Layered Silicon-Graphite Anode Structure for Longer Battery Life
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Solution Overview
Problem
Lithium secondary batteries face challenges with low energy density due to the low theoretical capacity of graphite and the issue of large volume expansion in Si-based materials, leading to deteriorated battery life characteristics.
Innovation Solution
The solution involves a negative electrode structure with a silicon-based material in a lower layer and a graphite-based active material with a high surface area in an upper layer, along with the use of CNT conductive material to prevent isolation due to volume expansion and improve adhesive properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si-based material is used as negative electrode active material, then energy density is improved, but battery life characteristic is deteriorated due to large volume expansion
Solution Approach 1:
The negative electrode is divided into multiple layers: a first negative electrode active material layer containing Si-based material and a second negative electrode active material layer containing graphite-based material. This segmentation allows the Si-based material to provide high capacity while the graphite layer buffers volume expansion and maintains structural integrity, resolving the contradiction between energy density and battery life.
Solution Approach 2:
The patent uses a composite structure combining Si-based active material with graphite-based active material in a layered configuration. The Si-based layer provides high theoretical capacity (3580 mAh/g) while the graphite layer (372 mAh/g) provides structural stability and accommodates volume changes, creating a composite system that achieves both high energy density and improved reliability.
2Stability of the object's composition
If SiOx material is used to reduce volume expansion, then volume expansion rate is reduced, but interfacial resistance is increased and electrode adhesive strength is reduced
Solution Approach 1:
The patent applies different materials with different properties to different locations: the SiOx-based material is placed in the first negative electrode active material layer where volume expansion control is needed, while graphite-based material is placed in the second layer where adhesive strength and electrical conductivity are critical. This local differentiation allows each material to perform its optimal function without compromising overall electrode performance.
3Reliability
If graphite-based active material is used, then battery life is improved, but energy density is reduced due to low theoretical capacity
Solution Approach 1:
The negative electrode is segmented into two functional layers: the first layer uses Si-based or SiOx-based material optimized for high capacity and volume expansion control, while the second layer uses graphite-based material optimized for structural stability and long cycle life. This segmentation allows the system to achieve both high energy density from the Si-based layer and improved battery life from the graphite layer.
Solution Approach 2:
The patent merges two different active material systems (Si-based and graphite-based) into a single layered electrode structure. The Si-based layer contributes high theoretical capacity (3580 mAh/g) to boost energy density, while the graphite layer contributes structural stability and long-term cycling performance, achieving a synergistic effect that combines the advantages of both materials.
Data Source
AI summary
Provided are a negative electrode for a lithium secondary negative electrode battery including: a current collector; a first negative electrode active material layer disposed on the current collector and including a silicon-based active material, a first graphite-based active material, and a linear conductive material; and a second negative electrode active material layer disposed on the first negative electrode active material layer and including a second graphite-based active material. The first graphite-based active material has a carbon coating layer on at least a part of a surface. Also provided is a lithium secondary battery including the negative electrode.