Positive Electrode Particle Size Mix for Low-Conductive Cathodes
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Solution Overview
Problem
Nonaqueous electrolyte energy storage devices experience a significant decrease in capacity retention ratio after charge-discharge cycles when the content of the conductive agent in the positive active material layer is reduced, leading to particle cracking and pulverization of active material particles.
Innovation Solution
A positive electrode with a positive active material layer containing first particles with a Feret diameter of 5 μm or less and second particles with a Feret diameter greater than 5 μm, along with a conductive agent content less than 1.1% by mass, where the first particles are secondary particles with an average secondary particle size to average primary particle size ratio of 3 or less, or primary particles that are not substantially aggregated, effectively suppressing particle cracking and pulverization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional positive electrode without protective coating is used, then the electrode structure is simple and manufacturing is easier, but the electrode deteriorates due to contact with the electrolyte solution, causing performance degradation and shortening battery life
Solution Approach 1:
The patent applies composite materials by forming a protective coating layer comprising inorganic particles embedded in a resin matrix on the positive electrode. This composite structure combines the electrical functionality of the base electrode with the protective and conductive properties of the coating layer, resolving the contradiction between electrode stability and structural complexity.
Solution Approach 2:
The protective coating layer is designed with porous characteristics that allow electrolyte penetration while providing protection. The porous structure enables ion transport necessary for battery operation while maintaining the protective function against electrode deterioration, thus improving reliability without excessively complicating the electrode structure.
2Reliability
If a protective coating layer is formed on the positive electrode to prevent deterioration, then electrode stability improves, but high-frequency impedance increases and battery output performance deteriorates
Solution Approach 1:
The patent optimizes several parameters of the protective coating layer to balance stability and performance: controlling particle concentration (0.1-10 wt%), particle size distribution, resin-to-conductive-agent ratio, and coating thickness. These parameter adjustments ensure the coating provides protection while maintaining adequate ion and electron transport for high-rate charge-discharge operation.
Solution Approach 2:
The coating layer uses a composite formulation combining resin materials with conductive agents (such as carbon black or graphite particles) in specific ratios. This composite approach maintains electrical conductivity throughout the coating, preventing excessive impedance buildup that would limit charge-discharge rates, while still providing the protective function.
3Reliability
If the positive electrode potential is controlled to prevent electrolyte decomposition, then electrolyte stability improves, but the battery capacity and output performance are limited
Solution Approach 1:
The protective coating layer acts as an intermediary between the positive electrode and the electrolyte solution. It enables the electrode to operate at higher potentials that would otherwise cause electrolyte decomposition, while the coating itself prevents direct harmful interactions. This mediator approach allows the battery to achieve higher capacity without sacrificing electrolyte stability.
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 configuration enhances the capacity retention ratio of nonaqueous electrolyte energy storage devices by minimizing particle cracking and pulverization, even with reduced conductive agent content, while maintaining high energy density and durability during charge-discharge cycles.
Implementation Method 1
a protective coating layer which comprises: inorganic particles serving as a scaffold
Implementation Method 2
resin material serving as a matrix in a case where the inorganic particles serve as a scaffold
Implementation Method 3
the protective coating layer has a porous structure
Implementation Method 4
containing a conductive agent
Data Source
Figure 1~2
AI summary
A positive electrode for a nonaqueous electrolyte energy storage device according to one aspect of the present invention includes a positive active material layer containing: first positive active material particles having a Feret diameter of 5 µm or less in a projection image obtained by scanning electron microscope (SEM) observation; second positive active material particles having a Feret diameter of more than 5 µm in a projection image obtained by SEM observation; and a conductive agent, wherein a content of the conductive agent in the positive active material layer is less than 1.1% by mass, and the first positive active material particles are secondary particles having a ratio of an average secondary particle size to an average primary particle size of 3 or less, or primary particles which are not substantially aggregated.