Composite Cathode Active Material with Dual-Layer Coating for High-Voltage Stability
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Solution Overview
Problem
Lithium cobalt acid-based cathode active materials experience degradation in cycle characteristics and energy density when charge voltage is increased, due to sintering and coating layer issues, leading to particle binding and surface damage.
Innovation Solution
A composite oxide cathode active material with a coating layer containing lithium, nickel, and manganese, and a surface layer of silicon, tin, phosphorus, magnesium, boron, zinc, tungsten, aluminum, or zirconium, formed through a hydroxide coating process followed by a heating step, to enhance chemical stability and prevent sintering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the charge voltage is raised to increase energy density, then the energy density is improved, but the cycle characteristics deteriorate
Solution Approach 1:
The cathode active material is divided into two distinct layers: a core layer containing lithium cobalt acid for high energy density, and a surface layer containing lithium manganese oxide for stability. This segmentation allows each layer to perform its specialized function - the core provides high capacity while the surface protects against degradation at high voltages.
Solution Approach 2:
The invention uses a composite structure combining lithium cobalt acid (LiCoO2) and lithium manganese oxide (LiMn1-xMxO2) in a core-shell configuration. This composite material approach leverages the high energy density of lithium cobalt acid while incorporating the superior chemical stability of lithium manganese oxide at the surface, resolving the contradiction between energy density and cycle life.
2Use of energy by moving object
If the charge voltage is raised, then the energy density is improved, but sintering and coating layer issues occur leading to particle binding
Solution Approach 1:
The surface layer of lithium manganese oxide is formed on the cathode active material before the high-voltage charging process. This preliminary coating action prevents sintering and particle binding from occurring during subsequent high-voltage operation, allowing the material to withstand elevated charge voltages without structural degradation.
Solution Approach 2:
The invention changes the chemical composition parameter at the particle surface by introducing lithium manganese oxide with different stoichiometric ratios (LiMn1-xMxO2 where M is a divalent or trivalent metal). This parameter change in surface composition provides resistance against sintering and maintains particle integrity at high charge voltages.
3Reliability
If a coating layer is applied to improve cycle characteristics, then the cycle characteristics are improved, but manufacturing complexity increases
Solution Approach 1:
The invention combines the coating material (lithium manganese oxide) and the base material (lithium cobalt acid) into a single integrated core-shell structure. This merging approach eliminates the need for separate coating processes by forming both layers simultaneously through co-precipitation or solid-state reaction, thereby improving cycle characteristics without significantly increasing manufacturing complexity.
Solution Approach 2:
The surface layer of lithium manganese oxide serves a dual function: it protects the lithium cobalt acid core from degradation (improving cycle characteristics) and also provides structural stability against sintering. This self-service approach allows a single layer to perform multiple protective functions, reducing the need for additional complex coating processes.
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 improves the chemical stability and charge/discharge cycle characteristics of the cathode active material, maintaining high capacitance and energy density even at high charge voltages by preventing particle binding and surface damage.
Implementation Method 1
a coating layer which is provided in at least a part of the composite oxide particle and includes an oxide containing lithium Li and a coating element of at least one of nickel Ni and manganese Mn
Implementation Method 2
formed through a hydroxide coating process followed by a heating step
Data Source
AI summary
A cathode active material is provided. The cathode active material includes: a composite oxide particle including at least lithium and cobalt; a coating layer which is provided in at least a part of the composite oxide particle and includes an oxide including lithium and a coating element of at least one of nickel and manganese; and a surface layer which is provided in at least a part of the coating layer and includes at least one element selected from the group consisting of silicon, tin, phosphorus, magnesium, boron, zinc, tungsten, aluminum, titanium, and zirconium.