The solid lithium-ion electrolyte ''Li 7 La 3 Zr 2 O 12 '' (LLZO) with a garnet-type structure has been prepared in the cubic and tetragonal modification following conventional ceramic syntheses routes. Without aluminium doping tetragonal LLZO was obtained, which shows a two orders of magnitude lower room temperature conductivity than the cubic modification. Small concentrations of Al in the order of 1 wt% were sufficient to stabilize the cubic phase, which is known as a fast lithium-ion conductor. The structure and ion dynamics of Al-doped cubic LLZO were studied by impedance spectroscopy, dc conductivity measurements, 6 Li and 7 Li NMR, XRD, neutron powder diffraction, and TEM precession electron diffraction. From the results we conclude that aluminium is incorporated in the garnet lattice on the tetrahedral 24d Li site, thus stabilizing the cubic LLZO modification. Simulations based on diffraction data show that even at the low temperature of 4 K the Li ions are blurred over various crystallographic sites. This strong Li ion disorder in cubic Al-stabilized LLZO contributes to the high conductivity observed. The Li jump rates and the activation energy probed by NMR are in very good agreement with the transport parameters obtained from electrical conductivity measurements. The activation energy E a characterizing longrange ion transport in the Al-stabilized cubic LLZO amounts to 0.34 eV. Total electric conductivities determined by ac impedance and a four point dc technique also agree very well and range from 1 Â 10 À4 Scm À1 to 4 Â 10 À4 Scm À1 depending on the Al content of the samples. The room temperature conductivity of Al-free tetragonal LLZO is about two orders of magnitude lower (2 Â 10 À6 Scm À1 , E a = 0.49 eV activation energy). The electronic partial conductivity of cubic LLZO was measured using the Hebb-Wagner polarization technique. The electronic transference number t eÀ is of the order of 10 À7. Thus, cubic LLZO is an almost exclusive lithium ion conductor at ambient temperature.

Piezoelectric actuators convert electrical into mechanical energy and are implemented for many large-scale applications such as piezoinjectors and ink jet printers. The performance of these devices is governed by the electric-field-induced strain. Here, the authors describe the development of a class of lead-free (0.94−x)Bi0.5Na0.5TiO3–0.06BaTiO3–xK0.5Na0.5NbO3 ceramics. These can deliver a giant strain (0.45%) under both unipolar and bipolar field loadings, which is even higher than the strain obtained with established ferroelectric Pb(Zr,Ti)O3 ceramics and is comparable to strains obtained in Pb-based antiferroelectrics.

Available online xxx a b s t r a c tThis overview addresses the atomistic aspects of degradation of layered LiMO 2 oxide Li-ion cell cathode materials, aiming to shed light on the fundamental degradation mechanisms especially inside active cathode materials and at their interfaces. It includes recent results obtained by novel in situ/in operando diffraction methods, modelling, and quasi in situ surface science analysis. Degradation of the active cathode material occurs upon overcharge, resulting from a positive potential shift of the anode. Oxygen loss and eventual phase transformation resulting in dead regions are ascribed to changes in electronic structure and defect formation. The anode potential shift results from loss of free lithium due to side reactions occurring at electrode/electrolyte interfaces. Such side reactions are caused by electron transfer, and depend on the electron energy level alignment at the interface. Side reactions at electrode/electrolyte interfaces and capacity fade may be overcome by the use of suitable solid-state electrolytes and Licontaining anodes.

costs are required. Current state-of-theart LIBs using, e.g., well-established LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111) cathode material are yet not able to fulfill all these demands. In order to increase the energy density of LIBs, battery produ cers and researchers pursue various strategies. Substitution of expensive Co by Ni to achieve LiNi 1−x−y Co x Mn y O 2 compounds with x < 0.3 in order to increase the structural stability at high state-of-charge (SOC) is one possible approach. Another promising material class is represented by Li-rich high-energy NCM (HE-NCM) materials (cLi 2 MnO 3 ⋅[1 − c]LiTMO 2 [TM = Ni, Co, Mn, etc.]). All of these subgroups of layered oxides have in common a crystal structure that is prone to irreversible changes and fatigue during continuous Li (de-)intercalation. The relevant changes in electronic and crystal structure strongly depend on the particular cathode composition and micro/nanostructure. The development of a target-oriented roadmap to improved LIBs that meet the above requirements must address the underlying mechanisms on different cell levels, i.e., from the atomic level to the electrode level. A comprehensive summary of the properties and developments in the field of Ni-rich NCM [1][2][3][4][5][6][7][8][9] and Li-rich HE-NCM [10][11][12][13][14][15][16] has been presented recently In order to satisfy the energy demands of the electromobility market, both Ni-rich and Li-rich layered oxides of NCM type are receiving much attention as high-energy-density cathode materials for application in Li-ion batteries. However, due to different stability issues, their longevity is limited. During formation and continuous cycling, especially the electronic and crystal structure suffers from various changes, eventually leading to fatigue and mechanical degradation. In recent years, comprehensive battery research has been conducted at Karlsruhe Institute of Technology, mainly aiming at better understanding the primary degradation processes occurring in these layered transition metal oxides. The characteristic process of formation and mechanisms of fatigue are fundamentally characterized and the effect of chemical composition on cell chemistry, electrochemistry, and cycling stability is addressed on different length scales by use of state-of-the-art analytical techniques, ranging from "standard" characterization tools to combinations of advanced in situ and operando methods. Here, the results are presented and discussed within a broader scientific context. by several authors. Here, we focus on the detailed characterization of these materials on different length scales, including the processes during formation and fatigue.After a brief introduction of the different materials addressed here, their characteristic process of formation and mechanisms of fatigue are discussed with respect to cell chemistry, electrochemistry, and cycling stability. Based on the fundamental results of our experimental studies on the material level, the effect of formation and fatigue on different cell levels is evalu...

The thermodynamic stability of Li 2 MnSiO 4 polymorphs and their electrochemical properties as electrode for Li batteries are investigated combining experimental and computational methods. Three possible Li 2 MnSiO 4 forms have been considered crystallizing in Pmnb, Pmn2 1 (β-Li 3 PO 4 derivatives) and P2 1 /n (γ-Li 3 PO 4 derivative) space groups (S.G.). We have first demonstrated that the relative stability of βand γ-Li 3 PO 4 polymorphs is well-reproduced by density functional theory (DFT) methods (LDA, GGA). For Li 2 MnSiO 4 , the Pmnb form is predicted to be 2.4 meV/f.u. and 65 meV/f.u. more stable than the Pmn2 1 and P2 1 /n forms, respectively (GGA + U results). Computational results indicate that the denser Pmn2 1 polymorph can be obtained by high pressure/high temperature treatment of the other polymorphs or their mixtures. A sample of Li 2 MnSiO 4 prepared at 900 °C consists of a mixture of polymorphs, as detected by XRD and confirmed by means of SAED and 6 Li MAS-NMR. As expected from DFT results, exposing the as-prepared Li 2 MnSiO 4 sample to high pressure/high temperature (pressure range 2-8 GPa, temperature range 600-900°C) allows to isolate the Pmn2 1 polymorph. The crystal structure has a minor impact in the average lithium intercalation voltage for the two electron process (GGA+U calculated voltages are 4.18, 4.19,and 4.08 V for Pmnb, Pmn2 1 and P2 1 /n, respectively). Major structural rearrangements are expected under lithium deinsertion from the P2 1 /n polymorph, as previously found for the β-Li 3 PO 4 derivatives, rendering any MnSiO 4 delithiated hosts prompt to transform into a more stable structure or a mixture of them.

In situ synchrotron diffraction revealed a stepwise appearance of two new phases upon electrochemical lithium extraction from LiCoPO 4 . These phases were demonstrated to have the same olivine-like structure as the pristine compound. The lithium-deficient phases were proposed to be Li 0.7 CoPO 4 and CoPO 4 . The completely delithiated phase appears to be unstable in air and undergoes amorphization. The phase transitions are reversible, but a slow kinetics of the initial delithiation was identified by in situ synchrotron diffraction and the potentiostatic intermittent titration technique. We demonstrated that the electrochemical extraction of lithium is accompanied by significant electrolyte decomposition, contributing to the capacity loss upon cycling. The galvanostatic intermittent titration technique combined with impedance spectroscopy revealed self-discharge of the cell in the charged state. This study argues different mechanisms of lithium extraction from LiCoPO 4 in comparison with LiFePO 4 and LiMnPO 4 .

Sodium-ion batteries operating at ambient temperature hold great promise for use in grid energy storage owing to their significant cost advantages. However, challenges remain in the development of suitable electrode materials to enable long lifespan and high rate capability. Here we report a sodium super-ionic conductor structured electrode, sodium vanadium titanium phosphate, which delivers a high specific capacity of 147 mA h g−1 at a rate of 0.1 C and excellent capacity retentions at high rates. A symmetric sodium-ion full cell demonstrates a superior rate capability with a specific capacity of about 49 mA h g−1 at 20 C rate and ultralong lifetime over 10,000 cycles. Furthermore, in situ synchrotron diffraction and X-ray absorption spectroscopy measurement are carried out to unravel the underlying sodium storage mechanism and charge compensation behaviour. Our results suggest the potential application of symmetric batteries for electrochemical energy storage given the superior rate capability and long cycle life.

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