Production Scheduling for Battery Manufacturing (Li-ion)

This guide walks production planners and operations managers through configuring and scheduling a Li-ion battery production line in Schantt — from slurry mixing through cell testing and packaging. You will build a hybrid-flowshop model with batch mixing, continuous coating, parallel machines at every stage, and chemistry-driven changeovers.

This guide follows a fictional composite company built from industry research on lithium-ion battery manufacturing; all names, parameters, and figures are illustrative.

Industry context

A Li-ion battery production line spans electrode preparation, cell assembly, and finishing. The process starts with slurry mixing — blending active materials, binders, and solvents in large mixers to produce a uniform electrode paste. The slurry is coated onto metal foil, dried, and calendered to compress the electrode to a precise thickness. The coated foil is slit into narrower strips and notched to shape, then assembled into cells by winding (cylindrical) or stacking (pouch) the electrode layers together. Assembled cells are filled with electrolyte, subjected to a formation charge-discharge protocol, aged, and finally tested and packaged.

The production environment presents several structural complexities. It mixes batch and flow processing — mixing is a discrete batch operation, while every stage downstream runs as a continuous or semi-continuous flow. Multiple parallel machines operate at each stage, some stage-specific (winders for cylindrical cells, a stacker for pouch cells) and some interchangeable. Chemistry changeovers impose directional cleaning times that differ significantly depending on the from-to pair. A multi-hour formation-and-aging hold separates cell filling from testing, and several stages share a dry-room atmosphere whose quarterly maintenance window halts all machines inside the envelope.

Celerion runs approximately 85 people at a single 2,800 m² facility, producing two product classes — NMC-cylindrical cells (the full eight-stage route) and LCO-pouch-formation-free cells (skipping the formation stage) — across 8 ordered production stages. A 3-person planning team (a planner, a shift supervisor, and the plant manager) manages 8–12 active SKUs in typical run quantities of 10,000–50,000 cells per SKU, working to confirmed purchase orders on a 1–4 week horizon. The plant operates on a two-shift calendar, Monday through Friday, 16 production hours per day (06:00–22:00), for an 80-hour working week, with three annual calendar exceptions and a quarterly 12-hour dry-room HVAC maintenance window.

Process overview

flowchart LR
  A["Slurry mixing"]
  B["Coating & drying"]
  C[Calendering]
  D["Slitting & notching"]
  E[Cell assembly]
  F[Electrolyte filling]
  G["Formation & aging"]
  H["Cell testing & packaging"]
  A --> B --> C --> D --> E --> F --> G --> H
  F -.-> H

The Li-ion battery manufacturing process flows left to right through eight stages. A dashed route shows the formation-skip path for pre-lithiated (formation-free) cell variants.

Note on skip routing. For product classes that skip the formation and aging stage — such as the pre-lithiated LCO-pouch-formation-free variant — the schedule bridges directly from electrolyte filling to cell testing and packaging with a short handling-only transfer time, bypassing the multi-hour formation dwell.

Scheduling challenges and how Schantt handles them

In a typical Li-ion battery plant, the schedule is driven by confirmed purchase orders across a 1–4 week horizon. If your plant is driven by forecasts or a build-to-stock model, the scheduling setup remains the same — only the input source changes. Schantt optimizes to minimise total production time — the overall completion time across all scheduled jobs — scheduling forward from a chosen start date. For plant runs that span a full week, the practical horizon of this guide is one week of production, which is enough to capture the chemistry changeovers, formation dwells, and maintenance windows that characterise Li-ion lines. In Auto mode, Schantt decides the job sequence, machine assignments, and exact timing. In Semi-Auto mode, you set the production order and the system optimises machine assignments within that fixed sequence.

What Schantt handles well

• Sequential multi-stage production. Schantt models the ordered electrode-to-packaging line as a stage sequence with transfer times. Each product's route chains through its required stages in order.

• Multi-machine stages with automatic assignment. Each stage has multiple parallel machines (mixers, coaters, winders, fill stations). In Auto and Semi-Auto modes, Schantt selects which machine handles each job.

• Mixed batch-and-flow pipelines. Slurry mixing (batch) feeds continuous coating (flow), then further stages — all in one routing. The simulation handles supply starvation with material-wait pauses and supports partial transfers where realistic.

• Sequence-dependent changeovers. Chemistry-clean durations (mixing vessels, coating dies, fill-head plumbing) are modelled as directional, per-machine changeover times. The optimizer favours sequences that reduce total changeover time.

• Calendar-aware availability and downtimes. Working shifts, planned maintenance windows, dry-room regeneration outages, and holidays are modelled via calendars and machine downtimes. Timing routes work around non-working periods and planned outages.

• Per-class routing with stage skipping. A product class that skips formation uses a routing that omits that stage, with a bridging transfer time across the skip.

How Schantt handles each challenge

1. Chemistry-driven changeovers.

• The plant runs NMC and LCO-pouch product classes on shared equipment. A chemistry switch on a mixer can take up to 4 hours of cleaning (240 minutes from NMC to LCO), while the reverse takes 2.5 hours (150 minutes). Coating dies take 90–150 minutes per switch, and fill-station plumbing takes 60–90 minutes. With 3–4 chemistry switches per week, the plant loses 18–28 hours of productive capacity to changeovers.

• Schantt models changeovers as directional, per-machine durations — you enter each from-to pair on the machine detail page (for example, 240 minutes on Mixer-C for NMC-cylindrical to LCO-pouch-formation-free, and 150 minutes for the reverse). Because changeover time is folded into each operation's start and therefore into total production time, the optimizer naturally favours sequences that group same-chemistry jobs together, reducing the overall time spent on changeovers. In Auto mode the system reorders jobs to find a lower-changeover sequence; in Semi-Auto mode it holds your fixed order while still managing changeover time through machine assignment choices. You enter the durations based on your own chemistry policies — Schantt uses the directional times you provide without deriving or validating the reason behind the asymmetry.

2. Batch-to-flow interface starvation.

• Slurry mixing operates in batch mode — each mixer produces a 200 kg batch over 170–225 minutes — while the coating line runs continuously at 3,000–3,600 cells per hour. This handoff creates recurring starvation: when a coating line finishes its current buffer before the next batch is ready, production pauses. Plant records show 2–4 such starvation events per week.

• Schantt handles this through its mixed batch-and-flow pipeline model. Each stage is typed batch (slurry mixing) or flow (all downstream stages), and the simulation feeds each downstream stage from its upstream stage's completions using the transfer time of 15 minutes between mixing and coating. When the coating line runs out of material before the next batch lands, the schedule inserts a material-wait pause — visible on the Gantt as a labelled segment with the reason on hover — so you can see the exact timing and impact of each starvation event. The handoffs are timed realistically through chain timing and the transfer time settings, and you verify on the Gantt that downstream start times fall inside the viable electrode-moisture exposure window.

3. Job-to-machine assignment complexity.

• With 18 machines across 8 stages — some with a single machine (calendering), others with three parallel units (mixing, slitting) or four (cell assembly) — the planner faces 40–60 individual job-to-machine assignment decisions each week. Every decision ripples through downstream capacity and changeover timing.

• In Auto and Semi-Auto modes, Schantt handles machine assignment automatically. Each machine belongs to exactly one stage, and the system explores which machine handles each job at each stage, restricted to machines capable of that product class. Auto mode explores both job sequence and machine assignments together; Semi-Auto mode keeps your fixed order and optimises assignments within it. The Gantt shows the resulting machine on each operation's row, and you can group the view by machine to see each stage's capacity lanes. Where a product class uses multiple machines in a stage — for example, three slitters for NMC and three for LCO — partial transfers can be enabled at critical handoffs: at the slitting-to-assembly interface, set to a quantity of one electrode roll, so cell assembly begins on the first usable portion while slitting continues.

4. Formation gap extending across weekends and holidays.

• The formation and aging stage imposes a timed hold of approximately 24 hours on every cell — a combination of electrolyte wetting, formation charge-discharge cycles, and short-term aging. Because this hold elapses in wall-clock time, a batch that finishes filling on Friday evening does not exit formation until late Saturday or early Sunday — non-working hours — pushing the start of testing to Monday morning. The effective gap extends to about 60 hours for a Friday-evening batch.

• Schantt models the formation dwell as a timed transfer from electrolyte filling to cell testing and packaging — a forward-only delay of 1,440 minutes (24 hours) that elapses continuously rather than being advanced through the working calendar. For product classes that skip formation, a bridging transfer of 30 minutes bypasses the dwell entirely. The schedule chains each subsequent stage to start only after the dwell completes, and non-working weekend time renders as shaded overlays on the Gantt so you can see exactly why some operations span several calendar days. You verify manually that concurrent cell batches do not exceed the available formation rack positions, since Schantt schedules the delay but does not track rack occupancy. Facilities running a multi-day aging protocol split the schedule into two groups — pre-formation and post-formation — to keep the scheduling horizon manageable.

5. Shared dry-room dependency.

• Twelve machines across five stages — coating and drying, calendering, slitting and notching, cell assembly, and electrolyte filling — operate inside a dry-room enclosure. When the quarterly 12-hour dry-room HVAC maintenance window arrives for desiccant regeneration and filter replacement, every machine in the envelope must stop. Entering this as a single factory-wide shutdown on the calendar would halt the entire plant including stages outside the dry-room.

• In Schantt, you enter the 12-hour maintenance window as an individual downtime entry on each machine within the dry-room envelope: Coater-1, Coater-2, Calender-1, Slitter-1, Slitter-2, Slitter-3, Winder-1, Winder-2, Winder-3, Stacker-1, Fill-1, and Fill-2. The algorithm routes work around each machine's unavailable period individually while leaving unaffected upstream stages (slurry mixing) and downstream stages (cell testing and packaging) free to continue. The downtimes render as shaded bands on the Gantt with the maintenance reason visible on hover. You apply the same window to each machine rather than entering a single propagating event.

What to model in Schantt

The Celerion plant is configured from five first-class entities, which you create as top-level objects:

Additional sub-configuration — per-class routings, transfer times, changeovers, calendar exceptions, and machine downtimes — is set on the detail pages of these entities.

Step-by-step setup

1. Create the stages in order. Add eight stages from slurry mixing (position 1) through cell testing and packaging (position 8). Set slurry mixing as batch type and all others as flow. On each stage's detail page, enter the transfer times between consecutive stages:

• Slurry mixing → Coating and drying: 15 minutes
• Coating and drying → Calendering: 10 minutes
• Calendering → Slitting and notching: 10 minutes
• Slitting and notching → Cell assembly: 15 minutes
• Cell assembly → Electrolyte filling: 10 minutes
• Electrolyte filling → Formation and aging: 1,440 minutes (24-hour formation dwell)
• Formation and aging → Cell testing and packaging: 30 minutes

For the formation-skip route, also add a bridging transfer directly from electrolyte filling to cell testing and packaging: 30 minutes.

2. Add the machines to each stage. Create the 18 machines distributed across the eight stages:

• Slurry mixing: Mixer-C, Mixer-A, Mixer-S (3 batch mixers)
• Coating and drying: Coater-1, Coater-2 (2 flow coaters)
• Calendering: Calender-1 (1 flow calender)
• Slitting and notching: Slitter-1, Slitter-2, Slitter-3 (3 flow slitters)
• Cell assembly: Winder-1, Winder-2, Winder-3 (cylindrical winding), Stacker-1 (pouch stacking)
• Electrolyte filling: Fill-1, Fill-2 (2 flow fill stations)
• Cell testing and packaging: Tester-1, Tester-2, Pack-1 (testing and final packing)

3. Create the product classes and define per-class routing. Add two classes:

• NMC-cylindrical — route through all 8 stages in order
• LCO-pouch-formation-free — route through stages 1–6 and 8, skipping formation and aging

On each product class's detail page, enable partial transfer at the slitting and notching stage with a quantity of 1 (one electrode roll). This allows cell assembly to begin on the first usable electrode portion while slitting continues, reducing the material exposure window.

4. Add one product per class. Create two representative SKUs:

• NMC-18650-2.5Ah (grey) — belonging to the NMC-cylindrical class
• LCO-pouch-1.8Ah (teal) — belonging to the LCO-pouch-formation-free class

5. Set each machine's capacity parameters and changeovers. With product classes created, configure each machine's per-class parameters on its detail page:

• Batch mixers — cycle duration and batch size:
• Mixer-C: 210 min / 200 kg (NMC), 195 min / 200 kg (LCO)
• Mixer-A: 180 min / 200 kg (NMC), 170 min / 200 kg (LCO)

• Mixer-S: 225 min / 200 kg (NMC), 210 min / 200 kg (LCO)

• Flow machines — throughput per hour:

• Coater-1: 3,200 (NMC), 3,600 (LCO); Coater-2: 3,000 (NMC), 3,400 (LCO)
• Calender-1: 3,500 (NMC), 3,800 (LCO)
• Slitter-1: 3,400 (NMC), 3,700 (LCO); Slitter-2: 3,200 (NMC), 3,500 (LCO); Slitter-3: 3,600 (NMC), 3,800 (LCO)
• Winder-1/2/3: 2,400 (NMC only); Stacker-1: 960 (LCO only)
• Fill-1: 1,200 (NMC); Fill-2: 960 (LCO)

• Tester-1/2: 800 (both classes); Pack-1: 1,600 (both classes)

• Changeover times (directional, per machine):

• Mixer-C and Mixer-S: NMC→LCO 240 min, LCO→NMC 150 min
• Coater-1 and Coater-2: NMC→LCO 150 min, LCO→NMC 90 min
• Slitter-1/2/3: 15 min both directions
• Calender-1: 0 min (no changeover time between these classes)
• Fill-1 and Fill-2: NMC→LCO 90 min, LCO→NMC 60 min

6. Configure calendars, exceptions, and downtimes (optional). The default calendar is already set to Monday–Friday, 06:00–22:00, 80 hours per week. Add three calendar exceptions: New Year's Day (Jan 1, non-working), International Workers' Day (May 1, non-working), and year-end shutdown (Dec 31, non-working). Add the quarterly dry-room HVAC maintenance as a 12-hour downtime (06:00–18:00) on each dry-room machine — Coater-1, Coater-2, Calender-1, Slitter-1 through Slitter-3, Winder-1 through Winder-3, Stacker-1, Fill-1, and Fill-2 — plus a year-end transition shutdown window.

For step-by-step instructions on configuring each of these in Schantt, see the Schantt documentation.

Common mistakes

1. Using a single blanket changeover instead of directional per-pair times. The NMC-to-LCO changeover on a mixer is 240 minutes, while the reverse is 150 minutes. Entering one averaged value misrepresents the true sequence-dependent penalty, causing the optimizer to undervalue or overvalue specific product transitions. Fix: Enter both directional durations for each machine pair — the from-to and to-from values shown in the changeover table above.

2. Modelling the formation dwell as a stage with machines. Formation and aging is a timed hold where cells sit in racks for approximately 24 hours with no machine activity. Creating a formation machine assigns capacity and availability logic that does not physically exist. Fix: Model the dwell as a transfer time (1,440 minutes) between electrolyte filling and cell testing and packaging. Verify formation rack occupancy manually on the Gantt when several batches are in formation concurrently.

3. Assigning all cell assembly work to winders, ignoring the dedicated stacker. Cylindrical cells use winding (Winder-1, Winder-2, Winder-3 at 2,400 cells per hour), while pouch cells require stacking (Stacker-1 at 960 cells per hour). Routing pouch cells to a winder produces an incorrect assembly operation that does not match the physical process. Fix: Configure each product class to route only to the machines intended for its assembly method — winders handle only the NMC-cylindrical class; Stacker-1 handles the LCO-pouch-formation-free class.

4. Omitting the bridging transfer for the formation-skip route. Without a direct transfer from electrolyte filling to cell testing and packaging, the LCO-pouch-formation-free class has no valid path — the schedule has no route from the last pre-skip stage to the first post-skip stage. Fix: Add a bridging transfer time (30 minutes, handling only) between electrolyte filling and cell testing and packaging.

5. Entering the dry-room maintenance as a single factory-wide downtime instead of per-machine. A factory-wide downtime halts all stages including slurry mixing and cell testing and packaging, which sit outside the dry-room envelope and could continue working. Fix: Apply the 12-hour quarterly maintenance window individually to each machine in the dry-room stages (coaters, calender, slitters, winders and stacker, fill stations). Slurry mixing and cell testing and packaging remain available through the window.

What a good schedule looks like

A well-configured Li-ion battery schedule in Schantt shows each chemistry class running in compact blocks, machine loads balanced across parallel resources, and the formation dwell cleanly separating filling from testing without creating phantom capacity constraints.

Before (weekly planner in a spreadsheet):
- 18–28 hours of productive capacity consumed by chemistry changeovers each week, with switches dispersed across the schedule rather than grouped
- 2–4 starvation events at the batch-to-flow interface, each requiring manual rescheduling of the coating line mid-week
- 40–60 manual job-to-machine decisions by the planner, often yielding suboptimal assignments by late in the week
- A Friday-evening formation batch silently delaying testing start until Monday, hidden in the spreadsheet's row logic

After (Schantt Auto mode):
- Changeover time visibly reduced — the optimizer naturally sequences NMC and LCO batches into contiguous runs, eliminating unnecessary back-and-forth chemistry switching
- Batch-to-flow starvation predictable — material-wait segments on the Gantt show exactly where and when the coating line pauses, enabling you to adjust mixer-to-coater timing in the next schedule cycle
- Machine assignment handled automatically across all 18 parallel resources — the planner reviews assignments rather than building them from scratch each week
- Formation dwell rendered as a clean 24-hour timed gap between filling and testing, with weekend non-working time shown as shaded overlays — you can see at a glance why Monday-morning testing starts later for Friday-evening batches