Low-EC Electrolyte for Cobalt-Free Lithium Battery Cathode Stability
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Solution Overview
Problem
Cobalt-free lithium nickel manganese-based oxide positive electrodes in rechargeable lithium batteries experience structural collapse and transition metal elution under high-voltage and high-temperature conditions, leading to gas generation, capacity reduction, and increased battery resistance.
Innovation Solution
A rechargeable lithium battery design incorporating a layered positive electrode active material with a cobalt-free lithium nickel manganese-based oxide and an electrolyte solution containing a non-aqueous organic solvent with ethylene carbonate in less than 5 wt% and an additive, which reduces transition metal elution and structural collapse, enhancing high-voltage and high-temperature characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If cobalt-free lithium nickel manganese-based oxide is used as positive electrode active material to achieve high energy density and economic benefits, then energy density and cost-performance are improved, but structural collapse and transition metal elution occur under high-voltage conditions leading to capacity reduction and gas generation
Solution Approach 1:
A coating layer comprising at least one of an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxy carbonate of a coating element is formed on the surface of the positive electrode active material. This coating layer acts as an intermediary barrier between the positive electrode active material and the electrolyte solution, preventing direct contact and chemical reactions that cause structural collapse and transition metal elution under high-voltage conditions, thereby maintaining structural stability while preserving high energy density
Solution Approach 2:
The positive electrode is constructed as a composite structure combining the cobalt-free lithium nickel manganese-based oxide active material with a protective coating layer of metal oxide/hydroxide compounds. This composite material approach allows the core active material to maintain its high capacity characteristics while the outer coating layer provides structural reinforcement and chemical stability under high-voltage operation
2Use of energy by moving object
If positive electrode including cobalt-free lithium nickel manganese-based oxide is used in high-voltage environment to increase energy density, then energy density is improved, but transition metals are eluted causing gas generation and capacity reduction
Solution Approach 1:
The coating layer serves as a protective intermediary that physically separates the positive electrode active material containing transition metals from the electrolyte solution. This prevents the elution of transition metals into the electrolyte, thereby eliminating the harmful effects of gas generation and capacity reduction while allowing the high-voltage operation needed for high energy density
Solution Approach 2:
The coating process transforms the potentially harmful direct exposure of the positive electrode active material to the electrolyte into a beneficial protective interface. The coating layer, formed through controlled chemical reactions, converts the reactive surface into a stable barrier that prevents transition metal elution and electrolyte decomposition, turning a vulnerability into a protective feature
3Temperature
If cobalt-free lithium nickel manganese-based oxide positive electrode is used under high-temperature conditions, then high-temperature operation capability is improved, but transition metal elution increases causing side reactions and increased battery resistance
Solution Approach 1:
The coating layer acts as a thermally stable intermediary barrier that remains intact under high-temperature conditions. It prevents the accelerated transition metal elution that normally occurs at elevated temperatures, thereby preventing side reactions with the electrolyte and maintaining low battery resistance and good cycle-life characteristics during high-temperature operation
4Reliability
If electrolyte solution is designed to protect positive electrode under high-voltage and high-temperature conditions, then high-voltage and high-temperature characteristics are improved, but electrolyte composition constraints increase
Solution Approach 1:
The coating layer on the positive electrode acts as a protective intermediary that reduces the demands on the electrolyte solution. By preventing direct contact between the positive electrode active material and the electrolyte, the coating layer allows the use of simpler electrolyte compositions that would otherwise be too aggressive and cause rapid degradation, thereby achieving high-voltage and high-temperature characteristics with less complex electrolyte formulations
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 effectively suppresses structural collapse and side reactions, improving battery stability, cycle-life, and reducing internal resistance, thereby enhancing the battery's high-voltage and high-temperature performance.
Implementation Method 1
an electrolyte solution effectively protecting a positive electrode including the positive electrode active material to reduce transition metal elution under high-voltage and high-temperature conditions and suppress structural collapse of the positive electrode
Data Source
Figure 1
AI summary
Disclosed are a rechargeable lithium battery including an electrolyte solution including a non-aqueous organic solvent, a lithium salt, and an additive; a positive electrode including a positive electrode active material; and a negative electrode including a negative electrode active material, wherein the non-aqueous organic solvent includes ethylene carbonate in an amount of less than about 5 wt%, and the additive includes a compound represented by Chemical Formula 1, and the positive electrode active material is represented by Chemical Formula 2. Chemical Formula 1 and Chemical Formula 2 are the same as defined in the specification.