Tri-Layer Silicon-Graphite Negative Electrode for Lithium Battery
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Solution Overview
Problem
Lithium secondary batteries face issues with non-uniform swelling and separation of electrodes due to the volumetric changes of silicon-based negative electrode active materials, leading to performance degradation and safety concerns.
Innovation Solution
A tri-layer structure for the negative electrode is introduced, comprising a silicon-based active material layer sandwiched between two layers of carbonaceous active materials with different shapes and surface treatments, enhancing adhesion and conductivity to prevent swelling and improve electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode active material is used to increase lithium capacity, then energy density is improved, but volume expansion during charge/discharge causes electrode separation and performance degradation
Solution Approach 1:
The negative electrode is divided into multiple layers: a first carbonaceous layer directly on the current collector, a silicon-based active material layer in the middle, and a second carbonaceous layer on top. This segmentation isolates the silicon layer's volume expansion from the current collector and outer electrode surface, preventing electrode separation while maintaining high lithium capacity.
Solution Approach 2:
The negative electrode uses a composite structure combining carbonaceous materials (graphite or hard carbon) with silicon-based active material. The carbonaceous layers provide structural stability and accommodate volume changes, while the silicon layer provides high lithium capacity, creating a composite that balances both requirements.
2Quantity of substance
If silicon-based negative electrode active material is used to increase lithium capacity, then energy density is improved, but contact resistance between particles increases due to volume expansion
Solution Approach 1:
The silicon-based active material layer is segmented and surrounded by conductive carbonaceous materials on both sides. This segmentation ensures that even when silicon particles expand, they remain in electrical contact with the conductive carbon network, maintaining reliable electron transport pathways.
Solution Approach 2:
The carbonaceous materials act as intermediary conductive phases between the silicon particles and the current collector. These intermediaries maintain electrical contact during volume expansion, preventing increase in contact resistance while allowing the silicon to undergo lithiation/delithiation.
3Reliability
If graphite-based particles are used to surround silicon negative electrode active material to improve conductivity, then electrical conductivity is improved, but contact between graphite particles and silicon particles degrades due to volume expansion
Solution Approach 1:
The carbonaceous particles (graphite or hard carbon) form flexible surrounding layers that can accommodate the volume expansion of silicon particles during lithiation. These flexible carbon shells maintain contact with the silicon particles throughout the charge/discharge cycles, preserving both conductivity and contact stability.
Solution Approach 2:
The negative electrode creates a composite structure where carbonaceous materials and silicon-based active material are intimately mixed and coated together. This composite approach ensures that the carbon particles remain in stable contact with silicon particles even during volume expansion, maintaining both conductivity and structural integrity.
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 tri-layer structure effectively inhibits non-uniform swelling and separation, enhancing the adhesion between the electrode and current collector, and significantly improving output and life characteristics of the battery.
Implementation Method 1
the first carbonaceous negative electrode active material includes spherical shaped particles, which spherical shaped particles having a sphericity of 0.90-0.99, said spherical shaped particles including an oxidized surface portion
Implementation Method 2
said spherical shaped particles including an oxidized surface portion and/or carbon-coated surface portion, and the second carbonaceous negative electrode active material includes flake shaped particles having a sphericity of 0.70-0.89, said flake shaped particles including a carbon-coated surface portion
Implementation Method 3
various types of carbonaceous materials capable of lithium intercalation/deintercalation
Implementation Method 4
various types of carbonaceous materials capable of lithium intercalation/deintercalation
Data Source
AI summary
A negative electrode for a lithium secondary battery (and a lithium secondary battery including the same) including: a negative electrode current collector; a first negative electrode mixture layer present on at least one surface of the negative electrode current collector and including a first carbonaceous negative electrode active material, a first polymer binder and a first conductive material; a second negative electrode mixture layer present on a top surface of the first negative electrode mixture layer and including a silicon-based negative electrode active material, a second polymer binder and a second conductive material; and a third negative electrode mixture layer present on a top surface of the second negative electrode mixture layer and including a second carbonaceous negative electrode active material, a third polymer binder and a third conductive material.