Gradient Prussian Blue Cathode for Water-Resistant Sodium-Ion Batteries
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Solution Overview
Problem
Existing prussian blue materials for sodium-ion batteries suffer from deterioration in electrochemical performance during long-term storage, leading to poor storage and cycle performance due to water absorption issues.
Innovation Solution
A prussian blue material with a compound structure represented by NaxAyM1[M2(CN)6]δ·zH2O, where A is an alkali or alkaline earth metal with a larger ionic radius than sodium, and M1 and M2 are transition metals, is developed. This material has a gradient layer with decreasing A element content from the surface to the interior, improving storage and cycle performance without significantly reducing specific capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If prussian blue materials are used as positive electrode active material, then high capacity, high-voltage platform, and fast sodium ion transport are achieved, but storage performance deteriorates due to water absorption
Solution Approach 1:
The patent applies local quality by creating a gradient distribution of element A within the prussian blue particle structure. The outer layer has a higher concentration of element A (alkali metal or alkaline earth metal with larger ionic radius than sodium) compared to the inner core. This gradient structure provides water resistance at the surface where water contact occurs, while maintaining the electrochemical activity and sodium ion transport channels in the interior, thus resolving the contradiction between storage performance and specific capacity.
Solution Approach 2:
The patent creates a composite material system by doping prussian blue with element A having larger ionic radius than sodium (such as potassium, rubidium, cesium, calcium, strontium, or barium). This composite structure combines the high capacity and fast ion transport properties of prussian blue with the water resistance properties of the larger-radius element A, achieving both improved storage performance and maintained specific capacity.
2Reliability
If element A with larger ionic radius than sodium is doped into prussian blue material, then storage performance and cycle performance are improved, but specific capacity may decrease
Solution Approach 1:
The gradient distribution of element A concentrates the water-resistant and structurally stabilizing properties at the outer layer, while the inner core retains the original prussian blue composition with high electrochemical activity. This local differentiation allows the material to achieve both improved cycle performance (through the protective outer layer) and maintained specific capacity (through the active inner core).
Solution Approach 2:
The patent optimizes the concentration parameter of element A, controlling it to be within 0.01 to 0.5 atomic ratios. By precisely controlling this parameter and creating a gradient distribution rather than uniform doping, the material achieves structural stability and water resistance without excessive substitution of electrochemically active sodium sites, thus maintaining specific capacity while improving cycle performance.
3Stability of the object's composition
If prussian blue material absorbs water during storage, then electrochemical performance deteriorates, but water absorption is inherent to the material structure
Solution Approach 1:
The patent applies preliminary anti-action by pre-introducing element A with larger ionic radius than sodium into the prussian blue structure, particularly at the outer layers. This element A creates a protective effect that preemptively counteracts water absorption before it can occur during storage. The larger ionic radius of element A creates a more stable crystal structure with reduced water affinity, thus preventing the harmful water absorption effect before it deteriorates electrochemical performance.
Solution Approach 2:
The patent converts the potential harm of water absorption into a benefit by using element A to create a gradient structure where the outer layer specifically targets water interaction. The element A-doped outer layer acts as a protective barrier that converts the harmful water absorption into a controlled interface phenomenon, preventing water from penetrating to the electrochemically active interior, thus protecting performance while allowing controlled surface interaction.
Data Source
AI summary
The present application provides a positive electrode active material which may be in a particulate form and comprise a compound represented by Formula 1:NaxAyM1[M2(CN)6]δ·zH2O Formula 1wherein, A is selected from at least one of an alkali metal element and an alkaline earth metal element, and the ionic radius of A is greater than the ionic radius of sodium; M1 and M2 are each independently selected from at least one of a transition metal element, 0<y≤0.2, 0<x+y≤2, 0<δ≤1, and 0≤z≤10; and the particles of the positive electrode active material may have a gradient layer in which the content of the A element decreases from the particle surface to the particle interior.