Lithium-Nickel Cathode Particle Structure for Longer Cycle Life
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Solution Overview
Problem
Lithium-nickel composite oxides used in lithium-ion secondary batteries exhibit poor cycle characteristics and significant battery expansion due to gas generation during charge and discharge cycles.
Innovation Solution
A positive electrode active material for lithium-ion secondary batteries is developed, comprising a lithium-nickel composite oxide with a hexagonal layered structure, consisting of either single primary particles or secondary particles with a small number of aggregated primary particles, and a specific mole ratio of lithium, nickel, and optional elements like cobalt, manganese, and aluminum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium-nickel composite oxide is used as positive electrode active material, then battery capacity and energy density are improved, but cycle characteristic deteriorates and battery expansion occurs
Solution Approach 1:
The lithium-nickel composite oxide is divided into multiple primary particles that aggregate to form secondary particles. This segmentation reduces the size of individual particles, minimizing strain during lithium ion insertion/extraction cycles and preventing particle cracking that leads to capacity fade and battery expansion.
Solution Approach 2:
The invention uses a composite structure where multiple primary particles aggregate to form secondary particles with controlled morphology. This composite architecture combines the high capacity benefits of lithium-nickel oxide with improved structural stability, as the aggregated structure distributes mechanical stress during cycling.
2Ease of manufacture
If secondary particles with multiple aggregated primary particles are used, then manufacturing is easier, but particle cracking occurs at interfaces reducing cycle life
Solution Approach 1:
The invention optimizes the local quality at particle interfaces by controlling the aggregation of primary particles into secondary particles with specific morphological characteristics. This local optimization reduces stress concentration at grain boundaries while maintaining the benefits of aggregated structure for manufacturability.
3Power
If charge and discharge are repeated, then battery output is maintained, but gas generation causes battery expansion
Solution Approach 1:
By segmenting the active material into small primary particles that form aggregated secondary particles, the invention reduces the volume expansion stress during cycling. The smaller particle size and aggregated structure accommodate gas generation and dimensional changes more effectively, preventing overall battery expansion while maintaining output capacity.
Data Source
AI summary
A positive electrode active material for a lithium ion secondary battery, including a lithium-nickel composite oxide having a hexagonal layered structure and configured by particles including at least either single primary particles or secondary particles with a plurality of aggregated primary particles, wherein the particles included in the positive electrode active material have a cross section having one or more crystal faces, and the one or more crystal faces in the particles have an average misorientation of 0.7° or less from a reference orientation of each of the one or more crystal faces.