Abstract
The environmental and economic importance of recycling spent lithium iron phosphate battery (LiFePO4 battery) has gained significant attention in recent years. This study presents a novel sodium salt roasting followed by water leaching process for recovering lithium from spent lithium iron phosphate battery (LiFePO4 battery). The effects of sodium sulfate addition, roasting temperature, and roasting time on lithium extraction were systematically investigated. Characterization techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to analyze the roasted products. Under optimal conditions (sodium sulfate to LiFePO4 cathode powder mass ratio of 1.6, roasting temperature of 650°C, roasting time of 2.0 hours, and water leaching time of 15 minutes), a lithium extraction efficiency of 96.81% was achieved, yielding lithium sulfate with a purity of 97.36%. Compared to traditional methods, this process boasts advantages such as the absence of strong acids, high lithium-iron separation efficiency, and a simplified recovery procedure, making it an attractive industrial application.
Introduction
Lithium-ion batteries (LIBs) have become indispensable components in various applications, including electric vehicles (EVs) and energy storage systems. The two dominant cathode materials in LIBs are lithium nickel manganese cobalt oxide (NMC) and lithium iron phosphate battery (LiFePO4 battery). Among these, lithium iron phosphate battery (LiFePO4 battery) is preferred due to its long cycle life, low cost, and excellent safety profile [1-3]. With the increasing demand for LIBs, the disposal of spent batteries has emerged as a critical environmental challenge, necessitating efficient and eco-friendly recycling methods [4-6].
Spent lithium iron phosphate battery (LiFePO4 battery) contain valuable metals such as lithium, iron, and phosphorus, making their recycling not only environmentally beneficial but also economically viable . However, conventional recycling processes often suffer from low metal recovery rates, complex procedures, and environmental hazards associated with the use of strong acids . Therefore, the development of an efficient, cost-effective, and environmentally friendly recycling method for spent lithium iron phosphate battery (LiFePO4 battery) is crucial.
This study introduces a sodium salt roasting followed by water leaching process for extracting lithium from spent lithium iron phosphate battery (LiFePO4 battery). The process involves mixing the cathode powder with sodium sulfate, roasting at an optimal temperature, and leaching the roasted product in water to selectively extract lithium. The performance of this novel process is evaluated by studying the effects of various process parameters, such as sodium sulfate addition, roasting temperature, and roasting time.
Materials and Methods
2.1 Materials
- Spent LiFePO4 batteries: Provided by a local lithium battery recycling company in Jiangxi Province, China.
- Sodium sulfate (Na2SO4): Analytical grade, purchased from a reputable chemical supplier.
2.2 Experimental Procedure
The experimental procedure for extracting lithium from spent lithium iron phosphate battery (LiFePO4 battery) involves several steps, including pretreatment, sodium salt roasting, and water leaching.
2.2.1 Pretreatment
- Discharge: The spent lithium iron phosphate battery (LiFePO4 battery) were fully discharged in a 1.0 mol/L sodium sulfate solution for 48 hours.
- Dismantling: The batteries were manually disassembled to obtain the cathode sheets.
- Thermal Decomposition: The cathode sheets were thermally decomposed at 550°C under an inert (N2) atmosphere for 2 hours to remove organic binders.
- Grinding and Sieving: The thermally decomposed cathode sheets were ground and sieved to obtain fine lithium iron phosphate battery (LiFePO4 battery) cathode powder.
2.2.2 Sodium Salt Roasting
- Mixing: The lithium iron phosphate battery (LiFePO4 battery) cathode powder and sodium sulfate were mixed in predetermined mass ratios using a ball mill.
- Roasting: The mixture was roasted in a tube furnace under an oxidizing atmosphere at a specified temperature for a given duration.
- Cooling and Pulverization: The roasted product was allowed to cool naturally and then pulverized into a fine powder.
2.2.3 Water Leaching
- Leaching: The pulverized roasted product was leached in distilled water for 15 minutes to extract lithium.
- Filtration and Evaporation: The leachate was filtered to separate the solids, and the filtrate was evaporated to obtain lithium sulfate crystals.
2.3 Characterization Techniques
- X-ray Diffraction (XRD): Used to analyze the phase composition of the raw lithium iron phosphate battery (LiFePO4 battery) cathode powder and the final lithium sulfate product.
- Scanning Electron Microscopy (SEM): Employed to examine the morphology of the raw material and the roasted product before and after leaching.
- Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES): Used to determine the elemental composition of the lithium iron phosphate battery (LiFePO4 battery) cathode powder and the lithium extraction efficiency.
2.4 Data Analysis
The lithium extraction efficiency (Q) was calculated using the following equation:
Q=(mC×V)×100%
where C is the concentration of lithium in the leachate (g/L), V is the volume of the leachate (L), and m is the mass of lithium in the raw lithium iron phosphate battery (LiFePO4 battery) cathode powder (g).
Results and Discussion
3.1 Effect of Sodium Sulfate Addition
The effect of sodium sulfate addition on lithium extraction efficiency was investigated by varying the mass ratio of sodium sulfate to lithium iron phosphate battery (LiFePO4 battery) cathode powder from 1.4 to 1.9, while keeping the roasting temperature and time constant at 650°C and 2.0 hours, respectively. the lithium extraction efficiency initially increased with increasing sodium sulfate addition, reaching a maximum of 96.81% at a mass ratio of 1.6. Further increases in sodium sulfate addition did not significantly improve the extraction efficiency, indicating that the optimal mass ratio for maximum lithium recovery had been achieved.
3.2 Effect of Roasting Temperature
The roasting temperature was varied from 400°C to 800°C, while keeping the sodium sulfate to lithium iron phosphate battery (LiFePO4 battery) cathode powder mass ratio and roasting time constant at 1.6 and 2.0 hours, respectively. the lithium extraction efficiency increased with increasing roasting temperature, reaching a maximum of 96.81% at 650°C. At higher temperatures, the extraction efficiency slightly decreased, possibly due to sintering effects or phase transformations that hindered lithium leaching.
3.3 Effect of Roasting Time
The effect of roasting time on lithium extraction was studied by varying the roasting duration from 0.5 to 3.0 hours, while keeping the sodium sulfate to lithium iron phosphate battery (LiFePO4 battery) cathode powder mass ratio and roasting temperature constant at 1.6 and 650°C, respectively. the lithium extraction efficiency increased with increasing roasting time, reaching a peak of 96.81% at 2.0 hours. Prolonged roasting did not significantly improve the extraction efficiency, suggesting that the optimal roasting time had been achieved.
3.4 Characterization Results
3.4.1 X-ray Diffraction (XRD)
XRD patterns of the raw lithium iron phosphate battery (LiFePO4 battery) cathode powder and the final lithium sulfate product. The raw material exhibited the characteristic peaks of lithium iron phosphate battery (LiFePO4 battery), while the product after roasting and leaching showed the formation of pure lithium sulfate with no observable impurities.
3.4.2 Scanning Electron Microscopy (SEM)
SEM images of the raw lithium iron phosphate battery (LiFePO4 battery) cathode powder and the roasted product before and after leaching are presented. The raw material showed agglomerated particles with irregular shapes, while the roasted and leached product exhibited a more homogeneous and smooth surface, indicating effective lithium extraction and separation from iron and phosphorus.
3.5 Comparison with Traditional Methods
The proposed sodium salt roasting process offers several advantages over traditional recycling methods for spent lithium iron phosphate battery (LiFePO4 battery):
- Absence of Strong Acids: The process avoids the use of hazardous strong acids, reducing environmental risks and safety concerns.
- High Lithium-Iron Separation Efficiency: The process achieves efficient separation of lithium from iron and phosphorus, yielding high-purity lithium sulfate.
- Simplified Recovery Procedure: The relatively straightforward procedure simplifies the overall recycling process, making it more amenable to industrial-scale applications.
Conclusion
This study successfully demonstrated a novel sodium salt roasting followed by water leaching process for extracting lithium from spent lithium iron phosphate battery (LiFePO4 battery). The optimal conditions for maximum lithium extraction (96.81%) were determined to be a sodium sulfate to lithium iron phosphate battery (LiFePO4 battery) cathode powder mass ratio of 1.6, a roasting temperature of 650°C, a roasting time of 2.0 hours, and a water leaching time of 15 minutes. Characterization results confirmed the formation of pure lithium sulfate with a high purity of 97.36%. Compared to traditional recycling methods, this process offers significant advantages in terms of environmental friendliness, separation efficiency, and process simplicity, making it a promising candidate for industrial-scale applications.