A study on the surface modification of electrodes via utilization of thin film engineering for advanced lithium metal batteries

Abstract

Over the past decades, global exertion to shift energy paradigm from fossil fuel to renewable energy have rapidly increased the demands for energy storage systems with a high-energy density. Accordingly, lithium ion battery (LiB) systems that are first commercialized in 1991 have been continuously evolved to meet the demands. However, unfortunately, the prevailing opinion in research society is that the evolution of the system has almost reached to the limitation given by materials. In this regard, recently, lithium metal anodes (LMAs) have widely gain attention due to their outstanding natures such as extra-high capacity (3,860 mAh g-1) and low working potential (-3.040 V vs standard hydrogen electrode) both which can guide the highest energy density among the known anode candidates. Besides, it can double the energy density of current LiBs in the case that low-capacity graphite can be successfully replaced by LMA resulting in decreases of volume and/or weight of anode compartment. Despite its potentials, unfortunately, LMA has been suffered from both the problematic growth of Li dendrites and the formation of fragile native solid-electrolyte interphases (SEIs). The obstacles induce a vicious cycle that the growing dendrite breaks the native SEIs, and then the interphase is recovered by consuming active Li+ ions. Such process results in low cycling efficiency, and ultimately cause an electrically isolated metallic Li called dead Li. Furthermore, a growing dendrite may potentially reach to cathode compartments leading to short-circuit that would cause a dangerous combustion. Therefore, alleviating the Li dendrites, thereby prolonging cycle life of lithium metal batteries (LMBs) have been considered as top priority to be solved. In order to mitigate the notorious Li dendrites, in this thesis, strategies based on the surface modification of electrodes (mainly current collectors) will be suggested. In particular, to modify the surface, approaches based on thin film engineering are intensively studied, because it is not only considered as an industrially mature technology, but it can also provide many advantages such as material diversity, good adhesion properties, high-reproducibility and excellent uniformity. Throughout the thesis, the following contents will be introduced. 1. First of all, an entire review will be presented in the first chapter, including brief introduction of lithium metal battery systems, critical drawbacks, literature survey, and so forth.

2. In the subsequent chapter, a topic related to lithiophilic property of metallic elements and its effective utilization will be discussed. Specifically, this topic will contain a method to provide lots of lithiophilic metal nanoparticles on the surface of electrodes via regulation of evaporation conditions during deposition process of metal thin films.

3. Finally, the remainder chapter will be filled with a study on a novel lithiophobic properties of metals that inhibits the electrodeposition reaction of Li. In addition, a simple but effective fabrication strategy for preparation of host structures to stably accommodate LMA is developed by exploiting the unprecedented lithiophobicity of metal thin films. In this section, bottom-up deposition of Li which is favorable deposition characteristics for stable LMAs will be demonstrated with the developed approach.