BASIC KNOWLEDGE - SODIUM ION BATTERY What is a sodium-ion battery? Definition, structure, and more

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What exactly is a sodium-ion battery, what makes them different from mainstream alternatives like lithium-ion batteries, and what sort of applications could they help to transform? We’re going to explore all this and more in this comprehensive breakdown of this potential breakthrough battery technology.

Sodium-ion batteries are currently evolving as a viable substitute for lithium-ion batteries because of the abundant availability and reasonable cost of sodium. They hold great promise due to their properties; they’re energy dense, non-flammable, and can operate well in cold temperatures. They’re also much better for the environment than other mainstream alternatives, but the performance of SIBs has so far been limited due to their poor durability. All this, as we will explore in this article, could be about to change if recent developments in the SIB space are to be believed.

What is a sodium-ion battery?

A sodium-ion battery is a type of rechargeable battery comparable to the ubiquitous lithium-ion battery, but it uses sodium ions (Na+) as the charge carriers rather than lithium ions (Li+). The working principles behind and cell construction of a sodium-ion battery is virtually identical to those of lithium-ion batteries, but sodium compounds are used instead of lithium compounds.

Sodium-ion batteries are currently emerging as a potential alternative to current lithium-ion battery technology due to their lower cost, higher availability, and reduced impact on the environment. Since sodium-ion batteries use cheap and abundant materials—sodium and aluminum rather than lithium and copper—they could be transformative in some applications.

The structure and composition of a sodium-ion battery

A sodium-ion battery is made up of an anode, cathode, separator, electrolyte, and two current collectors, one positive and one negative. The anode and cathode store the sodium whilst the electrolyte, which acts as the circulating “blood” that keeps the energy flowing. This electrolyte forms by dissolving salts in solvents, resulting in charged ions that are then carried by the electrolyte from the anode to the cathode and vice-versa through the separator.

The movement of sodium ions creates free electrons in the anode, and this creates a charge at the positive current collector. The current then flows from the current collector through the device that’s being powered by the battery, such as a smartphone, to the negative current collector. The separator blocks the flow of electrons inside the battery.

While a sodium-ion battery is discharging and providing a current, the anode releases sodium ions to the cathode, generating a flow of electrons from one side to the other. When plugging in the device, the opposite happens: Sodium ions are released by the cathode and received by the anode.

Sodium-ion batteries can use aqueous as well as non-aqueous electrolytes. When aqueous electrolytes are used, the limited electrochemical stability window of water results in batteries with lower voltages and limited energy densities. To get around this, the same non-aqueous carbonate ester polar aprotic solvents used in lithium-ion batteries, such as dimethyl carbonate and propylene carbonate, can be used. Currently, the most widely used non-aqueous electrolyte uses sodium hexafluorophosphate.

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What’s the difference between a sodium-ion battery vs lithium-ion battery?

As we mentioned at the beginning of this article, there’s not a whole lot of difference between sodium-ion vs lithium-ion batteries; they’re both built and perform in virtually the same way, and both can for the most part be used in the same applications.

The biggest difference and advantage of sodium-ion vs lithium-ion batteries stems from the high natural abundance of sodium (23,600ppm) in the earth’s crust compared to lithium (20 ppm), and the overall lower cost of extraction and purification of sodium when compared to lithium also. In addition, sodium-containing metal oxide and polyanion cathode materials can be fabricated from naturally abundant metals such as iron and titanium, which makes sodium-ion batteries far more sustainable and affordable.

Indeed, a close examination of lithium-ion and sodium-ion batteries confirms that it is indeed the use of sodium and thus nature of the cathode material that is the main difference between the two. Since the preparation cost of the cathode from raw materials is more or less the same for both lithium-ion and sodium-ion battery technologies, the major cost reduction for sodium-ion batteries comes from their raw materials: sodium and aluminum.

Here’s a breakdown of some of the key differences between sodium-ion and lithium-ion battery technology:

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Key sodium-ion battery applications

Research has shown that replacing lithium-ion batteries with sodium-ion alternatives can lead to meaningful outcomes, and many studies have supported the use of sodium-ion batteries to meet the growing demands of cleaner, greener energy.

Although sodium-ion batteries can be used to power virtually any application that currently relies on lithium-ion batteries, some of the applications where sodium-ion technology could make the biggest difference include:

• Automotive: With EV sales expected to skyrocket over the next few years, sodium-ion technology is the obvious better choice because not only are they cheaper, which will make EVs more accessible, but they’re also cleaner, lighter, and more stable.

• Power grids: Smart grids rely on reliable power, meaning an intermittent power supply can cause them to malfunction. Sodium-ion batteries could be used to optimize solar and wind energy to meet grid energy storage requirements.

• Industrial mobility: Industrial mobility: The properties of sodium-ion batteries mean that they can be used to maximize asset utilization and reduce operating costs with a constant state of readiness and high peak power.

The latest research in sodium-ion battery technology

Although sodium-ion batteries hold much promise, they do have some limitations that have thus far held back their commercialization. One of the biggest limitations has been pure durability, but recent, widely celebrated research means that this is likely to change for the better.

A research team from the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) has developed a sodium-ion battery with greatly extended longevity. The team’s findings, which were published in the journal Nature Energy earlier this year, provide a promising recipe for a battery that may one day power electric vehicles and store solar energy.

In their work, the researchers shifted the ingredients that compose the battery’s liquid core, which ultimately prevented the performance issues that have previously plagued sodium-ion technology. “Here, we have shown in principle that sodium-ion batteries have the potential to be a long-lasting and environmentally friendly battery technology,” the research team said in June.

As the team explains, the electrochemical reactions inside batteries that keeps energy flowing become sluggish over time, meaning that the battery can no longer be recharged. In current sodium-ion technology, this process takes place much faster than in lithium-ion technology.

The PNNL team solved this problem by switching out the liquid solution and the type of salt flowing through it to create a new electrolyte recipe. This enabled the team, for the first time ever, to greatly extend the number of charging cycles to 300 or more with a minimal loss of capacity in a coin-sized battery.

The research team explains that the current electrolyte recipe for sodium-ion batteries creates a protective film on the anode that dissolves over time. This film is important because it enables sodium ions to pass through while preserving battery life. In contrast, the research team’s technology works by stabilizing this protective film, contributing to its extended durability.

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The future of sodium-ion technology

Sodium-ion battery technology has benefitted from huge amounts of recent research activity, with developments in the space being particularly rapid due to their similarity to lithium-ion battery systems.

With recent discoveries such as hard carbon as a more suitable anode material and increasing demand in large-scale electrical energy storage, progress towards the commercialization of sodium-ion batteries is gaining traction.

Indeed, with the great pace of improvements that we’re seeing in sodium-ion battery technology, it can be anticipated that the technology will soon emerge as a serious challenger to lithium-ion in the rechargeable battery space. This, however, can only be achieved through further investment in research and development of sodium-ion batteries in order to commercialize this technology for cheap, scalable, and large-scale electrical energy storage.

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