Silicon Negative Electrode Projections for Battery Expansion
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Solution Overview
Problem
Nonaqueous electrolytic secondary cells with silicon-based negative electrodes face challenges in maintaining high charge/discharge characteristics due to expansion and contraction issues, leading to reduced electrolyte retention and ion conductivity, especially at high rates and low temperatures.
Innovation Solution
A negative electrode design featuring column-shaped active material bodies with projections on their side surfaces, which prevent adjacent bodies from contacting each other and maintain a space for electrolyte retention, alleviating expansion stress on the current collector and improving charge/discharge performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used to increase capacitance density, then the theoretical capacitance density increases from 372 mAh/g (carbon) to 4200 mAh/g (silicon), but the volume expansion reaches 4.12 times when lithium ions are occluded, causing detachment from current collector and buckling of wound electrode assembly
Solution Approach 1:
The active material is divided into granular particles with diameters of 0.1 to 10 μm, which are then sintered to form porous sintered bodies. This segmentation allows each particle to expand and contract independently during charge/discharge cycles, preventing catastrophic volume changes at the electrode level while maintaining high capacitance density through the high surface area of numerous small particles.
Solution Approach 2:
The invention uses porous sintered bodies formed by sintering granular active material particles. The porous structure provides expansion space within the sintered body, accommodating volume changes during lithium occlusion/release without causing detachment from the current collector. The porosity also facilitates electrolyte penetration and ion transport while maintaining structural integrity during cycling.
2Productivity
If active material layer is deposited as thin film to form negative electrode, then the electrode structure is compact and efficient, but the closeness of contact between active material layer and current collector is reduced due to expansion/contraction, possibly causing detachment
Solution Approach 1:
The porous sintered body acts as a flexible matrix that can accommodate the expansion and contraction of granular active material particles during charge/discharge cycles. This flexible structure maintains continuous contact with the current collector while allowing individual particles to change volume, preventing detachment and ensuring reliable electrical connection throughout cycling.
Solution Approach 2:
The electrode is constructed as a composite structure combining granular active material particles with a binder matrix to form porous sintered bodies. This composite approach allows the binder to hold particles together and maintain contact with the current collector, while the porous structure accommodates volume changes, ensuring both reliability and charge/discharge efficiency.
3Duration of action of moving object
If charge/discharge cycle is repeated, then the cell achieves practical use, but the closeness of contact between active material layer and current collector is progressively reduced, leading to performance degradation
Solution Approach 1:
The porous structure of the sintered body provides pre-configured expansion space that cushions the volume changes of granular active material during charge/discharge cycles. This beforehand cushioning prevents stress concentration and maintains contact between the active material and current collector throughout cycling, ensuring long-term durability without performance degradation from contact loss.
4Quantity of substance
If active material bodies are made larger to increase capacitance, then the cell capacity increases, but the expansion stress increases, causing current collector to expand beyond elastically deformable threshold and buckle
Solution Approach 1:
The total cell capacity is achieved through numerous small granular particles (0.1 to 10 μm diameter) rather than a few large particles. Each small particle experiences minimal expansion stress, and the collective capacity of many particles provides high cell capacity. The granular structure distributed throughout the porous sintered body prevents stress concentration that would occur with larger active material bodies.
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 design enhances electrolyte retention and ion conductivity, maintaining high charge/discharge rates and capacitance while preventing active material detachment and current collector deformation.
Implementation Method 1
a negative electrode active material for occluding or releasing lithium metal, lithium alloy or lithium ions
Implementation Method 2
plurality of projections are formed on a part of a side surface of each active material body
Implementation Method 3
maintain a space for electrolyte retention
Data Source
AI summary
A negative electrode 100 for a nonaqueous electrolytic secondary cell includes a current collector 1 and a plurality of active material bodies 2 formed on a surface of the current collector 1 at intervals; each active material body 2 contains a material for occluding or releasing lithium; and a plurality of projections 3 are formed on a part of a side surface of each active material body 2.