Single-Particle Ni-Rich Cathode Coating Against Rock-Salt Degradation
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Solution Overview
Problem
Lithium transition metal oxides used in lithium secondary batteries face limitations in thermal stability and capacity due to nickel content, leading to poor battery performance and safety issues like gas generation and swelling.
Innovation Solution
A positive electrode active material with a lithium transition metal oxide containing 60 mol% or greater nickel, coated with a metal oxide layer of specific elements like Ni, Co, Mn, Al, B, Ti, Ta, or Nb, is developed, with controlled particle sizes to enhance stability and prevent rock-salt structure formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the nickel content in lithium transition metal oxide is increased to achieve high capacity (200 mAh/g), then the reversible capacity is improved, but the thermal stability deteriorates and the material decomposes causing battery rupture and ignition
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core (lithium transition metal oxide with high Ni content) provides high capacity while the outer shell (coating layer with different composition) provides thermal stability. The coating layer has a different chemical composition and structure than the core, giving different local properties to different regions of the particle.
Solution Approach 2:
The patent uses composite materials by combining lithium transition metal oxide with a coating layer made of different materials (such as lithium phosphate, lithium oxide, or other metal oxides). This composite structure allows the high-capacity core material to be protected by a stable shell material, achieving both high capacity and thermal stability.
2Quantity of substance
If the nickel content is increased to improve capacity characteristics, then the reversible capacity increases, but lithium by-products (LiOH or Li2CO3) are formed on the surface due to Ni2+ remaining tendency
Solution Approach 1:
The patent converts the harmful effect of Ni2+ remaining on the surface into a beneficial process by controlling the firing conditions to intentionally form a specific surface layer composition. The heat treatment at 800-890°C transforms the unwanted Ni2+ surface accumulation into a controlled surface modification that prevents further harmful by-product formation during battery operation.
Solution Approach 2:
The patent applies parameter changes by precisely controlling the firing temperature (800-890°C) and atmosphere (oxygen) to modify the surface composition and oxidation state of nickel. This parameter control transforms the surface properties to reduce lithium by-product formation while maintaining high bulk nickel content for capacity.
3Reliability
If a coating layer is added to improve thermal stability and suppress rock-salt structure formation, then the battery stability and lifespan are improved, but the device complexity increases
Solution Approach 1:
The patent applies preliminary action by forming the coating layer during the initial firing process (800-890°C) rather than as a separate subsequent step. The coating material is mixed with the lithium transition metal oxide before firing, and the coating layer forms in-situ during the sintering process, integrating structure formation with material synthesis.
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 solution improves battery stability, capacity retention, and lifespan by suppressing rock-salt structure diffusion and enhancing particle strength, leading to better resistance and cycle performance.
Implementation Method 1
a coating layer which is placed on a surface of the lithium transition metal oxide and contains a metal oxide
Implementation Method 2
the lithium transition metal oxide is a single particle including primary particles having an average particle diameter (D50) of 0.7 to 3 μm
Data Source
AI summary
A positive electrode active material includes a lithium transition metal oxide comprising nickel in an amount of 60 mol % or greater with respect to a total number of moles of transition metals excluding lithium and a coating layer placed on a surface of the lithium transition metal oxide. The coating layer has a metal oxide and the lithium transition metal oxide is a single particle containing primary particles having an average particle diameter (D50) of 0.7 to 3 μm. The metal oxide is primary particles having an average particle diameter (D50) of 0.5 μm or less and has at least one metal element selected from the group consisting of Ni, Co, Mn, Al, B, Ti, Ta, W, and Nb.