Fluorine-Coated Lithium Nickel Manganese Cobalt Cathode
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Solution Overview
Problem
Lithium secondary batteries require improved rate characteristics for high-capacity and long-term use in electric vehicles, with existing cathode active materials like LiCoO2 facing safety and resource issues, and LiMn2O4 experiencing capacity reduction and degradation due to electrolyte decomposition.
Innovation Solution
A lithium nickel-manganese-cobalt cathode active material with a layered structure and a fluorine-coated surface, featuring a spinel-like phase, is developed, with a composition of at least 50 wt% Mn and Co, and a fluorine coating thickness of 2 nm to 20 µm, enhancing stability and reducing reactivity with electrolytes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiCoO2 is used as cathode active material, then cycle characteristics are excellent, but safety is low and cost is high
Solution Approach 1:
A fluorine-containing compound coating layer is introduced as an intermediary between the LiCoO2 cathode active material and the electrolyte solution. This coating layer acts as a protective barrier that prevents direct contact and harmful reactions between the cathode material and electrolyte, thereby improving safety while maintaining good cycle characteristics.
Solution Approach 2:
A thin film coating of fluorine-containing compound is applied on the surface of the cathode active material particles. This thin film forms a protective shell that is thin enough to allow lithium ion diffusion but thick enough to provide safety protection and prevent electrolyte decomposition.
2Ease of manufacture
If LiMn2O4 is used as cathode active material, then cost is reduced and resources are abundant, but capacity reduction occurs and cycle characteristics degrade at high temperature
Solution Approach 1:
A fluorine-containing compound coating layer is applied on the surface of LiMn2O4 particles to act as a protective intermediary. This coating prevents direct contact between the cathode material and electrolyte, suppressing electrolyte decomposition and manganese ion dissolution, thereby dramatically improving cycle characteristics at high temperatures while maintaining cost advantages.
Solution Approach 2:
The surface chemistry of LiMn2O4 is modified by coating with fluorine-containing compounds, which changes the surface properties to be more stable and less reactive. This parameter change in surface composition prevents the Jahn-Teller distortion and manganese dissolution that cause capacity reduction and poor cycle life.
3Reliability
If lithium nickel-manganese-cobalt composite oxide is used, then battery performance balance is improved, but rate characteristics need improvement
Solution Approach 1:
A thin film coating of fluorine-containing compound is applied on the surface of the lithium nickel-manganese-cobalt composite oxide particles. This thin film is designed to be sufficiently thin to allow rapid lithium ion diffusion (improving rate characteristics) while still providing protective functions (improving performance balance).
Solution Approach 2:
The surface properties of the composite oxide are modified by fluorine coating, which changes the surface conductivity and wettability parameters. These parameter changes facilitate faster lithium ion transport kinetics while maintaining the balanced performance characteristics of the composite material.
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 fluorine-coated lithium nickel-manganese-cobalt cathode active material improves charging/discharging characteristics, thermal safety, and rate capabilities, providing a high-capacity power source suitable for medium- and large-sized devices like electric vehicles.
Implementation Method 1
a fluorine-coated surface has a spinel-like phase
Implementation Method 2
the fluorine-coated surface has a spinel-like phase
Data Source
Figure 1a
Figure 1b
Figure 2a
AI summary
The present disclosure relates to a cathode active material for a lithium secondary battery with improved rate characteristics in which a spinel surface structure is formed by fluorine coating on a surface of layered lithium nickel-manganese-cobalt cathode active material and a method for manufacturing the same, and according to the present disclosure, there is provided a lithium secondary battery with improved rate characteristics that may be charged to a capacity close to a full charge in a short time when compared to a related art and thus is suitable for high capacity of a secondary battery.