Recently, news that CATL will launch sodium-ion batteries has repeatedly made headlines in various media outlets, and sodium-ion batteries have also attracted significant market attention.
In fact, sodium-ion batteries are not a new invention. Sodium-ion batteries are also a type of rechargeable battery, which mainly relies on the movement of sodium ions between the positive and negative electrodes to work, similar to the working principle of lithium-ion batteries.
During charging and discharging, Na+ ions move back and forth between the two electrodes, inserting and de-inserting: during charging, Na+ ions are de-inserted from the positive electrode and inserted into the negative electrode through the electrolyte; the opposite occurs during discharging.
In other words, sodium-ion batteries use sodium ion transfer (rather than lithium ion) to store and release electrical energy.
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 requirements are not critical.
Compared to lithium-ion batteries, sodium-ion batteries have the following advantages:
(1) Sodium salt raw materials are abundant and inexpensive. Compared with ternary cathode materials for lithium-ion batteries, the raw material cost of using iron-manganese-nickel-based cathode materials is reduced by half.
(2) Due to the properties of sodium salts, it is permissible to use low-concentration electrolytes (for the same concentration of electrolyte, sodium salt conductivity is about 20% higher than that of lithium electrolytes), thus reducing costs;
(3) Sodium ions do not form alloys with aluminum, and aluminum foil can be used as the current collector for the negative electrode, which can further reduce the cost by about 8% and the weight by about 10%;
(4) Sodium-ion batteries have no over-discharge characteristics, allowing them to 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, and are expected 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.
Because sodium ions are relatively larger, they require more energy to move, which was once the biggest headache for new battery technology. However, scientists, like with carbon-core batteries, have used carbon as the driving medium, enabling sodium-ion batteries to achieve up to seven times the energy efficiency of lithium-ion batteries and allowing for more rechargeable cycles. Furthermore, the challenge of sodium ion liquid memory has also been overcome.
However, despite the abundance of nano-ion resources, CATL also stated that its current nano-ion batteries are slightly more expensive than lithium-ion batteries, which are already widely used.
Therefore, reducing the cost of nano-ion batteries will be a challenge that needs to be overcome in the future.
