title: Using X-ray Microscopy To Understand How Nanoporous Materials Can Be Used To Reduce the Large Volume Change in Alloy Anodes.
abstract: Tin metal is an attractive negative electrode material to replace graphite in Li-ion batteries due to its high energy density. However, tin undergoes a large volume change upon alloying with Li, which pulverizes the particles, and ultimately leads to short cycling lifetimes. Nevertheless, nanoporous materials have been shown to extend battery life well past what is observed in nonporous material. Despite the exciting potential of porous alloying anodes to significantly increase the energy density in Li-ion batteries, the fundamental physics of how nanoscale architectures accommodate the electrochemically induced volume changes are poorly understood. Here, operando transmission X-ray microscopy has been used to develop an understanding of the mechanisms that govern the enhanced cycling stability in nanoporous tin. We found that in comparison to dense tin, nanoporous tin undergoes a 6-fold smaller areal expansion after lithiation, as a result of the internal porosity and unique nanoscale architecture. The expansion is also more gradual in nanoporous tin compared to the dense material. The nanoscale resolution of the microscope used in this study is ∼30 nm, which allowed us to directly observe the pore structure during lithiation and delithiation. We found that nanoporous tin remains porous during the first insertion and desinsertion cycle. This observation is key, as fully closed pores could lead to mechanical instability, electrolyte inaccessibility, and short lifetimes. While tin was chosen for this study because of its high X-ray contrast, the results of this work should be general to other alloy-type systems, such as Si, that also suffer from volume change based cycling degradation.
authors.affiliation: Department of Chemistry and Biochemistry, UCLA , Los Angeles, California 90095, United States.
authors.forename: John B
authors.initials: JB
authors.lastname: Cook
authors.affiliation: Department of Chemistry and Biochemistry, UCLA , Los Angeles, California 90095, United States.
authors.forename: Terri C
authors.initials: TC
authors.lastname: Lin
authors.affiliation: Department of Chemistry and Biochemistry, UCLA , Los Angeles, California 90095, United States.
authors.forename: Eric
authors.initials: E
authors.lastname: Detsi
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
authors.forename: Johanna Nelson
authors.initials: JN
authors.lastname: Weker
authors.affiliation: Department of Chemistry and Biochemistry, UCLA , Los Angeles, California 90095, United States.|Department of Materials Science and Engineering, UCLA , Los Angeles, California 90095, United States.|The California NanoSystems Institute, UCLA , Los Angeles, California 90095, United States.
authors.forename: Sarah H
authors.identifier: 0000-0001-9969-1582
authors.initials: SH
authors.lastname: Tolbert
keywords: Li-ion battery; alloy anodes; in situ; operando; porous silicon; porous tin; tin; transmission X-ray microscope