Core-Shell Lithium Battery Cathode for High Capacity and Cycle Life
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in achieving high capacity and excellent cycle-life characteristics, particularly for use in downsized mobile devices and as power sources for hybrid or electric vehicles, where rapid charging and discharging with stable performance are required.
Innovation Solution
A positive active material for rechargeable lithium batteries is developed, comprising a core compound represented by LiaNxCoyMezM1kO2−pFp, where 0.9≤a≤1.1, 0.7≤x≤0.93, 0<y≤0.3, 0<z≤0.3, 0≤k≤0.005, and x+y+z+k=1, with a structure-stabilizing compound such as Al2O3 or Co3O4 coated on the surface to enhance lithium ion mobility and structural stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high nickel content compounds (LiNi0.9Co0.05Al0.05O2) are used to increase capacity, then discharge capacity is improved, but structural stability and cycle-life deteriorate
Solution Approach 1:
The patent applies composite material principle by creating a core-shell structure where the core is LiNi0.9Co0.05Al0.05O2 high-nickel compound and the shell is a structure-stabilizing compound. This composite structure allows the high-capacity core material to be protected by the stable shell material, simultaneously achieving high discharge capacity and excellent cycle-life characteristics.
Solution Approach 2:
The patent applies local quality principle by modifying only the surface region of the positive active material with a structure-stabilizing compound while maintaining the high-nickel composition in the bulk. This localized modification preserves the high capacity of the core material while providing structural stability at the surface where degradation typically occurs during cycling.
2Power
If rapid charging and discharging is implemented to improve power delivery, then rate capability is improved, but heat generation and structural degradation increase
Solution Approach 1:
The patent applies parameter changes principle by modifying the surface composition and structure of the positive active material. The structure-stabilizing compound on the surface changes the electrochemical parameters at the electrode-electrolyte interface, enabling faster lithium ion transport and electron transfer, thereby improving rate capability while maintaining thermal stability.
3Reliability
If surface coating with structure-stabilizing compound is applied to improve cycle-life, then structural stability is improved, but discharge capacity may be reduced due to increased impedance
Solution Approach 1:
The patent applies local quality principle by providing structure-stabilizing compound only at the surface region rather than throughout the bulk material. This localized coating approach minimizes the amount of inactive material, thereby reducing impedance increase while still providing sufficient structural stabilization to maintain excellent cycle-life characteristics.
Solution Approach 2:
The patent applies composite material principle by creating an optimized core-shell structure where the ratio of core to shell is carefully controlled. This composite structure ensures that the structure-stabilizing compound provides adequate protection for cycle-life while minimizing the thickness to reduce impedance and preserve high discharge capacity.
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 improved discharge capacity and cycle-life characteristics, with the positive active material exhibiting capacities greater than 180 mAh/g and cycle-life retention of over 85% when the structure-stabilizing compound is present in the range of 1.5 wt% to 3 wt% based on the core, effectively addressing the need for high-capacity and durable battery performance.
Implementation Method 1
a structure-stabilizing compound on a surface of the core. The structure-stabilizing compound includes an Al compound or a Co compound
Data Source
AI summary
A positive active material for a rechargeable lithium battery includes a core including a compound represented by Chemical Formula 1 and a structure-stabilizing compound on a surface of the core. The structure-stabilizing compound includes an Al compound or a Co compound. Chemical Formula 1 is LiaNixCoyMezM1kO2−pFp where 0.9≤a≤1.1, 0.7≤x≤0.93, 0<y≤0.3, 0<z≤0.3, 0≤k≤0.005, x+y+z+k=1, 0≤p≤0.005, Me is Mn or Al, and M1 is Mg, Ba, B, La, Y, Ti, Zr, Mn, Si, V, P, Mo, W, or a combination thereof.