Cation-Disordered Rocksalt Cathodes for High Energy Density
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Solution Overview
Problem
Cation-disordered lithium transition metal oxides face challenges in achieving high energy density and stability due to oxygen loss, polarization, and the presence of heavy inactive metals, limiting their electrochemical performance as cathode materials in lithium-ion batteries.
Innovation Solution
Development of lithium metal oxides and oxyfluorides with a cation-disordered rocksalt structure, specifically formulated as LixM′aM″bO2-yFy, where M′ is a low-valent transition metal and M″ is a high-valent transition metal, optimized to balance lithium and transition metal capacity, and incorporating fluorine substitution to enhance structural stability and electrochemical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cation-disordered lithium transition metal oxides are used to achieve high capacity, then lithium diffusion can be facilitated through percolating networks, but oxygen loss occurs which degrades the percolation network and reduces cyclability
Solution Approach 1:
The patent extracts and removes oxygen from the lattice by operating at high voltages (>4.5V vs Li/Li+) to induce controlled oxygen loss. This intentional extraction transforms the harmful uncontrolled oxygen loss into a beneficial design feature, creating surface-enriched disordered rocksalt phases with improved electrochemical stability and sustained percolation networks for high capacity and cyclability
Solution Approach 2:
The patent applies preliminary anti-action by pre-forming surface-disordered rocksalt phases through high-voltage charging before cycling. This preliminary treatment creates a stable surface structure that prevents subsequent harmful oxygen loss and maintains the percolation network integrity throughout cycling, thereby improving cyclability while preserving high lithium diffusion capacity
2Quantity of substance
If heavy transition metals are included to increase capacity, then energy density can be improved, but the materials become less electrochemically active and more polarized
Solution Approach 1:
The patent applies local quality by creating a spatially heterogeneous structure where the surface region has disordered rocksalt phase with high electrochemical activity, while the bulk contains the heavy transition metals for high capacity. This local differentiation allows the surface to provide low polarization and high reactivity, while the bulk provides the desired energy density
Solution Approach 2:
The patent creates a composite material system consisting of surface-enriched disordered rocksalt phase combined with bulk heavy transition metal oxides. This composite structure integrates the advantages of both components: the surface phase provides low polarization and high electrochemical activity, while the bulk phase provides high capacity and energy density
3Quantity of substance
If oxygen redox is utilized to achieve high capacity, then energy density increases, but structural stability decreases due to lattice densification and oxygen loss
Solution Approach 1:
The patent performs preliminary action by conducting high-voltage charging treatment before normal cycling to pre-form the surface-disordered rocksalt phase. This preliminary structural transformation stabilizes the surface composition and prevents subsequent harmful oxygen loss and lattice densification during cycling, thereby maintaining structural stability while preserving the high capacity enabled by oxygen redox
Solution Approach 2:
The patent applies beforehand cushioning by creating a stable surface-disordered rocksalt phase that acts as a protective layer. This surface phase cushions and prevents the propagation of harmful lattice densification and oxygen loss into the bulk material during cycling, thereby protecting the overall structural stability while allowing high capacity oxygen redox reactions
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 resulting materials exhibit high discharge capacities (250-400 mAh/g) and energy densities (700-900 Wh/kg) with improved reversibility and cyclability, overcoming previous limitations of disordered rocksalt systems by maximizing transition metal capacity and minimizing oxygen redox.
Implementation Method 1
facile Li diffusion is possible in disordered structures once enough excess Li is introduced, which, in turn, introduces a percolating network of facile Li diffusion channels (0-TM channels) through which Li diffusion can be facile in the disordered structure due to weak electrostatic repulsion on the activated Li+ ion upon Li diffusion by the lack of repulsive TM ions
Implementation Method 2
oxygen oxidation, which is often necessary to achieve high capacity from disordered materials, can trigger oxygen loss via lattice densification, which degrades 0-TM percolation (and hence Li diffusion) in the disordered materials by reducing the Li-excess level
Data Source
AI summary
A disordered rocksalt lithium metal oxide and oxyfluoride as in manganese-vanadium oxides and oxyfluorides well suited for use in high capacity lithium-ion battery electrodes such as those found in lithium-ion rechargeable batteries. A lithium metal oxide or oxyfluoride example is one having a general formula: LixM′aM″bO2-yFy, with the lithium metal oxide or oxyfluoride having a cation-disordered rocksalt structure of one of (a) or (b), with (a) 1.09≤x≤1.35, 0.1≤a≤0.7, 0.1≤b≤0.7, and 0≤y≤0.7; M′ is a low valent transition metal and M″ is a high-valent transition metal; and (b) 1.1≤x≤1.33, 0.1≤a≤0.41, 0.39≤b≤0.67, and 0≤y≤0.3; M′ is Mn; and M″ is V or Mo. The oxides or oxyfluorides balance accessible Li capacity and transition metal capacity. An immediate application example is for high energy density Li-cathode battery materials, where the cathode energy is a key limiting factor to overall performance. The second structure (b) is optimized for maximal accessible Li capacity.