Literature | A Comprehensive View of Science PopularizationEditor | Science Popularization OverviewintroductionWith the continuous growth of energy demand in human society, traditional fossil fuels are no longer able to meet people's needs, so the research and application of new energy technologies have become increasingly important. During this process, batteries, as an energy storage device, have received widespread attention and research

Literature | A Comprehensive View of Science Popularization

Editor | Science Popularization Overview

introduction

With the continuous growth of energy demand in human society, traditional fossil fuels are no longer able to meet people's needs, so the research and application of new energy technologies have become increasingly important. During this process, batteries, as an energy storage device, have received widespread attention and research.

In recent years, magnesium ion batteries have gradually become a research hotspot. Today I will take you allExplore the advantages of magnesium batteries in various aspects, thereby proving why magnesium batteries are the breakthrough direction for the next generation of high-performance batteries.

1 Magnesium ions carry more charge and have a higher energy density

The divalent nature of magnesium ions allows them to carry and store more charges, which means they have higher volume 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 hydrogen batteries, and lithium-ion batteries. And its volume to capacity ratio is as high as 3833mAh/cm-3,This means that magnesium ion batteries can store more electricity in the same volume.

2 No dendrites generated, better safety performance

With the popularization 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 issues in the use of lithium-ion batteries, among which dendrite growth is one of the most fundamental issues.

Dendritic growth can lead to internal short circuits in batteries, causing uncontrolled heating, and even causing hazards such as fire and explosion.Therefore, how to effectively control the dendritic growth of lithium-ion batteries has become one of the hotspots in lithium-ion battery technology research.

The dendritic growth of lithium-ion batteries is mainly due to the formation of dendritic metallic lithium during the charging process when lithium ions are reduced.These lithium dendrites will rapidly grow on the electrode surface, disrupting the stable interface between the electrode and electrolyte, and leading to internal instability in the battery, increasing the risk of battery accidents.

Unlike lithium-ion batteries, magnesium ion batteries do not exhibit magnesium dendrites on the negative electrode surface during the charging and discharging process. This is because the deposition performance of magnesium ions is better than that of lithium ions,Therefore, there will be no phenomenon similar to the dendritic growth in lithium batteries that punctures the separator and causes battery short circuits, fires, explosions, etc.

3 China has abundant magnesium resources and strong autonomy and controllability

Lithium and magnesium are two important metal elements that have wide applications in the energy field, especially in lithium-ion and magnesium batteries. As a new generation of energy storage, lithium battery and magnesium battery have the advantages of high efficiency, environmental protection and long life,It is an indispensable energy source in the field of new energy vehicles and energy storage.

However, the natural reserves of lithium resources are relatively low, and China's domestic supply capacity is limited. With the large-scale application of energy storage equipment and new energy vehicles,The problems of low reserves and high costs of lithium resources are gradually emerging.

According to statistics, the lithium reserves in the crust are only 0.0065%, and China's lithium resource reserves are only 7% of the global level. Most lithium mines rely on imports, and the existing lithium resource supply system has a high degree of external dependence, which poses a constraint on the development of new energy vehicles and energy storage in China.

In contrast, China has abundant magnesium resources. China is one of the countries with the most abundant magnesium resources in the world, with a wide range of magnesium ore types and distribution.

At the same time, China is the world's largest producer of primary magnesium, accounting for over 80% of global production.This means that once magnesium batteries are industrialized in the future,China's dependence on overseas lithium resources in the field of new energy will significantly decrease, while battery manufacturing costs will be significantly reduced.

4 The working principle of magnesium batteries

Magnesium secondary battery is a new type of rechargeable battery with good development prospects, which is proposed based on the principle of lithium-ion batteries.In rechargeable magnesium batteries, magnesium ions are removed from the positive electrode active material and migrate through the electrolyte to the negative electrode under the driving force of external voltage. At the same time, magnesium ions are embedded in the negative electrode active material. Due to charge balance, an equal amount of electrons are required to flow from the positive electrode to the negative electrode in the wires of the external circuit.

The result of charging is that the negative electrode is in a magnesium rich state, while the positive electrode is in a high energy state of magnesium poor state. During discharge, the opposite is true. The flow of electrons in the external circuit forms a current, achieving the conversion of chemical energy to electrical energy.

The research focus of magnesium secondary batteries is on electrolytes and positive electrode 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 positive electrode materials, it is necessary to search for materials with high electrochemical activity and stability.

The positive electrode material is one of the key materials for magnesium ion batteries, which directly affects the working voltage and charge discharge specific capacity of the battery.The ideal positive electrode material for magnesium ion batteries should meet the requirements of large capacity, high voltage platform, good reversibility, high cycling efficiency, safety and stability, abundant resources, and easy preparation.

At present, research on positive electrode materials for magnesium secondary batteries mainly focuses on transition metal sulfides, transition metal oxides, polyanionic compounds, sulfur and sulfur compounds, organic compounds, and composite materials. Among them,The insertion and detachment type positive electrode material is the most commonly used type of 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 positive electrode material, achieving electrochemical reactions. Transition metal sulfides, oxides, and sulfur and sulfur compounds all belong to this category of materials.Compared with the embedded and stripped materials in lithium ion batteries, the materials in magnesium ion batteries have larger ionic radius and stronger ion polarization effect, and need higher reactivity to meet the needs of batteries.

Another common type of positive electrode material is conversion type material.The principle of this type of material is that during the charging and discharging process, the positive electrode material undergoes chemical changes, transforming from one compound to another. The advantage of conversion materials lies in their high theoretical specific capacity and high working voltage, but their complex reaction mechanism leads to a shorter cycle life. At present, transition metal oxides are the main representative of conversion type positive electrode materials.

5 Homogeneous deposition of metallic magnesium is an ideal negative electrode material

Developing magnesium ion batteries faces some challenges, one of which is to find suitable negative electrode materials. The negative electrode material needs to have the ability of reversible deposition and dissolution, which is necessary for the normal operation of magnesium ion batteriesAt present, researchers mainly focus on two types of negative electrode materials: metal magnesium and alloy based plug-in negative electrode materials.Magnesium metal is an excellent negative electrode material because it can be uniformly deposited on the surface of the negative electrode.

However,The polar organic compounds or aqueous electrolytes in traditional electrolytes can form a passivation film on the negative electrode surface, preventing magnesium ions from effectively contacting the negative electrode material, thereby affecting battery performance.To address this issue, researchers have started using nanostructured magnesium or alloy based plug-in negative electrode materials.

Nanostructured magnesium negative electrode materials can effectively reduce the thickness of the passivation film.For example, magnesium negative electrodes with a diameter of 2.5nm exhibit good performance in magnesium oxygen battery systems. In addition, alloy based plug-in negative electrode materials have also attracted the attention of researchers. This material includes alloy negative electrode materials such as bismuth, antimony, and tin.

The Mg3Bi2 nanoclusters as negative electrodes can achieve electrochemical performance of 360mAhg-1 in LiCl-APC electrolyte, and maintain relatively stable performance even after 200 cycles.During the insertion and removal process of magnesium, Bi nanotubes evolved into interconnected nanopores, exhibiting excellent cycling stability and rate performance.

Magnesium ion batteries are a battery technology with great potential, but there are still many challenges. Finding suitable negative electrode materials is one of them.Nanostructured magnesium or alloy based plug-in negative electrode materials are expected to solve the problem of traditional electrolyte passivation films 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.

6 A suitable electrolyte is crucial as a bridge connecting the anode and cathode

Electrolytes play an important role in the transport of magnesium ions in rechargeable magnesium batteries.Electrolytes should be able to transfer ions between electrodes while also limiting charge transfer within the electrolyte. Therefore, an ideal electrolyte should have high ion transport efficiency and high ion selectivity, allowing only specific ions to pass through.

At present, the electrolytes of rechargeable magnesium batteries are mainly divided into two types: liquid electrolyte and solid electrolyte.The liquid electrolyte mainly consists 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.

The magnesium perchlorate electrolyte is composed of a mixture of high concentration of Mg (ClO4) 2 and organic solvents such as ethylene glycol dimethyl ether.Liquid electrolytes have relatively high ion transfer efficiency and good electrochemical performance, but they have disadvantages such as poor heat resistance, volatility, and poor safety.

In contrast, solid-state electrolytes have better stability and safety.Solid electrolytes are generally composed of a mixture of porous materials and magnesium salts, which can provide stable ion transport channels and effectively suppress the formation of passivation layers on the electrode surface.

Currently, solid-state electrolytes are mainly prepared from materials such as magnesium oxide, alumina, and magnesium sulfide. Among them, magnesium oxide electrolyte has high ion transfer efficiency and high ion selectivity, as well as good mechanical and thermal stability, making it an electrolyte material with broad application prospects.

conclusion

Although the application of magnesium secondary batteries is still in the early exploration stage, it has great potential in improving the energy density of secondary batteries, extending their lifespan, reducing the cost of secondary batteries, and reducing environmental pollution.

Compared to lithium-ion batteries and lead-acid batteries, magnesium batteries have higher specific energy and capacity,A higher operating voltage window and richer resources are expected to become an important alternative in the fields of power batteries, energy storage, and consumer electronics.

In fact, the EU has invested over 6.5 million euros in the magnesium battery project (E-MAGIC) under its "Outlook 2020" scientific research plan, in order to replace lithium-ion batteries.

At present, the technology route of magnesium batteries is diversified, in addition to magnesium ion batteries, there are also magnesium primary batteries, magnesium fuel cells, and magnesium seawater batteries.Among them, magnesium ion batteries are 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, thus having broad application prospects in fields such as power batteries and energy storage batteries.

Magnesium secondary batteries and magnesium fuel cells are mainly used in fields such as disposable consumer goods and mobile devices,These batteries can provide higher energy density and longer service life.Magnesium seawater batteries are a technology route with great potential,It can extract magnesium ions from seawater for energy supply, with extremely high energy storage density and environmental friendliness.

Author's viewpoint

The diversification and widespread 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.

reference:

1. Research progress on performance improvement strategies for magnesium battery cathode materials [J]. Zeng Jing; Wu Dongzheng; Zhuang Yichao; Zhao Jinbao. Materials Engineering, 2021

2. Current Status and Prospects of Power Lithium Battery Recycling and Utilization [J]. Zan Wenyu; Ma Beiyue; Liu Guoqiang. Rare Metals and Hard Alloys, 2020

3. Research progress in cathode materials for magnesium secondary batteries [J]. Li Yanyang; Xiong Yue; Zhang Jianmin; Chen Weihua. Material Introduction, 2015

4. Research progress in magnesium seawater batteries and magnesium anode materials [J]. Lin Yaqing; Wang Wei; Sanglin. Material Protection, 2015

5. Preparation and Performance Study of Magnesium Alloy Anode Materials for Seawater Batteries [J]. Jia Wenbin; Fang Wa; Huang Ruini; Sun Kai. Power Technology, 2016

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