Li-Free Cathode Mixture for All-Solid-State Batteries
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Solution Overview
Problem
Current sulfur-based batteries face challenges with high irreversible capacity, which degrades battery performance, particularly due to the presence of Li elements in cathode mixtures, leading to low ion conductivity and capacity loss.
Innovation Solution
A cathode mixture comprising sulfur, a phosphorus-containing sulfur compound, and a conductive auxiliary material with minimal Li content, characterized by a specific diffraction intensity ratio, is developed to reduce irreversible capacity and enhance ion conductivity, along with an all-solid-state battery structure and production method that includes mechanical milling and initial high-temperature discharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Li element is included in cathode mixture to enable ion conduction, then ion conductivity is improved, but irreversible capacity increases and degrades battery performance
Solution Approach 1:
The invention extracts and removes the Li element from the cathode mixture by using a Li-free composition (sulfur, phosphorus sulfide, and conductive carbon). This extraction eliminates the source of irreversible capacity while maintaining ion conductivity through alternative mechanisms in the Li-free cathode mixture.
Solution Approach 2:
The invention changes the compositional parameters of the cathode mixture by eliminating Li content and optimizing the ratio of sulfur to phosphorus sulfide. This parameter change transforms the system from a Li-containing to a Li-free composition, fundamentally altering how ion conduction occurs while reducing irreversible capacity.
2Stability of the object's composition
If mechanical milling is applied to cathode mixture to improve homogeneity, then mixing uniformity is improved, but particle size reduction may increase surface reactivity and capacity loss
Solution Approach 1:
The invention changes the milling parameters by optimizing the milling time and intensity to achieve sufficient homogeneity without excessive particle size reduction. The Li-free composition also changes the chemical reactivity parameters, reducing surface reactivity and associated capacity loss despite mechanical activation.
3Quantity of substance
If high sulfur content is used to increase theoretical capacity, then battery capacity is improved, but ion conductivity and mixture homogeneity deteriorate
Solution Approach 1:
The invention creates a composite cathode mixture where sulfur particles are dispersed in a matrix of phosphorus sulfide and conductive carbon. This composite structure maintains high sulfur content for capacity while the phosphorus sulfide and carbon matrix provide ion conduction pathways and electrical conductivity, preventing the deterioration that would occur with pure high-sulfur composition.
Solution Approach 2:
The phosphorus sulfide acts as an intermediary material between sulfur and the electrolyte, facilitating ion transport in the high-sulfur composition. The conductive carbon also serves as an intermediary for electron transport, enabling the system to maintain both high capacity and good conductivity through these mediating substances.
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 cathode mixture exhibits reduced irreversible capacity and improved high-rate properties, inhibiting capacity degradation and enhancing overall battery performance by securing an ion conducting path and maintaining high ion conductivity.
Implementation Method 1
conducting mechanical milling to a mixture of sulfur (S), P2S5, and Ketjen black
Implementation Method 2
initial high-temperature discharging
Implementation Method 3
when a diffraction intensity at 2θ=15.5° in an X-ray diffraction measurement using a CuKα ray is regarded as I15.5
Data Source
AI summary
An object of the present disclosure is to produce a cathode mixture with less irreversible capacity. The present disclosure achieves the object by providing a cathode mixture comprising: a cathode active material including a S element; a sulfur containing compound including a P element and a S element; a conductive auxiliary material; and substantially no Li element; wherein when a diffraction intensity at 2θ=15.5° in an X-ray diffraction measurement using a CuKα ray is regarded as I15.5, a diffraction intensity at 2θ=25° is regarded as I25, and a diffraction intensity at 2θ=40° is regarded as I40, a standard value defined by the following formula is more than 1.2.Standard value=(I15.5−I40)/(I25−I40)