Solid Electrolyte Gradient for Li Metal Battery Stability
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Solution Overview
Problem
Lithium secondary batteries with metallic Li and sulfide-based solid electrolytes face challenges in achieving high capacity and stable charge/discharge cycling characteristics, particularly at low temperatures, due to electrochemical instability and limited heat resistance.
Innovation Solution
A battery structure with a solid electrolyte layer composed of Li, phosphorus, boron, sulfur, oxygen, and nitrogen, featuring a two- or three-layered configuration with controlled atomic fractions and functional gradients, enhancing electrochemical stability and ionic conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If metallic Li is used for a negative electrode in batteries using an organic electrolytic solution, then discharge capacity per unit volume is improved, but charge/discharge cycling characteristics deteriorate due to needle crystal formation and short circuiting
Solution Approach 1:
The invention changes the physical state parameter of the electrolyte from liquid (organic electrolytic solution) to solid (solid electrolyte layer), which fundamentally alters the interaction between Li metal and the electrolyte. This parameter change prevents needle crystal formation and maintains electrochemical stability during repeated charging and discharging cycles.
Solution Approach 2:
The invention uses a composite structure consisting of a solid electrolyte layer (made from Li compounds containing P, S, O, and Nb/Ta) in contact with the Li metal negative electrode. This composite material system provides both high capacity and stable cycling characteristics by combining the high capacity advantage of Li metal with the stability advantage of solid electrolytes.
2Quantity of substance
If batteries using an organic electrolytic solution are designed for high capacity, then discharge capacity is improved, but heat resistance deteriorates and cannot withstand reflow solder mounting process temperatures
Solution Approach 1:
The invention changes the electrolyte from liquid organic solution to solid state material, which fundamentally improves the thermal stability and heat resistance of the battery system, enabling it to withstand reflow solder mounting process temperatures while maintaining high discharge capacity.
3Temperature
If Li metal is used in batteries requiring improved heat resistance, then melting point concerns arise at about 180° C., but solid electrolyte provides sufficient heat resistance in reflow solder mounting process
Solution Approach 1:
The solid electrolyte layer acts as an intermediary barrier between the Li metal negative electrode and the external environment. This intermediary layer protects the Li metal from direct exposure to high temperatures and reactive substances, maintaining electrochemical stability while enabling the battery to withstand reflow solder mounting process temperatures.
4Power
If sulfide-based solid electrolytes are used to improve ionic conductivity, then current density is improved, but electrochemical stability against negative electrode containing metallic Li deteriorates
Solution Approach 1:
The invention uses a composite solid electrolyte material system containing Li compounds with P, S, O, and Nb/Ta elements. This composite material combines the high ionic conductivity advantage of sulfide-based electrolytes with the electrochemical stability provided by phosphate and oxide components, achieving both high current density and stable cycling characteristics.
Solution Approach 2:
The invention introduces local compositional variations within the solid electrolyte layer, with different regions having optimized compositions for specific functions. The solid electrolyte contains P and S for ionic conductivity, while O and Nb/Ta provide electrochemical stability, creating local quality differences that address multiple requirements simultaneously.
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 battery structure achieves high current density and stable charge/discharge cycling characteristics at low temperatures, with improved lithium ionic conductivity and reduced degradation, ensuring increased capacity and efficiency.
Implementation Method 1
the solid electrolyte layer has a chemical composition... aLi·bX·cS·dY... improving lithium ionic conductivity
Implementation Method 2
a solid electrolyte layer is disposed between a positive electrode layer... and a negative electrode layer... the metallic Li may react with the organic electrolytic solution to form needle crystals
Data Source
AI summary
A battery structure includes a positive electrode layer, a solid electrolyte layer, and a negative electrode layer disposed in that order, wherein the solid electrolyte layer has a chemical composition, excluding incidental impurities, represented by the formula aLi·bX·cS·dY, where X is at least one element of phosphorus (P) and boron (B), Y is at least one element of oxygen (O) and nitrogen (N), the sum of a, b, c, and d is 1, a is 0.20 to 0.52, b is 0.10 to 0.20, c is 0.30 to 0.55, and d is 0 to 0.30. The solid electrolyte layer includes a portion A in contact with the negative electrode layer and a portion B in contact with the positive electrode layer, and d in the portion A is larger than d in the portion B. A lithium secondary battery includes the battery structure.