Positive Electrode Flaked Graphite for Battery Distortion
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries for EVs and HEVs face challenges in achieving high output characteristics and safety due to distortion in positive electrode plates during compression, leading to rolling gaps and potential inner short circuits, which are exacerbated by the high internal resistance variations with state of charge.
Innovation Solution
Incorporating a positive electrode mixture with 5 to 15% by mass of conductive material, predominantly flaked graphite particles with an average diameter of 5 to 30 μm and thickness of 0.1 to 1.0 μm, and a packing density of 2.00 to 2.80 g/cc, to minimize distortion and reduce rolling gaps during electrode preparation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a positive electrode plate is compressed to reduce thickness and increase capacity, then energy density is improved, but distortion occurs leading to rolling gaps and inner short circuits
Solution Approach 1:
The patent changes the physical parameters of the conductive material by specifying flaked graphite with controlled particle size (5-30 μm) and aspect ratio (5-30), and optimizes its content (5-15 mass%) to balance electrode integrity and electrical conductivity, preventing distortion during compression while maintaining energy density
Solution Approach 2:
The patent creates a composite positive electrode mixture containing lithium transition metal oxide (70-90 mass%), conductive binder (0.5-5 mass%), and specifically controlled flaked graphite (5-15 mass%), where the composite structure provides both mechanical stability during compression and sufficient electrical conductivity
2Power
If rapid discharge or charging is performed to improve output characteristics, then power delivery is improved, but internal resistance variations with state of charge increase
Solution Approach 1:
The patent optimizes the conductive material parameters (flaked graphite with specific particle size 5-30 μm and aspect ratio 5-30) and concentration (5-15 mass%) to maintain stable electrical pathways throughout charge-discharge cycles, reducing internal resistance variations while enabling rapid power delivery
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 results in a nonaqueous electrolyte secondary battery with reduced distortion, lower internal resistance, and improved safety and performance, suitable for EVs and HEVs, by maintaining a low and constant internal resistance across varying states of charge.
Implementation Method 1
a positive electrode mixture with 5 to 15% by mass of conductive material, predominantly flaked graphite particles... to minimize distortion and reduce rolling gaps during electrode preparation... lower internal resistance
Implementation Method 2
a laser beam is irradiated... FIG. 6 is a partially broken elevation view showing a state where the collector plate is pressed to the rolled electrode and a laser beam is irradiated
Data Source
AI summary
A nonaqueous electrolyte secondary battery of the present invention includes a positive electrode plate 21 having an uncoated part along at least one long side of a continuous positive electrode substrate 211 coated with a positive electrode mixture layer 212 containing a positive electrode active material. In the nonaqueous electrolyte secondary battery, the positive electrode mixture layer 212 includes a lithium transition-metal compound capable of insertion and separation of lithium ion and 5 to 15% by mass of a conductive material with respect to the positive electrode mixture, the conductive material contains 70% by mass or more of flaked graphite particles with an average particle diameter (D50) of 5 to 30 μm and an average thickness of 0.1 to 1.0 μm with respect to the whole amount of the conductive materials, and a packing density of the positive electrode mixture layer is 2.00 to 2.80 g/cc.