Titanium Oxynitride Cap Layer for Lithium Cobalt Oxide Cycle Stability
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Solution Overview
Problem
Lithium-ion secondary batteries face issues with charge and discharge characteristics, cycle performance, reliability, safety, and cost, particularly due to side reactions at the interfaces between the positive electrode active material and electrolyte or current collector, leading to reduced capacity and structural instability during repeated charging and discharging.
Innovation Solution
A positive electrode structure comprising a base film and a cap layer, where the base film and cap layer contain titanium oxynitride, is introduced to inhibit side reactions and maintain the crystal structure of the lithium cobalt oxide active material, enhancing cycle performance and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If charge and discharge are repeated to improve battery capacity utilization, then the crystal structure of the positive electrode active material breaks, but cycle performance deteriorates
Solution Approach 1:
A cap layer is formed on the surface of the lithium cobalt oxide particles before charge and discharge cycles begin. This cap layer, containing titanium compound and having oxygen excess, is prepared in advance to prevent crystal structure breakdown during subsequent repeated charging and discharging operations.
Solution Approach 2:
The cap layer acts as an intermediary between the lithium cobalt oxide active material and the electrolyte. It mediates the interaction by providing a protective interface that prevents direct contact and harmful reactions, while still allowing lithium ion transport, thus preventing crystal structure breakdown during cycling.
2Quantity of substance
If the positive electrode active material is improved to enhance capacity, then charge and discharge capacity increases, but side reactions occur at interfaces leading to reduced cycle performance
Solution Approach 1:
The cap layer serves as an intermediary protective layer between the lithium cobalt oxide active material and both the electrolyte and current collector. It prevents side reactions at these interfaces while maintaining good electrical contact and lithium ion transport, thereby improving cycle performance without sacrificing capacity.
Solution Approach 2:
The positive electrode uses a composite structure where lithium cobalt oxide particles are coated with a cap layer containing titanium compound. This composite material combines the high capacity properties of lithium cobalt oxide with the protective and conductive properties of the titanium-based cap layer, achieving both high capacity and improved cycle performance.
3Reliability
If a cap layer containing titanium compound with oxygen excess is formed, then side reactions are inhibited and crystal structure stability improves, but device complexity increases
Solution Approach 1:
The cap layer is formed as a thin film coating on the lithium cobalt oxide particles. This thin film approach provides the necessary protective function against side reactions and crystal structure breakdown while minimizing the added complexity and maintaining a relatively simple overall electrode structure.
Data Source
AI summary
A positive electrode for a secondary battery having excellent cycle performance is provided. The positive electrode for a secondary battery includes a positive electrode current collector layer, a base film, a positive electrode active material layer, and a cap layer; the base film contains titanium nitride; the positive electrode active material layer contains lithium cobalt oxide; and the cap layer contains titanium oxide. The use of titanium nitride for the base film can inhibit oxidation of the positive electrode current collector and diffusion of metal atoms while ensuring an adequate conductivity. The use of titanium oxide for the cap layer can inhibit a side reaction between the positive electrode active material layer and an electrolyte and collapse of a crystal structure of the electrode active material, improving the cycle performance.