Porous Silicon Anode Core-Shell Structure for Stable Li-Ion Cycling
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Solution Overview
Problem
Lithium-ion batteries face challenges in energy density and cycle life due to volume expansion and contraction of silicon negative electrodes, leading to material crushing and instability of the SEI film, which affects their efficiency and capacity retention.
Innovation Solution
A porous silicon negative electrode material with a sparse-silicon inner core, transition ring, and dense-silicon ring, combined with a carbon coating layer, is designed to buffer volume expansion and improve electrical conductivity, featuring sequentially decreasing porosity and increasing silicon distribution density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon negative electrode material is used to increase capacity, then the theoretical capacity increases significantly (about 10 times graphite), but volume expansion and contraction during lithium intercalation causes material crushing and SEI film instability
Solution Approach 1:
The silicon negative electrode is divided into multiple silicon particles distributed within a graphite matrix, rather than using bulk silicon. This segmentation reduces the volume of individual silicon particles, allowing them to expand and contract without crushing the overall electrode structure, thus maintaining cycle stability while preserving high capacity
Solution Approach 2:
A composite material structure is created by combining silicon particles with graphite to form a porous negative electrode. The graphite component provides structural stability and accommodates silicon volume changes, while silicon contributes high capacity. This composite approach resolves the contradiction between high capacity and cycle stability
2Strength
If porous structure is introduced to reduce volume stress, then the compressive strength increases and expansion stress is reduced, but the electrode complexity increases with multiple layers (sparse-silicon inner core, transition ring, dense-silicon ring)
Solution Approach 1:
Different regions of the porous silicon negative electrode are designed with different silicon distribution densities: a sparse-silicon inner core, a transition ring with intermediate density, and a dense-silicon ring at the periphery. This local variation in silicon density optimizes both compressive strength and stress reduction while maintaining a manageable three-layer structure
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 porous silicon structure enhances compressive strength, reduces stress, and stabilizes the electrode, resulting in improved battery capacity retention and cycle performance.
Implementation Method 1
intercalation and deintercalation processes of a large number of lithium ions are accompanied by volume expansion and contraction of a silicon negative electrode material
Implementation Method 2
deterioration of electrical contact
Data Source
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AI summary
Disclosed is a porous silicon negative electrode material, comprising a sparse-silicon inner core, and a transition ring, a dense-silicon ring and a carbon coating layer which are sequentially coated on the surface of the sparse-silicon inner core. In the sparse-silicon inner core, the transition ring and the dense-silicon ring, the porosity sequentially decreases, and the silicon density sequentially increases. Further disclosed are a negative electrode sheet and a lithium-ion battery which are prepared from the described porous silicon negative electrode material. The porous silicon negative electrode material of the present disclosure effectively reduces the expansion and contraction stress of the electrode material during cycle and slows down the capacity attenuation, and thus the battery capacity retention rate is high, and the cycle performance is stable.