Cathode Active Material ZrO2 F Coating Stability
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Solution Overview
Problem
Lithium secondary batteries face issues with stability and cycle characteristics due to the reaction between impurities on the cathode active material surface and hydrofluoric acid in the electrolyte, leading to structural collapse and gas generation, which causes swelling and deteriorates high-temperature stability.
Innovation Solution
A method of manufacturing a cathode active material by dry mixing lithium metal oxide with a precursor containing zirconium and fluorine, followed by heat-treatment to form a ZrO2 and F coating layer, which prevents contact with impurities and hydrofluoric acid, stabilizing the surface and suppressing gas generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium secondary batteries use electrolyte containing lithium salts with fluorine (such as LiBF4, LiPF6), then solubility and chemical stability are improved, but hydrofluoric acid (HF) is generated through reaction with water, which decomposes the electrode and causes structural collapse
Solution Approach 1:
A coating layer comprising ZrO2 and F is applied to the surface of the cathode active material particles. This coating layer acts as an intermediary barrier between the electrode material and the electrolyte, preventing direct contact and reaction that would generate HF, while still allowing lithium ion transport. The coating layer specifically prevents contact between impurities (Li2CO3 and LiOH) on the cathode surface and hydrofluoric acid in the electrolyte.
Solution Approach 2:
A thin film coating layer comprising ZrO2 and F is formed on the surface of the cathode active material particles. This thin film provides protective function while maintaining ion conductivity, preventing harmful reactions between the electrode and electrolyte without significantly increasing cell volume or resistance.
2Quantity of substance
If lithium carbonate (Li2CO3) impurity reacts with hydrofluoric acid (HF) in electrolyte, then solubility increases causing elution, but carbon dioxide (CO2) gas is generated leading to swelling and high temperature stability deterioration
Solution Approach 1:
The ZrO2 and F coating layer serves as a protective intermediary that prevents direct contact between Li2CO3 impurities on the cathode surface and HF in the electrolyte. By blocking this contact, the coating prevents the chemical reaction that would generate CO2 gas, thereby avoiding battery swelling and maintaining high-temperature stability.
Solution Approach 2:
The coating layer is applied in advance to the cathode active material surface before battery assembly and operation. This preliminary protective action prevents the harmful reaction between Li2CO3 and HF from occurring in the first place, rather than attempting to address gas generation after it has been produced.
3Ease of manufacture
If cathode active material surface contains impurities (Li2CO3 and LiOH), then manufacturing is simplified, but contact with hydrofluoric acid causes structural collapse and deteriorates cycle characteristics
Solution Approach 1:
Instead of requiring complete removal of surface impurities through complex additional processing steps, a ZrO2 and F coating layer is applied to create a protective barrier. This intermediary layer allows the impurities to remain on the surface while preventing their harmful interaction with HF, thus maintaining ease of manufacture while improving cycle characteristics.
Solution Approach 2:
The coating layer transforms the situation by preventing the harmful reaction between surface impurities and HF. The impurities that would normally cause structural collapse are now isolated by the coating, converting a potentially harmful configuration into a stable system where the impurities are contained without affecting long-term battery 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 ZrO2 and F coating layer enhances the stability and cycle characteristics of lithium secondary batteries by preventing structural collapse and minimizing swelling, thereby improving the battery's overall performance.
Implementation Method 1
changing a precursor containing zirconium and fluorine into ZrO2 and substituting some oxygen (O) anions with F by heat-treatment after the dry mixing
Implementation Method 2
a precursor containing zirconium and fluorine is changed into ZrO2 and substituting some oxygen (O) anions with F
Implementation Method 3
the ZrO2 film may react with the hydrofluoric acid (HF) in the electrolyte and thereby stable ZrO2·5HF·H2O may be formed
Data Source
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AI summary
Disclosed are a cathode active material and a lithium secondary battery including the same, and a method of manufacturing the cathode active material, the method including: (a) manufacturing a lithium metal oxide according to formula 1 below: Li1+zNiaMnbCo1-(a+b)O2 (1) wherein 0≤z≤0.1, 0.1≤a≤0.8, 0.1≤b≤0.8 and a+b<1; (b) dry mixing the lithium metal oxide, and a precursor including zirconium and fluorine; and (c) changing the precursor including zirconium and fluorine into ZrO2 and substituting some of oxygen (O) anions with F by heat-treatment after dry mixing of step (b), wherein the cathode active material is coated with ZrO2 and F.