Positive Electrode Particle Blend for Lower AC Resistance
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Solution Overview
Problem
Energy storage devices using single particle-based positive active material particles exhibit high initial alternating-current resistance, which increases with charge-discharge cycles, leading to decreased capacity retention.
Innovation Solution
The energy storage device incorporates a positive active material layer containing a combination of first positive active material particles (single particle-based) and second positive active material particles (secondary particle-based) along with fibrous carbon, where the first particles have a particle size ratio of 3 or less to their average primary particle size, and the second particles have a particle size ratio greater than 3.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If single particle-based positive active material particles are used, then capacity retention is improved, but initial alternating-current resistance increases
Solution Approach 1:
The patent combines single particle-based positive active material particles with fibrous carbon to create a composite structure. The fibrous carbon forms a conductive network that bridges the single particles, reducing overall resistance while preserving the advantages of single-particle architecture for capacity retention.
Solution Approach 2:
The invention creates a composite material system consisting of single particle-based positive active material particles embedded in a fibrous carbon matrix. This composite structure integrates the high capacity retention of single particles with the low resistance characteristics of conductive carbon networks.
2Reliability
If single particle-based positive active material particles are used, then capacity retention is improved, but alternating-current resistance increases with charge-discharge cycles
Solution Approach 1:
The fibrous carbon is incorporated beforehand to create a pre-established conductive network that cushions against resistance increases during cycling. This network provides stable electrical pathways that prevent the formation of high-resistance regions that would otherwise develop during charge-discharge cycles.
Solution Approach 2:
The fibrous carbon acts as an intermediary conductive phase between single particle-based positive active material particles. It mediates electron transport between particles, maintaining stable alternating-current resistance by providing alternative conduction paths that are not affected by particle degradation during cycling.
3Object-affected harmful factors
If secondary particles with many primary particles aggregated are used, then alternating-current resistance is reduced, but capacity retention deteriorates due to grain boundary cracking
Solution Approach 1:
The invention segments the positive active material into single particles or minimally aggregated secondary particles, preventing the formation of large aggregates with numerous grain boundaries. This segmentation eliminates the grain boundary cracking issue while the fibrous carbon provides the necessary conductive network.
Solution Approach 2:
The invention applies different structural characteristics to different components: single particle-based positive active material particles provide high capacity retention by eliminating grain boundaries, while fibrous carbon provides low resistance through its continuous conductive network. Each component optimizes its local function to overcome the limitations of the other.
Data Source
AI summary
An energy storage device according to an aspect of the present invention includes a positive electrode including a positive active material layer, the positive active material layer contains first positive active material particles, second positive active material particles, and fibrous carbon, the first positive active material particles are primary particles or secondary particles of primary particles aggregated, the ratio of a particle size to an average primary particle size for the first positive active material particles is 3 or less, the second positive active material particles are secondary particles of primary particles aggregated, and the ratio of a particle size to an average primary particle size for the second positive active material particles is more than 3.