All-solid-state Battery Mixed Layer for Adhesion and Conductivity
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Solution Overview
Problem
All-solid-state lithium secondary batteries face challenges with lithium-ion conductivity at the solid-solid interface between the solid electrolyte and active material, leading to insufficient energy density due to inadequate adhesion and potential degradation at high sintering temperatures, and existing methods like gas-phase methods are not productive for increasing energy density.
Innovation Solution
A mixed layer containing a positive-electrode active material and (Lix(1−α), Mxα/β)γ+(B1−y, Ay)z+O2−δ is formed in close contact with the solid electrolyte, where M and A represent elements like C, Al, Si, Ga, Ge, In, and Sn, to increase the energy density by enhancing lithium-ion conductivity without degrading the materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If external pressure is applied to bind the solid electrolyte and active material, then adhesion is improved, but strong adhesion is not obtained and lithium-ion conductivity remains insufficient
Solution Approach 1:
A glassy carbon layer is introduced as an intermediary substance between the solid electrolyte and the active material. This intermediate layer facilitates strong adhesion through effective contact while simultaneously providing a pathway for lithium-ion conduction, thereby resolving the contradiction between achieving strong adhesion and maintaining lithium-ion conductivity.
2Strength
If sintering is performed at high temperature to increase adhesion, then adhesion is improved, but the solid electrolyte and active material degrade and third phases form that increase interface resistance
Solution Approach 1:
The glassy carbon layer serves as a protective intermediary that enables adhesion enhancement through lower-temperature processing. This intermediate layer allows the solid electrolyte and active material to be bound together without requiring high-temperature sintering, thereby preventing material degradation and the formation of harmful third phases while still achieving strong adhesion.
Solution Approach 2:
The introduction of glassy carbon changes the processing parameters, allowing adhesion to be achieved at lower temperatures. This parameter change prevents the thermal degradation that would occur with high-temperature sintering while still providing effective bonding between the solid electrolyte and active material.
3Reliability
If gas-phase methods are used to form the active material layer, then lithium-ion conductivity is improved, but productivity decreases and energy density needs to be increased by other methods
Solution Approach 1:
The glassy carbon intermediate layer provides a pathway that enables conventional manufacturing methods to achieve good lithium-ion conductivity. This allows the use of more productive, conventional fabrication techniques rather than requiring specialized gas-phase methods, thereby improving manufacturing efficiency while maintaining adequate lithium-ion conductivity.
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 increases the energy density of all-solid-state lithium secondary batteries by providing a lithium-ion-conducting path and preventing degradation, thereby improving the battery's performance without using gas-phase methods.
Implementation Method 1
a solid electrolyte arranged between the positive electrode and the negative electrode, the solid electrolyte conducting lithium ions
Data Source
AI summary
An all-solid-state lithium secondary battery includes a positive electrode; a negative electrode; and a solid electrolyte arranged between the positive and negative electrodes, to conduct lithium ions. In the all-solid-state lithium secondary battery, a mixed layer is in close contact with a surface of the solid electrolyte adjacent to the positive electrode, the mixed layer containing the positive-electrode active material and (Lix(1−α), Mxα/β)γ+(B1−y, Ay)z+O2−δ (wherein in the formula, M and A each represent at least one or more elements selected from C, Al, Si, Ga, Ge, In, and Sn, α satisfies 0≤α<1, β represents the valence of M, γ represents the average valence of (Li+x(1−α), Mα), y satisfies 0≤y<1, z represents the average valence of (B1−y, Ay) and x, α, β, γ, z, and γ satisfy the relational expression (x(1−α)+xα/β)γ+z=2δ) serving as a matrix.