The cover picture shows the sweet-water snail Biomphalaria glabrata. Its shell consists of calcium carbonate in the aragonite modification (see the packing plot, upper left). The composition of the shell in embroynic and adults snails was studied with high-end solid state chemical methods, that is synchrotron powder diffractometry (EXAFS, upper right). The delicate structure of the shell and the extraordinary hardness compared with ªsimpleº calcium carbonate is due to the biological control of the crystallization process. If calcium carbonate is crystallized in the laboratory, usually the calcite modification (lower right) is obtained. This work is described in more detail by M. Epple et al. on p. 3679 ff.

Ni-rich layered oxides are one of the most attractive cathode materials in high-energy-density lithium-ion batteries, their degradation mechanisms are still not completely elucidated. Herein, we report a strong dependence of degradation pathways on the long-range cationic disordering of Co-free Ni-rich Li 1À m -(Ni 0.94 Al 0.06 ) 1 + m O 2 (NA). Interestingly, a disordered layered phase with lattice mismatch can be easily formed in the near-surface region of NA particles with very low cation disorder (NA-LCD, m � 0.06) over electrochemical cycling, while the layered structure is basically maintained in the core of particles forming a "coreshell" structure. Such surface reconstruction triggers a rapid capacity decay during the first 100 cycles between 2.7 and 4.3 V at 1 C or 3 C. On the contrary, the local lattice distortions are gradually accumulated throughout the whole NA particles with higher degrees of cation disorder (NA-HCD, 0.06 � m � 0.15) that lead to a slow capacity decay upon cycling.

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Herein, an eco‐friendly and high safety aqueous Mg‐ion electrolyte (AME) with a wide electrochemical stability window (ESW) ≈3.7 V, containing polyethylene glycol (PEG) and low‐concentration salt (0.8 m Mg(TFSI)2), is proposed by solvation structure reorganization of AME. The PEG agent significantly alters the Mg2+ solvation and hydrogen bonds network of AMEs and forms the direct coordination of Mg2+ and TFSI‐, thus enhancing the physicochemical and electrochemical properties of electrolytes. As an exemplary material, V2O5 nanowires are tested in this new AME and exhibit initial high discharge/charge capacity of 359/326 mAh g‐1 and high capacity retention of 80% after 100 cycles. The high crystalline α‐V2O5 shows two 2‐phase transition processes with the formation of ε‐Mg0.6V2O5 and Mg‐rich MgxV2O5 (x ≈1.0) during the first discharge. Mg‐rich MgxV2O5 (x ≈1.0) phase formed through electrochemical Mg‐ion intercalation at room temperature is for the first time observed via XRD. Meanwhile, the cathode electrolyte interphase (CEI) in aqueous Mg‐ion batteries is revealed for the first time. MgF2 originating from the decomposition of TFSI‐ is identified as the dominant component. This work offers a new approach for designing high‐safety, low‐cost, eco‐friendly, and large ESW electrolytes for practical and novel aqueous multivalent batteries.

electric vehicles (HEVs), next-generation lithium-ion batteries (LIBs) that utilize high-energy cathode materials are crucially needed. [1][2][3] Among various types of cathode materials, Li-and Mn-rich layered oxides (LMLOs) are regarded as one of the most promising cathode candidates owing to their high capacity (≥250 mAh g −1 ) and low cost. [4][5][6][7] The high capacity of LMLOs is widely believed to originate predominantly from the reversible cationic and anionic redox activities, [8][9][10] which remarkably overcome the capacity limitations of conventional cathode materials (<200 mAh g −1 ) like olivine LiFePO 4 (space group: Pnma), [11,12] spinel LiMn 2 O 4 (Fd3m), [13,14] and layered Li[Ni,Co,Mn]O 2 (NCM, square brackets represent transition metal ions located on octahedral positions, R3m) [15][16][17][18] because of the sole transition metal (TM) redox activity in these cathodes. Nevertheless, LMLOs always undergo a severe voltage decay upon cycling, [19,20] which seriously hinders the practical application of LMLOs. Over the last two decades, a series of attempts have been made to reveal the underlying structural degradation mechanism and mitigate the voltage decay during extended cycling.Lithium-and manganese-rich layered oxides (LMLOs, ≥ 250 mAh g −1 ) with polycrystalline morphology always suffer from severe voltage decay upon cycling because of the anisotropic lattice strain and oxygen release induced chemo-mechanical breakdown. Herein, a Co-free single-crystalline LMLO, that is, Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 (LLNMO-SC), is prepared via a Li + /Na + ionexchange reaction. In situ synchrotron-based X-ray diffraction (sXRD) results demonstrate that relatively small changes in lattice parameters and reduced average micro-strain are observed in LLNMO-SC compared to its polycrystalline counterpart (LLNMO-PC) during the charge-discharge process. Specifically, the as-synthesized LLNMO-SC exhibits a unit cell volume change as low as 1.1% during electrochemical cycling. Such low strain characteristics ensure a stable framework for Li-ion insertion/extraction, which considerably enhances the structural stability of LLNMO during long-term cycling. Due to these peculiar benefits, the average discharge voltage of LLNMO-SC decreases by only ≈0.2 V after 100 cycles at 28 mA g −1 between 2.0 and 4.8 V, which is much lower than that of LLNMO-PC (≈0.5 V). Such a single-crystalline strategy offers a promising solution to constructing stable high-energy lithium-ion batteries (LIBs).

One of the major challenges facing the application of layered LiNiO 2 (LNO) cathode materials is the oxygen release upon electrochemical cycling. Here it is shown that tailoring the provided lithium content during synthesis process can create a disordered layered Li 1-x Ni 1+x O 2 phase at the primary particle surface. The disordered surface, which serves as a self-protective layer to alleviate the oxygen loss, possesses the same layered rhombohedral structure (R3m) as the inner core of primary particles of the Li 1-x Ni 1+x O 2 (x ≈ 0). With advanced synchrotron-based x-ray 3D imaging and spectroscopic techniques, a macroporous architecture within the agglomerates of LNO with ordered surface (LNO-OS) is revealed after only 40 cycles, concomitant with the reduction of nickel on the primary particle surface throughout the whole secondary particles. Such chemomechanical degradation accelerates the deterioration of LNO-OS cathodes. Comparably, there are only slight changes in the nickel valence state and interior architecture of LNO with a thin disordered surface layer (LNO-DS) after cycling, mainly arising from an improved robustness of the oxygen framework on the surface. More importantly, the disordered surface can suppress the detrimental H2 ⇋ H3 phase transition upon cycling compared to the ordered one.

Previous investigations on porous NCM particles with shortened diffusion paths and an enlarged interface between active material and electrolyte showed improved rate capability and cycle stability compared to compact particles. Due to the additional intragranular porosity of the active material, the pore structure of the overall electrode, and, as consequence, the ionic transport in the pore phase, is altered. In addition, the particle morphology influences the ohmic contact resistance between the current collector and electrode film. These effects are investigated using impedance spectroscopy in symmetrical cells under blocking conditions. The ionic resistance and the tortuosity of the electrodes are determined and analyzed by a transmission line model. Tortuosity is higher for porous particles and increases more during calendering. This limits the options for densifying these electrodes to the same level as with compact particles. In a further approach, the method is used to explain the drying related performance differences of these electrodes. At higher drying rates, the contact and the ionic resistance of electrodes with compact particles increases more strongly as for electrodes with porous particles. These investigations provide new insights into the ion transport behavior and enable a better understanding of the impact of the electrode processing condition.

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