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Organisationseinheit der BAM
Porous carbons are promising anode materials for next generation lithium batteries due to their large lithium storage capacities. However, their highsloping capacity during lithiation and delithiation as well as capacity fading due to intense formation of solid electrolyte interphase (SEI) limit their gravimetric and volumetric energy densities. Herein we compare a microporous carbide-derived carbon material (MPC) as promising future anode for all solid-state batteries with a commercial high-performance hard carbon anode. The MPC obtains high and reversible lithiation capacities of 1000 mAh g−1carbon in half-cells exhibiting an extended plateau region near 0 V vs. Li/Li+ preferable for full-cell application. The well-defined microporosity of the MPC with a specific surface area of >1500 m2 g−1 combines well with the argyrodite-type electrolyte (Li6PS5Cl) suppressing extensive SEI formation to deliver high coulombic efficiencies. Preliminary full-cell measurements vs. nickel-rich NMC-cathodes (LiNi0.9Co0.05Mn0.05O2) provide a considerably improved average potential of 3.76 V leading to a projected energy density as high as 449 Wh kg−1 and reversible cycling for more than 60 cycles. 7Li Nuclear Magnetic Resonance spectroscopy was combined with ex-situ Small Angle X-ray Scattering to elucidate the storage mechanism of lithium inside the carbon matrix. The formation of extended quasi-metallic lithium clusters after electrochemical lithiation was revealed.
Hard carbon is the material of choice for sodium ion battery anodes. Capacities comparable to those of lithium/graphite can be reached, but the understanding of the underlying sodium storage mechanisms remains fragmentary. A two‐step process is commonly observed, where sodium first adsorbs to polar sites of the carbon (“sloping region”) and subsequently fills small voids in the material (“plateau region”). To study the impact of nitrogen functionalities and pore geometry on sodium storage, a systematic series of nitrogen‐doped hard carbons is synthesized. The nitrogen content is found to contribute to sloping capacity by binding sodium ions at edges and defects, whereas higher plateau capacities are found for materials with less nitrogen content and more extensive graphene layers, suggesting the formation of 2D sodium structures stabilized by graphene‐like pore walls. In fact, up to 84% of the plateau capacity is measured at potentials less than 0 V versus metallic Na, that is, quasimetallic sodium can be stabilized in such structure motifs. Finally, gas physisorption measurements are related to charge discharge data to identify the energy storage relevant pore architectures. Interestingly, these are pores inaccessible to probe gases and electrolytes, suggesting a new view on such “closed pores” required for efficient sodium storage.
Cadmium benzylphosphonate Cd(O3PBn)·H2O and its fluorinated derivates Cd(O3PBn-3F)·H2O, Cd(O3PBn-4F)·H2O, and Cd(O3PBn-F5)·H2O were synthesized mechanochemically. The Crystal structures of the compounds were determined based on powder X-ray diffraction (PXRD) data. The influence of the ligand substitution on the crystal structure of the metal phosphonate was determined. The hydrophobicity as a function of degree of fluorination was investigated using dynamic vapor sorption.