Nonaqueous Electrolyte Battery SEI Coat Uniformity
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face non-uniform infiltration of coat-forming agents, leading to uneven SEI coat formation on the negative electrode active material layer, particularly in large batteries, causing localized degradation and reduced performance.
Innovation Solution
Incorporating a crown ether into the nonaqueous electrolyte to trap sodium ions, preventing the formation of insoluble salts and ensuring uniform infiltration and decomposition of oxalato complex compounds, thereby forming a homogeneous coat on the negative electrode active material layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an oxalato complex compound is added to the nonaqueous electrolyte as a coat-forming agent, then a stable SEI coat can be formed on the negative electrode active material layer, but non-uniform infiltration occurs into the active material layer particularly in large batteries, leading to non-uniform SEI coat formation
Solution Approach 1:
The patent changes the chemical parameters of the electrolyte by adding crown ether compounds with specific molecular structures (15-crown-5, 18-crown-6, or dibenzo-18-crown-6) at controlled concentrations (0.01-5 mass%). This parameter change modifies the electrolyte's ability to dissolve sodium ions, thereby preventing the formation of insoluble sodium salts and ensuring uniform infiltration of the oxalato complex compound throughout the active material layer, especially in large batteries.
Solution Approach 2:
The crown ether acts as an intermediary substance that mediates between the sodium ions present in the electrolyte and the oxalato complex compound. By forming soluble complexes with sodium ions, the crown ether prevents direct reaction between sodium ions and oxalato complex compounds, thereby eliminating the formation of insoluble precipitates that cause non-uniform infiltration and enabling uniform SEI coat formation.
2Reliability
If sodium ions are present in the nonaqueous electrolyte, then the electrolyte can conduct lithium ions, but sodium ions react with oxalato complex compounds to form insoluble salts that precipitate and cause non-uniform infiltration
Solution Approach 1:
The patent converts the harmful effect of sodium ions (which cause precipitation and non-uniform infiltration) into a beneficial effect by using crown ether compounds to selectively complex with sodium ions. This allows the electrolyte to maintain ionic conductivity while preventing the formation of insoluble sodium salts, as the crown ether-sodium ion complexes remain soluble and do not precipitate.
Solution Approach 2:
The crown ether serves as an intermediary that binds to sodium ions, preventing them from reacting with oxalato complex compounds. This intermediary action maintains the beneficial ionic conductivity of the electrolyte while eliminating the harmful precipitation effect, as the crown ether-sodium ion complexes are stable and soluble.
3Ease of manufacture
If the nonaqueous electrolyte infiltrates the electrode assembly during manufacture, then the electrolyte can reach the active material layers, but the coat-forming agent infiltrates non-uniformly causing localized degradation and reduced battery performance
Solution Approach 1:
The patent modifies the chemical parameters of the electrolyte by incorporating crown ether compounds at specific concentrations (0.01-5 mass%). This parameter change alters the electrolyte's interaction with sodium ions and oxalato complex compounds, ensuring uniform distribution and infiltration throughout the electrode assembly during manufacturing, thereby preventing localized degradation and ensuring consistent SEI coat formation.
Solution Approach 2:
The crown ether acts as an intermediary during the electrolyte infiltration process, preventing premature reaction between sodium ions and oxalato complex compounds. This ensures uniform infiltration of the coat-forming agent throughout the active material layer, as the crown ether maintains the oxalato complex compound in a soluble, non-reactive state during the infiltration process.
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
This approach results in improved cycling characteristics and battery performance by maintaining uniform current distribution and preventing localized deterioration of the negative electrode active material.
Implementation Method 1
a crown ether which forms a complex with sodium ions
Implementation Method 2
a solid electrolyte interface (SEI) coat is formed on the surface of the negative electrode active material by reductive decomposition of part of the nonaqueous electrolyte at the negative electrode
Data Source
AI summary
Provided is a nonaqueous electrolyte secondary battery with better battery performance than in the past, by forming an SEI coat with very little non-uniformity on the surface of the negative electrode active material layer. The invention provides a nonaqueous electrolyte secondary battery in which an electrode assembly including a positive electrode, a separator, and a negative electrode, and a nonaqueous electrolyte are contained in a battery case. In this secondary battery, the nonaqueous electrolyte contains a crown ether that forms a complex with a sodium ion, and the negative electrode includes a negative current collector, a negative electrode active material layer containing a negative electrode active material formed on the surface of the current collector, and a coat including an oxalato complex structure and provided on at least part of the surface of the negative electrode active material layer.