Rock-Salt Cathode Composition for Higher Li-Ion Discharge Capacity
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Solution Overview
Problem
Existing positive electrode active materials for lithium ion secondary batteries, such as those disclosed in PTL 1, have insufficient capacity increasing effects, leaving room for improvement.
Innovation Solution
A positive electrode active material containing a lithium metal composite oxide with a rock salt structure belonging to the space group Fm-3m, incorporating a trace amount of element A1 (selected from Fe, Ca, Cr, Na, Al, Si, Mg, Cu, Zn, Pb, Sb, and W) in the range of 10 ppm to 1000 ppm by mass, and being cation-rich with a mole ratio of cation elements other than the trace amount of element A1 to anion elements larger than 1.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cobalt atoms are replaced with nickel atoms to increase capacity, then the capacity of lithium ion secondary battery is increased, but the structural stability and safety deteriorate due to the high reactivity of nickel
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the central part contains high-nickel content (0.6-0.8) for high capacity, while the outer shell contains low-nickel content (0.0-0.2) for structural stability. This spatial differentiation of composition allows simultaneous achievement of high capacity and structural stability that cannot be obtained with uniform composition.
Solution Approach 2:
The patent uses composite materials by combining nickel-rich lithium transition metal oxide core with nickel-poor protective shell, creating a composite structure that integrates the high capacity advantage of nickel-rich materials with the structural stability advantage of nickel-poor materials.
2Quantity of substance
If Li-rich lithium metal composite oxides are used to achieve high energy density, then the energy density is increased, but the discharge capacity and cycling stability deteriorate due to structural degradation
Solution Approach 1:
The patent applies beforehand cushioning by pre-forming a protective shell structure around the Li-rich core before electrochemical cycling begins. This shell acts as a cushion that prevents structural degradation and capacity fading during cycling, allowing the Li-rich core to maintain its high energy density advantage without suffering from typical cycling instability.
Solution Approach 2:
The patent uses a thin shell structure (containing 5-50 atom% of the metal elements) that is flexible enough to accommodate volume changes during lithium insertion/extraction while providing protective coverage. This thin flexible shell maintains electrical contact and prevents structural collapse during cycling.
3Quantity of substance
If the nickel content in lithium transition metal oxide is increased to improve capacity, then the discharge capacity is increased, but the material becomes more susceptible to structural phase transitions and oxygen release
Solution Approach 1:
The patent applies local quality by concentrating the high-nickel content (0.6-0.8) in the core region where high capacity is needed, while placing low-nickel content (0.0-0.2) material in the outer shell that is directly exposed to the electrolyte and subjected to structural stress. This spatial distribution minimizes the harmful effects of high nickel content while preserving its capacity benefits.
Solution Approach 2:
The patent introduces an intermediary shell layer composed of nickel-poor material that acts as a mediator between the high-nickel core and the external environment. This intermediary shell protects the nickel-rich core from direct exposure to electrolyte, preventing structural degradation and oxygen release while allowing lithium ion transport.
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 proposed solution achieves a significant increase in discharge capacity and energy density of secondary batteries, with a remarkable effect of improving discharge properties due to the facilitation of electron tunneling and lithium ion diffusibility.
Implementation Method 1
the facilitation of electron tunneling and lithium ion diffusibility
Implementation Method 2
the facilitation of electron tunneling and lithium ion diffusibility
Data Source
AI summary
A positive electrode active material for a secondary battery contains a lithium metal composite oxide having a crystal structure based on a rock salt structure belonging to the space group Fm-3m. The lithium metal composite oxide contains at least one element A1 selected from the group consisting of Fe, Cr, Na, Mg, Cu, Zn, Pb, Sb, and W. The content of the element A1 in the lithium metal composite oxide is 10 ppm by mass or more and 1000 ppm by mass or less with respect to the total amount of the lithium metal composite oxide.