Effect of the Calcination Duration on the Electrochemical Properties of Na2Ti3O7 as Anode Material for Na-Ion Batteries

peer reviewedThe growing interest in Na-ion batteries as a “beyond lithium” technologies for energy storage drives the research for high-performance and environment-friendly materials. Na2Ti3O7 (NTO) as an eco-friendly, low-cost anode material shows a very low working potential of 0.3 V vs. Na+/Na but suffers from poor cycling stability, which properties can be significantly influenced by materials synthesis and treatment. Thus, in this work, the influence of the calcination time on the electrochemical performance and the reaction mechanism during cycling were investigated. NTO heat-treated for 48 h at 800 °C (NTO-48h) demonstrated enhanced cycling performance in comparison to NTO heat-treated for only 8 h (NTO-8h). The pristine material was thoroughly characterized by X-ray diffraction, laser granulometry, X-ray photoelectron spectroscopy, and specific surface area measurements. The reaction mechanisms induced by sodiation/desodiation and cycling were investigated by operando XRD. Electrochemical impedance spectroscopy was used to evidence the evolution of the solid electrolyte interface layer (SEI) and modification of charge transfer resistances as well as the influence of cycling on capacity decay. The evolution of the crystallographic structure of NTO-48h revealed a more ordered structure and lower surface contamination compared to NTO-8h. Moreover, the residual Na4Ti3O7 phase detected after the sodium extraction step in NTO-8h seems correlated to the lower electrochemical performance of NTO-8h compared to NTO-48h

Spray-drying de matériaux à base de titane pour batteries Li/Na-ion : développement d’électrodes flexibles à base de Li4Ti5O12 et caractérisations in-situ de Na2Ti3O7

Rechargeable batteries occupy a predominant position in energy storage systems, thanks to their versatility and performance. Indeed, they can be used in a wide range of applications such as portable devices, electric vehicles or grid storage. The development of high-performance energy storage systems has to meet actual energy and technology needs and requirements but also fulfill environmental considerations. In this context, this thesis included two research axes: the development of green and flexible Li4Ti5O12 electrodes for Li-ion batteries, based on aqueous formulation, and the study and optimisation of Na2Ti3O7 anode material for Na-ion batteries. Therefore, the first part of this thesis concerned the development of new aqueous suspensions for the preparation of free-standing and flexible electrodes. Li4Ti5O12, which is a promising anode material for Li-ion batteries, was synthesized via a spray-drying route in aqueous media. Crack-free and free-standing electrodes were obtained with the use of polyvinyl alcohol and polyethylene glycol as the binder and plasticizer, respectively. Good electrochemical performance was obtained in half-cell configuration and also in full-cell configuration with LiFePO4 flexible cathode. The second part of this thesis concerns the development of Na2Ti3O7 (NTO) as anode material for Na-ion batteries. In-situ high-temperature XRD was coupled with ex-situ XRD, TGA/DSC, SEM and TEM to investigate the formation of NTO. Na2Ti6O13 and Na4Ti5O12 were identified as intermediate phases and the chemical equations for a three-step formation mechanism were established. The observed influence of the heat-treatment duration on the electrochemical performance of NTO material was elucidated by in-situ XRD technique. Indeed, for the first time different mechanisms for Na+ ions insertion/extraction in the structure were identified and studied, regarding the calcination time. Rietveld refinement showed that the increase of the calcination duration leads to a more ordered structure, which explained the higher performance and stability of the material heat-treated 48 h compared to 8 h. In addition to this study, the formation of in-situ carbon was considered in order to decrease the irreversibility at the first cycle and limiting the surface degradation of Na2Ti3O7 during cycling. Finally, the electrochemical performance in Na-ion full-cell configuration was investigated using Na3V2(PO4)2F3 (NVPF) as cathode material. The system NTO/NVPF has been reported for the first time in this study. A high excess of NVPF was required to compensate the sodium consumption due to SEI formation and side reactions at NTO anode. Moreover, the presodiation of the NTO anode allowed to improve the stability and enhance the performance of the NVPF/NTO batteries of more than 300 % during the rate capability test, compared to the batterie assembled with non-presodiated NTO

Synthesis and shaping of flexible anodes based on Li4Ti5O12 for lithium-ion batteries

Les dispositifs de stockage d’énergie électrique sont devenus une nécessité de par l’utilisation quotidienne de nombreux appareils électriques et électroniques. Dans le but de développer des systèmes performants, des accumulateurs au lithium sont étudiés. De plus, les nouvelles technologies flexibles (vêtements intelligents, smatphone, etc.) demandent le développement d’accumulateurs eux-aussi flexibles. Le but de ce mémoire était de mettre au point une anode à base de Li4Ti5O12 (LTO) sous forme d’un film mince et flexible. La synthèse de la poudre de LTO a été réalisée par spray-drying, au départ d’une suspension aqueuse de TiO2 et LiOH. Les particules obtenues ont un diamètre d’environ 10 µm. Cependant, dans l’optique de réaliser des suspensions stables et d’augmenter les performances électrochimiques, il était impératif de diminuer cette taille en procédant à un broyage. Des suspensions avec ce LTO broyé ont été préparées en y ajoutant différents additifs afin de pouvoir réaliser les électrodes de travail. Les suspensions ont ensuite été mises en forme pour réaliser des films minces. Ces films sont homogène (macroscopiquement et microscopiquement), flexibles et montrent de bonnes performances électrochimiques

Films minces flexibles pour électrodes de pile/batterie

publication date: 2018-08; filing date: 2017-01A composition comprising: a. An at least partially hydrolysed polyvinyl acetate component having an hydrolysation degree of at least 5%, b. A polyalkylene glycol component having a number average molecular mass Mn lower than 9000 g/mol and consisting of one or more substances selected from the group consisting of polyethylene glycol, polypropylene glycol, copolymers of ethylene glycol and propylene glycol, and their derivatives, c. a positive or negative electrode active component, and d. a conductive component, wherein the mass ratio between the at least partially hydrolysed polyvinyl acetate component and the positive or negative electrode active component equals at least 0.12 and at most 0.30, and wherein the mass ratio between the polyalkylene glycol component and the positive or negative electrode active component equals at least 0.012 and at most 0.10L'invention concerne une composition comprenant : a. un composant d'acétate de polyvinyle au moins partiellement hydrolysé ayant un degré d'hydrolyse d'au moins 5 % ; b. un composant polyalkylène glycol ayant une masse moléculaire moyenne en nombre Mn inférieure à 9000 g/mol et constitué d'une ou plusieurs substances choisies dans le groupe constitué par le polyéthylène glycol, le polypropylène glycol, les copolymères d'éthylène glycol et de propylène glycol, et leurs dérivés ; c. un composant actif d'électrode positive ou négative ; et d. un composant conducteur. Le rapport massique entre le composant d'acétate de polyvinyle au moins partiellement hydrolysé et le composant actif d'électrode positive ou négative est compris entre 0,12 et 0,30 inclus, et le rapport massique entre le composant polyalkylène glycol et le composant actif d'électrode positive ou négative est compris entre 0,012 et 0,10 inclus

Spray-drying of electrode materials for lithium- and sodium-ion batteries

The performance of electrode materials in lithium-ion (Li-ion), sodium-ion (Na-ion) and related batteries depends not only on their chemical composition but also on their microstructure. The choice of a synthesis method is therefore of paramount importance. Amongst the wide variety of synthesis or shaping routes reported for an ever-increasing panel of compositions, spray-drying stands out as a versatile tool offering demonstrated potential for up-scaling to industrial quantities. In this review, we provide an overview of the rapidly increasing literature including both spray-drying of solutions and spray-drying of suspensions. We focus, in particular, on the chemical aspects of the formulation of the solution/suspension to be spray-dried. We also consider the post-processing of the spray-dried precursors and the resulting morphologies of granules. The review references more than 300 publications in tables where entries are listed based on final compound composition, starting materials, sources of carbon etc. © 2018 by the authors

Spray-drying synthesis of Na2Ti3O7 and electrochemical characterization using different electrolytes

Na2Ti3O7 is considered as a promising intercalation anode material for sodium ion batteries thanks to its low insertion potential (0.3V vs Na0/Na+) and relatively good theoretical capacity (178 mAh/g) [1,2,3]. Nevertheless, it has a poor long term cycling stability that still needs to be solved. Besides, the importance of the choice of the electrolyte for Na-ion batteries was recently reviewed [4]. We report here a new spray-drying synthesis of Na2Ti3O7. By contrast to the solid-state synthesis, the advantages of the spray-drying method are a high homogeneity of the precursors and good control of the particle size and morphology (typically spherical particles of 3-30 µm, depending on the injection mode, concentration, pressure, temperature, etc.). Therefore, the heat treatment time is decreased. In this work, we studied the formation mechanism of Na2Ti3O7. We identified sequences of intermediate phases, starting from spray-dried TiO2 and NaOH or Na2CO3 precursors. In order to improve the performances of our material, we also tested the influence of the electrolyte on the electrochemical performances in half cell. The effect of the solvent (PC, EC, DMC and Diglyme) but also of the salt (NaClO4, NaPF6, NaTFSI, NaFSI and NaOTf) was examined and significant differences were observed. [1] Zukalová et al., Journal of Solid State Electrochemistry, 2018, 22, 2545–2552 [2] J. Nava-Avendaño et al., Journal of Material Chemistry A, 2015, 3, 22280-22286 [3] M. Zarrabeitia et al., Acta Materialia, 2016, 104, 125-130 [4] A. Ponrouch et al., Journal of Material Chemistry A, 2015, 3, 22-4

Comparison of the electrochemical performance of Li4Ti5O12 spinel as negative electrodes for lithium-ion batteries prepared by sol gel and spray drying methods

Energy is considered as the lifeblood of modern society. Rechargeable batteries are the most promising to meet the human needs concerning the energy storage thanks their high energy density and high energy efficiency. Most difficult challenges of the development of promising rechargeable batteries concern the electrode materials. Li4Ti5O12 (LTO) is one the most promising anode materials for Li-ion batteries, as it demonstrates very stable cycling stability and excellent safety. Its high operating potential (~1.5 V) allows to avoid the formation of SEI during the first cycle. The three-dimensional structure offers LTO excellent reversibility due to the near zero volume strain during the Li+ ion intercalation and deintercalation cycling. The main objective of this study on LTO samples was to evidence the effect of synthesis method and thermal conditions on their structural, morphological and electrochemical properties [1, 2]. The results demonstrate the strong influence of the synthesis route (Sol-Gel and spray-drying methods) and the thermal treatment on the capacity, cyclability and rate capability of the LTO spinel in Li-half-cell and Li-ion full-cell (see Figure 1). References [1] A. Mahmoud, J. M. Amarilla, K. Lasri, I. Saadoune, Electrochim. Acta 93 (2013) 163-172. [2] A. Mahmoud, J. M. Amarilla, I. Saadoune, Electrochim. Acta 163 (2015) 213-222.RESIBAT n° 1510399, Batwa