LiF Coated Carbon Negative Electrode for Rapid Charging
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Solution Overview
Problem
Lithium secondary batteries using carbon-based negative electrodes face challenges with rapid charging capability, safety during overcharge and high-temperature exposure, and potential short-circuit risks due to the formation of a thick solid electrolyte interface (SEI) and reactivity with lithium.
Innovation Solution
A negative electrode with a carbon-based active material layer coated with a LiF layer containing amorphous LiF (30 mol% or more) and additional components like Li2O, Li2CO3, or LiOH (3 wt% to 90 wt%), which helps in forming an appropriate SEI thickness, enhancing rapid charging and providing safety by acting as a protective and insulating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick SEI is formed on the surface of the negative electrode to improve safety and prevent short-circuits, then reliability is improved, but rapid charging capability is reduced
Solution Approach 1:
The patent changes the chemical composition parameters of the SEI layer by incorporating LiF and specific organic compounds (Li2CO3, LiOH, LiO2) in controlled ratios. This compositional parameter change allows the SEI to maintain appropriate thickness for safety while improving ion conductivity for rapid charging.
Solution Approach 2:
The patent creates a composite SEI layer combining inorganic LiF with organic compounds (Li2CO3, LiOH, LiO2). This composite structure leverages the protective properties of inorganic materials while incorporating organic components that facilitate ion transport, resolving the contradiction between safety and charging speed.
2Reliability
If a LiF layer is formed on the negative electrode to improve safety and reduce calorific value, then reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The LiF layer with specific composition is formed on the negative electrode before battery assembly and initial charging. This preliminary action ensures the protective layer is already in place, reducing manufacturing complexity during final assembly while maintaining safety improvements.
Solution Approach 2:
The patent specifies precise compositional parameters (LiF content and ratios of organic compounds) that can be controlled during deposition. By defining clear parameter ranges, the manufacturing process becomes more standardized and less complex, despite the additional functional requirements.
3Use of energy by moving object
If carbon-based compound is used as negative electrode active material to achieve low discharge voltage and good cycle life, then energy efficiency is improved, but safety at overcharge and high temperature deteriorates
Solution Approach 1:
The LiF-based protective layer acts as an intermediary between the carbon-based active material and the electrolyte. This intermediate layer prevents direct harmful interactions at high temperatures and overcharge conditions while allowing beneficial electrochemical reactions to proceed, thus improving safety without compromising energy efficiency.
Solution Approach 2:
The LiF layer with specific composition is formed in advance to prevent harmful reactions before they can occur. By establishing this protective barrier beforehand, the carbon-based material's vulnerability to thermal runaway and overcharge damage is preemptively counteracted, maintaining both energy efficiency and safety.
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 LiF layer improves rapid charging characteristics, reduces calorific values during overcharge and high-temperature exposure, and enhances safety by preventing short-circuits, thus addressing the limitations of carbon-based electrodes.
Implementation Method 1
a LiF layer which is formed on the negative electrode active material layer and comprises amorphous LiF in an amount of 30 mol% or more based on a total number of moles of LiF included in the LiF layer
Implementation Method 2
The ion tunnel may prevent the collapse of a structure of the carbon negative electrode due to the co-intercalation of the carbon negative electrode and organic solvents of the electrolyte solution
Data Source
AI summary
A negative electrode for a lithium secondary battery, in which a LiF layer comprising amorphous LiF in an amount of 30 mol% or more is formed on a negative electrode active material layer comprising a carbon-based active material, a lithium secondary battery comprising the same, and a preparation method thereof.