Silicon-Anode Battery Charging Profile to Limit Cracking
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Solution Overview
Problem
Charging non-aqueous electrolyte secondary batteries with silicon compounds as a negative electrode active material faces challenges of cracking and deterioration, leading to poor cycle characteristics, while low charging currents result in prolonged charging times.
Innovation Solution
A charging method involving multiple stages with specific current values, including a first constant current step, a second reduced current step, and a large current step, tailored to the capacity ratio of silicon compounds, to optimize charging efficiency and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the charging current is increased to reduce charging time, then charging efficiency is improved, but cracking of the silicon compound occurs and cycle characteristics deteriorate
Solution Approach 1:
The charging process is divided into multiple stages with different current values. The charging current is segmented into a first current value (I1st) for initial charging and a second current value (I2nd) for subsequent charging, where I2nd < I1st. This segmentation allows the battery to accept higher current initially when the silicon compound is less susceptible to cracking, then reduces current to prevent cracking as charging progresses and the silicon compound becomes more vulnerable.
Solution Approach 2:
The charging current is made dynamic rather than constant. The charging method adjusts the current value based on the charging state and the ratio of silicon compound capacity to rated capacity (x). When x is within the range 0.1 ≤ x ≤ 0.5, the method dynamically switches from a higher first current value to a lower second current value, adapting the charging rate to the real-time condition of the silicon compound to prevent cracking while maximizing charging efficiency.
2Reliability
If the charging current is reduced to prevent silicon compound cracking, then cycle characteristics are improved, but charging time is prolonged
Solution Approach 1:
The charging process is divided into multiple stages with different current values. The charging current is segmented into a first current value (I1st) for initial charging and a second current value (I2nd) for subsequent charging, where I2nd < I1st. This segmentation allows the battery to accept higher current initially when the silicon compound is less susceptible to cracking, then reduces current to prevent cracking as charging progresses and the silicon compound becomes more vulnerable.
Solution Approach 2:
The charging current is made dynamic rather than constant. The charging method adjusts the current value based on the charging state and the ratio of silicon compound capacity to rated capacity (x). When x is within the range 0.1 ≤ x ≤ 0.5, the method dynamically switches from a higher first current value to a lower second current value, adapting the charging rate to the real-time condition of the silicon compound to prevent cracking while maximizing charging efficiency.
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 method enables efficient charging in a short time while maintaining favorable cycle characteristics by minimizing silicon compound cracking and enhancing lithium ion occlusion.
Implementation Method 1
a silicon compound such as silicon oxide represented by SiO x can occlude more lithium ions per unit volume than a carbon material such as graphite
Data Source
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AI summary
A charging method of a non-aqueous electrolyte secondary battery involves a first charging step in which, defining x as the ratio of the capacity of a silicon compound to the rated capacity Q (0.1 ≤ x ≤ 0.5), charging is performed at a first fixed current value I1st that satisfies the expression below; and a high current charging step in which after completion of the first charging step, charging is performed at a fixed current value Imax higher than the first fixed current value I1st. Expression: 82 / (81.8x + 64) × (0.3 /0.7) - α ≤ I1st / Imax ≤ 82/(81.8x + 64) × (0.3 /0.7) + α (α = 0.3)