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In this paper, we report on a novel RbVPO4F fluoride phosphate, which adopts the KTiOPO4 (KTP) type structure and complements the AVPO4F (A = alkali metal) family of positive electrode (cathode) materials for metal-ion batteries. RbVPO4F was synthesized via a freeze-drying assisted solid-state route and characterized via structural, computational and electrochemical methods. RbVPO4F represents the first example of reversible electrochemical Rb+ de/insertion in a crystalline oxypolyanionic framework. The electrochemical measurements on RbVPO4F in a three-electrode cell configuration in RbClO4-saturated propylene carbonate (PC) electrolyte revealed that the material exhibits reversible Rb+ de/insertion within the 0.4–1.3 V vs. Ag+/Ag potential range (∼3.9–4.8 V vs. K+/K) displaying rather high diffusion coefficients of (0.3–1.0) × 10−11 cm2 s−1 comparable to those of K+ in KVPO4F that supports reasonably fast ionic mobility in the KTP structure despite the large ionic radius of the Rb+ ions. The energy barriers of Rb+ ion transport are exceptionally low not exceeding 0.2 eV along the c-axis and correlating well with diffusion coefficients estimated using the DFT+U-NEB methodology and with the experimentally determined transport properties. These results suggest a new paradigm for the development of materials that support many monovalent ion reversible de/insertion processes in a single prototypical structural oxypolyanionic framework.

In this work, we provide a structural and computational investigation of the Li2CoPO4F high-voltage cathode material by means of neutron powder diffraction (SG Pnma, a = 10.4528(2) A, b = 6.38667(10) A, c = 10.8764(2) A, RF = 0.0145), crystal chemistry approaches (Voronoi–Dirichlet partitioning and bond valence sums mapping), and density functional theory. The material reveals low energy barriers (0.12–0.43 eV) of Li hopping and a possible 3D channel system for Li-ion migration. It is found that only one Li per formula unit can be extracted within the potential stability window of the commercially available electrolytes. The interrelation between dimensionality, topology and energetics of Li-ion diffusion and peculiarities of the Li2CoPO4F crystal structure are discussed in detail.

Composite electrode materials based on LiFeBO3 are synthesized under different conditions and studied as the cathodic materials for lithiumion batteries. Composites with different degrees of iron oxidation are synthesized by annealing in a closed system with the use of metal-oxide getters. Based on the results of cyclic voltammetry and galvanostatic cycling of samples with different Fe(II) contents, it is concluded that the surface composition is the determining factor for applicability of materials to reversible processes of inter-calation-deintercalation.

The crystal structures of various mixed Li and transition metal fluoride phosphates are reviewed, with a special focus on their applicability as cathode materials for Li-ion batteries., To satisfy the needs of rapidly growing applications, Li-ion batteries require further significant improvements of their key properties: specific energy and power, cyclability, safety and costs. The first generation of cathode materials for Li-ion batteries based on mixed oxides with either spinel or rock-salt derivatives has already been widely commercialized, but the potential to improve the performance of these materials further is almost exhausted. Li and transition metal inorganic compounds containing different polyanions are now considered as the most promising cathode materials for the next generation of Li-ion batteries. Further advances in cathode materials are considered to lie in combining different anions [such as (XO4)n− and F−] in the anion sublattice, which is expected to enhance the specific energy and power of these materials. This review focuses on recent advances related to the new class of cathode materials for Li-ion batteries containing phosphate and fluoride anions. Special attention is given to their crystal structures and the relationships between structure and properties, which are important for their possible practical applications.

A new model of lithium-ion transport processes in the LiFePO 4 electrode is proposed. This model takes into account the phase transition LiFePO 4 ↔ FePO 4 accompanying reversible lithium intercalation into the electrode during potential or current steps. The diffusion coefficient of Li + ion and its dependence on the LiFePO 4 /FePO 4 phase ratio have been determined by means of processing of experimental potential and current transients in accordance with the model's equations. The results of galvanostatic and potentiostatic intermittent titration techniques are in good agreement. The value of diffusion coefficient varies within 10 −10 –10 −16 cm 2 s −1 depending on the lithium content in solid solution Li X FePO 4 and Li 1− X FePO 4 ( X 4 /FePO 4 phase ratio.

L batteries originally developed for portable devices can now be found in applications as diverse as power tools, electric vehicles, and stationary energy storage. To satisfy the need of current and new applications, Li-ion batteries require further improvement in terms of performance properties (energy and power density, safety, and cost). Transition metal compounds containing different polyanion units (XO4) m− (X = P, S, Si) are considered as the most promising cathode materials for the next generation of Li-ion batteries due to increased redox potential caused by an inductive effect and remarkable electrochemical and thermal stability ascribed to a three-dimensional structure. Further advances in the polyanion cathodes are related to combining (XO4) m− and F− in the anion sublattice, which is expected to enhance the operating voltage due to the higher ionicity of the M−F bond. Indeed, various fluorophosphates (LiVPO4F, Na2FePO4F) and fluorosulphates (LiMSO4F) have been reported to exhibit attractive electrochemical performance. Among fluorophosphates, compounds of the general formula A2MPO4F (A = Na, Li; M = Fe, Mn, Co, Ni) have received particular interest due to their potential to operate on more than one alkali atom per formula unit (f.u.), which would result in higher specific capacity and energy density. The A2MPO4F fluorophosphates crystallize in three different structure types. While the coordination polyhedra of transition metal, MO4F2 octahedra, is the same for all three, the means of their conjugation varies from edge-shared in Li2MPO4F (M = Ni, Co) and corner-shared in Na2MnPO4F to mixed face-shared and corner-shared in Na2FePO4F, resulting in different architectures. The three-dimensional (3D) Na2MnPO4F and the layered Na2FePO4F were shown to operate as positive electrode material in Naand Li-ion cells with reversible capacity of about 120 mAh g−1 (∼0.8 electron per f.u.). Moreover, the capacity improvement up to ∼180 mAhg−1 (∼1.46 electrons per f.u.) was observed for nanostructured Na2FePO4F cycled at elevated temperature. 12 Several groups reported on high voltage electrochemical performance of Li2CoPO4F and Li2NiPO4F. 8,14−16 These fluorophosphates possess a three-dimensional structure and, by analogy with the olivine phase, are expected to demonstrate good stability and reversibility upon cycling. The complete evaluation of these materials is restrained by the absence of commercial high-voltage electrolytes stable above 4.8 V. The exploration of corresponding Feor Mn-based fluorophosphates with lower redox potentials might provide an advantage in the energy and power density over the LiFePO4 cathode materials. So far, these fluorophosphates have not been identified: apparently, the structure framework could not adopt the Fe and Mn ions, which are larger compared to Co and Ni. In our previous paper, we showed that upon the first charge Li2CoPO4F undergoes structural transformation with the large volume expansion (∼5%) demonstrating the framework flexibility. Considering this “structure pliability” we attempted to stabilize Fe-based fluorophosphate by “expanding” the framework through the substitution of Li ions located in the structure voids by larger Na ions; as a result, we succeeded in synthesis of a new NaLiFePO4F phase isostructural to Li2NiPO4F (Figure 1). Upon preparing this communication, we have found a short report by Mizuta et al., where electrochemical properties measured on the multiphase NaLiFePO4F sample were described. 17 Here, we report on the synthesis employed for obtaining the pure NaLiFePO4F phase, its structure determination, and electrochemical activity. We demonstrate that electrochemical replacement of Na by Li in

The structure of a superconducting oxide (K0.87Bi0.13)BiO3(Tc≈10.2 K) prepared under high pressure was analyzed by time-of-flight neutron powder diffraction. Rietveld refinement showed this compound to be a cubic perovskiteABO3with space groupPm 3 m(No. 221) and lattice parametera=4.23377(3) A. Refinement of occupation factors revealed the absence of oxygen vacancies and the substitution of Bi3+ions for 13% of K+ions at theAsite, presenting evidence for electron doping in this superconductor. Extraordinarily large atomic displacement parameters for theAand O sites are believed to reflect pronounced positional disorder mainly arising from the large difference in size between the K+and Bi3+ions.

NaLiFePO4F is prepared by annealing a stoichiometric mixture of LiFePO4 and NaF (Ar flow, 650—700 °C, 2 h).

Dicopper(II) dilanthanum pentaoxide, La 2 Cu 2 O 5 , has been prepared using a high-pressure technique. Its structure at 296 and 10 K was analyzed by Rietveld refinements using neutron powder diffraction data. The structure of La 2 Cu 2 O 5 comprises CuO 5 square pyramids connected to each other in three dimensions by corner sharing and ten-coordinate La 3+ ions occupying positions next to oxygen vacancies which form tunnels along the c axis.

Ca2Sr2Cu3GaO9 with a Tc of 73 K was prepared at 1250°C and 6 GPa. Its neutron powder diffraction data were analyzed on the basis of Ima2, Imcm and P21ab space groups. Imcm gave the best approximation to the actual superstructure with a doubled b dimension. Ca2Sr2Cu3GaO9 belongs to a homologous series of oxides (R1−xCax)n−1Sr2CunGaO2n+3 (R: rare-earth metals). In its structure, GaO4 tetrahedra form (GaO33−)∞ chains running parallel with the c-axis. Sr2GaO3 blocks composed of the infinite chains and Sr2+ ions alternate with (Ca)2(CuO2)3 sheets along the a-axis. Two types of the infinite chains with different orientations of GaO4 tetrahedra alternate along the b-axis, which is the reason for the 2b superstructure. The Cu(1)O5 pyramid tilts owing to the tetrahedral coordination of Ga. The intermediate Cu(2)O2 sheet is nearly flat with each Cu(2) atom having four equivalent CuO bonds. Sr2+ and Ca2+ ions are completely ordered on two different sites. Full occupation of Ca2+ ions at an eight-coordinated site, which is obtained only at high pressure, permits adequate hole doping of the CuO2 sheets, where the formal oxidation state of Cu is +2.33.

Wadsley–Roth phase Li x Nb 9 PO 25 has been studied as a potential candidate for anode material of Li-ion batteries. Its crystal structure, which consists of ReO 3 -type blocks of NbO 6 octahedra connected with PO 4 tetrahedra, provides a good stability and performance during Li + insertion/removal. Li-ion chemical diffusion coefficient ( D chem ) in Li x Nb 9 PO 25 was determined by means of potentiostatic intermittent titration technique and electrochemical impedance spectroscopy. Different data treatments (classical Warburg equation or the model of an electrode system with ohmic potential drop and/or slow kinetics of the interfacial Li + ion transfer across the electrode/electrolyte interface) were used for calculation of D chem of the Li ion inside this material; their applicability is discussed in the article. D chem changes with the Li-ion doping degree, x, in Li x Nb 9 PO 25 and has a sharp minimum near the two-phase region at appr. 1.7 V vs. Li + /Li. These values of D chem in Li x Nb 9 PO 25 (∼10 −9 –10 −11 cm 2 s −1 ) were found to be in average noticeably higher than in the widely studied anode material, Li 4 Ti 5 O 12 .

The crystal structure of Li2CoPO4F is completely solved from precession electron diffraction data, including the location of the Li atoms.

The crystal structure of the Li2CoPO4F high-voltage cathode for Li ion rechargeable batteries has been completely solved from precession electron diffraction (PED) data, including the location of the Li atoms. The crystal structure consists of infinite chains of CoO4F2 octahedra sharing common edges and linked into a 3D framework by PO4 tetrahedra. The chains and phosphate anions together delimit tunnels filled with the Li atoms. This investigation demonstrates that PED can be successfully applied for obtaining structural information on a variety of Li-containing electrode materials even from single micrometer-sized crystallites.

Dicopper(II) dilanthanum pentaoxide, La 2 Cu 2 O 5 , has been prepared using a high-pressure technique. Its structure at 296 and 10 K was analyzed by Rietveld refinements using neutron powder diffraction data. The structure of La 2 Cu 2 O 5 comprises CuO 5 square pyramids connected to each other in three dimensions by corner sharing and ten-coordinate La 3+ ions occupying positions next to oxygen vacancies which form tunnels along the c axis.

A new potassium palladate KPd2O3 was synthesized by the reaction of KO2 and PdO at elevated oxygen pressure. Its crystal structure was solved from powder X-ray diffraction data in the space group R3m (a = 6.0730(1) A, c = 18.7770(7) A, and Z = 6). KPd2O3 represents a new structure type, consisting of an alternating sequence of K+ and Pd2O3− layers with ordered Pd2+ and Pd4+ ions. The presence of palladium ions in di- and tetravalent low-spin states was confirmed by magnetic susceptibility measurements.

A new potassium palladate KPd(2)O(3) was synthesized by the reaction of KO(2) and PdO at elevated oxygen pressure. Its crystal structure was solved from powder X-ray diffraction data in the space group R3m (a = 6.0730(1) A, c = 18.7770(7) A, and Z = 6). KPd(2)O(3) represents a new structure type, consisting of an alternating sequence of K(+) and Pd(2)O(3)(-) layers with ordered Pd(2+) and Pd(4+) ions. The presence of palladium ions in di- and tetravalent low-spin states was confirmed by magnetic susceptibility measurements.