Li-Ion Cathode Composition Balancing Ru Reduction and Capacity
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Solution Overview
Problem
The partial replacement of Ru with Mn in Li2RuO3 for Li-ion secondary batteries reduces discharge capacity and may affect cycle life due to suppressed oxygen extraction, leading to reduced energy density and durability issues, especially at high temperatures.
Innovation Solution
Replacing part of Ru with trivalent Mn (Mn3+) in Li2RuO3 to maintain charge compensation through valence change, and optionally adding electrochemically inert transition metals like Ti to improve durability and suppress oxygen extraction, resulting in a Li-transition metal composite oxide with a layered rock salt crystal structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Ru is replaced with Mn in Li2RuO3 to reduce cost, then the amount of expensive Ru is reduced, but discharge capacity decreases and oxygen extraction is suppressed leading to reduced energy density
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Mn content parameter (x in formula (1)) to be within 0.1≤x≤0.9, with preference for 0.3≤x≤0.7. This quantitative parameter optimization resolves the contradiction by finding the optimal balance point where Ru is sufficiently reduced for cost reasons while discharge capacity and oxygen extraction suppression remain adequate for energy density requirements
Solution Approach 2:
The patent creates a composite material system with the formula (1−x)Li2RuO3—xLiMnO2, combining Ru-based and Mn-based compounds in specific proportions. This composite approach allows the material to benefit from both Ru's electrochemical properties and Mn's cost advantages, resolving the contradiction between reducing Ru quantity and maintaining discharge capacity through synergistic material composition
2Quantity of substance
If Ru is replaced with Mn to reduce cost, then material cost is reduced, but oxygen extraction is suppressed leading to reduced energy density
Solution Approach 1:
The patent uses parameter changes by optimizing the Mn content parameter (x) within specific ranges to balance cost reduction with energy density maintenance. The controlled substitution parameter ensures that oxygen extraction capability is preserved sufficiently while achieving cost reduction through Ru reduction
Solution Approach 2:
The composite material formula (1−x)Li2RuO3—xLiMnO2 creates a synergistic system where the combination of Ru and Mn compounds maintains oxygen extraction capability better than pure Mn substitution, thereby preserving energy density while still achieving cost reduction through partial Ru replacement
3Productivity
If Mn is added to replace Ru, then discharge capacity may be maintained through charge compensation, but durability at high temperatures deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Mn content parameter (x) within 0.1≤x≤0.9, preventing excessive Mn substitution that would cause high-temperature durability deterioration. This parameter optimization maintains discharge capacity through charge compensation while limiting the harmful effects on thermal stability
Solution Approach 2:
The patent strategically uses Mn (a cheaper metal) to replace part of Ru, accepting that Mn has lower high-temperature durability but compensating by limiting the substitution ratio. This controlled use of cheaper material achieves cost reduction while managing the trade-off in durability through precise compositional 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 use of trivalent Mn ensures high discharge capacity and improved durability, particularly at high temperatures, while reducing the amount of expensive Ru, and the addition of inert metals like Ti enhances crystal stability and cycle life.
Implementation Method 1
valence change of Mn (Mn3+ to Mn4+) is caused at the time of charge and discharge. This valence change can act as charge compensation similarly to the valence change of Ru
Implementation Method 2
Ru is a metal element having high electronic conductivity, and exhibits reversible anionic redox of oxygen through electron transfer. This anionic redox acts as charge compensation, and hence contributes to capacity increase as well as charge compensation due to valence change of a Ru ion (Ru4+ to Ru5+)
Implementation Method 3
In Li2RuO3, oxygen extraction is difficult to proceed owing to strong covalency between a Ru ion and an oxide ion, and therefore, oxygen extraction caused in a Li-transition metal composite oxide of Mn or the like is difficult to occur
Data Source
AI summary
The present invention relates to a positive electrode active material for a Li-ion secondary battery containing a Li-transition metal composite oxide. This Li-transition metal composite oxide has a layered rock salt crystal structure, and is represented by a formula (1): (1−x)Li2RuO3—xLiMnO2 (Mn is trivalent Mn, and x is a real number satisfying 0<x<1). In addition, when part of Ru and/or Mn of the Li-transition metal composite oxide is replaced with a metal M such as Ti, durability can be improved. According to the present invention, a reduced amount of Ru but a higher capacity can be achieved for a positive electrode active material containing Li2RuO3.