Positive Electrode Active Material Void Ratio Distribution
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Solution Overview
Problem
Existing positive electrode active materials for nonaqueous electrolyte secondary batteries face challenges in achieving high energy density and cycle stability due to low fillability and increased reaction resistance caused by voids and coat layers, respectively.
Innovation Solution
A lithium-metal composite oxide with a specific particle structure, including a void ratio distribution and tap density, is developed, utilizing a crystallization process to control the morphology of the nickel-cobalt-manganese composite hydroxide, resulting in a positive electrode active material with improved charging and discharging capacities and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the average particle diameter is reduced to 2-8 μm with narrow size distribution to improve cycle characteristic and output, then charging and discharging capacity is improved, but volume-based energy density decreases due to low fillability
Solution Approach 1:
The invention segments the particle structure into hierarchical levels: secondary particles (2-8 μm) composed of multiple primary particles (0.5-2 μm), which in turn consist of finer sub-primary particles. This segmentation allows the secondary particles to maintain small overall size for good fillability and cycle characteristics, while the internal porous structure of primary particles provides high surface area for electrochemical reactions, thus resolving the contradiction between particle size and energy density.
Solution Approach 2:
The invention introduces a controlled porous structure within primary particles, where the porosity ratio is specifically controlled at 10-50%. This porous structure increases the effective surface area for lithium ion insertion/extraction reactions without significantly increasing the external particle size, thereby improving volumetric energy density while maintaining the small secondary particle size needed for good fillability and cycle stability.
2Power
If voids are formed inside secondary particles to improve initial charging and discharging capacities, then capacity is enhanced, but reaction resistance increases and cycle durability decreases
Solution Approach 1:
The invention applies local quality by creating voids only in specific regions of the particle structure - specifically within primary particles but not throughout the entire secondary particle. The voids are localized to occupy 10-50% of the primary particle volume, while the outer shell of primary particles remains dense. This localized porosity provides reaction sites for high capacity while the dense outer structure maintains structural integrity for good cycle durability.
Solution Approach 2:
The invention uses controlled porosity within primary particles rather than large voids throughout secondary particles. The porosity ratio of 10-50% creates a hierarchical porous structure that facilitates ion transport and provides reaction sites without creating the large internal voids that cause structural collapse and high resistance. This resolves the contradiction by providing capacity enhancement through controlled local porosity rather than global void formation.
3Reliability
If a coat layer of inorganic lithium compound is applied on the surface of primary particles to improve cycle durability, then stability is enhanced, but reaction resistance increases and charging/discharging capacity decreases
Solution Approach 1:
The invention extracts or eliminates the need for thick protective coat layers by utilizing the inherent stability of the spinel phase on the particle surface. The controlled porous structure and small primary particle size (0.5-2 μm) inherently provide sufficient surface area and stability, making additional thick coat layers unnecessary. This removes the harmful effect of coat layers while preserving cycle durability through the stable spinel phase that forms naturally on the particle surface during 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 enhances the energy density and cycle stability of nonaqueous electrolyte secondary batteries by optimizing the particle structure, leading to higher battery capacity retention and reduced reaction resistance, while also enabling cost-effective industrial-scale production.
Implementation Method 1
a crystallization process of crystallizing a nickel-cobalt-manganese composite hydroxide
Implementation Method 2
the material undergoes an electrochemical reaction uniformly
Data Source
AI summary
Provided are a positive electrode active material with which a secondary battery having high charging and discharging capacities and an excellent cycle characteristic can be obtained, and a method for producing the same. A positive electrode active material for a nonaqueous electrolyte secondary battery includes a lithium-metal composite oxide represented by a general formula: LiaNixCoyMnzMtO2+α and containing a secondary particle formed of a plurality of flocculated primary particles. A void ratio obtained from an image analysis result of a cross section of the secondary particle, the image thereof being obtained by a scanning electron microscope, is at least 5% and up to 50% in a first area that is from a central part of the secondary particle to one half of a radius of the secondary particle, and is up to 1.5% in a second area that is outside the first area.