Cathode Active Material Coating for Battery Safety
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Solution Overview
Problem
Lithium secondary batteries with high potential cathode active materials are prone to internal shorts, leading to sudden heat generation, fire, or explosion due to rapid electron and lithium ion flow, and decomposition at high temperatures, exacerbated by side reactions with electrolytes.
Innovation Solution
Coating the entire surface of a first lithium-containing metal composite oxide cathode active material with a second lithium-containing metal composite oxide having higher resistance and lower potential, which acts as a significant internal resistance layer during high-rate discharges, thereby slowing down lithium ion and electron intercalation and inhibiting side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a high potential cathode active material is used to achieve high energy density, then the battery capacity increases, but the risk of internal short and heat generation increases
Solution Approach 1:
A coating layer comprising a lithium-containing metal composite oxide with lower potential and higher resistance is applied on the surface of the high-potential cathode active material particles. This coating layer acts as an intermediary that reduces the direct contact between the high-potential material and the electrolyte, thereby lowering the risk of internal short and heat generation while maintaining the high energy density benefits
Solution Approach 2:
The invention changes the surface properties of the cathode active material by coating it with a material having different electrochemical parameters (lower potential and higher resistance). This parameter change at the surface level allows the bulk material to maintain high energy density while the surface provides safety through reduced reactivity and lower potential
2Temperature
If the cathode active material is exposed at high temperature, then the battery operates at higher temperature, but the cathode active material decomposes and generates oxygen causing fire or explosion
Solution Approach 1:
The coating layer serves as a protective intermediary between the cathode active material and the external environment, particularly at high temperatures. It prevents direct exposure of the cathode material to oxygen and reduces the likelihood of decomposition reactions that would generate oxygen and cause fire or explosion
Solution Approach 2:
The invention converts the potential harm of high-temperature decomposition into a benefit by using a coating material that is thermally stable and prevents decomposition. The coating layer itself acts as a thermal barrier that protects the underlying cathode material from reaching decomposition temperatures
3Ease of operation
If side reactions occur between cathode active material and nonaqueous electrolyte, then the battery functions, but exothermic reactions may cause explosion
Solution Approach 1:
The coating layer acts as an intermediary barrier that prevents direct contact and side reactions between the cathode active material and the nonaqueous electrolyte. This eliminates the exothermic side reactions that could lead to explosion while still allowing the battery to function through the controlled electrochemical reactions of the coating material itself
4Productivity
If internal short occurs with high potential cathode material, then large amount of electrons and lithium ions flow rapidly, but heat generation occurs causing safety issues
Solution Approach 1:
The coating layer changes the electrical parameters at the surface of the cathode material by introducing higher resistance. This resistance limitation prevents the rapid flow of electrons and lithium ions that occurs during internal short, thereby controlling the heat generation and preventing safety issues while still allowing normal battery operation
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
This approach enhances battery safety by preventing heat generation during over-current events, increasing the decomposition temperature of the cathode active material, and improving thermal stability while maintaining high energy density and cycle life performance.
Implementation Method 1
the second lithium-containing metal composite oxide having a higher resistance and a lower potential vs. lithium potential
Implementation Method 2
when lithium ions are intercalated and deintercalated at the cathode and the anode, oxidation/reduction reactions generate electrical energy
Implementation Method 3
prevent heat generation caused by the temporary occurrence of over-current
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
Disclosed are a cathode active material and a secondary battery including the same. Herein, the cathode active material includes (a) a first lithium-containing metal composite oxide and (b) a second lithium-containing metal composite oxide coated on an entire particle surface of the first lithium-containing metal composite oxide, the second lithium-containing metal composite oxide having a higher resistance and a lower potential vs. lithium potential (Li/Li"1) than the first lithium-containing metal composite oxide. In the disclosed cathode active material, an entire surface of a first lithium-containing metal composite oxide is coated with a second lithium-containing metal composite oxide having a high resistance value and a low potential vs. lithium potential. Therefore, during an internal short of a secondary battery, it is possible to slow down the moving rate of a large amount of lithium ions and electrons from an anode to a cathode, and thus to prevent heat generation caused by the occurrence of temporary over-current. Also, it is possible to increase the temperature where a cathode active material is decomposed and gas is generated, and to improve thermal stability by inhibiting side reactions of the cathode active material and electrolyte.