Silicon-Carbon Negative Electrode Sheet With Interface Buffer Layer
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Solution Overview
Problem
The low cycle life of silicon-containing negative electrode lithium-ion batteries is due to the poor compatibility and volume expansion issues between silicon and graphite materials, leading to reduced electrochemical performance and lithium intercalation capacity.
Innovation Solution
A negative electrode sheet is designed with a silicon-containing layer, an intermediate layer containing a conductive agent and a binder, and a carbon layer stacked sequentially on a current collector, enhancing interface compatibility and adhesion, and forming a stable electronic and ion transmission channel to alleviate lithium precipitation and prolong battery life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon material is used as negative electrode material to achieve high theoretical capacity, then energy density is improved, but volume expansion during lithium intercalation causes poor interface compatibility and reduced cycle life
Solution Approach 1:
The negative electrode is segmented into three distinct layers: a silicon-containing layer (providing high capacity), an intermediate layer (providing mechanical support and interface stability), and a carbon layer (providing structural stability and lithium intercalation sites). This segmentation allows each layer to specialize in addressing specific problems, enabling the silicon to deliver high energy density while the other layers ensure cycle life through volume expansion accommodation.
Solution Approach 2:
The patent employs a composite structure combining silicon-containing material, conductive agents, binders, and carbon materials in a layered configuration. The intermediate layer acts as a buffer zone that accommodates silicon's volume expansion while maintaining electrical conductivity through conductive agents and mechanical integrity through binders, thus resolving the contradiction between high capacity and cycle stability.
2Quantity of substance
If silicon material is mixed with graphite material to improve lithium intercalation performance, then capacity is enhanced, but interface compatibility deteriorates due to difference in lithium intercalation performance between the two materials
Solution Approach 1:
Different regions of the negative electrode are assigned different compositions and functions: the silicon-containing layer is optimized for high lithium intercalation capacity, the intermediate layer is optimized for mechanical flexibility and electrical conductivity to handle interface stresses, and the carbon layer is optimized for structural stability. This local quality differentiation allows each region to perform its specialized function without compromising overall interface compatibility.
Solution Approach 2:
The intermediate layer serves as a mediator between the silicon-containing layer and the carbon layer. It contains conductive agents to maintain electrical continuity and binders to provide mechanical adhesion, thereby bridging the interface compatibility gap between silicon and graphite materials that have different lithium intercalation characteristics.
3Use of energy by moving object
If silicon-containing layer is made thicker to increase capacity, then energy density is improved, but adhesion between layers deteriorates due to expansion during charging and discharging
Solution Approach 1:
The intermediate layer is designed with dynamic mechanical properties that allow it to flex and deform elastically during charging and discharging cycles, accommodating the expansion and contraction of the silicon-containing layer. This dynamic response maintains adhesion throughout the cycle, preventing delamination even when the silicon layer is thickened to increase capacity.
Solution Approach 2:
The intermediate layer acts as a pre-configured cushioning layer that anticipates and absorbs the mechanical stress from silicon expansion before it can propagate to the carbon layer. By providing this beforehand cushioning, the structure prevents adhesion failure and layer separation, enabling the use of thicker silicon-containing layers for higher energy density.
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
The solution effectively improves the cycle life and energy density of lithium-ion batteries by stabilizing the silicon-containing layer and carbon layer interface, reducing internal resistance, and preventing layer separation during volume expansion.
Implementation Method 1
the intermediate layer including the conductive agent and the binder constructs a stable electronic and ion transmission channel between the carbon layer and the silicon-containing layer
Implementation Method 2
adhesion and interfacial stress between the two layers are enhanced, to avoid separation of the two layers due to expansion of the silicon-containing layer
Implementation Method 3
adhesion and interfacial stress between the two layers are enhanced, to avoid separation of the two layers due to expansion of the silicon-containing layer
Implementation Method 4
the intermediate layer including the conductive agent and the binder constructs a stable electronic and ion transmission channel between the carbon layer and the silicon-containing layer
Data Source
AI summary
Negative electrode sheets are disclosed. The negative electrode sheets comprise a current collector, and a silicon-containing layer, an intermediate layer and a carbon layer which are stacked in sequence on at least one side of the current collector, wherein the intermediate layer comprises a first conductive agent and a first binder.