CO2 Battery

Concept and Terminology

• Not a chemical battery; it’s mechanical/thermal storage via compressing and liquefying CO₂, then expanding it through a turbine to generate power.
• Several comments note this is essentially a flavored form of compressed-gas / CAES-style storage with a phase change.

Performance vs Lithium-Ion

• Stated round‑trip efficiency ~75% vs ~85–90% for modern Li-ion grid batteries; some think 75% is optimistic, others note similar concepts model at ~65%.
• Expected drawbacks vs Li-ion:
  • Lower volumetric energy density (especially once the low‑pressure dome volume is included).
  • Larger physical footprint (≈5 ha for 200 MWh mentioned).
  • Significant mechanical complexity: compressors, turbines, heat exchangers, moving parts, and phase-change management.
  • Slower, more bespoke deployment vs commodity Li-ion packs and standard inverters.
• Claimed advantages:
  • Potentially lower $/kWh at large scale and long life.
  • Avoids lithium/cobalt supply chains; uses mostly standard industrial components.

Thermodynamics and Working Fluid

• Key to claimed efficiency is storing and reusing compression heat in a separate thermal store (TES: gravel/ceramic-like solids), then feeding that heat back during expansion.
• CO₂ chosen for:
  • Liquefaction at “moderate” pressures, allowing compact high‑energy reservoir plus low‑pressure dome.
  • Non-flammability, non-corrosiveness, industrial familiarity.
• Some discussion of temperature limits (critical point ~31°C): may need cooling or burial in hot climates.

Economics, Scale, and Use Cases

• Website criticized as data-poor: little on $/kWh, $/kW, real project costs, or degradation.
• Power vs energy scaling: more tanks add capacity cheaply; more/bigger compressors and turbines needed to add power.
• Seen as potentially suited to 8–10 hour solar shifting, not true multi‑month “long-duration” storage; economics become challenging if cycled infrequently.
• Compared with rapidly falling Li-ion prices, some see this as a risky niche bet; others note compressed-gas storage could scale without EV-driven supply volatility.

Environmental and Resource Considerations

• Attraction: no dependence on lithium, cobalt, nickel, manganese; uses abundant materials.
• Some argue Li-ion externalities may be overstated vs fossil fuels; others worry about imperfect recycling and mining impacts.
• CO₂ source likely from industrial capture, not air; concern that at end of life it may simply be vented unless sequestered.

Safety and Engineering Risks

• Concerns about:
  • Large quantities of CO₂ in domes; risk of suffocation if a major release occurs (analogy to limnic eruptions).
  • Structural fatigue from pressure and temperature cycling.
  • Inevitable leakage over time despite “no leaks” marketing.
• Counterpoint: compared to many industrial plants, hazards are familiar and manageable with siting and setbacks.

Comparison to Other Storage (CAES, Pumped Hydro)

• Similar in principle to CAES but uses CO₂ to avoid cryogenic temperatures and to reduce required storage pressure.
• Efficiency compared to pumped hydro seen as roughly comparable; advantage is not needing special geography or elevation changes.

Overall Sentiment

• Mixed but engaged:
  • Enthusiasm for diversification of storage tech and reduced reliance on lithium.
  • Significant skepticism about marketing claims, real-world costs, land/volume requirements, and whether it can beat or even match mature Li-ion systems outside specific niches.