Hard carbons are the material of choice as negative electrode in sodium ion batteries. Despite being extensively studied, there is still debate regarding the mechanisms responsible for storage in low- and high-potential regions. This work presents a comprehensive approach to elucidate the involved storage mechanisms when Na ions insert into such disordered structures. Synchrotron X-ray total scattering experiments were performed to access quantitative information on atomic ordering in these materials at the nanoscale. Results prove that hard carbons undergo an atomic rearrangement as the graphene layers cross-link at intermediate temperatures (1200–1600 °C), resulting in an increase of the average interplanar distance up to 1400 °C, followed by a progressive decrease. This increase correlates with the positive trend in the reversible capacity of biomass-derived carbons when processed up to 1200–1600 °C due to an increased capacity at low potential (≤0.1 V vs Na/Na+). A decrease in achievable sloping capacity with increasing heat-treatment temperature arises from larger crystalline domains and a lower concentration of defects. The observed correlation between structural parameters and electrochemical properties clearly supports that the main storage of Na ions into a hard-carbon structure is based on an adsorption–intercalation mechanism.

6Porous graphitic carbons were successfully obtained from wood precursors through 7 pyrolysis using a transition metal as catalyst. Once the catalyst is removed, the resulting 8 material mimics the microstructure of the wood and presents high surface area, open and 9 interconnected porosity and large pore volume, high crystallinity and good electrical 10 conductivity, making these carbons interesting for electrochemical devices. Carbons 11 obtained were studied as electrodes for supercapacitors in half cell experiments, obtaining 12high capacitance values in a basic media (up to 133 F·g -1 at current densities of 20 mA·g -1 13 and 35 F·g -1 at current densities of 1 A·g -1 ). Long-cycling experiments showed excellent 14 stability of the electrodes with no reduction of the initial capacitance values after 1000 15 cycles in voltammetry. 16

Graphitized carbon materials from biomass resources were successfully synthesized with an iron catalyst, and their electrochemical performance as anode materials for lithium-ion batteries (LIBs) was investigated. Peak pyrolysis temperatures between 850 and 2000 °C were covered to study the effect of crystallinity and microstructural parameters on the anodic behavior, with a focus on the first-cycle Coulombic efficiency, reversible specific capacity, and rate performance. In terms of capacity, results at the highest temperatures are comparable to those of commercially used synthetic graphite derived from a petroleum coke precursor at higher temperatures, and up to twice as much as that of uncatalyzed biomass-derived carbons. The opportunity to graphitize low-cost biomass resources at moderate temperatures through this one-step environmentally friendly process, and the positive effects on the specific capacity, make it interesting to develop more sustainable graphite-based anodes for LIBs.