Direct Internal Recycling (DIR)

• Direct Internal Recycling (DIR) is a method for preserving active battery and magnet materials by retaining their functional structure for reuse within the same production chain.
• In EV batteries, DIR involves mechanical pre-processing, selective separation, and relithiation, while in magnets it uses hydrogen decrepitation and re-sintering to maintain alloy integrity.
• DIR offers improved performance and energy savings by avoiding full chemical breakdown, though challenges remain in standardization, scalability, and feedstock variability.

Searching arXiv for the cited papers and topic-specific context. Direct Internal Recycling (DIR) denotes a class of recycling routes in which functional materials are retained in a form suitable for reuse in the same manufacturing value chain, rather than being fully reduced to elemental metals or salts. In electric-vehicle lithium-ion batteries, DIR is described under the broader heading of direct recycling and corresponds to process routes where the functional battery components—especially the cathode active material—are recovered and re-used essentially as cathode material again, after limited reconditioning such as relithiation, impurity removal, and re-processing (Narisetty et al., 2024). In permanent magnets, DIR denotes the direct re-use of the magnet alloy as magnet material, without full chemical dissolution or high-temperature extraction and refining; the hydrogen decrepitation plus re-sintering route for SmCo₅ is a representative example (Eldosouky et al., 2019). Taken together, these uses suggest a broader closed-loop concept in which material value is preserved at the level of active phases, particle morphology, or alloy composition.

1. Conceptual definition and scope

In the battery-recycling literature, direct recycling is defined as a class of techniques that preserve the active electrode materials, mainly the cathode and in some cases the anode, rather than decomposing them to base metals. Its objective is to reuse the same active materials in new battery cells, thereby avoiding the full chemical “reset” characteristic of pyrometallurgical smelting and fully metal-focused hydrometallurgy (Narisetty et al., 2024). In a narrow sense, DIR denotes the closed-loop, internal reuse of active cathode material, and possibly other functional components, within the EV battery value chain. The associated term “closed-loop recycling” occupies the same conceptual space, emphasizing that cathode-grade or electrode-grade materials are returned to battery production.

For permanent magnets, the same logic appears in alloy-preserving routes. DIR of permanent magnets means direct re-use of the magnet alloy as magnet material, without full chemical dissolution and without pyrometallurgical separation of rare-earth and transition metals. In the SmCo₅ case, hydrogen decrepitation is used simply to break the sintered magnet into powder, after which the powder is milled, pressed, and sintered to make a new magnet using standard SmCo₅ processing (Eldosouky et al., 2019). The alloy is therefore kept essentially intact, and composition and basic phase framework are largely preserved.

This common formulation distinguishes DIR from commodity recovery. In battery systems, the intended loop is “battery → refurbished cathode → new battery”; in magnet systems, it is “magnet → powder → re-sintered magnet.” A plausible implication is that DIR is best understood not as a single unit operation but as a recycling philosophy centered on preserving functional material value.

2. Process architectures in batteries and magnets

For EV batteries, the paper embeds recycling in a multi-stage lifecycle: “Begin of life → Battery 1st life → 2nd life in smart grid → End of life recycling” (Narisetty et al., 2024). After collection, packs are assessed, discharged, and routed to recycling. Mechanical pre-processing then includes physical dismantling of packs and mechanical recycling by crushing, grinding, and sieving to liberate electrode coatings from current collectors. The resulting “black mass” contains cathode particles, anode graphite, conductive additives, binder, and residual electrolyte. Direct routes then require selective separation of cathode material from graphite and other fractions, followed by healing or reconditioning of cathode material. The core objective is to retain the crystal structure and morphology of cathode powders such as NMC, NCA, and LFP while restoring lithium content and removing surface contamination or degraded binder and electrolyte residues. The relithiation step is represented as

$$\text{Li}_{1-x}\text{MO}_2 + x\text{Li}^+ + x e^- \rightarrow \text{LiMO}_2$$

where $M = \text{Ni, Co, Mn, etc.}$. Recovered and reconditioned cathode powders are then re-coated onto fresh current collectors with new binder and conductive carbon and assembled into new cells (Narisetty et al., 2024).

For SmCo₅ magnets, the process is more explicitly specified. Industrial sintered SmCo₅ cylindrical magnets of composition 36.30 wt% Sm, 63.22 wt% Co, and 0.37 wt% O were processed in 200 g batches in a 100 mL stainless steel jar. After evacuation, the jar was filled with high-purity hydrogen $(> 99.999\%)$ to pressures of 1, 2.5, 4, or 9.5 bar and rotated in a planetary ball mill for 3 h at 250 rpm, with repressurization every 15 minutes to compensate for hydrogen uptake (Eldosouky et al., 2019). Decrepitated powder with maximum particle size below 200 µm was removed in a glove box with $\text{O}_2 < 10$ ppm, jet-milled in nitrogen to below 20 µm, compacted by isostatic pressing, and sintered at $1170\,^\circ\text{C}$ with post-sintering heat treatment at $880\,^\circ\text{C}$.

These process descriptions illustrate a key distinction. Battery DIR attempts to preserve active particles through separation and relithiation, whereas magnet DIR preserves an alloy system through hydrogen-assisted comminution followed by conventional powder metallurgy. In both cases, the short loop is the defining feature.

3. Relation to pyrometallurgical, hydrometallurgical, and indirect routes

In EV battery recycling, the three principal routes are pyrometallurgy, hydrometallurgy, and direct recycling. Pyrometallurgy relies on high-temperature smelting or incineration of whole cells or black mass to produce a metal-rich alloy and slag. The paper notes that nickel, cobalt, and copper are largely recovered, while lithium and aluminum are largely lost in slag; it further describes this route as energy-intensive, environmentally unfavorable, and limited in circularity because active structures are destroyed (Narisetty et al., 2024).

Hydrometallurgy uses leaching with acids and other aqueous chemistries, followed by solvent extraction, precipitation, and related separation steps. Its advantages include higher recovery rates of lithium, cobalt, and nickel and more selective modern processes, potentially with lower energy intensity than pyrometallurgy. Its drawbacks are challenges related to chemical disposal and scalability, together with the loss of the original active-material value because the cathode is still broken down to elemental or ionic form (Narisetty et al., 2024).

DIR differs because it attempts to preserve active materials as active materials. The contrast is summarized below.

Route	Core operation	Product form
Pyrometallurgy	High-temperature smelting or incineration	Metal-rich alloy and slag
Hydrometallurgy	Acid leaching and aqueous separation	Elemental or ionic forms, then salts or precursors
Direct Internal Recycling	Mechanical liberation, separation, and reconditioning	Refurbished cathode or preserved alloy for reuse

In permanent magnets, the same contrast is explicit. The SmCo₅ route contains no hydrometallurgical or pyrometallurgical refining steps. Hydrogen is introduced temporarily, causes physical decrepitation, and is later released during processing. The powder is then fed directly back into conventional SmCo₅ sintering, just like virgin powder (Eldosouky et al., 2019). This makes DIR less a matter of recovering raw elements than of recovering engineering effort embodied in a functional material.

4. Materials science basis and performance retention

The materials-science rationale for battery DIR is preservation of the crystal structure and morphology of cathode powders. Direct recycling attempts to restore stoichiometry and performance at the material level rather than dissolving the transition metals into solution. The paper associates this with low-temperature solid-state relithiation, hydrothermal relithiation, and mild annealing in the underlying review literature, and states that direct recycling seeks to maintain battery performance while reducing energy consumption (Narisetty et al., 2024). This suggests that phase integrity and morphology retention are central technical assets, not incidental by-products.

In SmCo₅ recycling, the underlying mechanism is hydrogen-assisted comminution. Hydrogen is absorbed intergranularly, especially by Sm-rich phases, and interstitially in the main hard-magnetic phase. This leads to hydride formation, Co-rich residual phases, and volume expansion; prior work cited in the paper reports about 10 vol% expansion for SmCo₅H$_x$ at high hydrogen pressures. Internal stresses then generate cracks along grain boundaries and through grains, so that the bulk magnet falls apart into powder (Eldosouky et al., 2019). X-ray diffraction showed that the overall diffraction patterns of decrepitated powders were similar to the original magnet, the Sm₂Co₇ peak disappeared, and weak peaks attributable to Sm-hydrides, Sm-oxides, and Co-rich phases appeared. After pressure release, interstitial hydrogen desorbed and the hexagonal SmCo₅ structure was recovered; after sintering and heat treatment, the typical SmCo₅ + Sm₂Co₇ + Sm-rich phase/Sm-oxide microstructure was reestablished.

The recycled SmCo₅ magnet not only retained functionality but exhibited higher reported magnetic metrics than the original. The original magnet had remanence $B_r = 0.915\ \text{T}$ and maximum energy product $(BH)_{\max} = 156.92\ \text{kJ/m}^3$, whereas the recycled magnet reached $B_r = 0.945\ \text{T}$ and $M = \text{Ni, Co, Mn, etc.}$0 (Eldosouky et al., 2019). The maximum energy product is defined as

$M = \text{Ni, Co, Mn, etc.}$1

The recycled magnet also showed a slightly higher density, 8.33 g/cm$M = \text{Ni, Co, Mn, etc.}$2 versus 8.28 g/cm$M = \text{Ni, Co, Mn, etc.}$3, and a modest oxygen increase from 0.37 wt% to 0.48 wt%. The paper attributes the performance improvement to microstructural refinement, slightly higher density, and the use of isostatic pressing rather than axial pressing. In DIR terms, this is a particularly clear demonstration that preservation of the alloy system can be compatible with equal or better end-use performance.

5. Industrial implementation and circular-economy integration

The EV battery overview identifies several industrial examples that embody direct-recycling or DIR-adjacent concepts. Redwood Materials is listed as using “Direct Recycling & Hydrometallurgy,” with emphasis on scaling direct recycling and operating an integrated closed-loop model that captures batteries from automaker partners, recovers high-value materials, and feeds them back into new battery production; its stated challenge is “sourcing enough batteries” (Narisetty et al., 2024). Duesenfeld GmbH is described explicitly as “Direct Recycling (Cathode Recovery)” and is credited with “Over 90% recovery of materials” and “Reduced energy consumption,” while also facing “Limited supply of suitable batteries” and “High initial cost of scaling.” BASF & Aurora are presented as “Hydrometallurgical & Closed-Loop,” with achievement defined as a “Circular supply chain for EV batteries. Recycled materials used in new battery production,” and with challenges of “Logistical challenges; high capital investment; complex integration with existing processes.”

These industrial cases place DIR within a broader circular-economy framework. The paper explicitly emphasizes “closed-loop systems for battery production and recycling” and links recycling to reduced dependence on mining and raw-material extraction (Narisetty et al., 2024). It also stresses design-for-recycling, stating that modular battery designs allowing easier disassembly can make recycling more efficient and cost-effective, and that standardized chemistries and components would simplify recycling and make it more economically viable. DIR benefits particularly strongly from such design changes because it requires clean separation of electrodes and consistent chemistries that can share relithiation and annealing recipes.

The SmCo₅ study points to an analogous manufacturing integration pathway in permanent magnets. The work used industrially produced magnets and originated from an industrial magnet producer, Magneti Ljubljana, which strongly suggests in-plant integration for internal scrap or controlled return streams (Eldosouky et al., 2019). Potential uses include recycling in-plant rejects, machining swarf, off-spec magnets, and end-of-line scrap, as well as end-of-life magnets of known and compatible composition. In this form, DIR becomes not merely an end-of-life strategy but an internal manufacturing loop.

6. Limitations, standardization, and strategic implications

DIR is technically attractive precisely because it is technically demanding. In EV batteries, the paper identifies the need for chemistry-specific reconditioning recipes and high-purity separation of cathode from anode and other materials (Narisetty et al., 2024). It further notes that EV batteries vary in chemistry, form factor, and pack design, so each may need different DIR protocols; lack of standardization is explicitly highlighted as a major obstacle. Additional barriers include the high cost of scaling, underdeveloped infrastructure for collection and pre-processing, limited supply of suitable batteries because many EV packs remain in first or second life, and regulatory and logistical hurdles associated with hazardous-waste transport and OEM–recycler integration.

In SmCo₅ magnets, the main limitations are oxidation, contaminant carry-through, composition drift, and uncertain multi-cycle behavior. Even with glove-box transfer and nitrogen jet milling, oxygen increased from 0.37 wt% to 0.48 wt% after a single recycling loop (Eldosouky et al., 2019). The paper identifies oxygen accumulation, repeated-loop performance, feedstock variability, and uncharacterized mechanical properties as open issues. It also notes that DIR is more constrained than full chemical recycling because it requires relatively clean, known-composition feed magnets and is less suitable for mixed or heavily corroded waste streams.

Strategically, the battery paper presents DIR as a key next-generation technology that is complementary to, rather than yet a complete replacement for, hydrometallurgical and pyrometallurgical routes (Narisetty et al., 2024). It is described as lower energy and potentially lower chemical-intensity than those routes, with higher product value because the recovered output is closer to electrode-grade material, but with correspondingly higher technical specificity and current scale challenges. The paper further states that improved recycling, especially closed-loop routes, could reduce the overall cost of battery production by as much as 20%, and that by 2030 the market for recycled materials from EV batteries could be worth over $10 billion.

Across both batteries and permanent magnets, DIR can therefore be understood as the most direct form of circularity: it seeks to preserve active functionality, embedded manufacturing energy, and value-chain continuity. The available examples also show its boundary conditions. DIR is most effective when feedstocks are compositionally known, contamination is controlled, atmosphere management is robust, and downstream reconditioning or sintering routes are tightly matched to material chemistry. Under those conditions, the approach can shorten the recycling loop from raw-material recovery to functional-material recovery, which is its defining technical and economic distinction.