CN115172923B - Method for recycling battery powder through low-temperature pyrolysis - Google Patents

Abstract

The invention discloses a method for recovering battery powder by low-temperature pyrolysis and desorption, wherein the waste battery crushed material is reacted in a mixed atmosphere with a pressure of 3-8 MPa and a temperature of 120-150°C, wherein the mixed atmosphere is a mixed gas of _CO2 , NO, and _O2 , and the obtained reaction materials are reacted at a negative pressure and 310-360°C, and then the copper-aluminum foil and the battery powder are sorted. The invention adopts a combined process of low-temperature and high-pressure pyrolysis and medium-temperature and negative-pressure pyrolysis, and the temperature of the whole process is controlled below 400°C, so as to achieve the purpose of separation from the current collector, realize the chain breaking of the polymer, and avoid the oxidation of copper and aluminum.

Description

Method for recovering battery powder by low temperature pyrolysis desorption

Technical Field

The invention belongs to the technical field of battery recycling, and in particular relates to a method for recycling battery powder by low-temperature thermal desorption.

Background Art

Lithium-ion batteries have a complex structure, consisting of multiple parts such as the outer shell, diaphragm, positive electrode, and negative electrode. In the process of recycling used batteries, it is necessary to separate the different parts through a series of methods. Among them, the negative electrode is composed of graphite, binder, conductive agent and current collector copper foil, and the positive electrode is made of active material powder, binder and conductive agent coated on the current collector aluminum foil. The positive electrode active material powder _mainly includes _{LiCoO2 , LiNiO2} , _LiMnO2 , LiFePO4 and _{LiNixCoyMn1 -xyO2 ,} etc.

The pre-treatment process of recycling waste lithium-ion batteries usually requires certain technical means to desorb and separate the active material powder from the current collector.

At present, the separation of active materials and current collectors mainly starts from three aspects: ① Based on the characteristic that metal aluminum can be dissolved in alkaline solution, the positive electrode core can be immersed in alkaline solution to achieve the purpose of separating positive electrode powder from current collector. This method has the advantages of low energy consumption and strong operability, but the current collector aluminum foil enters the solution in the form of ions and needs further recycling. In addition, this process requires a large amount of alkaline solution. In order to prevent secondary pollution from the alkaline solution, neutralization treatment is required, which will require additional cost expenditure. In order to avoid the introduction of alkaline solution to pollute the powder, the desorbed active material must be fully rinsed or acid-neutralized during the filtration process; ② The binder PVDF is dissolved by organic solvents so that the current collector metal foil can be recovered in solid form, but the price of organic solvents is usually expensive and not suitable for large-scale industrial applications; ③ Directly heating to a specific temperature in the air can inactivate the binder to achieve the purpose of separating the current collector aluminum foil, which is also the most reported lithium battery recycling pyrolysis pretreatment process.

The pyrolysis pretreatment process is widely used in existing industrial production, but there are also some major problems, such as: ① The temperature of conventional pyrolysis is above 500°C. Due to the complex types of materials, at this temperature, the electrolyte and diaphragm will burn, which can easily cause violent local reactions in the pyrolysis furnace and cause temperature out of control. The aluminum metal in the battery will undergo a thermite reaction at above 600°C, resulting in a sharp rise in instantaneous temperature, burning through the pyrolysis furnace, and posing a greater safety risk; ② At this temperature, the metallic copper and aluminum in the battery are oxidized in large quantities, resulting in a high impurity content in the battery powder, and during the subsequent acid leaching, the oxides dissolve to produce a large amount of copper and aluminum slag, which brings great pressure to the subsequent purification.

Summary of the invention

The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a method for recovering battery powder by low-temperature pyrolysis desorption, which can separate the active materials of waste batteries from the current collector at a relatively low temperature.

According to one aspect of the present invention, a method for recovering battery powder by low-temperature pyrolysis is proposed, comprising the following steps:

S1: Waste batteries are discharged, disassembled and crushed to obtain crushed materials;

S2: reacting the crushed material in a mixed atmosphere with a pressure of 3-8 MPa and a temperature of 120-150° C., wherein the mixed atmosphere is a mixed gas of CO2, NO, and O2 in a volume ratio of 100:(10-15):(0-2);

S3: reacting the reaction materials obtained in step S2 under negative pressure at 310-360° C., and then sorting to obtain copper-aluminum foil and battery powder.

In some embodiments of the present invention, in step S1, the particle size of the crushed material is less than 5 cm.

In some embodiments of the present invention, in step S1, the waste battery is at least one of a ternary lithium-ion battery, a lithium iron phosphate battery, a lithium cobalt oxide battery, a lithium manganese oxide battery or a lithium nickel oxide battery.

In some embodiments of the present invention, in step S2, the reaction time is 3-5 hours.

In some embodiments of the present invention, in step S2, the reaction is carried out in a pyrolysis furnace, and the filling rate of the crushed material in the pyrolysis furnace is controlled to be 5-15%.

In some embodiments of the present invention, in step S3, the negative pressure is -0.01 to -0.08 MPa.

In some embodiments of the present invention, in step S3, the reaction time is 1-3 hours.

In some embodiments of the present invention, after the reaction in step S2 is completed, the pressure in the pyrolysis furnace is released to normal pressure at a rate of 0.1-0.5 MPa/min, and then the vacuum pump is started to evacuate to the negative pressure.

In some embodiments of the present invention, in step S3, heating is performed to the reaction temperature at a heating rate of 5-10°C/min.

In some embodiments of the present invention, the copper content of the copper-aluminum foil obtained in step S3 is not less than 45wt%, and the aluminum content is not less than 35wt%.

In some embodiments of the present invention, the aluminum content in the battery powder obtained in step S3 is not higher than 0.5 wt %.

In some embodiments of the present invention, in step S3, the sorting process is: using a double-layer sieve for screening, and the upper layer obtained is the copper-aluminum foil, and the bottom layer is the battery powder.

According to a preferred embodiment of the present invention, at least the following beneficial effects are achieved:

1. In the scheme of the present invention, in order to solve the problem that waste batteries are prone to safety hazards and large-area oxidation of copper and aluminum at high pyrolysis temperatures, a combined process of low-temperature and high-pressure pyrolysis and medium-temperature and negative-pressure pyrolysis is adopted, and the temperature of the whole process is controlled below 400°C. The medium-temperature and negative-pressure pyrolysis is carried out under anaerobic conditions, which avoids the combustion of electrolyte and diaphragm in the crushed material and the phenomenon of temperature runaway, protects the pyrolysis furnace, and reduces the degree of copper and aluminum oxidation.

2. When high-pressure mixed gas is introduced, NO is used as a single-electron free radical, which has high activity above 100°C. Under the catalysis of trace oxygen, it can randomly attack the carbon-carbon bonds in organic polymers, causing the polymer chains to break to form small molecular compounds, thereby reducing the thermal decomposition temperature of the polymer. Refer to the following reaction formula:

·NO+[-CH ₂ -CF ₂ -]→R1-CH ₂ -N=O+R ₂ -CF ₂ -N=O.

By utilizing PVDF's unique absorption characteristics for carbon dioxide, a large volume expansion can occur, causing certain mechanical damage to PVDF, which is conducive to NO's deeper chain breaking of carbon-carbon bonds.

At a relatively low temperature, the polymer chain is broken, the oxidation of copper and aluminum is avoided, and the occurrence of thermite reaction is avoided.

3. During negative pressure pyrolysis, the organic polymer after chain breaking can be decomposed and carbonized at a slightly higher temperature without heating to above 500°C. The electrolyte in it can easily reach the boiling point under negative pressure and enter the exhaust gas treatment system in gaseous state. At the same time, copper and aluminum will not be oxidized, and thermite reaction will not occur, thus achieving the purpose of separating and desorbing battery powder from copper and aluminum foil.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

Fig. 1 is a process flow chart of the present invention.

DETAILED DESCRIPTION

The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

Example 1

A method for recovering battery powder by low-temperature pyrolysis and desorption, referring to FIG1 , the specific process is as follows:

Step 1, after the waste ternary lithium-ion batteries are discharged and disassembled, they are crushed into crushed materials with a particle size of less than 5 cm;

Step 2, add the crushed material into the pyrolysis furnace, control the filling rate of the pyrolysis furnace to 5%, and introduce high-pressure mixed gas, close the furnace, control the pressure in the pyrolysis furnace to 3MPa, the temperature to 120℃, and continue for 5h. The high-pressure mixed gas is a mixed gas of _CO2 , NO, and _O2 , with a volume ratio of 100:10:0.1;

Step 3: After the reaction is completed, the pressure in the furnace is released to normal pressure at a rate of 0.1 MPa/min, and the vacuum pump is started to extract negative pressure, the pressure in the pyrolysis furnace is controlled to be -0.01 MPa, and the temperature is increased to 310°C at a heating rate of 5°C/min for 3 hours;

Step 4, after the pyrolysis reaction is completed, the material in the pyrolysis furnace is screened using a double-layer screen to obtain an upper layer of copper and aluminum foil after pyrolysis and a bottom layer of battery powder removed during the pyrolysis process.

Monitoring the situation in the pyrolysis furnace: During high-pressure pyrolysis, only droplets were observed to dissolve out of the surface of the crushed material, and the volume expanded slightly, and no other obvious changes were observed; during negative-pressure pyrolysis, the temperature in the furnace remained constant, the powder fell off obviously, and a metallic luster appeared.

Example 2

A method for recovering battery powder by low-temperature pyrolysis desorption, the specific process is as follows:

Step 1, after the waste ternary lithium-ion batteries are discharged and disassembled, they are crushed into crushed materials with a particle size of less than 5 cm;

Step 2, adding the crushed material into the pyrolysis furnace, controlling the filling rate of the pyrolysis furnace to 10%, and introducing high-pressure mixed gas, sealing, controlling the pressure in the pyrolysis furnace to 5MPa, the temperature to 130°C, and continuing for 4h; the high-pressure mixed gas is a mixed gas of CO2, NO, and O2, with a volume ratio of 100:13:1;

Step 3: After the reaction is completed, the pressure in the furnace is released to normal pressure at 0.3 MPa/min, and the vacuum pump is started to extract negative pressure, the pressure in the pyrolysis furnace is controlled to be -0.04 MPa, and the temperature is increased to 340°C at a heating rate of 8°C/min for 2 hours;

Step 4, after the pyrolysis reaction is completed, the material in the pyrolysis furnace is screened using a double-layer screen to obtain an upper layer of battery material after pyrolysis and a bottom layer of battery powder removed during the pyrolysis process.

Monitoring the situation in the pyrolysis furnace: During high-pressure pyrolysis, only droplets were observed to dissolve out of the surface of the crushed material, and the volume expanded slightly, and no other obvious changes were observed; during negative-pressure pyrolysis, the temperature in the furnace remained constant, the powder fell off obviously, and a metallic luster appeared.

Example 3

A method for recovering battery powder by low-temperature thermal desorption, the specific process is as follows:

Step 1, after the waste ternary lithium-ion batteries are discharged and disassembled, they are crushed into crushed materials with a particle size of less than 5 cm;

Step 2, adding the crushed material into the pyrolysis furnace, controlling the filling rate of the pyrolysis furnace to 15%, and introducing high-pressure mixed gas, sealing, controlling the pressure in the pyrolysis furnace to 8MPa, the temperature to 150°C, and continuing for 3h; the high-pressure mixed gas is a mixed gas of CO2, NO, and O2, with a volume ratio of 100:15:2;

Step 3: After the reaction is completed, the pressure in the furnace is released to normal pressure at a rate of 0.5 MPa/min, and the vacuum pump is started to extract negative pressure, the pressure in the pyrolysis furnace is controlled to be -0.08 MPa, and the temperature is increased to 360°C at a heating rate of 10°C/min for 1 hour;

Step 4, after the pyrolysis reaction is completed, the material in the pyrolysis furnace is screened using a double-layer screen to obtain an upper layer of battery material after pyrolysis and a bottom layer of battery powder removed during the pyrolysis process.

Monitoring the situation in the pyrolysis furnace: During high-pressure pyrolysis, only droplets were observed to dissolve out of the surface of the crushed material, and the volume expanded slightly, and no other obvious changes were observed; during negative-pressure pyrolysis, the temperature in the furnace remained constant, the powder fell off obviously, and a metallic luster appeared.

Comparative Example 1

A method for recovering battery powder by pyrolysis desorption is different from Example 1 in that low-temperature and high-pressure pyrolysis is not performed. The specific process is as follows:

Step 1, after the waste ternary lithium-ion batteries are discharged and disassembled, they are crushed into crushed materials with a particle size of less than 5 cm;

Step 2, adding the crushed material into the pyrolysis furnace, and controlling the filling rate of the pyrolysis furnace to be 5%;

Step 3, start the vacuum pump to draw negative pressure, control the pressure in the pyrolysis furnace to -0.01 MPa, and heat up to 310°C at a heating rate of 5°C/min for 3 hours;

Step 4, after the pyrolysis reaction is completed, the material in the pyrolysis furnace is screened using a double-layer screen to obtain an upper layer of battery material after pyrolysis and a bottom layer of battery powder removed during the pyrolysis process.

Monitoring the conditions in the pyrolysis furnace: During negative pressure pyrolysis, the temperature in the furnace remains constant, molten droplets appear on the surface of the crushed materials, and agglomerate after cooling, without showing obvious metallic luster.

Comparative Example 2

A method for recovering battery powder by pyrolysis desorption is different from Example 2 in that low-temperature and high-pressure pyrolysis is not performed. The specific process is as follows:

Step 1, after the waste ternary lithium-ion batteries are discharged and disassembled, they are crushed into crushed materials with a particle size of less than 5 cm;

Step 2, adding the crushed material into the pyrolysis furnace, and controlling the filling rate of the pyrolysis furnace to be 10%;

Step 3, start the vacuum pump to draw negative pressure, control the pressure in the pyrolysis furnace to -0.04 MPa, and heat up to 340°C at a heating rate of 8°C/min for 2 hours;

Step 4, after the pyrolysis reaction is completed, the material in the pyrolysis furnace is screened using a double-layer screen to obtain an upper layer of battery material after pyrolysis and a bottom layer of battery powder removed during the pyrolysis process.

Monitoring the conditions in the pyrolysis furnace: During negative pressure pyrolysis, the temperature in the furnace remains constant, molten droplets appear on the surface of the crushed materials, and agglomerate after cooling, without showing obvious metallic luster.

Comparative Example 3

A method for recovering battery powder by pyrolysis desorption, which differs from Example 3 in that low-temperature and high-pressure pyrolysis is not performed, and the specific process is as follows:

Step 1, after the waste ternary lithium-ion batteries are discharged and disassembled, they are crushed into crushed materials with a particle size of less than 5 cm;

Step 2, adding the crushed material into the pyrolysis furnace, and controlling the filling rate of the pyrolysis furnace to be 15%;

Step 3, start the vacuum pump to draw negative pressure, control the pressure in the pyrolysis furnace to -0.08MPa, and heat up to 360°C at a heating rate of 10°C/min for 1h;

Step 4, after the pyrolysis reaction is completed, the material in the pyrolysis furnace is screened using a double-layer screen to obtain an upper layer of battery material after pyrolysis and a bottom layer of battery powder removed during the pyrolysis process.

Monitoring the conditions in the pyrolysis furnace: During negative pressure pyrolysis, the temperature in the furnace remains constant, molten droplets appear on the surface of the crushed materials, and they agglomerate after cooling, without showing obvious metallic luster.

Comparative Example 4

A method for recovering battery powder by pyrolysis desorption is different from that in Example 2 in that low-temperature and high-pressure pyrolysis is not performed and the pyrolysis temperature of step 3 is increased. The specific process is as follows:

Step 1, after the waste ternary lithium-ion batteries are discharged and disassembled, they are crushed into crushed materials with a particle size of less than 5 cm;

Step 2, adding the crushed material into the pyrolysis furnace, and controlling the filling rate of the pyrolysis furnace to be 10%;

Step 3, start the vacuum pump to draw negative pressure, control the pressure in the pyrolysis furnace to -0.04 MPa, and heat up to 450°C at a heating rate of 8°C/min for 1 hour;

Step 4, after the pyrolysis reaction is completed, the material in the pyrolysis furnace is screened using a double-layer screen to obtain an upper layer of battery material after pyrolysis and a bottom layer of battery powder removed during the pyrolysis process.

Monitoring the situation inside the pyrolysis furnace: During negative pressure pyrolysis, when the temperature inside the furnace reaches 450°C, flames appear, the temperature becomes uncontrolled and rises on its own, sparks quickly fly, and the material appears in a red molten state. After cooling, no obvious metallic luster appears.

The battery powder and metal foil obtained in Examples 1-3 and Comparative Examples 1-4 were tested, and the results are shown in Table 1.

Table 1

In Comparative Examples 1-3, a large amount of transition metal remained in the metal foil, indicating that the pyrolysis temperature was insufficient and the pyrolysis reaction was difficult to occur completely; in Comparative Example 4, an aluminothermic reaction obviously occurred, and basically all the aluminum was oxidized into the black powder, and no formed aluminum foil was obtained.

The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims (10)

1. The method for recycling the battery powder by low-temperature pyrolysis is characterized by comprising the following steps of:

s1: discharging, disassembling and crushing the waste batteries to obtain crushed materials;

S2: the crushed materials react under the mixed atmosphere with the air pressure of 3-8MPa and the temperature of 120-150 ℃, and the mixed atmosphere is the mixed gas of CO ₂、NO、O₂ with the volume ratio of 100: (10-15): (0.1-2);

s3: and (3) reacting the reaction material obtained in the step (S2) under negative pressure at 310-360 ℃, and then separating to obtain copper-aluminum foil and battery powder.

2. The method according to claim 1, wherein in step S1, the particle size of the crushed material is 5cm or less.

3. The method of claim 1, wherein in step S1, the waste battery is at least one of a ternary lithium ion battery, a lithium iron phosphate battery, a lithium cobalt oxide battery, a lithium manganate battery, or a lithium nickelate battery.

4. The method according to claim 1, wherein in step S2, the reaction time is 3-5 hours.

5. The method according to claim 1, characterized in that in step S2 the reaction is performed in a pyrolysis furnace, the filling rate of the crushed material in the pyrolysis furnace being controlled to be 5-15%.

6. The method according to claim 1, wherein in the step S3, the negative pressure is-0.01 to-0.08 MPa.

7. The method according to claim 1, wherein in step S3, the reaction time is 1-3 hours.

8. The method according to claim 5, wherein after the reaction in step S2 is completed, the pressure in the pyrolysis furnace is released to normal pressure at a rate of 0.1 to 0.5MPa/min, and the vacuum pump is started to the negative pressure.

9. The method according to claim 1, wherein in step S3, the reaction temperature is heated at a heating rate of 5-10 ℃/min.

10. The method according to claim 1, wherein in step S3, the sorting process is: and screening by using a double-layer screen, wherein the upper layer is the copper aluminum foil, and the bottom layer is the battery powder.