Sodium ion battery vs Lithium ion battery: Competition or Coexistence?

Sodium ion battery vs Lithium ion battery, Looking at the whole country, the popularity of sodium ion batteries is rising rapidly. As the “king” of lithium batteries, CATL released its first generation of sodium ion batteries, and claimed that the energy density of a single cell can reach 160Wh/kg, and the batteries will be industrialized this year; Recently, Jiangsu Azure Corporation, which is also a leader in lithium batteries industry, also announced that it intends to jointly develop cylindrical sodium ion batteries with Zhongke Haina, and the latter is the first company in China to focus on the development of sodium ion batteries, its valuation has skyrocketed several times in the latest round of financing.

Leading industries in this field have begun to invest capital in the research of sodium ion batteries, making the competition between lithium ion and sodium ion batteries reappear.

Why Lithium?

Why “lithium”? Lithium element is located in the upper left corner and is the first metal element. Lithium itself has a small atomic weight, its activity is high, and the electrode potential is the most ‘negative’, so batteries with higher energy density can be made theoretically.

According to statistics, since 2014, China has been the world’s largest lithium ion battery production and manufacturing country. In 2014, China’s overall lithium ion battery shipments accounted for 42.1% of the world, and this figure reached 59.4% in 2021. Behind this, the energy density of ternary batteries and lithium iron phosphate batteries reached respectively an average of 280Wh/kg and 170Wh/kg, the cycle life of the battery system of key enterprises exceeds 5,000 times, which has obvious advantages.

Nowadays, the lithium ion battery industry is becoming more and more mature, which can be said to be “in the ascendant”, and thanks to the demand of the downstream industries such as new energy vehicles is strong, the production capacity of lithium ion batteries is increasing rapidly, and the technology is also constantly improving. And its mainstream position is difficult to be shaked move.

Why do we need sodium ion batteries?

Lithium ion batteries are in the ascendant, why should we develop sodium ion batteries?

Lithium is an ideal material for batteries, but it is not abundant in the earth’s crust.   The tight supply of lithium resources has caused the price of lithium carbonate to rise steadily in the past two years, from tens of thousands of yuan per ton jumping to hundreds of thousands of yuan per ton, which has driven up the price of the entire industry chain, and has obvious side effects on the healthy development of the industry.

Sodium is one of the most abundant elements on the earth. For example, there is a large amount of sodium salt in seawater. Its mining and preparation process is also simpler, so it can effectively solve the problems of insufficient resources and uneven distribution, and has advantages in terms of cost. There are obvious sodium cost advantages when the price of lithium is getting higher and higher.

In addition, the physical and chemical properties of sodium are similar to lithium, which is also an important reason for attracting researchers. “On the periodic table, sodium, it is a ‘neighborhood’ with lithium and they are both the metal element of group I. ” Gao Jian said that since they are both “rocking chair batteries”, the principle is the same. And the success of lithium ion batteries also provides many mature ideas for the development of sodium ion batteries, such as in the design of the material system, most of today’s sodium ion batteries refer to lithium ion batteries.

How is the sodium ion battery research going?

Although the physical and chemical properties are similar, sodium has obvious shortcomings in front of lithium. Due to the greater atomic weight, the sodium ion has a larger radius than lithium. “To store the same amount of electricity, the number of ions that need to migrate is the same, but the weight required for sodium ion batteries is heavier.

How sodium ion battery catch up? The key is still the material.

Cathode materials have the greatest impact on energy density. According to the composition, the mainstream sodium ion battery cathode materials can be divided into transition metal oxide, polyanion compound and Prussian blue compound system, which can roughly correspond to the ternary of lithium ion batteries cathode materials, lithium iron phosphate materials and organic materials. “Lithium ion batteries provide ideas, and sodium ion batteries still need. Adjust according to your own characteristics.

In addition to pursuing energy density, cycle life is also an important goal. The charging process of sodium ion batteries is to insert sodium ions into the negative electrode. Due to the larger size of sodium ions, it is more difficult to insert the negative electrode, and the cycle life is naturally longer than that of lithium ions. Batteries are shorter.

What is the difference between sodium ion battery vs lithium ion battery?

Similar to a lithium battery, a sodium ion battery is a “rocking chair” secondary battery that also includes a positive electrode, a negative electrode, a separator, an electrolyte, and a current collector.

• When charging, Na + comes out from the positive electrode, and is inserted into the negative electrode through the electrolyte through the separator, so that the positive electrode is in a high potential sodium poor state, and the negative electrode is in a low potential sodium rich state. The discharge process is the opposite. To maintain the balance of charge, the same number of electrons are transferred through the external circuit during charging and discharging and migrate between the positive and negative electrodes together with Na+ so that the positive and negative electrodes undergo oxidation and reduction reactions respectively. The de-intercalation working principle of sodium ion batteries is similar to that of lithium ion batteries, laying a solid foundation for the industrialization of sodium ion batteries.
• Sodium ion batteries have better safety performance. The internal resistance of sodium ion batteries is slightly higher than that of lithium batteries, resulting in less instantaneous heat generation and lower temperature rise in safety tests such as short circuits. In the tests of all safety items such as overcharge, overdischarge, short circuit, acupuncture, extrusion, etc., no fire or explosion was found in the sodium ion battery.
• Na ion batteries have better high and low temperature performance. The high temperature discharge capacity (55°C and 80°C) exceeds 100% of the rated capacity, and the low temperature -40°C discharge capacity exceeds 70% of the rated capacity. And it can realize 0.1C charging and discharging at low temperature -20°C, and its charging and discharging efficiency is close to 100%, which has better low temperature charging performance than lithium batteries.
• Na ion batteries have better rate performance. The Stokes diameter of sodium ions is smaller than that of lithium ions, and the electrolyte with the same concentration has higher ionic conductivity than lithium salt electrolytes. The solvation energy of sodium ions is lower than that of lithium ions, resulting in faster kinetics and interfacial diffusion properties in the electrolyte
• There is still room for improvement in the energy density and cycle times of Na ion batteries. The energy density of sodium ion batteries is about 100-150Wh/kg, which is higher than that of lead acid batteries and comparable to some lithium iron phosphate batteries. The energy density of the sodium ion battery released by Ningde Times is as high as 160Wh/kg, and the research and development goal of the energy density of the next generation sodium ion battery is more than 200Wh/kg. In terms of cycle times, sodium ion batteries exceed 2,000 times, which still has a certain gap with lithium iron phosphate batteries.
• It is expected that sodium ion batteries will first replace lead acid batteries and enter low speed two wheel vehicles, and then cut into energy storage and A00 class vehicles, partially replacing lithium iron phosphate batteries. Sodium ion batteries can be used in fields that require lower energy density. More than 70% of the national two wheel electric vehicle battery market is lead acid batteries. The overall performance of sodium ion batteries is higher than that of lead acid batteries, and they are more environmentally friendly. It is expected to promote the implementation of lead free low speed electric vehicles and start stop power supplies. With the rapid development of domestic electrochemical energy storage,sodium ion batteries are expected to penetrate the energy storage market by virtue of low cost and resource advantages. However, A00-class vehicles are more sensitive to battery costs, and sodium ion batteries have advantages.
• Under ideal conditions, sodium ions can be completely reversibly extracted and intercalated without causing damage to the crystal structure. Electrode materials are crucial to sodium ion batteries, and the development of ideal cathode materials for sodium ion batteries is the key to advancing sodium ion batteries. The current cathode materials for sodium ion batteries mainly include transition metal layered oxides, polyanion compounds and Prussian blue compounds.

The three positive electrode routes have their own strengths and may coexist in the future. The preparation method of the layered oxide system is simple, the specific capacity and voltage are high, but the stability in air is poor. The polyanion system has good rate performance and cycle performance, but the conductivity is generally poor. Carbon coating and doping are used to increase the energy density.

Prussian blue compounds have good structural stability and rate capability, but there are problems such as difficult removal of crystal water and dissolution of transition metal ions. The layered oxide system has a high degree of maturity and is expected to be the first to realize industrialization. The Prussian blue type has low cost, high specific capacity and energy density, excellent rate performance, and great potential in the future. The preparation techniques of Prussian blue compound cathode materials mainly include: co-precipitation method, hydrothermal synthesis method, ball milling method, etc. The co-precipitation method is the most mainstream synthesis method, with low production cost and easy adjustment of the synthesis process, but it takes a long time and is prone to crystal lattice defects and crystal water. The hydrothermal synthesis method can speed up the reaction rate and the product has high dispersibility, but it requires high production equipment. The ball milling method has a simple operation process and can reduce the crystal water of the material, but the particles are easy to agglomerate and easily mixed with impurities.

Summarize:

1. From the perspective of safety: sodium ion batteries are safer, and the higher the current density of lithium ion batteries, the faster the growth of dendrite lithium, piercing the internal structure of the battery, causing short circuit spontaneous combustion. However, the probability of sodium ions to generate dendrites is very low, and the probability of spontaneous combustion is very low.
2. From a technical point of view: sodium ion batteries are worse than lithium ion batteries in terms of energy density and power density. The main reason is that sodium ions are twice as large as lithium ions to carry the same charge. If a sodium ion battery is a donkey, a lithium ion battery is a horse, with better explosive power and endurance, but donkeys can do things that are not in a hurry, such as grinding and grinding. In addition, the cycle life of sodium ion batteries is also longer than that of ternary batteries. Lithium battery low;
3. From the point of view of resources: the reserves of lithium in the world are not particularly rich, but the distribution of sodium on the earth is much more, especially in the ocean, sodium is equivalent to inexhaustible, but due to sodium The manufacturing cost of ion batteries is not much cheaper than that of lithium ion batteries, and requires technical research and scale effects. In theory, the cost will be lower than that of lithium iron phosphate.