Moreover, sulfide SEs in contact with an inactive component of conductive carbon additives are oxidatively decomposed at the entire range of operating voltages of Li [Ni,Mn,Co]O 2 , leading to the lowered initial Coulombic efficiency (ICE) and gradual capacity fading upon cycling. [49] Owing to the incompressible feature of SEs, electrochemomechanical effects on the performance are also critical for allsolid-state batteries. [37,50,51] Even slight volumetric strains of a few percentages in LiMO 2 during charge and discharge induces loosening and/or loss of interfacial ionic contacts. [18,37,38,52] Moreover, very recently, our group demonstrated that commercial-grade LiNi 0.80 Co 0.10 Mn 0.10 O 2 , consisting of randomly oriented grains, was susceptible to severe disintegration of the secondary particles even at the initial charge and discharge due to the anisotropic volumetric strains, which led to poor electrochemical performance of low ICE and degradation of cycling retention. [37] In this regard, recently emerging research directions for cathodes in advanced LIBs based on LEs, the development of cracking-free single-crystalline Ni-rich layered oxides, [30,[53][54][55][56][57][58] could be in the same vein for the development of practical ASLBs.The recent discovery of halide SEs (Li 3 YX 6 (X = Cl, Br)) with Li + conductivities of over 10 −4 S cm −1 has opened new opportunities due to their excellent electrochemical oxidation stability (>4 V vs Li/Li + ) and much better chemical stability (more oxygen-resistant and no H 2 S evolution), compared to sulfide SEs, as well as deformability. [59,60] By exploration of the Li 3 YX 6 analogs, highly Li + conductive halide SEs of Li 3 InCl 6 (1.5 mS cm −1 ), [61] Li 3 ErCl 6 (0.33 mS cm −1 ), [62] Li 3 ScCl 6 (3.0 mS cm −1 ), [63,64] and Li 3−x M 1−x Zr x Cl 6 (M = Y, Er, 1.4 mS cm −1 ), [65] Li 2+x Zr 1−x Fe x Cl 6 (max. ≈ 1 mS cm -1 ) [66] were identified. By employing these new halide SEs, uncoated LiCoO 2 electrodes showed good electrochemical performance, which was attributed to their high electrochemical oxidation stability. [65,66,67] To date, reports on the application of halide SE for Ni-rich layered oxides are scarce. [64,66] The aforementioned advances in understanding the failure modes of Ni-rich layered oxides in terms of electrochemical and electrochemo-mechanical stabilities, advanced Ni-rich layered oxides with electrochemo-mechanically compliant microstructures, and new halide SEs led us, herein, to the rigorous investigation of all-solid-state cells with variations in Ni-rich layered oxides (single-crystalline LiNi 0.88 Co 0.11 Al 0.01 O 2 (single-NCA) vs conventional polycrystalline LiNi 0.88 Co 0.11 Al 0.01 O 2 (poly-NCA)) and SEs (halide SE Li 3 YCl 6 (LYC) vs conventional sulfide SE Li 6 PS 5 Cl 0.5 Br 0.5 (LPSX)). Notably, several critical counteracting pros and cons of two sets of NCAs and SEs, summarized in Figure 1a, pose intriguing questions on the type of factors that are critical from the viewpoint of designing ASLBs. First, compared to poly-...

No abstract

The recent discovery of reversible plating and alloying of calcium has invoked considerable interest in calcium-based rechargeable batteries toward overcoming the limitations of conventional Li-ion batteries. However, only a few cathode materials have been tested thus far, and these exhibit low energy-storage capability and poor cyclability. Herein, the highly reversible Ca-intercalation capability of NASICON-type NaV2(PO4)3 makes it a potential cathode material for nonaqueous Ca-ion batteries, with high capacity and voltage and good cyclability (90 mA h g–1 and ∼3.4 V at 11.7 mA g–1 and 75 °C; 70 mA h g–1 and ∼3.2 V at 5.85 mA g–1 and 25 °C). Although this work shows only the capability of the cathode, not a full-cell performance, it does demonstrate experimentally that a poly-oxyanionic material can provide an outstanding host structure for Ca diffusion at room temperature with high energy-storage capability.

In this study, we developed a doping technology capable of improving the electrochemical performance, including the rate capability and cycling stability, of P2-type Na 0.67 Fe 0.5 Mn 0.5 O 2 as a cathode material for sodium-ion batteries. Our approach involved using titanium as a doping element to partly substitute either Fe or Mn in Na 0.67 Fe 0.5 Mn 0.5 O 2 . The Ti-substituted Na 0.67 Fe 0.5 Mn 0.5 O 2 shows superior electrochemical properties compared to the pristine sample. We investigated the changes in the crystal structure, surface chemistry, and particle morphology caused by Ti doping and correlated these changes to the improved performance. The enhanced rate capability and cycling stability were attributed to the enlargement of the NaO 2 slab in the crystal structure because of Ti doping. This promoted Na-ion diffusion and prevented the phase transition from the P2 to the OP4/″Z″ structure.

Magnesium batteries have received attention as a type of post-lithium-ion battery because of their potential advantages in cost and capacity. Among the host candidates for magnesium batteries, orthorhombic α-VO is one of the most studied materials, and it shows a reversible magnesium intercalation with a high capacity especially in a wet organic electrolyte. Studies by several groups during the last two decades have demonstrated that water plays some important roles in getting higher capacity. Very recently, proton intercalation was evidenced mainly using nuclear resonance spectroscopy. Nonetheless, the chemical species inserted into the host structure during the reduction reaction are still unclear (i.e., Mg(HO), Mg(solvent, HO), H, HO, HO, or any combination of these). To characterize the intercalated phase, the crystal structure of the magnesium-inserted phase of α-VO, electrochemically reduced in 0.5 M Mg(ClO) + 2.0 M HO in acetonitrile, was solved for the first time by the ab initio method using powder synchrotron X-ray diffraction data. The structure was tripled along the b-axis from that of the pristine VO structure. No appreciable densities of elements were observed other than vanadium and oxygen atoms in the electron density maps, suggesting that the inserted species have very low occupancies in the three large cavity sites of the structure. Examination of the interatomic distances around the cavity sites suggested that HO, HO, or solvated magnesium ions are too big for the cavities, leading us to confirm that the intercalated species are single Mg ions or protons. The general formula of magnesium-inserted VO is MgHVO, (0.66 ≤ x ≤ 1.16). Finally, density functional theory calculations were carried out to locate the most plausible atomic sites of the magnesium and protons, enabling us to complete the structure modeling. This work provides an explicit answer to the question about Mg intercalation into α-VO.