Pseudo-Spinel Cathode Material for High-Voltage Cycle Stability
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges with reduced capacity and cycle performance due to structural changes during high-voltage charge and discharge cycles, leading to instability and decreased reliability.
Innovation Solution
A positive electrode active material with a pseudo-spinel crystal structure containing lithium, cobalt, magnesium, oxygen, and fluorine, along with optional titanium or aluminum, is developed to minimize structural changes between charged and discharged states, enhancing stability and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional positive electrode active materials are used for high-voltage charge and discharge, then capacity and power output can be increased, but structural changes occur during cycling leading to reduced capacity and cycle performance
Solution Approach 1:
The patent employs a composite material strategy by combining lithium cobalt oxide (LiCoO2) with lithium nickel oxide (LiNiO3) or lithium manganese oxide (LiMnO3) to form a spinel structure. This composite approach allows the material to achieve high capacity and power output while the spinel crystal structure provides inherent structural stability during charge-discharge cycles, preventing the degradation that would otherwise occur with conventional materials at high voltages.
Solution Approach 2:
The patent modifies the crystal structure parameter by transitioning from conventional layered structures to a spinel crystal structure. This structural parameter change enables the material to maintain stability during high-voltage cycling while still achieving high capacity. The spinel structure's three-dimensional lithium ion diffusion pathways and stable framework allow parameter optimization for both high power output and sustained cycle performance.
2Quantity of substance
If high voltage charging is applied to increase capacity, then energy density improves, but structural integrity deteriorates leading to reduced reliability
Solution Approach 1:
The spinel composite material combines multiple metal oxides (LiCoO2, LiNiO3, LiMnO3) in a unified crystal structure that provides both high capacity and structural integrity. The spinel framework accommodates lithium extraction and insertion at high voltages without collapsing, maintaining structural integrity while achieving high capacity through the synergistic properties of the constituent materials.
Solution Approach 2:
The patent applies local quality by creating a surface coating or modification on the spinel particles. This local treatment enhances the surface properties to resist structural degradation during high-voltage cycling, while the bulk material maintains its high capacity characteristics. The local modification protects the crystal structure from irreversible changes that would otherwise occur at high voltages.
Data Source
AI summary
A positive electrode active material having high capacity and excellent cycle performance is provided. The positive electrode active material has a small difference in a crystal structure between the charged state and the discharged state. For example, the crystal structure and volume of the positive electrode active material, which has a layered rock-salt crystal structure in the discharged state and a pseudo-spinel crystal structure in the charged state at a high voltage of approximately 4.6 V, are less likely to be changed by charge and discharge as compared with those of a known positive electrode active material.