Sodium-ion Battery Industry Research

Na Ion Battery Future Is Promising

The working principles of sodium-ion batteries and lithium-ion batteries are very similar, but there are certain differences in battery materials. Sodium-ion batteries use sodium ions to repeatedly embed and detach in the positive and negative electrode materials during charging and discharging, resulting in a reversible oxidation-reduction reaction. Therefore, its working principle is similar to that of lithium-ion batteries. The differences in battery materials are mainly reflected in the positive electrode, negative electrode and current collector. There are three main routes for positive electrodes, and layered oxide is expected to be the first to be produced on a large scale. Layered oxides have high specific capacity and high compacted density, but their air stability is average. Sodium layered oxide is compatible with the production equipment of lithium battery ternary cathodes and is expected to be the first to be mass-produced. Prussian blue/white compounds have high specific capacity and low price, but the presence of crystal water will affect the electrochemical performance. Polyanionic compounds have good stability, good cycle performance, and high operating voltage, but have low specific capacity and poor conductivity.

The negative electrode is mainly made of hard carbon and supplemented by soft carbon. As a sodium electronegative electrode, hard carbon has a high specific capacity, but because most of its raw materials are biomass, the yield is low and the cost is high. There are various hard carbon raw materials, among which the preparation of hard carbon from biomass raw materials is the mainstream choice. Soft carbon is more structurally ordered than hard carbon, so its specific sodium storage capacity is lower, but its cost is low when using raw materials such as coal and asphalt. The material cost of sodium batteries has dropped significantly compared with lithium batteries. The material cost has been reduced by 30%-40%. The main reasons for the cost reduction are: 1. The metal sodium has high abundance in the earth's crust and its price is much lower than that of lithium. 2. The current collectors are different. The negative electrode current collector of lithium batteries must be copper foil, while the positive and negative electrode current collectors of sodium batteries can both be cheaper aluminum foil.

Sodium-ion battery demand is expected to grow rapidly. Sodium-ion batteries are superior to lithium iron phosphate batteries in terms of raw material cost, capacity retention at low temperatures, and over-discharge resistance, and their performance in all aspects surpasses lead-acid batteries. They are expected to be used in electric two-wheelers (replacing lead-acid batteries), A00 level electric vehicles and energy storage fields (replacing lithium iron phosphate batteries). According to estimates, global demand for sodium-ion batteries is expected to grow from 3.6GWh in 2023 to 65.8GWh in 2025, with huge room for growth.

01. Composition of sodium-ion battery

1.1. Working principle and battery materials of sodium electricity

1.2. Sodium cathode route

There are three routes for the positive electrode of sodium-ion batteries, each with its own advantages and disadvantages in terms of performance. Layered oxides have high specific capacity and high compacted density, but their air stability is average. Prussian blue/white compounds have high specific capacity and low price, but the presence of crystal water will affect the electrochemical performance. Polyanionic compounds have good stability, good cycle performance, and high operating voltage, but have low specific capacity and poor conductivity.

The preparation methods of sodium layered oxide cathode and lithium battery ternary cathode are similar. The preparation methods mainly include solid phase method and liquid phase method. Among them, the solid phase method uses ball milling of metal oxides and sodium sources to mix them evenly, and then calcines them at high temperature. This method has a simple process, but requires higher temperatures and has poor product uniformity. The liquid phase method first performs a co-precipitation reaction between metal salts and alkali solutions to generate precursors, and then mixes sodium sources and calcinations to obtain layered oxides. Although this method has more processes than the solid-phase method, it can prepare products with better uniformity and higher tap density by controlling the reaction conditions. The sodium layered oxide cathode is compatible with the production equipment of lithium battery ternary cathodes and is suitable for mass production.

Prussian blue cathodes are usually prepared by co-precipitation method. Prussian blue cathodes can be synthesized by thermal decomposition, hydrothermal, and co-precipitation methods. Among them, thermal decomposition method and hydrothermal method have low production efficiency and yield, and the synthesis process can easily cause ferrocyanide to decompose and produce poisonous gas. Co-precipitation method can be regarded as a safe and environmentally friendly method that can prepare such materials on a large scale. The process is simple, does not require high-temperature sintering, and is low-cost. It is mainly prepared by co-precipitation reaction of sodium ferrocyanide, transition metal salts, complexing agents, etc. The addition of complexing agent can reduce the reaction speed of transition metal salt and sodium ferrocyanide, thereby reducing the formation of vacancies and crystal water. The purpose of adding antioxidants and using an inert protective atmosphere is to keep the transition metal ions in a low valence state, thereby ensuring a higher sodium content in the final product.

Crystallization water and vacancies can be reduced by surface coating, metal element doping, and improved processes. Xingkong Nadian has disclosed a method of using calcium oxide to reduce the crystal water content of Prussian blue (Patent Publication No. CN115180634A). After grinding and mixing calcium oxide and Prussian blue, they heat it in an inert atmosphere without destroying the crystal structure of Prussian blue. At the same time, water is effectively removed.

The mainstream polyanion cathodes are phosphate polyanions and sulfate polyanions, such as sodium vanadium phosphate and sodium iron sulfate. The price of vanadium is high and fluctuates violently with the price. The cost of vanadium sources is as high as 96% of the cost of sodium cathode raw materials. "Vanadium reduction" from sodium vanadium phosphate to manganese phosphate/sodium iron vanadium system is expected to reduce costs. ZhongNa Energy mainly promotes the sodium ferric sulfate system, which can be prepared by using simple industrial-grade raw materials of ferrous sulfate and sodium sulfate, paired with carbon nanotubes, mixed and then calcined. Its advantages are: 1) The material is very pure and 100% of the raw materials are utilized. 2) Energy consumption is very low. 3) Environmentally friendly, simple process, no pollution or by-products. 4) The sintering temperature of the material is relatively low, compared to the temperature of lithium batteries and layered oxides which are above seven or eight hundred degrees. In addition, the existing lithium iron phosphate production equipment can be directly used.

1.3. Sodium cathode route

Sodium electrodes mainly use hard carbon and soft carbon. Graphite is a commercial anode material for lithium-ion batteries. However, because the radius of sodium ions is larger than that of lithium ions, the interlayer spacing of graphite is too small for sodium electricity, and it is difficult for sodium ions to embed and detach between graphite layers. Therefore, it is a negative electrode material for sodium-ion batteries. Using amorphous carbon (including hard carbon and soft carbon) whose structure contains a large number of defects, its sodium storage capacity is greater than that of graphite. Soft carbon refers to carbon materials that can be graphitized at temperatures above 2500°C, otherwise it is hard carbon. As a sodium electronegative electrode, hard carbon has a high specific capacity, but because most of its raw materials are biomass, the yield is low and the cost is high. Soft carbon is more structurally ordered than hard carbon, so it has a lower specific sodium storage capacity. However, it uses raw materials such as coal and asphalt, and its cost is low.

At present, the layout of mainstream manufacturers on sodium electrolyte anodes is mainly hard carbon and supplemented by soft carbon. There are various hard carbon raw materials, among which the preparation of hard carbon from biomass raw materials is the mainstream choice. Biomass raw materials can be selected from a variety of sources (coconut shells, straw, moso bamboo, etc.), and the hard carbon produced has moderate comprehensive properties, but problems such as stable supply of raw materials and product consistency need to be solved; polymer raw materials (phenolic resin, etc.) The prepared hard carbon has high specific capacity, uniform product, and easy control of structure, but the cost is high. Although the cost of raw materials such as asphalt and anthracite is low, the specific capacity of the prepared hard carbon is relatively low.

1.4. Sodium electrolyte

The formula of sodium-ion battery electrolyte is similar to that of lithium-ion battery electrolyte, both consisting of electrolyte, solvent and additives. Carbonate solvents EC and PC have the advantages of wide electrochemical window, large dielectric constant and good chemical stability. They are excellent organic solvents for sodium batteries. Ether solvents, because they have better resistance to oxidation and reduction in sodium battery systems, can generate a thin and stable SEI film and high first Coulomb efficiency on the surface of the negative electrode. They can also be used in sodium batteries, but they are rarely used in lithium batteries. used in batteries. The solute is changed from lithium hexafluorophosphate (LiPF6) in lithium batteries to sodium hexafluorophosphate (NaPF6) in sodium batteries. The synthesis principles and technical routes of the two are similar, and sodium hexafluorophosphate is easy to mass-produce. In terms of additives, there is not much difference between sodium battery and lithium battery systems. They mainly include film-forming additives, flame retardant additives, overcharge protection additives, etc.

1.5. Others

In terms of current collectors, both the positive and negative current collectors of sodium batteries use cheap aluminum foil, but the negative current collectors of lithium batteries must be copper foil. This is because aluminum and sodium do not undergo alloying reactions at low potentials, while aluminum and lithium easily undergo this reaction at low potentials. Therefore, the amount of aluminum foil used in sodium batteries has doubled compared to lithium batteries. In terms of separators, both sodium batteries and lithium batteries can use PP and PE separators.

02. Cost and performance of sodium-ion batteries

2.1. Sodium electricity cost

The material cost of sodium batteries has dropped significantly compared with lithium batteries. The material cost has been reduced by 30%-40%. The main reasons for the cost reduction are: 1. The metal sodium has a high abundance in the earth's crust and its price is much lower than that of lithium. In addition, the cathode of sodium batteries also uses metals such as iron, copper, and manganese that are abundant in resources. Therefore, the price of cathode materials has dropped significantly, and the proportion of cathodes in lithium batteries has dropped from 43% to 26%. 2. The current collectors are different. The negative electrode current collector of lithium batteries must be copper foil, while the positive and negative electrode current collectors of sodium batteries can both be aluminum foil. Aluminum prices are much lower than copper.

2.2. Sodium electrical properties

Sodium-ion batteries have advantages in terms of cost and low-temperature performance. Although there is a gap between sodium-ion batteries and lithium iron phosphate batteries in terms of energy density and cycle life, their raw material costs are about 30% lower than that of lithium iron phosphate batteries, and their capacity retention rate at low temperatures and over-discharge resistance are both excellent. For lithium iron phosphate batteries. Sodium batteries can be discharged to 0V and are more stable than lithium batteries in terms of storage and transportation. Comparing sodium-ion batteries with lead-acid batteries, it can be found that sodium-ion batteries surpass lead-acid batteries in all aspects of performance and are expected to replace lead-acid batteries in mainstream application scenarios.

03. Market space of sodium-ion batteries

Sodium-ion battery demand is expected to grow rapidly. Based on the above performance of sodium-ion batteries, we infer that in the future they will be mainly used in fields that require low energy density but are sensitive to cost, such as electric two-wheeled vehicles (replacing lead-acid batteries), A00-level electric vehicles, and energy storage fields ( Replaces lithium iron phosphate batteries). According to estimates, global demand for sodium-ion batteries is expected to grow from 3.6GWh in 2023 to 65.8GWh in 2025, with huge room for growth.

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