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The relationship between structure and lithium storage capacity of different titanate samples as anode materials for lithium-ion batteries is discussed. Li 4 Ti 5 O 12 , Na 2 Ti 3 O 7 and Na 2 Ti 6 O 13 were synthesized by solid-state reaction. The structure, surface and morphology of the samples were characterized by SEM, XRD and RAMAN spectroscopy. The electrochemical performance was studied by galvanostatic charge-discharge cycling, cyclic voltammetry, electrochemical impedance spectroscopy and rate capability. The lithium titanate presented the highest capacity of the three electrodes, together with the most reversible potential plateau at 1.6 V vs. Li + /Li 0 and the best response in rate capability. Apparent diffusion coefficients of Li + ions into the titanate matrices were obtained, showing the highest value for the lithium titanate compound. Between both sodium titanates, Na 2 Ti 6 O 13 presented the highest specific capacity and the best discharge retention.

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The Nobel Prize in Chemistry 2019 recognized the importance of Li-ion batteries and the revolution they allowed to happen during the past three decades. They are part of a broader class of electrochemical energy storage devices, which are employed where electrical energy is needed on demand and so, the electrochemical energy is converted into electrical energy as required by the application. This opens a variety of possibilities on the utilization of energy storage devices, beyond the well-known mobile applications, assisting on the decarbonization of energy production and distribution. In this series of reviews in two parts, two main types of energy storage devices will be explored: electrochemical capacitors (part I) and rechargeable batteries (part II). More specifi cally, we will discuss about the materials used in each type of device, their main role in the energy storage process, their advantages and drawbacks and, especially, strategies to improve their performance. In the present part, electrochemical capacitors will be addressed. Their fundamental difference to batteries is explained considering the process at the electrode/electrolyte surface and the impact in performance. Materials used in electrochemical capacitors, including double layer capacitors and pseudocapacitive materials will be reviewed, highlighting the importance of electrolytes. As an important part of these strategies, synthetic routes for the production of nanoparticles will also be approached (part I).