Nickel-Rich Cathode Composition With Surface Doping for Thermal Stability
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Solution Overview
Problem
The increase in nickel content in ternary positive electrode materials leads to decreased thermal stability, lattice oxygen evolution, internal cracks, transition metal dissolution, and poor interface stability, resulting in deteriorated cycling and storage performance.
Innovation Solution
A positive electrode material with a chemical formula LiaNixCoyMn1-x-yMbO2-cQc, doped with high-valence cations like Mo6+, Sb5+, Zr4+, Ti4+, Nb5+, W6+, Y5+, Ta5+, and anions like S2−, Se2−, Te2−, P3−, combined with a selenium-containing substance coating layer to stabilize the bulk structure and interface, inhibit side reactions, and enhance lithium ion transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If nickel content in ternary positive electrode materials is increased to improve energy density, then reversible capacity is improved, but thermal stability deteriorates
Solution Approach 1:
The patent applies local quality by implementing surface gradient doping with anions (S, Se, Te, or P) specifically at the surface region of the nickel-rich ternary positive electrode material, while the bulk maintains high nickel content (x≥0.6) for high capacity. This creates a composition gradient where the surface has different chemical properties than the interior, allowing the surface to provide stability while the bulk provides capacity.
Solution Approach 2:
The patent creates a composite structure by combining nickel-rich ternary material (LiaNixCoyMn1-x-yO2) with doped anions (S, Se, Te, or P) at the surface. This composite approach integrates the high capacity characteristics of nickel-rich materials with the stabilizing effects of anion doping, achieving both high reversible capacity and improved thermal stability.
2Quantity of substance
If nickel content is increased to improve energy density, then capacity is improved, but interface stability deteriorates due to surface residual lithium compounds
Solution Approach 1:
The patent addresses interface stability by applying local quality through surface-specific anion doping. The surface gradient doping creates a region with modified chemical composition that specifically targets interface-related issues such as residual lithium compounds and poor interface stability, while preserving the high-nickel bulk composition for energy density.
Solution Approach 2:
The patent converts the harmful effect of surface residual lithium compounds into a benefit by using anion doping to transform the surface composition. The doped anions react with or modify the residual lithium compounds, converting them from harmful surface phases into stable surface structures that improve interface stability and reduce side reactions.
3Quantity of substance
If nickel content is increased to improve energy density, then capacity is improved, but cycling performance deteriorates
Solution Approach 1:
The patent improves cycling performance by implementing local quality through surface gradient anion doping. This surface modification specifically addresses degradation mechanisms that occur during cycling, such as surface reconstruction and side reactions with electrolyte, while maintaining the high-capacity nickel-rich bulk composition.
Solution Approach 2:
The patent applies preliminary action by pre-doping the surface with anions before the material undergoes cycling degradation. This preliminary surface modification creates a stable surface structure that prevents or mitigates degradation processes during subsequent cycling, thereby improving long-term cycling performance.
4Quantity of substance
If nickel content is increased to improve energy density, then capacity is improved, but storage performance deteriorates
Solution Approach 1:
The patent improves storage performance by applying local quality through surface gradient anion doping. The modified surface composition specifically addresses storage-related degradation mechanisms such as electrolyte decomposition and surface instability during stationary storage, while preserving the high-energy-density nickel-rich bulk.
5Quantity of substance
If nickel content is increased to improve energy density, then capacity is improved, but lattice oxygen evolution increases
Solution Approach 1:
The patent suppresses lattice oxygen evolution by implementing local quality through surface gradient anion doping. The doped anions at the surface strengthen the metal-oxygen bonds and stabilize the surface structure, preventing oxygen release during high-voltage operation and delithiation, while maintaining the high-capacity nickel-rich bulk composition.
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 solution stabilizes the bulk structure and interface, reduces side reactions and transition metal dissolution, improves cycling stability and high-temperature storage performance, and accelerates lithium ion migration.
Implementation Method 1
A high-valence cation doped into a nickel-rich positive electrode material can affect the crystal growth direction of the positive electrode material and thus lead to grain refinement, eliminate harmful stresses caused by H2-H3 phase transition lattice contraction through fracture toughening
Implementation Method 2
A doped anion can replace an oxygen site, enhance a metal-oxygen bond, inhibit lattice oxygen evolution
Implementation Method 3
reduce an interaction force between a lithium layer and an oxygen layer to increase the spacing between the lithium layer and the oxygen layer, reduce the migration barrier of lithium ions, and accelerate the transmission of lithium ions
Data Source
AI summary
A positive electrode material is disclosed, represented by the formula LiaNixCoyMn1-x-yMbO2-cQc, where 0.2≤a≤1.2, x≥0.6, y>0, b>0, and c>0. M comprises a high-valence cation and Q comprises an anion. The doping of a high-valence cation and an anion in a nickel-rich ternary material stabilizes the bulk structure during lithium deintercalation, reduces side reactions, lattice oxygen release, and transition metal dissolution, and improves cycling stability, high-temperature storage, and rate capability. The outer surface of the positive electrode material may further include a selenium-containing coating layer that reacts with residual lithium compounds and binds released lattice oxygen to suppress electrolyte oxidation. A conductive coating layer may be formed on the selenium-containing layer to prevent direct contact with the electrolyte and inhibit side reactions.