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Deep Dive – Catholyte Options & Selection
Version: 2024-06-17, for paid subscribers
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Introduction
One of the main advantages of all-solid and semi-solid electrolyte cell designs is that a differentiation between the electrolytes that can migrate to the interface of the positive and the negative electrode is possible, allowing for the separate definition of anolytes (electrolytes in the vicinity of anode) and catholytes (electrolytes in the vicinity of cathode, Figure C-1).
Figure C-1: cell in which liquid transfer from 'catholyte' to 'anolyte' regions is blocked or substantially slowed down by a solid or semi-solid electrolyte layer
The most important implication of this differentiation between anolytes and catholytes is that no simultaneous stability at low potentials (0 V vs. Li+/Li) and high potentials (≥4 V vs. Li+/Li) is necessary for anolyte and catholyte components, as compared to fully liquid electrolytes that simultaneously have to be stable at the anode and the cathode, or form a stable SEI layer.
Promising electrolyte components that thus far were not frequently used in commercial cells because of insufficient stability at the negative electrode therefore stand the chance of gaining prominence in future commercial catholytes.
Prevention of parasitic shuttling (such as by leaked transition metal ions) between electrodes is a major advantage of all-solid and semi-solid cells that eliminates cell aging and failure mechanisms that have tended to slow down the move to higher energy / power and lower cost active materials in both electrodes.
In case of semi-solid or partially porous solid electrolyte layers, the rate of migration of catholyte and anolyte components has to be checked and needs to be sufficiently mitigated as not to cause parasitic reactions that reduce longevity or safety.
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The sections below are included in the full version.
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All-solid vs. Semi-solid vs. Liquid Catholytes and Anolytes – General Considerations
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Why Liquid Catholytes Should Not Be Forfeited Prematurely
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Is Transition Metal-dissolution in Catholytes a Problem?
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Arguments for All-solid and Semi-solid Catholytes
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Summary – Catholyte Component Options and Trade-offs
Table C-1 (full version: 21 entries): Catholyte component selection trade-offs (listed in black in left column: components that were clearly identified as having been used as catholyte components according to patent applications, listed in gray in left column: components used as electrolyte components according to patent applications, explicit use as catholyte component was not identified in the patent literature during preparation of this chapter)
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Estimate of Current State of the Art
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Liquid Catholyte Components
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Solid Catholyte Components
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Under-explored Materials & Chemicals
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Liquid Catholyte Components
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Solid Catholyte Components
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Document size: 4,189 words, 4 figures, 1 table
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