Cylindrical Battery Anode Layering for Fast Charging and Low Swelling
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Solution Overview
Problem
Large-size cylindrical secondary batteries face issues with fast charging characteristics, side reactions, gas generation, swelling, and lithium plating due to high current application, which affect their performance and durability in medium and large-scale devices like vehicles.
Innovation Solution
A cylindrical secondary battery design with a negative electrode active material layer divided into three regions: a lower layer with silicon-containing compounds and natural graphite, a mixed region with both silicon-containing and artificial graphite, and an upper layer with artificial graphite, enhancing adhesion strength and reducing side reactions and swelling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If large-size cylindrical secondary batteries are designed for high capacity and fast charging, then energy density and charging speed are improved, but side reactions, gas generation, swelling and lithium plating occur due to high current application
Solution Approach 1:
The negative electrode active material layer is divided into three distinct regions along the thickness direction: a lower layer region containing silicon-containing compound and natural graphite, a middle layer region containing silicon-containing compound and artificial graphite, and an upper layer region containing artificial graphite. This segmentation allows different material compositions to handle different aspects of the charging process, with silicon providing high capacity in the lower regions and artificial graphite providing stability in the upper regions closer to the separator.
Solution Approach 2:
Different active materials are strategically distributed at different positions within the negative electrode active material layer. Silicon-containing compounds are concentrated in the lower layer and middle layer regions where they can provide high capacity without causing excessive swelling, while artificial graphite is predominantly placed in the upper layer region closer to the separator to provide structural stability and reduce side reactions at the electrode-electrolyte interface.
2Quantity of substance
If large-size cylindrical secondary batteries are designed for high capacity, then energy density is improved, but swelling caused by side reaction and gas generation increases
Solution Approach 1:
The negative electrode active material layer is segmented into three regions with varying compositions of silicon-containing compound and graphite. This segmentation allows the battery to achieve high capacity through silicon while distributing the swelling effects across different layers, with the artificial graphite in the upper layer providing a stable framework that constrains overall volume expansion.
Solution Approach 2:
The negative electrode active material layer employs a composite structure combining silicon-containing compounds with natural graphite and artificial graphite in different proportions across three regions. This composite material approach leverages the high capacity of silicon while using graphite's dimensional stability to counteract swelling, achieving both high capacity and reduced volume expansion.
3Speed
If large-size cylindrical secondary batteries are designed for fast charging, then charging speed is improved, but lithium plating occurs due to high current application
Solution Approach 1:
The negative electrode active material layer is divided into three regions with gradient composition of silicon-containing compound and artificial graphite. During fast charging, the artificial graphite in the middle and upper layers provides stable lithium insertion/extraction pathways that reduce current density hotspots, preventing lithium plating while maintaining high charging speed capability.
Solution Approach 2:
Artificial graphite is strategically distributed in the middle layer and upper layer regions closer to the separator, creating zones with different electrochemical properties. This local quality variation ensures that regions closer to the electrolyte interface have materials (artificial graphite) that are less prone to lithium plating during fast charging, while silicon in the lower regions provides high capacity.
Data Source
AI summary
A secondary battery including an electrode assembly having a jelly-roll shape, a positive electrode, and a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector. The negative electrode active material layer includes a first region in contact with the negative electrode current collector including a silicon-containing compound and natural graphite as an active material, a mixed region in contact with the first region including a silicon-containing compound, natural graphite and artificial graphite as an active material, and a second region in contact with the mixed region including a silicon-containing compound and artificial graphite as an active material. The secondary battery has a high form factor applied to medium and large scale devices and may be a cylindrical secondary battery with improved fast charging characteristics, reduced swelling, suppressed lithium plating and high capacity characteristics.