The global imperative to mitigate climate change has solidified carbon neutrality as a universal goal. In the transportation sector, the electrification of vehicles is a central pillar of this transition. While conventional lithium-ion batteries (LIBs) have enabled the first wave of electric vehicles, they face inherent limitations regarding safety, energy density, and resource sustainability. Solid-state batteries (SSBs), which replace the flammable liquid electrolyte with a solid ion conductor, are widely regarded as the next evolutionary step, promising superior safety, higher energy densities, and wider operational temperature ranges. As the core component differentiating SSBs, the solid electrolyte determines the battery’s key performance metrics. However, the environmental footprint of manufacturing these advanced materials must be scrutinized to ensure the sustainable development of this promising technology. This assessment focuses on the production phase of solid electrolytes, evaluating their environmental impact through a comprehensive “footprint family” lens to inform greener material choices for the future of solid-state battery technology.
The methodology employed in this study is based on the Life Cycle Assessment (LCA) framework, a standardized tool (ISO 14040/44) for evaluating the potential environmental impacts associated with all stages of a product’s life. The study follows the four phases of LCA: goal and scope definition, life cycle inventory (LCI), life cycle impact assessment (LCIA), and interpretation. The system boundary is defined as “cradle-to-gate,” encompassing the extraction of raw materials, their transportation, and the manufacturing processes up to the production of 1 kg of solid electrolyte. The life cycle inventory data for the electrolyte compositions were compiled from published scientific literature and laboratory data.
To provide a multi-faceted environmental profile, we adopt a “footprint family” approach. This framework integrates several footprint indicators, each capturing different aspects of environmental pressure and resource use. For this assessment of solid-state battery electrolytes, we calculate the following footprints:
- Carbon Footprint: Quantifies greenhouse gas emissions, expressed in kg CO2-equivalents, using the IPCC 2013 GWP 20a method.
- Water Footprint: Assesses water consumption and degradation, expressed in m³, using the AWARE method, which considers water scarcity.
- Material Footprint: Evaluates the depletion of abiotic resources, split into Mineral Resource Depletion and Fossil Resource Depletion, expressed in USD (2013).
- Ecological Footprint: Measures the biologically productive land and water area required to provide resources and absorb emissions, expressed in global square meter-years (m²·a).
- Health Footprint: Estimates impacts on human health, encompassing categories like carcinogens, non-carcinogens, respiratory effects, ionizing radiation, and ozone layer depletion, using the IMPACT 2002+ methodology.
The functional unit for comparison is 1 kilogram (kg) of manufactured solid electrolyte. We selected 22 distinct solid electrolytes, categorizing them into three main families prevalent in solid-state battery research: Inorganic Solid Electrolytes (ISE), Solid Polymer Electrolytes (SPE), and Composite Solid Electrolytes (CSE). Their compositions and key properties are summarized in Table 1.
| Type | Abbreviation | Composition | Ionic Conductivity (S/cm) |
|---|---|---|---|
| Inorganic (ISE) | ISE-1 | Li0.34La0.56TiO3 | 2 × 10-5 (25°C) |
| ISE-2 | Li4Al0.33Si0.33P0.33O4 | 1 × 10-3 (200°C) | |
| ISE-3 | Li10.42Ge1.5P1.5Cl0.08O11.92 | 3.7 × 10-5 (27°C) | |
| ISE-4 | Na3.1Zr1.95Mg0.05Si2PO12 | 1.33 × 10-3 (25°C) | |
| ISE-5 | Li1.2Mg0.1Zr1.9(PO4)3 | 2.8 × 10-5 (25°C) | |
| ISE-6 | Li1.3Al0.3Ti1.7(PO4)3 | 4.46 × 10-5 (25°C) | |
| ISE-7 | Li1.5Al0.5Ge1.5(PO4)3 | 2 × 10-5 (25°C) | |
| ISE-8 | Li7La3Zr1.7Sn0.3O12 | 2.52 × 10-5 (25°C) | |
| ISE-9 | Li7La2.75Ca0.25Zr1.75Nb0.25O12 | 2.2 × 10-4 (22°C) | |
| ISE-10 | Li2S-P2S5 | 7.9 × 10-5 (25°C) | |
| ISE-11 | Li10GeP2S12 | 2.02 × 10-3 (25°C) | |
| ISE-12 | 98Li7P3S11-2Li3SI | 2.3 × 10-4 (25°C) | |
| ISE-13 | Li3YCl6 | 5.1 × 10-4 (25°C) | |
| ISE-14 | Li3.6PO3.4N0.6 | 5.0 × 10-6 (70°C) | |
| ISE-15 | Li6PS5Cl | 1.4 × 10-5 (25°C) | |
| Polymer (SPE) | SPE-1 | C2F6LiNO4S2 + Propylene Carbonate | 3.0 × 10-4 (20°C) |
| SPE-2 | C2F6LiNO4S2 + Poly(ethylene oxide) | 2.8 × 10-4 (25°C) | |
| SPE-3 | C2BF2LiO4 + Poly(vinyl acetate) | 9.82 × 10-5 (50°C) | |
| Composite (CSE) | CSE-1 | LiB3O5 + Li3BO3-Li6.5La3Zr1.5Ta0.5O12 | 4.5 × 10-5 (25°C) |
| CSE-2 | Li1.5Al0.5Ge1.5(PO4)3 + LiClO4 + Oxypolyethelene | 2.6 × 10-4 (55°C) | |
| CSE-3 | Li7La3Zr2O12 + LiClO4 + Poly(vinylidene fluoride) | 1.16 × 10-4 (30°C) | |
| CSE-4 | Li1.5Al0.5Ge1.5(PO4)3 + C2F6LiNO4S2 + PEO + PEGDME | 1.67 × 10-4 (25°C) |
The impact assessment was conducted using the LCA software SimaPro. The specific methods and units for each footprint category within the footprint family are detailed in Table 2.
| Footprint Indicator | Impact Category | Calculation Method | Unit |
|---|---|---|---|
| Carbon Footprint | Global Warming Potential | IPCC 2013 GWP 20a | kg CO2-eq |
| Water Footprint | Water Scarcity | AWARE | m³ |
| Material Footprint | Mineral Resource Depletion | ReCiPe 2016 Endpoint (E) | USD2013 |
| Fossil Resource Depletion | |||
| Ecological Footprint | Carbon Dioxide Uptake | Ecological Footprint V1.01 | m²·a |
| Nuclear Energy | |||
| Land Occupation | |||
| Health Footprint | Carcinogens | IMPACT 2002+ | kg C2H3Cl-eq |
| Non-carcinogens | kg C2H3Cl-eq | ||
| Respiratory Inorganics | kg PM2.5-eq | ||
| Ionizing Radiation | kBq C-14-eq | ||
| Ozone Layer Depletion | kg CFC-11-eq | ||
| Respiratory Organics | kg C2H4-eq |
The footprint calculations are based on aggregating the impacts from all constituent materials and energy inputs. A generalized expression for calculating a footprint (F) for an electrolyte can be represented as:
$$ F = \sum_{i} (m_i \times EF_i) + \sum_{j} (E_j \times EF_j) $$
where $m_i$ is the mass of raw material $i$, $EF_i$ is its specific environmental footprint factor, $E_j$ is the amount of energy type $j$ consumed, and $EF_j$ is the corresponding footprint factor for that energy. The water footprint specifically considers different water types:
$$ WF = WF_{blue} + WF_{green} + WF_{grey} $$
representing consumption of surface/groundwater, rainwater, and the volume of water needed to dilute pollutants, respectively.
The analysis of the carbon footprint, a critical metric for climate impact, reveals a clear hierarchy among electrolyte families. The average carbon footprint for producing 1 kg of material was found to be 3.348 kg CO2-eq for SPEs, 8.127 kg CO2-eq for ISEs, and 15.685 kg CO2-eq for CSEs. SPEs demonstrate the lowest impact, primarily because their polymer matrices are synthesized from organic monomers through polymerization, processes that are generally less energy and material-intensive compared to metallurgy. ISEs, containing significant amounts of various metals, incur a higher burden. Notably, CSEs exhibit the highest carbon footprint, even though they contain polymer components. This is attributed to their complex manufacturing processes, which often involve energy-intensive steps like high-temperature sintering or calcination of the inorganic fillers. For instance, CSE-1, a composite of two ceramic materials (Li6.5La3Zr1.5Ta0.5O12 and Li3BO3), has the highest individual carbon footprint at 36.956 kg CO2-eq. Among ISEs, those containing lanthanum compounds (e.g., ISE-1, ISE-8, ISE-9) and several sulfide/halide-based electrolytes (e.g., ISE-10 to ISE-15) also show elevated carbon emissions.
The water footprint assessment, evaluating water consumption and scarcity-weighted use, follows a similar trend: SPEs have the lowest average impact (1.957 m³), followed by ISEs (5.231 m³), and then CSEs (9.017 m³). This reinforces that the production processes for composite and inorganic solid-state battery electrolytes are more demanding on water resources. While CSE-1 again has the highest water footprint, CSE-3 shows a relatively lower value, indicating that different electrolyte compositions have varying sensitivities to different footprint categories. A notable finding is the high water footprint of ISE-7 (Li1.5Al0.5Ge1.5(PO4)3), which is attributed primarily to the germanium (Ge) content in its composition.
The material footprint, split into mineral and fossil resource depletion, provides insight into non-renewable resource use. For mineral resource depletion, the averages are 0.013 USD for SPEs, 0.247 USD for ISEs, and 0.821 USD for CSEs. For fossil resource depletion, the averages are 0.448 USD (SPE), 0.632 USD (ISE), and 1.563 USD (CSE). The significantly higher fossil resource depletion across all types highlights the energy-intensive nature of advanced material synthesis. CSE-1 dominates both mineral and fossil depletion categories. Polymer electrolytes show a negligible mineral footprint, consistent with their organic nature, but still contribute to fossil depletion through energy inputs. ISE-7 and the nitride-based ISE-14 show high mineral depletion potentials, while ISE-13 (halide), ISE-8, and ISE-1 exhibit high fossil resource depletion.
The ecological footprint, translating impacts into a land-area equivalent, consolidates pressures from carbon emissions, nuclear energy use, and direct land occupation. The results strongly indicate that CSE production imposes the greatest demand on the planet’s biocapacity. CSEs account for approximately 59% of the total carbon dioxide uptake footprint and 76% of the land occupation footprint among the three families. While SPEs and ISEs have similar contributions to the nuclear energy footprint, CSEs again lead. CSE-1 has the highest impact in all three sub-categories. Among ISEs, those with lanthanum (ISE-1, ISE-8, ISE-9) and sulfide/halide/nitride types contribute significantly to the CO2 uptake footprint. Niobium chloride (in ISE-9) and lithium metaphosphate (in ISE-14) are key drivers for the land occupation impact.
The health footprint analysis presents a comprehensive view of potential human health damages. Across all six impact categories—carcinogens, non-carcinogens, respiratory inorganics/organics, ionizing radiation, and ozone depletion—CSEs consistently show the highest average impacts, followed by ISEs and then SPEs. For example, CSEs contribute about 57-71% of the total impact in categories like respiratory inorganics and non-carcinogens. CSE-1 is the most impactful individual electrolyte in every health category. Lanthanum-containing electrolytes (ISE-1, ISE-8, CSE-3) are major contributors to carcinogens, respiratory organics, ozone depletion, and ionizing radiation. Germanium-containing compositions (ISE-3, ISE-7, CSE-2, CSE-4) are linked to high impacts for non-carcinogens and respiratory inorganics (PM2.5). Furthermore, sulfide-type (ISE-10, ISE-11, ISE-12), nitride-type (ISE-14), and argyrodite-type (ISE-15) ISEs, along with the lithium salt C2F6LiNO4S2 used in some SPEs, contribute significantly to ionizing radiation.
In conclusion, this comprehensive footprint family assessment of solid-state battery electrolytes reveals a consistent environmental hierarchy: Composite Solid Electrolytes (CSEs) generally have the highest environmental burden across almost all footprint categories, followed by Inorganic Solid Electrolytes (ISEs), with Solid Polymer Electrolytes (SPEs) presenting the lowest impact profile for an equivalent mass produced. This pattern holds true for climate change (carbon footprint), water scarcity, resource depletion, ecological land use, and human health impacts. The high impact of CSEs, despite containing organic polymer phases, underscores the dominant role of energy-intensive ceramic processing and the compounding effects of combining multiple inorganic materials. Specific elements like lanthanum and germanium are identified as significant contributors to various footprints. These findings highlight a critical trade-off in solid-state battery development: while composite and inorganic electrolytes may offer superior ionic conductivity or stability, their environmental cost at the production stage is substantially higher. To support a truly sustainable transition to next-generation solid-state battery technology, research must focus not only on electrochemical performance but also on developing greener synthesis routes for high-impact materials, exploring alternative chemistries with lower footprint elements, and prioritizing polymer-based systems where performance requirements allow. This multi-criteria footprint analysis provides a valuable framework for guiding the eco-design of future solid-state battery components.