Magnesium Battery – High Performance Batteries With Unlimited Potential
- The concept of magnesium battery
- Magnesium battery cathode material
- Metal magnesium that can be deposited uniformly
- The right electrolyte is critical
- Rechargeable magnesium batteries have great potential
- Diversification of magnesium battery technology routes
- Magnesium-ion batteries have broad application space in the future
Magnesium battery is currently mainly focused on positive electrode materials and electrolytes. Cathode materials mainly include insertion-extraction type cathode materials, conversion type cathode materials, organic cathode materials, etc. Electrolytes mainly include liquid electrolytes and solid electrolytes.
Different cathode materials and electrolytes have their own characteristics and advantages. At present, the undetermined technical route of magnesium battery has become a major obstacle restricting the commercial application of magnesium battery.
The concept of magnesium battery
Magnesium battery is a new battery with great potential. Compared with lithium, magnesium is a more ideal metal anode.
- Magnesium metal has high energy density and low electrode potential, which is conducive to improving the energy density of the battery;
- Magnesium is abundant in the earth’s crust, and its price is much lower than that of lithium, which is conducive to reducing battery costs;
- Magnesium deposition is not easy to produce dendrites, so the safety of magnesium batteries is higher. Magnesium batteries are still in the primary research stage, and there is still a long way to go before commercialization.
Magnesium battery works similarly to lithium-ion batteries. When charging, magnesium ions are released from the positive electrode active material, and driven by the external voltage, they migrate to the negative electrode through the electrolyte.
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 be transferred from the wire of the external circuit to the negative electrode.
The result of charging is that the negative electrode is in a magnesium-rich state, and the positive electrode is in a high-energy state of a magnesium-poor state, and the opposite is true during discharge.
Magnesium battery cathode material
At present, the research on cathode materials for magnesium secondary batteries mainly focuses on transition metal sulfides, transition metal oxides, polyanionic compounds, sulfur and chalcogenides, organic compounds, and composite materials.
The current collector needs to have characteristics such as corrosion resistance and good stability, and will not chemically react with other substances. At present, the current collector commonly used in magnesium battery is stainless steel foil.
Cathode material is one of the key materials of magnesium battery, which directly affects the working voltage and charge-discharge specific battery capacity. An ideal cathode material for magnesium-ion batteries should meet the requirements of large capacity, high voltage platform, good reversibility, high cycle efficiency, safety and stability, abundant resources, and easy preparation.
The types of cathode materials involved in the current research mainly include intercalation-extraction cathode materials, conversion cathode materials, and organic cathode materials.
- Insertion-extraction cathode material
Generally speaking, intercalation-extraction materials, also known as intercalation materials, can maintain structural stability during cycling and can achieve stable cycling, and are the most widely studied cathode materials in magnesium battery. Due to their successful application in Li-ion battery systems, these intercalation compounds are also considered as potential candidate cathodes for Mg-ion battery systems.
- Conversion type cathode material
Compared with intercalation compounds, conversion-type cathode materials have been studied relatively late in Mg-ion batteries. Conversion-type cathode materials have higher theoretical capacity and energy density, which can reach several times that of intercalation materials. Such materials mainly include some transition metal sulfides and oxides.
- Organic cathode materials
Organic materials have attracted increasing attention due to their richness, diversity, structural flexibility, and tunability. Due to the weak intermolecular force in organic materials with redox activity, Mg2+ can achieve rapid diffusion. The development of organic cathode materials provides new opportunities for the development of magnesium ion cathode materials.
Metal magnesium that can be deposited uniformly
The requirement of the negative electrode material is that magnesium ions can be reversibly deposited and dissolved. According to the choice of electrolyte, it is generally metal magnesium or activated carbon/carbon cloth, and the corresponding electrolyte is usually ether electrolyte or magnesium perchlorate electrolyte. The uniform deposition behavior of metallic magnesium during cycling makes it a good anode material in itself.
The right electrolyte is critical
The electrolyte is the carrier of magnesium ion transport in rechargeable magnesium batteries, providing electrochemical performance through electron transfer or ion transfer. The voltage window of the electrolyte will affect the selection of cathode materials, and the electrolyte also has a significant impact on the electrochemical performance of the battery.
The electrolyte system of magnesium batteries is different from that of lithium-ion batteries. For lithium ion battery electrolyte, electrolyte solutions are usually prepared by dissolving simple salts with anions such as perchlorate (ClO4) and hexafluorophosphate (PF6) in carbonate/aprotic solvents from which lithium can be reversible deintercalation.
However, magnesium metal will form a passivation layer on the negative electrode surface in an aprotic solvent, which is unfavorable to the electrochemical migration and reversible deposition and dissolution of magnesium ions. Therefore, it is very important for the development of Mg-ion batteries to develop an electrolyte that can realize the reversible deposition of Mg without producing a passivation layer.
At present, electrolyte materials for magnesium battery can be divided into liquid electrolytes and solid electrolytes according to their phase states.
Liquid electrolyte is one of the most suitable electrolytes for current magnesium-ion battery systems. Compared with solid electrolytes, liquid electrolytes have higher ionic conductivity, better reversibility and cycle performance, are easier to prepare, and have lower viscosity.
The liquid electrolytes of magnesium-ion battery systems mainly include inorganic electrolytes, boron-based electrolytes, magnesium organohalogenaluminate-based electrolytes, phenate or alkoxide-based electrolytes, and non-nucleophilic electrolytes.
Solid electrolytes have the advantages of good safety performance, excellent mechanical properties, wide voltage window and high energy density. Electrolytes can be divided into inorganic solid electrolytes, organic solid electrolytes and organic-inorganic composite solid electrolytes according to their composition.
Currently, research on magnesium solid electrolytes is at a preliminary stage. The solid electrolytes used in magnesium solid-state batteries are basically divided into inorganic systems (phosphates, borohydrides, chalcogenides, metal-organic framework materials), organic polymer systems (addition of magnesium salts, and possible addition of inorganic fillers) and organic-inorganic composite solid-state electrolytes Wait.
Rechargeable magnesium batteries have great potential
Although the large-scale application of magnesium secondary batteries is still in the initial stage of exploration, it has important potential in improving the safety of secondary batteries, reducing the cost of secondary batteries, and alleviating the pollution of secondary batteries. Some fields replace lithium batteries or lead-acid batteries, such as power batteries, energy storage, and consumer electronics.
Diversification of magnesium battery technology routes
Magnesium battery technology routes are diversified. In addition to magnesium battery, currently researched batteries are divided into magnesium primary batteries, fuel cells and magnesium seawater batteries.
Magnesium primary battery
Due to the active nature of magnesium, magnesium is easily oxidized to magnesium oxide in the air, resulting in the formation of a passivation film on the surface of the magnesium electrode, which hinders the battery reaction and produces hysteresis, which cannot meet the high-rate discharge requirements.
At the same time, magnesium is also easy to react with water to generate hydrogen and heat, which promotes the shedding of the passivation film and causes the anode corrosion reaction to continue. Therefore, the storage capacity of the magnesium battery decreases after being discharged, which cannot meet the intermittent use.
Magnesium seawater battery
Magnesium seawater batteries have obvious advantages and unique principles. Magnesium seawater batteries generally refer to chemical power sources that work in marine environments and use seawater as an electrolyte, which is characterized by the fact that no additional electrolyte is required.
Magnesium seawater batteries have obvious advantages. Different types of batteries have different structures and principles, but some or all of them use seawater as the electrolyte, so there is no need to carry electrolytes, which simplifies the battery structure, reduces the mass, and increases the unit energy density.
At the same time, the polarization of the reactant to the electrode is eliminated to a certain extent, so that the discharge performance of the electrode is stable and the efficiency of the electrode is improved. The above characteristics make magnesium seawater batteries play an important role in marine exploration, resource utilization, military defense and other fields.
Magnesium-air batteries are also called magnesium metal fuel cells. Magnesium or magnesium alloys are used as the negative electrode, air is used as the positive electrode, and the electrolyte is generally an inorganic salt solution. Traditional fuel cells use hydrogen or hydrocarbons as fuel.
Magnesium-air batteries are a new type of fuel cells that use metal as fuel and rationally utilize oxygen in the air. They are safe, reliable, low in cost, pollution-free, stable in discharge, and relatively High energy advantages. Magnesium-air battery is known as the new energy source with the most development and application prospects in the future.
Magnesium-ion batteries have broad application space in the future
In the current situation where the proportion of new energy power generation has increased significantly, the problem of the consumption of renewable energy has become prominent, and the coordinated development of energy storage is required. The focus of energy storage on the power generation side and the grid side is mainly on economy, safety and lifespan.
The characteristics of magnesium battery are highly compatible with the requirements of energy storage scenarios, and the future development space in the field of energy storage will continue to expand with technological progress. It is estimated that the potential market size of the world’s energy storage is expected to exceed 250GWh by 2025.
Magnesium battery has the advantages of high energy density and low cost. After the technology matures, they can partially replace lithium batteries in the field of new energy electric vehicles. With the rapid growth of the penetration rate of new energy vehicles, the healthy development of the industrial chain, China’s power battery market will continue to grow.
It is estimated that the installed capacity of power batteries will reach 229.9GWh in 2022. Magnesium battery have the advantages of high energy density and low cost. After the technology matures, they can partially replace lithium batteries in the field of new energy electric vehicle power batteries.
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Magnesium battery have stable high-power output capabilities and good cycle times. Features, cost-effective potential, and a wide range of work, can adapt to cold weather and long-term work, and has good penetration potential in this field.