Kelimah Elong

Solid Solutions of LiCo1-xNixO2(x=0,0.1,...,0.9) Obtained via a Combustion Synthesis Route and Their Electrochemical Characteristics.

Pure, single-phase and layered materials with good cation ordering are not easy to synthesize. In this work, solid solutions of (x = 0, 0.1, …, 0.9) are synthesized using a self-propagating combustion route and characterized. All the materials are observed to be phase pure giving materials of hexagonal crystal system with R-3m space group. The RIR and R factor values of stoichiometries of (x = 0.1, 0.2, 0.3, 0.4, and 0.5) show good cation ordering. Their electrochemical properties are investigated by a series of charge-discharge cycling in the voltage range of 3.0 to 4.3 V. It is found that some of the stoichiometries exhibit specific capacities comparable or better than those of LiCoO2, but the voltage plateau is slightly more slopping than that for the LiCoO2 reference material.

Effect of High-Energy Ball Milling on the Charge-Discharge Behaviour of LiCo0.3Ni0.7O2

Li-ion cathode materials in the nanodimension should show improvement in capacity retention from the normal material. This is because the electrochemical performance of the cathode material in lithium secondary batteries depends on the electrochemical redox reaction which is affected by the surface area to volume ratio of the particles. In this work, LiCo0.3Ni0.7O2 powder will be prepared via a self-propagating combustion method and the high-energy ball milling method will be used to prepare LiCo0.3Ni0.7O2 nanopowders. X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) are used to characterize the materials. The materials are observed to be phase pure. Li-ion cells are then fabricated and tested. The cells are subjected to a series of charge-discharge cycling in the voltage range of 3.0 to 4.3 V. It was found that the nanomaterial exhibit specific capacities less than that of the normal material.

Mn Substitution with Co in LiCo(1-X)MnxO2 Cathode Materials and their Charge-Discharge Characteristic

LiCoO2 has been used as a cathode material in commercial Li-ion batteries. This is due to advantageous properties of the LiCoO2 like ease of preparation and good electrochemical characteristics. However, the high cost and toxicity of Co has limited its use. Therefore, the substitution of Co in the LiCoO2 by non-toxic and inexpensive transition metallic element is needed. Mn is considered as one of the promising candidates to fulfill all the requirements. Partial substitution of Co by Mn has also been considered to enhance the stability of LiCoO2 lattice, minimize capacity fading and increase cycle life of the Li-ion battery. LiCo(1-x)MnxO2 (x= 0.1, 0.2, 0.3) were prepared by using a self-propagating combustion (SPC) method. X-ray diffraction (XRD) of the samples were carried out for phase analysis and showed that all the materials are pure. The samples were also analyzed using the Field Emission Scanning Electron Microscope (FESEM) to study its morphology and particle size. Finally cathodes were fabricated and assembled in an inert gas-filled fabrication box. Discharge profiles of the materials were carried out in the voltage range of 4.3 V – 3 V. The materials obtained were phase pure and improved the capacity fading of the materials compared to LiCoO2. All of the materials exhibited less than 10% capacity loss even though it does not improve the first cycle discharge capacity.

Ti Doped LiMn1/3Co1/3Ni1/3O2 for Li-Ion Battery Application

Single phase LiMn0.3Co0.3Ni0.3Ti0.1O2 materials are prepared using a self-propagating combustion method. The structure and morphology of the materials were characterized using X-Ray powder diffraction (XRPD) and Field Emission Scanning Electron Microscopy (FESEM). The electrochemical performances of the materials were characterized by means of galvanostatic charge-discharge test on the fabricated cells. XRD results showed that the materials are impurity-free and single phase with well ordered hexaganol structure of Rm space group. The compound was annealed at 700 °C and 800 °C for 24 h. The discharge capacities obtained was 143 mAhg-1 in the first cycle for both materials. The voltage range was between 2.5 to 4.2 V. The 30th cycle, however, revealed that the material annealed at 700 °C shows the better performance. The capacity fading is only about 14% compared to 17% for the 800 °C sample. This implies that LiMn0.3Co0.3Ni0.3Ti0.1O2 material is sensitive to annealing temperature. They exhibited good specific capacity values and looked promising for Li-ion battery application.

Electrochemical performance of overlithiated Li1+xNi0.8Co0.2O2: structural and oxidation state studies

Pure, layered compounds of overlithiated Li1+xNi0.8Co0.2O2 (x = 0.05 and 0.1) were successfully prepared by a modified combustion method. XRD studies showed that cell parameters of the material decreased with increasing the lithium content. SEM revealed that the morphology of particles changed from rounded polyhedral-like crystallites to sharp-edged polyhedral crystals with more doped lithium. EDX showed that the stoichiometries of Ni and Co agrees with calculated synthesized values. Electrochemical studies revealed the overlithiated samples have improved capacities as well as cycling behavior. The sample with x = 0.05 shows the best performance with a specific capacity of 113.29 mA·h·g−1 and the best capacity retention of 92.2% over 10 cycles. XPS results showed that the binding energy of Li 1s is decreased for the Li doped samples with the smallest value for the x = 0.05 sample, implying that Li+ ions can be extracted more easily from Li1.05Ni0.8Co0.2O2 than the other stoichiometries accounting for the improved performance of the material. Considerations of core level XPS peaks for transition metals reveal the existence in several oxidation states. However, the percentage of the +3 oxidation state of transition metals for the when x = 0.1 is the highest and the availability for charge transition from the +3 to +4 state of the transition metal during deintercalation is more readily available.

Influence of Carbon Additives on Cathode Materials, LiCoO2 and LiMn2O4

Carbon additives are very important components of cathodes in Li-ion batteries. This is because carbon is an electronic conductor whereas cathode materials are ionic conductors. Without the presence of carbon, the electrons will not be able to flow and there will be space charge built-up in the materials. Carbon therefore facilitates the conductivity of charged species in the cathode materials and help to disperse the negative charge accumulation which may otherwise impede Li-ion diffusion within the cathodes. In this work, two types of carbon, namely, activated carbon (micron sized) and Denka Black (nano sized) were used in conjunction with the cathode materials LiCoO2 and LiMn2O4. The amounts of cathode materials were kept constant while the amounts of carbon additives were varied. Galvanostatic charge-discharge was done over a voltage range of 4.2 V to 3.2 V. Results showed that Denka Black gives improved performance for both cathode material. This is believed to be due to the effect of nano sized particles of Denka Black.

Fe doped in LiCo0.6Ni0.4O2 and their electrochemical behaviour

LiCo0.6Ni0.4O2 was introduced as one of the most promising candidates for a cathode material as it had higher practical capacity compared to LiCoO2. However, it still can be improved further by using Fe as a dopant producing LiCo0.55Ni0.4Fe0.05O2 novel stoichiometry. The materials were prepared by using a self-propagating combustion method. The materials were found to be single phase and pure of the hexagonal structure and R3¯m space group. LiCo0.55Ni0.4Fe0.05O2 materials were annealed at fixed temperature of 800 °C with different annealing times to optimize the thermal process. Results showed that the Fe doped materials annealed at 800 °C for 24 h performs better than the undoped material in terms of first cycle capacity and capacity retention. The initial discharge capacity showed a 1.7 % improvement compared to the undoped material. Although the improvement in the first cycle is quite small, the cycle stability has improved when Fe was substituted. All of the Fe doped materials annealed at 24 h, 48 h, ...

The Effect of Fe and Al Substitution in LiNi0.8Co0.2O2 Cathode Material

The effect of different cation substitution on the electrochemical performance of layered LiNi0.8-xCo0.2MxO2 (M= Fe, Al; x=0.1) cathode materials were investigated. LiNi0.8-xCo0.2MxO2 (M= Fe, Al; x=0.1) cathode materials were successfully synthesized by a combustion method with an annealing temperature of 800 °C for 24h. The physical and electrochemical properties of the materials were examined using X-ray Diffractometer (XRD), Field Emission Scanning Electron Microscopy (FESEM) and electrochemical charge-discharge. The XRD data showed that all the materials are single phase, hexagonal α-NaFeO2 type structure. The initial discharge capacity showed that Fe and Al substituted materials gave 8 % and 10 % improvement compared to LiNi0.8Co0.2O2 material. The discharge cycling also showed that the cycle stability has improved when Fe and Al was substituted. In view of electrochemical performance, Al containing sample was found to be superior to those of LiNi0.8Co0.2O2 and Fe substituted cathode materials.

Effect of Calcination Time on the Specific Capacities of LiNi0.4Co0.55Ti0.05O2 Cathode Materials

One of the main goals for most of the research in advanced Li-ion batteries is to develop cathode materials with improvement on cost and toxicity. This is to replace the existing commercial cathode material, LiCoO2. LiNi0.4Co0.6O2 was introduced as one of the most promising candidates for a cathode material due to its lower cost and higher capacity compared with LiCoO2. Modification of cathode materials by substituting with other materials is one of the alternative ways to improve the electrochemical performance of the material. In this case, a little amount of Ti was substituted to replace Co in order to give the material LiNi0.4Co0.55Ti0.05O2. Results showed that the substituition of some Co with Ti improves the electrochemical behavior of the material.

Electrochemical Behavior of LiCo(1-x)MnxO2 Crystalline Powders

LiCoO2 is a well-known cathode material used in commercial Li-ion batteries but it has its own limitations in terms of cost and toxicity. Improvement of the material by partial substitution of Co with other transition metals is one of the alternative and effective ways to overcome the limitations and improve the electrochemical performance of cathode materials. The transition metal element used for the substitution has to be cheaper and non-toxic thus Mn is chosen here. LiCo(1-x)MnxO2 (x= 0.1, 0.2, 0.3) we synthesized by a novel route using a self-propagating combustion (SPC) method. The samples are analyzed using X-Ray Diffraction (XRD) for phase purity and Field Emission Scanning Electron Microscopy (FESEM) for morphology and particle size studies. The materials obtained are phase pure. In terms of electrochemical activity, though it does not show better first cycle discharge capacity, the Mn doped materials have improved capacity retention. Results showed that LiCo0.9Mn0.1O2 and LiCo0.8Mn0.2O2 exhibited less than 8 % capacity loss in the 20th cycle compared to 12 % for LiCoO2.