All-solid-state batteries (ASSBs) that rely on the use of solid electrolytes (SEs) with high ionic conductivity are the holy grail for future battery technology, since it could enable both greater energy density and safety. However, practical application of ASSBs is still being plagued by difficulties in mastering the SE–electrode interphases. This calls for a wide exploration of electrolyte candidates, among which halide-based Li+ conductors show promise despite being not stable against Li or Li x In y negative electrodes, hence the need to assemble cells with a dual SE design. In the work described herein, we studied the electrochemical/chemical compatibility of Li3InCl6 against layered oxide positive electrode (LiNi0.6Mn0.2Co0.2O2, NMC622), carbon additive, and Li6PS5Cl under both cycling and aging conditions. Combining electroanalytical and spectroscopic techniques, we provide evidence for the onset of electrochemically driven parasitic decomposition reactions between Li3InCl6 and NMC622/carbon at lower potentials (3.3 V vs LiIn/In) than theoretically predicted in the literature. Moreover, to combat chemical incompatibility between dual SEs, we propose a new strategy that consists of depositing a nanometer-thick (1 or 2 nm) surface protective layer of Li3PO4 made by atomic layer deposition between Li3InCl6 and Li6PS5Cl. Through this surface engineering process with highly conformal and pinhole-free thin films, halide-based solid-state cells showing spectacular capacity retention over 400 cycles were successfully assembled. Altogether, these findings position halide SEs as serious contenders for the development of ASSBs.
Li-ion batteries are the key stones of electric vehicles, but with the emergence of solid-state Li batteries for improving autonomy and fast charging, the need for mastering the solid electrolyte (SE)/electrode material interfaces is crucial. All-solid-state-batteries (ASSBs) suffer from long-term capacity fading with enhanced decomposition reactions. So far, these reactions have not been extensively studied in Li6PS5Cl-based systems because of the complexity of overlapping degradation mechanisms. Herein, those reactions are studied in depth. We investigated their effects under various operating conditions (temperature, C-rate, voltage window), types of active materials, and with or without carbon additives. From combined resistance monitoring and impedance spectroscopy measurements, we could decouple two reactions (NMC/SE and VGCF/SE) with an inflection dependent on the cutoff potential (3.6 or 3.9 V vs Li-In/In are studied) on charge and elucidate their distinct repercussions on cycling performances. The pernicious effect of carbon additives on both the first cycle and power performances is disclosed, so as its long-term effect on capacity retention. As a mean to resolve these issues, we scrutinized the benefits of a coating layer around NMC particles to prevent high potential interactions, minimize the drastic loss of capacity observed with bare NMC, and simply propose to get rid of carbon additives. Altogether, we hope these findings provide insights and novel methodologies for designing innovative performing solid-state batteries.
Composites made of high-capacity and highpotential LiNi x Mn y Co 1−x−y O 2 (NMC) lamellar transition-metal oxides and S-based ionic conductors are primarily used as positive electrodes in all-solid-state batteries (ASSBs). However, NMC coatings are necessary to prevent the chemical reactivity of oxygen and sulfur at the expense of some penalty in capacity and in ionic conduction. To overcome these problems, the current trend is to move to S-based positive electrodes, which exhibit higher electronic and ionic conductivities and no S−O reactivity. Herein we succeed in preparing highly divided O3-Li x TiS 2 powders by ball milling, which can be used as a positive electrode free of the electrochemically dead solid electrolyte (SE) in ASSBs that shows energy densities of more than 350 Wh/kg and stable cycling under low pressures down to 1 bar. These enhanced performances were rationalized by 7 Li NMR measurements that revealed a decrease in the site-to-site activation energy barrier with increasing ballmilling time. This finding, based on diffusion considerations associated with particle size reduction, can be generalized to other 3D metal sulfides and provides insights on the benefits of using a SE-free and C-free design relying on highly divided Li-containing sulfides to boost energy densities in ASSBs. KEYWORDS: all-solid-state lithium batteries, lithiated titanium disulfide, O3-Li x TiS 2 , low pressure, SE-free cathode, chalcogenides
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