Lithium Battery Positive Electrode Coating for Thermal Safety
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Solution Overview
Problem
Lithium secondary batteries face challenges in achieving improved thermal safety and cycle-life characteristics, with existing electrodes often compromising on safety and energy density due to issues with electron conductivity and particle size of active materials.
Innovation Solution
A positive electrode design featuring a current collector with an active material layer and a coating layer containing a compound of Chemical Formula Li a Fe 1-x M x PO 4, where 0.90 ≤ a ≤ 1.8 and 0 ≤ x ≤ 0.7, with an average particle diameter of 0.2 µm to 1 µm, and an aqueous binder, which enhances thermal stability and cycle-life by optimizing the thickness ratio and using an oxidation-resistant binder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating layer with fine particles (D50 ≤ 2 μm) is formed on the active material layer, then thermal safety and cycle-life characteristics are improved, but manufacturing complexity increases
Solution Approach 1:
The positive electrode is segmented into two distinct functional layers: an active material layer for high capacity and a coating layer with fine particles (D50 ≤ 2 μm) for thermal safety. This segmentation allows each layer to perform its specific function optimally, resolving the contradiction between reliability improvement and structural complexity by creating a modular, functionally-separated structure.
Solution Approach 2:
The coating layer is formed as a composite material system combining fine particles (such as Al2O3, SiO2, TiO2, or LiFePO4) with a binder and conductive agent. This composite structure provides both thermal stability and electrical conductivity, enabling the coating layer to improve reliability without excessive complexity increase.
2Temperature
If the coating layer thickness is increased to improve thermal safety, then thermal stability improves, but electron conductivity and energy density deteriorate
Solution Approach 1:
The thickness of the coating layer is precisely controlled within the range of 1-13 μm, representing a critical parameter optimization. This parameter change allows the coating layer to provide sufficient thermal protection while maintaining adequate electron conductivity and energy density, resolving the contradiction between thermal stability and electrical performance.
Solution Approach 2:
The coating layer is applied locally on the active material layer surface rather than throughout the entire electrode structure. This local quality approach concentrates the thermal protection function where it is most needed (at the particle surfaces) while minimizing the overall impact on electron conductivity and energy density.
3Ease of manufacture
If LiFePO4 with larger particle diameter is used, then manufacturing is easier, but electron conductivity and utilization rate decrease
Solution Approach 1:
The particle diameter of LiFePO4 in the coating layer is controlled within the optimal range of 0.2-1 μm (D50). This parameter optimization balances manufacturing feasibility with electrical performance, ensuring that particles are fine enough to maintain good electron conductivity and high utilization rate while still beingprocessable using conventional manufacturing techniques.
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 proposed electrode structure significantly enhances thermal safety and cycle-life characteristics by maintaining electron conductivity and energy density, while minimizing resistance and the risk of short circuits, leading to improved battery performance.
Implementation Method 1
a compound capable of intercalating and deintercalating lithium
Implementation Method 2
The aqueous binder may be an aqueous binder having oxidation resistance
Data Source
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AI summary
The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery comprising the same, wherein the positive electrode comprises: a current collector; an active material layer formed on the current collector and comprising a compound capable of intercalating and deintercalating lithium; and a coating layer formed on the active material layer and comprising an aqueous binder and a compound of Chemical Formula 1 having an average particle diameter (D50) of 2 µm or less. [Chemical Formula 1] LiaFe1-xMxPO4 (In Chemical Formula 1, 0.90 ≤ a ≤ 1.8, 0 ≤ x ≤ 0.7, and M is Mg, Co, Ni, or a combination thereof)