Cathode Particle Composition to Limit Oxygen Release in Batteries
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Solution Overview
Problem
Secondary batteries with high capacity, particularly those using lithium cobalt oxide as a positive electrode active material, face safety issues due to thermal runaway caused by excessive lithium ion extraction, leading to oxygen release and potential thermal runaway.
Innovation Solution
A positive electrode active material comprising cobalt, oxygen, magnesium, and nickel, with a median diameter between 1 μm and 12 μm, and a conductive material adhering to specific planes, inhibits oxygen release by creating a region with higher resistance and bonding strength, enhancing safety and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium cobalt oxide with layered rock-salt crystal structure is used as positive electrode active material, then high capacity is achieved through two-dimensional lithium ion diffusion, but safety deteriorates due to crystal structure collapse from excessive lithium ion extraction leading to thermal runaway
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the surface region has different composition and properties from the interior. The surface is modified with elements like fluorine, aluminum, or magnesium to form a protective layer that prevents crystal structure collapse during charging, while the interior maintains the high-capacity layered rock-salt structure. This local differentiation allows the surface to provide safety protection while the bulk material delivers high capacity.
Solution Approach 2:
The patent employs composite materials by combining lithium cobalt oxide with other elements forming a core-shell or doped structure. The composite consists of the high-capacity LiCoO2 core and a protective shell or doped regions containing elements like F, Al, or Mg. This composite structure integrates the high capacity of LiCoO2 with the structural stability and safety of the protective components, preventing thermal runaway while maintaining performance.
2Reliability
If the amount of lithium ions extracted is limited to maintain crystal structure stability, then safety is improved, but capacity deteriorates due to restricted charge voltage
Solution Approach 1:
The surface-modified or doped structure allows different regions to serve different functions: the surface/protected regions maintain structural stability at high voltages, enabling greater lithium extraction, while the bulk material provides the pathway for lithium diffusion. This local differentiation removes the need to limit overall lithium extraction, as the protective surface prevents collapse even when more lithium is extracted than would be safe in conventional materials.
Solution Approach 2:
The patent changes the chemical and structural parameters of the material surface or composition through doping or coating with specific elements. This parameter modification raises the charge voltage limit at which the material can operate safely, allowing extraction of more lithium ions without triggering thermal runaway. The modified material can sustain higher states of charge that would be dangerous in conventional LiCoO2.
3Quantity of substance
If additive elements are added to lithium cobalt oxide to increase capacity, then capacity is improved, but manufacturing precision deteriorates due to difficulty in controlling element distribution and concentration
Solution Approach 1:
The patent applies segmentation by separating the additive elements into distinct structural roles: some elements form the core LiCoO2 matrix while others form a surface shell or occupy specific crystallographic sites. This segmentation allows each element to be optimized independently and reduces the complexity of controlling overall distribution, as the synthesis process naturally separates elements into their functional zones during formation.
Solution Approach 2:
The patent uses intermediary substances or methods during synthesis to control element distribution. For example, precursor compounds or surfactants may be used as intermediaries to ensure uniform doping or coating during the formation process. These intermediaries facilitate controlled incorporation of additive elements, achieving the desired concentration and distribution without requiring extremely precise manufacturing control.
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 provides a battery with high capacity and improved safety by preventing thermal runaway through controlled lithium ion extraction and oxygen release, even under high charge voltages.
Implementation Method 1
a conductive material adhering to part of a plane other than a (001) plane of the positive electrode active material
Implementation Method 2
lithium ions can move two-dimensionally between layers composed of CoO6 octahedrons
Data Source
AI summary
A secondary battery with high capacity and a high level of safety is provided. The battery includes a positive electrode including a positive electrode active material and a conductive material. The positive electrode active material contains cobalt, oxygen, magnesium, and nickel. A median diameter of the positive electrode active material is greater than or equal to 1 μm and less than or equal to 12 μm. In EDX line analysis in a depth direction on a region of the positive electrode active material having a plane other than a (001) plane, a distribution of the magnesium partly overlaps with a distribution of the nickel. The conductive material adheres to part of the plane other than the (001) plane of the positive electrode active material.