Gradient Silicon Negative Electrode Plate for SEI and Expansion Control
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Solution Overview
Problem
Silicon-based negative electrode materials exhibit poor cycle performance and storage performance due to the continuous generation of a new solid electrolyte interface (SEI) caused by silicon particle expansion and pulverization, which consumes active lithium from the positive electrode.
Innovation Solution
A negative electrode plate design with a layered structure comprising a first part close to the current collector having a higher mass percentage of silicon-based material and a second part further away with a lower percentage, where lithium is preferentially intercalated into the second part during charging, reducing overall expansion and improving efficiency, cycle performance, and storage performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based material is used as negative electrode material to achieve high gram capacity, then the capacity increases, but the cycle performance and storage performance deteriorate due to continuous SEI generation from expansion and pulverization
Solution Approach 1:
The negative electrode active material layer is divided into a first part (close to current collector) and a second part (far from current collector) with different silicon-based material mass percentages. The first part has higher silicon content (5-20 wt%) while the second part has lower silicon content (0-5 wt%), creating gradient structures that segment the expansion stress and prevent uniform pulverization, thereby improving cycle performance while maintaining high capacity
Solution Approach 2:
Different regions of the negative electrode active material layer are assigned different silicon-based material concentrations. The first part near the current collector has higher silicon content to provide high capacity, while the second part farther away has lower silicon content to reduce expansion and pulverization. This local quality variation optimizes both capacity and reliability in different spatial zones
2Quantity of substance
If silicon-based material expands during lithium intercalation, then the capacity increases, but the continuous generation of new SEI consumes active lithium and deteriorates performance
Solution Approach 1:
The negative electrode plate is pre-designed with a gradient silicon distribution structure before battery operation. The first part with higher silicon content is positioned close to the current collector, while the second part with lower silicon content is positioned farther away. This preliminary structural arrangement ensures that during initial charging cycles, lithium preferentially intercalates into the second part first, allowing the formation of stable SEI before the silicon-rich first part undergoes full expansion, thereby reducing active lithium consumption
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 layered structure alleviates silicon-based material expansion, enhancing the battery's first efficiency, cycle performance, and storage performance by optimizing lithium intercalation distribution, thereby improving overall electrochemical performance.
Implementation Method 1
During charging and discharging, lithium is preferentially intercalated into the second part
Data Source
AI summary
A negative electrode active material layer includes a first part and a second part in a thickness direction, and the first part is a part close to a negative electrode current collector is described. During charging of a battery, a lithiation state at the second part is higher, and a lithiation state at the first part is lower. When a mass percentage of a silicon-based material in the first part is greater than a mass percentage of a silicon-based material in the second part, expansion of the silicon-based material in the negative electrode active material layer can be alleviated. Charging and discharging of the battery can be met without full intercalation for the silicon-based material in the first part, and the silicon-based material in the first part does not need to operate at full load.