Aspects of popular science
Editor|Aspects of popular science
introduction
With the increasing demand for energy in human society, traditional fossil fuels can no longer meet people's needs, so the research and application of new energy technologies have become more and more important. In this process, the battery, as an energy storage device, has received extensive attention and research.
In recent years, magnesium-ion batteries have gradually become a research hotspot. Today I will take you to explore the advantages of magnesium batteries in all aspects, so as to prove why magnesium batteries are the breakthrough direction of the next generation of high-performance batteries.
First, magnesium ions carry more charge and have higher energy density
The divalent properties of magnesium ions allow them to carry and store more charge, which means it has a higher volumetric specific capacity and theoretical energy density.
Specifically, the theoretical energy density of magnesium-ion batteries can reach 150-200Wh/kg, which is much higher than traditional battery technologies such as lead-acid batteries, nickel-metal hydride batteries and lithium-ion batteries. Its volume specific capacity is as high as 3833 mAh/cm-3, which means that magnesium-ion batteries can store more electricity in the same volume.
Second, it will not produce dendrites, and the safety performance is better
With the popularity of electronic devices and new energy vehicles, lithium-ion batteries have become one of the most important battery technologies today. However, there are some safety problems in the use of lithium-ion batteries, of which dendrite growth is one of the most fundamental problems.
Dendrite growth can lead to a short circuit inside the battery, causing thermal runaway and even causing hazards such as fire and explosion. Therefore, how to effectively control the dendrite growth of lithium-ion batteries has become one of the hot spots in lithium-ion battery technology research.
The dendrite growth of lithium-ion batteries is mainly due to the formation of dendritic metallic lithium when lithium ions are reduced during charging. These lithium dendrites will grow rapidly on the electrode surface, disrupt the stable interface between the electrode and the electrolyte, and cause instability inside the battery, increasing the risk of battery accidents.
Unlike lithium-ion batteries, magnesium-ion batteries do not appear magnesium dendrites on the negative electrode surface during charging and discharging. This is because the deposition performance of magnesium ions is better than that of lithium ions, so there will be no dendrite growth similar to that in lithium batteries that pierce the diaphragm and cause battery short circuit, fire, explosion and other phenomena.
Third, the mainland has abundant magnesium resources and strong independent controllability
Lithium and magnesium are two important metal elements that have a wide range of applications in the energy sector, especially in lithium-ion and magnesium batteries. As a new generation of energy storage technology, lithium batteries and magnesium batteries have the advantages of high efficiency, environmental protection and long life, and are indispensable energy sources in the field of new energy vehicles and energy storage.
However, lithium resources have low natural reserves and limited local supply capacity in the mainland. With the large-scale application of energy storage equipment and new energy vehicles, the problems of low reserves and high cost of lithium resources have gradually emerged.
According to statistics, the lithium reserves in the earth's crust are only 0.0065%, and the continental lithium resource reserves are only 7% of the world. Most lithium mines rely on imports, and the existing lithium resource supply system is extremely dependent on foreign countries, which restricts the development of new energy vehicles and energy storage in the mainland.
In contrast, the continent is very rich in magnesium resources. Mainland China is one of the countries with the richest magnesium resources in the world, and magnesium resources and ores are all types and widely distributed.
At the same time, the mainland is the world's largest producer of raw magnesium, accounting for more than 80% of the world's total production. This means that once magnesium batteries are industrialized in the future, the dependence of lithium resources required by mainland China in the field of new energy will be greatly reduced, and battery manufacturing costs will be significantly reduced.
Fourth, the working principle of magnesium battery
Magnesium secondary battery is a new battery proposed with reference to the principle of lithium-ion batteries, which is known as a new rechargeable battery with good development prospects. In the rechargeable magnesium battery, magnesium ions are separated from the positive electrode active material, driven by the external voltage through the electrolyte to migrate to the negative electrode, and the magnesium ion is embedded in the negative electrode active material, due to the charge balance, so the same amount of electrons are required to flow from the positive electrode to the negative electrode in the wire of the external circuit.
The result of charging is that the negative electrode is in a magnesium-rich state, the positive electrode is in a magnesium-poor high-energy state, and the opposite is true when discharging. The flow of electrons in the external circuit forms a current, which realizes the conversion of chemical energy into electrical energy.
The research focus of magnesium secondary batteries is electrolyte and cathode materials. In terms of electrolyte, it is necessary to find materials with high ionic conductivity and high chemical stability to ensure the stability and safety of the battery. In terms of cathode materials, it is necessary to look for materials with high electrochemical activity and stability.
The cathode material is one of the key materials of magnesium-ion batteries, which directly affects the working voltage and charge-discharge specific capacity of the battery. The ideal magnesium-ion battery cathode material should meet the requirements of large capacity, high voltage platform, good reversibility, high cycle efficiency, safety and stability, abundant resources, and easy preparation.
At present, the research on cathode materials of magnesium secondary batteries mainly focuses on transition metal sulfides, transition metal oxides, polyanionic compounds, sulfur and chalcogenides, organic compounds and composite materials. Among them, the embedded detachment cathode material is the most commonly used material in magnesium-ion batteries.
The basic principle of this type of material is that during the charging and discharging process, magnesium ions are embedded and removed from the lattice of the cathode material to achieve an electrochemical reaction. Transition metal sulphides, oxides and sulfur and chalcogenides fall into this category. Compared with the embedded detachment material in lithium-ion batteries, the materials in magnesium-ion batteries have a larger ion radius and stronger ion polarization effect, and require higher reactivity to meet the needs of the battery.
Another common class of cathode materials is conversion type materials. The principle of this type of material is that during the charge and discharge process, the cathode material undergoes chemical changes to change from one compound to another. The advantages of conversion materials are high theoretical specific capacity and high operating voltage, but their reaction mechanism is complex, resulting in short cycle life. At present, transition metal oxides are the main representatives of conversion cathode materials.
Fifth, magnesium metal that can be uniformly deposited is an ideal anode material
Developing magnesium-ion batteries faces some challenges, one of which is finding suitable anode materials. The negative electrode material needs to have the ability to be reversible deposition and dissolve, which is necessary for the normal operation of magnesium-ion batteries. At present, researchers mainly focus on two anode materials: metal magnesium and alloy insertion anode materials. Magnesium metal is an excellent anode material because it can be uniformly deposited on the negative electrode surface.
However, the polar organic matter or aqueous electrolyte in the traditional electrolyte will form a passivation film on the surface of the negative electrode, so that magnesium ions cannot effectively contact the negative electrode material, thereby affecting battery performance. To solve this problem, researchers began to use nanostructured magnesium or alloy insertion anode materials.
Nanostructured magnesium anode materials can effectively reduce the thickness of the passivation film. For example, a magnesium anode with a diameter of 2.5 nm shows better performance in a magnesium-oxygen battery system. In addition, the alloy method insert anode material has also attracted the attention of researchers. This material includes bismuth, antimony, tin and other alloy anode materials.
The nanocluster Mg3Bi2 as the negative electrode can obtain the electrochemical performance of 360 mAhg-1 in LiCl-APC electrolyte, and it can still maintain relatively stable performance during 200 cycles. During the magnesium insertion and removal process, Bi nanotubes evolve into interconnected nanopores, showing good cycle stability and rate performance.
Magnesium-ion batteries are a battery technology with great potential, but there are still many challenges. Finding the right anode material is one of them. Nanostructured magnesium or alloy plug-in anode materials are expected to solve the problem of traditional electrolyte passivation film and improve the performance of batteries. With the continuous development and progress of technology, it is believed that magnesium-ion batteries are expected to become an important member of the future battery field.
Sixth, the bridge connecting the anode and the cathode, the appropriate electrolyte is crucial
The electrolyte plays an important role in magnesium ion transport in rechargeable magnesium batteries. The electrolyte needs to be able to transfer ions between electrodes while also limiting charge migration within the electrolyte. Therefore, the ideal electrolyte should have high ion transport efficiency, but also high ion selectivity, i.e. only specific ions can be allowed to pass through.
At present, the electrolyte of rechargeable magnesium batteries is mainly divided into two types: liquid electrolyte and solid electrolyte. The liquid electrolyte is mainly composed of ether electrolyte and magnesium perchlorate electrolyte. Ether electrolytes are generally composed of solvents such as ethylene oxide, dimethyl ether and diethylene glycol methyl ether mixed with magnesium salts.
Magnesium perchlorate electrolyte is a mixture of organic solvents such as Mg(ClO4)2 and ethylene glycol dimethyl ether with high concentrations. Liquid electrolyte has relatively high ion transport efficiency and good electrochemical performance, but it has the disadvantages of poor heat resistance, volatility and poor safety.
In contrast, solid electrolytes have better stability and safety. Solid electrolytes are generally made of porous materials and magnesium salts, which can provide stable ion transport channels and effectively inhibit the formation of passivation layers on the electrode surface.
At present, solid electrolytes are mainly prepared from materials such as magnesium oxide, alumina and magnesium sulfide. Among them, magnesium oxide electrolyte has high ion transport efficiency and high ion selectivity, as well as good mechanical and thermal stability, and is an electrolyte material with broad application prospects.
conclusion
Although the application of magnesium secondary batteries is still in the early stage of exploration, it has great potential in improving the energy density of secondary batteries, extending the battery life of secondary batteries, reducing the cost of secondary batteries and reducing environmental pollution.
Compared with lithium-ion batteries and lead-acid batteries, magnesium batteries have higher specific energy and specific capacity, higher operating voltage window, and more abundant resources, so they are expected to become an important alternative in the field of power batteries, energy storage and consumer electronics.
In fact, the EU has invested more than 6.5 million euros in the magnesium battery project (E-MAGIC) under its "Vision 2020" research program to replace lithium-ion batteries.
At present, the technical route of magnesium batteries is diversified, in addition to magnesium-ion batteries, there are magnesium primary batteries, magnesium fuel cells and magnesium seawater batteries. Among them, magnesium-ion battery is currently the most widely studied battery technology route. Compared with lithium-ion batteries, magnesium-ion batteries have higher ion transfer rates and better safety performance, so they have broad application prospects in the fields of power batteries and energy storage batteries.
Magnesium secondary batteries and magnesium fuel cells are mainly used in disposable consumer goods and mobile devices, which can provide high energy density and long service life. The magnesium seawater battery is a technical route with great potential, which can extract magnesium ions from seawater for energy, with extremely high energy storage density and environmental friendliness.
The author's opinion
The diversification and wide application of magnesium battery technology will provide more choices and opportunities for future energy and environmental protection. Although there are still some challenges and limitations in this technology, I believe that with the continuous development and improvement of technology, magnesium batteries will become a more excellent and sustainable energy storage and supply technology.
Bibliography:
1. Research progress on performance improvement strategies of cathode materials for magnesium batteries[J]. ZENG Jing; Wu Dongzheng; Zhuang Yichao; ZHAO Jinbao. Materials Engineering, 2021
2. Current situation and prospect of recycling of power lithium battery[J]. ZAN Wenyu; Ma North Vietnam; LIU Guoqiang. Rare Metals and Tungsten Carbide, 2020
3. Research progress of cathode materials for magnesium secondary batteries[J]. Li Yanyang; Xiong Yue; ZHANG Jianmin; CHEN Weihua. Materials Reports, 2015
4. Research progress of magnesium seawater battery and magnesium anode materials[J]. LIN Yaqing; Wang Wei; Sang Lin. Material Protection, 2015
5. Preparation and properties of magnesium alloy anode materials for seawater batteries[J]. JIA Wenbin; Fangwa; HUANG Ruini; SUN Kai. Power Technology, 2016