High-Ni NCM Cathode Coating for Thermal Stability at High Voltage
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Solution Overview
Problem
High-Ni NCM-based lithium composite transition metal oxides face challenges with thermal stability and capacity retention due to rapid oxygen deintercalation, leading to structural instability and performance deterioration, especially at high voltages.
Innovation Solution
A method involving the preparation of a high-Ni NCM-based positive electrode active material with a fluorine and boron coating, achieved through dry mixing and heat treatment of lithium composite transition metal oxides with MgF2 and H3BO3, to enhance surface stability and electrochemical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the nickel content in NCM-based lithium composite transition metal oxide is increased to 60 mol% or more, then the capacity is improved, but the thermal stability deteriorates due to rapid oxygen deintercalation and structural instability
Solution Approach 1:
A coating layer comprising fluorinated boron-containing compound is introduced as an intermediary between the high-Ni NCM-based lithium composite transition metal oxide and the external environment. This coating layer mediates the interaction by suppressing oxygen deintercalation and preventing direct contact between the electrolyte and the unstable high-Ni material surface, thereby resolving the contradiction between high capacity and thermal stability
Solution Approach 2:
The invention creates a composite structure by combining high-Ni NCM-based lithium composite transition metal oxide with a fluorinated boron-containing compound coating layer. This composite material approach allows the core high-Ni material to provide high capacity while the coating layer provides thermal stability and structural protection, effectively resolving the contradiction between capacity and reliability
2Reliability
If a coating technique is applied to suppress oxygen deintercalation and improve thermal stability, then the stability is improved, but the capacity and output properties deteriorate due to coating material resistance
Solution Approach 1:
The invention optimizes the coating parameters by controlling the thickness, composition ratio, and fluorine content of the boron-containing compound coating layer. By adjusting these parameters, the coating provides sufficient thermal stability while maintaining adequate lithium ion and electron transport, thus resolving the contradiction between stability and capacity
Solution Approach 2:
The coating layer is applied selectively on the surface of the high-Ni NCM-based lithium composite transition metal oxide particles, providing localized protection where oxygen deintercalation and electrolyte contact occur most frequently. This localized quality enhancement maintains the bulk material's high capacity properties while providing surface-level thermal stability
3Quantity of substance
If the charge depth is increased to utilize the high capacity of nickel-rich material, then the capacity is improved, but the structural stability deteriorates due to lattice collapse from oxygen deintercalation
Solution Approach 1:
The fluorinated boron-containing compound coating layer is applied in advance before the high-Ni NCM-based lithium composite transition metal oxide undergoes deep charging. This preliminary protective action prevents oxygen deintercalation and lattice collapse during subsequent deep charge cycles, enabling the material to achieve its full capacity potential without structural degradation
Solution Approach 2:
The coating layer acts as a cushioning barrier that absorbs and mitigates the harmful effects of oxygen deintercalation and electrolyte contact before they can cause lattice collapse. This beforehand cushioning allows the material to withstand deep charging conditions that would otherwise lead to structural failure
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 solution effectively suppresses resistance increase and output reduction, while ensuring excellent thermal stability and electrochemical performance even at high voltages of 4.3 V or higher, thereby improving the structural and chemical stability of the battery.
Implementation Method 1
subjecting the lithium composite transition metal oxide, MgF2 as a fluorine (F) coating source, and a boron (B) coating source to dry mixing and heat treatment to form a coating portion on the particle surface
Implementation Method 2
The deintercalated oxygen reacts with an electrolyte to change the intrinsic properties of a material, and has a problem of causing the instability of a lattice structure
Data Source
AI summary
A method for preparing a positive electrode active material for a secondary battery is provided. The method includes preparing a lithium composite transition metal oxide including nickel, cobalt, and manganese (Mn), wherein the content of the nickel in the total content of the transition metal is 60 mol % or greater. The lithium composite transition metal oxide, MgF2 as a fluorine (F) coating source, and a boron (B) coating source undergoes dry mixing and heat treatment to form a coating portion on the particle surface of the lithium composite transition metal oxide. In addition, a positive electrode active material prepared as described above, is also provided.