**5. Life Cycle Impact Assessment—LCIA**

In an LCA, the impacts evaluation phase (Life Cycle Impact Assessment—LCIA) allows the assessment of potential impacts extent using data collected in the LCI. This operation links inventory data with specific impact categories and indicators, in order to better evaluate these impacts. The LCIA phase gives important information for life cycle results interpretation. Since different studies rely on different hypotheses, make use of different databases for background data and, above all, use different Life Cycle Impact Assessment Methods with their own unit, results cannot be compared easily with each other [20]. Nevertheless, some general conclusions may be drawn. First of all, for almost all impact categories, results show that the environmental major impacts of batteries life cycle occur during the production phase [7] and are due to energy consumption during materials and component

production [11,16]. In particular, anode production process is responsible for the greatest impacts for impact categories such as eutrophication and acidification, whereas the cathode has major impacts for global warming and abiotic depletion [17]. Coming to the amount of the environmental impacts, results show great variability. Variability is due to, as mentioned, the use of different hypotheses and databases, but it is also linked to the different batteries' chemistry. As discussed, global warming is the most investigated impact category, since EV market penetration is mainly driven by transport sector decarbonization. Figure 2 summarizes results variability linked to greenhouse gas emissions per kWh of batteries capacity, relating to batteries production phase. These values are extracted or inferred by the assessed studies in this literature review. Depending on the different technologies and on the age of the studies, greenhouse gas emissions per kWh batteries capacity can range from 53 kg CO2eq/kWh to more than 300 kg CO2eq/kWh.

**Figure 2.** Variability of the global warming potential indicator (kg CO2eq/kWh) for batteries production phase (LCO: Lithium Cobalt Oxide; LFP: Lithium iron phosphate; LFP-LTO: Lithium iron phosphate-Lithium Titanate; LMO: Lithium Manganese Oxide; LMO-NCM: Lithium Manganese Oxide-Lithium Nickel Cobalt Manganese; NCA: Lithium Nickel Cobalt Aluminum Oxide; NCM: Lithium Nickel Cobalt Manganese Oxide).

Considering a modern EV equipped with a 40 kWh battery lasting for 210,000 km [3], the lower and the upper values in Figure 2 correspond to an emission per km ranging from less than 10 g CO2eq/km to almost 60 g CO2eq/km. Nevertheless, despite this high variability, if we consider for the other vehicles life cycle phases, the CO2eq/km reported in reference [3], the total CO2eq/km life cycle emissions of an average middle size EV equipped with a 40 kWh battery, are lower than those of similar diesel or petrol cars, no matter if we consider the upper or the lower bound of battery CO2eq emission variability (see Table 3).

A similar range of variability can be found for other, less investigated, environmental impact categories (see Figures 3–6). Again, if we consider a 40 kWh battery lasting for 210,000 km, and we consider the results from reference [1] for the other life stages, we can see that while for some impact categories for which EV perform worst, like eutrophication [1], the variability of the impacts associated with battery production does not affect the environmental ranking among EV and the corresponding ICE Vehicle. For categories like acidification, the use of the lower bound value implies that EV performs better than ICE Vehicle, while the use of the upper bound value implies that the ICE Vehicle is the best performer (see Table 4).

**Table 3.** Effects of the variability of CO2eq emission per kWh of battery on the life cycle comparison among a middle size electric, diesel and petrol car. Battery CO2eq emission per km derives from Figure 2**,** considering 40 kWh of capacity and 210,000 km of life. CO2eq emission per km of remaining life cycle phases are taken from reference [1].


**Figure 3.** Variability of acidification potential (kg SO2eq/kWh) for batteries production phase (LCO: Lithium Cobalt Oxide; LFP: Lithium iron phosphate; LMO: Lithium Manganese Oxide; NCM: Lithium Nickel Cobalt Manganese Oxide); \*\* data from reference [11] have been updated using Ecoinvent v 3.5.

**Figure 5.** Variability of eutrophication potential (kg Peq/kWh) for batteries production phase (LFP: Lithium iron phosphate; LMO: Lithium Manganese Oxide; LMO-NCM: Lithium Manganese Oxide-Lithium Nickel Cobalt Manganese; NCM: Lithium Nickel Cobalt Manganese Oxide); \* data from reference [7] are calculated on the basis of the total amount and the percentage for battery production, \*\* data from reference [11] have been updated using Ecoinvent v 3.5.

**Figure 6.** Variability of particulate matter formation potential (kg PM10eq/kWh) for batteries production phase (LFP: Lithium iron phosphate; LMO: Lithium Manganese Oxide; NCM: Lithium Nickel Cobalt Manganese Oxide); \*\* data from reference [11] have been updated using Ecoinvent v 3.5.

**Table 4.** Effects of the variability of acidification potential (g SO2eq) and eutrophication potential (g PO4eq) per kWh of battery on the life cycle comparison among a middle size electric, diesel and petrol car. Battery Emissions per km derives from Figures 3 and 5, considering 40 kWh of capacity and 210,000 km of life. Emissions per km of remaining life cycle phases are taken from reference [1].


Of course, many of the impacts associated with battery production could be lowered by recycling battery components and using recycled materials for battery production. Recycling may reduce material production energy demand up to 50% and can help to decrease environmental impacts for all the impact categories assessed [4]. Although there are a number of technologies and combinations of technologies being developed for batteries recycling (hydrometallurgy is close at hand, and can potentially extract more materials than pyrometallurgy) [12], battery recycling options are not always included in the analysis, due to the lack of relevant and reliable information [20]. Recently, a very careful recycle phase analysis has been realized in reference [7]. This work states that the environmental credits associated with materials recovered through battery recycling processes exceed the environmental impacts associated with recycling processes in all the impact categories examined, with the exception of ozone depletion, ionizing radiation and freshwater ecotoxicity. The environmental credits are particularly relevant for some impact categories such as: marine eutrophication (−27%), human toxicity (about −20% for human toxicity no cancer effect and −40% for human toxicity cancer effect), particulate matter (−17%) and abiotic depletion (−16.4%). In particular, the environmental credits related to cobalt, nickel and manganese sulphates, copper and steel are really significant and rise up to almost 80% for an important category such as abiotic depletion. Moreover, the environmental benefits linked to recycling could be increased if other cell components/materials, such as graphite, electrolyte and aluminum, are recovered, i.e., by designing battery cells to make disassembling and separating the cell components easier and more secure [7]. Additionally, for climate change impact, recycling can gain relevant positive effects, and the saved emission can be in a range of 16–32 kg CO2eq/kWh [26]. For what concerns lithium recycling, instead, further research is still needed [19].

### **6. Sensitivity and Uncertainty Analysis**

In general, because of the lack of primary and reliable data from industry, several assumptions have to be made in LCA studies. For this reason, sensitivity analysis has an important role, especially in a traction battery LCA, where some data and information are difficult to be found or cannot be declared by battery manufacturers due to their confidentiality. Moreover, in comparative LCAs, sensitivity analysis is requested by the ISO 14040 standard. However, sensitivity analysis is realized only in eight studies out of seventeen, and the related parameters can be organized in three categories: energy, distance driven, battery components materials and their recycling rate. The first category refers mainly to the energy mix consumed during the use phase and in the battery manufacturing phase [4,7,10,11,14,21]. The energy mixes consumed can considerably affect the final results, especially if these mixes are characterized by a high rate of non-renewable energy sources. For this reason, it is important to consider an appropriate energy mix [1] or simulate different mixes or different daily charging period. Sensitivity analysis should also be applied to the amount of energy used for battery production and to the composition of the energy mix used in this life cycle stage, given its relevance in traction battery LCA [7,10]. The second category is linked with the total distance driven, during their entire lives, by the e-cars where batteries are deployed [7,10,11,14,17]. This parameter can influence the final results of the studies and for this reason, different distances can be considered in order to verify the robustness of the results. Finally, the third category refers to battery components' materials and their recycling rate during the end of life phase [7,11,14,16,21], which could represent a relevant parameter in an LCA study. The sensitivity analysis related to this parameter could help to identify the materials with higher environmental impacts and if material recovery can help to reduce environmental impacts or if recycling operations generate more impacts than components disposal.

### **7. Conclusions**

The review analyzed seventeen recent studies on automotive batteries LCA. This analysis is realized to give useful information to carry out new LCAs of automotive batteries and to provide a more complete picture of electric vehicle batteries LCAs. Almost all the assessed works have a good degree of compliance with the indications given by ISO 14040 [23] and ISO 14044 [24] international standards, but some documents do not fully comply with these two standards when they analyze batteries' impacts. We found that the functional unit definition is very heterogeneous and not always appropriate, and many studies consider different functional units, basing their choice on the analysis they have to realize. Consequently, the assessed works suggest many functional units: the whole battery pack, 1 kWh of storage capacity, 1 kg of battery, the distance travelled by the electric vehicle (equipped with the batteries) during its lifetime or 1 km. In view of the foregoing, the most suitable functional units for LCA of traction batteries seem to be 1 km of travel distance along the entire battery life cycle or, for sake of comparability with the existing literature, 1 kWh of battery storage capacity (specifying the battery's number of charging cycles during its lifetime). Many studies, except for [8,13,19], clearly define the system boundaries of their analysis. Only eight out of seventeen studies consider all impacts generated by the batteries during their life, realizing a cradle to grave assessment. The evaluated phases are: raw materials extraction and manufacturing, batteries production, transportation, use phase, and end of life with material recycling. Only few studies rely on primary data, while many of the assessed studies use secondary data, obtained from available literature documents or from the Ecoinvent LCA database. In general, we register a lack of primary data and of transparency both on bills of material and on energy consumption during the battery production phases. It seems important to encourage new automotive battery LCA using updated and reliable primary data, since using old data in a sector where technologies are evolving rapidly can lead to wrong conclusions and wrong decisions. For what concerns impact categories, there is a very heterogeneous situation, even if some impact categories are more frequently used (global warming, acidification, eutrophication) whereas others are used only in few studies (e.g., water use, land use, ionizing radiation). Basing on this literature review, to realize an automotive battery LCA authors suggest to consider the following: global warming, acidification, eutrophication, ozone depletion, particulate matter, abiotic depletion, human toxicity, ecotoxicity and CED (Cumulated Energy Demand). The review also underlines the importance of carrying out sensitivity analysis on some key parameters such as: battery lifetime, recycling/second life scenarios, energy mixes in production and use phase, percentage of recycled material used during the production phase.

As regards LCIA results, there is a great variability in all the impact categories that were comparable among different studies (global warming, ozone depletion, acidification, eutrophication and particulate matter formation). For global warming, one of the main impact categories under the spotlight, this variability ranges from 53 to 313 g CO2eq/kWh of battery capacity. Our analysis shows that no matter the value considered within this range, the EVs show lower impact in their life cycle when compared to diesel or petrol cars. For other analyzed impact categories we found similar variability but if for eutrophication EVs perform worse than ICE Vehicles for any value within the variability range, for impact categories such as acidification and particulate matter formation, the use of the lower or upper bound of the variability range completely change the comparison among EVs and ICE Vehicles. This confirms that other impact categories than global warming should be investigated in LCA of traction batteries. Moreover, our review shows that batteries components which generate the greatest impacts during the production phase are the cathode active material and the anode copper and aluminum. Key aspects that could be improved to reduce these impacts are: battery lifetime extension, increase in battery efficiency and energy density. In addition, energy mix considered during the battery different life phases could be very important to decrease impacts: an energy mix with an important contribution of renewable energy sources can reduce dramatically battery overall impacts. Many studies underline that battery second life, that is battery use in stationary storage systems after their use in the automotive field, can help to reduce storage systems overall impacts. Finally, although investigated by a relatively small number of studies, it appears that material recycling, especially cobalt and nickel, could represent another useful solution to further reduce batteries' overall impacts, avoiding virgin material use during storage devices' production.

**Author Contributions:** Conceptualization, A.T. and P.G.; Methodology, A.T. and P.G.; Software; Validation, M.L.C. and P.G.; Formal Analysis A.T. and M.L.C.; Investigation, A.T., M.L.C. and P.G.; Resources; Data Curation, A.T. and M.L.C.; Writing—Original Draft Preparation, A.T.; Writing—Review and Editing, A.T., M.L.C. and P.G.; Visualization, A.T. and M.L.C.; Supervision, P.G.; Project Administration, P.G.; Funding Acquisition. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work has been financed by the Research Fund for the Italian Electrical System in compliance with the Decree of 16 April 2018.

**Conflicts of Interest:** The authors declare no conflict of interest.
