With the rapid expansion of the electric vehicle market and the continuous acceleration of smart grid construction, the importance of energy storage technology is increasingly highlighted, and it has become one of the most concerned research hotspots in the global scientific and industrial circles.
Energy storage batteries, as a key technology in this field, directly affect the driving range, charging efficiency of electric vehicles, and the stable operation of smart grids. Therefore, breaking through the technical bottlenecks of energy storage batteries has become the main challenge to promote the development of electric vehicles and smart grids.
On April 5, 2024, scientists published an article on high-energy efficiency all-solid-state sodium-air batteries in the journal "Nature Communications", which is expected to activate the irreversible carbonate reactions in the battery through solid-state electrolytes, thereby improving the battery performance.
What is a sodium-air battery?
A sodium-air battery is a device that generates electrical energy through the chemical reaction between metallic sodium and the oxygen in the air. Compared with traditional lithium-ion batteries, sodium-air batteries have many advantages.
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Firstly, sodium metal is extremely abundant on Earth and has a low cost. Secondly, sodium-air batteries have a high energy density, which can store more electrical energy to meet people's growing energy needs. In addition, sodium-air batteries also have characteristics such as environmental protection and safety, which are in line with the direction of future energy development.
How to improve the performance of sodium-air batteries?
In actual use, for cost and convenience, the positive electrode of the sodium-air battery usually uses air as the fuel. The air involved in the reaction at the positive electrode of the battery is oxygen. However, carbon dioxide and water coexisting with oxygen in the air will cause serious irreversible reactions during the battery reaction process, such as the formation of carbonates and hydroxides, which reduce the battery performance.
Based on this, researchers have prepared a new type of high-efficiency sodium-air battery, which achieves a high voltage window, high energy density, and high energy efficiency by carrying out reversible carbonate reactions in the Na3Zr2Si2PO12 (Nasicon) solid-state electrolyte.Researchers first synthesized the Na3Zr2Si2PO12 (Nasicon) solid-state electrolyte using the solid-state reaction method, and then assembled a sodium-air battery with nickel as the air electrode, sodium as the anode, and Nasicon as the solid-state electrolyte.
The electrochemical test results show that the discharge product of the sodium-air battery can activate the reversible electrochemical reaction of carbonates by undergoing a chemical reaction with water to form a cathode electrolyte, which promotes the kinetic reaction process. This is due to the small charge-discharge potential difference of the carbonate reaction. This reaction process allows the battery to achieve higher energy efficiency.
Under the test conditions of 70% relative humidity, the voltage platform of the sodium-air battery can reach 3.4V, higher than other metal-air batteries.
Energy density, Coulomb efficiency, and energy efficiency are important parameters of a battery. The larger the energy density of a battery, the more electrical energy it can store. Coulomb efficiency is closely related to the performance degradation of the battery during the charge-discharge process. The higher the Coulomb efficiency, the less performance degradation and the longer the battery life. Energy efficiency is positively correlated with the ratio of electrical energy released and stored by the battery. The higher the energy efficiency, the higher the conversion efficiency of electrical energy.
The study shows that the battery can provide an energy density of 0.16mAh cm−2, the Coulomb efficiency can reach 99%, and the average energy efficiency is 82.1%, indicating that the battery can store more electrical energy, has a longer service life, and can efficiently achieve the storage and release of electrical energy.
In addition, once the reversible electrochemical reaction of carbonates is activated under high relative humidity conditions, it can still be maintained even under low relative humidity conditions.
Sodium-air battery performance (a-c. Performance of sodium-air batteries under 70% relative humidity, 25°C conditions; d-f. Performance of sodium-air batteries under 40% relative humidity, 25°C conditions; g. Comparison between superoxide metal-oxygen batteries and sodium-air batteries) (Image source: Reference 1)
The advantages of the sodium-air battery designed in this study are: no need for additional devices for gas purification and storage, simplifying the battery structure, which helps to improve the energy density of metal-air batteries; using sodium, which is abundant in the Earth's reserves, as the battery material, can further reduce the cost of the battery.Conclusion
The breakthrough in new energy vehicle (NEV) battery technology undoubtedly injects new vitality into the environmental protection cause and brings a completely new experience to consumers. With the continuous advancement and innovation in technology, we have reason to believe that NEVs will achieve greater breakthroughs in performance, safety, and intelligence, providing consumers with more convenient, comfortable, and green modes of transportation. Let us look forward to the arrival of this day and witness the brilliant future of the new energy vehicle industry together!