D.H Bradhurst

Nickel Hydroxide as an Active Material for the Positive Electrode in Rechargeable Alkaline Batteries

Spherical nickel hydroxide powders coprecipitated with the additives Ca(OH){sub 2}, Co(OH){sub 2}, and Zn(OH){sub 2} were prepared through a spraying technique. These powders, which have a higher tapping density and a much smaller pore volume and crystalline size than conventional powders, were used as the active materials of nickel hydroxide electrodes. The effects of the Ca(OH){sub 2}, Co(OH){sub 2}, and Zn(OH){sub 2} additions on electrode properties such as charge-discharge, reversibility of the electrode reaction, and cycle life, were studied. The relationship between the electrode swelling and the formation of {gamma}-NiOOH was also investigated. The results show that nickel hydroxide powders having a smaller crystallite size show better electrode characteristics such as lower overpotential, higher plateau discharge potential, and higher capacity. The utilization of the active material in the electrodes illustrates that for general use it is better to add Co{sub 2+}, while for a wider temperature range, it would be better to consider the addition of Ca{sup 2+}. The cycle life of the electrode containing Zn{sup 2+} was improved obviously because there was less electrode swelling due to much reduced formation of {gamma}-NiOOH.

Innovative nanosize lithium storage alloys with silica as active centre

Abstract Two types of nanosize intermetallic alloy powders, NiSi and FeSi, are prepared by high-energy ball-milling. The alloys are used as electrode materials in lithium test cells. During lithium insertion into the alloy electrodes, Si acts as active centres, which react with Li to form Li x Si alloys. A high lithium storage capacity of 1180 mA h g −1 is observed for the NiSi electrode, with some reversibility. A mechanism for the reaction of NiSi and FeSi with Li + is proposed.

Spinel Li[Li1/3Ti5/3]O4 as an anode material for lithium ion batteries

Abstract The spinel Li[Li1/3Ti5/3]O4 compound was synthesised via a solid-state method and its electrochemical performance in lithium ion cells was examined. Lithium ions intercalate into and deintercalate from Li[Li1/3Ti5/3]O4 with high reversibility. The spinel Li[Li1/3Ti5/3]O4 demonstrated a very stable structural characteristic for lithium ion insertion and extraction without passivation on its surface. The spinel Li[Li1/3Ti5/3]O4 as an anode material was coupled with LiCoO2 and LiMn2O4 as cathodes to construct lithium ion cells. These cells provide 2.4–2.5 V operating voltage and without the safety concerns associated with using lithium metal or carbon anodes.

Improvement of electrochemical properties of the spinel LiMn2O4 using a Cr dopant effect

Abstract A series of LiCr x Mn 2− x O 4 spinels were synthesised by the Pechini method which enables dopant Cr ions to distribute at Mn sites homogeneously. Neutron diffraction and EDS analysis confirmed that Cr ions do occupy 16d sites (octahedral intestial) evenly in the spinel structure. The Cr dopant effect improves the cyclability of spinel LiMn 2 O 4 electrodes and decreases the self-discharge rate substantially. Cyclic voltammetry and AC impedance spectroscopy were employed to characterise the reactions of lithium insertion into and extraction from LiCr x Mn 2− x O 4 electrodes. It was found that a thicker surface layer was formed on the surface of the pure LiMn 2 O 4 electrode than on the LiMn 2 O 4 electrode.

Secondary aqueous lithium-ion batteries with spinel anodes and cathodes

Abstract Secondary aqueous lithium-ion batteries with spinel Li 2 Mn 4 O 9 or Li 4 Mn 5 O 12 as the anode and LiMn 2 O 4 as the cathode are investigated. The aqueous electrolyte contains 6 M LiNO 3 and 0.0015 M OH − . The Li 2 Mn 4 O 9 /LiNO 3 /LiMn 2 O 4 and Li 4 Mn 5 O 12 /LiNO 3 /LiMn 2 O 4 aqueous cells deliver approximately 100 m Ah g −1 capacity at an average voltage of 1–1.1 V. This aqueous lithium-ion system eliminates safety concerns and offers considerably cost-effective technology for manufacturing.

LiAlδNi1-δO2 solid solutions as cathodic materials for rechargeable lithium batteries

Abstract Layered LiAl δ Ni 1− δ O 2 solid solutions were synthesised via a solid-state reaction at 750°C under an oxygen stream. Single phase LiAl δ Ni 1− δ O 2 compounds were obtained. The structural integrity of the electrode could be preserved via an inert Al 3+ dopant effect to prevent the overcharge of the electrode, which is beneficial for long cycle life of the cell. The LiAl δ Ni 1− δ O 2 electrode delivered approximately 150–160 mAh/g discharge capacity between 3 and 4.3 V, which is similar to LiNiO 2 . A.c. impedance spectroscopy was employed to characterise the kinetic parameters of LiAl δ Ni 1− δ O 2 electrodes in lithium cells combined with the galvanostatic intermittent titration technique (GITT). It was found that the Al 3+ dopant effect could decrease the charge-transfer resistance ( R CT ) and increase the Li-ion diffusion coefficient.

Synthesis and characterization of LiNiO2 compounds as cathodes for rechargeable lithium batteries

Abstract Layered LiNiO2 compounds are synthesized using a variety of conditions. Lithium hydroxide (LiOH·H2O) and nickel oxide (NiO) are used as precursors. Heat treatment at 750°C in oxygen is found to be an optimum synthesis condition. Excess lithium (Li:Ni=1∼1.1 in molar ratio) is essential to produce LiNiO2 compounds with good electrochemical performance. According to DTA/TG analysis, the LiNiO2 can decompose to Li1−xNi1+xO2, which has a detrimental effect on the electrochemical reactivity of the LiNiO2 compound. The kinetic parameters of LiNiO2 electrodes are characterized by AC impedance spectroscopy.

Lithium storage properties of nanocrystalline eta-Cu6Sn5 alloys prepared by ball-milling

Abstract Nanocrystalline eta-Cu6Sn5 alloy powders were prepared by high energy ball-milling. Lithium ions can be electrochemically inserted into Cu6Sn5 electrodes, alloying with Sn to form LixSn alloys. Simultaneously, an inactive Cu matrix is produced, which could buffer the volume expansion of the active Sn due to the formation of LixSn alloys. It appears that lithium can react reversibly with the nanocrystalline Cu6Sn5 alloy to some extent. A reversible capacity of ∼400 mAh/g has been achieved in preliminary tests. The results of ex-situ X-ray diffraction support the above proposal.

Structural, physical and electrochemical characterisation of LiNixCo1−xO2 solid solutions

Abstract LiNi x Co 1− x O 2 solid solutions are synthesised and their electrochemical performance as cathodes is examined in lithium cells. Through DTA/TG analysis and self-discharge tests, it is found that both the thermal stability at high temperature and the electrochemical stability in the fully-charged state for LiNi x Co 1− x O 2 increases with increasing content of cobalt in the compound. The average operating potentials for the solid solutions are lower than those for pure LiCoO 2 . This indicates that both cobalt and nickel take part in the redox reactions during lithium insertion and extraction. The substitution of Ni 3+ for Co 3+ in LiNi x Co 1− x O 2 can improve the specific capacity, but with a small sacrifice in cycleability.

Surface modification of Mg2Ni alloy in an acid solution of copper sulfate and sulfuric acid

Abstract A simple method of electroless copper plating for the surface modification of Mg 2 Ni alloy has been described in this paper. The plating solution contains only copper sulfate and sulfuric acid which are less toxic to the environment than the chemical reagents used in conventional copper plating solutions. Moreover, the coating process was very easy and fast to operate needing no special treatment for air-exposed samples before plating. The phase composition and microstructure of the modified and unmodified Mg 2 Ni alloy were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical characteristics and performance of the electrodes were examined using galvanostatic charge/discharge and cyclic voltammetry techniques. A discharge capacity of 210 mA·h·g −1 Mg 2 Ni has been obtained from the modified Mg 2 Ni alloy. The results show that the surface modification of the Mg 2 Ni alloy electrode can significantly improve its electrochemical characteristics and performance. It is suggested that this copper plating method is very promising for surface modification of the Mg 2 Ni alloy in hydride batteries.