Positive Electrode Material for Lithium Secondary Battery, and Positive Electrode for Lithium Secondary Battery and Lithium Secondary Battery Including the Same
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Solution Overview
Problem
Existing lithium secondary batteries face issues with structural collapse due to excess lithium release, leading to voltage sagging and reduced thermal stability, which affects their output and cycle characteristics.
Innovation Solution
A positive electrode material comprising a combination of large and small lithium composite transition metal oxide particles, where the large particles have a lithium-to-metal ratio of 1 to 1.5 or less and an average size of 7 to 20 μm, and the small particles have a lithium-to-metal ratio of 0.9 to 1 and a crystallite size of 180 nm or more, enhancing structural stability and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If excess lithium-containing lithium transition metal oxide is used as positive electrode active material to achieve high capacity and high output, then capacity and output characteristics are improved, but irreversible capacity increases and oxygen is released causing structural collapse and voltage sagging
Solution Approach 1:
The patent controls the lithium-to-transition metal ratio (Li/Me) within a specific range of 0.95 to 1.05, preventing excess lithium content that would cause oxygen release and structural collapse. This parameter control allows the material to achieve high capacity and output while maintaining structural stability during charge-discharge cycles.
Solution Approach 2:
The patent uses composite lithium transition metal oxides containing multiple transition metals (Ni, Co, Mn) in specific ratios. This composite structure provides both high capacity/output characteristics and enhanced structural stability, as the different metals complement each other's properties to prevent structural degradation while enabling excess lithium utilization.
2Quantity of substance
If high voltage activation is used to utilize surplus lithium, then capacity is improved, but oxygen is released to the outside causing active material structure collapse
Solution Approach 1:
The patent precisely controls the lithium-to-transition metal ratio (Li/Me) to be within 0.95 to 1.05, which allows sufficient lithium content for high capacity while preventing the excessive lithium that would decompose and release oxygen during high voltage activation. This parameter optimization enables safe utilization of lithium surplus.
Solution Approach 2:
The patent converts the potential harm of excess lithium (which would release oxygen and cause structural collapse) into a benefit by precisely controlling the Li/Me ratio. The controlled excess lithium provides high capacity and output characteristics without triggering oxygen release, transforming what would be a harmful condition into a beneficial one.
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 combination of particle sizes and lithium ratios improves high capacity, output, and thermal stability, reducing gassing and maintaining cycle characteristics by preventing structural degradation.
Implementation Method 1
produces electric energy through oxidation and reduction when a lithium ion is intercalated/deintercalated in/from the positive electrode and the negative electrode
Data Source
AI summary
A positive electrode material for a lithium secondary battery includes a first positive electrode active material and a second positive electrode active material, both of which are lithium composite transition metal oxides containing transition metals. The first positive electrode active material has a larger average particle size (D50) than the second positive electrode active material, wherein a ratio (Li/Me)1 of the mole number of lithium with respect to the total mole number of transition metals of the first positive electrode active material is more than 1 to 1.5 or less, and a ratio (Li/Me)2 of the mole number of lithium (Li) with respect to the total mole number of transition metals of the second positive electrode active material is 0.9 to 1. The second positive electrode active material has a crystallite size of 180 nm or more.