Efficient Lithium Recovery from Spent Lithium Iron Phosphate Batteries via Sodium Salt Roasting

The exponential growth of lithium iron phosphate (LiFePO₄) batteries in electric vehicles and energy storage systems has intensified the demand for sustainable recycling methods. Traditional hydrometallurgical approaches, while effective, often involve corrosive acids, generate excessive waste, and struggle with selective lithium recovery. This study introduces a sodium salt roasting-water leaching process that achieves high lithium selectivity without acid consumption, offering a scalable and eco-friendly solution for spent lithium iron phosphate battery recycling.

1. Methodology

Spent lithium iron phosphate batteries underwent systematic pretreatment:

Complete discharge in 1.0 mol/L Na₂SO₄ solution (48 h)
Mechanical dismantling to isolate cathode sheets
Thermal decomposition at 550°C under N₂ atmosphere (2 h)
Mechanical separation to obtain LiFePO₄ cathode powder (ICP composition: Li 4.17%, Fe 43.54%)

2. Process Optimization

The lithium extraction efficiency was quantified using:

$$ Q = \frac{C \times V}{m} \times 100\% $$

where C (g/L) and V (L) represent lithium concentration and leachate volume, respectively, and m denotes initial lithium mass.

Table 1. Effect of Na₂SO₄/LiFePO₄ mass ratio on lithium recovery (650°C, 2 h)
Mass Ratio	1.4	1.5	1.6	1.7	1.8	1.9
Li Recovery (%)	89.32	93.15	96.81	96.75	96.68	95.42

Table 2. Temperature influence on lithium extraction (Mass ratio 1.6, 2 h)
Temperature (°C)	400	500	600	650	700	800
Li Recovery (%)	51.23	68.95	87.41	96.81	96.78	94.56

3. Phase Transformation Mechanism

Roasting facilitates lithium sulfation through:

$$ 2\text{LiFePO}_4 + 2\text{Na}_2\text{SO}_4 + \frac{1}{2}\text{O}_2 \rightarrow \text{Li}_2\text{SO}_4 + 2\text{NaFe(SO}_4\text{)} + \text{P}_2\text{O}_5 $$

Water leaching subsequently dissolves Li₂SO₄ while leaving iron compounds insoluble, enabling efficient lithium-iron separation.

4. Industrial Implications

Compared with conventional acid leaching, this sodium salt roasting process demonstrates:

97.36% purity Li₂SO₄ recovery
96.81% lithium extraction efficiency
Zero acid consumption (pH-neutral wastewater)
20-35% lower energy consumption than pyrometallurgical alternatives

The developed methodology addresses critical challenges in lithium iron phosphate battery recycling through:

Selective lithium extraction without Fe co-dissolution
Closed-loop Na₂SO₄ regeneration potential
Direct synthesis of battery-grade lithium compounds

This advancement significantly enhances the economic viability and environmental sustainability of lithium iron phosphate battery recycling systems, particularly crucial as global LiFePO₄ battery deployments approach 250 GWh annual production capacity.