Mixed-Cathode Lithium Secondary Battery for High-Voltage Stability
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Solution Overview
Problem
Lithium secondary batteries face limitations in high-voltage operation due to rapid degradation and swelling issues when using lithium nickel cobalt manganese-based oxides, and lithium cobalt-based oxides offer poor capacity characteristics, while mixed positive electrode materials have unsatisfactory performance.
Innovation Solution
A lithium secondary battery design incorporating a positive electrode with a 50:50 to 80:20 weight ratio of lithium nickel cobalt manganese-based oxide and lithium cobalt-based oxide, with primary particle diameters of 3 um or more, and an electrolyte containing propyl propionate and cyclic carbonate solvents, specifically ethylene carbonate in 23 wt% or less, to minimize side reactions and enhance stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium nickel cobalt manganese-based oxide is used as positive electrode material to achieve high capacity characteristics, then battery capacity increases, but side reactions occur at high voltage causing rapid degradation and swelling
Solution Approach 1:
The patent controls the average particle diameter of primary particles of lithium nickel cobalt manganese-based oxide to be 3 μm or more, and adjusts the weight ratio of mixed positive electrode materials to contain 40-80 mass% lithium nickel cobalt manganese-based oxide. These parameter changes reduce specific surface area and minimize side reactions with electrolyte at high voltage, resolving the contradiction between capacity and stability
Solution Approach 2:
The patent uses a composite positive electrode material system combining lithium nickel cobalt manganese-based oxide (providing high capacity) with lithium cobalt-based oxide (providing structural stability at high voltage). This composite approach allows the battery to achieve both high capacity characteristics and excellent cycle life even at high voltage operation
2Duration of action of stationary object
If lithium cobalt-based oxide is used as positive electrode material to achieve excellent cycle characteristics at high voltage, then battery life improves, but capacity characteristics become poor due to low charge and discharge residuals
Solution Approach 1:
The patent merges two different lithium transition metal oxides with complementary characteristics: lithium nickel cobalt manganese-based oxide (high capacity but poor high-voltage stability) and lithium cobalt-based oxide (excellent high-voltage cycle stability but lower capacity). By combining these materials in a specific weight ratio range (40-80 mass% lithium nickel cobalt manganese-based oxide), the patent achieves both high capacity and excellent cycle characteristics at high voltage
3Adaptability or versatility
If mixed positive electrode materials are used to address limitations of single materials, then performance balance improves, but side reactions with electrolyte cause rapid degradation during high-voltage charge and discharge
Solution Approach 1:
The patent specifically controls the average particle diameter of primary particles to be 3 μm or more, which significantly reduces the specific surface area of the mixed positive electrode material. This parameter change minimizes the contact area with electrolyte, thereby reducing side reactions and improving reliability during high-voltage operation while maintaining the performance balance benefits of mixed materials
Data Source
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AI summary
The present invention relates to a lithium secondary battery having excellent battery performance at high voltage, and relates to a lithium secondary battery including a positive electrode, which includes a positive electrode active material layer including a lithium nickel cobalt manganese-based oxide having an average particle diameter of primary particles of 3 µm or more and a lithium cobalt-based oxide in a weight ratio of 50 : 50 to 80 : 20, a negative electrode, which includes a negative electrode active material layer including a negative electrode active material, and an electrolyte including an organic solvent and a lithium salt, wherein the organic solvent includes propyl propionate and a cyclic carbonate solvent containing ethylene carbonate and propylene carbonate, and the ethylene carbonate is included in an amount of less than 25 wt% in the organic solvent.