A sodium-ion battery is a type of rechargeable battery that works primarily by moving sodium ions between the positive and negative electrodes, similar to the working principle of a lithium-ion battery.
Working principle of sodium-ion batteries
During the charging and discharging process of a sodium-ion battery, Na+ ions move back and forth between the two electrodes: during charging, Na+ ions are extracted from the positive electrode and inserted into the negative electrode via the electrolyte; the reverse occurs during discharging. The new 18650 sodium-ion battery utilizes sodium-ion transfer (instead of lithium-ion transfer) to store and release electrical energy.
Advantages of sodium-ion batteries
Researchers have classified this particular material as a trade secret. Loç Simonin, a collaborating researcher at LITEN, noted, "Its energy density is comparable to that of lithium-ion batteries such as lithium iron phosphate."
Sodium-ion batteries primarily use sodium salts as electrode materials, which are more abundant and cheaper than lithium salts. Because sodium ions are larger than lithium ions, sodium-ion batteries are a cost-effective alternative when weight and energy density are not critical requirements. Compared to lithium-ion batteries, sodium-ion batteries offer the following advantages:
1. Sodium salt raw materials are abundant and inexpensive. Compared with ternary cathode materials for lithium-ion batteries, using iron-manganese-nickel-based cathode materials reduces raw material costs by half.
2. Due to the properties of sodium salts, lower concentration electrolytes can be used (for the same concentration, sodium salt electrolytes have a conductivity approximately 20% higher than lithium electrolytes), thus reducing costs;
3. Sodium ions do not form alloys with aluminum, so aluminum foil can be used as the current collector in the negative electrode, which can further reduce costs by about 8% and weight by about 10%.
4. Because sodium-ion batteries have no over-discharge characteristics, they can discharge to zero volts. Sodium-ion batteries have an energy density greater than 100Wh/kg, comparable to lithium iron phosphate batteries, but with a significant cost advantage, making them a promising candidate to replace traditional lead-acid batteries in large-scale energy storage.
Research on sodium-ion batteries began around the 1980s. Early electrode materials such as MoS2, TiS2, and NaxMO2 exhibited unsatisfactory electrochemical performance, leading to very slow development. Finding suitable sodium-ion electrode materials is one of the keys to realizing the practical application of sodium-ion energy storage batteries.
Since 2010, a series of positive and negative electrode materials have been designed and developed based on the characteristics of sodium-ion batteries, which have greatly improved capacity and cycle life. For example, hard carbon materials, transition metals and their alloy compounds are used as negative electrodes, while polyanionic, Prussian blue and oxide materials are used as positive electrodes. In particular, layered NaxMO2 (M=Fe, Mn, Co, V, Ti) and its binary and ternary materials have shown good charge-discharge specific capacity and cycle stability.
