Material and Energy Flow Analysis of Hydrometallurgical Recycling for Lithium-Ion Battery Based on Aspen Plus

Abstract

The exponential growth of global electric vehicle deployment has precipitated a critical need for the sustainable recycling of end-of-life lithium-ion batteries (LIBs), particularly nickel–cobalt–manganese (NCM) ternary cathodes, which dominate the retired battery stream. This study establishes an integrated Aspen Plus-based hydrometallurgical process model, focusing on “acid dissolution–LiOH precipitation–electrolysis” for closed-loop NCM recycling. Gibbs reactor-based dissolution kinetics is used for selective metal leaching (achieving > 99% efficiency at 185 kg/h acid flow), the thermodynamic prioritization of sequential hydroxide precipitation (Co → Ni → Mn at 10–60 kg/h LiOH), and the electrochemical regeneration of LiOH/H₂SO₄ from Li₂SO₄ (70.01 kg/h LiOH at 0.8 conversion). Material balance analysis confirms a net production of 10.01 kg LiOH per 100 kg of NCM feedstock with 41.87 kg of acid consumption, while the energy of electrolysis power is 452.96 kW at 6 V/1360 A/m². This work provides a techno-economic framework for industrial-scale battery recycling.

1. Introduction

The rapid development of the global electric vehicle industry has driven exponential growth in lithium-ion battery (LIB) demand [1]. Industry data project that the global volume of end-of-life power batteries will exceed 2 million tons by 2030 [2,3], over 60% of which comprise nickel–cobalt–manganese (NCM) ternary cathode materials rich in strategic metals like lithium, cobalt, nickel, and manganese [4,5]. These retired batteries represent valuable secondary resources, yet their indiscriminate disposal poses environmental risks due to heavy metal leaching [6,7]. Compounded by the geopolitical concentration of critical metals and escalating environmental pressures from mining, efficient recycling technologies have become essential for sustainable industry development.

Current mainstream LIB recycling technologies include hydrometallurgy, pyrometallurgy, and physical separation [5,8]. Pyrometallurgy employs high-temperature smelting (>1400 °C) to convert metals into alloys or slag phases, accommodating mixed battery streams without rigorous sorting [9,10]. However, it suffers from high energy costs, low lithium recovery (<30% in conventional processes), and significant dioxin/fluoride emissions requiring costly gas purification [11]. Physical separation recovers black mass and metal fragments through mechanical crushing and sieving [12]. While operationally simple with low capital investment, the resulting black mass typically contains copper/aluminum impurities. Hydrometallurgy, as the dominant industrial approach, selectively dissolves electrode-active materials in acidic media, followed by solvent extraction purification and precipitation, achieving high metal recovery rates (>90% for Ni, Co, Mn) [13,14]. Its advantages include superior product purity and lower energy intensity. Typical processes, such as the sulfuric acid-reductant system (H₂SO₄/H₂O₂), achieve > 90% leaching efficiency for Ni, Co, and Mn at 80 °C [15].

Recent advancements in hydrometallurgy focus on innovations in leaching and separation [16]. Extractants like tributyl phosphate (TBP) or di (2-ethylhexyl) phosphate effectively separate nickel, cobalt, and manganese, while sodium carbonate precipitation recovers high-purity lithium carbonate (>99.5%) [17,18]. Nevertheless, challenges persist, including poor lithium leaching selectivity and high acid/base consumption [16,19]. The multivariate nature of hydrometallurgical processes makes experimental optimization costly [20,21]. To address this issue, Li et al. [22] developed a microwave-assisted leaching technique using citric acid as a reductant for recovering valuable metals from spent NCM black mass. Compared to traditional reductants (H₂O₂ or ascorbic acid), citric acid exhibits synergistic advantages under microwave irradiation: its reductive properties and chelation of Cu/Fe ions promote reductive radical generation, significantly enhancing leaching efficiency. Under optimized conditions, leaching efficiencies reached 99.5% for Li, 99.7% for Mn, 99.5% for Co, and 99.3% for Ni. Dai et al. [23] proposed a high-temperature hydrothermal reduction method using eco-friendly starch as a reductant for selective lithium extraction from spent lithium manganate (LMO) cathode powder. At 240 °C with 40% starch dosage, lithium leaching efficiency exceeded 95% with selectivity > 92%, recovering lithium as lithium carbonate. Transition metals in the residue were subsequently extracted via ammonium salt roasting–water leaching at 350 °C, with 1.7 times stoichiometric ammonium sulfate, achieving > 99% extraction efficiency and yielding ammonium manganese sulfate double salt. For NCM material, Wang et al. [24] proposed a novel chromatographic process of recycling spent ternary lithium battery cathodes using amine-modified polyacrylonitrile fibers. The method achieved 99.4% lithium recovery with 100% purity under optimized conditions. While numerous novel methods have been proposed to optimize the recycling of lithium battery electrode materials, the scaling potential and industrialization prospects of these new recycling processes remain to be evaluated.

Aspen Plus, as a platform for chemical process simulation, provides critical theoretical support for process design and scale-up through material and energy balance modeling [25]. Asadi et al. [26] develops a sodium-free closed-loop process for recycling spent lithium nickel manganese cobalt oxide cathodes. Sulfuric acid and lithium hydroxide regeneration via electrodialysis was modeled using Aspen Plus. Batch electrodialysis increased lithium hydroxide recovery by twenty-five percent, while higher leaching temperatures improved lithium extraction by fifty-three percent. Kim et al. [27] utilized Aspen Plus and COMSOL to propose a novel sustainable LIB recycling system integrating electrodialysis for wastewater treatment, analyzing coupled electrochemical processing for metal recovery from lithium cobalt oxide (LCO). While hydrometallurgy achieves high leaching rates, the high-selectivity separation and enrichment of different metal ions from solution typically require multi-stage solvent extraction, chemical precipitation, or electrodeposition. While Aspen Plus has been applied to lithium battery recycling processes, research predominantly focuses on metal leaching rates. Insufficient attention has been given to energy release in reactors and system power consumption during reactions, and the limited research efforts constrain the potential assessment of industrialization.

This study focuses on NCM ternary cathode material recycling, constructing a comprehensive “sulfuric acid-reductant dissolution-LiOH precipitation-electrolysis” process model on the Aspen Plus platform. Leveraging Gibbs reactor principles, the model investigates the dissolution kinetics of NCM materials and the fractional precipitation process for nickel, cobalt, and manganese. An electrolysis regeneration module is developed to convert Li₂SO₄ into battery-grade LiOH and regenerate sulfuric acid via ion migration. Finally, the energy and material flow consumption of the integrated system is quantitatively evaluated. This research provides key technical support for the intelligent design and resource-closed-loop implementation of hydrometallurgical recycling processes.

2. Methods

Typically, end-of-life lithium-ion batteries undergo deep discharge in a 10 wt% NaCl solution for 48 h to achieve a residual voltage below 0.5 V, followed by cryogenic crushing at −196 °C in liquid nitrogen to prevent thermal runaway; the crushed material is sieved (<2 mm) and subjected to electrostatic separation (25 kV) to isolate the cathode-derived black mass, which is then thermally treated at 300 °C under a nitrogen atmosphere to decompose polyvinylidene fluoride binders, ultimately yielding purified NCM (LiNi_0.7Co_0.15Mn_0.15O₂) cathode active material with 95.2% purity [2]. In this study, to focus the material and energy flow analysis on the core hydrometallurgical recycling steps, purified NCM material is directly utilized as the feedstock, with no further simulation or analysis of the pretreatment stages.

A process model for the hydrometallurgical recovery of NCM cathode materials was developed using Aspen Plus (V11) with the flowsheet illustrated in Figure 1a. NCM material (LiNi_0.7Co_0.15Mn_0.15O₂, 100 kg/h) as feedstock and acid solution (a mixture of sulfuric acid and hydrogen peroxide with a mass ratio H₂SO₄:H₂O₂:H₂O = 10:1:2) are fed into a dissolution reactor (DIS, Gibbs reactor, 1 bar, 80 °C, possible reaction pathways: LiNi_0.7Co_0.15Mn_0.15O₂ + 1.5H₂SO₄ + H₂O₂ → 0.5Li₂SO₄ + 0.7NiSO₄ + 0.15CoSO₄ + 0.15MnSO₄ + 2.5H₂O + 0.75O₂↑) for dissolution. The reaction products subsequently enter a separator (SEP1, Flash separator, 1 bar, 80 °C) where gaseous products are removed. The resulting liquid phase proceeds to a precipitation reactor (PRE, Gibbs reactor, 1 bar, 80 °C, possible reaction pathways: CoSO₄ + 2LiOH → Co(OH)₂↓ + Li₂SO₄, NiSO₄ + 2LiOH → Ni(OH)₂↓ + Li₂SO₄ and MnSO₄ + 2LiOH → Mn(OH)₂↓ + Li₂SO₄), where lithium hydroxide is introduced to precipitate nickel, cobalt, and manganese metals. The slurry undergoes secondary separation (SEP2, Flash separator, 1 bar, 80 °C) to recover solid products. The residual lithium sulfate-dominated solution is directed to an electrolysis reactor (ELE, RStoic reactor, 1 bar, 80 °C) operating via the reaction Li₂SO₄ + 2H₂O → H₂SO₄ + 2LiOH, where electrochemically driven ion migration generates lithium hydroxide, sulfuric acid, and diluted lithium sulfate. These products undergo separation in dedicated cathode (CATHODE, Flash separator, 1 bar, 80 °C) and anode (ANODE, Flash separator, 1 bar, 80 °C) units. Key system evaluation parameters include acid solution consumption, lithium hydroxide consumption, oxygen production rate, dissolution reaction enthalpy, precipitation reaction enthalpy, electrolysis power consumption, electrolysis reactor heat release, feedstock dissolution efficiency, and target metal precipitation efficiency. The schematic diagram of key chemical reactions is shown in Figure 1b.

The model utilized the Aspen Plus solver with enhanced numerical stability settings: Stream relative convergence tolerance = 0.0001. Final constraint violation tolerance = 0.000001. Creep step size = 0.1, to resolve path-sensitive electrochemical reactions. State variables (pressure and enthalpy) verified at every iteration. Maximum flowsheet passes = 30 and basis iterations = 100. Stability search initiated after 4 stable steps via linear search.

3. Results

3.1. Process of Dissolution and Leaching

The dissolution and leaching of NCM metals constitute critical steps governing overall metal recovery efficiency. Figure 2 illustrates the leaching progression of the four major metals within the Gibbs reactor. Under a constant NCM feed rate of 100 kg/h, the acid solution flow rate was incrementally increased from 65 kg/h to 185 kg/h. As acid addition rises, metal dissolution progressively intensifies, while the solid residue phase diminishes correspondingly. At an acid flow rate of 65 kg/h, lithium is completely leached, yielding 61.7 kg/h of lithium sulfate. Manganese leaching commences at this stage, with dissolved manganese accounting for 46.76% of its total mass. Nickel and cobalt remain unreacted, persisting in their oxide forms. When acid addition reaches 95 kg/h, the complete leaching of lithium, manganese, and cobalt is achieved, while nickel leaching initiates. Further increasing the acid supply to 155 kg/h results in a nickel leaching efficiency of 73.47%. Ultimately, at a 185 kg/h acid flow rate, all metallic components are fully dissolved, with no residual solids remaining.

Figure 3 illustrates the sulfuric acid content profile within the leaching solution across varying acid flow rates. When the acid flow rate ranges from 65 to 155 kg/h, the Gibbs reactor configuration facilitates near-complete acid consumption, with sulfuric acid approaching full reaction conversion. However, at the elevated flow rate of 185 kg/h, a distinct residual sulfuric acid concentration of 7.56 kg/h emerges, indicating a reagent surplus beyond the stoichiometric requirement for metal dissolution under these operational conditions. The addition of hydrogen peroxide (H₂O₂) during the hydrometallurgical recovery of lithium battery materials enhances dissolution efficiency through combined reductive and acidifying effects. Cathode materials such as LiCoO₂ and NCM contain cobalt, nickel, and manganese predominantly in +3 or +4 valence states, which exhibit limited solubility in acidic media. In acidic environments, H₂O₂ decomposes to generate strongly reductive hydroxyl radicals (OH), which reduce high-valence metals to soluble lower-valence ions, significantly lowering the leaching energy barrier. This reduction mechanism is exemplified by the representative reaction: 2Co³⁺ + H₂O₂ → 2Co²⁺ + 2H⁺ + O₂, a process that substantially improves cobalt and nickel leaching efficiencies [18]. The reaction stoichiometry further reveals that oxygen gas evolves as a byproduct during H₂O₂ consumption, as a reductant. Figure 3 demonstrates the oxygen production profile under increasing acid solution flow rates, revealing a predominantly linear escalation from 0.99 kg/h to 2.82 kg/h, corresponding to the acid flow increment. This progressive increase directly correlates with the intensified decomposition of hydrogen peroxide reductant during the metal reduction process.

The exothermic reaction between NCM cathode materials and sulfuric acid fundamentally involves coupled processes of strong acid-induced lattice destruction and transition metal reduction. Protons (H⁺) penetrate the oxygen sublattice, triggering structural collapse where Li⁺ deintercalates from interlayers to form Li₂SO₄, releasing lattice energy (ΔH₁ ≈ −75 kJ/mol) in a step governed by interfacial mass transfer [28]. Concurrent side reactions include manganese disproportionation (2Mn⁴⁺ → Mn²⁺ + MnO₂↓), which consumes acid and forms passivating layers, while cobalt reduction (Co³⁺ → Co²⁺, ΔH₃ ≈ −156 kJ/mol) intensifies heat release [29]. The Gibbs reactor’s equilibrium-driven resolution of competing reactions inherently prioritizes Li leaching via direct H⁺ exchange [30], followed by Mn disproportionation [31], and finally Co/Ni reduction [32], as these pathways reflect progressively higher energy barriers. Figure 4 depicts the heat release profile within the dissolution reactor (DIS). The total heat output ranges between 40 and 50 kW, peaking at 47.5 kW under a 155 kg/h acid flow and reaching a minimum of 41.24 kW at 95 kg/h. Notably, heat release decreases as acid flow increases from 65 kg/h to 95 kg/h. Product analysis attributes this anomaly to the cessation of manganese hydroxide formation: at lower acid flows (65 kg/h), 9.87 kg/h of Mn(OH)₂ precipitates, whereas higher flows (≥95 kg/h) suppress this reaction entirely. The endothermic nature of Mn(OH)₂ formation thus critically modulates the net thermal signature. At a low acid flow (65 kg/h), residual Mn²⁺ reacts with OH⁻ impurities (from H₂O₂ decomposition: H₂O₂ ⇌ H⁺ + HO₂⁻) to form Mn(OH)₂ (ΔH = +83 kJ/mol), consuming latent heat. Higher acid influx (≥95 kg/h) prevents hydroxylation and unmasks the exothermic Co³⁺ reduction dominance (ΔH = −156 kJ/mol).

3.2. Process of Precipitation

Following the complete dissolution of NCM metals into sulfate species through acid excess, lithium hydroxide is employed to directly precipitate nickel, cobalt, and manganese, thereby bypassing complex solvent extraction processes. Figure 5 delineates the precipitation progression within the Gibbs reactor as the lithium hydroxide dosage increases from 10 to 60 kg/h. Augmenting alkali addition progressively drives the precipitation of all three target metals while diminishing dissolved sulfate concentrations. At 10 kg/h LiOH, cobalt initiates precipitation, yielding 12.24 kg/h of cobalt hydroxide, which constitutes 68.3% of the total mass of Co. Nickel and manganese remain unreacted in sulfate forms. When alkali dosage reaches 20 kg/h, nickel precipitation commences. At 50 kg/h LiOH, nickel achieves 100% precipitation efficiency, while manganese begins precipitating. The ultimate precipitation of all metals occurs at 60 kg/h. Cobalt’s priority precipitation results from its low dehydration barrier enabled by moderate hydration energy. This facilitates rapid Co(OH)₂ nucleation, while Mn²⁺’s weaker hydration demands a higher LiOH dosage (≥50 kg/h) to achieve critical supersaturation. Building upon the established material balance per 100 kg of NCM feedstock processed, the system yields 72.83 kg of nickel hydroxide, 15.65 kg of cobalt hydroxide, and 14.97 kg of manganese hydroxide, collectively constituting 103.45 kg of high-purity hydroxide products that directly serve as precursor materials for cathode resynthesis. This staged precipitation behavior demonstrates how controlled alkali addition governs metal-specific separation through thermodynamic prioritization in the Gibbs reactor system.

The precipitation of nickel, cobalt, and manganese sulfates with lithium hydroxide constitutes a coupled crystallization and exothermic neutralization process, where heat release originates from concurrent ion dehydration energy liberation and lattice formation. When sulfate solutions containing Ni²⁺, Co²⁺, and Mn²⁺ ions react with LiOH, instantaneous proton-hydroxide neutralization occurs first (H⁺ + OH⁻ → H₂O, ΔH ≈ −57.3 kJ/mol), rapidly elevating the system temperature. Subsequently, metal ions combine with hydroxyl groups to form crystalline hydroxides, releasing additional heat through the dehydration of hydrated ions and lattice ordering. The dominant thermal contribution arises from the dehydration of high-hydration-energy ions: Ni²⁺ (hydration energy −2106 kJ/mol) and Co²⁺ (−1990 kJ/mol) exhibit intense exothermic behavior during precipitation. In contrast, Mn²⁺ with lower hydration energy (−1880 kJ/mol) contributes minimally to heat release. This thermodynamic hierarchy is exemplified by the representative nickel precipitation reaction: NiSO₄ + 2LiOH → Ni(OH)₂↓ + Li₂SO₄ (ΔH ≈ −78 kJ/mol), where the net enthalpy change integrates neutralization, dehydration, and crystallization energetics. Given the comparable reaction enthalpies of nickel and cobalt precipitation, the heat release rate within the precipitation reactor increases approximately linearly, with the lithium hydroxide dosage between 10 and 50 kg/h, as shown in Figure 6. However, a distinct reduction in the heat release slope occurs when the dosage rises from 50 to 60 kg/h, attributed to the weakly exothermic nature of manganese precipitation. At this terminal dosage, the reactor achieves a heat output of 120.62 kW.

3.3. Process of Electrolysis

Following the precipitation and separation of nickel–cobalt–manganese hydroxides, the resulting concentrated lithium salt solution undergoes electrochemical processing. Within the electrolysis reactor, the directional migration of lithium ions and sulfate anions generates lithium hydroxide and regenerated sulfuric acid, significantly reducing fresh reagent consumption in the system. Figure 7 presents the operational voltage requirements and corresponding current densities across varying lithium sulfate conversion rates, with the current density calculated based on electron transfer stoichiometry, using an effective electrode area of 55.5 m². As the conversion rate increases from 0.4 to 0.8, applied cell voltages were set at 4, 4.5, 5, 5.5, and 6 V. At the established lithium hydroxide addition rate of 60 kg/h, the lithium sulfate feed flow measures 193.56 kg/h. The derived current densities—calculated from charge transfer requirements and the effective electrode area—correspond to 680, 850, 1020, 1190, and 1360 A/m², respectively, across the conversion rate gradient. These values align with the standard industrial operating ranges for electrochemical separation systems, validating the process’ scalability.

Figure 8a presents the primary product yields under varying lithium sulfate conversion efficiencies, demonstrating an inverse correlation between conversion rate and residual lithium sulfate flow. As conversion efficiency increases, the effluent lithium sulfate diminishes progressively, while lithium hydroxide and sulfuric acid production exhibit corresponding growth. At the 0.8 conversion benchmark, the system yields 70.01 kg/h of lithium hydroxide and 138.13 kg/h of sulfuric acid, with the residual lithium sulfate flow reduced to 38.71 kg/h. Material balance analysis per 100 kg of NCM feedstock, after accounting for internal reagent recycling, indicates a net consumption of 41.87 kg of sulfuric acid, alongside the production of 10.01 kg of battery-grade lithium hydroxide and 38.71 kg of residual lithium sulfate. Concurrent energy analysis at a 0.8 conversion efficiency (employing a 6 V potential and a 1360 A/m² current density from Figure 7) reveals an electrolysis reactor power consumption of 452.96 kW, with a concurrent heat release of 264.6 kW, as quantified in Figure 8b. This integrated assessment validates the closed-loop regeneration efficiency while delineating the operational energy boundaries.

4. Conclusions

This study establishes a robust Aspen Plus-based framework for the closed-loop hydrometallurgical recycling of NCM lithium-ion batteries, demonstrating high-efficiency metal recovery via integrated “acid dissolution–LiOH precipitation–electrolysis” processes. Key findings reveal that the acid flow rate (185 kg/h H₂SO₄/H₂O₂, 10:1:2 mass ratio) governs sequential metal leaching, achieving > 99% dissolution efficiency while generating 0.99–2.82 kg/h of oxygen as a reduction byproduct. Controlled LiOH addition (10–60 kg/h) enables the thermodynamic prioritization of hydroxide precipitation (Co → Ni → Mn), yielding 103.45 kg of Co/Ni/Mn hydroxides per 100 kg of NCM feedstock. Electrolysis regenerates 70.01 kg/h of LiOH at 0.8 Li₂SO₄ conversion, reducing the net fresh reagent consumption to 41.87 kg of H₂SO₄ and producing 10.01 kg of LiOH per 100 kg of NCM processed. Energy analysis confirms electrolysis as the dominant energy sink (452.96 kW at 6 V/1360 A/m²), underscoring the need for energy optimization in scaling up. These results provide a validated techno-economic blueprint for industrial implementation, where reagent circularity and selective recovery mitigate resource scarcity and environmental impacts. Future work will focus on optimizing acid/reductant stoichiometry to minimize residual sulfuric acid (7.56 kg/h observed at 185 kg/h flow), scaling electrolysis modules for higher Li₂SO₄ conversion rates and reduced voltage/current density, and evaluating process robustness against complex feedstocks containing aluminum/copper impurities at various temperatures.