STRUCTURAL AND SURFACE MODIFICATION OF HIGH CAPACITY LI-RICH CATHODE FOR LI-ION BATTERY APPLICATION

• Main Author: Karunawan, Jotti
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/80827
• Institution: Institut Teknologi Bandung

Lithium-ion batteries are currently the main choice as energy storage devices in portable electronic devices and electric vehicles. As a source of Li+ ions, the cathode material plays an important role in determining the capacity, working voltage, and other electrochemical performance of a lithium ion battery. In addition, the cathode material is also the most expensive part, so developing a cheaper cathode is also the main focus in the development of cathode materials. Various types of cathode materials have been developed and commercialized. The Li-rich cathode material with a layered-layered structure is one of the most potential types owing to high specific capacity of >200 mAh/g and a wide working voltage. In addition, the Li-rich cathode material only requires a small amount of cobalt (Co-less), potentially making this type of Li-rich cathode material cheaper. However, until now Li-rich cathode material has not been commercialized yet because it has several problems. The synthesized Li-rich cathode material often suffers from structural defects, including cation mixing, hexagonal structural defects, low c/a lattice parameters which results in a less specific capacity. In addition, the Li-rich cathode material has a poor capacity retention due to degradation reactions at the interface and surface. The anionic redox reaction which is irreversible will result in an O vacancy in the structure and the formation of O2 gas on the surface. O vacancies in the structure will trigger a phase transformation from layered to spinel resulting in voltage fading. In addition, O2 gas on the surface can act as a catalyst in electrolyte decomposition, thus triggering the formation of cathode electrolyte interphase (CEI) and transition metals dissolution. In this research, we have developed Co-less Li-rich Li1.2Ni0.13Co0.13Mn0.54O2 cathode material with structure and surface modification approach. Microwave assisted synthesis is able to increase the uniformity of layered structures which are characterized by low cation mixing and high hexagonal homogeneity resulting in high capacity (259 mAh/g). In addition, proper microwave irradiation can also increase the homogeneity of particle size so that the capacity retention increases. On the other hand, modification of the structure by combining the spinel structure with the layered-layered structure Li-rich to form a layered-layered-spinel multistructure can be carried out by means of calcination at high temperature (950 ?). At high temperature calcination, it will trigger the release of Li and O in the structure, making it easier for transition metals to fill Li sites. This phenomenon will trigger the formation of spinel structures. Layered-layered-spinel multistructure can produce good retention capacity (86.5% 100 cycles 0.2 C, Coulomb efficiency > 99%) and high rate capability. On the other hand, the working voltage greatly affects the electrochemical performance of the Li-rich cathode material. The wide working voltage (2 – 4.8 V) increases the surface degradation of the Li-rich cathode material resulting in significantly increased resistance. SiO2 coating on the Li-rich cathode material can increase the retention capacity which indicates SiO2 can reduce surface degradation. However, the higher SiO2 content on the surface will decrease the specific capacity and increase the charge transfer resistance. Urea treatment on Li-rich coated with SiO2 can significantly reduce resistance due to the presence of carbon nitride (CN) deposits on the surface. SiO2 and CN coatings are formed on the nanometer scale so that they do not reduce the specific capacity of the Li-rich cathode material. Furthermore, the synergistic coating of SiO2+CN can increase the retention capacity in both half-cell (vs. Li metal) and full cell (vs. graphite anode) configurations. In addition, SiO2+CN coating on the Li-rich cathode material is also able to increase rate capability and reduce voltage fading phenomena. This results indicate that SiO2+CN synergistically can reduce surface problems of the Li-rich cathode material.