Disordered Rocksalt Oxyfluoride Cathodes for High-Voltage Li-Ion Batteries
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Solution Overview
Problem
Current disordered rocksalt Li2MO2F compounds used in high-performance batteries operate at low voltages and have limited search space due to the requirement for metal species to be in their M3+ states, restricting the development of high capacity cathode materials with multiple redox couples.
Innovation Solution
The development of lithium metal oxides with a cation-disordered rocksalt structure, incorporating transition metals like Ni, Mn, Co, Fe, and high-valent charge balancing metals like Ti, Zr, Nb, which enable high voltage and energy density through both metal and oxygen redox processes, allowing for a broader range of compositions and eliminating the need for metals to be in their 3+ states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If metal species are restricted to M3+ states in Li2MO2F compounds, then the structure maintains stability, but the search space for high capacity cathode materials is significantly limited
Solution Approach 1:
The patent changes the oxidation state parameter of metal species from the conventional M3+ to include M4+ and M5+ states. This parameter change expands the search space for cathode materials while maintaining structural stability through the disordered rocksalt structure design, allowing exploration of high-capacity materials like Li2MO2F with M in higher oxidation states.
2Quantity of substance
If multiple redox couples are utilized to increase capacity, then energy density improves, but the operating voltage decreases to less than 3 volts
Solution Approach 1:
The patent creates composite cathode materials with multi-element compositions (e.g., Li2MO2F where M can be V, Cr, Mo, W in various oxidation states). This composite approach allows simultaneous utilization of multiple redox couples for high capacity while the specific composition design maintains higher operating voltages above 3 volts, resolving the trade-off between capacity and voltage.
3Speed
If high lithium content with Li:M=2:1 ratio is used to enable facile lithium diffusion, then ionic conductivity improves, but the voltage decreases to less than 2.8 V
Solution Approach 1:
The patent applies local quality by creating a disordered rocksalt structure where lithium atoms are strategically positioned in a percolating network for fast diffusion, while metal species in higher oxidation states (M4+, M5+) are localized at specific sites to maintain high voltage. This local differentiation allows simultaneous achievement of fast lithium diffusion and high operating voltage.
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
This approach results in lithium metal oxyfluorides that deliver high capacity and energy density above 300 mAh/g and 1000 Wh/kg, with average voltages exceeding 3 volts, significantly improving upon previous compounds by leveraging both metal and oxygen redox capabilities.
Implementation Method 1
metal species have been sought from either V3+ or Cr3+, and possibly to include Mo3+ or W3+, whose multiple redox couples (e.g., V3+/V4+ N5+, Cr3+/Cr4+/Cr5+, Mo3+/Mo4+/Mo5+) can compensate for all the charge capacity necessary to extract lithium ions
Implementation Method 2
Rechargeable lithium-ion, Li-ion, batteries consist of a negative electrode and a positive electrode between which lithium ions move during discharge and recharge
Data Source
AI summary
A lithium metal oxide suitable for use as a cathode material in a rechargeable battery having a general formula of: LixMzM′zOuFy, where x is 1.80<x<2.20, y=1, and more specifically 1.90<x<2.10, with 1.80<u<2.20. Preferably, 1.90<u<2.10, and 0.80<y<1.20, or more specifically, 0.90<y<1.10. The lithium metal oxide has a cation-disordered rocksalt structure, wherein M is a transition metal selected from a first group consisting of Ni, Mn, Co, Fe, and combinations thereof. M′ is a transition metal selected from a second group consisting of Ti, Zr, Nb, Mo, Sn, Hf, Te, Sb, and combinations thereof. M has a first oxidation state q and M′ has a second oxidation state q′, with (q/z)+(q′/z′)=+3, preferably +2.7≤q/z)+(q′/z′)≤+3.3.