Prussian-Blue Cathode Composition for Stable Sodium-Ion Battery Storage
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Solution Overview
Problem
Existing Prussian-blue materials for sodium ion secondary batteries suffer from deterioration of electrochemical properties during long-term storage, leading to poor cycling performance and rate performance.
Innovation Solution
A positive electrode active material comprising a compound represented by formula (NaxAy)a□bM1[M2(CN)6]δ, where A is an alkali metal with a larger ionic radius than sodium, is developed, with a specific pH value in an aqueous solution of 7.6 to 8.5, and a gradient layer of A element distribution, to reduce water absorption and enhance high-temperature cycling and rate performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Prussian-blue materials are used as positive electrode active material, then high capacity and high voltage plateau are achieved, but electrochemical properties deteriorate during long-term storage
Solution Approach 1:
The patent changes the chemical composition parameters by introducing alkali metal elements (K, Rb, or Cs) as dopants in specific amounts (0.01-0.50 mol per formula unit) and controlling the Na/A ratio (0.95-1.05), which modifies the crystal structure and electronic properties to improve storage stability while maintaining electrochemical performance
Solution Approach 2:
The patent creates a composite material system by combining Prussian-blue analogues with alkali metal elements, forming a doped composite structure (Na1-yAyM[Fe(CN)6] where A=K, Rb, or Cs) that synergistically improves both storage stability and electrochemical properties
2Speed
If Prussian-blue materials are used, then rapid sodium ion transport is achieved, but cycling performance deteriorates over time
Solution Approach 1:
The patent optimizes compositional parameters (Na content, A element content, M1/M2 ratios) to achieve a balance between ion transport channels and structural stability, enabling fast sodium ion diffusion while maintaining framework integrity during repeated cycling
Solution Approach 2:
The patent introduces local structural modifications through A element doping at specific lattice positions, creating regions with enhanced ion conductivity while maintaining overall structural stability, thus improving both rate performance and cycling life
3Ease of manufacture
If conventional Prussian-blue materials are used, then simple preparation is achieved, but water absorption increases during storage
Solution Approach 1:
The patent modifies the stoichiometric parameters and chemical composition by incorporating A elements and controlling Na/A ratios, which alters the surface chemistry and crystal structure to reduce hygroscopicity while maintaining ease of preparation through conventional synthesis methods
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 modified Prussian-blue materials exhibit improved high-temperature cycling and rate performance, reduced specific capacity loss, and simplified battery manufacturing, while maintaining structural integrity.
Implementation Method 1
a positive electrode active material comprising a compound represented by formula (NaxAy)a□bM1[M2(CN)6]δ, where A is an alkali metal with a larger ionic radius than sodium
Implementation Method 2
a gradient layer of A element distribution
Data Source
AI summary
A positive electrode active material is granular and comprises a compound represented by formula 1: (NaxAy)a□bM1[M2(CN)6]δ, wherein A is selected from at least one of alkali metal elements and has an ionic radius greater than that of sodium, M1 and M2 are each independently selected from at least one of transition metal elements, 0<y≤0.2, 0<x+y≤2, 0≤δ≤1, a+b=2, 0.85≤a≤0.98, □ represents a vacancy, and b represents the number of vacancies; and when the positive electrode active material is dissolved, at a temperature of 20° C., into an aqueous solution having a concentration of 5 g/100 g water, a pH value of the aqueous solution is in a range of 7.6 to 8.5. The positive electrode active material has good cycling and rate performance, and a high specific capacity.