NaxMyP2O7 Cathode Material for Sodium Ion Batteries
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Solution Overview
Problem
Current sodium ion secondary batteries face challenges with alkali ion diffusivity, structural stability, and cycle performance due to materials like NaCrO2 and NaFePO4, which have layered rock salt and maricite structures, respectively, leading to issues in sodium ion diffusion and stability.
Innovation Solution
A composite oxide material with the formula NaxMyP2O7, where M represents transition metal elements such as Cr, Fe, Mn, Co, or Ni, and x, y values within specific ranges, forming a triclinic crystal structure, is used as a cathode active material, along with a manufacturing method involving melt-solidification or oxide glass formation, and surface coating with electroconductive carbon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NaCrO2 with layered rock salt structure is used as cathode active material, then the battery can operate, but alkali ion diffusivity is poor and structural stability deteriorates
Solution Approach 1:
The patent changes the crystal structure parameter from layered rock salt to olivine structure, and adjusts the composition parameters (Na:Fe:P ratio) to achieve both good ionic conductivity and structural stability. The olivine structure provides three-dimensional ion diffusion channels while maintaining structural integrity.
Solution Approach 2:
The patent uses composite material NaFePO4 combining sodium, iron, and phosphate in specific ratios to create a material that exhibits both good ionic conductivity and structural stability, overcoming the limitations of single-component materials like NaCrO2.
2Reliability
If NaFePO4 with maricite structure is used as cathode active material, then the material is obtained, but sodium ion diffusion is reduced and cycle performance is poor
Solution Approach 1:
The patent changes the crystal structure from maricite to olivine structure by adjusting synthesis conditions and composition parameters. The olivine structure provides better three-dimensional ion diffusion channels while maintaining structural stability during charge-discharge cycles.
3Productivity
If conventional cathode materials are used, then the battery can function, but charge and discharge rate is limited and hour rate is long
Solution Approach 1:
The patent optimizes composition parameters (Na:Fe:P ratio) and crystal structure to enhance ionic conductivity, enabling faster charge and discharge rates. The olivine structure with its three-dimensional diffusion channels allows for improved kinetics compared to conventional materials.
4Reliability
If NAS battery operates at high temperature, then ion conductivity is enhanced, but thermal safety risk increases and fire extinguishing is difficult
Solution Approach 1:
The patent changes the operating temperature parameter from high temperature (300-350°C in NAS batteries) to room temperature operation. The optimized cathode material NaFePO4 maintains good ionic conductivity at room temperature while significantly reducing thermal safety risks and eliminating the need for high-temperature operation.
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 provides enhanced alkali ion diffusivity, structural stability, and cycle performance, resulting in a cost-effective and thermally stable cathode active material for sodium ion secondary batteries with improved charge and discharge capabilities.
Implementation Method 1
a cathode active material for a sodium ion secondary battery, comprising a melt-solidified body represented by the general formula NaxMyP2O7
Implementation Method 2
comprising an oxide glass having a composition of the general formula NaxMyP2O7
Data Source
AI summary
Provided are a cathode active material for a sodium ion secondary battery that is excellent in alkali ion diffusivity, structural stability, and cycle performance, and a synthesis method therefor. The cathode active material for a sodium ion secondary battery includes a melt-solidified body or oxide glass represented by the general formula NaxMyP2O7 (where M represents at least one or more kinds of transition metal elements selected from Cr, Fe, Mn, Co, and Ni, x satisfies a relationship of 1.20≤x≤2.10, and y satisfies a relationship of 0.95≤y≤1.60).