Abstract
This paper investigates the challenges associated with the separation of cathode and anode materials from spent lithium iron phosphate (LiFePO4) batteries through flotation. To overcome the difficulty of separating these materials, an oxidative roasting pretreatment method is proposed and evaluated. The results indicate that roasting the spent LiFePO4 battery powder at 500°C for 30 minutes significantly enhances the separation efficiency. The carbon grade of the recovered graphite anode material increases from 47.63% to 97.70%, while the carbon grade in the cathode product decreases from 24.00% to 1.01%. This improvement is attributed to the elimination of long-chain organic compounds on the surfaces of cathode and anode materials, which strengthens the surface property differences between them. The proposed method provides a feasible and efficient solution for recycling graphite anode materials from spent LiFePO4 batteries.
Keywords: Lithium Iron Phosphate battery, Lifepo4 battery, anode material recovery, oxidative roasting, surface modification, flotation, graphite anode material
Introduction
Lithium iron phosphate (LiFePO4) batteries have gained significant popularity in recent years due to their exceptional cycling performance, high safety, and environmental friendliness. As the market for electric vehicles and renewable energy storage systems expands, the production and consumption of LiFePO4 batteries are projected to increase substantially. Consequently, the volume of spent LiFePO4 batteries is expected to rise dramatically in the coming years.
The disposal of spent LiFePO4 batteries poses significant environmental and economic challenges. On the one hand, if not managed properly, the batteries can cause severe environmental pollution due to their toxic and hazardous components. On the other hand, LiFePO4 batteries contain valuable metals such as lithium, iron, and phosphorus, as well as graphite anode materials, which have high recycling potential.
Currently, most recycling efforts for LiFePO4 batteries focus on the recovery of cathode materials and the extraction of metals like lithium, iron, and phosphorus. However, the recovery of graphite anode materials has received relatively little attention. To address this gap and contribute to a more comprehensive recycling system for LiFePO4 batteries, this study explores the impact of oxidative roasting pretreatment on the recovery of graphite anode materials through flotation.
Literature Review
Several studies have been conducted on the recycling of spent LiFePO4 batteries, primarily focusing on the recovery of cathode materials and metal extraction. However, the recovery of graphite anode materials remains an understudied area. Some of the key findings and challenges in this field are discussed below.
Cathode Material Recovery
Several methods have been proposed for the recovery of cathode materials from spent LiFePO4 batteries, including direct recycling, pyrometallurgical processes, and hydrometallurgical processes. Direct recycling involves remanufacturing spent batteries into new ones, while pyrometallurgical processes involve high-temperature treatment to recover metals. Hydrometallurgical processes, on the other hand, use chemical leaching to extract metals from spent batteries [1, 2].
Metal Extraction
Metal extraction from spent LiFePO4 batteries has been extensively researched, with various solvents and acids being tested for their efficiency in leaching metals from cathode materials. Deep eutectic solvents and organic acids have shown promising results in selectively extracting lithium, iron, and phosphorus from spent batteries [3, 4].
Graphite Anode Recovery
Compared to cathode material recovery and metal extraction, the recovery of graphite anode materials from spent LiFePO4 batteries has received limited attention. A few studies have explored mechanical separation methods and chemical treatments for this purpose, but the overall recovery efficiency remains low [5, 6].
Materials and Methods
This study aims to evaluate the impact of oxidative roasting pretreatment on the recovery of graphite anode materials from spent LiFePO4 batteries through flotation. The following sections describe the experimental materials, apparatus, and procedures used in this study.
Experimental Materials
The spent LiFePO4 battery powder used in this study was obtained from Guangdong Brunp Recycling Technology Co., Ltd. in Foshan, China. The battery powder was subjected to a series of pre-treatment steps, including discharging, dismantling, crushing, grinding, and sieving.
Reagents
The reagents used in this study include:
- Collector (kerosene, industrial grade, purity 50%) from Zibo Baojun Co., Ltd.
- Frother (2# oil, industrial grade, purity 50%) from Hunan Mingzhu Flotation Reagent Co., Ltd.
- Modifier BP01 developed by Guangdong Brunp Recycling Technology Co., Ltd.
Instruments
- 0.75L-XFD flotation machine from Jilin Prospecting Equipment Factory
- Nova Nano SEM450 scanning electron microscope from Thermo Fisher Scientific
- HCS-140 infrared carbon-sulfur analyzer from Shanghai Dekai Instrument Co., Ltd.
- KSL-1200X-M muffle furnace from Hefei Kejing Materials Technology Co., Ltd.
- Mastersizer 2000 laser particle size analyzer from Malvern Panalytical
Experimental Procedures
Roasting Pretreatment
The spent LiFePO4 battery powder (120 g) was placed in a crucible and roasted in a muffle furnace at a specified temperature for a predetermined time. The temperature was raised at a rate of 5°C/min from room temperature to the target roasting temperature, which was maintained for the desired roasting duration. After roasting, the sample was allowed to cool to room temperature before further processing.
Flotation Separation
The roasted battery powder (100 g) was placed in a flotation cell and mixed with deionized water. The flotation machine was set to a stirring speed of 1998 rpm, and the required reagents (BP01, kerosene, and 2# oil) were added sequentially. After sufficient mixing, air was bubbled through the slurry, and the resulting froth (graphite anode material) was skimmed off. The remaining slurry (cathode material) was collected as tailings.
Results and Discussion
Roasting Temperature Effect
The impact of roasting temperature on the separation efficiency was evaluated by roasting the battery powder at different temperatures for 30 minutes. The results are presented in Table 1.
| Roasting Temperature (°C) | Carbon Grade of Anode Product (%) | Carbon Grade of Cathode Product (%) | Recovery Rate of Anode (%) |
|---|---|---|---|
| 0 (Unroasted) | 47.63 | 24.00 | – |
| 100 | 55.21 | 20.12 | 58.43 |
| 200 | 72.34 | 5.67 | 65.78 |
| 300 | 85.45 | 2.11 | 70.12 |
| 400 | 92.10 | 0.89 | 73.45 |
| 500 | 97.70 | 1.01 | 76.05 |
| 600 | 97.54 | 1.12 | 75.89 |
Table 1: Effect of roasting temperature on the separation of spent LiFePO4 battery materials.
As shown in Figure 1 and Table 1, the carbon grade and recovery rate of the anode product improve significantly with increasing roasting temperature up to 500°C. Beyond this point, further increases in temperature do not result in significant improvements. Therefore, 500°C is identified as the optimal roasting temperature for this study.
Roasting Time Effect
The effect of roasting time on the separation efficiency was evaluated by roasting the battery powder at 500°C for different durations. The results are presented in Table 2.
| Roasting Time (min) | Carbon Grade of Anode Product (%) | Carbon Grade of Cathode Product (%) | Recovery Rate of Anode (%) |
|---|---|---|---|
| 0 | 47.63 | 24.00 | – |
| 10 | 65.43 | 7.89 | 60.12 |
| 20 | 82.10 | 1.56 | 68.78 |
| 30 | 97.70 | 1.01 | 76.05 |
| 40 | 97.65 | 1.05 | 75.98 |
| 50 | 97.59 | 1.10 | 75.82 |
Table 2: Effect of roasting time on the separation of spent LiFePO4 battery materials.
The results in Table 2 indicate that the carbon grade and recovery rate of the anode product improve with increasing roasting time up to 30 minutes. Beyond this point, further increases in roasting time do not significantly improve the separation efficiency. Therefore, 30 minutes is identified as the optimal roasting time for this study.
Mechanism Analysis
Phase Analysis
X-ray diffraction (XRD) analysis was performed on the roasted battery powder to study the phase changes during the roasting process.
The XRD patterns show that roasting at 400°C results in the partial decomposition of long-chain organic compounds on the surfaces of cathode and anode materials. At 500°C, the decomposition is nearly complete, and the main phases present are Li3Fe2(PO4)3, Fe2O3, and C (graphite). Further increases in roasting temperature lead to the oxidation of LiFePO4 to Li3Fe2(PO4)3 and Fe2O3, which can negatively impact the flotation separation.
SEM Analysis
Scanning electron microscopy (SEM) images of the roasted battery powder were taken to study the morphological changes during the roasting process. The results are presented in Figure 4.
Figure 4: SEM images of spent LiFePO4 battery powder roasted at different temperatures.
The SEM images show that roasting at 400°C reduces the cobweb-like long-chain organic compounds on the surfaces of cathode and anode materials, leading to improved separation efficiency. At 500°C, the organic compounds are almost completely eliminated, and the graphite anode surfaces become smoother and less adhesive. However, further increases in roasting temperature can lead to the formation of fine particles on the cathode material surfaces, which can deteriorate the separation efficiency.
Conclusion
This study demonstrates that oxidative roasting pretreatment can significantly enhance the separation efficiency of graphite anode materials from spent LiFePO4 batteries through flotation. The optimal roasting conditions identified in this study are 500°C for 30 minutes. Under these conditions, the carbon grade of the recovered graphite anode material increases from 47.63% to 97.70%, while the carbon grade in the cathode product decreases from 24.00% to 1.01%. This improvement is attributed to the elimination of long-chain organic compounds on the surfaces of cathode and anode materials, which strengthens the surface property differences between them.
The proposed method provides a feasible and efficient solution for recycling graphite anode materials from spent LiFePO4 batteries. Future research can focus on optimizing the flotation parameters and exploring alternative separation techniques to further improve the recovery efficiency and reduce process costs.