F. Ronci

Transport and interfacial properties of composite polymer electrolytes

Lithium polymer electrolytes formed by dissolving a lithium salt LiX in poly(ethylene oxide) PEO, may find useful application as separators in lithium rechargeable polymer batteries. The main problems, which are still to be solved for a complete successful operation of these materials, are the reactivity of their interface with the lithium metal electrode and the decay of their conductivity at temperatures below 70°C. In this paper we demonstrate that a successful approach for overcoming these problems, is the dispersion of selected ceramic powders in the polymer mass, with the aim of developing new types of composite PEO–LiX polymer electrolytes characterized by enhanced interfacial stability, as well as by improved ambient temperature transport properties.

Nanocomposite polymer electrolytes and their impact on the lithium battery technology

Lithium polymer electrolytes formed by dissolving a lithium salt LiX in poly(ethylene oxide) PEO may find useful application as separators in lithium rechargeable polymer batteries. The main problems which are still to be solved for a complete successful operation of these materials are the reactivity of their interface with the lithium metal electrode and the decay of their conductivity at temperatures below 70°C. In this paper we demonstrate that a successful approach for overcoming these problems is the dispersion of selected, low-particle size ceramic powders in the polymer mass with the aim of developing new types of nanocomposite PEO-LiX polymer electrolytes characterized by enhanced interfacial stability as well as by improved ambient temperature transport properties.

A FTIR and Raman study of spontaneous reactions occurring at the LiNiyCo(1-y)O2 electrode/non-aqueous electrolyte interface

Spontaneous reactions occurring at the surface of LiNiyCo(1−y)O2-based electrodes during contact with non-aqueous organic electrolytes have been investigated by FTIR and Raman spectroscopy. It is found that several types of compounds and/or functional groups are formed on the electrode surface and that these compounds appear to be dependent on the type of electrolyte used. Thus, for a LiClO4-propylene carbonate (PC) electrolyte, the main reaction is formation of Li-carbonate, whereas in the case of LiPF6-ethylene carbonate/dimethyl carbonate (EC/DMC) electrolyte formation of P-, O- and F-containing compounds dominate. Spectroscopic data also show a variation of the LiNi(1−y)CoyO2 crystalline structure during storage in an electrolyte which probably is due to a spontaneous deintercalation of the Li ions. An analysis of the newly formed species is presented and possible reaction mechanisms are discussed.

Reactivity of lithium battery electrode materials toward non-aqueous electrolytes: spontaneous reactions at the electrode-electrolyte interface investigated by FTIR

Abstract Spontaneous reactions occurring at the surface of LiNi 0.8 Co 0.2 O 2 and LiMn 2 O 4 -based electrodes during the storage in organic non-aqueous electrolytes have been investigated by diffuse reflectance FTIR technique. It is found that both materials spontaneously form different inorganic and organic compounds on their surface when in contact with electrolyte solutions. The nature of these self-acting reactions is moreover found to be similar to that of the processes occurring during electrochemical cycling of the electrodes. Reaction mechanisms and the final products depend on both electrode surface chemistry and the nature of electrolyte used. It appears that the spontaneous reactions are initiated by lithium deintercalation from the electrode active material. The influence of different factors, e.g. degree of lithiation of the active material, roughness of the electrode surface and temperature on the reaction rate is discussed.

In situ studies of electrodic materials in Li-ion cells upon cycling performed by very-high-energy x-ray diffraction

A very high-energy synchrotron radiation source (87 keV) was utilized for in situ sampling of the structural changes occurring in the electrodic materials of a Li-ion cell during charge–discharge cycling. The real-time evolution of their crystal lattice was obtained as a function of the degree of Li intercalation. As a result, new information on two electrodic materials, Li–Ti “zero strain” and Li–Ni–Co oxide, both of extreme interest for generation of rechargeable batteries, was gained. The actual change of the Li–Ti oxide lattice parameter upon cycling was observed in greater detail than before, and provided evidence of unexpected behavior in some intervals of the cycle. In the Li–Ni–Co sample, a new phase formed during the early stages of cycling that remained stable in the subsequent cycles was revealed.

Refined, in-situ EDXD structural analysis of the Li[Li1/3Ti5/3]O4 electrode under lithium insertion–extraction

An in-situ energy dispersive X-ray diffraction (EDXD) analysis has been run on the Li[Li1/3Ti5/3]O4 compound upon Li intercalation–deintercalation process. The results confirm that this process is accompanied by a very small variation of the host lattice parameter, i.e., confined between 1‰ over the entire cycle. This value, which agrees with previous literature information, concurs to demonstrate that Li[Li1/3Ti5/3]O4 may indeed be considered as a zero-strain intercalation compound, this being a characteristic of key technological importance since lattice strains upon cycling are among the main causes of capacity decays in lithium battery electrodes. In addition, this work confirms that EDXD is a quite convenient technique for electrochemical measurements since, allowing in-situ lattice parameter determinations, may lead to a complete evaluation of the intermediate stages of the intercalation process and, possibly, to detect differences among the various cycles.

Thermal, electrochemical and structural properties of stabilized LiNiyCo1−y−zMzO2 lithium-ion cathode material prepared by a chemical route

Layered compounds, such as LiNiO2 and LiCoO2 , have been extensively studied as active cathodic materials in lithium-ion batteries. Mixed oxides having general formula LiNiyCo1−yO2 represent a good compromise between the limited cyclability of LiNiO2 and the high cost of LiCoO2. However, recent studies have demonstrated that LiNiyCo1−yO2 compounds are thermally unstable in their charged state, undergoing exothermic reactions that might cause thermal runaway and safety concern. The stability of the compounds may be greatly controlled by doping with a suitable metal, M = Al, Mg. In this work we further investigate the role of the doping metal on the thermal, electrochemical and structural characteristics of the LiNiyCo1−y−zMzO2 electrode materials. These materials were prepared using a soft chemistry route, to achieve the proper control of the chemical homogeneity and of the microstructural properties of the final samples. The thermal behavior of the doped LiNiyCo1−y−zMzO2, where M = Al, was studied using differential scanning calorimetry. The structural properties upon cycling were investigated by a recently, in-house developed, in situ energy dispersive X-ray diffraction (EDXD) technique. The reversibility and rate capabilities of the cathodes in lithium cells were characterized using electrochemical equipment.

Structural and electrochemical study on Li(Li1/3Ti5/3)O4 anode material for lithium ion batteries

Chemical and electrochemical studies have shown that various titanium oxides can incorporate lithium in different ratios. Other compounds with a spinel-type structure and corresponding to the spinel oxides LiTi2O4 and Li4Ti5O12 have been evaluated in rechargeable lithium cells with promising features. The spinel Li[Li1/3Ti5/3]O4 [1–5] compound is a very appealing electrode material for lithium ion batteries. The lithium insertion-deinsertion process occurs with a minimal variation of the cubic unit cell and this assures high stability which may reflect into long cyclability. In addition, the diffusion coefficient of lithium is of the order of 10−8 cm2s−1 [5] and this suggests fast kinetics which may reflect in high power capabilities.In this work we report a study on the kinetics and the structural properties of the Li[Li1/3Ti5/3]O4 intercalation electrode carried out by: cyclic voltammetry, galvanostatic cycling and in-situ X-ray diffraction.The electrochemical characterization shows that the Li[Li1/3Ti5/3]O4 electrode cycles around 1.56 V vs. Li with a capacity of the order of 130 mAhg−1 which approaches the maximum value of 175 mAhg−1 corresponding to the insertion of 1 equivalent per formula unit. The delivered capacity remains constant for hundred cycles confirming the stability of the host structure upon the repeated Li insertion-deinsertion process. This high structural stability has been confirmed by in situ Energy Dispersion X-ray analysis.

Long cycle life Li-Mn-O defective spinel electrodes

A Li–Mn–O defective spinel phase material has been synthesized through repeated grinding and heating (T<400°C) steps from a mixture of LiOH and MnO2. The sample has been characterized by X-ray diffraction, thermogravimetric analysis and elemental and oxidation state analyses. At a C/12 charge/discharge rate, the material showed a first-cycle capacity of almost 200 mAh/g that decreased upon cycling to a stable value of 120 mA h/g after the 20th cycle. At a higher rate (C/3.7), the material showed a long cycle life upon lithium insertion/deinsertion with more than 50% of the initial capacity delivered at the 750th cycle. The work was developed within the ALPE (Advanced Lithium Polymer Electrolyte) battery project, an Italian project devoted to the realization of lithium polymer batteries for electric vehicle applications.

Lithium-7 nuclear magnetic resonance and Ti K-edge X-ray absorption spectroscopic investigation of electrochemical lithium insertion in Li4/3+xTi5/3O4

Abstract The spinel compound Li4/3+xTi5/3O4 is known to undergo reversible lithium intercalation up to x=1 with almost no change in lattice parameters, hence its designation as a “zero strain” intercalation compound. Structural changes that accompany electrochemical Li intercalation into this compound were studied by both 7 Li nuclear magnetic resonance (NMR) and Ti K-edge X-ray absorption fine structure (XAFS). The NMR results demonstrate that Li occupancies do not follow a simple distribution between two possible sites, one tetrahedral and one octahedral. The presence of at least one additional octahedral site is suggested. Line width measurements show that the Li+ ions do not return to their original distribution after cycling. XAFS results indicate the presence of modest static disorder in TiO and TiTi distances above x=0.5. Both methods thus reveal subtle structural details previously unobserved by X-ray diffraction (XRD).