Segmented Silicon Negative Electrode for Battery Expansion Control
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Solution Overview
Problem
Silicon-based negative electrode materials in batteries suffer from poor cycle performance and storage performance due to particle expansion and pulverization, leading to continuous consumption of active lithium in the positive electrode.
Innovation Solution
The negative electrode active substance layer is structured into two portions along the thickness direction, with the portion closer to the current collector having a higher mass percentage of silicon-based material and a lower lithiation state, while the other portion preferentially intercalates lithium, maintaining a capacity ratio within 30% to 95% of the positive electrode, thereby mitigating expansion issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based material is used in the negative electrode to increase capacity, then the energy density is improved, but the cycle performance and storage performance deteriorate due to particle expansion and pulverization
Solution Approach 1:
The negative electrode active substance layer is divided into a first portion (close to current collector) and a second portion (far from current collector) with different silicon-based material mass percentages. This segmentation allows different regions to perform different functions: the first portion with higher silicon content provides capacity while the second portion with lower silicon content mitigates expansion, resolving the contradiction between energy density and cycle performance.
Solution Approach 2:
Different portions of the negative electrode active substance layer are assigned different local compositions: the first portion has a higher mass percentage of silicon-based material to maximize capacity, while the second portion has a lower mass percentage to reduce expansion and pulverization. This local quality differentiation enables simultaneous optimization of energy density and reliability.
2Quantity of substance
If silicon-based material is used in the negative electrode to increase capacity, then the energy density is improved, but the storage performance deteriorates due to continuous SEI generation consuming active lithium
Solution Approach 1:
The negative electrode is segmented into portions with different silicon content. The second portion (far from current collector) with lower silicon content generates less SEI and consumes less active lithium, thereby improving storage performance while the first portion maintains high capacity contribution.
Solution Approach 2:
The local composition is optimized by placing higher silicon content in the first portion and lower silicon content in the second portion. This reduces the overall SEI generation rate and active lithium consumption during storage, improving storage performance while maintaining high capacity.
3Reliability
If the second portion intercalates lithium preferentially to improve initial efficiency and cycling performance, then the lithiation state of the second portion increases, but the expansion of silicon-based material in the first portion must be controlled
Solution Approach 1:
The negative electrode active substance layer is segmented into a first portion and a second portion with different silicon-based material mass percentages. The second portion preferentially intercalates lithium during charging, achieving higher lithiation state for improved cycling performance, while the first portion with higher silicon content experiences controlled expansion due to its specific composition and position.
Solution Approach 2:
Different local regions are designed with different silicon content to achieve different functions: the second portion (far from current collector) with lower silicon content preferentially intercalates lithium to enhance cycling performance, while the first portion (close to current collector) with higher silicon content has its expansion controlled through compositional optimization.
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
This structure improves initial efficiency, cycling performance, and storage performance of silicon-based batteries by reducing silicon-based material expansion and fracture sites, enhancing electrochemical performance and energy density.
Implementation Method 1
the second portion will preferentially intercalate lithium, that is, during battery charging, the lithiation state of the second portion is relatively higher
Implementation Method 2
the silicon particles in the silicon-based negative electrode expand and pulverize, continuously generating new SEI
Data Source
Figure 1~2
Figure 3~4
AI summary
The present application relates to the technical field of batteries, and provides an electrode assembly, a secondary battery, and an electrical device. A negative electrode active material layer comprises a first part and a second part in the thickness direction; the first part is a part close to a negative electrode current collector, in the charging and discharging process, the second part would preferentially undergo lithium intercalation, when a battery is charged, the lithiation state of the second part is relatively high, the lithiation state of the first part is relatively low, and the improvement by the second part for the electrochemical performance of the battery is greater than the improvement by the first part for the electrochemical performance of the battery; when the mass percentage of a silicon-based material in the first part in the first part is greater than the mass percentage of a silicon-based material in the second part in the second part, the expansion problem of the silicon-based materials in the negative electrode active material layer can be ameliorated. By setting 30% ≤ C2/C1 ≤ 95%, the second part can bear 30%-95% of capacity from a positive electrode, thereby further improving the initial Coulombic efficiency and the cycle and storage performance of the battery.