Silicon Negative Electrode Additives Retard Oxidation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional secondary lithium batteries using silicon as a negative active material face challenges with oxidation of silicon during charge-discharge cycles, leading to reduced charge-discharge cycle characteristics and capacity retention due to expansion and porosity changes.
Innovation Solution
Incorporating additives such as acids, acid anhydrides, and lithium salts in the positive electrode, negative electrode, or separator to create a weak-alkaline or acidic atmosphere, which retards the oxidation of silicon, thereby suppressing expansion and improving cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as negative active material to increase capacity, then charge/discharge capacity per unit mass and volume increases, but oxidation of silicon during charge-discharge cycles occurs leading to deterioration of cycle characteristics
Solution Approach 1:
A columnar structure is introduced as an intermediary framework between the silicon active material and the current collector. This columnar structure accommodates the expansion and shrinkage of silicon during charge-discharge cycles, preventing direct stress transmission to the current collector and reducing delamination, thereby maintaining cycle characteristics while preserving high capacity
Solution Approach 2:
The silicon active material is formed as a thin film with controlled thickness (1-10 μm) deposited on the current collector. This thin film configuration allows the silicon to expand and contract during cycling without generating excessive stress, while maintaining electrical contact and preventing complete detachment, thus improving cycle stability
2Quantity of substance
If silicon thin film is used as negative active material, then superior charge/discharge capacity is achieved, but active material changes in properties and increases in porosity with repeated cycling
Solution Approach 1:
The thickness of the silicon thin film is precisely controlled within the range of 1-10 μm, and the film is formed with specific physical properties (amorphous or microcrystalline structure) through sputtering or CVD methods. These parameter optimizations ensure the silicon maintains structural integrity during cycling while achieving high capacity, preventing excessive porosity development and property changes
3Reliability
If columnar structure with gaps is provided in silicon thin film, then stress from expansion and shrinkage is reduced and delamination is prevented, but manufacturing complexity increases
Solution Approach 1:
The silicon thin film is segmented into a columnar structure with vertical gaps extending through the film thickness. This segmentation allows independent movement of each column during expansion and shrinkage, reducing internal stress and preventing delamination. The columnar structure is formed through controlled deposition processes that create self-organizing patterns, achieving stress relief without excessive manufacturing complexity
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 use of these additives effectively retards silicon oxidation, enhancing charge-discharge cycle characteristics and maintaining capacity retention by preventing excessive swelling and delamination of the active material from the current collector.
Implementation Method 1
oxidation of silicon during operation of a battery... oxidation of silicon during charge-discharge cycles... an atmosphere surrounding silicon is rendered weak-alkaline or acidic
Data Source
AI summary
Disclosed is a nonaqueous electrolyte secondary battery which has a negative electrode containing silicon as a negative active material, a positive electrode containing a positive active material, a nonaqueous electrolyte and a separator. Characteristically, an additive which retards oxidation of silicon during operation of the battery is contained either in an interior or surface portion of the positive electrode, or in an interior or surface portion of the negative electrode, or in an interior or surface portion of the separator.