Azira Azahidi

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.

The electrochemical performance of layered LiNi0.8-xCo0.2MxO2 (M = Fe and Al) cathode materials

The effects of Al and Fe 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 700 °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 39 % and 10 % improvement compared to the undoped 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 better to those of LiNi0.8Co0.2O2 and Fe substituted cathode materials.

Synthesis of LiMn1.9Ti0.1O4 via a combustion method

Lithium Manganese Oxide, LiMn2O4 is being considered as one of the favourable options to replace the current cathode material, LiCoO2. LiMn2O4 have several advantages such as lower cost and non-toxic. In this research, Mn has been partially substituted with Ti in order to overcome the problem of severe capacity fading. LiMn1.9Ti0.1O4 was prepared by a self-propagating combustion method (SPC). Thermal analysis was carried out by Simultaneous Thermogravinometric Analyzer (STA). The material was annealed at 800 °C for 24u2005h and 48u2005h respectively. The Phase analysis was done by performing X-Ray Diffraction (XRD) and also to check the purity of the materials.

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 24u2005h 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 24u2005h, 48u2005h, ...

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.

Investigation of the Overlithiation of Layered LiNi0.7Co0.2Fe0.1O2 Material

The purpose of this research was to investigate and compare the electrochemical characterization of new cathode materials LiNi0.7Co0.2Fe0.1O2 and Li1.1Ni0.6Co0.2Fe0.1O2. The materials were prepared using a combustion synthesis method. Composite cathodes were fabricated and assembled in a coin-type cell. The discharge profile showed plateaus at 3.7 V and 1.6 V. The overlithiated sample exhibited a 10.4% increase of discharge capacity in the first cycle of and an increase of 43.7% in the 5th cycle compared to the non-overlithiated sample.

Materials Characterization and Charge-Discharge Profile of LiNi1-XCoxO2 Cathodic Materials for Li-Ion Battery Application

Mixed lithium nickel cobalt oxides are advantageous over LiCoO2 due to decrease in cobalt content in the material. It is also better than LiNiO2 which is known to be difficult to synthesize and has poor electrochemical properties. Partial substitution of nickel in lithium nickel oxide with cobalt significantly improves its electrochemical properties. In this work, a combustion method was used for synthesis of LiNi1-xCoxO2 (x= 0.1 and 0.2). The starting materials used are nitrates of the metals or transition metals. The precursors obtained are used for thermal studies. The precursors of LiNi1-xCoxO2 were annealed at a temperature of 700 °C for 24h. X-ray diffraction (XRD) showed that the materials are pure. A composite cathode comprising of the cathode active material, binder and graphite was fabricated. Charge-discharge profiles of the materials with a voltage range of 0.5 V - 4.5 V vs Li/Li+ were obtained in order to study their electrochemical characteristics. The materials exhibited several voltage plateaus attributed to different electrochemical reactions.

Mn as a Substituted Cation in LiCoO 2 Cathode Materials

LiCoO2 is the commercial cathode material for Li-ion battery application with many advantages such as ease of preparation and good electrochemical properties. However, it has some limitations especially Co being expensive and toxic. Therefore, the substitution of Co in the LiCoO2 by non-toxic and inexpensive transition metal elements will be an improvement. Partial substitution of Co by Mn has been done in this work via the self-propagating combustion (SPC) method. The materials are then characterized. The materials obtained were phase pure but the electrochemical discharge capacity is about 24 – 27 % less than that of LiCoO2. However, the cycling behaviour of LiCo0.9Mn0.1O2 and LiCo0.8Mn0.2O2 over 15 cycles improved over that of LiCoO2.