Positive Electrode Active Material, All-Solid-State Battery, and Method of Producing Positive Electrode Active Material
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Solution Overview
Problem
Sulfide solid electrolytes in all-solid-state batteries deteriorate when directly contacted with positive electrode active material particles, leading to increased battery resistance, and existing coating films, while reducing deterioration, often result in undesirably high battery resistance due to their resistive nature.
Innovation Solution
A positive electrode active material with a coating film containing oxygen and glass-forming elements like phosphorus and silicon, where the Li composition ratio is limited to 2.5 or less, and silicon is introduced in a condensed phosphate compound with a high P2O5 concentration, forming a composite glass network to enhance ion conduction and reduce battery resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating film is formed on the active material particle surface, then the deterioration of the sulfide solid electrolyte is reduced, but the battery resistance increases
Solution Approach 1:
The patent changes the compositional parameters of the coating film by controlling the Li composition ratio to be 2.5 or less (Formula 1) and the Si composition ratio to be 0.05 or more (Formula 2). This parameter optimization allows the coating film to maintain protective function while reducing resistance, resolving the contradiction between deterioration resistance and battery resistance.
Solution Approach 2:
The patent creates a composite coating film containing multiple glass-forming elements (P, Si, and potentially other elements) with specific compositional ratios. This composite structure combines the protective properties of glass networks with controlled Li content, achieving both deterioration resistance and low resistance by leveraging the synergistic effects of different materials.
2Object-affected harmful factors
If the Li composition ratio in the coating film is increased, then the battery resistance is expected to be reduced, but the coating film becomes more resistive
Solution Approach 1:
The patent precisely controls the Li composition ratio parameter to be 2.5 or less, which is a critical threshold value. This parameter setting optimizes the balance between ion conduction (reducing battery resistance) and maintaining coating film integrity, preventing the coating film from becoming overly resistive while still achieving low battery resistance.
Solution Approach 2:
The patent references conventional findings where higher Li composition ratio was expected to reduce battery resistance, but applies the opposite approach by limiting Li to 2.5 or less. This inverted strategy, based on new experimental findings, achieves better results by copying the successful protective function while avoiding the resistance penalty of high Li content.
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 proposed solution significantly reduces battery resistance by promoting ion conduction through a mixed anion effect, improving the continuity of the glass network and ion conductivity, thereby achieving a desired battery performance.
Implementation Method 1
The glass network is considered to include two or more types of anions (PO43−, SiO44−, etc.). The coexistence of the two or more types of anions is expected to cause exhibition of a mixed anion effect. The mixed anion effect is expected to promote ion conduction.
Implementation Method 2
CLi, CX and CSi respectively represent element concentrations measured by X-ray photoelectron spectroscopy. The XPS acquires information of the outermost surface of a measurement target (positive electrode active material).
Data Source
AI summary
A positive electrode active material includes an active material particle and a coating film. The coating film covers at least a part of a surface of the active material particle. The coating film includes oxygen and a glass forming element. The glass forming element includes phosphorus and silicon. The positive electrode active material satisfies relationships of a formula (1) of “CLi/CX≤2.50” and a formula (2) of “0<CSi/CX”. CLi, CX and CSi respectively represent element concentrations measured by X-ray photoelectron spectroscopy. CLi represents an element concentration of lithium. CX represents a total element concentration of the glass forming element. CSi represents an element concentration of silicon.