All-solid-state battery electrolyte diffusion control
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Solution Overview
Problem
The diffusion of Li and M from the olivine-type positive electrode active material into the solid electrolyte during sintering reduces the active material amount and alters the properties of the solid electrolyte in all-solid-state secondary batteries, affecting charging and discharging performance.
Innovation Solution
Incorporating a NASICON-type phosphate solid electrolyte with a particulate precipitate of olivine-type crystal structure, including a transition metal element matching the positive electrode active material, to inhibit diffusion and maintain the integrity of both materials during sintering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the positive electrode active material and solid electrolyte are sintered at the same time to simplify the manufacturing process, then the manufacturing complexity is reduced, but Li and M diffuse from the positive electrode active material to the solid electrolyte, reducing the active material amount and altering the solid electrolyte properties
Solution Approach 1:
The solid electrolyte is pre-formed as a green sheet before sintering, and the positive electrode active material is applied on top. This preliminary arrangement allows both materials to be positioned correctly before the sintering process, enabling simultaneous sintering while controlling material diffusion through the pre-established layer structure
Solution Approach 2:
The sintering temperature is controlled within a specific range (900°C to 1100°C) to achieve densification and improve contact between materials while minimizing excessive diffusion. This parameter optimization allows simultaneous sintering to proceed without causing harmful material degradation or excessive diffusion
2Reliability
If the sintering temperature is increased to improve the contact between positive electrode active material and solid electrolyte, then the interface contact quality is improved, but the diffusion of Li and M from the positive electrode active material to the solid electrolyte is accelerated
Solution Approach 1:
The positive electrode active material is applied to the green sheet form of the solid electrolyte before sintering, establishing intimate contact between the two materials in advance. This preliminary contact arrangement ensures good interface quality without requiring excessively high sintering temperatures to achieve contact
Solution Approach 2:
The sintering temperature is optimized to a specific range (900°C to 1100°C) that provides sufficient thermal energy to improve interface contact and densification while remaining below the threshold that causes excessive material diffusion. This parameter control resolves the trade-off between contact quality and material loss
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 effectively prevents Li and M diffusion, maintaining the active material quantity and electrolyte properties, enhancing the battery's charging and discharging performance while allowing for a simplified manufacturing process.
Implementation Method 1
Li and M (M=Mn, Co, Ni) tend to diffuse out of the positive electrode active material (LiMPO4, M=Mn, Co, Ni) when sintered at the same time as the solid electrolyte
Implementation Method 2
sintering, at the same time together, a solid electrolyte layer containing a phosphate having a NASICON-type structure and a positive electrode active material layer formed of an olivine-type active material LiMPO4
Data Source
AI summary
An all-solid-state secondary battery, including: a solid electrolyte layer; a positive electrode layer including a positive electrode active material layer and a first current collector layer; a negative electrode layer including a second current collector layer, the positive electrode layer and the negative electrode layer sandwiching the solid electrolyte layer; and external electrodes connected respectively to the first current collector layer and the second current collector layer, wherein the positive electrode active material layer is formed of an olivine-type active material, wherein the solid electrolyte layer is formed of a phosphate having a NASICON-type structure, and wherein the solid electrolyte layer contains particulate precipitate having an olivine-type crystal structure that includes a same element as an element forming the positive electrode active material layer.