The constantly growing power requirements of portable electronic devices and the need for high-power batteries for electric vehicles have created a strong demand for new batteries or substantial improvements of existing ones.  Fundamental problems associated with complex interfacial processes in batteries must be resolved to enhance battery performance and lifetime.  An overview of the principles of electrode-electrolyte interfacial studies, experimental methods, recent results, and potential applications will be presented.  Advanced instrumental techniques and basic research approaches were employed to explore in detail fundamental interfacial processes.  Using current-sensing atomic forcemicroscopy (CSAFM), small variations in the electronic conductance of battery electrodes with sub-nanometer spatial resolution were detected and correlated with surface phenomena such as passive film formation and active material phase segregation. The presence of this passive film is believed to be a primary cause of unwanted battery power loss.  While using CSAFM as a diagnostic tool to characterize lithium manganese oxide electrode surfaces, we discovered that CSAFM could also be used to permanently alter the local conductivity of the electrode surface, and thereby carry out nanometer-scale electrochemical patterning, i.e. lithography.  An effort to improve the performance of advanced rechargeable alkaline batteries led to the development of a new inexpensive composite photochromic material that spontaneously switches from transparent to opaque upon exposure light, or by the application of a small voltage.