Si-Graphite Negative Electrode Layering to Limit Expansion
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Solution Overview
Problem
Negative electrodes containing silicon (Si) significantly expand during charging and discharging, leading to a reduction in the reaction force characteristics of the electrode plate, which affects the durability of electricity storage devices.
Innovation Solution
The negative electrode active material layer is partitioned into layers with Si-containing particles of varying hardness, using a first layer with relatively low hardness and a second layer with relatively high hardness, composed of composite particles with a graphite substrate and silicon within its void, to reduce resistance increase and suppress electrode plate expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is added to the negative electrode active material to increase capacity, then the electricity storage capacity is improved, but the electrode plate expands significantly during charging and discharging, leading to hardening and reduced reaction force characteristics
Solution Approach 1:
The negative electrode active material layer is divided into multiple layers (first layer and second layer) with different Si-containing particle hardness characteristics. This segmentation allows different regions to perform different functions: the first layer with softer particles suppresses expansion, while the second layer with harder particles maintains reaction force characteristics.
Solution Approach 2:
Different hardness characteristics are assigned to Si-containing particles in different layers. The first layer contains particles with relatively low hardness to suppress expansion, while the second layer contains particles with relatively high hardness to maintain reaction force characteristics. This local differentiation resolves the contradiction between expansion suppression and reaction force maintenance.
2Strength
If the negative electrode plate is hardened to improve structural stability, then the electrode plate strength is improved, but the reaction force characteristics are reduced, affecting durability
Solution Approach 1:
The active material layer is segmented into multiple layers with different particle hardness characteristics. The first layer contains softer particles that maintain reaction force characteristics, while the second layer contains harder particles that provide structural strength. This segmentation allows both strength and reliability to be maintained simultaneously.
Solution Approach 2:
The negative electrode uses a composite structure with Si-containing particles of different hardness characteristics distributed in different layers. This composite approach combines the benefits of soft particles (maintaining reaction force) and hard particles (providing structural strength), resolving the contradiction between strength and reliability.
3Device complexity
If a single-layer structure with uniform Si-containing particles is used to simplify manufacturing, then the device complexity is reduced, but the resistance increase rate and expansion rate cannot be effectively suppressed
Solution Approach 1:
The active material layer is divided into multiple layers with different Si-containing particle characteristics. This segmentation enables effective suppression of resistance increase rate and expansion rate by utilizing the different hardness characteristics of particles in different layers, while the manufacturing process remains relatively simple through sequential coating or mixing approaches.
Data Source
AI summary
Provided is a technology to reduce a resistance increase rate while suppressing increase in an electrode plate expansion rate after a charge-discharge cycle of an electricity storage device having a negative electrode containing Si. According to the technology disclosed herein, an electricity storage device including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector is disclosed. The negative electrode active material layer includes, as a negative electrode active material particle, a Si-containing particle that is a composite particle of a graphite substrate having a void and silicon disposed within the void of the graphite substrate. The hardness of the Si-containing particle contained in at least one of layers, into which the negative electrode active material layer is partitioned in a thickness direction thereof, is lower than a hardness of the Si-containing particle contained in the other layer.