Electrodeposition of Manganese Oxides for 3D Electrode Architectures

• Subiksha Baskaran, Chemical Engineering, University of Delaware

• Rachel Davidson, Chemistry and Biochemistry, University of Delaware

Manganese oxides are a class of low-cost, high-performance cathode materials for rechargeable lithium-ion batteries. Improving battery (dis)charging rates requires improving ion and electron transport. Recent single particle studies have shown that matrix effects in traditional composite electrodes, designed with inclusion of binding agents and conductive additives, significantly hinder (dis)charge kinetics. Electrodeposition of cathode materials can enable formation of well-adhered thin films, negating the need for incorporating binding agents. We utilize these pathways to achieve 1) direct deposition of crystalline films and 2) electrochemical printing of 3D electrode architectures using spatially resolved electrochemistry. Unfortunately, reported paths to form manganese oxides via electrodeposition typically require long deposition times and high-temperature annealing steps post-deposition and often produce films which are amorphous and/or exhibit film cracking. We have explored the indirect, cathodic electrodeposition of manganese oxides. These form via production of an electrogenerated base which causes precipitation of Mn(OH)2 or MnOOH species onto electrode surfaces. We have observed that the morphology of deposits can be controlled by changing the primary source of the electrogenerated base and adding structure directing ligands to the electrolyte, allowing us to produce well-adhered, crystalline deposits using room temperature reactions.  Lithium was incorporated into these deposits to form a common cathode structure, LiMn2O4 using a high-temperature and high-pressure hydrothermal reaction with LiOH serving as the source for lithium. We also explored the anodic, oxidative electrodeposition of manganese oxide from manganese sulfate precursors at room temperature and in neutral electrolytes, which formed a mixture of MnOOH and MnO2. Future work will investigate the influence of anodic and cathodic electrodeposition conditions on film crystallinity, particle morphology, and manganese oxide phase. We will also explore the influence of lithium incorporation conditions and final structures and begin testing the performance of films in lithium (dis)charge cycling. Scanning electrochemical cell microscopy (SECCM) will be used to enable the fabrication of 3-D self-supported nanostructured electrodes. These structures will offer shorter diffusion pathways, reducing tortuosity and improving rate capability, yielding more durable and fast-charging batteries.