Lithium Ion Battery Negative Electrode Crack Segmentation
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Solution Overview
Problem
Lithium ion secondary batteries using silicon as the negative electrode active material face issues with pulverization, warpage, and short cycle life due to lithium ion absorption and desorption, and existing methods to alleviate current path disconnection are not applicable to flat laminate-type batteries.
Innovation Solution
A lithium ion secondary battery design featuring a negative electrode with a metal collector and active material layer, where a crack reaching the collector and outer edge is formed by lithium doping, reducing detachment and disconnection of the active material layer during expansion and contraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as the negative electrode active material to increase capacity, then the energy density is improved, but pulverization occurs due to expansion and contraction during lithium ion absorption and desorption
Solution Approach 1:
The negative electrode is divided into multiple independent regions by forming cracks that extend from the inner peripheral edge to the outer peripheral edge. These cracks segment the electrode structure, allowing each segment to expand and contract independently during lithium ion absorption and desorption, thereby reducing overall pulverization and improving cycle life while maintaining high capacity.
2Quantity of substance
If the negative electrode active material layer is made thick to increase capacity, then the energy density is improved, but warpage and wrinkling of the electrode occur frequently due to expansion and contraction
Solution Approach 1:
By forming cracks that divide the thick active material layer into multiple segments, the electrode can accommodate expansion and contraction without developing warpage or wrinkling. Each segmented region can deform independently, preventing the accumulation of stress that would otherwise cause shape distortion.
Solution Approach 2:
The crack depth and positioning are optimized to create different structural characteristics in different regions of the electrode. The cracks extend from the inner peripheral edge toward the outer peripheral edge, creating a gradient structure that locally manages stress distribution and prevents uniform warpage across the entire electrode.
3Reliability
If a crack is formed in the molded negative electrode to alleviate disconnection of current collecting paths, then the cycle property is improved, but the method is only applicable to coin-type batteries and not flat laminate-type batteries
Solution Approach 1:
The crack formation method is designed to be universally applicable to both coin-type and flat laminate-type batteries. The cracks are formed in the negative electrode active material layer regardless of battery geometry, and the inner peripheral edge reference point adapts to different battery types, making the solution versatile across various battery configurations.
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 design enhances the charge and discharge cycle life by minimizing capacity loss and improving the battery's cycle properties, making it suitable for repeated use.
Implementation Method 1
a Li absorbing substance represented by a composition formula of LixA (A is an atom such as silicon or tin) that is alloyed with lithium is used as the negative electrode active material
Implementation Method 2
This Li absorbing substance can absorb and desorb a large amount of lithium ion with respect to the unit volume and has a high capacity
Implementation Method 3
by forming a crack which starts from the recessed portion along the thickness direction thereof is proposed... by forming a crack in the molded negative electrode, an effect is produced in which the disconnection of the current collecting paths along the thickness direction of the negative electrode is alleviated
Data Source
AI summary
The object of an exemplary embodiment of the invention is to provide a lithium ion secondary battery having an excellent charge and discharge cycle property. An exemplary embodiment of the invention is a lithium ion secondary battery, comprising a battery assembly in which a positive electrode and a negative electrode are stacked through a separator and a package in which the battery assembly and an electrolyte are placed; wherein the negative electrode comprises a negative electrode collector which is composed of a metal and a negative electrode active material layer which is formed on the negative electrode collector and which comprises a negative electrode active material and a binder; wherein the negative electrode collector and the negative electrode active material layer have a crack which is formed so as to be communicated with each of them; and wherein the crack reaches an outer peripheral edge from an inside of the negative electrode.