Amorphous Lithium Complex Oxide Cathode for Solid-State Batteries
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Solution Overview
Problem
The development of high-capacity thin film lithium secondary batteries is hindered by the low ionic and electron conductivity of lithium transition-metal oxides, such as LiFePO4, which results in high internal impedance and poor charge/discharge characteristics, making it difficult to commercialize batteries with thick cathode activating substance layers.
Innovation Solution
A solid-state electrolyte battery with a cathode activating substance layer composed of a lithium complex oxide in an amorphous state, expressed by Formula LixMyPO4−zNz, where M is a transition metal, x is the lithium composition ratio, y is the transition metal composition ratio, and z is the nitrogen composition ratio, providing high ionic conductivity without the need for annealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the cathode activating substance layer is increased to achieve high capacity, then the battery capacity is improved, but the internal impedance increases significantly due to low ionic and electron conductivity
Solution Approach 1:
The invention changes the physical state parameter of the cathode activating substance from crystalline to amorphous. This parameter change fundamentally alters the material's properties, enabling high ionic conductivity (comparable to liquid electrolytes) and electron conductivity simultaneously, thus resolving the contradiction between increasing layer thickness for capacity and maintaining low internal impedance
Solution Approach 2:
The invention uses a composite approach by combining transition metal elements (Fe, Co, Ni, Mn) with phosphorus and nitrogen in specific ratios within the amorphous structure. This composite material design achieves both high ionic conductivity and sufficient electron conductivity, allowing thick layers to be used without excessive impedance
2Stability of the object's composition
If conventional crystalline lithium transition-metal oxides are used as cathode activating substance, then the material is stable, but the ionic and electron conductivity are low resulting in poor charge/discharge characteristics
Solution Approach 1:
The invention changes the structural parameter from crystalline to amorphous state. This parameter change dramatically improves both ionic conductivity (enabling fast charge/discharge) and electron conductivity, while the amorphous structure itself provides inherent stability, resolving the contradiction between material stability and charge/discharge characteristics
Solution Approach 2:
The invention introduces local structural variations within the amorphous matrix by controlling the ratios of different transition metal elements and incorporating nitrogen. This creates localized regions with optimized electronic and ionic transport properties while maintaining overall structural stability
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 amorphous lithium complex oxide cathode activating substance layer enables high ionic conductivity and stable charge/discharge cycle characteristics, reducing manufacturing costs by eliminating the need for heat-resistant glass substrates and maintaining performance without annealing.
Implementation Method 1
The ionic conductivity of these materials is about 10−6 S/cm which is significantly lower than that of an ordinary liquid electrolyte of 10−2 S/cm
Data Source
AI summary
The present invention provides a solid-state electrolyte battery using a cathode activating substance which functions as such in an amorphous state and has a high ionic conductivity and provides a cathode activating substance used for the same. This solid-state electrolyte battery includes a laminated body. In the laminated body, a cathode-side current collector film, cathode activating substance film, solid-state electrolyte film, anode potential formation layer and anode-side current collector film are stacked above a substrate in this order. The cathode activating substance film is made of LixMyPO4−zNz, i.e., a lithium complex oxide in an amorphous state.