KR102050003B1 - Lithium anode comprising metal alloy foam, thermal battery comprising thereof and method for producing thereof - Google Patents

Abstract

A lithium negative electrode of a thermal battery according to an embodiment of the present invention comprises: a metal alloy foam having a plurality of openings and including nickel (Ni), iron (Fe), chrome (Cr) and molybdenum (Mo) mixed at a predetermined ratio; and lithium impregnated into the metal alloy foam in a melted form and accommodated in the openings. The chrome facilitates the impregnation of lithium into the openings and reduces the reactivity of the metal alloy foam to lithium at the operating temperature of the thermal battery. The molybdenum can prevent corrosion of the metal alloy foam by lithium.

Description

Lithium negative electrode comprising a metal alloy foam, a thermocell comprising the same and a method for manufacturing the same {LITHIUM ANODE COMPRISING METAL ALLOY FOAM, THERMAL BATTERY COMPRISING THEREOF AND METHOD FOR PRODUCING THEREOF}

The present invention disclosed by the present application relates to a lithium negative electrode including a metal alloy foam, a thermocell including the same, and a manufacturing method thereof.

Thermoelectric cells are non-rechargeable primary cells that remain inactive at room temperature and are activated by melting a solid electrolyte within seconds by ignition of a heat source. As there is little self-discharge during storage, it can be stored for more than 10 years without degrading performance. In addition, due to structural stability and reliability that can withstand vibration, shock, low temperature, and high temperature, thermoelectric batteries are mainly used as guided weapons and space launch vehicle power sources.

In particular, in the case of guided weapons, the life expectancy is 15 years or more, and since power is used only at the time of launching, self-discharing does not occur, which is an essential requirement of the power supply. In addition, the power source of the guided weapons must also meet the requirement for light weight for flight. Since the electrolyte has a solid state when the thermoelectric battery is inactivated, self-discharge may be blocked, and thus may be used as a power source for an induction weapon.

Lithium-silicon (Li-Si) alloys and liquid lithium in which iron powder is mixed with molten lithium are used as negative electrode materials for thermo batteries. However, the lithium-silicon (Li-Si) alloy has a limitation of molding because it is manufactured through powder molding method, and the open circuit voltage is 1.9V, which is 2.0V which is the open circuit voltage of the liquid lithium electrode. Has a lower problem. On the other hand, the liquid lithium electrode has the advantage of using pure lithium with excellent theoretical capacity, but the reduction of specific capacity inevitably occurs by using an excessive amount of iron powder in order to prevent leakage of molten lithium at high temperature, which is a thermal cell operating condition. .

Therefore, in order to solve the above-mentioned problems, researches on other types of thermocell anode materials that can replace the existing lithium-silicon (Li-Si) alloys and liquid lithium electrodes have been actively conducted.

In related prior documents, Korean Patent No. 10-1449597 for impregnating lithium in a metal alloy foam coated with a eutectic salt and Japanese Patent No. 1996-078023 for impregnating lithium in a porous nickel substrate have been disclosed.

An object according to an embodiment is to produce a lithium negative electrode by immersing a metal alloy foam prepared according to a predetermined composition ratio including chromium and molybdenum in molten lithium, and to provide a thermal battery including the same.

The problem to be solved is not limited to the above-described problem, and the problems that are not mentioned will be clearly understood by those skilled in the art from the present specification and the accompanying drawings.

According to one embodiment, a plurality of pores are formed, and a metal alloy foam (Ni) including nickel (Ni), iron (Fe), chromium (Cr) and molybdenum (Mo) mixed according to a predetermined composition ratio foam) and a metal alloy foam impregnated in a molten state, containing lithium contained in the voids, chromium in the composition ratio facilitates impregnation of lithium into the voids, molybdenum in the composition ratio, the metal alloy foam is lithium The lithium negative electrode of the thermoelectric battery may be provided to prevent the melted reaction.

In addition, the first composition ratio of the metal alloy foam may be 47 to 67 parts by weight of nickel, 1 to 33 parts by weight of iron, 13 to 33 parts by weight of chromium, and 1 to 14 parts by weight of molybdenum based on 100 parts by weight of the metal alloy foam. .

The second composition ratio of the metal alloy foam is 47 to 67 parts by weight of nickel, 1 to 33 parts by weight of iron, 13 to 33 parts by weight of chromium, 1 to 14 parts by weight of molybdenum and silicon, based on 100 parts by weight of the metal alloy foam. It may be 1 to 11 parts by weight.

It also does not include cups or meshes for retaining the form of the metal alloy foam.

According to another embodiment, a plurality of voids are formed, and a metal alloy foam including nickel (Ni), iron (Fe), chromium (Cr) and molybdenum (Mo) mixed according to a predetermined composition ratio a lithium anode comprising lithium contained in an alloy foam and a metal alloy foam in a molten state and contained in a void, a negative electrode current collector disposed on one side of the lithium negative electrode, an electrolyte disposed on the other side of the lithium negative electrode, It may include a cathode (cathode) disposed on the opposite side of the lithium negative electrode based on the electrolyte and a positive electrode current collector disposed on the opposite side of the electrolyte based on the positive electrode.

According to another embodiment, the step of melting lithium in an argon atmosphere glove box, a plurality of voids are formed, and mixed according to a predetermined composition ratio nickel (Ni), iron (Fe), chromium (Cr) and mol Immersing a metal alloy foam including molybdenum (Mo) in molten lithium and placing a negative electrode current collector on one side of the metal alloy foam, and an electrolyte, positive electrode and positive electrode collector on the other side of the metal alloy foam There may be provided a method of manufacturing a thermocell comprising the step of laminating the whole in order.

The metal alloy foam in which nickel, iron, chromium and molybdenum are present together according to an embodiment may prevent corrosion of the metal alloy foam by lithium and maintain its shape, thereby preventing leakage of lithium. Cups and meshes may not be used.

Effects are not limited to the above-described effects, and effects that are not mentioned will be clearly understood by those skilled in the art from the present specification and the accompanying drawings.

1 is a cross-sectional view of a conventional lithium anode commercially available.
2 is a flowchart illustrating a method of manufacturing a thermo battery using a metal alloy foam according to an embodiment as a negative electrode.
3 is a diagram schematically illustrating a method of manufacturing a metal alloy foam according to FIG. 2.
4 is a photograph of a metal alloy foam before and after lithium is impregnated according to one embodiment.
5 is a photograph taken of an electron microscope of the microstructure of the metal alloy foam before and after lithium is impregnated.
6 is a view illustrating a thermocell manufactured according to an embodiment and components thereof.
7 is a discharge test result for a unit cell of a thermo battery manufactured according to one embodiment.

1 is a cross-sectional view of a conventional lithium anode commercially available. Referring to FIG. 1, it can be seen that an electrode mixed with lithium 2000 and iron powder 2010 is contained in a nickel mesh 2020 and a cup 2030 made of nickel or iron.

Conventional commercially available lithium anodes are manufactured by splitting and injecting iron powder into molten lithium, and ingot making, pressing, rolling and punching ingot from lithium in which the solidified iron powder is mixed. It is manufactured to include a nickel mesh 2020 and a nickel or iron cup 2030 that can be accommodated therein.

The liquid lithium electrode undergoes a phase change from a solid to a liquid state at 400 to 500 ° C., which is an active temperature of a thermo battery. Lithium in the liquid state is flowable and may cause a short circuit of the battery when flowing to the positive electrode.

In order to control the flowability of lithium, the conventional lithium cathode manufacture uses a method in which a large amount of iron powder 201 is mixed and produced. The iron powder 201 may provide a supporting force for the molten liquid lithium to maintain its shape.

However, since the iron powder (2010) has to go through the process of physically mixing, there is a fear that the iron powder (2010) or lithium (2000) is unevenly distributed when completed in the ingot form. Therefore, the iron powder 2010 is mixed excessively for stable operation, resulting in a reduction of lithium specific capacity.

On the other hand, it is common to assemble a battery under a pressurized environment in order to reduce contact resistance. However, when lithium 2000 is melted by the operation of the thermoelectric battery in a state where lithium 2000 and the iron powder 2010 are partially unevenly mixed, deformation of the electrode necessarily occurs due to the pressing force applied during the assembly of the thermocell. When deformation of the electrode occurs, the molten lithium 2000 leaks out and moves to the positive electrode, which may cause a short circuit of the battery.

Therefore, a conventional lithium electrode is manufactured using a nickel mesh 202 and a cup 2030 made of nickel or iron in order to prevent leakage of lithium due to such deformation.

However, since the ratio of the weight of the nickel and iron cup 2030 and the nickel mesh 2020 to the total weight of the negative electrode reaches 30 to 40 wt%, a specific amount of lithium inevitably occurs. In addition, it is observed that after the discharge, the electrode analysis shows that the iron powder is agglomerated than before the discharge. Therefore, there is a disadvantage in that structural stability cannot be obtained when discharged under a pressurized environment.

In order to solve these problems, the lithium negative electrode according to the embodiments is manufactured through a process of impregnating lithium in a metal alloy foam prepared according to a predetermined composition ratio. Thus, the lithium anode manufacturing method according to the embodiments, the reactivity of the metal alloy foam to lithium is improved to improve the stability, and the wettability to lithium is improved. In addition, the lithium negative electrode does not use the cup 203 and the mesh 202, which have been previously used, and omits surface treatment using eutectic salts. Significant increases, streamlining manufacturing processes and improving productivity.

Hereinafter, a lithium negative electrode and a method of manufacturing the same according to the embodiments will be described in more detail.

FIG. 2 is a flowchart illustrating a method of manufacturing a thermal battery including a metal alloy foam according to an embodiment as a negative electrode, and FIG. 3 is a diagram illustrating a method of manufacturing a metal alloy foam according to FIG. 2.

2 and 3, first, lithium is heated and melted in a glove box in an argon atmosphere (S1100). Since lithium can easily react with oxygen and water in the air, a heating source 101 is installed in the glovebox to melt lithium in the glovebox 100 substituted with an argon atmosphere. For example, the heating source may be a heating mechanism such as a hot plate or induction. The heating source 101 heats the vessel 102 to 250 to 350 ° C. above the melting point of lithium (180 ° C.). For example, the container can be made of iron or stainless steel. Subsequently, lithium 103 is thrown into the container and melted. The impeller uniformly stirs the molten liquid lithium. When the lithium is fully melted, the impeller is removed.

Thereafter, the metal alloy foam 104 manufactured according to the predetermined composition ratio is introduced into the molten lithium, and the molten lithium is impregnated into the pores formed in the metal alloy foam 104 (S1200). As a result, a lithium negative electrode impregnated with lithium in the metal alloy foam 104 is produced.

Compared to a liquid lithium electrode containing a conventional lithium-silicon (Li-Si) alloy and iron powder, the metal alloy foam 104 controls the amount of lithium impregnation by controlling the size of the cells in the foam. It is freer in design of capacity than liquid lithium electrodes containing iron powder.

Reducing the time required to impregnate the molten liquid lithium in the molten state of the metal alloy foam 104 is an important technical problem as it directly leads to a reduction in process cost and productivity. The compositional design of the metal alloy foam 104 may find a composition ratio that allows molten lithium to be impregnated in a short time.

The metal alloy foam is impregnated with molten liquid lithium (Li) to form voids that can accommodate lithium. At this time, the pore diameter is 250 to 6000 m. More specifically, the diameter of the voids is 400 to 1200 μm.

The metal alloy foam 104 includes nickel (Ni), iron (Fe), chromium (Cr), and aluminum (Al) mixed according to a predetermined composition ratio.

Nickel has a high reactivity with lithium and is difficult to be used alone at a high operating temperature of a thermal battery. Nickel is also not suitable for thermoelectric electrode structures in pressurized environments due to its low strength.

On the other hand, iron has low reactivity with lithium, but it is difficult to impregnate lithium because of poor wettability with lithium.

Accordingly, the metal alloy foam 104 according to one embodiment may further include chromium and aluminum in addition to nickel and iron, thereby maintaining a low reactivity with lithium and facilitating impregnation of lithium.

The metal alloy foam 104 mixed with chromium has excellent low reactivity with lithium at high temperature. The metal alloy foam 104 mixed with chromium has a low level of reactivity with lithium at a high temperature of iron. Therefore, the metal alloy foam 104 mixed with chromium may ensure stability at the operating temperature of the thermocell. In addition, the metal alloy foam 104 mixed with chromium is easily impregnated with lithium.

In the metal alloy foam 104 mixed with aluminum, although the surface of the metal alloy foam 104 may react with lithium slightly, it has been observed that lithium does not penetrate into the surface of the metal alloy foam 104.

In other words, the metal alloy foam 104 mixed with aluminum exhibits some reaction at the surface when it is in contact with liquid lithium, but the reaction does not occur to a depth deeper than the surface of the metal alloy foam 104, so that the metal alloy foam 104 Can maintain its structure.

Therefore, the metal alloy foam 104 mixed with aluminum can be used as a thermoelectric electrode structure by protecting from reaction with lithium. In addition, the metal alloy foam 104 mixed with aluminum facilitates the impregnation of lithium. In addition, the metal alloy foam 104 mixed with aluminum may prevent nitriding.

That is, the metal alloy foam 104 mixed with chromium and aluminum facilitates impregnation of lithium. As lithium is melted at about 300-400 ° C., the melting temperature of lithium, impregnation of lithium occurs on the metal alloy foam 104 mixed with chromium and aluminum.

The first composition ratio of the metal alloy foam 104 is 22 to 42 parts by weight of nickel, 9 to 29 parts by weight of iron, 21 to 41 parts by weight of chromium and 9 to 29 parts by weight of aluminum, based on 100 parts by weight of the metal alloy foam.

The second composition ratio of the metal alloy foam 104 is 26 to 46 parts by weight of nickel, 6 to 26 parts by weight of iron, 18 to 38 parts by weight of chromium, and 10 to 30 parts by weight of aluminum, based on 100 parts by weight of the metal alloy foam.

The metal alloy foam 104 may further include an oxygen element (O) to facilitate the impregnation of lithium through oxidation. At this time, the third composition ratio of the metal alloy foam 104 is 10 to 30 parts by weight of nickel, 2 to 22 parts by weight of iron, 9 to 29 parts by weight of chromium, and 2 to 22 parts by weight of aluminum, based on 100 parts by weight of the metal alloy foam. And 9 to 29 parts by weight of the oxygen element.

Further, according to another embodiment, the metal alloy foam 104 further includes chromium, molybdenum (Mo;), and silicon (Si; silicon) in addition to nickel and iron to facilitate impregnation of lithium. At the same time, corrosion of the metal alloy foam 104 can be prevented.

Conventional metal alloy foam consisting of nickel and iron has a problem that melted due to the reaction with molten lithium at the operating temperature of the thermocell. This reaction may cause a decrease in lithium capacity during the discharge of the thermal cell. In particular, a phenomenon in which the metal alloy foam melts due to reaction with lithium occurs at a discharge temperature of 500 to 550 ° C. Therefore, the existing metal alloy foam consisting of nickel and iron should be essentially equipped with a mesh 202 and a cup 203 to prevent leakage of lithium.

However, when molybdenum is mixed with the metal alloy foam 104, the metal alloy foam 104 does not react with the molten lithium at the operating temperature of the thermocell, and can maintain its shape and is stable. Accordingly, the metal alloy foam 104 mixed with molybdenum can stably maintain the structure to prevent leakage of lithium and remove the mesh 202 and the cup 203 which occupy about 30% of the total cathode weight. It is possible to increase the specific capacity of the breakthrough lithium.

The fourth composition ratio of the metal alloy foam 104 including molybdenum is 47 to 67 parts by weight of nickel, 13 to 33 parts by weight of chromium and 1 to 14 parts by weight of molybdenum with respect to 100 parts by weight of the metal alloy foam.

The fifth composition ratio of the metal alloy foam 104 including molybdenum is 47 to 67 parts by weight of nickel, 13 to 33 parts by weight of chromium, 1 to 14 parts by weight of molybdenum and silicon based on 100 parts by weight of the metal alloy foam. 1 to 10 parts by weight.

The metal alloy foam 104 produced according to a predetermined composition ratio is superior in wettability to lithium as compared to the metal alloy foam 104 in which simple nickel and iron are mixed. For example, the molten lithium may be fully impregnated into the metal alloy foam 104 within tens of seconds or up to five minutes.

In addition, in the past, attempts were made to coat eutectic salts on the surface of nickel foam to improve wettability to lithium, or to deposit materials including silicon or gold on the surface of nickel foam using CVD (Chemical Vapor Deposition). In this case, process cost and time increase, which may lead to an increase in production cost of a thermo battery.

On the other hand, the wettability of the molten lithium may be improved without additional surface pretreatment including eutectic salts on the surface of the metal alloy foam 104 manufactured at a predetermined composition ratio according to the embodiment. As such, a good quality lithium negative electrode for a thermocell can be produced by simply immersing the metal alloy foam 104 in molten lithium without the need for pretreatment such as eutectic salt coating or silicon deposition.

In addition, the metal alloy foam 104 manufactured according to a predetermined composition ratio has a strength capable of withstanding a pressure of 4 to 7 kg / cm ² applied during the manufacturing process of the thermocell. As a result, the shape can be maintained without deformation in the pressurized environment, and no leakage of lithium occurs. Therefore, the unit cell of the thermo battery can be configured without using the nickel and iron cups 203 and the nickel mesh 202 which can prevent leakage of lithium.

Thereafter, the negative electrode current collector 147 is disposed on one surface of the lithium negative electrode 146, and the electrolyte 145, the positive electrode 144, and the positive electrode current collector 142 are sequentially stacked on the other surface of the lithium negative electrode 146. The unit cell 140 of the battery is manufactured (S1300).

The thermo battery may be configured of at least one thermo battery cell 140. The thermo battery cells 140 are connected in series, and as the number of the thermo battery cells 140 connected is increased, the output voltage of the thermo battery increases.

The thermo battery cell 140 includes a cathode 144, an electrolyte 145, a lithium anode 146, a heat source (not shown) for melting the electrolyte 145, a cathode current collector 142, and a cathode current collector. 147 may be included. The negative electrode current collector 147 is disposed on one surface of the lithium negative electrode 146. The positive electrode 144 is disposed opposite the lithium negative electrode 146 based on the electrolyte 145. The positive electrode current collector 142 is disposed on the opposite side of the electrolyte 145 based on the positive electrode 144.

The heat source (not shown) may be inserted and disposed between the positive electrode 144 and the current collector. In this case, for example, the positive electrode 144, the electrolyte 145, the negative electrode 146, and a heat source (not shown) may be formed of disk-shaped pellets to facilitate lamination.

The positive electrode current collector 142 and the negative electrode current collector 147 serve as a support for allowing the active material to exist in the thermoelectric battery in the form of a pole plate, and the electrical energy generated by the chemicals of the positive electrode 144 and the negative electrode 146. It is responsible for the transmission of electrical energy so that it can be connected to the circuit. The positive electrode current collector 142 and the negative electrode current collector 147 may be made of, for example, metal plates such as stainless steel (SUS) and nickel (Ni) plates.

4 is a photograph of a metal alloy foam before and after lithium is impregnated, and FIG. 5 is a photograph of an electron microscope of a microstructure of the metal alloy foam before and after lithium is impregnated.

Referring to FIG. 4, a plurality of voids are formed in the metal alloy foam before lithium is impregnated. When the metal alloy foam is immersed in the molten lithium, it can be confirmed that lithium is penetrated and accommodated in the plurality of pores.

Checking the microstructure with reference to Figure 5, it can be seen that before the impregnation of lithium there are pores of 400 to 1200 μm in diameter between the foam. After lithium is completely impregnated, it can be seen that there are no more voids than before impregnation. Therefore, it can be seen that lithium is impregnated into the alloy foam without empty space.

6 is a view illustrating a thermocell manufactured according to an embodiment and components thereof. Referring to FIG. 6, a negative electrode current collector 147 is disposed on one surface of a lithium negative electrode 146 including a metal alloy foam, and an electrolyte 145, a positive electrode 144, and a positive electrode collector are disposed on the other surface of the lithium negative electrode 146. The whole 142 may be stacked in order to form the unit cell 140 of the thermal battery. At this time, the lithium negative electrode 146 does not use the nickel and iron cups 203 and the nickel mesh 202 which are commonly used in the conventional lithium negative electrode due to the strength of the metal alloy foam, and the unit cell 140 of the thermal battery. ) Can be configured.

7 is a discharge test result for a unit cell of a thermo battery manufactured according to one embodiment.

Figure 7 (a) is a discharge test result of a thermal cell including a metal alloy foam composed of conventional nickel and iron. It was observed that the structure of the metal alloy foam collapsed due to the low stability of the metal alloy foam in molten lithium at the time of discharge at high temperature, and thus a sharp decrease in the voltage. Therefore, to prevent this, metal alloy foams composed of conventional nickel and iron must use cups and meshes.

On the other hand, Figure 7 (b) is a discharge test results of a thermal cell including a metal alloy foam 104 composed of nickel, iron, chromium and molybdenum. The metal alloy foam 104 has low reactivity with respect to molten lithium even at high temperatures and does not deform the structure because corrosion is prevented. Accordingly, the metal alloy foam 104 can be discharged without the cup 203 and the mesh 202.

In the conventional metal alloy foam composed of nickel and iron, the cup 203 and the mesh 202 account for at least 30% of the total weight of the thermoelectric cathode. The metal alloy foam 104 composed of nickel, iron, chromium and molybdenum does not include the cup 203 and the mesh 202, so that the cost can be increased by more than 30% over the same discharge performance. Accordingly, the application range of the thermal battery is dramatically widened due to the reduction in the overall weight compared to the same performance.

The description of the presented embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the invention. Thus, the present invention should not be limited to the embodiments set forth herein but should be construed in the broadest scope consistent with the principles and novel features set forth herein.

100 glovebox
101 heating source
102 containers
103 lithium
104 metal alloy foam
140 thermocell cells
142 anode collector
144 anodes
145 electrolyte
146 cathode
147 Cathode Current Collector

Claims (6)

As a lithium negative electrode of a thermocell disposed on the other side of the solid electrolyte layer on which one side of the solid electrolyte layer is disposed,
A metal alloy foam including a plurality of voids formed therein and including nickel (Ni), iron (Fe), chromium (Cr), and molybdenum (Mo) mixed according to a predetermined composition ratio; And
And impregnated in the molten state into the metal alloy foam to be accommodated in the pores.
In the composition ratio, chromium facilitates impregnation of lithium into the pores,
Molybdenum in the composition ratio prevents the metal alloy foam from reacting with lithium to melt
Lithium anode of thermo battery. According to claim 1,
The first composition ratio of the metal alloy foam is 47 to 67 parts by weight of nickel, 1 to 33 parts by weight of iron, 13 to 33 parts by weight of chromium and 1 to 14 parts by weight of molybdenum, based on 100 parts by weight of the metal alloy foam.
Lithium anode of thermo battery. According to claim 1,
The second composition ratio of the metal alloy foam is 47 to 67 parts by weight of nickel, 1 to 33 parts by weight of iron, 13 to 33 parts by weight of chromium, 1 to 14 parts by weight of molybdenum and silicon based on 100 parts by weight of the metal alloy foam. 1 to 11 parts by weight,
Lithium anode of thermo battery. According to claim 1,
Does not include a cup or mesh to maintain the shape of the metal alloy foam,
Lithium anode of thermo battery. A plurality of voids are formed, and the metal alloy foam and the metal alloy including nickel (Ni), iron (Fe), chromium (Cr) and molybdenum (Mo) mixed according to a predetermined composition ratio A lithium anode comprising lithium contained within the pores of the foam;
A negative electrode current collector disposed on one surface of the lithium negative electrode;
A solid electrolyte layer disposed on the other surface of the lithium negative electrode;
A cathode disposed opposite the lithium cathode based on the solid electrolyte layer; And
It includes; a positive electrode current collector disposed on the opposite side of the solid electrolyte layer relative to the positive electrode
Thermo battery. Melting lithium in an argon atmosphere glovebox;
A plurality of pores are formed, and the molten metal alloy foam including metal (Ni), iron (Fe), chromium (Cr) and molybdenum (Mo) mixed according to a predetermined composition ratio Preparing an anode by immersing in lithium; And
Disposing a negative electrode current collector on one surface of the negative electrode;
Disposing a solid electrolyte layer on the other side of the cathode;
Disposing an anode opposite the cathode based on the solid electrolyte layer; And
Disposing a positive electrode current collector on the opposite side of the solid electrolyte layer based on the positive electrode;
Thermocell manufacturing method.

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