Nonaqueous Battery Negative Electrode Mass Ratio Design
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Solution Overview
Problem
In nonaqueous electrolyte secondary batteries, the uneven distribution of active material layers on the inner and outer circumferences of the current collector leads to reduced mass per unit area on the outer circumference, causing lithium deposition when the negative electrode's load capacity exceeds its theoretical capacity, compromising battery capacity and cycle characteristics.
Innovation Solution
The battery design includes a wound electrode group with a porous insulating layer, where the negative electrode active material layers on both surfaces of the current collector have mass ratios that satisfy specific relational expressions to maintain the balance between the inner and outer circumferential masses, preventing lithium deposition and enhancing cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the mass of the negative electrode active material is reduced to increase battery capacity, then the load capacity of the negative electrode exceeds its theoretical capacity, but metal lithium deposits on the negative electrode active material layer formed on the outer circumference
Solution Approach 1:
The patent applies local quality by setting different active material masses M1 and M2 for the negative electrode layers on the outer and inner circumferences respectively. The mass ratio M1/M2 is specifically controlled to satisfy (R2+t/2)/(R2−t/2) ≤ M1/M2 ≤ (R1+t/2)/(R1−t/2), creating a non-uniform distribution that compensates for the extension effect during winding, preventing lithium deposition on the outer circumference while maintaining high battery capacity.
2Shape
If the active material layer on the outer circumference is extended during winding, then the mass per unit area is reduced, but the load capacity per unit area exceeds the theoretical capacity
Solution Approach 1:
The patent applies preliminary action by pre-adjusting the active material mass distribution before winding occurs. The masses M1 and M2 are set in advance to satisfy the specific ratio relationship, so that when the electrode group is wound and the outer circumference extends, the load capacity per unit area remains within the theoretical capacity limit, preventing lithium deposition.
3Duration of action of stationary object
If the filling amount of active material on the inner circumference is made smaller than on the outer circumference to improve cycle characteristics, then the mass distribution becomes uneven, but lithium deposition occurs when capacity is increased
Solution Approach 1:
The patent applies parameter changes by precisely controlling the mass ratio parameter M1/M2 within the mathematical bounds defined by the inner and outer radii. This quantitative parameter adjustment ensures that the load capacity distribution accounts for both cycle characteristics requirements and prevents lithium deposition, resolving the contradiction through mathematical optimization.
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 achieves a higher capacity nonaqueous electrolyte secondary battery with excellent cycle characteristics by maintaining the margin between the load capacity and theoretical capacity of the negative electrode, preventing lithium deposition and ensuring efficient lithium ion transfer.
Implementation Method 1
a porous insulating layer interposed therebetween
Implementation Method 2
the load capacity (mAh/g) is obtained by dividing the capacity per unit area (mAh/cm2) of the positive electrode in full charge by the mass per unit area (g/cm2) of the active material of the negative electrode
Data Source
AI summary
In a wound electrode group, a positive electrode includes positive electrode active material layers formed on both surfaces of a band-like positive electrode current collector, and a negative electrode includes negative electrode active material layers on both surfaces of a band-like negative electrode current collector. Charge capacity of the negative electrode falls within a range of 83-99% of theoretical capacity of the negative electrode in a full charge state of a nonaqueous electrolyte secondary battery. An active material mass M1 per unit area of a negative electrode active material layer formed on an outer circumference of the negative electrode current collector, and an active material mass M2 per unit area of a negative electrode active material layer formed on an inner circumference satisfy a relational expression of M1/M2<(R1+t/2)/(R1−t/2), where the electrode group has an innermost diameter of R1, and the negative electrode has a thickness of t.