Bimodal Cathode Material for High-Density Stable Lithium Batteries
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Solution Overview
Problem
Lithium nickel-cobalt-manganese oxide positive electrode materials for lithium secondary batteries face challenges with low roll-pressing density, reduced energy density, and poor high-temperature stability, leading to issues like internal short circuits and reduced lifespan.
Innovation Solution
A bimodal particle size distribution is employed, with large-diameter lithium composite transition metal oxide particles having 80% nickel content and small-diameter particles containing nickel, cobalt, and aluminum at specific ratios, enhancing roll-pressing density and high-temperature stability.
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, decreasing energy density
Solution Approach 1:
The patent changes the particle size distribution parameter by creating a bimodal distribution with small particles (D50: 3-8 μm) and large particles (D50: 10-20 μm). This parameter change allows high Ni content (80-85 at%) for capacity while the small particles fill voids to maintain high roll-pressing density, resolving the contradiction between capacity and energy density
Solution Approach 2:
The patent creates a composite particle system where small high-Ni particles and large high-Ni particles are combined in a bimodal distribution. This composite structure allows the small particles to pack efficiently in interstices, achieving both high capacity (from high Ni content) and high roll-pressing density simultaneously
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, deteriorating high-temperature lifespan
Solution Approach 1:
The patent changes the compositional parameters by precisely controlling Ni content (80-85 at%) and introducing Al (0.01-0.1 at%) with specific Co/Al ratios (1.5-5). This parameter optimization maintains high capacity while improving structural stability at high temperatures, as evidenced by DSC analysis showing higher exothermic onset temperatures
Solution Approach 2:
The patent applies local quality by creating a bimodal particle size distribution where small and large particles have different roles. The small particles provide high capacity density while the larger particles provide structural stability, and together they achieve both high capacity and thermal stability
3Volume of stationary object
If an electrode is roll-pressed hard to increase the roll-pressing density, then the energy density is improved, but the current collector breaks and the positive electrode material cracks
Solution Approach 1:
The patent changes the particle size distribution parameter to bimodal, which allows achieving high roll-pressing density (4.8-5.2 g/cm³) through optimized particle packing rather than excessive mechanical pressure. This eliminates the need for hard roll-pressing that would damage the electrode structure
Solution Approach 2:
The bimodal particle distribution creates an optimized porous structure where small particles fill voids between large particles. This natural packing achieves high density without requiring excessive compression force, preventing current collector breakage and material cracking
Data Source
AI summary
A positive electrode material and a positive electrode and a lithium secondary battery including the same are provided. The positive electrode material having a bimodal particle size distribution which includes large-diameter particles and small-diameter particles having different average particle diameters (D50), wherein the large-diameter particles are lithium composite transition metal oxide having a nickel content of 80 atm % or more in all transition metals thereof, and the small-diameter particles are a lithium composite transition metal oxide including nickel, cobalt, and aluminum, having a nickel content of 80 atm % to 85 atm % in all transition metals, and having an atomic ratio of the cobalt to the aluminum (Co/Al) of 1.5 to 5.