Silicon Negative Active Material with Oxide and Conductive Layers
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in achieving stable cycle-life characteristics and initial efficiency due to issues with silicon-based negative active materials, such as particle breakage and uneven lithium distribution, caused by inadequate oxide layer thickness and exposure to electrolytes.
Innovation Solution
A negative active material for rechargeable lithium batteries is developed, comprising a silicon particle core with a micrometer-sized particle size and an oxide layer of specific thickness (65 nm to 450 nm) and a conductive layer, which prevents direct contact with the electrolyte and ensures stable lithium ion diffusion, enhancing cycle-life characteristics and initial efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based negative active material is used to obtain high capacity, then energy density is improved, but particle breakage and uneven lithium distribution occur due to inadequate oxide layer protection
Solution Approach 1:
The patent uses a composite structure consisting of a silicon core particle surrounded by a silicon oxide layer. This composite material approach allows the silicon core to provide high capacity while the oxide layer provides protection, resolving the contradiction between high energy density and reliable cycle-life characteristics.
Solution Approach 2:
The silicon oxide layer is formed beforehand on the silicon particle surface to prevent particle breakage and provide structural support during lithium ion insertion/extraction cycles. This prior cushioning effect protects the silicon core from mechanical stress, maintaining cycle-life stability while preserving high capacity.
2Reliability
If oxide layer thickness is increased to prevent particle breakage, then cycle-life characteristics are improved, but lithium ion conductivity may be reduced
Solution Approach 1:
The patent optimizes the oxide layer thickness to a specific range (65-450 nm) to balance protection and conductivity. This parameter optimization ensures the oxide layer is thick enough to prevent particle breakage and improve cycle-life, while remaining thin enough to maintain adequate lithium ion conductivity for high initial efficiency.
3Productivity
If silicon particle size is reduced to improve lithium distribution, then charging-discharging performance is improved, but particle breakage becomes more severe without adequate protection
Solution Approach 1:
The composite structure of silicon core with silicon oxide shell provides both improved lithium distribution (due to smaller effective particle size) and enhanced particle stability (due to the protective oxide layer). The oxide layer acts as a structural reinforcement that prevents breakage of the smaller silicon particles.
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 proposed negative active material achieves excellent initial efficiency and stable cycle-life characteristics by preventing particle breakage and maintaining lithium ion conductivity, as demonstrated by the thickness range of the oxide layer and the inclusion of a conductive layer.
Implementation Method 1
an oxide layer having a thickness in a range of about 65 nm to about 450 nm, on the silicon particle core
Implementation Method 2
a conductive layer on the oxide layer
Implementation Method 3
a silicon particle core including a silicon particle having a particle size in a micrometer range
Data Source
AI summary
Disclosed are a negative active material for a rechargeable lithium battery and a rechargeable lithium battery including the same. The negative active material includes: a silicon particle core comprising a silicon particle having a particle size in a micrometer range; an oxide layer having a thickness in a range of about 65 nm to about 450 nm, on the silicon particle core; and a conductive layer on the oxide layer.