Core-Shell Solid-State Electrolyte Coating for HF-Stable Cathodes
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Solution Overview
Problem
Existing solid-state electrolytes, such as Li3AlF6, exhibit poor lithium ion conductivity and limited cycle stability, leading to issues like capacity reduction and HF corrosion of positive electrodes in lithium-ion batteries, while other coatings fail to provide comprehensive improvements in electrochemical performance and stability.
Innovation Solution
A core-shell glassy solid-state electrolyte material composed of LiAlPO4(OH)xFx as the core and Al(H2PO4)3 as the shell, combined with Li3AlF6, enhances lithium ion conductivity and stability by forming a robust structure that protects against HF attack and inhibits transition metal dissolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Li3AlF6 is used as solid-state electrolyte coating, then electrochemical window is widened, but lithium ion conductivity is poor
Solution Approach 1:
The patent creates a composite solid-state electrolyte coating by combining Li3AlF6 with LiAlPO4(OH)xF1-x and Al(H2PO4)3. This composite structure integrates the wide electrochemical window advantage of Li3AlF6 with the high lithium ion conductivity of the phosphate-based components, achieving both properties simultaneously rather than relying on a single material
2Reliability
If solid-state electrolyte coating is applied to positive electrode, then side reactions are suppressed, but capacity is reduced
Solution Approach 1:
The coating is designed with a core-shell structure where the inner core (LiAlPO4(OH)xF1-x) provides high lithium ion conductivity to maintain capacity, while the outer shell (Al(H2PO4)3) provides robust protection against side reactions and HF corrosion. This localized functional differentiation allows simultaneous achievement of both protection and capacity retention
3Reliability
If conventional solid-state electrolyte coating is used, then transition metal dissolution is mitigated, but structural stability is limited
Solution Approach 1:
The composite coating combines multiple materials with complementary properties: Li3AlF6 provides chemical stability and HF resistance, LiAlPO4(OH)xF1-x provides structural framework stability, and Al(H2PO4)3 provides surface protection. Together they create a synergistic system that simultaneously achieves dissolution mitigation and enhanced structural stability
Solution Approach 2:
The coating forms a thin film structure that maintains flexibility and adhesion to the positive electrode surface while providing comprehensive protection. The thin film design ensures minimal interference with lithium ion transport while delivering effective protection against dissolution and structural degradation
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 core-shell structure improves lithium ion diffusion, maintains structural stability, and ensures good electrochemical performance by converting residual lithium into conductive Li3PO4, providing excellent ionic conductivity and thermal stability, thus mitigating capacity reduction and corrosion.
Implementation Method 1
improve electronic and ionic conductivity
Implementation Method 2
the solid-state electrolytes can act as a physical barrier to suppress side reactions and mitigate transition metal dissolution
Implementation Method 3
modify surface chemistry to promote interfacial ion charge transfer
Implementation Method 4
stabilize structure to reduce phase transition stress
Implementation Method 5
converting residual lithium into conductive Li3PO4
Data Source
Figure 1~2
AI summary
Provided in the present disclosure is a composite material, which comprises LiAlPO4(OH)xF1-x and Al(H2PO4)3 compounded on the surface of the LiAlPO4(OH)xF1-x, wherein 0≤x≤1. A corresponding core-shell/glassy solid-state electrolyte material is also prepared in the present disclosure. The composite solid electrolyte has good ionic conductivity, good flexibility, a stable composite structure and thermal stability, such that when being applied to positive electrode coating, the composite solid electrolyte can slow down reduction in the capacity of a positive electrode by a coating layer, effectively remove alkaline residual lithium left on the surface in the preparation process of a positive electrode material, and convert the residual lithium into Li3PO4 favorable for ionic conductivity of the coating layer and AlPO4 capable of protecting the positive electrode. Moreover, Li3AlF6 is more stable to HF, and the good flexibility of a glassy structure thereof is beneficial to effective interfacial contact between the positive electrode and an electrolyte solution of the electrolyte, such that good interfacial ion conduction is achieved.