Si-Carbon Negative Electrode SOC Control for Cycle Stability
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Solution Overview
Problem
Secondary batteries using silicon-based materials face issues with cracking and detachment of electrode active materials due to volumetric swelling, leading to degradation of electrical contact and rapid capacity loss, and mixing with carbonaceous materials worsens energy density performance.
Innovation Solution
A secondary battery design incorporating a mixed active material layer of silicon-based and carbonaceous materials, with controlled state-of-charge (SOC) limits set based on their weight and capacity ratios, ensuring discharge to specific voltage thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based active material is used to increase theoretical capacity, then energy density is improved, but volumetric swelling causes cracking and detachment of electrode active materials
Solution Approach 1:
The patent applies the nesting principle by placing silicon-based active material particles inside a carbonaceous matrix structure. The carbonaceous material forms a container or framework that encapsulates the silicon particles, allowing the high-capacity silicon to be protected while maintaining electrical contact. This nested structure prevents the silicon from detaching during volumetric expansion and contraction cycles.
Solution Approach 2:
The patent employs a flexible carbonaceous matrix that can accommodate the volumetric changes of silicon-based active material during lithiation and delithiation. The carbonaceous structure acts as a flexible shell or binding network that maintains structural integrity while allowing controlled expansion, preventing cracking and detachment of the silicon particles.
2Quantity of substance
If hybrid type negative electrode with mixture of silicon-based and carbonaceous active materials is applied, then energy density is improved, but performance of secondary battery is degraded
Solution Approach 1:
The patent applies local quality by creating regions with different compositions and functions within the negative electrode. The carbonaceous active material provides structural stability and electrical conductivity in certain regions, while silicon-based active material provides high capacity in other regions. This spatial differentiation of material properties allows the electrode to simultaneously achieve high energy density and maintained performance.
Solution Approach 2:
The patent uses composite materials by combining silicon-based active material with carbonaceous active material in a specifically designed hybrid structure. The composite nature allows the electrode to leverage the high theoretical capacity of silicon while the carbonaceous component provides structural support, electrical conductivity, and stability, resulting in a material that achieves both high energy density and reliable performance.
3Reliability
If graphite is used as negative electrode active material, then stability is maintained, but theoretical capacity is limited to 372 mAh/g
Solution Approach 1:
The patent merges graphite with silicon-based active material in a hybrid negative electrode structure. The graphite provides the stable framework and electrical conductivity characteristics, while the silicon-based material contributes high theoretical capacity. This combination allows the electrode to achieve both the stability of graphite and the high capacity of silicon, exceeding the 372 mAh/g limitation of pure graphite.
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
This approach enhances cycle characteristics and energy density by preventing material degradation, maintaining battery performance through controlled SOC limits.
Implementation Method 1
silicon (Si) having a theoretical capacity of 4200 mAh/g corresponding to about 10 times or more of the theoretical capacity of graphite has been given many attentions. Besides silicon, use of various non-carbonaceous materials showing high theoretical capacity by forming an alloy with lithium as a novel material substituting for carbonaceous active materials
Implementation Method 2
Graphite, which is a commercially available negative electrode active material for a lithium ion battery, has a limited theoretical capacity of 372 mAh/g
Data Source
AI summary
A secondary battery including a positive electrode, a negative electrode and a separator interposed between the negative electrode and the positive electrode. The negative electrode includes: a negative electrode current collector; and a negative electrode active material layer on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a mixed active material comprising a carbonaceous active material and a Si-based active material. The secondary battery is controlled by setting a lower limit of state-of-charge (SOC) during operation of the secondary battery depending on a weight mixing ratio of the Si-based active material to the carbonaceous active material. The capacity ratio of the Si-based active material to the carbonaceous active material.