Nonaqueous Electrolyte for Low-Co Cathodes With Stable Cycling
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Solution Overview
Problem
The increasing cost of Co in lithium-transition metal composite oxides for nonaqueous electrolyte secondary batteries leads to deterioration in cycle characteristics due to unstable lattice structures and side reactions, especially when Co content is reduced.
Innovation Solution
A nonaqueous electrolyte secondary battery design featuring a positive electrode active material with high Ni and Al content, and low or no Co, combined with an organophosphorus compound in the nonaqueous electrolyte to stabilize the crystal structure and prevent metal leaching, thereby improving cycle characteristics and reducing internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Co content is reduced in lithium-transition metal composite oxide, then cost is reduced, but cycle characteristics deteriorate due to unstable lattice structure
Solution Approach 1:
The patent changes the chemical composition parameters of the lithium-transition metal composite oxide by reducing Co content to 1.5 atm% or less and adjusting Ni, Mn, and Al proportions. This parameter change resolves the contradiction by finding an optimal composition that maintains lattice stability while reducing costly Co content.
Solution Approach 2:
The patent uses a composite material approach by combining multiple transition metals (Ni, Mn, Al, and reduced Co) in specific proportions within the lithium-transition metal composite oxide. This composite structure stabilizes the lattice and prevents degradation, allowing Co content reduction while maintaining cycle characteristics.
2Quantity of substance
If Co content is reduced in lithium-transition metal composite oxide, then cost is reduced, but side reactions are accelerated
Solution Approach 1:
The patent modifies the compositional parameters of the positive electrode active material by optimizing the ratios of Ni, Mn, Al, and reduced Co. This parameter optimization suppresses side reactions between the electrolyte and positive electrode, resolving the contradiction between cost reduction and harmful side reactions.
Solution Approach 2:
The patent introduces an organophosphorus compound as an intermediary substance in the nonaqueous electrolyte. This compound mediates the interaction between the electrolyte and the reduced-Co positive electrode, forming a protective interface that suppresses side reactions while allowing the cost-reducing low-Co composition to function properly.
3Quantity of substance
If Ni content is increased in lithium-transition metal composite oxide, then capacity is improved, but lattice stability decreases
Solution Approach 1:
The patent employs a composite material strategy by combining high-Ni content with specific proportions of Mn, Al, and reduced Co in the lithium-transition metal composite oxide. This composite composition leverages the high capacity of Ni while the other elements stabilize the lattice structure, resolving the contradiction between capacity improvement and lattice stability.
Solution Approach 2:
The patent applies local quality by distributing different transition metal elements in specific proportions within the composite oxide structure. The high-Ni regions provide capacity while Mn, Al, and Co regions provide structural stability, allowing the overall material to achieve both high capacity and lattice stability.
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 battery exhibits excellent cycle characteristics and reduced internal resistance, even with low Co content, by forming a stable surface film on the positive electrode active material that suppresses metal leaching and oxidation, enhancing capacity retention and charge/discharge efficiency.
Implementation Method 1
forming a stable surface film on the positive electrode active material that suppresses metal leaching and oxidation
Implementation Method 2
The nonaqueous electrolyte includes an organophosphorus compound represented by a general formula (1)... forming a stable surface film
Data Source
AI summary
A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode includes a positive electrode active material, the positive electrode active material includes a lithium-transition metal composite oxide containing Ni, Mn, and Al, and the proportions of Ni, Mn, and Al in metal elements other than Li contained in the lithium-transition metal composite oxide are, respectively, Ni: 50 atm % or more, Mn: 10 atm % or less, and Al: 10 atm % or less. When the lithium-transition metal composite oxide contains Co, the proportion of Co in the metal dements other than Li is 1.5 atm % or less. The nonaqueous electrolyte includes an organophosphorus compound represented by a general formula (1). In the general formula (1), R1 and R2 are each independently an alkyl group with 1 to 4 carbon atoms, and R3 is a fluorinated alkyl group with 1 to 4 carbon atoms.