The intercalation of solvated sodium ions into graphite from ether electrolytes was recently discovered to be a surprisingly reversible process. The mechanisms of this “cointercalation reaction” are poorly understood and commonly accepted design criteria for graphite intercalation electrodes do not seem to apply. The excellent reversibility despite the large volume expansion, the small polarization and the puzzling role of the solid electrolyte interphase (SEI) are particularly striking. Here, in situ electrochemical dilatometry, online electrochemical mass spectrometry (OEMS), a variety of other methods among scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) as well as theory to advance the understanding of this peculiar electrode reaction are used. The electrode periodically “breathes” by about 70–100% during cycling yet excellent reversibility is maintained. This is because the graphite particles exfoliate to crystalline platelets but do not delaminate. The speed at which the electrode breathes strongly depends on the state of discharge/charge. Below 0.5 V versus Na+/Na, the reaction behaves more pseudocapacitive than Faradaic. Despite the large volume changes, OEMS gas analysis shows that electrolyte decomposition is largely restricted to the first cycle only. Combined with TEM analysis and the electrochemical results, this suggests that the reaction is likely the first example of a SEI‐free graphite anode.

In order to understand the compound stability of binary alkali metal graphite intercalation compounds, the interplay between the binding energy and the structural deformation energy contributions is investigated.

The lack of description of van der Waals interactions in layered materials such as graphite and binary graphite intercalation compounds remains a main drawback of conventional density functional theory. Two fundamentally different approaches to overcome this issue are the employment of semiempirical dispersion correction scheme such as Grimme dispersion correction or nonlocal density functionals. We carefully compare these two approaches for the description of the geometric structure and the thermodynamic stability of pure graphite and Li-GICs at different lithium concentrations and stages. Based on the computed formation energies, we also evaluate the lithium-graphite intercalation potential. We find that PBE-D3(BJ) accurately reproduces the lattice parameters and the interlayer binding energy of graphite, although it underestimates the thermodynamic stability of stage-II Li-GICs mainly due to overbinding of carbon atoms in pure graphite. The nonlocal van der Waals functionals optB88-vdW, optB86b-vdW, and revPBE-vdW show a good agreement with experiments concerning stability of Li-GICs of different stages, although they overestimate the van der Waals interactions in graphite. The experimentally determined decreasing step-function behavior of Li-graphite intercalation potential can be qualitatively reproduced only by employing the revPBE van der Waals functional, whereas the other density functionals fail in the description.

growth reactions from continuing toward bulk metal chalcogenides by kinetic stabilization. [1] In most cases, phosphine ligands were used for this purpose, [2] sometimes being supported by additional organic substituents on the chalcogen atoms. [3] Ternary clusters have also been reported that include a second type of metal atoms, [4] which enables tuning of structural and physical features within the range of the respective binary compounds. [5] Diversity can be further enhanced by attachment of functional organic ligands to the metal atoms of the clusters for tailoring material properties for optoelectronics or solar cells. [6] Recently, our group has reported on the outstanding nonlinear optical properties of adamantane-type clusters with the general composition [(RT) 4 S 6 ] (R = organic substituent; T = Si, Ge, Sn). [7] We found that amorphous compounds with aromatic ligands transform infrared laser light into highly directional white light, while crystalline compounds or those with aliphatic ligands show strong second harmonic generation. Yet, the prerequisites for white-light generation are still under debate, and it is not clear whether the strong optical nonlinearities are an inherent molecular property or have their origin in the cluster habitus.To shed light onto this physical scenario, we combined the adamantane-type clusters with metal complexes. [8] This allowed In order to gain more information on the white-light generation by amorphous molecular materials, the influence of metal complex substituents on the photophysical properties of potential white-light emitters is investigated. Three compounds of the general type [{(R 3 P) 3 MSn}{PhSn} 3 S 6 )], with R/M = Me/Au (1), Et/Ag (4), and Me/Cu (5), are produced by reactions of the organotin sulfide cluster [(PhSn) 4 S 6 ] (A) with the corresponding coinage metal complexes [M(PR 3 ) 3 Cl]. Excess of the gold complex in the reaction leads to rearrangement and formation of [Au(PMe 3 ) 4 ][Au(PMe 3 ) 2 ][(PhSnCl) 3 S 4 ] (2). The use of PMe 3 instead of PEt 3 in the reaction with the silver salt causes decomposition and affords [(Me 3 P) 3 AgSnCl 3 ](3). All compounds are structurally characterized, and the necessity of sterically stabilizing PEt 3 groups at the silver complex in 4 are rationalized by density functional theory (DFT) calculations. Measurements of the photophysical properties of 1, 4, and 5 show that the introduction of the metallo-ligands indeed affects the materials properties, and at the same time confirm that the reduction of the molecular symmetry alone is not a sufficient condition for white-light generation (WLG), which still requires amorphicity of the compound. This is realized for 1 and 4 in situ, while reabsorption processes inhibit WLG in case of the copper compound 5.

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