Guidelines for All-Solid-State Battery Design and Electrode Buffer Layers Based on Chemical Potential Profile Calculation

Abstract

Protective coatings on cathode active materials have become paramount for the implementation of solid-state batteries; however, the development of coatings lacks the understanding of the necessary coating properties. In this study, guidelines for the design of solid electrolytes and electrode coatings in all-solid-state batteries are proposed from the viewpoint of the steady-state Li chemical potential profile across the battery cell. The model calculation of the (electro)chemical potential profile in all-solid-state batteries is established by considering the steady-state mixed ionic and electronic conduction in the solid electrolyte under the assumption of local equilibrium. For quantitative discussion, the potential profiles within oxygen ion conductors are calculated instead of Li/Na ion conductors as their partial electronic conductivities have not been reported so far in sufficient detail. Based on the calculated chemical potential profile, two main conclusions are obtained: (1) the decisive factor for the formation of the chemical potential profile of the neutral mobile component (e.g., oxygen or lithium) in the solid electrolyte is its electronic conductivity (and the activity dependence), and (2) a particularly large potential drop is formed in a region where the electronic conductivity becomes small. While these conclusions are valid and general for any solid electrolyte device, they are particularly important for the design of protective coatings and the understanding of the functionality of selfassembled solid electrolyte interphases in all-solid-state batteries. To protect the solid electrolyte from decomposition by reduction/oxidation at the anode/cathode interfaces, a sufficient chemical potential drop is necessary within the coating layer or directly at the interphase layer. To achieve this situation, the coating/interphase materials need to have a lower electronic conductivity than the solid electrolyte.

A Flexible Electron-blocking Interfacial Shield for Dendrite-free Solid Lithium Metal Batteries

“…In contrast, the EBS protected LLZTO prevents electrons from entering the electrolyte, avoiding dendrite formation (Fig. 6c) 46 . The exible LiPAA polymer maintains interfacial contact by accommodating the Li volume change during cycling.…”

From Liquid- to Solid-State Batteries: Ion Transfer Kinetics of Heteroionic Interfaces

“…Hardly any solid electrolyte is equally suited for reducing and oxidizing conditions at an anode and a cathode [77]. One method to solve this problem is the introduction of coating layers with low electronic conductivity between the SE and the electrode [34]. Although the SE and the coating have to be precisely matched, it is not possible to find the perfect coating material for every SE, however.…”

“…Ideally, one electrolyte is stable against reduction in contact with the anode and the other one is stable against oxidation in contact with the cathode [30]. This concept is successfully used in solid oxide fuel cells, where CeO 2 is protected against reduction by yttria-stabilized zirconia (YSZ) [34]. setup consisting of the polymer electrolyte (PE) and the SE with a cathode composite comprised of a transition metal oxide and an SE.…”

Ionic Transport in Potential Coating Materials for Mg Batteries

“…In general, higher electronic conductivity in coatings compared to electrolytes is detrimental to electrolyte stability and can cause battery self-discharge. 23 Ideally, coatings in Mg batteries should: i ) be inexpensive, ii ) involve simple equipments, and iii ) not alter the composition/properties of electrodes and electrolytes. Several strategies exist to introduce coating materials onto electrodes in Li-ion batteries, as summarized recently by Culver et al 35 Inexpensive and simpler techniques include wet and chemical spray coating, while expensive and advanced techniques include ALD, PLD, and chemical vapor deposition.…”

“…This is because the drop/gain in chemical potential across the coating may not be sufficient enough to protect the electrolyte from reduction/oxidation. 23 Additionally, a thicker coating layer accommodates a higher chemical potential difference and becomes more suitable for accommodating an electrolyte with a small ESW. Hence, the choice and thickness of a coating (and its electronic conductivity) can be calibrated depending on the intrinsic electronic conductivity of the electrolyte in ex situ methods.…”