Nickel-Rich Cathode Material With Cobalt Gradient for Thermal Stability
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Solution Overview
Problem
There is a demand for a positive electrode active material with high nickel content that exhibits improved structural stability and suppressed gas generation at high temperatures, while maintaining high capacity properties.
Innovation Solution
A method for preparing a positive electrode active material involving the preparation of a precursor with nickel, cobalt, and manganese, followed by primary and secondary heat treatments, and a boron coating process to form a cobalt-containing coating layer, enhancing structural stability and reducing gas generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the nickel content in lithium-nickel-cobalt metal oxide is increased to increase capacity properties, then the reversible capacity is improved, but the thermal stability and structural stability are degraded
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of cobalt within the crystal structure. The cobalt content is higher at the surface region (7.0 mol% or greater) and decreases toward the interior, forming a core-shell like structure. This localized distribution allows the surface to provide thermal stability while the nickel-rich interior maintains high capacity, resolving the contradiction between capacity and stability.
Solution Approach 2:
The patent creates a composite structure within the lithium-nickel-cobalt-metal oxide by combining nickel-rich regions (for high capacity) with cobalt-rich regions (for thermal stability). This internal composite architecture, achieved through controlled cobalt distribution during synthesis, allows both high reversible capacity and improved thermal stability to coexist.
2Quantity of substance
If the nickel content in lithium-nickel-cobalt metal oxide is increased to increase capacity properties, then the reversible capacity is improved, but the structural stability is degraded
Solution Approach 1:
The patent implements local quality by establishing a spatial gradient of cobalt concentration within the particle structure. The surface layer contains 7.0 mol% or greater cobalt content, providing structural stability, while the interior maintains high nickel content for capacity. This localized compositional variation resolves the contradiction between capacity and structural stability.
Solution Approach 2:
The patent applies parameter changes by controlling the cobalt concentration parameter as a function of position within the particle. By varying the cobalt content from surface to interior, the patent optimizes both structural stability (through high cobalt at surface) and capacity (through high nickel at interior), resolving the contradiction between these two properties.
3Quantity of substance
If heat treatment temperature is increased to improve material properties, then the capacity properties are improved, but the gas generation and lifespan properties are degraded
Solution Approach 1:
The patent applies parameter changes by optimizing the heat treatment temperature to a specific range (660-800°C) and controlling the duration. This controlled thermal parameter regime allows sufficient capacity development while preventing excessive gas generation and degradation, resolving the contradiction between capacity improvement and harmful gas generation.
Solution Approach 2:
The patent applies preliminary anti-action by conducting heat treatment under controlled conditions that prevent the formation of harmful byproducts. By carefully controlling temperature and time parameters during synthesis, the patent anticipates and prevents gas generation issues that would otherwise occur with higher temperature or prolonged treatment, thereby improving lifespan properties while maintaining 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 approach results in a positive electrode active material with improved high-temperature lifespan properties and reduced gas generation, effectively addressing the limitations of existing materials.
Implementation Method 1
mixing the positive electrode active material precursor with a lithium raw material and performing primary heat treatment thereon at 660° C. to 800° C. to form a lithium transition metal oxide
Implementation Method 2
mixing the lithium transition metal oxide with a cobalt ion-containing source and performing secondary heat treatment thereon at 640° C. to 800° C. to form a secondary heat-treated product
Implementation Method 3
mixing the lithium transition metal oxide with a cobalt ion-containing source and performing secondary heat treatment thereon at 640° C. to 800° C.
Implementation Method 4
dry-mixing the washed secondary heat-treated product with a boron coating source and performing heat treatment thereon
Data Source
AI summary
A positive electrode active material for a lithium secondary battery includes a lithium transition metal oxide containing nickel, cobalt, and manganese and a cobalt-containing coating layer. The lithium transition metal oxide is in the form of a secondary particle in which primary particles are aggregated. The coating layer is formed at interface between the primary particles positioned on the surface and inside of the lithium transition metal oxide secondary particle. A spectrum measured for the lithium transition metal by TEM-EELS includes a first peak in a region from a surface of a primary particle in a surface portion of the secondary particle to a depth of 50 nm, and a second peak in a region from the surface of a primary particle in a core portion of secondary particle to a depth of 50 nm. A method for preparing the positive electrode active material is also provided