Gradient Design for High‐Energy and High‐Power Batteries

Abstract

lithium-ion batteries (LIBs) with intercalation-type cathodes, liquid electrolytes, and graphite anodes are approaching the energy-density limits; therefore, exploring new redox chemistries or battery configurations is needed to improve the performance of batteries. [3] On the one hand, high-capacity active materials (AMs) such as sulfur-or Li-rich cathodes are extensively explored to offer new chemistries for higher theoretical capacities. [4,5] On the other, increasing efforts are being made to optimize the microstructures of the cathode, anode, and electrolyte to improve the charge-transport kinetics and cell-level energy/power density. [6,7] Charge transport in batteries includes metal-ion transport in the electrolyte, charge transfer at the electrolyte/electrode interphase, solidstate diffusion inside the electrode, and electron transport along the conductive pathways. [8,9] At a low current density, the charge-transfer process dominates the electrochemical kinetics. As current density increases, ion diffusion in the electrolyte plays a major role. [10] Ion transport in the electrolyte is determined by the porous structure of the electrodes and separators. [11,12] In LIBs with a liquid electrolyte, ion diffusion in the porous electrodes is the rate-limiting process. The typical LIB electrodes are isotropic at the macroscale structure, made of a homogeneous mixture of AMs, conductive agents, binders, interconnected pores, etc. The limited ion mobility in the tortuous pores and the anisotropic electric field during operation inevitably cause heterogeneous mass transport through the thickness direction of the electrode. [13] Due to concentration gradients, the reaction kinetics can be different at different depths, and not all the AMs are accessed and activated at the same time. [14,15] The disparity in charge-transport dynamics and reaction kinetics results in underuse of the AMs and reaction polarization, especially at high C-rates, and at a certain C-rate, reaction polarization increases proportionally with electrode thickness due to the lengthened diffusion pathway. [16] Therefore, it is critical to design electrodes with a rational architecture to regulate charge transport. In particular, constructing electrodes with varying microstructures or compositions along the depth direction would allow us to reduce increasing resistances along the charge-transport direction and thus compensate the reaction polarization, which supports high energy and fast charging capacity.The lithium (Li)-metal anode, with the highest gravimetric energy density of 3860 mAh g −1 and the lowest redox potential (−3.04 V vs the standard hydrogen electrode), is considered the Charge transport is a key process that dominates battery performance, and the microstructures of the cathode, anode, and electrolyte play a central role in guiding ion and/or electron transport inside the battery. Rational design of key battery components with varying microstructure along the charge-transport direction to realize optimal local charge-transport dyn...

Toward High‐Areal‐Capacity Electrodes for Lithium and Sodium Ion Batteries

“…High-tap-density active electrode also tends to provide excellent high power density performance. [31] Traditionally, the most intuitive and common ways to achieve high power and/or rate performance are to create nanosized or porous (usually hierar-chical) structure, which minimizes the Li + ion solid-state diffusion distances and increases the surface area of the electrode materials in contact with the electrolyte. [32] However, this strategy is contrary to the high-tap-density and high-areal-mass [27] Copyright 2018, Royal Society of Chemistry.…”

Regulating Lithium Ion Transport by a Highly Stretchable Interface for Dendrite-Free Lithium Metal Batteries

“…The lithium metal anode has been regarded as one of the most promising anode materials for high-energy-density Li-ion secondary batteries due to its high theoretical specific capacity (3680 mAh g –1 ) and lowest electrochemical potential (−3.04 V vs the standard hydrogen electrode). − However, the practical development of lithium metal batteries (LMBs) is hindered by uncontrollable lithium dendrite growth, which is caused by the heterogeneous diffusion and deposition of lithium ions. − The continuous proliferation of dendrites during cycling results in irreversible morphology changes, continuous side reactions, and accumulated dead Li, − which further causes low Coulombic efficiency, poor cycling performance, short circuit, and serious safety issues. Therefore, it is desirable to effectively inhibit uneven lithium deposition for the practical applications of Li metal anodes. − …”

Gradient Designs for Efficient Sodium Batteries

“…Finally, the remaining challenges and future directions related to gradient sodium batteries are discussed. To the best of our knowledge, such reviews have not been available except few overviews on gradient lithium electrodes. , Hopefully, this review would provide valuable insight and stimulate new activity in the future research of gradient designs for sodium and other rechargeable systems.…”