Cathode Solid-Electrolyte Coating for Low-Gas Li-Ion Batteries
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Solution Overview
Problem
Conventional lithium ion secondary batteries face challenges in suppressing gas generation when using high-potential positive electrode active materials, as the oxidative decomposition of nonaqueous electrolytes leads to increased gas production, which is not effectively mitigated by existing coating films.
Innovation Solution
A positive electrode composite active material is developed, where the surface of the high-potential positive electrode active material is coated with a layered oxide-based solid electrolyte, specifically Li1+p+q+rAlpGaq(Ti,Ge)2−p−qSirP3−rO12, with a thickness between 5 nm and 50 nm, containing both amorphous and crystalline portions, to prevent direct exposure to the nonaqueous electrolyte and reduce gas generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a high-potential positive electrode active material (4.5 V or more) is used to improve energy density, then the energy density is improved, but gas generation increases due to oxidative decomposition of the nonaqueous electrolyte
Solution Approach 1:
A solid electrolyte coating layer is introduced as an intermediary between the high-potential positive electrode active material and the nonaqueous electrolyte. This coating prevents direct contact and oxidative decomposition reactions, suppressing gas generation while allowing lithium ion transport. The solid electrolyte acts as a protective mediator that enables the use of high-potential materials without the harmful side reactions.
Solution Approach 2:
A thin film coating of solid electrolyte (5 nm to 50 nm thickness) is applied to the surface of the positive electrode active material. This thin film provides protection against electrolyte decomposition while maintaining electrical conductivity and lithium ion transport. The flexible thin film structure allows the coating to conform to the electrode material surface and maintain functionality during battery operation.
2Object-generated harmful factors
If a coating film is formed on the positive electrode by adding additive to the nonaqueous electrolyte to suppress gas generation, then gas generation is suppressed to some extent, but the suppression effect is insufficient due to inadequate oxidation resistance
Solution Approach 1:
The approach changes from using chemical additives in the electrolyte to applying a physical coating of solid electrolyte material on the electrode surface. This parameter change from chemical to physical protection method provides superior oxidation resistance. The solid electrolyte coating has inherent high oxidation stability that conventional electrolyte additives cannot achieve, providing reliable and sufficient gas generation suppression.
Solution Approach 2:
A composite structure is created by coating the positive electrode active material with solid electrolyte material. This composite structure combines the high energy density characteristics of the active material (such as lithium nickel manganate or lithium cobalt oxide) with the high oxidation resistance of the solid electrolyte coating, achieving both high energy density and effective gas suppression.
3Object-generated harmful factors
If the surface of the positive electrode active material is coated with solid electrolyte to suppress gas generation, then gas generation is suppressed, but resistance may increase
Solution Approach 1:
The solid electrolyte coating is applied locally and uniformly on the surface of the positive electrode active material particles, creating a localized protective layer. This local coating approach ensures that only the surface is protected while the bulk material maintains its intrinsic conductivity. The thin film structure (5-50 nm) minimizes the impact on overall electrical resistance while providing sufficient gas suppression.
Solution Approach 2:
Instead of using a thick coating that would significantly increase resistance, a thin partial coating (5-50 nm) is applied. This partial action provides sufficient protection against gas generation while minimizing the added resistance. The coating thickness is optimized to provide just enough protection without excessive resistance penalty.
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
This approach significantly reduces gas generation and maintains low resistance, ensuring both effective lithium ion conductivity and gas suppression, even at high potentials, thereby enhancing the performance and stability of lithium ion secondary batteries.
Implementation Method 1
the positive electrode active material is coated with the oxide-based solid electrolyte... to prevent direct exposure to the nonaqueous electrolyte and reduce gas generation
Implementation Method 2
ensuring both effective lithium ion conductivity and gas suppression
Data Source
AI summary
A positive electrode composite active material, a lithium ion secondary battery, a method for producing a positive electrode composite active material, a method for producing a lithium ion secondary battery, and a composite active material is provided. The positive electrode composite active material includes a positive electrode active material and an oxide-based solid electrolyte. The positive electrode active material is coated with the oxide-based solid electrolyte. The oxide-based solid electrolyte is represented by Li1+p+q+rAlpGaq(Ti,Ge)2−p−qSirP3−rO12 (0<p≤1, 0≤q<1, 0≤r≤1). The oxide-based solid electrolyte is layered and has a coating thickness of 5 nm or more and 50 nm or less. In the oxide-based solid electrolyte, an amorphous portion and a crystalline portion are mixed, and the amorphous portion is in contact with the positive electrode active material.