Dual-Particle Nickel Cathode Coating for Crack-Resistant Cycle Life
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Solution Overview
Problem
Rechargeable lithium batteries using lithium nickel-based oxide materials face issues with structural collapse and cracking during repeated charges and discharges, leading to reduced long-term cycle-life and increased resistance, which affects capacity and energy density.
Innovation Solution
A positive active material for lithium batteries is developed, comprising lithium nickel-based composite oxides with secondary particles and single particles coated with a cobalt layer, featuring high and low concentration cobalt regions on the surface, enhancing structural stability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium nickel-based oxide materials are used as positive active material, then high capacity and high energy density are achieved, but structure collapses or cracks during repeated charges and discharges leading to deteriorated long-term cycle-life
Solution Approach 1:
The patent uses a composite material structure consisting of lithium nickel-based composite oxide particles coated with a lithium nickel manganese cobalt composite oxide layer. This composite structure combines the high capacity characteristics of lithium nickel-based oxide with the structural stability of lithium nickel manganese cobalt composite oxide, thereby maintaining high capacity while improving cycle-life characteristics.
Solution Approach 2:
The patent modifies the surface composition parameters of the positive active material by forming a coating layer with specific elemental ratios (Ni:Mn:Co = 7:2:1 to 3:2:5). This parameter change in the surface composition provides structural stability to prevent collapse and cracking during charge-discharge cycles, thereby improving cycle-life while maintaining high capacity.
2Quantity of substance
If lithium nickel-based oxide materials are used to achieve high energy density, then capacity is improved, but resistance increases during repeated charges and discharges
Solution Approach 1:
The composite material structure with lithium nickel manganese cobalt composite oxide coating layer reduces resistance by providing a stable surface that prevents degradation during charge-discharge cycles. The coating layer acts as a protective barrier that maintains low resistance while allowing the inner high-capacity lithium nickel-based oxide to function effectively.
Solution Approach 2:
The patent changes the surface composition parameters by introducing Mn and Co elements in specific ratios (Ni:Mn:Co = 7:2:1 to 3:2:5). This parameter modification reduces resistance by creating a more stable surface chemistry that prevents the formation of high-resistance surface films during repeated cycling.
3Quantity of substance
If conventional positive active materials are used, then high capacity is achieved, but structure collapses during repeated charges and discharges
Solution Approach 1:
The patent creates a composite material where lithium nickel-based oxide particles (providing high capacity) are coated with lithium nickel manganese cobalt composite oxide (providing structural stability). This composite structure prevents structural collapse during repeated charges and discharges while maintaining high capacity characteristics.
Solution Approach 2:
The patent applies local quality modification by creating a surface coating layer with different composition (Ni:Mn:Co = 7:2:1 to 3:2:5) than the core material. This local compositional change provides enhanced structural stability at the surface where structural degradation typically occurs, while the inner core maintains high 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 improves initial charge/discharge efficiency, cycle-life characteristics, and safety while achieving high capacity and energy density, as demonstrated by increased cobalt content on the surface and inside the particles, leading to enhanced battery performance.
Implementation Method 1
a cobalt coating portion on a surface of the secondary particles; and a cobalt coating portion on a surface of the single particles
Implementation Method 2
performing a first heat treatment to prepare a first nickel-based oxide; performing a second heat treatment to prepare a second nickel-based oxide; performing a third heat treatment to obtain the positive active material
Data Source
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AI summary
Disclosed a positive active material for a rechargeable lithium battery, a preparing method thereof, and a rechargeable lithium battery including the same, the positive active material for a rechargeable lithium battery including a first positive active material including a lithium nickel-based composite oxide and including secondary particles in which a plurality of primary particles are aggregated and a cobalt coating portion on a surface of the secondary particles; and a second positive active material including a lithium nickel-based composite oxide and including single particles and a cobalt coating portion on a surface of the single particles, wherein on the surface of the single particles of the second positive active material, there are a high-concentration coating region having a cobalt content of greater than or equal to about 30 at% and a low-concentration coating region having a cobalt content of less than or equal to about 25 at% based on the total amount of nickel and cobalt, and a difference between a cobalt content based on the total amount of nickel and cobalt in the high-concentration coating region and a cobalt content based on the total amount of nickel and cobalt in the low-concentration coating region is about 20 at% to about 50 at%.