Positive electrode material for secondary batteries
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Solution Overview
Problem
Existing positive electrode materials for secondary batteries, such as those described in Patent Literature 1, face challenges in maintaining high resistance during heat-generating events like short circuits, which can lead to safety issues and performance deterioration.
Innovation Solution
A positive electrode material comprising secondary particles with a specific structure, where first, second, and third primary particles are arranged differently, and a second metal oxide is selectively attached to the surfaces of the first and second primary particles, but not or minimally to the third primary particles, enhancing safety and maintaining electronic and ionic conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electrical conductivity of the powder compact is controlled to improve thermal stability, then safety is improved, but battery resistance increases causing deterioration in battery performance
Solution Approach 1:
The patent applies local quality by differentiating the treatment of primary particles based on their position within secondary particles. Surface-exposed primary particles receive the second metal oxide coating to enhance safety, while internal primary particles maintain their original conductivity properties. This localized differentiation resolves the contradiction by applying resistance-enhancing measures only where needed for safety (surface particles) while preserving battery performance (internal particles).
Solution Approach 2:
The patent uses composite materials by combining the first metal oxide (positive electrode active material) with a second metal oxide having different properties. The second metal oxide is selectively attached to form a composite structure on surface particles, creating a material system that exhibits both high resistance (for safety) and maintained conductivity (for performance) through the synergistic combination of different oxide phases.
2Reliability
If a specialized composition like lithium-nickel composite oxide is used to improve thermal stability, then safety is improved, but versatility is reduced
Solution Approach 1:
The patent achieves universality by developing a generalizable coating approach that can be applied to various positive electrode active materials, not limited to lithium-nickel composite oxide. The method of selectively attaching a second metal oxide to surface-exposed primary particles can be adapted to different material systems (layered oxides, spinel structures, olivine structures), making the safety improvement versatile across multiple battery chemistries and material types.
Solution Approach 2:
The patent applies local quality by targeting only the surface-exposed primary particles for coating modification, while leaving internal particles unchanged. This localized approach allows the same treatment strategy to be effectively applied regardless of the specific material composition, as it addresses the critical surface region where short-circuit risks are highest without requiring material-specific bulk modifications.
3Object-generated harmful factors
If the short-circuited portion expands and short-circuit current increases, then Joule heat generation increases, but this accelerates temperature rise creating a positive feedback loop
Solution Approach 1:
The patent applies preliminary anti-action by pre-modifying the surface of primary particles with a second metal oxide coating before short-circuit events can occur. This preliminary modification increases the resistance of surface-exposed particles, creating an opposing effect that counteracts the expansion of short-circuited portions and limits Joule heat generation before the positive feedback loop of temperature acceleration can begin.
Solution Approach 2:
The patent converts the harmful effect of surface particle conductivity (which enables short-circuit current flow) into a benefit by selectively modifying surface particles with a second metal oxide. This transformation increases resistance precisely where short-circuit risks originate (at particle surfaces), turning the previously harmful conductivity into a controlled resistance that limits harmful current while maintaining overall battery functionality.
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 proposed positive electrode material effectively maintains high resistance during heat-generating events, ensuring safety and performance of the secondary battery, while avoiding the limitations of specialized compositions like lithium-nickel composite oxides.
Implementation Method 1
the electrical conductivity σ at 25° C. of a powder compact at a compression density of 4.0 g/cm3 is within the range of 5×10−2>σ>5×10−4 [S/cm]
Implementation Method 2
the Joule heat generated by short-circuit current melts the separator, to form a larger short-circuited portion
Data Source
AI summary
A positive electrode material for a secondary battery includes a secondary particle that is an aggregate of a plurality of primary particles. The primary particles contain a first metal oxide as a positive electrode active material. The primary particles include first primary particles disposed at a surface of the secondary particle, second primary particles disposed inside the secondary particle in contact with the first primary particles, and third primary particles disposed inside the secondary particle not in contact with the first primary particles. The positive electrode material further includes a second metal oxide attached at least to surfaces of the first primary particles and the second primary particles and having a composition different from the first metal oxide. The second metal oxide is not attached to surfaces of the third primary particles, or an amount attached thereto is smaller than an amount attached to the second primary particles.