Research status and development trend of aluminum air battery -Lithium - Ion Battery Equipment
The theoretical specific energy of aluminum air fuel cell can reach 8100Wh/kg, which has the advantages of low cost, high specific energy density and specific power density. As a special fuel cell, aluminum air battery has great commercial potential in special, civil, underwater power system, backup power source of telecommunication system, portable power supply and other applications.
Overview of metal air battery
Lithium ion battery has a high specific energy, which is a secondary battery with mature research and large-scale commercial use. However, in recent years, facing the huge development of mobile electronic equipment and electric vehicles and other fields, lithium ion battery has been difficult to meet its demand for large capacity, especially the power battery system with strong dependence on energy. Therefore, metal air batteries, which are several times larger than the specific capacity of lithium ion batteries, have emerged as the times require, such as zinc air batteries, aluminum air batteries, magnesium air batteries, lithium air batteries, etc.(Lithium - Ion Battery Equipment)
Since the positive active substance of this type of battery mainly comes from oxygen in the air, the theoretical amount of positive active substance is infinite, so the theoretical capacity of the battery mainly depends on the amount of negative metal, and this type of battery has a larger specific capacity.
Among them, the theoretical specific energy of aluminum air fuel cell can reach 8100Wh/kg, which has the advantages of low cost, high specific energy density and specific power density. As a special fuel cell, aluminum air battery has great commercial potential in special, civil, underwater power system, backup power source of telecommunication system, portable power supply and other applications.
Structure and principle of aluminum air battery
According to the existing research results and battery characteristics, aluminum air battery has the following characteristics:
(1) High specific energy. The aluminum air battery is a new type of battery with high specific energy. The theoretical specific energy can reach 8100Wh/kg. The currently developed products can reach 300-400Wh/kg, which is much higher than the specific energy of various types of batteries today.
(2) Medium specific power. As the working potential of the air electrode is far away from its thermodynamic equilibrium potential, its exchange current density is very small, and the polarization of the battery is very large when discharging, resulting in the specific power of the battery only reaching 50-200W/kg.
(3) Long service life. The aluminum electrode can be replaced continuously, so the life of aluminum air battery depends on the working life of the air electrode.
(4) It is non-toxic and free of harmful gas. The electrochemical reaction of the battery consumes aluminum, oxygen and water to produce Al2O3 ˙ NH2O can be used for drying adsorbent and catalyst carrier, grinding and polishing abrasives, ceramics and excellent precipitators for sewage treatment.
(5) Strong adaptability. The battery structure and raw materials used can be changed according to the practical environment and requirements, with strong adaptability.
(6) Aluminum is cheap and easy to get. Compared with other metals, the price of metal aluminum is relatively low, and the manufacturing process of metal anode is relatively simple.
Aluminum anode (negative pole)
Aluminum (Al) is an ideal electrode material. The theoretical energy density of metal aluminum is 8.2W ˙ H/g, second only to 13.3W of lithium in common metals ˙ H/g, the electrode potential is relatively negative, which is the light metal battery material with the highest mass specific energy except lithium metal. The mass specific energy of aluminum air battery can actually reach 450Wh/kg, and the specific power can reach 50~200W/kg. It has the advantages of high theoretical capacity, low consumption rate, light weight, negative potential, rich resources and easy processing, and has been widely studied.
However, because aluminum is a very active amphoteric metal, the development of aluminum anode is still affected by the following problems.
(1) There is a passivation film on the surface of aluminum, which affects the electrochemical activity of aluminum.
(2) Aluminum is an amphoteric metal element, which determines that it is prone to hydrogen evolution corrosion in strong alkaline environment, affecting electrode potential, and the product floats in the electrolyte to affect the entire electrochemical reaction.
(3) The unique semi open system of the air battery makes the air electrode vulnerable to the influence of external humidity, resulting in "flooding" or "drying" of the aluminum anode, or even "alkali climbing" or "liquid leakage", which will damage the entire air battery structure. In order to solve the above problems, domestic and foreign scholars have studied from the following three aspects:
1. Aluminum anodic alloying
Industrial grade aluminum (99.0%) contains many impurities, such as iron (0.5%), silicon, copper, manganese, magnesium and zinc, which will aggravate the hydrogen evolution corrosion of aluminum at the phase interface. In particular, iron will form a local galvanic cell with aluminum, causing the electrochemical corrosion to multiply. Alloy components that can improve both chemical activity and corrosion resistance can be added to aluminum.
The elements to be added for aluminum alloy alloying shall meet the following conditions: ① the melting point of alloy elements shall be lower than that of metal Al; ② The solid saturation is higher in Al; ③ The electrochemical activity was higher than that of Al; ④ High solubility in electrolyte; ⑤ It has high hydrogen evolution overpotential. In addition, the anode efficiency can be further improved by processing the anode metal into ultra-fine grain materials.
2. Slow release agent added to electrolyte
Because of the cost of anodic alloying, people often choose to add some slow release agents in the electrolyte to ensure the performance of aluminum air battery. Some carboxylic acid, amine and amino acid slow-release agents and their inhibition efficiency on aluminum corrosion are shown in Table 1:
The researchers used natural substances as inhibitors of aluminum corrosion, and the experiments proved that organic amines, pyrrole, etc. have obvious inhibitory effects on aluminum corrosion. The electrochemical behavior of aluminum metal anode was studied by adding organic substances and water-soluble compounds to the strong alkaline electrolyte to reduce the corrosion rate of aluminum, thereby improving the performance of aluminum air battery.
3. Heat treatment process
Heat treatment affects the properties of aluminum alloy by changing the distribution of trace elements in aluminum alloy and the microstructure of the alloy surface, which belongs to the research field of technology. The best heat treatment process can be found through suitable orthogonal experiments.
electrolyte
The electrolyte of aluminum air battery is mostly neutral salt solution or strong alkaline solution. When the neutral electrolyte is used, the self corrosion of the anode is small, but the surface of the aluminum anode is seriously passivated, which reduces the working voltage, makes it difficult to increase the power and current of the battery, and also causes the voltage lag, and the product aluminum hydroxide colloid will also settle and block the electrolyte, so this type of battery can only be used as a small power output device.
When strong alkaline electrolyte is used, the passivation of aluminum is reduced, and the alkaline solution can absorb a certain amount of reaction product aluminum hydroxide. The performance of the battery is relatively good, but aluminum is an amphoteric metal. In a strong alkaline environment, strong hydrogen evolution corrosion will occur, releasing a lot of hydrogen, reducing the output power of the battery and the utilization rate of the anode, especially under high current density. To solve the above problems simply, we can choose to replace the electrolyte regularly and add additives that can activate the aluminum anode surface and inhibit aluminum hydrogen evolution corrosion to the electrolyte to solve the appeal problem.
Air electrode (positive pole)
The cathode is the reaction site of O2, which is breathable, conductive, waterproof, anti-corrosion and catalytic. It is also often called the air electrode. The air electrode generally consists of a porous catalytic layer, a conductive collector and a waterproof and breathable layer. The porous catalytic layer is the main place where oxygen is reduced, where the oxygen diffused into, the oxygen reduction catalyst and the thin layer electrolyte form a three-phase interface electrochemical active site; The conductive collector mainly plays the role of conducting electricity and mechanical support; The waterproof and breathable layer has a loose porous hydrophobic structure, which not only provides the catalytic layer with the gas required for reaction, but also prevents the electrolyte from flooding the gas diffusion channel.
The catalytic layer is the most critical part of the air electrode and plays a decisive role in its electrochemical performance. The performance of aluminum air battery largely depends on the cathode catalyst selected. The performance of air electrode can directly affect the electrode reaction balance. Therefore, improving its performance can improve the utilization rate of aluminum air battery anode to a certain extent and inhibit the self corrosion of aluminum anode.
The commonly used catalysts of aluminum air battery are as follows:
(1) Precious metal catalyst. Platinum and silver are commonly used, with high catalytic activity and stable performance. However, due to the high price and shortage of resources, the adoption rate is not high.
(2) Metal macrocyclic compound catalyst. Organometallic macrocyclic compounds have good catalytic activity for oxygen reduction, especially when they are adsorbed on carbon with large surface area. Their activity and stability can be significantly improved by heat treatment. Therefore, it is expected to replace noble metal oxygen reduction catalyst. The common synthesis methods of metal macrocyclic compounds include thermal decomposition and precursor preparation. However, due to the heat treatment process of thermal decomposition method will lead to the reaction between metal macrocyclic compounds and carbon matrix, and the catalyst prepared by precursor method has poor activity, so there are some problems in its application.
(3) Perovskite type oxide catalyst. Perovskite type oxides have high catalytic activity for the reduction and precipitation of oxygen and are cheap, so they have broad application prospects in aluminum air cells and fuel cells. The current research on perovskite oxygen electrode catalysts mainly focuses on improving the preparation methods and searching for new replacement elements to improve the catalytic performance. Amorphous precursor method, especially malic acid precursor method, can prepare perovskite oxides with fine grains and large specific surface area, thus greatly improving their catalytic activity. It is a better method to prepare perovskite oxides at present.
(4) Cheap catalyst. The most important representative is the manganese dioxide catalyst. Its greatest advantage is that it has rich raw materials and low cost, and can be widely used in batteries with aqueous or non-aqueous electrolytes. However, the single manganese dioxide electrocatalytic activity has certain limitations, so people never stop researching in this area.
(5) AB2O4 spinel oxide catalyst. The crystal lattice of spinel is face centered cubic. There are 32 close packed 02 ions in the unit cell, 64 tetrahedral voids and 32 octahedral voids are occupied by metal ions. The dehydration activity of spinel is related to the fraction of B ions in the tetrahedral space. The higher the fraction, the more acidic the catalyst surface and the more dehydration activity. Generally, aluminum air batteries do not use this catalyst.
(6) Other metal and alloy catalysts. Nickel is relatively cheap, and has high corrosion resistance under anodic polarization conditions in alkaline electrolyte. At the same time, nickel has the highest oxygen evolution efficiency among metal elements. Therefore, nickel is traditionally used as the anode material in alkaline water electrolysis. Nickel iron, nickel cobalt and other alloy catalysts are also often used, which have good catalytic activity and corrosion resistance, and are also a possible catalyst direction for aluminum air battery.
(7) Composite catalyst. The catalytic activity of the air electrode of aluminum air battery can be better improved by combining two or more catalysts.
Application prospect of aluminum air battery
At present, aluminum air battery has not been widely used in industrial and civil fields, mainly because the material preparation technology needs to be improved and the understanding of its concept of secondary charge and discharge.
Overview of metal air battery
Lithium ion battery has a high specific energy, which is a secondary battery with mature research and large-scale commercial use. However, in recent years, facing the huge development of mobile electronic equipment and electric vehicles and other fields, lithium ion battery has been difficult to meet its demand for large capacity, especially the power battery system with strong dependence on energy. Therefore, metal air batteries, which are several times larger than the specific capacity of lithium ion batteries, have emerged as the times require, such as zinc air batteries, aluminum air batteries, magnesium air batteries, lithium air batteries, etc.(Lithium - Ion Battery Equipment)
Since the positive active substance of this type of battery mainly comes from oxygen in the air, the theoretical amount of positive active substance is infinite, so the theoretical capacity of the battery mainly depends on the amount of negative metal, and this type of battery has a larger specific capacity.
Among them, the theoretical specific energy of aluminum air fuel cell can reach 8100Wh/kg, which has the advantages of low cost, high specific energy density and specific power density. As a special fuel cell, aluminum air battery has great commercial potential in special, civil, underwater power system, backup power source of telecommunication system, portable power supply and other applications.
Structure and principle of aluminum air battery
According to the existing research results and battery characteristics, aluminum air battery has the following characteristics:
(1) High specific energy. The aluminum air battery is a new type of battery with high specific energy. The theoretical specific energy can reach 8100Wh/kg. The currently developed products can reach 300-400Wh/kg, which is much higher than the specific energy of various types of batteries today.
(2) Medium specific power. As the working potential of the air electrode is far away from its thermodynamic equilibrium potential, its exchange current density is very small, and the polarization of the battery is very large when discharging, resulting in the specific power of the battery only reaching 50-200W/kg.
(3) Long service life. The aluminum electrode can be replaced continuously, so the life of aluminum air battery depends on the working life of the air electrode.
(4) It is non-toxic and free of harmful gas. The electrochemical reaction of the battery consumes aluminum, oxygen and water to produce Al2O3 ˙ NH2O can be used for drying adsorbent and catalyst carrier, grinding and polishing abrasives, ceramics and excellent precipitators for sewage treatment.
(5) Strong adaptability. The battery structure and raw materials used can be changed according to the practical environment and requirements, with strong adaptability.
(6) Aluminum is cheap and easy to get. Compared with other metals, the price of metal aluminum is relatively low, and the manufacturing process of metal anode is relatively simple.
Aluminum anode (negative pole)
Aluminum (Al) is an ideal electrode material. The theoretical energy density of metal aluminum is 8.2W ˙ H/g, second only to 13.3W of lithium in common metals ˙ H/g, the electrode potential is relatively negative, which is the light metal battery material with the highest mass specific energy except lithium metal. The mass specific energy of aluminum air battery can actually reach 450Wh/kg, and the specific power can reach 50~200W/kg. It has the advantages of high theoretical capacity, low consumption rate, light weight, negative potential, rich resources and easy processing, and has been widely studied.
However, because aluminum is a very active amphoteric metal, the development of aluminum anode is still affected by the following problems.
(1) There is a passivation film on the surface of aluminum, which affects the electrochemical activity of aluminum.
(2) Aluminum is an amphoteric metal element, which determines that it is prone to hydrogen evolution corrosion in strong alkaline environment, affecting electrode potential, and the product floats in the electrolyte to affect the entire electrochemical reaction.
(3) The unique semi open system of the air battery makes the air electrode vulnerable to the influence of external humidity, resulting in "flooding" or "drying" of the aluminum anode, or even "alkali climbing" or "liquid leakage", which will damage the entire air battery structure. In order to solve the above problems, domestic and foreign scholars have studied from the following three aspects:
1. Aluminum anodic alloying
Industrial grade aluminum (99.0%) contains many impurities, such as iron (0.5%), silicon, copper, manganese, magnesium and zinc, which will aggravate the hydrogen evolution corrosion of aluminum at the phase interface. In particular, iron will form a local galvanic cell with aluminum, causing the electrochemical corrosion to multiply. Alloy components that can improve both chemical activity and corrosion resistance can be added to aluminum.
The elements to be added for aluminum alloy alloying shall meet the following conditions: ① the melting point of alloy elements shall be lower than that of metal Al; ② The solid saturation is higher in Al; ③ The electrochemical activity was higher than that of Al; ④ High solubility in electrolyte; ⑤ It has high hydrogen evolution overpotential. In addition, the anode efficiency can be further improved by processing the anode metal into ultra-fine grain materials.
2. Slow release agent added to electrolyte
Because of the cost of anodic alloying, people often choose to add some slow release agents in the electrolyte to ensure the performance of aluminum air battery. Some carboxylic acid, amine and amino acid slow-release agents and their inhibition efficiency on aluminum corrosion are shown in Table 1:
The researchers used natural substances as inhibitors of aluminum corrosion, and the experiments proved that organic amines, pyrrole, etc. have obvious inhibitory effects on aluminum corrosion. The electrochemical behavior of aluminum metal anode was studied by adding organic substances and water-soluble compounds to the strong alkaline electrolyte to reduce the corrosion rate of aluminum, thereby improving the performance of aluminum air battery.
3. Heat treatment process
Heat treatment affects the properties of aluminum alloy by changing the distribution of trace elements in aluminum alloy and the microstructure of the alloy surface, which belongs to the research field of technology. The best heat treatment process can be found through suitable orthogonal experiments.
electrolyte
The electrolyte of aluminum air battery is mostly neutral salt solution or strong alkaline solution. When the neutral electrolyte is used, the self corrosion of the anode is small, but the surface of the aluminum anode is seriously passivated, which reduces the working voltage, makes it difficult to increase the power and current of the battery, and also causes the voltage lag, and the product aluminum hydroxide colloid will also settle and block the electrolyte, so this type of battery can only be used as a small power output device.
When strong alkaline electrolyte is used, the passivation of aluminum is reduced, and the alkaline solution can absorb a certain amount of reaction product aluminum hydroxide. The performance of the battery is relatively good, but aluminum is an amphoteric metal. In a strong alkaline environment, strong hydrogen evolution corrosion will occur, releasing a lot of hydrogen, reducing the output power of the battery and the utilization rate of the anode, especially under high current density. To solve the above problems simply, we can choose to replace the electrolyte regularly and add additives that can activate the aluminum anode surface and inhibit aluminum hydrogen evolution corrosion to the electrolyte to solve the appeal problem.
Air electrode (positive pole)
The cathode is the reaction site of O2, which is breathable, conductive, waterproof, anti-corrosion and catalytic. It is also often called the air electrode. The air electrode generally consists of a porous catalytic layer, a conductive collector and a waterproof and breathable layer. The porous catalytic layer is the main place where oxygen is reduced, where the oxygen diffused into, the oxygen reduction catalyst and the thin layer electrolyte form a three-phase interface electrochemical active site; The conductive collector mainly plays the role of conducting electricity and mechanical support; The waterproof and breathable layer has a loose porous hydrophobic structure, which not only provides the catalytic layer with the gas required for reaction, but also prevents the electrolyte from flooding the gas diffusion channel.
The catalytic layer is the most critical part of the air electrode and plays a decisive role in its electrochemical performance. The performance of aluminum air battery largely depends on the cathode catalyst selected. The performance of air electrode can directly affect the electrode reaction balance. Therefore, improving its performance can improve the utilization rate of aluminum air battery anode to a certain extent and inhibit the self corrosion of aluminum anode.
The commonly used catalysts of aluminum air battery are as follows:
(1) Precious metal catalyst. Platinum and silver are commonly used, with high catalytic activity and stable performance. However, due to the high price and shortage of resources, the adoption rate is not high.
(2) Metal macrocyclic compound catalyst. Organometallic macrocyclic compounds have good catalytic activity for oxygen reduction, especially when they are adsorbed on carbon with large surface area. Their activity and stability can be significantly improved by heat treatment. Therefore, it is expected to replace noble metal oxygen reduction catalyst. The common synthesis methods of metal macrocyclic compounds include thermal decomposition and precursor preparation. However, due to the heat treatment process of thermal decomposition method will lead to the reaction between metal macrocyclic compounds and carbon matrix, and the catalyst prepared by precursor method has poor activity, so there are some problems in its application.
(3) Perovskite type oxide catalyst. Perovskite type oxides have high catalytic activity for the reduction and precipitation of oxygen and are cheap, so they have broad application prospects in aluminum air cells and fuel cells. The current research on perovskite oxygen electrode catalysts mainly focuses on improving the preparation methods and searching for new replacement elements to improve the catalytic performance. Amorphous precursor method, especially malic acid precursor method, can prepare perovskite oxides with fine grains and large specific surface area, thus greatly improving their catalytic activity. It is a better method to prepare perovskite oxides at present.
(4) Cheap catalyst. The most important representative is the manganese dioxide catalyst. Its greatest advantage is that it has rich raw materials and low cost, and can be widely used in batteries with aqueous or non-aqueous electrolytes. However, the single manganese dioxide electrocatalytic activity has certain limitations, so people never stop researching in this area.
(5) AB2O4 spinel oxide catalyst. The crystal lattice of spinel is face centered cubic. There are 32 close packed 02 ions in the unit cell, 64 tetrahedral voids and 32 octahedral voids are occupied by metal ions. The dehydration activity of spinel is related to the fraction of B ions in the tetrahedral space. The higher the fraction, the more acidic the catalyst surface and the more dehydration activity. Generally, aluminum air batteries do not use this catalyst.
(6) Other metal and alloy catalysts. Nickel is relatively cheap, and has high corrosion resistance under anodic polarization conditions in alkaline electrolyte. At the same time, nickel has the highest oxygen evolution efficiency among metal elements. Therefore, nickel is traditionally used as the anode material in alkaline water electrolysis. Nickel iron, nickel cobalt and other alloy catalysts are also often used, which have good catalytic activity and corrosion resistance, and are also a possible catalyst direction for aluminum air battery.
(7) Composite catalyst. The catalytic activity of the air electrode of aluminum air battery can be better improved by combining two or more catalysts.
Application prospect of aluminum air battery
At present, aluminum air battery has not been widely used in industrial and civil fields, mainly because the material preparation technology needs to be improved and the understanding of its concept of secondary charge and discharge.
