Nickel Oxide Cathode Particles With Porosity Gradient for Fast Charging
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in achieving high energy density while maintaining lithium ion permeability and preventing dendrite formation, which can lead to safety issues and reduced battery life.
Innovation Solution
A positive active material for rechargeable lithium batteries is developed, comprising secondary particles of nickel-based transition metal oxide with a dense inner portion and a porous outer portion, featuring protruding portions that enhance lithium ion diffusion and charging efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If porosity of electrode is increased to enhance lithium ion mobility, then lithium ion permeability is improved, but electrical contact surface area decreases and energy density is lowered
Solution Approach 1:
The positive active material employs a core-shell structure where the core region has higher porosity (0.4-0.6) to facilitate lithium ion diffusion, while the shell region has lower porosity (0.2-0.4) to maintain electrical contact and structural stability. This spatial differentiation of porosity allows simultaneous optimization of ion mobility and energy density.
Solution Approach 2:
The positive active material is designed as a composite structure combining nickel-based transition metal oxide with controlled internal porosity distribution. The composite architecture integrates dense regions for electrical conductivity with porous regions for ion transport, achieving both high energy density and high rate charging capability.
2Productivity
If charge rate is increased to achieve high-rate charging, then charging speed is improved, but battery performance deteriorates and safety issues arise
Solution Approach 1:
The positive active material incorporates a controlled porous structure with total porosity of 0.2-0.4, with enhanced internal porosity (0.4-0.6) in the core region. This porous architecture facilitates rapid lithium ion diffusion throughout the particle interior, enabling high-rate charging while maintaining structural integrity and preventing dendrite formation.
Solution Approach 2:
The invention introduces a radial porosity gradient from the particle center to the surface, creating a three-dimensional porosity distribution. This dimensional approach allows lithium ions to access the particle interior more efficiently, reducing polarization and enabling high-rate charging without compromising performance.
3Speed
If porosity is increased to improve lithium ion diffusion, then ion mobility is enhanced, but structural stability decreases leading to particle cracking
Solution Approach 1:
The positive active material features a core-shell structure with differentiated porosity: the core has high porosity (0.4-0.6) for rapid ion diffusion, while the shell has low porosity (0.2-0.4) for structural stability. This local quality differentiation allows the particle to withstand mechanical stress during charging-discharging cycles while maintaining high ion mobility in the core region.
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 proposed positive active material achieves improved high-rate charging capabilities and cycle-life characteristics, maintaining structural stability and preventing particle cracking during charging and discharging processes.
Implementation Method 1
the inner portion has a dense structure having a higher density than the outer portion, the secondary particles of the nickel-based transition metal oxide have a plurality of protruding portions on the surface thereof
Data Source
AI summary
Disclosed is a positive active material for a rechargeable lithium battery including secondary particles of a nickel-based transition metal oxide composed of an inner portion and an outer portion, wherein the inner portion has a dense structure having a higher density than the outer portion, the secondary particles of the nickel-based transition metal oxide have a plurality of protruding portions on the surface thereof, and the positive active material has an area ratio of 25% to 30% occupied by the protruding portions calculated by Equation 1 based on a cross-section of the secondary particles of the nickel-based transition metal oxide.