Sodium-Doped LiCoO2 Coating for Low-Impedance High-Voltage Cathodes
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Solution Overview
Problem
The elevated voltage in lithium-ion batteries leads to interface reactions between the positive electrode material and the electrolyte, causing phase transformation, deactivation, and increased impedance, resulting in rapid capacity decay.
Innovation Solution
A positive electrode material with a lithium cobalt composite oxide having a coating layer with distinct regions of P63mc and R-3m crystal structures doped with sodium, enhancing structural stability and lithium-ion channels, thereby reducing interface impedance and suppressing phase transformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the voltage platform of lithium-ion batteries is increased to meet high energy density requirements, then the energy density is improved, but interface reactions between the positive electrode material and the electrolyte are intensified, leading to phase transformation, deactivation, increased impedance, and capacity loss
Solution Approach 1:
A coating layer comprising Li2SiO3 and Li4SiO4 is formed on the surface of the lithium cobalt composite oxide particles. This coating layer acts as an intermediary barrier between the positive electrode material and the electrolyte, suppressing interface reactions, preventing phase transformation and deactivation, and reducing impedance increase during cycling, thereby improving cycling performance while maintaining high energy density
Solution Approach 2:
The surface composition and crystal structure of the lithium cobalt composite oxide are modified by forming a specific coating layer with controlled thickness and composition ratios. The coating layer contains Li2SiO3 and Li4SiO4 in a molar ratio of 1:9 to 9:1, which changes the surface properties to reduce reactivity with the electrolyte while maintaining structural stability at high voltage platforms
2Use of energy by moving object
If the voltage platform is elevated to achieve high energy density, then the energy density is improved, but impedance increases due to interface reactions and byproduct formation, resulting in rapid capacity decay
Solution Approach 1:
The Li2SiO3-Li4SiO4 coating layer serves as a protective intermediary that prevents direct contact between the lithium cobalt composite oxide and the electrolyte, blocking the formation of resistive byproducts and suppressing impedance-increasing side reactions, thereby maintaining low interface impedance under high voltage conditions
Solution Approach 2:
A composite coating structure comprising Li2SiO3 and Li4SiO4 is created on the particle surface. This composite material combines the benefits of both compounds to form a stable, low-impedance interface that resists electrolyte decomposition and prevents capacity decay while enabling high energy density 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
The solution improves the cycling performance and high-temperature storage performance of the electrochemical device under high voltage by stabilizing the electrode structure and reducing interface reactions.
Implementation Method 1
Element Na can be doped at lithium sites, thereby expanding lithium-ion channels and stabilizing the structure of the surface layer
Implementation Method 2
reducing interface impedance during lithium-ion intercalation and deintercalation
Implementation Method 3
suppress phase transformation and deactivation of the surface layer of the positive electrode material
Implementation Method 4
the electrolyte is oxidized on the material surface, generating byproducts that further increase impedance
Data Source
AI summary
A positive electrode material, including a lithium cobalt composite oxide, where the lithium cobalt composite oxide includes a matrix and a coating layer located on a surface of the matrix, the coating layer includes a first region and a second region, the first region has a P63mc crystal structure, the second region has an R-3m crystal structure, and both the first region and the second region contain element Na. The positive electrode material of this application can reduce interface impedance during lithium-ion intercalation and deintercalation, improving high-temperature storage performance and cycling performance of the electrochemical device under high voltage.