Nickel Cathode Surface Doping for High-Voltage Cycle Stability
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Solution Overview
Problem
Existing positive-electrode active materials for nonaqueous electrolyte secondary batteries face challenges in maintaining charge/discharge capacities and cycle characteristics at high voltages, often requiring large amounts of aluminum additives that lead to capacity reduction.
Innovation Solution
A positive-electrode active material comprising lithium transition metal composite oxide particles with a layered structure, containing nickel, and oxides adhering to the surface, including lithium-aluminum and lithium-boron oxides, where the aluminum is present in a solid solution in the surface layer and boron is distributed to enhance cycle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large amounts of aluminum additives are used to improve cycle characteristics at high voltage, then charge/discharge cycle characteristics are improved, but charge/discharge capacities are reduced
Solution Approach 1:
The patent applies local quality by creating an aluminum-rich surface layer on the lithium transition metal composite oxide particles. The aluminum content is specifically concentrated in the surface region (within 10 nm from the surface) rather than being uniformly distributed throughout the bulk material. This localized aluminum enrichment provides protective effects at the surface where electrochemical reactions occur, improving cycle characteristics without requiring large amounts of aluminum that would otherwise reduce overall capacity.
Solution Approach 2:
The patent employs parameter changes by precisely controlling the aluminum concentration gradient from the surface inward. The aluminum content in the surface layer is maintained at 0.01-0.10 atomic ratio (Al/(Li+Ni+Co+Mn)), which is higher than the bulk composition. This controlled parameter variation optimizes both cycle stability and capacity retention by balancing surface protection with bulk electrochemical activity.
2Stability of the object's composition
If aluminum is added to stabilize the structure at high voltage, then structure stability is improved, but capacity is reduced due to aluminum occupying lithium sites
Solution Approach 1:
The patent segments the aluminum distribution into two distinct regions: an aluminum-enriched surface layer and an aluminum-poor bulk interior. The surface layer (depth 0-10 nm) contains aluminum at 0.01-0.10 atomic ratio to stabilize the crystal structure during cycling, while the bulk material maintains low aluminum content to preserve lithium sites and maximize capacity. This spatial segmentation resolves the contradiction between structure stability and capacity.
Solution Approach 2:
The patent introduces an intermediate surface layer that acts as a mediator between the bulk material and the electrolyte. This surface layer, enriched with aluminum and potentially other elements, provides structural stability and protects the bulk material from degradation, while allowing efficient lithium ion transport. The intermediate layer thus enables both structure stability and high capacity to coexist.
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 effectively stabilizes the structure of the lithium transition metal composite oxide, improving charge/discharge capacities and cycle characteristics at high voltages while minimizing capacity reduction, by diffusing aluminum into secondary particles and forming protective surface oxides.
Implementation Method 1
a solid solution of aluminum in a surface layer
Implementation Method 2
The lithium transition metal composite oxide particles include secondary particles formed by aggregation of primary particles containing a solid solution of aluminum in a surface layer
Implementation Method 3
heat-treating the provided mixture
Implementation Method 4
heat-treating the provided mixture
Implementation Method 5
an oxide containing lithium and aluminum and an oxide containing lithium and boron adhering to a surface of the lithium transition metal composite oxide particles
Data Source
AI summary
Provided is a positive-electrode active material for a nonaqueous electrolyte secondary battery, including a lithium transition metal composite oxide particle having a layered structure and containing nickel, and an oxide containing lithium and aluminum and an oxide containing lithium and boron adhering to a surface of the lithium transition metal composite oxide particle. The lithium transition metal composite oxide particle includes a secondary particle formed by aggregation of primary particles containing a solid solution of aluminum in a surface layer. The lithium transition metal composite oxide particles have a composition with a difference of more than 0.22 mol % and less than 0.6 mol % between a ratio of the number of moles of aluminum in the solid solution in the surface layer of the primary particles relative to a total number of moles of metal other than lithium and a ratio of the number of moles of aluminum present in a region other than the surface layer of the primary particles relative to the total number of moles of metal other than lithium.