Lithium Iron Phosphate Electrode with Etched Aluminum Foil
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Solution Overview
Problem
Lithium ion secondary batteries using olivine lithium oxide as positive electrode material face significant degradation in charge and discharge cycle properties, particularly high-rate discharge polarization, due to low conductivity and poor adhesiveness with current collectors, leading to reduced battery performance and increased manufacturing costs.
Innovation Solution
A lithium ion secondary battery design featuring a positive electrode active material with an average primary particle size of 0.50 µm to 2 µm and a surface roughness of 0.2 µm to 0.6 µm on the current collector, using lithium iron phosphate with carbon coating to enhance conductivity and adhesiveness, and employing an etched aluminum foil with controlled surface roughness to improve mechanical strength and battery capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If olivine lithium oxide is used as positive electrode material, then cost is reduced, but adhesiveness with current collector is low
Solution Approach 1:
A binder is introduced as an intermediary substance that adheres to both the olivine lithium oxide particles and the current collector surface. This binder creates strong interfacial adhesion, ensuring good contact between the active material and current collector, which is essential for electron transport and mechanical stability.
Solution Approach 2:
The electrode composite includes binder components that provide adhesive functionality, creating a tri-phase composite system (olivine lithium oxide, conductive agent, binder) that simultaneously achieves cost-effectiveness, electrical conductivity, and mechanical adhesion to the current collector.
2Reliability
If small particle size is used, then polarization is reduced, but fill density and overall energy density are reduced
Solution Approach 1:
The positive electrode active material is segmented into fine primary particles with controlled size distribution. This segmentation reduces the diffusion path length for lithium ions, thereby reducing polarization during charge-discharge cycles. The segmented particles are then aggregated into larger secondary particles that achieve optimal fill density in the electrode.
Solution Approach 2:
Different regions of the electrode structure exhibit different particle size characteristics. Primary particles have small sizes (0.5-2 µm) to reduce polarization, while the overall packing arrangement and secondary particle formation create local density variations that optimize fill density. This local quality differentiation allows simultaneous achievement of low polarization and high energy density.
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 solution significantly increases battery capacity retention rate after repeated high-rate charge and discharge cycles, improving battery performance and reducing manufacturing costs while maintaining mechanical strength of the current collector.
Implementation Method 1
lithium iron phosphate with carbon coating to enhance conductivity
Implementation Method 2
etched aluminum foil with controlled surface roughness to improve mechanical strength and battery capacity retention
Data Source
AI summary
A lithium ion secondary battery that can increase battery capacity retention rate after repeated high-rate charge and discharge is provided. A lithium ion secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode has a positive electrode active material-containing layer containing a positive electrode active material represented by formula (I) below formed on a positive current collector, and in the lithium ion secondary battery, the average primary particle size of the positive electrode active material is 0.50 µm or more and 2 µm or less, and the average surface roughness Ra of the surface of the positive current collector in contact with the positive electrode active material-containing layer is 0.2 µm or more and 0.6 µm or less. In formula (I) below, M is at least one metal atom selected from the group consisting of Co, Ni, Fe, Mn, Cu, Mg, Zn, Ti, Al, Si, B, and Mo, and 0<X<2. LixMPO4 ... (I)