Composite particle, positive electrode, all-solid-state battery, and method of producing composite particle
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Solution Overview
Problem
Existing all-solid-state batteries face challenges in reducing initial resistance and post-endurance-test resistance increment, particularly in sulfide-type batteries, where conventional coating films like Li3PO4 exhibit high initial resistance and significant resistance increases over time.
Innovation Solution
A composite particle is developed with a coating film containing a phosphorus compound, where the particle surface composition ratio of lithium to phosphorus (Li/P) is maintained at 2.5 or less, achieved by using a coating liquid with diphosphorus pentoxide (P2O5) in a mass fraction of 72% or more, along with a molar ratio of lithium to phosphorus (nLi/nP) less than 1.1, to form a coating film that significantly decreases initial resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional coating film material (Li3PO4) is used, then the coating film can be formed on the positive electrode active material particle, but the initial resistance remains high
Solution Approach 1:
The patent changes the chemical composition parameters of the coating film by using a phosphorus compound with controlled Li/P ratio (2.5 or less) instead of conventional Li3PO4. This parameter change in composition enables marked decrease in initial resistance while maintaining coating film formation capability.
Solution Approach 2:
The patent employs a composite coating film structure comprising a phosphorus compound combined with lithium compound, creating a new composite material system. This composite approach achieves both low initial resistance and good Li-ion conductivity that neither material alone could provide.
2Reliability
If the particle surface composition ratio (Cli/Cp) is increased to improve Li-ion conductivity, then initial resistance decreases, but post-endurance-test resistance increment increases
Solution Approach 1:
The patent optimizes the Li/P composition ratio parameter to 2.5 or less, which represents a precise parameter adjustment that simultaneously achieves low initial resistance and minimal resistance increment after endurance testing. This optimal parameter balance resolves the contradiction between initial performance and long-term stability.
Solution Approach 2:
The patent employs X-ray photoelectron spectroscopy (XPS) to measure and control the particle surface composition ratio, implementing a feedback mechanism to ensure the Li/P ratio remains at or below 2.5. This measurement and control feedback enables consistent achievement of both low initial resistance and low resistance increment.
3Reliability
If a coating film with high Li-ion conductivity is formed, then initial resistance decreases, but the covering rate and composition control become more difficult
Solution Approach 1:
The patent controls the phosphorus compound composition and Li/P ratio as key parameters during coating film formation. By precisely controlling these composition parameters, the patent achieves uniform covering with 83% or more coverage rate while maintaining the optimal Li/P ratio for low resistance.
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 approach results in a marked decrease in initial resistance and a lower post-endurance-test resistance increment, enhancing the battery's performance and longevity by optimizing the Li-ion conductivity and covering rate of the coating film.
Implementation Method 1
A coating film is required to have Li-ion conductivity. The higher the Li-ion conductivity is, the more decreased the initial resistance is expected to be.
Implementation Method 2
By using X-ray photoelectron spectroscopy (XPS), it is possible to identify the composition of a particle surface (namely, the composition of the coating film).
Data Source
Figure 1~2
Figure 3~4
AI summary
A composite particle includes a positive electrode active material particle and a coating film. The coating film covers at least part of a surface of the positive electrode active material particle. The coating film includes a phosphorus compound. The composite particle satisfies a relationship of "CLi/CP ≤ 2.5". "CLi" represents a concentration of Li element measured by XPS. "CP" represents a concentration of P element measured by XPS.