Si-Graphite Anode Layer Hardness Gradient for Low Expansion
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Solution Overview
Problem
Negative electrodes containing silicon (Si) significantly expand during charging and discharging, leading to a reduction in reaction force characteristics and durability of the electrode plate in electricity storage devices.
Innovation Solution
The negative electrode active material layer is partitioned into layers with Si-containing particles of varying hardness, where one layer contains Si-containing particles with relatively low hardness and the other with relatively high hardness, composed of a graphite substrate with silicon within its void, to reduce resistance increase and electrode plate expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon is added to the negative electrode active material to increase capacity, then the energy density is improved, but the electrode plate expansion rate increases during charge-discharge cycles
Solution Approach 1:
The patent applies local quality by creating a multi-layer structure where different layers have different hardness characteristics. Specifically, a soft layer containing Si-containing particles with lower hardness (compression modulus 1000-3000 MPa) is placed adjacent to the current collector, while a hard layer containing Si-containing particles with higher hardness (compression modulus 2000-5000 MPa) is placed on the outer side. This gradient structure allows the soft layer to accommodate expansion locally near the current collector while the hard layer maintains overall structural stability, thereby suppressing electrode plate expansion rate while preserving the high energy density benefits of silicon.
Solution Approach 2:
The patent employs composite materials by combining Si-containing particles with different hardness values in a layered configuration. The composite structure integrates particles with compression moduli ranging from 1000-5000 MPa, creating a material system that exhibits both high capacity (from silicon content) and suppressed expansion (from hardness differentiation). This composite approach allows the electrode to benefit from silicon's high energy density while mitigating its expansion issues through the combined properties of particles with varying mechanical characteristics.
2Stability of the object's composition
If the negative electrode active material layer is made harder to reduce expansion, then the electrode plate expansion rate is suppressed, but the resistance increase rate increases
Solution Approach 1:
The patent applies local quality by creating a multi-layer structure where different layers have different hardness characteristics. Specifically, a soft layer containing Si-containing particles with lower hardness (compression modulus 1000-3000 MPa) is placed adjacent to the current collector, while a hard layer containing Si-containing particles with higher hardness (compression modulus 2000-5000 MPa) is placed on the outer side. This gradient structure allows the soft layer to accommodate expansion locally near the current collector while the hard layer maintains overall structural stability, thereby suppressing electrode plate expansion rate while preserving the high energy density benefits of silicon.
Solution Approach 2:
The patent employs parameter changes by varying the compression modulus of Si-containing particles across different layers. The compression modulus parameter is changed from 1000-3000 MPa in the soft layer to 2000-5000 MPa in the hard layer. This parameter gradient allows the electrode to achieve both low expansion (through the hard outer layer) and low resistance increase (through the soft inner layer that maintains good contact with the current collector)
Data Source
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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 (100) including a negative electrode current collector (62, 262) and a negative electrode active material layer (64, 264) disposed on the negative electrode current collector (62, 262) is disclosed. The negative electrode active material layer (64, 264) 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 (64, 264) is partitioned in a thickness direction thereof, is lower than a hardness of the Si-containing particle contained in the other layer.