Battery material leaching method based on in-situ current collector reduction and citric acid gradient regulation

Abstract

The invention relates to a battery material leaching method based on in-situ current collector reduction and citric acid gradient regulation and control, which comprises the following steps: 1, raw material treatment: crushing a battery with a reserved positive pole piece and current collector metal copper foil and aluminum foil; 2, adding a citric acid solution; 3, heating to 60-80 DEG C, continuously reacting, and keeping the pH stable by virtue of self-buffering of citric acid; and 4, continuing to heat to 85-95 DEG C, and completing the continuous reaction. According to the method, the negative electrode metal Cu foil of the waste battery is adopted as a reducing agent, no other external reducing reagent needs to be added, the method is more economical, the Cu foil serves as an anode to release electrons (Cu0-Cu < 2 + >), Co < 3 + > and Mn < 4 + > in a positive electrode material serve as a cathode acceptor to be reduced and dissolved, no HO is added, Cu < 2 + > in leachate can be circularly used for copper powder preparation, and the environmental protection property is improved; according to the method, only a battery shell needs to be disassembled, the battery shell is cut into small slices smaller than 5 cm, and then the small slices are ground into small slices smaller than 100 microns, no high-temperature treatment is needed, the process is simpler, the levigation treatment can improve the leaching efficiency, the disassembling step is omitted, and the labor cost is reduced by 30%.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery recycling and treatment, and particularly to a method for leaching battery materials based on in-situ current collector reduction and citric acid gradient regulation. Background Art

[0002] A lithium-ion battery generally consists of five major components: a positive electrode (positive electrode active material + metal Al foil), a negative electrode (graphite + metal Cu foil), an organic electrolyte, a separator, and a casing. In the existing small-scale recycling of waste ion batteries, the casing is first removed, and the positive and negative electrodes are manually separated. The positive electrode is calcined at high temperature to strip the positive electrode active material and the metal Al foil, and then the positive electrode active material is leached with acid. The existing technology has complex processes, is time-consuming, and requires manual disassembly. In industry, on a large scale, the positive and negative electrodes are broken together, and then the powder after crushing is leached with acid, resulting in a large amount of Al 3+ entering the solution, and separating the impurity Al 3+ will result in the loss of valuable metals such as Ni, Co, and Mn, and will also affect the purity of valuable metal products such as Ni, Co, and Mn.

[0003] Problems of the existing technology:

[0004] 1. The traditional leaching process requires manual disassembly of the battery to separate the positive electrode material from the current collector (Cu / Al foil), with complex processes and high costs;

[0005] 2. The high-valence metals (Co 3+ , Mn 4+ ) in the positive electrode material need to rely on external reducing agents (such as HO, NaHSO, Na2S2O3, etc.) for dissolution, resulting in high acid consumption and difficult treatment of waste liquid;

[0006] 3. It is difficult to inhibit the corrosion of the Al foil during the leaching process, resulting in the mixing of aluminum and valuable metals into the leaching solution (the leaching rate of Al is as high as 30%), and it is difficult to separate Al 3+ from other metal ions subsequently, which will affect the purity of the subsequent valuable metal recovery products. Summary of the Invention

[0007] In view of the deficiencies of the existing technology, the present invention proposes a leaching process that is free of disassembly and without adding external reducing agents. By utilizing the synergistic effect of the Cu current collector and the citric acid system, a method for leaching battery materials based on in-situ current collector reduction and citric acid gradient regulation is realized, which can achieve efficient leaching of all components of the positive electrode material of the lithium-ion battery and protective separation of the aluminum foil. The specific technical solutions are as follows:

[0008] A method for leaching battery materials based on in-situ current collector reduction and citric acid gradient regulation, the specific steps are as follows:

[0009] Step 1: Raw material treatment, crushing the battery with the positive electrode plate, the current collector metal copper foil, and the aluminum foil retained;

[0010] Step 2: Add citric acid solution;

[0011] Step 3: Heat to 60 - 80 °C and continue the reaction, relying on the self-buffering of citric acid to maintain a stable pH;

[0012] Step 4: Continue to heat to 85 - 95 °C and complete the reaction.

[0013] No disassembly is required. Just remove the battery case, in-situ reduce the cathode material using the Cu current collector inside the battery, and use the self-buffering of citric acid to maintain the solution pH (H3Cit → H2Cit - → Hcit 2- → Cit 3- , gradually release H + , control the pH), control the reaction potential, achieve an Al leaching rate of less than 5%, reduce the leaching of Al, and facilitate subsequent metal separation.

[0014] As an optimization: In the above-mentioned Step 1, the process of battery crushing is to crush the battery to a particle size of 3 - 5 cm and then grind it to less than 100 microns. After removing the case, the disassembly step is omitted, reducing the labor cost by 30%.

[0015] As an optimization: In the above-mentioned Step 2, the concentration of the citric acid solution is 0.4 - 0.6 mol / L citric acid solution, and the liquid-solid ratio is 8:1 - 12:1. Since citric acid is a tricarboxylic acid weak acid (pKa = 3.13, pKa = 4.76, pKa = 6.40), within this concentration range, the solution has its own pH buffering ability and can resist the drastic fluctuation of pH during the reaction through the dissociation equilibrium Auto-compensation during the reaction process, acid consumption: The dissolution of the cathode metals (Li / Ni / Co / Mn) requires reaction with H + , resulting in a decrease in H + and an increase in pH; Acid generation compensation: The Cu current collector is oxidized as the anode (Cu 0 → Cu 2+ + 2e - ), the released electrons participate in the cathode reaction (such as Co 3+ + e - → Co 2+ ), and at the same time Cu 2+ combines with citric acid to form a complex (Cu 2+ + Cit 3- → CuCit - ), releasing a small amount of H + during the process to offset the consumption of H + and maintain a stable pH.

[0016] As an optimization: During the reaction process, the pH of the citric acid solution is controlled at 2.5 - 3.0. When pH > 3.0, citric acid with a concentration of 0.1 mol / L is injected into the reaction system. If pH < 2.5, a NaOH solution with a concentration of 0.1 mol / L is added dropwise for adjustment. Initial acidity calibration: The initial pH of the leaching solution is monitored online in real time by a pH meter. If it exceeds the range of 2.5 - 3.0, an appropriate amount of citric acid solution or deionized water is added for adjustment. Temperature control in stages:

[0017] In the first stage, low temperature 60 - 80°C: H + is consumed slowly, and the system can maintain a stable pH relying on the self - buffering of citric acid;

[0018] In the second stage, high temperature 85 - 95°C: The increase in temperature accelerates the dissolution of metals, but the oxidation rate of Cu increases along with the generation of H + to avoid a large increase in pH.

[0019] Emergency adjustment mechanism: When pH > 3.0, a trace amount of citric acid with a concentration of 0.1 mol / L is injected into the reaction system; if pH < 2.5, a 0.1 mol / L NaOH solution is added dropwise for adjustment.

[0020] As an optimization: In step three, heat to 60 - 80°C and react for 15 - 25 minutes. In step four, continue to heat to 85 - 95°C and react for 45 - 55 minutes. The leaching rates of Li, Ni, Co, and Mn are ≥92%, and the reaction time is shortened to 1 hour, while the existing process requires ≥2 hours.

[0021] As an optimization: The redox potential Eh of the reaction system is measured in real time. When the reduction potential Eh reaches 0.15 V, it indicates that Cu begins to oxidize significantly, triggering the reduction of Co / Mn; if the reduction potential Eh exceeds 0.25 V, the temperature needs to be reduced or citric acid needs to be added to prevent the activation corrosion of Al; during the process of continuing to heat to 85 - 95°C, the high temperature promotes the oxidation of Cu, and the reduction potential Eh gradually rises to 0.2 V. If Eh > 0.25 V, the temperature is reduced briefly to delay the Cu oxidation rate and avoid breaking through the potential threshold.

[0022] The potential Eh is monitored in real time to control the reaction. The preferential reaction of Cu causes the formation of an AlO3 passivation layer on the surface of the aluminum foil, inhibiting the dissolution of Al, and the leaching rate < 5%.

[0023] The beneficial effects of the present invention are as follows: 1. Using the negative - electrode metal Cu foil of the waste battery itself as a reducing agent, no other external reducing reagents need to be added, which is more economical. The Cu foil releases electrons as the anode (Cu 0 →Cu 2+ ), and Co 3+ , Mn 4+is reduced and dissolved as a cathode acceptor, without adding HO, and Cu in the leaching solution 2+ can be recycled for the preparation of copper powder, improving environmental protection;

[0024] 2. For this application, only the battery case needs to be removed, cut into small slices less than 5 cm, and then ground into particles less than 100 microns, without any high-temperature treatment. The process is simpler, and the grinding treatment can improve the leaching efficiency, omitting the disassembly step and reducing the labor cost by 30%;

[0025] 3. The solid-liquid mass-volume ratio of the patented battery powder to the citric acid solution is higher, reaching 50 g / L - 150 g / L, the leaching efficiency is faster, the leaching rates of Li, Ni, Co, and Mn are ≥ 92%, the reaction time is shortened to 1 hour, while the traditional process requires ≥ 2 hours;

[0026] 4. The potential Eh is monitored in real time to control the reaction. The preferential reaction of Cu causes the formation of AlO 3 passivation layer on the surface of the aluminum foil, inhibiting the dissolution of Al, and the leaching rate < 5%. Detailed implementation mode

[0027] The following elaborates on the preferred embodiments of the present invention so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0028] Example 1:

[0029] A method for leaching battery materials based on in-situ current collector reduction and citric acid gradient regulation, the specific steps are as follows:

[0030] S1. Raw material treatment: Remove the case of the waste LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 battery, retain the positive electrode plate and the current collector metal Cu / Al foil, crush it to a particle size of 3 - 5 cm, and then grind it to less than 100 microns;

[0031] S2. Leaching conditions: The concentration of citric acid is 0.5 mol / L, the liquid-solid ratio is 10:1 (10 g / L), and the stirring speed is 200 rpm;

[0032] S3. React at 70 °C for 20 minutes in the first stage, and then raise the temperature to 90 °C and react for 50 minutes in the second stage;

[0033] S4. Control the pH to 2.5 - 3.0 and the potential Eh to 0.15 - 0.25 V during the experiment;

[0034] The specific control method is as follows: Set the initial acidity of the citric acid self-buffer system:

[0035] When preparing the leaching solution, the initial concentration of citric acid is 0.4 - 0.6 mol / L, corresponding to a pH of 2.5 - 3.0, measured at room temperature. Since citric acid is a tricarboxylic acid weak acid (pKa = 3.13, pKa = 4.76, pKa = 6.40), within this concentration range, the solution itself has pH buffering ability and can maintain pH stability through dissociation equilibrium. Resist the drastic fluctuation of pH during the reaction process.

[0036] Automatic compensation during the reaction process:

[0037] Acid consumption: The dissolution of the positive electrode metal (Li / Ni / Co / Mn) requires reaction with H + (such as Co 3+ + 3H + → Co 3+ + 1.5H2), resulting in a decrease in H + and an increase in pH;

[0038] Acid generation compensation: The Cu current collector is oxidized as the anode (Cu 0 → Cu 2+ + 2e - ), and the released electrons participate in the positive electrode reaction (Co 3+ + e - → Co 2+ ), and at the same time Cu 2+ combines with citric acid to form a complex (Cu 2+ + Cit 3- → CuCit - ), and a small amount of H + is released during the process, offsetting the consumption of H + and maintaining pH stability.

[0039] Practical operation steps for dynamic regulation

[0040] Initial acidity calibration: Online real-time monitor the initial pH of the leaching solution through a pH meter. If it exceeds the range of 2.5 - 3.0, supplement citric acid solution or deionized water for adjustment.

[0041] Temperature control in stages:

[0042] In the first stage, low temperature 70°C: The consumption of H + is slow, and the system can maintain pH stability relying on the self-buffering of citric acid;

[0043] In the second stage, high temperature 90°C: Heating accelerates the dissolution of the metal, but the oxidation rate of Cu increases accompanied by the generation of H + to avoid a large increase in pH.

[0044] Emergency adjustment mechanism: when pH > 3.0, a small amount of citric acid (concentration 0.1 mol / L) is automatically injected into the reaction system; if pH < 2.5, NaOH solution (0.1 mol / L) is added dropwise for adjustment.

[0045] In this example, the potential control in the actual process

[0046] On-line potential Eh monitoring: the redox potential (Eh) of the reaction system is measured in real time using a platinum electrode and a reference electrode (Ag / AgCl);

[0047] When Eh reaches 0.15 V, it indicates that Cu starts to oxidize significantly, triggering the reduction of Co / Mn; if Eh exceeds 0.25 V, the activation corrosion of Al may occur, and the temperature needs to be reduced or citric acid needs to be added.

[0048] Temperature-Eh linkage control:

[0049] When heating up to 90 °C in the second stage, the high temperature promotes the oxidation of Cu, and Eh gradually rises to 0.2 V, being in the optimal window;

[0050] If Eh > 0.25 V, the temperature is reduced briefly. In this example, it is selected to 85 °C to slow down the oxidation rate of Cu and avoid breaking through the potential threshold.

[0051] Detection results: the leaching rates of Li, Ni, Co, and Mn are 93.2%, 92.8%, 91.5%, and 94.1% respectively; the Al leaching rate is 4.3%.

[0052] Example 2: A method for leaching battery materials based on in-situ current collector reduction and citric acid gradient regulation, the specific steps are as follows:

[0053] S1. Raw material treatment: Remove the outer shell of the waste LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 battery, retain the positive electrode sheet and the current collector metal Cu / Al foil, crush it to a particle size of 3 - 5 cm, and then grind it to less than 100 microns;

[0054] S2. Leaching conditions: citric acid concentration 0.5 mol / L, liquid-solid ratio 10:1 (10 g / L), stirring at 200 revolutions per minute;

[0055] S3. React at 70 °C for 60 minutes; do not control pH and Eh;

[0056] Detection results: the leaching rates of Li, Ni, Co, and Mn are 75.8%, 72.3%, 78.4%, and 74.6% respectively; the Al leaching rate is 24.5%.

[0057] Example 3: A method for leaching battery materials based on in-situ current collector reduction and citric acid gradient regulation, the specific steps are as follows:

[0058] S1. Raw material treatment: Remove the outer shell of the waste LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 battery, retain the positive electrode plate and the current collector metal Cu / Al foil, crush it to a particle size of 3 - 5 cm, and then grind it to less than 100 microns;

[0059] S2. Leaching conditions: Citric acid concentration is 0.5 mol / L, liquid-solid ratio is 10:1 (10 g / L), stir at 200 revolutions per minute;

[0060] S3. React at 90 °C for 60 minutes, without controlling pH and Eh;

[0061] Detection results: The leaching rates of Li, Ni, Co, and Mn are 90.8%, 90.4%, 93.8%, and 91.7% respectively; the leaching rate of Al is 32.6%.

[0062] Example 4: A method for leaching battery materials based on in-situ current collector reduction and citric acid gradient regulation, the specific steps are as follows:

[0063] S1. Raw material treatment: Remove the outer shell of the waste LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 battery, select the positive electrode plate (LiNi 1 / 3 Mn 1 / 3Co 1 / 3 O2 and metal Al foil), then calcine it at a temperature of 600 °C for 2 h, and then peel off the powder containing only LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, and only leach this powder in subsequent experiments;

[0064] S2. Leaching conditions: Citric acid concentration is 0.5 mol / L, liquid-solid ratio is 10:1 (10 g / L), stir at 200 revolutions per minute;

[0065] S3. React at 90 °C for 60 minutes, without controlling pH and Eh;

[0066] Detection results: The leaching rates of Li, Ni, Co, and Mn are 64.7%, 47.8%, 44.5%, and 38.3% respectively.

[0067] Example 5: A method for leaching battery materials based on in-situ current collector reduction and citric acid gradient regulation, the specific steps are as follows:

[0068] S1. Raw material treatment: Remove the outer shell of the waste LiNi 1 / 3Mn 1 / 3 Co 1 / 3 Remove the outer shell of the O2 battery and select the positive electrode sheet (LiNi 1 / 3 Mn 1 / 3Co 1 / 3 O2 and metallic Al foil), then crush the positive electrode sheet to a particle size of 3 - 5 cm, and then grind it to less than 100 microns. In subsequent experiments, the leaching only includes the powder of LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 and metallic Al foil;

[0069] S2. Leaching conditions: citric acid concentration is 0.5 mol / L, liquid-solid ratio is 10:1 (10 g / L), stir at 200 rpm;

[0070] S3. React at 90 °C for 60 minutes without controlling pH and Eh;

[0071] Test results: The leaching rates of Li, Ni, Co, and Mn are 68.7%, 49.5%, 48.7%, and 43.6% respectively; the leaching rate of Al is 28.7%.

[0072] By comparing Example 1 with the other four examples, it can be concluded that in Example 1, there is no need to disassemble the battery, no external reducing agent is added. By selecting a suitable citric acid, monitoring and controlling the potential Eh and pH value in real time, and utilizing the synergistic effect of the Cu current collector and the citric acid system, efficient leaching of all components (Li, Ni, Co, Mn) of the positive electrode material of the ternary lithium-ion battery and protective separation of the Al foil are achieved, with the Al leaching rate less than 5%, reducing the leaching of Al.

Claims

1. A method for leaching battery materials based on in-situ current collector reduction and citric acid gradient regulation, characterized in that, The specific steps are as follows: Step 1: Raw material treatment, crushing the battery that retains the positive electrode plate and the current collector metal copper foil and aluminum foil; Step 2: Adding a citric acid solution; Step 3: Heating to 60 - 80 °C and continuously reacting, relying on the self-buffering of citric acid to maintain a stable pH; Step 4: Continuing to heat to 85 - 95 °C and completing the continuous reaction.

2. The battery material leaching method according to claim 1, wherein: In the said Step 1, the process of battery crushing is to crush the battery to a particle size of 3 - 5 cm and then grind it to less than 100 microns.

3. The battery material leaching method according to claim 1, wherein: In the said Step 2, the concentration of the citric acid solution is 0.4 - 0.6 mol / L citric acid solution, and the liquid-solid ratio is 8:1 - 12:

1.

4. The battery material leaching method according to claim 1, characterized in that: During the reaction process, the citric acid solution controls the pH to be 2.5 - 3.

0. When pH > 3.0, inject 0.1 mol / L citric acid into the reaction system. If pH < 2.5, then add a 0.1 mol / L NaOH solution dropwise for adjustment.

5. The battery material leaching method according to claim 1, wherein: In the said Step 3, heat to 60 - 80 °C and continuously react for 15 - 25 minutes. In the said Step 4, continue to heat to 85 - 95 °C and continuously react for 45 - 55 minutes.

6. The battery material leaching method according to claim 1, wherein: Measure the redox potential (Eh) of the reaction system in real time. When the reduction potential Eh reaches 0.15 V, it indicates that Cu begins to be significantly oxidized, triggering the reduction of Co / Mn; if the reduction potential Eh exceeds 0.25 V, it is necessary to lower the temperature or add citric acid to prevent the activation corrosion of Al from occurring; During the process of continuing to heat to 85 - 95 °C, the high temperature promotes the oxidation of Cu, and the reduction potential Eh gradually rises to 0.2 V. If Eh > 0.25 V, then lower the temperature briefly to delay the oxidation rate of Cu and avoid breaking through the potential threshold.