The all-solid-state sodium-air battery is launched. 1 article amazing makes it clear!

The all-solid-state sodium-air battery is launched

The all-solid-state sodium-air battery is launched

Metal-air battery: received widespread attention

The all-solid-state sodium-air battery is launched. In recent years, due to the need for the development of electric vehicles and energy storage systems, the development of secondary battery technology has been rapid, and the technical routes are constantly enriched. However, electric vehicles still have some disadvantages, such as long charging time, limited driving range, and high battery cost, which restrict their widespread popularity. Among various battery technology routes, metal-air batteries have attracted widespread attention due to their high energy density.

Among various battery technology routes, metal-air batteries have attracted widespread attention due to their high energy density.

Metal-air batteries are electrochemical batteries with metals and air as positive and negative electrodes. The reactants of this battery are generally oxygen in the air, which is superior to other secondary batteries in terms of mass and volume.

Technical advantages

For a long time, lithium batteries have dominated the application of secondary batteries.

However, with the advancement of lithium-air battery research and development, the energy density and performance of lithium batteries have been significantly improved. However, considering the shortage of lithium metal resources, the abundant and low-cost sodium metal has similar physical and chemical properties to lithium metal, and replacing lithium metal with sodium metal has also become a hot spot in battery research.

For transportation and grid energy storage, the commercial battery energy density requirement is about 1700Wh/kg, while sodium air batteries can reach 1600Wh/kg, which meets the energy density requirements.

Sodium air batteries also have the advantages of low charging voltage, abundant resources, and suitability for large-scale production and application.

However, although lithium or sodium metal-air batteries have received much attention in recent years, the development of these two batteries also faces many challenges.

Current metal-air batteries mainly rely on pure oxygen rather than ambient air for reaction.

This is because carbon dioxide (CO2) and water (H2O) in the ambient air will inevitably react chemically with the discharge products to form insoluble carbonates. These products are not only non-conductive but also block the gas channels, resulting in poor battery cycle stability, and are difficult to decompose by electrochemical methods.

To separate pure oxygen from the air, the battery module also needs to add additional devices that can purify and store oxygen (such as oxygen-permeable membranes), which will greatly increase the weight and volume of the battery module and reduce the energy density.

Therefore, how to avoid the formation of carbonates and directly use ambient air for reactions has become a core issue.

The new electric car prototype boasts an innovative air battery for extended range
The new electric car prototype boasts an innovative air battery for extended range

Breakthrough of Nasicon solid electrolyte

Recently, researchers from Pohang University of Science and Technology (POSTECH) in South Korea introduced a sodium-air battery. The team used Nasicon (a sodium superionic conductor) solid electrolyte (Na3Zr2Si2PO12) to activate a reversible carbonate reaction. The battery has a discharge potential of 3.4 V, which is much higher than other metal-air batteries, and therefore has a high energy density.

The biggest breakthrough of this all-solid-state sodium-air battery is that it effectively solves the problem of insoluble carbonate products, so ambient air can be used without any special equipment. The research results were published in the journal Nature Communications.

Electrochemical reactions of sodium-air batteries

The research team built a sodium-air battery based on the Nasicon solid electrolyte, whose air electrode consists of Nasicon (Na3Zr2Si2PO12) as an ion conductor and nickel (Ni) metal instead of carbon as an electronic conductor.

Caption: a is a schematic diagram of a sodium-air battery based on Nasicon SE; b and c are a cross-section of the air electrode and a top view of the air electrode; d and e are optical images of the air electrode and the anode side of the battery.

Nasicon contains elements such as sodium (Na), silicon (Si), and zirconium (Zr), allowing ions to move in the solid state. At the same time, Nasicon can also maintain high chemical stability in ambient air and will not react with water, oxygen, or carbon dioxide.

In addition, the use of solid electrolytes helps protect the sodium metal anode from air erosion, while the use of carbon-free air electrodes can mitigate unpredictable side reactions usually caused by carbon.

When the battery is discharged, the Na metal electrode loses electrons, while the Na ions near the air electrode gain electrons and react with water and oxygen in the air to produce NaOH precipitation.

Based on the study of the discharge products of the air electrode in the sodium-air battery, the staff found that the discharge of the air electrode based on the Nasicon solid electrolyte simultaneously formed NaOH and Na2CO3·H2O.

The formation of Na2CO3·xH2O (x=1 or 0) may be caused by the chemical reaction of NaOH with CO2 and H2O in the ambient air during or after the first discharge.

When the discharge product NaOH is exposed to humid air, it also tends to form NaOH·H2O with moisture in the air, thereby generating an in-situ cathode electrolyte. This phenomenon is also common in lithium-air battery electrolytes. It can act as both an electrolyte and an active material, enabling rapid conduction of sodium ions within the electrode, and unexpectedly activating a reversible carbonate reaction in a large active reaction area, thereby increasing the achievable capacity and enhancing the electrochemical kinetics.

This “activation” can be understood as that at first, it should be NaOH that participates in the reversible reaction with the charge and discharge cycle, but then NaOH forms an in-situ cathode electrolyte with water, which is also applicable in lithium-air battery electrolytes, so the main participant in the redox reaction becomes Na2CO3.

The researchers found that the formed Na2CO3·H2O will decrease with the electrochemical decomposition during the charging process.

After the first cycle of discharge and charge in the experiment, the in-situ Raman spectroscopy of the air electrode further confirmed the formation and decomposition of Na2CO3·H2O (x = 0 or 1) in the Nasicon-based sodium-air battery. The in-situ differential electrochemical mass spectrometry (DEMS) analysis also confirmed the decomposition of Na2CO3·H2O.

The in-situ DEMS clearly shows that CO2 gas is released during the charging process. Considering the reaction-based gas release rate, part of the released CO2 is stored in the air electrode (especially in the absorbed H2O).

After in-situ measurements of the air electrode after 10 cycles, the researchers concluded that NaOH and Na2CO3·xH2O were electrochemically formed at low potentials (~2.0 V) and high potentials (~3.4 V), respectively.

After the electrochemical reaction of Na2CO3·xH2O was activated in the sodium-air battery, it became the main redox reaction with the number of cycles, and the voltage platform was also stabilized at around 3.4 V.

This is the first report of a reversible reaction of carbonate compounds electrochemically formed in a lithium/sodium ambient air battery.

This reversible electrochemical reaction involving carbonates increases the operating voltage and increases the energy density of the battery, while significantly reducing the voltage difference during charging and discharging, thereby improving energy efficiency.

These excellent electrochemical properties indicate that Nasicon-based sodium-air batteries can operate in relatively humid ambient air using the reversible electrochemical reaction of sodium carbonate/hydroxide.

Professor Kang Bingyu, who led the research, said: “We have invented a method to utilize carbonates, which has been a long-standing challenge in the development of metal-air batteries. We hope to lead the field of next-generation all-solid-state metal-air batteries using a solid electrolyte-based battery platform.”

Consumer electronics are increasingly adopting air battery systems for their sustainability
Consumer electronics are increasingly adopting air battery systems for their sustainability