Core-Shell LiCoO2 Cathode Material for High-Voltage Stability
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Solution Overview
Problem
Lithium cobalt oxide-based cathode materials suffer from structural instability and reduced performance at high voltages above 4.5 V, leading to rapid deterioration of lifetime characteristics and safety concerns due to reactions with electrolytes.
Innovation Solution
A lithium cobalt-doped oxide with a core-shell structure, where the core and shell contain three kinds of dopants with specific oxidation number ratios and contents, maintaining structural stability and preventing irreversible phase changes at high voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LiCoO2 is used as cathode active material to achieve high energy density, then rolling density and discharge voltage are improved, but structural stability deteriorates at high voltage above 4.5 V and lifetime characteristics rapidly deteriorate
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the core region maintains high LiCoO2 content for energy density while the shell region contains dopant elements for structural stability. This spatial differentiation allows each region to perform its specialized function - the core provides capacity while the shell provides protection against structural degradation at high voltages.
Solution Approach 2:
The patent employs composite materials by combining LiCoO2 with dopant elements (such as Al, Ti, Mg, or Zr) in a core-shell configuration. This composite structure integrates the high energy density characteristics of LiCoO2 with the structural stability of dopant-containing phases, resolving the contradiction between energy storage capability and structural integrity at elevated voltages.
2Duration of action of stationary object
If doping elements are added to LiCoO2 to improve structural stability, then lifetime characteristics are improved, but charging/discharging current amount decreases
Solution Approach 1:
By concentrating dopant elements in the shell region rather than uniformly distributing them throughout the material, the patent preserves the high conductivity and current transfer capabilities of the LiCoO2 core while providing structural stability through the doped shell. This localized doping approach minimizes the negative impact on power characteristics.
Solution Approach 2:
The patent applies partial doping by introducing dopant elements at controlled concentrations (50 ppm to 8000 ppm) specifically in the shell region. This partial action provides sufficient structural stabilization without excessive doping that would severely compromise the charging/discharging current capacity of the overall material.
3Stability of the object's composition
If coating layer is applied to surface of LiCoO2 to improve stability, then structural stability is improved, but Li ion transfer is interrupted and capacity decreases
Solution Approach 1:
The patent employs porous or nanostructured shell materials that provide structural stability while maintaining ion transport pathways. The porous architecture of the shell allows Li ions to penetrate through to the active LiCoO2 core, preventing the shell from acting as a complete barrier while still providing protective stabilization effects.
Solution Approach 2:
The patent utilizes thin film shell structures that are sufficiently thin to allow Li ion diffusion while providing the necessary structural stabilization. These thin protective layers maintain structural integrity at high voltages without creating significant resistance to ion transport, thus preserving capacity while improving stability.
4Use of energy by moving object
If operating voltage is increased to 4.3 V or more to develop high capacity batteries, then energy density is improved, but crystal structure becomes unstable and lifetime characteristics rapidly deteriorate
Solution Approach 1:
The patent creates a composite core-shell structure where the doped shell phase provides structural stability that enables the battery to operate at high voltages (4.3 V or more) without rapid degradation. This composite architecture allows the system to access higher voltage regimes for improved energy density while the stable shell prevents the crystal structure collapse that would otherwise occur.
Solution Approach 2:
The patent applies preliminary action by pre-doping the shell region with stabilizing elements before the battery enters high-voltage operation. This preliminary structural reinforcement prepares the material to withstand the stresses of high-voltage charging and discharging, preventing structural degradation and maintaining lifetime characteristics even when operating at elevated voltages for high energy density.
Data Source
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Figure 1b
AI summary
The present invention relates to a positive electrode active material for a lithium secondary battery including a lithium cobalt oxide having a core-shell structure, wherein the lithium cobalt-doped oxide of the core and the lithium cobalt-doped oxide of the shell include each independently three kinds of dopants and satisfy specific conditions, a method for producing the same, and a positive electrode and a secondary battery containing the positive electrode active material.