Our group is focused on investigating the fundamentals of electrochemistry in solid-state ion batteries and using this knowledge to develop novel energy storage systems that utilize architected materials as electrodes. These 3D lattice-type electrodes are designed with full control over the surface area, active material loading, geometry, and size such that it is possible to elicit the desired energy or power density, as well as cyclability and capacitance. The aim of these efforts is to overcome some of the key limitations of high-energy-density electrode materials that undergo alloying or conversion reactions upon lithiation: mechanical failure, sluggish kinetics, and low active material loading.
We utilize various 3D lithographic patterning techniques and often utilize additional nano-fabrication techniques, i.e. electrodeposition, sputtering, chemical vapor deposition, plasma etching, and pyrolisis to create architected anode and cathode materials, as well as electrolytes, to construct battery cells. We conduct cycling and in-situ electrochemical-mechanical experiments in a custom instrument that allows cycling of the cells while simultaneously visualizing the lithiation/delithiation process and/or electrodeposition and dendrite growth.Projects:
- Developing All-Solid-State Li-ion Batteries
- Lithium Oxygen Batteries
- Nanomechanics of Lithium
- Design and in situ Lithiation of Mechanically Robust, Nano-architected Battery Electrodes
Developing All-Solid-State Li-ion Batteries
Researchers: Dr. Heng Yang (post-doc), Kewei Xu (Ph.D. student in Chemistry), Kai Narita (Ph.D. student in Materials Science)
Current battery technologies are inadequate to meet the performance and cost targets of electric vehicles. The limited range of the vehicles resulting from insufficient energy densities of todays’ (lithium-ion) batteries and their high costs (~ 2X over the target) are preventing their widespread adoption. It is necessary to develop new battery technologies, with advanced chemistries, higher energy densities, lower cost and improved safety.
Our team is focused on designing, fabricating, and testing nano-architected all-solid-state Li-ion battery cells that consist of i) nano-architected, mechanically resilient anodes made of variety of different materials, ii) thin and conformal coating of solid electrolytes with high Li-ion conductivity, and iii) high areal capacity, inter-digitated cathodes.
Beyond developing novel electrode geometries for better battery cell performance, this research addresses fundamental questions about mechanisms of ion transport through solid electrolytes, reaction mechanisms, and electrochemistry of architected anodes/cathodes.
Lithium Oxygen Batteries
Researchers Dylan Tozier (Ph.D. student in Materials Science)
State of the art commercial lithium ion batteries use cathodes such as lithium cobalt oxide which rely on insertion and removal of lithium ions from a host material. Insertion cathode materials are limited in their capacity, replacing them with a cathode that employs growth and dissolution of new phases could significantly increase a battery’s energy density. For example, oxygen and sulfur cathodes have been widely researched to this end, with both cases involving the growth of a lithium-rich compound on a current collector/catalyst support.
While the lithium-oxygen battery is promising with regard to its energy density, there are many practical challenges that remain to be solved. For instance, traditional organic electrolytes decompose in the presence of superoxide anions, intermediates in the growth of the lithium peroxide discharge product. Replacing the organic electrolyte with a molten salt in a process pioneered by our collaborators at Liox Power, the organic electrolyte decomposition can be avoided. The morphology of the lithium peroxide grown in this molten salt lithium-oxygen battery is notably different from that previously observed in literature: instead of thin films, platelets, and “toroids” on the order of several hundred nanometers, we observe much larger (several micron) structures shaped consistent with the Wulff construction of lithium peroxide.
The electrochemical growth and dissolution of such large particles presents an interesting problem with respect to design of the cathode geometry. By architecting a cathode to best accommodate this new form of lithium peroxide, we can possibly tune properties such as energy density and power density independently of each other. Such cathode design principles could be extended to other phase-forming chemistries.
Nanomechanics of Lithium
Researchers: Dr. Heng Yang (post-doc), Mike Citrin (Ph.D. student in Materials Science)
Lithium metal is the most energy dense anode material, with a gravimetric energy density over ten times as high as the carbon anodes used in most lithium ion batteries. Commercialization of lithium anode rechargeable batteries has mainly been limited by dendrite formation during cycling, which produces inactive lithium and eventually can short circuit the cell. One promising method to inhibit lithium dendrite formation is to use a robust solid electrolyte with sufficient stiffness and strength that mechanically suppresses dendrite formation.
In this project, we investigate the mechanical properties of Lithium produced through electrochemical cycling of batteries and their link to its atomic-level microstructure at the length scale that are relevant to dendrite dimensions. We first fabricate isolated lithium samples with micro- and nano-dimensions and then conduct nanomechanical experiments using a custom in-situ nanomechanical instrument inside a scanning electron microscope (SEM) under vacuum. Findings from this research have direct implications in the design and safe operation of next-generation lithium anode batteries.
Design and in situ Lithiation of Mechanically Robust, Nano-architected Battery Electrodes
Researchers: Dr. Heng Yang (post-doc), Xiaoxing Xia (Ph.D. student in Materials Science)
Silicon anodes for Li-ion batteries have a 10-fold enhancement in theoretical capacity compared with intercalation-type graphite anodes. The alloying nature of Li insertion in Si allows each Si atom to accommodate up to four Li atoms, but it also causes up to ∼300% Si volume expansion/contraction during lithiation/delithiation, which leads to mechanical degradation and a reduced cycling life. Nano-structuring Si can alleviate this problem for each nanoscale element such as nanowires and nanoparticles but the traditional slurry fabrication method, suitable for intercalation materials with minimal volume expansion, does not provide efficient and reliable assembly of the nanoscale Si building blocks.
We design and create 3D nano-architected electrodes that could potentially resolve some of the key limitations of high-energy-density electrode materials that undergo alloying or conversion reactions upon lithiation: mechanical failure, sluggish kinetics, and low active material loading.