Layered Positive Electrode Structure for High-Voltage Gas Suppression
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries with high Ni content lithium complex oxides experience excessive gas generation under high voltage due to stress-induced cracking of the positive electrode active material, leading to side reactions with the electrolyte.
Innovation Solution
A multilayer positive electrode structure is implemented, with a dense first layer and a porous second layer containing a covering element like boron, where the second layer's porosity and covering element distribution minimize surface reactions and gas generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high Ni content lithium complex oxide (70 mol% or more) is used as positive electrode active material to improve energy density, then energy density is improved, but gas generation increases under high voltage due to stress-induced cracking
Solution Approach 1:
The positive electrode active material layer is divided into two distinct layers: a first layer containing high Ni content lithium complex oxide with porosity of 0.1% or less (for high energy density), and a second layer containing high Ni content lithium complex oxide with porosity of 2% or more and covering element (for suppressing gas generation). This segmentation allows each layer to fulfill different functions simultaneously.
Solution Approach 2:
Different regions of the positive electrode are given different properties: the first layer (closer to current collector) has low porosity for high energy density, while the second layer (outer layer) has higher porosity and contains covering elements on particle surfaces to prevent side reactions and gas generation under high voltage stress.
2Use of energy by moving object
If positive electrode is pressed with high pressure to increase energy density, then energy density is improved, but cracking occurs in positive electrode active material on front surface side
Solution Approach 1:
The second layer with higher porosity and covering elements is positioned in advance on the front surface side of the positive electrode, where it acts as a cushioning layer that absorbs pressing stress and prevents cracking of the active material particles during high-pressure compression to increase energy density.
3Object-generated harmful factors
If covering element is added to second high Ni content lithium complex oxide to suppress side reactions, then gas generation is reduced, but manufacturing complexity increases
Solution Approach 1:
The porosity of the second high Ni content lithium complex oxide is controlled within a specific range (2% or more and 20% or less), and the covering element content is optimized (0.5 mol% or more and 3 mol% or less based on total metal elements). These parameter optimizations ensure effective suppression of side reactions while maintaining ease of manufacture through conventional processes.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A positive electrode (50) of a nonaqueous electrolyte secondary battery (100) disclosed herein includes a positive electrode active material layer (54) with a multilayer structure including a positive electrode lower layer (54A) close to a positive electrode current collector (52) and a positive electrode upper layer (54B) far from the positive electrode current collector (52). The positive electrode lower layer (54A) includes a first positive electrode active material (1) including a first Ni content lithium complex oxide (1A) with a porosity of less than 2%. The positive electrode upper layer (54B) includes a second positive electrode active material (2) including a second Ni content lithium complex oxide (2A) that is in a form of a secondary particle in which primary particles (2p) are aggregated, has a porosity of 2 to 20%, and does not include a larger space than an average cross-sectional area of the primary particles (2p) inside the secondary particle, and a covering element (4). The ratio of the covering element (4) is 0.5 to 3 mol% when the total of metal elements of the second Ni content lithium complex oxide (2A) is 100 mol%.