LCO Cathode Powder Composition for Capacity and Cycle Life Balance
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Solution Overview
Problem
Lithium cobalt-based oxide (LCO) cathode active material powders for lithium-ion secondary batteries face challenges in achieving high first discharge capacity and low capacity fading rate, with existing materials showing suboptimal performance in terms of cycle life and discharge capacity.
Innovation Solution
A lithium cobalt-based oxide cathode active material powder with a specific range of LiNaSO4 content (0.4wt.% to 1.1wt.%) and S/Na atomic ratio (0.80 to 1.20) is developed, incorporating a primary phase of Li, Co, and O, and a secondary phase of LiNaSO4, optimized through sintering and milling processes to enhance electrochemical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the content of LiNaSO4 secondary phase is increased to improve capacity fading rate, then cycle life is improved, but first discharge capacity decreases
Solution Approach 1:
The patent optimizes the content of LiNaSO4 secondary phase within a specific range (0.5-5 wt%) to achieve the best balance between cycle life and first discharge capacity. This parameter optimization resolves the contradiction by identifying the optimal concentration that simultaneously improves reliability while maintaining adequate quantity of active material.
Solution Approach 2:
The patent creates a composite cathode active material consisting of a core phase (LiCoO2 or LiNi0.8Co0.1Mn0.1O2) and a secondary phase (LiNaSO4). This composite structure allows the secondary phase to improve cycle life through surface protection and structural stabilization, while the core phase maintains high discharge capacity, thus resolving the contradiction between reliability and quantity.
2Stability of the object's composition
If the content of LiNaSO4 secondary phase is increased to stabilize particle structure, then capacity fading rate is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent combines the formation of LiNaSO4 secondary phase with the main sintering process by adding sodium sulfate precursor to the cathode material mixture before sintering. This merging of steps allows the secondary phase to form in-situ during the standard manufacturing process, stabilizing particle structure while avoiding additional complex manufacturing steps.
Solution Approach 2:
The patent incorporates sodium sulfate precursor into the cathode material mixture before sintering, so that the LiNaSO4 secondary phase forms in-situ during the sintering process. This preliminary action ensures proper phase formation and distribution without requiring separate coating or treatment steps, thus maintaining manufacturing simplicity while achieving structure stability.
3Quantity of substance
If washing process is applied to remove excess LiNaSO4, then first discharge capacity is improved, but cycle life deteriorates
Solution Approach 1:
The patent optimizes the content of LiNaSO4 secondary phase within a specific range (0.5-5 wt%) that provides sufficient surface protection for good cycle life while avoiding excessive amounts that would reduce discharge capacity. This parameter optimization resolves the contradiction by identifying the optimal concentration that balances both requirements without needing washing.
Solution Approach 2:
The patent converts the potentially harmful effect of excess LiNaSO4 (which would reduce discharge capacity if washed away) into a beneficial surface coating that protects the cathode material. By controlling the content within the optimal range, the LiNaSO4 phase that would otherwise be considered excess or harmful becomes a protective layer that improves cycle life while maintaining adequate discharge capacity.
Data Source
Figure 1.1~1.2
Figure 2.1~2.2
Figure 3~4
AI summary
A lithium cobalt-based oxide cathode active material powder having: - a primary phase comprising Li, Co, and O, and - a secondary phase comprising LiNaSO4, wherein the content of said LiNaSO4 secondary phase in said powder is of at least 0.4wt.% and inferior or equal to 1.1wt.% with respect to a total weight of the cathode active material powder, said cathode active material powder being characterized in that it has a S/Na atomic ratio superior or equal to 0.80 and inferior or equal to 1.20.