Gradient-Doped Cathode Coating for Li-Ion Cycle Life and Safety
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium-ion secondary batteries face challenges with rapid capacity reduction, low energy density, and safety concerns, especially at high temperatures, due to existing doping and surface coating modifications of positive active materials.
Innovation Solution
A positive active material is developed with a doped layer of M elements (Mg, Ca, Ce, Ti, Zr, Al, Zn, B) on the surface and a coating layer of N elements (Mg, Ca, Ce, Ti, Zr, Al, B) oxide on the outer surface, where the content of M elements decreases from the surface towards the core, and N elements are present in higher concentrations in the coating layer, improving structural stability and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If doping modification and surface coating modification of the positive active material are performed to improve cycle performance and safety performance, then cycle performance and safety performance are improved to some extent, but capacity and energy density are sacrificed
Solution Approach 1:
The patent applies local quality by creating a doped layer only on the surface of the active material particles rather than throughout the bulk. The doping concentration is highest at the surface and decreases toward the core, allowing surface protection while preserving the bulk material's high capacity characteristics. This resolves the contradiction by localizing the modification to where it is most needed for safety and cycle life, without compromising overall energy density.
Solution Approach 2:
The patent employs parameter changes by precisely controlling the doping concentration gradient from surface to core, and by optimizing the thickness of the doped layer. These parameter optimizations ensure that the doped layer provides sufficient protection for cycle performance and safety while minimizing the volume fraction of doped material, thereby preserving capacity and energy density.
2Reliability
If doping modification and surface coating modification of the positive active material are performed to improve cycle performance and safety performance, then safety performance is improved to some extent, but energy density is sacrificed
Solution Approach 1:
The doped layer is applied locally on the surface where it provides maximum safety benefit by stabilizing the crystal structure and preventing oxygen release during charging. The localized surface modification achieves safety improvement without requiring bulk doping that would consume valuable energy-storing material, thus preserving energy density.
Solution Approach 2:
The patent creates a composite structure with a doped surface layer and an undoped or lightly-doped core. This composite approach allows the surface to provide safety functions while the core maintains high energy density, effectively combining the benefits of both doped and undoped regions without the drawbacks of either extreme.
3Reliability
If doping modification and surface coating modification of the positive active material are performed to improve cycle performance, then cycle performance is improved to some extent, but capacity is sacrificed
Solution Approach 1:
The doped layer is confined to the surface region where it provides cycle life improvement by stabilizing the material during repeated charge-discharge cycles. The bulk material remains largely undoped and retains its high capacity characteristics, thus achieving cycle performance improvement without significant capacity sacrifice.
Solution Approach 2:
The patent applies partial doping action by creating a doped layer of optimized thickness that provides sufficient cycle performance improvement. The doping concentration is carefully controlled to be just enough to stabilize the structure during cycling, without excessive doping that would reduce capacity. The gradient concentration profile ensures partial action at the surface with minimal impact on bulk capacity.
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 configuration enhances the capacity, energy density, cycle performance, and safety of lithium-ion secondary batteries, maintaining high rate performance while preventing side reactions and reducing volume expansion at high temperatures.
Implementation Method 1
the surface of the active material bulk particle is doped with M element to form a doped layer
Implementation Method 2
a coating layer of an oxide containing N element coated on an outer surface of the active material bulk particles
Data Source
AI summary
A positive active material comprising active material bulk particles and a coating layer of an oxide containing N element is disclosed, wherein the surface of the active material bulk particle is doped with M element to form a doped layer, and the content of the M element is 400 ppm to 3000 ppm, and the content of the M element gradually decreases from the outer surface of active material bulk particles towards the core direction; wherein the content of the N element in the coating layer is 100 ppm to 2000 ppm; wherein the average content of the N element per unit volume of the coating layer is greater than the average content of the M element per unit volume of the doped layer; wherein the M element and the N element are each independently selected from one or more of Mg, Ca, Ce, Ti, Zr, Al, Zn, and B.