Battery Passport — Carbon Footprint as Competitive Advantage
Can a sodium-ion startup prove its carbon advantage with numbers that trace to their source — and hold up when emission factors change?
The scenario
Polar Cells AB manufactures sodium-ion battery cells in Skelleftea for stationary energy storage — grid-scale batteries, industrial UPS systems, telecom backup. Their chemistry uses iron, manganese, and sodium. No cobalt. No lithium. No nickel. This is not a compromise — it is a strategic choice. Sodium-ion cells are cheaper, safer, use abundant materials, and have a significantly lower carbon footprint than lithium-ion. For stationary storage where energy density matters less than cost and cycle life, the chemistry is ideal.
Under the Battery Regulation, carbon footprint declarations have been required since February 2025. Digital passports become mandatory in February 2027 for industrial batteries above 2 kWh. Polar Cells’ standard product — a 48V 280Ah sodium-ion module (13.4 kWh) — is well above the threshold.
Here is the thing: Polar Cells’ carbon footprint is their competitive advantage. Their cradle-to-gate calculation shows roughly 1.3 kgCO₂e/kWh for Na-ion modules, versus approximately 4 kgCO₂e/kWh for a comparable lithium-ion NMC module calculated using the same methodology. That roughly 68% advantage is traceable to specific material choices, specific suppliers, and Sweden’s low-carbon electricity grid. But only if the numbers are provable.
The pipeline
RAW MATERIAL SOURCING
─────────────────────────────────────────────────────
Iron (cathode) Manganese (cathode) Sodium carbonate
LKAB, Kiruna, Sweden South African mine, Domsjo Fabriker,
Hotazel, Northern Cape Ornskoldsvik, Sweden
│ │
│ │
┌──────────────────────┼──────────────────────────┼─────────┐
│ │ │ │
▼ ▼ ▼ │
┌─── material sourcing evidence ───────────────────────────┐ │
│ │ │
│ Iron: LKAB Kiruna │ │
│ emission factor: 1.06 tCO₂/t iron (LKAB EPD 2025) │ │
│ transport: 950 km rail Kiruna→Skelleftea │ │
│ sha256:4a22... │ │
│ │ │
│ Manganese: South Africa │ │
│ emission factor: 1.83 tCO₂/t Mn ore (actual, v2025) │ │
│ transport: 14,200 km sea + 320 km rail │ │
│ due diligence: OECD Annex II compliant │ │
│ sha256:b7c1... │ │
│ │ │
│ Sodium carbonate: Domsjo │ │
│ emission factor: 0.41 tCO₂/t Na₂CO₃ (biorefinery) │ │
│ transport: 380 km road Ornskoldsvik→Skelleftea │ │
│ sha256:e3d9... │ │
└────────────────────┬─────────────────────────────────────┘
│
▼
┌─── emission factor registry ─────────────────────────────┐
│ │
│ Versioned reference data │
│ │
│ emission-factors-v2025: │
│ Swedish grid mix: 7.1 gCO₂/kWh (Energimynd. 2025)│
│ LKAB iron (EPD): 1.06 tCO₂/t │
│ SA manganese (actual): 1.83 tCO₂/t │
│ Domsjo Na₂CO₃ (EPD): 0.41 tCO₂/t │
│ Road transport SE: 0.062 kgCO₂/tkm │
│ Rail transport SE: 0.005 kgCO₂/tkm │
│ Sea transport: 0.008 kgCO₂/tkm │
│ sha256:91f7... │
│ │
│ When factors update → this version is superseded → │
│ all downstream calculations automatically refresh │
└────────────────────┬─────────────────────────────────────┘
│
▼
┌─── carbon footprint calculation ─────────────────────────┐
│ │
│ Per 48V 280Ah module (13.4 kWh): │
│ │
│ 1. Raw material acquisition 12.8 kgCO₂e │
│ ├── Iron (cathode active): 4.2 kgCO₂e │
│ ├── Manganese (cathode active): 3.9 kgCO₂e │
│ ├── Sodium carbonate (cathode): 1.1 kgCO₂e │
│ ├── Aluminium (current collector): 2.4 kgCO₂e │
│ └── Other (electrolyte, separator): 1.2 kgCO₂e │
│ │
│ 2. Raw material transport 2.6 kgCO₂e │
│ ├── Iron (950 km rail): 0.1 kgCO₂e │
│ ├── Manganese (14,200 km sea + 1.9 kgCO₂e │
│ │ 320 km rail): │
│ ├── Sodium carbonate (380 km road): 0.4 kgCO₂e │
│ └── Other materials: 0.2 kgCO₂e │
│ │
│ 3. Cell manufacturing 1.4 kgCO₂e │
│ ├── Electrode preparation: 0.5 kgCO₂e │
│ ├── Cell assembly (dry room): 0.4 kgCO₂e │
│ ├── Formation cycling: 0.3 kgCO₂e │
│ └── Quality testing: 0.2 kgCO₂e │
│ (all powered by Swedish grid: 7.1 gCO₂/kWh) │
│ │
│ 4. Module assembly 0.6 kgCO₂e │
│ ├── BMS electronics: 0.3 kgCO₂e │
│ └── Housing, wiring, assembly: 0.3 kgCO₂e │
│ │
│ ────────────────────────────────────────────────── │
│ Total: 17.4 kgCO₂e per module │
│ Per kWh: 17.4 / 13.4 = 1.30 kgCO₂e/kWh │
│ │
│ For comparison (same calculation, NMC811 Li-ion): │
│ Raw materials: 41.2 kgCO₂e (cobalt, lithium) │
│ Transport: 3.1 kgCO₂e │
│ Cell mfg: 8.7 kgCO₂e (higher energy) │
│ Module assembly: 0.8 kgCO₂e │
│ Total: 53.8 kgCO₂e → 4.01 kgCO₂e/kWh │
│ │
│ Polar Cells advantage: ~68% lower carbon footprint │
│ │
│ sha256:c54b... │
└────────────────────┬─────────────────────────────────────┘
│
▼
┌─── manganese due diligence ──────────────────────────────┐
│ │
│ Battery Regulation Art. 52: supply chain due diligence │
│ for cobalt, lithium, nickel, natural graphite, AND │
│ manganese (added in Annex X). │
│ │
│ Polar Cells uses no cobalt, lithium, or nickel. │
│ But manganese requires OECD Annex II due diligence. │
│ │
│ Supplier: Hotazel Manganese Mines │
│ Country: South Africa (not conflict-affected) │
│ OECD Step 1-5 assessment: COMPLIANT │
│ Third-party audit: Bureau Veritas, 2025-09-12 │
│ Certification: sha256:7d83... │
│ │
│ Decision: "Manganese sourced from South Africa, │
│ OECD-compliant, audited. No conflict mineral risk. │
│ Na-ion chemistry eliminates cobalt/lithium/nickel │
│ due diligence requirements entirely." │
│ (decision recorded) │
└────────────────────┬─────────────────────────────────────┘
│
▼
┌─── quality and performance data ─────────────────────────┐
│ │
│ Nominal capacity: 280 Ah │
│ Nominal voltage: 48V (16S configuration) │
│ Energy: 13.4 kWh │
│ Cycle life: >4,000 cycles at 80% DoD │
│ Round-trip efficiency: 92% │
│ Operating temp: -20°C to +60°C │
│ Expected lifetime: 15 years │
│ Recyclability: 87% (iron and manganese recoverable) │
│ sha256:a2e6... │
└────────────────────┬─────────────────────────────────────┘
│
▼
┌─── compose passport ─────────────────────────────────────┐
│ │
│ Passport ID: PC-NAI-48V280-2026-00142 │
│ Manufacturer: Polar Cells AB, Skelleftea, Sweden │
│ Chemistry: Sodium-ion (Prussian White cathode) │
│ Carbon footprint: 1.30 kgCO₂e/kWh │
│ breakdown: materials 12.8 + transport 2.6 + │
│ manufacturing 1.4 + assembly 0.6 │
│ Mineral due diligence: Mn (compliant), no Co/Li/Ni │
│ Recyclability: 87% │
│ Performance class: A (per forthcoming classification) │
│ │
│ passport-PC-NAI-48V280-2026-00142.json: sha256:e1f3... │
│ seal.json: sha256:39b2... │
└────────────────────┬─────────────────────────────────────┘
│
▼
┌─── register with EU battery passport system ─────────────┐
│ │
│ Upload passport to EU registry │
│ Generate QR code link │
│ Battery Passport ID: EU-BP-2026-SE-004781 │
└──────────────────────────────────────────────────────────┘
│
▼
Battery Passport
sha256:e1f3...
┌──────────────────────┐
│ [QR] <- passport URL │
│ Polar Cells AB │
│ Na-ion 48V 280Ah │
│ 1.30 kgCO₂e/kWh │
│ Seal: 39b2... │
└──────────────────────┘What happens when emission factors update: In March 2026, Energimyndigheten publishes updated Swedish grid emission factors: 6.8 gCO₂/kWh (down from 7.1). The emission factor registry is updated. All downstream calculations that depend on it automatically refresh: material sourcing data is unchanged, but the manufacturing stage recalculates using the new grid factor. Cell manufacturing drops from 1.4 to 1.34 kgCO₂e. The passport regenerates. Every passport issued before the update still references the old factor version — verifiably. Every passport issued after references the new one. No ambiguity about which factors were in effect for which product.
The sodium-ion advantage, proven: Any competitor can claim lower emissions. Polar Cells can prove it: the 1.30 kgCO₂e/kWh figure traces through every lifecycle stage to specific suppliers, specific emission factors, and a specific electricity grid. A potential customer can verify the calculation. A regulator can audit it. The 68% advantage over lithium-ion NMC is not a marketing number — it is a sealed, reproducible computation.
What you can ask afterward
| Question | How it’s answered |
|---|---|
| ”Where does the 1.30 kgCO₂e/kWh figure come from?” | Trace the carbon footprint calculation (sha256:c54b…): 12.8 (materials, from supplier EPDs and actuals) + 2.6 (transport, from distances × modal factors) + 1.4 (manufacturing, from facility energy × grid factor) + 0.6 (assembly). Each term traces to a versioned emission factor and a measured quantity. |
| ”Which emission factor version was used for this passport?” | The passport references emission-factors-v2025 (sha256:91f7…). The registry contains every factor with its source and publication date. Passports issued after the March 2026 update reference emission-factors-v2026 (sha256:44c2…). |
| ”Does Polar Cells meet the manganese due diligence requirement?” | Decision record: manganese sourced from Hotazel Manganese Mines, South Africa. OECD Annex II Steps 1-5 assessment: compliant. Third-party audit by Bureau Veritas (certification sha256:7d83…). Na-ion chemistry eliminates cobalt, lithium, and nickel from the due diligence scope entirely. |
| ”How does this compare to a lithium-ion alternative?” | The same calculation run with NMC811 inputs produces 4.01 kgCO₂e/kWh. Both calculations use the same emission factor registry and methodology. The difference is in the inputs — materials, energy intensity, supply chain distances — not in the method. An evaluator can verify both share the same structure. |
| ”What if the manganese supplier changes?” | New supplier → new sourcing evidence → carbon footprint recalculates → passport regenerates. Due diligence assessment re-runs for the new supplier. Old passports remain valid for products already manufactured (they reference the original supplier’s sealed data). |
Before and after
Today: Polar Cells calculates their carbon footprint in a spreadsheet. They collect supplier EPDs by email, look up grid emission factors on Energimyndigheten’s website, and enter numbers into a calculation template. When a customer asks how their footprint compares to lithium-ion, they send a PDF. When an auditor asks where the 1.06 tCO₂/t iron figure comes from, they search for the LKAB EPD email. When emission factors update, someone remembers to update the spreadsheet — or doesn’t. The 68% advantage over lithium-ion is a claim. A credible one, but a claim.
With provenance: The carbon footprint is a reproducible computation. Every number traces to a versioned source. When factors update, affected passports are automatically identified and recalculated. The comparison with lithium-ion uses the same methodology and the same emission factor versions — the difference is in the chemistry, provably. The 68% advantage is not a claim. It is a sealed, tamper-evident record.
Looking for battery manufacturers, especially alternative chemistries (Na-ion, LFP), preparing for the February 2027 digital passport deadline. [Contact ->]