Superior "green" electrode materials for secondary batteries: through the footprint family indicators to analyze their environmental friendliness.

As secondary batteries are becoming the popular production of industry, especial for lithium ion batteries (LIBs), the degree of environmental friendliness will gather increasing attention to their products of the whole life cycle. The research combines the life cycle assessment (LCA) and footprint family definition to establish a framework to calculate the footprint family of secondary battery materials. Through the method, we calculated the values of carbon footprint, water footprint, and ecological footprint about this eight kinds of secondary cathode battery materials with Ni-MH, Li1.2Ni0.2Mn0.6O2/C, LiNi1/3Co1/3Mn1/3O2/C, LiNi0.8Co0.2O2/C, LiFePO4/C, LiFe0.98Mn0.02PO4/C, FeF3(H2O)3/C, and NaFePO4/C. When comparing and analyzing their values in each footprint, it can summarize the evaluation method for some secondary batteries by footprint indicators and construct the evaluation system. Through the comprehensive evaluation of footprint family system, the NaFePO4/C battery gets the best performance of three main footprints when combining 1 kg of cathode materials, while Ni-MH is opposite. Hence, among these eight batteries environmental impacts evaluation, the NaFePO4/C battery is regarded as the superior "green" battery, albeit the current application is restricted because of the synthesis limitation on large scale and energy density of storage. In LIBs comparison, the FeF3(H2O)3 material shows its characteristics of environmental friendliness, which is expected to be a greener battery material of LIB. In conventional LIBs, the iron-containing cathode materials show lower environmental burden than ternary cathode materials. We can reduce environmental impacts through developing new advanced materials and reducing the content of high sensitivity element in raw materials.