Carbon-Coated Olivine Cathode for Low-Temperature Power Retention
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Solution Overview
Problem
Nonaqueous electrolyte energy storage devices using olivine-type positive active materials face challenges in achieving optimal power characteristics, especially in low temperature environments, due to limitations in electron conductivity and ion diffusibility.
Innovation Solution
A positive electrode with a composite layer containing a carbon-coated olivine-type positive active material, where the carbon's pore specific surface area is between 20% to 50% of the composite material's surface area, and the density is between 1.80 g/cm3 and 2.10 g/cm3, enhancing electron conductivity and ion diffusibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface of olivine-type positive active material is coated with carbon to improve electron conductivity, then electron conductivity is improved, but power characteristics in low temperature environment are still insufficient
Solution Approach 1:
The patent uses a composite structure where carbon coats the surface of olivine-type positive active material (LiFexMn1-xPO4). This composite material combines the high voltage characteristics of olivine-type materials with the high conductivity of carbon, achieving both improved electron conductivity and enhanced power characteristics in low temperature environments.
Solution Approach 2:
The patent specifies that the pore specific surface area of carbon should be 1.0 m2/g or more and 5.5 m2/g or less, and the proportion of carbon's pore specific surface area to the composite positive active material's pore specific surface area should be 20% or more and 50% or less. This porous structure facilitates electrolyte penetration and ion diffusibility, improving power characteristics in low temperature environments.
2Productivity
If the pore specific surface area of carbon is increased to improve ion diffusibility, then ion diffusibility is improved, but density decreases
Solution Approach 1:
The patent optimizes the pore specific surface area of carbon within a specific range (1.0-5.5 m2/g) and controls the proportion of carbon's pore specific surface area to the composite material's pore specific surface area (20%-50%). It also specifies the density of the positive composite layer should be 1.80 g/cm3 or more and 2.10 g/cm3 or less. These parameter optimizations balance ion diffusibility and density, ensuring both high productivity and appropriate weight.
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
This configuration improves the initial power performance and capacity retention of nonaqueous electrolyte energy storage devices in low temperature environments by optimizing lithium ion diffusibility and reducing contact resistance.
Implementation Method 1
it is difficult to obtain a discharge capacity close to the theoretical capacity, but a technique of coating a surface with carbon for improving the electron conductivity has been proposed
Implementation Method 2
a proportion of a pore specific surface area of the carbon to a pore specific surface area of the composite positive active material is 20% or more and 50% or less
Data Source
AI summary
A positive electrode for nonaqueous electrolyte energy storage device according to an aspect of the present invention includes a positive composite layer containing a composite positive active material in which at least part of a surface of a positive active material is coated with carbon, a proportion of a pore specific surface area of the carbon to a pore specific surface area of the composite positive active material is 20% or more and 50% or less, a density of the positive composite layer is 1.80 g/cm3 or more and 2.10 g/cm3 or less, and the positive active material is a compound represented by the following Formula 1.LiFexMn(1-x)PO4(0≤x≤1) 1