(Report Producer/Author: Founder Securities, Shen Jianguo)
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The principle of sodium-ion batteries is consistent with lithium-ion batteries
Sodium-ion batteries are rocking chair type secondary batteries, which are consistent with the principle of lithium-ion batteries. Sodium and lithium belong to the same main group of elements, and both exhibit similar "rocking chair" electrochemical charge-discharge behaviors in battery operation. Sodium ion battery in the charging process, sodium ions from the cathode out of the cathode and embedded in the anode, while the electron through the external circuit, embedded in the anode of the sodium ions, the higher the charging capacity; when discharging, the reverse process occurs, the more sodium ions back to the positive electrode, the higher the discharge capacity.
Consistent with the internal structure of lithium-ion batteries, sodium ions replace lithium ions. Like lithium batteries, sodium batteries are mainly composed of positive electrode, negative electrode, fluid collector, electrolyte and separator. Since the radius of sodium ions is relatively large, the cathode material preferentially chooses a regular layered structure, and the design through the layer spacing is the key parameter of the performance performance of sodium batteries.
The development of sodium batteries has lasted for more than fifty years, and there is no obvious gap at home and abroad
Sodium-ion and lithium-ion battery research began in the 1970s, due to the growing demand for energy storage, the demand for low-cost energy storage battery technology has become more and more urgent, sodium-ion battery research has made rapid progress in the past decade.
Early: Basic research on sodium ions began in the 1970s and was mainly used in energy storage scenarios
In the late 1970s, people carried out research on sodium-ion batteries and lithium-ion batteries almost simultaneously, but due to the limitations of the research conditions at that time and the strong interest in lithium-ion batteries, sodium-ion batteries were slow and stagnant in early research, and early sodium-ion battery research was mainly concentrated in sodium-sulfur batteries. Sodium-sulfur batteries were first proposed in 1966 by Kummer and Weber, who worked at Ford in the United States, and early research focused on the application of electric vehicles. Early sodium-sulfur batteries, with their obvious advantages in low cost and energy density, have been widely studied and applied in large-scale energy storage systems.
In the medium term: the tension of lithium resources is highlighted, and the research of sodium-ion batteries begins to receive attention
Sodium-ion battery research has received attention, mainly due to: 1) lead-acid battery environmental pollution is inevitable: its solid-state, gaseous pollution may be eliminated, but it is impossible to avoid the pollution of water-soluble lead heavy metal ions; 2) lithium resource reserves are limited: at present, 70% of the world's lithium resources are distributed in South America, 80% of China's lithium resources rely on imports, lithium-ion batteries are difficult to take into account the needs of electric vehicles and grid energy storage two major industries; 3) sodium-ion battery cost advantage: the current price of battery-grade lithium carbonate has risen to about 90,000 yuan / ton, Sodium is easy to obtain, and the cost advantage of sodium-ion batteries is obvious.
At present: from the laboratory to the practical stage, there have been a number of enterprise layouts
Domestic sodium-ion battery technology research is now at the forefront of the world. Zhejiang Sodium Innovation Energy prepared a sodium ion soft-packed battery cell with NaNi1/3Fe1/3Mn1/3O2 ternary layered oxide cathode-hard carbon anode system, with an energy density of 100~120Wh/kg, and a capacity retention rate of more than 92% after 1000 cycles. Relying on the technology of the Institute of Physics of the Chinese Academy of Sciences, Zhongke HaiNa Company has developed a sodium-ion battery with an energy density higher than 135Wh/kg, with an average working voltage of 3.2V, a capacity retention rate of 91% after 100% deep discharge, 1000 cycles, and has now realized the 100-ton preparation of positive and negative electrode materials and small batch supply, sodium ion batteries also have MWh-level manufacturing capabilities, and take the lead in completing the demonstration role in low-speed electric vehicles and 30kW, 100kWh energy storage power stations.
Overseas also has a number of enterprises to lay out sodium-ion batteries: 1) the British Faradion company earlier to carry out the research and development of sodium-ion battery technology, its cathode material is nickel, manganese, titanium layered oxide, anode material using hard carbon, and the company has developed a 10Ah soft pack battery sample, energy density of 140Wh/kg, the average battery operating voltage is 3.2V, and the cycle life prediction at 80% discharge depth can exceed 1000 times; 2) Natron in the United States Energy uses Prussian blue materials to develop high-magnification aqueous sodium-ion batteries, with a cycle life of 10,000 times at 2C magnification; 3) The Battery Research Department of Toyota Corporation of Japan announced the development of a new cathode material system for sodium-ion batteries in 2015.
The downstream application of sodium-ion batteries overlaps with lithium iron phosphate
Due to the limitation of energy density, the application scenarios of sodium ions are more in the fields of energy storage and two-wheeled vehicles. Sodium-ion batteries have a complementary relationship with NCM, and there is a certain replacement relationship with LFP. The AB sodium-lithium battery solution announced by CATL may broaden the application scenarios in the field of passenger cars.
<h1 class="pgc-h-arrow-right" data-track="122" > comparison between sodium batteries and lithium batteries</h1>
The capacity density of sodium-ion batteries is 70-200Wh/Kg, and the cycle can reach 10,000 times
Energy density, sodium ion battery capacity density of 70-200Wh/Kg, and NCM lithium battery 240-350Wh/Kg energy density range does not conflict, theoretically high-energy sodium batteries and LFP batteries at the same level, the current stage of sodium batteries are mainly concentrated in the 130-150Wh/Kg range. From the perspective of circulation, the theoretical cycle of sodium batteries can reach 10,000 times, and at this stage, it is about 3,000-4,000, which is still a little gap with LFP lithium batteries.
Sodium-ion batteries have better fast charging performance than lithium-ion batteries
Sodium ion compared to lithium ion: 1) Stokes diameter is smaller, the same concentration of electrolyte has a higher ion conductivity than lithium salt electrolyte, or lower concentration of electrolyte can achieve the same ion conductivity, fast charging performance is good; 2) although the sodium ion is larger than the radius of lithium ions, it is difficult to embed in the electrode crystal structure resulting in a slower movement rate, but the disadvantage can be improved by changing the characteristics of the negative electrode material. As early as 2017, the team of the School of Materials Science and Engineering of Hefei University of Technology used the sodium chloride template method combined with the optimized carbon source composition to prepare a three-position amorphous carbon material, which realized the effective regulation of its microscopic pores and microstructure.
Sodium-ion batteries are safer than lithium-ion batteries
According to incomplete statistics, a total of 32 energy storage power station fire and explosion accidents occurred in the world from 2011 to 2021, of which 26 were ternary lithium-ion batteries. The electrochemical performance of sodium-ion batteries is relatively stable, and it is easy to passivate and inactivate during thermal runaway, and the safety experiment performance is better than that of lithium-ion batteries. At present, the sodium ion battery has passed the detection of the China Automobile Center, and does not smoke, fire, or explode when acupuncture, and does not catch fire and burn after withstanding experiments such as short circuit, overcharge, over-discharge, and extrusion. Compared with lithium-ion batteries, the starting self-heating temperature reaches 165 °C, and the sodium-ion battery reaches 260 °C; and the maximum self-heating rate of sodium-ion batteries in the ARC test is significantly lower than that of lithium-ion batteries, which indicate that sodium-ion batteries have better thermal stability.
<h1 class="pgc-h-arrow-right" data-track="123" > third, sodium battery process and materials</h1>
Structure and process of sodium batteries
There is no longer a lithium ion in the sodium battery, and the raw materials except the isolation film have changed, and the lithium battery equipment is basically reused. Like the lithium battery structure, it is also composed of a positive electrode material, a negative electrode material, a fluid collector, a separation film, an electrolyte and a housing, and a top cover. The faster progress of the cathode material is the nickel iron manganese/copper ferromanganese system of copper oxides and the Prussian compound route; the rapid progress of the negative electrode material is carbon-based material; the main salt of the electrolyte has changed from lithium hexafluorophosphate to sodium hexafluorophosphate; the negative collector can change from copper foil to aluminum foil; the isolation film maintains the original product; the battery factory production line can be completely reused, and the small upgrade of equipment can be achieved, and there is basically no additional fixed asset investment.
Cathode route: four main routes of transition metal oxides, polyanionic compounds, Prussian compounds and amorphous materials
There are four main routes for the cathode, focusing on the excess metal oxide and Prussian compound routes
The cathode route mainly includes: transition metal oxides, polyanionic compounds, Prussian compounds and amorphous materials. Transition metal oxides are currently the most popular cathode materials, such as sodium ferric phosphate, sodium iron manganate, sodium titanium manganate, etc. Zhongke Sea Sodium, Sodium Innovation Energy and Faradion are the main companies in this route. Prussian materials, with good electrochemical properties, with low cost, good stability and other advantages, but in the preparation process there are problems such as coordination water content is difficult to control, Ningde era, Starry Sky Sodium Electricity and Natron Energy are the main companies of the route. Poly-negative ionized materials, good stability and cycle life, compound families have diversity, but the low intrinsic electronic conductivity limits the practical application of such materials.
Negative electrode route: metal compounds, carbon-based materials, alloy materials, non-metallic elements four types of routes
Metal compounds: metal oxides, sulfides and selenides as the main representative, metal alloy materials in the discharge process of low potential and sodium alloying reaction, charging process high potential when the de-alloying reaction, the type of material is often the theoretical reversible specific capacity is high, the output potential is low (<1V), but the volume of the reaction process changes greatly (often > 200%), so that the material in the cycle process is easy to rupture affecting performance.
Alloy materials: Rely on the interaction of the negative electrode material with lithium or sodium to form an alloy, which in turn produces an electrochemical reaction to ensure the normal operation of the battery. What is obviously different from lithium-ion batteries is that the sodium ion itself has a larger ion radius relative to the lithium ion, so the volume expansion caused by the metal sodium and the negative electrode material when forming an alloy is also more obvious.
Non-metallic elements: elements homogeneous with carbon, phosphorus and silicon have become the direction of recent rise, and the research maturity is not high. Among them, purple phosphorus heating is easy to form white phosphorus, white phosphorus has unstable chemical properties, purple phosphorus and white phosphorus can not be used as electrode materials; red phosphorus conductivity is low and the problem of volume expansion is difficult to solve; black phosphorus has a wrinkled layered structure, high conductivity and other characteristics, but it is difficult to prepare.
The negative carbon-based material is preferably hard carbon, and the more stable structure corresponds to the higher cycle life of the battery
Graphite is usually replaced with hard carbon as a negative electrode active material, and graphite has poor storage capacity for sodium ions
Graphite materials cannot provide sufficient mobile space for sodium ions because of their structural relationship. Although soft carbon has a certain sodium storage capacity, its own low sodium storage capacity and high charging potential shortcomings limit soft carbon as an ideal high specific energy carbon sodium storage anode material. The carbon sheet layer of carbon microcrystalline inside soft carbon presents a chaotic layer accumulation structure with high electrical conductivity, and the sodium storage mechanism is mainly manifested as the adsorption of Na+ by the edge of the carbon layer, the surface of the carbon layer and the microcrystalline gap. (Research Progress on Carbon-based Anode Materials for CNKI Sodium-Ion Batteries)
Amorphous carbon is applied to the anode material of sodium-ion batteries, which starts with soft carbon, but its sodium storage capacity is not ideal at this stage. Different from soft carbon, hard carbon is difficult to appear graphitization even after high temperature treatment, showing stronger sodium storage capacity and lower working potential, which is more suitable for use as a sodium-ion battery anode material.
The negative collector is changed from copper foil to aluminum foil, and the cost is further reduced
In addition to positive and negative electrode materials, fluid collectors play an important role as materials that carry positive and negative electrode activity and collect electrons. Sodium-ion batteries have a similar working principle to lithium-ion batteries, but the cations flowing in the electrolyte are sodium ions instead of lithium ions. Unlike lithium, sodium does not undergo electrochemical alloying reactions with aluminum at room temperature, so copper collectors can be replaced by cheaper aluminum.
<h1 class="pgc-h-arrow-right" data-track="124" >4. Analysis of sodium battery industry chain</h1>
Sodium battery industry chain
The main changes in the sodium battery industry chain are in the midstream and the positive electrode. The industrial chain structure of sodium batteries is similar to that of lithium batteries, and the negative electrode, electrolyte, and diaphragm basically maintain the current competitive pattern, and the collector no longer needs copper foil. Battery companies with major technical routes are different, and the cathode materials required or their key materials are also different. Since the industrial system is in the early stage of commercialization, the competitive landscape still needs to be tracked, and the relevant leading enterprises still have the advantage of being the first mover.
Prussian compound - sodium ferrocyanide
Prussian materials are mainly composed of sodium ferrocyanide, with good electrochemical properties, clear cost advantages, through the surface modification treatment, increase the cycle life, the rate of use of active materials, enhance the thermal stability of the battery and reversible specific capacity. Cyanide is widely used in industry, mainly in paints, dyes, rubber and other industries. Since the battery field did not involve the use of the product before, and the total amount of use in other industries is not large, the current sodium battery industry chain environment is still a blue ocean.
Transition metal oxide - iron/manganese/sodium copper
Transition oxidation materials have large S-shaped channels and small hexagonal channels, Na ions can diffuse quickly and have good structural stability, thus showing considerable discharge specific capacity and excellent cycle performance. The mainstream system is manganese / iron / cobalt / nickel / copper oxide, sodium manganate compared with other compounds, due to the comprehensive performance of performance and cost is better, is the current development of faster materials.
Hard carbon is more suitable as an anode material than soft carbon, and existing faucets have technical reserves
The difference between soft carbon and hard carbon: According to whether the carbon material can be fully graphitized under high temperature heat treatment at 2800 °C, the carbon material can be divided into hard carbon or soft carbon. When the temperature rises, the change rate of soft carbon in the interlayer distance and microcrystalline will be much greater than that of hard carbon, soft carbon will be fully graphitized by high temperature heat treatment, and the graphitization of hard carbon is difficult to carry out. Although both have graphite microcrystals, the microcrystallines inside soft carbon are larger in size and have higher orderliness. If soft carbon is not carbonized by high-temperature heat treatment, it will lead to the reversibility of sodium storage, poor cycle stability, and delay in voltage.
At present, hard carbon is the mainstream material, and the main negative electrode enterprises have technical reserves. In addition to the use of synthetic hard carbon precursors, many natural organic matter in nature is also a good precursor for the preparation of hard carbon materials, and they also have the advantages of wide range, low price and environmental protection. Compared with graphite, hard carbon is mainly improved in microstructure and preparation process, and the main negative electrode enterprises have technical reserves.
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