Graphite Anode Protective Film for Fast-Charging Secondary Batteries
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Solution Overview
Problem
Existing lithium-ion batteries face challenges with poor fast charging performance due to metallic lithium precipitation on the negative electrode surface, leading to decreased reversible capacity, high internal polarization, and shortened cycle life.
Innovation Solution
A secondary battery design featuring a negative electrode with a protective film, controlled particle size distribution, and optimized thickness ratios of the negative electrode active material layer and protective film, combined with a specific organic electrolyte composition, enhances fast charging capability and cycle life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-rate charging is performed on a lithium-ion battery with graphite negative electrode, then charging speed is improved, but metallic lithium precipitation occurs on the negative electrode surface causing decreased reversible capacity and shortened cycle life
Solution Approach 1:
A protective film is pre-formed on the surface of the negative electrode active material layer before high-rate charging operations. This protective film, with controlled thickness (0.05-0.5 μm) and composition (fluorinated polymer with 1-20 wt% fluorine), is prepared in advance to prevent metallic lithium precipitation during subsequent fast charging, thereby resolving the contradiction between charging speed and cycle life
Solution Approach 2:
The protective film acts as an intermediary layer between the negative electrode active material and the electrolyte. This intermediate layer prevents direct contact that would lead to lithium precipitation, while still allowing lithium ion transport. The film's specific composition (fluorinated polymer with controlled fluorine content) and thickness enable it to mediate the interaction, permitting fast charging without sacrificing cycle life
2Quantity of substance
If graphite is used as negative electrode material for high theoretical capacity, then energy density is improved, but fast charging performance deteriorates due to lithium precipitation and high internal polarization
Solution Approach 1:
The protective film is applied locally on the surface of the negative electrode active material layer, creating a region with different properties (fluorinated polymer composition, controlled porosity of 30-50%, and specific thickness) than the bulk electrode material. This local modification enables fast charging capability at the electrode surface while maintaining the high capacity graphite material in the bulk, thus resolving the contradiction between energy density and fast charging performance
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 high-rate charging and discharging performance while maintaining high energy density and extended cycle life through the formation of a resistant protective film that prevents electrolyte decomposition and lithium ion co-intercalation.
Implementation Method 1
a surface of the negative electrode active material layer is provided with a protective film
Implementation Method 2
the battery achieves high-rate charging and discharging performance while maintaining high energy density and extended cycle life through the formation of a resistant protective film that prevents electrolyte decomposition
Data Source
Figure 1
AI summary
A secondary battery and an electric device. The secondary battery includes a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active substance, and a surface of the negative electrode active material layer is provided with a protective film. The negative electrode plate satisfies: 0.05<Dv50/A<0.25, 300≤A/B≤5000, and a<Dv50<25, wherein Dv50 is the corresponding particle size when the cumulative volume percentage of the negative electrode active substance reaches 50%, with the unit thereof being µm; A is the thickness of the negative electrode active material layer, with the unit thereof being µm; and B is the thickness of the protective film, with the unit thereof being µm. The secondary battery has the characteristic of excellent dynamic performance, and can take into account the characteristics of a long cycle life and a high energy density simultaneously, thereby solving the problem of relatively poor fast charging performance of the battery on the premise of a high energy density.