, with 15 years a widely quoted industry target. However, the longevity of the most common Li-ion battery types in consumer applications such as mobiles, where they are typically charged to the maximum allowable voltage, is set to continue to be limited.

To help improve the specific energy of li-ion products, silicon nanowire anodes are being used which deliver enhanced watthours per kg (Wh/kg) – typically up to twice that of commercial Li-ion cells. However, like all Si nanowire-based structures, their cycle life is limited. Microscale Si islands can develop under the nanowire arrays, with cycling that results not only in stress and cracking, but also in capacity loss emanating from reduced contact with current collectors.

Unsurprisingly, the search for the ‘perfect’ battery solution continues unabated. With almost all battery types, development time is typically extended – 10 years is commonplace – with many concepts abandoned in the laboratory, and others having their initial launch dates put back, often multiple times, when these are found to be unrealistic. This extended development time makes battery manufacture an unattractive proposition for investors – meaning it takes real commitment and patient, understanding benefactors to bring a new type of battery to market. It is hardly surprising, therefore, that the successful launch of a new battery is not only a rarity but a major event – and that some proven technologies that were previously put aside for commercial reasons are enjoying renewed focus and investment.

One of these is sodium ion batteries. Advances in this technology area kept pace with lithium ion products in the 1970s and 1980s, but the spotlight turned to lithium from that point. However, with concerns over remaining global supplies of lithium, and associated higher costs, the search for more available and cost-effective alternatives has intensified. Sodium is the sixth most abundant element in the Earth’s crust and can also be extracted from seawater, meaning that supplies are potentially almost infinite.

While not boasting the same energy density as lithium-ion batteries, there are notable advantages in the areas of safety and cost, with sodium able to operate across a broader range of temperatures.

Sodium ions have similar intercalation (charging) chemistry to lithium ions meaning many of the materials being tested for sodium batteries are similar to those used for lithium. However, graphite cannot be employed as the anode in sodium-ion batteries, as it is not energetically favourable to put sodium in between the individual layers. Some companies are using hard carbon anodes, with an NaPF6 electrolyte. The most widely seen design for sodium ion batteries is similar to the most common lithium counterparts: a sodium oxide cathode, a carbon-based anode and a non-aqueous solvent electrolyte. The manufacturing processes are also similar, so any factories producing lithium-ion batteries will be fully adaptable towards sodium-ion technology.

This is key given that one recent analysis by Bloomberg New Energy Finance forecast that demand for lithium will grow 1500 times by 2030. This has the potential to push prices for lithium higher, and making alternative battery types could then be an economic necessity rather than a novelty.

Performance is not an issue either. Indeed, in June last year it was revealed that one particular solution developed by a team from Washington State University (WSU) and Pacific Northwest National Laboratory (PNNL) was able to deliver a capacity similar to some lithium-ion batteries and to recharge successfully, keeping more than 80 percent of its charge after 1,000 cycles.

 

Figure 2: The Blueline 3743 LA charger is one of an extensive range from Mascot which are suitable for charging sodium ion batteries as well as other battery types

 

Sodium ions are larger than lithium ions, meaning the energy density of batteries containing them is naturally lower, making sodium particularly well suited to stationary applications where battery size is less important.

Many of the first applications are likely to be as replacements for lead-acid batteries where sodium-ion technology can deliver much higher energy density and performance at similar cost. Such applications include smart grids, grid-storage for renewable power plants, car SLI batteries, UPS, telecoms, home storage and other stationary energy storage applications.

Any applications in extreme temperature locations – high or low – such as weather stations, field work, pipeline inspections equipment, communication links or the likes, are also suitable for sodium-ion batteries.

Transport is another possible application for the higher energy density types of sodiumion batteries, typically those using non-aqueous electrolytes – in effect any application currently served by lithium-ion batteries. Power tools, drones, low speed electric vehicles, e-bikes, e-scooters and e-buses would all potentially benefit from the lower costs of sodium-ion batteries with respect to those of lithium-ion batteries at similar performance levels.

In the longer term, continued rapid development will see sodium-ion batteries deployed in very high-density applications, such as long-range electric vehicles and consumer electronics such as mobile phones and laptops, which are currently served by highercost lithium-ion batteries.

A number of companies have identified the potential of sodium-ion batteries and are committed to developments in this area, notably Faradion, Tiamat, Aquion Energy,
Novasis, Nitron and Altris.

Any battery of course is only effective as how rapidly and safely as it can be charged. During charging of sodium ion batteries, positive sodium ions are extracted from the cathode and transferred to the anode, while the electrons travel through the external circuit; for discharging, the process is reversed.

The good thing seems to be that charging time is comparable with alternative battery types and that there is no need for specialist charging equipment – meaning that, depending on the application, a switch to sodium ion products can be made without significant cost or inconvenience in this area.

 

This article originally appeared in Bodo’s Power Systems magazine.

 

About the Author

Dag Pedersen received a degree name Quartermaster from a Commandant School for the Coastal Artillery, then Bachelor of Commerce in the Field of Business at Aarhus University, and an MBA at Oregon State University. He worked as a Marketing manager at Mascot AS.