Positive Electrode Coating Structure for High-Voltage Cycling Stability
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Solution Overview
Problem
Lithium cobalt oxide materials used in lithium-ion batteries suffer from rapid cycling degradation at high voltages due to irreversible phase transitions and interface side reactions, leading to poor cycling stability and capacity retention.
Innovation Solution
A positive electrode material with a P63mc matrix and an R-3m coating structure is developed, where the coating material undergoes a spinel phase transition to form a stable spinel phase transition layer, inhibiting transition metal dissolution and enhancing high-voltage cycling stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the charge voltage of lithium cobalt oxide is increased to extract more lithium ions, then the energy density is improved, but the cycling stability deteriorates due to rapid cycling degradation at high voltage
Solution Approach 1:
A coating layer comprising lithium cobalt oxide with R-3m structure is introduced as an intermediary between the P63mc matrix and the electrolyte. This coating layer mediates the interaction at the interface, preventing direct contact between the matrix and electrolyte that would cause degradation, while still allowing lithium ion transport. The coating layer thus enables high voltage operation (improving energy density) without suffering from the associated cycling degradation (maintaining reliability).
Solution Approach 2:
The invention changes the crystal structure parameter of the surface layer from P63mc to R-3m through controlled synthesis conditions (lower temperature treatment). This parameter change in the coating layer's crystal structure provides enhanced stability at high voltage compared to the P63mc structure, allowing the material to operate at higher charge voltages while maintaining cycling stability.
2Quantity of substance
If lithium cobalt oxide operates at high voltage, then more lithium ions can be extracted for higher capacity, but irreversible phase transitions occur causing rapid cycling degradation
Solution Approach 1:
The invention applies local quality by having the surface coating layer undergo spinel phase transition at high voltage while the bulk matrix maintains its P63mc structure. This localized phase transition in the coating layer protects the bulk material from irreversible transformations, enabling high lithium ion capacity extraction without compromising overall phase stability.
Solution Approach 2:
The R-3m structured coating layer acts as a protective cushion formed beforehand on the matrix surface. This pre-formed layer absorbs and mitigates the harmful effects of high voltage stress and prevents irreversible phase transitions in the bulk material, cushioning against degradation before it can occur in the main body of the material.
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 R-3m@P63mc coating structure achieves high reversible capacity and improved cycling stability at high voltages, providing effective protection for the matrix and inhibiting transition metal dissolution, thus extending the battery's service life.
Implementation Method 1
the R-3m structure of the coating material can undergo a spinel phase transition to form a stable spinel phase transition layer
Data Source
AI summary
A positive electrode material, including a matrix and a coating material located on at least a portion of a surface of the matrix. The matrix includes a first compound having a P63mc structure, and the coating material includes a second compound having an R-3m structure. The positive electrode material can have a high gram capacity and cycling stability at a high voltage.