Selective lithium extraction and green regeneration method for waste lithium titanate battery

Abstract

The invention discloses a selective lithium extraction and green regeneration method for a waste lithium titanate battery. The method comprises the following steps: firstly, pretreating the waste lithium titanate battery to obtain black powder containing lithium titanate; then selectively leaching lithium by adopting a quaternary ammonium salt / gluconic acid / ethylene glycol-based eutectic solvent to obtain a lithium-rich leaching solution and leaching slag containing a titanium compound; the leachate is circularly used for leaching lithium in the black powder until the lithium is saturated, a saturated sodium carbonate solution is added for reaction, washing and drying are performed after solid-liquid separation, and battery-grade lithium carbonate is obtained; the leaching residues are subjected to impurity removal, washing and drying, and a titanium compound is obtained; and finally, preparing the lithium titanate negative electrode material by taking the lithium titanate and battery-grade lithium carbonate as a precursor. According to the method, a traditional strong acid leaching process is replaced with the environment-friendly green solvent, the method has the remarkable advantages that the process is simple, the solvent can be recycled, and secondary pollution is avoided, efficient selective extraction of lithium in the waste lithium titanate battery and green short-process regeneration of the lithium titanate negative electrode material are achieved, and the method has excellent industrial application prospects.

Description

Technical Field

[0001] This invention relates to the field of recycling technology for retired power batteries, and more specifically, to a method for selective lithium extraction and green regeneration of waste lithium titanate battery anode materials. Background Technology

[0002] With the rapid development of new energy vehicles, large-scale energy storage systems, and high-end portable electronic devices, the global demand for lithium-ion batteries, as a core energy storage unit, continues to rise. Among many anode materials, lithium titanate, with its unique "zero-strain" crystal structure, excellent safety characteristics, and ultra-long cycle life, has established an irreplaceable position in fields with stringent requirements for power output, durability, and safety, such as electric buses, grid frequency regulation energy storage, and vehicle start-stop systems. However, as early commercially applied lithium titanate batteries gradually enter the end-of-life stage, how to achieve efficient, economical, and environmentally friendly recycling and regeneration of its key components, especially lithium titanate material itself, has become a key technological issue for promoting sustainable resource recycling and addressing environmental challenges.

[0003] Currently, research and industrial application of lithium-ion battery recycling technology mainly focus on high-value cathode materials (such as ternary materials and lithium iron phosphate) and anode graphite. In contrast, existing mainstream recycling technologies for the chemically stable lithium titanate anode have significant limitations. Traditional pyrometallurgical technology, while capable of handling complex materials, requires extremely high temperatures exceeding 1400°C. This not only consumes enormous amounts of energy but also completely destroys the lithium titanate framework structure in a strongly reducing atmosphere, leading to lithium volatilization and titanium loss, ultimately resulting in low-value "downgraded recycling" that fails to preserve the material's high-end electrochemical performance and generates harmful gases with high waste gas treatment costs. Widely used hydrometallurgical technology, namely strong acid leaching, typically relies on high concentrations of sulfuric acid, hydrochloric acid, or even hydrofluoric acid, and requires strong oxidants such as hydrogen peroxide under harsh conditions of high temperature and pressure to dissolve the metal ions in lithium titanate. This process not only causes severe equipment corrosion and generates large amounts of difficult-to-treat acidic wastewater containing heavy metals, but more importantly, it indiscriminately leaches lithium and titanium ions. This necessitates complex separation and purification steps to obtain a single component, resulting in a lengthy process, high chemical reagent consumption, and a significant environmental footprint, contradicting the core principles of green recycling. On the other hand, the simpler direct physical remediation method, which involves dismantling and heat treatment to remove organic matter and then recovering lithium titanate powder, while concise, cannot effectively remove electrolyte decomposition products, metal impurities from the cathode, and residual carbon materials accumulated during long-term battery cycling. These impurities severely damage the electrode interface stability of the recycled materials, causing their electrochemical performance, especially initial coulombic efficiency, rate performance, and long-cycle stability, to fall far short of the application standards for power batteries, greatly limiting their recycling value.

[0004] In summary, existing technologies reveal a fundamental contradiction when dealing with the unique material lithium titanate: the excellent stability that lithium titanate provides for batteries becomes a formidable obstacle in its recycling process. Neither highly destructive pyrometallurgical methods, heavily polluting strong acid wet processes, nor purely physical methods with insufficient purity can simultaneously meet the triple requirements of efficient recycling, environmental friendliness, and high-performance regeneration. Therefore, developing a new process capable of selectively extracting valuable components under mild conditions and directly regenerating them into high-performance electrode materials has become a clear and urgent technological development direction in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for selective lithium extraction and green recycling of waste lithium titanate batteries. This method uses an environmentally friendly eutectic solvent as the leaching medium to achieve selective lithium leaching under relatively mild conditions. Through subsequent replenishment of the lithium source and heat treatment, the lithium titanate material is directly regenerated. The entire process is simple, low-cost, and environmentally friendly, achieving efficient and selective lithium extraction and green recycling of lithium titanate anode materials, and has excellent prospects for industrial application.

[0006] The specific technical solution of this invention is as follows:

[0007] A method for selective lithium extraction and green recycling of waste lithium titanate batteries includes the following steps:

[0008] (1) Pre-treatment of waste lithium titanate batteries by discharging, crushing and sorting to obtain black powder rich in lithium titanate negative electrode active material;

[0009] (2) Mix quaternary ammonium salt, gluconic acid, ethylene glycol and water, heat at a constant temperature and stir to obtain a eutectic solvent solution;

[0010] (3) The black powder obtained in step (1) is added to the eutectic solvent solution obtained in step (2) and heated and stirred to react. After the reaction is completed, solid-liquid separation is carried out to achieve selective leaching of lithium, and a filtrate rich in lithium ions and a filter residue mainly composed of titanium compounds and graphite are obtained.

[0011] (4) Add saturated sodium carbonate solution to the filtrate obtained in step (3), and after washing and drying several times, obtain battery-grade lithium carbonate with a purity higher than 99.5%;

[0012] (5) Remove the graphite from the filter residue obtained in step (3) by flotation, and then remove impurities, wash and dry to obtain a titanium-containing compound;

[0013] (6) The battery-grade lithium carbonate obtained in step (4) and the titanium-containing compound obtained in step (5) are used as precursors for lithium titanate anode material. After being fully mixed, lithium titanate anode material is prepared by high-temperature calcination, realizing the green short-process regeneration of lithium titanate anode material in waste lithium titanate batteries.

[0014] In this invention, in step (1), the waste lithium titanate battery is disassembled after discharge to obtain positive and negative electrode materials, organic separator and shell; the negative electrode material is cut into slices, put into N-methylpyrrolidone NMP solution and stirred, then solid-liquid separation, washing and drying are performed to remove aluminum foil and obtain waste lithium titanate battery negative electrode active material powder.

[0015] In this invention, in step (2), the eutectic solvent solution contains 5-25 wt.% quaternary ammonium salt, the molar ratio of gluconic acid to ethylene glycol is 1:3-3:1, and the water content is 10-60 wt.%.

[0016] In this invention, in step (2), the quaternary ammonium salt is any one or more of betaine, betaine hydrochloride, choline chloride, or acetylcholine.

[0017] In this invention, in step (2), the reaction temperature is 50-100℃, the reaction time is 30-150min, and the stirring speed is 300-800rpm.

[0018] In this invention, in step (3), the liquid-solid ratio of the eutectic solvent solution to the black powder is 10-30 mL / g, the leaching temperature is 60-110℃, the leaching time is 60-120 min, and the stirring speed is 300-800 rpm.

[0019] In this invention, in step (3), the filtrate is recycled and used to leach lithium from the black powder obtained in step (1) 3 to 10 times until saturation.

[0020] In this invention, in step (4), a saturated sodium carbonate solution is added at a temperature of 80-100°C, and the reaction continues for 30-180 minutes after the addition is complete. After the reaction is completed, the mixture is filtered, and the filter residue is washed multiple times with hot water at 55-65°C and then dried at a temperature of 100-110°C.

[0021] In this invention, in step (6), the high-temperature calcination temperature is 700-950℃ and the calcination time is 6-24h; the molar ratio of lithium atoms in battery-grade lithium carbonate to titanium atoms in the titanium-containing compound obtained in step (5) is controlled to be 0.84:1-0.88:1.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. This invention provides a selective lithium extraction and green recycling method for waste lithium titanate batteries. A quaternary ammonium salt-gluconic acid-ethylene glycol eutectic solvent is used as the leaching agent to efficiently and selectively leach lithium from the negative electrode material of waste lithium titanate batteries. Under optimized process conditions, the lithium leaching rate can reach 100%, while the titanium leaching rate is effectively suppressed to below 1.08%, achieving efficient selective lithium leaching and one-step efficient separation of titanium. The filter residue obtained after leaching mainly consists of titanium-containing compounds, which can be directly used as a precursor for synthesizing lithium titanate negative electrode materials, thereby realizing the selective extraction and closed-loop recycling of valuable components from waste lithium titanate batteries.

[0024] 2. This invention replaces the strong acids, strong alkalis, and additional reducing agents in traditional recycling processes with an environmentally friendly eutectic solvent. It has significant advantages such as simple process, recyclable solvent, and avoidance of secondary pollution from the source. It realizes efficient and selective lithium extraction and green regeneration of waste lithium titanate battery anode materials, and has good prospects for industrial application. Attached Figure Description

[0025] Figure 1 The process flow diagram for selective lithium extraction and green recycling of waste lithium titanate batteries provided by the present invention is shown.

[0026] Figure 2 This illustrates the effect of leaching time on the metal leaching rate in waste lithium titanate black powder in Example 1 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, the specific steps of the selective lithium extraction and green recycling process for waste lithium titanate batteries proposed in this invention are as follows:

[0029] (1) Black powder rich in lithium titanate anode active material is obtained by pre-treatment such as discharge, crushing and sorting of waste lithium titanate batteries;

[0030] (2) After mixing quaternary ammonium salt, gluconic acid, ethylene glycol and water in a certain ratio, heat at a constant temperature and stir to obtain a eutectic solvent solution;

[0031] (3) Add the black powder obtained in step (1) to the eutectic solvent solution obtained in step (2) and heat and stir at a constant temperature. After the reaction is completed, perform solid-liquid separation to obtain a filtrate rich in lithium ions and a filter residue mainly composed of titanium compounds and graphite.

[0032] (4) The filtrate obtained in step (3) can be recycled to leach the black powder obtained in step (1) until the lithium ions in the leachate reach saturation. After solid-liquid separation, a saturated sodium carbonate solution is added to the final leachate. After multiple washing and drying, battery-grade lithium carbonate with a purity higher than 99.5% is obtained.

[0033] (5) Remove the graphite from the filter residue obtained in step (3) by flotation, and then remove impurities, wash and dry to obtain titanium-containing compounds (complexes formed by organic matter and titanium ions); the impurities of waste lithium titanate anode material are mainly waste graphite used as a conductive agent, which can be effectively removed by flotation; finally, the lithium / titanium content in the anode black powder after impurity removal is measured by ICP-OES, and the purity is determined and used as a precursor for regenerated lithium titanate anode material;

[0034] (6) The battery-grade lithium carbonate obtained in step (4) and the lithium titanate anode material precursor obtained in step (5) are fully mixed in a certain proportion and then calcined at high temperature to prepare lithium titanate anode material, thus realizing the green recycling of anode material in waste lithium titanate batteries.

[0035] In step (2) above, the eutectic solvent solution contains 5 to 25 wt.% quaternary ammonium salt, the molar ratio of gluconic acid to ethylene glycol is 1:3 to 3:1, and the water content is 10 to 60 wt.%.

[0036] In step (2) above, the quaternary ammonium salt is any one or more of betaine, betaine hydrochloride, choline chloride or acetylcholine.

[0037] In step (2) above, the reaction temperature is 50-100℃, the reaction time is 30-150min, and the stirring speed is 300-800rpm.

[0038] In step (3) above, the liquid-solid ratio of the eutectic solvent solution to the black powder is 10-30 mL / g, the leaching temperature is 60-110℃, the leaching time is 60-120 min, and the stirring speed is 300-800 rpm.

[0039] In step (3) above, the filtrate is recycled and used to leach lithium from the black powder in step (1) 3 to 10 times until saturation.

[0040] In step (4) above, a saturated sodium carbonate solution is added at a temperature of 80-100°C, and the reaction continues for 30-180 minutes after the addition is complete. After the reaction is complete, the mixture is filtered, and the filter residue is washed several times with hot water at 55-65°C and then dried at a temperature of 100-110°C.

[0041] In step (6) above, the high-temperature calcination temperature is 700-950℃ and the calcination time is 6-24h; the molar ratio of lithium atoms in battery-grade lithium carbonate to titanium atoms in the titanium-containing compound obtained in step (5) is controlled to be 0.84:1-0.88:1.

[0042] Example 1

[0043] A method for selective lithium extraction and green recycling of waste lithium titanate batteries, the specific steps of which are as follows:

[0044] (1) Sample pretreatment

[0045] Waste lithium titanate batteries were discharged in a 1 wt.% sodium chloride solution for more than 12 hours, then disassembled to obtain positive and negative electrode materials, an organic separator, and a casing. The negative electrode material was cut into approximately 1 cm × 1 cm sheets and placed in an NMP solution to promote the dissolution of the PVDF binder in the electrode sheets. The liquid-to-solid ratio was 20 mL / g, and the stirring time was 40 min. The mixture was then filtered, washed with water, and dried at 110 °C. The aluminum foil was removed by sieving to obtain the negative electrode active material powder from the waste lithium titanate batteries.

[0046] (2) Determination of metal content in samples

[0047] A 0.1g sample of dried waste lithium titanate anode material powder was placed in a digestion vessel, followed by the addition of 6mL concentrated hydrochloric acid, 2mL concentrated nitric acid, and 2mL deionized water. The digestion vessel was then placed in a microwave digestion apparatus. After digestion, the volume was adjusted to 100mL, and the solution was diluted 10-fold. The content of metal components was then quantitatively determined using an ICP-OES (iCAP7000) instrument from Thermo Fisher Scientific. The results are shown in Table 1.

[0048] Table 1 Main components of black powder from waste lithium titanate battery anode

[0049]

[0050] (3) Preparation of betaine hydrochloride-gluconic acid-ethylene glycol eutectic solvent solution

[0051] The eutectic solvent solution contained 15 wt.% betaine hydrochloride, 2:1 molar ratio of gluconic acid to ethylene glycol, and 40 wt.% water. It was added to a sealed glass bottle and placed in an oil bath for constant temperature heating with magnetic stirring. The reaction temperature was 70℃, the reaction time was 30 min, and the stirring speed was 500 rpm to obtain the eutectic solvent solution.

[0052] (4) Leaching metal with eutectic solvent solution

[0053] Take 1g of black powder and place it in a glass bottle containing prepared solvent. Control the liquid-to-solid ratio of the eutectic solvent solution to the black powder to be 15mL / g. The reaction temperature is 100℃, the rotation speed is 600rpm, and the reaction time is 90min. After the reaction is complete, separate the mixed sample by vacuum filtration to obtain a filtrate mainly composed of lithium ions and a filter residue mainly composed of titanium compounds.

[0054] The content of metal ions in the filtrate was measured using ICP-OES, and the lithium leaching rate was calculated using the following formula.

[0055]

[0056]

[0057] In the formula, η is the leaching rate of metal M;

[0058] C L The concentration of the metal in the leachate, in g / L;

[0059] V1 is the volume of the leachate, in L;

[0060] m0 and C0 are the mass (g) and concentration (g / L) of metal M, respectively.

[0061] V0 is the volume (in L) of metal M after digestion and constant volume.

[0062] f is the dilution factor of metal M after digestion and volume adjustment.

[0063] The leaching rate of lithium was as high as 100% in the system using a betaine hydrochloride-gluconic acid-ethylene glycol eutectic solvent solution as the leaching agent, while the leaching rate of titanium was only 1.08% (see...). Figure 2 This means that selective leaching of lithium from waste lithium titanate battery anode material black powder has been achieved.

[0064] (5) Metal recovery of negative electrode materials

[0065] The filtrate obtained after leaching is used to leach black powder 3-10 times until lithium ions in the leaching solution reach saturation. A saturated sodium carbonate solution is added, and the mixture is filtered, washed with water at 60°C, and dried at 105°C to obtain battery-grade lithium carbonate with a purity higher than 99.5%. The filter residue, mainly composed of titanium compounds and graphite, is subjected to flotation to remove graphite. The resulting titanium-containing leaching residue is then subjected to impurity removal, washing with dilute acid and hot water, and vacuum drying at 100°C to obtain a lithium titanate anode material precursor. The impurity removal process includes mixing the titanium-containing leaching residue with water to form a homogeneous slurry, adding 2wt% NaOH solution, and stirring at 70°C for 1 hour. This allows amphoteric metal impurities such as iron and aluminum, present in the form of hydroxides, to dissolve into the liquid phase, while titanium elements remain in the solid phase as titanium compounds. After the reaction is completed, the mixture is filtered to obtain preliminarily purified titanium-rich slag; dilute acid washing is used to neutralize the alkaline substances remaining in the titanium-rich slag and dissolve trace amounts of amphoteric metal impurities, and hot water washing is used to ensure that sodium ions and other soluble salts are fully removed.

[0066] (6) Synthesis of lithium titanate anode material

[0067] The lithium carbonate obtained in step (5) and the cathode material precursor were fully mixed at a ratio of n(Li):n(Ti) = 0.85:1 and then calcined in air at a temperature of 850°C for 12 hours. After calcination, the lithium titanate anode material was obtained.

[0068] Example 2

[0069] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the content of betaine hydrochloride in step (3) is 5 wt.%.

[0070] Example 3

[0071] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the content of betaine hydrochloride in step (3) is 25 wt.%.

[0072] Example 4

[0073] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the liquid-solid ratio of black powder to eutectic solvent in step (4) is 10 mL / g.

[0074] Example 5

[0075] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the liquid-solid ratio of black powder to eutectic solvent in step (4) is 30 mL / g.

[0076] Example 6

[0077] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the leaching reaction temperature in step (4) is 60°C.

[0078] Example 7

[0079] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the leaching reaction temperature in step (4) is 110°C.

[0080] Example 8

[0081] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the leaching reaction time in step (4) is 60 min.

[0082] Example 9

[0083] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the leaching reaction time in step (4) is 120 min.

[0084] Example 10

[0085] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the eutectic solvent solution in step (3) is gluconic acid and ethylene glycol in a molar ratio of 3:1.

[0086] Example 11

[0087] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the eutectic solvent solution in step (3) is gluconic acid and ethylene glycol in a molar ratio of 1:3.

[0088] Example 12

[0089] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the water content of the eutectic solvent solution in step (3) is 10% wt.%.

[0090] Example 13

[0091] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that the water content of the eutectic solvent solution in step (3) is 60% wt.%.

[0092] Example 14

[0093] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that: in step (3), the quaternary ammonium salt is composed of betaine hydrochloride and choline chloride in a molar ratio of 1:1.

[0094] Example 15

[0095] A selective lithium extraction and green recycling method for waste lithium titanate batteries is the same as in Example 1, except that: in step (3), the quaternary ammonium salt is composed of betaine hydrochloride, choline chloride and acetic acid choline in a molar ratio of 1:1:1.

[0096] The leaching rates of lithium and titanium in waste lithium titanate battery black powder from different embodiments are shown in Table 2.

[0097] Table 2. Leaching rates of lithium and titanium in different embodiments

[0098]

[0099] As shown in Table 2, using a eutectic solvent solution composed of quaternary ammonium salt, gluconic acid, ethylene glycol, and water as a leaching agent for waste lithium titanate battery black powder can achieve selective leaching of lithium. It also solves the problems of high secondary pollution risk, difficult treatment of hydrometallurgical wastewater, and high cost associated with recycling technologies using strong acids, strong alkalis, and reducing agents as leaching agents. This enables the recovery of metals from waste lithium titanate battery black powder and the green regeneration of cathode materials.

[0100] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Those skilled in the art should understand that various modifications, substitutions, or combinations in form or detail can be made to the technical solutions disclosed in the foregoing embodiments without departing from the spirit and scope defined by the appended claims. All such modifications, substitutions, or combinations fall within the protection scope of the present invention. The protection scope of the present invention should be determined by the claims and covered by equivalent technical solutions.

Claims

1. A method for selective lithium extraction and green recycling of waste lithium titanate batteries, characterized in that, Includes the following steps: (1) Pre-treatment of waste lithium titanate batteries by discharging, crushing and sorting to obtain black powder rich in lithium titanate negative electrode active material; (2) Mix quaternary ammonium salt, gluconic acid, ethylene glycol and water, heat at a constant temperature and stir to obtain a eutectic solvent solution; (3) The black powder obtained in step (1) is added to the eutectic solvent solution obtained in step (2) and heated and stirred to react. After the reaction is completed, solid-liquid separation is carried out to achieve selective leaching of lithium, and a filtrate rich in lithium ions and a filter residue mainly composed of titanium compounds and graphite are obtained. (4) Add saturated sodium carbonate solution to the filtrate obtained in step (3), and after washing and drying several times, obtain battery-grade lithium carbonate with a purity higher than 99.5%; (5) Remove the graphite from the filter residue obtained in step (3) by flotation, and then remove impurities, wash and dry to obtain a titanium-containing compound; (6) The battery-grade lithium carbonate obtained in step (4) and the titanium-containing compound obtained in step (5) are used as precursors for lithium titanate anode material. After being fully mixed, lithium titanate anode material is prepared by high-temperature calcination, realizing the green short-process regeneration of lithium titanate anode material in waste lithium titanate batteries.

2. The method for selective lithium extraction and green recycling of waste lithium titanate batteries according to claim 1, characterized in that, In step (1), the waste lithium titanate battery is disassembled after discharge to obtain positive and negative electrode materials, organic separator and shell; the negative electrode material is cut into slices, put into N-methylpyrrolidone NMP solution and stirred, then solid-liquid separation, washing and drying are performed, aluminum foil is removed and waste lithium titanate battery negative electrode active material powder is obtained.

3. The method for selective lithium extraction and green recycling of waste lithium titanate batteries according to claim 1, characterized in that, In step (2), the eutectic solvent solution contains 5-25 wt.% quaternary ammonium salt, 1:3-3:1 molar ratio of gluconic acid to ethylene glycol, and 10-60 wt.% water.

4. The method for selective lithium extraction and green recycling of waste lithium titanate batteries according to claim 1, characterized in that, In step (2), the quaternary ammonium salt is any one or more of betaine, betaine hydrochloride, choline chloride or acetylcholine.

5. The method for selective lithium extraction and green recycling of waste lithium titanate batteries according to claim 1, characterized in that, In step (2), the reaction temperature is 50-100℃, the reaction time is 30-150 min, and the stirring speed is 300-800 rpm.

6. The method for selective lithium extraction and green recycling of waste lithium titanate batteries according to claim 1, characterized in that, In step (3), the liquid-solid ratio of the eutectic solvent solution to the black powder is 10-30 mL / g, the leaching temperature is 60-110℃, the leaching time is 60-120 min, and the stirring speed is 300-800 rpm.

7. The method for selective lithium extraction and green recycling of waste lithium titanate batteries according to claim 1, characterized in that, In step (3), the filtrate is recycled and used to leach lithium from the black powder obtained in step (1) 3 to 10 times until saturation.

8. The method for selective lithium extraction and green recycling of waste lithium titanate batteries according to claim 1, characterized in that, In step (4), a saturated sodium carbonate solution is added at a temperature of 80-100°C, and the reaction continues for 30-180 minutes after the addition is complete. After the reaction is complete, the mixture is filtered, and the filter residue is washed several times with hot water at 55-65°C and then dried at a temperature of 100-110°C.

9. The method for selective lithium extraction and green recycling of waste lithium titanate batteries according to claim 1, characterized in that, In step (6), the high-temperature calcination temperature is 700-950℃ and the calcination time is 6-24h; the molar ratio of lithium atoms in battery-grade lithium carbonate to titanium atoms in the titanium-containing compound obtained in step (5) is controlled to be 0.84:1-0.88:1.

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