Sodium Cathode Coating Layer for Residual Alkali Control
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Solution Overview
Problem
Conventional sodium-ion secondary batteries suffer from inferior cycle performance due to residual alkali (Na2CO3 and NaOH) on the surface of the positive electrode material, leading to irreversible capacity loss and deterioration, which existing methods like water washing or dry-mix coating fail to adequately address without disrupting the crystal structure.
Innovation Solution
A sodium-containing positive electrode material with a NaxMyO2 coating layer, where M includes B, Si, or P, is applied using surface heat treatment with a coating modifier to consume residual alkali, isolate the material from air, and enhance bonding, thereby improving cycle stability and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If water washing or dry-mix coating is used to remove residual alkali, then residual alkali content is reduced, but crystal structure integrity is disrupted
Solution Approach 1:
The patent changes the chemical composition parameters of the coating layer by incorporating multiple elements (M, N, O) with specific ratios. The coating layer has a controlled thickness (5-50 nm) and specific chemical formula NaxMyOz, where the parameters are optimized to consume residual alkali while maintaining crystal structure integrity through in-situ formation rather than external coating applications.
Solution Approach 2:
The coating layer acts as an intermediary between the positive electrode material substrate and the residual alkali. It provides a protective interface that consumes residual alkali through chemical reactions while preventing direct contact between washing/coating agents and the crystal structure, thereby mediating the interaction to achieve alkali removal without structural damage.
2Object-affected harmful factors
If conventional coating methods are applied, then surface protection is improved, but bonding strength between coating and substrate deteriorates
Solution Approach 1:
The coating layer is formed through in-situ generation from coating modifiers that decompose and react directly on the substrate surface during battery manufacturing processes. This self-service mechanism ensures the coating is inherently bonded to the substrate without requiring separate coating applications, achieving both surface protection and strong bonding simultaneously.
Solution Approach 2:
The patent merges the coating formation process with the battery manufacturing process itself. The coating modifiers are incorporated into the electrode slurry or applied during sintering, combining the coating application with the electrode fabrication steps, thereby ensuring intimate contact and strong bonding between the coating layer and substrate while providing surface protection.
3Ease of manufacture
If residual alkali is not removed, then manufacturing process is simple, but cycle performance deteriorates due to irreversible capacity loss
Solution Approach 1:
The coating modifiers act as intermediaries that are easily incorporated into the manufacturing process. They decompose during standard sintering or formation cycles to generate the protective coating in-situ, maintaining manufacturing simplicity while effectively removing residual alkali to improve cycle performance and reduce irreversible capacity loss.
Solution Approach 2:
The patent utilizes standard battery manufacturing parameters (sintering temperature, formation cycle conditions) to trigger the decomposition and reaction of coating modifiers. By optimizing the coating modifier composition and processing parameters within existing manufacturing ranges, the process maintains simplicity while achieving effective residual alkali removal and improved cycle performance.
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 method effectively reduces residual alkali content, maintains the crystal structure integrity, and enhances the cycle performance of the sodium-ion battery by forming a stable NaxMyO2 coating layer that prevents continuous reaction with air components, leading to improved intercalation and deintercalation efficiency.
Implementation Method 1
The NaxMyO2 formed in the coating layer can consume residual alkali (Na2CO3 and NaOH) on the surface of the sodium-containing positive electrode material substrate
Implementation Method 2
the coating layer can isolate the sodium-containing positive electrode material substrate from the air, avoid exposure of the sodium-containing positive electrode material substrate to the air, and prevent continuous reaction of the material with components (water and carbon dioxide) in the air
Implementation Method 3
The superficial doping can form a chemical bond between the element M and the sodium-containing positive electrode material substrate, thereby further increasing the bonding force of adhesion to the sodium-containing positive electrode material substrate
Data Source
AI summary
A positive electrode material includes a sodium-containing positive electrode material substrate and a coating layer covering at least a part of a surface of the sodium-containing positive electrode material substrate. The coating layer includes NaxMyO2, where M includes at least one of B, Si, or P, x>0, and y>0.