LiVOPO4 Coated LiCoO2 Cathode for Thermal Stability
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Solution Overview
Problem
Lithium ion secondary batteries face issues with thermal stability and discharge energy due to the reactivity of oxygen atoms in LiCo(1-x)MxO2 and Mn3+ ion dissolution in LiMn2O4, leading to instability and reduced performance at high temperatures.
Innovation Solution
A core particle coated with LiVOPO4, which provides structural stability and high conductivity, preventing direct contact between the core particles and electrolyte, thereby suppressing oxygen release and Mn3+ elution, and enhancing discharge voltage and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LiCo(1-x)MxO2 is used as positive electrode active material, then high capacity and high discharge voltage are achieved, but thermal stability deteriorates due to oxygen atom reactivity with electrolyte
Solution Approach 1:
The invention uses a composite structure where LiCo(1-x)MxO2 core particles are coated with LiFePO4 material to form a composite active material. This composite structure allows the core to provide high capacity and voltage while the coating layer provides thermal stability by preventing oxygen release and electrolyte decomposition.
Solution Approach 2:
The LiFePO4 coating material acts as an intermediary layer between the LiCo(1-x)MxO2 core and the electrolyte. This intermediate layer suppresses direct contact between the reactive core material and electrolyte, preventing harmful reactions while allowing ionic transport.
2Use of energy by moving object
If Li(Mn(1-y)My)2O4 is used as positive electrode active material, then high theoretical capacity and high discharge voltage are achieved, but stability deteriorates due to Mn3+ ion dissolution in electrolyte at high temperature
Solution Approach 1:
The invention creates a composite active material where Li(Mn(1-y)My)2O4 core particles are coated with LiFePO4 material. The core provides high capacity and voltage while the coating prevents Mn3+ ion dissolution into the electrolyte at elevated temperatures.
Solution Approach 2:
The LiFePO4 coating serves as an intermediary barrier between the Li(Mn(1-y)My)2O4 core and the electrolyte, preventing direct interaction that would cause Mn3+ ion elution and subsequent negative electrode deterioration.
3Reliability
If LiFePO4 coating is applied to improve high-temperature stability, then thermal stability is improved, but discharge energy deteriorates due to low discharge voltage
Solution Approach 1:
The invention applies local quality by using a core-shell structure where the core material (LiCo(1-x)MxO2 or Li(Mn(1-y)My)2O4) provides high discharge energy characteristics, while the shell material (LiFePO4) provides high-temperature stability. Each material is placed where its specific properties are most needed.
Solution Approach 2:
The composite active material combines the high-energy core material with the stable coating material in a controlled ratio and structure, achieving overall performance that balances both discharge energy and thermal stability rather than sacrificing one for the other.
4Reliability
If coating material is applied to suppress oxygen release and Mn3+ elution, then crystal structure stability is improved, but conductivity deteriorates
Solution Approach 1:
The invention optimizes parameters including coating thickness (0.1-10 μm), coating ratio (5-50 wt%), and sintering conditions to achieve a balance where the coating provides sufficient protection while maintaining adequate ionic and electronic conductivity for 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 coated active material achieves high thermal stability and discharge energy, maintaining capacity and voltage stability even at elevated temperatures, ensuring reliable battery performance.
Implementation Method 1
the surface of LiCo(1-x)MxO2 having a layer-like structure which is likely to come into contact with and react with an electrolyte at a high temperature and/or the surface of Li(Mn(1-y)My)2O4 from which Mn3+ ions are likely to be eluted into the electrolyte at the high temperature is covered with the coating part containing LiVOPO4 which is excellent in structural stability at the high temperature, whereby the core particle and the electrolyte can be restrained from coming into direct contact with each other
Implementation Method 2
LiVOPO4 which is excellent in structural stability at the high temperature
Implementation Method 3
LiVOPO4 is easy to insert and release Li ions, functions as an active material, and has not only a sufficiently high theoretical capacity but also a sufficiently high discharge voltage of 3.8 to 3.9 V vs. lithium
Data Source
AI summary
An active material comprises a core particle containing LiCo(1-x)MxO2 and/or Li(Mn(1-y)My)2O4, and a coating part covering at least part of a surface of the core particle, while the coating part contains LiVOPO4. Here, M is at least one element selected from the group consisting of Al, Mg, and transition elements, 0.95≧x≧0, 0.2≧y≧0, and V in LiVOPO4 may partly be substituted by at least one element selected from the group consisting of Ti, Ni, Co, Mn, Fe, Zr, Cu, Zn, and Yb.