The preparation and electrochemical characterization of a new material consisting of carbon coated ZnFe 2 O 4 nanoparticles is presented. This material, which offers an interesting combination of alloying and conversion mechanisms, is capable of hosting up to nine equivalents of lithium per unit formula, corresponding to an exceptional specifi c capacity, higher than 1000 mAh g − 1 . Composite electrodes of such a material, prepared using environmentally friendly sodium carboxymethyl cellulose as binder, showed the highest, ever reported, specifi c capacity and high rate performance upon long-term testing. Furthermore, in situ X-ray diffraction analysis allowed identifying the reduction process occurring upon initial lithiation. 514 wileyonlinelibrary.com

Herein, we present a new synthesis method for transition-metal-doped zinc oxide nanoparticles utilized and characterized for the first time as anode material for lithium-ion batteries. In fact, the introduction of a transition metal (for instance, iron or cobalt) into the zinc oxide lattice results in an advanced performance with reversible lithium storage capacities exceeding 900 mAh g–1, i.e., more than twice that of graphite. In situ XRD analysis reveals the electrochemical reduction of the wurtzite structure and the reversible formation of a LiZn alloy. The additional application of a carbon coating of such nanoparticles enables further improvement in terms of capacity retention and high rate (dis)charge capability. Moreover, the newly developed, simple, and environmentally friendly synthesis of these n-type doped nanoparticles is considered to be also applicable to other transition metals, presumably showing comparable electrochemical performances.

Today, it is common knowledge, that materials science in the field of electrochemical energy storage has to follow a system approach as the interactions between active materials, electrolyte, separator and various inactive materials (binder, current collector, conductive fillers, cell-housing, etc.) which are of similar or even higher importance than the properties and performance parameters of the individual materials only. In particular, for lithium-ion batteries, it is widely accepted that the electrolyte interacts and reacts with the electrodes. Here, we report how reactions at a graphite anode (involving electrolyte decomposition and solid electrolyte interphase (SEI) formation), affect the performance of a LiCoO2 (LCO) cathode and the full lithium-ion cell during cycling. We discuss effects of the SEI-forming electrolyte additive vinylene carbonate (VC) and the influence of graphite anodes with different surface areas on the cycling stability, end of charge (EOC) and end of discharge (EOD) potentials of the LCO cathode. We will thus elucidate the failure mechanism of LCO/graphite cells by showing that the formation and growth of SEI on the anode, resistance increase in the cathode, electrode and electrolyte degradation in general, as well as capacity and power fade of the lithium ion cell are in fact strongly interrelated processes.

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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