Silicon Composite Negative Electrode for Stable Battery Cycling
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges with the degradation of negative electrodes due to the expansion and contraction of silicon-based active materials, leading to reduced capacity and cycle life.
Innovation Solution
A negative electrode comprising composite particles with a silicon-based active material and a titanium-based functional material, where the functional material has a higher Young's modulus than the active material, is used to alleviate stress and maintain conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used to increase capacity, then the theoretical capacity increases dramatically from 372 mAh/g to 4200 mAh/g, but the material expands and contracts during charge and discharge cycles causing loss of conductive path and contact between active material and current collector
Solution Approach 1:
A conductive layer is introduced as an intermediary between the silicon-based active material and the current collector. This conductive layer maintains electrical connection even when the silicon expands and contracts during charge-discharge cycles, preventing loss of conductive path and ensuring stable electron transport throughout the battery's operational life.
Solution Approach 2:
The negative electrode is constructed as a composite structure combining silicon-based active material with conductive materials. This composite approach allows the high capacity of silicon to be utilized while the conductive components maintain structural integrity and electrical connectivity during volume changes, resolving the contradiction between capacity and cycle stability.
2Quantity of substance
If silicon-based active material is used to increase capacity, then the theoretical capacity increases dramatically, but the material deforms or breaks leading to separation from current collector and pulverization
Solution Approach 1:
The conductive layer serves as a protective intermediary that constrains the silicon-based active material during expansion and contraction. This layer prevents direct deformation and breaking of the silicon particles, maintaining their structural integrity and preventing separation from the current collector throughout repeated charge-discharge cycles.
3Quantity of substance
If the amount of carrier ions occluded by the material increases, then the capacity increases, but the contact states between active material and conductive additive, between active materials, and between active material and current collector become worse
Solution Approach 1:
The conductive layer acts as a stable intermediary network that maintains contact between active material particles, conductive additives, and the current collector. Even as more carrier ions are occluded and the silicon expands, this conductive framework preserves electrical pathways, preventing degradation of contact states and ensuring continuous conductivity throughout the battery's operational life.
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 proposed solution enhances the cycle characteristics and charge/discharge efficiency of lithium-ion secondary batteries by mitigating the mechanical stress on the silicon-based active material and maintaining a conductive path.
Implementation Method 1
the functional material has a higher Young's modulus than the active material, is used to alleviate stress
Implementation Method 2
maintaining a conductive path
Data Source
AI summary
A power storage device having high capacitance is provided. A power storage device with excellent cycle characteristics is provided. A power storage device with high charge and discharge efficiency is provided. A power storage device including a negative electrode with low resistance is provided. A negative electrode for a power storage device includes a number of composites in particulate forms. The composites include a negative electrode active material, a first functional material, and a compound. The compound includes a constituent element of the negative electrode active material and a constituent element of the first functional material. The negative electrode active material includes a region in contact with at least one of the first functional material or the compound.