Degradation of Li S battery electrodes on 3D current collectors studied using x ray phase contrast tomography

Lithium sulphur batteries are promising candidates for future energy storage systems, mainly due to their high potential capacity. However low sulphur utilization and capacity fading hinder practical realizations. In order to improve understanding of the system, we investigate Li S electrode morphology changes for different ageing steps, using X ray phase contrast tomography. Thereby we find a strong decrease of sulphur loading after the first cycle, and a constant loading of about 15 of the initial loading afterwards. While cycling, the mean sulphur particle diameters decrease in a qualitatively similar fashion as the discharge capacity fades. The particles spread, migrate into the current collector and accumulate in the upper part again. Simultaneously sulphur particles lose contact area with the conducting network but regain it after ten cycles because their decreasing size results in higher surface areas. Since the capacity still decreases, this regain could be associated with effects such as surface area passivation and increasing charge transfer resistanc

A Biomass-Based Integral Approach Enables Li-S Full Pouch Cells with Exceptional Power Density and Energy Density

Lithium-sulfur (Li-S) batteries, as part of the post-lithium-ion batteries (post-LIBs), are expected to deliver significantly higher energy densities. Their power densities, however, are today considerably worse than that of the LIBs, limiting the Li-S batteries to very few specific applications that need low power and long working time. With the rapid development of single cell components (cathode, anode, or electrolyte) in the last few years, it is expected that an integrated approach can maximize the power density without compromising the energy density in a Li-S full cell. Here, this goal is achieved by using a novel biomass porous carbon matrix (PCM) in the anode, as well as N-Co9S8 nanoparticles and carbon nanotubes (CNTs) in the cathode. The authors' approach unlocks the potential of the electrodes and enables the Li-S full pouch cells with unprecedented power densities and energy densities (325 Wh kg−1 and 1412 W kg−1, respectively). This work addresses the problem of low power densities in the current Li-S technology, thus making the Li-S batteries a strong candidate in more application scenarios

Influence of the binder and preparation process on the positive electrode electrochemical response and Li/S system performances

International audienceIn this study, the effect of the binder (PVdF and CMC/NBR) and the preparation process of sulfur electrode ink/slurry on electrochemical performance and cycling behaviour of Li/S cells was investigated. Well-dispersed and homogeneous slurries obtained using high-energy mechanical dispersion (Dispermat®) permit to decrease the impedance response of the electrodes and thus to improve the cycling performances at high C-rates. The main effect of CMC/NBR binder was mostly related to electrode adhesion properties, resulting in better cycle life. A detailed analysis of EIS data gives us an insight into electrode impedance response and their variation depending on the electrode fabrication process and nature/type of a binder

Non-woven carbon paper as current collector for Li-ion/Li2S system: Understanding of the first charge mechanism

International audienceThe use of porous 3D current collectors, especially carbon-based ones, has already been demonstrated as a concept of choice as alternative to standard 2D aluminium foil in sulfur positive electrodes. In this study, we investigated non-woven carbon (NwC) as a 3D current collector for Li2S positive electrodes. Improved charge and discharge capacities, and capacity retention were obtained, as compared with electrodes containing Al-foil current collector. However, irrespective of the current collector used, the initial charge presents a particular and weakly reproducible voltage shape. By applying GITT and XRD measurements an electrochemical mechanism was proposed to explain the initial charge profile, in terms of equilibrium potential and polarization phenomenon. During the 1st charge, competitive oxidation reactions can be evoked involving both Li2S and long polysulfide intermediates (Li2Sn), in the main part of the charge process. While the oxidation of Li2S is thermodynamically favorable over the oxidation of Li2Sn, the kinetics of the latter is much more rapid

Functionalized carbon nanotubes fir Lithium-Sulphur and Lithium-Organic batteries

International audienceLithium batteries are among the most promising systems for electrochemical energy storage. However, their capacity and cost-efficiency have to be improved for further applications, for instance in electric vehicles. Lithium/organic and lithium/sulfur batteries offer an interesting alternative to the classical Li-ion systems due to their high theoretical specific capacity and potential low cost. However, two major roadblocks currently prevent industrial development of these kind batteries: (i) the progressive dissolution of active material in the electrolyte, which hinders cyclability of the devices and; (ii) the electrical insulating nature of organic or sulfur materials. Here, we develop a new positive electrode material avoiding the dissolution of the active material in the electrolyte upon cycling, by grafting new diazonium derivatives containing active disulfide groups onto multi-walled carbon nanotubes (MWNTs). The MWNTs insure a well distributed electronic conductivity inside the positive electrode and serve as a support for a covalent immobilization of the thiolated active species. Compared to electrodes formed by simply mixing carbon nanotubes with thiol-containing molecules, covalently functionalized MWNT materials present an excellent stability over prolonged cycling and a promising specific capacity, in the range of 100 mAh·g$_{electrode}^{-1}$ , i.e. including carbon and current collector masses

Investigation of non-woven carbon paper as a current collector for sulfur positive electrode—Understanding of the mechanism and potential applications for Li/S batteries

International audiencePorous 3-D current collectors have been shown to be the primary choice in replacing classical 2D aluminum foil in applicable developments, especially those using carbon-based current collectors. In this study, we investigated the impact of using a non-woven carbon (NWC) based current collector for sulfur electrodes, in terms of performance and practical use in a commercial battery, keeping in mind the simplicity of electrode preparation method. The benefits of using NWC as a 3D current collector include high sulfur utilization for even highly loaded electrodes, lower polarization, and the provision of an efficient electrolyte reservoir. High discharge capacities up to ∼1200 mAh g−1 can be obtained at moderate C-rates, with relatively good capacity retention (<1% loss per cycle) and practical loadings as high as 8 mAh cm−2