Cathode Active Material Structure for Lithium-Ion Diffusion and Capacity
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Solution Overview
Problem
The addition of niobium, tungsten, or molybdenum to lithium metal composite oxides in lithium secondary batteries can hinder sintering and crystal growth, leading to reduced initial discharge capacity, efficiency, and cycle characteristics due to smaller average crystallite diameters of positive electrode active material particles.
Innovation Solution
A positive electrode active material comprising lithium metal composite oxide with secondary particles having gaps among primary particles, where a lithium-ion conductive oxide containing niobium, tungsten, or molybdenum is present in these gaps, optimizing the crystallite diameter, particle size distribution, and specific surface area to enhance battery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a compound containing niobium, tungsten, or molybdenum is added to lithium metal composite oxide, then battery characteristics are improved, but sintering and crystal growth are hindered resulting in smaller average crystallite diameter
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the central part contains the lithium metal composite oxide with niobium/tungsten/molybdenum compound for improved battery characteristics, while the outer peripheral part contains a lithium compound that promotes sintering and crystal growth. This spatial differentiation allows different regions to have different functions: the core provides enhanced electrochemical performance while the shell ensures adequate crystallite diameter through promoted sintering.
2Volume of moving object
If the average crystallite diameter of positive electrode active material particles is reduced, then particle size is decreased, but initial discharge capacity, initial efficiency, and cycle characteristic are reduced
Solution Approach 1:
The patent creates a differentiated structure where the central part has smaller crystallite diameter for reduced particle size, while the outer peripheral part has larger crystallite diameter for maintaining initial discharge capacity and efficiency. This local differentiation resolves the contradiction by allowing different regions to optimize for different performance aspects.
Solution Approach 2:
The patent uses composite materials by combining lithium metal composite oxide containing niobium/tungsten/molybdenum with a lithium compound in a core-shell configuration. This composite structure allows the inner core to provide high capacity through smaller crystallites while the outer shell provides structural support and maintains efficiency through larger crystallites, achieving both reduced particle size and maintained productivity.
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 solution results in lithium secondary batteries with improved initial discharge capacity, efficiency, and cycle characteristics by effectively diffusing lithium ions and reducing resistance during insertion and desorption, while maintaining particle integrity and stability.
Implementation Method 1
the Li—X compound is a lithium-ion conductive oxide
Data Source
AI summary
A positive electrode active material for a lithium secondary battery, containing a lithium metal composite oxide and an Li—X compound containing Li and an element X, in which the Li—X compound is a lithium-ion conductive oxide, the lithium metal composite oxide contains secondary particles, which are aggregates of primary particles, the secondary particles have gaps among the primary particles, the Li—X compound is present at least in the gap, the element X is one or more elements selected from the group consisting of Nb, W, and Mo, and the positive electrode active material for the lithium secondary battery satisfies (A).4.95≤LA/Lav (A)