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Towards future-proofed battery solutions


A group of quality and certification managers at power supply and battery charger manufacturer Mascot, examine current advances in battery technology


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ithium-ion batteries have lately become the preferred choice in numerous applications. 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 rapid chargeability.


Furthermore, they are highly versatile, boast high energy density and low self-discharge and require little maintenance. They can also provide instant start-up when needed. But they have their limitations: transportation issues are well-documented while they are also subject to aging, even when not in use, while a protection circuit is invariably needed to maintain voltage and current within safe limits.


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 resulting in stress and cracking, and capacity loss emanating from reduced contact with current collectors.


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. A successful new battery launch is therefore not only a rarity but a major event – and some proven technologies previously shelved for commercial reasons are enjoying renewed focus and investment.


Among these is sodium ion batteries, where advances kept pace with Li-ion until the 1980s, when the spotlight turned to lithium. However, with concerns over remaining global lithium supplies, the search for more available, cost-effective alternatives has intensified. Sodium is the sixth most abundant element in the Earth’s crust


Developments continue apace in lithium-ion batteries, specifically through using a single crystal cathode material instead of graphite. This will deliver major benefits in the rapidly developing electric vehicle sector. 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, will continue to be limited.


To help improve the specific energy of Li-ion products, silicon nanowire anodes are being used which deliver enhanced watthours


www.cieonline.co.uk


and can be extracted from seawater, making supplies potentially almost infinite. While not boasting the same energy density as lithium-ion batteries, there are notable advantages in safety and cost, with sodium able to operate across a broader temperature range.


Sodium ions have similar intercalation chemistry to lithium ions meaning many 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 Li-ion counterparts: a sodium oxide cathode, carbon-based anode and non-aqueous solvent electrolyte. Manufacturing processes are similar, so any factories producing lithium-ion batteries will be fully adaptable towards sodium-ion technology. This is key given recent analysis by Bloomberg New Energy Finance forecasting demand for lithium will grow 1500 times by 2030. This could increase lithium prices. making alternative battery types an economic necessity.


Performance is not an issue either. In June 2020 it was revealed that one solution developed by Washington State University and Pacific Northwest National Laboratory could deliver similar capacity to some lithium-ion batteries and retain more than 80 percent of its charge after 1,000 cycles.


Sodium ions are larger than lithium ions, meaning energy density of batteries containing them is lower, making sodium particularly well-suited to stationary applications. Many early applications will replace lead- acid batteries where sodium-ion technology can deliver higher energy density and performance at similar cost. Such applications include smart grids, grid-storage for renewable power plants, car SLI batteries, UPS, telecoms and home storage.


Extreme temperature applications such as weather stations, fieldwork, pipeline


inspections equipment and communication links are also suitable.


Transport is another possible application for higher energy density sodium-ion batteries, typically those using non-aqueous electrolytes – in effect any application currently using 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 compared with lithium- ion batteries at similar performance levels. Further ahead, sodium-ion batteries will be deployed in very high-density applications, such as long-range electric vehicles and consumer electronics, which are currently served by higher-cost lithium-ion batteries. Any battery is only as 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.


Charging time is comparable with alternative battery types with 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. As an independent global leader on power supply and charging technology, Mascot AS can recommend the best future-proofed charging solution.


mascot.no Components in Electronics April 2021 27


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