JP7707443B2 - Thermal treatment method for lithium-ion battery waste - Google Patents

Description

This specification discloses a method for thermally treating lithium ion battery waste.

In recent years, recovery of valuable metals from lithium-ion battery waste that has been discarded due to product life, manufacturing defects, or other reasons has been widely considered from the perspective of effective resource utilization.

When recovering valuable metals from lithium-ion battery waste, the lithium-ion battery waste may be subjected to heat treatment, crushing, sieving, etc. to obtain battery powder that contains as much of the metal of the positive electrode active material as possible while removing metals that are impurities that are not subject to recovery. Then, as a wet process, a process may be performed in which the metals in the battery powder are leached with acid, etc., and various metals are recovered from the resulting leaching solution.

Among these, techniques related to heat treatment include those described in Patent Documents 1 to 4, for example.

Patent Document 1 describes a method for heating and treating a lithium ion battery enclosed in a casing containing aluminum, which method controls the rate at which the temperature of the lithium ion battery is increased to above 400°C, thereby terminating the outflow of gas from within the casing of the lithium ion battery while the temperature of the lithium ion battery is within the range of 200°C to 400°C.

Patent Document 2 describes a method for treating lithium ion batteries containing cobalt and nickel, comprising: a heating step of heating the lithium ion battery and maintaining the temperature of the lithium ion battery at 550°C to 650°C for 1 to 4 hours; and a leaching step of adding the battery powder obtained after the heating step to a leaching solution containing 0.9 to 1.5 molar equivalents of sulfuric acid required to dissolve all of the metal components contained in the battery powder, and heating the leaching solution to a temperature of 60°C to 80°C to leach the battery powder.

Patent Document 3 describes "a method for treating lithium ion batteries, comprising a heating step of heating lithium ion batteries to 450°C to 650°C, and a leaching step of leaching the battery powder obtained after the heating step with a leaching solution containing 0.9 to 1.5 molar equivalents of sulfuric acid required to dissolve all metal components contained in the battery powder, and terminating the leaching before the oxidation-reduction potential ORP value (based on silver/silver chloride potential) of the leaching solution exceeds 0 mV."

Patent Document 4 describes a method for treating a lithium ion battery, "wherein a lithium ion battery enclosed in a casing containing aluminum is placed in a battery heating space and hot gas is fed into the battery heating space to heat and treat the lithium ion battery, the method comprising: setting the temperature of the hot gas fed into the battery heating space to less than 450°C; and, while the temperature of the lithium ion battery heated by the hot gas is within the range of 200°C to 400°C, causing battery gas to flow out from within the casing of the lithium ion battery and terminating the flow of the battery gas."

JP 2020-73732 A JP 2017-36490 A JP 2017-36489 A JP 2017-37818 A

Incidentally, lithium-ion battery waste may be heated in a heat treatment furnace under a specified atmosphere in order to perform heat treatment in an inert atmosphere. During this process, a relatively large amount of flammable gases derived from the electrolyte and other components may be generated from the lithium-ion battery waste. In order to combust and detoxify such generated gases, it is considered to install a gas combustion furnace next to the heat treatment furnace.

In a gas combustion furnace, fuel is supplied to burn the generated gas. In such a gas combustion furnace, when lithium-ion battery waste is heated in a heat treatment furnace, it is desirable to control the temperature in the gas combustion furnace to be constant by changing the amount of fuel supply. For example, when a large amount of generated gas is sent from the heat treatment furnace, the amount of fuel supply can be adjusted to be reduced in order to suppress the temperature rise caused by the combustion of a large amount of generated gas in the gas combustion furnace. As an example, in the case of a gas combustion furnace that uses LPG as fuel, the amount of LPG combustion flow supplied to the gas combustion furnace may be adjusted to be reduced, and the amount of reduction in the LPG combustion flow rate in the gas combustion furnace (reduction in the amount of fuel) at this time is called ΔLPG.

Here, it was found that when the temperature inside the heat treatment furnace is raised to heat the lithium-ion battery waste, at a certain time, the reduction in the amount of fuel in the gas combustion furnace becomes large, i.e., the amount of fuel supply is greatly reduced. When the reduction in the amount of fuel becomes large, the load on the gas combustion furnace becomes large. Specifically, when the reduction in the amount of fuel is large, the amount of fuel supply reaches the minimum flow (the minimum amount of fuel supply) and the amount of fuel supply cannot be further reduced, and as a result, the rise in the internal temperature cannot be suppressed, and the temperature rises, and there is a risk that the equipment will become worn out or burn out. This becomes apparent when a small gas combustion furnace is used due to restrictions on installation space, etc.

This specification provides a method for thermally treating lithium-ion battery waste that can reduce the load on gas combustion furnaces.

The heat treatment method for lithium ion battery waste disclosed in this specification includes a battery heating process for heating the lithium ion battery waste in a heat treatment furnace, and a gas combustion process for sending the gas generated in the heat treatment furnace into a gas combustion furnace, supplying LPG as fuel in the gas combustion furnace to combust the generated gas, and changing the LPG combustion flow rate, which is the fuel supply amount, according to the temperature in the gas combustion furnace, and during the temperature rise in the heat treatment furnace, there are two or more ΔLPG increase periods in which ΔLPG, which is the throttle amount of the LPG combustion flow rate in the gas combustion furnace, is increased to 0.5 ^Nm3 /h or more, and during at least a part of at least the second ΔLPG increase period, the temperature rise rate in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained.

In addition, the heat treatment method for lithium ion battery waste disclosed in this specification targets lithium ion battery waste containing resin and includes a battery heating process for heating the lithium ion battery waste in a heat treatment furnace, and a gas combustion process for sending gas generated in the heat treatment furnace to a gas combustion furnace, supplying fuel in the gas combustion furnace to combust the generated gas, and changing the amount of fuel supply depending on the temperature in the gas combustion furnace, and during the temperature rise in the heat treatment furnace, the rate of temperature rise in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained, at least for at least a part of the period during which the resin is thermally decomposed.

The heat treatment method for lithium ion battery waste disclosed in this specification includes a battery heating process for heating the lithium ion battery waste in a heat treatment furnace, and a gas combustion process for sending gas generated in the heat treatment furnace into a gas combustion furnace, supplying fuel in the gas combustion furnace to combust the generated gas, and changing the amount of fuel supply depending on the temperature in the gas combustion furnace, and during heating in the heat treatment furnace, the rate of heating in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained, at least for at least a portion of the period during which the temperature of the lithium ion battery waste reaches 380°C to 530°C.

The above-mentioned thermal treatment method for lithium-ion battery waste can reduce the load on the gas combustion furnace.

1 is a graph showing an example of changes over time in the temperature of lithium ion battery waste when the lithium ion battery waste is heated and in the LPG combustion flow rate of a gas combustion furnace. 1 is a graph showing the change over time in the set temperature in a heat treatment furnace, the temperature of lithium-ion battery waste, and the LPG combustion flow rate in a comparative example, and a graph showing the same in schematic form. 3 is a graph showing the change over time of the difference in LPG combustion flow rate obtained by subtracting the LPG combustion flow rate in the graph showing the change over time of the LPG combustion flow rate when the heat treatment furnace in the comparative example is operated without placing lithium ion battery waste in the furnace from the LPG combustion flow rate in the graph in FIG. 2 . 1 is a graph showing the change over time in the set temperature in a heat treatment furnace, the temperature of lithium-ion battery waste, and the LPG combustion flow rate in an embodiment, and a schematic graph showing the same. 5 is a graph showing the change over time of the difference in LPG combustion flow rate obtained by subtracting the LPG combustion flow rate in the graph showing the change over time of the LPG combustion flow rate when the heat treatment furnace in the embodiment is operated without placing lithium ion battery waste in the furnace from the LPG combustion flow rate in the graph in FIG.

Hereinafter, an embodiment of the above-mentioned method for heat treating lithium ion battery waste will be described in detail.
The thermal treatment method for lithium-ion battery waste includes a battery heating step and a gas combustion step. In the battery heating step, the lithium-ion battery waste is heated in a thermal treatment furnace. In the gas combustion step, the gas generated in the thermal treatment furnace is sent to a gas combustion furnace, fuel is supplied in the gas combustion furnace to combust the generated gas, and the amount of fuel supplied is changed according to the temperature in the gas combustion furnace.

As an example, in a gas combustion furnace where the fuel is LPG, the generated gas is burned by an LPG burner that uses LPG. In such a gas combustion furnace, when the amount of generated gas being processed increases, the fuel supply amount may be reduced to prevent the internal temperature from rising above a predetermined value. For example, when the fuel is LPG, the LPG combustion flow rate (LPG combustion flow rate) as the fuel supply amount is reduced, and this reduction in the LPG combustion flow rate is referred to here as ΔLPG.

In one embodiment, during heating in the heat treatment furnace, there are two or more ΔLPG increase periods (fuel reduction increase periods) in which ΔLPG is increased to 0.5 ^Nm3 /h or more, and during at least a portion of at least the second ΔLPG increase period, the heating rate in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained. In another embodiment, during heating in the heat treatment furnace, the heating rate in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained at least during at least a portion of the period in which the resin is thermally decomposed. In yet another embodiment, during heating in the heat treatment furnace, the heating rate in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained at least during at least a portion of the period in which the temperature of the lithium ion battery waste is 380°C to 530°C.

During the above period, the more the LPG combustion flow rate reaches the minimum flow (the smallest amount of LPG combustion flow rate), the larger ΔLPG can become. If ΔLPG becomes too large and the LPG combustion flow rate cannot be further reduced, there is a concern that the temperature inside the gas combustion furnace will exceed a predetermined temperature. In response to this, if the rate of temperature rise inside the heat treatment furnace is reduced or the temperature inside the heat treatment furnace is maintained during at least a portion of the period, the flow rate of gas generated from the lithium-ion battery waste is suppressed, and the amount of gas generated in the gas combustion furnace that needs to be processed is reduced. As a result, the load on the gas combustion furnace can be reduced.

(Lithium ion battery waste)
The lithium-ion battery waste targeted here is lithium-ion secondary batteries for in-vehicle or consumer use that have been discarded due to the end of the battery product's life, manufacturing defects, or other reasons. Examples of lithium-ion secondary batteries for in-vehicle use include those contained in in-vehicle battery packs installed in vehicles such as hybrid cars and electric cars. Examples of lithium-ion secondary batteries for consumer use include those used in mobile phones and various other electronic devices. From the perspective of effective resource utilization, it is desirable to recover valuable metals such as cobalt, nickel, and others from such lithium-ion battery waste.

An on-board battery pack including an on-board lithium-ion secondary battery generally comprises a metal case that forms the surrounding housing, a battery such as a lithium-ion secondary battery having multiple battery cells housed inside the case, and other components. The multiple battery cells may be bundled together and included in the on-board battery pack as a battery module. On-board battery packs come in a variety of shapes depending on the space constraints of the vehicle in which they are mounted, but some have an external shape that is elongated in one direction, such as a rectangular parallelepiped that is roughly rectangular in plan view.

Lithium-ion battery waste usually contains a positive electrode material in which a positive electrode active material made of one or more single metal oxides of lithium, nickel, cobalt, and manganese, or a composite metal oxide of two or more types, is coated and fixed on an aluminum foil (positive electrode substrate) with, for example, polyvinylidene fluoride (PVDF) or other organic binder, a negative electrode material made of a carbon-based material, and an organic electrolyte solution such as ethylene carbonate or diethyl carbonate or other electrolyte. Lithium-ion battery waste may also contain copper, iron, etc.

Lithium ion battery waste includes battery cells removed from in-vehicle battery packs and the like. Battery modules made by bundling battery cells may be treated as lithium ion battery waste. Furthermore, aluminum foil-attached positive electrode material or battery powder that has been removed from battery cells and the like and subjected to any processing as necessary may also be treated as lithium ion battery waste. In other words, the heat treatment method of this embodiment can be applied to in-vehicle battery packs, battery cells, battery modules, aluminum foil-attached positive electrode material or battery powder, etc.

Lithium-ion battery waste may contain electrolyte and resin in the battery cells. As an example, one battery module of lithium-ion battery waste may contain 662 g of electrolyte and 230 g of resin. When lithium-ion battery waste containing electrolyte and resin is heated, gas is generated.

(Battery heating process)
In the battery heating step, the lithium ion battery waste is heated in an inert atmosphere such as nitrogen, carbon dioxide and/or water vapor while supplying an inert gas in a heat treatment furnace, and the temperature is maintained at, for example, 300° C. to 650° C.

When heat treatment is performed in an inert atmosphere, explosive combustion of electrolytes and the like that may be contained in lithium-ion battery waste is suppressed, making it easier to control the temperature inside the heat treatment furnace, and the recovery rate of valuable metals is increased by suppressing the generation of nickel oxide and cobalt oxide and promoting the generation of metals such as cobalt and nickel that are easily soluble in acid. A certain amount of oxygen may be contained, and the oxygen partial pressure during heat treatment is measured with a zirconia type oxygen concentration meter and maintained within the range of, for example, 0 atm to 4 x ^10-2 atm. The flow rate of the inert gas supplied into the heat treatment furnace is preferably 6 ^Nm3 /h to 60 ^Nm3 /h.

When lithium-ion battery waste is heated in the heat treatment furnace as described above, gas resulting from the electrolyte, resin, etc. is generated from within the casing of the lithium-ion battery waste. Such generated gas is flammable and needs to be burned, so it is sent from the heat treatment furnace to a gas combustion furnace and burned in the gas combustion furnace in the gas combustion process.

There are two main types of gases that are generated: gas derived from the electrolyte and resin decomposition gas (CH gas, etc.) produced by thermal decomposition of the resin.

Depending on the type of electrolyte, gas derived from the electrolyte may be generated when the temperature of lithium-ion battery waste reaches 150°C to 190°C. In many cases, when lithium-ion battery waste is heated, the components of the electrolyte inside evaporate in order, starting with those with low boiling points, and when the temperature reaches the above range, a certain internal pressure is reached, causing the safety valve to open and generating gas derived from the electrolyte.

In addition, resin decomposition gas tends to be released from lithium ion battery waste when the temperature of the lithium ion battery waste is between 380°C and 530°C. This temperature range depends on the decomposition (vaporization) temperature of the resin attached to the battery modules of the lithium ion battery waste. Typically, resin decomposition gas begins to be generated at around 400°C. In addition, resin decomposition gas is often a mixture of multiple hydrocarbon compounds.

As the heat treatment furnace, it is possible to use a continuous furnace in which lithium ion battery waste is heated while being moved inside the furnace. On the other hand, it is preferable to use a batch furnace in which lithium ion battery waste is heated without being moved inside the furnace, since this allows heat treatment to be performed with a simple structure.

If necessary, the lithium ion battery waste may be subjected to a heat treatment while blowing air into a heat treatment furnace or a heat treatment 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. Heat treatment in an air atmosphere does not require adjustment of the atmosphere, and the lithium ion battery waste can be heated in the air to reach and maintain a temperature of 300°C to 650°C.

(Gas Combustion Process)
In the gas combustion process, the generated gas sent from the heat treatment furnace to the gas combustion furnace is combusted at a predetermined high temperature in the gas combustion furnace to be rendered harmless. The gas after combustion is discharged from the gas combustion furnace as combusted gas and sent to a gas treatment facility for further treatment.

The temperature inside the gas combustion furnace may be preferably maintained at 800°C to 1000°C, more preferably 850°C to 900°C. If the temperature inside the gas combustion furnace is too low, there is a concern that the generated gas will not burn effectively, while if the temperature is too high, there may not be enough time for the generated gas to burn effectively inside the gas combustion furnace, or the capacity of the downstream gas treatment equipment may be exceeded.

Examples of fuels for gas combustion furnaces include liquefied petroleum gas (LPG) whose main component is propane or butane, liquefied natural gas (LNG) whose main component is methane and used as city gas, heavy oil, recycled oil, etc. Here, a gas combustion furnace whose fuel is LPG will be described in detail. However, in addition to gas combustion furnaces that burn LPG, gas combustion furnaces that use CO2 _- free fuels such as hydrogen or ammonia or a mixed gas of these, and gas combustion furnaces that use dimethyl ether (DME) or synthetic natural gas (SNG) as fuel may also be used. The above-mentioned DME and SNG can be synthesized from gas derived from woody biomass, gas whose main components are hydrogen ( _H2 ) and carbon monoxide (CO), etc.

In a gas combustion furnace that uses LPG, LPG is supplied to an LPG burner, which burns the generated gas. The LPG combustion flow rate (fuel supply amount), which is the flow rate of LPG supplied to the LPG burner, can be changed according to temperature fluctuations in the gas combustion furnace that accompany the combustion of the generated gas. For example, when the amount of generated gas being processed in the gas combustion furnace increases, the fuel supply amount can be reduced, specifically the LPG combustion flow rate, in order to prevent the temperature inside the gas combustion furnace from rising above a predetermined temperature.

For example, the graph shown in FIG. 1 shows how the temperature of the lithium ion battery waste (LIB temperature) increases with time after the heating of the lithium ion battery waste is started by raising the temperature inside the heat treatment furnace. At this time, if the LPG combustion flow rate does not reach the minimum flow, the LPG combustion flow rate can be reduced to suppress an excessive increase in temperature inside the gas combustion furnace due to the combustion of the generated gas. The above minimum flow can be set to a flow rate greater than 0 Nm ³ /h (when a certain amount of LPG continues to be supplied even when the LPG combustion flow rate is reduced to the maximum) or to 0 Nm ³ /h (when the supply of LPG is stopped). In either case, when the LPG combustion flow rate reaches the minimum flow, it cannot be reduced any further, and it becomes impossible to prevent the temperature from exceeding the limit.

In Figure 1, there are two periods when ΔLPG becomes large; the first is when a large amount of gas originating from the electrolyte is generated, and the second is thought to be when resin decomposition gas is generated due to thermal decomposition of the resin. When the residual voltage of lithium-ion battery waste is high, ΔLPG tends to become large when gas originating from the electrolyte is generated.

In addition, since LPG burners often mix LPG with air and burn it, the LPG combustion flow rate and ΔLPG mentioned above refer to the flow rate of LPG, not the flow rate of the gas mixed with air.

(Temperature control in heat treatment furnace)
During the temperature rise in the heat treatment furnace, there may be two or more fuel reduction and increase periods during which the fuel supply amount is significantly reduced, i.e., periods during which the ΔLPG of the gas combustion furnace increases to 0.5 ^Nm3 /h or more (ΔLPG increase periods). For example, when the residual voltage of the lithium-ion battery waste is low, the ΔLPG tends to be relatively larger in the second ΔLPG increase period than in the first ΔLPG increase period, and the LPG combustion flow rate may reach the minimum flow. In contrast, in one embodiment, during at least a part of the second ΔLPG increase period, the temperature rise rate in the heat treatment furnace is reduced from the previous period, or the temperature in the heat treatment furnace is maintained.

In addition, when the resin contained in the lithium ion battery waste is thermally decomposed, the amount of gas generated from the lithium ion battery waste increases due to the generation of resin decomposition gas caused by the thermal decomposition of the resin, and ΔLPG increases. To address this, in another embodiment, the rate of temperature rise in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained for at least a portion of the period during which the resin is thermally decomposed.

In addition, ΔLPG tends to increase when the temperature of the lithium ion battery waste reaches 380° C. to 530° C. Therefore, in yet another embodiment, the rate of temperature rise in the treatment furnace is reduced or the temperature in the heat treatment furnace is maintained during at least a portion of the period during which the temperature of the lithium ion battery waste reaches 380° C. to 530° C.

As described above, if the heating rate in the heat treatment furnace is reduced or the temperature is maintained, the outflow of gas generated from the lithium-ion battery waste slows. Therefore, by reducing the heating rate in the heat treatment furnace or maintaining the temperature during at least part of the period when ΔLPG increases (the second ΔLPG increase period, the period when the resin is thermally decomposed, and the period when the temperature of the lithium-ion battery waste reaches 380°C to 530°C), the gas generated from the lithium-ion battery waste is suppressed, and the amount of gas generated that needs to be treated in the gas combustion furnace is reduced. This reduces the load on the gas combustion furnace.

The ΔLPG increase period can be determined as follows. When lithium ion battery waste is placed in the heat treatment furnace and the heat treatment furnace and the gas combustion furnace are operated, a graph showing the change over time of the LPG combustion flow rate as illustrated in FIG. 1 is obtained. In addition, when the heat treatment furnace and the gas combustion furnace are operated under the same conditions except that lithium ion battery waste is not placed in the heat treatment furnace, a graph showing the change over time of the LPG combustion flow rate without the influence of the gas generated from the lithium ion battery waste is obtained. Then, for each time point during the operation, the LPG combustion flow rate of the graph when lithium ion battery waste is placed in the heat treatment furnace is subtracted from the LPG combustion flow rate of the graph when lithium ion battery waste is placed in the heat treatment furnace. In the graph showing the change over time of the difference in the LPG combustion flow rate obtained in this way, the period from the start to the end of the peak (mountain) at which ΔLPG becomes 0.5 Nm ³ /h or more is defined as the ΔLPG increase period. The start and end of the peak are respectively the points on both sides of the peak top on the graph of the time-dependent change in the difference in the LPG combustion flow rate described above that are closest in time to the peak top and where the value of the difference in the LPG combustion flow rate becomes 0. In other words, the region between the points on both sides of the peak top that are adjacent to the peak top and where the value of the difference in the LPG combustion flow rate becomes 0 is the ΔLPG increase period.

The period during which the resin is thermally decomposed means the period during which the temperature of the lithium ion battery waste is within the temperature range in which at least one type of resin in the lithium ion battery waste is thermally decomposed, during the period during which the LPG combustion flow rate is reduced as the temperature in the heat treatment furnace rises. The period during which gas derived from the electrolyte is generated means the period during which the temperature of the lithium ion battery waste is within the temperature range in which gas is generated from the electrolyte in the lithium ion battery waste, during the period during which the LPG combustion flow rate is reduced as the temperature in the heat treatment furnace rises. The temperature range in which the resin is thermally decomposed and the temperature range in which gas is generated from the electrolyte can be confirmed by examining the resin and electrolyte contained in the lithium ion battery waste. As described above, the electrolyte evaporates in order from the components with the lowest boiling points, and the gas derived from the electrolyte is released to the outside of the lithium ion battery waste only when a certain pressure is reached and the safety valve is opened. For this reason, the temperature range in which gas is generated from the electrolyte in the lithium ion battery waste depends on the ratio of the components constituting the electrolyte and the mechanism of the safety valve, and may be higher than the boiling point of the electrolyte.

The period during which the temperature of the lithium ion battery waste reaches a specified temperature (380°C to 530°C, 150°C to 190°C described below) refers to the period during which the temperature of the lithium ion battery waste is within that temperature range when the temperature is rising in the heat treatment furnace.

In any embodiment, it is sufficient that the rate of temperature rise in the heat treatment furnace is reduced or the temperature is maintained during at least a portion (temporary period) of the second ΔLPG increase period, the period during which the resin is thermally decomposed, or the period during which the temperature of the lithium ion battery waste reaches 380° C. to 530° C. Preferably, the rate of temperature rise in the heat treatment furnace is reduced or the temperature is maintained throughout the entire period from the start to the end.

Depending on the type of resin contained in the lithium-ion battery waste and other conditions, the period during which the resin thermally decomposes may correspond to the second ΔLPG increase period. Also, the period during which the temperature of the lithium-ion battery waste reaches 380°C to 530°C may correspond to the second ΔLPG increase period.

It is preferable to reduce the heating rate or maintain the temperature in the heat treatment furnace not only during the second ΔLPG increase period among the two or more ΔLPG increase periods, but also during at least a part of the first ΔLPG increase period. It is also preferable to reduce the heating rate or maintain the temperature in the heat treatment furnace not only during the period in which the resin is thermally decomposed, but also during at least a part of the period in which gas derived from the electrolyte is generated. It is also preferable to reduce the heating rate or maintain the temperature in the heat treatment furnace at least during a part of the period in which the temperature of the lithium ion battery waste is 150°C to 190°C. The first ΔLPG increase period may correspond to the period in which gas derived from the electrolyte is generated and/or the period in which the temperature of the lithium ion battery waste is 150°C to 190°C. This is because ΔLPG increases to a certain extent during such periods as well.

Inside the heat treatment furnace, the heating rate is usually (when the heating rate is not reduced) set to 100°C/h to 200°C/h in order to complete heating of the lithium-ion battery waste within a relatively short period of time. In contrast, when the heating rate inside the heat treatment furnace is reduced during the above-mentioned period, it is preferable to set the heating rate to 0°C/h to 50°C/h. If the heating rate is faster than this, there is a concern that ΔLPG may not be effectively reduced.

Whether the heating rate in the heat treatment furnace has decreased or the temperature has been maintained is confirmed by measuring the actual temperature in the heat treatment furnace. When the actual temperature in the heat treatment furnace fluctuates in small increments at relatively short time intervals, as shown in Figures 2 and 4 in the examples described later, the temperature setting value in the heat treatment furnace set in the heat treatment furnace is referred to to determine whether the heating rate has decreased or the temperature has been maintained. Specifically, the time points at which the heating rate has decreased or the temperature has been maintained are confirmed on a graph showing the change over time in the temperature setting value of the heat treatment furnace, and when the slope of the line segment connecting the plots at the start and end points on the graph showing the change over time in the actual furnace temperature is relatively small, it is recognized that the heating rate has decreased or the temperature has been maintained. The slope of the line segment is the heating rate described above. It should be noted that if the heating rate in the heat treatment furnace is maintained within the range of 0°C/h to 10°C/h for 45 minutes or more, the temperature in the heat treatment furnace can be considered to be maintained. During the temperature holding in the heat treatment furnace, the temperature may be maintained at a temperature rise rate of 5° C./h to 10° C./h for 30 to 45 minutes.

As described above, when reducing the temperature rise rate or maintaining the temperature in the heat treatment furnace for a predetermined period of time, the temperature rise rate in the heat treatment furnace can be changed according to the change in the LPG combustion flow rate of the gas combustion furnace. In other words, the temperature rise rate in the heat treatment furnace may be automatically controlled to change based on the change in the LPG combustion flow rate. Specifically, for example, the LPG combustion flow rate of the gas combustion furnace is constantly monitored, and when the LPG combustion flow rate begins to decrease to a certain extent, the temperature rise rate in the heat treatment furnace is adjusted to decrease, and then, when the LPG combustion flow rate exceeds its peak and begins to increase, the temperature rise rate in the heat treatment furnace is adjusted to increase, thereby controlling the temperature rise rate in the heat treatment furnace. This makes it possible to keep ΔLPG around the peak small.

As described above, when the temperature in the heat treatment furnace rises, there are two or more periods during which ΔLPG becomes large. According to the embodiment described here, by slowing down the rate of temperature rise in the heat treatment furnace or maintaining the temperature, it is possible to reduce the maximum value of ΔLPG regardless of the period during which the maximum value occurs. As a result, the load on the gas combustion furnace can be effectively reduced.

Specifically, ΔLPG may vary depending on whether the lithium ion battery waste explodes during the heat treatment, the residual voltage of the lithium ion battery waste, etc. Regarding the residual voltage, when the residual voltage of the lithium ion battery waste is relatively low (for example, when the residual voltage per battery cell of the lithium ion battery waste is less than 2.1 V/cell), ΔLPG tends to be larger during the second ΔLPG increase period (or the period during which the resin is thermally decomposed or the period during which the temperature of the lithium ion battery waste is 380°C to 530°C) than during the first ΔLPG increase period (or the period during which gas derived from the electrolyte is generated or the period during which the temperature of the lithium ion battery waste is 150°C to 190°C). Therefore, in this case, if the rate of temperature rise in the heat treatment furnace is reduced or the temperature is maintained during at least a part of the second ΔLPG increase period, the maximum value of ΔLPG during the entire heat treatment can be reduced.

On the other hand, in lithium ion battery waste with a relatively high residual voltage (for example, lithium ion battery waste with a residual voltage per battery cell of 2.1 V/cell or more), the ΔLPG tends to be large during the first ΔLPG increase period (or the period during which gas derived from the electrolyte is generated or the period during which the temperature of the lithium ion battery waste is 150°C to 190°C). Therefore, in this case, it is desirable to reduce the heating rate or maintain the temperature in the heat treatment furnace during the first ΔLPG increase period in addition to the second ΔLPG increase period (or the period during which the resin is thermally decomposed or the period during which the temperature of the lithium ion battery waste is 380°C to 530°C). In this way, when deciding whether to reduce the heating rate or maintain the temperature during the first ΔLPG increase period, the magnitude of ΔLPG during the first ΔLPG increase period, which depends on the residual voltage of the lithium ion battery waste, can be taken into consideration.

(post-process)
The lithium ion battery waste that has been subjected to the above-mentioned battery heating process can be subjected to a crushing process, a crushing/pulverization process, and a sieving process, as necessary.
The crushing is performed by removing the battery from the case of the lithium ion battery waste such as an in-vehicle battery pack, destroying the battery case, and selectively separating the positive electrode active material from the aluminum foil to which the positive electrode active material is applied. Various known devices or equipment can be used here, and specific examples thereof include impact crushers that can crush the lithium ion battery waste by applying impact while cutting it, such as sample mills, hammer mills, pin mills, wing mills, tornado mills, hammer crushers, etc. Note that a screen can be installed at the outlet of the crusher, and the battery is crushed to a size that can pass through the screen and then discharged from the crusher through the screen.

After crushing, the crushed batteries may be lightly crushed into powder as necessary, and then sieved using a sieve with appropriate mesh size. Crushing and pulverization improve the separation of the positive electrode active material that was adhered to the aluminum foil from the aluminum foil. However, crushing and pulverization may be omitted. This leaves aluminum, copper, etc. on the sieve, and a battery powder containing lithium, cobalt, nickel, etc. with some of the aluminum, copper, etc. removed can be obtained below the sieve.

The above battery powder is subjected to a lithium dissolution process as necessary, followed by an acid leaching process. In the lithium dissolution process, the battery powder is brought into contact with either a weak acid solution, water, or an alkaline solution, and the lithium contained in the battery powder is dissolved in the solution to obtain a lithium solution. The lithium solution can be subjected to processes such as solvent extraction, neutralization, and carbonation to recover the lithium in the lithium solution as lithium carbonate.

In the acid leaching process, the residual battery powder that remains in the lithium dissolution process and does not dissolve in water or solution is extracted by solid-liquid separation using a filter press, thickener, etc., and then leached in acid. The acid leaching process can be carried out by known methods or conditions. For example, the pH may be 0.0 to 3.0.

The post-leaching liquid obtained from the acid leaching process and solid-liquid separation can be subjected to processes such as neutralization, solvent extraction, and other processes to recover various metals such as cobalt and nickel.

Next, the above-mentioned heat treatment method for lithium-ion battery waste was experimentally carried out, and its effects were confirmed, which will be described below. However, the description here is merely for illustrative purposes and is not intended to be limiting.

Comparative Example
A test was conducted in which a battery module including 12 battery cells was used as lithium-ion battery waste, and three of the lithium-ion battery wastes were heated simultaneously in a heat treatment furnace at the same temperature rise rate, while the generated gas in the heat treatment furnace was sent to a gas combustion furnace for combustion. Each lithium-ion battery waste had been discharged, and its residual voltage was approximately 0 V/cell. In the heat treatment furnace, the temperature was set so that the temperature rise rate in the heat treatment furnace was approximately constant at 100°C/h during heating of the lithium-ion battery waste. Nitrogen was also supplied into the heat treatment furnace at this time, and the supply flow rate of the nitrogen was set to 140 L/min. In the gas combustion furnace, the LPG combustion flow rate was changed within the range of 0.3 ^Nm3 /h to ³ Nm3/h so that the internal temperature was 850°C.

As a result, a graph showing the change over time in temperature inside the heat treatment furnace and in the LPG combustion flow rate (LPG flow rate) was obtained, as shown in Fig. 2. In this test, as shown in the schematic graph in Fig. 2, ΔLPG (electrolyte load) due to gas derived from the electrolyte was 0.51 ^Nm3 /h, and ΔLPG (CH gas load) due to thermal decomposition of the resin was 1.09 ^Nm3 /h.

In addition, the heat treatment furnace and the gas combustion furnace were operated under the same conditions as described above, except that no lithium ion battery waste was placed in the heat treatment furnace. The LPG combustion flow rate in the graph showing the time-dependent change in the LPG combustion flow rate obtained thereby (without lithium ion battery waste placed) was subtracted from the LPG combustion flow rate in the graph of FIG. 2 (with lithium ion battery waste placed) to obtain a graph of the difference in the LPG combustion flow rate. This is shown in FIG. 3. From the difference graph in FIG. 3, it can be seen that there were two ΔLPG increase periods having a peak in which ΔLPG was 0.5 Nm ³ /h or more. The two ΔLPG increase periods were the period when the temperature of the lithium ion battery waste was 181°C to 234°C (the period when gas derived from the electrolyte was generated) and the period when it was 414°C to 509°C (the period when the resin was thermally decomposed) when lithium ion battery waste was placed.

(Example)
A test was conducted substantially similarly to the comparative example, except that the temperature inside the heat treatment furnace was set so as to maintain the temperature without increasing it when the temperature inside the heat treatment furnace reached 290°C and 470°C (when the temperature of the lithium ion battery waste reached 170°C and 410°C), respectively.

As a result, a graph showing the change over time in temperature and LPG combustion flow rate (LPG flow rate) in the heat treatment furnace was obtained, as shown in Fig. 4. In this test, as shown in the schematic graph in Fig. 4, ΔLPG (electrolyte load) due to gas derived from the electrolyte was 0.36 ^Nm3 /h, which was about 30% lower than the similar ΔLPG in the test of the comparative example. In addition, ΔLPG (CH gas load) due to thermal decomposition of the resin was 0.35 ^Nm3 /h, which was about 60 to 70% lower than the similar ΔLPG in the test of the comparative example.

As shown in FIG. 4, there were two ΔLPG increase periods (periods during which ΔLPG increased to 0.5 Nm ³ /h or more) during the temperature rise in the heat treatment furnace. The first ΔLPG increase period was approximately the same as the period during which the temperature of the lithium ion battery waste reached 150° C. to 190° C., and the second ΔLPG increase period was approximately the same as the period during which the temperature of the lithium ion battery waste reached 380° C. to 530° C. These temperature ranges are substantially the same as the temperature range during which gas derived from the electrolyte in the lithium ion battery waste is generated and the temperature range during which the resin in the lithium ion battery waste is thermally decomposed, respectively. Therefore, it is considered that the first ΔLPG increase period is the period during which gas derived from the electrolyte is generated, and the second ΔLPG increase period is the period during which the resin is thermally decomposed.

In addition, the heat treatment furnace and the gas combustion furnace were operated under the same conditions as described above, except that no lithium ion battery waste was placed in the heat treatment furnace. The LPG combustion flow rate in the graph showing the time-dependent change in the LPG combustion flow rate obtained thereby (without lithium ion battery waste placed) was subtracted from the LPG combustion flow rate in the graph of FIG. 4 (with lithium ion battery waste placed) to obtain a graph of the difference in the LPG combustion flow rate. This is shown in FIG. 5. From the difference graph in FIG. 5, it can be seen that there were two ΔLPG increase periods having a peak in which ΔLPG was 0.5 Nm ³ /h or more. The two ΔLPG increase periods were the period when the temperature of the lithium ion battery waste was 188°C to 217°C (the period when gas derived from the electrolyte was generated) and the period when it was 414°C to 500°C (the period when the resin was thermally decomposed) when the lithium ion battery waste was placed.

From the above, it was found that the above-mentioned thermal treatment method for lithium-ion battery waste can reduce the load on the gas combustion furnace.

Claims (11)

A method for heat treating lithium ion battery waste, comprising:
A battery heating step of heating the lithium ion battery waste in a heat treatment furnace;
a gas combustion process in which the gas generated in the heat treatment furnace is fed into a gas combustion furnace, LPG is supplied as fuel into the gas combustion furnace to combust the generated gas, and a fuel supply amount, i.e., an LPG combustion flow rate, is changed according to a temperature in the gas combustion furnace;
A method for heat treatment of lithium ion battery waste, in which, during heating in the heat treatment furnace, there are two or more ΔLPG increase periods in which ΔLPG, which is the throttling amount of the LPG combustion flow rate in the gas combustion furnace, is increased to 0.5 ^Nm3 /h or more, and the heating rate in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained during at least a portion of at least the second ΔLPG increase period. The method for heat treatment of lithium ion battery waste described in claim 1, wherein the rate of temperature rise in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained during at least a portion of the first ΔLPG increase period. A method for heat treating lithium ion battery waste containing resin, comprising:
A battery heating step of heating the lithium ion battery waste in a heat treatment furnace;
a gas combustion process for feeding the gas generated in the heat treatment furnace into a gas combustion furnace, supplying fuel in the gas combustion furnace to combust the generated gas, and varying the amount of fuel supply in accordance with the temperature in the gas combustion furnace;
A method for heat treating lithium ion battery waste, comprising: reducing a temperature increase rate in the heat treatment furnace or maintaining a temperature in the heat treatment furnace during at least a portion of a period during which the resin is thermally decomposed. The lithium ion battery waste contains an electrolyte,
4. The method for heat treatment of lithium ion battery waste according to claim 3, wherein during the temperature rise in the heat treatment furnace, the rate of temperature rise in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained during at least a portion of the period during which gas derived from the electrolyte is generated. A method for heat treating lithium ion battery waste, comprising:
A battery heating step of heating the lithium ion battery waste in a heat treatment furnace;
a gas combustion process for feeding the gas generated in the heat treatment furnace into a gas combustion furnace, supplying fuel in the gas combustion furnace to combust the generated gas, and varying the amount of fuel supply in accordance with the temperature in the gas combustion furnace;
The method for heat treating lithium ion battery waste comprises, during heating in the heat treatment furnace, reducing a heating rate in the heat treatment furnace or maintaining the temperature in the heat treatment furnace at least during at least a part of a period during which the temperature of the lithium ion battery waste reaches 380°C to 530°C. A method for heat treating lithium ion battery waste as described in claim 5, wherein, during heating in the heat treatment furnace, the rate of temperature rise in the heat treatment furnace is reduced or the temperature in the heat treatment furnace is maintained during at least a portion of the period during which the temperature of the lithium ion battery waste reaches 150°C to 190°C. A method for heat treatment of lithium ion battery waste as described in any one of claims 1 to 6, wherein the temperature rise rate in the heat treatment furnace when reduced is set to 0°C/h to 50°C/h. A method for heat treatment of lithium ion battery waste as described in any one of claims 1 to 6, wherein the heating rate in the heat treatment furnace when not reduced is 100°C/h to 200°C/h. A method for heat treatment of lithium ion battery waste as described in any one of claims 1 to 6, in which the rate of temperature rise in the heat treatment furnace is changed in response to changes in the amount of fuel supplied. The lithium ion battery waste used in the battery heating step includes a battery cell,
The method for heat treating lithium ion battery waste according to any one of claims 1 to 6, wherein the residual voltage per battery cell of the lithium ion battery waste is less than 2.1 V/cell. The lithium ion battery waste used in the battery heating step includes a battery cell,
The method for heat treatment of lithium ion battery waste according to any one of claims 1 to 6, wherein the residual voltage per battery cell of the lithium ion battery waste is 2.1 V/cell or more.

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