Nickel-Rich Cathode Material With Core-Shell Stability Gradient
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Solution Overview
Problem
Nickel-based lithium metal oxide positive active materials for lithium rechargeable batteries become structurally unstable and exhibit increased resistance when nickel content is high, especially in high-temperature environments, affecting cycle-life and capacity characteristics.
Innovation Solution
A nickel-based lithium metal oxide particle with a core-shell concentration gradient and a coating layer of rare earth oxyhydroxide, doped with Zr and Al, is used to maintain structural stability and reduce nickel content in the shell portion, enhancing resistance and capacity characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the nickel content is increased to achieve higher capacity, then the battery capacity is improved, but the structural stability deteriorates and resistance increases significantly in high temperature environments
Solution Approach 1:
The positive active material is divided into a core portion with high nickel content (0.8-0.95) for high capacity and a shell portion with reduced nickel content (0.6-0.8) for structural stability. This core-shell segmentation allows the inner core to provide high capacity while the outer shell protects against structural degradation and resistance increase at high temperatures.
Solution Approach 2:
Different regions of the particle have different nickel concentrations - the core has high nickel content optimized for capacity, while the shell has lower nickel content optimized for stability. This local quality variation resolves the contradiction by allowing each region to perform its specific function optimally.
2Quantity of substance
If the nickel content is increased to achieve higher capacity, then the battery capacity is improved, but the resistance increases significantly in high temperature environments
Solution Approach 1:
The particle structure is segmented into core and shell regions, where the high-nickel core provides capacity while the low-nickel shell minimizes resistance increase at high temperatures. This segmentation allows the material to achieve high capacity without suffering from the resistance problems associated with uniformly high nickel content.
Solution Approach 2:
The positive active material forms a composite structure with different nickel concentrations in core and shell regions. This composite approach combines the high-capacity advantage of high-nickel materials with the low-resistance advantage of lower-nickel materials, achieving both high capacity and stable resistance characteristics.
3Reliability
If a coating layer is added to improve resistance characteristics, then the resistance stability is improved, but the device complexity increases
Solution Approach 1:
The protective function is merged into the shell portion of the core-shell structure itself, rather than adding a separate coating layer. The shell with reduced nickel content (0.6-0.8) inherently provides protection against resistance increase, eliminating the need for additional coating materials and simplifying the overall structure.
Solution Approach 2:
The shell portion serves multiple functions: it maintains structural stability, prevents resistance increase at high temperatures, and eliminates the need for separate coating layers. This multi-functionality reduces device complexity while achieving the desired resistance characteristics.
Data Source
AI summary
The present disclosure relates to a positive active material for a lithium rechargeable battery and a lithium rechargeable battery including the same, which include a first compound represented by Chemical Formula 1 and a second compound represented by Chemical Formula 2, and a content of the first compound is 65 wt % or more based of the positive active material of 100 wt %.Lia1Nib1Coc1Mnd1M1e1M2f1O2-f1[ Chemical Formula 1]Lia2Nib2COc2Mnd2M3e2M4f2O2-f2[ Chemical Formula 2]Chemical Composition 1 and 2 of each composition and molar ratio is as defined in the specification. Each composition and molar ratio of Chemical Formula 1 and 2 is as defined in the specification.