The movement of lithium ions into and out of electrodes is central to the operation of lithium-ion batteries. Although this process has been extensively studied at the device level, it remains insufficiently characterized at the nanoscale level of grain clusters, single grains and defects. Here, we probe the spatial variation of lithium-ion diffusion times in the battery-cathode material LiCoO(2) at a resolution of ∼100 nm by using an atomic force microscope to both redistribute lithium ions and measure the resulting cathode deformation. The relationship between diffusion and single grains and grain boundaries is observed, revealing that the diffusion coefficient increases for certain grain orientations and single-grain boundaries. This knowledge provides feedback to improve understanding of the nanoscale mechanisms underpinning lithium-ion battery operation.

No abstract

The ability to engineer electrode microstructures to increase power and energy densities is critical to the development of high-energy density lithium-ion batteries. Because high tortuosities in porous electrodes are linked to lower delivered energy and power densities, in this paper, we experimentally and computationally study tortuosity and consider possible approaches to decrease it. We investigate the effect of electrode processing on the tortuosity of in-house fabricated porous electrodes, using three-dimensionally reconstructed microstructures obtained by synchrotron x-ray tomography. Computer-generated electrodes are used to understand the experimental findings and assess the impact of particle size distribution and particle packing on tortuosity and reactive area density. We highlight the limitations and tradeoffs of reducing tortuosity and develop a practical set of guidelines for active material manufacture and electrode preparation.

Starting from three-dimensional X-ray tomography data of a commercial LiMn 2 O 4 battery electrode, the effect of microstructure on the electrochemical and chemo-mechanical response of lithium-ion batteries is analyzed. Simulations show that particle size polydispersity impact the local chemical and electrical behavior of a porous electrode, while particle-particle mechanical interactions favor intercalation induced stress accumulation, resulting in a mechanically unreliable electrode microstructure. Simulations based on computer-generated electrode microstructures demonstrate that broad particle size distributions deliver up to two times higher energy density than monodisperse-sized particles based electrodes for low Crates. However, monodisperse particle size distribution electrodes deliver the highest energy and power density for high discharge rates due to a higher surface area of reactive material per unit volume. Calculations show that the surface roughness in experimentally determined electrodes is 2.5 times higher than the one delivered by perfectly smooth spherical particles in computer generated electrodes, and provide high instantaneous power performance, but accelerate side reactions that impact negatively on power performance. The combined experimental and modeling approach demonstrates that porous electrodes with spatially uniform microstructural features improve electrochemical performance and mechanical reliability, especially for high power density applications.

No abstract