Investigation of Lignocellulosic Waste-Derived Hard Carbons and Binders as Electrode Materials for Li-ion and Na-ion Batteries

In the present thesis work, the valorization of lignocellulosic waste has been pursued through the production of Hard Carbon active material and binders that can be used as electrode materials for both lithium- and sodium-ion batteries. In order to suppress the ever-rising greenhouse gases emissions, energy transition toward clean energy sources is mandatory. In this context, the development of rechargeable batteries to store electricity produced by renewable energy sources is fundamental and therefore is attracting great attentions in the last decade. However, the huge increase in the global demand of lithium- ion batteries mainly driven by transport electrification is posing serious concerns associated with the future availability of the so-called “critical raw materials”, motivating the investigation of an alternative, MWh-scalable battery technology composed of low-cost and sustainable materials. In this context, sodium-ion batteries can potentially fulfill these requirements, although the cost- competitiveness of these systems strictly depends on the achievable energy density and the electrode materials cost. At anode side, biomass-derived Hard Carbons are appealing candidates thanks to their good electrochemical performance coupled with technical aspects of low-cost and sustainability of the synthesis. Also the development of bio-based binders and eventually aqueous electrode processing is beneficial for the breakdown of the electrode manufacturing process. In this regard, an abundant and widely distributed agricultural by-product such as corncob has been used as raw material for both the production of Hard Carbon and for the extraction of cellulose for the synthesis of the sodium carboxymethylcellulose. Moreover, the bio-based electrode was used to study the sodium storage mechanism into Hard Carbon, which is fundamental to understand the structure-capacity relationship and open the path to the structural design and optimization of the electrochemical performance of Hard Carbons. The bio- based anode was deeply characterized at materials level as well as the electrochemical performance and interfacial properties. The results show that the corncob-derived anode possess good specific capacity with a promising capacity retention and good rate capability in sodium- ion system as a consequence of the high reaction kinetic and interfacial stability. Moreover, the sodium storage arises from the capacitive-controlled adsorption on surface active sites in the sloping region, while the diffusion-controlled intercalation is the predominant process approaching the low-voltage plateau. Additionally, the corncob waste-derived electrode has been evaluated also in Li-ion system both as active materials, investigating the capabilities of Hard Carbon to replace the graphite in some specific applications, and also as buffer matrix for SnO2, an interesting high-energy density anode material for lithium-ion batteries, whose development is hindered by the rapid capacity fading as a consequence of the huge volume changes during lithiation and de-lithiation. In the first application, corncobs electrodes show the same features experimented in sodium analogue, i.e. good specific capacity, long cycling stability and rate capability, while in the second application, the corncob-derived HC reveals that the mitigation of capacity fade is remarkable whit low content of SnO2 and 2% of vinylene carbonate is added to the electrolyte, promoting the formation of a thin and stable electrode/electrolyte, which increases the capacity retention. Parallelly, forestry scraps, another abundant and renewable sources of lignocellulosic materials, have been used to produce Hard Carbons and to isolate cellulose and lignin, which are in turn processed for the preparation of binders. The obtained bio-based materials have been characterized and then combined for the fabrication of anode electrodes for sodium-ion batteries. Particular emphasis has been given to the extraction and valorization of lignin as binder material for Hard Carbon anodes. The lignin extractions have been conducted using an organsolv method with two different bio-based solvents, γ-Valerolactone and Dihydrolevoglucosenone, observing that the first is more selective respect to the latter toward delignification of the biomass. The electrochemical performances of the obtained electrodes were investigated in Na half-cells. When Cyrene extracted lignin is used as binder, the electrodes show impressively long cycling stability, which can be ascribed to the high hydrogen bonding ability of the binder. The long cycling stability as well as the coulombic efficiency is enhanced when Cyrene extracted lignin is used also in Na3(VO)2(PO4)2F cathode electrode. Finally, the best Hard Carbon anode have been employed with Na3(VO)2(PO4)2F cathode in full-cell application, evaluating the electrochemical performance in terms of specific capacity and capacity retention especially at high-current rates, where this kind of cathode find its most important application. The obtained specific capacities at different current rates are good and have been confirmed also when the commercial CMC is replaced with Cyrene extracted lignin as binder at anode side. Additionally, in order to evaluate an alternative strategy for the anode preconditioning respect to the electrochemical presodiation with metallic sodium, sodium mesoxalate Na2C3O5 has been evaluated as sacrificial salt to overcome the drawback of low initial coulombic efficiency of Hard Carbon, although unsuitable results have been preliminary obtained.