Hydrated Manganese Cathode Material for Reversible Phase Transitions
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Solution Overview
Problem
Existing cathode active materials for secondary batteries, such as LiCoO2, suffer from low reversible capacity and poor life characteristics due to irreversible structural changes during charging/discharging, especially under high voltage conditions, limiting their energy density and performance in devices requiring better electrochemical properties.
Innovation Solution
A cathode active material comprising crystal water and manganese-based metal oxide with a two-dimensional and three-dimensional crystal structure, where the manganese fills octahedral and tetrahedral sites, allowing for reversible phase transitions between stable and metastable phases, enhancing capacity and life characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LiCoO2 is used as cathode active material, then high energy density is achieved, but irreversible structural changes occur during charging/discharging leading to poor life characteristics
Solution Approach 1:
The patent changes the crystal structure parameters by introducing a three-dimensional spinel phase alongside the two-dimensional layered phase. This structural parameter change allows reversible phase transitions during charging/discharging, preventing irreversible structural degradation while maintaining high energy density through the layered phase's capacity for lithium insertion/extraction.
Solution Approach 2:
The patent creates a composite cathode active material containing both two-dimensional layered structure and three-dimensional spinel phase. The layered phase (e.g., LiCoO2) provides high energy density, while the spinel phase (e.g., LiMn2O4) provides structural stability and reversible phase transition capability, together resolving the contradiction between energy density and life characteristics.
2Power
If high voltage charging/discharging is performed, then power output is improved, but structural changes become irreversible reducing capacity
Solution Approach 1:
The patent utilizes reversible phase transitions between the two-dimensional layered phase and three-dimensional spinel phase during high voltage charging/discharging. The spinel phase acts as a buffer that undergoes reversible structural changes, accommodating the stress of high voltage operation and preventing irreversible degradation of the layered phase, thus maintaining both power output and structural stability.
3Reliability
If reversible phase transitions are enabled, then capacity characteristics are improved, but crystal structure complexity increases
Solution Approach 1:
The patent segments the cathode active material into distinct two-dimensional layered phase and three-dimensional spinel phase components. Each phase performs a specific function: the layered phase handles lithium insertion/extraction for high capacity, while the spinel phase provides reversible phase transition pathways. This segmentation enables complex reversible behavior through the combination of simpler individual phases, managing overall structural complexity.
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 cathode active material exhibits excellent capacity and life characteristics by maintaining reversible phase transitions, achieving capacity close to theoretical limits and improving battery performance even under repetitive high-voltage charging/discharging.
Implementation Method 1
the first crystal phase and the second crystal phase may have a reversible phase transition relationship
Implementation Method 2
a reversible phase transition between the first crystal phase and the second crystal phase may occur depending on oxidation or reduction of manganese
Data Source
AI summary
Provided are a cathode active material, a cathode comprising same, and a secondary battery. The cathode active material contains crystal water and a manganese-based metal oxide and has a first crystal phase having a two-dimensional crystal structure and a second crystal phase having a three-dimensional crystal structure, wherein the three-dimensional crystal structure is formed by the combination of manganese in the manganese-based metal oxide and oxygen in the crystal water.