Solid-State Lithium Battery Thermal Stability via Phosphate Ester
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Solution Overview
Problem
Solid-state lithium batteries using oxide active materials and sulfide solid electrolytes with iodine face thermal instability issues due to exothermic reactions at high temperatures, necessitating improved thermal stability.
Innovation Solution
Incorporating a specific phosphate ester into the cathode active material layer, represented by general formulas (1) or (2), which contains carbon-based groups like C6H5, C6F5, C6H4(CH3), or CF3 at the terminus, to shift the exothermic peak temperature to higher values, thereby enhancing thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sulfide solid electrolyte material containing iodine is used as solid electrolyte material, then Li ion conductivity is improved, but thermal stability deteriorates due to exothermic reactions with oxide active material at high temperature
Solution Approach 1:
A coating layer comprising Li ion conductive oxide is formed on the surface of the oxide active material to act as an intermediary barrier between the oxide active material and the sulfide solid electrolyte material containing iodine. This coating layer prevents direct contact and exothermic reaction between these two materials, thereby improving thermal stability while maintaining Li ion conductivity through the coating layer.
Solution Approach 2:
The invention uses a composite structure where the oxide active material is coated with Li ion conductive oxide, creating a multi-layer composite material. This composite approach allows combining the high Li ion conductivity of sulfide solid electrolyte with the thermal stability provided by the oxide coating layer, resolving the contradiction between conductivity and thermal stability.
2Reliability
If safety devices are installed in lithium batteries using liquid electrolytes, then safety is improved, but device complexity and production cost increase
Solution Approach 1:
The invention extracts and eliminates the need for separate safety devices by replacing the liquid electrolyte with a solid electrolyte layer. The solid electrolyte inherently provides safety by being non-flammable and stable, thereby removing the requirement for additional safety components while maintaining or improving battery safety.
Solution Approach 2:
The invention changes the physical state parameter of the electrolyte from liquid to solid, fundamentally altering the safety characteristics. This parameter change eliminates flammability and thermal instability issues associated with liquid electrolytes, providing inherent safety without requiring additional safety devices.
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 addition of the phosphate ester significantly improves thermal stability by suppressing exothermic reactions, as evidenced by a shifted exothermic peak temperature and reduced heat generation, maintaining battery performance and capacity.
Implementation Method 1
an exothermic reaction due to the reaction of the oxide active material and the sulfide solid electrolyte material may occur
Data Source
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Figure 3~4
AI summary
The main object of the present invention is to provide a solid-state lithium battery in which a thermal stability is improved. The present invention solves the problem by providing a solid-state lithium battery comprising a cathode active material layer containing a cathode active material, an anode active material layer containing an anode active material, and a solid electrolyte layer formed between the cathode active material layer and the anode active material layer, characterized in that the cathode active material is an oxide active material; at least one of the cathode active material layer and the solid electrolyte layer contains a sulfide solid electrolyte material; the sulfide solid electrolyte material comprises the element Li, the element P, the element S, and the element I; and the cathode active material layer contains a specific phosphate ester.