Method for extracting lithium from waste ternary positive electrode material

Abstract

The invention discloses a method for extracting lithium from a waste ternary positive electrode material, and belongs to the technical field of lithium battery recovery. The lithium extraction method comprises the following steps: S1, mixing a waste ternary material, elemental sulfur and a biomass carbon source, heating to a temperature T1 and a heat preservation time t1 in an inert gas atmosphere, then heating to a temperature T2 and a heat preservation time t2, and maintaining the inert gas atmosphere until cooling to room temperature to obtain a sintered product; s2, mixing the sintered product with water, adjusting the pH value, carrying out first stirring and water leaching, and filtering to obtain a first filter residue and a first lithium-containing solution; mixing the primary filter residue with water, adjusting the pH value, carrying out secondary stirring and water leaching, and filtering to obtain a secondary filter residue and a secondary lithium-containing solution; and mixing the primary lithium-containing solution and the secondary lithium-containing solution to obtain a lithium-containing mother solution, and purifying to obtain a recycled lithium material. According to the method, lithium can be efficiently extracted from the waste ternary material at low cost, and meanwhile, emission of pollutants such as acid waste gas is reduced.

Description

Technical Field

[0001] This invention relates to the field of lithium battery recycling technology, and in particular to a method for extracting lithium from waste ternary cathode materials. Background Technology

[0002] The demand for lithium-ion batteries is increasing daily, resulting in a large amount of waste lithium-ion batteries. Waste ternary cathode materials are rich in high-value metals such as lithium, cobalt, nickel, and manganese. Efficient and environmentally friendly recycling of these materials has significant economic value. In the recycling process, selectively extracting lithium from the complex cathode materials is key to simplifying subsequent metal separation and purification processes and reducing recycling costs.

[0003] Currently, the common methods for extracting lithium from waste ternary materials are carbothermal reduction and sulfation roasting. The principle of sulfation roasting is as follows: sulfuric acid / sulfate is mixed with ternary materials and then calcined. At high temperature, the cathode material reacts with sulfuric acid / sulfate, and lithium is preferentially converted into soluble lithium sulfate. Most of the nickel, cobalt and manganese elements are retained in the solid phase, thus achieving preferential lithium extraction.

[0004] For example, patent CN 114291854A discloses a method for the resource recovery of waste battery cathode materials, which involves mixing at least one of sulfur, sulfite, and sulfide with ternary materials and calcining at 600℃~700℃ to extract lithium. Patents CN 114574705A and CN 117049575A involve mixing sulfuric acid / sulfate with ternary materials and then calcining twice to extract lithium. Patent CN 119581719A discloses a method for the efficient stepwise recovery of valuable metals from waste ternary cathode materials, which recovers lithium from ternary materials through a reduction roasting method using a sodium thiosulfate and glucose composite salt.

[0005] However, during sulfation roasting, due to the rapid decomposition of sulfuric acid / sulfate, excessive amounts of sulfuric acid roasting aids are usually added to ensure complete reaction. This results in the generation of large amounts of acidic waste gas during roasting, posing a risk of environmental pollution and easily causing equipment corrosion. Furthermore, nickel and cobalt in ternary cathode materials typically exist in high valence states, and sulfation roasting is insufficient for reducing these high-valence metals, leading to low lithium recovery rates.

[0006] Therefore, providing an efficient, environmentally friendly method for extracting lithium from waste ternary cathode materials with a high lithium recovery rate is an urgent problem to be solved in this field. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, this invention provides a method for extracting lithium from waste ternary cathode materials, which can efficiently and cost-effectively extract lithium from waste ternary materials with an ideal lithium extraction rate.

[0008] The technical solution of the present invention is as follows: This invention provides a method for extracting lithium from waste ternary cathode materials, comprising the following steps: S1. Mix waste ternary materials, elemental sulfur, and biomass carbon source. In an inert gas atmosphere, heat to temperature T1, hold for t1, then heat to temperature T2, hold for t2, and maintain the inert gas atmosphere until cool to room temperature to obtain sintered product. S2. Mix the sintered product with water, adjust the pH, and perform a first stirring and water soaking. Filter to obtain a primary filter residue and a primary lithium-containing solution. Mix the primary filter residue with water, adjust the pH, and perform a second stirring and water soaking. Filter to obtain a secondary filter residue and a secondary lithium-containing solution. Mix the primary and secondary lithium-containing solutions to obtain a lithium-containing mother liquor, purify it, and obtain the recovered lithium material.

[0009] Preferably, in step S1, the mass ratio of the waste ternary material, elemental sulfur, and biomass carbon source is 1:(0.2~0.3):(0.2~0.3).

[0010] Preferably, in step S1, the biomass carbon source has a mesh size of 200-300 mesh.

[0011] Preferably, in step S1, the biomass carbon source includes at least one of pine wood chips, fir wood chips, bamboo chips, and coconut shell chips.

[0012] Preferably, in step S1, the sulfur element has a mesh size of 200-300 mesh.

[0013] Preferably, in step S1, The inert gas includes at least one of nitrogen and argon; The temperature T1 is 250~350℃, and the heat preservation time t1 is 2~3h.

[0014] Preferably, in step S1, The heating rate is 2~3℃ / min; The temperature T2 is 600~700℃; the heat preservation time t2 is 1~2h.

[0015] Preferably, in step S2, The pH was adjusted using dilute sulfuric acid during the first stirring and soaking. During the first stirring and water soaking, the mass of water should be 4 to 5 times the mass of the sintered product. The temperature of the first stirring and soaking water is 50~80℃, the pH is 6~7, and the time is 1~1.5h.

[0016] Preferably, in step S2, The pH was adjusted using dilute sulfuric acid during the second stirring and soaking process. During the second stirring and soaking, the mass of the water should be 4 to 5 times the mass of the filter residue from the first soaking. The second stirring and soaking water temperature is 50~80℃, pH is 6~7, and the time is 1~1.5h.

[0017] Preferably, in step S2, the purification includes: removing calcium and magnesium from the lithium-containing mother liquor, heating it to 85-90°C, and passing a hot sodium carbonate solution through it to carry out a lithium precipitation reaction. After the reaction is completed, the lithium carbonate material is obtained by centrifugation, washing, drying, air jet milling and demagnetization, i.e., the recovered lithium material.

[0018] The beneficial technical effects of this invention are as follows: This invention utilizes low-cost elemental sulfur and biomass carbon source as composite additives, combined with a two-stage heating and water immersion process, to extract lithium from waste ternary materials. During the first heating stage, a portion of the elemental sulfur preferentially reacts with the biomass carbon source, fixing the sulfur element within the biomass material to form a sulfurized biomass material. This material is stable at lower temperatures and does not react with the ternary material, laying the foundation for the efficient synergistic reaction in the second stage. Simultaneously, the remaining elemental sulfur undergoes a reduction reaction with the ternary material, forming lithium sulfate and metal sulfides, completing the initial lithium extraction. The generated metal sulfides can then be further used as a reducing agent in the second stage at high temperatures to extract lithium.

[0019] After entering the second stage of heating and holding, the sulfurized biomass material generated in the first stage acts as a highly efficient reducing agent, undergoing decomposition at high temperatures to release reducing gases such as methane, hydrogen, and carbon monoxide, as well as sulfidation / sulfation gases such as hydrogen sulfide, sulfur dioxide, and sulfur trioxide. This allows the carbothermic reduction and sulfation reactions to proceed synergistically within the same system, significantly improving the lithium extraction efficiency of the ternary material. This reaction not only allows the reduction and sulfation reactions to occur simultaneously, but also, throughout the process, the lithium oxide or lithium carbonate generated by carbothermic reduction can rapidly react with sulfur trioxide in the system to convert into water-soluble lithium sulfate. This process consumes the reduction products, thus greatly promoting the forward progress of the carbothermic reduction reaction. On the other hand, the continuous carbothermic reduction also guides the decomposition of sulfides and the release of sulfur oxide gases, providing stable and continuous reactants for the sulfation reaction. These two reactions synergistically promote each other, significantly accelerating the overall reaction rate and improving the lithium conversion efficiency.

[0020] Compared to the traditional carbothermal reduction method, the lithium extraction method of this invention can be carried out efficiently at lower temperatures, thereby significantly reducing production energy consumption. Furthermore, compared to the traditional sulfation roasting method, the reactants in this invention are generated in situ and immediately participate in the reaction, resulting in more uniform mixing, more thorough contact, and a more complete reaction. This improves the utilization rate of additives, achieves a higher lithium extraction yield, and reduces the emission of pollutants such as acidic waste gas. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the embodiments.

[0022] A method for extracting lithium from waste ternary cathode materials includes the following steps: S1. Mix waste ternary materials, elemental sulfur, and biomass carbon source. In an inert gas atmosphere, heat to temperature T1, hold for t1, then heat to temperature T2, hold for t2, and maintain the inert gas atmosphere until cool to room temperature to obtain sintered product. S2. Mix the sintered product with water, adjust the pH, and perform a first stirring and water soaking. Filter to obtain a primary filter residue and a primary lithium-containing solution. Mix the primary filter residue with water, adjust the pH, and perform a second stirring and water soaking. Filter to obtain a secondary filter residue and a secondary lithium-containing solution. Mix the primary and secondary lithium-containing solutions to obtain a lithium-containing mother liquor, purify it, and obtain the recovered lithium material.

[0023] In the preparation method of this invention, waste ternary materials, elemental sulfur, and biomass carbon source are mixed and sintered at 250-350°C for 2-3 hours for the first stage. During this process, some sulfur reacts with the ternary materials, reducing them to form metal sulfides. Simultaneously, the generated sulfides promote partial decomposition of the biomass carbon source, generating unsaturated bonds. These unsaturated bonds react with sulfur to produce a large amount of cross-linked sulfur and doped sulfur. The possible reactions during this process are as follows: 3S + 2LiMeO2 = 2MeS + Li2SO4 Ph-OCH3 + S8 → Ph-S-OCH3 + byproduct (Ph-OCH3: a functional group in biomass carbon; metal sulfides can catalyze this sulfidation reaction, the same below) Ph-O• + S8 → Ph-OSSO-Ph (Ph-O•: a functional group in biomass carbon;) Ph-OH + S₂ + HO-Ph′ → Ph-S x Ph′+H2O (Ph-OH: a functional group in biomass carbon;) CH2=CH-R+ x S•→CH2 S x CH2 R (CH2=CH-R: a functional group in biomass carbon;) Further, the temperature is raised to 600-700℃ and held for 1-2 hours for the second stage of sintering. During the reheating and holding stage, the sulfurized biomass carbon source decomposes and oxidizes, producing gases such as methane, ethylene, carbon monoxide, hydrogen, hydrogen sulfide, sulfur dioxide, and sulfur trioxide. These gases reduce the ternary material for subsequent lithium extraction. The possible reactions in this process are as follows: LiMeO2+H2 / CO / CH4→Li2O / Li2CO3+Me+ MeO LiMeO2+C-SO x (Sulfur-doped carbon) → Li₂SO₄ + Me + MeO + SO₂ + SO₃ SO2 / SO3 / H2S+LiMeO2→Li2SO4+ Li2S+MeS+O2+H2O SO3 + Li2O / Li2CO3 = Li2SO4 + CO2 2MeS + 4LiMeO2 = 2Li2S + 6MeO + O2 2Li₂S + 4SO₂ = 2Li₂SO₄ + 4S Subsequently, the calcined product was subjected to water leaching to extract lithium, yielding filter residue and a lithium-containing solution.

[0024] The elemental sulfur and biomass carbon source used in the following embodiments and comparative examples of the present invention can all be purchased.

[0025] Example 1 A method for extracting lithium from waste ternary cathode materials includes the following steps: S1. Mix 100g of waste ternary material (LiNi0.6Co0.2Mn0.2O2) with a particle size ≤100μm, 25g of elemental sulfur (250 mesh, purity ≥99%), and 25g of pine wood chips (280 mesh, dried to a moisture content ≤5%). Under a nitrogen atmosphere, heat to 300℃ and hold for 2.5h. Then, heat to 650℃ at 3℃ / min and hold for 1.5h while maintaining a nitrogen atmosphere. Cool to room temperature to obtain the sintered product.

[0026] S2. The sintered product is mixed with deionized water at a mass ratio of 1:5, and the pH is adjusted with dilute sulfuric acid. The first stirring leaching is carried out at 60℃ and pH=7.0 for 1 hour. After filtration, a primary lithium-containing solution and filter residue are obtained. The primary filter residue is mixed with deionized water at a mass ratio of 1:4, and the pH is adjusted with dilute sulfuric acid. The second stirring leaching is carried out at 60℃ and pH=6.5 for 1 hour. After filtration, 114.2g of secondary filter residue and secondary lithium-containing solution are obtained. The primary and secondary lithium-containing solutions are mixed to obtain a lithium-containing mother liquor. After calcium and magnesium removal, the lithium-containing mother liquor is heated to 85℃ and hot sodium carbonate solution is introduced to carry out a lithium precipitation reaction. After the reaction is completed, the lithium carbonate material is obtained by centrifugation, washing, drying, air jet milling and demagnetization, i.e., the recovered lithium material.

[0027] According to the national standard YS / T 1006.2-2014, the lithium content in the filter residue was tested using inductively coupled plasma atomic emission spectrometry and found to be 0.38 wt%, indicating a lithium extraction rate of 93.8%.

[0028] Example 2 A method for extracting lithium from waste ternary cathode materials includes the following steps: S1. Mix 100g of waste ternary material (LiNi0.8Co0.1Mn0.1O2) with a particle size ≤100μm, 30g of elemental sulfur (200 mesh, purity ≥99%), and 20g of bamboo shavings (200 mesh, dried to a moisture content ≤5%). Under a nitrogen atmosphere, heat to 250℃ and hold for 3h. Then, heat to 700℃ at 3℃ / min and hold for 1h while maintaining a nitrogen atmosphere. Cool to room temperature to obtain the sintered product.

[0029] S2. The sintered product is mixed with deionized water at a mass ratio of 1:4.5, and the pH is adjusted with dilute sulfuric acid. The first stirring leaching is carried out at 60℃ and pH=6.5 for 1.5 hours. After filtration, a primary lithium-containing solution and filter residue are obtained. The primary filter residue is mixed with deionized water at a mass ratio of 1:5, and the pH is adjusted with dilute sulfuric acid. The second stirring leaching is carried out at 60℃ and pH=6.5 for 1.5 hours. After filtration, 111.3g of secondary filter residue and a secondary lithium-containing solution are obtained. The primary and secondary lithium-containing solutions are mixed to obtain a lithium-containing mother liquor. After calcium and magnesium removal, the lithium-containing mother liquor is heated to 90℃ and hot sodium carbonate solution is introduced to carry out a lithium precipitation reaction. After the reaction is completed, the lithium carbonate material is obtained by centrifugation, washing, drying, air jet milling and demagnetization, i.e., the recovered lithium material.

[0030] The lithium content in the filter residue was tested using the method described in Example 1 and found to be 0.42 wt%, indicating a lithium extraction rate of 93.3%.

[0031] Example 3 A method for extracting lithium from waste ternary cathode materials includes the following steps: S1. Mix 100g of waste ternary material (LiNi0.5Co0.3Mn0.2O2) with a particle size ≤100μm, 20g of elemental sulfur (300 mesh, purity ≥99%), and 30g of coconut shell scraps (300 mesh, dried to a moisture content ≤5%). Under a nitrogen atmosphere, heat to 350℃ and hold for 2h. Then, heat to 600℃ at 3℃ / min and hold for 2h while maintaining a nitrogen atmosphere. Cool to room temperature to obtain the sintered product.

[0032] S2. The sintered product is mixed with deionized water at a mass ratio of 1:4, and the pH is adjusted with dilute sulfuric acid. The first stirring leaching is carried out at 60℃ and pH=6 for 1.2h. After filtration, a primary lithium-containing solution and filter residue are obtained. The primary filter residue is mixed with deionized water at a mass ratio of 1:4.5, and the pH is adjusted with dilute sulfuric acid. The second stirring leaching is carried out at 60℃ and pH=6.5 for 1.2h. After filtration, 121.5g of secondary filter residue and secondary lithium-containing solution are obtained. The primary and secondary lithium-containing solutions are mixed to obtain a lithium-containing mother liquor. After calcium and magnesium removal, the lithium-containing mother liquor is heated to 90℃ and hot sodium carbonate solution is introduced to carry out a lithium precipitation reaction. After the reaction is completed, the lithium carbonate material is obtained by centrifugation, washing, drying, air jet milling and demagnetization, i.e., the recovered lithium material.

[0033] The lithium content in the filter residue was tested using the method described in Example 1 and found to be 0.29 wt%, indicating a lithium extraction rate of 95.0%.

[0034] Comparative Example 1 A method for extracting lithium from waste ternary cathode materials is basically the same as that in Example 1, except that: S1. Mix 100g of waste ternary material (LiNi0.6Co0.2Mn0.2O2) with a particle size ≤100μm with 30g of graphite powder, and heat to 900℃ at 5℃ / min under a nitrogen atmosphere, and hold for 3h to obtain the sintered product.

[0035] In this comparative example, the lithium extraction rate was 88.7%. Furthermore, it was observed that there were obvious unreacted ternary material particles in the filter residue.

[0036] Comparative Example 2 A method for extracting lithium from waste ternary cathode materials is basically the same as that in Example 1, except that: S1. Mix 100g of waste ternary material (LiNi0.6Co0.2Mn0.2O2) with a particle size ≤100μm with 50g of pine wood chips (280 mesh, dried to a moisture content ≤5%). Under a nitrogen atmosphere, heat to 300℃ and hold for 2.5h. Then, heat to 650℃ at 3℃ / min and hold for 1.5h while maintaining a nitrogen atmosphere. Cool to room temperature to obtain the sintered product.

[0037] In this comparative example, the lithium extraction rate was 82.7%. Furthermore, it was observed that there were obvious unreacted ternary material particles in the filter residue.

[0038] Comparative Example 3 A method for extracting lithium from waste ternary cathode materials is basically the same as that in Example 1, except that: S1. 100g of waste ternary material (LiNi0.6Co0.2Mn0.2O2) with a particle size ≤100μm was mixed with 50g of elemental sulfur (250 mesh, purity ≥99%) and heated to 300℃ under a nitrogen atmosphere, and held at that temperature for 2.5h; then the temperature was increased to 650℃ at 3℃ / min and held for 1.5h while maintaining a nitrogen atmosphere, and then cooled to room temperature to obtain the sintered product.

[0039] In this comparative example, the lithium extraction rate was 80.2%.

[0040] In this comparative example, a large number of clumps appeared in the filter residue, making leaching more difficult than in the example.

[0041] Comparative Example 4 A method for extracting lithium from waste ternary cathode materials is basically the same as that in Example 1, except that: S1. Mix 100g of waste ternary material (LiNi0.6Co0.2Mn0.2O2) with a particle size ≤100μm, 10g of elemental sulfur (250 mesh, purity ≥99%), and 40g of pine wood chips (280 mesh, dried to a moisture content ≤5%). Under a nitrogen atmosphere, heat to 300℃ and hold for 2.5h. Then, heat to 650℃ at 3℃ / min and hold for 1.5h while maintaining a nitrogen atmosphere. Cool to room temperature to obtain the sintered product.

[0042] In this comparative example, the lithium extraction rate was 86.7%.

[0043] Comparative Example 5 A method for extracting lithium from waste ternary cathode materials is basically the same as that in Example 1, except that: S1. Mix 100g of waste ternary material (LiNi0.6Co0.2Mn0.2O2) with a particle size ≤100μm, 25g of elemental sulfur (250 mesh, purity ≥99%), and 25g of pine wood chips (280 mesh, dried to a moisture content ≤5%). Under a nitrogen atmosphere, heat the mixture to 650℃ at 3℃ / min, hold for 4h while maintaining the nitrogen atmosphere, and cool to room temperature to obtain the sintered product.

[0044] In this comparative example, the lithium extraction rate was 83.5%.

[0045] Comparative Example 6 A method for extracting lithium from waste ternary cathode materials is basically the same as that in Example 1, except that: S1. Mix 100g of waste ternary material (LiNi0.6Co0.2Mn0.2O2) with a particle size ≤100μm, 25g of elemental sulfur (250 mesh, purity ≥99%), and 25g of pine wood chips (280 mesh, dried to a moisture content ≤5%). Under a nitrogen atmosphere, heat to 400℃ and hold for 2.5h. Then, heat to 650℃ at 3℃ / min and hold for 1.5h while maintaining a nitrogen atmosphere. Cool to room temperature to obtain the sintered product.

[0046] In this comparative example, the lithium extraction rate was 86.9%.

[0047] Comparative Example 7 A method for extracting lithium from waste ternary cathode materials is basically the same as that in Example 1, except that: S1. Mix 100g of waste ternary material (LiNi0.6Co0.2Mn0.2O2) with a particle size ≤100μm, 25g of elemental sulfur (250 mesh, purity ≥99%), and 25g of pine wood chips (280 mesh, dried to a moisture content ≤5%). Under a nitrogen atmosphere, heat to 300℃ and hold for 2.5h. Then, heat to 550℃ at 3℃ / min and hold for 1.5h while maintaining a nitrogen atmosphere. Cool to room temperature to obtain the sintered product.

[0048] In this comparative example, the lithium extraction rate was 78.6%.

[0049] Comparing Comparative Example 1 with Example 1, it can be seen that, compared with the preparation method of the present invention, Comparative Example 1 uses the traditional carbothermal reduction method, only uses graphite powder as an additive and performs single-stage sintering, resulting in poor reaction uniformity and obvious unreacted ternary material particles in the filter residue; the final lithium extraction rate is 88.7%, which is lower than the lithium extraction rate of 93.8% in Example 1, and also lower than the other examples of the present invention.

[0050] Comparing Comparative Example 2 with Example 1, it can be seen that, compared with the preparation method of the present invention, Comparative Example 2 only uses pine wood chips as a biomass carbon source as an auxiliary agent and does not add elemental sulfur. The reaction uniformity of biomass carbon is poor, resulting in poor lithium extraction effect. The final lithium extraction rate is only 82.7%, which is much lower than that of Example 1 and the other examples of the present invention.

[0051] Comparing Comparative Example 3 with Example 1, it can be seen that, compared with the preparation method of the present invention, Comparative Example 3 only uses elemental sulfur as an auxiliary agent and does not add biomass carbon source. There are a large number of clumps in the filter residue, which increases the difficulty of lithium extraction. The final lithium extraction rate is only 80.2%, which is much lower than Example 1 and the other examples of the present invention.

[0052] Comparing Comparative Example 4 with Example 1, it can be seen that, compared with the preparation method of the present invention, the amount of elemental sulfur added in Comparative Example 4 is too small, the amount of biomass carbon source added is too large, the reaction is incomplete, and the final lithium extraction rate is 86.7%, which is much lower than that of Example 1 and the other examples of the present invention.

[0053] Comparing Comparative Example 5 with Example 1, it can be seen that, compared to the preparation method of the present invention, Comparative Example 5, which only uses a single-stage sintering method, achieved a final lithium extraction rate of 83.5%, which is far lower than that of Example 1 and the other examples of the present invention. The likely reason is that during single-stage sintering, the excessively high temperature causes premature volatilization of elemental sulfur, reducing the reactants, and making it difficult for the reduction and sulfation reactions to proceed in synergy.

[0054] Comparing Comparative Example 6 with Example 1, it can be seen that, compared to the preparation method of the present invention, the temperature during the first stage sintering in Comparative Example 6 is higher, resulting in a final lithium extraction rate of 86.9%, which is lower than that of Example 1 and the other examples of the present invention. The likely reason is that the excessively high temperature during the first stage sintering causes partial volatilization of sulfur, leading to insufficient sulfur source in the reaction system, incomplete reaction, and thus reduced lithium extraction rate.

[0055] Comparing Comparative Example 7 with Example 1, it can be seen that, compared to the preparation method of the present invention, the second stage temperature in Comparative Example 7 is lower, resulting in a final lithium extraction rate of 78.6%, which is far lower than that of Example 1 and the other examples of the present invention. The likely reason is that the excessively low temperature during the second-stage sintering makes it difficult to achieve the reduction reaction of the ternary cathode material. This not only inhibits the cracking process of the sulfurized biomass material but also leads to insufficient release of reducing gas, ultimately resulting in incomplete metal reduction and a decrease in lithium conversion rate, thus significantly reducing the overall lithium extraction efficiency.

[0056] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A method for extracting lithium from waste ternary cathode materials, characterized in that, Includes the following steps: S1. Mix waste ternary materials, elemental sulfur, and biomass carbon source. In an inert gas atmosphere, heat to temperature T1, hold for t1, then heat to temperature T2, hold for t2, and maintain the inert gas atmosphere until cool to room temperature to obtain sintered product. S2. Mix the sintered product with water, adjust the pH, and perform a first stirring and water soaking. Filter to obtain a primary filter residue and a primary lithium-containing solution. Mix the primary filter residue with water, adjust the pH, and perform a second stirring and water soaking. Filter to obtain a secondary filter residue and a secondary lithium-containing solution. Mix the primary and secondary lithium-containing solutions to obtain a lithium-containing mother liquor, purify it, and obtain the recovered lithium material.

2. The method for extracting lithium from waste ternary cathode materials according to claim 1, characterized in that, In step S1, the mass ratio of the waste ternary material, elemental sulfur, and biomass carbon source is 1:(0.2~0.3):(0.2~0.3).

3. The method for extracting lithium from waste ternary cathode materials according to claim 1, characterized in that, In step S1, the biomass carbon source has a mesh size of 200-300 mesh.

4. The method for extracting lithium from waste ternary cathode materials according to claim 1 or 3, characterized in that, In step S1, the biomass carbon source includes at least one of pine wood chips, cedar wood chips, bamboo chips, and coconut shell chips.

5. The method for extracting lithium from waste ternary cathode materials according to claim 1, characterized in that, In step S1, the sulfur element has a mesh size of 200-300 mesh.

6. The method for extracting lithium from waste ternary cathode materials according to claim 1, characterized in that, In step S1, The inert gas includes at least one of nitrogen and argon; The temperature T1 is 250~350℃, and the heat preservation time t1 is 2~3h.

7. The method for extracting lithium from waste ternary cathode materials according to claim 1, characterized in that, In step S1, The heating rate is 2~3℃ / min; The temperature T2 is 600~700℃; the heat preservation time t2 is 1~2h.

8. The method for extracting lithium from waste ternary cathode materials according to claim 1, characterized in that, In step S2, The pH was adjusted using dilute sulfuric acid during the first stirring and soaking. During the first stirring and water soaking, the mass of water should be 4 to 5 times the mass of the sintered product. The temperature of the first stirring and soaking water is 50~80℃, the pH is 6~7, and the time is 1~1.5h.

9. The method for extracting lithium from waste ternary cathode materials according to claim 1, characterized in that, In step S2, The pH was adjusted using dilute sulfuric acid during the second stirring and soaking process. During the second stirring and soaking, the mass of the water should be 4 to 5 times the mass of the filter residue from the first soaking. The second stirring and soaking water temperature is 50~80℃, pH is 6~7, and the time is 1~1.5h.

10. The method for extracting lithium from waste ternary cathode materials according to claim 1, characterized in that, In step S2, the purification includes: removing calcium and magnesium from the lithium-containing mother liquor, heating it to 85-90°C, and passing hot sodium carbonate solution through it to carry out a lithium precipitation reaction. After the reaction is completed, the lithium carbonate material is obtained by centrifugation, washing, drying, air jet milling and demagnetization, i.e., the recovered lithium material.