Multilayer Positive Electrode for Secondary Battery Cycle Life
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Solution Overview
Problem
Conventional secondary batteries with multilayer positive electrodes suffer from capacity deterioration and inadequate internal short circuit resistance, particularly when repeatedly charged and discharged, and are prone to heat generation during internal short circuits.
Innovation Solution
A positive electrode with a multilayer structure, where the second layer has a specific capacity greater than 17 mAh/g and at most 30 mAh/g, and the first layer has a specific capacity of 2 mAh/g or more and 17 mAh/g or less, using lithium composite oxides with high Ni content, and optionally doped with Ti or Zr, to enhance cycle characteristics and internal short circuit resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a multilayer structure with high-capacity materials is used in the lower layer and high-output materials in the upper layer, then energy density and output density are improved, but cycle characteristics deteriorate due to capacity deterioration during repeated charging and discharging
Solution Approach 1:
The positive electrode active material layer is divided into two distinct layers: a lower layer (first layer) containing high-capacity materials and an upper layer (second layer) containing high-output materials. This segmentation allows each layer to perform its specific function while working together to resolve the contradiction between energy density and cycle characteristics.
Solution Approach 2:
Different regions of the positive electrode are assigned different material compositions and properties. The lower layer uses materials optimized for capacity (high Ni content), while the upper layer uses materials optimized for output and stability (high Co content). This local differentiation enables the electrode to simultaneously achieve high energy density and good cycle characteristics.
2Power
If conventional multilayer structures are used, then output density is improved, but internal short circuit resistance is insufficient causing excessive heat generation during internal short circuits
Solution Approach 1:
The invention changes the material composition parameters of the positive electrode layers. The upper layer contains high-Co materials with specific capacity ranges (17-30 mAh/g) that provide both high output density and excellent internal short circuit resistance, thereby reducing heat generation during internal short circuits while maintaining high power output.
Data Source
AI summary
A positive electrode includes a current collector, and an active material layer provided on the current collector. The active material layer has a first layer located on the current collector side and a second layer located on a surface layer side of the active material layer. A proportion of a thickness of the second layer to a total thickness of the first and second layers is from 0.20 to 0.80. When each specific capacity of a potential flat portion near 4.2 V in a charging voltage curve is measured for the first and second layers, the above specific capacity of the second layer is larger than that of the first layer. The above specific capacity of the second layer is greater than 17 mAh/g and at most 30 mAh/g. The above specific capacity of the first layer is from 2 mAh/g to 17 mAh/g.