Separator Conductive Layer for Silicon Anode Crack Tolerance
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Solution Overview
Problem
Lithium secondary batteries with silicon negative electrodes face issues of conductive network breakage due to overexpansion and overcontraction, leading to increased resistance and performance deterioration, which existing technologies fail to adequately address.
Innovation Solution
An electrode assembly with a separator featuring a conductive layer on its surface, where the conductive layer's thickness is greater than 50% of the D50 particle size of the silicon active material, functions as a supplementary conductive network to prevent electron path interruption and maintain ionic conductivity, even when cracks form in the negative electrode mixture layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the negative electrode mixture layer is increased to raise energy capacity, then the energy capacity per unit volume increases, but the negative electrode mixture layer becomes prone to breakage and separation from the current collector
Solution Approach 1:
The patent uses a composite structure consisting of the negative electrode mixture layer and a conductive layer formed on the separator. The conductive layer contains conductive particles that create alternative electron transport paths, compensating for breaks in the negative electrode mixture layer's conductive network. This composite approach allows thicker electrode layers to maintain both high capacity and structural integrity.
2Length of moving object
If silicon active material is used to reduce electrode thickness and solve breakage problems, then the electrode thickness is reduced, but the conductive network is short-circuited due to expansion and contraction during charging and discharging
Solution Approach 1:
The conductive layer on the separator acts as an intermediary that provides alternative electron transport paths. When silicon particles expand and contract, causing breaks in the negative electrode mixture layer's conductive network, electrons can travel through the conductive layer on the separator instead, maintaining electrical continuity and preventing short-circuiting of the conductive network.
Solution Approach 2:
The invention introduces a new dimension for electron transport by forming a conductive layer on the separator surface. This creates a two-path electron transport system: through the negative electrode mixture layer and through the conductive layer on the separator. This dimensional addition provides redundancy that compensates for volume changes in silicon particles.
3Reliability
If a conductive layer is formed on the separator to prevent conductive network breakage, then the conductive network continuity is improved, but the thickness of the separator increases
Solution Approach 1:
The patent optimizes the thickness parameter of the conductive layer to balance its dual functions. The conductive layer is made thin enough to minimize separator thickness increase and maintain ionic conductivity, while still being thick enough to provide sufficient conductive particles for electron transport when the negative electrode mixture layer breaks. The thickness is specifically controlled to be greater than 50% of the D50 particle size of the silicon active material.
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 solution effectively prevents electron path interruption and maintains ionic conductivity, allowing for higher energy density and improved cycle characteristics by supplementing the conductive network of the silicon negative electrode, while controlling the thickness of the conductive layer to avoid deterioration in output characteristics.
Implementation Method 1
a conductive layer is formed on at least one surface of the separator... functions as a supplementary conductive network to prevent electron path interruption and maintain ionic conductivity
Data Source
AI summary
An electrode assembly including a positive electrode current collector having at least one surface, positive electrode having a positive electrode mixture layer on at least one surface of the positive electrode current collector, a negative electrode current collector having at least one surface, a negative electrode having a negative electrode mixture layer on at least one surface of the negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode. The negative electrode mixture layer includes silicon active material particles, a conductive layer on at least one surface of the separator, and the thickness of the conductive layer is greater than 50% of the D50 particle size of the silicon active material particles, and a battery cell including the same.