Olivine Positive Electrode Material for Low-Temperature Discharge
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Solution Overview
Problem
Olivine-type positive active materials for energy storage devices face challenges in achieving high rate discharge capacity in low temperature environments due to limitations in electron conductivity and lithium ion diffusibility, despite surface carbon coating.
Innovation Solution
The positive active material has an olivine-type crystal structure with a carbon-coated surface, specifically optimized with pore volumes and surface areas within certain ranges, and controlled X-ray diffraction peak ratios to enhance lithium ion diffusibility and electron conductivity, thereby improving discharge capacity at low temperatures.
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 lithium ion diffusibility remains insufficient in low temperature environments
Solution Approach 1:
The patent applies composite materials by combining olivine-type positive active material with a specific porous coating layer. This coating layer has controlled pore volume (0.03-0.50 mL/g) and pore size (5-50 nm) to simultaneously improve electron conductivity through carbon content while maintaining lithium ion diffusibility through optimized pore structure, resolving the contradiction between these two properties in low temperature environments
Solution Approach 2:
The patent utilizes porous materials by introducing a coating layer with specific porosity characteristics (pore volume 0.03-0.50 mL/g, pore size 5-50 nm). This porous structure provides channels for lithium ion transport while the carbon content within the pores enhances electron conductivity, thereby solving the contradiction between lithium ion diffusibility and electron conductivity
2Productivity
If the pore volume is increased to improve lithium ion diffusibility, then lithium ion diffusibility is improved, but the density and energy density of the electrode may decrease
Solution Approach 1:
The patent applies parameter changes by precisely controlling the pore volume within the range of 0.03-0.50 mL/g and pore size within 5-50 nm. This optimized parameter range ensures sufficient lithium ion diffusibility while maintaining acceptable electrode density, as the porous structure provides ion transport pathways without excessive volume occupation that would reduce overall electrode density
3Reliability
If the carbon coating is applied to enhance electron conductivity, then electron conductivity is improved, but the cost of material preparation increases
Solution Approach 1:
The patent applies local quality by implementing carbon coating only in the porous structure of the coating layer rather than uniform thick coating. This localized approach places carbon specifically where it is needed for electron conductivity enhancement at particle interfaces and surfaces, while minimizing overall carbon content and associated costs
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 optimization significantly increases the energy storage device's capacity during high rate discharge in low temperature environments by improving lithium ion diffusibility and electron conductivity, ensuring better performance in cold conditions.
Implementation Method 1
a pore volume in the range of a pore size of 60 nm or more and 200 nm or less determined by a BJH method from a desorption isotherm using a nitrogen gas adsorption method is 0.05 cm3/g or more and 0.25 cm3/g or less
Implementation Method 2
a pore volume in the range of a pore size of 60 nm or more and 200 nm or less determined by a BJH method from a desorption isotherm using a nitrogen gas adsorption method
Implementation Method 3
Since this olivine-type positive active material has low electron conductivity, it is difficult to obtain a discharge capacity close to the theoretical capacity, but a technique of coating a surface with carbon for improving electron conductivity has been proposed
Implementation Method 4
A full width at half maximum ratio (200)/(131) of a peak corresponding to the (200) plane to a peak corresponding to the (131) plane by a powder X-ray diffraction method using a CuKa ray in a charged state is 1.10 or less
Data Source
AI summary
The positive active material for an energy storage device according to one aspect of the present invention has an olivine-type crystal structure, has a surface at least partially coated with carbon, and satisfies either (A) or (B) below. (A) a pore volume in a range of a pore size of 60 nm or more and 200 nm or less determined by a BJH method from a desorption isotherm using a nitrogen gas adsorption method is 0.05 cm3/g or more and 0.25 cm3/g or less, and a pore specific surface area in a range of a pore size of 10 nm or more and 200 nm or less using a nitrogen gas adsorption method is 5 m2/g or more; (B) a full width at half maximum ratio (200)/(131) of a peak corresponding to a (200) plane to a peak corresponding to a (131) plane by a powder X-ray diffraction method using a CuKα ray in a charged state is 1.10 or less.