Phosphorus Coating for Solid-State Cathodes Under High Voltage
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Solution Overview
Problem
Sulfide solid electrolytes in all-solid-state batteries degrade when directly contacting positive electrode active material particles, leading to increased battery resistance, which is mitigated by forming a coating film on the particles, but existing materials like LiNbO3 have limitations in durability under high voltage.
Innovation Solution
A phosphorus-based coating film with a specific composition ratio of lithium, glass network-forming elements, and transition elements is developed, which includes a phosphorus compound with a lithium concentration of 2.5 or less, incorporating elements like boron, silicon, or transition metals to enhance ionic conduction and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiNbO3 coating film is used to reduce battery resistance, then ionic conduction is improved, but durability under high voltage deteriorates
Solution Approach 1:
The patent uses a composite coating film made of Li3PO4 and Li2SiO3 instead of a single material. Li3PO4 provides high voltage durability while Li2SiO3 contributes to low resistance through its glass network structure. This composite approach combines the advantages of both materials to achieve both durability and low resistance simultaneously.
Solution Approach 2:
The patent changes the compositional parameters of the coating film by controlling the molar ratio of Li3PO4 to Li2SiO3 within 95:5 to 50:50. By adjusting these parameters, the film achieves optimal balance between voltage durability (from Li3PO4) and ionic conduction (from Li2SiO3), resolving the contradiction between durability and resistance.
2Reliability
If Li3PO4 coating film is used to improve high voltage durability, then reliability is improved, but battery resistance increases
Solution Approach 1:
The patent creates a composite coating film combining Li3PO4 (for durability) with Li2SiO3 (for low resistance). The Li2SiO3 component forms a glass network structure that facilitates ion transport, compensating for the higher resistance of pure Li3PO4 while maintaining its voltage durability benefits.
Solution Approach 2:
The coating film exhibits local quality differentiation where Li3PO4 domains provide high voltage stability while Li2SiO3 domains provide low resistance pathways. This spatial distribution of different material properties allows the film to simultaneously achieve both durability and 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 phosphorus-based coating film achieves resistance as low as or lower than LiNbO3, while maintaining durability under high voltage and supporting high output, by facilitating carrier migration through mixed anion effects and structural defects.
Implementation Method 1
the sulfide solid electrolyte can degrade. Degradation of the sulfide solid electrolyte (ionic conduction paths) can increase the battery resistance
Implementation Method 2
Carrier (cation) migration can be facilitated by the mixed anion effect. Moreover, as the number of carriers may be small, carrier migration is considered to be further facilitated.
Data Source
AI summary
A composite particle includes a positive electrode active material particle and a coating film. The coating film covers at least a part of a surface of the positive electrode active material particle. The coating film includes a phosphorus compound. The phosphorus compound includes either or both of a first element and a second element, and phosphorus. The first element is a glass network-forming element. The second element is a transition element. The relationship of CLi/(CP+CE1+CE2)≤2.5 is satisfied, where CLi, CP, CE1, and CE2 represent elemental concentrations obtained by measuring the composite particle by X-ray photoelectron spectroscopy, CLi represents an elemental concentration of lithium, CP represents an elemental concentration of phosphorus, CE1 represents an elemental concentration of the first element, and CE2 represents an elemental concentration of the second element.