Introduction: A Model of Cross-Disciplinary Innovation in the Circular Economy
Amid the global wave of energy transition, the popularity of electric vehicles has brought about an increasingly severe challenge—the fate of a large number of retired lithium iron phosphate (LFP) power batteries. Traditional hydrometallurgical recycling primarily focuses on extracting lithium, which is economically suboptimal and fails to fully utilize the phosphorus resource that constitutes nearly 40% of the battery’s mass. Simultaneously, modern agriculture faces the dual challenges of acidic soil remediation and low phosphorus fertilizer efficiency. A groundbreaking technology ingeniously connects these two seemingly unrelated problems. Through innovative chemical processes, it directly converts retired LFP batteries into a slow-release phosphorus fertilizer that performs exceptionally well in acidic soils. This is not only a major innovation in the field of resource recovery but also opens a new path for nutrient supply in green agriculture, serving as a vivid practice of the circular economy concept at the intersection of new energy and agriculture.
I. Core Technology: A Four-Step Transformation from Battery to Fertilizer
This technology follows a clear, efficient, and environmentally friendly process route, divided into four key steps that achieve the precise conversion from waste electrode materials to functional fertilizer.
Step 1: Mild and Efficient Electrode Delamination
The process begins with separating the battery cathode active material from the aluminum foil current collector. Unlike traditional strong acid stripping or high-temperature incineration, this technology employs a mild chemical stripping solution assisted by ultrasonic treatment. The cavitation effect generated by ultrasound efficiently breaks the adhesion of the binder (e.g., PVDF) while avoiding harsh reactions that could damage the crystal structure of the active material. This step yields uniform, high-purity lithium iron phosphate (LiFePO₄) black powder, laying the foundation for subsequent selective extraction.
Step 2: Selective Lithium Extraction and Retention of Phosphorus-Iron Solid Phase
This is the key to the economic viability of the entire process. Using mild oxidants such as sodium persulfate (Na₂S₂O₈) under specific conditions, lithium ions (Li⁺) in LiFePO₄ are selectively oxidized and leached into the solution, while iron (Fe) and phosphorus (P) elements are retained in the solid phase as insoluble iron phosphate (FePO₄). This method achieves efficient, high-purity lithium recovery (which can be subsequently converted into lithium carbonate products) while ensuring that phosphorus and iron resources are not lost. This precise separation creates the conditions for the targeted utilization of phosphorus.
Step 3: Efficient Phosphorus Release and Resource Conversion
The solid phase after delithiation is mainly FePO₄, from which phosphorus needs to be released and converted into a plant-available form. Through reaction with reagents such as sodium sulfide (Na₂S), phosphorus is efficiently transferred into an aqueous solution in the form of specific ions (e.g., dihydrogen phosphate, H₂PO₄⁻). The phosphorus recovery rate in this step is extremely high, exceeding 99.5% under laboratory conditions, ensuring maximum resource utilization. It is worth noting that the by-products of this reaction (e.g., iron sulfide) also have potential value as photocatalytic materials, further embodying the zero-waste concept of “utilizing everything to the fullest.”
Step 4: Synthesis of Acid-Resistant Slow-Release Phosphorus Fertilizer
This is the functional core of the technology. The obtained phosphorus-containing solution (containing precisely controlled molar ratios of hydrogen phosphate, HPO₄²⁻, and dihydrogen phosphate, H₂PO₄⁻) is used as a functional monomer and mixed with raw materials such as acrylic acid and urea. In the presence of an initiator and under nitrogen protection, free radical polymerization is carried out at 50-80°C. The key to this reaction is that phosphate ions act as cross-linking agents and stabilizers, forming a dense hydrogen bond network with the carboxyl groups on the polyacrylic acid chains and creating an interpenetrating structure with urea, ultimately building a stable three-dimensional polymer hydrogel network. The fertilizer nutrient (phosphorus) is chemically bonded or physically encapsulated within this network.
II. Core Advantages: Triple Breakthroughs in Economics, Performance, and Environmental Protection
The disruptive potential of this technology stems from its significant advantages across multiple dimensions.
- Disruptive Economic Model:Traditional LFP battery recycling suffers from poor economics due to the lack of high-value cobalt and nickel. This technology adopts a “lithium + phosphorus” dual-recovery model, converting the phosphorus that constitutes the bulk of the battery mass into high-value-added agricultural products. Calculations estimate that introducing this technology can yield a net profit of approximately $2,035 per ton of retired batteries processed, completely reversing the “unprofitable” situation of LFP recycling and providing strong commercial drivers for the recycling industry.
- Outstanding Acid-Resistant Slow-Release Performance:Traditional polymer slow-release fertilizers tend to have their network structure collapse due to protonation in acidic soils, leading to nutrient “burst release” or failure. In the fertilizer synthesized by this technology, phosphate groups play a dual role: first, as strong hydrophilic groups and cross-linking points, they enhance the stability and water retention of the network in acidic environments; second, they possess pH buffering capacity, partially neutralizing soil acidity and providing an ideal microenvironment for steady, long-lasting nutrient release. This makes it particularly suitable for the vast areas of acidic red and yellow soils in southern China.
- Green and Environmentally Friendly Throughout the Process:The entire process avoids the use of strong acids, strong alkalis, or high-temperature calcination. The reagents are mild, and by-products can be resource-utilized, basically generating no difficult-to-treat secondary pollution. The transformation from electronic waste to an environmentally friendly fertilizer achieves true clean production and a closed resource loop.
III. Application Prospects and Future Directions
The successful development of this technology holds broad application value and profound social significance.
In Agriculture: It provides an innovative product to address the worldwide challenges of severe phosphorus fixation in acidic soils and low fertilizer efficiency. Preliminary experiments indicate that this fertilizer can effectively promote the growth of crops like corn. It can achieve the same or even higher yields while reducing phosphorus fertilizer application by 30%-50%, significantly lowering the risk of phosphorus loss through runoff. This has a positive effect on protecting water bodies and preventing eutrophication.
In Resource Circulation: It points the way for the high-value, resource-based utilization of millions of tons of retired LFP batteries annually. It is a key technological node in constructing the grand cycle of “battery production – use – recycling – material regeneration – agricultural feedback,” strongly supporting the sustainable development of the new energy vehicle industry.
Future Development Focus: Current research is primarily at the laboratory stage. Future work will focus on: 1) Process Engineering Scale-up: Optimizing continuous production processes, reducing equipment and operational costs, and promoting the industrialization of the technology; 2) Systematic Agricultural Validation: Conducting large-scale, long-term field trials on various types of acidic soils and multiple crops to comprehensively evaluate its agronomic effects and environmental benefits; 3) Product Series Development: Building on the existing phosphorus fertilizer, introducing potassium, calcium, magnesium, and trace elements to develop specialized compound slow-release fertilizers for different scenarios such as dryland farming, protected horticulture, and economic forests; 4) Technology Extension Applications: Exploring the application of this technological concept to the resource treatment of other phosphorus-containing wastes (e.g., phosphorus-rich sludge, phosphogypsum), expanding its application boundaries.
Converting discarded lithium iron phosphate batteries into acid-resistant, slow-release phosphorus fertilizer is a cutting-edge technology that integrates materials science, environmental engineering, and agronomy. It cleverly solves the dual challenges of “difficult disposal of waste batteries” and “difficult fertilization of acidic soils,” achieving a transformative “waste-to-resource” solution. This technology not only demonstrates the immense potential of interdisciplinary resource recycling but also provides a highly promising technological blueprint for the green transformation of global agriculture and the closed-loop development of the new energy industry. As the technology matures and is widely adopted, we have reason to believe that these batteries, which once powered electric vehicles and traveled thousands of miles, will continue to nourish the earth in another form after their retirement, sustaining life for generations to come.
A Circular Blueprint: From Batteries to Farmland
The conversion of spent lithium iron phosphate batteries into acid-resistant, slow-release phosphorus fertilizer represents a paradigm shift in resource recovery. This interdisciplinary innovation addresses both critical waste management and sustainable agriculture challenges, creating a truly circular “waste-to-resource” pathway with significant environmental and economic potential.
To scale this transformative process, the recovered nutrient materials can be integrated into conventional fertilizer granulation processes. The phosphorus-rich compound can be blended into formulations using an npk blending machine and then shaped into uniform granules via advanced granulation technology. Depending on the desired product characteristics, a disc granulator (as part of a disc granulation production line) or a double roller press granulator can be employed within a complete npk fertilizer production line. This integration with professional fertilizer manufacturing equipment ensures the final product meets agronomic standards for efficient, controlled-release application.
Ultimately, this technology exemplifies a powerful synergy between the new energy and agriculture sectors. It promises a future where batteries, after powering our vehicles, can be reborn as vital nutrients that nourish crops and regenerate soils, closing the loop in a truly sustainable economy.