Silicon Particle Circularity for Battery Capacity and Lifespan
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Solution Overview
Problem
Silicon-based negative active materials in lithium secondary batteries face challenges due to volume expansion and contraction during charging and discharging, leading to irreversible reactions, reduced lifespan, and decreased capacity, limiting their commercialization.
Innovation Solution
The use of silicon particles with controlled circularities between 0.5 and 0.9, combined with optional silicon oxide, silicon carbide, and conductive layers, to reduce tensile hoop stress and enhance the structural integrity of the particles, thereby improving capacity and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as negative material to achieve high capacity, then battery capacity increases, but volume variation during charging and discharging causes active material isolation and lifespan degradation
Solution Approach 1:
The silicon negative material is divided into particles with controlled circularity (0.5-0.9), creating multiple small units that can independently accommodate volume changes during lithiation and delithiation, preventing catastrophic failure and maintaining structural integrity over multiple cycles
Solution Approach 2:
The patent employs composite structures where silicon particles are combined with materials having different mechanical properties, creating a composite negative material that leverages the high capacity of silicon while the composite structure mitigates volume expansion issues and improves cycle stability
2Reliability
If silicon particles are reduced in size to minimize volume expansion damage, then particle damage decreases, but capacity is reduced
Solution Approach 1:
The patent optimizes the circularity parameter of silicon particles to a specific range (0.5-0.9), which represents a critical parameter change that balances volume expansion tolerance with capacity retention, achieving both particle integrity and high capacity simultaneously
3Reliability
If silicon particles with high circularity are used to improve structural integrity, then volume variation is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent defines a practical circularity range (0.5-0.9) that achieves structural integrity benefits without requiring extreme precision, representing an optimized parameter range that balances performance with manufacturability
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 controlled circularity of silicon particles effectively suppresses crack formation and irreversible reactions, leading to improved energy density, capacity retention, and extended lifespan of lithium secondary batteries.
Implementation Method 1
The circularities of the particles are determined by equation 1 below, and the circularities are 0.5 or greater and 0.9 or less... effectively suppresses crack formation and irreversible reactions
Implementation Method 2
since silicon expands about four times greater in volume during a charging operation than during a discharging operation
Implementation Method 3
crystalline carbon such as graphite and artificial graphite or carbon based active material such as soft carbon or hard carbon capable of intercalating and deintercalating lithium ions
Data Source
AI summary
Provided is a negative active material and a lithium secondary battery including the negative active material. The negative active material for a secondary battery includes silicon particles, wherein circularities of the particles are determined by equation 1 below, and the circularities are 0.5 or greater and 0.9 or less,Circularity=2(pi×A)1/2/P [Equation 1]where A denotes a projected area of the silicon particle that is two-dimensionally projected, and P denotes a circumferential length of the silicon particle that is two-dimensionally projected.