Positive Electrode Active Material for Safe Lithium Secondary Batteries
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Solution Overview
Problem
Lithium secondary batteries face delayed activation of current interrupt devices during overcharge due to reduced contact surface area and diffusion issues in positive electrode active materials with increased density and particle size, leading to potential overcharge risks.
Innovation Solution
A positive electrode active material comprising lithium transition metal oxide with a layered structure, specifically Li1+αNixCoyMnzCaβMγO2, is developed, which includes calcium as a structural element to enhance gas generation and discharge paths, ensuring early activation of the current interrupt device during overcharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the density of the positive electrode active material layer is increased through adjustment of particle size, then energy density is improved, but the contact surface area between electrode and electrolyte solution is reduced, causing delayed gas generation during overcharge
Solution Approach 1:
The patent applies local quality by creating a hierarchical particle size distribution where fine particles (5-20 μm) provide high surface area for rapid gas generation and overcharge protection, while coarse particles (50-150 μm) contribute to high energy density. Different regions of the electrode layer thus have different functional characteristics - the fine particles ensure safety response while coarse particles maximize capacity.
Solution Approach 2:
The patent uses composite materials by combining positive electrode active material particles of different size ranges (fine particles of 5-20 μm and coarse particles of 50-150 μm) in specific proportions (fine particles: 10-50 wt%, coarse particles: 50-90 wt%). This composite structure allows the electrode to simultaneously achieve high energy density from coarse particles and rapid overcharge protection response from fine particles.
2Quantity of substance
If the particle size of positive electrode active material is increased to improve energy density, then capacity is enhanced, but diffusion paths for gas are narrowed, preventing smooth gas discharge
Solution Approach 1:
The patent applies segmentation by dividing the particle size distribution into distinct segments - fine particles (5-20 μm) that create adequate void spaces for gas diffusion, and coarse particles (50-150 μm) that provide high capacity. The fine particle segment ensures sufficient diffusion paths for smooth gas discharge, while the coarse particle segment maximizes energy capacity.
Solution Approach 2:
The patent utilizes porous materials principles by maintaining a specific void volume ratio (0.2-0.8 mL/g) through the inclusion of fine particles. These fine particles create a porous network structure that provides adequate diffusion paths for gas to escape smoothly, even when coarse particles are present for high capacity.
3Quantity of substance
If the voids of positive electrode active material layer are reduced to increase density, then energy density improves, but reaction sites between electrode and electrolyte solution decrease, slowing gas generation during overcharge
Solution Approach 1:
The patent applies preliminary action by pre-distributing fine particles (5-20 μm) throughout the electrode structure before overcharge occurs. These fine particles are strategically positioned to provide immediate reaction sites when overcharge happens, ensuring rapid gas generation without compromising the overall high density achieved by coarse particles.
Solution Approach 2:
The patent uses parameter changes by optimizing the particle size distribution parameters - specifically setting fine particles at 5-20 μm and coarse particles at 50-150 μm, with fine particles comprising 10-50 wt% of the total. This parameter optimization balances the void volume ratio (0.2-0.8 mL/g) to maintain both high energy density and sufficient reaction sites for rapid gas generation.
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 material achieves high energy density, cycle characteristics, and reliable overcharge resistance by promoting prompt gas generation and discharge, thereby ensuring safe and efficient battery operation.
Implementation Method 1
a positive electrode active material for lithium secondary batteries, comprising a lithium transition metal oxide (hereafter, 'LNCMC oxide') of a layered structure
Implementation Method 2
gas might not be discharged smoothly from an electrode active material layer, due to narrowing diffusion paths of the generated gas
Data Source
AI summary
A positive electrode active material for lithium secondary batteries disclosed herein comprises a lithium transition metal oxide of a layered structure, represented by formula Li1+αNixCoyMnzCaβMγO2 (where −0.05≤α≤0.2, x+y+z+β+γ≅1, 0.3≤x≤≤0.7, 0.1≤y≤0.4, 0.1≤z≤0.4, 0.0002≤β≤0.0025, 0.0002≤β+γ≤0.02, and in a case where γ>0, M is absent or represents one, two or more elements selected from the group consisting of Na, Mg, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W). The tap density of the positive electrode active material ranges from 1.8 to 2.5 g/cm3.