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Sodium-ion batteries, a minority, not the mainstream

Nov 16,2021 | Hui Zeng

On July 29, 2021, CATL officially released the first-generation sodium-ion battery(SIB). SIBs are not the latest scientific and technological ideas. In fact, as early as 2010, the development of SIBs has already begun. Compared with lithium-ion batteries(LIBs), SIBs have the advantages of abundant reserves, low cost, low price, and high safety. But there are also disadvantages of low energy density and short cycle life. For now, SIBs can be used in low-end energy storage, electric bicycles, electric scooters, and other niche fields at most. It is difficult to use in high-end electric vehicles, home energy storage, and large and medium-sized energy storage. If SIBs are truly commercialized, they will bring all-around benefits from cost to safety. But for now, how far is SIB from commercialization? Can it replace the current mainstream LIBs?

 

First of all, let us understand what is a SIB?

 

I.  What is a SIB?

SIB is a kind of secondary battery, also called the rechargeable battery. The charging principle is to realize charging and discharging by using the intercalation and deintercalation process of sodium ions between the positive and negative electrodes. The intercalation process here means that sodium ions leave the positive electrode during charging, and then enter the negative electrode through the electrolyte. At the same time, the compensation charge of the electrons also comes to the negative electrode through the external circuit, thus ensuring the charge balance of the positive electrode. The process during discharge is reversed. Simply put, SIBs mainly rely on the movement of sodium ions between the positive and negative electrodes to work. Actually, sodium and lithium belong to the same main group in the periodic table of elements and have similar physical and chemical properties. Therefore, the working principle of SIBs is similar to that of LIBs.

 

Na-ion Battery (Image: Materials Views China)

 

II. Compared with LIBs, what are the advantages of SIBs?

  1. Abundant reserves.As the sixth richest element in the earth's crust, sodium is inexpensive and has potential cost advantages on the raw material side compared with lithium. LIBs are currently the most widely used battery type, and their demand is also growing rapidly with the expansion and change of downstream demand, resulting in an increasingly tight supply of lithium resources. At present, the world has identified about 62 million tons of lithium resources, and the reserves are relatively small (reserves 0.002%). The abundance of sodium ions in the crust is about 2.36%, which is much higher than 0.002% of lithium ions. In addition, the distribution of global lithium reserves is mainly concentrated in Chile, Australia, and Argentina, and the distribution is extremely uneven. In contrast, all countries can use seawater to prepare sodium salt, and sodium resources are evenly distributed;

 

Parameters

Na

Li

Abundance in Crust (mg kg-1)

23.6*103

20

Source: CNKI, HUAAN Securities Research Institute

 

  1. The raw material cost of SIBsis lower. Since lithium and aluminum easily react to form lithium aluminum alloy, relatively low-priced aluminum foil can be used as anode material for lithium batteries, but copper foil can only be used as anode material. However, sodium ions do not form an alloy with aluminum, so the aluminum foil can be used as the current collector for both the positive and negative electrodes, thereby further reducing the cost by about 8% and the weight by about 10%. The price of sodium ion compounds is stable and low, about $39 per ton, which is about 1/50 of the price of battery-grade lithium carbonate. According to data from Hina BATTERY(A company that develops and produces SIBs), the BOM(Bill of Material) cost of SIBs is about 30% lower than that of LIBs;

 

 

Sodium-ion Battery

Lithium Iron Phosphate Battery

Raw Material Costs ($/Wh)

0.03-0.05

0.05-0.06

Source: HUAAN Securities Research Institute

 

  1. The electrochemical performance of SIBis relatively stable and safer. Conventional LIBs operate at temperatures between -20 and 60 degrees Celsius. SIBs can adapt to high and low temperatures between -30 and 80 degrees Celsius without much energy attenuation. Moreover, through a variety of impact and pressure tests such as acupuncture, the SIB also shows good stability. So in terms of safety, SIBs are better than LIBs.

 

Sodium-ion Battery System (Image: OF week)

 

Why can't SIBs with low cost, good safety, and stable performance at extreme temperatures replace LIBs? Although CATL released the first generation of SIBs and plans to mass-produce SIBs in 2023. However, it is not the beginning of replacing LIBs. At this stage, the development of SIB technology is more of a supplement to LIBs rather than a replacement. The fundamental reason is that SIBs also have very significant disadvantages.

 

III.  Disadvantages of SIBs

  1. Low energy density. Sodium and lithium are in the same main group of the periodic table and have similar properties. Compared with lithium, sodium has a larger atomic mass and a high standard electrode potential, so the energy density of sodium ions is lower than that of lithium-ion. In addition, the ionic radius of sodium ions is larger than that of lithium ions, so the volumetric energy density is also lower than that of lithium ion. To describe it simply: Assuming that lithium-ion is the size of a ping-pong ball, and sodium ion is much larger than lithium ion, so it can be assumed to be a football. Therefore, the speed of sodium ions is slower when they are wandering, and it is not easy to penetrate the battery separator. At the same time, the amount of electrons carried by this "plus-size man" is lower than that of lithium ions, which leads to a very specific shortcoming, that is, lower energy density. The energy density of the first-generation SIB released by the CATL is 160Wh/kg, while the energy density of the LIB has easily exceeded 200Wh/kg. And the battery's energy density is as important to an electric vehicle as the heart is to the human body. The performance, range, and reliability of an electric vehicle depend on the number of batteries in its battery pack and the energy density within a single battery. Here's a formula to help you understand: Total power = number of batteries * energy density per battery;

 

Parameters

Na

Li

Atomic Mass (g mol-1)

22.99

6.94

Ionic Radius (angstrom)

1.02

0.76

Standard Potential (V vs SHE)

-2.71

-3.04

Source: CNKI, HUAAN Securities Research Institute

 

Chemical Properties

Lead-acid Battery

Sodium-ion Battery

Lithium-ion Battery

Energy Density (Wh/kg)

40-50

90-160

160-300

Source: HUAAN Securities Research Institute

 

  1. Short battery cycle.The battery cycle of SIBsis between that of lead-acid batteries and LIBs. At present, the cycles of lithium iron phosphate batteries(LFP) can reach 6000 times or even higher, while SIBs can only reach 2000 times. What is the battery life cycle? Taking LFP as the standard, under normal circumstances, the life cycle of 2000 times can be used for 7 to 8 years. Therefore, according to the current energy storage requirements for more than 10 years, or even 20 years on the new energy side, the battery cycle of SIBs is still not enough;

 

Chemical Properties

Lead-acid Battery

Sodium-ion Battery

Lithium-ion Battery

Voltage (V)

~2

2.8-3.5

3.0-4.5

Life Cycle (times)

~300

1000-4000

2000-15000

Source: HUAAN Securities Research Institute

 

  1.  Low cost performance.Although the raw material cost of SIBsis lower than that of LIBs, due to low energy density and short life cycle, SIBs need to consume more auxiliary materials and higher costs per kilowatt-hour. On the whole, the price performance of SIBs is not high. According to a report by the Huaan Securities Research Institute, ignoring the price difference of other auxiliary materials, the total raw material cost of SIBs can theoretically be saved by about 25.3%. Despite the theoretical raw material cost of SIBs being 25.5% lower than that of LFP, considering the cycle performance of LFP, the cost performance of SIBs is much lower than that of LFP. In other words, the life cycle of SIBs must reach 7500-11000 times or even higher to be comparable to LFP.

 

 

Sodium-ion Battery

Lithium Iron Phosphate Battery

Raw Material Cost ($/Wh)

0.03-0.05

0.05-0.06

Life Cycle (times)

1000-4000

6000-15000

Life Cycle Cost ($/kWh)

0.008-0.05

0.003-0.006

Source: HUAAN Securities Research Institute

 

  1. The industry chain is still incomplete.The product performance, cost control, and application of SIBs need to be further tested.

 

Volumetric Energy Density of Different Batteries (Image: Science Direct)

 

IV.Application

In terms of application, SIBs are difficult to apply to the mainstream applications, such as mid-to-high-end automobiles, home energy storage, and large and medium-sized energy storage. However, around the advantages of SIBs, it is not difficult to find that it has certain advantages in specific scenarios. In fields where energy density or battery cycle are not high, the cost-effective advantages of SIBs are indeed prominent, such as small power batteries (electric bicycles, etc.) or low-end energy storage (low battery cycle). 1) In the field of energy storage, due to the large scale of investment and the use of SIBs to reduce the initial capital investment, from the perspective of capital costs, SIBs may have more advantages. 2) In the extreme temperature scenarios, SIBs can take advantage of their good performance at low temperatures. Compared with lithium-titanate batteries(LTO) with the same performance and faster charging, the cost of SIBs is lower, but the number of cycles is less than that of LTO. 3) As for the high-power field, SIBs can be used in conjunction with LIBs in the power battery. In point of fact, LTO has already played this role. 4) On the contrary, in the fields of new energy vehicles, energy storage, 5G base stations, two-wheeled vehicles, heavy trucks, electric ships, etc., there are more applications of LFP. Among them, the application of new energy vehicles accounts for the largest proportion, including new energy passenger vehicles, new energy buses, and new energy special vehicles. The energy storage field currently uses more than 94% of LFP. Meanwhile, according to an article in the Journal of Cleaner Production, the water footprint of SIBs is far large compared with Li-S batteries.

 

Application of Lithium-ion Batteries (Image: Springer Link)

 

V. Conclusion

Regarding the development background of SIBs, CATL mentioned at the press conference that the new energy industry has entered a multi-level, multi-type, and diversified development stage and increasingly segmented markets have put forward differentiated needs for batteries.

 

The implication is that the SIB is a supplement, not a substitute.

 

For this reason, CATL also particularly emphasizes the compatibility and complementarity of SIBs and LIBs. CATL has developed the AB battery system solution, that is, the SIBs and the LIBs are mixed and matched in a certain ratio, integrated into the same battery system, and the balance control of different battery systems is performed through the BMS precise algorithm. The AB battery system solution not only makes up for the energy density shortcomings of SIBs at this stage, but also exerts its advantages of high power and good low-temperature performance.

 

Obviously, CATL also hopes to expand the scope of application of SIBs through a "mix and match" approach. Of course, there may be more innovative applications in the future. But in general, SIBs are more like snacks than staples. SIBs are less likely to replace LIBs. The two are more complementary, each meeting the application needs of different market segments, but SIBs are expected to replace lead-acid batteries in the future.

 

With the diversification of applications, battery types will gradually be enriched. On the basis of LIBs, there are not only SIBs, but also vanadium matte batteries, zinc-ion batteries, and other batteries. Under the background of the continuous expansion of the market and the continuous refinement of application, it is no longer possible to get everything done with one trick. SIBs are just the beginning.

 

Electrochemical Energy Storage and Conversion (Image: Science Direct)

 

Reference

[1] Lei Wang, JianxingHu, YajuanYu, KaiHuang and YuchenHua, Lithium-air, lithium-sulfur, and sodium-ion, which secondary battery category is more environmentally friendly and promising based on footprint family indicators? Journal of Cleaner Production, 2020, 276.

[2] Xiao Chen, Yitian Bie, Fei Teng, Sodium battery positioning energy storage and lead-acid replacement, lithium battery is still the mainstreamNew Energy Lithium Battery Series Report No. 5, Huaan Securities, 2021.

 

By Hui Zeng

November 16, 2021

Reprinting is prohibited without the author's authorization.

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