Structure Of LiCoO2 Research Articles

Clarifying Anionic Redox Chemistry in LiCoO2 By Direct Detection of O-O Bond Length and First-Principle Investigations

Developing high energy density lithium ion battery cathode materials requires exploring novel chemistries that go beyond the conventional redox couple which is solely based on transition metal. Anionic redox reaction that activates lattice oxygen anions during charging and discharging can almost double the capacity of conventional cathode and thereby significantly increases the energy density. The nature of chemical bonding, in particular whether or not oxygen anions can bond in forming dimers or peroxo-like species, is critical to the reversibility of anionic redox couple and consequent cyclability of the material. Unfortunately, because oxygen scatters X-ray weakly and dimers may form locally rather than globally, it is very challenging to characterize the oxygen-oxygen bond unambiguously using conventional structural study tools like XRD. Here it is shown that neutron pair distribution function (NPDF) analysis is an effective tool in probing the existence of oxygen dimers without limitation to long range order. This technique is applied to LiCoO2 which still attracts lots of attention due to its high packing density and potential high energy density (delivers around 220 mAh/g when charged to 4.6 V). Through combining experimental results with theoretical calculations, the nature of anionic redox reaction is unraveled and it is shown that the structure of LiCoO2 can be fairly robust against oxygen release, suggesting the relative stability of the bulk structure and the possibility of fulfilling its potential of high energy density. Acknowledgement The work done at Brookhaven National Laboratory were supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program, including Battery500 Consortium under contract DE-SC0012704. Research conducted at ORNL's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

Effect of short-time external short circuiting on the capacity fading mechanism during long-term cycling of LiCoO2/mesocarbon microbeads battery

Commercial LiCoO2/mesocarbon microbeads (MCMB) batteries (CP475148AR) are short circuited by different contact resistances (0.6 mΩ and 5.0 mΩ) for short times. The short circuited battery is cycled for 1000 times, and the effect of the short-time external short circuiting on the capacity fading mechanism during long-term cycling of LiCoO2/MCMB battery is studied by analyzing the morphology, structure, and electrochemical performance. The results of SEM indicates that the morphology of LiCoO2 material is almost unchanged, except that the particle surface becomes smooth, and the solid electrolyte interphase (SEI) film on the surface of MCMB electrode becomes nonuniform due to the high temperature caused by short circuiting. The lithium ions are more difficult to de-intercalate from the anode and the lattice structure of LiCoO2 degrades according to the results of X-ray diffraction (XRD). The high discharge current caused by short circuiting can damage electrodes, leaving vacancies in structure. The damage of electrode structure can lead to a decrease of diffusion coefficient of lithium (D), so polarization increases and mainly caused by the LiCoO2 electrode. The capacity deterioration of short circuited battery during long-term cycling is mainly caused by the increase of polarization and capacity loss of electrodes.

Effect of Mg Substitution in the Structural and Electrochemical Properties of Li2MnO3

The revolutionary concept of energy storage is constantly changing due to the increasing demand of high energy density devices. However, issues such as safety, high temperature performance, cost, and environmental concerns need to be addressed, especially for the high power applications. Among the cathode materials investigated, lithium manganese oxides have been exploited due to the abundance of Mn in earth, low toxicity and safety. In this family of oxides, Li2MnO3 possess monoclinic structure having c2/m space group symmetry with a layered arrangement of Li[Li1/3Mn2/3]O2, thus resembling the ideal layered structure of LiCoO2. Li2MnO3 is known to be electrochemically inactive due to the presence of Mn in tetravalent oxidation state. Substitutions of ions in the structure allow possible reduction of the valance state of manganese and electrochemically activating the material. In the present study, we investigated the electrochemical and structural properties of Li2MnO3at room temperature by partially substituting lithium with magnesium using the Pechini synthesis method. Li2MnO3, Li1.5Mg0.25MnO3, Li1.0Mg0.50MnO3 and Li0.5Mg0.75MnO3 compositions were prepared by the Pechini synthesis method. These substitutions were chosen balancing the charge of the cations. For the individual compounds the synthesis was carried out using lithium nitrate [LiNO3], manganese nitrate [Mn(NO3)2], magnesium nitrate [Mg(NO3)2•6H2O], ethylene glycol [C2H6O2] and citric acid [H3C6H5O7] as precursors materials.The molar ratio of M:CA:EG used was 1:1.2:1.2, where M is the sum of all metal ions. Stoichiometric ratios of the metals corresponding to each composition were measured and dissolved in deionized water (H2O) along with citric acid (CA), which behaves as a chelating reagent. The resulting compound was placed in an oven at 130oC for 24 h to complete the drying process, followed by annealing of the powder at 750oC for 8h in air to obtain desire phase. The final heat treated powder samples were mixed with polyvinylidenefloride (PVDF) and carbon black in the wt % ratio of 80:1010, respectively. A slurry paste was prepared using 1-methyl 2-pyrolidone as solvent and was coated on Al foil substrates to form a homogeneous layer. Electrodes were punched out for the fabrication of 2032 coin cells. Metallic Li was used as the counter electrode along with 1.2M LiPF6in EC:DMC (1:1) as electrolyte. The charge and discharge analysis was performed at 10mAh/g within a potential window of 2.0V- 4.8V. The structural phase formation of the materials and presence of any crystalline impurities in the compounds were studied with X-ray diffraction (XRD). Figure 1 shows XRD patterns for Li2MnO3, Li1.5Mg0.25MnO3, Li1.0Mg0.50MnO3 and Li0.5Mg0.75MnO3 synthesized at 7500C for 8h. The formation of single phase material was confirmed for Li2MnO3 and a combination of monoclinic/spinel phases (Li2-xMn1-yMgx+yO3+z) was observed for the Mg-substituted compounds. X-ray photoelectron spectroscopy (XPS) was used to study the valance state of the manganese ion after magnesium substitution. Figure 2 shows XPS pattern for Mn 2p of pristine and partially Mg-substituted samples. A shift to a lower binding energy is observed for Li1.0Mg0.50MnO3 and Li0.5Mg0.75MnO3, indicating a decrease in the tetravalent state of manganese. Therefore, an improvement in electrochemical cycling performance is expected. Preliminary results shown in Figure 3 indicate that partial Mg-substitution enhances the cycleability of Li2MnO3 and increase the capacity to ~90mAh/g. All the electrochemical performance of Li2MnO3, Li1.5Mg0.25MnO3, Li1.0Mg0.50MnO3 and Li0.5Mg0.75MnO3 cathodes will be presented in detail. Figure 1

Cobalt and lithium recovery from active mass of spent Li-ion batteries: Theoretical and experimental approach

The paper is focused on the experimental study of cobalt and lithium recovery from active mass of spent lithium batteries with theoretical explanation of behavior of components in this process. Two leaching agents — H2SO4 and HCl were used in order to compare their effects on cobalt and lithium extraction. It follows from the results that using HCl as a leaching reagent is more appropriate than using H2SO4. Optimal conditions for cobalt and lithium recovery were: 2M HCl, 60–80°C, leaching time 90min. The work also explains the influence of temperature on cobalt and lithium extraction from active mass by activation energy in case of both leaching agents. It was found that the cobalt extraction in sulfuric acid occurs in two time periods. In the first time period, in 15 to 20min from the beginning of leaching, the process is controlled by the rate of a chemical reaction (Ea(Co)=43–48kJ·mol−1). In second time period, the process changes to diffusion controlled, as it is evidenced from the value of Ea(Co)=3–3.5kJ·mol−1. In the case of HCl, cobalt extraction in first time period is controlled by the rate of chemical reaction, Ea(Co)=40–44kJ·mol−1. In the second time period, process is converted to a mixed mechanism, Ea(Co)=20–26kJ·mol−1. Lithium extraction is controlled by the diffusion in both of time periods, or occurs in mixed mode. Ea(Li) is between 2 and 20kJ·mol−1 in both of leaching agent. The study of the fine structure confirmed the hypothesis that on the cobalt and lithium extraction affects the internal structure of the active mass, which consists primarily of LiCoO2 and the cobalt extraction is dependent on lithium extraction from the LiCoO2 structure.

Microscopy Study of Structural Evolution in Epitaxial LiCoO2 Positive Electrode Films during Electrochemical Cycling.

The evolution of interface between the epitaxial thin film LiCoO2 (LCO) electrode and liquid electrolyte and inside the LCO film during electrochemical cycling has been analyzed by high resolution scanning transmission electron microscopy. Relaxation of sharp translational domain boundaries with mismatched layers of CoO2 octahedra occurs during cycling and results in formation of continuous CoO2 layers across the boundaries. The original trigonal layered structure of LiCoO2 tends to change into a spinel structure at the electrode/electrolyte interface after significant extraction of Li from LCO. This change is more pronounced at 4.2 V peak of CV, indicating lower stability of the layered LCO structure near its surface after Li is extracted above 60%. The transformed structure is identified to be close to Co3O4, with Co both on tetrahedral and octahedral sites, rather than to LiCo2O4 as it was suggested in earlier publications. Electron energy-loss spectroscopy measurements also show that Co ions oxidation state is reduced to mixed valence state Co(2+)/Co(3+) during the structure changes to spinel rather than oxidized.

Synthesis of LiCoO2 Prepared by Sol–gel Method

LiCoO2 was synthesized by sol–gel method using lithium acetate and cobalt acetate as the precursors and citric acid as the chelating agent. The solutions were stirred for different stirring times with a magnetic stirrer, followed by heating at 80°C under vigorous stirring until a viscous gel was formed. The as-formed gel was calcined at 700°C for 7 h in air. Structural analysis confirmed that the layered hexagonal structure of LiCoO2 was formed. The synthesized LiCoO2 exhibited the highest intensity, thereby confirming that 30 h is the optimum stirring time. Clear splitting of the (006)/(102) and (108)/(110) hexagonal doublets in the X-rays diffraction patterns indicated that the materials formed a well-ordered hexagonal structure. No impurity phases were observed in the range of stirring times studied probably because of the homogeneous mixing of the precursors.

Enhanced electrochemical performance of surface modified LiCoO2 for all-solid-state lithium batteries

Li2CO3-coated LiCoO2 powders are prepared from a lithium hydroxide solution via low-temperature heat treatment and the effects on the electrochemical performance of all-solid-state lithium ion batteries (ASS-LIBs) using Li2S-P2S5 glass-ceramic solid electrolytes are investigated. A combination of X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analyses reveals that the Li2CO3 particles on the surface of LiCoO2 particles are formed without significant change in LiCoO2 structure. While the Li2CO3 is regarded as an impurity phase in lithium battery systems using liquid electrolytes due to its detrimental effects on electrochemical performance, we show that optimal amounts of Li2CO3 coating effectively suppress interfacial side reactions without a significant decrease in interfacial kinetics for all-solid-state lithium battery systems using sulfide solid electrolytes.

Electrochemical and Structural Properties of Rh Substituted Li2MnO3

Commercial realization of rechargeable Li-ion batteries has revolutionized portable electronic industry, especially microelectronics in recent years. However, issues such as safety, high temperature performance, cost, and environmental concerns need to be addressed, especially for high power applications. Among the cathode materials investigated, lithium manganese oxides have been exploited due to the abundance of Mn in earth, low toxicity and safety. In this family of oxides, Li2MnO3 possess monoclinic structure having c2/m space group symmetry with a layered arrangement of Li[Li1/3Mn2/3]O2, thus resembling the ideal layered structure of LiCoO2. Li2MnO3 is known to be electrochemically inactive due to the presence of Mn in tetravalent oxidation state. Substitutions of ions in the structure allow the reduction of the valance state of manganese, electrochemically activating the material. In the present study, we investigated the electrochemical and structural properties of Li2MnO3at room temperature by partially substituting Mn site with rhodium via the solid state synthesis method. Li2MnO3, Li2RhO3 and Li2Mn0.5Rh0.5O3 compositions were prepared by a solid state synthesis method. For the individual compounds the synthesis was carried out using lithium carbonate [Li2CO3], manganese oxide [MnO2] and rhodium chloride [RhCl3] as precursor materials. Stoichiometric ratios of the metals corresponding to each composition were measured and carefully ground using a pestle and mortar for 1 hour. The resulting mixture was calcined in air at a ramp rate of 100oC h-1 to a final temperature of 600oC for Li2CO3/MnO2, 850oC for Li2CO3/RhCl3 and 900oC for Li2CO3/MnO2/RhCl3.The final heat treated powder samples were mixed with polyvinylidenefloride (PVDF) and carbon black in the wt % ratio of 80:10:10, respectively. A slurry paste was prepared using 1-methyl 2-pyrolidone as solvent and was coated on Al foil substrates to form a homogeneous layer. Electrodes were punched out for the fabrication of 2032 coin cells. Metallic Li was used as the counter electrode along with 1.2M LiPF6in EC:DMC (1:1) as electrolyte. The charge and discharge analysis was performed at 10mAh/g within a potential window of 2.0V- 4.8V. The structural phase formation of the materials and presence of any crystalline impurities in the compounds were studied with X-ray diffraction (XRD). Figure 1 shows XRD spectra for Li2MnO3 600o C -8h, Li2Mn0.5Rh0.5O3 900o C -24h and Li2RhO3 850o C-24h. X-ray photoelectron spectroscopy (XPS) was obtained to study the valance state of the manganese ion after rhodium substitution. Figure 2 shows XPS pattern for Mn 2p of pristine and partially Rh-substituted samples. The Mn 2p1/2 and Mn 2p3/2 peaks for Li2MnO3 are 654.25eV and 642.50eV, respectively, being in agreement with those reported in literature [3]. A slightly shift to a lower binding energy is observed for Li2Mn0.5Rh0.5O3, indicating a decrease in the tetravalent state of manganese. Therefore, an improvement in electrochemical performance is expected. Preliminary results shown in Figure 3 indicate that partial Rh-substitution enhances the cycleability of Li2MnO3 and increases the capacity by 64mAh/g. Electrochemical performance of Li2MnO3, Li2RhO3 and Li2Mn0.5Rh0.5O3 cathodes will be presented in detail. Figure 1

Improvement of the cycling performance of LiCoO2 with assistance of cross-linked PAN for lithium ion batteries

LiCoO2 has been widely used in lithium ion batteries for digital electronic products. However, the limited cycling performance under high cut-off voltage hinders its commercial application. Many metal oxides and/or phosphorus coating have been reported to improve the cycling performance of LiCoO2. In this paper, we report on cross-linked PAN coated LiCoO2 composite as a cathode material for lithium ion batteries. The coating layer was obtained by intermolecular crosslinking of PAN polymer chain by heat treatment at high temperature in air. The air heating process avoids the possible damage arising from the carbon thermal reduction to the surface structure of LiCoO2. Electrochemical test indicates that the LiCoO2 with the cross-linked PAN coating layer shows much improved cycle performance compared with that of bare and Al2O3 coated LiCoO2. These findings might also open new avenues to explore polymer coating for other cathode materials of lithium ion batteries.

Cycling-Induced Changes in the Entropy Profiles of Lithium Cobalt Oxide Electrodes

Entropy profiles of lithium cobalt oxide (LiCoO2) electrodes were measured at various stages in their cycle life to examine performance degradation and cycling-induced changes, or lack thereof, in thermodynamics. LiCoO2 electrodes were cycled at C/2 rate in half-cells (vs. lithium anodes) up to 20 cycles or C/5 rate in full cells (vs. MCMB anodes) up to 500 cycles. The electrodes were then subjected to entropy measurements (∂E/∂T, where E is open-circuit potential and T is temperature) in half-cells at regular intervals over the approximate range 0.5 ≤ x ≤ 1 in LixCoO2. Despite significant losses in capacity, the cycling did not result in any change to the overall shape of the entropy profile, indicating retention of the LiCoO2 structure, lithium insertion mechanism, and thermodynamics. This confirms that cycling-induced performance degradation in LiCoO2 electrodes is primarily caused by kinetic barriers that increase with cycling. Electrodes cycled at C/5 exhibited a subtle, quantitative, and gradual change in the entropy profile in the narrow potential range of the hexagonal-to-monoclinic phase transition. The observed change is indicative of a decrease in the intralayer lithium ordering that occurs at these potentials, and it demonstrates that a cycling-induced structural disorder accompanies the kinetic degradation mechanisms.

Mg doping and zirconium oxyfluoride coating co-modification to enhance the high-voltage performance of LiCoO2 for lithium ion battery

Mg doping and zirconium oxyfluoride (ZrOxFy) coating are introduced simultaneously to improve the high-voltage performance of LiCoO2 cathode material. XRD, TEM and XPS analysis confirm that the doping element (Mg) is incorporated into the lattices of the modified samples and there is a compact ZrOxFy coating layer on the surface of the co-modified sample. In addition, DSC results indicate that the modified samples show better thermal stability at the charged state. Electrochemical tests demonstrate that the cycling capability of co-modified sample is enhanced apparently, which maintains 76.3% of its initial capacity after 100cycles at 1C in the voltage range of 3.0–4.6V. That is much more than 19.5% for the pristine sample. Moreover, EIS, XRD, TEM and Co dissolution tests of the cycled electrodes reveal that Mg-doping stabilizes the crystal structure of LiCoO2 and ZrOxFy-coating alleviates unwanted interfacial side reactions between the cathode and electrolyte, thereby suppressing Co dissolution and the impedance growth during prolonged cycling.

Improving the cycling stability of LiCoO2 at 4.5 V through co-modification by Mg doping and zirconium oxyfluoride coating

The co-modification by Mg doping and zirconium oxyfluoride (ZrOxFy) coating is employed to improve the cycling stability of LiCoO2 in the voltage range of 3.0–4.5V. SEM, TEM images and EDS mappings of the modified sample confirm that there is a compact ZrOxFy coating layer on the surface of the cathode particles and the doping element (Mg) distributes uniformly in the modified sample. Electrochemical tests demonstrate that the co-modified sample exhibits obviously enhanced cycling stability in the voltage range of 3.0–4.5V, which maintains 91.2% of its initial capacity after 100 cycles at 1C rate. That is much more than 64.4% for the pristine sample. Moreover, EIS, XRD and Co dissolution tests of the cycled electrodes reveal that Mg doping stabilizes the crystal structure of LiCoO2 and ZrOxFy coating alleviates unwanted interfacial side reactions between the cathode and electrolyte, thereby suppressing Co dissolution and the growth of impedance during prolonged cycling.

Analysis for the Electronic Structure at Cathode/Electrolyte Interface in Lithium-Ion Battery Via In Situ Total Reflection Fluorescence X-ray Absorption Spectroscopy

Several research groups have reported that the cathode/electrolyte interface plays an essential role for the deterioration of lithium ion batteries [1, 2]. To further enhance the cycle time of lithium-ion batteries, it is important to understand the reactions at the cathode/electrolyte interface. However, the mechanisms of such interface reactions have not been fully understood due to the difficulty of their direct observation at the nanometer scale. Recently, we have developed a new technique named in-situ total-reflection fluorescence X-ray absorption spectroscopy (in-situ TRF-XAS) to analyze directly the electronic structure at the cathode/electrolyte interface under operating condition [3, 4]. By using in-situ TRF-XAS, we investigate the electronic structure of LiCoO2 and/or LiFePO4/electrolyte interface under battery operation condition and discuss the correlation between the electronic structure at the interface and durability of the active materials. LiCoO2 is one of the most popular active materials whose capacity easily fades with the long charge/discharge cycling [5]. On the other hand, LiFePO4 exhibits a more stable capacity with cycling compared to LiCoO2 [6].LiCoO2 and LiFePO4 thin-films were prepared on Pt and Au polycrystalline substrate by pulsed layer deposition (PLD), respectively. In-situ TRF-XAS measurements were performed at the BL01B1, BL28XU and BL37XU at SPring-8 (Japan) using a home-made cell with a counter electrode of Li foil (Fig. 1). The separator (CELGARD®3501) was immersed with 1 mol dm-3 LiClO4 in a 1:1 volumetric mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The TRF-XAS measurements were conducted under setting the X-ray incident angle at 0.17-0.20° and the generated fluorescence X-ray was detected with a solid state detector. In-situ TRF XAS spectra corresponding to the information at cathode/electrolyte interface of the LiCoO2 and LiFePO4 thin films were analyzed before and after electrolyte immersion. The XANES spectrum of the LiCoO2 surface was shifted to lower energy upon electrolyte immersion, meaning the reduction of the Co ions at the surface. In contrast to LiCoO2, the XANES spectrum of the LiFePO4 surface did not show any shift upon electrolyte immersion, meaning that no reduction of the Fe ions at the surface occurred. At the electrode/electrolyte interface, the electrochemical potential gap between the two phases should be compensated. The potential change at the electrode side and the electrolyte side forms space charge layer and electrical double layer, respectively. For LiCoO2, the reduction of the surface means the formation of the space charge layer via electron transfer form the electrolyte and therefore the potential gap is compensated by both the space charge layer and the electrical double layer (Fig. 2 (a)). As for LiFePO4, the space charge layer hardly forms at the surface because the surface was not reduced via electron transfer from the electrolyte. Therefore, the electrical double layer contributes locally to the potential compensation for LiFePO4 (Fig. 2(b)). The durability of the electrode materials depends on the formation of the space charge layer. Acknowledgments This work was partially supported by New Energy and Industrial Technology Department Organization (NEDO), Japan, for Research and Development Initiative for Scientific Innovation of New Generation Battery (RISING) project.

Performance improvement of LiCoO2 by MgF2 surface modification and mechanism exploration

LiCoO2 cathode material synthesized by a sol-gel method is modified by different contents of MgF2 via simple chemical deposition. The structure and morphology of pristine and MgF2-coated LiCoO2 are investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). It is found that the homogeneous MgF2 surface modification does not change the bulk structure of LiCoO2. The effects of MgF2 on the electrochemical behaviors of LiCoO2 are studied. Comparatively, 1wt.% MgF2-coated LiCoO2 exhibits the best electrochemical performances. Cyclic voltammetry (CV) results confirm that MgF2 surface coating decreases the electrode polarization and improves the structural stability of LiCoO2 during cycling. The results of electrochemical impedance spectroscopy (EIS) and Fourier transform infrared (FTIR) for pristine and 1wt.% MgF2-coated LiCoO2 further demonstrates that modification layer suppresses the undesirable growth of solid electrolyte interface (SEI) film, which greatly contributes to the improved electrochemical performances after surface modification. Differential scanning calorimetry (DSC) tests show that MgF2 coating also improves the thermal stability of LiCoO2 electrode.

Enhanced electrochemical performance of Mg-doped LiCoO2 synthesized by a polymer-pyrolysis method

LiCo1−xMgxO2(x=0, 0.01, 0.03, and 0.05) was synthesized by a polymer-pyrolysis method. The effect of Mg doping on the structure and electrochemical properties of LiCoO2 was investigated. XRD analysis showed that all the samples obtained had the well-ordered layer structure. SEM image showed that the powders consist of well-crystallized particles with hexagonal form. The charge–discharge tests showed that the increase of Mg content in LiCoO2 pronouncedly improved the cycling performance of samples although it slightly decreased the initial discharge capacity. LiCo0.97Mg0.03O2 demonstrated an initial discharge capacity of 169.2mAhg−1 and the best cyclic performance as it retained 91.1% of the initial capacity after 50 cycles when cycled at 50mAg−1 between 3.0 and 4.5V. Cyclic voltammagram demonstrated that the Mg doping can distinctly stabilize the crystal structure of LiCoO2 by suppressing the phase transition of the cathode during lithium ion deintercalation and intercalation.

Effect of Potassium on the Steadiness of the Structure of LiCoO2

The aim of this study was to improve the properties of cathode material for Li-ion batteries based on LiCoO2. As a method of manufacturing of the doped base material was chosen the solid phase reaction method, which has been already tested for the production of the basic material. The main goals were reducing the capacity loss during cycling of the material, maintaining the same or achieving higher capacity or increasing the current carrying capacity of the material LiCoO2 by doping the base material with varying amounts of potassium ions or by substitution of lithium by potassium.

Electrochemical features of combustion-synthesized lithium cobaltate as cathode material for lithium ion battery

Lithium cobaltate (LiCoO2) was produced by carbon combustion synthesis of oxide (CCSO) using carbon nanoparticles as a fuel. In this method, the exothermic oxidation of carbon nanoparticles with an average size of 5 nm (specific surface 80 m2/g) gives rise to a self-propagating thermal wave with maximum temperatures of up to 900°C. The thermal front rapidly propagates through the mixture of solid reactants converting it to lithium cobaltate. XRD data suggest that the as-synthesized products were single phase. Carbon is not incorporated in the product and is evolved from the reaction zone as gaseous CO2. Thermogravimetric analysis was used to identify the features of interaction in the LiNO3-Co3O4-C system. The key features affecting the process-carbon pre-concentration in the reacting mixture and oxygen infiltration to the reaction zone-led to the formation of layered structure of LiCoO2 and affected the particle sizes. The synthesized crystalline nanoparticles were nearly spherical, and their average particle diameters ranged between 60 and 200 nm.

Effect of Mg doping on the local structure of LiMgyCo1−yO2 cathode material investigated by X-ray absorption spectroscopy

A higher capacity and better cyclability are apparent when magnesium is introduced into the structure of LiCoO2 (y = 0.15). XRD analysis of LiMgyCo1−yO2 (y = 0, 0.1, 0.15), synthesized at 800 °C using a microwave assisted method, shows that the material is in the R-3m space group and to have a slightly expanded unit cell that increases with greater magnesium doping. Structural analysis by X-ray absorption spectroscopy (XAS) at the Co K-edge, L-edge and O K-edge shows that the magnesium is located in the transition metal layer rather than in the lithium layer and the charge balance results from the formation of oxygen vacancies rather than Co4+, while cobalt remains in the 3+ oxidation state. Interestingly, oxygen is found to participate in the charge compensation. Both magnesium, in the transition metal layer, and the Co-defect structure are attributed to the contribution towards structural stabilization of LiCoO2, thereby resulting in its enhanced electrochemical performance.

Heat treatment of LiCoO2 recovered from cathode scraps with solvent method

Solvent method was used to recover LiCoO2 scrap materials, and the effects of heat treatment on the scrap materials for Li-ion battery were investigated in detail. SEM results showed that heat treatment could slightly reduce the degree agglomeration of the scrap materials. XRD results showed that the layer structure of LiCoO2 was partly destroyed during the recovery process. Low temperature heat treatment could contribute to restore the original layer structure of LiCoO2, however, high temperature heat treatment could lead to the further damage of the layer structure. Compared with the unheat-treated scrap materials, the discharge capacity and the cycle life of the pristine scrap materials heat-treated at 200 °C, 250 °C and 300 °C were obviously improved, Especially after heat-treated at 250 °C, the discharge capacity could reach about 154.6 mAh g−1 and the capacity retention rate still remained at 92.0% after 360 cycles. Particle size distribution, tap density and recovery rate of scrap materials were also investigated.

Investigations on the influence of the substrate on the crystal structure of sputtered LiCoO2

The influence of the uppermost substrate layer on the structural properties of sputtered lithium cobalt oxide (LiCoO2) is discussed in this work. For this purpose, bare, oxidized, and platinum-coated silicon wafers, as well as stainless steel and titanium sheets, were used as substrates. The resulting crystal structure of LiCoO2 deposited on these substrates was analyzed and discussed. The LiCoO2 thin films were deposited by RF magnetron sputtering with different film thicknesses. A subsequent annealing step at 700 °C was performed to induce the crystallinity of LiCoO2. The crystal orientation was determined by X-ray diffraction. The obtained results show a strong dependency of LiCoO2's crystal structure on the surface the film is deposited on. However, the strong influence of the film thickness reported in previous publications could not be observed. If LiCoO2 is deposited on the substrates with a metallic surface, a strong (003) preferential orientation is obtained for a wide range of film thicknesses. In contrast, sputtering of LiCoO2 on bare and on oxidized silicon wafers results in a (101) dominated crystal structure for the different film thicknesses. These experiments show the importance of the characterization of LiCoO2's crystal structure in the intended battery setup.