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Difference between sodium ion battery and lithium ion battery

Similar to lithium battery, sodium ion battery is a "rocking chair" secondary battery. The sodium ion battery also includes positive electrode, negative electrode, diaphragm, electrolyte and current collector. ? During charging, Na+is released from the positive electrode and inserted into the negative electrode through the electrolyte through the diaphragm, 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 opposite. Keep the charge balance. During the charging and discharging process, the same number of electrons are transferred through the external circuit 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-inserted working principle of sodium ion battery is similar to that of lithium ion battery, which lays a solid foundation for the industrialization of sodium ion battery.

Sodium ion battery cell of Zhejiang Changyi Sodium Power

The safety performance of sodium ion battery is more excellent. The internal resistance of the sodium ion battery is slightly higher than that of the lithium battery, resulting in less instantaneous heating and lower temperature rise in the short circuit and other safety tests. In the tests of all safety items such as overcharge, over-discharge, short circuit, puncture and extrusion, no fire and explosion were found in the sodium ion battery.

? The sodium ion battery has better high and low temperature performance. The discharge capacity at high temperature (55 ° C and 80 ° C) exceeds 100% of the rated capacity, and the discharge capacity at low temperature - 40 ° C exceeds 70% of the rated capacity. Moreover, 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 battery.

? The rate performance of sodium ion battery is more excellent. The Stokes diameter of sodium ion is smaller than that of lithium ion, and the electrolyte with the same concentration has higher ionic conductivity than that of lithium salt electrolyte. The solvation energy of sodium ion is lower than that of lithium ion, so it has faster kinetic and interfacial diffusion properties in the electrolyte.

? There is still room for improvement in the energy density and cycle times of the sodium ion battery. The energy density of sodium ion battery is about 100-150Wh/kg, which is higher than that of lead-acid battery and equivalent to some lithium iron phosphate batteries. The energy density of sodium ion batteries released by Ningde Times is as high as 160Wh/kg, and the research and development goal of the energy density of the next generation of sodium ion batteries is more than 200Wh/kg. In terms of cycle times, the sodium ion battery has more than 2000 cycles, which still lags behind the lithium iron phosphate battery.

? It is expected that the sodium ion battery will first replace the lead acid battery to enter the low-speed two-wheeled vehicle, and then enter the energy storage and A00 class vehicle, and partially replace the lithium iron phosphate battery. Sodium ion batteries can be used in fields with low energy density requirements. More than 70% of the national second-wheel electric vehicle battery market is lead-acid battery. The comprehensive performance of sodium ion battery is higher than that of lead-acid battery, and it is 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 with low cost and resource advantages. However, A00 vehicles are more sensitive to battery costs, and sodium ion batteries have advantages.

? Under ideal conditions, sodium ions can be completely and reversibly removed and embedded without damaging the crystal structure. The electrode material is very important to the sodium ion battery. The research and development of ideal cathode material for sodium ion battery is the key to promote the sodium ion battery. At present, the cathode materials of sodium ion batteries mainly include transition metal layered oxides, polyanions and Prussian blue compounds.

? The three positive electrode routes have their own advantages and may coexist in the future. The preparation method of layered oxide system is simple, and its specific capacity and voltage are high, but its stability in air is poor. The polyanion system has good rate performance and cycling performance, but its conductivity is generally poor. Carbon coating and doping are used to improve the energy density. Prussian blue compounds have good structural stability and magnification performance, but there are problems such as difficult removal of crystal water and dissolution of transition metal ions. The layered oxide system is highly mature and is expected to take the lead in industrialization. Prussian blue has low cost, high specific capacity and energy density, excellent magnification performance and great potential in the future.

The preparation processes of Prussian blue compound cathode materials mainly include: coprecipitation method, hydrothermal synthesis method, ball milling method, etc. Coprecipitation method is the most mainstream synthesis method with low production cost and easy adjustment of synthesis process, but it takes a long time and is easy to produce lattice defects and crystal water. Hydrothermal synthesis can accelerate the reaction rate, and the product dispersion is high, but it requires high production equipment. The operation process of ball milling method is simple, which can reduce the crystal water of the material, but the particles are easy to agglomerate and easily mixed with impurities.

Summary: 1. From the perspective of safety: sodium ion batteries are safer. The higher the current density of lithium ion batteries is, the faster the dendritic lithium grows, which punctures the internal structure of the battery, causing short circuit spontaneous combustion. The probability of sodium ion producing dendrite is very low, and the probability of spontaneous combustion is very low.

2. Technically, sodium ion batteries are worse than lithium ion batteries in terms of energy density, power density and other indicators. The main reason is that when carrying the same charge, sodium ion is twice larger than lithium ion. If the sodium ion battery is a donkey, the lithium ion battery is a horse, which has better explosive power and endurance, but pulling and grinding can be done by the donkey, and the cycle life of the sodium ion battery is also lower than that of the ternary lithium battery;

3. From the perspective of resources, lithium reserves in the world are not particularly rich, while sodium is much more distributed on the earth, especially in the ocean. Sodium is equivalent to an inexhaustible supply. However, since the manufacturing cost of sodium ion batteries is not much cheaper than lithium ion batteries, it requires technical research and scale effects, and the theoretical cost will be lower than lithium iron phosphate.