Recently, the domestic power battery leader CATL stated that it is committed to promoting the industrialization of sodium-ion batteries in 2023.
The so-called industrialization of sodium-ion batteries includes not only the mass production of batteries, but also the establishment of upstream industrial chains. Among the sodium-ion batteries that CATL is expected to put into production next year, there are both sodium-ion power batteries for electric vehicles and sodium-ion energy storage batteries for energy storage power stations.
A sodium-ion battery is a secondary battery that relies on the movement of sodium ions between the positive and negative electrodes to complete charge and discharge. Its working principle is similar to that of a lithium-ion battery. During charging, sodium ions are extracted from the positive electrode and inserted into the negative electrode through the electrolyte; the opposite is true when discharging.
Globally, research on sodium-ion battery technology can be traced back to the 1970s, or even slightly earlier than lithium-ion batteries, but in the 1990s, lithium-ion batteries were successfully commercialized due to their superior performance. The development of sodium-ion batteries was once silent. Since 2010, with the shortage of lithium resources and the safety of lithium-ion batteries, sodium-ion batteries have once again appeared on the stage.
On July 29, 2021, CATL released its first-generation sodium-ion battery. According to the company's introduction in the press conference, the energy density of the battery cell reached 160Wh/kg; after 15 minutes of charging at room temperature, the power can reach 80%. In the low temperature environment of -20°C, it also has a discharge retention rate of more than 90%; the system integration efficiency can reach more than 80%. CATL stated that the energy density of the second-generation sodium-ion battery cell will exceed 200Wh/kg.
Compared with lithium-ion batteries, sodium-ion batteries are not very dominant in terms of energy density. At present, the energy density of ternary lithium batteries can reach 200-350 Wh/kg, but the low-temperature performance of sodium-ion batteries, Fast charging and safety are theoretically better.
The outstanding advantages of sodium-ion batteries are more reflected in the cost of raw materials. Sodium ranks sixth in the crustal element content, which is abundant compared to the scarce lithium resources. The average price of domestic lithium carbonate for batteries has risen from about 40,000 yuan/ton in 2020 to about 500,000 yuan/ton at present, while the average price of industrial sodium carbonate is always within 3,000 yuan/ton.
In addition, aluminum foil can be used for the positive and negative current collectors of sodium ion batteries, and since aluminum current collectors are prone to alloy reaction with lithium at low potentials, only more expensive copper foils can be used for the negative electrodes of lithium ion batteries.
In terms of manufacturing process, CATL said that sodium-ion batteries can be compatible with lithium-ion battery production equipment and processes, and production lines can be quickly switched to complete the rapid layout of production capacity. In terms of battery system integration, CATL has developed an AB battery solution, which can realize the integrated hybrid sharing of sodium-ion batteries and lithium-ion batteries.
In the view of industry insiders, sodium-ion batteries have put forward higher requirements for the positive and negative electrode materials and electrolyte materials of the battery, which has also become the reason why their industrialization has not been realized.
On the one hand, compared with lithium ions, the mass and radius of sodium ions are larger, and the ion diffusion rate is lower, which is reflected in the battery performance. At present, layered oxides, polyanionic compounds and Prussian blue compounds are the three main development directions of sodium ion cathode materials.
On the other hand, despite the large internal resistance of sodium-ion batteries, the instantaneous heat release during short circuit is less than that of lithium-ion batteries, and the temperature rise is lower, which has inherent advantages in safety. However, the sodium ion electrolyte is flammable, and the growth of sodium dendrites in the negative electrode can easily lead to short circuit. These safety problems need to be solved by the negative electrode material and the electrolyte material. At present, the anode materials of sodium-ion batteries mainly include amorphous carbon (hard carbon, soft carbon), alloys, transition metal oxides, etc.
In the selection of materials for sodium-ion batteries, the CATL used Prussian white materials with high gram capacity (Prussian white belongs to one of the Prussian blue compounds, which is white due to high sodium content, called Prussian white) as the positive electrode material. , the charge rearrangement of the bulk phase structure of the material solves the problem of rapid capacity decay of Prussian white during cycling. In terms of anode materials, CATL has developed a hard carbon material with a unique pore structure, which has the characteristics of high gram capacity, easy de-intercalation, and excellent cycle.
In terms of electrolyte, CATL said that it has developed a new and unique electrolyte system suitable for cathode and anode materials, which is compatible with the current lithium-ion battery manufacturing process and equipment in terms of manufacturing process.
However, the large-scale preparation of these materials still faces many challenges. Take the Prussian blue material of the positive electrode as an example. At present, the Prussian blue material is usually prepared by the co-precipitation method. Before realizing large-scale preparation, it is necessary to solve the problems of crystal water, structural defects and low production efficiency caused by this preparation method.
The hard carbon material of the negative electrode is more expected to take the lead in achieving industrialization breakthrough. Hard carbon is a carbon that is difficult to graphitize even at high temperatures above 2800 degrees Celsius. However, hard carbon materials also have low first Coulomb efficiency (a performance index to quantify negative electrode materials for lithium batteries, that is, the ratio of discharge capacity to charge capacity in the first charge-discharge cycle of the battery), low long-term cycle stability and low compaction density. question. Low Coulombic efficiency will seriously affect the battery capacity, which needs to be improved by means of structural design, cation doping, surface functionalization, and pre-sodiumization.
Many people in the industry believe that in the field of electric vehicles, from a technical point of view, sodium-ion batteries are supplements to lithium-ion batteries, which cannot completely change the development direction of electric vehicle batteries, but will have a certain impact on the current market pattern. In the field of miniature pure electric vehicles of 30,000-50,000 yuan, sodium-ion batteries will have great market prospects.
Not only that, in the case of the soaring prices of upstream raw materials for lithium-ion batteries represented by lithium carbonate, the CATL promotes the industrialization of sodium-ion batteries, in a sense, it can send a signal to the upstream raw material suppliers of lithium-ion batteries, In the future, the growth of demand for lithium battery raw materials may slow down, thereby stabilizing or even lowering the price of lithium battery raw materials.
In addition, in terms of the comprehensive performance of sodium-ion batteries, compared with electric vehicles, it may be a more suitable scenario for energy storage.
