Lithium-Ion Cathode Electrolyte Additives for Voltage Drop Suppression
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Solution Overview
Problem
Lithium-ion batteries face issues with high-temperature stability, cycle characteristics, and abnormal voltage drops due to the elution of transition metals from the positive electrode, leading to capacity degradation and structural instability, especially when using high-Ni content positive electrode active materials.
Innovation Solution
A lithium secondary battery design incorporating a positive electrode active material represented by LiaNixCoyM1zM2wO2 and a non-aqueous electrolyte solution with specific additives, such as an imidazole-based compound and lithium difluorophosphate, to form a stable ion conductive film on the electrode surface, preventing metal elution and side reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-Ni content positive electrode active material is used to increase capacity, then battery capacity is improved, but transition metal elution and structural collapse occur leading to capacity degradation and voltage drop
Solution Approach 1:
A protective film comprising a first region and a second region is formed as an intermediary layer between the positive electrode and electrolyte solution. The first region contains a metal element from the positive electrode material, while the second region contains a metal element from the additive, creating a barrier that prevents direct contact and reduces transition metal elution into the electrolyte solution.
Solution Approach 2:
The protective film is constructed as a composite material with two distinct regions: a first region containing metal elements from the positive electrode active material and a second region containing metal elements from the additive. This composite structure provides both adhesion to the electrode and effective barrier properties against metal elution.
2Quantity of substance
If high-Ni content positive electrode active material is used, then battery capacity is improved, but structural stability deteriorates due to crystal structure deformation and collapse
Solution Approach 1:
The protective film is formed beforehand on the surface of the positive electrode active material to provide cushioning protection. This pre-formed barrier prevents direct exposure of the high-Ni content material to the electrolyte solution and harsh conditions, thereby preventing crystal structure deformation and collapse during battery operation.
3Ease of manufacture
If conventional electrolyte solution is used, then manufacturing simplicity is maintained, but Lewis acid generation erodes passivation film causing metal elution
Solution Approach 1:
The invention converts the harmful effect of Lewis acid generation into a benefit by using the additive that reacts with Lewis acids to form a protective film. The same chemical reactions that were previously harmful (Lewis acid generation from electrolyte decomposition) are now utilized to create the protective barrier, turning the harmful process into a useful film-forming mechanism.
4Device complexity
If no protective film is formed, then manufacturing process is simple, but transition metal elution occurs leading to voltage drop and abnormal phenomena
Solution Approach 1:
The protective film is formed preliminarily during the battery manufacturing process or initial charging cycles, before the battery enters service. This preliminary action ensures that the protective barrier is already in place to prevent transition metal elution and maintain voltage stability throughout the battery's operational life.
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 enhances high-temperature stability, cycle performance, and prevents abnormal voltage drops by forming a robust film that scavenges Lewis acids, thereby improving the overall durability and capacity retention of the battery.
Implementation Method 1
two additives capable of forming a stable ion conductive film on the electrode surface
Implementation Method 2
form a stable film on the surface of an electrode, together with a positive electrode comprising a positive electrode active material of a specific constituent
Implementation Method 3
an electrolyte solution which is a medium for transferring lithium ions
Implementation Method 4
The positive electrode stores energy through a redox reaction of transition metal
Data Source
AI summary
The present disclosure relates to a lithium secondary battery in which an abnormal voltage drop phenomenon is improved. The lithium secondary battery comprises a negative electrode comprising a negative electrode active material, a positive electrode comprising a positive electrode active material represented by Formula 1, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution comprises a lithium salt, a non-aqueous organic solvent, a compound represented by Formula 2 as a first additive, and lithium difluorophosphate as a second additive:LiaNixCOyM1zM2wO2 [Formula 1]wherein all the variables are described herein.