Positive-Electrode Plate Trilithium Phosphate Distribution
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Solution Overview
Problem
In lithium-ion secondary batteries, the decomposition of electrolytes leads to the elution of transition metals from positive-electrode active materials, reducing capacity maintenance and battery durability due to inadequate distribution of trilithium phosphate, which fails to react with hydrofluoric acid effectively.
Innovation Solution
A positive-electrode plate with a positive-electrode active material layer containing trilithium phosphate, where the trilithium phosphate is evenly distributed with a dispersion index value of 0.8 or less, ensuring high reaction frequency with hydrofluoric acid and maintaining a high electric potential, thereby preventing metal elution and enhancing battery durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If trilithium phosphate is added to the positive-electrode active material layer to prevent transition metal elution, then battery durability is improved, but the distribution of trilithium phosphate becomes uneven, reducing its effectiveness in reacting with hydrofluoric acid
Solution Approach 1:
The patent applies local quality by controlling the particle size distribution of trilithium phosphate to create different functional zones. Small particles (≤1 μm) are strategically distributed to ensure adequate spacing between active material particles, creating localized regions where trilithium phosphate can effectively react with hydrofluoric acid. This resolves the contradiction by making the distribution non-uniform in a controlled way that enhances reactivity where needed while maintaining overall composition stability.
Solution Approach 2:
The patent changes the particle size parameter of trilithium phosphate from conventional larger sizes to specifically ≤1 μm. This parameter change enables the material to fill spaces between active material particles more effectively and increases the surface area for reaction with hydrofluoric acid. The parameter transformation resolves the distribution issue by allowing trilithium phosphate to reach locations where hydrofluoric acid is generated, thereby improving both durability and distribution effectiveness.
2Power
If the positive-electrode active material layer contains high electric potential materials to increase operating voltage, then battery power is improved, but electrolyte decomposition increases, leading to transition metal elution
Solution Approach 1:
The patent introduces trilithium phosphate as an intermediary substance between the high electric potential active material and the electrolyte. This intermediary reacts with hydrofluoric acid generated from electrolyte decomposition, forming a protective coating that prevents transition metal elution. The intermediary resolves the contradiction by allowing high voltage operation while mitigating the harmful effects of electrolyte decomposition through chemical buffering and protective film formation.
Solution Approach 2:
The patent converts the harmful hydrofluoric acid generated during electrolyte decomposition into a beneficial protective coating. By providing trilithium phosphate that reacts with hydrofluoric acid, the harmful byproduct of high-voltage operation is transformed into a protective layer that prevents further degradation and metal elution. This resolves the contradiction by making the harmful effect serve the protective function needed for high-voltage stability.
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 even distribution of trilithium phosphate in the positive-electrode active material layer effectively reacts with hydrofluoric acid, forming a protective coating that inhibits transition metal elution, increases reaction frequency, and reduces internal resistance, thereby enhancing battery performance and durability.
Implementation Method 1
trilithium phosphate is reacted with hydrofluoric acid (HF) generated in the electrolyte, thereby functioning as an acid-consuming material
Data Source
AI summary
In a positive-electrode active material layer of a positive-electrode plate for a non-aqueous electrolyte secondary battery, a dispersion index value C determined from a small-size-particle ratio A and a coefficient B of variation and expressed by an expression, C=B/A3, is 0.8 or less. The small-size-particle ratio A is a ratio of the number of small-size-particle-containing spots where a detected intensity of phosphorus is equal to or lower than a detected density of trilithium phosphate having a particle size of 1 μm or less, to the number of phosphorus-containing spots among the analyzed spots. The coefficient B of variation is a ratio of a standard deviation of segmented-region accumulated values to an arithmetic mean of the segmented-region accumulated values each of which is the sum of detected intensities in the phosphorus-containing spots in a corresponding one of the segmented regions obtained through segmentation of the analyzed region.