Lithium Battery Passivation Layer Thickness Control
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining high initial efficiency and capacity while suppressing thickness increase during charging and discharging, as conventional passivation layers exhibit significant thickness changes and resistance increases over cycles.
Innovation Solution
A lithium secondary battery design featuring a passivation layer with a film-like thickness of 10 nm or greater and a particulate passivation layer with a three-dimensional structure, formed on the negative electrode, which includes organic and inorganic compounds, inhibiting oxidation and reduction reactions and maintaining resistance levels, thereby extending lifespan and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional passivation layer is used on the negative electrode, then the battery can operate with basic protection, but the passivation layer exhibits significant thickness changes and resistance increases over charging-discharging cycles, leading to reduced lifespan and capacity
Solution Approach 1:
The patent applies composite materials by forming a passivation layer containing both organic compounds (from vinylene carbonate and vinyl ethylene carbonate) and inorganic compounds (such as lithium fluoride and lithium oxalate). This composite structure provides superior stability compared to conventional single-component passivation layers, preventing significant thickness changes and resistance increases over charging-discharging cycles, thereby extending battery lifespan while maintaining capacity.
2Reliability
If the passivation layer is made thinner to reduce resistance, then resistance levels decrease, but the layer becomes insufficient to protect the electrode surface, leading to increased oxidation and reduction reactions
Solution Approach 1:
The patent applies parameter changes by optimizing the thickness and composition of the passivation layer. The layer is maintained at a specific thickness range (10-100 nm) and contains specific organic-inorganic compounds that provide both protective functionality and low resistance. This optimized parameter configuration allows the passivation layer to effectively protect the electrode surface from oxidation and reduction reactions while maintaining low resistance levels for efficient ion transport.
3Reliability
If the passivation layer thickness increases to improve protection, then electrode protection improves, but the battery thickness increases and capacity decreases
Solution Approach 1:
The patent applies flexible shells and thin films by forming a passivation layer with controlled thickness in the range of 10-100 nm. This thin film structure provides sufficient protection against oxidation and reduction reactions while minimizing the increase in battery thickness. The passivation layer acts as a protective shell that prevents harmful reactions without significantly increasing the overall battery volume, thereby maintaining high capacity.
4Reliability
If a thick passivation layer is formed to suppress oxidation and reduction reactions, then electrode protection improves, but the initial efficiency and capacity of the battery decrease
Solution Approach 1:
The patent applies parameter changes by optimizing the passivation layer thickness to 10-100 nm and controlling the composition ratios of organic and inorganic compounds. This optimized configuration provides sufficient protection against oxidation and reduction reactions while minimizing the impact on initial charging-discharging efficiency and capacity. The thin film structure allows efficient ion transport, maintaining high productivity without compromising electrode protection.
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 battery achieves long lifespan and high capacity by maintaining small thickness changes and resistance levels, with the passivation layer effectively formed on a significant portion of the negative electrode surface, ensuring efficient charging and discharging cycles.
Implementation Method 1
When the electrolyte is brought into contact with active materials of the electrodes, oxidation and reduction reactions of components of the electrolyte occur. Although some products of these reactions are desorbed or eluted therefrom, others are deposited on the surface of the electrode to form a passivation layer on the surface of an active material.
Implementation Method 2
Since the behavior of the passivation layer is similar to that of a solid electrolyte, due to a very low electronic conductivity and a very high lithium ion conductivity, the passivation layer is also referred to as a solid electrolyte interphase (SEI) layer.
Data Source
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AI summary
Provided is a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode, wherein a passivation layer is formed on at least one portion of a surface of the negative electrode after one cycle of charging and discharging of the lithium secondary battery, and the passivation layer includes a particulate passivation layer and a film-like passivation layer.