Cathode Precursor pH Control for Bimodal Particle Packing
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Solution Overview
Problem
Current methods for preparing positive electrode active material precursors for lithium secondary batteries are inefficient, requiring separate reactors and processes for small- and large-diameter precursors, leading to increased costs and time, and resulting in low thermal stability and capacity.
Innovation Solution
A method is developed to simultaneously prepare bimodal-type positive electrode active material precursors with different average particle diameters in a single reactor by controlling pH levels during co-precipitation, forming a mixture of first and second precursor particles with specific diameters and ratios, enhancing packing density and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate reactors and processes are used to prepare small-diameter and large-diameter precursors, then particle size control is improved, but preparation costs and preparation time increase
Solution Approach 1:
The patent combines the preparation processes for small-diameter and large-diameter precursors into a single reactor by controlling pH levels at different stages. The method adds basic aqueous solution in two stages: first to form small-diameter precursor particles, then additional base to form large-diameter precursor particles, eliminating the need for separate reactors and reducing preparation time
2Manufacturing precision
If separate reactors and processes are used to prepare small-diameter and large-diameter precursors, then particle size control is improved, but preparation costs increase
Solution Approach 1:
The patent merges multiple preparation processes into one reactor system, eliminating the need for separate equipment for preparing small and large diameter precursors. This consolidation reduces capital investment, operational costs, and complexity while maintaining precise particle size control through staged pH adjustment
Solution Approach 2:
The single reactor is designed to perform multiple functions: preparing both small-diameter and large-diameter precursor particles, controlling different pH ranges, and producing bimodal particle size distributions. This multi-functional approach eliminates the need for dedicated reactors for each particle size category
3Reliability
If lithium-nickel-cobalt metal oxide is used to improve thermal stability, then thermal stability is improved, but capacity decreases
Solution Approach 1:
The patent creates a bimodal particle size distribution with both small and large diameter precursors, where each size category can be optimized for different properties. The smaller particles provide high surface area for capacity, while the larger particles contribute to overall structural stability, achieving both thermal stability and high capacity
4Quantity of substance
If increasing nickel content is used to increase capacity, then capacity is improved, but thermal stability decreases
Solution Approach 1:
The patent optimizes nickel content locally within different particle size categories of the bimodal distribution. By having both small and large diameter precursors with potentially different compositions, the system can achieve high overall capacity while maintaining thermal stability through the larger particles that provide structural framework
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
This approach improves productivity, reduces preparation costs and time, and enhances the packing density and high-capacity properties of the positive electrode active material precursors, addressing the limitations of existing methods.
Implementation Method 1
adding the metal aqueous solution, an ammonium cation complex forming agent, and a basic aqueous solution into a reactor, co-precipitating a resulting mixture at pH 11 to less than pH 13 to form nuclei of first positive electrode active material precursor particles
Implementation Method 2
adjusting input amount of the basic aqueous solution to increase the pH in the reactor to a range of 0.8 to 1.5 compared to that of Step 2, thereby forming nuclei of second positive electrode active material precursor particles
Data Source
AI summary
A method for preparing a positive electrode active material precursor includes preparing a metal aqueous solution including a nickel raw material, a cobalt raw material, and a manganese raw material (step 1); adding the metal aqueous solution, an ammonium cation complex forming agent, and a basic aqueous solution into a reactor, co-precipitating the mixture at pH 11 to less than pH 12 to form nuclei of first positive electrode active material precursor particles and growing the nuclei (step 2); adjusting input amount of the basic aqueous solution to increase the pH in the reactor to a range of 0.8 to 1.5 compared to that of step 2; and adjusting input amount of the basic aqueous solution to change the pH in the reactor to pH 11 to less than pH 12 (step 4). A positive electrode active material precursor prepared by the above preparation method has an improved packing density.