Exploring sodium ion battery technology-are they better than lithium

Principle of sodium ion battery

Sodium ion battery technology continues to evolve, with batteries operating on a similar working principle to lithium ion batteries, with the cathodes and anodes consisting of two different sodium ion intercalation compounds.

When charging, Na+ is detached from the cathode and embedded in the anode by the electrolyte. At the same time, the compensation charge of the electrons is supplied to the anode through the external circuit to ensure the cathode and anode charge balance.

On the contrary, on discharge, Na+ is de-intercalated from the anode and embedded in the cathode through the electrolyte. You can read how do batteries work for more in-depth understanding.

Materials for sodium ion batteries

Cathode material

At present, the cathode materials selected for sodium ion batteries mainly include: transition metal oxides, Prussian blue/white compounds, and polyanionic compounds.

● The layered oxide material is not only similar to the lithium battery material in structure, but also similar in the production process of sodium ion battery technology.

However, the choice of transition metal elements for the cathode of sodium ion batteries is wider and the price is low.

The price of layered oxides for lithium ion batteries is relatively high. The layered oxide cathode material has high energy density, high voltage platform, good rate performance and excellent comprehensive performance.

At the same time, its synthesis process is simple, and there are many transition metal elements to choose from. Therefore, it is the main choice of sodium ion battery technology route for enterprises.

●  The Prussian blue compound is a typical cubic crystal structure. It allows free insertion and deinsertion of sodium ions, and has excellent theoretical rate performance and cycle performance. Meanwhile, that energy density is high and the cost is relatively low.

The defects of Prussian Blue technology path are also obvious.

First of all, even with the assistance of sodium ion battery technology, it will still participate in various side reactions, seriously affecting the battery capacity and cycle performance of the battery;

Secondly, Prussian blue compound has poor thermal stability. It reacts with water to produce toxic HCN, posing safety concerns and environmental handling challenges.

● Polyanionic compounds have a firm and open three-dimensional network structure, high thermal stability and electrochemical stability.

So the cycle performance is better than that of layered oxides and Prussian blue, but the material cost is relatively high, the energy density is low, and the rate performance is poor.

Anode material

The atomic radius of sodium ion is more than 35% larger than that of lithium ion. The graphite cathode of lithium ion battery cannot meet the requirements of sodium ion battery cathode.

Therefore, the anode materials of sodium ion batteries are mainly selected for hard carbon and soft carbon.

● Soft carbon has a low cost, but low sodium storage because of its graphitized-like structure. Although the capacity can be increased by the pore making process, it will increase the cost in the practical application of sodium ion battery technology.

The merits of soft carbon lie in the strong conductivity and high cycling performance.

● Hard carbon materials store sodium in a variety of locations and forms, and sodium ion battery technology enables anodes to better achieve fast charging. This not only solves the safety problem of overdischarge, but also opens up the breadth of sodium battery applications, with a theoretical capacity of 350-400 mAh/g.

Also hard carbon has many problems: such as low first coulombic efficiency, short cycle life and structural consistency.

Electrolyte

The electrolyte system of sodium ion battery is the same as that of lithium ion batteries, including solutes, solvents, and additives.
Sodium ion battery solute is to replace lithium salt with sodium salt;

Many additives of lithium battery are not necessarily suitable for sodium battery. Many enterprises still use ester solvents now, and the proportion of solvents used for different material systems is different;

At the additive level, sodium ions have higher molar conductivity and low electrolyte concentration. The proportion and requirements for additives are lower than those of lithium batteries, reducing part of the material cost.

Separator

The direct use of lithium battery separator technology in sodium ion battery technology will cause poor liquid retention ability and affect the cycle performance of the battery;

Sodium dendrites are easy to produce on the surface of the anode, resulting in a short circuit and affecting the safety performance. So the requirements for the porosity of sodium and lithium battery separators will be different.

In lithium ion batteries, the cathodecurrent collector is aluminum foil, and the anode is copper foil. This avoids alloying of aluminum and lithium under low potential conditions. In sodium ion batteries, sodium does not alloy with aluminum. Therefore, aluminum foil can be used for cathode and anode current collectors, which can reduce costs.

Sodium ion battery vs lithium ion battery-pros and cons

Compared with lithium batteries, the advantages of sodium batteries are:

1. Abundant resources and low cost:

Compared with the scarcity of lithium ions, sodium ions are more abundant in energy storage in the elements of the earth’s crust, so the cost is low.

As of November 2022 data, the price of sodium carbonate is about 1/200 of the price of lithium carbonate. And aluminum foil is used for both the cathodes and anodes of sodium batteries to further reduce costs;

2.Wide temperature range:

Good capacity retention in the temperature rate range of -40 °C ~ 80 ° C;

3.Fast charging and good rate:

The same concentration of sodium-ion battery electrolyte has higher ionic conductivity than lithium-ion battery electrolyte in sodium-ion battery technology applications. And the sodium ions have lower solvation energy in polar solvents. It has higher conductivity;

4.Safety:

Sodium batteries can be stored and transported under zero voltage, no transportation safety risks, less self-heating heat in short circuit, no hidden dangers such as fire/explosion;

5.Production:

It has a similar working principle and material composition of sodium ion battery technology as lithium-ion batteries, and production experience and equipment can be partially compatible.

Compared with lithium batteries, the disadvantages of sodium batteries are:

1.Sodium ion battery technology is difficult to put into practical use.

The mass of sodium ions is heavier than lithium ions, and the electronegativity is not as good as lithium, so the energy density is not as good as lithium.

In addition, the voltage of sodium ion batteries is lower than that of lithium ion batteries, so sodium ion batteries have a lower specific capacity and low energy density.

2.Sodium ions are larger in volume and have poor cycling performance.

The radiu of that sodium ion is larger than that of the lithium ion, so that the sodium ion is relatively stable in a rigid structure and is difficult to reversibly deintercalate.

Even if intercalation can occur, it is easy to cause irreversible phase changes in the structure of the electrode material, thereby reducing the cycling performance of the battery.

Current situation of sodium ion battery industry

The terminal application of sodium battery has broad prospects, and the market and capital are hot.

However, the current sodium ion battery technology is not advanced. The actual production cost does not have advantages, and large-scale commercial use is still obstructive and long.

The main route of the sodium ion battery technology industry is relatively clear.

Main development direction of cathode materials

Electrode material is the key to improve its energy density, voltage and cycle performance.

Layered oxide is the main direction of the existing cathode materials for sodium ion batteries.

At present, layered oxide is the cathode material with the fastest development progress, and it is expected to be the first to achieve mass production by relying on sodium ion battery technology.

The research and development of layered oxides mainly needs to overcome key scientific problems such as complex structural evolution, irreversible phase transformation, poor transport kinetics, and poor air stability.

Mainstream materials of anode materials

Amorphous carbon materials are preferred among carbon-based materials.

At present, carbon-based materials that can be used as battery anode materials mainly include graphite carbon materials and amorphous carbon (hard carbon and soft carbon) materials.

Graphite materials commonly used in the anode of lithium ion batteries cannot form stable compounds with sodium ions due to thermodynamic reasons. Therefore, sodium ion batteries are difficult to use graphite as the anode material.

Amorphous carbon materials with large layer spacing have high sodium storage capacity and excellent cycle stability. Hard carbon materials are preferred among amorphous carbon materials. The hard carbon material has the advantages of high sodium storage specific capacity, low sodium storage voltage, good cycle performance and the like.

And it also has the advantages of rich carbon source, low cost, no toxicity, environmental protection and the like. This is friendly to the development of sodium ion battery technology.

Hard carbon also has some disadvantages when used as an anode material. Such as low electrode potential and poor cycle stability, which poses obstacles to the industrial application of hard carbon-based anode materials.

The electrolyte field

The electrolyte of sodium ion batteries is similar to that of lithium ion batteries, and some of the production equipment and technologies of existing lithium ion batteries can be used.

In the realization of sodium ion battery technology, compared with the traditional sodium salts NaPF6 and NaClO4, sodium salts containing fluorosulfonyl groups (NaTFSI, NaFTFSI, NaFSI, etc.) have high thermal stability and non-toxic characteristics.

However, due to their anion corrosive effect on aluminum foil current collector, they are rarely used as a separate sodium salt in sodium-ion battery technology.

Application scenarios and cost analysis

Low-speed electric bicycle

On the electric bicycle, 0.6 kilowatt-hour products, equipped with 32 soft package sodium ion batteries, the system efficiency can achieve 98%. The core is cost.

48V12AH lead-acid two-wheeler battery pack, consumer purchase price is 680RMB. Assuming a 5-year life cycle, the battery pack is replaced once in the middle, the replacement price is 180RMB, and the final recycling price is 200RMB.
The total cost of consumers = 680 + 480 – 200 = 960 RMB.

Assuming that the dealer’s gross profit is 20%, recycling gross profit of 40%, the dealer can earn = 2 * 680 * 0.2 + 2 * 200 * 0.4 = 272 + 160 = 432 RMB. The manufacturer’s tax price = 680 * 0.8 = 544 RMB. Converted into kWh tax-inclusive delivery price = 900 RMB.

After switching to sodium ion batteries, one-time consumption is not allowed to replace them, because sodium ion batteries have no recycling value. To guarantee the dealer’s profits unchanged, the sodium battery equivalent ex-factory price = 900 – 160/0.6 = 630 RMB/degree.

After deducting 15% of the comprehensive tax burden, it is equal to 535 RMB/kWh, including pack cost. According to the battery and pack cost 7:3, battery price = 535 * 0.7 = 374 RMB/degree. Assuming 15% of the gross profit, the battery cost price = 318 RMB/degree.

After preliminary calculation, the cost price of sodium ion battery cells reached 318 RMB/kWh (0.32 RMB/wh), equivalent to that of lead acid. The net profit margin of the enterprise is about 3% (refer to the lithium battery industry).

In China, the cost of electric bicycles is about 40 million vehicles/year, 1 kilowatt hour/car, so 40 Gwh batteries a year. According to the penetration rate of 30% of sodium electricity in 2025, corresponding to 12 Gwh, the total net profit = 12 * 3.74 * 0.03 = RMB 134 million.

Low-speed passenge car scenario

With Hongguang mini EV 13 kilowatt hour version as reference, it provides 96 v driving voltage, limit power 10 kw, Max power 20 kw.

LFP about 32 string 2 and a total of 64 batteries. Haina 32138 cylindrical sodium ion battery requires 32 strings of 36 and a total of 1152. Penghui 41030 cylindrical requires 32 strings of 24 and a total of 768. Polyfluoro 61030 cylindrical sodium ion battery requires 576.

The discharge efficiency of LFP battery reaches 99%. The larger the sodium ion battery, the lower the efficiency. And the discharge efficiency can only be 89% after the large cylindrical pack with more fluorine.
Energy storage scenario

The problems encountered by sodium batteries in energy storage are that: the system integration density and the energy conversion efficiency are too low.

Sodium battery power stations are spent heavily on components such as chassis, cabinets and cables.

The true cost of sodium ion battery technology is simply impossible to estimate.

Summary:
1. Sodium ion battery does not see obvious bottleneck on low-speed electric bicycle, depending on cost competitiveness.

2. sodium ion batteries can be used in low-speed electric vehicles, but the group efficiency is low. The lower the charge, the more feasible.

3. In the energy storage scenario (large storage and small storage), the group efficiency of sodium ion battery is too low to be applicable.

Cost analysis

In terms of cost, the cost of sodium ion battery is about 30% lower than that of lithium ion battery from anode to cathode, but the cost of separator will increase by about 40%.

Battery industry experts said that if sodium batteries achieve large-scale production in the future. Then using sodium ion battery technology, the material cost can be as low as 0.25RMB/watt-hour, and the manufacturing cost is 0.1RMB/watt-hour, which is significantly lower than the current power battery.

Future development of sodium ion batteries

Material system innovation

Find cathode and anode materials for sodium ion batteries with higher specific capacity and voltage;

Relying on sodium ion battery technology, we develop anode materials with long cycle life, low cost and high sodium storage capacity; Sodium-ion battery technology is supported.

The electrolyte formula is optimized to make sodium ion batteries have high charge and discharge rates in a wide temperature range and have long cycle life required for large-scale energy storage applications.

Industrial chain construction

The commercialization of sodium ion batteries is currently in its infancy, and a complete and mature industrial chain has not yet formed.

In August 2022, the Chinese government issued relevant documents to develop new batteries such as sodium ion batteries.

Because of this, many related companies have laid out the research and development and production of sodium-ion battery materials, upgraded sodium ion battery technology and invested more.

It is expected that in the next 2-3 years, the sodium ion industry chain will be significantly reduced with the continuous improvement of sodium power planning.

Scenario expectations

Due to the limitation of energy density, sodium batteries cannot be applied to consumer batteries and new energy vehicles with high energy density requirements.

With the continuous advancement of technology, the cost of sodium electricity continues to decrease.

The industrial chain continues to improve, it is expected that around 2025, sodium ion battery technology will carry out large-scale demonstration applications in the field of power energy storage.

Through demonstration verification, sodium ion batteries have the conditions for application in the field of power energy storage.

Standard development

The Chinese government issued relevant documents in resent years.

The standard specifies the corresponding requirements and test methods, which can provide a test reference for manufacturers, owners and investors to understand product performance. The standard is prepared by many companies in the lithium battery industry.