LiCoO2 Cathode Surface Doping for Nail Penetration Safety
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Solution Overview
Problem
Lithium cobalt oxide (LiCoO2) in lithium-ion secondary batteries experiences low thermal stability, leading to thermal runaway and safety concerns during nail penetration tests due to oxygen release and reaction with the electrolyte, which can cause ignition.
Innovation Solution
A battery design with a positive electrode active material having a first region closer to the surface containing lithium, cobalt, and magnesium or nickel, and a second region deeper in the material with lithium and cobalt, where the first region has a thickness of 1-20 nm and a magnesium concentration of 0-10 atomic %, and is coated with fluorine to inhibit oxygen release and enhance thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium cobalt oxide with layered rock-salt crystal structure is used to achieve high capacity, then the battery capacity is improved, but the thermal stability deteriorates and thermal runaway occurs during nail penetration tests
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the surface region (shell) has different composition and properties from the interior (core). The surface contains magnesium or nickel at 0-10 atomic % concentration to suppress oxygen release, while the interior maintains high lithium cobalt oxide content for capacity. This local differentiation resolves the contradiction by protecting the high-capacity material thermally without sacrificing capacity.
Solution Approach 2:
The patent uses composite materials by combining lithium cobalt oxide with magnesium or nickel to form a composite positive electrode active material. The composite structure integrates the high capacity of LiCoO2 with the thermal stability of Mg/Ni-containing phases, achieving both high capacity and improved thermal stability simultaneously.
2Reliability
If a protective layer is disposed between positive electrode composite layer and current collector to suppress temperature increase, then thermal stability is improved, but the device structure becomes more complex
Solution Approach 1:
The patent merges the protective layer function directly into the positive electrode active material itself by forming a core-shell structure where the shell region contains magnesium or nickel for thermal protection. This integration eliminates the need for separate protective layers between the active material and current collector, reducing structural complexity while maintaining thermal stability.
Solution Approach 2:
The patent extracts the protective function from a separate layer and incorporates it into the active material composition itself. By including magnesium or nickel within the active material structure, the protective functionality is embedded directly in the electrode material, simplifying the overall device structure.
3Quantity of substance
If lithium ions are extracted to enable high capacity in lithium cobalt oxide, then battery capacity is improved, but crystal structure collapses and thermal runaway occurs
Solution Approach 1:
The patent applies preliminary action by pre-forming a magnesium or nickel-containing surface region in the positive electrode active material before battery operation. This pre-established protective shell prevents crystal structure collapse during subsequent lithium ion extraction cycles, enabling high capacity operation without structural degradation or thermal runaway.
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 battery exhibits reduced temperature increase and prevents ignition during nail penetration tests, maintaining safety and capacity while inhibiting thermal runaway by controlling oxygen release and stabilizing the crystal structure.
Implementation Method 1
fluorine is adsorbed onto the surface of the positive electrode active material
Implementation Method 2
the first region contains lithium, cobalt, magnesium, and oxygen; the first region contains lithium, cobalt, magnesium, nickel, and oxygen
Implementation Method 3
lithium ions can move two-dimensionally between layers composed of CoO6 octahedrons
Implementation Method 4
a phase change from the hexagonal phase to the monoclinic phase occurs in lithium cobalt oxide when lithium ions are extracted
Data Source
AI summary
To provide a high-safety battery. The battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte solution. The positive electrode active material includes a first region and a second region. The first region contains cobalt, magnesium, fluorine, and oxygen. The second region contains cobalt and oxygen. The first region is closer to a surface of the positive electrode active material than the second region is. The negative electrode active material contains graphite. The electrolyte solution contains a mixed organic solvent. When the battery in a fully charged state undergoes a nail penetration test in which the nail diameter is 3 mm and the nail penetration speed is 5 mm/sec, the voltage of the battery decreases from a first voltage Vb to a second voltage Vc and then exceeds the second voltage Vc.