Sodium Transition Metal Pyrophosphate Cathode for Ion Intercalation
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Solution Overview
Problem
Sodium secondary batteries face challenges with reversible ion intercalation and deintercalation due to the large size of sodium ions, leading to unsatisfactory dynamic properties and performance limitations in existing olivine phosphate-based cathode materials.
Innovation Solution
A cathode active material comprising sodium transition metal pyrophosphate with a specific chemical formula (Na3.12−x2Acx1M1ay1M2by2(P2O7)2) is developed, which includes elements like Co, Ni, Fe, Mn, and Li, with a triclinic phase and P-1 space group structure, enabling efficient intercalation and deintercalation of sodium ions and improving charge and discharge rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If olivine phosphate material (NaMPO4) is used as cathode material in sodium secondary battery, then structural stability is improved due to strong P-O bond, but reversible intercalation/deintercalation of sodium ions deteriorates due to large ion size
Solution Approach 1:
The patent changes the crystal structure parameter from olivine to pyrophosphate structure, and modifies compositional parameters by introducing multiple transition metals (Fe, Mn, Co, Ni) and carbon coating, thereby improving both structural stability and ion intercalation performance simultaneously
Solution Approach 2:
The patent creates a composite material system combining multiple transition metals (Fe, Mn, Co, Ni) in specific ratios within the pyrophosphate structure, with additional carbon coating, to achieve synergistic effects that resolve the contradiction between structural stability and ion intercalation reversibility
2Ease of manufacture
If conventional cathode materials are used in sodium secondary battery, then manufacturing simplicity is maintained, but dynamic properties (kinetic aspects) deteriorate due to poor ion intercalation
Solution Approach 1:
The patent optimizes compositional parameters (metal ratios, carbon content) and structural parameters (pyrophosphate configuration) to achieve excellent dynamic properties while maintaining relatively simple synthesis procedures through conventional solid-state reaction 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 sodium transition metal pyrophosphate material provides enhanced structural stability and reversibility during charging and discharging, significantly improving the charge and discharge rate and capacity of sodium secondary batteries.
Implementation Method 1
reversible intercalation/deintercalation of sodium ions is not performed well due to the ion size
Implementation Method 2
allowing very fast ion intercalation-deintercalation in a structure
Data Source
AI summary
Provided is a cathode active material for a secondary battery, specifically, a cathode active material for a secondary battery including sodium transition metal pyrophosphate satisfying Na3.12−x2Acx1M1ay1M2by2 (P2O7)z, which has an advantage of structural stability due to a strong P—O bond of sodium transition metal phosphate having an olivine structure, and also performs proper intercalation and deintercalation of Na ions having a large ion radius, thereby significantly improving reversibility during charging and discharging, and a charge and discharge rate.