Multilayer Positive Electrode Surfactant Distribution for Gas Suppression
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Solution Overview
Problem
Surfactants incorporated into the positive electrode active material layer of nonaqueous electrolyte secondary batteries degrade at high voltages, leading to gas generation when lithium composite oxides with high nickel content are used, compromising the battery's performance.
Innovation Solution
A positive electrode with a multilayer structure in its active material layer, where one layer has a higher surfactant mass percentage and another layer has a lower mass percentage, with specific ratios and coverage, is designed to enhance electrolyte impregnation and suppress gas generation, using a nonionic surfactant and optimizing surfactant distribution to prevent degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a surfactant is incorporated into the positive electrode active material layer to enhance electrolyte impregnation, then the impregnating ability of the nonaqueous electrolyte solution is improved, but the surfactant degrades at high voltages leading to gas generation
Solution Approach 1:
The positive electrode active material layer is divided into multiple layers with different surfactant mass percentages. The layer closer to the electrolyte interface has a higher surfactant content (1.0-10 mass %) to enhance impregnation, while the layer closer to the current collector has a lower surfactant content (0.03-0.5 mass %) to minimize degradation and gas generation. This spatial segmentation allows each layer to perform its specific function optimally.
Solution Approach 2:
Different regions of the positive electrode active material layer are assigned different surfactant concentrations based on their functional requirements. The outer layer (facing electrolyte) receives higher surfactant concentration for improved wettability and impregnation, while the inner layer (facing current collector) receives lower surfactant concentration to reduce harmful degradation effects. This local quality differentiation resolves the contradiction between impregnation enhancement and gas suppression.
2Quantity of substance
If a high nickel content lithium composite oxide is used as positive electrode active material to increase capacity, then the energy density is improved, but the surfactant degradation and gas generation are exacerbated
Solution Approach 1:
The multilayer structure segments the surfactant distribution to isolate the high-nickel active material's aggressive electrochemical environment from the bulk surfactant. By concentrating surfactant only in the outer layer (1.0-10 mass %) where it contacts the electrolyte, and minimizing it in the inner layer (0.03-0.5 mass %) adjacent to the high-Ni active material, the system maintains capacity while reducing degradation-driven gas generation.
3Productivity
If the surfactant mass percentage is increased throughout the entire positive electrode active material layer to improve impregnation, then the electrolyte wettability is enhanced, but the gas generation increases
Solution Approach 1:
Rather than uniformly increasing surfactant content throughout the entire active material layer, the invention segments the layer into regions with different surfactant concentrations. The outer layer contains 1.0-10 mass % surfactant to ensure good electrolyte impregnation, while the inner layer contains only 0.03-0.5 mass % surfactant to minimize gas generation. This segmented approach achieves effective impregnation without the penalty of uniform high surfactant content.
Solution Approach 2:
The invention applies local quality by assigning different surfactant concentrations to different spatial locations within the active material layer. The region requiring maximum wettability (outer layer facing electrolyte) receives high surfactant content (1.0-10 mass %), while the region where degradation is most problematic (inner layer near high-Ni active material) receives low surfactant content (0.03-0.5 mass %). This localized optimization resolves the contradiction between overall impregnation performance and local gas generation suppression.
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 multilayer structure effectively improves the impregnation of the nonaqueous electrolyte solution into the positive electrode active material layer while significantly reducing gas generation at high voltages, enhancing the battery's performance and cycle characteristics.
Implementation Method 1
the ability of the nonaqueous electrolyte solution to impregnate into the positive electrode active material layer is enhanced by incorporating a surfactant into the positive electrode active material layer so as to improve the wettability of the positive electrode active material layer with the nonaqueous electrolyte solution
Data Source
AI summary
The positive electrode is provided with a positive electrode current collector and a positive electrode active material layer that is supported on the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and a surfactant. The positive electrode active material contains a lithium composite oxide that has a nickel content, with respect to the metal atoms other than lithium, of at least 70 mol %. The positive electrode active material layer has a multilayer structure that includes at least two layers that have different mass percentages of the surfactant with respect to the total of the positive electrode active material and the surfactant. The mass percentage of the surfactant in a layer that has a larger mass percentage of surfactant, of the layers present in the multilayer structure is not less than 1.0 mass % and not more than 10 mass %.