Aluminum electrodes have been considered for use in lithium and lithium ion batteries for nearly four decades. Although the Al-Li equilibrium phase diagram contains multiple Al-Li phases, only β-AlLi forms during room temperature cycling. Al 2 Li 3 can be formed when electrochemically inserting Li at temperatures above 400°C, and Al 4 Li 9 is occasionally detected after extended room temperature cycling. Here, four equilibrium phases of Al-Li (β-AlLi, Al 2 Li 3 , AlLi 2−x , Al 4 Li 9 ) were produced by the electrochemical lithiation and delithiation of 1100-series aluminum foil at moderate to intermediate temperatures (30-150°C) using a carbonate-based electrolyte. Phase identification was performed using ex-situ X-ray diffraction and coulometry, after accounting for the consumption of lithium in electrolyte breakdown products. After overcoming an initial nucleation barrier, β-AlLi formed at all temperatures, Al 2 Li 3 and AlLi 2−x formed at temperatures above 60°C at moderate rates, and above 35°C at low rates, and Al 4 Li 9 formed at temperatures above 100°C. All expected phases were also encountered during delithiation. The effects of nucleation and diffusion on observed phases and capacities are also discussed.

No abstract

The trade-off between energy density and power capabilities is a challenge for Li-ion battery design as it highly depends on the complex porous structures that holds the liquid electrolyte. Specifically, mass-transport limitations lead to large concentration gradients in the solution-phase and subsequently to crippling overpotentials. The direct study of these solution-phase concentration profiles in Li-ion battery positive electrodes has been elusive, in part because they are shielded by an opaque and paramagnetic matrix. Herein we present a new methodology employing synchrotron hard X-ray fluorescence to observe the concentration gradient formation within Li-ion battery electrodes in operando. This methodology is substantiated with data collected on a model LiFePO 4 /Li cell using a 1 M LiAsF 6 in 1:1 ethylene carbonate/dimethyl carbonate (EC/DMC) electrolyte under galvanostatic and intermittent charge profiles. As such, the technique holds great promise for optimization of new composite electrodes and for numerical model validation.

Lithium ion battery performance becomes increasingly limited by ionic transport as the current demand increases. Especially detrimental is the transport within the liquid electrolyte that fills the porous electrode, yet reliable measurement of practical lithium diffusivity within this complex structure has been a longstanding challenge. In this work, we have developed a “single sided” analytical technique to determine the diffusivity in porous networks using scanning electrochemical microscopy (SECM) and a molecular redox marker. SECM surface mapping of porous films shows measurement consistency, and diffusion limited currents through a test structure with well-defined geometry matches the results of numerical modeling within 10%. Diffusivity measurement shows significant deviation from the Bruggeman model for porosities below 60%. The developed technique is applicable to all porous structures independent of their electronic conductivity. Importantly, for lithium-ion batteries the technique does not require free-standing electrodes and therefore is applicable to industrially relevant high power electrodes as a tool for optimization as well as for quality control.