Letteratura scientifica selezionata sul tema "Spinel LiNi0.5Mn1.5O4"

The presence of water inside a lithium ion (Li-ion) battery causes several interconnected chemical mechanisms that lead to material degradation including transition metal dissolution. [1-4]. As a result, cell performance is reduced, and the cell capacity rapidly fades. To mitigate transition metal dissolution caused by trace water, research groups have proposed various approaches to scavenge and neutralize the water within different components of the cell [4-6]. These methods include using a dehydratable molecular sieve within the cathode active material powder [6], direct dosing of the electrolyte with a water scavenging additive [5], and introducing a metal organic framework with water scavenging properties by mixing it with a polymer binder to create a film for use as a separator. Results from these studies show promise in improving the cycling stability of cells under abuse conditions, such as elevated temperature and high water content in the electrolyte. While these water scavenging techniques show clear benefits to cell capacity retention, they come with the trade-off of higher material cost, more complex production processes, and lower energy density, which have limited their widespread adoption in Li-ion batteries. This study focuses on the use of “cellulose”, a cheap, abundant and naturally dehydrating biopolymer, as a separator material. Cellulose-based separators have been used in Li-ion batteries and shown to be advantageous for capacity retention of the cells. The benefits of the cellulose separators have been attributed to their superior wettability, uniform pore size distribution, high porosity, and low electrical resistance [7-10]. Despite their well-known hydrophilicity, their water scavenging capabilities have not been thoroughly evaluated. In this work, we present new insights into the interaction of water with cellulose-based separator. The water scavenging properties of the cellulose separator are investigated both outside of the battery using the Karl-Fischer Coulometric Titration technique, and inside of the battery through cycling tests. As shown in Figure 1, replacing the conventional polymer-based separator with a cellulose-based nonwoven separator resulted in a significant improvement in cycle life. Furthermore, the water scavenging mechanism of cellulose-based nonwoven separator is studied using surface chemistry characterizations, suggesting water scavenging by the naturally occurring hydrogen bonding sites of cellulose. Additional discussion on drying conditions and the impact of other fiber types are also provided. References: Etacheri, V.; Marom, R.; Elazari, R.; Salitra, G.; Aurbach, D. Challenges in the development of advanced Li-ion batteries: a review. Energy & Environmental Science 2011, 4 (9), 3243-3262. Yoon, T.; Park, S.; Mun, J.; Ryu, J. H.; Choi, W.; Kang, Y.-S.; Park, J.-H.; Oh, S. M. Failure mechanisms of LiNi0. 5Mn1. 5O4 electrode at elevated temperature. Journal of power sources 2012, 215, 312-316. Lux, S.; Lucas, I.; Pollak, E.; Passerini, S.; Winter, M.; Kostecki, R. The mechanism of HF formation in LiPF6 based organic carbonate electrolytes. Electrochemistry Communications 2012, 14 (1), 47-50 Chang, Z.; Qiao, Y.; Deng, H.; Yang, H.; He, P.; Zhou, H. A stable high-voltage lithium-ion battery realized by an in-built water scavenger. Energy & Environmental Science 2020, 13 (4), 1197-1204. Sheha, E.; Refai, H. Water scavenger as effective electrolyte additive and hybrid binder‐free organic/inorganic cathode for Mg battery applications. Electrochimica Acta 2021, 372, 137883. Zhang, H.; Shi, L.; Zhao, Y.; Wang, Z.; Chen, H.; Zhu, J.; Yuan, S. A simple method to enhance the lifetime of Ni-rich cathode by using low-temperature dehydratable molecular sieve as water scavenger. Journal of Power Sources 2019, 435, 226773. Gwon, H.; Park, K.; Chung, S.-C.; Kim, R.-H.; Kang, J. K.; Ji, S. M.; Kim, N.-J.; Lee, S.; Ku, J.-H.; Do, E. C. A safe and sustainable bacterial cellulose nanofiber separator for lithium rechargeable batteries. Proceedings of the National Academy of Sciences 2019, 116 (39), 19288-19293. Jiang, F.; Yin, L.; Yu, Q.; Zhong, C.; Zhang, J. Bacterial cellulose nanofibrous membrane as thermal stable separator for lithium-ion batteries. Journal of Power Sources 2015, 279, 21-27. Wang, Y.; Liu, X.; Sheng, J.; Zhu, H.; Yang, R. Nanoporous regenerated cellulose separator for high-performance lithium ion batteries prepared by nonsolvent-induced phase separation. ACS Sustainable Chemistry & Engineering 2021, 9 (44), 14756-14765. Lv, D.; Chai, J.; Wang, P.; Zhu, L.; Liu, C.; Nie, S.; Li, B.; Cui, G. Pure cellulose lithium-ion battery separator with tunable pore size and improved working stability by cellulose nanofibrils. Carbohydrate polymers 2021, 251, 116975. Figure 1

Cette thèse visait à mieux comprendre la structure, les propriétés électrochimiques, la surface et les propriétés de transport des phases spinelles haut potentiel LiNi0. 5Mn1. 5O4 sous forme de poudre et de films minces, matériaux de cathode potentiel pour les batteries Li-ion. L'effet des paramètres de synthèse sur la stœchiométrie en oxygène et sur les phases formées a été examiné. Nous avons proposé une transformation de phase de type peritectoid pour expliquer la formation de phases de type NaCl. Les films minces de LiNi0. 5Mn1. 5O4 ont été déposés par Ablation Laser Pulsée. L'impact de la pression et de la température de dépôt sur la microstructure, la morphologie et les propriétés électrochimiques a été étudié. Le coefficient apparent de diffusion du lithium dans ces phases a été estimé à 1~2 ×10−12 cm2 s–1. Nous avons de plus mis en évidence l'effet bénéfique sur les retentions de capacité d'enrobages à base d'aluminium déposé par la méthode ALD et traité thermiquement. Enfin, les propriétés de transport des films mince de LiMn1. 5Ni0. 5O4-δ ont été mesurées. La stœchiométrie en oxygène apparaît comme le facteur principal qui contrôle la conductivité électronique
The thesis objectives were to obtain a deeper understanding of the structure, electrochemical properties, surface modification, and transport properties of high voltage spinel LiNi0. 5Mn1. 5O4 powders and thin films as cathode material in lithium ion battery. The effect of synthesis parameters on oxygen deficiency and the formed phases were investigated. We proposed a peritectoid phase transition to explain the presence of some rock salt impurities. LiNi0. 5Mn1. 5O4 thin films were deposited by Pulsed Laser Deposition (PLD) method. The effect of deposition pressure and temperature on microstructure, morphology, and electrochemical properties was investigated. The apparent lithium diffusion coefficient was estimated to a value of 1~2 ×10−12 cm2 s–1. We evidenced the beneficial effect of ALD prepared Al2O3-based coating when an annealing treatment was performed at 600oC. We propose that this is linked with the formation of LiAlx(Ni0. 5Mn1. 5)yO4 lithium ion conductor thus allowing improving the capacity retention. The transport properties of LiMn1. 5Ni0. 5O4-δ thin film via PLD were measured. It is demonstrated that the oxygen stoichiometry is the main factor for controlling the electronic conductivity

La batterie lithium-ion est l’une des technologies de stockage de l’énergie les plus prometteuses pour permettre le développement des transports propres. Dans ce but il est cependant nécessaire de rechercher des matériaux d’électrode de batterie lithium-ion adaptés et qui satisfont différentes conditions de : (i) fortes capacités spécifique (Ah. Kg-1) et volumétrique (Ah. L-1); (ii) grande différence de potentiel entre les deux électrodes ; (iii) haute sécurité et respect de l’environnement. Ainsi, une transition du graphite au silicium de forte capacité et des composés à base de cobalt ou de fer au matériau à haut potentiel LiNi0. 5Mn1. 5O4 (LNMO) est examinée ici. Dans cette étude, nous avons identifié des formulations d’électrodes optimisées, premièrement pour un Si nanométrique avec de la carboxymethyl cellulose (CMC), de l’acide poly(acrylique-co-maléique) et du graphene à la négative ; deuxièmement pour un LNMO micrométrique avec du polyfluorure de vinylidène (PVdF) et des nanofibres de carbone (CNF) à la positive. Ces formulations possèdent de bonnes performances électrochimiques et ont des propriétés appropriées à leur mise en oeuvre sur des machines d’enduction industrielles. Pour atteindre ces buts, nous avons fait des investigations sur les encres d’électrode (comportement rhéologique, granulométrie, potentiel zéta, tests de sédimentation) et des caractérisations sur les électrodes (analyse de leur texture par MEBEDX, porosité, comportements mécanique, électrique, et électrochimique)
Rechargeable lithium-ion battery is one of the most promising energy storage technologies to enable a various range of clean transportations. To meet requirements of these automotive applications, it is necessary to find suitable electrode materials which satisfy several conditions: (i) high specific capacity (Ah. Kg-1) and volumetric capacity (Ah. L-1); (ii) high difference of potential between positive and negative electrodes; (iii) high safety and environmental standards. This way, a shift from graphite to much higher capacity siliconbased and from cobalt or iron-based to high voltage LiNi0. 5Mn1. 5O4 (LNMO) is examined here. This study successfully defined the optimized electrode formulations first with nanometric Si coupled with carboxymethyl cellulose (CMC), poly (acrylic-co-maleic) acid (PAMA) and graphene at the negative side; then for micrometric LNMO material coupled with polyvinylidene fluorine (PVdF) and carbon nanofibres (CNF) at the positive side. These formulations possess good electrochemical performance and satisfactory properties for processing on industrial coating machine. In order to achieve this purpose, characterization of electrode slurries (e. G. , rheological behaviour, particle size distribution, zeta potential measurements, settling tests) were investigated together with elaboration (e. G. , tape casting, calendaring, drying) and characterization of the electrodes (e. G. , texture analysis through SEM, EDX observations, measurements of porosity, mechanical, electrical and electrochemical behaviours)

This doctoral thesis deals with properties of cathode materials for Lithium-Ion accumulators. The theoretical part consists of an overview of the cathode materials and a brief introduction into the very wide area of Lithium-Ion accumulators. The goal of this work was to study the LiCoO2 cathode material and to prepare some modifications of it by doping with other elements. This work was then extended with the study of the new generation of high-voltage cathode materials. The aim of this part was to study their synthesis, their physical and electrochemical properties and the influence of used electrolytes on their electrochemical stability. The work then focuses on the influence of doping these materials and the influence of another part of the battery – the separator – on the overall properties of these types of cathode materials. The results show that doping the LiCoO2 cathode material with sodium and potassium lead to an enhancement of some electrochemical properties as stability during cycling or stability at higher loads and also the long-term stability during aging is better. The LiNi0,5Mn1,5O4 high voltage material was synthetized in both its forms in comparable or even better quality compared with the results from foreign laboratories. The synthesis process was watched in-situ by SEM, thanks to which a unique study of the ongoing changes during synthesis was done. Also the best suitable electrolytes for this material were identified from the viewpoint of stability at high voltages, which is important for the future practical use. Doping of the material with chromium resulted in better stability and capacity both during cycling at standard conditions and at higher temperature and load. A significant impact of the separators on the overall electrochemical properties of the cathode materials was proved, which could be a big benefit for their future usage.

This thesis in its first part deals especially with characteristic of lithium ion accumulators in terms of their structure, electrochemical properties and also features of the most commonly used cathode materials. Especial attention is given to the high-voltage cathode material LiNi0,5Mn1,5O4 which cell voltage is close to 5V. The second practical part deals with the preparation of cathode materials based on LiNi0,5Mn1,5O4 with different temperatures in the second stage of annealing and analyzing them in terms of structure and electrochemical properties using appropriate measuring methods.