Coated Negative Electrodes for Solid-State Cells
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Solution Overview
Problem
The fabrication of solid-state electrochemical cells faces challenges with lithium metal negative electrodes due to safety concerns, limited high-rate charge-discharge capabilities, and difficulties in integrating gel-polymer electrolytes with high-capacity negative active materials like silicon, which restricts their performance and application.
Innovation Solution
The method involves fabricating negative electrodes using coating techniques without electrolytes initially, then integrating them with a gel-polymer electrolyte layer that provides ionic conductivity and supports high-rate applications, using materials like silicon and graphite, and incorporating a polymer base to trap and release liquid electrolyte for enhanced ionic transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium metal is used to form negative electrodes, then high capacity is achieved, but safety concerns arise and dendrite growth occurs
Solution Approach 1:
The patent replaces lithium metal with graphite-based negative electrodes that have a more stable and safer electrochemical profile. While graphite has slightly lower theoretical capacity than lithium metal, it eliminates dendrite formation and safety hazards, making it a practical substitute for mass-market applications.
2Quantity of substance
If lithium metal is used in solid-state cells, then high capacity is achieved, but charge-discharge rate is limited to less than 1 mA/cm2
Solution Approach 1:
The patent changes the material parameter from lithium metal to graphite, which has different electrochemical properties that enable higher charge-discharge rates. The graphite structure allows for faster ion transport kinetics, breaking the 1 mA/cm2 limitation that constrains lithium metal-based cells.
3Reliability
If gel-polymer electrolyte is integrated into negative electrodes during fabrication, then robust electrode-electrolyte interface is achieved, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-coating the negative electrode with a thin layer of liquid electrolyte before assembling the cell. This pre-treatment ensures immediate and uniform contact between the gel-polymer electrolyte and the electrode surface upon assembly, creating a robust interface without requiring complex in-situ electrolyte distribution mechanisms during cell fabrication.
4Quantity of substance
If high-capacity negative active materials like silicon are used, then capacity is improved, but volume expansion and low conductivity issues arise
Solution Approach 1:
The patent applies local quality by using silicon nanoparticles dispersed within a graphite matrix rather than bulk silicon. The graphite provides a stable structural framework that accommodates silicon's volume expansion locally at the nanoparticle level, while maintaining overall electrode structural integrity and electrical conductivity through the conductive graphite network.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables solid-state electrochemical cells to operate at charge and discharge rates greater than 1 mA/cm2, utilizing high-capacity negative active materials without sacrificing performance, and reduces the need for separators, enhancing the volumetric and gravimetric capacity compared to liquid-based cells.
Implementation Method 1
The gel-polymer electrolyte layer provides ionic conductivity between the positive electrode and the negative electrode
Implementation Method 2
The polymer base traps the liquid electrolyte
Implementation Method 3
The gel-polymer electrolyte layer releases some of its liquid electrolyte after the interface with the negative electrode is formed
Data Source
AI summary
Provided are new solid-state electrochemical cells and methods for fabricating these cells. In some examples, a solid-state electrochemical cell is assembled using a negative electrode, a positive electrode, and a gel-polymer electrolyte layer, which is disposed and provides ionic communications between these electrodes. Prior to this assembly, the negative electrode is free from electrolytes. The negative electrode is fabricated using a coating technique, e.g., forming a slurry, comprising a polymer binder and one or more negative active materials structures, such as silicon, graphite, and the like. The porosity, size, and other characteristics of the negative active materials structures and of the resulting coated later are specifically controlled to ensure operation with the gel-polymer electrolyte layer or, more specifically, high-rate charge and discharge, e.g., greater than 1 mA/cm2. The gel-polymer electrolyte layer releases some of its liquid electrolyte after the interface with the negative electrode is formed.