Aluminum-Doped Lithium Cobalt Oxide Cathode for High-Voltage Stability
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Solution Overview
Problem
Lithium cobalt oxide (LiCoO2) used in lithium secondary batteries undergoes irreversible phase transitions at high voltages, leading to cobalt dissolution, oxygen formation, and cell swelling, which deteriorates high-temperature lifespan and storage characteristics.
Innovation Solution
Doping lithium cobalt oxide with aluminum (4,000 ppm to 6,500 ppm) to control phase transitions, incorporating large and small particle sizes, and specific heat treatment processes to stabilize the material at high voltages, resulting in a lithium cobalt-based oxide with improved phase stability and charge-discharge efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lithium cobalt oxide is used at high voltages to achieve high energy density, then energy density is improved, but phase transition occurs causing cobalt dissolution and oxygen formation which deteriorates battery lifespan and storage characteristics
Solution Approach 1:
The patent applies parameter changes by precisely controlling the aluminum content (4,000-6,500 ppm) and lithium excess ratio (1.03-1.05) to modify the crystal structure stability of lithium cobalt oxide, preventing phase transition at high voltages while maintaining high energy density
Solution Approach 2:
The patent creates a composite material system by doping aluminum into lithium cobalt oxide and controlling particle size distribution (bimodal distribution with 3-5 μm and 7-10 μm particles), resulting in a material that combines high voltage stability with improved lifespan characteristics
2Stress or pressure
If lithium cobalt oxide undergoes phase transition at high voltages, then high voltage operation is achieved, but irreversible structure formation causes gas generation and cell swelling
Solution Approach 1:
The patent changes the chemical composition parameters by adding aluminum at 4,000-6,500 ppm and controlling lithium excess ratio to 1.03-1.05, which stabilizes the layered crystal structure and prevents irreversible phase transition to spinel structure at high voltages
Solution Approach 2:
Aluminum acts as an intermediary element that stabilizes the crystal structure between the lithium layers and cobalt layers, preventing the structural collapse that would otherwise occur during high voltage charging cycles
3Power
If surface electrolytes disintegrate at high voltages, then high voltage charging is achieved, but gas is generated causing swelling of pouch-type cells
Solution Approach 1:
The patent modifies the surface chemistry parameters by controlling aluminum content (4,000-6,500 ppm) and particle size distribution, which reduces surface reactivity and prevents electrolyte decomposition at high voltages, thereby eliminating gas generation
Solution Approach 2:
The patent converts the potentially harmful high voltage operation into a beneficial process by using aluminum doping to stabilize the surface, allowing high voltage charging to proceed without the harmful side effect of electrolyte disintegration and gas generation
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 approach enhances high-temperature lifespan and continuous charging characteristics by reducing irreversible phase transitions, maintaining battery performance and capacity over multiple cycles.
Implementation Method 1
Doping lithium cobalt oxide with aluminum (4,000 ppm to 6,500 ppm) to control phase transitions
Implementation Method 2
performing a first heat treatment on the first mixture; performing a second heat treatment on the second mixture; performing a third heat treatment on the third mixture
Data Source
AI summary
Disclosed are a lithium cobalt-based oxide for a lithium secondary battery, a method of preparing the lithium cobalt-based oxide, and a lithium secondary battery including a cathode including the lithium cobalt-based oxide, wherein the lithium cobalt-based oxide includes aluminum in an amount of 4,000 ppm to 6,500 ppm based on the total weight of lithium cobalt-based oxide and includes large particles and small particles, and in a differential capacity (dQ/dV)-voltage charge-discharge graph of the lithium secondary battery, discharge peaks appearing at a voltage in a range of 4.7 V to 3 V include Peak 1 appearing at a discharge voltage of 4.6 V or more, and Peak 2 appearing at a discharge voltage of 4.55 V or less, in which Peak 2 has a greater intensity than that of Peak 1.