Heat Treatment Method for Lithium-Ion Battery Waste

Abstract

Provided is a heat treatment method for lithium ion battery waste, said method comprising: a battery heating step for heating lithium ion battery waste while supplying an inert gas in a heat treatment furnace 1; and a gas combustion step for sending gas that is produced in the heat treatment furnace 1 to a gas combustion furnace 2 and combusting said gas in the gas combustion furnace 2, wherein in the battery heating step, when the lithium ion battery waste is heated while supplying the inert gas in the heat treatment furnace 1, the gauge pressure in the heat treatment furnace 1 is maintained in the range of -0.20 to -0.01 kPa.

Description

Technical Field

[0001] This specification discloses a heat treatment method for lithium-ion battery waste.

Background Art

[0002] In recent years, recovering valuable metals from lithium-ion battery waste discarded due to product lifespan, manufacturing defects, or other reasons has been widely studied from the perspective of effective resource utilization.

[0003] Regarding this, Patent Document 1 describes that "when recovering lithium from battery waste, after heating and heat-treating the battery waste in a heat treatment furnace, the lithium in the battery powder obtained by performing crushing, sieving, etc. is leached into water", and "by heat treatment, the lithium in lithium compounds such as lithium composite oxides that may be contained in the battery waste is changed into a form of lithium carbonate that is easily leached into water".

[0004] And in Patent Document 1, for the purpose of "stably generating lithium carbonate", "a method for heat-treating battery waste containing lithium, in which an atmosphere gas containing oxygen and at least one selected from the group consisting of nitrogen, carbon dioxide, and water vapor is flowed in a heat treatment furnace in which the battery waste is disposed, and the battery waste is heated while adjusting the oxygen partial pressure in the furnace" is proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, since lithium-ion battery waste is heat-treated in an inert atmosphere, it may be heated while supplying an inert gas into a heat treatment furnace. At this time, a relatively large amount of combustible gas or the like derived from the electrolytic solution and other components may be generated from the lithium-ion battery waste. In order to burn such generated gas, it is conceivable to install a gas combustion furnace in parallel with the heat treatment furnace.

[0007] Here, when the generated gas is sent from the heat treatment furnace to the gas combustion furnace and burned in the gas combustion furnace, the oxygen concentration in the heat treatment furnace may not become low to a certain extent, or the generated gas may leak to the outside of the heat treatment furnace.

[0008] This specification provides a heat treatment method for lithium-ion battery waste that can suppress leakage of gas generated from lithium-ion battery waste to the outside while maintaining a relatively low oxygen concentration in the heat treatment furnace.

Means for Solving the Problems

[0009] The heat treatment method for lithium-ion battery waste disclosed in this specification includes a battery heating step of heating the lithium-ion battery waste while supplying an inert gas in a heat treatment furnace, and a gas combustion step of sending the generated gas in the heat treatment furnace into a gas combustion furnace and burning the generated gas in the gas combustion furnace. In the battery heating step, when heating the lithium-ion battery waste while supplying an inert gas into the heat treatment furnace, the gauge pressure in the heat treatment furnace is maintained within a range of -0.20 kPa to -0.01 kPa.

Advantages of the Invention

[0010] According to the above heat treatment method for lithium-ion battery waste, it is possible to suppress leakage of gas generated from lithium-ion battery waste to the outside while maintaining a relatively low oxygen concentration in the heat treatment furnace.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the above-described heat treatment method for lithium ion battery waste will be described in detail. In the heat treatment method of one embodiment, for example, in the heat treatment furnace 1 in the facility as shown in FIG. 1, a battery heating step of heating the lithium ion battery waste while supplying an inert gas, and a gas generated in the heat treatment furnace 1 in the battery heating step (generated gas) is sent into the gas combustion furnace 2, and a gas combustion step of burning the generated gas in the gas combustion furnace 2 are included.

[0013] In the battery heating step, the lithium ion battery waste is heated while supplying an inert gas to adjust the furnace atmosphere. At this time, if the oxygen concentration in the heat treatment furnace 1 is lowered to a certain extent, the metal contained in the lithium ion battery waste can be effectively changed into a form that is easy to process later. If the pressure in the heat treatment furnace 1 is lower than the atmospheric pressure, it becomes easier for the air outside the furnace to flow into the heat treatment furnace 1. Therefore, if the purpose is only to lower the oxygen concentration in the heat treatment furnace 1, it is also considered desirable to maintain the heat treatment furnace 1 at an internal pressure equal to or higher than the atmospheric pressure (that is, a positive pressure).

[0014] On the other hand, in the heat treatment furnace 1, when the lithium-ion battery waste is heated, combustible gases such as those derived from the electrolyte and other components contained in the lithium-ion battery waste are generated from the lithium-ion battery waste. Such generated gases are sent to and burned in a gas combustion furnace 2 connected to the heat treatment furnace 1. Here, if the inside of the heat treatment furnace 1 is maintained at a positive pressure, the generated gases will leak to the outside of the heat treatment furnace 1. In order to suppress the leakage of the generated gases, it is preferable to make the inside of the heat treatment furnace 1 negative pressure. However, if the internal pressure of the heat treatment furnace 1 is made too low, air or outside air will flow into the heat treatment furnace 1, and it will be impossible to maintain a predetermined low oxygen concentration.

[0015] From such a perspective, in this embodiment, in the battery heating step, when heating the lithium-ion battery waste while supplying an inert gas into the heat treatment furnace 1, the gauge pressure inside the heat treatment furnace 1 is maintained within the range of -0.20 kPa to -0.01 kPa. Thereby, while suppressing the leakage of the generated gases, the inside of the heat treatment furnace 1 can be maintained at a desired low oxygen concentration.

[0016] (Lithium-ion battery waste) The lithium-ion battery waste targeted is a lithium-ion secondary battery for in-vehicle use or household use, etc., which has been discarded due to the life of the battery product, manufacturing defects, or other reasons. Examples of the in-vehicle lithium-ion secondary battery include those included in in-vehicle battery packs mounted on vehicles such as hybrid vehicles and electric vehicles. Examples of the household lithium-ion secondary battery include those used in mobile phones and various other electronic devices. Recovering cobalt, nickel, and other valuable metals from such lithium-ion battery waste is required from the perspective of effective utilization of resources. Lithium-ion battery waste refers to lithium-ion batteries targeted for recycling, regardless of whether the lithium-ion batteries are traded at a valuable price, or are traded free of charge or as industrial waste.

[0017] An in-vehicle battery pack including a lithium-ion secondary battery generally includes a metal case that constitutes its surrounding housing, and a battery such as a lithium-ion secondary battery having a plurality of battery cells and other components housed inside the case. The plurality of battery cells may be included in the in-vehicle battery pack as a battery module in which they are bundled. In-vehicle battery packs come in various shapes according to restrictions on the space of the vehicle on which they are mounted. For example, there are those having a vertically long outer shape that is long in one direction, such as a rectangular parallelepiped shape that is substantially rectangular in plan view.

[0018] Lithium-ion battery waste usually consists of a positive electrode active material made of one or more single metal oxides or two or more composite metal oxides of lithium, nickel, cobalt, and manganese, etc., coated and fixed on an aluminum foil (positive electrode substrate) by, for example, polyvinylidene fluoride (PVDF) or other organic binders, etc., a negative electrode material made of a carbon-based material, etc., and an organic electrolyte such as ethylene carbonate or diethyl carbonate or other electrolytes. In addition, copper, iron, etc. may be included in the lithium-ion battery waste.

[0019] Lithium-ion battery waste includes, in addition to in-vehicle battery packs, battery cells removed from in-vehicle battery packs, etc. A battery module in which battery cells are bundled may also be used as lithium-ion battery waste. The battery cells may contain an electrolyte or resin, and when heated, generated gas is produced, so there may be a need to prevent leakage of the generated gas and maintain the oxygen concentration in the heat treatment furnace 1 as described above. Furthermore, a positive electrode material with an aluminum foil or battery powder taken out from battery cells, etc. and optionally subjected to any treatment may also be used as lithium-ion battery waste. That is, the heat treatment method of this embodiment can be applied to in-vehicle battery packs, battery cells, battery modules, positive electrode materials with aluminum foils, or battery powder, etc.

[0020] (Battery Heating Step) In the battery heating process, while supplying an inert gas in the heat treatment furnace 1, the above-mentioned lithium-ion battery waste is heated under an inert atmosphere.

[0021] When heat treatment is performed under an inert atmosphere, explosive combustion of organic electrolytes and the like that may be contained in the lithium-ion battery waste is suppressed, making it easier to control the temperature in the heat treatment furnace 1. In addition, the production of nickel oxide and cobalt oxide is suppressed, and the recovery rate of valuable metals is increased by promoting the production of metals such as cobalt and nickel that are easily soluble in acids.

[0022] In addition, when it becomes difficult to control the temperature in the heat treatment furnace 1, aluminum such as aluminum foil melts, and valuable metals such as cobalt and nickel can be incorporated into the molten aluminum and solidified. In this case, there is a concern that the valuable metals will be removed together with the aluminum in the subsequent sieving process, resulting in a decrease in the recovery rate of the valuable metals. If the temperature in the heat treatment furnace 1 can be controlled, the formation of powdered lithium aluminate due to the reaction between aluminum and lithium oxide can be suppressed. Note that the formation of lithium aluminate promoted under high temperature and high oxygen partial pressure causes a decrease in the lithium leaching rate when leaching lithium in the subsequent lithium dissolution process because lithium aluminate has a lower solubility in water than lithium carbonate. In addition, the aluminum foil that has not reacted to form lithium aluminate can be easily separated in the sieving process. On the other hand, when lithium aluminate is formed, the aluminum foil becomes brittle and is likely to be mixed into the battery powder in the sieving process.

[0023] To make the inside of the heat treatment furnace 1 an inert atmosphere, an inert gas is supplied into the heat treatment furnace 1. Specifically, the inert gas can be a gas containing at least one selected from the group consisting of nitrogen, carbon dioxide, and water vapor. Among them, a gas mainly containing nitrogen is preferable. Oxygen may be contained in a certain trace amount. The oxygen partial pressure during heat treatment is, for example, in the range of 0 atm to 4×10 -2 atm, preferably 1×10 -2 atm or less, more preferably 1×10 -3Maintain it below atmospheric pressure. By doing so, embrittlement of aluminum in lithium-ion battery waste can be suppressed. If aluminum becomes embrittled during heat treatment, there is concern that the separability of aluminum will deteriorate during the subsequent screening process. The oxygen concentration in the heat treatment furnace 1 is, for example, 0.05 vol% to 4.00 vol%, preferably less than 1 vol%, more preferably less than 0.1 vol%. The oxygen partial pressure and oxygen concentration in the heat treatment furnace 1 are desirably kept low as described above from the time when the lithium-ion battery waste is heated and the temperature is raised until it is maintained at a predetermined temperature. In this case, the generated gas (such as gas derived from electrolyte or resin decomposition) generated during heating is not ignited in the heat treatment furnace 1 and can be burned in the gas combustion furnace 2 as intended. The oxygen partial pressure and oxygen concentration can be measured by a zirconia oxygen concentration meter. The above-described oxygen partial pressure and oxygen concentration mean that at least the measured value when the measurement is possible should be within the range. For example, when the organic electrolyte volatilizes, it may not be possible to measure, but the oxygen partial pressure and oxygen concentration during such unmeasurable periods are not a concern.

[0024] The supply flow rate of the inert gas into the heat treatment furnace 1 is 1 Nm 3 / h to 60 Nm 3 / h, and more preferably 6 Nm 3 / h to 60 Nm 3 / h, and particularly preferably 7 Nm 3 / h to 12 Nm 3 / h. If the flow rate of the inert gas is too high, there is concern that the temperature distribution during heat treatment will become large and heat treatment cannot be performed at an optimal temperature. On the other hand, if the flow rate of the inert gas is too low, there is a risk that the oxygen partial pressure distribution during heat treatment will become large and heat treatment cannot be performed at an optimal oxygen partial pressure.

[0025] Also, in the battery heating process, the lithium-ion battery waste can be heated and maintained at a temperature of 300°C to 800°C.

[0026] When the lithium-ion battery waste is heated in the heat treatment furnace 1 as described above, gas caused by the electrolyte or the like is generated from within the housing of the lithium-ion battery waste. Since such generated gas is flammable and needs to be combusted, it is sent from the heat treatment furnace 1 to the gas combustion furnace 2 and combusted within the gas combustion furnace 2 in the gas combustion process.

[0027] Here, when heating the lithium-ion battery waste while supplying an inert gas into the heat treatment furnace 1, the gauge pressure (that is, the pressure obtained by subtracting the atmospheric pressure from the absolute pressure) within the heat treatment furnace 1 is set to -0.20 kPa to -0.01 kPa.

[0028] By heating the lithium-ion battery waste while making the inside of the heat treatment furnace 1 slightly negative in pressure in this way, leakage of the generated gas to the outside of the heat treatment furnace 1 is prevented, and in addition, the inflow of oxygen into the heat treatment furnace 1 is suppressed, making it easier to maintain a predetermined oxygen concentration within the heat treatment furnace 1. That is to say, if the gauge pressure within the heat treatment furnace 1 is made higher than -0.01 kPa, there is a risk that the generated gas will leak from within the heat treatment furnace 1. On the other hand, if the gauge pressure within the heat treatment furnace 1 is made lower than -0.20 kPa, there is concern that outside air will flow into the heat treatment furnace 1 and the desired oxygen concentration cannot be achieved.

[0029] Furthermore, in this embodiment, by setting the gauge pressure in the heat treatment furnace 1 to -0.20 kPa to -0.01 kPa, the load on the gas combustion furnace 2 that burns the generated gas sent from the heat treatment furnace 1 can be reduced. As a result, a relatively small gas combustion furnace 2 can be used. In other words, if the gauge pressure in the heat treatment furnace 1 is set higher than -0.01 kPa to make the inside of the heat treatment furnace 1 positive pressure, the generated gas in the heat treatment furnace 1 will not easily flow into the gas combustion furnace 2. After accumulating in the heat treatment furnace 1, it will be sent to the gas combustion furnace 2 all at once at a certain timing. At this time, since the generated gas is combustible, it is necessary to limit the heat supply from the heat source of the gas combustion furnace 2 to keep the temperature in the gas combustion furnace 2 at a constant temperature. However, when the generated gas is sent to the gas combustion furnace 2 all at once, it becomes difficult to maintain the temperature in this gas combustion furnace 2. Also, if the gauge pressure in the heat treatment furnace 1 is set lower than -0.20 kPa, the generated gas will immediately flow into the gas combustion furnace 2, so in this case as well, the load on the gas combustion furnace 2 will increase.

[0030] Also, as shown in FIG. 1, the heat treatment furnace 1 and the gas combustion furnace 2 can be connected by a connecting pipe 3. The generated gas in the heat treatment furnace 1 is guided to the gas combustion furnace 2 through the connecting pipe 3. In this case, when the pressure in the heat treatment furnace 1 is high, the flow rate of the generated gas from the heat treatment furnace 1 to the gas combustion furnace 2 becomes slow, and the tar flowing into the gas combustion furnace 2 together with the generated gas aggregates in the connecting pipe 3, and clogging in the connecting pipe 3 is likely to occur. On the other hand, in this embodiment, since the internal pressure of the heat treatment furnace 1 is lowered as described above, it is also possible to effectively suppress the aggregation and clogging of tar in the connecting pipe 3.

[0031] From the above viewpoints, it is even more preferable that the gauge pressure in the heat treatment furnace is further set to -0.16 kPa to -0.13 kPa. The gauge pressure in the heat treatment furnace 1 can be measured by a pressure gauge. Specifically, for example, a measuring pipe may be inserted into the heat treatment furnace 1, and the pipe may be connected to a pressure gauge installed outside the heat treatment furnace 1, and the gauge pressure in the heat treatment furnace 1 may be measured by the pressure gauge.

[0032] Incidentally, on the downstream side in the gas flow direction of the heat treatment furnace 1 and the gas combustion furnace 2, as illustrated in FIG. 1, a gas treatment facility 4 for treating the exhaust gas discharged from the gas combustion furnace 2 after combustion of the generated gas may be provided. The gas treatment facility 4 is not particularly limited as long as it can appropriately treat the exhaust gas derived from, for example, electrolytic solution or the like. For example, it may include a gas cooling device 5 for cooling the exhaust gas and a gas washing device 6 for washing the exhaust gas that has passed through the gas cooling device 5.

[0033] On the downstream side in the gas flow direction of the heat treatment furnace 1 and the gas combustion furnace 2, it is preferable to provide a furnace pressure adjustment mechanism for adjusting the internal pressure of the heat treatment furnace 1 as described above. In the example shown in FIG. 1, as this furnace pressure adjustment mechanism, a valve 7 and an exhaust fan 8 are provided on the downstream side of the heat treatment furnace 1 and the gas combustion furnace 2 in the gas flow direction, and further on the downstream side of the gas treatment facility 4. In the illustrated example where it is connected by a closed pipeline without being open to the atmosphere from the heat treatment furnace 1 to the gas treatment facility 4, the internal pressure of the heat treatment furnace 1 can be controlled by automatically or manually adjusting the opening degree of the valve 7 and / or the rotation speed of the exhaust fan 8 on the downstream side of the gas treatment facility 4. In this example, since either one of the valve 7 or the exhaust fan 8 can adjust the internal pressure of the heat treatment furnace 1, either one of the valve 7 or the exhaust fan 8 may be omitted. Note that regardless of the configuration of the furnace pressure adjustment mechanism, as described above, by adjusting the gauge pressure in the heat treatment furnace 1 within a predetermined range, the effects of suppressing the leakage of the generated gas to the outside and maintaining the oxygen concentration in the heat treatment furnace 1 can be obtained. Therefore, as the furnace pressure adjustment mechanism, various configurations can be used, not limited to the valve 7 and the exhaust fan 8 shown in FIG. 1.

[0034] As the heat treatment furnace 1, a special furnace such as a vacuum furnace may be used, but it is also possible to use a general furnace whose sealing property is not as high as that of a vacuum furnace. In such a general furnace, a small amount of air (oxygen) can flow in from the outside, but as described above, by adjusting the internal pressure and other conditions, the oxygen concentration in the furnace can be maintained sufficiently low. In a vacuum furnace, a seal structure for the furnace door, a chamber for creating a vacuum environment, installation of a vacuum pump and vacuum valves for creating a vacuum, strengthening of the seal of the mounting port for instrumentation for measuring the temperature and pressure inside the furnace, etc. can be carried out. Also, depending on the vacuum furnace, there are some that are not suitable for processes that generate a relatively large amount of gas, such as the heat treatment of lithium-ion battery waste. On the other hand, in a general furnace, since such a structure etc. is not provided, it is possible to keep the installation cost and the cost required for maintenance low, and the heat treatment of lithium-ion battery waste can be effectively carried out. The heat treatment furnace 1 can be not only a batch type but also a continuous type. This embodiment can also be applied when using a continuous heat treatment furnace 1. The heat treatment furnace 1 can be a furnace in which the heat source is exposed to the object to be heat-treated (such as lithium-ion battery waste), but it may also be a muffle furnace in which the object to be heat-treated is isolated from the heat source. The muffle furnace has a high degree of sealing, can suppress the inflow of outside air, and can eliminate the influence of oxygen release from the refractory. Therefore, when the heat treatment furnace 1 is a muffle furnace, the supply flow rate of the inert gas into the heat treatment furnace 1 may be reduced in some cases. When it is desired to reduce the supply flow rate of the inert gas, for example, to 6 Nm 3 / h or less, etc., it is desirable to adopt a muffle furnace as the heat treatment furnace 1.

[0035] Note that the lithium-ion battery waste may be heat-treated in an air atmosphere before or after the heat treatment in an inert atmosphere as described above, preferably after the heat treatment in an inert atmosphere. The heat treatment in an air atmosphere is preferable in that the adjustment of the atmosphere becomes unnecessary and it can be carried out simply. In the heat treatment in an air atmosphere, the lithium-ion battery waste can be heated and maintained at a temperature of 300°C to 800°C.

[0036] (Gas combustion process) In the gas combustion process, the generated gas sent from the heat treatment furnace 1 to the gas combustion furnace 2 is burned at a predetermined high temperature inside the gas combustion furnace 2 to be rendered harmless. The gas after combustion is discharged from the gas combustion furnace 2 as exhaust gas and may be sent to the gas treatment facility 4 as described above.

[0037] By maintaining the internal pressure in the heat treatment furnace 1 within a predetermined range in the battery heating process, in the gas combustion process, the generated gas flows into the gas combustion furnace 2 at an appropriate flow rate. As a result, the load on the gas combustion furnace 2 is kept small, so the generated gas can be processed by a relatively small gas combustion furnace 2.

[0038] The inside of the gas combustion furnace 2 can preferably be maintained at 800°C to 1000°C, more preferably 850°C to 900°C. If the temperature inside the gas combustion furnace 2 is too low, there is concern that the generated gas will not burn effectively. On the other hand, if the temperature is too high, there may be a risk that the time for the generated gas to burn effectively cannot be ensured inside the gas combustion furnace 2, or that the capacity of the subsequent gas treatment facility 4 will be exceeded.

[0039] In the gas combustion furnace 2, the temperature tends to rise easily due to the combustion of the generated gas. In that case, it is preferable to adjust the temperature inside the gas combustion furnace 2 by changing the amount of heat supplied from the heat source of the gas combustion furnace according to the combustion of the generated gas inside the gas combustion furnace 2.

[0040] Specifically, if the heat source is LPG gas used in an LPG burner, in order to ensure that the temperature inside the gas combustion furnace 2 does not exceed a predetermined temperature during the combustion of the generated gas, the supply amount of LPG gas can be controlled to decrease. For example, in the graph shown in Fig. 2, as time elapses after starting to heat the lithium-ion battery waste inside the heat treatment furnace 1, the temperature of the lithium-ion battery waste (LIB temperature) is shown to increase. At this time, when the generated gas inside the heat treatment furnace 1 flows into the gas combustion furnace 2 and burns inside the gas combustion furnace 2, in response to the combustion, the combustion flow rate of the LPG gas, which is the heat source of the gas combustion furnace 2 (LPG combustion flow rate), is adjusted to decrease so that the temperature inside the gas combustion furnace 2 does not exceed a predetermined temperature. LPG burners usually mix LPG gas and air for combustion. Here, the aforementioned LPG combustion flow rate and ΔLPG described later refer to the flow rate of LPG gas, not the flow rate of the mixed gas with air.

[0041] Here, when a relatively large amount of generated gas flows into the gas combustion furnace 2, the combustion becomes intense and the temperature inside the gas combustion furnace 2 can rise rapidly. To suppress this, it is desirable to quickly reduce the LPG combustion flow rate. The amount of reduction of the LPG combustion flow rate is referred to as ΔLPG here. If ΔLPG becomes too large, the LPG combustion flow rate will reach the minimum flow (the minimum amount of the LPG combustion flow rate), and as a result, the LPG combustion flow rate cannot be reduced further, raising the concern that the temperature inside the gas combustion furnace 2 will exceed the predetermined temperature. As the above-mentioned minimum flow, there are cases where a flow rate greater than 0 Nm 3 / h is set (when a certain amount of LPG gas continues to be supplied even when the LPG combustion flow rate is reduced to the maximum), and cases where it is 0 Nm 3 / h (when the supply of LPG gas is stopped). In any case, when the LPG combustion flow rate reaches the minimum flow, it cannot be reduced further, and it becomes impossible to prevent the temperature from exceeding the limit. In Fig. 2, the LPG combustion flow rate is rapidly reduced twice. The first time is considered to be when a large amount of gas generated from the electrolyte is generated, and the second time is when CH-based gas is generated due to resin decomposition.

[0042] In this embodiment, by maintaining the gauge pressure in the heat treatment furnace 1 within the above-mentioned range during the battery heating process, the generated gas flows into the gas combustion furnace 2 at an appropriate flow rate, so that ΔLPG can be suppressed to a small value. Depending on the lithium-ion battery waste to be processed, for example, in the case of in-vehicle battery packs, ΔLPG per battery module is 1.0 Nm 3 / hr or less, further 0.40 Nm 3 / hr or less, particularly 0.37 Nm 3 / hr or less, typically 0.15 - 0.25 Nm 3 / hr can be suppressed, and when CH-based gas is generated by resin decomposition, it is 1.0 Nm 3 / hr or less, further 0.40 Nm 3 / hr or less, particularly 0.29 Nm 3 / hr or less, typically 0.25 - 0.35 Nm 3 / hr may be suppressed. Also, ΔLPG per unit mass (1 kg) of the electrolyte contained in the lithium-ion battery waste is 1.5 Nm 3 / hr or less, further 0.60 Nm 3 / hr or less, particularly 0.56 Nm 3 / hr or less, typically 0.20 - 0.40 Nm 3 / hr may be suppressed. Also, ΔLPG per unit mass (1 kg) of the resin contained in the lithium-ion battery waste is 4.5 Nm 3 / hr or less, further 1.8 Nm 3 / hr or less, particularly 1.3 Nm 3 / hr or less, typically 1.1 - 1.6 Nm 3It may be possible to suppress it to / hr. Here, when gas generated from the electrolytic solution is mentioned, it means when the temperature of the lithium-ion battery waste reaches 150°C to 190°C. Typically, it is around 170°C. In many cases, when the lithium-ion battery waste is heated, the low-boiling components in the electrolytic solution evaporate sequentially from the inside, and when the above temperature range is reached, the inside reaches a predetermined pressure, and the safety valve opens to generate gas derived from the electrolytic solution. Also, when CH-based gas is generated, it means when the temperature of the lithium-ion battery waste reaches 380°C to 420°C. This temperature range coincides with the decomposition (vaporization) temperature of the resin attached to the battery module of the lithium-ion battery waste, and is typically around 400°C. Note that the resin decomposition gas is often a mixture of multiple hydrocarbon-based compounds. Per unit of lithium-ion battery waste, the electrolytic solution may contain 662 g, and the resin may contain 230 g. Note that ΔLPG can vary depending on the presence or absence of rupture of the lithium-ion battery waste during heat treatment, the residual voltage of the lithium-ion battery waste described later, etc. However, if various conditions are substantially the same, maintaining the gauge pressure in the heat treatment furnace within the range of -0.20 kPa to -0.01 kPa can reduce ΔLPG compared to the case outside this range.

[0043] In the battery heating step described above, it is preferable to subject the lithium-ion battery waste with a residual voltage of less than 2.4 V to heating. When the residual voltage is high, ΔLPG tends to increase when gas generated from the electrolytic solution is generated.

[0044] On the other hand, even if the residual voltage of the lithium-ion battery waste is 2.4 V or more, as described above, by controlling the gauge pressure in the heat treatment furnace 1, it is possible to suppress the increase in ΔLPG to a certain extent. Therefore, in this embodiment, even such lithium-ion battery waste with a relatively high residual voltage can be the object of heat treatment. To lower the residual voltage of the lithium-ion battery waste, an additional step of discharging the lithium-ion battery waste is required, but by making even the lithium-ion battery waste with a relatively high residual voltage the object of heat treatment, this discharging step can be made unnecessary.

[0045] In addition, even when treating lithium-ion battery waste with a relatively high residual voltage by heat treatment, a discharging process may be omitted for some lithium-ion battery waste, such as performing a discharging process on lithium-ion battery waste with a residual voltage higher than a predetermined voltage and not performing a discharging process on lithium-ion battery waste with a residual voltage lower than the predetermined voltage. Even in this case, the throughput of the discharging process can be reduced, and the cost required for the discharging process can be kept low.

[0046] The reason why ΔLPG changes depending on the residual voltage is presumed as follows. When the battery cell of the lithium-ion battery waste is heated and the temperature rises, a short circuit occurs due to the softening of the separator and the pressure applied inside the battery cell, and the temperature of the battery cell rises rapidly. The degree of the rapid rise becomes larger as the residual voltage becomes higher. And when the temperature of the battery cell rises rapidly, the evaporation of the electrolyte proceeds rapidly. Therefore, when the safety valve of the battery cell opens, the discharge rate of the discharged electrolyte becomes larger. As a result, it is considered that ΔLPG becomes larger.

[0047] When the internal pressure of the heat treatment furnace 1 deviates from the predetermined range, the inflow rate of the generated gas into the gas combustion furnace 2 increases and ΔLPG increases. Therefore, it is necessary to secure a difference between the LPG combustion flow rate and the minimum flow rate that can absorb such a large ΔLPG, that is, a large LPG combustion flow rate is required. As a result, the gas combustion furnace 2 has to be enlarged. As an example, when the gauge pressure in the heat treatment furnace is made smaller than -0.20 kPa to about -0.30 kPa, ΔLPG may increase from 0.64 Nm 3 / hr to 1.0 Nm 3 / hr. In addition, as the heat source of the gas combustion furnace, in addition to the above LPG gas (liquefied petroleum gas whose main components are propane and butane), LNG gas (liquefied natural gas whose main component is methane and is used as city gas etc.), heavy oil, recycled oil, etc. may also be used.

[0048] (Subsequent process) For the lithium-ion battery waste that has undergone the above-described battery heating process, a crushing process, a pulverizing and powdering process, and a screening process can be performed as necessary. Crushing is performed to remove the battery from the case of lithium-ion battery waste such as in-vehicle battery packs, destroy the battery housing, and selectively separate the positive electrode active material from the aluminum foil coated with the positive electrode active material. Here, various known apparatuses or devices can be used. Specific examples thereof include impact crushers that can crush while cutting lithium-ion battery waste, such as sample mills, hammer mills, pin mills, wing mills, tornado mills, hammer crushers, and the like. A screen can be installed at the outlet of the crusher, and thereby, the battery is discharged through the screen from the crusher when it is crushed to a size that can pass through the screen.

[0049] After crushing, the crushed battery may be lightly pulverized into a powder as necessary, and then screened using a sieve with an appropriate mesh size. By pulverizing and powdering, the separability of the positive electrode active material adhered to the aluminum foil from the aluminum foil is improved. However, the pulverizing and powdering may be omitted. As a result, on the sieve residue, for example, aluminum, copper, etc. remain, and battery powder containing lithium, cobalt, nickel, etc. from which aluminum, copper, etc. have been removed to some extent can be obtained under the sieve.

[0050] The above battery powder is brought into contact with any one of a weakly acidic solution, water, or an alkaline solution in the lithium dissolution step to dissolve the lithium contained in the battery powder in the solution. For the lithium dissolution solution, lithium in the lithium dissolution solution can be recovered as lithium carbonate by performing treatments such as solvent extraction, neutralization, carbonation, etc.

[0051] The residue that remained undissolved in water or the solution during the lithium dissolution step can be taken out by solid-liquid separation using a filter press, a thickener, or the like, and then leached with an acid in the acid leaching step. The acid leaching step can be carried out by a known method or conditions. For example, the pH may be set to 0.0 to 3.0.

[0052] For the leachate obtained by acid leaching and solid-liquid separation in the acid leaching step, various metals such as cobalt and nickel can be recovered by performing, for example, neutralization, solvent extraction, and other steps.

Example

[0053] Next, the above-described heat treatment method for lithium-ion battery waste was experimentally carried out to confirm its effect, and the explanation is given below. However, the explanation here is for the purpose of mere illustration and is not intended to be limited thereto.

[0054] Using a predetermined heat treatment furnace and a gas combustion furnace, while supplying nitrogen gas in the heat treatment furnace, the lithium-ion battery waste was heated to 600 °C, and the generated gas was burned in the gas combustion furnace. The lithium-ion battery waste subjected to heat treatment was three battery modules in which battery cells included in an in-vehicle battery pack were bundled. The supply flow rate of nitrogen gas into the heat treatment furnace was 7.8 Nm 3 / h, and the LPG combustion flow rate and the like were adjusted so that the temperature in the gas combustion furnace was maintained at 850 °C.

[0055] (Example 1) The internal pressure (gauge pressure, furnace pressure) of the heat treatment furnace was controlled within the range of -0.16 kPa to -0.13 kPa. As a result, the oxygen concentration in the heat treatment furnace could be reduced to less than 0.1% by volume. The oxygen partial pressure in the heat treatment furnace was 0.998×10 -3 atm. Also, no leakage of the generated gas to the outside of the heat treatment furnace was confirmed. The flow rate of the gas (generated gas and nitrogen gas) in the connecting pipe connecting the heat treatment furnace and the gas combustion furnace was 28.2 m 3 / h. ΔLPG was relatively small and could be suppressed in both the case of gas generation from the electrolyte and the case of CH-based gas generation, as shown in Table 1. The residual voltage (cell voltage) of the battery cells in the lithium-ion battery waste before heat treatment was almost 0 V. Here, since three battery modules were the objects of treatment, the overall ΔLPG (total ΔLPG) was approximately three times the ΔLPG per module in Table 1, and was about 0.67 Nm 3 / h at the time of electrolyte gas generation and 0.86 Nm 3 / h at the time of CH-based gas generation.

[0056] (Example 2) The same procedure as in Example 1 was followed, except that the residual voltage of the lithium-ion battery waste before heat treatment was 2.4 V. As a result, ΔLPG at the time of gas generation from the electrolyte became slightly larger than that in Example 1. The oxygen concentration and oxygen partial pressure in the heat treatment furnace were the same as in Example 1. The total ΔLPG was about 1.11 Nm 3 / h at the time of electrolyte gas generation and about 0.86 Nm 3 / h at the time of CH-based gas generation.

[0057] (Comparative Example 1) The same procedure as in Example 1 was followed, except that the internal pressure of the heat treatment furnace was in the range of -0.50 kPa to -0.30 kPa. In this case, the oxygen concentration in the heat treatment furnace could not be reduced to 0.1% by volume. This is considered to be due to air flowing into the furnace from the outside. In Comparative Example 1, since the oxygen concentration did not become less than 0.1% by volume, the heating test of the lithium-ion battery waste could not be carried out.

[0058] (Comparative Example 2) The same procedure as in Example 1 was followed, except that the internal pressure of the heat treatment furnace was 0 kPa. In this case, it was confirmed that the generated gas leaked outside the heat treatment furnace. Therefore, in Comparative Example 2 as well, the heating test of the lithium-ion battery waste could not be carried out.

[0059]

Table 1

[0060] From the above, it was found that according to the heat treatment method described above, it is possible to maintain a relatively low oxygen concentration in the heat treatment furnace while suppressing the leakage of gas generated from the lithium-ion battery waste to the outside of the heat treatment furnace.

Explanation of symbols

[0061] 1 Heat treatment furnace 2 Gas combustion furnace 3 Connecting pipe 4 Gas treatment equipment 5 Gas cooling device 6 Gas cleaning device 7 Valve 8 Exhaust fan

Claims

1. A heat treatment method for lithium-ion battery waste, comprising: a battery heating step of heating the lithium-ion battery waste while supplying an inert gas in a heat treatment furnace; a gas combustion step of sending the generated gas in the heat treatment furnace into a gas combustion furnace and burning the generated gas in the gas combustion furnace; and in the battery heating step, when heating the lithium-ion battery waste while supplying an inert gas into the heat treatment furnace, maintaining the gauge pressure in the heat treatment furnace within a range of -0.20 kPa to -0.01 kPa.

2. The heat treatment method according to claim 1, wherein in the battery heating step, when heating the lithium-ion battery waste while supplying an inert gas into the heat treatment furnace, maintaining the oxygen concentration in the heat treatment furnace at less than 1% by volume from the time of temperature rise of the lithium-ion battery waste.

3. When heating the lithium-ion battery waste while supplying an inert gas into the heat treatment furnace in the battery heating step, from the time when the temperature of the lithium-ion battery waste starts to rise, maintain the oxygen partial pressure in the heat treatment furnace at 1×10 -2 atm or less. The heat treatment method according to claim 1 or 2.

4. In the battery heating step, the supply flow rate of the inert gas is 1 Nm 3 / h to 60 Nm 3 / h, and the lithium-ion battery waste is heated to a temperature of 300°C to 800°C. The heat treatment method according to claim 1 or 2.

5. The heat treatment method according to claim 1 or 2, wherein the exhaust gas from the gas combustion furnace is treated by gas treatment equipment provided downstream in the gas flow direction of the heat treatment furnace and the gas combustion furnace.

6. The heat treatment method according to claim 1 or 2, wherein the gauge pressure in the heat treatment furnace is adjusted by a furnace pressure adjustment mechanism provided downstream in the gas flow direction of the heat treatment furnace and the gas combustion furnace.

7. The heat treatment method according to claim 1 or 2, wherein in the gas combustion step, in response to the combustion of the generated gas in the gas combustion furnace, changing the amount of heat supplied from the heat source of the gas combustion furnace to control the temperature in the gas combustion furnace.

8. The heat treatment method according to claim 7, wherein the heat source of the gas combustion furnace is LPG gas, LNG gas or heavy oil.

9. The lithium-ion battery waste is an in-vehicle battery pack, and the heat source of the gas combustion furnace is LPG gas. In the gas combustion process, ΔLPG per battery module is 1.0 Nm 3 / hr or less when gas derived from the electrolytic solution is generated, and 1.0 Nm 3 / hr or less when CH-based gas is generated. The heat treatment method according to claim 8.

10. In the gas combustion step, ΔLPG per unit mass (1 kg) of the electrolytic solution contained in the lithium ion battery waste is 1.5 Nm 3 / hr or less at the time of generation of the gas derived from the electrolytic solution, and the heat treatment method according to claim 8.

11. In the gas combustion step, the ΔLPG per unit mass (1 kg) of the resin contained in the lithium-ion battery waste is 4.5 Nm 3 / hr or less during the generation of CH-based gas. The heat treatment method according to claim 8.

12. The heat treatment method according to claim 1 or 2, wherein in the battery heating step, heating the lithium-ion battery waste having a residual voltage of less than 2.4 V.

13. The heat treatment method according to claim 1 or 2, wherein in the battery heating step, heating the lithium-ion battery waste having a residual voltage of 2.4 V or more.

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