Science or engineering related to anodes made from aluminum alloy for aluminum-air batteries

Background of the Invention

Metal-air batteries have more capacity for energy than lithium-ion batteries such as zinc- air batteries, magnesium- air batteries, aluminum-air batteries. Significant interest has been shown in metal-air batteries because materials have high safety and are easily available. Metal-air batteries have high theoretical energy density. This type of batteries was developed for use in automobiles. When properties of various types of metal-air batteries are considered, aluminum- air batteries can be seen to be suitable for development and use as anodes to react with oxygen in the air because aluminum-air batteries have higher energy density than lithium-ion batteries in addition to having a high energy capacity, a long shelf life, and the ability to charge quickly. However, aluminum anodes continue to have limitations in commercial use. After reactions occur, an oxide layer is usually created such as aluminum oxide, which obstructs currents. In addition, aluminum anodes have high rates of corrosion with alkaline electrolytes. Therefore, other elements such as magnesium, zinc, indium, and tin are added to increase aluminum anode efficiency. Studies were conducted in the past on aluminum anodes of metal-air batteries in the following examples:

In a study on use of alloy to replace industrial pure aluminum in aluminum-air batteries such as aluminum-gallium at 0.1% by weight, aluminum- indium at 0.1% by weight and aluminum-tin at 0.1% by weight, etc. for one mole of potassium hydroxide solution, the selfcorrosion rate at the alloy anode was lower than for pure aluminum. In addition, anodes from the aforementioned aluminum alloy demonstrated excellent discharge efficiency and high efficiency as anodes (90.4%) (Sun, Z., Lu, H., Fan, L., Hong, Q., Leng, J., Chen, C., (2015) Performance of Al-Air Batteries Based on Al-Ga, Al-In and Al-Sn Alloy Electrodes, Journal of the Electrochemical Society, 162, A2116).

In another study, the addition of zinc in aluminum anodes reduced aluminum-air discharge efficiency while adding indium in aluminum-zinc anodes helped to reduce formations of zinc films, causing anode efficiency and discharge efficiency of aluminum-zinc-indium alloy anodes of aluminum-air batteries to be at 73.5%, which was similar to industrial pure aluminum. In addition, corrosion rates at anodes of the aluminum-zinc-indium alloy were lower than those of an aluminum-zinc alloy not added with indium (Park, I.J., Choi, S.R., Kim, J.G., (2017) Aluminum anode for aluminum-air battery - Part II: Influence of In addition on the electrochemical characteristics of Al-Zn alloy in alkaline solution, Journal of Power Sources, 57, 47-55.).

In a study on effects from reducing grain size in the structure of aluminum anodes for metal-air batteries in alkaline electrolytes, electrochemical properties were found to be dependent on reductions to grain size in the structure. Smaller and finer grains were able to suppress hydrogen evolution and modify electrochemical activity. Smaller and finer grains were able to modify and enhance anode efficiency for metal-air batteries (Fan, L., Lu, H., (2015) The effect of grain size on aluminum anodes for Al-air batteries in alkaline electrolytes, Journal of Power Sources, 409- 4 1 5 , 284 . and Liu, L., Li, Y., Wang, F., (20 1 0 ) Electrochemical corrosion behavior of nanocrystalline materials-a review, Journal of Materials Science and Technology, 26(1), 1-14.).

Furthermore, research and studies have found aluminum anodes with corrosion problems which had internal grains modified to be smaller and finer were able to resist corrosion. Grain size in the structure of aluminum used as anodes had influence over changes in electrochemical efficiency and enabled storage of charges and energy density at higher levels.

From the abovementioned information, the addition of elements such as zinc and indium to manufacture aluminum alloy anodes for metal-air batteries and the reduction of grain sizes to be consistent in the micrometer housing such as by using equal channel angular pressing were able to enhance anode efficiency better than the abovementioned works, which can lead to further development of the electric vehicle industry.

Some patents already appear to describe production processes of alloys for enhancing electrochemical properties or for use as anodes of metal-air batteries. For example:

A Thai invention patent, application number 2001001598 describes a production process of alloys for enhancing electrochemical properties consisting of melting aluminum with zinc at a zinc ratio of 0.1-5% of aluminum weight or at an appropriate zinc ratio of 2-3% of aluminum weight in an inert atmosphere for 1-4 hours, casting alloy pieces and inducing zinc distribution in the aluminum in alloy pieces under specified temperature conditions before reducing grain size through use of an equal channel angular pressing machine at 60-150 degrees, turning work pieces at 70-110 degrees per time in the same direction before the next pressing and pressing until grain size is at 0.05-5 micrometers.

A Chinese patent, publication number CN111560544A describes a material for anodes in aluminum-air batteries consisting of industrial pure aluminum with titanium at 5-10%, boron at 0.1-0.5% and lanthanum at 0.5-1% of aluminum weight. Additional components consist of zinc at 0.05-0.2%, gallium at 0.2-0.05%, tin at 0.01-0.05%, indium at 0.05-0.1%, bismuth at 0.1-0.2%, magnesium at 0.5-1%, cerium at 0.1-0.3% of aluminum weight. This alloy can be prepared by melting industrial pure aluminum at a temperature of 800-850 degrees Celsius, adding binding agent powders consisting of potassium fluoroborate (KBF4) and potassium fluotitanate (K2TIF6) to melted industrial pure aluminum for 15-30 minutes, adding high purity ruthenium at the old temperature for 20-40 minutes, adding additional components consisting of zinc, gallium, tin, indium, bismuth, magnesium and cerium at a total amount of 0.3-0.5% of aluminum weight, shaping and annealing at a temperature of 450-500 degrees Celsius for 10-15 hours by increasing temperature by 10-15 degrees Celsius/minute, cooling at room temperature, removing the oxide layer, shaping as aluminum plates and annealing again at a temperature of 400-120 degrees Celsius for 30-40 minutes before cooling at room temperature.

A Chinese patent, publication number CN113097471 A describes a material for anodes in alkaline aluminum-air batteries containing zinc at 0.5- 1.2%, indium at 0.05-0.1%, tin at 0.05-0.1% and other adulterants at no more than 0.01% of aluminum weight. The material was prepared by the following method: Melt aluminum, zinc, and tin inside an aluminum block under inert gas conditions by providing a temperature of 800-850 degrees Celsius for 30-50 minutes. Cool the temperature down to 760-780 degrees Celsius and adding the remaining materials along with heating for another 20-40 minutes before lowering the temperature and casting the materials in a graphite mold. After cooling, cut the material for the desired thickness for anodes.

A United States patent, publication number US 20120251897A1 describes the production of aluminum-air batteries with anodes made of aluminum coated over with a zinc alloy containing any one of indium, gallium, lead, thallium, mercury, or combination thereof. The battery housing and electrolytes such as potassium hydroxide and/or sodium hydroxide are around anodes for charge exchange.

A Chinese patent, publication number CN 105140595A describes an aluminum-air battery with anodes, cathodes, and electrolyte solutions. The anodes consist of zinc at 0.05-6%, gallium at 0.05-4% and indium at 0.01-2% of aluminum weight. Production was done by mixing all components under an inert gas condition and heating at temperatures of 730-780 degrees Celsius for 4-10 minutes before shaping by rolling the material into sheets with a thickness of 0.5-4 millimeters at temperatures of 150-200 degrees Celsius.

A Chinese patent, publication number CN109461942A describes anodes of aluminum-air batteries consisting of zinc at 0.05-5%, magnesium at 0.02-3%, indium at 0.01-3%, gallium at 0.02-5% and antimony at 0.05-5% of aluminum weight, which can be manufactured by blending all components under an inert gas condition and heating at a temperature of 730-780 degrees Celsius for 5-10 minutes before shaping by rolling the material into sheets with a thickness of 0.3- 5 millimeters at a temperature of 140-210 degrees Celsius and annealing the material at 350-570 degrees Celsius for 4-10 hours.

A South Korean patent, publication number KR1020140143528A describes a material for anodes in aluminum-air batteries consisting of an aluminum alloy with aluminum content at 99.8% by weight, zinc at 1.0-10.0% by weight, indium at 0.01-10.05% by weight, silicon at 0.005-0.5% by weight and phosphorus at 0.02% by weight with manganese, copper, and iron.

Noticeably, despite description of inventions of anodes from aluminum alloy for aluminum-air batteries with zinc and/or indium components in the abovementioned works, in production processes, no production of anodes from aluminum alloy for aluminum-air batteries with zinc and indium components by reducing grain size through equal channel angular pressing (ECAP) was found. After research and development of the process, the process was found to be able to improve anode efficiency of the aluminum- zinc-indium alloy for use in metal-air batteries. The key factor increasing anode efficiency is an appropriate amount of zinc and indium added to an aluminum alloy. Adding zinc helps improve ion solubility equilibrium and adding indium stimulates anode electrochemical activity. When added together in the production process to reduce grain size at the micrometer level, this causes the alloy to have a large number of grain boundary, which reduces corrosion more than large grains and reduces problems of anodes used in metal-air batteries which usually have high self-corrosion, which is a reason causing commercial use of metal-air batteries to not be widespread. The aluminum alloy product for manufacturing anodes in metal-air batteries made from the aluminum-zinc-indium alloy by reducing grain size in the lattice to be small and fine down to the micrometer level within the specified range of this invention has higher functional efficiency, discharge density, voltage and energy density than industrial aluminum pure anodes with inner grain sizes reduced by equal channel angular pressing.

Summary of the Invention

Anodes from the aluminum alloy for aluminum-air batteries consist of zinc at 3-5% of aluminum weight and indium at 0.01-0.05% of aluminum weight. The production method of anodes from the aluminum alloy for aluminum-air batteries has steps consisting of:

A. Alloy melting by preparing the aluminum-zinc-indium alloy and melting the alloy until the chemical compositions are one

B . Alloy casting in a mold by casting the liquid metal obtained from step A in a mold, leaving the alloy to cool and quenching the alloy to cool the alloy down again

C. Homogenized heat treatment of the aluminum alloy obtained from step B and quenching of the alloy in water D. Grain size reduction by using ECAP on the aluminum alloy obtained from step C until grain size of the aluminum alloy is less than 10 micrometers

The objective of the invention is to produce and modify the inner structure of the aluminum- zinc-indium alloy which passed the casting process by reducing grain size to be at the micrometer level by using equal channel angular pressing along with adding zinc and indium to produce anodes made of the aluminum-zinc-indium alloy for use in metal-air batteries. Adding zinc helps improve ion solubility equilibrium and adding indium stimulates anode electrochemical activity. In addition, reducing grain size to the micrometer level causes the alloy to have a large number of grain boundary, which reduces corrosion more than large grains. This increased anode efficiency and solved problems caused by high self-corrosion of anodes used in metal-air batteries.

Brief Description of the Drawings

Figure 1 - Polarization graph of industrial pure aluminum and the aluminum-zinc-indium alloy with a tiny grain size

Figure 2 - Corrosion rates of industrial pure aluminum and the aluminum-zinc-indium alloy with a tiny grain size

Figure 3 - Anode efficiency of industrial pure aluminum and the aluminum-zinc-indium alloy with a tiny grain size

Figure 4 - Charge Density of industrial pure aluminum and the aluminum-zinc-indium alloy with a tiny grain size

Figure 5 - Voltage of industrial pure aluminum and the aluminum-zinc-indium alloy with a tiny grain size

Figure 6 - Energy density of industrial pure aluminum and the aluminum-zinc-indium alloy with a tiny grain size

Figure 7 - Discharge behavior of (A) the industrial pure aluminum and (B) the aluminum- zinc-indium alloy with a tiny grain size

Detailed Description of the Invention

The current invention concerns anodes from aluminum alloy for aluminum air batteries, which can be explained based on the following invention characteristics:

Any characteristics shown herein mean and include applications to other characteristics of this invention unless specified otherwise.

Technical or scientific terms used in this place were defined as understood by a person with expertise in this field of art or science unless specified otherwise. Any tools, equipment, method, or chemicals describes here are to mean tools, equipment, methods, or chemicals generally practiced or used by experts in this field of art or science unless clearly specified as special tools, equipment, methods or chemicals specific to this invention.

The following shows details of the invention without any purpose to limit the scope of the invention.

This invention concerns anodes from aluminum alloy for aluminum air batteries consisting of the following constituents: zinc at 3-5% of aluminum weight indium at 0.01 - 0.05% of aluminum weight

Production methods of anodes from aluminum alloy for aluminum-air batteries have the following steps:

A. Alloy melting by preparing the aluminum-zinc-indium alloy and melting the alloy at temperatures of 530-1,200 degrees Celsius until the chemical compositions are one

B . Alloy casting in a mold by casting the liquid metal obtained from step A in a mold at temperatures of 600-950 degrees Celsius, leaving the alloy to cool and quenching the alloy to cool the alloy down again

C. Homogenized heat treatment of the aluminum alloy obtained from step B at temperatures of 200-600 degrees Celsius for 30 minutes - 72 hours and quenching of the alloy in water

D. Grain size reduction by using ECAP on the aluminum alloy obtained from step C and rotating aluminum alloy pieces by 90 degrees at a time along the cross-section before the next pressing and continue pressing until grain size of the aluminum alloy is less than 10 micrometers.

In one characteristic, step A: alloy melting has suitable temperatures for melting the aluminum alloy at 700-950 degrees Celsius with the most suitable temperature being 900 degrees Celsius.

In one characteristic, step B: casting has suitable temperatures for casting at 600-800 degrees Celsius with the most suitable temperature being 750 degrees Celsius.

In another characteristic, step B: casting has the cooling rate for the alloy in the mold at 10 degrees Celsius per minute. One example of the most suitable cooling period in the mold is 7 minutes.

In one characteristic, step C: homogenized heat treatment of the aluminum alloy has suitable temperatures for annealing at 400-600 degrees Celsius with the most suitable temperature being 550 degrees Celsius. In one characteristic, step D: grain size reduction requires the mold to have a channel angle of 60-160 degrees and an angle of curvature of 0-90 degrees.

In another characteristic, the number of times for equal channel angular pressing in step D: grain size reduction is dependent on the channel angle.

In another characteristic, step D: grain size reduction has a lower number of times in ECAP when the channel angle is smaller or a higher number of times in ECAP when the channel angle is larger.

One example of a characteristic of step D: grain size reduction is such that the aluminum alloy from step C has grain size reduced through ECAP at a channel angle of 90 degrees and at an angle of curvature of 20 degrees by using molds with a diameter of 20 millimeters. ECAP of aluminum alloy ingots use a degree of rotation of 90 degrees along the cross-section every time when pressed and use an equal number of equal channel angular pressings starting from 1 to 8 times.

Anodes from the aluminum alloy for aluminum-air batteries in this invention have a suitable aluminum alloy grain size after equal channel angular pressing through the mold at less than 10 micrometers.

One characteristic of the range of grain sizes obtained is such that grain size after ECAP for four times is at a range of 0.30-8.03 micrometers or 0.17 to 8.24 micrometers after ECAP for eight times when starting grain size before equal channel angular pressing is at the range of 18.30- 1,380.80 micrometers.

The following examples are only demonstrations of one characteristic of this invention to make the invention clearer without any objective to limit the scope of the invention and the scope of the invention will be consistent with attached claims:

Example 1 - Results from comparing corrosion potential between the aluminum-zinc- indium alloy with a tiny size and industrial pure aluminum

When the aluminum- zinc-indium alloy with a tiny grain size in this invention was studied for corrosion potential, corrosion potential of the aluminum-zinc-indium alloy was found to be lower when compared to industrial pure aluminum. This is because aluminum-air batteries are normally limited by high self-corrosion at the anodes due to a parasitic reaction of aluminum in high- alkalinity environments. Moreover, aluminum-air battery voltages are lower than theory because growth of the oxide layer at aluminum anode surfaces obstructs electrochemical reactions. However, the aluminum-zinc-indium alloy in this invention can increase aluminum-air battery voltages by triggering electrochemical activity through increase of grain boundary and triggering anodic dissolution by adding zinc and indium. These behaviors re shown by reductions to corrosion potential of the aluminum-zinc-indium alloy when compared to industrial pure aluminum as shown in Table 1 and Figure 1.

Table 1 - Variables connected to results from comparing corrosion potential between the aluminum-zinc-indium alloy with a tiny size and industrial pure aluminum

The aluminum-zinc-indium alloy with a tiny grain size has a lower corrosive potential than industrial pure aluminum by 6.55% and has a higher rate of corrosion than industrial pure aluminum by 5.24%. These behaviors show that the alloy of aluminum, zinc, and indium with a tiny grain size at the micrometer level has higher electrochemical activity than industrial pure aluminum despite having a higher rate of corrosion than industrial pure aluminum when not used.

Example 2 - Results from experimenting with anode efficiency of the aluminum-zinc- indium alloy with a tiny crystal size when compared to industrial pure aluminum

A test of anode efficiency was carried out on materials. According to a principle, an assessment can be carried out to determine that a material with low self-corrosion has high anode efficiency and, on the contrary, materials with high self-corrosion will have lower anode efficiency. From testing of anode efficiency of the aluminum-zinc-indium alloy with a tiny crystal size by comparing with industrial pure aluminum in Figures 2-6, corrosion rates, anode efficiency and charge density of both metals were found to have no significant differences in the current density range of 20 - 40 milli-amperes per square centimeters. However, at the current density of 80 - 100 milli-amperes per square centimeter, industrial pure aluminum has a significantly higher corrosion rate than the aluminum-zinc-indium alloy with a tiny crystal size, which causes anode efficiency and charge density to be significantly lower than the aluminum-zinc-indium alloy with a tiny crystal size. Furthermore, the aluminum-zinc-indium alloy with a tiny crystal size showed higher voltages at every current density range than industrial pure aluminum. Moreover, energy density of the aluminum-zinc-indium alloy with a tiny crystal size was significantly higher than industrial pure aluminum at the current density range of 80-100 milli-amperes per square centimeter. Comparison of anode efficiency between the aluminum-zinc-indium alloy with a tiny crystal size and industrial pure aluminum at a current density of 100 milli-amperes per square meter is as shown in Table 2.

Table 2 - Comparison of anode efficiency between the aluminum- zinc-indium alloy with a tiny crystal size and industrial pure aluminum at a current density of 100 milli-amperes per square centimeter

From Table 2, the aluminum-zinc-indium alloy with a tiny crystal size has higher anode efficiency at a current density of 100 milli-amperes per square centimeter than industrial pure aluminum while having a corrosion rate that is 11.50% lower than industrial pure aluminum. Anode efficiency was higher than industrial pure aluminum by 13.01%. charge density was higher than industrial pure aluminum by 12.98%. Voltage was higher than industrial pure aluminum by 51.49% and energy density was higher than industrial pure aluminum by 71.27%.

Example 3 - Discharge behavior of industrial pure aluminum and the aluminum-zinc- indium alloy with a tiny crystal size

Although anode efficiency of the aluminum-zinc-indium alloy with a tiny crystal size is higher than industrial pure aluminum as shown in Figure 7, discharge behavior of the aluminum- zinc-indium alloy with a tiny crystal size tested at a current density of 60-80 milli-amperes per square centimeter was found to have voltage fluctuations due to formations alternated with dissolution of the aluminum- zinc oxide layer that are a product of corrosion of the aluminum-zinc alloy. Therefore, in use of aluminum-air batteries with the aluminum-zinc-indium alloy with a tiny crystal size, there must be awareness of voltage fluctuations when using at the current density. However, discharge behavior of the aluminum-zinc-indium alloy with a tiny crystal size when tested at a current density of 20-40 milli-amperes per square meter had more consistent voltage and higher stability than industrial pure aluminum because the aluminum-zinc oxide layer helped to stabilize reactions at the alloy surface along with reducing formation of aluminum hydroxide layers that are the cause of delays against voltages reaching a point of balance. At the same time, in the area of discharge efficiency of the aluminum-zinc-indium alloy at a current density of 100 milli-amperes per square meter, the voltage was slow in reaching the point of balance because the aforementioned alloy’s surface had no aluminum-zinc oxide layer, causing formation of the aluminum hydroxide layer to obstruct discharges and causing the voltage to reach a point of balance late by more than 60 minutes.

Therefore, aluminum-air batteries with anodes made of the aluminum-zinc-indium alloy with a grain size at the micrometer level are suitable for real uses where there is a need for speed in discharging immediately after an electrochemical reaction occurs through use at a current density lower than 40 milli-amperes per square centimeter. However, for uses where there is need for anode efficiency worthy of anode weight loss in aluminum-air batteries without considering time when battery pressure reaches the point of balance, aluminum-air batteries should be used at a current density above 100 milli-amperes per square centimeter. If there is need to use aluminum- air batteries at a current density of 60-80 milli-amperes per square centimeter, devices that regulate outgoing voltage should be installed before connecting the circuit to electrical appliances to prevent danger from unstable electricity voltages.

Any modifications or changes may be clearly understood and carried out by a person skilled in the art and may fall under the scope and intention of this invention as shown in the attached claims.

Best Mode of the Invention

As described in Detailed Description of the Invention