Zinc-air and metal-air batteries use a metal anode and an air-breathing cathode, theoretically delivering very high energy density and low materials cost. In practice, most metal-air systems remain at the pilot or early commercial stage, with unresolved issues around reversibility, electrode degradation, and system-level efficiency.
- Theoretical energy density for zinc-air is far higher than lithium-ion, but practical stationary systems focus more on cost per kWh and cycle life than volumetric density.
- Reversible zinc-air systems targeting daily cycling typically reach 50–60% round-trip efficiency at the stack level; system-level AC–AC efficiency can be lower.
- Emerging metal-air vendors aim for CAPEX in the 50–120 USD/kWh range at scale, but current deployments are likely higher and bankability is still developing.
- Best-fit applications are 10–40 hour storage where low $/kWh and high cycle counts matter more than top-tier efficiency.
1. Technology benchmarks: zinc-air vs. lithium-ion and flow
Metal-air batteries encompass several chemistries (zinc, aluminum, lithium, iron), but zinc-air is the most advanced for stationary storage. The table below compares representative zinc-air systems with lithium-ion and vanadium flow batteries for long-duration use cases.
| Parameter | Zinc-air (rechargeable) | Li-ion LFP (grid) | Vanadium flow |
|---|---|---|---|
| Target duration | 10–40 hours | 2–8 hours | 8–20 hours |
| Round-trip efficiency (AC–AC) | 45–60% | 85–92% | 65–80% |
| Cycle life (equiv. full cycles) | 3,000–8,000 (targets) | 3,000–7,000 | >10,000 |
| Energy density (Wh/L, system) | 40–120 | 80–200 | 20–50 |
| Materials risk | Moderate (zinc supply, catalysts) | Moderate–high (metals, Li) | Moderate (vanadium) |
For stationary LDES, zinc-air’s volumetric energy density is less critical than its potential for low $/kWh and use of abundant materials. However, efficiency and cycle life must meet minimum thresholds for projects to be bankable.
2. Economics: CAPEX, LCOS, and where metal-air could land
Many public claims about zinc-air economics are based on pilot-scale data and optimistic scale-up assumptions. A more cautious view is to consider ranges for initial and mature deployments.
| Metric | Early zinc-air projects | Mature zinc-air (target) | Li-ion (LFP, 8h) |
|---|---|---|---|
| CAPEX (USD/kWh) | 200–350 | 70–150 | 150–250 |
| CAPEX (USD/kW) | 700–1,200 | 400–800 | 500–900 |
| LCOS, 10–20h (USD/MWh discharged) | 180–280 | 110–190 | 130–190 |
These indicative numbers suggest that, if technology targets are met, zinc-air could become competitive for ultra-long durations where Li-ion becomes expensive and flow batteries face scale or complexity limits. However, today’s bankable projects are still rare.
Use Energy Solutions tools to stress-test metal-air business cases
Because metal-air technology metrics are still evolving, LCOS results are highly sensitive to assumptions on efficiency, lifetime, and CAPEX. Our tools help teams run structured sensitivities rather than relying on single-point vendor claims.
3. Use cases: where metal-air could be attractive
If technical hurdles are addressed, zinc-air and other metal-air systems could serve specific niches:
- Ultra-long duration behind-the-meter for critical loads that need multi-day autonomy but have space for lower-power, high-energy systems.
- Remote and island grids where fuel logistics are costly and storage of large energy volumes is needed.
- Grid-connected LDES where low-cost $/kWh for 10–40 hours is more important than high round-trip efficiency.
Developer note: treat metal-air as an option alongside flow batteries, thermal storage, and hydrogen—not an automatic replacement for Li-ion for 4–8 hour services.
4. Constraints and technical challenges
The main barriers to bankable metal-air deployments include:
- Air cathode durability: catalysts and supports degrade due to CO2, contaminants, and cycling, limiting lifetime.
- Dendrite formation and shape change on metal anodes, leading to losses in capacity and safety concerns.
- Carbonation of electrolytes when exposed to air, impacting conductivity and performance.
- System complexity: managing air handling, humidity, and contaminants adds BOS costs.
Bankability warning: until multi-year field data is available at commercial scale, investors will treat metal-air cautiously. Projects may need strong balancesheet support or pilot/demonstration frameworks.
5. Global perspective: where metal-air R&D is focusing
R&D activity for zinc-air and metal-air batteries is concentrated in a few key regions:
- North America and Europe: start-ups and research labs focusing on reversible zinc-air and long-lifetime air electrodes.
- Asia: interest in metal-air for mobility and backup, with some spill-over into stationary.
- Public funding programs targeting ultra-long duration storage (100h+) where metal-air competes with hydrogen, flow systems, and thermal concepts.
6. Outlook to 2035: realistic role for metal-air in LDES
By 2035, metal-air could occupy a modest but important niche in LDES portfolios if key hurdles are overcome. Several scenarios are plausible:
- Optimistic scenario: a few vendors achieve robust, 10,000-cycle zinc-air systems at <100 USD/kWh, leading to multi-GWh deployments in remote grids and long-duration services.
- Base case: metal-air achieves modest scale in specific segments, while flow batteries, pumped hydro, and hydrogen dominate most LDES capacity.
- Downside: durability or economics fail to meet expectations, confining metal-air to small pilots and niche applications.
7. Implementation guide: how to approach metal-air projects today
Given current maturity, metal-air projects should be treated as structured pilots rather than mainstream assets:
7.1 Screening questions
- Is there a clear value gap that existing technologies cannot fill (e.g., 30-hour autonomy in a remote site)?
- Can the project be structured as a demonstration with risk-sharing from vendors and public funding?
- Is there a plan to monitor and publish performance data to build confidence and learning?
7.2 Commercial structuring
Early projects may use availability-based contracts, vendor performance guarantees, or joint ventures to align incentives. Traditional project finance will be challenging until references accumulate.
8. FAQ: common questions on zinc-air and metal-air LDES
Are metal-air batteries really rechargeable?
Some metal-air systems are designed as primary (non-rechargeable) batteries, while others aim for full rechargeability. Reversible zinc-air remains technically challenging; several vendors report progress, but long-term cycle data at commercial scale is still limited.
Why is the round-trip efficiency so much lower than lithium-ion?
Losses occur at both the air cathode and metal anode, and overpotentials are typically higher than in lithium-ion systems. Auxiliary loads for air handling and conditioning add further losses. As a result, practical AC–AC efficiency often sits in the 45–60% range for early systems.
Could metal-air ever replace lithium-ion in mainstream grid batteries?
It is unlikely that metal-air will displace lithium-ion for 1–4 hour services in the near term. Instead, metal-air may complement existing technologies by serving longer-duration niches where low $/kWh is more important than peak efficiency or power density.
What level of technology readiness should we assume today?
Most zinc-air and metal-air systems for stationary LDES are at TRL 5–7: advanced pilots and early demonstrations, but few fully bankable commercial references. Developers should calibrate expectations accordingly and build redundancy into critical applications.
How should we include metal-air in resource planning studies?
Planners can treat metal-air as a candidate option in long-term scenarios, with conservative cost and performance assumptions and explicit flags for technology risk. Comparative LCOS and system value analysis against pumped hydro, flow batteries, hydrogen, and thermal storage remains essential.