Synthesis of Manganese-Based Electrode Materials Prepared by a Novel Dynamic Floating Electrodeposition (DFE) Method for Energy Storage Devices

• Author / Creator

  Gao, Mingwen

• Electrochemical energy storage and conversion devices such as batteries and supercapacitors have been widely applied in many different fields. Electrode materials play a key role in improving the electrochemical performance of energy storage devices. Among various electrode materials, Mn-based electrode materials have attracted considerable interests, however the complicated methods for synthesizing nano-sized manganese-based materials hinder their commercialization. The aim of this thesis is to cultivate an efficient method, Dynamic Floating Electrodeposition (DFE), to synthesize high performance – manganese based electrode materials. The method can be widely used to fabricate MnOx, MnCO3, Cobalt-doped MnCO3 and LiMn2O4 crystals. In this research, carbon nanotubes (CNTs) were added into fabrication systems to improve the electrochemical performance of the final products. CNTs were processed in an acidic solution to obtain functionalized CNTs. Nano-crystal active materials can only be electrodeposited on the walls of functionalized CNTs. MnO2-CNT composites can deliver a superior electrochemical performance when used as an anode of Lithium Ion Batteries (LIBs). The capacity of MnO2-CNT can achieve to 1003 mAh/g, which is close to the theoretical capacity of MnO2, 1230 mAh/g. The mechanism of the charging-discharging process is also discussed to gain a better understanding of the MnO2-CNTs composites’ electrochemical behavior.A one-step process, Dynamic Floating Electrodeposition (DFE), was developed to synthesize graphene-wrapped MnCO3 mesoporous single crystals (MSCs). In this method, graphene oxide sheets (GOs) were added into electrolytes. The electrodeposition was made through a special setup that can simultaneously achieve the following three goals: the reduction of GOs to reduced graphene oxides (RGOs), the deposition of MnCO3 on RGOs and the wrapping of MnCO3 by RGOs. The as-deposited MnCO3 was characterized to be submicron single crystals and highly porous. Graphene-wrapped MnCO3 MSCs delivered more than 1,000 mAh/g after 130 cycles, demonstrating their significant potential to be used as anodes in LIBs. It is the first time that such a high performance has been achieved on MnCO3 for lithium-ion storage. The graphene-wrapped MnCO3 MSCs synthesized through DFE were electrochemically converted to graphene-wrapped amorphous (GWA) MnOx. The latter was investigated as electrodes for a pseudocapacitor. Such GWA manganese oxide composites showed distinct microstructural features between 0.7 – 2.8 V. The highest capacitance was measured to be 430 F/g at a sweeping rate of 0.2 mV/s. A capacitance of 200 F/g was also obtained under a high sweeping rate of 10 mV/s. The capacitance of GWA manganese oxide composites can maintain 86% even after 2,000 cycles. It was found, for the first time, that GWA manganese oxide composites showed high pseudo-capacitive performance in the potential range of 0.7 – 2.8 V. In order to further explore the potential of the DFE method in fabricating electrode materials, cobalt-containing compounds were introduced into an electrodeposition solution to fabricate Co-doped MnCO3. Different cobalt-doped Co-MnCO3 crystals were successfully fabricated, and the morphology of the Co-MnCO3 crystals could also be altered by adjusting the conditions of electro-deposition. The dumbbell-shaped Co-MnCO3 structure exhibited outstanding electrochemical performance as an anode for LIBs. The specific capacities can reach to 1000 mAh/g at 100 mA/g current density, and 400mAh/g at 1000mA/g current density. These doped manganese-carbonate crystals provide a new strategy and possibility for synthesizing advanced electrode materials for LIBs. Finally, and surprisingly, cathode material LiMn2O4 crystals were able to be synthesized using DFE. This is also the first time that spinel LiMn2O4 crystals have been synthesized at 210oC under atmospheric pressure in a relatively short processing time (five hours). The eutectic molten salts method was utilized to provide a liquid environment for DFE. By performing electrochemical synthesis using DFE in molten salts, porous spinel LiMn2O4 crystals were fabricated and characterized. The synthesized final products exhibited good rate capability. The specific discharge capacity reached 117, 63 and 45 mAh/g at 1, 2 and 4C, respectively. The good rate performance and good cyclability are believed to be rooted to the graphene-wrapped porous structure, which is the one of the prominent features of DFE.

• Subjects / Keywords

  • Electrochemcial Deposition
  • Lithium Manganese Carbonates
  • Pseudocapacitors
  • Lithium Ion Batteries
  • Manganese Carbonates
  • Single Crystals

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3S46HJ6X

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.