Carbon Footprint is a 2-axis Problem

The total lifetime emissions of a battery is dependent on the emissions generated in making it and how long it lasts, hence “Carbon Footprint is a 2-axis Problem”. Hence if we select a chemistry that has higher initial emissions but lasts much longer we could overall have a lower impact on the planet.

Carbon Footprint vs Cell Chemistry

The carbon footprint of manufacturing a battery cell varies significantly, with estimates ranging broadly from 10 to 394 kg CO2-equivalent per kilowatt-hour (kg CO2-eq/kWh). These emissions are heavily influenced by the region of production and the carbon intensity of its local electricity grid; for example, current average footprints are around 69 kg CO2-eq/kWh in the European Union and 87 kg CO2-eq/kWh in China.

We can calculate the carbon intensity over the cycle life for a given Greenhouse Gas (GHG) Intensity. This GHG Intensity is the emissions from the manufacture of 1 kWh of batteries.

When we look at the chemistry cycle life numbers we get typical values:

• LFP – 3,000 to 6,000+ cycles
• NMC/NCA – 500 to 1,000+ cycles
• LTO – 10,000 to 20,000+ cycles
• Sodium-ion – 1,000 to 2,000+ cycles
• NiMH – 500 to 800 cycles

That means the lifetime carbon intensity per kWh of energy throughput:

• LFP – 7 to 33 gCO2e/kWh
• NMC/NCA – 79 to 329 gCO2e/kWh

LTO has a very high cycle life of 10,000 to 20,000 and a very high GHG intensity 200 to 500 kg CO2-eq/kWh – the result is a lifetime carbon intensity per kWh of energy throughput of 14 to 71 gCO2e/kWh, beating NMC/NCA.

Note: we had to extend the GHG Intensity scale a long way to fit LTO onto the map.

However, this cycle life depends on other factors:

• Depth of Discharge (DoD) – using 100% of a battery’s capacity per cycle causes more stress than partial discharges. Narrowing the window can extend the life
• Temperature – high temperatures (above ~35°C) accelerate degradation, while extremely low temperatures reduce performance
• Charge Rate (C-rate) – fast charging (high C-rate) increases heat and internal stress, shortening life faster than slow charging
• Voltage Limits – operating at very high (100% SoC) or very low (0% SoC) voltages accelerates chemical degradation

If we are going to produce a battery that ages over years we also need to consider calendar ageing.

• Li-ion (NMC/NCA) – typically 10+ years
• Li-ion (LFP) – known for superior longevity, often surpassing 15+ years

Calendar life also depends on:

• Temperature – temperatures above ~35°C exponentially increase degradation.
• State of Charge (SoC) – storing batteries at very high (100%) or very low (0%) voltage shortens life.

Plus, we need to think about the application as increased mass can mean more energy required to move the transport. We could increase the size of a stationary energy storage pack, hence bringing the C-rate down and removing the need to thermally manage the system. Hence removing the energy required for the thermal management and all of the emissions that relate to that. But what about the calendar ageing? The pack ages even if we don’t use it and a larger pack => more GHG emissions in the production of it.

We originally stated that carbon footprint is a 2-axis problem, but in fact it is a multi-dimensional problem once we look at the system. Hence the need to build up a model of the system to truly understand the total lifetime emissions and to optimise the battery to get the best result for the EU Battery Passport.

Related: for a formal breakdown of what these gCO2e/kWh figures actually include (GWP, Scope 1/2/3, and the cradle-to-gate vs cradle-to-grave boundary question), see Embodied Carbon & GWP: Definitions and System Boundaries.