Fibrous Carbon Electrode Layer for Low Resistance Thick Batteries
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving low electric resistance with thicker electrode layers, as increased electrode density can lead to porosity issues and higher resistance, and methods to orient fibrous carbon for improved conductivity are time-consuming and may damage separators.
Innovation Solution
A thicker-film electrode mixture layer is formed using fibrous carbon with an average effective length of 10 μm or more, three-dimensionally dispersed in a random manner, with a surface layer oriented in the in-plane direction to create a long conductive path, reducing electric resistance and enabling high output capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the electrode layer is thickened to increase the support amount of electrode active material, then the energy density is improved, but the conductive path formation is insufficient and electric resistance increases
Solution Approach 1:
The patent changes the physical parameters of the conductive agent by using fibrous carbon with specific aspect ratios (length/diameter) greater than 3, and controlling its content at 0.1-5 mass%. This parameter optimization enables effective conductive network formation in thick electrode layers without excessive resistance
Solution Approach 2:
The patent creates a composite structure combining fibrous carbon with specific morphology (high aspect ratio) and electrode active material. This composite approach forms a three-dimensional conductive network that effectively addresses the conductive path formation issue in thick electrodes
2Reliability
If the electrode density is increased to reduce resistance, then the electric resistance is reduced, but the porosity becomes low and substance dispersion is inhibited leading to resistance rise
Solution Approach 1:
The patent utilizes the porous structure inherent in fibrous carbon materials to maintain electrode porosity even at high densities. The fibrous network creates interconnected pores that allow substance dispersion while providing conductive pathways, resolving the contradiction between density and porosity
3Reliability
If fibrous carbon is oriented in the film thickness direction to generate electrostatic field and improve conductivity, then the conductive direction is improved, but the process is time-consuming and may damage separator
Solution Approach 1:
The patent changes the orientation parameter of fibrous carbon, specifying that the degree of orientation should be 0.7 or less. This allows the conductive agents to maintain adequate conductivity without requiring intensive orientation processes that would consume time or damage the separator
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 approach results in excellent rate characteristics and low electric resistance for thick-film electrodes, allowing for high-output nonaqueous electrolyte secondary batteries with enhanced battery capacity, particularly for lithium ion batteries.
Implementation Method 1
a conductive path to a current collector is not formed sufficiently, an electric resistance of an electrode is increased
Implementation Method 2
by adding fibrous carbon as a conductive agent and generating an electrostatic field, the fibrous carbon is oriented in a film thickness direction of an electrode
Data Source
AI summary
The present invention provides an electrode mixture layer for nonaqueous electrolyte secondary batteries, which contains an electrode active material, a carbon-based conductive agent containing fibrous carbon having an average effective length of 10 μm, and a binder, and which has a thickness of 50 μm or more. This electrode mixture layer has an inner layer portion where the fibrous carbon is three-dimensionally dispersed in a random manner.