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Mechanochemical synthesis of Cu3P in the presence of n‐dodecane results in a material with a secondary particle size distribution of 10 μm, secondary particles which consist of homogeneously agglomerated 20 nm primary particles. The electrochemical performance of Cu3P with lithium is influenced by the reaction depth, in other words by the lower potential cut‐off. During the electrochemical reaction, the displacement of copper by lithium from the Cu3P structure until the formation of Li3P and Cu deteriorates the capacity retention. Improved performance was obtained when the charge potential was limited to 0.50 V (vs. Li/Li+) and the formation of the LixCu3‐xP phase (0 ≤ × ≤ 2). In this case, when the potential is limited to 0.5 V, the capacity is stable for more than 50 cycles. Acceptable electrochemical performances in Li‐ion cells within the voltage range 0.50–2.0 V (vs. Li/Li+) were shown when Cu3P was used as an anode and Li1.2(Ni0.13Mn0.54Co0.13)O2 and LiNi0.5Mn1.5O4 as positive electrode materials.

LiM0.5Mn1.5normalO4 ( M=Fe , Co, Ni) normal spinel oxides were prepared by a citric acid assisted Pechini synthesis with different thermal treatments and compared with respect to their electrochemical performance as cathodes in lithium-ion batteries. Characterization methods include X-ray diffraction, neutron diffraction, inductively coupled plasma optical emission spectroscopy analysis, and scanning electron microscopy. While LiM0.5Mn1.5normalO4 samples crystallize for M=Fe and Co with the 3d cation-disordered cubic spinel-like structure ( Fd3m space group), the 600°C annealed LiNi0.5Mn1.5normalO4 shows a partially ordered structure (belonging to the P4332 space group). The absolute discharge capacity is slightly higher for the Ni-doped samples in comparison with the Co- and Fe-doped spinels. 1000°C annealed samples show an improved cyclability in comparison with the 600°C annealed samples. At elevated temperatures, Co- and Fe-doped samples show much faster degradation in comparison with the Ni-doped sample. The responsible mechanisms are discussed.

Conversion and alloying type negative electrodes attracted huge attention in the present research on lithium/sodium-ion batteries (LIBs/SIBs) due to the high capacity delivered. Among these, SnO 2 is investigated intensively in LIBs due to high cyclability, low reaction potential, cost-effectiveness, and environmental friendliness. Most of the LIB electrodes are explored in SIBs too due to expected similar electrochemical performance. Though several LIB negative electrode materials successfully worked in SIBs, bare SnO 2 shows very poor electrochemical performance in SIB. The reason for this difference is investigated here through combined in operando and ex situ X-ray absorption spectroscopy (XAS). For this, the electrodes of SnO 2 (space group P 4 2 / mnm synthesized via one-pot hydrothermal method) were cycled in Na-ion and Li-ion half-cells. The Na/SnO 2 half-cell delivered a much lower discharge capacity than the Li/SnO 2 half-cell. In addition, higher irreversibility was observed for Na/SnO 2 half-cell during electrochemical investigations compared to that for Li/SnO 2 half-cell. In operando XAS investigations on the Na/SnO 2 half-cell confirms incomplete conversion and alloying reactions in the Na/SnO 2 half-cell, resulting in poor electrochemical performance. The difference in the lithiation and sodiation mechanisms of SnO 2 is discussed in detail.

the LiNi 0.5 Mn 1.5 O 4 material is intensively investigated due to its high-voltage electrochemical activity, excellent rate capability as well as cycling stability. [2][3][4][5][6][7] LiNi 0.5 Mn 1.5 O 4 exists mainly in two crystallographic structures according to the oxygen stoichiometry in the material. [ 2,[8][9][10] The cation-ordered spinel (space group P 4 3 32) which is oxygen-stoichiometric, contains all the Mn ions in their tetravalent form. [ 11 ] At the same time in the cation-disordered structure (space group Fd 3 m) , in addition to the tetravalent Mn species, some of the Mn ions exist in the trivalent form as a result of oxygen deficiency from the crystal lattice. [ 12 ] This is mainly associated with the synthesis temperature. According to Pasero et al. [ 10 ] when the synthesis temperature exceeds ≈650 °C, the structure of LiNi 0.5 Mn 1.5 O 4 transforms gradually from the cationordered to cation-disordered. In the cation-ordered structure, the only electrochemically active species is Ni 2+ . The electrochemical reaction takes place at ≈4.7 V with two plateaus corresponding to Ni 2+ / Ni 3+ and Ni 3+ /Ni 4+ reactions, respectively. [ 2,12 ] Meanwhile, in the cation-disordered structure, a slight electrochemical activity is observed around 4.0 V versus Li/Li + as a result of Mn 3+ /Mn 4+ electrochemical reaction. [ 12 ] However, this material offers only a theoretical capacity of ≈148 mAh g −1 in the usual cycling voltage range 3.5-5.1 V. [ 13 ] It is possible to intercalate a second Li + into the material at voltage <3.0 V which in turn increases the capacity delivered. [ 1,14 ] For this purpose a Li excess electrode must be used as the counter electrode during cycling. Moreover, this process is believed to induce Jahn-Teller distortion of the structure due to the existence of excessive amount of Mn 3+ which in turn results in an average oxidation state of Mn less than +3.5. [ 1,14,15 ] The layered lithium-rich (Li-rich) materials with a general composition x Li 2 MnO 3 · (1 -x ) LiMO 2 (M = Mn, Co, Ni) are known to deliver capacities >250 mAh g −1 when cycled within the voltage range 2.0-4.8 V. [ 16 ] This material has a complex structure which is reported either as composites with nanodomains of Li 2 MnO 3 -and LiMO 2 -like features or as their solid solutions. [17][18][19][20] The powder diffraction patterns of this material

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Mixed transition‐metal ferrites with the chemical formula MFe2O4 (M=Co, Ni), synthesized through an inverse co‐precipitation route, were characterized by using scanning electron microscopy and powder X‐ray diffraction, which demonstrate phase‐pure compounds with particle sizes of about 100 nm. Cyclic voltammetry investigations in lithium half‐cells revealed a difference between the first cycle and the following charge–discharge cycles, which is characteristic for conversion‐type electrode systems. To understand the mechanism of the electrochemical reaction in the first cycle, in situ X‐ray absorption spectroscopy was performed during cycling at a charge–discharge rate of C/10. During the first discharge process, the crystalline Co and Ni ferrites undergo reduction. A coexistence of binary metal oxides (CoO/NiO and Fe2O3) and metallic phases were observed during the discharge. At the end of discharge, only the existence of metallic nanoclusters was observed. In the subsequent charging process, Fe was found to undergo complete oxidation in both ferrites. In contrast, almost 60 % of the Co or Ni remained in the metallic state at the end of the charge (end of first cycle). This incomplete oxidation of Co and Ni in the applied voltage range could be the main reason behind the irreversible capacity loss and low coulombic efficiency often reported for these conversion electrode systems.

Careful development and optimization of negative electrode (anode) materials for Na-ion batteries (SIBs) are essential, for their widespread applications requiring a long-term cycling stability. BiFeO3 (BFO) with a LiNbO3-type structure (space group R3c) is an ideal negative electrode model system as it delivers a high specific capacity (770 mAh g–1), which is proposed through a conversion and alloying mechanism. In this work, BFO is synthesized via a sol–gel method and investigated as a conversion-type anode model-system for sodium-ion half-cells. As there is a difference in the first and second cycle profiles in the cyclic voltammogram, the operating mechanism of charge–discharge is elucidated using in operando X-ray absorption spectroscopy. In the first discharge, Bi is found to contribute toward the electrochemical activity through a conversion mechanism (Bi3+ → Bi0), followed by the formation of Na–Bi intermetallic compounds. Evidence for involvement of Fe in the charge storage mechanism through conversion of the oxide (Fe3+) form to metallic Fe and back during discharging/charging is also obtained, which is absent in previous literature reports. Reversible dealloying and subsequent oxidation of Bi and oxidation of Fe are observed in the following charge cycle. In the second discharge cycle, a reduction of Bi and Fe oxides is observed. Changes in the oxidation states of Bi and Fe, and the local coordination changes during electrochemical cycling are discussed in detail. Furthermore, the optimization of cycling stability of BFO is carried out by varying binders and electrolyte compositions. Based on that, electrodes prepared with the Na-carboxymethyl cellulose (CMC) binder are chosen for optimization of the electrolyte composition. BFO–CMC electrodes exhibit the best electrochemical performance in electrolytes containing fluoroethylene carbonate (FEC) as the additive. BFO–CMC electrodes deliver initial capacity values of 635 and 453 mAh g–1 in the Na-insertion (discharge) and deinsertion (charge) processes, respectively, in the electrolyte composition of 1 M NaPF6 in EC/DEC (1:1, v/v) with a 2% FEC additive. The capacity values stabilize around 10th cycle and capacity retention of 73% is observed after 60 cycles with respect to the 10th cycle charge capacity.