Transformation of β-Ni(OH)2to NiO nano-sheets via surface nanocrystalline zirconia coating: Shape and size retention

Shape and size of the synthesized NiO nano-sheets were retained during transformation of sheet-like β-Ni(OH)2to NiO at elevated temperatures via nano-sized zirconia coating on the surface of β-Ni(OH)2. The average grain size was 6.42 nm after 600 °C treatment and slightly increased to 10 nm after 1000 °C treatment, showing effective sintering retardation between NiO nano-sheets. The excellent thermal stability revealed potential application at elevated temperatures, especially for high temperature catalysts and solid-state electrochemical devices

Photochemical versus Thermal Synthesis of Cobalt Oxyhydroxide Nanocrystals

Photochemical methods facilitate the generation, isolation, and study of metastable nanomaterials having unusual size, composition, and morphology. These harder-to-isolate and highly reactive phases, inaccessible using conventional high-temperature pyrolysis, are likely to possess enhanced and unprecedented chemical, electromagnetic, and catalytic properties. We report a fast, low-temperature and scalable photochemical route to synthesize very small (~3 nm) monodisperse cobalt oxyhydroxide (Co(O)OH) nanocrystals. This method uses readily and commercially available pentaamminechlorocobalt(III) chloride, [Co(NH3) 5Cl]Cl2, under acidic or neutral pH and proceeds under either near-UV (350 nm) or Vis (575 nm) illumination. Control experiments showed that the reaction proceeds at competent rates only in the presence of light, does not involve a free radical mechanism, is insensitive to O 2, and proceeds in two steps: (1) Aquation of [Co(NH3) 5Cl] 2+ to yield [Co(NH3) 5(H2O)] 3+, followed by (2) slow photoinduced release of NH3 from the aqua complex. This reaction is slow enough for Co(O)OH to form but fast enough so that nanocrystals are small (ca. 3 nm). The alternative dark thermal reaction proceeds much more slowly and produces much larger (~250 nm) polydisperse Co(O)OH aggregates. UV-Vis absorption measurements and ab initio calculations yield a Co(O)OH band gap of 1.7 eV. Fast thermal annealing of Co(O)OH nanocrystals leads to Co3O4 nanocrystals with overall retention of nanoparticle size and morphology. Thermogravimetric analysis shows that oxyhydroxide to mixed-oxide phase transition occurs at significantly lower temperatures (up to T = 64 degrees C) for small nanocrystals compared with the bulk

Ozonation: A unique route to prepare nickel oxyhydroxides. Synthesis optimization and reaction mechanism study

This paper details the reacting paths involved during the oxidation of αII-Ni(OH)2 and βII-Ni(OH)2 with ozone, which is compared to the oxidation process conducted in aqueous solution. The main advantage of the ozone method lies in the control of the reaction medium steps owing to the feasibility of operating in the presence or absence of alkaline cations. This enables the preparation of the pure βIII-NiOOH phase, well-known to be difficult to obtain in aqueous media without γIII-NiOOH traces. The reaction mechanisms for both oxidation processes were found to be similar, and to yield the same final products, except for αII-Ni(OH) 2, where ozonation allowed the preparation of a new oxidized phase that was isolated and characterized by means of complementary techniques such as X-ray diffraction, chemical analysis, HRTEM, TGA, and FT-IR. A mechanism to account for the formation of this phase is proposed

In situ neutron diffraction study of the nickel oxihydroxide electrode upon discharge

The redox discharge process of the nickel oxihydroxide electrode (NOE) were followed by in situ neutron diffraction with the aim of getting a deeper insight into the phases and mechanisms involved, paying special attention to the second plateau. A set of deuterated samples was prepared to be used as a reference for the interpretation of the in situ patterns. Neutron diffraction experiments indicate that redox process is the same over both the first and second plateaus and corresponds to a phase transformation over the main part of the oxidation/reduction range and hence indicates that this phenomenon should not be associated to a structural transformation. © 2004 Elsevier B.V. All rights reserved

Composite polymer electrolytes based on LLZO in a cross-linked PEO matrix for all solid state Li metal batteries

Possible concerns about the safety of rechargeable lithium metal batteries has postponed their introduction into the smart electronics or automotive industries and have promoted advances in the field of non-flammable solid electrolytes. Among the oxide ceramic super lithium ion conductors, garnet-type Li7La3Zr2O12 (LLZO) has recently attracted much attention because of its relatively high ionic conductivity at room temperature (>10-4 S cm–1), negligible electronic conductivity and absence of harmful decomposition products upon contact with atmospheric moisture. Anyway, processing LLZO in pellets by sintering, results in brittle and more or less porous electrolytes, which often display poor interfacial contact with Li metal electrodes. Moreover, there are some reports of lithium dendrite growth and instability towards the cathode material - especially while processing of the electrode at high temperature - referred to cells assembled with this electrolyte family. To circumvent these problems, recent efforts have been dedicated to the formulation of composite hybrid polymer electrolytes (CPEs), where the ceramic material is embedded in a polymeric matrix. As compared to the pristine components, CPEs are stiff while preserving flexibility, are easily processed, and can be conceived to attain improved ionic conductivity and interfacial contact with the electrodes. In this work, a polymer based matrix containing poly(ethylene oxide) (PEO), lithium bis (trifluoromethylsulphonyl)imide (LiTFSI), tetra(ethylene glycol dimethyl ether) (G4) and a photoinitiator was added with LLZO particles, thoroughly mixed, formed into a film and cross-linked under UV radiation to obtain a composite hybrid electrolyte. This easy procedure allows obtaining self-standing CPEs with desirable properties of flexibility, shape retention upon thermal stress, improved interfacial contact with the electrodes and ionic conductivity suitable for practical application. Lab-scale lithium metal cells assembled with the CPEs and lithium iron phosphate (LFP) cathodes demonstrated specific capacities up to 125 mAh g1 at 1C rate and could work for hundreds of cycles at ambient temperature

In situ neutron powder diffraction of a nickel hydroxide electrode

The redox processes occurring at the nickel oxyhydroxide electrodes were followed by in situ neutron diffraction. The aim was to get a deeper insight into the existing phases and the reactivity mechanisms involved in the reduction process, paying special attention to the so-called "second plateau" phenomenon, occasionally appearing during electrochemical reduction at a potential of 0.8 V vs Hg/HgO. Chemically prepared protonated or deuterated nickel hydroxides, having different phase compositions, oxidation state, and particle size were studied to serve as reference samples. The electrochemically driven structural evolution of four samples upon discharge and charge was followed by in situ neutron powder diffraction using a specially designed cell. For both γ and β-NiOOH phases, the neutron diffraction results evidenced a direct and continuous structural transformation into the β-Ni(OH)2 phase upon reduction, on both the first and the second plateau, with no discontinuity when encountering the second plateau. This confirms that the second plateau phenomenon is not due to any intrinsic structural properties of the active material but is related to its surface properties being prone to be strongly dependent upon the electrode preparation

Towards Solid Batteries Operating at Ambient Temperature Exploiting (Composite) Polymer Electrolytes based on Cross-linked PEO

Profoundly ion conducting, self-standing and tack-free ethylene oxide based polymer electrolytes are successfully prepared via rapid and easily up-scalable free radical polymerization (UV/thermal-curing), which is highly advantageous due to its easiness and rapidity in processing, high efficiency and eco-friendliness as the use of solvent is avoided. All of the prepared materials are thoroughly characterized in terms of their physico-chemical, morphological and electrochemical properties. The crosslinking produced during curing allows the incorporation of high amount of RTIL (e.g., imidazolium, pyrrolidinium) or tetraglyme and lithium salt (TFSI– anion), leading to a material with remarkable homogeneity and robustness. The polymer network can efficiently hold plasticizers without leakage. Samples are thermally stable up to 375 °C under inert conditions, which is particularly interesting for application in Li-ion batteries with increased safety. Excellent ionic conductivity (>0.1 mS cm–1 at 25 °C), wide electrochemical stability (> 5 V vs. Li), stable interfacial properties and dendrite nucleation/growth resistance are obtained. The lab-scale Li-polymer cells assembled with different electrode materials (e.g., LiFePO4, Li-rich NMC, TiO2) show stable charge/discharge characteristics with limited capacity fading upon very long-term reversible cycling. More recently, efforts are dedicated to the formulation of composite hybrid polymer electrolytes that, compared to the pristine components, are stiff while preserving flexibility and can be conceived to attain improved transport properties and interfacial stability. The overall remarkable performance of the novel (composite) polymer electrolytes postulates the possibility of effective implementation in the next generation of safe, durable and high energy density secondary lithium polymer batteries working at (sub)-ambient temperature

Assessing Si-based anodes for Ca-ion batteries: Electrochemical decalciation of CaSi2

Density functional theory (DFT) calculations are used to investigate the basic electrochemical characteristics of Si-based anodes in calcium ion batteries (CIBs). The calculated average voltage of Ca alloying with fcc-Si to form the intermetallic CaxSi phases (0.5 < x ≤ 2) is of 0.4 V, with a volume variation of 306%. Decalciation of the lower Ca content phase, CaSi2, is predicted at an average voltage between 0.57 V (formation of Si-fcc, 65% volume variation) and 1.2 V (formation of metastable deinserted-Si phase, 29% volume variation). Experiments carried out in conventional alkyl carbonate electrolytes show evidence that electrochemical “decalciation” of CaSi2 is possible at moderate temperatures. The decalciation of CaSi2 is confirmed by different characterization techniques. Keywords: Ca-ion batteries, Si anode, CaSi alloys, CaSi

Towards solid-state batteries operating at ambient temperature: (composite) polymer electrolytes in a cross-linked poly(ethylene oxide) matrix

Among the oxide ceramic super lithium ion conductors, garnet-type Li7La3Zr2O12 (LLZO) has recently attracted much attention because of its relatively high ionic conductivity at room temperature (>10-4 S cm–1), negligible electronic conductivity and absence of harmful decomposition products upon contact with atmospheric moisture. Recent efforts have been dedicated to the formulation of composite hybrid polymer electrolytes (CPEs), where the ceramic material is embedded in a polymeric matrix. CPEs are stiff while preserving flexibility, are easily processed, and can be conceived to attain improved ionic conductivity and interfacial contact with the electrodes. Here, a polymer based matrix containing poly(ethylene oxide) (PEO), lithium bis (trifluoromethylsulphonyl)imide (LiTFSI), tetra(ethylene glycol dimethyl ether) (G4) and a photoinitiator was added with LLZO particles, thoroughly mixed, formed into a film and crosslinked under UV radiation to obtain a composite hybrid electrolyte. This easy procedure allows obtaining self-standing CPEs with desirable properties of flexibility, shape retention upon thermal stress, improved interfacial contact with the electrodes and ionic conductivity suitable for practical application. Lab-scale lithium metal cells assembled with the CPEs and LiFePO4 cathodes demonstrated specific capacities up to 125 mAh g-1 at 1C rate and could work for hundreds of cycles at ambient temperature