Research and application analysis of magnesium secondary 18650 li ion rechargeable battery materials

Energy is an important foundation for human survival and development. In order to save energy, power electrification is an inevitable trend. As a chemical power source for alternative energy to vehicle fuel, it has both good development opportunities and huge challenges.

People began to notice that magnesium is in a diagonal position with lithium on the periodic table. The two have similar physical and chemical properties. Magnesium is rich in reserves, low in price, low in electrode potential, high in energy density, safe and pollution-free, and is more convenient to process than lithium. It is considered to be another promising 18650 li ion rechargeable battery negative electrode material.

Magnesium secondary 18650 li ion rechargeable battery is a new type of secondary 18650 li ion rechargeable battery with great potential in the field of energy science in recent years. In addition, magnesium is low in price, pollution-free to the environment, and easy to operate. Magnesium secondary 18650 li ion rechargeable battery is considered to be a green rechargeable 18650 li ion rechargeable battery that is expected to be used in large-scale equipment. The author of this article, Zhang Wenyu, mainly introduces the advantages of magnesium as a 18650 li ion rechargeable battery material, as well as the current status and application of magnesium secondary batteries, including as electrolyte solution, positive electrode material and negative electrode material.

Current status of research on magnesium secondary 18650 li ion rechargeable battery materials

Magnesium secondary 18650 li ion rechargeable battery is a new type of rechargeable 18650 li ion rechargeable battery with great potential developed in recent years. The working principle of magnesium secondary 18650 li ion rechargeable battery is the same as that of lithium ion secondary 18650 li ion rechargeable battery. The core of magnesium secondary 18650 li ion rechargeable battery is Mg anode, electrolyte solution and positive electrode material that can embed Mg2+. Magnesium secondary 18650 li ion rechargeable battery uses Mg as negative electrode, requiring Mg/Mg2+ to be deposited/dissolved reversibly electrochemically. Since Mg is more active, it is only suitable for this reaction in organic non-protonic polar solvents.

Due to its safety and price factors, magnesium secondary 18650 li ion rechargeable battery has potential advantages in large-load applications. Therefore, it is considered to be a new type of green 18650 li ion rechargeable battery that is expected to be suitable for electric vehicles. At the same time, it is also a new 18650 li ion rechargeable battery proposed after the primary 18650 li ion rechargeable battery based on the principle of lithium ion 18650 li ion rechargeable battery. It is called a new type of rechargeable 18650 li ion rechargeable battery with good development prospects.

In 2000, Aurbach et al. developed a relatively complete magnesium secondary 18650 li ion rechargeable battery system, which made a breakthrough in the research of magnesium secondary 18650 li ion rechargeable battery. At present, the research focus of magnesium secondary 18650 li ion rechargeable battery is on finding a suitable electrolyte system and a positive electrode material that can be reversibly deintercalated, while there are relatively few reports on the research of negative electrode materials, and generally magnesium metal is used as the negative electrode. Similar to lithium batteries, magnesium metal as a negative electrode material may have the following problems: in the long-term cycle process, magnesium dendrites are easily formed on the electrode surface, resulting in poor 18650 li ion rechargeable battery performance and even short circuit.

Since the research on magnesium batteries is still in its infancy, the research on the synthesis of electrode materials and electrolyte materials and their electrochemical properties is not perfect. Magnesium secondary batteries have the advantages of being cheap, safe, and environmentally friendly. Compared with lead-acid and nickel-cadmium batteries, they can provide high energy density. However, the development of magnesium secondary batteries has been hindered by two aspects: on the one hand, due to the electrochemical activity of magnesium, magnesium will form a surface passivation film in most solutions. It is difficult for divalent magnesium ions to pass through this passivation layer, making it difficult for magnesium to dissolve and deposit, thereby limiting its electrochemical activity; on the other hand, divalent magnesium ions have a large charge density and strong solvation, making it difficult to insert into many matrices.

At present, people's research on magnesium secondary batteries is still in its infancy. There are relatively few positive electrode embedding materials developed, and most of them have poor cycle performance. In terms of electrolytes, there is still the problem of how to improve conductivity and stability. Therefore, finding a suitable electrolyte electrolyte system and positive electrode material is the key to the research of magnesium secondary batteries.

Magnesium positive electrode material

The ideal positive electrode material for secondary magnesium batteries has high specific energy, high electrode potential, good reversibility of charge and discharge reactions, high electronic conductivity, abundant resources, low price, good chemical stability in electrolyte and low solubility (low self-discharge). For secondary magnesium batteries, the positive electrode embeddable materials are mostly inorganic transition metal compounds, mainly oxides, sulfides, borides, polyanion compounds and sulfur-containing conductive materials.

Magnesium is mainly embedded and de-embedded in positive electrode materials. At present, the main research direction of positive electrode materials is to find materials that can reversibly insert and de-embed magnesium ions and can stably exist in electrolytes. The selection of positive electrode materials is generally concentrated on inorganic transition metal oxides, sulfides, borides, phosphates and other compounds.

Gregory et al., who first assembled and studied the secondary magnesium 18650 li ion rechargeable battery, used Co3O4 as the positive electrode material and found that most oxides and sulfides cannot be used in magnesium secondary batteries, and only Co3O4, Mn2O3, RuO2, ZrS2, etc. may be used in magnesium secondary batteries.

In 2008, Nuliyanna's research group used the sol-gel method to synthesize the Mg1.03Mn0.97SiO4 positive electrode material. Due to its poor conductivity, the material showed a relatively low reversible specific capacity in 0.25mol/LMg (AlCl2EtBu) 2/THF solution. After using the modified sol-gel and carbon coating method, a discharge specific capacity of up to 224mAh/g was obtained. The high discharge specific capacity and good cycle performance make this material a promising positive electrode material for magnesium secondary batteries.

Compared with the widely used lithium-ion batteries, the research on magnesium secondary batteries is still relatively limited. There are two main factors that hinder the development of magnesium secondary batteries. First, the limitation of positive electrode materials. Mg2+ has a large charge density and is more easily solvated than Li+, so it is more difficult to embed Mg2+ and move in the positive electrode material. Second, the electrolyte limitation. In most electrolytes, magnesium forms a dense passivation film on the surface, which prevents Mg2+ from passing through. Therefore, finding a positive electrode material suitable for magnesium embedding and moving in it and an electrolyte that can reversibly deposit and dissolve magnesium is the key to the research.

Magnesium negative electrode material

During the operation of magnesium batteries, magnesium ions are reversibly deposited and dissolved on the surface of negative electrode materials. Magnesium easily forms a relatively dense passivation film on the surface, which makes it difficult for magnesium ions to pass through, affecting the dissolution/deposition of magnesium. In addition, after multiple cycles, magnesium dendrites are easily formed on the surface of magnesium, which deteriorates the 18650 li ion rechargeable battery performance and even causes the 18650 li ion rechargeable battery to short-circuit.

The negative electrode material of magnesium secondary batteries requires that magnesium ions can be reversibly deposited and dissolved. At present, the research on magnesium secondary batteries focuses on positive electrode materials and electrolytes, and pure magnesium is generally used as the negative electrode material. There are relatively few reports on other negative electrode materials. Negative electrode passivation, dendrites and other problems affect the performance of the 18650 li ion rechargeable battery to a certain extent. Therefore, on the basis of certain improvement in the performance of the positive electrode material and the electrolyte, researching and developing new negative electrode materials is an important way to obtain a stable and high-performance magnesium secondary 18650 li ion rechargeable battery system.

At present, the negative electrode materials mainly include metal magnesium, magnesium alloys, organic polymers and inorganic embedded materials (laminated graphite, acetylene black, microbead carbon, petroleum coke, carbon fiber and other embedded materials).

The negative electrode material of magnesium secondary 18650 li ion rechargeable battery requires that magnesium ions can be reversibly deposited and dissolved, and its deposition-dissolution electrode potential is low. Because Mg is relatively active, it is easy to react with water and atmospheric impurities, and a passivation film will be formed on the surface. This covering layer of lithium is loose and easy for lithium ions to pass through, and it is conducive to the stability of lithium metal. However, the passivation layer of magnesium is dense, and magnesium ions are not easy to pass through, making the reversible dissolution and precipitation of magnesium in the electrolyte difficult. At present, the research on magnesium secondary batteries focuses on positive electrode materials and electrolytes. Pure magnesium is generally used as the negative electrode material, and there are relatively few research reports on other negative electrode materials.

Application of magnesium secondary 18650 li ion rechargeable battery materials

Currently, Aurbach et al. have assembled an experimental "button" rechargeable magnesium 18650 li ion rechargeable battery with a cathode capacity of up to 100mA/g. At a discharge rate of 0.1-1mA/cm2, a discharge depth of 100%, and a temperature range of -20-80°C, the cathode capacity decay is less than 15% over more than 2000 charge and discharge cycles. It should also be noted that magnesium batteries are not designed to compete with lithium batteries for small-scale applications (such as portable electronic devices) in terms of energy density, but are used in large-load applications that lithium batteries (due to their safety issues and relatively high prices) cannot replace.

With the increasing demand for environmentally friendly, low-cost large-load energy in modern society, the long-term cycle stability of rechargeable "green" magnesium batteries shows its unique advantages compared to lead-acid and nickel-cadmium batteries with adverse environmental impacts. The utilization rate of active materials in magnesium batteries is very high, with the cathode being greater than 90% and the anode being close to 100%. The proportion of passive additives in the cathode is also very low (less than 5%), and the amount of electrolyte solution is very small and does not participate in the 18650 li ion rechargeable battery reaction. It can be expected that by adopting good process technology, rechargeable Mg/MgxMo3S4 batteries with large size and energy density greater than 60Wh/kg can be obtained.

The characteristics of high performance, low cost and non-toxicity make magnesium secondary batteries have excellent application prospects and development space. At present, magnesium secondary batteries are theoretically and technically feasible, but their research and development work is not satisfactory, and many studies still need major breakthroughs. The research results of lithium-ion batteries provide reference and basis for the research of magnesium secondary batteries, but magnesium secondary batteries also need to find another way.

It is theoretically and technically feasible to assemble magnesium secondary batteries. This type of 18650 li ion rechargeable battery has many advantages, especially the hope of being used in electric vehicles, which is irreplaceable by all existing batteries. However, there are few international studies at present, and research work in this area has not yet been carried out in my country. The main problem at present is that the only electrolytes that can be used for reversible electrodeposition of Mg/Mg2+ are Green salts and their derivatives that require an anhydrous environment, while Mg also requires an anhydrous condition, and the solvent used is also easy to absorb water. This brings great difficulties to research and development. Future research should focus on finding superior electrolytes and synthesizing better "embedded" cathode materials, such as improving Mo3S4 and finding oxide cathode materials. Study the negative and positive electrode processes from the microscopic and macroscopic perspectives, and finally assemble practical batteries.

Magnesium batteries meet people's needs for the development of high-performance, low-cost, safe and environmentally friendly large-scale rechargeable batteries. At present, the research on magnesium secondary batteries is still in its initial stage and is still some distance away from practical application. With the continuous deepening of research on magnesium secondary batteries, magnesium secondary batteries may become a new energy source for large-scale equipment.

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