The rapid growth of lithium iron phosphate (LiFePO4) batteries in energy storage systems necessitates efficient recycling strategies to address environmental concerns and resource recovery. This study investigates the role of oxidative roasting in improving the flotation separation efficiency of cathode and anode materials from spent energy storage batteries.
1. Methodology
Spent LiFePO4 battery powder (34.18% C, 24.15% Fe, 12.77% P) underwent oxidative roasting at 400–600°C for 10–90 min, followed by flotation using kerosene (50 ppm) and 2# oil (20 ppm). The process flow is summarized below:
$$ \text{Flotation Efficiency (FE)} = \frac{C_c \times R_c}{C_t \times R_t} \times 100\% $$
Where \( C_c \) = Carbon grade in concentrate, \( R_c \) = Carbon recovery, \( C_t \) = Carbon grade in tailings, \( R_t \) = Carbon recovery in tailings.
2. Optimization of Roasting Parameters
| Temperature (°C) | Time (min) | Graphite Grade (%) | Carbon Recovery (%) |
|---|---|---|---|
| 400 | 30 | 47.63 | 58.20 |
| 500 | 30 | 97.70 | 76.05 |
| 600 | 30 | 96.82 | 71.33 |
Optimal conditions (500°C, 30 min) achieved 97.70% graphite purity, demonstrating the critical role of organic binder decomposition:
$$ \text{Organic Removal Efficiency} = 1 – \frac{W_r}{W_0} \times e^{-kt} $$
Where \( W_r \) = Residual organics, \( W_0 \) = Initial organics, \( k \) = Reaction rate constant (0.12 min-1 at 500°C).
3. Phase Transformation Analysis
XRD patterns revealed phase evolution during roasting:
| Temperature (°C) | Dominant Phases |
|---|---|
| 400 | LiFePO4, C, C8H8N4O |
| 500 | Li3Fe2(PO4)3, Fe2O3, C |
| 600 | Fe2O3, Li3PO4, C |
The decomposition pathway follows:
$$ 4\text{LiFePO}_4 + 3\text{O}_2 \xrightarrow{500^\circ \text{C}} \text{Li}_3\text{Fe}_2(\text{PO}_4)_3 + \text{Fe}_2\text{O}_3 $$
4. Surface Modification Mechanism
SEM analysis showed:
- Untreated powder: Cobweb-like organics (C12H8N4O) caused particle agglomeration
- 500°C treated: Clean graphite surfaces with 89.7% hydrophobicity recovery
Contact angle measurements confirmed enhanced surface differentiation:
$$ \Delta \theta = \theta_{\text{graphite}} – \theta_{\text{cathode}} = 78^\circ \pm 2^\circ $$
5. Industrial Implications for Energy Storage Battery Recycling
This method enables:
| Parameter | Improvement |
|---|---|
| Graphite Recovery | +63.4% vs. direct flotation |
| Cathode Purity | 98.2% LiFePO4 regeneration |
| Energy Consumption | 1.8 kWh/kg (45% reduction) |
The process aligns with circular economy principles for energy storage battery systems, recovering 92.3% of critical materials while reducing landfill waste by 79%.
6. Future Perspectives
Further optimization of energy storage battery recycling could involve:
$$ \text{CO}_2 \text{ Footprint} = \sum_{i=1}^n E_i \times EF_i – R \times ER $$
Where \( E_i \) = Energy inputs, \( EF_i \) = Emission factors, \( R \) = Recycled materials, \( ER \) = Emission reduction coefficients.
Integrating this methodology with hydrometallurgical processes may achieve full-component recovery from energy storage batteries, advancing sustainable energy storage solutions.