Nickel-Lithium Cobalt Oxide Cathode With Li-Gradient Surface Layer
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Solution Overview
Problem
The structural stability of layered ternary cathode materials deteriorates with increasing nickel content, leading to irreversible phase transitions and internal stress, which causes cracking and pulverization of particles, affecting cycle life and safety performance.
Innovation Solution
A nickel-lithium cobalt oxide based composite oxide cathode material with a core and a surface reconstruction layer, where the Li molar content gradient is controlled to facilitate preferential lithium ion deintercalation in the surface layer, reducing lattice expansion/contraction stress and enhancing lithium ion conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If nickel content is increased to improve reversible specific capacity and energy density, then the discharge capacity and specific energy are improved, but the structural stability deteriorates and irreversible phase transitions occur
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the core region contains high nickel content (0.8-0.95) for high capacity, while the surface shell contains lower nickel content (0.5-0.7) for structural stability. This spatial differentiation of composition allows each region to perform its optimal function without compromising the other.
Solution Approach 2:
The patent uses composite materials by combining high-nickel cathode material with a protective surface coating layer. The composite structure integrates the high-capacity core material with a more stable surface material, achieving both high energy density and structural stability through material composition design.
2Quantity of substance
If nickel content is increased to improve discharge capacity, then the energy density is improved, but internal stress increases causing particle cracking and pulverization
Solution Approach 1:
The surface shell with lower nickel content and higher structural stability acts as a protective layer that distributes and reduces internal stress during lithium ion insertion/extraction cycles, preventing stress concentration that would lead to particle cracking and pulverization.
Solution Approach 2:
The stable surface shell serves as a pre-established protective barrier that cushions the high-nickel core material from mechanical stress during cycling, preventing damage before it occurs to the capacity-providing core region.
3Speed
If lithium ion deintercalation is promoted to improve rate performance, then the charging speed is improved, but lattice expansion stress increases causing structural degradation
Solution Approach 1:
The surface shell is designed with optimized lithium ion conductivity and structural stability to facilitate rapid lithium ion transport while simultaneously providing a stable framework that accommodates lattice expansion stress, enabling high rate performance without structural degradation.
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 cathode material exhibits improved cycle stability, increased withstand voltage, and enhanced rate performance by minimizing particle cracking and optimizing lithium ion distribution.
Implementation Method 1
During charging and discharging, the core has a lower lithium ion deintercalation reaction activity than that of the surface reconstruction layer, thus lithium ions are preferentially deintercalated in the surface reconstruction layer
Implementation Method 2
a lithium ion concentration gradient is formed between inner and outer layers of the cathode material, resulting in a reduced lattice expansion/contraction stress in the core
Implementation Method 3
a higher lithium ion molar content in the surface reconstruction layer further improve lithium ion conductivity of the cathode material
Data Source
AI summary
A cathode material, a preparation method thereof, and a battery provided. The cathode material is a nickel-lithium cobalt oxide based composite oxide including a core and a surface reconstruction layer arranged outside the core, where the surface reconstruction layer is a region etched away by dissolving the cathode material with 100 times diluted aqua regia for 30 minutes, with an ambient temperature controlled to be 300° C. during dissolution, and the core is a remaining region after the surface reconstruction layer is etched away from the cathode material, and where the core has a Li molar content of m1, the surface reconstruction layer has a Li molar content of m2, and 1.3≤m2/m1≤4.0. The cathode material provided is improved stability of crystal structure while having high capacity, thereby improving cycle stability of the cathode material and improving withstand voltage of the cathode material.