In-depth introduction to sodium-ion batteries(Ⅰ)

1.Introduction to Basic Information

Sodium-ion batteries are rechargeable batteries that primarily rely on the movement of sodium ions (Na+) between the positive and negative electrodes to function, similar to the working principle of lithium-ion batteries. During the charge and discharge process, Na+ shuttles between the two electrodes: during charging, Na+ is deintercalated from the positive electrode and intercalated into the negative electrode through the electrolyte, and during discharge, the process is reversed.

Research on sodium-ion battery began around the 1980s. In the early stages, electrode materials such as MoS2, TiS2, and NaxMO2 showed unsatisfactory electrochemical performance, leading to slow development progress. Finding suitable electrode materials for sodium-ion storage is one of the key challenges to practical applications of sodium-ion batteries. Since 2010, a series of positive and negative electrode materials have been designed and developed based on the characteristics of sodium-ion batteries, leading to significant improvements in capacity and cycle life. Materials such as hard carbon for the negative electrode, transition metals and their alloys, and materials like polyanionic compounds, Prussian blue analogs, and oxides for the positive electrode, especially layered NaxMO2 (M=Fe, Mn, Co, V, Ti) and its binary and ternary derivatives, have demonstrated excellent charge and discharge capacity and cycle stability.

2.The current situation of the sodium battery industry

In terms of the production process, the manufacturing of sodium-ion batteries is similar to that of lithium-ion batteries. It mainly involves electrode manufacturing (preparation of slurries for positive and negative electrodes, drying, coating, calendering, slitting……) , cell assembly (rolling, cutting, winding/stacking, sealingt……), testing( formation, capacity grading, etc.). The main difference lies in the fact that sodium-ion batteries can use aluminum foil as the current collector for the negative electrode, which allows both positive and negative electrodes to utilize the same aluminum tabs, simplifying related processes such as tab welding. As a result, existing lithium-ion battery assembly production lines can be slightly modified to produce sodium-ion batteries, and the cost of transitioning to sodium-ion battery production is relatively low.

3.Advantages and disadvantages of Sodium Batteries:

Advantage 1: Abundant Resources

• Abundant Sodium Resources: Sodium is abundant in the Earth’s crust, with an abundance of 2.3%, ranking as the sixth most abundant element, significantly higher than lithium, which has an abundance of 0.0017%. According to expert, the currently explored lithium resources worldwide can only meet the demand for 1.48 billion electric vehicles, highlighting the increasing pressure of lithium resource scarcity with the accelerating global electrification.

• More Even Distribution of Sodium Resources: According to the 2019 report from the United States Geological Survey, three South American countries, Argentina, Chile, and Bolivia, hold 52.10% of the global lithium resources, while China’s lithium resources account for only 7.26%, indicating a highly uneven distribution of resources. China relies on imports for more than 60% of its required lithium raw materials, resulting in a high level of external dependence. In contrast, sodium is widely present in the form of salts in both terrestrial and marine environments, making it easily accessible.

Advantage 2: Low Cost

The cost advantages of sodium-ion batteries are mainly reflected in the following aspects:Sodium salts replace lithium salts. The price of metallic sodium is CNY19,000 per ton, and the price of sodium carbonate is CNY3,000 per ton, significantly lower than the CNY2.98M per ton for metallic lithium and CNY484,000 per ton for lithium carbonate. The raw material prices are much cheaper.

Aluminum foil replaces copper foil. Assuming copper foil is priced at CNY110,000 per ton and aluminum foil is priced at CNY40,000 per ton, and assuming 1 GWh of lithium batteries requires 622 tons of copper foil and 400 tons of aluminum foil, while 1 GWh of sodium-ion batteries requires 800 tons of aluminum foil, the single Wh current collector cost for lithium batteries is CNY0.084, and for sodium batteries, it is CNY0.032, resulting in a cost reduction of CNY0.052/Wh.

Graphite anode is expected to be replaced with anthracite coal to lower costs. According to data from Hina Sodium, the material cost of sodium-ion batteries is about CNY0.37 /Wh, which is significantly better than the phosphate iron and ternary lithium battery systems.

Advantage 3: High Safety

Sodium-ion battery possess superior safety performance compared to other battery types:• Sodium-ion batteries have higher internal resistance, resulting in lower currents during short circuits and less instantaneous heating.

• The standard voltage of lithium is higher, making it more likely to lose electrons in an aqueous solution. Therefore, sodium-ion batteries exhibit higher stability.

• After undergoing tests such as short circuit, puncture, and compression, sodium-ion batteries show no signs of ignition or explosion. On the other hand, lithium-ion batteries are susceptible to over-discharge, leading to the dissolution of copper foils and irreversible capacity decay. Sodium-ion batteries do not experience over-discharge issues, as the positive electrode can be discharged to 0V without affecting subsequent use, thus enhancing the safety of the battery during storage and transportation. Additionally, sodium-ion batteries tend to passivate and deactivate during thermal runaway, resulting in better safety performance during safety testing.

Advantage 4: Excellent Low-Temperature Performance & High Rate Capability

• High rate capability: Sodium-ion batteries exhibit excellent solvation energy lower than lithium-ion batteries, leading to a stronger interface ion diffusion ability. The smaller Stokes radius of sodium ions, combined with higher ionic conductivity of sodium salt electrolytes at the same concentration compared to lithium salt electrolytes, results in better fast-charging performance. According to data from CATL, sodium-ion batteries can charge up to 80% in 15 minutes, while Hina Sodium claims their batteries can reach 90% charge within 12 minutes, both significantly outperforming the 30-minute charging time to 80% for normal lithium-ion batteries.

• Excellent low-temperature performance: The high ionic conductivity of sodium-ion batteries allows for lower electrolyte concentration requirements, resulting in lower electrolyte viscosity at low temperatures compared to lithium-ion batteries. This overall enhances the battery’s performance at low temperatures. Sodium-ion batteries can operate within a normal temperature range of -40°C to 80°C, and some products can maintain around 88% of their capacity at -20°C, which is significantly better than the 60-70% capacity retention of LFP batteries at the same temperature.

Disadvantages: Cycle Life and Energy Density Need Improve

• Cycle Life: Currently, the overall cycle life of sodium-ion batteries is around 2000 cycles, slightly lower than LFP batteries. There is still some gap compared to certain LFP batteries used in energy storage applications, which can exceed 5000 cycles.

• Energy Density: The energy density of innovative sodium-ion battery cells from companies like Natrium Innovations is over 130 Wh/kg, while other companies like LiFun Energy have achieved 140 Wh/kg, and Hina Sodium’s products have an energy density of 145 Wh/kg. However, there is still room for further optimization to enhance the energy density of sodium-ion batteries.

Sodium-ion battery application scenarios: