Low-Tortuosity Thick Electrodes with Active Materials Gradient Design for Enhanced Energy Storage

Abstract

The ever-growing energy demand of modern society calls for the development of high-loading and high-energy-density batteries, and substantial research efforts are required to optimize electrode microstructures for improved energy storage. Low-tortuosity architecture proves effective in promoting charge transport kinetics in thick electrodes; however, heterogeneous electrochemical mass transport along the depth direction is inevitable, especially at high C-rates. In this work, we create an active material gradient in low-tortuosity electrodes along iontransport direction to compensate for uneven reaction kinetics and the nonuniform lithiation/delithiation process in thick electrodes. The gradual decrease of active material concentration from the separator to the current collector reduces the integrated ion diffusion distance and accelerates the electrochemical reaction kinetics, leading to improved rate capabilities. The structure advantages combining low-tortuosity pores and active material gradient offer high mass loading (60 mg cm −2 ) and enhanced performance. Comprehensive understanding of the effect of active material gradient architecture on electrode kinetics has been elucidated by electrochemical characterization and simulations, which can be useful for development of batteries with high-energy/power densities.

Gradient Design for High‐Energy and High‐Power Batteries

“…Wu et al recently reported a low‐tortuosity electrode with an AM gradient using a phase‐inversion process under a magnetic field. [ 65 ] LFP decorated with superparamagnetic iron oxide (Fe 3 O 4 ) nanoparticles could be elevated by a magnet along the thickness direction in the slurry, which was then submerged into the nonsolvent to complete the phase‐inversion process. The gradient composition distribution was confirmed by both SEM and nano‐CT images (Figure 4c).…”

“…Recently, ice-templating and phase inversion have been demonstrated to produce low-tortuosity thick electrodes with gradient porosity or composition, which proves effective in further accelerating reaction kinetics. [41,42,65] More extensive approaches beyond the above are required to accurately control architecture in low-tortuosity electrodes, and the interplay between microstructure and properties should be carefully evaluated to provide further guidance for advanced battery design.…”

“…e) Rate performance and the corresponding overpotentials for the upward, downward, and homogenous electrodes at 60 mg cm −2 LFP loadings. c-e) Reproduced with permission [65]. Copyright 2022, American Chemical Society.…”

Low‐Tortuous MXene (TiNbC) Accordion Arrays Enabled Fast Ion Diffusion and Charge Transfer in Dendrite‐Free Lithium Metal Anodes

“…[ 28–31 ] According to the diffusion coefficient equation $$\left( {{D_{{\rm{eff}}}} = D \times \frac{\varepsilon }{\tau }} \right)$$ (ε is porosity and τ is tortuosity), the conductive pathways is decided by the ε and τ. [ 32–34 ] The randomly arranged structures of 3D thick electrodes possess high tortuosity, prolonging the electron transport path and ion diffusion pathway, resulting in the local polarization of the electric field and lithium‐ion flux inside the electrode. [ 32,35 ] Besides, the high tortuosity would cause the Li plating merely occur at circumscribed anode/electrolyte interfaces, giving rise to inferior rate performances (<1 mA cm −2 ).…”

Unraveling the Effects of Hierarchical Bimodal Microscale Porosity on Thick Electrodes

“…The parameter j lim mainly depends on the value of β, which is increased in thicker electrodes with a smaller porosity and a higher tortuosity. , Therefore, architectural design in thick electrodes is pursued to remain a less tortuous structure and a shorter lithium-ion pathway . Recently, tremendous research efforts have been made in the structural design of thick electrodes, such as vertically arranged pores, , gradient pore structure, , and gradient active material, , with various advanced fabrication methods, such as ice templating, ,, phase inversion, ,,, and solvent evaporation . Although the above design strategies can promote the mass transport kinetics by creating pores and channels inside the thick electrodes, a high porosity is often employed.…”