Nitrogen-Substituted Lithium Oxinitride Electrodes
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Solution Overview
Problem
Lithium battery electrode materials like Li2FeSiO4 have low gravimetric capacity and cycling instability due to lattice collapse when voltage exceeds 4V, and existing polyanionic materials require conductive carbon coatings, reducing packing density and energy density.
Innovation Solution
Development of lithium salts with nitrogen-substituted polyanionic frameworks, such as Li2SO4, Li3PO4, and Li4SiO4, which allow reversible lithium extraction and maintain thermal stability, enabling high electronic conductivity without the need for carbon coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the voltage cut-off upper limit is brought to 4.5 V to increase capacity, then the gravimetric capacity is improved, but the cycling stability deteriorates due to lattice collapse and Fe(IV) instability
Solution Approach 1:
The patent changes the chemical composition parameters by introducing nitrogen substitution (x value) and lithium deficiency (q value) to modify the electronic structure and stabilize the lattice at high voltages, enabling stable operation at 4.5V cutoff
Solution Approach 2:
The invention creates a composite material system combining transition metal (Fe, Mn, Co, Ni), nitrogen, and oxygen in a polyanionic framework, where the multifunctional components work together to provide both high capacity and stability
2Stability of the object's composition
If strictly oxides are used to maintain thermal stability, then the thermal stability is improved, but the electronic conductivity deteriorates requiring carbon coatings
Solution Approach 1:
The patent changes the chemical composition by introducing nitrogen substitution (x parameter) which modifies the electronic structure through orbital overlap, dramatically increasing electronic conductivity while preserving the oxide framework's thermal stability
Solution Approach 2:
The invention introduces nitrogen at specific lattice positions (substituting oxygen in the polyanionic framework) to create localized regions of high electronic conductivity without compromising the overall thermal stability of the oxide structure
3Reliability
If carbon coatings are applied to improve electronic conductivity, then the electronic conductivity is improved, but the packing density and energy density deteriorate
Solution Approach 1:
The patent makes the electrode material self-sufficient by incorporating nitrogen substitution that provides intrinsic electronic conductivity, eliminating the need for external carbon coatings and thereby maximizing packing density and energy density
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
These materials achieve large reversible capacities and higher electronic conductivity, enhancing electrochemical performance and energy density while maintaining thermal stability at elevated temperatures.
Implementation Method 1
The result is a much higher electronic conductivity, and the materials do not need, for electrochemical operation, the coating by a conductive material like carbon
Implementation Method 2
The metastability of these materials, as obtained, allows reversible extraction of lithium corresponding to the transition metals going from +II to +III to +IV
Data Source
AI summary
The present invention relates to lithium salts of formula Li2SO4, Li3PO4 and Li4SiO4 in which a fraction of the oxygen from the polyanionic framework is replaced by nitrogen, and which are also associated with a transition metal, its use as electrode materials and a electrochemical generator comprising said lithium salts as material of the positive electrode.