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Various powerful oxygenation approaches were tested in order to find the limits of the oxygen-storage capability of YBaCo 4 O 7þ . By means of extreme solid-medium high-pressure oxygenation employing KClO 3 as an oxygen generator the phase was successfully loaded with excess oxygen up to % 1:56.The YBaCo 4 O 7þ phase has a unique ability to reversibly intake/release appreciably large amounts of oxygen at low temperatures.1 Accordingly the phase is believed to be a promising candidate for an efficient oxygen storage/separator material. 2In its as-synthesized oxygen-poor ( ¼ 0) form, YBaCo 4 O 7þ (with the mean oxidation state of cobalt at +2.25) possesses a hexagonal crystal structure that consists of two types of layers of corner-sharing CoO 4 tetrahedra in a 1:3 ratio.3 Through atmospheric-pressure oxygen annealing at low temperatures it is possible to load the as-synthesized samples with excess oxygen up to % 1:3.1 In the present work, a variety of powerful post-synthesis oxidation methods were tested for their capability to oxygenate the YBaCo 4 O 7þ phase. The purpose was to establish the maximum amount of excess oxygen that can be incorporated into the YBaCo 4 O 7þ lattice.High-pressure (HP) techniques have proven their superiority in stabilizing unusually high oxidation states of transition metals in their oxides. 4 In the present work, we employed two different HP approaches, i.e. gas-medium (10-100 atm O 2 ) and solidmedium (1-5Á10 4 atm plus KClO 3 as an oxygen generator) treatments. From previous works on various functional cobalt oxide materials, chemical oxidation methods have been found promising as well. 5,6 Therefore, in addition to the HP techniques we tested the capability of a Br 2 /H 2 O dispersion to oxidize YBaCo 4 O 7þ . Moreover, for the sake of comparison normalpressure annealing experiments in oxygen, air, and nitrogen atmospheres were performed.The master sample of YBaCo 4 O 7þ was synthesized by an EDTA chelation method.1 Stoichiometric amounts of Y 2 O 3 , Ba(NO 3 ) 2 , and Co(NO 3 ) 2 . 6H 2 O were dissolved in a concentrated HNO 3 solution from which the metal ions were chelated with an EDTA/NH 3 solution. After evaporating the solvent and burning the residue, the remaining ash was ground, pressed into pellets, and sintered in an N 2 gas flow at 1050 C for 20 h. From iodometric titration, oxygen content of the thus synthesized XRD-pure YBaCo 4 O 7þ sample (Sample B) was determined at ¼ 0:13. A nearly oxygen-stoichiometric sample of ¼ 0:03 (Sample A) was obtained by annealing a specimen of

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The recycling of used Li-ion batteries is important as the consumption of batteries is increasing every year. However, the recycling of electrode materials is tedious and energy intensive with current methods, and part of the material is lost in the process. In this study, an alternative recycling method is presented to minimize the number of steps needed in the positive electrode recovery process. The electrochemical performance of aged and re-lithiated MgÀ Ti-doped LiCoO 2 and stoichiometric LiCoO 2 was investigated and compared. The results showed that after re-lithiation the structure of original LiCoO 2 was restored, the capacity of an aged LiCoO 2 reverted close to the capacity of a fresh LiCoO 2 , and the material could thus be recovered. The re-lithiated MgÀ Ti-doped LiCoO 2 provided rate capability properties only slightly declined from the rate capability of a fresh material and showed promising cyclability in half-cells. trated acids, which easily generates large amounts of waste solutions. Pyrometallurgy-based methods have a high efficiency and they are easy to scale up. [16,17] On the other hand, the high temperatures needed in the processes lead to high energy consumption and emissions. In addition, the recovery of lithium is difficult. [7,17] Biometallurgy-based methods utilize bacteria to extract metals from the spent lithium-ion batteries. [18,19] The methods are usually quite inexpensive, but as a downside the extraction processes are slow. [20] Lithium-ion batteries can be recycled either by processing the whole battery, [21][22][23][24] or dismantling the cells before starting the recovery process. [5,6,9,12,14,19,[25][26][27][28][29][30][31] The latter has been more popular in the literature, but the dismantling can be a laborious process without proper equipment. One could argue that this method is not easy to scale-up for industrial purposes. However, for example Nan et al. [12] reported about 5000 spent cells dismantled in 1 h, which indicates that scaling up should be possible. The advantage of recycling a whole lithium-ion battery is that the possibly challenging dismantling process is skipped, and thus one process step is reduced. However, having all the battery components in the same material flow initially can increase the amount of impurities in the final product. Additional process steps might be necessary to reduce the impurity concentrations in the recycled material. [24] Even if most of the elements are recovered with the above-mentioned methods, the typical layered structure of the metal oxide intercalation compounds is almost certainly lost, and the material downgraded. Typically, the positive electrode materials are reduced to more low-value chemicals, such as CoSO 4 , [4,12,23,24,31] Co-(OH) 2 , [5,9,32] CoCO 3 , [8,22] and Li 2 CO 3 , [4,9,12,24,31,32] during the recycling process. To synthesize these compounds back to Li-ion battery electrode materials requires energy. Therefore, if the structure of the original electrode material can be spared during the recycling process,...

Various chemical oxidants were investigated for their capability to oxidize brownmillerite SrCoO 2:5 to perovskite SrCoO 3À . Among the oxidants tested, KMnO 4 /HCl was found to be the strongest to yield SrCoO 3À with % 0:06.The perovskite SrCoO 3À system is known for its wide range of oxygen nonstoichiometry. Hence, it serves as a kind of prototype for the recently highlighted functional oxides of mixed-valent (III/IV) cobalt. With the proper choice of process parameters it can be obtained as different types of metastable single phases with orthorhombic (0:5 < < 0:6), 1,2 tetragonal (0:1 < < 0:25) 2,3 or cubic ( % 0) 3-5 symmetry. Synthesis of the oxidized phases usually goes through the orthorhombic brownmillerite phase SrCoO 2:5 , 1 which has ordered oxygen vacancies such that the structure is composed of alternately stacked layers of corner-sharing CoO 4 tetrahedra and CoO 6 octahedra. For the oxidation of SrCoO 2:5 , electrochemical [3][4][5] and high-pressure 2,6 techniques have been employed. Possibility to utilize chemical ways for the control of oxygen content was brought up by Nemudry et al.3 who oxidized SrCoO 2:5 by immersing the sample into an aqueous solution of Br 2 and NaOH. Compared to the other methods chemical oxidation requires only a very simple experimental set up. In the present work, several other chemical oxidizing agents are utilized.The SrCoO 2:5 precursor was prepared from Co and SrCO 3 powders, dissolved in stoichiometric amounts in 3 M HNO 3 solution and then chelated by EDTA/NH 3 solution containing EDTA in 50% excess. The solution was dried, burned and then calcined at 900 C. The calcination product was ground and pressed into pellets for the final heat treatment in air at 1000 C for 40 h, followed by quenching to room temperature. The X-ray diffraction pattern for the product revealed a singlephase brownmillerite with an oxygen content of 2.50 per formula unit, as determined by iodometric titration.For the oxidation experiments, the SrCoO 2:5 pellets were crushed and ground. Four different oxidizing media were employed: (1) aqueous solution of 0.2 M KMnO 4 and HCl in various concentrations, (2) aqueous solution of Na 2 S 2 O 8 saturated at room temperature, (3) 1:1 dispersion of Br 2 and H 2 O, and (4) aqueous solution of 0.3 M Br 2 and 5 M NaOH. The experiments were carried out for 50-mg samples in 2-mL plastic vials except for experiment (4), which was carried out for a 200-mg sample in a 20-mL glass tube. Immersion time varied from 1 to 24 h. Temperature was controlled using a water or an ice bath and a thermometer. After the oxidation treatment, the sample powder was washed with deionized water plus ethanol [(1) and (2)] or CH 3 CN plus ethanol [(3) and (4)] and subsequently dried in air at room temperature.X-ray diffraction (XRD) patterns were collected for the samples with a Rigaku RINT2550 diffractometer equipped with a rotating Cu anode. Software JANA 2000 was used in the profile-fitting mode for the lattice-parameter refinements [in space groups, I4=mmm (SrCoO 3À ) and P...

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