Sustainable Electrodes and Cell Configurations for Li-ion and Na-ion Batteries

In the present thesis work, two types of electrochemical energy storage systems have been studied, focusing on the sustainability of materials and applicability in practical applications: a Si-based composite anode for Lithium-ion batteries and a Na-ion full cell employing a green presodiation additive. In order to face the ever-rising greenhouse gases emissions associated with the use of fossil fuels for energy production, transport electrification and renewable energy sources are rapidly starting to grow. In this context, the use of new materials for powering electric vehicles while still granting a high driving range per single charge is required to achieve desirable energy densities from next-generation Li-ion batteries. Moreover, the use of Na-ion batteries for stationary storage, coupled to the intermittent renewable energy sources, will be the key systems for production and storage of greener and cheaper energy. These goals towards a low-carbon society can however be achieved only by focusing on several practical aspects, considering either performance or sustainability of the materials employed in the final system. Concerning Li-ion batteries, the state-of-the-art graphite serving as the anode material is likely to be replaced in next-generation batteries, due to its relatively low theoretical specific capacity (372 mAh g-1 ), which is unable to meet the required densities for efficiently powering electric vehicles, and due to its introduction in the list of critical raw materials by the European Union in recent years, although its simple preparation and low cost are still desirable properties for battery manufacturing. Silicon is considered the best candidate anode for its replacement, as it is able to deliver a specific capacity almost ten times higher than graphite (3579 mAh g-1 ), hence being suitable for high-energy density applications. In addition, it is environmentally friendly and abundant all over the Earth’s crust. However, it suffers from fast capacity fade due to the large volume changes upon cycling. In this regard, a hard carbon from waste corn-cobs was synthesized and employed in combination with commercial Si to act as a buffering matrix for volume changes, also using a crosslinked chitosan-based binder to provide better electrode integrity compared to commercial PVdF. The composite anode was deeply characterized in terms of performance and interfacial and structural properties. As a result, the studied Si/Hard Carbon anode offers promising performance in terms of specific capacity, rate capability, and structural and interfacial stability upon cycling, with a good energy efficiency when coupled to a commercial LiFePO4 cathode in full cell configuration. Concerning Na-ion batteries, a layered cathode Na0.66Mn0.75Ni0.2Mg0.05O2 was used in combination with the same hard carbon employed as the buffering matrix for Si in a full cell configuration, and the compatibility of the two materials has been evaluated. A green sacrificial salt (sodium squarate) was synthesized and used as a cathode additive to provide an appropriate amount of additional Na and address the SEI formation at the anode side, in order to make the full cell more viable for practical applications. As a result, the two materials display good compatibility in full cell configuration, with performance decreasing due to the irreversible SEI formation. The sacrificial additive is found to provide additional sodium during the first charge, hence being suitable to address the abovementioned issue, but it also affects the structural and interfacial stability upon cycling. An in-depth study of interfaces and structural evolution reveals that the phase transitions and SEI composition and thickness are indeed affected by the decomposition of sodium squarate, highlighting the necessity to further optimize the system.