Bimodal NCM Positive Electrode Material for Dense High-Ni Batteries
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Solution Overview
Problem
Lithium nickel-cobalt-manganese oxides used in lithium secondary batteries face limitations in thermal stability and energy density, leading to issues with high-temperature lifespan and roll-pressing density, particularly when nickel content is increased to enhance capacity properties.
Innovation Solution
A positive electrode material comprising a bimodal particle size distribution of lithium composite transition metal oxides with a nickel content of 80% or greater, combining two types of active materials with specific compositions and particle sizes, enhancing high-temperature lifespan and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the content of Ni is increased to increase capacity properties, then the reversible capacity is improved, but the roll-pressing density of particles is lowered
Solution Approach 1:
The positive electrode active material is divided into two distinct particle size groups: large diameter particles (D50: 10-20 μm) and small diameter particles (D50: 1-7 μm). This segmentation allows each size fraction to contribute differently to overall performance, with larger particles providing capacity and smaller particles filling void spaces to increase density.
Solution Approach 2:
Small diameter particles are positioned to fill the interstitial spaces between large diameter particles, creating a nested arrangement. This maximizes the packing efficiency of the electrode material, thereby increasing roll-pressing density while maintaining high nickel content for capacity.
2Quantity of substance
If the content of Ni is increased to increase capacity properties, then the reversible capacity is improved, but the structural stability is reduced at high temperatures
Solution Approach 1:
Different particle size fractions are used with potentially different compositional characteristics. The large particles provide the primary nickel-rich capacity, while the small particles can have optimized composition for stability, creating local quality variations that resolve the contradiction.
Solution Approach 2:
The positive electrode active material is a composite of two different particle size fractions of lithium nickel-cobalt-manganese oxide. This composite structure allows the system to benefit from both high nickel content (for capacity) and optimized particle morphology (for stability).
3Volume of stationary object
If an electrode is roll-pressed hard to increase the roll-pressing density, then the density is improved, but the current collector breaks and positive electrode material cracks
Solution Approach 1:
The invention changes the particle size distribution parameters to achieve high density without excessive roll-pressing force. The bimodal distribution allows natural packing that achieves high density with gentle pressing, preserving mechanical integrity.
Data Source
AI summary
A positive electrode material including a first positive electrode active material represented by Formula 1 and a second positive electrode active material represented by Formula 2, a positive electrode including the same, and a lithium secondary battery including the positive electrode are provided. The positive electrode material has a bimodal particle size distribution including large diameter particles and small diameter particles, and the difference in average particle diameter (D50) between the large diameter particles and the small diameter particles is 3 μm or greater.