All-Solid Battery Electrode Structure for Polysulfide Isolation
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Solution Overview
Problem
All-solid secondary batteries face challenges with side reactions between polysulfide and lithium metal, disconnection of ion and electron transfer paths, and defects in the solid electrolyte layer leading to potential fires or explosions, especially during charging and discharging.
Innovation Solution
The battery design includes a lithium-containing sulfide-based positive electrode active material, a ratio-controlled negative electrode active material layer, and an inactive member on the positive electrode layer to prevent side reactions, maintain ion and electron transfer paths, and reduce defects in the solid electrolyte layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a sulfur-based material is used as positive electrode active material to increase capacity, then the battery capacity increases, but polysulfide is generated and moves to the negative electrode causing side reactions that degrade lifespan
Solution Approach 1:
A buffer layer is introduced as an intermediary between the positive electrode (containing sulfur-based material) and the negative electrode. This buffer layer prevents polysulfide generated during charging/discharging from directly contacting and reacting with the lithium metal negative electrode, thereby eliminating the harmful side reactions while maintaining the high capacity benefits of sulfur-based materials.
Solution Approach 2:
The harmful polysulfide intermediate is effectively removed from the reaction pathway by the buffer layer, which extracts or blocks the polysulfide from reaching the negative electrode. This separation prevents the degradation mechanism while preserving the electrochemical performance of the sulfur-based positive electrode.
2Quantity of substance
If the volume of sulfur-based material increases during initial discharging, then the capacity is utilized, but the transfer path of ions and/or electrons in the electrode becomes disconnected during volume changes
Solution Approach 1:
The buffer layer acts as a flexible thin film structure that can accommodate the volume expansion and contraction of the sulfur-based material during charging/discharging cycles. This flexible buffer layer maintains continuous contact and prevents disconnection of the ion and electron transfer paths, ensuring reliable electrochemical performance throughout the volume change process.
3Object-affected harmful factors
If a solid electrolyte layer is used to improve safety, then fire and explosion risks are reduced, but defects and cracks occur during manufacturing and charging/discharging processes leading to short circuits
Solution Approach 1:
The buffer layer is positioned beforehand between the solid electrolyte layer and the positive electrode to cushion and distribute mechanical stresses during manufacturing and charging/discharging processes. This prior cushioning prevents the formation and propagation of cracks in the solid electrolyte layer, maintaining its integrity and preventing short circuits while preserving the safety advantages of solid electrolytes.
4Quantity of substance
If lithium metal is used in the negative electrode to achieve high capacity, then the energy density increases, but side reactions with polysulfide occur degrading the battery lifespan
Solution Approach 1:
The buffer layer serves as a protective intermediary that physically separates the lithium metal negative electrode from polysulfide generated at the positive electrode. This intermediary prevents direct contact and harmful side reactions between lithium metal and polysulfide, thereby preserving the high energy density benefits of lithium metal while eliminating the lifespan degradation issue.
Data Source
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AI summary
An all-solid secondary battery includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer includes a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes a lithium-containing sulfide-based positive electrode active material, the lithium-containing sulfide-based positive electrode active material includes Li2S, a Li2S-containing composite, or a combination thereof, the all-solid secondary battery includes a first inactive member on one surface of the positive electrode layer, the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer, a ratio of initial charge capacity of the first negative electrode active material layer to an initial charge capacity of the positive electrode active material layer is in a range of about 0.005 to about 0.45.