Si-Containing Negative Electrode for Stable SEI and Cycle Life
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Solution Overview
Problem
Conventional lithium secondary batteries with graphite negative electrodes have low energy density and poor battery life due to volume expansion issues with silicon-based materials, making it difficult to confirm the life characteristics of new negative electrode materials in real battery operations.
Innovation Solution
A negative electrode for lithium secondary batteries is developed using a Si-containing active material, with specific formulations and manufacturing methods to control the (SEI n and T n ) values, ensuring excellent life characteristics by suppressing electrolyte decomposition and irreversible reactions, including SiO x , Si/C composites, and lithium silicate with controlled particle sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based negative electrode material is used to improve energy density, then theoretical capacity increases from 372 mAh/g to 3580 mAh/g, but battery life characteristics deteriorate due to large volume expansion (~400%) during repeated charging and discharging
Solution Approach 1:
The patent applies the nesting principle by encapsulating silicon-based negative electrode particles within a porous carbon structure. The silicon particles are nested inside the carbon matrix, allowing the carbon to accommodate the volume expansion of silicon during lithiation/delithiation cycles while maintaining structural integrity. This nested configuration resolves the contradiction by enabling high capacity silicon to function reliably within a protective carbon framework.
Solution Approach 2:
The patent applies local quality by creating a heterogeneous composite structure where different regions have different functions: the porous carbon structure provides mechanical stability and ion transport pathways, while the silicon particles provide high capacity. The carbon coating on silicon particles creates local regions with different properties - the core silicon for capacity and the shell carbon for stability - resolving the contradiction between energy density and reliability.
2Reliability
If silicon oxide-based negative electrode material or prelithiation treatment is used to improve battery life characteristics, then volume expansion is reduced, but it becomes more difficult to confirm life characteristics in real lithium secondary battery operations due to diversified component development
Solution Approach 1:
The patent applies the intermediary principle by introducing a porous carbon structure as a mediator between the silicon particles and the electrolyte. This carbon intermediary provides a stable interface that facilitates lithium ion transport while protecting the silicon from direct contact with the electrolyte, reducing side reactions. The porous structure acts as a buffer that mediates the mechanical stress during volume expansion, enabling reliable long-term operation that can be properly evaluated.
3Reliability
If graphite-based negative electrode material is used, then battery life characteristics are maintained, but energy density remains low due to theoretical capacity limitation of 372 mAh/g
Solution Approach 1:
The patent applies the composite materials principle by creating a hybrid negative electrode consisting of silicon particles embedded in a porous carbon matrix, with additional carbon coating. This composite structure combines the high capacity of silicon (3580 mAh/g) with the structural stability and ion conductivity of carbon. The composite enables the battery to achieve high energy density while maintaining good cycle life, overcoming the limitations of pure graphite (372 mAh/g) or pure silicon.
Data Source
AI summary
Provided are a negative electrode for a lithium secondary battery and a method of manufacturing the same. An implementation may provide a negative electrode for a lithium secondary battery including: a Si-containing negative electrode active material, wherein when a value derived according to the following Equation (1) by charging/discharging a lithium secondary battery including a negative electrode and a positive electrode including a Li-containing positive electrode active material n times, discharging the battery to 2.5 V, disassembling the battery to obtain the negative electrode and the positive electrode, and analyzing the negative electrode and the positive electrode is SEIn, a (SEI100 - SEI5) value is 10 or less: SEIn=Si0/Sin−1−CLL*CW/CMW*1−MLi/MTM*LiMW/ALL.