Image courtesy of Bruce Dunn, UCLA
The crystal structure of the niobium pentoxide (Nb2O5) electrode allows for 2-dimensional diffusion of lithium ions during charging and discharging cycles.
A new mechanism, termed “intercalation pseudocapacitance” was discovered for high-rate lithium-ion energy storage that overcomes lithium-ion diffusion limitations. The new mechanism combines surface adsorption with diffusion of ions into the bulk of the electrode.
This discovery could lead to the design of high performance electrode systems that are more robust and long lasting than the state-of-the-art for numerous applications including grid energy storage.
Electrochemical energy storage devices are currently able to deliver either high power or high energy densities, but not both. For high-power, electrochemical capacitors store energy when charged species, called ions, from the electrolyte adsorb on the surface of the electrode. However, this surface-dominated process results in low energy densities because the bulk of the electrode material is not utilized. On the other hand, lithium-ion batteries have high energy densities but are limited in power because charging is limited by diffusion of the lithium ions through the bulk of the electrode material. With the goal of improving the energy densities of electrochemical capacitors while retaining their high rate capabilities, a team of scientists from two Energy Frontier Research Centers, MEEM at the University of California – Los Angeles and EMC2 at Cornell University, evaluated an electrode material (orthorhombic Nb2O5) that exhibits a charging mechanism they termed “intercalation pseudocapacitance” – meaning that the kinetics of charging include both surface adsorption and diffusion of the charged ions into the bulk of the electrode. Through the quantification of the kinetics for charge storage, the team defined the characteristics necessary for this mechanism: (1) a crystalline structure that offers 2-dimensional transport pathways for ion diffusion and does not change structure during charge/discharge processes, (2) currents that are inversely proportional to the charging time, and (3) charge storage capacity that is mostly independent of charging rate, even at high power. High levels of charge storage achieved within short periods of time through the newly discovered mechanism could expand the possibilities for materials design for various high-performance energy storage applications including storage of energy generated by renewable energy sources for later use on the grid.
Bruce Dunn (Co-Director) and Vidvuds Ozolins (Director)
Molecularly Engineered Energy Materials (MEEM) EFRC, University of California at Los Angeles
Director, emc2 EFRC
DOE Office of Science, Office of Basic Energy Sciences, Energy Frontiers Research Centers Program; operation of the Cornell High Energy Synchrotron Source is supported by NSF and NIH; US DOD National Defense Science and Engineering Fellowship (author MAL); Delegation Generale pour l'Armement (author JC); and the European Research Council and EADS Foundation (authors P.S. and P-L.T.)
Veronica Augustyn, Jérémy Come, Michael A. Lowe. Jong Woung Kim, Pierre-Louis Taberna, Sarah H. Tolbert, Héctor D. Abruña, Patrice Simon, Bruce Dunn, “High-rate electrochemical energy storage through Li+ intercalation pseudocapacitance”, Nature Materials, 12, 518-522, (2013). [DOI: 10.1038/nmat3601]
Molecularly Engineered Energy Materials (MEEM) EFRC
Energy Materials at Cornell (emc2) EFRC
Collaborations, Non-DOE Interagency Collaboration, International Collaboration