Coated Cathode Active Material for Battery Cells
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Solution Overview
Problem
Conventional lithium-ion battery cells experience capacity fade and increased internal resistance due to reactions between the cathode active material and electrolyte at high voltages, leading to reduced service life and capacity loss.
Innovation Solution
A cathode active material coated with a thin, uniform layer of lithium ion-conducting solid electrolyte, such as LiTiCoO4 or lithium phosphorus oxynitride, is used to prevent direct contact between the active material and electrolyte, allowing lithium ions to pass through while blocking transition metal ions, thereby maintaining stable capacity and internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional liquid electrolyte is used in lithium-ion battery cells, then lithium ion transport between electrodes is enabled, but reactions occur between the cathode active material and electrolyte at high voltages leading to capacity fade and increased internal resistance
Solution Approach 1:
A protective layer made of lithium ion-conducting solid electrolyte material is introduced as an intermediary between the cathode active material and the liquid electrolyte. This protective layer physically separates the two components, preventing direct harmful reactions while allowing lithium ions to pass through via ionic conduction. The solid electrolyte coating acts as a barrier that blocks the oxidation of liquid electrolyte and dissolution of transition metal ions, thereby resolving the contradiction between enabling lithium ion transport and preventing harmful reactions.
Solution Approach 2:
The protective layer is applied as a thin film coating on the surface of the cathode active material particles. This thin film structure provides effective protection against harmful reactions while minimizing the additional resistance introduced by the coating. The thin film approach ensures that lithium ions can efficiently transport through the protective layer without significant impedance, thus maintaining good electrochemical performance while extending service life.
2Reliability
If the cathode active material is coated with a protective layer of lithium ion-conducting solid electrolyte, then harmful reactions are prevented and service life is extended, but the coating adds resistance to lithium ion transport
Solution Approach 1:
The protective layer is designed as an ultrathin film with controlled thickness to minimize the resistance added by the coating. By keeping the film thickness minimal while maintaining continuous coverage, the coating provides sufficient protection against harmful reactions without creating significant barriers to lithium ion transport. This thin film approach optimizes the balance between protection and ionic conductivity.
Solution Approach 2:
The protective layer is engineered with optimized material composition and thickness parameters to achieve the desired balance between protection and ionic conductivity. By carefully controlling the thickness and selecting appropriate solid electrolyte materials with high ionic conductivity, the coating provides effective protection while introducing minimal resistance to lithium ion transport, thus minimizing energy loss.
3Use of energy by moving object
If high-energy cathode materials such as NCM electrodes are used to achieve high energy density, then the battery cell provides high energy storage capacity, but the materials are more prone to oxidation and reactions with the electrolyte at high voltages
Solution Approach 1:
The lithium ion-conducting solid electrolyte coating serves as a protective intermediary between the high-energy cathode material (such as NCM electrodes) and the liquid electrolyte. This protective layer is particularly important for high-voltage materials that are more susceptible to oxidation. The coating physically isolates the high-energy material from the liquid electrolyte, preventing harmful oxidation reactions while allowing lithium ions to pass through, thus enabling the use of high-energy materials without suffering from their inherent instability at high voltages.
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 coating significantly increases the service life of battery cells by preventing oxidation of the electrolyte and dissolution of transition metal ions, ensuring stable lithium ion intercalation and release, thus maintaining capacity and reducing internal resistance over time.
Implementation Method 1
A material that includes Al2O3 and Si3N4 is provided for the protective layer
Implementation Method 2
this may result in changes in the active material of the electrode (in particular the positive electrode) and in the electrolyte (oxidation of the electrolyte at the cathode active material)
Implementation Method 3
The positive and negative active material is characterized in particular in that it is capable of reversible intercalation and deintercalation of lithium ions
Data Source
AI summary
A cathode active material for a battery cell is described. A protective layer is at least partially applied to the cathode active material, and the protective layer is made of a lithium ion-conducting solid electrolyte layer.