The rapid progress in mass-market applications of metal-ion batteries intensifies the development of economically feasible electrode materials based on earth-abundant elements. Here, we report on a record-breaking titanium-based positive electrode material, KTiPO 4 F, exhibiting a superior electrode potential of 3.6 V in a potassium-ion cell, which is extraordinarily high for titanium redox transitions. We hypothesize that such an unexpectedly major boost of the electrode potential benefits from the synergy of the cumulative inductive effect of two anions and charge/vacancy ordering. Carbon-coated electrode materials display no capacity fading when cycled at 5C rate for 100 cycles, which coupled with extremely low energy barriers for potassium-ion migration of 0.2 eV anticipates high-power applications. Our contribution shows that the titanium redox activity traditionally considered as "reducing" can be upshifted to near-4V electrode potentials thus providing a playground to design sustainable and cost-effective titanium-containing positive electrode materials with promising electrochemical characteristics.

O3 type layered sodium transition metal oxides, e.g. NaNi 0.5 Mn 0.5-z Ti z O 2 , having one sodium per transition metal ion could be attractive positive electrode materials for achieving high energy density sodium-ion batteries provided we can reversibly utilize their full Na content. However, the layered structure on cycling undergoes series of phase transitions in which the fully desodiated O1 phase shows huge reduction in cell volume together with cation migration both of which are detrimental for long term cycling performance. Hence, the practical capacity of layered oxides is restricted to solely ~0.5-0.6 Na (oxidation up to ~4 V vs Na + /Na 0 ), avoiding the complete removal of sodium. Herein, we show that the partial substitution of a redox-active Ni 2+ cation by an inactive one (e.g. Zn 2+ to form NaNi 0.45 Zn 0.05 Mn 0.4 Ti 0.1 O 2 ) suppresses the phase transitions at high voltage (>4 V vs Na + /Na 0 ), and helps in utilizing the maximum capacity of the material (170 mAh g -1 with ~0.8 Na) without much degradations upon long cycling. The fully charged phase (Na 0.2 Ni 0.45 Zn 0.05 Mn 0.4 Ti 0.1 O 2 ), as determined by high resolution electron transmission microscopy, shows P3-O1 intergrowth structure in which the O1 phase is present only locally as nanoscale domains. We believe that the formation of P3-O1 intergrowths in the Zn-substituted material, in contrast to the distinct O1 phase for unsubstituted NaNi 0.5 Mn 0.4 Ti 0.1 O 2 , restricts structural degradations during cycling and improves the long term cycling stability.Similar substitution chemistry can be extended to Cu 2+ , Mg 2+ ions as well. The NaNi 0.45 Zn 0.05 Mn 0.4 Ti 0.1 O 2 positive electrode material on implementation in 18650 Na-ion cells show electrochemical performances comparable to that of polyanionic Na 3 V 2 (PO 4 ) 2 F 3 /C cells.

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A novel approach to obtain exchange-coupled sandwiched nanoparticles in which cobalt ferrite outer layers are epitaxially grown on single crystalline hard magnetic strontium hexaferrite seeds.

To realize high-power performance, lithium-ion batteries require stable, environmentally benign, and economically viable noncarbonaceous anode materials capable of operating at high rates with low strain during charge–discharge. In this paper, we report the synthesis, crystal structure, and electrochemical properties of a new titanium-based member of the MPO4 phosphate series adopting the α-CrPO4 structure type. α-TiPO4 has been obtained by thermal decomposition of a novel hydrothermally prepared fluoride phosphate, NH4TiPO4F, at 600 °C under a hydrogen atmosphere. The crystal structure of α-TiPO4 is refined from powder X-ray diffraction data using a Rietveld method and verified by electron diffraction and high-resolution scanning transmission electron microscopy, whereas the chemical composition is confirmed by IR, energy-dispersive X-ray, electron paramagnetic resonance, and electron energy loss spectroscopies. Carbon-coated α-TiPO4/C demonstrates reversible electrochemical activity ascribed to the Ti3+/Ti2+ redox transition delivering 125 mAh g–1 specific capacity at C/10 in the 1.0–3.1 V versus Li+/Li potential range with an average potential of ∼1.5 V, exhibiting good rate capability and stable cycling with volume variation not exceeding 0.5%. Below 0.8 V, the material undergoes a conversion reaction, further revealing capacitive reversible electrochemical behavior with an average specific capacity of 270 mAh g–1 at 1C in the 0.7–2.9 V versus Li+/Li potential range. This work suggests a new synthesis route to metastable titanium-containing phosphates holding prospective to be used as negative electrode materials for metal-ion batteries.