Dual-Layer ALD Cathode Coating for High-Ni NMC Stability
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Solution Overview
Problem
High nickel lithium nickel manganese cobalt oxide (high Ni NMC) materials used in lithium-ion batteries face stability issues due to transition metal dissolution and surface cracking, and existing coatings either impede performance or have low stability when reacting with the electrolyte.
Innovation Solution
A cathode comprising two layers: a conductive metal oxide first coating layer and a passivating metal oxide second coating layer, applied using atomic layer deposition (ALD), where the second layer is in contact with the first layer to enhance stability and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high nickel lithium nickel manganese cobalt oxide (high Ni NMC) materials are used to increase energy density and improve rate performance, then energy density and rate performance are improved, but stability decreases due to transition metal dissolution and surface cracking
Solution Approach 1:
The patent applies a segmented coating approach by dividing the protective coating into two distinct layers: a first coating layer (conductive metal oxide or compound) and a second coating layer (passivating metal oxide). This segmentation allows each layer to perform its specific function optimally - the first layer maintains conductivity and prevents dissolution, while the second layer provides robust stability and prevents surface cracking, thereby resolving the contradiction between high energy density and stability.
Solution Approach 2:
The patent employs composite materials by combining two different types of metal oxides in a layered structure. The first coating layer uses conductive metal oxides (such as RuO2, IrO2, OsO2, or their mixed oxides) to maintain electrical conductivity, while the second coating layer uses passivating metal oxides (such as Al2O3, TiO2, SiO2, or ZrO2) to provide stability. This composite structure enables the cathode to simultaneously achieve high energy density and improved stability.
2Reliability
If a coating is applied to protect the cathode active material surface during charging cycles, then stability is improved, but an inactive phase forms on the surface which may impede overall performance
Solution Approach 1:
The patent applies local quality by creating different functional zones through the two-layer coating structure. The first coating layer (conductive metal oxide) is positioned directly on the cathode active material surface to maintain local electrical conductivity and prevent dissolution, while the second coating layer (passivating metal oxide) is applied on top to provide localized stability and crack prevention. This spatial differentiation of functional properties ensures both protection and performance without forming a completely inactive phase.
Solution Approach 2:
The patent utilizes parameter changes by carefully controlling the thickness, composition, and properties of each coating layer. The first layer uses conductive metal oxides with specific conductivity parameters to maintain electron transport, while the second layer uses passivating metal oxides with appropriate thickness and crystalline structure to provide stability. By optimizing these parameters, the coating system achieves both stability and performance without forming impeding inactive phases.
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 dual-layer coating significantly improves the cathode's stability, prevents transition metal leaching, and maintains high electronic conductivity, leading to enhanced cycling performance and capacity retention.
Implementation Method 1
depositing a passivating metal oxide on the cathode layer to form a second coating layer by atomic layer deposition
Data Source
Figure 1a~1b
Figure 2a~2b
AI summary
The present disclosure relates to a coated cathode for a lithium ion cell comprising a first coating layer and a second coating layer, with both layers being applied by atomic layer deposition. The first coating layer provides improved conductivity, while the second coating layer provides improved stability. Methods of forming the coated cathode by sequential atomic layer deposition are also disclosed.