Chapter 6 Nickel Hydroxides James McBreen, James McBreenSearch for more papers by this author James McBreen, James McBreenSearch for more papers by this author Book Editor(s):Prof. Dr. Jürgen O. Besenhard, Prof. Dr. Jürgen O. Besenhard Institut für Chemische Technologie Anorganischer Stoffe, Technische Universität Graz, Stremayrgasse 16/III, A-8010 Graz, AustriaSearch for more papers by this author First published: 10 December 1998 https://doi.org/10.1002/9783527611676.ch6Citations: 1 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter contains sections titled: Introduction Nickel Hydroxide Battery Electrodes Solid State Chemistry of Nickel Hydroxides Electrochemical Reactions References Citing Literature Handbook of Battery Materials RelatedInformation

In order to study the electronic structure changes of the electrochemically delithiated Li1−xFe0.5Co0.5PO4 system, in situ Fe and Co K-edge XAS and ex situ P K-edge XAS have been carried out during the first charging process. The Fe and Co K-edge XAS results showed that the major charge compensation at the metal sites during charge is achieved by the oxidation of Fe2+ ions at lower potential plateau (∼3.6 V) and the oxidation of Co2+ ions at higher potential plateau (∼5.0 V). The gradual shift of main edge features in P K-edge XANES spectra showed that PO bonds become less covalent during delithiation, due to the increased covalency of Fe3+O bonds via the inductive effect. From the observation of pre-edge peaks, it is concluded that the electrochemical delithiation of Li1−xFePO4 result in the hybridization of P 3p states with the metal 3d states.

This paper gives a brief review of the application of synchrotron X-ray techniques to the study of lithium-ion battery materials. The two main techniques are X-ray absorption spectroscopy (XAS) and high-resolution X-ray diffraction (XRD). Examples are given for in situ XAS and XRD studies of lithium-ion battery cathodes during cycling. This includes time-resolved methods. The paper also discusses the application of soft X-ray XAS to do ex situ studies on battery cathodes. By applying two signal detection methods, it is possible to probe the surface and the bulk of cathode materials simultaneously. Another example is the use of time-resolved XRD studies of the decomposition of reactions of charged cathodes at elevated temperatures. Measurements were done both in the dry state and in the presence of electrolyte. Brief reports are also given on two new synchrotron techniques. One is inelastic X-ray scattering, and the other is synchrotron X-ray reflectometry studies of the surface electrode interface (SEI) on highly oriented single crystal lithium battery cathode surfaces.

Electrocatalysis for the oxygen reduction reaction (ORR) on five binary Pt alloy electrocatalysts (PtCr/C, P W C , PtFe/C, PtCo/C and PtNiiC) supported on carbon have been investigated. The electrochemical characteristics for ORR in a proton conducting fuel cell environment has been correlated with the electronic and structural parameters determined under in situ conditions using XANES and EXAFS technique respectively. The results indicate that all the alloys possess higher Pt 5d band vacancies as compared to Pt/C. There is also evidence of lattice contraction in the alloys (supported by XRD results). Further, the Pt/C shows increase in Pt 5 d band vacancies during potential transitions &om 0.54 to 0.84 V vs. RHE, which has-been rationalized on the basis of OH type adsorption. In contrast to this, the alloys do not exhibit such an enhancement. Detailed E M S analysis supports the presence of OH species on Pt/C and its relative absence in the alloys. Correlation of the electrochemical results with bond distances and dband vacancies show a volcano type behavior with the PtCr/C on top of the curve.

In situ hard X-ray absorption spectroscopy (XAS) at metal K-edges and soft XAS at O K-edge and metal L-edges have been carried out during the first charging process for the layered Li1−xNi0.8Co0.15Al0.05O2 cathode material. The metal K-edge XAS results show that the major charge compensation at the metal site during Li-ion deintercalation is achieved by the oxidation of Ni ions, while the cobalt ions remain mostly unchanged in the Co3+ state. Ni LII,III-edge and O K-edge XAS results in both the fluorescence yield (FY) and partial electron yield (PEY) modes show that substantial amount of Ni ions at the surface of LiNi0.8Co0.15Al0.05O2 powders exist as Ni2+, whereas most of Ni ions in the bulk are in the form of Ni3+. Therefore, if the PEY mode, which is a surface-sensitive technique, is used alone, the interpretation of the results is limited to the surface structures only. In order to get the full picture of both the surface and the bulk, the FY mode and PEY mode should be used simultaneously.

In this program, two different approaches were undertaken to improve the role of electrolyte at low temperature performance - through the improvement in (i) ionic conductivity and (ii) interfacial behavior. Several different types of electrolytes were prepared to examine the feasibil.ity of using these new electrolytes in rechargeable lithium-ion cells in the temperature range of +40°C to -40°C. The feasibility studies include (a) conductivity measurements of the electrolytes, (b) impedance measurements of lithium-ion cells using the screened electrolytes with di.fferent electrochemical history such as [(i) fresh cells prior to formation cycles, (ii) after first charge, and (iii) after first discharge], (c) electrical performance of the cells at room temperatures, and (d) charge discharge behavior at various low temperatures. Among the different types of electrolytes investigated in Phase I and Phase II of this SBIR project, carbonate-based LiPF6 electrolytes with the proposed additives and the low viscous ester as a third component to the carbonate-based LiPF6 electrolytes show promising results at low temperatures. The latter electrolytes deliver over 80% of room temperature capacity at -20{degrees}C when the lithium-ion cells containing these electrolytes were charged at -20 °C. Also, there was no lithium plating when the lithium­-ion cells using C-C composite anode and LiPF{sub 6} in EC/EMC/MP electrolyte were charged at -20{degrees}C at C/5 rate. The studies of ionic conductivity and AC impedance of these new electrolytes, as well as the charge discharge characteristics of lithium-ion cells using these new electrolytes at various low temperatures provide new findings: The reduced capacity and power capability, as well as the problem of lithium plating at low temperatures charging of lithium-ion cells are primarily due to slow the lithium-ion intercalation/de-intercalation kinetics in the carbon structure.

Synchrotron based in situ X-ray diffraction technique has been used to study the mechanism of capacity fading of LiCoO2 cycled to a higher voltage above the normal 4.2V limit and to investigate the mechanism of capacity retention improvement by ZrO2 surface coating on LiCoO2. It was found that the capacity fading of LiCoO2 cycled at higher voltage limit is closely related to the increased polarization rather than the bulk crystal structure damage. The capacity of uncoated LiCoO2 sample dropped to less than 70mAhg−1 when charged to 4.8V after high voltage cycling. However, when the voltage limit was further increased to 8.35V, the capacity was partially restored and the corresponding structural changes were recovered to the similar level as seen in fresh sample. This indicates that the integrity of the bulk crystal structure of LiCoO2 was not seriously damaged during cycling to 4.8V. The increased polarization seems to be responsible for the fading capacity and the uncompleted phase transformation of LiCoO2. The polarization-induced capacity fading can be significantly improved by ZrO2 surface coating. It was proposed that the effect of ZrO2-coating layer on the capacity retention during high voltage cycling is through the formation of protection layer on the surface of LiCoO2 particles, which can reduce the decomposition of the electrolyte at higher voltages.

The application of lithium-ion batteries has been expended rapidly into cell phones, notebook computers, and consumer electronics. However, the more important step will be the commercialization of its use in electric and hybrid electric vehicles (EV and HEV). In order to do so, materials with lower cost, longer cycling life, and better safety characteristics need to be developed. Nickelbased layered materials being developed are considered to have lower cost and higher capacity than the most widely used LiCoO2 cathode materials. However, the safety is still a major concern. Safety characteristics is related to the exothermic reactions in charged (especially over charged) batteries at elevated temperatures that ultimately results in thermal runaway and catastrophic failure of the battery. The thermal runaway has been ascribed to reactions between the charged electrodes and the electrolyte. Therefore, it is very important to study the reactions between the electrodes and electrolyte when the battery is being heated. Calorimetric analysis (DSC, ARC and microcalorimetry), the chemical analysis of electrolyte and gasses evolved have been utilized to investigate the cell component reactions which contribute to the complex thermal behaviors of Li-ion cells. However, not much work has been reported on the very important issue, the interactions between the electrolyte and the cathode during heating and their effects on the structural changes and thermal stability of the cathode. Unfortunately, most temperature dependent x-ray diffraction studies of the charged electrodes reported in the literature were performed in the absence of electrolyte/solvents, therefore not fully reflecting the real situation of the cell during thermal runaway. Recently, we have developed a technique using the combination of a high intensity synchrotron x-ray beam and a fast image plate detector to do time resolved x-ray diffraction during the thermal decomposition of charged cathode materials in the presence of electrolyte. In order to understand the controlling mechanism of thermal runaway of the electrodes in Li-ion cells, we have monitored the structural changes of the charged nickelbased cathode materials in the presence of electrolyte. The cathodes were incorporated into cells with a Li foil anode, a Celgard separator, and a 1 M LiPF6 electrolyte in a 1:1 EC: DMC solvent (LP 30 from EM Industries, Inc.). The cells were charged to various stages of charge, outside the glove box. The cells were then transferred to the glove box for disassembly and transfer of charged cathode materials to 0.3 mm or 0.5mm quartz capillaries. The capillaries were mounted in the thermal stage of diffractometers on beamline X7B, at National Synchrotron Light Source (NSLS) located at Brookhaven National Laboratory (BNL). The XRD spectra were recorded as a set of circles on a Mar 345-image plate detector in the transmission mode. A complete XRD spectrum was taken on the image plate within ~1 min exposure time. Most of the capillaries were heated up to 450°C at a heating rate of 2.4°C /min while XRD patterns were continuously collected. Helped by the high sensitivity and fast data collection rate using the synchrotron X-ray and a twodimensional image detector, we observed new intermediate structure related to the reduction of Ni and oxygen release process. Although the observation of spinel and NiO structures during thermal decomposition have been reported in the literature, nothing has been reported on this intermediated structure, which we assigned as Ni2O3 structure. As shown in figure 1, the Bragg reflections marked with asterisks represent the intermediate structure, which can be assigned to the Ni2O3 structure as reported by Aggarwal et al. with a = 4.61 A and c = 5.61 A in a hexagonal unit cell. The phase transitions from the disordered spinel to the Ni2O3 and NiO start at almost the same temperature, accompanied with the reduction of Ni to Ni and Ni respectively. The structural changes, especially the Ni-O bond length change accompanied with the Ni cation reduction (from Ni in the disordered spinel to the Ni in rock salt type NiO) are quite large, which can be seen in the two-theta angle shifts between the corresponding Bragg reflections (hkl) in Fm3m rock salt structure vs 2x(hkl) in spinel Fd3m structure). The formation of the intermediate structure Ni2O3 with Ni serves as a bridge in the large gap between Ni and Ni. We believe that the formation of the Ni2O3 structure plays an important role in initiating and assisting the phase transition from disordered spinel to rock salt type NiO structure. More detailed discussion will be presented at the meeting.

P K-edge X-ray absorption spectroscopy (XAS) has been carried out to investigate the electronic structure of the electrochemically delithiated Li1-xFePO4 for Li rechargeable batteries. The gradual shift of main edge features to higher energy side showed that P-O bonds become less covalent during delithiation due to the more covalent Fe3+-O bonds via the inductive effect. A principal component analysis of P K-edge XAS spectra of the electrochemically delithiated Li1-xFePO4 reveals that this set of spectra can be well represented by two primary components, in good agreement with a first-order phase transition involving the LiFePO4 and FePO4 phases. From the observation of pre-edge peaks, it is concluded that electrochemical delithiation of Li1-xFePO4 results in the hybridization of P 3p states with the Fe 3d states. (c) 2006 The Electrochemical Society.