Porous Silicon Negative Electrode Structure for Thickness Stability
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Solution Overview
Problem
Conventional secondary battery negative electrodes experience significant changes in thickness and increased resistance due to the expansion and contraction of active materials during charging and discharging, leading to excessive restraint pressure.
Innovation Solution
A secondary battery negative electrode with an active material layer comprising porous silicon particles and a binder, where the porosity is greater than 15%, and the composite particles have an aspect ratio of 2.5 or more, combined with a sulfide solid electrolyte to reduce thickness change and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the active material layer has low porosity (15% or less), then the density and energy density are improved, but the thickness change during charging and discharging increases significantly
Solution Approach 1:
The patent applies porous materials by designing the active material layer with a controlled porosity of 15% or less, creating a compact structure that reduces volume expansion during lithium insertion. The porous structure allows accommodation of expansion stress while maintaining overall density, preventing excessive thickness change during charging-discharging cycles
Solution Approach 2:
The patent uses composite materials by combining the active material (containing Si, P, and Li elements) with a binder and conductive additive to form a composite active material layer. This composite structure provides mechanical stability and flexibility, allowing the layer to withstand expansion-contraction stress while maintaining electrical conductivity and structural integrity
2Productivity
If the active material undergoes expansion and contraction during charging and discharging, then the charge-discharge capacity is improved, but the resistance of the negative electrode increases
Solution Approach 1:
The patent applies parameter changes by optimizing the composition ratios of Si, P, and Li elements, controlling the porosity at 15% or less, and adjusting the particle size distribution. These parameter optimizations ensure good electrical contact between particles during expansion-contraction cycles, maintaining low resistance while preserving high charge-discharge capacity
3Stability of the object's composition
If the composite particles have high aspect ratio (2.5 or more), then the thickness change is suppressed, but the manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-forming composite particles with controlled aspect ratios of 2.5 or more before assembling the active material layer. This preliminary particle preparation ensures that the particles have the appropriate shape to suppress thickness change during charging-discharging, while the aspect ratio control is achieved through standardized particle synthesis methods
Data Source
AI summary
The secondary battery negative electrode of the present disclosure includes an active material layer, the active material layer includes a sulfide solid electrolyte and composite particles as an active material, the composite particles include a plurality of porous silicon particles and a binder, and the active material layer has a porosity of more than 15%.