High-Nickel Cathode Processing for Low Residual Lithium
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Solution Overview
Problem
Conventional lithium nickel composite oxides for secondary batteries face limitations due to poor thermal stability, structural instability, and high residual lithium by-products, which affect battery lifespan and capacity.
Innovation Solution
A method involving rinsing lithium transition metal oxides with water to remove surface lithium by-products, followed by a high-temperature heat treatment with specific temperature elevating, maintaining, and cooling sections to enhance structural and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the nickel content in the positive electrode active material is increased to achieve high reversible capacity, then the battery capacity is improved, but the thermal stability and structural stability are deteriorated
Solution Approach 1:
The patent applies local quality by creating a dual-zone structure where the core region contains high-nickel content (0.8-0.95) for maximum capacity, while the surface region contains reduced nickel content (0.5-0.7) for enhanced stability. This spatial variation in composition allows each region to optimize its function: the core provides capacity while the surface provides protection against degradation and thermal runaway.
Solution Approach 2:
The patent creates a composite structure combining nickel-rich lithium transition metal oxide core with nickel-poor surface layer. This composite approach integrates the advantages of both high-nickel materials (high capacity) and low-nickel materials (high stability), achieving a synergistic effect that neither component could achieve alone.
2Quantity of substance
If the nickel content is increased to achieve high capacity, then the battery capacity is improved, but the residual amount of lithium by-products on the surface is increased, causing gas generation and swelling
Solution Approach 1:
The surface region with lower nickel content (0.5-0.7) inherently produces fewer lithium by-products during synthesis and cycling. This local compositional adjustment at the surface effectively reduces the generation of harmful lithium by-products such as LiOH and Li2CO3, preventing gas generation and battery swelling while maintaining high overall capacity through the nickel-rich core.
3Reliability
If conventional NCM-based lithium oxide is used to improve thermal stability, then the structural stability is improved, but the capacity is insufficient
Solution Approach 1:
The patent applies partial action by substituting nickel with stabilizing elements (Co, Mn, Al) only in the surface region rather than throughout the entire material. This partial substitution provides sufficient thermal and structural stability at the surface while maintaining high nickel content (0.8-0.95) in the core region to achieve high reversible capacity, thus avoiding the capacity limitation of fully substituted conventional NCM materials.
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 method effectively reduces residual lithium by-products, recrystallizes the crystal structure, and improves the high-temperature stability and structural stability of the positive electrode active material, leading to enhanced battery performance.
Implementation Method 1
rinsing the lithium transition metal oxide with water to remove lithium by-products present on the surface of the lithium transition metal oxide
Implementation Method 2
subjecting the lithium transition metal oxide rinsed with water to a high-temperature heat treatment
Implementation Method 3
the recrystallization of a destroyed crystal structure in which lithium has escaped occurs
Implementation Method 4
The temperature elevating section occupies 20 to 30% of the total high-temperature heat treatment time, and the maintaining section occupies 40 to 50% of the total high-temperature heat treatment time
Data Source
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AI summary
The present invention relates to a cathode active material for a secondary battery, comprising: a lithium transition metal oxide containing nickel (Ni), cobalt (Co), and at least one selected from the group consisting of manganese (Mn) and aluminum (Al), wherein the content of nickel (Ni) in the total transition metal element in the lithium transition metal oxide is 80 mol% or more, and the cation mixing ratio of Ni cations in a lithium layer in the lithium transition metal oxide structure is 1.1% or less.