1.1 Lithium and sodium are of the same family, and their physical and chemical properties are similar.
Lithium, sodium and potassium are both alkali metal elements in Group IA of the Periodic Table of Elements, and they are similar in physical and chemical properties, so they can all be used as metal ion carriers of secondary batteries in theory.
lithium has a smaller ionic radius, a higher standard potential and a much higher specific capacity than sodium and potassium, so it has been used in secondary batteries earlier and more widely.
However, the global reserves of lithium resources are limited. With the development of new energy vehicles, the demand for batteries has risen sharply, and the bottleneck at the resource end has gradually emerged. As a result, the periodic fluctuation of lithium supply and demand has a negative impact on the operation of battery enterprises and OEMs. Therefore, the research and mass production process of battery systems with richer resource reserves and lower cost has been accelerated within the industry, and sodium has emerged as a substitute for lithium, which has attracted more and more attention in the battery field.
1.2 The comprehensive performance is better than that of lead-acid battery, and the energy density is short.
The working principle of sodium ion battery is similar to that of lithium ion battery. Similar to other secondary batteries, sodium ion batteries also follow the working principle of deintercalation. In the process of charging, sodium ions emerge from the positive electrode and are embedded in the negative electrode. The more sodium ions are embedded in the negative electrode, the higher the charging capacity is. When discharging, the process is reversed. The more sodium ions return to the positive electrode, the higher the discharge capacity.
the energy density is weaker than that of lithium battery and stronger than that of lead acid.
in terms of energy density, the battery core energy density of sodium ion battery is 1-16Wh/kg, which is much higher than that of lead-acid battery (3-5Wh/kg), and there is also an overlapping range compared with that of lithium iron phosphate battery (12-2Wh/kg).
At present, the energy density of ternary batteries in mass production is generally above 2Wh/kg, and the high nickel system even exceeds 25Wh/kg, which has obvious leading advantages for sodium batteries.
In terms of cycle life, the sodium battery is more than 3 times, which is also far more than the lead-acid battery's 3 times.
therefore, only from the perspective of energy density and cycle life, sodium batteries are expected to replace lead-acid and lithium iron phosphate batteries, such as start-stop, low-speed electric vehicles, energy storage and other markets, but it is difficult to be applied to electric vehicles and consumer electronics, where lithium batteries will remain the mainstream choice.
high safety and excellent high and low temperature performance.
The internal resistance of sodium ion battery is higher than that of lithium battery, and it has less instantaneous calorific value, lower temperature rise, and higher thermal runaway temperature than lithium battery, so it has higher safety. Therefore, for the tests of overcharge, overdischarge, short circuit, acupuncture and extrusion, the sodium battery can not catch fire or explode.
On the other hand, the sodium ion battery can work normally in the temperature range of -4 to 8, and the capacity retention rate is close to 9% in the environment of -2, and its high and low temperature performance is superior to other secondary batteries.
the rate performance is good, and fast charging has advantages.
depending on the open 3D structure, sodium ion battery has good rate performance, and can adapt to responsive energy storage and scale power supply, which is another advantage of sodium battery in the field of energy storage.
In terms of fast charging ability, the charging time of sodium ion battery is only about 1 minutes. Comparatively speaking, it usually takes 3 minutes to charge the ternary lithium battery from 2% to 8% even with the help of DC fast charging, and it takes about 45 minutes in Ferrous lithium phosphate.
2.1 resource end: overcoming the bottleneck of lithium battery
Lithium battery is facing a resource bottleneck, and sodium resources are relatively abundant. The abundance of lithium in the crust is only .65%.
according to the report of the U.S. geological survey, with the increasing exploration of lithium ore resources, the global lithium ore reserves will increase to 21 million tons of lithium metal equivalent (equivalent to 112 million tons of lithium carbonate) in 22, with a year-on-year increase of 23.5%; If 5kg lithium carbonate is used for each electric vehicle and other downstream markets of lithium carbonate are not considered, the current lithium reserves can only meet the demand of 2 billion vehicles, so there is a bottleneck at the resource end.
in terms of regions, the lithium reserves of major lithium mine resource countries in the world have all increased to varying degrees, with Australia and China increasing more, among which Australia's lithium reserves have increased from 2.8 million tons in 219 to 4.7 million tons of lithium metal equivalent, while China's lithium reserves will increase by 5% to 1.5 million tons of lithium metal equivalent in 22.
overall, Chile and Australia are still the top two countries with lithium resources in the world, accounting for about 43.8% and 22.4% of the global lithium resources in 22, respectively.
In contrast, the crustal abundance of sodium resources is 2.74%, which is 44 times that of lithium resources. At the same time, it is widely distributed and simple to extract, and sodium ion batteries have strong advantages in the resource end.
the increase of lithium price brings the disturbance of enterprise cost.
in the short term, due to the increasing demand for lithium since 221, and the shrinking supply and destocking of upstream lithium ores, the prices of lithium ores and lithium salts will bottom out in 22, and the prices will rebound greatly in the first half of 221; In the long run, the capacity bottleneck of lithium resources has triggered the market's expectation that the lithium price center will move up.
for enterprises, long-term stable raw material prices are of great significance to their normal operations, and the continuous rise of lithium prices may accelerate the process of enterprises looking for more cost-effective substitutes.
China's lithium resources are highly dependent on foreign countries.
China lithium mines are mainly distributed in Qinghai, Tibet, Xinjiang, Sichuan, Jiangxi, Hunan and other provinces, including spodumene, lepidolite and salt lake brine.
Limited by objective factors such as lithium extraction technology, geographical environment and traffic conditions, the development of lithium resources in China has been slow for a long time, mainly relying on imports; In recent years, with the downstream demand growth and technological progress, the development progress of lithium resources in China has been accelerated.
In 22, the dependence of China lithium industry on external resources will exceed 7%, maintaining a high level, regardless of inventory.
the development of sodium ion batteries is of strategic significance.
the purpose of developing new energy vehicles in China is not only to reduce carbon emissions and solve environmental problems, but also to reduce the import dependence on traditional fossil fuels.
therefore, if the resource bottleneck problem cannot be effectively solved, the significance of developing electric vehicles will be discounted.
In addition to lithium resources, other aspects of lithium batteries, such as cobalt and nickel, are also facing import dependence and price fluctuation, so the development of sodium ion batteries has strategic significance at the national level.
In 22, the U.S. Department of Energy explicitly adopted sodium ion batteries as the development system of energy storage batteries; The "Battery 23" project of the EU energy storage plan ranks sodium ion battery at the top of the non-lithium ion battery system, and the "Horizon 22 Research and Innovation Plan" of the EU takes sodium ion material as a key development project for manufacturing durable batteries for non-automotive applications. The Guiding Opinions on Accelerating the Development of New Energy Storage issued by two ministries and commissions in China put forward that energy storage technologies should be diversified, and large-scale experiments and demonstrations of flywheel energy storage, sodium ion batteries and other technologies should be accelerated.
sodium ion batteries have attracted the attention and support of more and more countries.
2.2 material end: highlighting the cost advantage
cathode material
the cathode material uses sodium ion active material, and the selection is diversified.
The cathode material is the key factor to determine the energy density of sodium ion batteries. At present, materials with potential for mass production include transition metal oxide system, polyanion (phosphate or sulfate) system and Prussian blue (ferricyanide) system.
transition metal oxides are the mainstream choice of cathode materials at present.
layered transition metal oxide 2(M is a transition metal element) has a high specific capacity and many similarities with cathode materials of lithium batteries in synthesis and battery manufacturing, and is one of the mainstream materials with potential for commercial production of cathode materials of sodium ion batteries.
However, the layered transition metal oxides are prone to structural phase transition during charging and discharging, and their capacity decays seriously during long-cycle and high-current charging and discharging, which makes them have low reversible capacity and poor cycle life.
The common improvement methods mainly include bulk doping and surface coating of cathode materials.
The P2-type copper-based oxide (P2-Na.9Cu.22Fe.3Mn.48O2) was used in Zhongkehai sodium, which significantly improved the capacity level of the cathode material and the energy density of the battery reached 145 Wh/kg.
O3-NaFe.33Ni.33Mn.33O2, which is used in sodium innovative energy, has high gram capacity (over 13mAh/g) and good cycle stability.
Faradion company in Britain adopts nickel-based oxide material, and the energy density of the battery exceeds 14Wh/kg.
sodium vanadate phosphate is one of the mainstream research directions.
polyanionic compound, Na[()] (M is a metal ion with changeable valence state such as Fe and V, and X is an element such as P and S), has the advantages of higher voltage, higher theoretical specific capacity and stable structure, but the low electronic conductivity limits the specific capacity and rate performance of the battery.
At present, the most studied materials in the industry mainly include sodium ferric phosphate, sodium vanadate phosphate, sodium ferric sulfate, etc., and the conductivity and capacity are improved by carbon coating and adding fluorine.
sodium innovative energy takes sodium vanadate phosphate as one of the key cathode materials for sodium batteries, and Dalian Institute of Physics and Chemistry of Chinese Academy of Sciences has realized efficient synthesis and application of sodium vanadate trifluoride.
Prussian blue material has higher theoretical capacity.
Prussian blue material, Na[()6] (Fe, Mn, Ni and other elements) has an open frame structure, which is beneficial to the rapid migration of sodium ions; Theoretically, it can realize two-electron reaction, so it has high theoretical capacity.
However, in the preparation process, it is difficult to control the structural water content, and it is prone to phase change and side reaction with electrolyte, resulting in poor cycle performance.
Liaoning Xingkong Sodium Power Co., Ltd. is committed to the industrialization research of Na1.92FeFe(CN)6, with a theoretical capacity of 17 mAh/g; Contemporary Amperex Technology Co., Limited used the Prussian white (Nan[Fe()6]) material, and innovatively rearranged the charge of the bulk structure of the material, which solved the core problem that the capacity of Prussian white rapidly decayed during the cycle.
sodium ion batteries have significant cost advantages at the material end.
Because the price of sodium carbonate is much lower than that of lithium carbonate, and the cathode materials of sodium ion batteries usually use bulk metal materials such as copper and iron, the cost of cathode materials is lower than that of lithium batteries.
According to the data of official website of Zhongke Haina, the anode material cost of sodium battery using NaCuFeMnO/ soft carbon system is only 4% of that of lithium battery using Ferrous lithium phosphate/graphite system, while the total material cost of the battery is 3%-4% lower than that of the latter.
negative electrode materials
negative electrode materials of sodium ion batteries mainly include carbon-based materials (hard carbon and soft carbon), alloys (Sn, Sb, etc.), transition metal oxides (titanium-based materials) and phosphate materials.
The radius of sodium ion is larger than that of lithium ion, so it is difficult to embed graphite materials, so the traditional graphite negative electrode of lithium battery is not suitable for sodium battery.
Alloys generally have large volume changes and poor cycle performance, while metal oxides and phosphates generally have low capacities. Amorphous carbon is the mainstream material of sodium battery.
Among the reported anode materials for sodium ion batteries, amorphous carbon materials have become the most promising anode materials for sodium ion batteries because of their relatively low sodium storage potential, high sodium storage capacity and good cycle stability.
The precursors of amorphous carbon materials can be divided into soft carbon and hard carbon precursors. The former is cheap, can be completely graphitized at high temperature and has excellent electrical conductivity. The latter is expensive (1,-2, yuan/ton) and cannot be completely graphitized at high temperature, but the specific capacity of sodium storage and the first-week efficiency of carbon materials obtained after carbonization are relatively high.
Coal-based materials, such as sub-bituminous coal, bituminous coal and anthracite, have the characteristics of abundant resources, low price and high carbon yield. The negative electrode material of sodium ion battery prepared from coal-based precursors has a sodium storage capacity of about 22mAh/g and a first-cycle efficiency of 8%, which is the most cost-effective carbon-based negative electrode material of sodium ion battery at present. However, this kind of material has many characteristics, such as micro powder, low tap density and irregular shape, which is not conducive to processing in the process of battery production.
with sub-bituminous coal, lignite, bituminous coal, anthracite and other coal-based materials as the main materials, and soft carbon precursors such as asphalt, petroleum coke and needle coke as the auxiliary materials, Zhongke Haina proposed a method to improve the processability and electrochemical performance of coal-based sodium ion battery cathode materials. The preparation process is simple and the cost is low, and the battery cathode materials with low micro-powder content and high tap density can be obtained.
Contemporary Amperex Technology Co., Limited has developed a hard carbon material with unique pore structure, which has the characteristics of easy deintercalation and excellent cycle. The specific capacity is as high as 35mAh/g, which is equivalent to the level of power graphite.
The electrode current collectors are all made of aluminum foil, so the cost is lower.
In graphite-based lithium-ion batteries, lithium can react with aluminum to form an alloy, so aluminum can not be used as the current collector of the negative electrode, and copper can only be used instead.
The anode and cathode current collectors of sodium ion battery are all aluminum foil, so the price is lower; According to the official website data of Zhongke Haina, the current collector (aluminum-aluminum) cost of sodium battery using NaCuFeMnO/ soft carbon system is only 2%-3% of the current collector (aluminum-copper) cost of lithium battery using Ferrous lithium phosphate/graphite system.
besides the positive electrode, the material cost of the current collector is the most different from that of the lithium battery.
Electrolyte
Similar to lithium ion batteries, the electrolytes in sodium ion batteries are mainly divided into three categories: liquid electrolyte, solid-liquid composite electrolyte and solid electrolyte.
in general, the ionic conductivity of liquid electrolyte is higher than that of solid electrolyte.
at the solvent level, ester electrolyte and ether electrolyte are the two most commonly used organic electrolytes, among which ester electrolyte is the main choice for lithium-ion battery system because it can be effectively used on graphite negative electrode surface.