Sodium-ion batteries have a cost advantage over lithium-ion batteries

Why sodium batteries?

This is not the first time in the history of sodium-ion and lithium-ion batteries that sodium batteries have been used as battery materials. Since Na and Li belong to the same group of alkali metals, the research on sodium-ion batteries started at the same time as that on Li-ion batteries.
Both sodium-ion and lithium-ion batteries were first studied in the late 1970s, but the performance of lithium-ion batteries led scientists to abandon sodium-ion batteries, and lithium-ion batteries have made huge strides in the past 50 years. In particular, SONY commercialized the lithium-ion battery technology in 1990, which made the lithium-ion battery technology develop rapidly, but the research on the sodium-ion battery was relatively stagnant in the same period. It was not until 2010 that the research of sodium-ion batteries reached a turning point. Subsequently, sodium-ion batteries made continuous breakthroughs in electrode materials, electrolyte materials, characterization analysis, exploration of sodium-storage mechanism, and cell technology.

In fact, as a branch of the diversified development of power batteries, the theoretical basis and battery structure of sodium-ion batteries and lithium-ion batteries are very close. The structure of a liquid sodium ion battery also includes a positive electrode, a negative electrode, a collector, an electrolyte, and a diaphragm.

Due to the difference between the characteristics of sodium ion and lithium-ion, the positive and negative materials of sodium ion need to choose materials suitable for sodium ion migration, which is also the core of sodium-ion battery technology. According to Guotai Junan’s research report, elements such as copper and iron, which can not be used as cathode materials in lithium-ion batteries, have a good performance in sodium-ion batteries.

At present, the cathode materials of sodium-ion batteries are mainly divided into five types: oxide, polyanion, Prussian blue, fluoride and organic compounds. Among them, the first three types have the highest maturity and have entered the early stage of industrialization.

In the selection of anode materials for sodium-ion batteries, because the radius of sodium ions is much larger than that of lithium ions, it also makes the graphite materials widely used in lithium batteries have poor sodium storage performance. However, some amorphous carbon anode has relatively low sodium storage potential. It has the advantages of high sodium storage capacity and good cycling stability, which makes it the most promising anode material for sodium-ion batteries. At present, the anode materials for sodium-ion batteries are mainly divided into four categories: carbon anode materials, conversion anode materials, titanate anode materials, and alloy anode materials. Among them, carbon-based materials have the highest technical maturity and rich resources and are expected to take the lead in realizing industrialization.

In terms of battery production, similar to lithium-ion batteries, the production of sodium ion batteries also needs to go through the pulp, coating, assembly, liquid injection, formation, and other processes. Among them, the assembly link is mainly to assemble the finished positive and negative electrode sheets through the diaphragm sandwich, establish the sodium ion pathway inside the battery, and isolate the positive and negative electrodes to prevent internal short circuits. The assembly process follows the lithium-ion battery technology, which is divided into winding and laminating processes, and the former is further divided into cylindrical winding and square winding. In addition, the structure design and packaging process of sodium ion battery products are basically similar to that of the lithium-ion batteries, and the appearance is roughly divided into three categories: cylinder, soft package, and square hard shell. In addition, the sodium battery electrolyte and diaphragm also basically follow the lithium-ion battery system.

In other words, the production of sodium-ion batteries can be made directly using the existing lithium-ion battery production line, without the need to rebuild a new production line. In some ways, the sodium-ion battery is the closest battery route to mass at this stage.

In addition, from the perspective of cost, theoretically, sodium-ion batteries have a significant cost advantage in terms of materials. For example, the cathode material with the largest cost ratio is lower than that of lithium carbonate because the price of sodium carbonate is much lower than that of lithium carbonate, and the cathode material of sodium ion battery usually uses bulk metal materials such as copper and iron, so the cathode material cost is lower than that of lithium battery. According to Ping An Securities, the cathode material cost of sodium batteries using NaCuFeMnO/ soft carbon system is only 40% of that of lithium iron phosphate/graphite system, and the total material cost of batteries is 30% to 40% lower than that of the latter.

At the same time, the sodium ion battery collector (the fluid collector is a base component attached to active materials of positive and negative electrodes, accounting for about 10-13% of the battery weight, which is used to collect the current generated by electrode materials and release and conduct) can use aluminum foil for both positive and negative electrodes, while the copper foil is needed for the negative electrode of lithium-ion batteries (because sodium ions will not react with aluminum ions in the negative electrode). This also reduces the cost of the sodium-ion battery collector.

Each indicator has its own advantages and is complementary rather than a substitute

Back to the battery itself, battery safety and energy density have always been the core indicators reflecting the overall performance of the battery, and also the competitiveness of each battery manufacturer. Sodium-ion batteries are no exception. In comparison, in terms of energy density, the cell energy density of sodium-ion batteries is 100-160Wh/kg. Compared with lithium-ion batteries, there is still a big gap in the energy density of sodium-ion batteries. At present, the energy density of lithium iron phosphate batteries is 120-200Wh/kg, and the energy density of ternary lithium battery cells can reach 200-350Wh/kg. Moreover, in terms of cycle life, the sodium battery can reach about 1000-3000 cycles, and the lithium-ion battery cycle life is more than 3000 cycles.

In terms of battery safety, because the internal resistance of a sodium ion battery is higher than that of a lithium battery, it has less instantaneous heat in the case of a short circuit, lower temperature rise, and higher thermal runaway temperature than a lithium battery, so it has higher safety. On the other hand, lithium-ion batteries will discrete lithium when charged at low temperatures, while sodium batteries will not discrete, so sodium-ion batteries have a wider operating temperature range. The sodium-ion battery can work normally in the temperature range of -40℃ to 80℃, and the capacity retention rate is close to 90% at -20℃. The high and low-temperature performance of the sodium-ion battery is better than that of lithium-ion batteries.

In addition, in terms of the fast charging capacity, the charging time of 80% of the sodium ion battery is about 15 minutes. In the mainstream battery of the current mass production, the terpolymer lithium battery under the DC fast charging, the charge from 20% to 80% usually takes 30 minutes, and the lithium iron phosphate takes about 45 minutes.

Obviously, for new energy vehicles and other fields with high requirements for energy density and driving range, the defect of low energy density is the main weakness of sodium-ion batteries. Energy density constraints also make it difficult to form a serious disruptive alternative between sodium-ion batteries and lithium-ion batteries. However, sodium-ion battery technology in communication base stations, low-speed electric vehicles, electric bicycles, electric energy storage, solar street lighting and other fields with relatively low demand for energy density, or will be a good complement to the lithium battery technology route.

Especially in the field of energy storage, the performance of sodium-ion batteries is more suitable to the requirements of energy storage system standards.

Generally, large energy storage systems have low requirements on the energy density of batteries used for energy storage, and higher requirements on safety and economy. Therefore, energy storage systems may become an important scene for the landing application of sodium batteries. Moreover, the cost advantage of sodium ion battery makes it more economical in energy storage application scenarios. In addition, due to the wide temperature zone characteristic of the sodium-ion battery itself, the energy storage system built on the basis of the sodium-ion battery can adapt to the climatic conditions in different latitudes, effectively improve the permeability of distributed power supply, and improve the stability and economy of the operation of the distribution network.

In the energy storage market, the burst of demand for policy support is rapidly driving downstream demand for energy storage batteries. According to GGII data, the newly installed capacity of new energy storage in the first half of 2022 was 12.7GW, 3.7 times that of the whole year of 2021 (3.4GW). The shipment volume of lithium energy storage battery is 44.5GWh, which has exceeded the annual level in 2021, and lithium-ion battery has taken up more than 90% of the market share of new energy storage.

But it’s important to note that the market’s expectations for sodium-ion batteries depend largely on their theoretical cost advantage. However, on the whole, the actual production cost of sodium-ion batteries is above 1 yuan /wh, much higher than that of lithium-ion batteries, due to the lack of supporting facilities and scale effect in the current industrial chain. In addition, the performance, cost control, and adaptation of sodium-ion batteries need to be further tested, and there is still a certain distance between real industrial application and popularization. Moreover, the high price of lithium carbonate has magnified the market’s recognition of the advantages of sodium-ion batteries. If the price of lithium falls in the future, the promotion of sodium batteries may still need to draw a question mark.